Corrected edition · JAPAN ASSOCIATION FOR QUATERNARY RESEARCH

Inventory of Quaternary Outcrops —Tephras in Japan—

Japan Association for Quaternary Research · Original publication: 1996

About this corrected and translated edition
This unofficial corrected and translated edition was prepared by Fumihiko Ikegami, who reformatted the OCR text and adjusted the layout based on the publicly distributed PDF of Inventory of Quaternary Outcrops—Tephras in Japan (edited by the volume’s editorial committee and published by the Japan Association for Quaternary Research in 1996). The English text was produced using automated translation with GPT-6.1 Sol. The corrections, translation, figure alt text and lettering transcriptions, and additional editorial notes in this edition were prepared after the original publication.

Ages, place and stratigraphic names, interpretations, and outcrop conditions retain their historical context. Automated processing and the low resolution of the source material may leave transcription or translation errors; please also consult the Association’s original PDF when using or citing this work for research. Unreadable passages and inconsistencies in the original are documented in the editorial review notes.

Four entries on original pp. 157–159 and 164 were removed from the public edition following the Association’s assessment of material associated with the Paleolithic fabrication scandal; editorial notes explain their absence at the corresponding locations. See the Association’s distribution page for the public-edition policy.

All four documents share an external image folder. Expand the panel below a figure in the HTML to read its extracted lettering and translation. Separate data include Japanese figure text, English figure text, bilingual alt and figure-text JSON, and the terminology glossary.

Cover

Inventory of Quaternary Outcrops —Tephras in Japan—

Special publication commemorating the 40th anniversary of the Japan Association for Quaternary Research

Japan Association for Quaternary Research
40th Anniversary Special Publication

日本第四紀学会 — Japan Association for Quaternary Research

Color plates: 1–3

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1. Post-caldera tephras overlying the Shikotsu tephra at Bibi on the Ishikari Plain. The yellow tephra is Eniwa-a, and the dark orange tephra is Tarumae-d; Tarumae-c and -b overlie them. See WS-7-1. Photograph: 町田洋 (Hiroshi Machida).

2. Tephras from Kutcharo and Mashu volcanoes at Shari in eastern Hokkaido. The Aso-4 tephra is preserved within this succession. See WS-9-4. Photograph: 奥村晃史 (Koji Okumura).

3. Tephra involutions at Nakashunbetsu on the Konsen Plain. There is a marked contrast between tephras disturbed during the last glacial period (oxygen isotope stage 2) and the Mashu-1 tephra, which was affected relatively little. All are products of Mashu stratovolcano. Photograph: 岩田修二 (Shuji Iwata).

Cover photograph: The Great Geological Section at Senbazaki, Izu-Oshima. Scoria beds of the Older Oshima Group. See KT-47. Photograph: 新川和範.

Original Japanese lettering

1. 石狩平野美々において、支笏テフラの上にのる後カルデラテフラ群。黄色のテフラが恵庭a、濃いオレンジ色のテフラが樽前d、その上位に樽前c、bがのる。本文WS-7-1参照。町田洋撮影。

2. 道東斜里における屈斜路および摩周火山のテフラ群。これらの中に阿蘇4テフラが保存されている。本文WS-9-4参照。奥村晃史撮影。

3. 根釧原野、中春別におけるテフラのインボリューション。最終氷期（酸素同位体ステージ2）に擾乱をうけたテフラとあまり受けなかった摩周1テフラとの対照が顕著。どれも摩周成層火山の噴出物。岩田修二撮影。

表紙写真：伊豆大島千波崎地層大切断面。古期大島層群のスコリア層。本文KT-47参照。新川和範撮影。

1. Post-caldera tephras overlying the Shikotsu tephra at Bibi on the Ishikari Plain. The yellow tephra is Eniwa-a, and the dark orange tephra is Tarumae-d; Tarumae-c and -b overlie them. See WS-7-1. Photograph: 町田洋 (Hiroshi Machida).

2. Tephras from Kutcharo and Mashu volcanoes at Shari in eastern Hokkaido. The Aso-4 tephra is preserved within this succession. See WS-9-4. Photograph: 奥村晃史 (Koji Okumura).

3. Tephra involutions at Nakashunbetsu on the Konsen Plain. There is a marked contrast between tephras disturbed during the last glacial period (oxygen isotope stage 2) and the Mashu-1 tephra, which was affected relatively little. All are products of Mashu stratovolcano. Photograph: 岩田修二 (Shuji Iwata).

Cover photograph: The Great Geological Section at Senbazaki, Izu-Oshima. Scoria beds of the Older Oshima Group. See KT-47. Photograph: 新川和範.

Color plates: 4–6

4. The Shimosueyoshi Formation and tephras at Chitose, Kawasaki. This has been one of the reference outcrops since the early studies of the Kanto Loam. Although urbanization has advanced, part of the outcrop survives. The basement consists of sandstone and mudstone of the Kazusa Group. Apart from valley-filling sediments, the Shimosueyoshi Formation consists of very thin wave-cut platform deposits, overlain by the Shimosueyoshi Loam and younger layers. The tephras appearing white are derived from Hakone volcano. Photograph: 貝塚爽平 (Sohei Kaizuka).

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Signs appear near the top of the photograph; part of their lettering is illegible.

Original Japanese lettering

写真上部に札があるが、文字の一部は判読不明。

Reading notes

写真中の札の全字は低解像度のため確定できない。

5. A section through the Tama Loam exposed during construction of the Kawasaki interchange of the Tomei Expressway. The Oshinuma sand and gravel bed is visible at the foot of the cliff, overlain by marker tephras including Gomashio, Doran, and Baya-rees (バヤリース). Photograph: 貝塚爽平 (Sohei Kaizuka).

6. Early Pleistocene Shirakawa pyroclastic-flow deposits, widely distributed in southern Tohoku. Above the intervening alternation of fallout tephra and soil is the Saigo pyroclastic-flow deposit; below it is the Ashino pyroclastic-flow deposit. The Saigo deposit is weakly welded. See TH-27. Photograph: 鈴木毅彦 (Takehiko Suzuki).

Color plates: 7–9

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Numerals indicating a photographic date occur at lower right; some digits are illegible.

Original Japanese lettering

右下に撮影日を示す数字がある。一部判読不明。

Reading notes

撮影日の年は確定せず。

7. Products of the large eruption that generated the Kikai-Akahoya tephra: a pumice-fall deposit and two pyroclastic-flow deposits (Takeshima, Kikai caldera, southern Kyushu). At the far left is the Nagase pyroclastic-flow deposit, the proximal pyroclastic-flow deposit associated with the Kikai-Tozurahara tephra. See WS-2-1. Photograph: 町田洋 (Hiroshi Machida).

8. The large-scale tephra deposits that produced the Aira-Tn tephra (Shibushi coast, southern Kyushu): the Osumi pumice-fall deposit and the Ito pyroclastic-flow deposit. Beneath them occur various slightly pedogenically altered Late Pleistocene tephras. See WS-5-1. Photograph: 町田洋 (Hiroshi Machida).

9. Sueyoshi stage I tephras of Higashiyama volcano on Hachijojima and the intercalated Aira-Tn tephra (the white volcanic-ash layer on the left). See KT-50. Photograph: 菅香世子.

Color plates: 10–12

10. The Sannai-Maruyama archaeological site in Aomori. An embankment constructed during the Early Jomon period stands in the center of the valley and is covered by deposits consisting mainly of abundant pottery. See TH-3. Photograph: 辻誠一郎 (Seiichiro Tsuji).

11. Tephras at the Iwajuku archaeological site, Gunma Prefecture. The Paleolithic artifacts first excavated here were recovered from volcanic-ash soil approximately halfway between the ground surface and the Haruna-Hassaki tephra (the white pumice layer), approximately at the stratigraphic horizon of the Aira-Tn tephra. See KT-12. Photograph: 町田洋 (Hiroshi Machida).

Show extracted lettering and translation

English translation of figure lettering

Numerals indicating a photographic date appear at lower left, but the complete date is illegible.

Original Japanese lettering

左下に撮影日を示す数字があるが、全桁は判読不明。

Reading notes

写真中の撮影日全桁は判読不明。

12. The Atotsugawa fault in the upper Makawa valley, Toyama Prefecture. Granite lies on the left (northwestern) side and terrace gravel on the right (southeastern) side. See CB-27. Photograph: 町田洋 (Hiroshi Machida).

Contents

III. Individual entries

Four entries on original pp. 157–159 and 164 were removed from the Association’s public edition. Their contents links lead to explanatory editorial notes.

1. Widespread tephras throughout Japan

1. Widespread tephras throughout Japan

2. Hokkaido

2. Hokkaido

3. Tohoku

3. Tohoku

4. Kanto

4. Kanto

5. Chubu

5. Chubu

6. Kinki

7. Chugoku and Shikoku

7. Chugoku and Shikoku

8. Kyushu and the Nansei Islands

Preface

Research concerning the Quaternary has become increasingly integrated in recent years and has expanded to encompass a broad range of subjects, including the reconstruction of former land–sea distributions, sea levels, vegetation, climate, and other aspects of past environments; the activity histories of active faults; and archaeological excavations and changes in human culture. Strata, landforms, and soils record in detail the histories of these terrestrial ecosystems and human activities. Outcrops enable us to encounter strata, landforms, and soils of many different ages, and the significance of outcrops and boreholes is therefore increasing. The outcrops that constitute the main subject of this book are the most readily accessible places where anyone can observe, collect samples, and unravel the record of the Earth's activity at any time. Borehole cores become important in settings where outcrops are intrinsically scarce, including sea floors, lake beds, embayments, plains, basins, and wetlands. The importance of research using borehole cores from land, sea floors, and lake beds needs no emphasis, but only a small selection is included here. We hope to compile these materials on another occasion.

Outcrops that provide such important information are precious assets for humanity and a combined natural and cultural heritage. There is consequently an extremely strong need to preserve them. Many Japanese Quaternary outcrops, however, are artificial exposures, including those created by archaeological excavations, and often disappear very quickly. The situation is particularly serious in urban areas. Even exposures of the Shimosueyoshi Formation and Shimosueyoshi Loam, which document the Shimosueyoshi transgression 125,000 years ago, have become almost impossible to see in the Yokohama–Kawasaki area. It is no exaggeration to describe the loss of these precious records in the course of “development” as a modern form of “book burning.”

There are, on the other hand, a few examples of outcrops being used for tourism, education, and research. At the “Great Geological Section” on Izu-Oshima (cover photograph), the town has installed explanatory signs and continually manages and conserves the exposure, which attracts many visitors. Various ways of preserving archaeological and active-fault exposures have also begun to be considered. At present, however, only a very small number of Quaternary exposures, such as lava caves and coral reefs, have been designated natural monuments. There is an urgent need to preserve particularly valuable reference outcrops of Quaternary strata. A variety of approaches will be necessary according to the value and condition of each exposure: preserving the site itself, taking and preserving an outcrop peel, and preserving samples, including borehole cores. Consideration should also be given to a system of emergency investigation of outcrops exposed by construction and similar activities, analogous to rescue excavations at archaeological sites, so that at least a description is made. Cooperation from museums and other public institutions will be indispensable for preserving peels and samples. For conservation in the field, it is important to secure the understanding of the Agency for Cultural Affairs, local authorities, and other relevant bodies regarding designation as cultural properties or natural monuments. Installing appropriate explanatory signs at outcrops with the cooperation of local boards of education would also be highly significant.

This book selects and describes 274 sites, principally terrestrial outcrops containing tephra in the Japanese archipelago. It introduces a variety of exposures: representative widespread tephras and their characteristics in source regions and at distant localities; regional tephra stratigraphies; relationships between regional and widespread tephras; exposures bearing on past environments to which tephra provides a chronological framework, including glacial and periglacial features, Jomon transgression deposits, and peat; active-fault exposures; and exposures associated with archaeological sites. It also includes a considerable number of important exposures in which no tephra has so far been found, for example those associated with active faults, archaeological sites, and coral reefs. Some of the selected outcrops have already disappeared. One purpose of the book is to preserve descriptive records of type localities and other important exposures that can serve in their place.

We have focused on tephra-bearing outcrops because tephra is the most effective means in the Japanese archipelago of providing a time axis for the various records that outcrops reveal. In general, a tephra is an excellent time-marker bed that covers extensive land and water areas at a geologically instantaneous moment. If its eruption age is known, it has a significance equivalent to an absolute age.

A major characteristic of the Japanese archipelago is that very many strata contain tephra—volcaniclastic material such as volcanic ash—and many landforms are mantled by it. Regional tephra stratigraphies have long been studied in Japan. Tephra has been used to correlate and establish chronologies for strata, landforms, and soils, and to provide a chronological framework for environmental changes, geological events, and human activities. Together with the accumulation of age determinations by various methods, these developments have made the account of the Quaternary drama unfolding in and around the Japanese archipelago far more detailed, and are making it possible to place it within global environmental change. In this sense, research on tephra and tephrochronology, alongside research on dating methods, is among the most fundamental and broadly applicable areas of Quaternary research.

At the general meeting of the Japan Association for Quaternary Research held at Tokyo Metropolitan University in August 1994, publication of an inventory of Quaternary outcrops was approved as a project commemorating the Association's 40th anniversary. Against the background of advances in tephrochronology, its purpose is, above all, to give young researchers, graduate students, and students who will carry the field forward an opportunity to learn how to examine outcrops: to pass on existing knowledge in front of surviving exposures, to identify what information should be obtained from them, and to discern what has been established and what problems remain. It also aims to make the wider public aware of the importance of outcrops and the significance of conserving them. We hope that this book will be widely used in these ways.

The contents of this book are not necessarily complete, and there will undoubtedly be many corrections and additions. In that sense, it is a starting point for further research. We hope readers will take it into the field and use it to deepen discussion.

Building on the history and tradition of tephrochronology developed in Japan, continuing efforts will be needed to describe outcrops accurately—including those that have disappeared—to preserve their records, and to pass them on to the next generation. Unremitting efforts will also be needed to conserve outcrops of great significance to Quaternary research. We therefore hope that this project will continue.

During the editing of this book, 貝塚爽平 (Sohei Kaizuka) initially contributed to the formulation of the project as chair of the Planning and Editorial Committee, the predecessor of the present committee. He, 新井房夫 (Fusao Arai), and 新川和範 also supplied the color plates and cover photograph. 吉田浩, 小林淳, and 是枝若奈 assisted with the editorial work. Over two terms, the Executive Board of the Japan Association for Quaternary Research delegated three executive members to the committee and provided extensive assistance throughout the planning and editing process. We express our sincere thanks to all these individuals and organizations.

1 July 1996

Editorial Committee for the Inventory of Quaternary Outcrops

遠藤邦彦、熊井久雄、町田洋、奥村晃史、清水長正
鈴木毅彦、渡辺満久、上杉陽、池田安隆、辻誠一郎

I. Explanatory chapters

1. Tephra research in Japan and Quaternary science

Today, whatever the subject, no discussion of the Quaternary in the Japanese archipelago can dispense with tephra or the methods of tephrochronology. The late 小林国夫 (Kunio Kobayashi), formerly a professor at Shinshu University, established a Commission on Tephrochronology within the International Union for Quaternary Research (INQUA) and became its first chair. The commission was active from 1961 to 1983. It was revived in 1988, and 町田洋 (Hiroshi Machida) has chaired it since 1992; Japanese researchers have thus also played central roles internationally. One reason for this is the long history of vigorous tephra research throughout Japan and the major role of tephra in establishing regional Quaternary stratigraphies. The Japan Association for Quaternary Research has held three symposia on tephrochronology, publishing special issues in The Quaternary Research, volume 3, numbers 1–2; volume 11, number 4; and volume 30, number 5 (1992).

In 1976, a thin white ash bed within the Kanto Loam mantling slopes across the Tanzawa Mountains—the Tanzawa Pumice (Machida et al., 1971)—was named the Aira-Tn tephra (AT). When it was shown to derive from the great eruption about 24,000 years ago that discharged the Ito pyroclastic flow from Aira caldera and formed the extensive Shirasu plateaus (Machida and Arai, 1976), the Japanese earth-science community was profoundly surprised and took considerable time to accept this interpretation. The advances in tephrochronology initiated by the discovery of this widespread tephra are nevertheless clearly evident in the course of research during the ensuing 20 years. Following the discovery of AT in 1976, widespread tephras were identified one after another, and the field advanced to a qualitatively higher level. Thirty years have now passed since the special issue on tephrochronology appeared in volume 3, numbers 1–2 of The Quaternary Research, and 20 years since the discovery of AT. The tephra symposium held at Meiji University in 1990 (published as a special issue in volume 30, number 5 of The Quaternary Research) and the Atlas of Tephra (Machida and Arai, 1992), which brings together the work of those two researchers, have documented the present state of knowledge concerning the characteristics, distributions, and ages of major tephras, particularly widespread tephras, and have demonstrated their substantial usefulness and potential for application.

2. Fundamentals of tephra research

a. What is tephra?

Tephra comprises pyroclastic (volcaniclastic) material, such as pumice and scoria of various sizes (Table 1), generated by explosive volcanic eruptions. It is synonymous with volcanic ash in the broad sense.

During an explosive volcanic eruption, magma rising through the conduit is fragmented and ejected upward as it cools and solidifies. An eruption column forms above the crater, consisting of magma fragments, volcanic gases, and air entrained from the surroundings. As particles of various sizes within the column are transported by wind, coarse particles fall to the ground near the crater and progressively finer particles fall farther away. In this way, fallout tephra that is size-sorted according to distance from the crater is deposited.

Pyroclastic-flow and pyroclastic-surge deposits, on the other hand, form when material containing particles of various sizes flows downslope during partial collapse of an eruption column, overflow of the eruption cloud from the crater, or the formation of an inclined eruption column from the outset. Pyroclastic flows can also be generated by collapse of a lava dome. Pyroclastic-surge deposits associated with laterally directed eruption clouds produced by phreatomagmatic explosions are called base-surge deposits. Debris-avalanche deposits generated by collapse of a volcanic edifice and deposits of water-bearing mudflows or debris flows often consist of pyroclastic material and are included in tephra in the broad sense (Table 2).

The term “volcanic ash,” often used synonymously with tephra, properly refers to particles finer than 2 mm. Using it to include coarse pumice or scoria therefore remains somewhat incongruous. For this reason, “tephra” has increasingly been used as the collective term for volcaniclastic (pyroclastic) material. With some exceptions, Machida and Arai (1992) replaced “ash” with “tephra” in tephra names. Although a distal tephra may be fine-grained and appropriately called ash, near its source volcano it commonly occurs as fallout tephra rich in coarse particles or as a pyroclastic-flow deposit. Accordingly, this book uses “tephra” as the general term for pyroclastic material and indicates correspondence with the tephra names (“… tephra”) of Machida and Arai (1992). Where the name “ash” is already well established, however, especially for units named and defined regionally as “… volcanic-ash bed,” the original term has sometimes been retained.

Table 1. Classification of tephra by grain size and other characteristics

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Grain size	Classification and characteristics
Coarser than 64 mm	Volcanic blocks
2–64 mm	Lapilli; pumice (vesiculated white particles); scoria (vesiculated black particles)
Finer than 2 mm	Volcanic ash: coarse ash (volcanic sand) and fine ash

Original Japanese lettering

粒径	分類・性状
64 mmより粗粒	火山岩塊
2–64 mm	火山礫；軽石（発泡した白色粒子）；スコリア（発泡した黒色粒子）
2 mmより細粒	火山灰：粗粒火山灰（火山砂）、細粒火山灰

Table 2. Classification of tephra by transport process

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Classification by transport process	Subdivisions
Fallout tephra	Pumice fall, scoria fall, ash fall (volcanic sand)
Pyroclastic-flow deposits	—
Pyroclastic-surge deposits	—
Ballistically ejected material	—
Debris-avalanche deposits	—
Mudflows, debris flows, and slushflows	—

Figure 1. Distribution limits of representative Late Pleistocene widespread tephras in Japan and adjacent regions (Machida and Arai, 1992). Volcanoes (stars): Kc, Kutcharo; S, Toya; On, Ontake; D, Daisen; Sb, Sambe; Aso, Aso; A, Aira; Ata, Ata; K, Kikai; B, Baitoushan; U, Ulleung.

Tephra abbreviations in the map: Aso-4, B-Tm, AT, K-Tz, Spfa-1, Kc-Sr, Kc-Hb, Toya, SK, K-Ah, U-Oki, DKP, On-Pm1. Longitude ticks: 126°, 130°, 134°, 138°, 142°, 146°E. Latitude ticks: 46°N, 42°, 38°, 34°, 30°, 26°, 22°. Scale: 0–500 km.

Original Japanese lettering

運搬過程による分類	細分
降下テフラ	降下軽石、降下スコリア、降下火山灰（火山砂）
火砕流堆積物	—
火砕サージ堆積物	—
弾道噴出物	—
岩屑なだれ堆積物	—
泥流・土石流・スラッシュフロー	—

図1. 日本とその周辺地域における更新世後期の代表的広域テフラの分布範囲（町田・新井、1992）。火山（星印）：Kc（屈斜路）、S（洞爺）、On（御岳）、D（大山）、Sb（三瓶）、Aso（阿蘇）、A（姶良）、Ata（阿多）、K（鬼界）、B（白頭山）、U（鬱陵）。

図中のテフラ略号：Aso-4、B-Tm、AT、K-Tz、Spfa-1、Kc-Sr、Kc-Hb、Toya、SK、K-Ah、U-Oki、DKP、On-Pm1。経度目盛：126°、130°、134°、138°、142°、146°E。緯度目盛：46°N、42°、38°、34°、30°、26°、22°。縮尺：0–500 km。

Figure 1. Distribution limits of representative Late Pleistocene widespread tephras in Japan and adjacent regions (Machida and Arai, 1992). Volcanoes (stars): Kc, Kutcharo; S, Toya; On, Ontake; D, Daisen; Sb, Sambe; Aso, Aso; A, Aira; Ata, Ata; K, Kikai; B, Baitoushan; U, Ulleung.

Tephra abbreviations in the map: Aso-4, B-Tm, AT, K-Tz, Spfa-1, Kc-Sr, Kc-Hb, Toya, SK, K-Ah, U-Oki, DKP, On-Pm1. Longitude ticks: 126°, 130°, 134°, 138°, 142°, 146°E. Latitude ticks: 46°N, 42°, 38°, 34°, 30°, 26°, 22°. Scale: 0–500 km.

Table 3. Widespread tephras from giant eruptions in Japan and adjacent regions during the late Quaternary (approximately the past 130,000 years)

(Revised and supplemented from Machida and Arai, 1992.)

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Tephra (symbol)	Age, ka (dating method)	Eruption/deposition modes and sequence	Total tephra volume (bulk, km³)	Juvenile tephra: volcanic glass, n	Juvenile tephra: phenocrysts	References and other information
Baitoushan–Tomakomai (B-Tm)	10th century (A, C, V)	pfa, pfl, pfa, pfl (coign.)	>50	pm, bw; 1.511–1.522	af, (am, cpx); af 1.521–1.525	Machida et al. (1981); Machida et al. (1990)
Kikai-Akahoya (K-Ah)	6.3 (C)	pfa, pfl, afa (coign.)	>170	bw, pm; 1.508–1.516	opx, cpx; opx 1.708–1.713	Machida and Arai (1978)
Ulleung-Oki (U-Oki)	9.3 (C)	pfa, pfl	>10	pm; 1.518–1.524	bi, am, cpx; af 1.522–1.524; ho 1.726–1.740	Machida et al. (1984)
Towada-Hachinohe (To-H)	12.6 (C)	pfa, afa, pfl	>50	pm; 1.502–1.509 (1.503–1.508)	opx, cpx, ho; opx 1.705–1.708; ho 1.669–1.673	Hayakawa (1983)
Aira-Tn (AT)	c.24 (C)	pfa, pfl (pp), pfl, afa (coign.)	>450	bw, pm; 1.498–1.501	opx, cpx, (ho; qt); opx 1.728–1.734	Machida and Arai (1976)
Towada-Ofudo (To-Of)	>33 (C)	pfa, afa, pfl	>50	pm>bw; 1.505–1.511 (1.506–1.508)	opx, cpx; opx 1.707–1.711	Hayakawa (1985)
Kutcharo-Shoro (Kc-Sr)	30–32 (C)	afa, pfl, afa (coign.?)	100	pm, bw; 1.502–1.505	opx, cpx; opx 1.707–1.710	Arai et al. (1986); Okumura (1988)
Shikotsu-1 (Spfa-1, Spfl)	c.40 (C)	pfa, pfl	200	pm, bw; 1.500–1.505	opx, ho, (cpx); qt; opx 1.729–1.735; ho 1.688–1.691	Katsui (1958); Arai et al. (1986)
Daisen-Kurayoshi (DKP)	43–55 (U, ST)	pfl, pfa	>20	pm; 1.508–1.514	ho, opx, (bi); opx 1.702–1.708; ho 1.673–1.680	Machida and Arai (1979)
Aso-4 (Aso-4)	85–90 (ST, FT, etc.)	pfl, afa (coign.)	>600	bw, pm; 1.506–1.510	ho, opx, cpx; opx 1.699–1.701; ho 1.685–1.691	Machida et al. (1985)
Kikai-Tozurahara (K-Tz)	90–95 (ST, TL)	afa (pp), pfl, afa (coign.)	150?	bw, pm; 1.494–1.500	opx, cpx; qt; opx 1.705–1.709	Machida and Arai (1992)
Ontake-1 (On-Pm1)	c.95 (FT, KA)	pfa	50	pm, (bw); 1.500–1.503	ho, bi, (opx); opx 1.706–1.711; ho 1.681–1.690	Kobayashi et al. (1967); Machida (1990)
Sambe-Kisuki (SK)	c.100 (ST)	pfa	20	pm; 1.494–1.498	bi; qt	豊倉 et al. (1991)
Ata (Ata)	c.105 (ST)	afa (pp), pfa, pfl, afa (coign.)	>300	bw, pm; 1.508–1.512	opx, cpx, (ho); opx 1.704–1.708	Ota and Machida (1987)
Toya (Toya)	90–120 (FT, ST)	afa (pp), pfl, afa (coign.)	>150	pm, bw; 1.494–1.498	(opx, cpx, ho; qt); opx 1.711–1.761; ho 1.674–1.684	Machida et al. (1987)
Aso-3 (Aso-3)	105–125 (FT, ST)	pfa, pfl, afa (coign.)	>150	pm, bw; 1.512–1.540	opx, cpx; opx 1.702–1.705	Machida and Arai (1992, 1994)
Kutcharo-Haboro (Kc-Hb)	100–130 (FT, ST)	afa·pfa, pfl, afa (coign.)	>150	bw, pm; 1.502–1.506	opx, cpx; opx 1.705–1.710	Katsui and Sato (1963); Arai et al. (1986); Okumura (1988)

Original Japanese lettering

テフラ名（記号）	年代 ka（測定方法）	噴火・堆積様式と順序	全テフラ量（みかけ、km³）	本質テフラ粒：火山ガラス、n	本質テフラ粒：斑晶	文献・その他
白頭山苫小牧 (B-Tm)	10世紀 (A, C, V)	pfa, pfl, pfa, pfl (coign.)	>50	pm, bw; 1.511–1.522	af, (am, cpx); af 1.521–1.525	町田ほか (1981); Machida et al. (1990)
鬼界アカホヤ (K-Ah)	6.3 (C)	pfa, pfl, afa (coign.)	>170	bw, pm; 1.508–1.516	opx, cpx; opx 1.708–1.713	町田・新井 (1978)
鬱陵隠岐 (U-Oki)	9.3 (C)	pfa, pfl	>10	pm; 1.518–1.524	bi, am, cpx; af 1.522–1.524; ho 1.726–1.740	町田ほか (1984)
十和田八戸 (To-H)	12.6 (C)	pfa, afa, pfl	>50	pm; 1.502–1.509 (1.503–1.508)	opx, cpx, ho; opx 1.705–1.708; ho 1.669–1.673	早川 (1983)
姶良Tn (AT)	c.24 (C)	pfa, pfl (pp), pfl, afa (coign.)	>450	bw, pm; 1.498–1.501	opx, cpx, (ho; qt); opx 1.728–1.734	町田・新井 (1976)
十和田大不動 (To-Of)	>33 (C)	pfa, afa, pfl	>50	pm>bw; 1.505–1.511 (1.506–1.508)	opx, cpx; opx 1.707–1.711	Hayakawa (1985)
クッチャロ庶路 (Kc-Sr)	30–32 (C)	afa, pfl, afa (coign.?)	100	pm, bw; 1.502–1.505	opx, cpx; opx 1.707–1.710	Arai et al. (1986); Okumura (1988)
支笏第1 (Spfa-1, Spfl)	c.40 (C)	pfa, pfl	200	pm, bw; 1.500–1.505	opx, ho, (cpx); qt; opx 1.729–1.735; ho 1.688–1.691	勝井 (1958); Arai et al. (1986)
大山倉吉 (DKP)	43–55 (U, ST)	pfl, pfa	>20	pm; 1.508–1.514	ho, opx, (bi); opx 1.702–1.708; ho 1.673–1.680	町田・新井 (1979)
阿蘇4 (Aso-4)	85–90 (ST, FTなど)	pfl, afa (coign.)	>600	bw, pm; 1.506–1.510	ho, opx, cpx; opx 1.699–1.701; ho 1.685–1.691	町田ほか (1985)
鬼界葛原 (K-Tz)	90–95 (ST, TL)	afa (pp), pfl, afa (coign.)	150?	bw, pm; 1.494–1.500	opx, cpx; qt; opx 1.705–1.709	町田・新井 (1992)
御岳第1 (On-Pm1)	c.95 (FT, KA)	pfa	50	pm, (bw); 1.500–1.503	ho, bi, (opx); opx 1.706–1.711; ho 1.681–1.690	小林ほか (1967); 町田 (1990)
三瓶木次 (SK)	c.100 (ST)	pfa	20	pm; 1.494–1.498	bi; qt	豊倉ほか (1991)
阿多 (Ata)	c.105 (ST)	afa (pp), pfa, pfl, afa (coign.)	>300	bw, pm; 1.508–1.512	opx, cpx, (ho); opx 1.704–1.708	Ota and Machida (1987)
洞爺 (Toya)	90–120 (FT, ST)	afa (pp), pfl, afa (coign.)	>150	pm, bw; 1.494–1.498	(opx, cpx, ho; qt); opx 1.711–1.761; ho 1.674–1.684	町田ほか (1987)
阿蘇3 (Aso-3)	105–125 (FT, ST)	pfa, pfl, afa (coign.)	>150	pm, bw; 1.512–1.540	opx, cpx; opx 1.702–1.705	町田・新井 (1992, 1994)
クッチャロ羽幌 (Kc-Hb)	100–130 (FT, ST)	afa·pfa, pfl, afa (coign.)	>150	bw, pm; 1.502–1.506	opx, cpx; opx 1.705–1.710	勝井・佐藤 (1963); Arai et al. (1986); Okumura (1988)

Table 4. Widespread tephras from giant eruptions in Japan during the middle and early Quaternary

(Revised and supplemented from Machida and Arai, 1992.)

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English translation of figure lettering

Tephra (symbol)	Age, ka (dating method)	Eruption/deposition modes and sequence	Total tephra volume (bulk, km³)	Juvenile tephra: volcanic glass, n	Juvenile tephra: phenocrysts	References and other information
Ata-Torihama (Ata-Th)	230–250 (ST, FT)	pfa, pfl, afa (coign.)	≫100	bw, pm; 1.498–1.500	ho, opx, bi; qt; opx 1.714–1.718; ho 1.670–1.674	Machida and Arai (1992)
Aso-1 (Aso-1)	260–280 (FT)	pfa, afa, pfl, afa (coign.)	≫100	pm, bw; 1.518–1.521	(cpx, opx); opx 1.710–1.715	Shirai and Tada (1996); Fukuoka et al. (1996). Lake Biwa, mountains of central Japan, Oga Peninsula, Sea of Japan
Ng-1 (Ng-1)	260–300 (ST)	? afa	?	pm; 1.498–1.499	bi, ho; ho 1.685–1.687	Mizuno and Yoshikawa (1991). Osaka Group [Hatta and Wada], Oiso [Tl1 58 up], Ehime [Nomura 2]
Kakuto (Kkt)	>300 (FT)	pfl, afa (coign.)	≫100	bw, pm; 1.500–1.501	opx, cpx, (ho); opx 1.718–1.725	Machida and Arai (1992)
Omachi APm tephra group (A₁Pm–A₅Pm)	Mainly >300 (FT, ST)	pfa, partlypfl	?	pm; 1.497–1.499	bi, ho, opx; qt; opx 1.730–1.734; ho 1.688–1.693	Suzuki and Hayakawa (1990). Refractive-index values are for A₃Pm
Kobayashi-Kasamori (Kb-Ks)	400–500 (FT)	pfa, pfl, afa (coign.)	≫100	bw, pm; 1.503–1.507	bi, ho; ho 1.677–1.685	Machida and Arai (1992). Osaka Group [Sakura], Kazusa Group [Kasamori 11]
Seiganji–Toga (Se-Tg)	c.600 (FT)	pfa	?	pm; 1.500–1.505 (1.501–1.502)	(ho, bi); ho 1.671–1.677	Mizuno et al. (1989); Yoshikawa et al. (1991). Hiroshima [Okago (岡郷)], Osaka [Toga]
Shishimuta-Azuki (Ss-Az)	c.900 (FT, KA, ST)	pfa, pfl	≫100	bw, pm; 1.512–1.516 (1.513–1.515)	(opx, cpx); opx 1.706–1.710	Shimokawa et al. (1986); Kamata et al. (1994). Oita [Magari, Imaichi], Osaka Group [Azuki], Kazusa Group [Kokumoto Ku6C]
Yabakei-Pink (Yb-Pk)	1 Ma (FT, ST)	afa, pfl, afa (coign.)	≫100	bw, pm; 1.500–1.502	ho, opx; opx 1.706–1.709; ho 1.674–1.679	Kamata (1989); Kikkawa et al. (1993); Danhara et al. (1992). Osaka Group [Pink], Kazusa Group [Otadai 7]
Fukuda (Fkd)	1.75 Ma (FT, ST)	pfl, afa	?	pm, bw; 1.502–1.504	(ho, opx, cpx); opx 1.755; ho 1.689–1.695	Yoshikawa et al. (1995). Niigata [Tsujimatagawa], Kazusa Group [Kiwada 38]. Refractive-index values are for Tsujimatagawa

Abbreviations for Tables 3 and 4

• Dating methods: C, radiocarbon; FT, fission track; KA, potassium–argon; TL, thermoluminescence; ST, age inferred from stratigraphic position based on radiometric ages, biostratigraphy, magnetostratigraphy, etc.; U, uranium series; V, varve chronology.
• Eruption/deposition modes are listed in eruption order: pfa, pumice fall; pfl, pyroclastic-flow deposit; afa, ash fall; pp, phreatoplinian ash; coign., ash fall contemporaneous with a large pyroclastic flow; afa·pfa, alternating eruptions of the two types.
• Volcanic glass: pm, pumice-type glass; bw, bubble-type glass. Numerical n values are refractive indices. Parentheses indicate minor components.
• Phenocrysts: af, alkali feldspar; am, amphiboles; ho, hornblende; cpx, clinopyroxene; opx, orthopyroxene; bi, biotite; qt, quartz. Parentheses indicate minor components. Numerical values are refractive indices (n₁ for af, γ for opx, and n₂ for ho; measured by Fusao Arai).

Original Japanese lettering

テフラ名（記号）	年代 ka（測定方法）	噴火・堆積様式と順序	全テフラ量（みかけ、km³）	本質テフラ粒：火山ガラス、n	本質テフラ粒：斑晶	文献・その他
阿多鳥浜 (Ata-Th)	230–250 (ST, FT)	pfa, pfl, afa (coign.)	≫100	bw, pm; 1.498–1.500	ho, opx, bi; qt; opx 1.714–1.718; ho 1.670–1.674	町田・新井 (1992)
阿蘇1 (Aso-1)	260–280 (FT)	pfa, afa, pfl, afa (coign.)	≫100	pm, bw; 1.518–1.521	(cpx, opx); opx 1.710–1.715	白井・多田 (1996); 福岡ほか (1996)。琵琶湖、中部山岳、男鹿半島、日本海
Ng-1 (Ng-1)	260–300 (ST)	? afa	?	pm; 1.498–1.499	bi, ho; ho 1.685–1.687	水野・吉川 (1991)。大阪層群〔八田・和田〕、大磯〔Tl1 58 up〕、愛媛〔野村2〕
加久藤 (Kkt)	>300 (FT)	pfl, afa (coign.)	≫100	bw, pm; 1.500–1.501	opx, cpx, (ho); opx 1.718–1.725	町田・新井 (1992)
大町APm群 (A₁Pm–A₅Pm)	主として>300 (FT, ST)	pfa, 一部pfl	?	pm; 1.497–1.499	bi, ho, opx; qt; opx 1.730–1.734; ho 1.688–1.693	鈴木・早川 (1990)。屈折率の値はA₃Pm
小林笠森 (Kb-Ks)	400–500 (FT)	pfa, pfl, afa (coign.)	≫100	bw, pm; 1.503–1.507	bi, ho; ho 1.677–1.685	町田・新井 (1992)。大阪層群〔サクラ〕、上総層群〔笠森11〕
誓願寺–栂 (Se-Tg)	c.600 (FT)	pfa	?	pm; 1.500–1.505 (1.501–1.502)	(ho, bi); ho 1.671–1.677	水野ほか (1989); 吉川ほか (1991)。広島〔岡郷〕、大阪〔栂〕
猪牟田アズキ (Ss-Az)	c.900 (FT, KA, ST)	pfa, pfl	≫100	bw, pm; 1.512–1.516 (1.513–1.515)	(opx, cpx); opx 1.706–1.710	下川ほか (1986); 鎌田ほか (1994)。大分〔曲、今市〕、大阪層群〔アズキ〕、上総層群〔国本 Ku6C〕
耶馬渓ピンク (Yb-Pk)	1 Ma (FT, ST)	afa, pfl, afa (coign.)	≫100	bw, pm; 1.500–1.502	ho, opx; opx 1.706–1.709; ho 1.674–1.679	Kamata (1989); Kikkawa et al. (1993); 檀原ほか (1992)。大阪層群〔ピンク〕、上総層群〔大田代7〕
福田 (Fkd)	1.75 Ma (FT, ST)	pfl, afa	?	pm, bw; 1.502–1.504	(ho, opx, cpx); opx 1.755; ho 1.689–1.695	Yoshikawa et al. (1995)。新潟〔辻又川〕、上総層群〔黄和田38〕。屈折率の値は辻又川

表3・4の略記

• 年代測定法：C＝放射性炭素法；FT＝フィッショントラック法；KA＝カリウムアルゴン法；TL＝熱ルミネッセンス法；ST＝放射年代、生層序、地磁気層序などに基づく層位からの推定；U＝ウラン系列法；V＝年縞法。
• 噴火・堆積様式：噴火順に示した。pfa＝降下軽石；pfl＝火砕流堆積物；afa＝降下火山灰；pp＝水蒸気プリニアン火山灰；coign.＝大火砕流と同時の降下火山灰；afa·pfa＝交互に噴出したことを示す。
• 火山ガラス：pm＝軽石型ガラス；bw＝バブル型ガラス。数値nは屈折率。括弧内は少量含まれるもの。
• 斑晶：af＝アルカリ長石；am＝角閃石類；ho＝普通角閃石；cpx＝単斜輝石；opx＝斜方輝石；bi＝黒雲母；qt＝石英。括弧内は少量含まれるもの。数値は屈折率（afはn₁、opxはγ、hoはn₂の値を示す。測定者：新井房夫）。

Reading notes

Ng-1の対比欄、大磯［Tl1 58 up］ — 細い縦画が判別しづらく、Tl1の末尾は数字1/小文字lの可能性が残る。原図も併載し、符号の読みを確定していない。

Abbreviations for Tables 3 and 4

• Dating methods: C, radiocarbon; FT, fission track; KA, potassium–argon; TL, thermoluminescence; ST, age inferred from stratigraphic position based on radiometric ages, biostratigraphy, magnetostratigraphy, etc.; U, uranium series; V, varve chronology.
• Eruption/deposition modes are listed in eruption order: pfa, pumice fall; pfl, pyroclastic-flow deposit; afa, ash fall; pp, phreatoplinian ash; coign., ash fall contemporaneous with a large pyroclastic flow; afa·pfa, alternating eruptions of the two types.
• Volcanic glass: pm, pumice-type glass; bw, bubble-type glass. Numerical n values are refractive indices. Parentheses indicate minor components.
• Phenocrysts: af, alkali feldspar; am, amphiboles; ho, hornblende; cpx, clinopyroxene; opx, orthopyroxene; bi, biotite; qt, quartz. Parentheses indicate minor components. Numerical values are refractive indices (n₁ for af, γ for opx, and n₂ for ho; measured by Fusao Arai).

b. Widespread tephras

Widespread tephras are deposits from extremely large eruptions, with total erupted tephra volumes reaching 10–1,000 km³, and commonly extend over an area larger than a single region. Because many tephras are dispersed eastward by westerly winds, however, even a large deposit may extend predominantly over the sea rather than across several land regions. Figure 1 shows the distribution of late Quaternary widespread tephras in Japan and adjacent regions.

As shown in Table 3, 17 widespread tephras that fell during the past 125,000 years (the late Quaternary) have now been identified. In recent years, tephras long known in the Osaka and Kazusa groups, such as Kobayashi-Kasamori (Kb-Ks), Shishimuta-Azuki (Ss-Az), and Yabakei-Pink (Yb-Pk), have been traced as far as Kyushu (Table 4). Nearly 30 widespread tephras are known for the Quaternary as a whole. Detailed tephra-based time scales combining widespread tephras with local tephra stratigraphies of various scales, and the application of tephrochronology based on regional “standard tephra stratigraphies,” have become indispensable.

c. Modes of tephra deposition

Matsuda and Nakamura (1966) classified the processes from volcanic eruption to tephra deposition according to where the material was erupted, how it was transported, and the type of setting in which it was deposited. Eruption sites are divided into terrestrial (A) and subaqueous (W). Transport is divided into travel through the air from an eruption column (A) and transport through water (W). Deposition is divided into deposition on dry land (A) and in water (W). These three elements are expressed by arranging their symbols in this order. Thus, material erupted on land, transported through the air, and deposited on dry land is type AAA. A subaqueous eruption followed by airborne (wind) transport and deposition in water is type WAW.

Frequently, only the transport and deposition processes are expressed, omitting the eruption site. In that usage, type AA means airborne transport and deposition on land, while type WW means transport through water and deposition in water.

Stranded pumice (drift pumice) is described in WS-12-2, WS-13-4, and TH-15. These are examples of AWW and AAW tephras. Tephra is well preserved in peat, and this book presents many examples. Tephra falls into damp settings such as wetlands or shallow water and is deposited there without further transport. This may be considered intermediate between AA and AW, and is sometimes called “water-associated tephra” (mizutsuki tephra, 水つきテフラ). Identifying the depositional environment helps reveal the processes of emergence and conversion to land following a rise in sea level.

The environment in which tephra is deposited produces large differences in its weathering conditions. Depositional settings favorable for preservation include (1) quiet-water environments (swamps and peatlands, lake beds, and deep-sea floors), (2) places where material covering the tephra accumulates rapidly (near volcanoes, in dunes, and elsewhere), and (3) cold regions, where weathering proceeds slowly. Poor preservation occurs in (1) terrestrial settings generally, especially projecting features such as ridges, cliff edges, steep slopes, and windward slopes; (2) tropical and subtropical regions, where weathering is rapid; and (3) urban areas, where material is removed by human activities. On land, weathering may destroy the volcanic glass that constitutes the main component of tephra, leaving only minerals. Conversely, particular minerals may dissolve, destroying the original mineral assemblage. Care is therefore necessary. Tephra deposited under water is also strongly affected by sorting according to particle density and size; coarse, low-density pumice does not necessarily accumulate together with fine volcanic ash.

Table 5. Methods of tephra identification (expanded from Machida and Arai, 1992)

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English translation of figure lettering

Method	Level or criterion	Features observed or analyzed
Stratigraphic methods (mainly field investigation)	Stratigraphic position	Stratigraphy: distinction of fall and flow units, beds, and members; buried soils; stratigraphic relationships
Same	Age	Various radiometric ages, microfossil ages, paleomagnetic ages, and ages of cultural horizons
Same	Facies	Thickness, grain size, color, apparent density, fallout units, types and proportions of juvenile/accessory/accidental material, weathering, induration, and sedimentary structures
Petrographic methods (mainly laboratory investigation)	Rock level: texture	Vesiculation style, vesicularity, phenocryst/glass ratio, and groundmass texture
Same	Rock level: mineral assemblage	Ratios of phenocryst minerals and of heavy to light minerals
Same	Rock level: chemical composition	Whole-rock analysis: XRF and wet-chemical methods
Same	Volcanic-glass and mineral level: morphology	Crystal habit; shape, color, and crystallite characteristics of volcanic glass
Same	Volcanic-glass and mineral level: refractive index	Volcanic glass and minerals, including pyroxenes and amphiboles
Same	Volcanic-glass and mineral level: thermomagnetic properties	Curie temperatures of ferromagnetic minerals, etc.
Same	Volcanic-glass and mineral level: chemical composition	Relative abundances of major and trace elements in volcanic glass and phenocryst minerals: EPMA, XRF, AA, ICP, INAA
Same	Volcanic-glass and mineral level: other properties	Lattice constants of particular minerals, Sr isotope ratios of volcanic glass, etc.

Original Japanese lettering

方法	レベル・項目	観察・分析する特徴
層位学的方法（主に野外調査による）	層位	層序：降下・流下単位／単層／部層の区分、埋没土壌、層位関係
同上	年代	各種放射年代、微化石年代、古地磁気年代、文化層年代
同上	層相	層厚、粒度、色調、見掛け密度、降下ユニット、本質／類質／異質物質の種類と割合い、風化度、固結度、堆積構造
岩石記載的方法（主に室内実験による）	岩石レベル：組織	発泡様式、発泡度、斑晶・ガラス比、石基組織
同上	岩石レベル：鉱物組合せ	斑晶鉱物比、重・軽鉱物比
同上	岩石レベル：化学組成	全岩分析：XRF、湿式
同上	火山ガラス・鉱物レベル：形態	晶癖、火山ガラスの形・色・晶子の特徴
同上	火山ガラス・鉱物レベル：屈折率	火山ガラス、鉱物：輝石、角閃石など
同上	火山ガラス・鉱物レベル：熱磁気的性質	強磁性鉱物のキュリー温度など
同上	火山ガラス・鉱物レベル：化学組成	火山ガラス、斑晶鉱物などの主要元素や微量元素の量比：EPMA、XRF、AA、ICP、INAA
同上	火山ガラス・鉱物レベル：その他	特定鉱物の格子常数値、火山ガラスのSr同位体比など

d. Tephra identification

Identification of tephra requires an integrated examination, beginning with the characteristics of the stratigraphic unit, proceeding to the various properties of individual pumice, scoria, and ash particles, and extending to the properties of their constituent volcanic glass and phenocryst and microphenocryst minerals (Table 5). We wish to emphasize the importance of thoroughly establishing the tephra stratigraphy and all characteristics observable in the field before undertaking laboratory analysis. For details of analytical methods, see Methods for the Analysis of Quaternary Samples (Editorial Committee for Methods for the Analysis of Quaternary Samples, 1993a).

e. Dating methods

Tephras whose stratigraphy is established serve as marker beds and key beds for correlating landforms and strata and assigning ages to them. This is because many tephras have been dated and checked directly or indirectly by radiometric methods—including radiocarbon (¹⁴C), fission-track (FT), thermoluminescence (TL), and uranium-series methods—as well as paleomagnetic chronology, archaeological methods, and their positions within oxygen isotope stratigraphy. For details, see Methods for the Analysis of Quaternary Samples (Editorial Committee, 1993b).

3. Future research issues

With the successive recognition of widespread tephras of the early and middle Quaternary and the identification of tephra in marine sediments, Japanese tephrochronology may be said to have begun ascending to its next stage (Machida and Arai, 1992). This book describes a considerable number of such tephras, including Ata-Torihama (Ata-Th; 230–250 ka), Seiganji–Toga (Se-Tg; approximately 0.6 Ma), and Shishimuta-Azuki (Ss-Az; approximately 1 Ma). These nevertheless represent only a small fraction of the tephras described, and further discoveries are awaited.

Although tephra research has advanced greatly, many problems and tasks remain: tephras with unknown sources, unknown ages, or poorly understood distributions and eruption styles, among others. Only a very small number are well understood in terms of their effects on people and their lives. The older the period, the more unresolved questions accumulate. We hope readers will learn from this book both what has become known and what remains unknown.

Future work will need to focus on tephras in marine areas such as the Pacific Ocean, the Sea of Japan, and the Sea of Okhotsk, and in lake sediments. Large-scale volcanism and global upper-atmospheric winds must have transported and deposited tephra on a hemispheric scale. Research on these exceptionally widespread tephras is another task. It is also necessary to establish how such volcanic activity affected the Earth's environment, vegetation, and human life, and what benefits and disasters it brought. At the global scale, tephra in ice-sheet cores is a further subject for future work. Moreover, a succession of tephras directly records the activity history of a volcano, leaving substantial scope for volcanological research. Another issue concerns the brown loam layers widely distributed on the Sea of Japan side of the archipelago, which recent research has suggested are derived from loess. The stratigraphy of this loess (loam) is being elucidated by intercalated tephras and paleosols. The establishment of a new time scale combining loess and tephra is anticipated.

References

• Machida, H. (町田洋) (1971). Tephrochronology of southern Kanto I: Sources and stratigraphic ages of tephras since the Shimosueyoshi period. The Quaternary Research, 10: 1–20.
• Machida, H., and Arai, F. (町田洋・新井房夫) (1976). Widespread volcanic ash: Discovery of the Aira-Tn ash and its significance. Kagaku (科学), 46: 339–347.
• Machida, H., and Arai, F. (1992). Atlas of Tephra: The Japanese Archipelago and Its Surroundings (火山灰アトラス―日本列島とその周辺). University of Tokyo Press, 276 pp.
• Matsuda, T., and Nakamura, K. (松田時彦・中村一明) (1966). Characteristics and classification of volcanic deposits accumulated under water. Mining Geology (鉱山地質), 20: 129–142.
• Editorial Committee for Methods for the Analysis of Quaternary Samples (第四紀試料分析法編集委員会) (1993a). Tephra. In Japan Association for Quaternary Research (ed.), Methods for the Analysis of Quaternary Samples 2 (第四紀試料分析法2). University of Tokyo Press, pp. 136–224.
• Editorial Committee for Methods for the Analysis of Quaternary Samples (1993b). Dating methods. In Japan Association for Quaternary Research (ed.), Methods for the Analysis of Quaternary Samples 1 (第四紀試料分析法1). University of Tokyo Press, pp. 51–68.

II. A guide to using this book

The 274 outcrops included in this book extend throughout the Japanese archipelago, from Hokkaido in the north to Ishigakijima in the southwestern islands in the south. They include both surviving and vanished exposures. Although the focus is on tephra-bearing outcrops, some contain no tephra. This section explains the tephra names, age notation, and citation practices used in the book.

1. Tephra names

It is not uncommon for a single tephra to have several names. In particular, the recent discovery of widespread tephras in regions with a long history of Quaternary stratigraphic research has created circumstances in which established local names and new widespread-tephra names must be used together. Regional differences in names and informal names, and differences in tephra numbering between researchers, have their respective histories and are in some respects unavoidable. Nevertheless, it is preferable for the same tephra to bear the same name; at the very least, failure to clarify the relationships between names causes inconvenience to those using them. In their Atlas of Tephra, Machida and Arai (1992) presented a standardized naming scheme. In principle, a tephra name combines the name of its source volcano with the locality name of its reference exposure or discovery site. Abbreviations are given on the same basis: for example, the Aira AT tephra (AT) and Kikai-Tozurahara tephra (K-Tz). Many tephras, however, have unknown source volcanoes, and efforts to identify them are needed. At the same time, with some exceptions, “… ash” was expressed as “… tephra.” Since the names proposed in the Atlas currently provide a common standard for the largest number of tephras, this book gives both established tephra names and those used in that volume. Treatment of tephras described regionally under well-established names is not straightforward. Standardization should be sought, but further consideration is needed.

2. Age notation

Radiocarbon (¹⁴C) ages are expressed, for example, as 2,980 ± 150 yr B.P. (GaK-55555). This gives the number of years before AD 1950. The parenthetical expression is the laboratory's sample code. In general, it is impossible to list every available age determination, so an appropriate representative value or a range is often given. In these cases, and also for other dating methods, ages on the scale of tens to hundreds of thousands of years are expressed in ka. One ka means 1,000 years; 25 ka means 25,000 years ago, and 175 ka means 175,000 years ago. Ma is used for units of one million years. Where ages are given in Ma, some ages of several hundred thousand years are also expressed in Ma for comparison.

The dating method used is indicated as far as possible. In addition to radiometric methods, these include paleomagnetic dating, archaeological chronology, and loess chronometry. Radiocarbon ages are based on Libby's half-life and are generally given without calibration. Where calibration has been applied, this is stated.

3. Citing this book

The nature of the description varies between outcrops, ranging from reviews based on previously published work to original accounts first published here. Even in the former case, the original description may have been expanded or revised, and photographs, sketches, or stratigraphic columns may be original. In all cases, responsibility for the content rests with the author of the individual outcrop description. Citations to this book must therefore be made at the level of the individual outcrop entry. Where an original description is cited, readers should consult and cite the original source.

Precautions for outcrop investigations and visits

In general, the outcrops described in this book are not places where readers may freely enter or collect samples. Before visiting, obtain permission from the landowner or manager. Explain the purpose of the visit, including the information you hope to obtain, and help them understand the importance of outcrop investigation. In every case, treat the exposure with care, keep cleaning and sampling to the necessary minimum, restore the site by backfilling where appropriate after the investigation, leave it tidy, and express your thanks. At localities yielding rare fossils in particular, avoid purposeless collection or destruction of finite research material. Conduct that might lead to visits being prohibited because of a few inconsiderate individuals must be strictly avoided.

Outcrops are places where danger is close at hand: investigators may slip and fall, encounter falling rocks, or enter habitats of poisonous plants or animals. The exposures introduced in this book are not necessarily safe. Investigations and visits should be undertaken at your own responsibility and with due attention to safety. When organizing group visits, give careful consideration to safety measures and encourage participants to take out accident insurance in advance.

1. Widespread Tephras in Japan

WS-1-1 Baitoushan–Tomakomai Tephra on the Eastern Foot of Changbai Mountain, China

Hiroshi Machida

• Locality: Yuanchi (圓池), southern Antu County, Jilin Province, People's Republic of China
• Latitude and longitude: N42°1′30″ E128°27′30″
• Elevation: approximately 1,250m
• Outcrop type and current condition: pumice extraction site; extant
• Deposit types and age: pumice fall and pyroclastic-flow deposits; first half of the 10th century
• Date of description: 1994
• Keywords: Changbai Mountain; Baitoushan; Baitoushan pumice fall; Changbai pyroclastic-flow deposit; Baitoushan–Tomakomai tephra (白頭山苫小牧テフラ)

Changbai Mountain volcano (Korean name: Baekdusan (白頭山)) is the volcanic cone forming the highest peak in a major volcanic region straddling the border between northeastern China and North Korea. Its summit contains a caldera (Tianchi) 4–5km in diameter, and the highest peak on the caldera rim reaches 2,749m. The volcano has extensive lower slopes, passing into a vast basalt lava plateau 30–50km from the summit. Volcanic activity in this region began in the early Miocene or later and formed a lava plateau consisting of numerous shield volcanoes. With time, however, explosive eruptions of trachyte and rhyolite became more frequent, forming several volcanic cones. Baitoushan is the youngest of these large volcanoes. Records suggest eruptions in 1597, 1668, and 1702, but before these it produced an enormous eruption in the first half of the 10th century, ejecting pumice fall and large-scale pyroclastic flows. The co-ignimbrite ash from that eruption is widely distributed on the floor of the northern Sea of Japan and in northern Japan.

The extensive volcanic slopes and foot are covered by this young pyroclastic-flow deposit. Near Yuanchi on the China–North Korea border at the eastern foot, approximately 30km east of the summit of Changbai Mountain, several outcrops permit a comprehensive observation of the stratigraphy of these tephra layers. Figure 2 shows the distribution of these tephras and the outcrop locations. There, the Changbai pyroclastic-flow deposit (unit C), the preceding Baitoushan Plinian pumice-fall deposit (unit B), and pumice-fall and scoria layers (unit E) separated from them by a thin soil can be observed (Fig. 1). B is the first product of the series of major eruptions and is a pure white, alkali-rhyolitic pumice-fall deposit. Its principal distribution axis extends southeastward, and it is thick within North Korean territory. At this outcrop the pyroclastic-flow deposit is thin because it lies at the edge of its distribution, but on the mountain foot farther west and northwest it is several tens of metres thick. The lower part of the Changbai pyroclastic-flow deposit is a pumice-flow deposit containing abundant grayish-white felsic pumice clasts; upward it grades into a scoria-flow deposit consisting mainly of dark glassy volcanic ash. Both are nonwelded and fill the upper valleys of rivers such as the Yalu (鴨緑江) and Songhua (松花江), developing terrace landforms and badlands (Fig. 2). Meanwhile, large volumes of volcanic mudflow material generated from the pyroclastic flows (unit D) travelled farther down these valleys. These deposits can be traced even more than 100km from the volcano, indicating that the disaster extended along rivers to distant lowlands. The Changbai pyroclastic-flow deposit also contains abundant charred wood (Fig. 3), and the region east of Changbai Mountain is now an extensive area of pure larch forest. This suggests that destruction of vegetation by the eruption affected a vast area.

The tephra of unit E shown in Figure 1 consists of 2–4 pumice-fall and volcanic-ash layers. They are probably products of the eruptions recorded in historical documents. Their distribution is confined to the eastern side of Changbai Mountain and is not very extensive.

References: 町田・新井 (1992); 町田ほか (1981); Machida et al. (1990); 町田・新井 (1992)

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English translation of figure lettering

0m; 1; 2; 3; 4; 5 E-6; E-5; E-4; E-3; E-2; E-1 — Yuanchi plinian fall C-pfl: Changbai pyroclstic flow B-pfa: Baegudu plinian fall A-dfl: Erdaobaihe debris flow soil; older tephra fall

Original Japanese lettering

0m; 1; 2; 3; 4; 5 E-6; E-5; E-4; E-3; E-2; E-1 — Yuanchi plinian fall C-pfl: Changbai pyroclstic flow B-pfa: Baegudu plinian fall A-dfl: Erdaobaihe debris flow soil; older tephra fall

Figure 1. Stratigraphy of products of the major Baitoushan eruption approximately 1000 years ago (partly modified from Machida et al., 1990).

Unit E probably represents products of the eruptions of 1597, 1668, and 1702.

[Original printed page: 2]

WS-1-1 (continued)

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WS-1-1; N; Baitoushan (Changbai Mountain); Yuanchi (圓池); Changbai; Yalu River; Tumen River; B; >0; 100; 200; 1000; 1500; 2000; 0; 30km

Original Japanese lettering

WS-1-1; N; 白頭山（長白山）; 圓池; 長白; 鴨緑江; 豆満江; B; >0; 100; 200; 1000; 1500; 2000; 0; 30km

Reading notes

豆満江 — 地図の薄い河川名は低コントラストで一部不鮮明；読みは暫定。

Figure 2. Distribution of products of the major Baitoushan eruption approximately 1000 years ago.

Solid lines are isopachs (cm) of the preceding fallout tephra. The screened area represents the Changbai pyroclastic-flow deposit. ● indicates the distribution of mudflow deposits. ▲ indicates deposits of the rock avalanche that occurred immediately before the eruption.

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Figure 3. Wood buried in the pyroclastic-flow deposit (mostly charred).

Original Japanese lettering

図3 火砕流堆積物に埋まった材（大部分炭化している）

Figure 3. Wood buried in the pyroclastic-flow deposit (mostly charred).

[Original printed page: 3]

WS-1-2 Baitoushan–Tomakomai Tephra in the Alluvial Deposits of Tomakomai Port

Hiroshi Machida

• Locality: Tomakomai Port, Tomakomai City, Hokkaido
• Latitude and longitude: N42°39′8″ E141°42′3″
• Elevation: 1–2m
• Outcrop type and current condition: cliff exposed during quay construction; unknown
• Deposit types and age: volcanic ash, pumice, and peat; first half of the 10th century
• Date of description: 1979–1980
• Keywords: Baitoushan–Tomakomai tephra; Tarumae-b tephra; Tarumae-c tephra

This outcrop is the type locality from which the tephra takes its name. It lies at the innermost (eastern) part of Tomakomai Port and exposes a section through the alluvial deposits of the Yufutsu Plain. The uppermost pumice layer is Tarumae-b (Ta-b) of AD1667; the lower pumice layer enclosed within thick peat is Tarumae-c (Ta-c), erupted at 2.5–3ka. Baitoushan–Tomakomai tephra (B-Tm) can be observed somewhat discontinuously as a white volcanic-ash layer 2–3cm thick in the upper part of the thick peat layer in the photograph, where the shovel has been inserted. In the alluvial lowlands of Hokkaido it commonly occurs well preserved within peat, as at this outcrop (see Biruwa, HK-10); on uplands it can also commonly be found as a yellowish-white volcanic-ash layer. Its foremost petrographic characteristic is the alkali-rich volcanic glass; under the microscope it is characterized by fine-grained glass with few phenocrysts, strong curvature, and abundant striations. This tephra occurs in Satsumon pottery cultural layers in Hokkaido and in Haji pottery cultural layers in northern Honshu. It is therefore also important for correlating the two cultures.

References: 町田ほか (1980); Machida et al. (1987)

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1:50,000 “Tomakomai” map sheet (Tomakomai No. 5); golf course

Original Japanese lettering

5万分の1『苫小牧』（苫小牧5号）; ゴルフ場

1:50,000 “Tomakomai” map sheet (Tomakomai No. 5).

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English translation of figure lettering

Ta-b; ←B-Tm; Ta-c

Original Japanese lettering

Ta-b; ←B-Tm; Ta-c

[Original printed page: 4]

WS-1-3 Baitoushan–Tomakomai Tephra and Towada-a Tephra in the Tashirotai Wetland, Hakkoda

Hiroshi Machida

• Locality: Tashirotai, Aomori City
• Latitude and longitude: N40°38′30″ E140°55′17″
• Elevation: 570m
• Outcrop type and current condition: along a small stream in peatland and in a roadside ditch; extant
• Deposit types and age: glassy volcanic ash; first half of the 10th century
• Date of description: 1980 onward
• Keywords: Baitoushan–Tomakomai tephra; Towada-a tephra; peat layer

The Tashirotai Wetland at the northeastern foot of Hakkoda volcano developed within the Tashirotai caldera and preserves useful paleoenvironmental records, including tephra (八甲田湿原研究グループ, 1969). In the raised peatland here, two extremely thin volcanic-ash layers occur one above the other at the top of strongly decomposed deposits (black mud). In the low-lying peatland, however, peat deposition continues today, so these ashes can be observed clearly separated. The upper yellowish-white volcanic-ash layer is Baitoushan–Tomakomai tephra (B-Tm), and the lower white volcanic-ash layer is Towada-a ash (To-a) (町田ほか, 1981). The characteristics of the former differ little from those in Hokkaido (see Tomakomai Port, WS-1-2). The latter is somewhat coarser than the former, contains phenocrysts such as pyroxene, is somewhat colored, and consists of thick volcanic-glass shards.

To-a is a tephra that widely covers the six prefectures of Tohoku. It occurs within Heian-period cultural layers or overlying artifacts of that period, as at the Tagajo archaeological site. At Mutsu Kokubunji in particular it intervenes between artifact-bearing layers thought to date to 870 and 934 (白鳥, 1980). Moreover, wood from houses buried by the pyroclastic-flow and mudflow deposits accompanying To-a (see Kemanai, TH-13) is known to yield a tree-ring date of >903AD (奈良文化財研究所, 1990). The tephra eruption is therefore considered to correspond to the account in the Fusō Ryakki reporting from Dewa Province in Engi 15 (915) that ash fell to a depth of 2 sun, and so forth. If To-a is an AD915 eruptive product, the eruption of B-Tm immediately above it is considered to have occurred several to ten-odd years after To-a. The two tephras occur superposed with an observable stratigraphic relationship in the field mainly within Aomori Prefecture.

References: 八甲田湿原研究グループ (1969); 町田ほか (1981); 奈良文化財研究所 (1990); 白鳥 (1980)

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Tashiro Motoyu; Tashirotai hot spring; Hakkoda hot spring; wetland plant community; Tashirotai; Koma River (駒川); 563; 596.1; 1:50,000 “Aomori Tobu” (Aomori No. 4)

Original Japanese lettering

田代元湯; 田代平温泉; 八甲田温泉; 湿原植物群; 田代平; 駒川; 563; 596.1; 5万分の1『青森東部』（青森4号）

1:50,000 “Aomori Tobu” map sheet (Aomori No. 4).

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←B-Tm; ←To-a

Original Japanese lettering

←B-Tm; ←To-a

[Original printed page: 5]

WS-2-1 Kikai-Akahoya Tephra on Takeshima, Kikai Caldera, Southern Kyushu

Hiroshi Machida

• Locality: Takeshima, Mishima Village, Kagoshima Prefecture
• Latitude and longitude: N30°48′25″ E130°24′54″
• Elevation: 80m
• Outcrop type and current condition: sea cliff and roadside; extant
• Deposit types and age: fallout tephra and pyroclastic-flow deposits; 6.3ka
• Date of description: 1976
• Keywords: Kikai-Akahoya tephra; Funakura pumice fall; Funakura pyroclastic-flow deposit; Takeshima pyroclastic-flow deposit; Nagase pyroclastic-flow deposit

Around Kikai caldera, the source of Kikai-Akahoya tephra, the stratigraphy and facies of this tephra can be observed best on Takeshima. These have been described in detail by 小野ほか (1982). Although this tephra can be observed at various places on the island, the outcrop facing Funakura Port on its northern side is described here (Fig. 1). As shown in Figure 2, the tephra overlying the kuroboku (black humic soil) layer comprises, from bottom to top, Plinian pumice fall (Funakura pumice fall), welded tuff (Funakura pyroclastic flow), and a nonwelded pyroclastic-flow deposit (Takeshima pyroclastic flow). A glassy volcanic-ash layer can sometimes be seen above the pyroclastic-flow deposit, but it is rather discontinuous. Pumice at every horizon is extremely well vesiculated and light. The total thickness at this outcrop is slightly more than 10m, but the thickness of the pyroclastic-flow deposit varies with the terrain and exceeds 30m in places. In some places the Takeshima pyroclastic-flow deposit also truncates protruding parts of the underlying beds and overlies them unconformably (Fig. 3). The principal distribution axis of the Plinian pumice fall is east-southeastward; it also occurs on the Osumi Peninsula (see Onejime, WS-2-2). Rather than all of the material identified as the Funakura pyroclastic-flow deposit having been deposited by pyroclastic flow, some portions are welded pumice fall.

The Takeshima pyroclastic flow was the product of an enormous eruption. Many lithic fragments within it are rounded (Figs. 2, 3). This suggests that the eruption occurred on a shallow seabed and entrained deposits from submarine wave-cut platforms. This pyroclastic flow crossed the sea, travelling to and depositing on Yakushima as well as the Osumi and Satsuma peninsulas. In Osumi and Satsuma it corresponds to what was called the Koya pyroclastic-flow deposit (宇井, 1973). Characteristics of these eruptive deposits include a small aspect ratio and the release of large quantities of glassy volcanic ash into the atmosphere, forming ash fall. This fallout ash is the Kikai-Akahoya tephra (K-Ah), which widely covered the Japanese archipelago and surrounding seabed (町田・新井, 1978).

The tephra labeled Nagase pyroclastic flow below the Funakura pumice fall in Figure 3 is a large-scale white rhyolitic tephra and the source of Kikai-Tozurahara ash (K-Tz), described later. Several fallout tephras are also recognized in the kuroboku layer overlying the Takeshima pyroclastic-flow deposit. These are thickly developed on Satsuma Iwojima and are eruptive products of Iwojima volcano. The numerous tephras below the Funakura pumice fall are likewise considered to be mainly products of the central-cone group of Kikai caldera. This caldera formed through the cumulative effects of several enormous eruptions since the Middle Pleistocene, rather than solely through the eruption of Kikai-Akahoya tephra.

References: 町田・新井 (1978); 小野ほか (1982); 宇井 (1973)

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Figure 1; 1:25,000 “Satsuma Takeshima” (Kaimondake No. 12-1); Mishima Village; Takeshima; village office branch; heliport; Abi-yama (アビ山); Onbo Point (オンボ崎); Utsun Point (ウツン崎); 東風泊 [reading uncertain]; Kutsu-se (クツ瀬); 71; 73; 89; 39; 133; 168; 203.1

Original Japanese lettering

図1; 2.5万分の1『薩摩竹島』（開聞岳12号-1）; 三島村; 竹島; 役場支所; ヘリポート; アビ山; オンボ崎; ウツン崎; 東風泊; クツ瀬; 71; 73; 89; 39; 133; 168; 203.1

Reading notes

島東北端の小地名 — 小さい文字が不鮮明で全字を確定できない。（未確定候補 / Unconfirmed candidate: [判読不明]崎，江鼻）

Figure 1. 1:25,000 “Satsuma Takeshima” map sheet (Kaimondake No. 12-1).

[Original printed page: 6]

WS-2-1 (continued)

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Figure 2; Takeshima pyroclastic-flow deposit; Funakura pyroclastic-flow deposit; Funakura pumice fall

Original Japanese lettering

図2; 竹島火砕流堆積物; 船倉火砕流堆積物; 船倉降下軽石

Figure 2.

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Figure 3; Takeshima pyroclastic-flow deposit; Nagase pyroclastic-flow deposit; Funakura pyroclastic-flow deposit; Funakura pumice fall

Original Japanese lettering

図3; 竹島火砕流堆積物; 長瀬火砕流堆積物; 船倉火砕流堆積物; 船倉降下軽石

Figure 3.

[Original printed page: 7]

WS-2-2 Kikai-Akahoya Tephra near Onejime, Osumi Peninsula

Hiroshi Machida

• Locality: Hananomoto (花之本), Nejime Town, Kagoshima Prefecture
• Latitude and longitude: N31°13′28″ E130°48′43″
• Elevation: 180m
• Outcrop type and current condition: cutting for farmland development; unknown
• Deposit types and age: pumice-fall and pyroclastic-flow deposits
• Date of description: 1984
• Keywords: Kikai-Akahoya tephra; Aira-Ito pyroclastic flow; Aira-Osumi pumice fall; Kikai-Tozurahara tephra; Ata tephra

Throughout southern Kyushu, yellowish-red, volcanic-glass-rich Kikai-Akahoya tephra (K-Ah), locally called Akahoya or Imogo, can be observed near the ground surface. Whereas the coarse-grained tephra layers above and below it pinch out in different regions, K-Ah remains well continuous, although its degree of preservation varies with its cover.

On the Osumi Peninsula south of a line running east–west near Kanoya, Kikai-Akahoya tephra can be divided into three units. At this outcrop, from below, Koya pumice fall (the Funakura pumice fall on Takeshima), the Koya pyroclastic-flow deposit (the Takeshima pyroclastic-flow deposit), and Kikai-Akahoya ash are seen. The Koya pyroclastic-flow deposit is thin and continuous irrespective of topographic irregularities, as though it were fallout tephra. Its components, however, are more poorly sorted than those of the other units, with pumice clasts coexisting with fine volcanic ash, showing the characteristics of a pyroclastic-flow deposit. There are parts at the base where fine lithic fragments and phenocryst minerals are concentrated. The pyroclastic flow is considered to have been extremely gas-rich and highly mobile (宇井, 1973). Above this pyroclastic-flow deposit lies a normally graded volcanic-ash layer with a layer of accretionary lapilli at its base. This is the widespread K-Ah. The ash consists of bubble-type and pumice-type volcanic glass of pyroxene-rhyolitic to dacitic composition. It is generally yellowish-red in the field, but is pale yellowish-white where covered by thick tephra or intercalated in water-laid strata.

The tephra above K-Ah at this outcrop, separated from it by a thin kuroboku layer, is the Ikedako fallout tephra erupted from the Ikedako caldera at approximately 5.7ka (pumice fall with volcanic ash and scoria at its base; 成尾・小林, 1984). At the site marked ■, members of the Aira-Tn tephra (mainly the Ito pyroclastic flow, A-Ito, or the Osumi pumice fall, A-Os), Kikai-Tozurahara tephra (K-Tz), and Ata tephra (Ata) can be observed below K-Ah, separated by thick volcanic-ash soil. On the upland formed by the Ata pyroclastic flow near Onejime and Nejime, there are many other outcrops where K-Ah and associated tephras can be seen in almost the same mode of occurrence, although these exposures repeatedly appear and disappear.

In southern Kyushu, it is known that the types of Jomon pottery excavated from volcanic-ash soils above and below K-Ah differ across this boundary (新東, 1978). This major eruption probably greatly changed the landforms and ecosystems, including vegetation and fauna, of Kyushu, Shikoku, and Chugoku. It is anticipated that Jomon culture in this region suffered a severe blow and that cultural replacement occurred (Machida, 1984).

References: 宇井 (1973); Machida (1984); 町田・新井 (1978); 新東 (1978); 成尾・小林 (1984)

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1:50,000 “Onejime” (Kaimondake No. 1-4); 城; 上宇都; 山添; Hananomoto (花之本); 浦; 久保 [small place-name readings unverified]; 41.5; 77.6; 83.6; 172; Kikai-Akahoya ash; accretionary lapilli; Koya pyroclastic-flow deposit; Koya pumice fall

Original Japanese lettering

5万分の1『大根占』（開聞岳1号-4）; 城; 上宇都; 山添; 花之本; 浦; 久保; 41.5; 77.6; 83.6; 172; 鬼界アカホヤ火山灰; 火山豆石; 幸屋火砕流堆積物; 幸屋降下軽石

1:50,000 “Onejime” map sheet (Kaimondake No. 1-4).

[Original printed page: 8]

WS-2-3 Kikai-Akahoya Tephra in Holocene Marine-Terrace Deposits of the Miyazaki Plain

長岡信治

• Locality: bank of the 鬼付女 River at Minashiro (三納代), Shintomi Town, Miyazaki Prefecture, in front of the Koyu Poultry Agricultural Cooperative
• Latitude and longitude: N32°4′8″ E131°29′38″
• Elevation: 6m
• Outcrop type and current condition: river-improvement works; now covered with concrete
• Deposit types and age: water-laid tephra; Holocene
• Date of description: February 1993
• Keywords: Kikai-Akahoya tephra; Shimotajima I surface; Miyazaki Plain; 鬼付女 River

Because the Miyazaki Plain is uplifting, at least four levels of Holocene terraces have developed (長岡ほか, 1991). Of these, the highest, Shimotajima I surface, is a marine terrace that emerged at approximately 5–6ka (長岡ほか, 1991). The Shimotajima I terrace consists of more than 50m of transgressive deposits and contains Kikai-Akahoya tephra (K-Ah), deposited on the seabed, in its upper part. At this outcrop, K-Ah and the marine strata of the Shimotajima I surface can be observed. Below K-Ah lies a marine clay layer containing abundant inner-bay molluscan fossils. K-Ah reaches a maximum thickness of 5m and, unlike its terrestrial counterpart, consists of fresh, translucent grayish-white, glassy coarse volcanic ash with well-developed cross-lamination and trace fossils. K-Ah pinches out upstream, toward the former shoreline. Above K-Ah is a cover of marine and fluvial sand approximately 1m thick. The fluvial sand often contains fragments of Yayoi pottery. Although most of the outcrop here is now covered, some portions remain visible. Similar outcrops also occur on the Ishizaki River. Confirmation with a hand auger or similar equipment should be possible.

Reference: 長岡ほか (1991)

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English translation of figure lettering

1:25,000 “Sadowara” (Nobeoka No. 12-2); Minashiro (三納代); 一丁田; 二丁田; 新町; 鬼付女; 一池; 下城島 [place-name readings unverified]; 84; 4.90

Original Japanese lettering

2.5万分の1『佐土原』（延岡12号-2）; 三納代; 一丁田; 二丁田; 新町; 鬼付女; 一池; 下城島; 84; 4.90

1:25,000 “Sadowara” map sheet (Nobeoka No. 12-2).

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English translation of figure lettering

NW; N; sand layer; K-Ah; marine clay layer; 1m; photographed in February 1993

Original Japanese lettering

NW; N; 砂層; K-Ah; 海成粘土層; 1m; 1993年2月撮影

Photographed in February 1993.

[Original printed page: 9]

WS-2-4 Kikai-Akahoya Tephra in Uplifted Holocene Terrace Deposits — Nakamurahara, Kanagawa Prefecture

Hiroshi Machida and 松島義章

• Locality: Obune, Odawara City, beneath the Tokaido Shinkansen bridge
• Latitude and longitude: N35°17′54″ E139°14′0″
• Elevation: 19–25m
• Outcrop type and current condition: riverbank cliff; extant, but difficult to approach in summer because of vegetation in the riverbed
• Deposit types and age: marine strata, marine molluscan fossils, and volcanic ash; Holocene
• Date of description: 1979
• Keywords: marine alluvial deposits; marine molluscan fossils; Kikai-Akahoya tephra

The coastal zone from Oiso to Kozu in Kanagawa Prefecture is known as one of Japan's greatest areas of seismic uplift. Holocene marine strata reach elevations above 20m and form terraces. At this outcrop the upper part of these alluvial deposits can be observed, and a thin layer of Kikai-Akahoya tephra (K-Ah) is recognized within it. Below 19m above sea level, alternating sand and silt containing fossils of inner-bay molluscs (Anadara subclenata, Anomalocardea squamosa, etc.) are observed. Above them lie sand containing wood fragments, wetland silt, and fluvial sand and gravel. Detailed examination of the silt near 20.5m above sea level reveals a white volcanic-ash layer several mm thick. It consists of bubble-type volcanic glass and is identified as Kikai-Akahoya tephra (K-Ah) from its characteristics and stratigraphic position (松島, 1980; Machida et al., 1984; 遠藤ほか, 1979). Because K-Ah here occurs within terrestrial rather than marine strata, it must have been deposited as fallout when the coast had begun to pass from transgression to regression. In contrast, in coastal areas of central Honshu and farther west, K-Ah was generally deposited slightly before the peak of transgression (see, for example, the Miyazaki Plain, WS-2-3). This difference is explained by regional differences in uplift rate (町田・新井, 1980).

References: 遠藤ほか (1979); 松島 (1980); 町田・新井 (1980); Machida et al. (1980)

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1:25,000 “Odawara Hokubu” (Yokosuka No. 13-1); Tokaido; Odawara–Atsugi Road; Nakamura River; Yamanishi; Obune; Ninomiya; mountain shrine (山神社); 32.11; 85.9; 76; 20; 73.1

Original Japanese lettering

2.5万分の1『小田原北部』（横須賀13号-1）; 東海道; 小田原厚木道路; 中村川; 山西; 小船; 二宮; 山神社; 32.11; 85.9; 76; 20; 73.1

1:25,000 “Odawara Hokubu” map sheet (Yokosuka No. 13-1).

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English translation of figure lettering

25.5m; 20; 15; 13.8; Yayoi pottery; K-Ah; y.B.P.; 6250±150 w; 7340±230 s; 7410±190 s; 7750±270 w; loam; tephra; sand and gravel layer; silt; humus; wood; molluscan fossils; sand pipes

Original Japanese lettering

25.5m; 20; 15; 13.8; 弥生式土器; K-Ah; y.B.P.; 6250±150 w; 7340±230 s; 7410±190 s; 7750±270 w; ローム; テフラ; 砂礫層; シルト; 腐植; 材; 貝化石; サンドパイプ

Outcrop stratigraphic column (松島, 1980).

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M; 30; 20; 10; 0; -10; Tokaido railway; Kawawa (川勾); Nakamurahara; Shinkansen; Obune; Odawara–Atsugi bypass; Odake (小竹); 0; 500m; geological section along the Nakamura River (遠藤ほか, 1979)

Original Japanese lettering

M; 30; 20; 10; 0; -10; 東海道線; 川勾; 中村原; 新幹線; 小船; 小田原・厚木バイパス; 小竹; 0; 500m; 中村川沿いの地質断面図（遠藤ほか，1979）

Reading notes

断面内の斜体地層略号 — 小さく低解像度で一部の文字を確定できない。（未確定候補 / Unconfirmed candidate: [判読不明]）

Geological section along the Nakamura River (遠藤ほか, 1979).

[Original printed page: 10]

WS-2-5 Kikai-Akahoya Tephra and Aira-Tn Tephra on the Kasari Peninsula, Amami Oshima

成尾英仁

• Locality: 喜子川 archaeological site, Tomori, Kasari Town, Kagoshima Prefecture, on the west side of the prefectural Akakina road
• Latitude and longitude: N28°27′33″ E129°43′14″
• Elevation: 12m
• Outcrop type and current condition: excavated exposure; only the western exposure remains as of 1996
• Deposit types and age: aeolian tephra; Late Pleistocene–Holocene
• Date of description: August 1988
• Keywords: Amami Oshima; Kasari Peninsula; Kikai-Akahoya tephra; Aira-Tn tephra; fingernail-impressed pottery

This is a good outcrop for confirming Kikai-Akahoya tephra (K-Ah; 6.3ka) in the Amami Islands. It lies at the edge of a low terrace facing the Pacific Ocean. Here the lower dune sand is hard and grayish-black, consisting mainly of foraminiferal sand, while the upper dune sand is unconsolidated and likewise mainly foraminiferal. Archaeological excavation has continued here since 1987, and the sequence has been divided into eight layers from the surficial black sand to the clayey weathered soil (maji layer). Unconsolidated brown sand forms the artifact-bearing layer and yields fingernail-impressed pottery. Below it is consolidated sand, the lower dune sand. Farther below, separated by black sand, K-Ah is deposited. It contains some foraminiferal sand but is a vivid yellowish-orange glassy volcanic ash. It occurs in blocks approximately 5cm thick and has good lateral continuity. Underlying it is reddish-orange clayey soil called the maji layer, containing abundant medium to large shale gravel derived from the bedrock. Although not distinguishable to the naked eye, Aira-Tn tephra (AT; 25ka) is scattered within this layer. K-Ah glass is light brown to dark brown, has a refractive index of 1.510–1.512, and has an average SiO₂ content of 76%. AT glass is colorless, transparent, and platy, with a refractive index of 1.497–1.498. Fingernail-impressed pottery in the Ryukyu Islands was formerly assigned to the Incipient Jomon period, approximately 10ka, as on the main islands. The recovery of this pottery above K-Ah, however, led to its assignment to the Initial Jomon period.

References: 成尾 (1988); 田村ほか (1988)

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English translation of figure lettering

Sakibaru (崎原); Tomori; 38; 1:25,000 “Akakina” (Amami Oshima No. 6-1)

Original Japanese lettering

崎原; 土盛; 38; 2.5万分の1『赤木名』（奄美大島6号-1）

1:25,000 “Akakina” map sheet (Amami Oshima No. 6-1).

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sand layer (artifact-bearing); K-Ah; maji layer

Original Japanese lettering

砂層（遺物包含）; K-Ah; マージ層

[Original printed page: 11]

WS-3-1 Late Pleistocene–Holocene Tephras of Ulleung Island, Korea

森脇 広

• Locality: Sokpo-dong (石圃洞), Ulleung Island, Korea
• Latitude and longitude: N37°32′28″ E130°54′18″
• Elevation: 270m
• Outcrop type and current condition: artificial; preserved as of July 1982
• Deposit types and age: aeolian tephra; Late Pleistocene and Holocene
• Date of description: July 1982
• Keywords: Korea; Ulleung Island; Ulleung-Oki tephra

Ulleung Island (Ururundo) is a Quaternary volcanic island in the Sea of Japan, 140km from the Korean Peninsula. Attention was drawn to Quaternary tephra from this volcano by the discovery, in Kansai and Chubu on the Japanese archipelago and on the floor of the southern Sea of Japan, of an early Holocene tephra thought to originate on Ulleung Island: Ulleung-Oki ash (U-Oki), an alkaline-rock tephra rare among tephras of the Japanese archipelago (町田ほか, 1981). A detailed tephra chronology for the island was established by 町田ほか (1984). The island is nearly circular, 12km east–west and 9km north–south. In its north-central part is a caldera 3.5km in diameter, with the central cone Al-bong (卵峰) in its northern part. The tephra stratigraphy can be established at Sokpo-dong in the northeastern part of the island, where a lava plateau remains (82.7-2 in Fig. 1), and on the small island Chuk-do (竹島; 82.7-1), 2km off its northeastern coast (Figs. 1, 3). At outcrop 82.7-2, seven tephra layers originating from Ulleung volcano are recognized and named U-1, U-2, …, U-7 from top downward (Fig. 2; 町田ほか, 1984). All are alkaline-rock tephras and differ greatly from the subalkaline-rock tephras originating in the Japanese archipelago.

The uppermost U-1 is a product of the latest eruptive stage of Ulleung volcano, recognized as a thin scoriaceous volcanic-ash layer. Its lower part is cement-like and consolidated; it is a product of a phreatomagmatic eruption of the central cone Al-bong. U-2 and the lower units are fallout tephras from Plinian eruptions, consisting of trachytic pumice and volcanic ash. U-5–U-7 are strongly weathered and differ in their mode of occurrence from the overlying U-2–U-4, which consist of fresh pumice. U-2 and U-3 are accompanied by pyroclastic flows in addition to pumice-fall layers. The U-3 pyroclastic-flow deposit also contains abundant accretionary lapilli. U-2, U-3, and U-4 show no significant differences in petrography or chemical composition; their eruption sizes are also similar. Their properties likewise resemble those of U-Oki, and they cannot be clearly distinguished on petrographic or chemical grounds. Nevertheless, U-2, which has the widest distribution, a southeastward distribution axis, and a distribution corresponding to that of U-Oki in Honshu, is correlated with U-Oki. Steep slopes are widespread on this island, and tephra preservation is poor, but U-2, a product of the latest caldera eruption, is relatively well preserved on slopes. The thick deposits on slopes around To-dong (道洞), the island's main settlement, are this U-2. The widespread tephras originating in southern Kyushu, Aira-Tn tephra (AT) and Kikai-Akahoya tephra (K-Ah), have been detected within kuroboku soil between U-4 and U-5 and between U-1 and U-2, respectively.

References: 町田ほか (1981, 1984)

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Cheonbu-dong; Pyongri; Hyangnamu-dong; Al-bong; Nari-kol; Seongin-bong; Sokpo-dong; Chuk-do; Jeo-dong; To-dong; 82.7-10; 82.7-5; 81.8-12; 82.7-2; 82.7-1; 83.10-4; 81.8-11; 300; 100; 10; 20; 0; 5km

Original Japanese lettering

Cheonbu-dong; Pyongri; Hyangnamu-dong; Al-bong; Nari-kol; Seongin-bong; Sokpo-dong; Chuk-do; Jeo-dong; To-dong; 82.7-10; 82.7-5; 81.8-12; 82.7-2; 82.7-1; 83.10-4; 81.8-11; 300; 100; 10; 20; 0; 5km

Figure 1. Outcrop locations on Ulleung Island, U-2 isopachs (heavy solid and dashed lines), and isopleths of grain size (dotted lines for pumice; dash-dot lines for lithic fragments).

[Original printed page: 12]

WS-3-1 (continued)

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WS-3-1; 82.7-10; 82.7-5; 81.8-12; 81.8-11; 83.10-4; 82.7-2; 82.7-1; U-1; U-2; U-3; U-4; U-5; U-6; U-7; K-Ah; AT; ?; 0; 3m; 20m; 3m; 4m; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10

Original Japanese lettering

WS-3-1; 82.7-10; 82.7-5; 81.8-12; 81.8-11; 83.10-4; 82.7-2; 82.7-1; U-1; U-2; U-3; U-4; U-5; U-6; U-7; K-Ah; AT; ?; 0; 3m; 20m; 3m; 4m; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10

Figure 2. Tephra stratigraphic columns on Ulleung Island (locations in Fig. 1). The two sites on the right are the type outcrops.

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U-2; U-3

Original Japanese lettering

U-2; U-3

Figure 3. Tephra outcrop on Chuk-do (竹島), Ulleung Island.

[Original printed page: 13]

WS-3-2 Ulleung-Oki Tephra at the Torihama Shell Midden and Lake Suigetsu, Fukui Prefecture

Hiroshi Machida

• Locality: Torihama, Mikata Town, Fukui Prefecture
• Latitude and longitude: N35°33′3″ E135°54′16″
• Elevation: -2–2m
• Outcrop type and current condition: excavation; disappeared; a peel specimen is preserved at the Wakasa Museum of History and Folklore
• Deposit types and age: alkaline-rock volcanic ash and mud; early Holocene
• Date of description: 1981
• Keywords: Ulleung-Oki tephra; early Holocene; Torihama Shell Midden; Lake Suigetsu

The Torihama Shell Midden near Lake Mikata is a representative Early Jomon lowland archaeological site, but also contains artifacts from the Incipient to Initial Jomon periods. Abundant human artifacts and clues to the natural environment of the time are well preserved here. Figure 2 is a composite geological column for Section 4 of the midden's 80L area and the western wall of Section 80L2 (町田, 1981). In wetland mud containing impressed-pattern pottery at 2.2m below sea level, there is a well-continuous grayish-white volcanic-ash layer 2–3cm thick (Figs. 2, 3). This is Ulleung-Oki tephra (U-Oki). Under the microscope it is seen to consist mainly of white to grayish-brown pumice-type volcanic glass with sponge-like vesiculation (mean maximum grain size 0.3mm), containing very small quantities of microphenocrysts of alkali feldspar, brown biotite, amphibole, and clinopyroxene. Correlative tephra has been found at several sites in Kinki and Tokai on Honshu. In the Sea of Japan it is intercalated in seabed deposits from Oki Bank to waters southeast of Ulleung Island. On Ulleung Island the second tephra from the top, U-2, corresponds to it (町田ほか, 1984). This tephra has a radiocarbon age of approximately 9.3ka and is an extremely important marker bed for resolving questions concerning early Holocene sea level, paleoclimate, and the inflow of the Tsushima Warm Current (新井ほか, 1981). K-Ah in the upper part of Figure 4 is not very well preserved, but lies below the layers containing Early Jomon Hashima Lower II-type and Kitashirakawa Lower II-type pottery.

It has also been reported that this tephra is intercalated at 11–12m below the lake floor in a drill core from Lake Suigetsu, one of the Mikata Five Lakes approximately 3km north of Torihama. Varves are recognized in these sediments, and counting them yielded an age of 10,738 years before AD1995 (福沢, 1995; Fig. 5).

References: 新井ほか (1981); 福沢 (1995); 町田 (1981); 町田ほか (1984)

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Figure 1; 1:25,000 “Mikata” (Miyazu No. 3-2); Torihama; Mikata; Mishima; 北前川 [reading unverified]; Obama railway; 2; 9 cm; 0; 50; 100; K-Ah glass; ○ sample; sand & gravel; shell bed; silt; U-Oki; K; D; n.a.; H; O; I.J. K, Kitashirakawa Lower II-type pottery; D, dugout canoe; n.a., no artifacts; H, Hashima Lower II-type pottery; O, impressed-pattern pottery; I.J., Incipient Jomon pottery Left column, top downward: −, −, −, −, −, −, −, − (8 points). Right column, top downward: +, +, +, +, +, ++, ++, +++, ++, ++++, ++++ (11 points).

Original Japanese lettering

図1; 2.5万分の1『三方』（宮津3号-2）; 鳥浜; 三方; 三島; 北前川; 小浜線; 2; 9 cm; 0; 50; 100; K-Ah glass; ○ sample; sand & gravel; shell bed; silt; U-Oki; K; D; n.a.; H; O; I.J. K，北白川下層Ⅱ式土器；D，丸木舟；n.a.，無遺物；H，羽島下層Ⅱ式土器；O，押型文土器；I.J.，縄文草創期土器 左柱状図：上から－，－，－，－，－，－，－，－（8点） 右柱状図：上から＋，＋，＋，＋，＋，＋＋，＋＋，＋＋＋，＋＋，＋＋＋＋，＋＋＋＋（11点）

Figure 1. 1:25,000 “Mikata” map sheet (Miyazu No. 3-2).

Figure 2. Schematic section showing the stratigraphic relationships between Jomon pottery and tephras (U-Oki, K-Ah) (町田ほか, 1984). The abundance of K-Ah volcanic glass is indicated by + and −.

[Original printed page: 14]

WS-3-2 (continued)

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English translation of figure lettering

←U-Oki; 9 30

Original Japanese lettering

←U-Oki; 9 30

Reading notes

写真右下の日付 — 左側の年・月部分は不鮮明で読み切れない。

Figure 3. U-Oki at the Torihama Shell Midden.

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0cm; 100; 200; K-Ah; clay; sand layer; impressed-pattern pottery; mud layer; U-Oki; Incipient Jomon pottery

Original Japanese lettering

0cm; 100; 200; K-Ah; 粘土; 砂層; 押型文土器; 泥層; U-Oki; 縄文草創期土器

Figure 4. Composite stratigraphic column at the Torihama Shell Midden.

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SGP2; SGP3; SGP4; SGB; Core Depth and Core Name of SGB K-Ah; U-Oki; Sakate; hiatus; ?; Younger Dryas?; Older Dryas?; Last Glacial Maximum?; 1m SG11: 8.95m–9.97m; SG12: 9.97m–10.45m; SG13: 10.45m–11.33m; SG14: 11.33m–12.25m; SG15: 12.25m–13.17m; SG16: 13.17m–14.08m; SG17: 14.08m–14.98m; SG18: 14.98m–15.89m; SG19: 15.89m–16.80m; SG20: 16.80m–17.71m; SG21: 17.71m–18.60m; SG22: 18.60m–19.39m tephra layer; upward fining silt layer; silty clay layer; mudflow layer including organic debris; organic debris; non-recovery horizons; siderite-rich varve horizon; joint positions of core sampler

Original Japanese lettering

SGP2; SGP3; SGP4; SGB; Core Depth and Core Name of SGB K-Ah; U-Oki; Sakate; hiatus; ?; Younger Dryas?; Older Dryas?; Last Glacial Maximum?; 1m SG11: 8.95m–9.97m; SG12: 9.97m–10.45m; SG13: 10.45m–11.33m; SG14: 11.33m–12.25m; SG15: 12.25m–13.17m; SG16: 13.17m–14.08m; SG17: 14.08m–14.98m; SG18: 14.98m–15.89m; SG19: 15.89m–16.80m; SG20: 16.80m–17.71m; SG21: 17.71m–18.60m; SG22: 18.60m–19.39m tephra layer; upward fining silt layer; silty clay layer; mudflow layer including organic debris; organic debris; non-recovery horizons; siderite-rich varve horizon; joint positions of core sampler

Figure 5. Stratigraphic columns of lake-floor sediment cores from Lake Suigetsu (福沢, 1995).

[Original printed page: 15]

WS-4-1 Towada-Hachinohe and Ofudo Pyroclastic-Flow Deposits around Ninokura Dam, Aomori Prefecture

Hiroshi Machida

• Locality: Ninokura Dam, Shingo Village, Aomori Prefecture
• Latitude and longitude: A: N40°25′9″ E141°3′53″; B: N40°25′34″ E141°4′59″
• Elevation: 300–340m
• Outcrop type and current condition: roadside cliffs; hidden by retaining walls
• Deposit types and age: pyroclastic-flow deposits and pumice fall; 12ka and 35ka
• Date of description: 1980
• Keywords: Towada-Ofudo tephra; Towada-Hachinohe tephra; Ninokura tephra group; Towada-Nanbu tephra; Towada-Chuseri tephra; Towada-b tephra; Towada-a tephra; Towada caldera; Ninokura Dam

Towada-Hachinohe tephra (To-H) and Ofudo tephra (To-Of) are considered to have been principally involved in the formation of Towada caldera. Both are large tephras of similar size, approximately 50km³ in volume, comprising pyroclastic-flow deposits accompanied by pumice fall. The pyroclastic-flow plateau in this area formed through their combination. Towada caldera also erupted numerous other large-scale tephras. At this outcrop, both the upper To-H and lower To-Of have preceding pumice-fall layers, respectively 250cm and 55cm thick, immediately beneath the pyroclastic-flow deposits that fill valleys thickly and form uplands (Fig. 2). On the upland north of Hachinohe, including Takadate, the type area of the Towada tephra group, these pumice-fall layers correspond to the tephras called Hachinohe Pumice (HP) and Biscuit 1 (BP1). HP is rich in volcanic ash and accretionary lapilli (早川, 1983). BP1 likewise has a pumice layer in its lower part but a fallout-ash layer above. To-H and To-Of are lithologically similar but can be distinguished by the more felsic composition of To-Of and the amphibole phenocrysts in To-H that are absent in To-Of. To-Of also contains a small amount of bubble-type volcanic glass.

The abundant charred wood in pyroclastic-flow deposits in this area clearly shows that To-H buried and destroyed a subarctic coniferous forest. Previous radiocarbon dates on this wood range from 10.4 to 14ka. Recent accelerator mass spectrometry, however, yielded 12.65ka and showed that the eruption occurred between autumn and spring (寺田ほか, 1994). In piston core KH77-1-6 off Sanriku, 300km east of Miyako, tephra identified as To-Of co-ignimbrite ash occurs 72cm above tephra identified as Shikotsu-1 (青木, 1996). Near Hachinohe, volcanic glass identified as AT also occurs in volcanic-ash soil between BP1 and BP2. Thus To-Of lies between AT and Spfa-1, nearer to the latter. Previous radiocarbon dates for this tephra range from 20ka to >33ka and are difficult to settle (町田・新井, 1992), but its age is probably closer to the older values.

Tephra layers from the latest Pleistocene through the Heian period overlie the depositional surface of To-H (Fig. 3). Unlike the other tephras, the lowest is not the product of a single eruption but consists of numerous scoria and volcanic-ash layers (To-Nk). These are thought to have been erupted during formation of the small Goshikiiwa stratovolcano in the southwestern part of the Nakako crater of Towada caldera. Their eruption ages are 10–13ka, and they are overlain by Initial Jomon cultural layers. Above them, separated by soils, lie Towada-Nanbu tephra (To-Nb), Towada-Chuseri tephra (To-Cu), Towada-b tephra (To-b), and Towada-a tephra (To-a), in that order. To-Nb is a marker tephra for the Initial Jomon period and To-Cu for the Early Jomon period. The latter is widely distributed throughout Tohoku, much like To-a.

References: 青木 (1996); 早川 (1983); Hayakawa (1985); 町田・新井 (1992); 寺田ほか (1994)

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Figure 1; 1:50,000 “Takko” (Hachinohe No. 14-2); Ninokura Dam; 羽井内; 迷川 [readings unverified]; 590; 398; 340.0; 375.1; 371.2; 502.9; 517.3; 468

Original Japanese lettering

図1; 5万分の1『田子』（八戸14号-2）; 二ノ倉ダム; 羽井内; 迷川; 590; 398; 340.0; 375.1; 371.2; 502.9; 517.3; 468

Figure 1. 1:50,000 “Takko” map sheet (Hachinohe No. 14-2).

[Original printed page: 16]

WS-4-1 (continued)

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English translation of figure lettering

To-H; To-HP; To-Of; To-BP1

Original Japanese lettering

To-H; To-HP; To-Of; To-BP1

Figure 2. Two large-scale Towada tephras.

Show extracted lettering and translation

English translation of figure lettering

To-Cu; To-Nb; To-Nk; To-H

Original Japanese lettering

To-Cu; To-Nb; To-Nk; To-H

Figure 3. Outcrop photograph at the site marked ▲ (published in Hayakawa, 1985).

[Original printed page: 17]

WS-5-1 Large-Scale Tephras Erupted from Aira Caldera at Shibushi Port

Hiroshi Machida

• Locality: sea cliff east of Shibushi Port, Shibushi Town, Kagoshima Prefecture
• Latitude and longitude: N31°28′14″ E131°6′58″
• Elevation: 0–50m
• Outcrop type and current condition: sea cliff; extant
• Deposit types and age: pumice-fall and pyroclastic-flow deposits
• Date of description: 1983
• Keywords: Aira-Osumi pumice fall; Aira-Ito pyroclastic-flow deposit; Aira-Tn tephra; Aira-Iwato tephra; Aira-Fukuyama tephra; Kikai-Tozurahara tephra; Ata tephra

The large-scale tephras erupted from Aira caldera at approximately 24ka form most of the shirasu uplands throughout southern Kyushu. The type locality differs for each member, but here the cliff east of Shibushi Port has been selected because the basic members have long been exposed there and are thought unlikely to disappear in the future (Figs. 1, 2). The lower stratified pumice layer is the Osumi pumice fall (A-Os); the inversely graded pyroclastic-flow deposit in the middle and upper parts is the Ito pyroclastic-flow deposit (A-Ito). Their distributions are shown in Figure 3. A-Os is one of Japan's largest pumice falls, with a volume of approximately 100km³ and a principal distribution axis extending southeast to east-southeast from near present-day Sakurajima. Its distribution on the upwind side as well suggests formation of a gigantic umbrella cloud. After the A-Os eruption, the Tsumaya pyroclastic flow (A-Ts) was erupted, a tephra consisting of fine-grained material produced by a phreatomagmatic eruption. A-Ito is the deposit of an immense pyroclastic flow with a volume of approximately 200km³. It widely covers southern Kyushu and forms most of the shirasu uplands. All these deposits are pyroxene-rhyolitic and extremely homogeneous regardless of member.

Volcanic ash consisting mainly of bubble-type volcanic glass, erupted into the atmosphere during the A-Ito eruption, is widely distributed over the Japanese archipelago and surrounding regions. Called Aira-Tn tephra (AT), it is frequently used as a marker bed in studies of Late Pleistocene questions (町田・新井, 1976). In Kyushu this tephra is recognized from near the edge of the A-Ito distribution outward, where it can be traced continuously as a glassy volcanic-ash layer slightly less than 1m thick. Around Shibushi, too, the uppermost part of A-Ito contains a volcanic-ash layer, locally with accretionary lapilli, that may be part of fallout AT.

East of this outcrop, various tephra layers beneath A-Os can be observed (Fig. 4). From the top downward they are Aira-Iwato tephra (A-Iw; a thin layer that is a clear marker bed on the Miyazaki Plain), Aira-Fukuyama tephra (A-Fk; rich in amphibole), Kikai-Tozurahara tephra (K-Tz; glassy volcanic ash weathered pink), and Ata tephra (Ata). Of these, the main body of Ata is welded tuff, overlain by weathered tephra consisting of accretionary lapilli, probably Ata co-ignimbrite ash.

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English translation of figure lettering

1:50,000 “Shibushi” (Miyazaki No. 16); 田畦敷; 大性院; 帖; 宇都; 西谷; 沢目; 若宮; 宝満; 志布志屋敷; 天神; 向川原; 有明; 関屋; 小西; 大黒; 新町; 内田 [local place-name readings unverified]; 59.6; 66.8; 36.6; 50.4; 9.9

Original Japanese lettering

5万分の1『志布志』（宮崎16号）; 田畦敷; 大性院; 帖; 宇都; 西谷; 沢目; 若宮; 宝満; 志布志屋敷; 天神; 向川原; 有明; 関屋; 小西; 大黒; 新町; 内田; 59.6; 66.8; 36.6; 50.4; 9.9

Figure 1. 1:50,000 “Shibushi” map sheet (Miyazaki No. 16).

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English translation of figure lettering

Figure 2; A-Ito; A-Os

Original Japanese lettering

図2; A-Ito; A-Os

Figure 2.

[Original printed page: 18]

WS-5-1 (continued)

References: Aramaki and Ui (1966); 町田・新井 (1976, 1992)

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English translation of figure lettering

6cm; 12; 25; 50; 100; 200; 400; 400; 800; >0; Kagoshima; Sakurajima; Miyazaki; 32°; 31°; 131°; 0; 30km

Original Japanese lettering

6cm; 12; 25; 50; 100; 200; 400; 400; 800; >0; 鹿児島; 桜島; 宮崎; 32°; 31°; 131°; 0; 30km

Figure 3. Isopachs of Osumi pumice fall (A-Os) and distributions of Tsumaya and Ito pyroclastic-flow deposits (A-Tm, A-Ito), etc.

Dots: Ito pyroclastic flow (A-Ito); horizontal lines: Tsumaya pyroclastic flow (A-Tm); diagonal lines: pyroclastic-flow deposits contemporaneous with Osumi pumice fall (A-Os).

町田・新井 (1992).

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English translation of figure lettering

Figure 4; A-Os; A-Iw; A-Fk; K-Tz; Ata

Original Japanese lettering

図4; A-Os; A-Iw; A-Fk; K-Tz; Ata

Figure 4.

[Original printed page: 19]

WS-5-2 Aira-Tn Tephra and Kikai-Akahoya Tephra in Southwestern Shikoku

Hiroshi Machida

• Locality: Ogawa (小川), Sukumo City, Kochi Prefecture, at the Kochi–Ehime prefectural boundary
• Latitude and longitude: N32°58′03″ E132°41′37″
• Elevation: 50–80m
• Outcrop type and current condition: farm-road cutting; unknown
• Deposit types and age: glassy volcanic ash; 6.3ka and 24ka
• Date of description: 1975
• Keywords: Aira-Tn tephra; Kikai-Akahoya tephra

Aira-Tn tephra (AT) and Kikai-Akahoya tephra (K-Ah) can be found throughout western Japan as representative widespread tephras of the Late Pleistocene and Holocene. Places where both layers occur together in a typical exposure, however, are not very numerous. This is a good outcrop 5km northwest of Sukumo City. The upper K-Ah is yellowish-red and the lower AT bright yellow. In Shikoku these were formerly called red onji (onji) and yellow onji. Talus deposits intervene between them. Detailed observation of AT shows that its lowermost 11cm consists of extremely fine volcanic ash, whereas the thick bright-yellow volcanic-ash layer above is normally graded. The base of the latter in particular consists of phenocrysts and coarse-sand-sized volcanic ash, with pumice fragments also present. From the middle to the top it becomes compact fine volcanic ash. This stratified structure can be observed from southern Kyushu to the Chugoku region. Various explanations had been proposed for the origin of the basal fine volcanic ash, but 町田・新井 (1992) interpreted it as fallout ash contemporaneous with the Tsumaya pyroclastic flow. The overlying normally graded volcanic ash is co-ignimbrite ash of the Ito pyroclastic flow.

References: 町田・新井 (1976, 1992)

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1:50,000 “Sukumo” (Uwajima No. 7); Ogawa; 野地; 東台地; 草木藪 [readings unverified]; 63; 62.12; 38.0; 25; 302.8

Original Japanese lettering

5万分の1『宿毛』（宇和島7号）; 小川; 野地; 東台地; 草木藪; 63; 62.12; 38.0; 25; 302.8

1:50,000 “Sukumo” map sheet (Uwajima No. 7).

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English translation of figure lettering

K-Ah; AT; 1m; P

Original Japanese lettering

K-Ah; AT; 1m; P

[Original printed page: 20]

WS-5-3 Aira-Tn Tephra within Mount Fuji Tephras — Along the Sakawa River, Kanagawa Prefecture

Hiroshi Machida

• Locality: Koichi (小市), Minamiashigara City, Kanagawa Prefecture (Oguchi Bridge)
• Latitude and longitude: N35°20′35″ E139°6′5″
• Elevation: 75–90m
• Outcrop type and current condition: riverbank; extant, but becoming covered by vegetation
• Deposit types and age: scoria fall and glassy volcanic ash; Late Pleistocene
• Date of description: 1992
• Keywords: Kanto Loam; Mount Fuji scoria layers; Aira-Tn tephra; Gotemba mudflow deposit

It is well known that thick Pleistocene tephras from Fuji and Hakone volcanoes have accumulated in the southwestern Kanto Plain. Scoria fall from Fuji volcano in particular appears to have been erupted and deposited quite frequently, preserving many tephras arriving from distant sources between its layers (see Kamishibanuta, Gotemba City, CB-16, and Ikudo Nishizawa, Oyama Town, WS-9-3). This outcrop is another such example. Because it lies approximately 30km east of Mount Fuji, it is important for connecting the stratified tephra sequences near their source at the foot of Fuji with the unstratified facies of the so-called Kanto Loam around Tokyo, approximately 100km away. As illustrated, approximately 10m of scoria fall overlies an erosion surface cut into the Hakone younger pyroclastic-flow deposit. Although the scoria layers show broad stratification, there are fewer conspicuous scoria beds than at Fuji's eastern foot. AT serves as a marker bed within them: a yellowish-white glassy volcanic-ash layer 5–10cm thick. Eastward from here, the scoriaceous volcanic-ash soils (Musashino Loam and Tachikawa Loam) gradually become thinner, but AT can be confirmed everywhere. In the Tanzawa Mountains and Oiso Hills the AT layer can be seen with the naked eye. Farther east, however, it generally forms a light-brown part mixed with scoria, requiring laboratory sample treatment and identification of its characteristic volcanic glass using a hand lens or microscope. When intercalated in water-laid strata, it can be observed in the field as a glassy volcanic-ash layer more than 5cm thick. The top of this outcrop contains stratified scoriaceous sand and gravel. This is the Gotemba mudflow deposit that flowed down following a major collapse of Mount Fuji at 2.4–2.5ka.

Reference: 町田・山崎 (1995)

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1:25,000 “Yamakita” (Tokyo No. 16-4); 行沢; 班目 [readings unverified]; 75; 110

Original Japanese lettering

2.5万分の1『山北』（東京16号-4）; 行沢; 班目; 75; 110

1:25,000 “Yamakita” map sheet (Tokyo No. 16-4).

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Gotemba mudflow deposit (Go-mf); Oguchi Bridge; Older Fuji tephra (Tachikawa Loam); AT; Hakone younger pyroclastic-flow deposit (TPfl); Sakawa River bed; 5m

Original Japanese lettering

御殿場泥流堆積物（Go-mf）; 大口橋; 古期富士テフラ（立川ローム）; AT; 箱根新期火砕流堆積物（TPfl）; 酒匂川河床; 5m

[Original printed page: 21]

WS-5-4 Vegetation Changes before and after Aira-Tn Tephra in the Kanto Plain

辻 誠一郎

• Localities: Irima-cho, Chofu City, Tokyo (site A); Shimo-oshima, Tsukuba City, Ibaraki Prefecture (site B)
• Latitude and longitude: N35°38′42″ E139°35′05″ (site A); N36°07′58″ E140°08′04″ (site B)
• Elevation: 27m (site A); 9m (site B)
• Outcrop type and current condition: artificial exposures; both artificially covered after completion of construction
• Deposit types and age: terrace-forming strata and water-laid strata; Late Pleistocene
• Date of description: November 1981 (site A); December 1980 (site B)
• Keywords: Aira-Tn tephra; fossil pollen assemblages; vegetation change; Kanto Plain

Recent radiocarbon dates for Aira-Tn tephra (AT) obtained using tandem accelerator mass spectrometry (AMS) cluster around 24ka. Pollen analyses of borehole samples from lake and wetland sediments throughout Japan are revealing that at this time ecosystems changed greatly, from deciduous broadleaved-tree dominance to conifer dominance. Surprisingly few sites, however, have provided outcrop confirmation of water-laid strata containing AT together with paleoenvironmental records. The two exposures at sites A and B in the central and southern Kanto Plain discussed here both appeared during riverbank protection works. As described below, 辻 (1992) reported pollen analyses for site A, and 遠藤ほか (1983) and 鈴木ほか (1993) for site B. They were valuable outcrops clearly recording substantial vegetation changes (Fig. 2). For the location map and tephra layers at site B, see KT-7 in this book.

Site A appeared during bank-protection works near Nogawa Bridge. At this exposure a sequence approximately 4m thick, comprising peat, peaty deposits, silt, and clay, overlies the Tachikawa Gravel. From bottom to top it indicates a change in depositional environment from riverbed to wetland. 千葉ほか (1982) called it the Nogawa Peat. AT intervenes in the lower part of the peat and peaty deposits in the middle of the Nogawa Peat, and a total of 36 fallout tephra layers, including AT, were distinguished. Most were approximately 3cm thick and consisted mainly of black scoria.

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Figure 1; 1:25,000 “Mizonokuchi” (Tokyo No. 7-3)

Original Japanese lettering

図1; 2.5万分の1『溝口』（東京7号-3）

Figure 1. 1:25,000 “Mizonokuchi” map sheet (Tokyo No. 7-3).

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B: Shimo-oshima, Tsuchiura City, Ibaraki Prefecture; m; 0; 1; 2; AT; phases: III, II, I; 0, 50, 100% A: Irima, Chofu City, Tokyo; m; 0; 1; 2; 3; 4; 5; AT; pollen zones and phases: CFI-IV—4, CFI-III—3, CFI-II—2, CFI-I—1; 0, 50, 100% Stratigraphic column: scoria; volcanic glass and pumice; humic soil; brown loam; clay; peaty deposits; sand; gravel; tuffaceous silt Pollen diagram: Abies and Tsuga; Picea; Pinus; Larix or Pseudotsuga; Quercus subgenus Quercus; Alnus; Betula; other woody pollen

Original Japanese lettering

B：茨城県土浦市下大島; m; 0; 1; 2; AT; 時期：Ⅲ，Ⅱ，Ⅰ; 0，50，100% A：東京都調布市入間; m; 0; 1; 2; 3; 4; 5; AT; 花粉帯・時期：CFI-Ⅳ—4，CFI-Ⅲ—3，CFI-Ⅱ—2，CFI-Ⅰ—1; 0，50，100% 柱状図：スコリア，火山ガラス・軽石，腐植土，褐色ローム，粘土，泥炭質堆積物，砂，礫，凝灰質シルト 花粉ダイアグラム：モミ属とツガ属，トウヒ属，マツ属，カラマツ属かトガサワラ属，コナラ属コナラ亜属，ハンノキ属，カバノキ属，その他の木本花粉

Figure 2. Composite pollen-analysis diagrams and correlation of sites A and B.

Column legend: scoria; volcanic glass and pumice; humic soil; brown loam; clay; peaty deposits; sand; gravel; tuffaceous silt.

Pollen-diagram legend: Abies and Tsuga; Picea; Pinus; Larix or Pseudotsuga; Quercus subgenus Quercus; Alnus; Betula; other woody pollen.

辻 (1992).

[Original printed page: 22]

WS-5-4 (continued)

Changes in fossil pollen assemblages at the two sites are broadly similar, but a typical succession can be seen at Shimo-oshima, site B (遠藤ほか, 1983). It is divided into a deciduous broadleaved-forest phase dominated by Quercus subgenus Quercus (phase ②), a coniferous-forest phase dominated by Pinus, Picea, and others (phase ④), and a mixed-forest phase transitional from ② to ④ (phase ③). Ecosystem changes in response to a cooler and colder climate can be clearly discerned (Fig. 2). Although there are some differences in the quantitative changes of deciduous broadleaved trees and conifers at Chofu, site A, the pattern of change is almost identical. What deserves attention is the recognition of two stages of increasing conifer dominance: gradual conversion to coniferous forest began before AT, followed by rapid conversion with the AT ash fall. Together with the abrupt changes also recognized in aquatic fossil diatom assemblages (Fig. 3), this suggests that the enormous eruption producing AT disturbed ecosystems and accelerated the direction of change expressed as increasing coniferous-forest dominance (Fig. 4; 辻・小杉, 1991).

References: 千葉ほか (1982); 遠藤ほか (1983); 鈴木ほか (1993); 辻 (1992); 辻・小杉 (1991)

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Eunotia; Pinnularia; Navicula contenta; Hantzschia amphioxys; Cymbella; Achnanthes lanceolata; Melosira ambigua; Cyclotella; Valve number per 1g of dry sediment; 0; 10; 10³; 10⁵; 10⁸; cm; 0; 5; AT; Peat; Tephra; 0; 10⁵; 10⁶; 10⁷ valve no./g

Original Japanese lettering

Eunotia; Pinnularia; Navicula contenta; Hantzschia amphioxys; Cymbella; Achnanthes lanceolata; Melosira ambigua; Cyclotella; Valve number per 1g of dry sediment; 0; 10; 10³; 10⁵; 10⁸; cm; 0; 5; AT; Peat; Tephra; 0; 10⁵; 10⁶; 10⁷ valve no./g

Figure 3. Changes in fossil diatom assemblages at site B. A: acidophilous benthic species; B: alkaliphilous benthic species; C: planktonic species. 辻・小杉 (1991).

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10⁴ y.B.P.; upland; valley floor; 2.2; 2.4; AT Cool-temperate coniferous forest comprising Baramomi-section spruce (バラモミ節), Korean pine, larch, Abies, and Tsuga. Communities of Poaceae and Sanguisorba; Korean-pine forest; Tilia forest; Quercus-subgenus forest; Cyperaceae wetland; Alnus wetland forest.

Original Japanese lettering

10⁴ y.B.P.; 台地; 谷底; 2.2; 2.4; AT バラモミ節・チョウセンゴヨウ・カラマツ・モミ属・ツガ属からなる冷温帯針葉樹林 イネ科やワレモコウ属の群落; チョウセンゴヨウ林; シナノキ属林; コナラ亜属林; カヤツリグサ科湿地; ハンノキ湿地林

Figure 4. Vegetation changes before and after AT fallout. 辻・小杉 (1991).

[Original printed page: 23]

WS-6-1 Kutcharo-Shoro Tephra at Shiranuka, Hokkaido

Hiroshi Machida

• Locality: Shoro, Shiranuka Town, Hokkaido
• Latitude and longitude: N43°59′30″ E144°10′05″
• Elevation: 45m
• Outcrop type and current condition: earth and sand quarry; probably extant
• Deposit types and age: marine-terrace deposits, pyroclastic-flow deposits, and volcanic ash; Late Pleistocene
• Date of description: 1984
• Keywords: Aso-4 tephra; Kutcharo-Shoro tephra; Shikotsu-1 tephra; Kuttara-8 tephra; Kutcharo-4 pyroclastic-flow deposit

One tephra widely distributed in eastern Hokkaido was named Kutcharo-Shoro tephra (Kc-Sr). It comprises the previously recognized Kutcharo-1 pyroclastic-flow deposit (勝井・佐藤, 1963) and its associated fallout ash. Many exposures of this tephra occur in eastern Hokkaido, but this outcrop has value as a type locality because the fallout ash can be recognized independently and its relationships with underlying tephras are clear.

Here approximately 4.5m of tephra overlies marine-terrace deposits of the Last Interglacial. The principal marker tephras, from below, are the Kutcharo-4 pyroclastic-flow deposit (Kc-4; the main component of Kc-Hb tephra), Aso-4 tephra (Aso-4), Kuttara-8 tephra (Kt-8), Shikotsu-1 tephra (Spfa-1), and Kutcharo-Shoro tephra. Kc-Sr is yellowish-white and consists mainly of pumice-type volcanic glass of pyroxene-rhyolitic to dacitic composition, with a small amount of bubble-type glass. It is probably co-ignimbrite ash of the Kutcharo-1 pyroclastic-flow deposit, but may be a product of a phreatomagmatic eruption early in the eruptive sequence. Its eruption age is considered to be 30–32ka from radiocarbon dates of charred wood fragments in the pyroclastic-flow deposit and its stratigraphic relationship with Spfa-1, but it may be slightly older. Generally it has undergone intense involution together with Spfa-1. At this outcrop, however, involution in this tephra is less conspicuous than in the underlying Spfa-1. For the Kutcharo-1 pyroclastic-flow deposit, refer to descriptions of outcrops at Koshimizu and Shari (WS-6-2, WS-9-4, HK-6, etc.).

References: 勝井・佐藤 (1963); Arai et al. (1986)

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1:50,000 “Shiranuka” (Kushiro No. 15); Nemuro Main Line; Shoro; 65; 54

Original Japanese lettering

5万分の1『白糠』（釧路15号）; 根室本線; 庶路; 65; 54

1:50,000 “Shiranuka” map sheet (Kushiro No. 15).

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Kc-Sr; Spfa-1; Kt-8; Aso-4; Kc-4(pfl); charred wood; Otanoshike Formation; basement; 5m

Original Japanese lettering

Kc-Sr; Spfa-1; Kt-8; Aso-4; Kc-4(pfl); 炭化材; 大楽毛層; 基盤; 5m

[Original printed page: 24]

WS-6-2 Kutcharo Pyroclastic-Flow Deposit I around Koshimizu, Hokkaido

奥村晃史

• Locality: left bank of the Ponyanbetsu River, Koshimizu Town, Hokkaido
• Latitude and longitude: N43°50′26″ E144°27′14″
• Elevation: 40m
• Outcrop type and current condition: artificial exposure; unknown
• Deposit types and age: pyroclastic-flow deposits and fallout tephra; Late Pleistocene
• Date of description: June 1984
• Keywords: Shari Plain; Kutcharo pyroclastic flow I; Kutcharo-Shoro tephra; eastern Hokkaido

Kutcharo pyroclastic-flow deposit I (KP I) is a large-scale felsic pyroclastic-flow deposit erupted contemporaneously with Kutcharo-Shoro tephra (KSr or Kc-Sr). It occurs mainly within approximately 50km west and north of Kutcharo caldera, with part reaching the Nemuro Strait [abbreviations follow 奥村 (1991); K.P. flow I: 勝井・佐藤 (1963); Kutcharo I, Kc-1: 町田・新井 (1992)]. At an outcrop 1km west of central Koshimizu (Loc. 1), KP I–KSr occupies a dissected valley in hills composed of tephras ranging from KP IV (WS-16-1) to Kpfa-2 (Kutcharo pumice fall II: 勝井・佐藤, 1963). Here an alternating sequence of fallout ash and pumice approximately 20cm thick covers an unconformity before emplacement of the pyroclastic flow, which then filled the valley. At this outcrop, the lowermost pyroclastic-flow deposit, more than 5m thick, is overlain successively by coarse pumice (15cm), well-sorted volcanic ash containing accretionary lapilli (approximately 1m), and a pyroclastic-flow deposit. At Minami 11-go, 8–9-sen, 5km east of Koshimizu (Loc. 2), a pyroclastic-flow deposit more than 5m thick is overlain by 3–5m of alternating coarse pumice, with grain sizes of 10–20cm, and well-sorted volcanic ash locally containing accretionary lapilli. Of these tephra units, the initially erupted alternating ash and pumice fall is ubiquitous around Koshimizu and Shari and shows the characteristics of fallout tephra, increasing in thickness eastward (WS-7-3). The mechanisms and distributions of eruption and deposition of the ash and pumice intercalated in the pyroclastic-flow deposits are unknown. These facies changes, however, suggest that the KP I–KSr eruption probably involved repeated violent phreatomagmatic explosions generating co-ignimbrite ash. KSr is considered to comprise fallout tephra immediately below the pyroclastic-flow deposit together with co-ignimbrite ash.

References: 勝井・佐藤 (1963); 町田・新井 (1992); 奥村 (1991)

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Loc.1; Loc.2; Koshimizu; Minami 9-go; Minami 11-go; 54; 65; 1:50,000 “Koshimizu” (Shari No. 9); 1:50,000 “Shari” (Shari No. 5)

Original Japanese lettering

Loc.1; Loc.2; 小清水; 南九号; 南十一号; 54; 65; 5万分の1『小清水』（斜里9号）; 5万分の1『斜里』（斜里5号）

1:50,000 “Koshimizu” (Shari No. 9); 1:50,000 “Shari” (Shari No. 5).

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Loc.1: 2m; 0; Kpfa-2; Kpfa-3; KPII/III; Aso-4; Kpfa-4; Kpfa-5; KPIV; KP I-KSr; massive pyroclastic flow; ash and accretionary lapilli; coarse pumice clasts; massive pyroclastic flow; alternation of ash and pumice falls. Loc.2: 2m; 0; Yambetsu Pfa; ash and pumice dune; ash and accretionary lapilli; coarse pumice clasts; massive pyroclastic flow; KP I-KSr. Basal KP I–KSr at Loc. 1 west of central Koshimizu; uppermost KP I–KSr at Loc. 2, Koshimizu Minami 11-go, 8–9-sen.

Original Japanese lettering

Loc.1: 2m; 0; Kpfa-2; Kpfa-3; KPII/III; Aso-4; Kpfa-4; Kpfa-5; KPIV; KP I-KSr; massive pyroclastic flow; ash and accretionary lapilli; coarse pumice clasts; massive pyroclastic flow; alternation of ash and pumice falls. Loc.2: 2m; 0; Yambetsu Pfa; ash and pumice dune; ash and accretionary lapilli; coarse pumice clasts; massive pyroclastic flow; KP I-KSr. Loc.1（小清水市街西方）のKPⅠ-KSr基底部；Loc.2（小清水南11号8–9線）のKPⅠ-KSr最上部

Basal KP I–KSr at Loc. 1, west of central Koshimizu.

Uppermost KP I–KSr at Loc. 2, Koshimizu Minami 11-go, 8–9-sen.

[Original printed page: 25]

WS-7-1 Shikotsu-1 Tephra and Overlying Tephra Layers at Bibi, Hayakita Town, Hokkaido

Hiroshi Machida and 山縣耕太郎

• Locality: Bibi, Hayakita Town, Hokkaido
• Latitude and longitude: N42°45′30″ E141°43′30″
• Elevation: 25m
• Outcrop type and current condition: cliff on factory premises; planted with vegetation
• Deposit types and age: fallout tephra and pyroclastic-flow deposits; Late Pleistocene–Holocene
• Date of description: 1990
• Keywords: Shikotsu-1 tephra; Eniwa-a tephra; Shikotsu caldera; fossil forest; Tarumae tephra group; Bibi

Shikotsu-1 tephra consists mainly of a large-scale pyroclastic-flow deposit (Spfl) and its preceding pumice fall (Shikotsu-1 Pumice; Spfa-1). The latter covers central to eastern Hokkaido and has been useful in chronology as a widespread marker tephra. This outcrop lies on an upland composed mainly of tephra, 25km east of the rim of Shikotsu caldera. This tephra and the overlying tephras erupted from Eniwa and Tarumae volcanoes form beautiful stripes. Shallow valleys dissect the upland, and the Bibi shell midden lies at a nearby valley head. Most of the exposure has now been planted, but several similar outcrops occur nearby. The basal pumice fall reaches 6m in thickness and is one of Japan's largest Plinian pumice tephras. It is an amphibole–pyroxene-rhyolitic tephra consisting of well-vesiculated, silky-lustered white and pink pumice. Both amphibole and orthopyroxene are iron-rich and have characteristically high refractive indices. Most of the pyroclastic-flow deposit has the same composition as the pumice fall, but its upper part becomes somewhat more mafic and locally changes to a scoria-flow deposit. A forest buried and charred by this tephra was reported nearby (勝井, 1958). Tree trunks stood upright in Spfa-1, as they also do at this outcrop, but were broken and fallen in Spfl. Repeated radiocarbon dating of charred wood fragments yielded a wide range of 31–40ka. The age is probably near 40ka (加藤ほか, 1995). A cold climate during and after the eruption is indicated not only by the buried vegetation but also by intense cryoturbation of Spfa-1 in many places. Whether its eruption age extends back to stage 4 of the marine-isotope chronology, however, requires evidence from marine-floor sediments containing this tephra.

Among the tephras above Shikotsu-1, Eniwa-a (En-a) is a marker tephra for the Last Glacial Maximum (stage 2), with radiocarbon dates of 15–17ka. It has been useful in studies of glacial landforms and deposits in the Hidaka Mountains and fluvial terraces on the Tokachi Plain. Tarumae-d (Ta-d) and Tarumae-c (Ta-c) are marker beds for the Initial and Final Jomon periods, respectively. Tarumae-b and -a (Ta-b, a) are fallout tephras of 1667 and 1739, respectively. All were accompanied by pyroclastic flows, but those flows did not reach this locality. Baitoushan–Tomakomai tephra (B-Tm) is recognized in patches in the volcanic-ash soil between Ta-c and Ta-b.

References: 勝井 (1958, 1959); 加藤ほか (1995)

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English translation of figure lettering

1:50,000 “Chitose” (Sapporo No. 8); Bibi; Bibi River; Gozen-sui (御前水); Tomioka; Chitose railway; 22.60; 22.7; 3.76; 7.80; 26.5

Original Japanese lettering

5万分の1『千歳』（札幌8号）; 美々; 美々川; 御前水; 富岡; 千歳線; 22.60; 22.7; 3.76; 7.80; 26.5

1:50,000 “Chitose” map sheet (Sapporo No. 8).

[Original printed page: 26]

WS-7-1 (continued)

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Ta-a,b; Ta-c; Ta-d; En-a (>1m); Spfl (7–8m); Spfa-1 (>6m); 20cm; Ta-a; Ta-b; B-Tm; Ta-c

Original Japanese lettering

Ta-a,b; Ta-c; Ta-d; En-a (>1m); Spfl (7–8m); Spfa-1 (>6m); 20cm; Ta-a; Ta-b; B-Tm; Ta-c

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English translation of figure lettering

Ta-a,b; Ta-c; Ta-d; En-a; Spfl; Spfa-1; photograph by 鈴木正章

Original Japanese lettering

Ta-a,b; Ta-c; Ta-d; En-a; Spfl; Spfa-1; 鈴木正章撮影

Photograph by 鈴木正章.

[Original printed page: 27]

WS-7-2 Relict Periglacial Features and Shikotsu-1 Tephra on the Tokachi Plain

平川一臣

• Locality: Sakae 8-go, 2-sen, Memuro Town, Kawanishi District (川西郡), Hokkaido
• Latitude and longitude: N42°49′24″ E143°05′00″
• Elevation: 280m
• Outcrop type and current condition: artificial exposure; disappeared
• Deposit types and age: aeolian tephra; Late Pleistocene
• Date of description: August 1980
• Keywords: Tokachi Plain; relict periglacial features; Shikotsu-1 tephra; Eniwa-a tephra

Tephra layers covering terrace landforms on the Tokachi Plain are known to have undergone disturbance related to freezing and thawing. These structures are called involutions, cryoturbation, or collectively relict periglacial features. Fresh exposures, such as slopes exposed during road construction, are needed to observe them. At this outcrop Shikotsu-1 tephra (Spfa-1), Eniwa-a tephra (En-a), and Tarumae-d tephra (Ta-d) are seen, with the first two disturbed. Disturbance in Spfa-1 is a typical example, showing various forms of deformation. En-a, by contrast, shows little intrusion into the overlying layer; the bed as a whole is flexed. Regarding the timing of disturbance, the Spfa-1 layer almost reaches the En-a horizon. Its disturbance therefore either continued until around the En-a fallout or occurred at about that time, rather than at the time of Spfa-1 fallout. Recent C-14 dates of 42ka for Spfa-1 (柳田, 1992) and 18ka for En-a (加藤, 1994) have been obtained. On the Tokachi Plain, underlying tephras down to Kuttara-1 (Kt-1), Kuttara-3 (Kt-3), and Shikotsu-7–10 (Spfa-7–10) also show conspicuous relict periglacial features similar to those in Spfa-1. These features do not provide direct evidence, but together with other types of relict periglacial features they suggest that permafrost developed on the Tokachi Plain during the coldest part of the Last Glacial.

References: 平川 (1984); 加藤 (1994); 柳田 (1992)

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1:25,000 “Kamiobihiro” (Obihiro No. 16-3); 8-go; 9-go; 127; 123; 131; 134; 142

Original Japanese lettering

2.5万分の1『上帯広』（帯広16号-3）; 八号; 九号; 127; 123; 131; 134; 142

1:25,000 “Kamiobihiro” map sheet (Obihiro No. 16-3).

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Ta-d; En-a; Spfa-1; Terrace gravel; m; 0; 1; 2; 3; 4; 5; 6; 0; 5; 10; 15; 20; 25; 30; 35; 40; 45; a; a′; ?

Original Japanese lettering

Ta-d; En-a; Spfa-1; Terrace gravel; m; 0; 1; 2; 3; 4; 5; 6; 0; 5; 10; 15; 20; 25; 30; 35; 40; 45; a; a′; ?

[Original printed page: 28]

WS-7-3 Shikotsu tephra 1 and Kutcharo pyroclastic-flow deposit I in the eastern Shari Plain

Koji Okumura

Locality: Shuen, Shari Town, Hokkaido. Coordinates: N43°53′34″ E144°45′08″. Elevation: 25 m. Exposure and present condition: artificial exposure; condition unknown. Deposit and age: tephra fall; Late Pleistocene. Date described: August 1985. Keywords: Shari Plain; Kutcharo pyroclastic-flow deposit I; involution.

Since the 1970s, Shikotsu tephra 1 (Spfa-1) had been correlated as a widespread tephra between the Ishikari Lowland and the Tokachi Plain. Okumura et al. (1985) and Arai et al. (1986) showed that it could be traced into eastern Hokkaido, where it lies immediately below Kutcharo pyroclastic-flow deposit I–Kutcharo-Shoro ash (KP I–Kc-Sr; WS-6). The abbreviations follow Okumura (1991). Spfa-1 in eastern Hokkaido consists of pumice-type volcanic glass resembling a finer-grained version of the pumice produced by the Plinian eruption farther west. This distinguishes it from other widespread tephras dominated by bubble-wall glass with a spherical-shell form. It contains almost none of the amphibole phenocrysts characteristic of Spfa-1 near its source, and the refractive indices of its orthopyroxene resemble those of Kutcharo-derived tephras. Nevertheless, its volcanic-glass chemistry differs from that of eastern Hokkaido tephras and agrees completely with Spfa-1 at the type locality (Okumura, 1991).

In the lower half of the Shuen exposure in Shari Town, alternating pumice- and scoria-fall layers, apparently derived from Kutcharo volcano, and volcanic-ash soil have been severely disturbed by periglacial processes. Spfa-1 is a yellowish-white, loose ash in the upper part of these disturbed tephra beds, deformed into pronounced undulations; its thickness varies from 0 to 20 cm. The ash-soil layer is overlain by alternating ash and pumice emitted during the early stage of the KP I eruption. The ash consists mainly of finely fragmented volcanic glass and contains abundant accretionary lapilli, indicating a large phreatomagmatic explosion preceding the emplacement of KP I (WS-6). Above this is volcanic-ash soil consisting chiefly of KP I glass and pumice fragments, with cross-lamination indicating secondary aeolian deposition. The KP I horizon and the overlying Yambetsu pumice fall (Sato, 1968) have undergone almost no disturbance since deposition, in contrast to the intense disturbance at the Spfa-1 horizon.

References: Arai et al. (1986); Okumura (1991); Okumura et al. (1985); Sato (1968).

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1:50,000 Shari (Shari sheet 5); 1:50,000 Minehama (Shari sheet 1). Shuen West; Shuen; Shuen East; stone circle; trunk line; Road No. 6; East Line 1; East Line 2. Legible numerical labels: 33.4, 34.7, 32, 19.8.

Original Japanese lettering

5万分の1『斜里』（斜里5号）；5万分の1『峰浜』（斜里1号）。朱円西，朱円，朱円東，ストーンサークル，幹線，道六号，東一線，東二線。可読数値：33.4，34.7，32，19.8。

Reading notes

地図内の微細な文字と数値 — 一部は解像度が低く確実に読めない。

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KPI afa/pfa; Spfa-1; Yambetsu Pfa. Photograph by Fusao Arai.

Original Japanese lettering

KPI afa/pfa；Spfa-1；Yambetsu Pfa；（新井房夫氏撮影）。

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Legend: topsoil; pumice; ash; aeolian sand; volcanic-ash soil. From top: Yambetsu pumice fall; secondary aeolian deposits of KP I; alternating ash and pumice falls from the early KP-I eruption; Spfa-1. Scale: 2 m, 0.

Original Japanese lettering

凡例：表土，軽石，火山灰，風成砂，火山灰土。上から：止別降下軽石；KP Iの風成二次堆積物；KP-I噴火初期の降下火山灰／軽石互層；Spfa-1。スケール：2m，0。

[Original printed page: 29]

WS-8-1 Daisen-Kurayoshi tephra and the tephra beds above and below it at Daisen Pond, Sekigane Town, on the eastern foot of Daisen

Hiroshi Machida

Locality: Daisen Pond, Sekigane Town, Tottori Prefecture. Coordinates: N35°22′21″ E133°43′33″. Elevation: 200 m. Exposure and present condition: reservoir cliff; extant. Deposit and age: pumice fall; Late Pleistocene. Date described: 1981. Keywords: Daisen-Kurayoshi tephra; Daisen-Sekigane tephra; Daisen-Namatake tephra; Aira-Tn tephra; Daisen-Hiruzen tephra; Daisen-Matsue tephra; Sambe-Kisuki tephra; Daisen-Sasaganaru tephra (笹ヶ平); Daisen-Higashidaisen tephra; Daisen volcano.

Daisen-Kurayoshi tephra was first described from a single thick pumice-fall bed seen at Dakeiji (駄経寺), Akiki (秋喜), and other localities in Kurayoshi City. Farther south, in Sekigane Town, however, several thick, weathered pumice-fall beds of similar appearance occur and must be distinguished. The exposure at Daisen Pond in Sekigane Town is therefore chosen here as the type locality. As this is an irrigation reservoir, the exposure can be examined only when the water level is low. Many similar exposures occur nearby. Three closely similar yellow-orange pumice beds occur below Aira-Tn tephra (AT), a yellowish-white glassy ash 20 cm thick. The uppermost is Daisen-Kurayoshi tephra (DKP). It is a biotite-bearing pyroxene–amphibole dacitic tephra. Although the pumice retains its grain shapes, it is almost completely weathered, so volcanic glass cannot be recovered. In distal areas from Hokuriku onward, DKP forms a vivid yellow, fine-grained pumice bed rich in phenocrysts as a result of weathering. Its names in Shinshu, such as “white sesame” and “yellow sesame,” likewise reflect these compositional characteristics. Orthopyroxene has a tabular habit with well-developed (100) faces. The underlying Daisen-Sekigane tephra (DSP) and Daisen-Namatake tephra (DNP) have similar phenocryst assemblages, but are distinguished by the refractive indices and crystal habits of orthopyroxene and amphibole (Machida and Arai, 1979). Few direct ages have been obtained for the DKP eruption; its stratigraphic relationships with other dated tephras suggest an age of approximately 50 ka. See, for example, the exposures in eastern Kanto and at Takano in Shinshu (WS-8-3, WS-9-2).

Tephras above AT are not well preserved at this exposure. Immediately above AT, however, are Daisen-Sasaganaru tephra (DSs), including a thin but widely distributed pyroclastic-flow deposit, and stratified Daisen-Higashidaisen tephra (DHg). Below DKP, Sambe-Kisuki tephra (SK), with marbled white pumice and quartz phenocrysts, can be identified with the naked eye between DNP and the Daisen-Hiruzen (DHP) and Daisen-Matsue (DMP) tephras (Tsukui and Sakuyama, 1981). Volcanic glass from K-Tz and Aso-4 can also be detected in weathered volcanic-ash soil above SK. This exposure thus establishes the stratigraphic relationships of Daisen-derived tephras to widespread tephras from Sambe and Kyushu.

References: Machida and Arai (1979); Tsukui (1984); Tsukui and Sakuyama (1981).

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1:25,000 Taikyuji (Matsue sheet 4-2). Daisen Pond; Taikyuji; Kurayoshi railway line; footpath; Daimyojin (大明神). 233.

Original Japanese lettering

2.5万分の1『泰久寺』（松江4号-2）。大山池，泰久寺，倉吉線，歩道，大明神。233。

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DKP; DSP; DNP.

Original Japanese lettering

DKP；DSP；DNP。

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Tephra stratigraphic column at Daisen Pond. Depth: 0, 5, 10 m. From top: DHg, DSs, AT, DKP, DSP, DNP, SK, DHP, DMP.

Original Japanese lettering

大山池のテフラ柱状図。深度：0，5，10 m。上から：DHg，DSs，AT，DKP，DSP，DNP，SK，DHP，DMP。

[Original printed page: 30]

WS-8-2 Daisen-Kurayoshi and Aira-Tn tephras on fluvial terraces of the Joganji River, Toyama Prefecture

Hiroshi Machida

Localities: 天林, Tateyama Town, Toyama Prefecture (site 1); Chigaki, Tateyama Town, Toyama Prefecture (site 2). Coordinates: N36°35′37″ E137°20′03″ (site 1); N36°34′23″ E137°22′28″ (site 2). Elevations: 260 m (site 1), 350 m (site 2). Exposure and present condition: roadside; extant. Deposits and age: volcanic-ash soil, pumice, and ash; Late Pleistocene. Date described: July 1995. Keywords: Daisen-Kurayoshi tephra; Aira-Tn tephra; Uwadann terrace; Awasuno terrace; Joganji River.

The Joganji River, which flows down from the Tateyama Range in the Northern Alps, has long been studied as a type area for fluvial terrace development (e.g., Fujii et al., 1966). In addition to landforms and sediments, widespread marker tephras assist research into the river's development. Of the Late Pleistocene terraces, the Uwadann (うわだん) and Awasuno (あわすの) terraces are well developed. Both are prominent aggradational terraces: the former occurs on the downstream alluvial fan, whereas the latter forms steeply sloping terraces in the upstream mountains. Site 1, in woodland a short distance from the road, shows Daisen-Kurayoshi tephra (DKP) and younger deposits resting on the Uwadann terrace at 天林. By pushing aside vegetation and carefully examining the brown volcanic-ash soil about 50 cm above the gravel, DKP can be recognized as a reddish-brown, patchy, fine-grained pumice bed 5 cm thick. The 60 cm of unstratified volcanic-ash soil above it is derived from DKP and contains orthopyroxene with a characteristic crystal habit, amphibole, and biotite. Above this is soil containing abundant volcanic glass derived from Aira-Tn tephra (AT). Site 2 is suitable for observing an unmixed AT bed. As shown in Figure 2, it occurs there as a striking white glassy ash bed between fine sand and gravel beds.

The deposits at site 2 represent the uppermost terrace sediments extending from Awasuno to Ashikuraji (芦峅寺). Farther upstream, on the Awasuno terrace, AT is deposited as a fairly thick brown ash layer over sand and gravel. These observations make clear that the Uwadann terrace formed before the DKP eruption and the Awasuno terrace before AT, in association with the downstream transport of large amounts of sand and gravel. An important question is whether these aggradational terraces formed through regionally shared causes related to climate and vegetation changes, or through local causes such as volcanic activity and frequent mountain-slope failures.

References: Fujii et al. (1966); Machida (1992).

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1:50,000 Gohyakukoku (Takayama sheet 9). Sites 1 and 2. Map place labels: 東中野, 新, 天林, 新村, 横江, 岡田, 尖山, Chigaki (千垣), 座主坊. Legible elevations and other numbers: 434, 559.4, 860, 263, 284.2.

Original Japanese lettering

5万分の1『五百石』（高山9号）。地点1，2。東中野，新，天林，新村，横江，岡田，尖山，千垣，座主坊。可読標高等：434，559.4，860，263，284.2。

Reading notes

地図内の天林付近の標高と微細な注記 — 小さく不鮮明で確定できない。

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DKP →; DKP resting on the Uwadann gravel bed at 天林; AT interbedded in sand and silt at Chigaki, on the Awasuno terrace.

Original Japanese lettering

DKP→；天林の上段礫層上にのるDKP；千垣の砂シルト層（粟巣野段丘上）中に挟まれるAT。

[Original printed page: 31]

WS-8-3 Stratigraphic position of Daisen-Kurayoshi tephra in Kanto: Daisen-Kurayoshi tephra immediately above Hakone-Tokyo tephra

Takehiko Suzuki

Locality: 房中, Dejima Village, Ibaraki Prefecture. Coordinates: N36°3′57″ E140°19′28″. Elevation: 22 m. Exposure and present condition: artificial exposure; extant. Deposit and age: aeolian tephra; Late Pleistocene. Date described: June 1996. Keywords: Lake Kasumigaura; Daisen-Kurayoshi tephra; Hakone-Tokyo tephra; Akagi-derived tephras.

Establishing the stratigraphic position of Daisen-Kurayoshi tephra (DKP) in Kanto was extremely important for determining its eruption age. The process of establishing that position was somewhat complicated. Initially, DKP at the foot of Akagi volcano in northern Kanto was placed below Haruna-Hassaki tephra and above Akagi-Yunokuchi tephra (Ag-UP) (Machida and Arai, 1979). Takemoto (1984) subsequently revised its position to below Ag-UP. Suzuki (1990a) then confirmed around Akagi volcano that DKP lies below Akagi-Namekawa tephra 2, itself below Ag-UP, and above Akagi-Mizunuma tephra 1. Although its stratigraphic position in northern Kanto had thus been defined in detail, its relationships with tephras distributed principally in southern Kanto remained unknown, because the southern limit of DKP passes through the southern parts of Gunma, Tochigi, and Ibaraki prefectures. Takemoto (1991), however, showed that DKP is mixed into the matrix in the uppermost part of Hakone-Tokyo tephra (Hk-TP), an important marker bed in southern Kanto.

At the present exposure near the shore of Lake Kasumigaura, both DKP and Hk-TP can be clearly identified in the field with the naked eye, making their relationship readily apparent. DKP occurs in patches 1–2 cm thick approximately 260 cm below the ground surface. Below it, separated by 8 cm of volcanic-ash soil, is Hk-TP, consisting of fine pumice 5 cm thick. Places where both can be clearly identified are limited, however. Radiometric ages for Hk-TP include the fission-track age of 49 ± 9 ka reported by Machida and Suzuki (1971) and, more recently, the ¹⁴C ages of 50–55 ka reported by Nakamura et al. (1992). Combining the latter measurements with ¹⁴C ages for the Kiso River mudflow deposit, Nakamura et al. (1992) placed the DKP fall at 50–52 ka.

References: Machida and Arai (1979); Machida and Suzuki (1971); Nakamura et al. (1992); Suzuki (1990a); Takemoto (1984, 1991).

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Overview: NW, N, NE; enlarged area; volcanic-ash soil; sand bed; photographed June 1996. Close-up: DKP, Hk-TP. Map: 1:25,000 Kihara (Mito sheet 12-4); 房中, 八田. Legible numbers: 24.3, 25.2, 33.3, 23.5. The cropped prose at upper left is included in the main text.

Original Japanese lettering

全景：NW，N，NE；拡大部分；火山灰土；砂層；1996年6月撮影。接写：DKP，Hk-TP。位置図：2.5万分の1『木原』（水戸12号-4）；房中，八田；可読数値24.3，25.2，33.3，23.5。画像左上の本文断片は本文欄に収録済み。

Reading notes

地形図の小さな文字・数値 — 不鮮明な箇所は読取りを確定できない。

[Original printed page: 32]

WS-9-1 Aso-4 pyroclastic-flow deposit southeast of Kuju volcano, Oita Prefecture

Koji Ono

Locality: cliff beside the prefectural road south of Nagayu, Naoiri Town, Naoiri District, Oita Prefecture. Coordinates: N33°03′48″ E131°23′03″. Elevation: 460 m. Exposure and present condition: artificial exposure; extant. Deposit and age: pyroclastic-flow deposit; Late Pleistocene. Date described: March 1996. Keywords: Imaichi pyroclastic-flow deposit; Aso-4 pyroclastic-flow deposit.

This exposure is beside a prefectural road 300 m south of Nagayu hot spring, southeast of Kuju volcano. A fault scarp cutting welded tuff of the Imaichi pyroclastic-flow deposit (“deposit” is omitted below in the original) extends for more than 10 km along the southern bank of the northeast-flowing Seri River, a tributary of the Oita River. The Aso-4 pyroclastic-flow deposit unconformably covers the base of this scarp and forms a surface along the Seri River about 100 m below the surface of the Imaichi pyroclastic-flow plateau to the south. Although the unconformity is not exposed here, the strongly welded zone near the base of Aso-4 and the upper weakly welded to nonwelded zone can be observed continuously over a distance of about 100 m.

In fact, this exposure lies below the base of the Imaichi pyroclastic-flow deposit. Aso-4 covers the weathered surface of pyroxene andesite underlying Imaichi, on a surface sloping gently toward the pre-Aso-4 Seri River. Consequently, foliation in the welded tuff consistently dips northwest toward the river. Along the road, progressively higher stratigraphic levels are exposed from south to north, continuously from the strongly welded zone at the southern end to the weakly welded zone at the northern end. Hardness changes with the degree of welding, as indicated by changes in the pitch produced by hammer blows. The welded tuff is largely glassy throughout the exposure. In its weakly welded part, flattened pumice stands out from the matrix on weathered surfaces (photograph). A small interval near the northern end is devitrified and has become pale grayish white overall. There, pumice weakened by vapor-phase crystallization is instead recessed below the matrix on weathered surfaces. At the northern end of the roadside exposure, the degree of welding falls to the very earliest stage of welding; the very weakly welded to nonwelded part forms a sand-extraction pit behind it. This exposure corresponds to Aso-4A of the Aso-4A and Aso-4B units of Ono et al. (1977). Watanabe (1978) divided Aso-4 west of the caldera into eight subunits. A unified re-examination of the entire Aso-4 pyroclastic-flow deposit is needed.

References: Ono (1963); Ono et al. (1977); Watanabe (1978).

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1:25,000 Asaji (Oita sheet 10-2). Nagayu; 栃原; public lodge; 田原. Legible numbers: 523, 587.3, 684.

Original Japanese lettering

2.5万分の1『朝地』（大分10号-2）。長湯，栃原，国民宿舎，田原。可読数値：523，587.3，684。

Reading notes

地図内の微細な標高・地名 — 一部が不鮮明で確実には読めない。

[Original printed page: 33]

WS-9-2 The lacustrine Takano Formation at Takano, Shinko Town, Nagano City: a host succession for widespread marker tephras spanning approximately 130,000 years

Jun-ichi Kimura

Locality: Takano area, Shinko Town, Nagano City. Coordinates: N36°32′35″–45″ E138°02′10″–20″. Elevation: 720–730 m. Exposure and present condition: cliffs along a small river; extant in August 1995, but generally poor except in a few places. Deposits and age: lacustrine clay and silt beds; Late Pleistocene. Date described: August 1986. Keywords: Takano Formation; Ontake-derived tephras; Tateyama-derived tephras; widespread tephras.

The Takano Formation accumulated through almost the entire Late Pleistocene in a narrow lake within the Saigawa Hills. It is one of the most valuable sources of information in central Japan. The formation consists predominantly of fine-grained silt and clay. Pumiceous tephras from Kiso-Ontake and Tateyama volcanoes, together with widespread tephras, are well preserved, allowing their stratigraphic relationships to be established clearly. By combining several small exposures, nearly the entire stratigraphy of the Takano Formation can be observed without gaps (Kimura, 1987a). Unfortunately, exposure conditions deteriorate each year, and some parts can now be observed only by excavating through collapsed material. Because the exposures are in walls of cultivated land, the landowner must be identified and permission obtained before excavation. The widespread and subregional tephras interbedded in the formation were correlated by Takemoto et al. (1987) and Kimura (1987b). The principal exposures are as follows (Figure 3).

Exposure 18: pumice thought to be derived from Tateyama (SyPm, possibly Omachi C scoria?) and an overlying gravel bed. Exposure 16: in ascending order, Tateyama D (Tt-D, the thickest tephra, composed of coarse pumice), Aso-3, Ontake tephra 1 (On-Pm1, Pm-1A/B), Kikai-Tozurahara (K-Tz), Ontake-Katamachi (On-Kt, Pm-2B), and Aso-4. Exposure 14: Aso-4 and Ontake-Nagawa (On-Ng, Pm-3C), with Tateyama E (Tt-E) at the top. Exposures 7–11: Daisen-Kurayoshi tephra (DKP) and thin basaltic-andesitic volcanic-sand beds. Exposure 12: above two thin basaltic-andesitic volcanic-sand beds are two further volcanic-sand beds, OL.S.; Aira-Tn tephra (AT) is interbedded at the top. The numerous basaltic-andesitic volcanic-sand beds from around Tt-E through OL.S. are regarded as scoria from Kiso-Ontake volcano. These tephras are well preserved because they are enclosed in fine-grained sediments.

The Takano Formation fills a small fault-angle depression bounded to the northwest by the east-downthrown Takanogawa Fault and to the southwest by the north-downthrown Karuizawa Flexure. The depositional surface lies at 730–740 m elevation and curves gently downward toward the center. The Takano River, flowing through the center of the basin, has incised gullies into this surface. Although the depositional area is small, approximately 1.5 × 1 km, drilling and electrical surveys show a maximum thickness of nearly 50 m (a cross-section is given in Kimura, 1987a). Minor nonsequences at the margins of the depositional basin provide the basis for dividing the formation into lower, middle, upper, and uppermost members. Apart from gravel beds at the base, its facies consist almost entirely of clay to silt, relatively rich in humic material, with plant fossils and precipitated vivianite. Interbeds of fine sand increase toward the margins, and at the outermost margins the succession consists entirely of fine sand. No pronounced erosion is recognized at the basin center, suggesting that the water body persisted. The cumulative thickness confirmed in exposures is about 25 m.

Taking Tt-D to be approximately 120 ka and AT approximately 25 ka, deposition of the Takano Formation is considered to span about 130,000 years, approximately 150–20 ka. The roughly 20 m between below Tt-D and AT records nearly continuous fine-sediment accumulation and is particularly suitable for analyzing paleoenvironmental change. Sakai (1988) reported changes in the formation's fossil pollen assemblages. The interval from below Tt-D to above On-Ng is considered to correspond to oxygen-isotope stages 5d–5a; Tt-E to early to middle stage 4; the interval around OL.S. to middle stage 3; and the beds above AT to stage 2.

References: Kimura (1987a, b); Sakai (1988); Takemoto et al. (1987).

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Figure 1. Route to the exposures. 1:25,000 Inariyama (Nagano sheet 13-4). Shinko Town; Takano; 島仁田; 郷津; 平条; Hikage. Numbers: 846, 828, 796, 752, 832. Figure 2. Detailed exposure-location map, modified from Kimura (1987a). 常安寺; Takano; Hikage; 島仁田; Takano River; 郷津. Sites: HB-1, TA-01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, SG-1. Contours: 800 m, 750 m. Coordinates: 138°02′10″, 36°32′40″. Distance: 0–200 m. The reference line at upper left is included in the main text.

Original Japanese lettering

図1。露頭のルート。2.5万分の1『稲荷山』（長野13号-4）。信更町，高野，島仁田，郷津，平条，日影。数値846，828，796，752，832。図2 露頭詳細位置図　木村(1987a)を一部改変。常安寺，高野，日影，島仁田，高野川，郷津。地点HB-1，TA-01，02，03，04，05，06，07，08，09，10，11，12，13，14，15，16，17，18，SG-1。等高線800m，750m。座標138°02′10″，36°32′40″。距離0～200m。画像左上の文献行は本文に収録済み。

[Original printed page: 34]

WS-9-2 (continued)

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Exposure numbers: 1–18. Scale: 0, 5 m. Legend: silt; sand; gravel; peat; peaty sediment. Volcanic-ash symbols: fine-grained; coarse-grained; pumice; lapilli; scoria. Correlation labels: AT, OL.S., DKP, Tt-E, Tt-D, basic ash, On-Ng, On-Kt, Aso-4, K-Tz, On-Pm1, Aso-3, Sy Pm. Members, from top: uppermost; upper; middle; lower. Correlation lines link equivalent horizons between columns; some are dotted.

Original Japanese lettering

露頭番号：1，2，3，4，5，6，7，8，9，10，11，12，13，14，15，16，17，18。スケール：0，5m。凡例：シルト，砂，礫，泥炭，泥炭質；火山灰：細粒，粗粒，軽石，ラピリ，スコリア。相関ラベル：AT，OL.S.，DKP，Tt-E，Tt-D，basic ash，On-Ng，On-Kt，Aso-4，K-Tz，On-Pm1，Aso-3，Sy Pm。部層（上から）：最上部層，上部層，中部層，下部層。相関線は各列間の同一層準を結び、一部は点線。

Figure 3. Stratigraphic columns of the exposures. Modified from Kimura (1987a); correlations after Takemoto et al. (1987).

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North arrow: N. Section lines: A–A′, B–B′. Takanogawa Fault; Karuizawa Flexure; Takano River. Place labels: 常安寺; Takano; Takano Elementary School; Hikage; 島仁田; 郷津. Survey points: E-1, E-2, E-3, E-4. Geological legend: alluvium; uppermost member (K N), upper member (OL.S.) (S G), middle member, lower member (Sy Pm), collectively the Takano Formation; 千石 Formation (CA 3); 灰原 Formation (M F); Tertiary volcanic rocks; fault; flexure. KEY BEDS. Distance: 0–200 m. Coordinates: 138°02′40″E, 36°32′20″N. Legible strike-and-dip and other numbers: 2, 4, 5, 7, 8, 10, 12, 14, 15, 16, 18, 20.

Original Japanese lettering

方位N。断面線A–A′，B–B′。高野川断層 Fault；軽井沢撓曲 flexure；高野川。常安寺，高野，高野小学校，日影，島仁田，郷津。測点E-1，E-2，E-3，E-4。地層凡例：沖積層；最上部層(K N)，上部層(OL.S.)(S G)，中部層，下部層(Sy Pm)〔以上高野層〕；千石層(CA 3)；灰原層(M F)；第三紀火山岩類；断層；撓曲。KEY BEDS。距離0～200m。座標138°02′40″E，36°32′20″N。可読の走向傾斜等数値：2，4，5，7，8，10，12，14，15，16，18，20。

Reading notes

地図の微細な数値とKEY BEDSの略記 — 多くが小さく、一部は数字・文字の区切りを確定できない。可読形を保持。

Figure 4. Geological map of the Takano Formation. From Kimura (1987a).

[Original printed page: 35]

WS-9-3 Aso-4 and other widespread tephras in the lower Fuji tephra succession on the eastern foot of Mount Fuji

Hiroshi Machida

Locality: upper Nishizawa, Ikido, Oyama Town, Shizuoka Prefecture. Coordinates: N35°22′33″ E139°00′34″. Elevation: approximately 450 m. Exposure and present condition: roadside cliffs and streamside exposures; extant. Deposits and age: ash, scoria beds, and sand and gravel beds; Late Pleistocene. Date described: 1983–1985. Keywords: Fuji-Yoshioka tephra; Hakone-Obaradai tephra; Daisen-Namatake tephra; Aso-4 tephra; Ontake-Ina tephra; Kikai-Tozurahara tephra; Ontake tephra 1; Aso-3 tephra.

Where the eastern edge of Mount Fuji's eastern foot meets the Tanzawa Mountains, a group of exposures provides one of Japan's richest records of volcanic activity, crustal deformation, climatic change, and related phenomena. From the settlement of Ikido in Oyama Town, across the river from JR Suruga-Oyama Station, a forest road follows the stream northward uphill. After about 2 km, an exposure of the southern branch of the Kannawa Fault occurs on the right (Machida et al., 1975). This area lies at the boundary between the alluvial fan of the Suruga Gravel and the Tanzawa Mountains. Sediments accumulated in a wetland dammed by the main stream are well preserved beneath Fuji tephras. Another 200 m uphill, a cliff on the left side of the road exposes the Suruga Gravel and tephras. This was the first locality where detailed stratigraphic relationships between the widespread Aso-4 ash and tephras from Fuji and Hakone were established (Machida et al., 1985). Examining the exposures from A to B in Figure 2, one can recognize, in descending order between brown scoria and sand and gravel beds, Fuji-Yoshioka tephra (F-YP), Hakone-Obaradai tephra (Hk-OP), Daisen-Namatake tephra (DNP), and Aso-4 (Figures 3 and 4). The first two are more distinct than the latter two. Aso-4 is a milky-white, sand-sized ash (Figure 4) containing characteristic bubble-type volcanic glass, brown amphibole, and orthopyroxene phenocrysts. Of the Kyushu-derived widespread tephras seen nearby, it is the coarsest and richest in phenocrysts.

To examine tephras below Aso-4, descend into the stream on the right, where erosion-control structures have been built, and walk along the valley floor upstream of the dam, near C in Figure 2. The orange pumice bed 1 m thick, exposed from the valley floor to the slope, is Ontake tephra 1 (On-Pm1). A peat bed at approximately the same horizon contains fossil trunks and roots of Hime-baramomi (Picea maximowiczii). Beneath this tephra are two pumice beds, as shown in Figure 3. Careful examination reveals a discontinuous white ash only a few millimeters thick immediately below the upper pumice bed (P-A). This is Aso-3 tephra (Machida and Arai, 1995). Recent sediment accumulation behind the dam has made it extremely difficult to observe. Aso-3 is also observed immediately below On-Pm1 at several places in Shinshu (see WS-9-2, for example).

To examine tephras above On-Pm1 and below Aso-4, climb the slope on the right bank or the small stream at D in Figure 2 and scrutinize the surfaces closely. The terrain is steep, wet, slippery, and dangerous. White ash rich in bubble-type volcanic glass is Kikai-Tozurahara tephra (K-Tz). If a fine-grained pumice bed resembling white ant eggs lies above it, that is Ontake-Ina tephra (On-In). Between On-In and Aso-4 is a glassy ash of unknown volcanic source.

References: Machida (1992, 1996); Machida and Arai (1995); Machida et al. (1975, 1985).

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Figure 1. 1:25,000 Yamakita and Suruga-Oyama (Tokyo sheet 16-4; Kofu sheet 4-2). Ikido; Oyama Town; Nakajima Falls; Ochiai; 三淵; Oyama; river. Fuji spinning factory (Kanegafuchi). Legible elevations and other numbers: 449.1, 416, 407, 293, 379.2, 350, 246, 300, 370.

Original Japanese lettering

図1。2.5万分の1『山北』・『駿河小山』（東京16号-4・甲府4号-2）。生土，小山町，中島滝，落合，三淵，小山，川。富士紡工場（かねがふち）。可読標高・数値：449.1，416，407，293，379.2，350，246，300，370。

Reading notes

富士紡工場の括弧内文字と地図の微細な注記 — 括弧内は「かねがふち」と読めるが解像度が低く、他の小文字も一部は確定不能。

[Original printed page: 36]

WS-9-3 (continued)

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From top: F-YP, Hk-OP, DNP, Aso-4, On-In, K-Tz, On-Pm1, P-A, Aso-3, P-B. Sites: A, B, D, C. Stratigraphic intervals: DNP to Aso-4, 5 m; Aso-4 to the indicated lower horizon, 4 m. Scale at left: 0–5 m.

Original Japanese lettering

上からF-YP，Hk-OP，DNP，Aso-4，On-In，K-Tz，On-Pm1，P-A，Aso-3，P-B。地点A，B，D，C。層位間隔：DNPからAso-4まで5m；Aso-4から下の指示層準まで4m。左のスケール0～5m。

Figure 3. Tephra stratigraphic column in upper Nishizawa, Ikido.

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Sites A, B, C, D; 500; 425.4; 100 m.

Original Japanese lettering

地点A，B，C，D；500；425.4；100m。

Figure 2. Route map of Nishizawa, Suruga-Oyama.

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← Aso-4.

Original Japanese lettering

←Aso-4。

Figure 4.

[Original printed page: 37]

WS-9-4 Kutcharo pyroclastic-flow deposits and Aso-4 tephra in the Shari Plain

Koji Okumura

Locality: Raiun, Shari Town, Hokkaido. Coordinates: N43°51′0″ E144°38′50″. Elevation: 40 m. Exposure and present condition: artificial exposure; extant. Deposits and age: pyroclastic-flow deposits and tephra fall; Late Pleistocene. Date described: June 1994. Keywords: Shari Plain; Kutcharo IV tephra; Kutcharo II/III tephra; Kutcharo I tephra; Aso-4 tephra; Toya tephra; Shikotsu tephra 1.

Aso-4 tephra (Machida et al., 1985) is well preserved at a thickness of about 15 cm around the Shari Plain in eastern Hokkaido, more than 1,500 km from its source at Aso caldera. This is attributed to deposition of Kutcharo pyroclastic-flow deposit (KP) II/III after only a short interval following the Aso-4 fall, protecting Aso-4 against erosion and weathering. [Abbreviations for Kutcharo tephras follow Okumura (1991). This unit is K.P. flow II or III of Katsui and Sato (1963); the two are written together because they are difficult to distinguish. It is Kutcharo 2–3 (Kc-2-3) of Machida and Arai (1992).] Consequently, the Shari Plain area provides the thickest unweathered Aso-4 outside central and southern Kyushu. The fine ash correlated with Aso-4 had been recognized by Katsui and Sato (1963) as the basal fine-grained part of KP II. Aso-4, however, contains small amounts of amphibole absent from Kutcharo volcanic tephras, which are mostly two-pyroxene andesitic to rhyolitic. Its volcanic-glass refractive indices and major- and trace-element compositions also differ markedly from Kutcharo-derived tephras (Machida et al., 1985). Discovery of Aso-4 and Toya ash (WS-13; Machida et al., 1987) made it possible for the first time to correlate the Late Pleistocene tephrochronology of eastern Hokkaido with that of central and western Hokkaido and then with the rest of Japan.

At the southern end of the Shari Plain, the end of a ridge-like pyroclastic-flow plateau extending south from Kawakami Bridge over the Shari River preserves a flat depositional surface of KP IV approximately 10 m above the alluvial surface. [This is the Kutcharo debris-flow deposit, K.S. flow, of Katsui and Sato (1963); see WS16-1 for the relationship between KP IV and K.S. flow.] More than 20 m of Late Pleistocene tephras overlie this surface. The exposure at Loc. 1 (Raiun) still exists, but its steep wall has prevented detailed description. Large exposures of KP IV through KP I are scattered south of Loc. 1 (Figure 1). Loc. 2, now lost, at the northern end of the plateau south of Kawakami Bridge, was the most thoroughly described nearby exposure and the subject of various analyses. Its stratigraphy is presented here (Figure 2).

Above KP IV, exposed at the base, lies 1.5 m of weathered volcanic-ash soil containing three reddish-brown pumice-fall beds, Nishiki pumices 1–3 (Sumita, 1988). Toya volcanic glass is concentrated in the upper part of this weathered ash soil, where a yellowish layer can be recognized within the reddish-brown soil. Above it, in ascending order, are a white pumice-fall bed about 1 m thick, 50 cm of volcanic-ash soil, and Aso-4.

Aso-4 is a loose beige ash that has undergone almost no weathering. Another characteristic is the glitter produced when its volcanic glass, shaped like spherical shells with low curvature, reflects light.

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1:50,000 Shari (Shari sheet 5). Sites 1, 2. Kawakami; Shari; Shari River; 羅萌; Raiun; 水無沢. Legible numbers: 45.8, 52.

Original Japanese lettering

5万分の1『斜里』（斜里5号）。地点1，2。川上，斜里，斜里川，羅萌，来運，水無沢。可読数値45.8，52。

Reading notes

地図内の微細な地名 — 一部は解像度が低い。

Figure 1.

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Scale: 0–5 m. From top: Yambetsu pumice²⁾; KP I-KSr—K.P. flow I¹⁾, Kc-1⁴⁾; Spfa-1; Kiyosato pumice 2³⁾; Kiyosato pumice 1³⁾; Tricolor—three-color ash³⁾; lithic Pm³⁾; Big Pm³⁾; KP II/III; Aso-4; Nishiki pumice 5³⁾; Toya; Nishiki pumice 3³⁾; Kpfa-4¹⁾—Nishiki pumice 2³⁾; Kpfa-5¹⁾—Nishiki pumice 1³⁾; KP IV—K.S. flow¹⁾, Kc-4⁴⁾. Sources: 1) Katsui and Sato (1963); 2) Sato (1968); 3) Sumita (1988); 4) Machida and Arai (1992); others from Okumura et al. (1985) and Okumura (1991).

Original Japanese lettering

スケール0～5m。上から：止別軽石²⁾；KP I-KSr―K.P. flow I¹⁾ Kc-1⁴⁾；Spfa-1；清里軽石-2³⁾；清里軽石-1³⁾；Tricolor―三色火山灰³⁾；岩片Pm³⁾；Big Pm³⁾；KP II/III；Aso-4；錦軽石-5³⁾；Toya；錦軽石-3³⁾；Kpfa-4¹⁾―錦軽石-2³⁾；Kpfa-5¹⁾―錦軽石-1³⁾；KP IV―K.S. flow¹⁾ Kc-4⁴⁾。出典：1)勝井・佐藤(1963)，2)佐藤(1968)，3)隅田(1988)，4)町田・新井(1992)，他は奥村ほか(1985)，奥村(1991)。

Figure 2.

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WS-9-4 (continued)

A soil layer approximately 1 cm thick separates Aso-4 from the overlying KP II/III, indicating a time interval between them. KP II/III is a somewhat firm, compact, gray pyroclastic-flow deposit containing abundant lithic fragments. At 130 cm above KP II/III is a distinctive ash with a combination of white, reddish-brown, and gray, called Tricolor (Okumura et al., 1985). Tricolor fell when the alluvial-fan surface forming most of the Koshimizu Plateau—the Bihoro surface of Sato (1968)—was becoming abandoned by water. The white tephra common to the upper parts of the exposures described here is KP I–Kc-Sr (WS-6). It is divided into a lower interval several tens of centimeters thick of striped alternating pumice and ash falls, and an overlying white pyroclastic-flow deposit. Yellowish-white Shikotsu pumice fall 1 (Spfa-1; WS-7) occurs approximately 30 cm below KP I–Kc-Sr. The subdivision and naming of tephra-fall beds in this region are described in detail in WS-6.

References: Katsui and Sato (1963); Machida and Arai (1992); Machida et al. (1985, 1987); Okumura (1991); Okumura et al. (1985); Sato (1968).

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KP I-KSr; KP II/III; KP IV.

Original Japanese lettering

KP I-KSr；KP II/III；KP IV。

Figure 3. Exposure south of Raiun. Its stratigraphy is nearly the same as at sites 1 and 2.

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KP I-KSr; Spfa-1; KP II/III; Aso-4; KP IV.

Original Japanese lettering

KP I-KSr；Spfa-1；KP II/III；Aso-4；KP IV。

Figure 4. Exposure south of Kawakami Bridge (site 2 in Figure 1; now lost).

[Original printed page: 39]

WS-10-1 Kikai-Tozurahara tephra and marine terraces on Tanegashima

Hiroshi Machida

Locality: Noma, Nakatane Town, Kagoshima Prefecture. Coordinates: N30°31′51″ E130°58′32″. Elevation: 110 m. Exposure and present condition: cliff at the Noma Junior High School playing field; extant? Deposits and age: marine-terrace sediments and ash; Late Pleistocene. Date described: 1983. Keywords: Kikai-Tozurahara tephra; Ata tephra; Tanegashima.

The most proximal deposit of Kikai-Tozurahara tephra (K-Tz) is the Nagase pyroclastic-flow deposit on Takeshima in Kikai caldera (see Takeshima, WS-2-1). Deposits indicating its widespread distribution can be readily observed on marine terraces of Yakushima and Tanegashima. The present exposure is at Noma in central Tanegashima. The tephras above the terrace sediments reach a total thickness of 6–7 m. K-Tz is the thickest of them: a vivid yellow-orange, pyroxene-rhyolitic glassy ash (Figure 2). This tephra, 1.7 m thick, is divided into a lower half consisting of finely stratified ash and coarse phenocryst minerals—feldspar and quartz—and an upper half of unstratified glassy ash. The lower half may be regarded as a type of pyroclastic surge lofted from the pyroclastic flow, and the upper half as co-ignimbrite ash. No Plinian pumice-fall unit occurs in this tephra. Its abundance of accretionary lapilli throughout suggests that it was produced by a large phreatomagmatic eruption.

In the upper part of the tephra succession here are vivid yellow-orange glassy ashes of Aira-Tn tephra (AT) and Kikai-Akahoya tephra (K-Ah). Although absent at this exposure, Ata pyroclastic-flow deposit, no more than 1 m thick, occurs below K-Tz on the western coast of central and southern Tanegashima and at Kaminaka in Minamitane Town. K-Tz is correlated with Tozurahara pumice I, described at Tozurahara in Uenohara Town, Yamanashi Prefecture (Minagawa, 1968, 1969; see the next entry, WS-10-2). It is an important marker bed for identifying marine terraces and other sediments of oxygen-isotope stage 5c throughout western and central Japan (Machida and Arai, 1992).

Tanegashima is an island of tilted, uplifted marine terraces and, together with the Miyazaki Plain, may be regarded as a type area for marine-terrace chronology in Kyushu. Marine terrace M1, corresponding to isotope stage 5e, and younger terraces are well developed. Their relationships with tephras are particularly clear between Hamatsuwaki and Fukagawa on the western coast of Nakatane Town, and between Sunasaka and Nishime on the southwestern coast of Minamitane Town (arrows in Figure 3). Based on these localities, Figure 4 schematically shows the relationships between marine terraces and tephras (Ota and Machida, 1987). Ata covers the M1 and M2 terrace surfaces and is interbedded in M3 terrace gravel. K-Tz, in contrast, also covers the scarp between M2 and M3. These observations suggest that M3 correlates with the Obaradai terrace in southern Kanto and formed in stage 5c, whereas M4 correlates with the Misaki terrace and formed in stage 5a. This leaves the question of what M2 represents; for the present, it is regarded as dating to an interval within stage 5e.

References: Machida and Arai (1992); Minagawa (1968, 1969); Ota and Machida (1987).

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Figure 2; photographic date stamp: 83 6 14.

Original Japanese lettering

図2；写真の日付表示：83 6 14。

[Original printed page: 40]

WS-10-1 (continued)

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1:50,000 Central Tanegashima (Yakushima sheet 1). Tanegashima Airport; equestrian training ground; 伏之前; 上方; Noma; Masuda; 野山崎; Central Park; 阿曽. Legible numbers: 142, 83, 6.

Original Japanese lettering

5万分の1『種子島中部』（屋久島1号）。種子島空港，乗馬訓練場，伏之前，上方，野間，増田，野山崎，中央公園，阿曽。可読数値：142，83，6。

Reading notes

地図の細かな地名・数値 — 一部不鮮明。読みの確認ができない地名は英訳でも日本語保持。

Figure 1.

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Legend: H₁ surface; H₂ surface; H₃ surface; M₁ surface; M₂ surface; M₃–M₄ surfaces; L surface. Place labels: Mageshima; 大広野; Nishinoomote; 田ノ脇; Masuda; Noma; Shimama; 長谷野; Cape Kadokura. Scale: 0–10 km. An arrow marks the southwestern coast.

Original Japanese lettering

凡例：H₁面，H₂面，H₃面，M₁面，M₂面，M₃面～M₄面，L面。地名：馬毛島，大広野，西之表，田ノ脇，増田，野間，島間，長谷野，門倉岬。スケール：0～10km。南西岸を矢印で示す。

Figure 3. Distribution of coastal terraces on Tanegashima (Machida, 1969).

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English translation of figure lettering

From landward to seaward: M1, M2, M3, M4. Tephras: K-Tz, Ata. Vertical scale: 0, 100 m. Horizontal scale: 0–1 km.

Original Japanese lettering

陸側から海側：M1，M2，M3，M4。テフラ：K-Tz，Ata。垂直スケール：0，100 m；水平スケール：0～1km。

Figure 4. Relationships between terraces and tephras in southern Tanegashima (Ota and Machida, 1987).

[Original printed page: 41]

WS-10-2 Kikai-Tozurahara and Aso-4 tephras around Tozurahara, Fujino Town, Kanagawa Prefecture

Hiroshi Yonezawa; Yo Uesugi; Kanto Quaternary Research Group

Locality: Shibata–Tozurahara, Fujino Town, Kanagawa Prefecture. Coordinates: N35°36′0″ E139°9′0″. Elevation: 180–230 m. Exposure and present condition: natural exposures; partly extant. Deposits and age: fluvial to lacustrine sediments; Late Pleistocene. Date described: December 1980. Keywords: Ontake tephra 1; Kikai-Tozurahara tephra; Aso-4 tephra.

Small bodies of standing water associated with deposition in the main channels occur at various places along rivers around the Tanzawa Mountains. Lacustrine to fluvial sediments of this period contain numerous tephras from the Fuji and Hakone volcanic systems, as well as many Late Pleistocene widespread tephras (e.g., Minagawa, 1969; Yonezawa, 1981; Uesugi and the Kanto Quaternary Research Group, 1994). On the right bank of Maedo Stream between Shibata and Tozurahara in Fujino Town, a thick succession of deposits forming the Sagamihara surface unconformably overlies basement rock (Yonezawa, 1981). This succession approximately corresponds to the Tozurahara Formation of Minagawa (1969). Around Tozurahara it comprises lower gravel about 8–9 m thick, middle alternating sand and mud about 35 m thick, and upper gravel about 8 m thick.

The middle alternating sand and mud contains Late Pleistocene widespread tephras in the following ascending order: Ontake tephra 1 (On-Pm1; tephra Y-1 of Uesugi et al., 1980, 1983; 80–90 ka); Kikai-Tozurahara tephra (K-Tz; Machida et al., 1985; tephra Y-19 of Uesugi et al., 1980, 1983; Migakizuna 1, or polishing sand 1; TzP-I of Minagawa, 1969; 75 ka); Ontake-Ina tephra (On-In; Machida et al., 1985; tephra Y-26 of Uesugi et al., 1980, 1983; “poppy-seed pumice”; TzP-II of Minagawa, 1969); Migakizuna 2 (tephra Y-36 of Uesugi et al., 1980, 1983; TzP-III of Minagawa, 1969); and Aso-4 tephra (Machida et al., 1985; Sagamihara City Geomorphology and Geology Research Group, 1986; 70 ka).

At the site marked ■ on the exposure-location map, at Tsurushima in Uenohara Town, Yamanashi Prefecture, two fine-grained glassy tephras are interbedded in peat (Kanto Quaternary Research Group, 1979). The lower, approximately 10 cm thick, has been correlated with Aso-4 (Sagamihara City Geomorphology and Geology Research Group, 1986; Machida and Arai, 1992). Pollen analysis of the peat indicates that coniferous forest comprising Picea, Pinus, Tsuga, Abies, and other taxa was widespread at the time of the Aso-4 ash fall (Kanto Quaternary Research Group, 1979; Sagamihara City Geomorphology and Geology Research Group, 1986).

References: Kanto Quaternary Research Group (1979); Machida et al. (1985); Machida and Arai (1992); Minagawa (1969); Sagamihara City Geomorphology and Geology Research Group (1986); Uesugi and the Kanto Quaternary Research Group (1994); Uesugi (1994); Uesugi et al. (1980, 1983); Yonezawa (1981).

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English translation of figure lettering

Map: 1:25,000 Yose (Tokyo sheet 15-1). Tozurahara; Shibata; Tsurushima; Uenohara Town; Sagami River; Uenohara Bridge (partly cropped at top). Legible numbers: 200, 250, 266.5. Column, from top: Hk-TP, Aso-4, TzP-III, On-In, K-Tz, On-Pm1. Scale: 0, 5, 10 m. Compiled from Yonezawa (1981) and Machida et al. (1985). The prose fragment at left is included in the main text.

Original Japanese lettering

位置図：2.5万分の1『与瀬』（東京15号-1）；葛原，芝田，鶴島，上野原町，相模川；上野原大橋（上部で一部切れる）。可読数値200，250，266.5。柱状図上から：Hk-TP，Aso-4，TzP-III，On-In，K-Tz，On-Pm1。スケール0，5，10m。米澤(1981)，町田ほか(1985)より作成。画像左側の本文断片は本文欄に収録済み。

Reading notes

地図中の小さな標高・地名 — 一部不鮮明で確定できない。

[Original printed page: 42]

WS-10-3 Kikai-Tozurahara tephra in marine sand forming the Naka Plateau, Joban coast

Takehiko Suzuki

Locality: Hetano, Hitachinaka City, Ibaraki Prefecture. Coordinates: N36°22′5″ E140°35′11″. Elevation: 30 m. Exposure and present condition: artificial exposure beside a paddy field; extant. Deposits and age: marine sand, AW-type tephra, and aeolian tephra; Late Pleistocene. Date described: June 1996. Keywords: Naka Plateau; Naka Plateau Sand and Gravel; upper member of the Miwa Formation; Kikai-Tozurahara tephra; Joban coast.

The exposure described here is presently the easternmost known terrestrial occurrence of Kikai-Tozurahara tephra (K-Tz). It lies on the Naka Plateau at the northeastern end of the Kanto Plain. This extensive plateau stretches northwest–southeast between the Kuji and Naka rivers at elevations of 25–55 m. Sakamoto (1972) called its marine sand the upper member of the Miwa Formation, interpreted it as deposits of the culmination of the Shimosueyoshi transgression, and correlated the plateau surface itself with the Shimosueyoshi surface in southern Kanto. Suzuki (1989) subsequently interpreted the Naka Plateau as a partly fluvial surface rather than a marine surface simply correlatable with Shimosueyoshi, and considered its emergence to have proceeded over a relatively long period from the peak of the last interglacial, the Shimosueyoshi period, to 75–80 ka. The strongest evidence for this timing was the discovery of K-Tz as AW-type tephra—wind-transported ash deposited on the bottom of a water body—in the uppermost terrace-forming sediments in the southeastern plateau.

At that time, the K-Tz fall was assigned an age of 75–80 ka. It is now considered somewhat older, 90–100 ka, and assigned to oxygen-isotope stages 5c–5b (Machida and Arai, 1994). Consequently, the Naka Plateau is considered to have formed during stages 5e–5c. The exposure shows approximately 3.6 m of volcanic-ash soil containing Akagi-Kanuma tephra (Ag-KP), overlying more than 1 m of sand. Their boundary is transitional; K-Tz occurs 60–100 cm below it. Rather than forming a bed, it occurs as lumps of fine ash several centimeters in diameter. At first glance, these resemble pumice pieces lined up in the sand. The characteristics of K-Tz at this site are described by Suzuki (1989, 1990b).

References: Machida and Arai (1994); Sakamoto (1972); Suzuki (1989, 1990b).

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English translation of figure lettering

1:25,000 Nakaminato (Mito sheets 6-2 and 6-4). Hetano; 原. Legible numbers: 36.6, 27.7, 30, 24.2.

Original Japanese lettering

2.5万分の1『那珂湊』（水戸6号-2・4）。部田野，原。可読数値：36.6，27.7，30，24.2。

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English translation of figure lettering

K-Tz (two labels at left, one at right); N, NE, E; photographed June 1996; Ag-KP; volcanic-ash soil; sand bed; enlarged area.

Original Japanese lettering

K-Tz（左に2箇所、右に1箇所）；N，NE，E；1996年6月撮影；Ag-KP；火山灰土；砂層；拡大部分。

[Original printed page: 43]

WS-11-1 Ontake tephra 1 on the eastern foot of Mount Fuji

Hiroshi Machida

Locality: upper Nakajima Stream, Oyama Town, Shizuoka Prefecture. Coordinates: N35°22′33″ E138°59′34″. Elevation: 390 m. Exposure and present condition: forest-road cutting; extant. Deposit and age: pumice-fall bed; Late Pleistocene. Date described: 1990. Keywords: Ontake tephra 1; Suruga-Oyama.

Proximal type exposures of Ontake tephra 1 (On-Pm1) occur at Kiso-Fukushima and Ina. They are generally strongly weathered, however, making the original character difficult to discern. The exposure considered here lies on Fuji's eastern foot. Burial beneath more than 100 m of tephras and other sediments has preserved this tephra exceptionally well, while its location provides evidence of the tephra's widespread extent. Its occurrence nearby in upper Nishizawa at Ikido, Oyama Town, is described separately (WS-9-3); preservation is better here. To reach the site, leave central Oyama northward and ascend the forest road along Nakajima valley. The landmark is the eastern wall of the forest road east of the reservoir, near the high-voltage power line.

The deposit consists chiefly of well-sorted pumice with a maximum grain size of 8 mm. It becomes finer in the middle to upper part, then coarsens again. The fine-grained interval suggests the possibility of pyroclastic-flow activity at that stage. Total thickness reaches 1 m. The pumice is pyroxene-bearing biotite–amphibole dacitic and highly vesicular, with a silky fibrous texture. It attracted attention as an unusual tephra in southern Kanto, where basaltic and andesitic tephras are abundant. Beneath it is a thick pumice bed identical to that labeled P-B at Ikido Nishizawa. Its source may be Komitake volcano. Kikai-Tozurahara and other tephras occur above (WS-9-3).

References: Machida (1990, 1996).

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English translation of figure lettering

1:25,000 Suruga-Oyama (Kofu sheet 4-2). Yanagishima. Legible elevations: 500, 394, 491, 359, 416.

Original Japanese lettering

2.5万分の1『駿河小山』（甲府4号-2）。柳島。可読標高：500，394，491，359，416。

[Original printed page: 44]

WS-11-2 Widespread tephras of the Isawa Plateau

Mitsuhisa Watanabe

Locality: Wakayanagi, Isawa Town, Isawa District, Iwate Prefecture. Coordinates: N39°7′6″ E140°58′47″. Elevation: 215 m. Exposure and present condition: artificial roadside exposure; extant. Deposits and age: fluvial sediments and tephras; Middle to Late Pleistocene. Date described: May 1987. Keywords: Isawa Plateau; Aso-4 tephra; Kitahara tephra; Ontake tephra 1; Sambe-Kisuki tephra; Toya tephra.

At this exposure, several widespread tephras overlying terrace gravel, the deposits forming the M1 surface, can be observed with the naked eye (Watanabe, 1991; Soda and Yagi, 1991; Machida and Arai, 1992). At the top is coarse Yakeishi-Yamagata tephra (Yk-Y; Yamagata pumice; Okami and Yoshida, 1984), derived from Yakeishidake, with slight involution on its upper surface. Below Yk-Y occur Aso-4, Kitahara (Kth), Atago (Atg), Ontake tephra 1 (On-Pm1), Sambe-Kisuki (SK), and Toya tephras. Each is only a few centimeters thick; the sketch exaggerates their thicknesses. These widespread ashes are clearly important for studying Late Quaternary landform development. Recognition of On-Pm1 at this exposure, near its currently known northern distribution limit, is especially significant. Together with Aso-4, it assists in establishing stratigraphic relationships with tephras in Chubu, Kanto, and Tohoku, and in correlating and dating landforms formed since the culmination of the last interglacial.

On-Pm1 is recognized as a yellow to yellowish-white, fine-grained glassy ash bed. Aso-4 is reddish orange, SK yellow, and Toya yellow to orange glassy ash. Kth is greenish gray and mixed with Atg, which contains abundant, relatively coarse high-temperature quartz.

The terrace gravel in the lower part of the exposure is buried by talus, but all the widespread ashes remain observable. They are easier to examine in the left half of the exposure. Because they commonly occur as scattered patches, however, collecting large quantities of samples will make them invisible unless the exposure is extensively cut back again. Care is needed to protect this exposure.

References: Machida and Arai (1992); Okami and Yoshida (1984); Soda and Yagi (1991); Watanabe (1991).

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English translation of figure lettering

1:25,000 Ishibuchi Dam (Shinjo sheet 2-1). 上愛宕; Atago; 中萱刈窪. Legible numbers: 198, 195, 203, 200.

Original Japanese lettering

2.5万分の1『石淵ダム』（新庄2号-1）。上愛宕，愛宕，中萱刈窪。可読数値：198，195，203，200。

Reading notes

小さな地名・数値 — 一部は不鮮明。

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English translation of figure lettering

Yk-Y′; Aso-4; On-Pm1; SK (left and right); Toya (left and right); Kth; Atg; M1 Terrace Gravel; Talus. Right-hand scale: 0–4 m.

Original Japanese lettering

Yk-Y′；Aso-4；On-Pm1；SK（左右）；Toya（左右）；Kth；Atg；M1 Terrace Gravel；Talus。右スケール0～4m。

[Original printed page: 45]

WS-12-1 Sambe-Kisuki tephra at Matsue

Hiroshi Machida

Locality: in front of the vehicle testing center, Yamashiro Town, Matsue City. Coordinates: N35°26′12″ E133°5′40″. Elevation: 20 m. Exposure and present condition: cutting; lost. Deposit and age: pumice-fall beds; Late Pleistocene. Date described: 1975. Keywords: Sambe-Kisuki tephra; Daisen-Matsue tephra; Matsue.

Sambe-Kisuki tephra, which extends over a broad area from Mount Sambe along the Sea of Japan to Tohoku, was formerly called Koshihara pumice (San'in Quaternary Research Group, 1969). The former type exposures at both Kisuki and Koshihara have now disappeared. New exposures are more likely to occur near Koshihara in southern Matsue, however, and Daisen-derived tephras can also be observed there; the former exposure is therefore described here. See also CG-8.

Two weathered pumice beds overlie red soil at this exposure. The lower, yellowish-brown bed was once described as Daisen-Kurayoshi pumice, but is actually the much older Daisen-Matsue tephra (DMP; Machida and Arai, 1979). The grayish-white to grayish-brown pumice bed above it, separated by soil, is Sambe-Kisuki tephra (SK). Whereas DMP is rich in mafic minerals, SK is biotite-rhyolitic, has few mafic minerals other than biotite, and is rich in quartz and feldspar. The unusually low refractive indices of its pumice-type volcanic glass, 1.494–1.498, are another distinguishing feature useful for regional correlation (Toyokura et al., 1991). In Tohoku, SK occurs between Ontake tephra 1 and Toya tephra (WS-11-2), suggesting an eruption age of 100–110 ka. DMP occurs immediately above Sashimi (差海) terrace deposits west of Lake Shinji [printed 穴道湖 in the original], considered to date to oxygen-isotope stage 5e, and is therefore thought to have erupted at 120–125 ka.

Among Sambe volcanic products, SK represents the largest Plinian eruption. An associated pyroclastic flow may have erupted, but this is uncertain near Mount Sambe because younger tephras cover the deposits. DMP is distributed both west and east of its source, Daisen volcano, and together with SK is an effective marker bed.

References: Machida and Arai (1979); San'in Quaternary Research Group (1969); Toyokura et al. (1991).

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English translation of figure lettering

1:50,000 Matsue (Matsue sheet 16). Asahi Town; Ohashi River; Nishitsuda; Higashitsuda Town; Agenogi Town; Koshihara Town. Legible numbers: 1.4, 2.2, 4.5, 2.3, 31.

Original Japanese lettering

5万分の1『松江』（松江16号）。朝日町，大橋川，西津田，東津田町，上乃木町，古志原町。可読数値：1.4，2.2，4.5，2.3，31。

Reading notes

地図の小さい数値・施設名 — 一部は解像度が低く確定できない。

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English translation of figure lettering

SK; DMP; old red soil. Scale: 0, 1, 2 m.

Original Japanese lettering

SK；DMP；古赤色土。スケール0，1，2m。

[Original printed page: 46]

WS-12-2 Sambe-Kisuki tephra washed ashore on the Echizen coast

Hiroshi Machida; Isamu Toyokura

Locality: Hamaji, Mikuni Town, Fukui Prefecture, on the shore at Midori-no-Hiroba. Coordinates: N36°15′8″ E136°10′57″. Elevation: 8.5 m. Exposure and present condition: sea cliff; extant. Deposits and age: beach sediments and water-deposited tephra; Late Pleistocene. Date described: 1989. Keywords: Sambe-Kisuki tephra; drift pumice; Echizen coast.

Sambe-Kisuki tephra (SK), whose distribution axis extends northeast to east-northeast from Mount Sambe, is an important marker linking Quaternary deposits of western and northern Japan. Material washed ashore is also found in water-laid beds on the Hokuriku coast and the Oga Peninsula (Toyokura et al., 1991). At this exposure, a yellowish-white ash bed and rounded pumice gravel immediately above it can be observed within coarse beach sand. The ash is a tephra-fall deposit; the pumice drifted with ocean currents and accumulated on the shore. Although both are strongly weathered, they can be identified by their characteristic biotite-rhyolitic composition. The ash bed has been disturbed by organisms.

Based on the eruption age of SK, the marine-terrace sediments are considered to correspond to oxygen-isotope stage 5c. The drift pumice suggests that a northward current along the Sea of Japan coast existed then, as it does today. Similar exposures of SK in marine sediments also occur on the Noto Peninsula (CB-28; Toyokura et al., 1991).

Reference: Toyokura et al. (1991).

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English translation of figure lettering

1:25,000 Kitagata and Mikuni (Kanazawa sheets 15-1 and 15-2). Mikuni Town; 城新田; Midori-no-Hiroba (two labels). Legible numbers: 33, 39.3.

Original Japanese lettering

2.5万分の1『北潟』・『三国』（金沢15号-1・2）。三国町，城新田，みどりの広場（2箇所）。可読数値33，39.3。

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English translation of figure lettering

Legible date stamp: 12 5 89. The reference line at the top is included in the main text.

Original Japanese lettering

日付表示の可読部分：12 5 89。上端の文献行は本文に収録済み。

Reading notes

12 5 89 — 日付表示の左側が不鮮明。順序・完全な日付は確定しない。

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English translation of figure lettering

Yellowish-brown soil (containing DKP and AT); dark-brown soil zone (containing K-Tz and Aso-4); SK. The cropped numbers at upper left belong to the adjacent photograph.

Original Japanese lettering

黄褐色土壌(DKP・ATを含む)；暗褐色土壌帯(K-Tz・Aso-4を含む)；SK。左上の数字断片は隣の写真の端部。

[Original printed page: 47]

WS-13-1 Stratigraphy of Toya tephra at the foot of Mount Usu

Hiroshi Machida; Kotaro Yamagata

Localities: village-boundary stream at Kaminagawa, Date City, Hokkaido (site 1); left bank of the Osaru River in the same area (site 2). Coordinates: N42°31′10″ E140°51′40″ (site 1); N42°31′10″ E140°52′24″ (site 2). Elevation: 80–120 m. Exposure and present condition: valley walls; extant. Deposits and age: pyroclastic-flow deposits, ash fall, pumice fall, and lava; Late Pleistocene. Date described: 1990. Keywords: Toya caldera; Toya tephra; Mount Usu.

The large pyroclastic-flow deposits forming plateaus around Toya caldera are the source deposits of Toya tephra, approximately 110 ka old and widespread throughout northern Japan. Their stratigraphy is fairly complex and has been studied mainly at the foot of Mount Usu south of the caldera. Site 1 is a valley wall along a steep small stream incising the Toya pyroclastic-flow depositional surface. Several units comprising Toya tephra can be readily observed here. Figure 2 is a stratigraphic column compiled by combining several exposures along this stream. Suzuki (1970) and Ikeda and Katsui (1986) divided Toya tephra into Toya pyroclastic-flow deposits Tpfl I–IV and Toya pyroclastic-fall deposits Tpfa. At this exposure, the following occur in ascending order: ash-rich pink to beige pyroclastic-flow deposit Tpfl II; ash fall containing abundant accretionary lapilli, Tpfa, with a pyroclastic-flow deposit interbedded within it; pink pyroclastic-flow deposit Tpfl III; and pumice-rich pyroclastic-flow deposit Tpfl IV, divided into several units. Tpfl IV has a basal concentration of lithic fragments, a lithic breccia. Of the four pyroclastic-flow units, Tpfl IV is the largest and most widely distributed. The widespread northern Japan Toya tephra is considered chiefly co-ignimbrite ash from this unit (Machida et al., 1987). It is a fairly homogeneous, glass-rich ash of amphibole-bearing pyroxene-rhyolitic composition. The glass is markedly felsic and predominantly pumice-type. The presence of orthopyroxene of eulite composition is also highly distinctive.

Toya tephra is overlain by its reworked deposits and then by Kuttara tephra 2 (Kt-2), a pumice fall dispersed west of its source at Kuttara volcano, formerly called N,Us-c; Nakajima-Osarugawa tephra (Nj-Os), derived from Nakajima, a post-caldera volcano of Toya; and ash and scoria falls from Usu volcano. These are covered by lava of the Usu stratovolcano.

At site 2 on the opposite bank of the Osaru River, beneath Tpfl II occupying the upper cliff, is Tpfl I, a unit consisting chiefly of beige ash with accretionary lapilli (Figure 3). This is the product of the initial phreatomagmatic eruption in the Toya caldera eruption sequence and resembles a pyroclastic-surge deposit. Below it, separated by soil, Osarugawa tephra (Osr), consisting mainly of another pyroclastic-flow deposit, the Osarugawa pyroclastic flow, rests on fluvial sand and gravel. From its stratigraphic position and elevation of about 15 m, this sand and gravel, the Kaminagawa Formation, is inferred to be terrace deposits of oxygen-isotope stage 5e.

References: Ikeda and Katsui (1986); Machida et al. (1987); Suzuki (1970).

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English translation of figure lettering

Figure 1. 1:50,000 Abuta (Muroran sheet 1). Sites 1, 2. Mount Usu; Usu-Shinzan; O-Usu; Ko-Usu; 有珠山方; Higashi-Maruyama; Showa-Shinzan; Sobetsu hot spring; Sobetsu Falls; Sobetsu Shrine; Date City; Kaminagawa Town; Kaminagawa post office; 西関内町; Osaru River. Legible numbers: 88.5, 84.9, 263, 86.6, 86.3, 60, 398, 38.50, 46.2, 82.6, 43, 29.0, 17.2, 80, 100, 200, 220, 300, 400, 500, 600.

Original Japanese lettering

図1。5万分の1『虻田』（室蘭1号）。地点1，2。有珠山，有珠新山，大有珠，小有珠，有珠山方，東丸山，昭和新山，壮瞥温泉，壮瞥滝，壮瞥神社，伊達市，上長和町，上長和郵，西関内町，長流川。可読数値：88.5，84.9，263，86.6，86.3，60，398，38.50，46.2，82.6，43，29.0，17.2，80，100，200，220，300，400，500，600。

Reading notes

地形図中の一部山名・微細な数値 — 不鮮明な文字は原図で確定できない。「有珠山方」は図上の可読形を保持。

[Original printed page: 48]

WS-13-1 (continued)

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English translation of figure lettering

Figure 2 column, from top: Us lava, Us pfa, Nj-Os, Kt-2 (N,Us-c), Tpfl IV, Tpfl III, Tpfl II, Tpfa, Tpfl I. Scale: 0, 1, 2, 3, 4, 5 m. Legend: pumice fall; ash fall; pyroclastic-flow deposit; lag breccia; lava; volcanic-ash soil. Figure 3 photograph: Tpfl I; Osr; Kaminagawa Formation. Legible date-stamp portion: 83 9.

Original Japanese lettering

図2柱状図の上から：Us lava，Us pfa，Nj-Os，Kt-2 (N,Us-c)，Tpfl IV，Tpfl III，Tpfl II，Tpfa，Tpfl I。スケール0，1，2，3，4，5m。凡例：降下軽石，降下火山灰，火砕流堆積物，lag breccia，溶岩，火山灰土。図3写真：Tpfl I，Osr，上長和層。日付の可読部分：83 9。

Reading notes

写真右下の日付 — 末尾の数字が白くかすれ、完全な日付を確定できない。

Figure 2. Stratigraphic column along the village-boundary stream.

Figure 3.

[Original printed page: 49]

WS-13-2 Toya tephra and overlying tephras at Date, Hokkaido

Kotaro Yamagata; Hiroshi Machida

Locality: along National Route 37, Tateyama Town, Date City, Hokkaido. Coordinates: N42°28′40″ E140°51′30″. Elevation: 45 m. Exposure and present condition: artificial exposure; extant. Deposits and age: pyroclastic-flow deposits and tephra fall; Late Pleistocene. Date described: August 1993. Keywords: Toya pyroclastic-flow deposit; Shikotsu pyroclastic-flow deposit; Usu volcano.

This exposure lies approximately 8 km southeast of Toya caldera on the depositional surface of the Toya pyroclastic flow (Toya pfl), erupted at about 110 ka. It is readily accessible and is the most suitable exposure for observing tephra beds younger than the Toya pyroclastic-flow deposit. The upper part of that deposit is exposed at a thickness of 4 m in the lower section. Overlying tephras occur in ascending order as follows: Aso-4 tephra and Nakajima-Date tephra (Nj-Dt) from Nakajima volcano in Toya caldera, neither particularly distinct to the naked eye; Kuttara tephra 2 (Kt-2, corresponding to N,Us-c), forming a thick pumice-fall bed; Nakajima-Osarugawa tephra (Nj-Os); grayish-white, laminated Shikotsu pyroclastic-flow deposit (Spfl); Usu-Kaminagawa tephra (Us-Ka) from Usu volcano; a group of volcanic-sand beds thought to have erupted during formation of the Usu stratovolcano; Nigorikawa tephra (Ng) from Nigorikawa volcano; and, in the uppermost black humic soil, Baitoushan–Tomakomai tephra (B-Tm), Komagatake d tephra (Ko-d), Usu b tephra (Us-b), and others. Spfl flowed down along the Osaru River; pronounced cross-lamination occurs in part of its upper interval. Thus, the eruption history of the Toya volcanic group can be read at this exposure from stratigraphic relationships established by widespread marker tephras.

Reference: Machida et al. (1987).

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English translation of figure lettering

1:50,000 Date (Muroran sheet 2). Tateyama Town; Asahi Town; Osaru Bridge; Osaru River; Iburi railway line; Shimura Chemical Works; Nishihama Town; 水水町; 日橋. Legible numbers: 53.8, 4, 3.5, 0.8, 5.2.

Original Japanese lettering

5万分の1『伊達』（室蘭2号）。館山町，旭町，長流橋，長流川，胆振線，志村化工，西浜町，水水町，日橋。可読数値53.8，4，3.5，0.8，5.2。

Reading notes

右端の町名「水水町」と「日橋」 — 一部切れて不鮮明なため読める形を仮に転記し、地名読みは確定しない。

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English translation of figure lettering

Left sketch: Us-b-, Spfl, Kt-2, Toya pfl; total height 12 m. Right column, from top: Us-b, Ko-d, Ng, volcanic sand, Spfl, Nj-Os, Kt-2, Nj-Dt, Aso-4, Toya pfl. Scale: 0–5 m. Legend: pumice fall; scoria fall; ash fall; pyroclastic-flow deposit; black humic soil; volcanic-ash soil.

Original Japanese lettering

左スケッチ：Us-b-，Spfl，Kt-2，Toya pfl；全高12m。右柱状図上から：Us-b，Ko-d，Ng，volcanic sand，Spfl，Nj-Os，Kt-2，Nj-Dt，Aso-4，Toya pfl。スケール0～5m。凡例：降下軽石，降下スコリア，降下火山灰，火砕流堆積物，クロボク，火山灰土。

[Original printed page: 50]

WS-13-3 Toya tephra as a terrace marker on the Shimokita Peninsula

Hiroshi Machida

Locality: 甲, Kazamaura Village, Aomori Prefecture. Coordinates: N41°27′28″ E141°6′47″. Elevation: 40 m. Exposure: road cutting. Deposits and age: terrace sand and gravel and ash fall; Late Pleistocene. Date described: August 1983. Keywords: Toya tephra; Hatajiri terrace; Shimokita Peninsula.

Of the marine terraces on the Shimokita Peninsula, the Hatajiri terrace, 40–60 m in elevation, is the most widely distributed. This exposure lies on its surface. A thin sand and gravel bed associated with a wave-cut platform is overlain by 3.5–4 m of brown volcanic-ash soil. The yellow tephra low in this soil frequently occurs on terraces from the Hachinohe area to this region. It was called “white tuff” at Hachinohe and “yellow pumice” near Misawa and Noheji (Tohoku Quaternary Research Group, 1969). Overall it is a fine-sand-sized glassy tephra. Tracing it northward from the south into Shimokita, one finds that grain size at its base increases. At this exposure the tephra is 18 cm thick, with a very clearly observable basal layer 2–3 cm thick of yellowish-white pumice ranging from coarse-sand size to several millimeters in diameter. This suggested a source farther north, in Hokkaido, and was strong evidence leading to the inference of a Toya caldera source (Machida et al., 1987). Here, 10–20 cm of volcanic-ash soil separates the terrace sand and gravel from Toya tephra, indicating that a substantial time elapsed after terrace emergence before the Toya ash fall.

References: Machida et al. (1987); Tohoku Quaternary Research Group (1969).

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English translation of figure lettering

1:50,000 Ohata (Shiriyazaki sheet 6). Shimofuro; Hatajiri; 鳥谷湯上; 甲; 甲崎; Akagawa; Osaki; Chijiri Beach; Sasuke River; 三角山; 道添; 岩角. Legible numbers: 6.6, 5.4, 282.0, 73, 7.2.

Original Japanese lettering

5万分の1『大畑』（尻屋崎6号）。下風呂，畑尻，鳥谷湯上，甲，甲崎，赤川，大崎，ちぢり浜，佐助川，三角山，道添，岩角。可読数値6.6，5.4，282.0，73，7.2。

Reading notes

地名甲・鳥谷湯上等 — 独立した読みを確認できず、英訳で日本語を保持。

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English translation of figure lettering

Photograph: ← Toya; photograph by Takahiro Miyauchi. Column: Toya; glassy ash; coarse-sand-sized pumice. Scale: 0–30 cm.

Original Japanese lettering

写真：←Toya；宮内崇裕撮影。柱状図：Toya，ガラス質火山灰，粗砂サイズの軽石。スケール0～30cm。

[Original printed page: 51]

WS-13-4 Marine Middle and Upper Pleistocene strata and widespread tephras, including Toya, on the Oga Peninsula, Akita Prefecture

Takeo Shiraishi (白石建雄); 的場保望

Locality: Anden, Oga City, Akita Prefecture. Coordinates: N39°58′10″ E139°51′00″. Elevation: 0–20 m. Exposure and present condition: sea cliff; extant. Deposits and age: chiefly coastal shallow-marine sediments; Middle to Late Pleistocene. Date described: May 1996. Keywords: Oga Peninsula; Shibikawa Formation; Anden Formation; Aso-4 tephra; Toya tephra; Aso-1 tephra; Baitoushan-Oga tephra.

The Oga Peninsula is one of the reference areas for the Neogene of the Sea of Japan coastal region and has long been the subject of numerous geological investigations. Marine terraces are also prominent, and studies of their landforms have a long history. Research on the Quaternary lagged somewhat, but since the 1970s advances combining magnetostratigraphy and microfossil stratigraphy have led to revised ages and established the presence of a thick marine Quaternary succession. More recently, successive discoveries of widespread tephras have also made the area important for Quaternary stratigraphy.

The present locality is a large sea-cliff exposure west of Anden village on the northern Oga coast. It is an important exposure where the stratigraphy and sedimentary facies of marine Middle and Upper Pleistocene strata, and their interbedded tephras, can be observed continuously. The formations seen here are, in ascending order, Wakimoto, Shibikawa, Anden, and Katanishi. Each formation from Shibikawa upward has been considered to overlie the underlying formation unconformably. New evidence has emerged concerning these divisions and stratigraphic relationships. Identification of widespread tephras, including Toya, has led to the view that the Anden Formation of Kitazato (1975) is part of the Katanishi Formation at its type locality (Katanishi Formation Collaborative Research Group, 1983; Machida et al., 1987; Miyauchi, 1988; Shiraishi et al., 1992). It has also been pointed out that the Anden and Katanishi formations at this exposure are conformable (Shiraishi et al., 1992). Re-examination is therefore underway, but the work is not yet complete; the conventional interpretation is presented here.

Because the beds dip eastward at this exposure, the succession described above can be observed starting from Anden village and proceeding west along the coast, continuously from the upper beds downward. The shore is sandy, the tidal range is small, and observations are possible at any time except during rough weather.

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English translation of figure lettering

1:25,000 Kitaura (Oga sheet 1-3). Anden.

Original Japanese lettering

2.5万分の1『北浦』（男鹿1号-3）。安田。

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English translation of figure lettering

Direction: NE. Exposure label: Aso-4. Column labels: Aso-4, Toya, pink tuff; Katanishi Formation; Anden Formation. Legend: silt; sandy silt; fine- to medium-grained sand; gravel; shell fossils. Horizontal scale: 100 m, 0; vertical scale: 0–30 m.

Original Japanese lettering

方位NE。露頭：Aso-4。柱状図：Aso-4，Toya，ピンクタフ；潟西層，安田層。凡例：シルト，砂質シルト，細～中粒砂，礫，貝化石。水平スケール100m、0；垂直スケール0～30m。

[Original printed page: 52]

WS-13-4 (continued)

The tephras identified at this exposure, in descending order, are Aso-4 (Shiraishi et al., 1992), Toya (Machida et al., 1987), Aso-1 (Shirai and Tada, 1996), Baitoushan-Oga (B-Og; Machida and Arai, 1992), and Oga pumice tuff (Oga; Kitazato, 1975). Aso-4 is 15 cm thick, at a horizon 1.8 m below a black silt bed in the middle Katanishi Formation. Although mixed with silt, a concentration of glass is visible to the naked eye near its center, and it is clearly primary ash fall. Immediately above it is drift pumice derived from the Aso-4 pyroclastic flow (Shiraishi et al., 1992). Toya is the thickest and most conspicuous tephra here: a 37 cm glassy ash bed intercalated in the lower Anden Formation, formerly called pink tuff. Aso-1 is a beige glassy ash bed about 10 cm thick intercalated in lignite in the middle Shibikawa Formation. This ash was briefly identified as Aso-3 (Machida and Arai, 1994), but Shirai and Tada (1996) revised the identification to Aso-1. B-Og (Machida and Arai, 1992, 1994) is a 2.5 cm bed of alkali-rhyolitic glassy ash intercalated near the base of a lignite bed immediately above Oga in the lower Shibikawa Formation. Unlike these widespread tephras, Oga is thick (1.5 m) and comprises alternating beds of coarse white pumice and ash. Its source is thought to be very close, and it has been correlated with the Toga Pumice Formation distributed around Toga Bay on the peninsula’s west coast (Fujioka, 1959). Machida and Arai (1994) express the same view. According to Shirai and Tada (1996), chronology based on Sea of Japan seafloor cores suggests eruption ages of about 250 ka for Aso-1 and about 440 ka for B-Og.

References: Fujioka (1959); Katanishi Formation Collaborative Research Group (1983); Kitazato (1975); Machida and Arai (1992, 1994); Machida et al. (1987); Miyauchi (1988); Shirai and Tada (1996); Shiraishi et al. (1992).

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English translation of figure lettering

Direction: SW. Toya; Aso-1; B-Og; Oga; lignite (three occurrences); Shibikawa Formation; Wakimoto Formation. Scale: 0, 40 m.

Original Japanese lettering

方位SW。Toya，Aso-1，B-Og，Oga；亜炭（3か所）；鮪川層，脇本層。スケール0，40m。

[Original printed page: 53]

WS-14-1 Ata tephra in the southern Osumi Peninsula

Shinji Nagaoka

Locality: valley floor south of 野尻野, Nejime Town, Kagoshima Prefecture. Coordinates: N31°6′36″ E130°45′29″. Elevation: 280 m. Exposure and present condition: artificial exposure; extant. Deposits and age: tephra fall and pyroclastic-flow deposits; Late Pleistocene. Date described: January 1996. Keywords: Ata pyroclastic-flow deposit; Kori ash fall; Ata pumice fall; Izashiki ash fall; Osumi Peninsula.

In the southern Osumi Peninsula, plateaus are developed on deposits of the Ata pyroclastic flow (Ata-pfl; 90–110 ka), one of southern Kyushu’s enormous pyroclastic flows. Strongly welded pyroclastic-flow deposits are exposed through most of the cliffs, which exceed 100 m in height. Earlier tephra-fall deposits occur at their base, but most are concealed by collapse debris and dense evergreen broadleaved forest. This is one of the few exposures where fallout tephras associated with the Ata eruption can be seen. Above the granite basement, the succession comprises 240 cm of Kori ash fall (Ko-A), 430 cm of Ata pumice fall (Ata-p; Aramaki and Ui, 1966), 95 cm of Izashiki ash fall (Iz-A), and more than 50 m of Ata pyroclastic-flow deposit (Ata-pfl) (Nagaoka, 1988). The Kori ash fall is poorly sorted ash containing pumice and occasionally accretionary lapilli. The Izashiki ash is rich in accretionary lapilli. Around Sata Town farther south, Sata pumice fall (St-p) is sometimes intercalated above the Izashiki ash fall. These fallout tephras indicate repeated Plinian and phreatomagmatic (phreatoplinian) eruptions preceding the Ata pyroclastic-flow eruption, suggesting that the sequence of the Ata eruption cycle took place under water (Nagaoka, 1988).

References: Aramaki and Ui (1966); Nagaoka (1988).

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English translation of figure lettering

1:25,000 Hetsuka (Kaimondake sheet 2-3). 野尻野; Kori; Izashiki; 別府; 唐栄. Legible numbers: 542, 384, 387, 396, 370.

Original Japanese lettering

2.5万分の1『辺塚』（開聞岳2号-3）。野尻野，郡，伊座敷，別府，唐栄。可読数値542，384，387，396，370。

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English translation of figure lettering

Direction: W. Ata-pfl; Izu-A; Ata-p; Ko-A. Scale: 2 m.

Original Japanese lettering

方位W。Ata-pfl，Izu-A，Ata-p，Ko-A。スケール2m。

Reading notes

Izu-A — 図中はIzu-A、本文はIz-Aと印刷されているため、それぞれ保持。

[Original printed page: 54]

WS-14-2 Pyroclastic-flow deposits from Aso, Ata, and other sources in the Hitoyoshi Basin

Hiroshi Machida

Locality: Yamashita, Nishiki Town, Kumamoto Prefecture. Coordinates: N32°13′17″ E130°49′44″. Elevation: 130–150 m. Exposure and present condition: excavation for earth and gravel; extant, but vegetation has begun to cover it. Deposits and age: pyroclastic-flow deposits; Late Pleistocene. Date described: 1987–1994. Keywords: Aso-3 pyroclastic-flow deposit; Ata pyroclastic-flow deposit; Aso-4 pyroclastic-flow deposit; Aira-Ito pyroclastic-flow deposit; Hitoyoshi Basin.

The Hitoyoshi Basin, opening within the Kyushu Mountains, received large pyroclastic flows from Aso caldera to the north and from Kakuto, Kobayashi, Aira, Ata, and other calderas to the south (all producing widespread tephras). It is consequently an excellent area for clarifying their relative stratigraphic positions. These pyroclastic-flow deposits are stacked in complex fashion throughout the hills on the right bank of the Kuma River in the northern basin. At this exposure one can observe the Aso-3, Ata, Aso-4, and Aira-Ito (A-Ito) pyroclastic-flow deposits.

Aso-3 at the bottom of the cliff contains large pumice clasts like Aso-4 but is somewhat more weathered. A thick soil developed between it and overlying Ata. Aso-3 identified in central Honshu and Pacific seafloor sediments occurs close to Ata stratigraphically and is considered to occupy isotope stage 5d (Machida and Arai, 1994).

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English translation of figure lettering

1:25,000 Hitoyoshi (Yatsushiro sheet 3-4). Yamashita; 野間; 新立; 滝の水; 由留木; 十日市; Nishiki Town; Kuma River. Legible numbers: 172, 163, 125, 134.4.

Original Japanese lettering

2.5万分の1『人吉』（八代3号-4）。山下，野間，新立，滝の水，由留木，十日市，錦町，球磨川。可読数値172，163，125，134.4。

Ata is the finest-grained of the four pyroclastic-flow deposits, rich in glassy ash containing accretionary lapilli. Its thickness exceeding 10 m at this distant locality, more than 100 km from its source, suggests that it was an eruption deposit of the largest class. Its basal portion contains abundant charcoal fragments.

Aso-4 here is an unwelded pyroclastic-flow deposit containing coarse pumice, but elsewhere it commonly forms grayish-black welded tuff. In some places its glass-rich basal portion can be seen.

The uppermost A-Ito is the whitest of the pyroclastic-flow deposits here and has stratification, resembling secondary shirasu. Elsewhere in the Hitoyoshi Basin it fills valleys and locally has a weakly welded facies.

References: Machida and Arai (1994); Machida et al. (1985).

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English translation of figure lettering

Conceptual sketch of the large Yamashita exposure. A-Ito; Aso-4 (twice); Ata (twice); Aso-3; road; cliff relief approximately 20 m.

Original Japanese lettering

山下の大露頭概念図。A-Ito；Aso-4（2か所）；Ata（2か所）；Aso-3；道路；崖の比高約20m。

[Original printed page: 55]

WS-14-3 Aso-4 and Ata tephras at the eastern foot of Aso

Hiroshi Machida

Locality: 野鹿, Ogi Town, Kumamoto Prefecture [as printed]. Coordinates: N38°56′17″ E131°18′48″ [as printed]. Elevation: 430 m. Exposure and present condition: tunnel walls, behind houses, and elsewhere; extant. Deposits and age: pyroclastic-flow deposits and tephra fall; Late Pleistocene. Date described: 1983–1996. Keywords: Aso-4 tephra; Kikai-Tozurahara tephra; Aso ABCD tephra; Ata tephra; Aso-3 tephra; 野鹿.

The stratigraphic relationships between Aso-4, Ata, and other large tephras representing Kyushu’s large pyroclastic-flow eruptions were unclear before widespread tephras were understood. At this exposure the problem can be solved using Aso-4 as a reference. Tephras from Aso-4 down to Aso-3 can be observed around the old-road tunnel and from there behind the settlement to the valley floor. The base of the Aso-4 pyroclastic-flow deposit is rich in coarse foreign lithic fragments. In places it erodes underlying tephras and often contains blocks of those tephras and volcanic-ash soil.

The tephra group between Aso-4 and Aso-3 is about 20 m thick, with more than ten units of scoria, pumice, and ash. Units with visibly different facies have been designated A–N (Ono et al., 1972). Between unit N and Aso-3C, where exposure is poor, there is more than 3 m of massive brown volcanic-ash soil with developed cracks. Units I–N cannot be observed in the tunnel exposure. Units ABCD form the largest continuous eruption sequence among the tephras between Aso-4 and Aso-3 and can be traced widely eastward. Where the volcanic-ash soil between Aso-4 and ABCD is well preserved, Kikai-Tozurahara tephra (K-Tz) can be identified as a concentration zone of bubble-wall glass shards.

About 20 cm below the ABCD tephra is an 11 cm bed of beige glassy ash. This is Ata co-ignimbrite ash, composed principally of bubble-wall glass shards. Its correlation and identification with Ata tephra (pumice-fall and pyroclastic-flow deposits) distributed across southern Kyushu are based on heavy-mineral assemblages, refractive-index characteristics, and other properties. Ata has few known terrestrial occurrences in the Japanese archipelago and is distributed chiefly in the sea south of Honshu. In Quaternary stratigraphy, Aso-4 and Ata lie after the culmination of the last interglacial, respectively in marine isotope stages 5b and 5c (Oba, 1991).

References: Machida et al. (1985); Oba (1991); Ono et al. (1972).

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Figure 1. 1:25,000 Sakuramachi (Oita sheet 11-3). 国方; 荻原; 仲村; 南河内; 野鹿. Legible numbers: 504, 465, 479, 429, 408.

Original Japanese lettering

図1。2.5万分の1『桜町』（大分11号-3）。国方，荻原，仲村，南河内，野鹿。可読数値504，465，479，429，408。

Reading notes

地図の細字注記 — 縦書きの小注記の一部が解像度により判読できない。

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English translation of figure lettering

Aso-4; K-Tz; A; B; C; D; Ata; F; I; K; L; M; N; Aso-3. Scale, m: 5, 0, 5, 10, 15.

Original Japanese lettering

Aso-4，K-Tz，A，B，C，D，Ata，F，I，K，L，M，N，Aso-3。スケールm：5，0，5，10，15。

Figure 2. Composite stratigraphic column (Ono et al., 1972).

[Original printed page: 56]

WS-14-3 (continued)

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English translation of figure lettering

Aso-4 basal portion; K-Tz; Aso-ABCD. Lettering on the vehicle tailgate is illegible.

Original Japanese lettering

Aso-4基底部，K-Tz，Aso-ABCD。車両荷台の文字は判読不明。

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English translation of figure lettering

Aso-ABCD; Ata (twice).

Original Japanese lettering

Aso-ABCD，Ata（2か所）。

[Original printed page: 57]

WS-15-1 Aso-3 pyroclastic-flow deposits along the Inaba River, Taketa City, Oita Prefecture—The Imaichi, Aso-1, Aso-3, and Aso-4 pyroclastic flows

Koji Ono

Locality: beside the entrance to the old national-road tunnel, north bank of the Inaba River, Shichiri, Taketa City, Oita Prefecture. Coordinates: N32°58′14″ E131°24′27″. Elevation: 250 m. Exposure and present condition: riverbank cliff; extant. Deposits and age: pyroclastic-flow deposits and wind-deposited tephra; Middle to Late Pleistocene. Date described: January 1996. Keywords: Imaichi pyroclastic flow; Aso-1 pyroclastic flow; Aso-3 pyroclastic flow; Aso-4 pyroclastic flow; fallout tephras between the pyroclastic-flow deposits.

Central Taketa lies near the eastern end of the pyroclastic plateau east of Aso caldera. The plateau is dissected by deep gorges of the Ono and Inaba rivers and others. Its principal component here is the Aso-3 pyroclastic-flow deposit (hereafter “deposit” is omitted); Aso-4 covers the plateau surface, but its base descends to the beds of the Inaba and other rivers (Figure 2). Aso-4 on the plateau is unwelded to weakly welded, whereas that on valley slopes and floors is strongly welded. The elevation difference between the base of Aso-4 on the plateau and the gorge floors of the Inaba and Ono rivers exceeds 80 m. At the time of Aso-4 emplacement, the terrain, much like that today, consisted of an Aso-3 pyroclastic plateau and deep, box-shaped gorges. Aso-4 filled the valleys and then covered the plateau, but strong welding of the thick valley-fill sections caused their surfaces to subside, accurately reproducing the pre-Aso-4 river courses.

This exposure is north of Oka Castle, east of the entrance to the tunnel through which former National Route 57 leaves the north bank of the Inaba River toward the north. A continuous section from Aso-1 to Aso-4 welded tuff is visible (Imaichi welded tuff was formerly exposed at the bottom but was buried during river improvement works). Above Aso-1, which is weakly welded and well laminated, successive beds separated by paleosols are Aso-2 tephra (Aso-2TL and 2T pumice- and scoria-fall beds; the Aso-2 pyroclastic-flow horizon lies between them), fallout tephras between Aso-3 and Aso-2 (Figure 4; Km is the weathered distal part of the Miyagi pyroclastic flow from Kuju volcano), the basal Aso-3W pumice fall, and the Aso-3A and B pyroclastic flows described below (Figures 3, 4). Aso-4 further covers the end of Aso-3B descending rightward toward the Inaba River, forming the valley wall (Figure 5). Aso-4 is strongly welded; locally even its matrix is dense black glass, making juvenile lenses difficult to see. Tensional joints formed through deformation during welding of the deep valley fill are observable in Aso-4. These precede columnar cooling joints; juvenile lenses protrude on the joint surfaces as a result of squeezing out (Watanabe et al., 1983).

On the eastern side of Aso caldera, Aso-3 can be divided, from bottom to top, into the Aso-3A, 3B, and 3C pyroclastic-flow subunits. Aso-3A is a white to brown dacitic pumice flow, strongly welded near the caldera; near Taketa it occurs only along valleys and is unwelded. Aso-3B is an aphyric andesitic scoria flow. It is absent from the caldera walls but is most voluminous west of Taketa, forming the main part of the pyroclastic plateau. It includes strongly welded portions west of Taketa and is weakly welded to unwelded around central Taketa. Aso-3C is an unwelded scoria-flow deposit of porphyritic andesite with abundant phenocrysts. Subunit distribution is not the same in every direction around the caldera; for example, Aso-3B has not yet been found on the western side of the caldera.

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English translation of figure lettering

Oka Castle; Inaba River; unconformity between 3 and 4. 1; 1M; 3; 4 (repeated).

Original Japanese lettering

岡城，稲葉川，3と4の不整合面。1，1M，3，4（複数箇所）。

Figure 2. Landform and constituents of the pyroclastic plateau at this exposure (left end, as in Figure 5) and across the Inaba River. Numbers identify the Aso pyroclastic flows, as in subsequent figures.

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English translation of figure lettering

Figure 1. 1:25,000 Taketa (Oita sheet 11-1). 城町; Shichiri; Inaba River; Taketa River; Taketa City; Taketa Town; Oka Castle ruins; 渡辺. Legible numbers: 300, 238, 322.

Original Japanese lettering

図1。2.5万分の1『竹田』（大分11号-1）。城町，七里，稲葉川，竹田川，竹田市，竹田町，岡城跡，渡辺。可読数値300，238，322。

[Original printed page: 58]

WS-15-1 (continued)

The Aso-3 pyroclastic flows at this exposure are Aso-3A and 3B. Aso-3A forms the lowermost several meters of the right half, where the beds descend toward the river (Figures 3, 5); Aso-3B occupies the left half and upper right part. Aso-3A here is a brown dacitic pumice flow composed of well-vesiculated pumice with elongated pores and glassy ash of the same composition (Figure 3). The lower part of Aso-3B is unwelded, with a dark-brown matrix containing abundant juvenile andesitic scoria, dense black andesitic glass nodules (juvenile?), brown pumice derived from Aso-3A, and foreign lithic fragments. It becomes weakly welded upward, with thick columnar joints.

In the valley wall descending from the plateau across the river, topped by Oka Castle, gentle slopes consist of Aso-4 welded tuff parallel to its lamination. Vertical cliffs expose the inner Aso-3B where the valley-wall Aso-4 has peeled away (Figure 2; Ono, 1965).

References: Ono (1965); Ono et al. (1977); Watanabe et al. (1983).

Note: Aso-II and III in Ono (1965) have now been revised to Aso-3 and Aso-4, respectively.

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English translation of figure lettering

3A; 3W; P; Q; 1 m.

Original Japanese lettering

3A，3W，P，Q，1m。

Extracted lettering and translation Figure 3. Sketch of the basal portion of the Aso-3 tephra.

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English translation of figure lettering

Scale in m: −2, −1, 0, 1, 2, 3, 4, 5, 6. From top: 3B: non-wd sc fl [unwelded scoria flow]; lithic conc [lithic concentration]; f. pm·lith -bg ash fl [fine pumice- and lithic-bearing ash flow]. 3W: c. pm [coarse pumice]; f. strat pm·lith [finely stratified pumice and lithics]. U: c. pm. O: grey ash/yel pm [yellow pumice], strat alt [stratified alternation]. P: c. pm. Q: black sdy ash [black sandy ash]. R: f–m. pm [fine to medium pumice]. Km: hb. biot-bg f. pm scatt [scattered hornblende- and biotite-bearing fine pumice]. S: m/c/f/m–c, pm [medium/coarse/fine/medium to coarse pumice]. 2T: ↑ f. strat sc [finely stratified scoria]; c. sc [coarse scoria]. 2TL: white·m·pm [white medium pumice].

Original Japanese lettering

スケールm：−2，−1，0，1，2，3，4，5，6。上から3B：non-wd sc fl；lithic conc；f. pm·lith -bg ash fl。3W：c. pm；f. strat pm·lith。U：c. pm。O：grey ash／yel pm，strat alt。P：c. pm。Q：black sdy ash。R：f–m. pm。Km：hb. biot-bg f. pm scatt。S：m／c／f／m–c，pm。2T：↑ f. strat sc；c. sc。2TL：white·m·pm。

Extracted lettering and translation Figure 4. Standard stratigraphic column from Aso-2 to Aso-3.

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English translation of figure lettering

3 and 4 (repeated); 3B (twice); 3A; 3/2; Q; 1.

Original Japanese lettering

3，4（複数箇所）；3B（2か所）；3A；3/2；Q；1。

Extracted lettering and translation Figure 5. Sketch of the eastern side of this exposure.

[Original printed page: 59]

WS-15-2 Aso-3 tephra intercalated in the Toriyamahama Formation at Kawaminami in the northern Miyazaki Plain

Hiroshi Machida

Locality: Toriyama 2 (通山二), Kawaminami Town, Miyazaki Prefecture. Coordinates: N32°9′3″ E131°32′45″. Elevation: 21 m. Exposure and present condition: valley wall; extant. Deposits and age: ash and sand-silt beds; Late Pleistocene. Date described: March 1994. Keywords: Aso-3 tephra; Toriyamahama Formation; Kawaminami; Miyazaki Plain.

Quaternary valley-fill deposits have long been known in the Miyazaki Plain. Otsuka (1930, 1932) described transgressive deposits overlain by the Chausubaru terrace deposits and named them the Toriyamahama Formation. The surroundings of this exposure are its type area. Many subsequent interpretations of its stratigraphic position have been reported, some placing it below and others above the last-interglacial Sanzaibaru terrace. Identification of its tephras provides the key to this question. It may contribute not only to regional stratigraphic chronology but also to the history of glacio-eustatic sea-level change. Figure 1 schematically illustrates the relationships between terraces and tephras in the northern plain. This exposure is at the base of valley-fill deposits underlying the deposits forming the Nyutabaru II surface.

To approach the exposure, enter a small valley from the coast. A basal gravel of boulders cutting into the Miyazaki Group can first be observed on the left. This is thought to be a steep-gradient river deposit formed during regression. Above it, sand and gravel continue for about 4 m. Following the valley on the left upstream, the sand and gravel soon change abruptly to silt, containing a yellowish-brown ash bed about 50 cm thick. Nagaoka (1986) and Endo and Suzuki (1986) described this as the Torihama Pumice and Torihama Tuff Bed, respectively. Machida and Arai (1992, 1994) correlated it with Aso-3 on petrographic characteristics (Figure 3). Because Aso-3 erupted during oxygen isotope stage 5d (Machida and Arai, 1994), its identification means that the Toriyamahama Formation represents transgressive deposits from stage 5d to 5c. This suggests both a major regression during 5d and a major transgression during 5c (Figure 4). The elevation difference between the former Sanzaibaru terrace shoreline and the base of the Toriyamahama Formation (Figure 1) implies a sea-level fall of as much as 70 m from stage 5e to 5d (Machida and Arai, 1994).

Marine beds between Aso-3 and Aso-4 have recently been reported in the Kumamoto Plain, in a situation similar to this locality (Ishizaka et al., 1995). Marine beds have also been observed between Aso-3 and K-Tz in the Oita Plain (Ono et al., 1996). All are considered products of the last interglacial. Globally, however, the last interglacial is often restricted to oxygen isotope stage 5e, with 5c regarded as an interstadial. Many researchers consider the last glacial to have begun in 5d, because warming and sea-level rise in 5c were smaller than in 5e, and a cold interval is thought to have occurred in 5d. Such chronological interpretations are nevertheless not without problems. Future research must improve precision by rechecking the position of Aso-3 within oxygen isotope stratigraphy in marine cores and collecting more data on identification and environments of stage 5e marine beds in Kyushu. Although the distribution of widespread Aso-3 was described in Machida and Arai (1992, 1994), it has since been found that Aso-1 was incorrectly identified as Aso-3 at several localities on the Oga Peninsula and in the Sea of Japan.

References: Endo and Suzuki (1986); Ishizaka et al. (1995); Machida and Arai (1992, 1994); Machida et al. (1993); Nagaoka (1986); Otsuka (1930, 1932); Ono et al. (1996).

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English translation of figure lettering

Kakuto; Ata-Torihama; Ata; Sanzaibaru; Nyutabaru I; Nyutabaru II; Aso-4; Aso-3. Elevation scale: 100 m, 50, 0.

Original Japanese lettering

Kakuto，Ata-Torihama，Ata，Sanzaibaru，Nyutabaru I，Nyutabaru II，Aso-4，Aso-3。標高スケール100m，50，0。

Extracted lettering and translation Figure 1. Relationships between terraces and marker tephras in the northern Miyazaki Plain (Kawaminami–Chausubaru), schematic (Machida and Arai, 1994).

[Original printed page: 60]

WS-15-2 (continued)

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Figure 2. 1:25,000 Kawaminami and Takanabe (Nobeoka sheets 7-4 and 8-3). 針池; Toriyama 2; Torihama; Toriyama; Kawaminami Town; Hirata. Legible numbers: 57, 56, 57.

Original Japanese lettering

図2。2.5万分の1『川南・高鍋』（延岡7号-4・8号-3）。針池，通山二，通浜，通山，川南町，平田。可読数値57，56，57。

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From left: this exposure; Hitoyoshi Basin; Taketa Basin; Takano, Shinshu; eastern foot of Fuji. Correlations and units: Aso-4; Ata; K-Tz (twice); Aso-3 (twice); Aso-3C; Aso-3A; Aso-3W; Tt-D; On-Pm1; P-A; P-B. Thicknesses: 4.3 m, 11 m, >10 m. Left scale in m: 0, 5; Takano scale in cm: 0, 500. Legend: paleosol; scoria; pumice; ash; pyroclastic flows; silt; sand & silt; gravel; basement; lignite.

Original Japanese lettering

左から：本露頭，人吉盆地，竹田盆地，信州高野，富士東麓。対比線・単位：Aso-4，Ata，K-Tz（2か所），Aso-3（2か所），Aso-3C，Aso-3A，Aso-3W，Tt-D，On-Pm1，P-A，P-B。厚さ：4.3m，11m，>10m。左スケールm：0，5；高野スケールcm：0，500。凡例：paleosol，scoria，pumice，ash，pyroclastic flows，silt，sand & silt，gravel，basement，lignite。

Extracted lettering and translation Figure 3. Stratigraphic columns centered on Aso-3 (partly modified from Machida and Arai, 1994).

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Tephra: K-Ah, AT, Aso-4, K-Tz, On-Pm1, Ata, Aso-3. Age (ka): 0, 50, 100, 130. Sea level: −100, 0, +100 m. 0.7 m/ka. ? (repeated).

Original Japanese lettering

Tephra：K-Ah，AT，Aso-4，K-Tz，On-Pm1，Ata，Aso-3。Age (ka)：0，50，100，130。Sea level：−100，0，+100m。0.7m/ka。?（複数箇所）。

Extracted lettering and translation Figure 4. Sea-level change over the last 130,000 years reconstructed from tephra and terrace stratigraphy in the Miyazaki Plain.

[Original printed page: 61]

WS-16-1 Kutcharo pyroclastic-flow deposit IV south of Abashiri—The source area of Kutcharo-Haboro tephra

Koji Okumura

Locality: upper Onnenai River, Abashiri City, Hokkaido. Coordinates: N43°55′6″ E144°23′6″. Elevation: 90 m. Exposure and present condition: artificial exposure; extant. Deposits and age: pyroclastic-flow deposits and tephra fall; Late Pleistocene. Date described: June 1994. Keywords: Kutcharo pyroclastic-flow deposit IV; eastern Hokkaido; Kutcharo-Haboro tephra; Abashiri.

Kutcharo pyroclastic-flow deposit IV (KP IV) is the largest of ten pyroclastic-flow deposits originating from Kutcharo caldera. It extends across an area about 70 km in diameter centered on the caldera [abbreviations follow Okumura, 1991; K.P. flow IV: Katsui and Sato, 1963; Kutcharo 4, Kc-4: Machida and Arai, 1992]. Kutcharo-Haboro ash (Kc-Hb), widely distributed in central and eastern Hokkaido, is considered the co-ignimbrite ash of KP IV on the basis of its petrographic characteristics and stratigraphy (Okumura et al., 1985; Okumura, 1991). At the upper Onnenai River exposure one can observe KP IV, the subsequent Late Pleistocene KP III, II, and I eruptions, and intercalated fallout tephras. Light-gray KP IV in the lower half overlies KP V and pink ash as a single flow unit more than 15 m thick. Its basal 1–2 m often lack coarse pumice clasts, but are considered part of the pyroclastic flow; no fallout tephra unit is recognized. In their description of KP IV, Katsui and Sato (1969) placed it west of a line connecting Higashimokoto Village and Abashiri, with a separate Kutcharo debris-flow deposit (KS) to the east. One reason was that KP IV is white to orange-white and contains no scoria, whereas KS is generally grayish-white to grayish-purple, occasionally black on the Konsen Plain, and contains small amounts of scoria and banded pumice. However, their superpositional relationship has not been confirmed, and changes in facies and color are gradual. Their petrographic characteristics also agree closely. Thus, although parts may have been deposited as different flow units, KP IV and KS are considered products of a continuous eruption sequence (Okumura et al., 1985).

A soil bed 1–2 cm thick between KP II and KP III indicates that the two pyroclastic flows erupted with a brief time interval between them. Aso-4 ash, 15 cm thick, occurs below KP III. Fine ash containing accretionary lapilli also occurs at the base of KP II; comparing the two provides a useful understanding of the characteristics of distant widespread ash.

References: Katsui and Sato (1963); Machida and Arai (1992); Okumura (1991); Okumura et al. (1985).

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English translation of figure lettering

1:50,000 Koshimizu (Shari sheet 9). Legible numbers: 80, 100.

Original Japanese lettering

5万分の1『小清水』（斜里9号）。可読数値80，100。

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KP I; Spfa-1; Kpfa-2; Kpfa-3; KP II; KP III; Aso-4; Kpfa-4; Kpfa-5; 20 m; KP IV; Pink; KP V. Left-hand scale visible on the original PDF: 2 m, 1, 0.

Original Japanese lettering

KP I，Spfa-1，Kpfa-2，Kpfa-3，KP II，KP III，Aso-4，Kpfa-4，Kpfa-5，20m，KP IV，Pink，KP V。左スケールは原PDF側に2m，1，0。

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English translation of figure lettering

KP I; KP II; KP III; KP IV.

Original Japanese lettering

KP I，KP II，KP III，KP IV。

[Original printed page: 62]

WS-16-2 Kutcharo-Haboro and other marker tephras at Haboro, Hokkaido

Hiroshi Machida; Hideki Miura; Koji Okumura

Locality: Nakanotaki, Haboro Town, Hokkaido. Coordinates: N44°21′30″ E141°41′48″. Elevation: 20 m. Exposure and present condition: sea cliff; extant. Deposits: marine sand and gravel, ash, and peat. Date described: May 1984. Keywords: Kutcharo-Haboro tephra; Toya tephra; Aso-4 tephra; Tomamae terrace; Haboro.

The Haboro–Tomamae area on the Sea of Japan coast of northwestern Hokkaido has well-developed marine terraces and was formerly considered a reference area for Hokkaido’s marine terraces (Sakaguchi, 1959). This exposure lies at the top of the sea cliff of the Tomamae terrace. On this terrace, wave-cut-platform sand and gravel truncating Neogene basement are overlain by peat and then Holocene dune sand. Three widespread ash beds are intercalated in the peat. All are thin, but the middle one, Toya, is most conspicuous: 10 cm of grayish-white glassy ash. Coarse sand at the top of the sand and gravel bed occurs 170 cm below it. Close examination reveals patchy coarse grayish-white ash less than 5 cm thick within this sand. It comprises slightly colored bubble-wall glass and phenocrysts. Refractive indices of glass and orthopyroxene permit correlation with Kutcharo 4 pyroclastic flow (Kc-4), Kutcharo caldera’s largest Quaternary pyroclastic-flow deposit. Recognition that ash fall was produced during this eruption and also deposited west of the source led to naming it Kutcharo-Haboro tephra (Kc-Hb) after this exposure (Arai et al., 1986). Here it lies approximately at the emergence horizon. Since the former shoreline of the Tomamae terrace is about 35 m above sea level, this tephra erupted and accumulated after sea level had fallen more than 15 m from its maximum. Likewise, on the Kushiro terrace in eastern Hokkaido, Kc-4 flowed and accumulated after the marine terrace surface had emerged over a substantial area. Yano (1970) reported remains of Larix Gmelini from mud below Toya and inferred a cold climate 2–5 degrees cooler than today. This may correspond to oxygen isotope stage 5d. It is unclear whether this horizon lies between Toya and Kc-Hb or below Kc-Hb, but the peat below Kc-Hb is thin, so the former is probably the case.

Of the three widespread ashes, Aso-4 came from the greatest distance. It is glassy ash with a characteristic brownish coloration and can also be observed in the terrace cliff at the entrance to Tomamae Port. Thus, this exposure both suggests the widespread distribution of these glassy ashes and provides information on environmental change since oxygen isotope stage 5e, when the Tomamae terrace formed.

References: Sakaguchi (1959); Yano (1970); Arai et al. (1986); Machida and Arai (1992).

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Upper section: vegetation cover; dune sand; humic layer; grayish-white clay, Spfa-1; organic clay; Aso-4; Toya; peat; Kc-Hb; marine sand. Horizontal scale: 0, 5, 10, 15 m; vertical: 0, 5. Lower section: horizontal 0, 300 m; vertical 10 m. Legend: dune sand; humic layer; brown clay; grayish-white clay; peat; marine sand; basement. Two question marks.

Original Japanese lettering

上図：植被，砂丘砂，腐植層，灰白色粘土 Spfa-1，有機質粘土，Aso-4，Toya，泥炭，Kc-Hb，海成砂層。水平0，5，10，15m；垂直0，5。下図：水平0，300m；垂直10m。凡例：砂丘砂，腐植層，褐色粘土，灰白色粘土，泥炭，海成砂層，基盤。疑問符2か所。

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English translation of figure lettering

1:50,000 Haboro (Haboro sheet 6). Haboro Town; Saiwai Town; Midori Town; 朝羽; Sakae Town; 寿. Legible numbers: 7.0, 3.5, 26.6, 27.5, 25, 64.0, 40.

Original Japanese lettering

5万分の1『羽幌』（羽幌6号）。羽幌町，幸町，緑町，朝羽，栄町，寿。可読数値7.0，3.5，26.6，27.5，25，64.0，40。

[Original printed page: 63]

WS-16-3 Late Pleistocene widespread tephras at Atsuma, Hokkaido—Widespread tephras from Aso, Toya, and Kutcharo

Kotaro Yamagata

Locality: Karumai, Atsuma Town, Hokkaido. Coordinates: N42°39′48″ E141°54′00″. Elevation: 15 m. Exposure and present condition: artificial exposure; mostly covered by talus. Deposits and age: tephra fall; Late Pleistocene. Date described: June 1987. Keywords: Aso-4 tephra; Toya tephra; Kutcharo-Haboro tephra; Atsuma Formation.

This exposure lies in a terrace cliff. At its bottom is a silt bed named the Atsuma Formation by the Umaoi Collaborative Research Group (1983) and considered a last-interglacial deposit. Several fine-grained tephra beds are intercalated in the lower peat. These include three particularly important Late Pleistocene widespread tephras in Hokkaido: Aso-4, Toya, and Kutcharo-Haboro (Kc-Hb). Kc-Hb and Toya correspond to Atsuma ash-fall deposits 3 and 2 of Kasugai et al. (1980). All are fine-grained glassy ashes; Kc-Hb and Aso-4 contain abundant bubble-wall glass. Atsuma ash-fall deposit 1 (Aafa1) is correlated with Kuttara tephra 8 (Kt-8) from Kuttara volcano. Aso-4 is recognizable as orange fine ash immediately below the thick Kt-6 pumice-fall bed (Mpfa3).

For the overlying Mukawa pumice-fall deposits (Mpfa1–3) and Shikotsu pumice-fall deposits (Spfa1–10), see the Genbu and Shiomi Sanku entries (HK-22, HK-23) and Yamagata (1994). Similar sections can currently be seen at several nearby localities, including Genbu, Ninomiya, and Toyoshiro, but exposure conditions mean that no exposure presently allows all of Spfa1, Aso-4, Toya, and Kc-Hb to be observed.

References: Arai et al. (1986); Kasugai et al. (1980); Machida and Arai (1992); Machida et al. (1987); Umaoi Collaborative Research Group (1983); Yamagata (1994).

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Map: 1:25,000 Karumai (Tomakomai sheet 1-1); Karumai; Karumai River; 正楽寺; legible numbers 30.0, 21, 1.5, 2. Column from top: Spfa1, Kt-1, Z-M, Kt-Tk, Kt-3, Spfa6, Kt-Hy, Ssfa, Yo-Mk, Kt-6, Aso-4, Kt-8, Toya, Kc-Hb, Aafa4. Scale: 0 m, 1, 2. Legend: pumice-fall deposit; scoria-fall deposit; ash fall; brown volcanic-ash soil; peat; clay.

Original Japanese lettering

地図：2.5万分の1『軽舞』（苫小牧1号-1）；軽舞，軽舞川，正楽寺；可読数値30.0，21，1.5，2。柱状図上から：Spfa1，Kt-1，Z-M，Kt-Tk，Kt-3，Spfa6，Kt-Hy，Ssfa，Yo-Mk，Kt-6，Aso-4，Kt-8，Toya，Kc-Hb，Aafa4。スケール0m，1，2。凡例：降下軽石堆積物，降下スコリア堆積物，降下火山灰，褐色火山灰土，泥炭，粘土。

[Original printed page: 64]

WS-17-1 Ata-Torihama tephra at Onejime on the Osumi Peninsula

Hiroshi Machida

Locality: Nakanishi, Onejime Town, Kagoshima Prefecture. Coordinates: N31°13′42″ E130°47′19″. Elevation: 30 m. Exposure and present condition: former excavation for earth and gravel; probably extant. Deposits and age: pumice fall and pyroclastic-flow deposits; 230–250 ka. Date described: March 1993. Keywords: Ata-Torihama tephra; Onejime.

The Torihama pyroclastic-flow deposit described on the Satsuma and Osumi peninsulas (Ui, 1971) is one of the large pyroclastic flows recognized at various localities in southern Kyushu. Its co-ignimbrite ash has also come to be identified throughout Honshu (Machida and Arai, 1992). This is one of the exposures closest to the source vent, where pumice fall and pyroclastic-flow deposits divided into several units can be observed. The middle flow unit contains andesite boulders, particularly somewhat rounded ones, at its base, suggesting that the eruption occurred on the nearby seafloor. At the ■ locality in Figure 1, the pyroclastic flow erodes the pumice fall and has basal rounded gravel thought to have lain on a shallow seafloor, with pyroclastic-surge deposits in its upper portion. Huge pumice clasts also occur in the pyroclastic-flow deposit across the bay on the Satsuma Peninsula. This distribution suggests a source within the conventionally defined Ata caldera, offshore Ibusuki, probably closer to the Satsuma Peninsula than the principal Ata tephra vent. This eruption sequence is called Ata-Torihama tephra (Ata-Th).

The tephra is biotite-bearing orthopyroxene-hornblende rhyolite containing some quartz. Southern Kyushu tephras with similar mineral assemblages include Hiwaki and Koseda, the latter considered to originate from Kikai caldera. They can be distinguished by differing refractive indices of orthopyroxene and hornblende. Glass in the co-ignimbrite ash is high-silica and of bubble-wall type. Considering its stratigraphic occurrences across Honshu, this tephra probably erupted during the transition from oxygen isotope stage 8 to 7, while sea level was still considerably low (Machida and Arai, 1992).

References: Machida and Arai (1992); Ui (1971).

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Map: 1:25,000 Onejime (Kaimondake sheet 1-4); 木場; 木原; 馬場; 山口; legible numbers 40, 61.0, 93. Column: pyroclastic-flow deposit; pumice fall; 5 m. No legible annotations within the photograph.

Original Japanese lettering

地図：2.5万分の1『大根占』（開聞岳1号-4）；木場，木原，馬場，山口；可読数値40，61.0，93。柱状図：火砕流堆積物，降下軽石，5m。写真自体に可読注記なし。

[Original printed page: 65]

WS-17-2 Ata-Torihama tephra and overlying tephras in the southwestern Miyazaki Plain

Shinji Nagaoka

Locality: Kamamuta, Aya Town, Miyazaki Prefecture. Coordinates: N31°59′17″ E131°11′43″. Elevation: 210 m. Exposure: road cutting. Deposits and age: wind-deposited tephra; Middle to Late Pleistocene. Date described: January 1996. Keywords: Kukino Gravel; Ata-Torihama tephra; Miyazaki Plain.

Middle Pleistocene fluvial terraces, including Chausubaru, Kukino, Higashibaru, and Shiibaru, are developed along the western and southwestern margins of the Miyazaki Plain (Nagaoka, 1986). Of these, the Kukino terrace in the southwestern plain is thickly covered by Middle Pleistocene to Holocene tephras deposited since the Kakuto pyroclastic-flow deposit (Nagaoka, 1984), providing a locality for confirming stratigraphic relationships among the principal southern Kyushu tephras. Here one can observe the tephras covering the Kukino Gravel (high-level terrace deposits; Noi, 1987). The lowermost Ata-Torihama tephra (Ata-Th; 230–250 ka) is a grayish-white, weathered, unwelded pyroclastic-flow deposit. Above it, the following can be identified: Kamamuta tephra (scoria) I (Km-I), II (Km-II), and III (Km-III); Ata; Kikai-Tozurahara (K-Tz); Aira-Fukuyama (A-Fk); Aya (Ay); Aira-Iwato (A-Iw); and Kirishima-Iwaokoshi (Kr-Iw). All except Ata are fallout tephras. Most are weathered and somewhat difficult to recognize, but Ata-Th and A-Fk, the latter yellowish-white fine-grained pumice containing hornblende, are conspicuous and serve as good marker beds. Tephras above Kr-Iw have been eroded here but can be seen where flat plateau surfaces are developed nearby. In the central part of the plateau south of the exposure, Kakuto tephra (Kkt), and also Kobayashi tephra (Kb-Ks; pyroclastic flow and pumice fall), can be identified within the Kukino Gravel (Noi, 1987).

References: Nagaoka (1984, 1986); Noi (1987).

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English translation of figure lettering

Directions: E, S. Kr-Iw; A-Iw; Ay; A-Fk; K-Tz; Ata; Km-III; Km-II; Km-I; Ata-Th; Kukino Gravel; road surface. 2 m.

Original Japanese lettering

方位E，S。Kr-Iw，A-Iw，Ay，A-Fk，K-Tz，Ata，Km-III，Km-II，Km-I，Ata-Th，久木野礫層，道路面。2m。

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English translation of figure lettering

1:25,000 Kamiya (Miyazaki sheet 13-1). 南俣; Kamamuta; 米田. Legible numbers: 202, 258, 225, 208.

Original Japanese lettering

2.5万分の1『紙屋』（宮崎13号-1）。南俣，釜牟田，米田。可読数値202，258，225，208。

[Original printed page: 66]

WS-17-3 Stratigraphic position of Ata-Torihama tephra in the Oiso Hills, southern Kanto

Takehiko Suzuki

Locality: Soga-Osawa, Odawara City, Kanagawa Prefecture. Coordinates: N36°58′53″ E139°10′35″ [as printed]. Elevation: 75 m. Exposure: natural exposure along a stream. Deposits and age: tephra fall and fine-grained glassy ash bed; Middle Pleistocene. Date described: March 1990. Keywords: Oiso Hills; Ata-Torihama tephra; beige tuff; upper Tama C tephra group; Tama Loam Formation.

Clarifying the stratigraphic position of Ata-Torihama tephra (Ata-Th) in the Oiso Hills was extremely important in determining its eruption age. The corresponding tephra was initially called beige tuff by Mori et al. (1982), who described it as a concentration zone of bubble-wall glass immediately below Tm-5 (Uesugi, 1976) in two small streams in the western Oiso Hills, A Stream and Magassawa (曲沢). Suzuki and Hayatsu (1991) established the petrographic characteristics of beige tuff and used these to show its correlation with Ata-Th from Ata caldera, southern Kyushu. At Oiso, Ata-Th lies below Tm-5, or TCu-3 (Machida et al., 1974), and above TCu-2. These relationships with Hakone-derived tephras and fission-track ages of other tephras suggested an Ata-Th eruption age of about 240 ka, around oxygen isotope stage 7 (Suzuki and Hayatsu, 1991). The lower-left figure shows the A Stream exposure. Both there and at Magassawa, it is a glassy fine ash bed 8–10 cm thick that can clearly be recognized in the field. At both sites, however, faults and fluvial gravel obscure its relationships with adjacent tephras. In contrast, tephras from TCu-1 to around TCu-4 are exposed in orderly succession in a tributary stream of the Kiku River to the north (■ locality). Volcanic-ash soil concentrated with Ata-Th glass has been confirmed between TCu-2 and TCu-3, between Tm-3 and Tm-4 of Uesugi (1976) (lower-right figure). Ata-Th here does not form a bed and is difficult to identify visually. In the classical Tama Loam stratigraphy of the Tama Hills, Ata-Th occupies an intermediate position between TCu-1 (Doran Pumice) and TB-1 (Bireley’s Pumice) within the Tama Loam above the Oshinuma Sand and Gravel.

References: Machida et al. (1974); Mori et al. (1982); Suzuki and Hayatsu (1991); Uesugi (1976).

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English translation of figure lettering

TB-8 (=Tm-19); ?; TCu-3 (=Tm-5); Ata-Th; TCu-1 (=Tm-2); fault; upstream; river; downstream; 2 m. Sketch of the Ata-Th exposure at A Stream.

Original Japanese lettering

TB-8 (=Tm-19)，?，TCu-3 (=Tm-5)，Ata-Th，TCu-1 (=Tm-2)，断層，上流，川，下流，2m。A沢でのAta-Th露頭スケッチ。

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English translation of figure lettering

TCu-4; TCu-3 (Tm-5); Tm-4; Ata-Th; TCu-2 (Tm-3); TCu-1; downstream; upstream; 1 m. Sketch of the Kiku River tributary exposure.

Original Japanese lettering

TCu-4，TCu-3 (Tm-5)，Tm-4，Ata-Th，TCu-2 (Tm-3)，TCu-1，下流，上流，1m。菊川支流露頭のスケッチ。

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English translation of figure lettering

1:25,000 Northern Odawara (Yokosuka sheet 13-1). 川原; Soga-Osawa; 井窪. Legible numbers: 130, 184, 193.4, 105, 83.

Original Japanese lettering

2.5万分の1『小田原北部』（横須賀13号-1）。川原，曽我大沢，井窪。可読数値130，184，193.4，105，83。

[Original printed page: 67]

WS-18-1 Aso-1 pyroclastic flow in central Taketa, Oita Prefecture—Aso-1, Aso-3/4 tephras, Imaichi, Takajomachi, and other pyroclastic flows

Koji Ono

Locality: cliff behind the martial-arts hall of Prefectural Taketa High School, Taketa, Taketa City, Oita Prefecture. Coordinates: N32°57′56″ E131°24′02″. Elevation: 250 m. Exposure and present condition: artificial exposure; extant, partly covered. Deposits and age: chiefly pyroclastic-flow deposits; Early to Late Pleistocene. Date described: February 1996. Keywords: Imaichi; Takajomachi; Aso-1; Aso-3; and Aso-4 pyroclastic flows.

Central Taketa lies near the eastern end of the pyroclastic plateau east of Aso caldera, where the Inaba, Tamara, and main Ono rivers and others converge in a fan-shaped pattern from the west. Thus many pyroclastic-flow deposits, including Imaichi, Aso-1, Aso-3, and Aso-4, here of valley-fill type, can be observed in a concentrated area. This exposure lies behind the former Taketa High School playing field, with the Inaba River on the left (site G in Figure 1). Much is covered by bamboo grass, obscuring most contacts, but the relative positions of the units are clear (Figure 2). At the bottom is the Imaichi pyroclastic-flow deposit (hereafter “deposit” is omitted), an unwelded pale-brown pumice flow, an unusual facies for Imaichi. Above and to its right are right-dipping Aso-1 welded tuff (described below) and the Aso-2T scoria-fall bed. Above these, Aso-3 extends to the summit on the right. Aso-4 welded tuff covers the left slope; at the summit its contact with Aso-3 is nearly vertical. Welding increases abruptly leftward from about 10 cm of yellow unwelded glassy ash, and the lamination changes from vertical to gently dipping. Going around behind the right side leads to the school playing field. A cutting on its eastern side provides a good section of Aso-3 from its base. The unwelded basal scoria flow forms a smooth slope, while the welded upper portion forms a vertical wall with columnar joints. The Aso-4/Aso-3 contact in Figure 2 is clearly controlled by the shape of this weathered Aso-3 surface. The Aso-4 welded tuff dipping toward the present valley here is a section through its cover of the pre-Aso-4 valley wall.

A small pedestrian tunnel is across the road in front of the school’s main gate. Passing through it leads to a Takajomachi pyroclastic-flow exposure on the right (site T on the map). It is white unwelded biotite-rhyolite pumice flow, between the Imaichi and Aso-1 flows. The nearby Inaba riverbed is chiefly red welded tuff in the vapor-phase crystallization zone of Imaichi. Aso-4 welded tuff is exposed at some points where the river crosses old channels filled by Aso-4. Here it is harder than Imaichi welded tuff, making the riverbed slightly higher.

The Aso-1 pyroclastic flow forms the lower part of the pyroclastic plateau around Aso caldera, and central Taketa is near the eastern margin of its present exposure. The facies of its strongly welded portion closely resemble those of underlying Imaichi, and sometimes it can be distinguished from reversely magnetized Imaichi only by the direction of magnetization.

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English translation of figure lettering

1; 3 (repeated); 4 (twice); 2T; IM (twice); 1F (twice).

Original Japanese lettering

1，3（複数箇所），4（2か所），2T，IM（2か所），1F（2か所）。

Extracted lettering and translation Figure 2. Sketch of this exposure. 1–4: Aso-1–Aso-4; IM: Imaichi tephra; 1F: Aso-1 fallout tephra; 2T: Aso-2 scoria fall.

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Figure 1. 1:25,000 Taketa (Oita sheet 11-1). G, T, K, U; Taketa Town; Taketa City; 渡辺; Inaba River; Taketa River. Legible numbers: 238, 322, 250.

Original Japanese lettering

図1。2.5万分の1『竹田』（大分11号-1）。G，T，K，U；竹田町，竹田市，渡辺，稲葉川，竹田川。可読数値238，322，250。

[Original printed page: 68]

WS-18-1 (continued)

Aso-1 welded tuff is thin but strongly welded, pinching out as a lens toward the upper left and accompanied below by white to pink Plinian pumice and ash. Most Aso-1 exposed in central Taketa has a facies similar to that here. Figure 3 shows a column of the exposure in front of the service gate south of Taketa High School, now concealed by concrete. Products of the Aso-1 cycle (A–D) are 2 m+ thick, with the upper surface unexposed; an upper unwelded portion, if present, was probably thin. A is yellowish-gray pumice fall. B also appears to be fallout, alternating black sandy ash with pinkish-white sand-sized pumice. C and D are pyroclastic-flow deposits. C is probably a surge deposit: unwelded, composed almost entirely of dark-brown sandy glassy ash, indistinctly stratified, with thin crystal-rich beds. D becomes abruptly welded above C, grading within about 30 cm into dark-brown dense glassy welded tuff. Its upper portion is reddish-brown from high-temperature oxidation, a color characteristic of the Aso-1 surface. Ellipsoidal black glassy juvenile lenses are small in the lower welded tuff but large and conspicuous above. Below Aso-1, separated by weathered soil, is the weathered surface portion of the Takajomachi pyroclastic flow. Exposures of this Aso-1 facies are distributed throughout the town, including localities south of Namese Bridge (site K on the map), as much as 50 m above the Ono riverbed, where they overlie Imaichi.

Aso-1 forms bedrock in the riverbed downstream on the right bank of Uozumi Dam (site U on the map). Valley-filling Aso-4 welded tuff overlies it across a clay bed containing gravel from riverbed deposits. Aso-1 here and nearby differs markedly in facies from the thin sections described above. It is several meters or more thick, with the lower part unexposed: dense, devitrified, purplish dark-gray welded tuff, extremely hard, probably owing to devitrification. It conspicuously contains flattened juvenile lenses and foreign lithic fragments. From the relative positions and facies, Aso-1 near site U is a thick deposit in the principal channel, filling a valley more than 50 m deep cut into Imaichi. The thin, often inclined, lens-shaped deposits that pinch out probably represent the wings along the valley walls.

Reference: Ono et al. (1977).

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m: 0, 1, 2. D: reddish brown wd tf with obsidian lens [reddish-brown welded tuff with obsidian lenses]; dark brown vitric wd tf [dark-brown glassy welded tuff]; coarser band. C: non-wd dark brown vitric ash [unwelded dark-brown glassy ash]; xl ash [crystal ash]. B: pink-white pm sd [pinkish-white pumice sand]; black sd [black sand]. A: white, clayey; yel gray fall pm [yellowish-gray pumice fall]. Below: humus soil; lighter color (pm bed?) [pumice bed?]; biot-bg soil [biotite-bearing soil].

Original Japanese lettering

m：0，1，2。D：reddish brown wd tf with obsidian lens；dark brown vitric wd tf；coarser band。C：non-wd dark brown vitric ash；xl ash。B：pink-white pm sd；black sd。A：white, clayey；yel gray fall pm。下位：humus soil；lighter color (pm bed?)；biot-bg soil。

Extracted lettering and translation Figure 3. Standard stratigraphic column showing the Aso-1 horizon.

[Original printed page: 69]

WS-18-2 Fine-grained glassy tephra at the eastern foot of Yatsugatake potentially correlatable with Aso-1

Takehiko Suzuki

Locality: Kawadaira, Minamimaki Village, Nagano Prefecture. Coordinates: N36°1′27″ E138°31′10″. Elevation: 1,150 m. Exposure: natural exposure on a terrace-cliff slope. Deposits and age: wind-deposited tephra and fine-grained glassy ash bed; Middle Pleistocene. Date described: July 1995. Keywords: eastern foot of Yatsugatake; Aso-1 tephra; Nuka 4.

Numerous wind-deposited tephra beds from Yatsugatake volcano accumulated at its eastern foot in central Japan. Several intercalated tephras consist principally of fine glass and appear to have arrived from distant volcanoes rather than Yatsugatake. These glassy ash beds were described by the Yatsugatake Collaborative Research Group (1988), Suzuki and Hayakawa (1990), Yoshikawa et al. (1990), and others. Nuka 4 of Suzuki and Hayakawa (1990) is a fine-grained glassy ash bed 20 cm thick, somewhat above Kakuto tephra (Kkt; ca. 300 ka; Machida and Arai, 1992; see WS-19-4) and the Omachi APm tephra group (300–350 ka; Suzuki and Hayakawa, 1990). Yoshikawa (1990) correlated it with Aso-1 (Ono et al., 1977). Exposures also occur around Kawadaira and in Kawakami Village farther upstream on the Chikuma River, but conditions are deteriorating as they become buried by talus and so forth. The exposure introduced here is difficult to find on a terrace-cliff slope, but should remain preserved for some time.

It is on a forest-covered mountain slope about 250 m west of Kawadaira village, at the top of a natural exposure about 3.5 m high. It is immediately overlain by Lw.O.P (Yatsugatake Research Group, 1988). Nuka 3, a glassy ash bed 2 cm thick, occurs 10.5 cm below it. Nuka 3 has characteristics closely resembling Nuka 4, including the refractive index of glass, leaving interesting questions about their relationship.

References: Yoshikawa (1990); Suzuki and Hayakawa (1990); Machida and Arai (1992); Ono et al. (1977); Yatsugatake Research Group (1988).

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English translation of figure lettering

Lw.O.P; Nuka 4, thickness 20 cm; Nuka 3, thickness 2 cm.

Original Japanese lettering

Lw.O.P，ヌカ4 層厚20cm，ヌカ3 層厚2cm。

Extracted lettering and translation Photographed in May 1995.

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1:25,000 Goshodaira (Kofu sheet 5-3). Kawadaira; Minamimaki Village; Hirose. Legible numbers: 1156, 1150, 1207.

Original Japanese lettering

2.5万分の1『御所平』（甲府5号-3）。川平，南牧村，広瀬。可読数値1156，1150，1207。

[Original printed page: 70]

WS-19-1 Ng-1 ash, a Middle Pleistocene widespread tephra in the Udo Hills, Shizuoka Prefecture

Kiyohide Mizuno

Locality: north of Ago (安居), Shizuoka City. Coordinates: N34°57′36″ E138°27′40″. Elevation: 50 m. Exposure and present condition: valley wall; extant. Deposits and age: marine beds; Middle Pleistocene, about 300 ka. Date described: January 1996. Keywords: Ng-1 ash; Negoya Formation; Udo Hills.

Ng-1 ash is a widespread tephra distributed in southwestern Japan, thought to have erupted from a volcano near the Northern Alps about 300 ka (Mizuno and Yoshikawa, 1991). Its type locality is in the Udo Hills, and it was named by Kondo (1985). The tephra is intercalated in marine to alluvial-fan deposits called the Negoya Formation, whose stratigraphy was described in detail by Kondo (1985). To reach this exposure, follow the stream west of Ago village northward for about 600 m, then enter an eastern tributary stream for about 50 m; a small check dam lies before the branch. Ng-1 is intercalated in alternating silt, sand, and gravel. Thick gravel is developed from about 5 m above the ash upward. The type locality of Kondo (1985) lies in the next stream to the north. Here Ng-1 is about 30 cm thick, consisting of grayish-white fine-grained glassy ash; the upper approximately 20 cm appears reworked. Petrographic characteristics are described in detail by Mizuno and Yoshikawa (1991).

References: Kondo (1985); Mizuno and Yoshikawa (1991).

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N; S. The interval between the arrows is the Ng-1 ash bed. Photographed in January 1996.

Original Japanese lettering

N，S。矢印の範囲がNg-1火山灰層。1996年1月撮影。

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1:25,000 Eastern Shizuoka (Shizuoka sheet 11-1). Kunozan; Negoya; Ago; Toshogu Shrine. Legible numbers: 246, 250, 50, 11.9, 12.

Original Japanese lettering

2.5万分の1『静岡東部』（静岡11号-1）。久能山，根古屋，安居，東照宮。可読数値246，250，50，11.9，12。

[Original printed page: 71]

WS-19-2 Ng-1 (Nomura 2) ash, a widespread tephra in high-level terrace deposits of the Nomura Basin, Ehime Prefecture

Kiyohide Mizuno

Locality: Ota, Nomura Town, Higashiuwa District, Ehime Prefecture. Coordinates: N33°21′36″ E132°39′4″. Elevation: 160 m. Exposure and present condition: artificial exposure; extant? Deposits and age: freshwater beds; Middle Pleistocene. Keywords: Nomura Basin; Ng-1 ash; high-level terrace.

Kashima et al. (1982) reported two tephras intercalated in the highest terrace deposits along the Uwa River at Nomura, Ehime Prefecture. Mizuno and Yoshikawa (1991) named them Nomura 1 and Nomura 2 in ascending order and correlated the lower tephra with Kakuto and the upper with Ng-1. Ng-1 is a widespread tephra thought to have erupted near the Northern Alps about 300 ka (Mizuno and Yoshikawa, 1991); this exposure is at the western end of its known distribution. The Nomura 2 ash bed, correlated with Ng-1, lies midway up the exposure and consists of about 50 cm of grayish-white glassy ash. Detailed examination distinguishes about six layers, possibly including portions reworked by water flow. Fine heavy-mineral grains can be seen scattered through it. About 5 m below is the glassy Nomura 1 ash bed, approximately 40 cm thick. An exposure slightly farther north contains peat with fossil wood at a horizon between the two tephras. Warm-climate taxa such as the evergreen-oak subgenus and the tung-tree genus occur mixed with Sawara cypress and the fir genus. About two carbonaceous silt beds also occur above Nomura 2; a spruce-genus cone, inferred to have fallen from them, was found nearby. All identifications are by 百原新 of Chiba University.

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1:25,000 Nomura (Matsuyama sheet 8-2). 山本; 中屋敷; 荒瀬; 中ノ村; Nomura; Ota. Legible numbers: 60, 61.5.

Original Japanese lettering

2.5万分の1『野村』（松山8号-2）。山本，中屋敷，荒瀬，中ノ村，野村，大田。可読数値60，61.5。

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English translation of figure lettering

Silt; gravel; Nomura 2 ash (Ng-1); carbonaceous silt–peat; Nomura 1 ash (Kkt). Scale: 5 m, 0. Described in March 1989.

Original Japanese lettering

シルト，礫，野村2火山灰(Ng-1)，炭質シルト-泥炭，野村1火山灰(Kkt)。スケール5m，0。1989年3月記載。

References: Kashima et al. (1982); Mizuno and Yoshikawa (1991).

[Original printed page: 72]

WS-20-1 Kakuto tephra in the Hitoyoshi Basin

Hiroshi Machida

Locality: Yamashita, Nishiki Town, Kumamoto Prefecture. Coordinates: N32°13′20″ E130°49′45″. Elevation: 150 m. Exposure and present condition: cliff cut for farmland development; probably extant. Deposits: wind-deposited tephra and pyroclastic-flow deposits. Date described: March 1993. Keywords: Kakuto tephra; Kakuto pyroclastic-flow deposit; Hitoyoshi Basin.

Pyroclastic-flow deposits formerly called Upper Kakuto, Shinkawa, Inuzako, Haginomoto, Chikuri, and other names according to locality and researcher across southern Kyushu are the same bed: a large Middle Pleistocene pyroclastic flow originating from Kakuto caldera (Machida and Arai, 1992). Kakuto tephra (Kkt) has no associated pumice fall and consists of pyroclastic-flow deposits and their co-ignimbrite ash. It commonly forms welded tuff in the Hitoyoshi Basin, but here is a weathered, unwelded pyroclastic-flow deposit. At this exposure Aso-4 and Aira-Ito (A-Ito) overlie it across a major erosional surface. At another nearby exposure, now destroyed, Ata and Aso-3 deposits also overlie it. In the Kogashira area of northern Kagoshima City, it lies below the Ata-Torihama pyroclastic-flow deposit (WS-20-2).

This tephra is pyroxene rhyolite, characterized by bubble-wall glass with a refractive index of 1.500–1.502, darkly colored here perhaps by high-temperature oxidation, and orthopyroxene with a somewhat high refractive index. Glassy ash with these characteristics has come to be recognized widely in Kyushu and Honshu, establishing that this eruption produced co-ignimbrite ash (Machida and Arai, 1992). Its stratigraphic occurrence clearly corresponds to the transgression of the major interglacial two cycles before oxygen isotope stage 5e. Considering radiometric ages and relationships with other tephras in central Japan, at the eastern foot of Yatsugatake, its eruption age is thought to be slightly older than about 300 ka, within oxygen isotope stage 9.

Reference: Machida and Arai (1992).

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1:25,000 Hitoyoshi (Yatsushiro sheet 3-4). 野間; Yamashita; 滝の水; 一野間; 山川. Legible numbers: 172, 156, 125.

Original Japanese lettering

2.5万分の1『人吉』（八代3号-4）。野間，山下，滝の水，一野間，山川。可読数値172，156，125。

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A-Ito (twice); Aso-4; Kkt; cliff relief approximately 10 m; farm road. Stratigraphy of the pyroclastic-flow deposits.

Original Japanese lettering

A-Ito（2か所），Aso-4，Kkt，崖の比高約10m，農道。火砕流堆積物の層序。

[Original printed page: 73]

WS-20-2 Large pyroclastic-flow deposits, including Kakuto and Hiwaki, at Kogashira, Kagoshima City

Hiroshi Machida

Locality: Kogashira, Kagoshima City. Coordinates: N31°39′03″ E130°30′40″. Elevation: 80–100 m. Exposure and present condition: quarry; extant. Deposits and age: pyroclastic-flow deposits and pumice fall; Middle Pleistocene. Date described: March 1969; 1994. Keywords: Kakuto tephra; Hiwaki tephra; Kogashira.

Around Kogashira in northern Kagoshima City, Early to Middle Pleistocene pyroclastic-flow deposits have been described together with marine beds (Oki and Hayasaka, 1970; Oki, 1974; and others). Their upper beds can be observed together at this exposure. Since this is an active quarry, the exposure changes continually. As shown, conspicuous welded tuffs occur in its upper and lower parts. Formerly called Inuzako above and Shimokado below, these correspond respectively to Kakuto (Kkt) and Hiwaki (Hw) pyroclastic-flow deposits. Valley-filling Kkt is a pyroxene-rhyolite deposit with basal breccia and an unwelded portion, truncated above by sand and gravel. At the ■ locality on the topographic map, Ata-Torihama overlies Kkt.

Hw overlies sand and gravel and is pyroxene-hornblende rhyolite; its strongly welded portion is used as building stone. Between Hw and Kkt are reworked Hw and another unnamed pyroclastic-flow deposit bounded above and below by red soils now unexposed. The intervening time was therefore probably considerable. Horizontal joints in strongly welded Hw are filled with unwelded ash. This ash differs lithologically from Hw and resembles the unnamed deposit above, so it probably entered the joints during that eruption.

Hw is also called the Lower Kakuto pyroclastic-flow deposit (Miyachi, 1987). Like Kkt, it erupted from Kakuto caldera and covers southern Kyushu widely. Its eruption age has been measured at 500–600 ka by fission-track dating. Finding ash fall formed during this eruption would clarify its chronological significance further.

Pyroclastic-flow deposits below Hw, including Kamagahara and Keno, and the marine Kogashira Formation can be observed in the Oyamada district to the west and at Kenoguchi to the south.

References: Machida and Arai (1992); Miyachi (1987); Oki (1974); Oki and Hayasaka (1970).

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English translation of figure lettering

Kkt; strongly welded portion; unwelded portion (twice); unnamed pyroclastic-flow deposit; Hw; welded portion; sand and gravel. Scale: 10 m, 0.

Original Japanese lettering

Kkt，強溶結部，非溶結部（2か所），未命名火砕流堆積物，Hw，溶結部，砂礫層。スケール10m，0。

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1:25,000 Northern Kagoshima (Kagoshima sheet 7-3). Oyamada Town; 稲村; 川田; 柿原; 柳瀬. Legible numbers: 186.6, 100, 200.

Original Japanese lettering

2.5万分の1『鹿児島北部』（鹿児島7号-3）。小山田町，稲村，川田，柿原，柳瀬。可読数値186.6，100，200。

[Original printed page: 74]

WS-20-3 High-level terrace and Kakuto tephra on the Nyu Plateau, Oita City

Hiroshi Machida

Locality: Tanegu, Nyu, Oita City, in front of Midorigaoka Hoyōen (緑が丘保養園). Coordinates: N33°12′30″ E131°42′15″. Elevation: 80 m. Exposure and present condition: excavation for earth and gravel; extant. Deposits: ash, sand and gravel, and silt. Date described: November 1990. Keywords: Kakuto tephra; Ozai Formation; Nyu Plateau.

At this exposure, ash fall (Kkt) contemporaneous with the Kakuto pyroclastic-flow deposit can be observed within high-level terrace deposits of the Nyu Plateau, Oita (Ozai Formation). This is a grayish-white ash bed around 40 cm thick within sand and gravel. At Sakotani, 1 km north, where housing development was underway in 1981, a 1 m thickness could be observed. Close examination reveals inverse grading. The bottom 3–4 cm is very fine-grained; above it lies about 10 cm of coarse ash containing pumice 2 mm in diameter, followed again by fine ash. Overall, it consists principally of transparent rhyolitic bubble-wall glass, with pyroxene phenocrysts and minor hornblende. Overlying silt has developed lamination and contains plant and shell fossils. This is the upper Ozai Formation, truncating the Oita Group and forming the high terrace of the Nyu Plateau. Intercalation of Kkt suggests correlation with oxygen isotope stage 9, that is, the Oshinuma Sand and Gravel of southern Kanto. The highest former shoreline of this age on the plateau is above 80 m elevation.

This exposure is at the top of a large cliff facing the Ono River lowland and is extremely dangerous.

Reference: Machida and Arai (1992).

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English translation of figure lettering

Well-stratified shell-fossil-bearing silt; Kkt; sand and gravel. Overall scale 5 m; enlarged interval 50 cm. No legible lettering within the photograph.

Original Japanese lettering

層理の発達した含貝化石シルト層，Kkt，砂礫層。全体5m；拡大50cm。写真に可読文字なし。

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1:25,000 Tsurusaki (Oita sheet 5-2). 西受; Ono River; 昭和井; Nyu; 野田岡; 浄願寺; Tanegu; 野間. Legible numbers: 81.5, 42.

Original Japanese lettering

2.5万分の1『鶴崎』（大分5号-2）。西受，大野川，昭和井，丹生，野田岡，浄願寺，種具，野間。可読数値81.5，42。

[Original printed page: 75]

WS-20-4 Kakuto tephra and marker tephras of Shinshu at the eastern foot of Yatsugatake

Hiroshi Machida

Locality: Hirose, Minamimaki Village, Nagano Prefecture. Coordinates: N36°0′0″ E138°31′13″. Elevation: 1,130 m. Exposure and present condition: cliff at a civil-engineering materials yard; extant. Deposits and age: ash fall, pumice fall, and scoria fall; Middle Pleistocene. Date described: May 1995. Keywords: Kakuto tephra; Omachi APm group; eastern foot of Yatsugatake.

Because tephras from Yatsugatake are thickly developed at its eastern foot (Yatsugatake Collaborative Research Group, 1988), intercalated Middle Pleistocene tephras arriving from distant sources are well preserved there (see WS-18-2). At this exposure, among Yatsugatake mudflow (debris-flow) deposits, scoria beds, and pumice beds, one can observe beige fine ash (Kakuto tephra; Kkt) and, below it, a pumice bed of the Omachi APm (crystal-ash) group and coarse pumice thought to originate from Yatsugatake. Kkt consists principally of bubble-wall glass slightly clouded by weathering, with sparse pyroxene phenocrysts. The underlying 30 cm pumice bed contains 1 cm pumice rich in biotite, hornblende, feldspar, and other phenocrysts. It corresponds to B2 of the three biotite-pumice beds distributed around Yatsugatake (Yatsugatake Collaborative Research Group, 1988) and is correlated with Omachi A3Pm (Suzuki and Hayakawa, 1990). Immediately beneath it, 1.2 m of coarse pumice characteristically contains abundant hornblende and corresponds to the hornblende-bearing white pumice described by the same group (1988). Immediately below that, one can also observe fine, phenocryst-rich pumice resembling B2, namely B1 of the group (1988). According to Suzuki and Hayakawa (1990), these tephras occur above Tama E-5 (TE-5) in the western Kanto Plain, for example at 安立, Chichibu City, linking the Middle Pleistocene of the central mountains and Kanto Plain. The pumice bed called BBP at the eastern foot of Yatsugatake (Iijima, 1967), correlated with Gomashio Pumice in southern Kanto (Arai, 1972), lies considerably above the horizons exposed here.

Kkt reaches 10 cm thickness, suggesting an extremely large eruption. It should therefore also be found farther east and is important for clarifying environmental changes during Middle Pleistocene oxygen isotope stage 9. Through Kkt, this exposure links the Middle Pleistocene tephras of Kyushu and central Honshu and has important significance for interpreting geological history.

References: Arai (1972); Iijima (1967); Suzuki and Hayakawa (1990); Yatsugatake Collaborative Research Group (1988).

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English translation of figure lettering

←Kkt; ←B2 (A3Pm).

Original Japanese lettering

←Kkt；←B2 (A3Pm)。

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English translation of figure lettering

Kkt; close-up.

Original Japanese lettering

Kkt，クローズアップ。

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English translation of figure lettering

1:25,000 Shinano-Nakajima (Nagano sheet 8-4); 1:25,000 Goshodaira (Kofu sheet 5-3). Koumi railway line; Hirose; Iwashita; Saku-Hirose. Legible numbers: 1100, 1257, 1156, 1219.

Original Japanese lettering

2.5万分の1『信濃中島』（長野8号-4）；2.5万分の1『御所平』（甲府5号-3）。小海線，広瀬，岩下，さくひろせ。可読数値1100，1257，1156，1219。

[Original printed page: 76]

WS-21-1 The Omachi APm tephra group, important Middle Pleistocene markers in central Japan

Takehiko Suzuki

Locality: Kambadaira (樺平), Ooka Village, Nagano Prefecture. Coordinates: N36°29′11″ E138°2′14″. Elevation: 1,230 m. Exposure and present condition: artificial exposure; extant. Deposits and age: tephra fall; Middle Pleistocene. Date described: September 1990. Keywords: Omachi APm tephra group; crystal ash; Kakuto tephra; central Japan; 水鉛谷 conduit; Momisawadake volcano.

The Omachi APm tephra group (APms), also called crystal ash for its characteristics, has attracted attention in central Japan for nearly 30 years as distinctive fallout tephras rich in biotite and quartz. Many researchers have investigated the group, and related reports continue to appear. Despite this long research history, its full nature cannot be said to be established. The group consists of a collection of deposits representing one eruption cycle; researchers disagree on individual distributions and local stratigraphic positions, and even on the number of beds. Under these circumstances, it is important to establish a well-exposed reference locality and proceed with correlations outward from it. Kambadaira is ideally suited to this role. It lies 50 km east-northeast of the 水鉛谷 conduit of Momisawadake volcano in the Northern Alps, considered the APms source (Harayama et al., 1991; see WS-21-2). Five Omachi APm beds are exposed here, named in ascending order A1Pm, A2Pm, …, A5Pm, or CA1, CA2, …, CA5 (Suzuki, 1992; Kimura, 1987). All are highly distinctive, biotite- and quartz-rich crystal tephras, with printed thicknesses of 30–106 m [unit as printed], separated by volcanic-ash soils indicating time intervals. Kakuto tephra from Kyushu (Kkt; see WS-19) is recognized between A4Pm and A5Pm here (Suzuki and Hayatsu, 1991).

Relationships with other tephras (see WS-21-4) and their stratigraphic horizons suggest that APms erupted during oxygen isotope stages 10 to 9, making them important Middle Pleistocene marker beds in central Japan.

References: Harayama et al. (1991); Kimura (1987); Suzuki (1992); Suzuki and Hayakawa (1990); Suzuki and Hayatsu (1991).

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English translation of figure lettering

NW, NE, SE; A4Pm, A3Pm, A2Pm, A1Pm; scale is 1 m. Omachi APm tephra group at Kambadaira, Ooka Village.

Original Japanese lettering

NW，NE，SE；A4Pm，A3Pm，A2Pm，A1Pm；スケールは1m。大岡村樺平における大町APmテフラ群。

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English translation of figure lettering

1:25,000 Omi (Nagano sheet 14-3). Kambadaira; Hijiriyama. Legible numbers: 1288, 1032, 1100, 1200.

Original Japanese lettering

2.5万分の1『麻績』（長野14号-3）。樺平，聖山。可読数値1288，1032，1100，1200。

[Original printed page: 77]

WS-21-2 Source conduit of the Omachi APm tephra group, widespread tephras from the Hida Range—The 水鉛谷 conduit

Satoru Harayama

Locality: 水鉛谷, a tributary of the Hidari-mata Valley of the Gamata River, Kamitakara Village, Yoshiki District, Gifu Prefecture. Coordinates: N36°20′17″ E137°37′13″. Elevation: 1,815 m. Exposure and present condition: natural exposure; extant as of October 1995. Rocks and age: conduit volcanic rocks; Middle Pleistocene. Date described: 1990. Keywords: Hida Range; Omachi APm tephras; Okuhida pyroclastic-flow deposit; 水鉛谷 conduit.

This exposure is the conduit that supplied the Omachi APm tephra group and Okuhida pyroclastic-flow deposits, an extremely rare example of a source conduit for widespread tephras and large pyroclastic flows exposed at the surface. It lies on the conduit’s northern margin, 1.3 km west-southwest of Yarigatake, along 水鉛谷, a tributary in the uppermost Hidari-mata Valley of the Gamata River. The conduit is elliptical, 600 m north–south and 500 m east–west, intruding Paleogene granite. It forms a volcanic neck rising above its surroundings in a pointed spire. Its principal rocks are pyroxene-hornblende-biotite rhyolitic tuff and compositionally equivalent granite porphyry; more mafic andesite, lava and tuff, is exposed only along the margin. Rhyolite (granite porphyry) and andesite have complex, interwoven relationships, interpreted as evidence for contemporaneous activity and mixing. For descriptions of the facies and discussion of correlations with tephras and pyroclastic-flow deposits, see the 1:50,000 Kamikochi and Yarigatake geological map sheets (Harayama, 1990; Harayama et al., 1991).

References: Harayama (1990); Harayama et al. (1991).

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English translation of figure lettering

1:25,000 Mitsumata-Rengedake (Takayama sheet 6-4); 1:25,000 Kasagatake (Takayama sheet 7-3). Hidari-mata Valley. Legible numbers: 2303, 205, 2105.

Original Japanese lettering

2.5万分の1『三俣蓮華岳』（高山6号-4）；2.5万分の1『笠ヶ岳』（高山7号-3）。左俣谷。可読数値2303，205，2105。

Reading notes

205 — 数値の一部が不鮮明で、全標高値は確定できない。

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English translation of figure lettering

N; Hidari-mata Valley; 水鉛谷; A, B; Tf, Gp (map and section). Contours: 1800 m, 1900 m, 2000 m, 2100 m, 2200 m, 2300 m, 2350 m (twice); summit 2270.7 m; dip values 75, 60. Section elevation, m: 1800, 2000, 2200. Horizontal scale: 0, 500 m. Legend: 水鉛谷熔結火道 [printed conduit designation]—tuff, granite porphyry; 奥丸沢 granite.

Original Japanese lettering

N；左俣谷，水鉛谷；A，B；Tf，Gp（平面図・断面図）。等高線1800m，1900m，2000m，2100m，2200m，2300m，2350m（2か所）；山頂2270.7m；走向傾斜75，60。断面標高m：1800，2000，2200。水平0，500m。凡例：水鉛谷熔結火道―凝灰岩，花崗斑岩；奥丸沢花崗岩。

Reading notes

凡例の水鉛谷熔結火道 — 細字の中央2字は不鮮明。英訳では印刷形を保持し、通常の地質用語への置換を避けた。

Extracted lettering and translation From Figure 68 of Harayama et al. (1991).

[Original printed page: 78]

WS-21-3 Okuhida pyroclastic-flow deposits at Kumonotaira, deep in the Northern Alps—Pyroclastic-flow deposits intercalated in the Kumonotaira Gravel

Shun Nakano

Locality: A Stream and elsewhere, Kumonotaira, Oyama Town, Toyama Prefecture. Coordinates: N36°25′28″ E138°33′46″ [as printed]. Elevation: 2,060 m. Exposure: natural exposure. Deposits and age: gravel and pyroclastic-flow deposits; Middle Pleistocene, 300–350 ka. Keywords: Kumonotaira Gravel; Okuhida pyroclastic-flow deposits; Omachi APm tephra group; crystal ash; Momisawadake volcano; Kumonotaira volcano.

The Kumonotaira Gravel, forming the lower part of Kumonotaira volcano, reaches about 200 m maximum thickness. Rounded gravel and sand derived from basement predominate, but lava and pyroclastic material from Kumonotaira volcano are occasionally intercalated. This gravel also contains about 2 m of unwelded pyroclastic-flow deposit, confirmed at three exposures, dominated by pumice fragments no larger than 3 cm rich in quartz, biotite, plagioclase crystals, and other minerals (Nakano, 1989). It is not a product of Kumonotaira volcano, but is correlated with the Okuhida pyroclastic-flow deposit (Okh). Near Momisawadake, about 6 km south-southeast of Kumonotaira, this deposit forms welded tuff about 200 m thick. Its source conduit has been discovered in 水鉛谷, about 10 km south-southeast of Kumonotaira (Momisawadake volcano). Erupted volume is estimated to exceed 10 km³. On its constituent minerals, this flow is correlated with one of the Omachi APm tephras (crystal ash). If so, its eruption age is estimated at 300–350 ka (Suzuki and Hayakawa, 1990).

References: Harayama et al. (1991); Nakano (1989); Suzuki and Hayakawa (1990).

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English translation of figure lettering

Site 1, right bank of A Stream: massive lava; 2100 m; tuffaceous sand; silt–coarse sand containing small gravel, with developed cross-stratification; pumice-flow deposit; 2050; gravel; 2000. Site 2, 600 m north of the Akagizawa confluence (right bank of the Kurobe River): massive portion; basal clinker; 2100 m; fine–medium sand with developed lamination; silt–coarse sand intercalated with small-gravel beds; fine–medium sand with developed lamination; 2050; Funatsu granitic rocks. Site 3, Jiji Stream: 2250 m (elevation); Jijidake lava; basal clinker; gravel; 2200; massive lava; 2150; pumice-flow deposit. Scale: 10 m.

Original Japanese lettering

地点1 A沢右岸：塊状溶岩；2100m；凝灰質砂層；シルト-粗粒砂層（小礫含），斜交層理発達；軽石流堆積物；2050；礫層；2000。地点2 赤木沢出合北600m（黒部川右岸）：塊状部，下部クリンカー，2100m；細-中粒砂層（葉理発達）；シルト-粗粒砂層（小礫層挟む）；細-中粒砂層（葉理発達）；2050；船津花崗岩類。地点3 祖父沢：2250m（標高）；祖父岳溶岩；下部クリンカー；礫層；2200；塊状溶岩；2150；軽石流堆積物。スケール10m。

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English translation of figure lettering

1:50,000 Yarigatake (Takayama sheet 6). Sites 1, 2, 3; Yakushizawa hut; A Stream; Kumonotaira (Okunotaira); Kumonotaira mountain lodge; Jiji Stream. Legible numbers: 2576, 2463.9, 1976.

Original Japanese lettering

5万分の1『槍ヶ岳』（高山6号）。地点1，地点2，地点3；薬師沢小屋，A沢，雲ノ平（奥ノ平），雲ノ平山荘，祖父沢。可読数値2576，2463.9，1976。

[Original printed page: 79]

WS-21-4 Omachi APm tephras and widespread tephras from Kyushu at Sugadaira, Shinshu

Stratigraphic relationships with Kakuto and Ata-Torihama tephras

Takehiko Suzuki

Locality: Nishigumi, Sugadaira, Sanada Town, Nagano Prefecture. Coordinates: N36°36′45″ E138°18′53″. Elevation: 1,270 m. Exposure and present condition: artificial exposure; extant. Deposits and age: tephra fall and fine-grained glassy ash beds; Middle Pleistocene. Date described: September 1989–May 1990. Keywords: Sugadaira Plateau; Omachi APm tephra group; Kakuto tephra; Sugadaira ash; Azumaya-蓑原 tephra; Ata-Torihama tephra; Azumaya volcano.

Gentle slopes are widely developed in the Sugadaira Basin, about 10 km west of Azumaya volcano. In places these slopes have remained stable since some time in the Middle Pleistocene and are covered by thick volcanic-ash soil. This Nishigumi exposure is in such an area. Tephras from the central mountains, including the Omachi APm group (APms; Suzuki and Hayakawa, 1990), and Middle Pleistocene widespread tephras are well preserved in the soil. It is therefore probably the most useful exposure for clarifying central Japan’s Middle Pleistocene tephra stratigraphy, including APms. It was discussed in detail by Suzuki and Hayakawa (1990) and Suzuki and Hayatsu (1991).

APms can be observed slightly right (west) of the exposure’s center. The two upper beds, A4Pm and A5Pm, are exposed, deposited above weathered basement across thin volcanic-ash soil. Their occurrence resembles that at the Kambadaira type locality, Ooka Village (WS-21-1), with a distinctive facies rich in biotite, quartz, and hornblende phenocrysts. Between them is orange fine-grained glassy ash of the Kyushu-derived Kakuto tephra (Kkt; see WS-19). The lower-middle part of the exposure, from the center leftward, contains a vivid vermilion fine tephra, Sugadaira ash (SgA). It apparently was originally glassy, suggesting a distant source, but loss of glass through weathering leaves its details unknown. Slightly above SgA is Azumaya-蓑原 tephra (Az-MiP), a Plinian fallout deposit. Coarse pumice and lithic fragments as large as 10 cm imply a nearby source, Azumaya volcano. At 1–1.5 m above Az-MiP is about 60 cm of yellow Plinian pumice, Sugadaira pumice 2 (SgP.2). Its pumice reaches 4 cm maximum diameter, likewise suggesting a nearby source, though no volcano has yet been identified. About 5 cm of volcanic-ash soil separates SgP.2 from an underlying olive-colored fine glassy ash bed about 6 cm thick. Initially called Sanada ash, it was later correlated with southern Kyushu’s Ata-Torihama tephra (Ata-Th; see WS-17). Iizuna-Nishiyama tephra (Iz-NY) also occurs above SgP.2. These relationships with widespread tephras show that APms erupted at least earlier than the approximately 240 ka Ata-Th eruption, within several tens of thousands of years before and after Kkt, whose eruption age is somewhat older than 300 ka (WS-19-1).

References: Suzuki and Hayakawa (1990); Suzuki and Hayatsu (1991).

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English translation of figure lettering

SE, SW, NW. Left: Iz-NY, Ata-Th, SgP.2, Az-MiP, SgA, A5Pm. Center: SgA. Right: A5Pm, A4Pm, Kkt. Exposure photograph at Nishigumi, Sugadaira Plateau.

Original Japanese lettering

SE，SW，NW。左部：Iz-NY，Ata-Th，SgP.2，Az-MiP，SgA，A5Pm。中央：SgA。右部：A5Pm，A4Pm，Kkt。菅平高原西組の露頭写真。

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English translation of figure lettering

1:25,000 Sugadaira (Nagano sheet 9-4). Nishigumi. Legible numbers: 1252, 1282, 1242, 1255, 1350.

Original Japanese lettering

2.5万分の1『菅平』（長野9号-4）。西組。可読数値1252，1282，1242，1255，1350。

[Original printed page: 80]

WS-22-1 Kobayashi–Kasamori tephra at Kukino, Miyazaki Prefecture—the home of the Sakura volcanic ash

Hiroshi Machida

Locality: Kukino, Takaoka Town, Miyazaki Prefecture. Coordinates: N37°57′23″ E131°13′38″. Elevation: 150 m.

Outcrop type and condition: roadside cliff; extant. Deposits and age: pumice fall, pyroclastic-flow deposits, and sand and gravel; Middle Pleistocene.

Date described: March 1995. Keywords: Kobayashi–Kasamori tephra; Kukino Formation.

High Middle Pleistocene terraces are well developed along the margins of the Miyazaki Plain. Among them, the hilly plateau around Kukino in Takaoka Town consists of thick sand and gravel reaching several tens to 100 m in thickness (Kino and Ota, 1976). These sand and gravel deposits contain several marker tephras composed chiefly of pyroclastic-flow deposits. One is the Kobayashi–Kasamori tephra (Kb-Ks). It consists chiefly of nonwelded pyroclastic-flow deposits containing pumice fall in their lower part, and its distinctive feature is the presence of biotite and hornblende phenocrysts. Outcrops at which this tephra can be observed at Kukino extend discontinuously for several tens of metres along the road. In the lower part, stratified pumice with a fallout facies overlies material with a pyroclastic-flow-like facies, with a single rounded-gravel bed between them. It is probably pumice fall deposited in a flowing-water environment. The middle and upper parts consist of nonwelded pyroclastic-flow deposits. Since their top is truncated by sand and gravel, the original deposit must have exceeded 30 m in thickness. From its distribution, the source of this tephra was considered to be Kobayashi caldera, and it was named the Kobayashi pyroclastic flow (Kino and Ota, 1976). However, it is difficult to identify the source volcano specifically as Kobayashi caldera, Kakuto caldera, or the Kirishima volcanic area. Around Kukino, sand and gravel separate this tephra from the overlying Kakuto pyroclastic-flow deposits (Kkt) and from the underlying Hiwaki pyroclastic-flow deposits (Hw).

The contemporaneous fallout tephra is called the Sakura volcanic ash in the Kinki region and Byobugaura 2 or Kasamori 11 in the Kanto region, and has been described as an important marker bed (Machida and Arai, 1992).

References: Kino and Ota (1976); Machida and Arai (1992).

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English translation of figure lettering

1:25,000 “Kamiya” (Miyazaki 13-1). Kukino; 東ヶ谷. Elevation and contour figures: 82, 80.2, 84, 130.

Original Japanese lettering

2.5万分の1「紙屋」（宮崎13号-1）。久木野；東ヶ谷。標高・等高線数字：82，80.2，84，130。

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English translation of figure lettering

From top: sand and gravel; pyroclastic-flow deposits; pumice-fall bed (water-laid?); ←rounded-gravel bed; ←sand and gravel. Kb-Ks extends from below the upper sand and gravel to above the lower sand and gravel. Forest road; scale 0, 10 m.

Original Japanese lettering

上から：砂礫層；火砕流堆積物；降下軽石層（水成？）；←円礫層；←砂礫層。Kb-Ksの範囲は上部砂礫層の下から下部砂礫層の上まで。林道；目盛0，10m。

WS-22-2 Kamiogi (Sakura) volcanic ash in the Katata Hills west of Lake Biwa—Kobayashi–Kasamori tephra

Hiroshi Machida

Locality: Kamiogi, Otsu City, Shiga Prefecture. Coordinates: N35°6′10″ E135°52′12″. Elevation: 180 m.

Outcrop type and condition: roadside; condition unknown. Deposit: volcanic ash. Date described: March 1978.

Keywords: Kamiogi volcanic ash; Sakura volcanic ash; Kobayashi–Kasamori tephra; Kobiwako Formation; Kamiogi; Katata Hills.

The Kobiwako Group, distributed in the Katata Hills west of Lake Biwa, is correlated with the Osaka Group and contains numerous Middle to Early Pleistocene tephras. Among them, the ash described as the Kamiogi volcanic ash (Yokoyama, 1975) is a marker tephra correlated with the Sakura volcanic ash of the Osaka Group (Hayashi, 1974; Machida et al., 1980, and others). At this outcrop, this 25-cm-thick volcanic-ash bed, with its characteristic cherry-blossom pink colour, can be observed between sand and silt beds. It is rich in bubble-type volcanic glass and contains small amounts of biotite, hornblende, and orthopyroxene. In both the Kinki region and southern Kanto, several tephras resemble this one in the refractive index of their volcanic glass (Sakura N and S in Kinki, and Kasamori 5 and 11 in Kanto). Because they also contain few phenocryst minerals, correlating and identifying these similar tephras requires combining major- and trace-element characteristics with the refractive index of volcanic glass. Sakura S and Kasamori 11 are correlated with this tephra (Machida and Arai, 1992). In the Kobiwako Group of the Katata Hills, this bed overlies the Kinugawa volcanic ash. In the Osaka Group, it occupies the horizon immediately below marine clay bed Ma7.

References: Hayashi (1974); Machida et al. (1980); Machida and Arai (1992); Yokoyama (1975).

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English translation of figure lettering

1:25,000 “Katata” (Kyoto and Osaka 2-1). Ogi Town; 192; 123.

Original Japanese lettering

2.5万分の1「堅田」（京都及大阪2号-1）。仰木町；192；123。

Sakura volcanic-ash bed

WS-22-3 Kobayashi–Kasamori tephra at Totsuka, Yokohama, and Futtsu on the Boso Peninsula

Hiroshi Machida

Localities: near Senshu Elementary School, Kosuzume Town, Totsuka Ward, Yokohama City; 上, Futtsu City, Chiba Prefecture.

Coordinates: N35°22′0″ E139°31′18″; N35°16′48″ E139°54′0″. Elevations: 26 and 30 m.

Outcrop type and condition: artificial exposures; condition unknown, probably destroyed. Deposits and age: volcanic ash, sand and gravel, and peat; Middle Pleistocene. Date described: 1979. Keywords: Kobayashi–Kasamori tephra; Byobugaura 2 tephra; Kasamori 11 tephra; Totsuka, Yokohama; Futtsu, Boso Peninsula.

At the Totsuka outcrop, peat and sand and gravel unconformably overlying the Taya Sand and Gravel (middle to upper part of the Naganuma Formation; Otsuka, 1937), together with several tephras including the Shimokurata pumice (Mitsunashi and Kikuchi, 1982), were observed. Among them, a pale pink glassy volcanic ash (10–15 cm thick) about 1.3 m below the Shimokurata pumice is correlated with the Kobayashi–Kasamori tephra (Kb-Ks; the Sakura volcanic ash in Kinki). Machida et al. (1980) described it here as the Byobugaura 2 volcanic ash (By2). It consists chiefly of bubble-type volcanic glass, with very small amounts of biotite and hornblende. Its correlation with the Kasamori 11 tephra (Ks11), a marker tephra within the Kasamori Formation on the Boso Peninsula, is evident from the characteristics of the tephra itself and from the occurrence of the complete set of tephras above and below it in both regions. In particular, the tephra immediately below By2 is a distinctive hornblende-rich tephra with a salt-and-pepper appearance (Byobugaura 1 volcanic ash; By1). It was also found in the Shunan–Sanuki Formation about 1.5 m below Ks11 at the outcrop at 上, Futtsu City, on the Boso Peninsula. These tephras aid correlation of the lower Byobugaura Formation in the Yokohama area with the upper Kasamori Formation and the Shunan–Sanuki Formation on the Boso Peninsula. They are considered to be tephras of the transition from oxygen-isotope stage 14 to 13.

References: Machida et al. (1980); Mitsunashi and Kikuchi (1982); Otsuka (1937).

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English translation of figure lettering

Upper map: 1:25,000 “Totsuka” (Tokyo 8-4); Kosuzume Town, Sumitomo Electric Yokohama Works, Taya Caves, Taya Town, Eishoji Temple. Elevations 2.0, 3.9; some small locality names are illegible. Lower map: locality 2; 1:25,000 “Kanozan” (Yokosuka 1-1); Futtsu City, 大堰, 上, 古谷, 新山, 前向谷, 後向, 百坂; elevations 24.0, 31.6.

Original Japanese lettering

上図：2.5万分の1「戸塚」（東京8号-4）；小雀町，住友電工横浜工場，田谷の洞窟，田谷町，永勝寺。標高2.0，3.9；一部の小字は判読不明。下図：地点2；2.5万分の1「鹿野山」（横須賀1号-1）；富津市，大堰，上，古谷，新山，前向谷，後向，百坂；標高24.0，31.6。

Reading notes

地図の細字地名 — 原画像でも一部は読み切れないため判読不明とした。

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English translation of figure lettering

1: Shimokurata pumice; laminated sand; By2; By-1; peaty layer; scale 0, 1, 2 m. 2: Standard Middle Pleistocene stratigraphy around Futtsu. From top: K2; Sn1 A, B, C; Sn2; Sn10=Ks11 (correlation line to By2); Ks11.2 (correlation line to By-1); Sn12; Sn14; Sn15; Ks15; Ku6 A, B, C, D, D′, E (overlapping lettering near D is indistinct); U1. Scale 0, 100, 200 m.

Original Japanese lettering

1：下倉田軽石；laminated sand；By2；By-1；peaty layer；目盛0，1，2m。2：富津周辺の更新世中期地層の標準層序。上からK2；Sn1 A・B・C；Sn2；Sn10=Ks11（By2と対比線）；Ks11.2（By-1と対比線）；Sn12；Sn14；Sn15；Ks15；Ku6 A・B・C・D・D′・E（D付近の重なりは不鮮明）；U1。尺度0，100，200m。

Reading notes

Ku6のD付近の枝番号 — 細字が重なりD・D′の並びは不鮮明。

WS-23-1 Seiganji Pumice Bed, a widespread tephra intercalated in the upper Oita Group

Kiyohide Mizuno, Hideo Hoshizumi, and Toshikazu Yoshioka

Locality: Seiganji, Nyu, Oita City, Oita Prefecture. Coordinates: N33°12′38″ E131°42′50″. Elevation: 20 m.

Outcrop type and condition: artificial exposure; extant in March 1996, partly vegetated. Deposits and age: freshwater deposits; approximately 0.6–0.7 Ma. Keywords: Seiganji Pumice Bed; Toga volcanic ash; Oita Group; Nyu, Oita.

The Seiganji Pumice Bed (Mizuno et al., 1989) is a tephra intercalated in the upper part of the Middle and Lower Pleistocene Oita Group (Shuto, 1953), which forms the hills around Oita City. It is a widespread tephra correlated with the Toga volcanic-ash bed of the Osaka Group (Yoshikawa, 1976) and other beds (Yoshikawa et al., 1991; Mizuno, 1992). However, the Seiganji Pumice Bed has been defined only in a conference abstract (Mizuno et al., 1989), so it is described here in detail. Its type exposures are at Seiganji, Nyu, Oita City (localities 1, 2, and 3 in the map), and it is distributed in the hills on both sides of the Ono River. At the type locality it is intercalated in freshwater deposits consisting chiefly of silt, whereas around Furushiroyama, about 7 km southwest of the type locality, and elsewhere, it is a terrestrial deposit. At locality 1, most of it is grass-covered and difficult to discern, but its entire facies can be observed by connecting the exposures along the road and watercourse toward localities 2 and 3 to the west. At locality 4, the lower part is easy to observe, but the upper part has been eroded away by terrace gravel. The lowermost approximately 50 cm consists of greyish-white to white pumice with grain sizes of 1 cm or less. This is overlain by approximately 20 cm of coarse volcanic ash containing pumice, and 20–40 cm of pumice with grain sizes of a few millimetres or less. Above these is an approximately 2-m-thick alternation of fine pumice and volcanic-ash beds, each 1–20 cm thick, with greyish-white, yellowish-brown, pale pink, and other colours. This alternation looks like “baumkuchen” and is the most distinctive feature of this tephra (photograph, locality 2). The uppermost approximately 2 m consists of massive grey to greyish-white fine pumice to volcanic ash. It contains two or three fine volcanic-ash beds 10–20 cm thick, possibly representing reworked material deposited under water. At the outcrop south of Sakanoichi, about 4 km northeast of this exposure, pumice-bearing volcanic ash overlies stratified pumice sand (Miyazaki and Yoshioka, 1994). This massive part looks like a pyroclastic-flow deposit. A characteristic of the volcanic glass forming this tephra is its abundance of brown blocky to granular types, which provides the most decisive evidence for widespread correlation. Orthopyroxene is the principal heavy mineral, with hornblende also present. Biotite is also visible to the naked eye. The tephra has normal paleomagnetic polarity. It lies slightly below the Yufugawa pyroclastic flow, whose age is estimated at approximately 0.6 Ma (Hoshizumi and Kamata, 1991; see KS-7) (Mizuno et al., 1989).

References: Hoshizumi and Kamata (1991); Yoshikawa et al. (1991); Miyazaki and Yoshioka (1994); Mizuno (1992); Mizuno et al. (1989); Shuto (1953); Yoshikawa (1976).

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English translation of figure lettering

1, 2, 3, 4; 1:25,000 “Tsurusaki” (Oita 5-2); Seiganji, Nyu, 下岡, Showa irrigation channel, Nyu branch office; elevations 86.5, 48.3, 81.5, 52.

Original Japanese lettering

1，2，3，4；2.5万分の1「鶴崎」（大分5号-2）；誓願寺，丹生，下岡，昭和井路，丹生出張所；標高86.5，48.3，81.5，52。

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English translation of figure lettering

SW; NE. Prose and references embedded above the photograph have been restored in the main text.

Original Japanese lettering

SW；NE。画像上部の本文と文献は本文に復元済。

The “baumkuchen-like” part in the middle of the Seiganji Pumice Bed. Cliff height approximately 1.5 m. Photographed in September 1985.

WS-23-2 Okago volcanic-ash bed intercalated in the Middle Pleistocene Saijo Formation, Hiroshima Prefecture—the widespread Seiganji–Toga tephra

Kiyohide Mizuno

Locality: south of Okago, Kurose Town, Kamo District, Hiroshima Prefecture. Coordinates: N34°18′48″ E132°41′30″. Elevation: 160 m.

Outcrop type and condition: artificial exposure; only a small part exposed because of vegetation in January 1996. Deposits and age: freshwater deposits; Middle Pleistocene, approximately 0.6 Ma. Date described: January 1996. Keywords: Okago volcanic ash; Saijo Formation; Seiganji–Toga tephra.

The Saijo Formation is a fluvial succession deposited approximately 0.7–0.5 Ma in the area centred on the Saijo and Kurose basins in Hiroshima Prefecture, and contains at least seven volcanic-ash beds. Of these, the Okago volcanic-ash bed in the middle of the succession is the most continuous and serves as a key bed (Higashimoto et al., 1985). This tephra is correlated with the Seiganji Pumice Bed of the Oita Group and the Toga volcanic-ash bed of the Osaka Group, and is recognized as a widespread tephra (Yoshikawa et al., 1991; Mizuno, 1992). This outcrop is the type locality of the Okago volcanic-ash bed. In 1982, 3–4 m of silt and sand could be observed both above and below the volcanic ash, but in January 1996 only an area about 1 m square around the ash bed was exposed. The tephra is an approximately 60-cm-thick, greyish-white glassy volcanic-ash bed composed chiefly of alternating thin beds a few centimetres thick. A fission-track age of 0.57±0.09 Ma was obtained from a sample at this outcrop (Higashimoto et al., 1985). Thin peat beds or carbonaceous silt are often developed immediately below the Okago volcanic-ash bed and have yielded plant fossils, including Korean pine and bogbean, indicating a cold to cool climate (Higashimoto et al., 1985).

References: Yoshikawa et al. (1991); Mizuno (1992); Higashimoto et al. (1985).

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English translation of figure lettering

1:25,000 “Aki-Uchinoumi” (Hiroshima 7-1). Okago, Kurose Town, 田津原, 川角. Elevations 161, 186, 160.9, 26.

Original Japanese lettering

2.5万分の1「安芸内海」（広島7号-1）。岡郷，黒瀬町，田津原，川角。標高161，186，160.9，26。

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English translation of figure lettering

Geological column; described in November 1982. From top: silt/sand; silt; volcanic ash; sand; ashy sand; Okago volcanic-ash bed; silt; peat; silt; sand; sandy silt. Scale 0, 1, 2 m.

Original Japanese lettering

地質柱状図；1982年11月記載。上から：シルト/砂；シルト；火山灰；砂；火山灰質砂；岡郷火山灰層；シルト；泥炭；シルト；砂；砂まじりシルト。尺度0，1，2m。

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English translation of figure lettering

Okago volcanic ash; photographed in January 1996.

Original Japanese lettering

岡郷火山灰；1996年1月撮影。

WS-24-1 Tephras in the lower Oita Group—with emphasis on the Magari pyroclastic-flow deposits correlated with the Azuki volcanic ash

Kiyohide Mizuno, Hideo Hoshizumi, and Toshikazu Yoshioka

Locality: Magari to Mera, Oita City, Oita Prefecture. Coordinates: N33°11′18″–N33°12′35″ E131°36′56″–E131°38′48″.

Elevation: 20–100 m. Outcrop type and condition: artificial and natural exposures; extant in March 1996. Deposits and age: freshwater deposits, partly eolian deposits; approximately 0.8–0.9 Ma. Keywords: Magari pyroclastic-flow deposits; Mera pyroclastic flow; Azuki volcanic ash; Oita Group.

The Oita Group is a Middle and Lower Pleistocene succession forming the hills around Oita City (Shuto, 1953), and contains numerous tephras. Among them, the deposits called the Magari pyroclastic-flow deposits (hereafter simply “pyroclastic flow”) were correlated with the Azuki volcanic ash, a representative tephra of the Osaka Group (Ichihara, 1993; approximately 0.85 Ma) (Shimokawa et al., 1986). Subsequently, the Magari pyroclastic flow was identified with the Imaichi pyroclastic flow erupted from Shishimuta caldera in Oita Prefecture, which is correlated with the Azuki volcanic ash (Kamata et al., 1994a, b). Since the tephras of the Oita Group have been discussed only in conference abstracts (Shimokawa et al., 1986; Mizuno et al., 1989), they are described here in detail, with some discussion of their correlation.

The Magari pyroclastic flow occurs between gravel and silt beds and is distributed from Magari to Mera in Oita City. It probably accumulated in a floodplain-like setting. Its type locality is the artificial exposure at locality 4. It is also continuously exposed in the valley near locality 8, where it is considered unlikely to disappear for some time. It consists of a lower greyish-white pumice-fall bed (2–4 m thick, divided into about ten fallout units) and upper dark brown pumice-bearing pyroclastic-flow deposits (approximately 4 m thick). Volcanic glass is the principal constituent, and the heavy minerals consist chiefly of orthopyroxene and clinopyroxene. This tephra has reversed paleomagnetic polarity, and a fission-track age of 1.3±0.2 Ma has been obtained for a pyroclastic-flow sample at locality 4 (Mizuno et al., 1989). Plant fossils are sometimes found in silt below the Magari pyroclastic flow, but they do not include elements of the so-called “Metasequoia flora” (Ichihara, 1960).

Tephras resembling the Magari pyroclastic flow include the Aso-4 pyroclastic flow (locality 3) and the Mera pyroclastic flow (Shimokawa et al., 1986). The type locality of the Mera pyroclastic flow is at localities 11–12; it is also seen at localities 1, 2, 10, and elsewhere. It lies approximately 20 m above the Magari pyroclastic flow. The Mera pyroclastic flow consists of a lower greyish-white pumice-fall bed (approximately 2 m thick, comprising four or five fallout units) and upper dark brown pumice-bearing pyroclastic-flow deposits (2–5 m thick). Its reversed paleomagnetic polarity and heavy-mineral composition, dominated by orthopyroxene and clinopyroxene, also resemble those of the Magari pyroclastic flow. However, they can be distinguished by the lower refractive indices of both volcanic glass and orthopyroxene in the Mera pyroclastic flow: n=1.508–1.512 and γ=1.700–1.707, respectively, compared with n=1.511–1.515 and γ=1.703–1.715 in the Magari pyroclastic flow. In addition, three pyroclastic flows occur above and below the Magari pyroclastic flow in the Hogawara area (localities 5–8). These are provisionally named Hogawara A, B, and C, in ascending order (see stratigraphic columns). Hogawara A and C consist chiefly of greyish-brown pyroclastic-flow deposits accompanied by pumice-fall beds in their lower parts. Their pyroclastic-flow colour and the low refractive index of volcanic glass, approximately n=1.500 in both, readily distinguish them from the Magari pyroclastic flow. The Hogawara B pyroclastic flow consists of lower dark brown fine-pumice to volcanic-sand fallout beds and an upper ashy pyroclastic-flow deposit. The flow deposit is compact and slightly welded. Its horizon is inferred to be immediately above the Magari pyroclastic flow, and it can be observed at localities 5 and 6. Its heavy minerals are chiefly orthopyroxene and clinopyroxene; the orthopyroxene refractive index is γ=1.699–1.712. Its volcanic glass consists chiefly of material with refractive indices of n=1.511–1.517, very similar to the Magari pyroclastic flow, but also includes high-index material reaching n=1.550. This tephra has reversed paleomagnetic polarity.

The petrographic characteristics of the Magari pyroclastic flow closely resemble those of the pumice-fall bed in the lower part of the Imaichi pyroclastic flow (Kamata et al., 1994a, b) at Kagonodai, Notsuharu Town, and of the nonwelded to weakly welded pyroclastic-flow deposits immediately above it. The Hogawara B pyroclastic flow above the Magari pyroclastic flow may also correlate with part of the Imaichi pyroclastic flow, but this remains a subject for future study. Shimokawa et al. (1986) correlated the Mera pyroclastic flow with the Imaichi pyroclastic flow. However, the sample they identified as Imaichi is from an exposure in Taketa City and has refractive indices different from those of the Imaichi pyroclastic flow at its type locality. Petrographic and stratigraphic investigation is also required for deposits collectively assigned to the Imaichi pyroclastic flow.

References: Ichihara (1960, 1993); Kamata et al. (1994a, b); Mizuno et al. (1989); Shimokawa et al. (1986); Shuto (1953).

WS-24-1 (illustrations, continued)

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WS-24-1. Maps: 1:25,000 “Oita” (Oita 5-4); 1:25,000 “Tsurusaki” (Oita 5-2). Localities 1–12 (the numeral near locality 1 overlaps another symbol and is indistinct); Magari, Mera, Hogawara, Tsumori, Katashima, 椎迫山, Shimogori, 和台 housing estate, Oomichi, 米竹新川 irrigation channel, golf course, Yokoo Waterworks, public-health nursing school. Elevation and other figures: 51.5, 68, 52, 97, 62, 90, 118.4, 129.4, 17, 33, 63.

Columns: localities 2, 4, 6, 7, 8, 9–10, 11–12. Legend: pyroclastic-flow deposits; pumice fall; volcanic-ash to volcanic-sand beds; silt; sand; gravel. Tephra labels: Mera; Hogawara C; Hogawara B; Hogawara A; Magari. Correlation lines link Magari, Hogawara B, Hogawara C, and Mera in ascending order, and Hogawara A below Magari. Scale 0, 10 m. Printed page 87.

Original Japanese lettering

WS-24-1。地図：2.5万分の1「大分」（大分5号-4）；2.5万分の1「鶴崎」（大分5号-2）。地点1～12（1付近の番号は他記号と重なり不鮮明）；曲，米良，芳河原，津守，片島，椎迫山，下郡，和台団地，大道，米竹新川井路，ゴルフ場，横尾浄水場，公衆衛生看護学院。標高等：51.5，68，52，97，62，90，118.4，129.4，17，33，63。

柱状図：地点2，地点4，地点6，地点7，地点8，地点9～10，地点11～12。凡例：火砕流堆積物；降下軽石；火山灰－火山砂層；シルト層；砂層；礫層。テフラ名：米良；芳河原C；芳河原B；芳河原A；曲。下位から曲、芳河原B、芳河原C、米良の対比線、曲より下位の芳河原Aの対比線。目盛0，10m。印刷ページ87。

Reading notes

地図内の地点1と一部細字 — 記号重なりと低解像度により一部は読み切れない。

WS-24-2 Imaichi pyroclastic-flow deposits in central Kyushu—the source pyroclastic flow of the Azuki volcanic ash of the Osaka Group

Hideo Hoshizumi and Hiroki Kamata

Locality: Kagonodai, Notsuharu Town, Oita Prefecture. Coordinates: N33°9′36″ E131°30′14″. Elevation: 210 m. Outcrop type and condition: artificial exposure revealed by road construction. Deposits and age: pyroclastic-flow deposits and pumice-fall beds; Early Pleistocene.

Date described: March 1996. Keywords: Imaichi pyroclastic-flow deposits; Shishimuta caldera; Azuki volcanic ash.

The Imaichi pyroclastic-flow deposits are large-volume pyroxene dacitic to pyroxene andesitic pyroclastic-flow deposits widely distributed from Oita to Kumamoto prefectures. Most form strongly welded pyroclastic-flow plateaus (Ono, 1963; Ono et al., 1977; Kamata et al., 1994a). K–Ar ages obtained for the deposits include 0.76±0.17 Ma (Uto and Suto, 1985) and several NEDO determinations ranging from 0.84±0.02 to 0.96±0.03 Ma (Hoshizumi and Morishita, 1993; p. 70, Appendix Table A-1). Three observations place the eruption of the Imaichi pyroclastic flow at approximately 0.9 Ma, in the reversed-polarity interval at the end of the Matuyama polarity chron (after the Jaramillo subchron): the deposits consistently have reversed polarity (Ono, 1963; Hoshizumi et al., 1988; Hayashida et al., 1996); the underlying Yabakei pyroclastic-flow deposits were erupted during the Jaramillo subchron (Uto and Suto, 1985); and the volcanic rocks above the Imaichi pyroclastic-flow deposits (Tokiyama andesite) erupted approximately 0.7–0.8 Ma (Hoshizumi and Kamata, 1991). The overall distribution and elevation of the flow suggest that its source was Shishimuta caldera north of Kuju volcano (Kamata et al., 1994a). The Imaichi pyroclastic-flow deposits are also correlated with the Azuki volcanic ash, an important key bed of the latest Early Pleistocene in the Osaka Group (discussed below) (Kamata et al., 1994b).

In most areas of the pyroclastic-flow plateau formed by the Imaichi deposits, erosion has removed the upper nonwelded part that must originally have been present, leaving only the welded part. Devitrification has also progressed in the welded part, crystallizing both juvenile lenses and matrix, so fresh glass samples are often unobtainable. This outcrop at Kagonodai, Notsuharu Town, is at the eastern edge of the Imaichi pyroclastic-flow plateau. Perhaps because it is near the distal limit of the distribution, glassy portions survive even within the welded part. The upper nonwelded part can also be identified locally on the plateau. The succession of eruptive products including the Imaichi pyroclastic-flow deposits in this area consists, in ascending order, of pumice fall and pyroclastic-flow deposits changing from nonwelded to weakly welded, strongly welded (glassy), strongly welded (devitrified), weakly welded, and nonwelded (Kamata et al., 1994b). Here the stratigraphic column of Kamata et al. (1994b) has been partly revised using information from a subsequently exposed new outcrop (locality 1). The revision adds a stratified part containing accretionary lapilli (55 cm thick) between the lower weakly welded part and the overlying strongly welded part. However, no weathering or erosional hiatus or soil is recognized in this interval, and the Imaichi pyroclastic-flow deposits as a whole are the product of one continuous episode of eruptive activity.

The pumice-fall bed at the base of the Imaichi pyroclastic flow has a total thickness of approximately 4–5 m and is divided into several fallout units, each several tens of centimetres to 1 m thick. Between the fallout units are fine volcanic-ash beds, approximately 1–4 cm thick, with greyish-black to reddish-purple-grey colours (locality 2; Hoshizumi et al., 1992; p. 106, Fig. 81) (locality 3). The phenocryst assemblage of the pumice is identical to that of the main pyroclastic-flow deposit. From its scale, this pumice fall is considered a deposit of a Plinian eruption from a high eruption column (Kamata et al., 1994b). Another exposure of the pumice-fall bed can be observed west of Motofukuso, Notsuharu Town (locality 4). Pumice fall has also been confirmed at the base of the pyroclastic flow at Sozu, Ajimu Town, approximately 25 km to the northwest (Hoshizumi, 1993; p. 33, Fig. 24), but that outcrop no longer survives. The pumice fall was followed by deposition of a nonwelded pumiceous ash flow (locality 5). The degree of welding increases upward in the pumiceous ash flow, forming a weakly welded part. The interval from this weakly welded part to the devitrified strongly welded part can be observed at locality 1. The uppermost 55 cm of the weakly welded part is faintly stratified and contains a small quantity of accretionary lapilli no larger than 1 cm. Strongly welded glassy pyroclastic-flow deposits overlie it, containing abundant black glassy lenses no larger than 10 cm and exhibiting a conspicuous eutaxitic texture. However, the basal 30 cm is strongly welded black glassy rock consisting solely of fine volcanic ash. Upward, devitrification gradually progresses in both matrix and juvenile lenses, with the matrix in particular becoming grey. The interval from weakly welded material through glassy strongly welded material to devitrified strongly welded material can also be observed near locality 6 beside the old road. Throughout the strongly welded part, columnar joints approximately 20–100 cm wide are developed. In the uppermost weakly welded part (locality 7) and nonwelded part (locality 8), the grey ash matrix contains, in addition to grey pumice, greyish-black scoria and banded scoria in which pumice and scoria glass are mixed.

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1:25,000 “Onoya” (Oita 9-2); “Oita” (Oita 5-4); “Bungo-Imaichi” (Oita 10-1); “Notsuharu” (Oita 6-3). Localities 1–12. Kagonodai, Fukuso, Motofukuso. Elevations 219, 240, 266, 24.

Original Japanese lettering

2.5万分の1「小野屋」（大分9号-2）；「大分」（大分5号-4）；「豊後今市」（大分10号-1）；「野津原」（大分6号-3）。地点1～12。籠ノ台，福宗，本福宗。標高219，240，266，24。

WS-24-2 (continued)

In this area, the stratigraphic relationships between the Imaichi pyroclastic-flow deposits and the Yabakei and Yufugawa pyroclastic-flow deposits, other large-volume deposits of central Kyushu, can be observed. A rounded-gravel bed lies immediately below the Imaichi deposits (locality 2), with nonwelded Yabakei pyroclastic-flow deposits below it (locality 9). The base of the Yabakei deposits includes a stratified part that conformably overlies sand beds of the underlying Wasada (東植田) Formation of the Oita Group (locality 10; Yoshioka and Hoshizumi, 1992; p. 101, Fig. 76). The welded part of the Yabakei deposits can be observed at locality 11 in Kaminakao, Hasama Town. Pumice fall of the Yufugawa pyroclastic flow also overlies the Imaichi deposits, with brown soil between them (locality 8; Yoshioka et al., 1997). At locality 12 on the plateau of the Imaichi deposits, a nonwelded part of the Yufugawa pyroclastic-flow deposits was confirmed.

Kamata et al. (1994b) measured, for the Imaichi pyroclastic-flow deposits (samples numbered in italics in the columns), the Azuki volcanic ash of the Osaka Group, and the Ku6C volcanic ash of the Kazusa Group: (1) the proportions of glass, plagioclase, and heavy minerals; (2) the proportions of orthopyroxene, clinopyroxene, and green common hornblende among the heavy minerals; and (3) the refractive indices of glass, orthopyroxene, and clinopyroxene. The results show systematic, matching compositional changes from felsic below to mafic above in the Imaichi deposits and in both the Azuki and Ku6C ashes, establishing their correlation. Thus, the Imaichi pyroclastic-flow deposits–Azuki volcanic ash–Ku6C volcanic ash were shown to constitute a widespread volcanic ash (Shishimuta–Azuki, Ss-Az) extending as far as 900 km from the source. Many similarities were also recognized between the basal pumice fall of the Imaichi deposits and the white fine volcanic ash (the so-called hakama) at the base of the Azuki and Ku-6C volcanic ashes. These results demonstrate that the Azuki and Ku6C ashes consist of both the distal facies of the main Imaichi pyroclastic flow (co-ignimbrite ash) and the distal facies of the pumice fall (distal plinian ash).

References: Hayashida et al. (1996); Hoshizumi (1993); Hoshizumi and Kamata (1991); Hoshizumi and Morishita (1993); Hoshizumi et al. (1988, 1992); Kamata et al. (1994a, b); Ono (1963); Ono et al. (1977); Uto and Suto (1985); Yoshioka and Hoshizumi (1992); Yoshioka et al. (1997).

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Left column, from top: Yufugawa pyroclastic-flow deposits: locality 12, nonwelded part (pumiceous ash flow); pumice-fall bed; brown soil. Imaichi pyroclastic-flow deposits: locality 8, sample 9, nonwelded part (pumice–scoria flow); locality 7, 8, weakly welded part (pumice–scoria flow); 7, devitrified strongly welded part; glassy strongly welded part, locality 6, 6; locality 1, glassy strongly welded ash flow; stratified weakly welded part (with accretionary lapilli); 5, weakly welded part (pumiceous ash flow). Scale 5 m. Right column, from top: Imaichi pyroclastic-flow deposits (continued); locality 5, 4, nonwelded part (pumiceous ash flow); locality 3, 3P; 2P, pumice-fall bed; locality 2, 1P; gravel. Yabakei pyroclastic-flow deposits: locality 9, nonwelded part (pumiceous ash flow); locality 10, stratified alternating pumice and volcanic-ash beds. Oita Group, Wasada (東植田) Formation; sand. Italic numerals designate samples. Arabic locality numerals designate outcrops.

Original Japanese lettering

左柱上から：由布川火砕流堆積物：地点12，非溶結部（軽石質火山灰流）；降下軽石層；褐色土壌。今市火砕流堆積物：地点8，試料9，非溶結部（軽石－スコリア流）；地点7，8，弱溶結部（軽石－スコリア流）；7，脱ガラス化した強溶結部；ガラス質の強溶結部，地点6，6；地点1，ガラス質の強溶結火山灰流；成層した弱溶結部（火山豆石入り）；5，弱溶結部（軽石質火山灰流）。尺度5m。 右柱上から：今市火砕流堆積物（続き）；地点5，4，非溶結部（軽石質火山灰流）；地点3，3P；2P，降下軽石層；地点2，1P；礫層。耶馬溪火砕流堆積物：地点9，非溶結部（軽石質火山灰流）；地点10，成層した軽石と火山灰の互層。大分層群東植田層；砂層。

WS-24-3 Kisen volcanic-ash bed in the Katata Hills west of Lake Biwa—the widely distributed Azuki volcanic ash

Kiyohide Mizuno

Locality: middle reaches of the Kisen River west of 高城, Shiga Town, Shiga District, Shiga Prefecture. Coordinates: N35°09′36″ E135°54′42″. Elevation: 120 m. Outcrop type and condition: artificial exposure; extant. Deposits and age: freshwater deposits; Early Pleistocene, approximately 0.85 Ma.

Date described: January 1996. Keywords: Kisen volcanic-ash bed; Azuki volcanic ash; Kobiwako Group; Katata Hills.

An outcrop of the Kisen volcanic-ash bed (Hayashi, 1974), correlated with the Azuki volcanic-ash bed, a representative tephra of the Osaka Group, occurs in the middle reaches of the Kisen River in the Katata Hills west of Lake Biwa. Yokoyama and Kusunoki (1967) had already identified it as the Azuki volcanic-ash bed, but here the local name Kisen volcanic-ash bed is used. The hills in this area consist of freshwater deposits of latest Early to Middle Pleistocene age called the Katata Formation of the Kobiwako Group (Hayashi, 1974; Yokoyama, 1975). This outcrop is a small cliff approximately 3 m high on the near right side when viewed from downstream of the Kisen River check dam, and the tephra is intercalated in silt.

The tephra should also be present in the cliff on the opposite bank, but it is difficult to observe. Its characteristics have been described in detail by Yokoyama and Kusunoki (1967), Yoshikawa (1983), Ito et al. (1989), Nishida and Wada (1991), and others. It is a glassy volcanic ash approximately 200 cm thick. The lowermost approximately 10 cm is greyish-white and, on close inspection, is divided into about five beds. This is overlain by a grey to dark grey part 10–25 cm thick. Above it are alternating grey to greyish-white beds, most likely representing secondary deposition. Excluding the secondarily deposited part, an upward change in chemical composition and other characteristics from dacitic to andesitic has been pointed out (Nishida and Wada, 1991, and others).

References: Hayashi (1974); Ito et al. (1989); Nishida and Wada (1991); Yokoyama (1975); Yokoyama and Kusunoki (1967); Yoshikawa (1983).

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1:25,000 “Katata” (Kyoto and Osaka 2-1). Kisen River, Kitahama, 高城, Shiga Town, Waninaka. Elevations 87, 162, 183.9.

Original Japanese lettering

2.5万分の1「堅田」（京都及び大阪2号-1）。喜撰川，北浜，高城，志賀町，和邇中。標高87，162，183.9。

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SW; NE. All material except the lowermost 10 cm is volcanic ash. Scale 1 m. Photographed in January 1996.

Original Japanese lettering

SW；NE。最下部10cm以外すべて火山灰．スケールは1m．1996年1月撮影。

WS-24-4 Ku6C tephra in the Kokumoto Formation of the Kazusa Group—a representative Early Pleistocene widespread tephra

Shigeo Sugihara

Locality: north of Umegase, Ichihara City, Chiba Prefecture (Umegase–Tsukizaki/Okubo forest road). Coordinates: N35°15′55″ E140°08′09″.

Elevation: 210 m. Outcrop type and condition: artificial exposure along a forest road; extant in June 1996. Deposits and age: marine deposits and fine glassy tephra; Early Pleistocene. Date described: June 1996. Keywords: Boso Peninsula; Kazusa Group; Kokumoto Formation; Ku6C tephra; Magari–Azuki tephra; Matuyama–Brunhes geomagnetic boundary.

Early to Middle Pleistocene strata (with a Pliocene lower part), called the Kazusa Group, are widely distributed in the central and northern Boso Peninsula. This locality is along a forest road approximately 2 km southwest of Kazusa-Okubo Station on the Kominato Railway. (Recently, portions of forest roads in this area have been closed owing to landownership issues; care is required when visiting the outcrop.) Among the widespread tephras intercalated in the Kazusa Group, this outcrop exposes the Ku6C tephra of the Kokumoto Formation, correlated with the Azuki volcanic ash of the Osaka Group. Most of the cliff face is covered with concrete, but fortunately the part containing the Ku6 tephra group in the mudstone (siltstone) of the Kokumoto Formation is exposed above the road surface. Five tephras, Ku6A through Ku6E, can be distinguished within the interval from the outcrop base to 2.5 m above it. Ku6C is the third bed from the top, a greyish-white fine glassy tephra less than or equal to 10 cm thick, and can be sampled at the outcrop. The significance of Azuki and Ku6C in Kansai and Kanto is that both lie just below the Matuyama–Brunhes geomagnetic boundary and occupy the lower parts of warm-water marine deposits indicating an interglacial (Ma3 and the lower Kokumoto Formation). A fission-track age of 870±20 ka is available for the Ku6C–Azuki volcanic ash (many other ages are also available). Recently, the Ku6C–Azuki ash has also been shown to correlate with the Magari tephra and the Imaichi pyroclastic-flow deposits and pumice fall of central Kyushu (WS-24-1, WS-24-2). This tephra is a first-class marker of the end of the Early Pleistocene.

References: Kamata et al. (1994); Machida et al. (1980); Mitsunashi et al. (1959); Niitsuma (1976).

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English translation of figure lettering

1:25,000 “Otaki” (Otaki 13-1). Ishizuka. Elevations 194, 239.3, 172, 188, 220.

Original Japanese lettering

2.5万分の1「大多喜」（大多喜13号-1）。石塚。標高194，239.3，172，188，220。

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English translation of figure lettering

From top: Ku6A, Ku6B, Ku6C, Ku6D, Ku6E.

Original Japanese lettering

上から：Ku6A，Ku6B，Ku6C，Ku6D，Ku6E。

WS-25-1 Yabakei pyroclastic-flow deposits in central Kyushu—the source pyroclastic flow of the Pink volcanic ash of the Osaka Group

Hiroki Kamata and Hideo Hoshizumi

Localities: Kaguma (鹿熊), Yabakei Town, Oita Prefecture (locality 2); Kasagiharu, Hijudai, Kusu Town, in the same prefecture (Self-Defense Forces Hijudai Training Area) (locality 4). Coordinates: N33°25′33″ E131°6′44″ (locality 2); N33°18′47″ E131°15′28″ (locality 4). Elevation: 230 m (locality 2); 600 m (locality 4). Outcrop type and condition: artificial exposure (locality 2); natural exposure (locality 4). Deposits and age: pyroclastic-flow deposits; latest Early Pleistocene. Dates described: March 1995 (locality 2); March 1987 (locality 4). Keywords: Yabakei pyroclastic-flow deposits; Pink volcanic ash; Shishimuta caldera; O7 volcanic ash; accretionary lapilli.

The Yabakei pyroclastic-flow deposits extend over a vast area spanning Kumamoto and Oita prefectures and are among the largest pyroclastic-flow deposits in central Kyushu. A K–Ar age of 0.99±0.03 Ma (Uto and Suto, 1985) and a fission-track age of 1.04±0.05 Ma (Danhara et al., 1994) have been obtained, and their magnetic polarity is normal. Because the overlying Imaichi pyroclastic-flow deposits have reversed polarity, the Yabakei eruption is considered to have occurred during the Jaramillo subchron (0.99–1.07 Ma). The surviving deposits cover approximately 480 km², have a maximum thickness of approximately 150 m, and have a surviving volume of approximately 40 km³ and an estimated volume of approximately 110 km³ (Kamata, 1989a). No crater landform or caldera corresponding to the source is presently identifiable at the surface. However, from the surface distribution and elevations of the deposits, drill-core samples, gravity anomalies, and other data, Kamata (1989a) postulated Shishimuta caldera near Shishimuta, Kokonoe Town, north of Kuju volcano, as the source of the Yabakei pyroclastic flow. The Yabakei deposits are correlated with the Pink volcanic ash of the Osaka Group and the O7 volcanic ash of the Kazusa Group, important key beds of the latest Early Pleistocene (Danhara et al., 1992; Hayashida et al., 1996). The evidence is as follows. In the Yabakei deposits and Pink ash: (1) the refractive indices of volcanic glass agree closely, with modal values of n=1.498–1.502; (2) phenocrysts of green common hornblende, orthopyroxene, clinopyroxene, zircon, apatite, and opaque minerals occur in approximately the same proportions, respectively about 40–70, 5–30, 1–10, 0–1, 1–2, and 10–30%; and (3) the refractive indices of green common hornblende and clinopyroxene agree closely, with modal values of n₂=1.673–1.679 and γ=1.706–1.710, respectively (Danhara et al., 1992). The Yabakei deposits, Pink ash, and O7 ash are also all characterized by normal polarity with a shallow inclination of approximately 30° (Hayashida et al., 1996).

The Yabakei pyroclastic-flow deposits consist chiefly of welded material, forming an extensive pyroclastic-flow plateau. Except for some black glassy facies, the welded part is extensively devitrified and grey. Columnar joints 0.5–2 m wide are developed. At devitrified outcrops, both matrix and juvenile lenses are grey and difficult to distinguish. Nonwelded parts occur at the base and top of the pyroclastic-flow deposits, but the upper nonwelded part has often been lost to erosion. The nonwelded part contains pale greyish-brown pumice, usually no larger than 10 cm but sometimes reaching 20 cm, in a greyish-white ash matrix. A characteristic of both welded and nonwelded deposits is the abundance of approximately 1–3 mm crystal fragments of plagioclase, common hornblende, and orthopyroxene in the matrix and juvenile lenses or pumice.

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Localities 1, 2, 3; 1:25,000 “Western Yabakei” (Nakatsu 16-3). Oshima, 奥鶴, 幸田, 金吉, 芝原, 鹿熊, Yabakei. Elevations 152, 366, 374; contour 200.

Original Japanese lettering

地点1，2，3；2.5万分の1「耶馬溪西部」（中津16号-3）。大島，奥鶴，幸田，金吉，芝原，鹿熊，耶馬溪。標高152，366，374；等高線200。

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Localities 4, 5; 1:25,000 “Hijudai” (Oita 9-3). 日出生, 長谷, Kasagiharu, 日出生 River. Elevations 690, 668, 678; contours 500, 600.

Original Japanese lettering

地点4，5；2.5万分の1「日出生台」（大分9号-3）。日出生，長谷，笠置原，日出生川。標高690，668，678；等高線500，600。

WS-25-1 (continued)

The exposures at localities 1, 2, and 3 (Kaguma, Yabakei Town) lie partway up the road ascending the plateau of the Yabakei pyroclastic-flow deposits. At locality 1, the nonwelded part directly overlies the underlying strata, with no basal fallout pyroclasts recognized. Locality 2 consists of black glassy strongly welded material, from which fresh, nondevitrified samples can be collected. Continuing up the road, successively higher facies can be observed continuously: a thick grey devitrified strongly welded part and a pale brown weakly welded to nonwelded part (left column). At locality 3, the uppermost nonwelded part of the Yabakei deposits has been lost, leaving the succession terminating in weakly welded material. The Imaichi pyroclastic-flow deposits overlie it with a weathered zone between (Kamata et al., 1994a).

At locality 4, in the Ground Self-Defense Force training area at Hijudai Kasagiharu, Kusu Town, a volcanic-ash fallout bed is recognized immediately below the Yabakei pyroclastic-flow deposits. The bed is pale greyish-brown throughout, approximately 60 cm thick, and composed chiefly of accretionary lapilli no larger than 1 cm (photograph) (Hoshizumi et al., 1988). Its uppermost part includes alternating volcanic-ash and volcanic-sand beds a few centimetres thick. The main nonwelded pyroclastic-flow deposit lies immediately above, with no weathering or erosional hiatus between them (right column). North of the road at this outcrop, nonwelded Kasagiharu pyroclastic-flow deposits occur below the Yabakei deposits, separated from them by the Onigahara debris deposits (stratified tuff breccia and other material). The Kasagiharu deposits originated from the rhyolitic lava plateau 2 km to the west (Komatsudai rhyolites, approximately 1.2 Ma) (Hoshizumi et al., 1988). Other exposures of fallout pyroclasts at the base of the Yabakei deposits have been confirmed along the national highway 100 m southeast of the 620 m elevation point southwest of Ishitobi, Kusu Town, and along a forest road 2.5 km east-southeast of Matsuki Dam (both within the 1:25,000 “Bungo-Mori” sheet). However, vegetation and other factors make the exposures rather poor.

References: Danhara et al. (1992, 1994); Hayashida et al. (1996); Hoshizumi et al. (1988); Kamata (1989a); Kamata et al. (1994a); Uto and Suto (1985).

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Legible tape-measure numerals: 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 12.

Original Japanese lettering

巻尺の可読目盛：1，2，4，5，6，7，8，9，10，11，12。

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Left column: localities 1, 2, 3 (Kaguma, Yabakei Town). From top: Imaichi pyroclastic-flow deposits: strongly welded part; weakly welded part; locality 3, weathered zone. Yabakei pyroclastic-flow deposits: weakly welded part; strongly welded part (devitrified); locality 1, strongly welded part (glassy); nonwelded part; locality 2; tuff–tuff breccia. Scale 2 m. Right column: locality 4 (Hijudai, Kusu Town). From top: Yabakei pyroclastic-flow deposits: nonwelded part (volcanic ash and pumice); alternating volcanic-ash and volcanic-sand fallout beds; locality 4, volcanic-ash fall (accretionary-lapilli fall). Onigahara debris deposits: tuff breccia–tuffaceous sandstone. Kasagiharu pyroclastic-flow deposits: nonwelded part (volcanic ash and pumice). Scale 2 m. Uto and Suto (1985) at the image top has been restored in the main references.

Original Japanese lettering

左柱：地点1，2，3（耶馬溪町鹿熊）。上から今市火砕流堆積物：強溶結部；弱溶結部；地点3，風化帯。耶馬溪火砕流堆積物：弱溶結部；強溶結部（脱ガラス化）；地点1，強溶結部（ガラス質）；非溶結部；地点2；凝灰岩－凝灰角礫岩。尺度2m。 右柱：地点4（玖珠町日出生台）。上から耶馬溪火砕流堆積物：非溶結部（火山灰及び軽石）；降下火山灰火山砂互層；地点4，降下火山灰（降下火山豆石）。鬼ヶ原岩屑堆積物：凝灰角礫岩－凝灰質砂岩。笠置原火砕流堆積物：非溶結部（火山灰及び軽石）。尺度2m。画像上端の宇都・須藤(1985)は本文文献に復元済。

WS-25-2 Dochu volcanic-ash bed, an Early Pleistocene widespread tephra at the earth pillars of Tokushima Prefecture—Osaka Pink volcanic ash

Kiyohide Mizuno

Locality: Awa-no-Dochu Natural Monument north of Sakuranooka, Awa Town, Awa District, Tokushima Prefecture. Coordinates: N34°05′20″ E134°12′34″.

Elevation: 120 m. Outcrop type and condition: natural exposure; extant. Deposits and age: freshwater deposits; Early Pleistocene, approximately 1.0 Ma. Date described: January 1996. Keywords: Dochu volcanic ash; Osaka Pink volcanic ash; Awa-no-Dochu.

Awa Town, Tokushima Prefecture, has “earth pillars” formed by erosion of strata consisting chiefly of fluvial gravel, and these have been designated a national natural monument. These strata are called the Dochu Formation. The intercalated Dochu volcanic-ash bed (Akoshima and Suyari, 1989) is correlated with the Pink volcanic-ash bed, one of the representative tephras of the Osaka Group erupted approximately 1.0 Ma (Mizuno, 1987). A column of the Dochu Formation by Suyari and Akoshima (1977) is presented here. The Dochu volcanic-ash bed in the middle of the succession consists of glassy volcanic ash approximately 40–100 cm thick, described in detail by Mizuno (1987) and Akoshima and Suyari (1989). Its paleomagnetic polarity is normal, and a fission-track age of 1.3±0.2 Ma has been obtained.

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Map: 1:25,000 “Nishi-Akadani” (Tokushima 16-1); Awa-no-Dochu, Hayashi, Sakuranooka, 名東岡, 十善地; elevations 203, 149.9, 84. Reference cross-section of Awa-no-Dochu (Hatodake); Yoshinogawa Group (1968); scale 2 m. Named landforms: Onami-Konami, Horaijima, Daitenchu–Daisekimon, Hakukuza, Oarizuka. Legend, retaining original English: boulder, angular, round; cobble; pebble; clayey. Bed numbers and original colour lettering:

Number	Legible colour or label
1	br.
2	illegible
3	br.
4	gray
5	brown br.
6	no colour lettering
7	brown br.
8	gray
9	grayey white
10	light brown; gray; light brown
11	Dochu volcanic-ash bed
12	brown
13	gray
14	brown
15	light brown

Original Japanese lettering

地図：2.5万分の1「西赤谷」（徳島16号-1）；阿波ノ土柱，林，桜ノ岡，名東岡，十善地；標高203，149.9，84。 阿波ノ土柱 模式断面図（波涛嶽）；吉野川グループ(1968)；尺度2m。地形名：大波小波，蓬莱島，大天柱・大石門，白狗座，大蟻塚。凡例：boulder, angular, round；cobble；pebble；clayey。層番号と原図色調：

番号	可読色調・ラベル
1	br.
2	判読不明
3	br.
4	gray
5	brown br.
6	色調文字なし
7	brown br.
8	gray
9	grayey white
10	light brown；gray；light brown
11	土柱火山灰層
12	brown
13	gray
14	brown
15	light brown

Reading notes

第2層の細字 — 原図上端の文字が重なり判読できない。br.とgrayey whiteは原図表記を保持。

References: Akoshima and Suyari (1989); Mizuno (1987); Suyari and Akoshima (1977); Yoshinogawa Group (1968).

WS-25-3 Pink volcanic ash, a representative widespread tephra of the lower Osaka Group

Kiyohide Mizuno

Locality: east of 富蔵, Sakai City, Osaka Prefecture. Coordinates: N34°28′18″ E135°31′42″. Elevation: 70 m.

Outcrop type and condition: natural exposure; extant in February 1996. Deposits and age: freshwater deposits, partly marine deposits; approximately 1.0 Ma. Keywords: Pink volcanic ash; Osaka Group; Sakai.

The Pink volcanic-ash bed is one of the representative tephras of the lower Osaka Group. Its horizon lies within the Jaramillo event, and numerous age determinations indicate approximately 1.0 Ma (Ishida et al., 1969; Danhara et al., 1992; Ichihara, 1993, and others). Widespread correlations of this tephra have also progressed. The name Pink volcanic ash was first used by Itihara (1953), and its type locality is in the Senri Hills. However, as development destroyed outcrops, the type area of the Osaka Group shifted to the Sennan and Senboku regions (Itihara et al., 1975; Yoshikawa, 1973). This outcrop forms part of that area, and its surroundings are expected to remain unaffected by development for some time. The exposure is approximately 10 m high, and the Pink volcanic-ash bed is intercalated in freshwater silt in its upper part. Below it lies the marine clay bed called Ma1, containing one extremely thin volcanic-ash bed. The geology around the outcrop is described by Yoshikawa (1973) and Itihara et al. (1975). Detailed features of the Pink ash can be observed in the valley to the southeast (the ■ locality on the map). The bed is approximately 70 cm thick, consists of greyish-white to pale pink glassy volcanic ash, and is divided into about six beds (Yoshikawa, 1984). In particular, coarse sandy beds occur at two middle horizons. Its petrographic characteristics are described in detail by Yokoyama and Kusunoki (1969), Yoshikawa (1976), Yoshikawa (1984), and others.

References: Danhara et al. (1992); Ishida et al. (1969); Itihara (1953); Ichihara (1993); Itihara et al. (1975); Yokoyama and Kusunoki (1969); Yoshikawa (1973); Yoshikawa (1976); Yoshikawa (1984).

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1:25,000 “Tondabayashi” (Wakayama 6-3). Sakai City, 富蔵, Sakasegawa, Kamamuro, Hata, Kannoji Temple. Elevations 59, 95.5, 145, 83, 66, 96.2.

Original Japanese lettering

2.5万分の1「富田林」（和歌山6号-3）。堺市，富蔵，逆瀬川，釜室，畑，感応寺。標高59，95.5，145，83，66，96.2。

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NW; SE; volcanic-ash bed; marine clay Ma1; 2 m; photographed in February 1996.

Original Japanese lettering

NW；SE；火山灰層；海成粘土Ma1；2m；1996年2月撮影。

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Facies of the Pink volcanic ash; scale 90 cm.

Original Japanese lettering

ピンク火山灰の層相；スケールは90cm。

WS-26-1 Fukuda volcanic-ash bed of the Osaka Group marking the Tertiary–Quaternary boundary horizon

Shusaku Yoshikawa

Locality: Mikeyama Town, Kishiwada City, Osaka Prefecture. Coordinates: N34°25′52″ E135°25′09″. Elevation: 60 m.

Outcrop type and condition: artificial exposure; destroyed by land development in 1992. Deposits and age: fluvial-lacustrine silt and sand, and volcanic ash; Pliocene and Early Pleistocene, 1.75 Ma. Date described: 1987. Keywords: Osaka Group; Fukuda volcanic-ash bed.

The most complete succession of the Osaka Group is developed in the Sennan and Senboku Hills of southern Osaka Prefecture. On the basis of plant-fossil occurrences, the group is divided into three parts: the lowermost part, representing the flourishing phase of the Metasequoia flora; the lower part, representing its disappearance phase; and the upper part. Their boundaries are placed at the top of the Fukuda volcanic-ash bed and the base of the Azuki volcanic-ash bed, respectively. The Fukuda horizon is considered the Tertiary–Quaternary boundary, with the Olduvai subchron of the paleomagnetic stratigraphy immediately below it (Ichihara, 1960; Yoshikawa, 1983; Ichihara, 1993). The exposure in Mikeyama Town, Kishiwada City, is the type locality of the Fukuda volcanic-ash bed. Fluvial-lacustrine silt and sand beds, locally sand and gravel, were present, and the Fukuda ash, 100–60 cm thick, was exposed within silt. An unnamed white fine volcanic-ash bed, 5–10 cm thick, could also be observed 10 cm below it. The Fukuda ash here consists of unit A, 14 cm of white to yellowish-white fine- to medium-grained glassy volcanic ash; unit B, 10 cm of reddish-purple fine- to medium-grained glassy volcanic ash; and unit C, 25–100 cm of yellowish-white to white fine glassy volcanic ash containing pumice. The Fukuda bed is continuously distributed in southern Osaka, and its equivalents have been found in the Kinki and Tokai regions, and farther afield in Niigata and on the Boso Peninsula. In Niigata it corresponds to the Tsujimatagawa volcanic-ash bed of the Uonuma Group, and in Boso to the Kd38 volcanic-ash bed of the Kazusa Group (Yoshikawa et al., 1995).

References: Ichihara (1960, 1993); Yoshikawa (1983); Yoshikawa et al. (1995).

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1:25,000 “Eastern Kishiwada” (Wakayama 10-1). Fukuda Town, Katsuragi Town, Oike. Elevations 69, 73.0, 74.

Original Japanese lettering

2.5万分の1「岸和田東部」（和歌山10号-1）。福田町，葛城町，大池。標高69，73.0，74。

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W, E on both photographs. Left photograph, from top: unit C; unit B; unit A1; silt; volcanic ash; silt. Photographed in March 1987.

Original Japanese lettering

左右ともW，E。左写真上から：ユニットC；ユニットB；ユニットA1；シルト；火山灰；シルト。1987年3月撮影。

WS-26-2 Tsujimatagawa volcanic-ash bed of the Uonuma Group marking the Tertiary–Quaternary boundary horizon

Shusaku Yoshikawa

Locality: Tsujimata, Yamato Town, Minamiuonuma District, Niigata Prefecture. Coordinates: N37°11′01″ E138°52′29″. Elevation: 210 m.

Outcrop type and condition: natural exposure; extant in September 1995. Deposits and age: fluvial-lacustrine silt, sand, sand and gravel, and volcanic ash; Pliocene to Early Pleistocene, 1.75 Ma. Date described: October 1989. Keywords: Uonuma Group; Tsujimatagawa volcanic ash; Fukuda volcanic ash.

The Pliocene–Pleistocene Uonuma Group is widely distributed in the Uonuma and Higashikubiki Hills of Niigata Prefecture. With a maximum thickness of approximately 3,000 m, it consists of marine or inland-water gravel, sand, and silt and contains approximately fifty volcanic-ash beds. The Tsujimatagawa volcanic-ash bed (Tzc) is intercalated in the upper part of the lower formation of the Uonuma Group, somewhat below the SK120 volcanic-ash bed and immediately above the Olduvai subchron in the paleomagnetic stratigraphy. The outcrop at Tsujimata, Yamato Town, Minamiuonuma District, is its type locality (Kazaoka et al., 1986). This is an approximately 3-m-high cliff on the east bank of the Tsujimata River, exposing fluvial-lacustrine silt, sand, and sand and gravel, locally with peat. The Tsujimatagawa ash, 120–100 cm thick, is exposed within this silt. Facies differences divide it, in ascending order, into units A1, A2, B, and C. Unit A1 is 16–23 cm of yellowish-white to white coarse- to fine-grained glassy volcanic ash. Unit A2 is 23 cm of white, salt-and-pepper-like, coarse- to medium-grained, somewhat crystal-rich volcanic ash. Unit B is 10 cm of reddish-purple fine- to medium-grained glassy volcanic ash. Unit C is 50–70 cm of yellowish-white to greyish-white to white fine- to coarse-grained glassy volcanic ash. The Tsujimatagawa bed is correlated with the Fukuda volcanic-ash bed of the Osaka Group (WS-26-1) and the Kd38 volcanic-ash bed of the Kazusa Group (WS-26-3) (Yoshikawa et al., 1994; Kurokawa and Tomita, 1995; Yoshikawa et al., 1996).

References: Kazaoka et al. (1986); Kurokawa and Tomita (1995); Yoshikawa et al. (1994, 1996).

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Map: 1:25,000 “Iwasawa” (Takada 1-4); 1:25,000 “Koide” (Takada 1-2). 下稲倉, Myojin, 上山; elevations 272, 194, 353, 424, 234.6. Photograph: NW, SE; Tsujimatagawa volcanic-ash bed; from top, units C, B, A2, A1; photographed in August 1995. Text fragments at the left edge are included in the main text.

Original Japanese lettering

地図：2.5万分の1「岩沢」（高田1号-4）；2.5万分の1「小出」（高田1号-2）。下稲倉，明神，上山；標高272，194，353，424，234.6。写真：NW，SE；辻又川火山灰層；上からユニットC，B，A2，A1；1995年8月撮影。画像左縁の本文断片は本文に収録済。

WS-26-3 Kd38 volcanic-ash bed of the Kazusa Group marking the Tertiary–Quaternary boundary horizon

Shusaku Yoshikawa

Locality: 加勢, Kimitsu City, Chiba Prefecture. Coordinates: N35°12′24″ E140°06′21″. Elevation: 100 m.

Outcrop type and condition: natural exposure; extant in June 1995. Deposits and age: marine silt and sand beds, and volcanic ash; Pliocene and Early Pleistocene, 1.75 Ma. Date described: June 1995. Keywords: Kazusa Group; Kiwada Formation; Kd38 volcanic-ash bed; Boso Peninsula.

The Pliocene and Lower Pleistocene Kazusa Group is widely distributed in the Kazusa Hills of the Boso Peninsula, Chiba Prefecture. It exceeds 3,000 m in maximum thickness and consists of alternating marine clay, sand, and silt beds, containing more than approximately 200 volcanic-ash beds. The Kd38 volcanic-ash bed is intercalated in the lower Kiwada Formation or the Kurotaki Formation of the Kazusa Group (Mitsunashi et al., 1959). It is an important key bed marking the Tertiary–Quaternary boundary horizon because it lies immediately below the FAD of Gephyrocapsa caribbeanica in the calcareous nannofossil stratigraphy (Takayama et al., 1995) and immediately above the Olduvai subchron in the paleomagnetic stratigraphy (Niitsuma, 1976). The outcrop at 加勢, Kimitsu City, is a cliff on the east bank of a tributary of the Obitsu River, just below the tunnel near the entrance to the University of Tokyo experimental forest at Orikizawa. Marine sand beds, locally silt, are exposed. An approximately 40-cm-thick Kd38 volcanic-ash bed is seen within this sand. Facies differences divide the ash, in ascending order, into units A1, A2, and B. Unit A1 is 12 cm of white medium- to fine-grained glassy volcanic ash containing 2–3 mm accretionary lapilli in its middle part. Unit A2 is 12 cm of greyish-white, salt-and-pepper-like, medium- to fine-grained, somewhat crystal-rich volcanic ash with developed parallel and cross-lamination. Unit B is 10–20 cm of reddish-purple fine- to medium-grained glassy volcanic ash. The Kd38 bed is correlated with the Fukuda volcanic-ash bed of the Osaka Group (WS-26-1) and the Tsujimatagawa volcanic-ash bed of the Uonuma Group (WS-26-2) (Yoshikawa et al., 1994; Kurokawa and Tomita, 1995; Yoshikawa et al., 1996).

References: Kurokawa and Tomita (1995); Mitsunashi et al. (1959); Niitsuma (1976); Takayama et al. (1995); Yoshikawa et al. (1994, 1996).

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1:25,000 “Sakahata” (Otaki 13-4). 加勢; 折 [remainder of locality name cropped]. Elevations 140, 204, 315.2.

Original Japanese lettering

2.5万分の1「坂畑」（大多喜13号-4）。加勢；折〔地名の残りは切れている〕。標高140，204，315.2。

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N; S; kd38 volcanic ash; from top, unit B, unit A2, unit A1; photographed in June 1995.

Original Japanese lettering

N；S；kd38火山灰；上からユニットB，ユニットA2，ユニットA1；1995年6月撮影。

2. Hokkaido region

HK-1 Late Pleistocene tephra beds from Rishiri volcano on plateaus around the Sarobetsu Plain, northern Hokkaido

Hideki Miura

Locality: 豊徳, Toyotomi Town, Hokkaido. Coordinates: N45°7′28″ E141°38′23″. Elevation: 26 m. Outcrop type and condition: artificial exposure; extant.

Deposits and age: eolian tephra and marine deposits; Late Pleistocene. Date described: May 1990.

Keywords: Rishiri-derived tephras; Rishiri–Wankonosawa tephra; Rishiri–豊徳 tephra; Sarobetsu Plain; cryoturbation.

All Late Pleistocene tephras derived from Rishiri volcano and distributed around the Sarobetsu Plain can be observed at this outcrop. Seven tephras are recognized directly above marine sand and gravel: Rishiri–Acharu 1 (Rs-Ac1), Acharu 2 (Rs-Ac2), Rishiri–Kabutonuma 1 (Rs-Kb1), Kabutonuma 2 (Rs-Kb2), Kabutonuma 3 (Rs-Kb3), Rishiri–Wankonosawa (Rs-Wn), and 豊徳 (Rs-Ho). At Kabutonuma on the Sarobetsu Plain, Rs-Ac1 lies above the 100–130 ka Kussharo–Haboro tephra (Kc-Hb), and Rs-Kb2 immediately below the 70–90 ka Aso-4 tephra. On the Tonbetsu Plain, Rs-Wn lies above the 31–42 ka Shikotsu-1 tephra (Spfa-1) (see Miura, 1995a, for outcrop locations and columns). The lowermost marine sand and gravel forming the plateau is called the Keihoku Formation (Sarabetsu Group et al., 1966) and has hitherto been regarded as Middle Pleistocene. However, because Rs-Ac1, Rs-Ac2, or Aso-4 directly overlies this sand and gravel at some sites, the traditionally defined Keihoku Formation is considered to include strata of differing Middle to Late Pleistocene ages (Miura, 1995b). The main distribution axis of Rs-Wn suggests a submerged depression offshore from Oniwaki, Rishiri Island (approximately 90 m below present sea level), as its crater. However, because no water-contact eruptive products are recognized in the tephra, it is expected to have erupted during a low-sea-level interval of the last glacial period. Rs-Ho is estimated to be latest Pleistocene (Miura, 1995a), rather than Holocene as previously considered (Sasaki et al., 1973; Tomioka and Otowa, 1973), because an approximately 8 ka radiocarbon age was obtained from acid-insoluble humus in the lower part of the overlying humic layer and its horizon is close to Rs-Wn. Cryoturbation is recognized at the Rs-Ho and Rs-Wn horizons, suggesting a cold environment after their deposition. This alone, however, does not directly demonstrate a permafrost environment at that time.

References: Sarabetsu Group et al. (1966); Sasaki et al. (1973); Tomioka and Otowa (1973); Miura (1995a, b).

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1:50,000 “Wakasakanai” (Teshio 6). Wankonosawa, Naganuma lake group, 豊徳, Seimei River. Elevations 5, 5.5, 57, 45, 56, 48.8, 8.7, 3.5, 51.5, 23, 55.2.

Original Japanese lettering

5万分の1「稚咲内」（天塩6号）。ワンコノ沢，長沼群，豊徳，清明川。標高5，5.5，57，45，56，48.8，8.7，3.5，51.5，23，55.2。

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S; N; Rs-Ho; Rs-Wn; Rs-Kb3; Rs-Kb2; Rs-Kb1; Rs-Ac2; Rs-Ac1; marine sand and gravel; photographed in May 1990.

Original Japanese lettering

S；N；Rs-Ho；Rs-Wn；Rs-Kb3；Rs-Kb2；Rs-Kb1；Rs-Ac2；Rs-Ac1；海成砂礫層；1990年5月撮影。

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Scale 0, 1, 2, 3 m. Ages: 8,180±180 yr BP (GaK-16786); 31–42 ka; 70–90 ka; 100–130 ka. From top: Rs-Ho; Rs-Wn; Spfa-1 (31–42 ka); Rs-Kb3; Aso-4 (70–90 ka); Rs-Kb2; Rs-Kb1; Rs-Ac2; Rs-Ac1; Kc-Hb (100–130 ka). Legend: humic layer; loam; volcanic ash; scoria; pumice; marine sand and gravel.

Original Japanese lettering

尺度0，1，2，3m。年代：8,180±180年BP（GaK-16786）；31–42ka；70–90ka；100–130ka。上からRs-Ho；Rs-Wn；Spfa-1（31–42ka）；Rs-Kb3；Aso-4（70–90ka）；Rs-Kb2；Rs-Kb1；Rs-Ac2；Rs-Ac1；Kc-Hb（100–130ka）。凡例：腐植層；ローム；火山灰；スコリア；軽石；海成砂礫層。

HK-2 Fossil frost-crack structures on the Tonbetsu Plain, northern Hokkaido—evidence of markedly low winter temperatures during the last glacial period

Hideki Miura

Locality: Ashino, Sarufutsu Village, Hokkaido (borrow pit near Ashino Elementary School). Coordinates: N45°17′50″ E142°11′05″. Elevation: 12 m.

Outcrop type and condition: artificial exposure; partly extant. Deposits and age: loam, eolian tephra, and marine deposits; Late Pleistocene.

Date described: December 1990. Keywords: Tonbetsu Plain; fossil frost-crack structures; Rishiri–Wankonosawa tephra; permafrost environment.

Strong winter cooling of the ground surface produces a temperature gradient within frozen ground, with greater contraction nearer the surface. Frost cracks form when the resulting tension exceeds the mechanical strength of the frozen ground. Numerous fossil frost-crack structures with this origin occur on plateaus around the Tonbetsu Plain in northern Hokkaido (outcrop maps and sketches are provided by Miura and Hirakawa, 1995). This outcrop contains the marine sand and gravel forming the Asachino surface (Asachino Formation; Heavy-Clay Land Group, 1964), overlain by dark brown fine sand with indistinct bedding, loam, and humic layers. Four frost-crack structures were confirmed in the approximately 30-m-wide southern exposure (extant; the left photograph shows one, 254 cm long from immediately below the humic layer to the crack tip). Five were confirmed in the adjacent approximately 40-m-wide northern exposure (the right photograph shows one, 238 cm long from immediately below the humic layer to the crack tip; this exposure has now disappeared). In the southern exposure, 1–2 mm pumice grains of the Rishiri–Wankonosawa tephra (Rs-Wn) form a continuous horizon approximately 40 cm below the humic layer, but are absent above the frost crack.

This indicates that the crack formed after the Rs-Wn fallout. Comparison of the theoretically calculated thickness of the contemporary freeze–thaw layer with the crack depth suggests that the photographed cracks are definite ice-wedge casts that extended below the permafrost table, implying a permafrost environment in this area during the latter half of the last glacial period. The approximately 1–2-cm-thick iron-oxide pan at the boundary between marine sand and gravel and loam in the right photograph may represent iron accumulated at a former permafrost table. Most exposures of fossil frost-crack structures around the Tonbetsu Plain have now disappeared, but the appearance of new outcrops should allow many more such structures to be discovered in this area.

References: Heavy-Clay Land Group (重粘地グループ) (1964); Miura (1995a); Miura and Hirakawa (1995).

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1:50,000 “Onishibetsu” (Esashi 9 and 13). Ashino, Sarukotsu, Lake Sarukotsu, Lake Kimoma. Elevations 20, 26.5, 11.3, 2.16, 6.

Original Japanese lettering

5万分の1「鬼志別」（枝幸9号・13号）。芦野，猿骨，猿骨沼，キモマ沼。標高20，26.5，11.3，2.16，6。

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Left: humic layer; Rs-Wn; loam; dark brown fine sand; marine sand and gravel (Asachino Formation). Right: loam; dark brown fine sand; iron-oxide pan; marine sand and gravel (Asachino Formation).

Original Japanese lettering

左：腐植層；Rs-Wn；ローム；暗褐色細粒砂層；海成砂礫層（浅茅野層）。右：ローム；暗褐色細粒砂層；酸化鉄の盤層；海成砂礫層（浅茅野層）。

Photographed in May 1991

HK-3 Middle Pleistocene marine terraces and tephras on the shores of Lake Saroma, southern coast of the Sea of Okhotsk

Koji Okumura

Locality: Horoiwa, Saroma Town, Hokkaido. Coordinates: N44°05′45″ E143°53′25″. Elevation: 5 m.

Outcrop type and condition: artificial exposure; condition unknown. Deposits and age: pyroclastic-flow deposits and fallout tephra; Middle Pleistocene.

Date described: August 1985. Keywords: Lake Saroma; tephras from Kussharo caldera; Mombetsu volcanic ash-1; Horoiwa volcanic ash; pollen analysis.

Around southeastern Lake Saroma lie the Horoiwa terrace observed at this outcrop, the Gifu Plateau at Tokoro, and a sandbar-like plateau separating the lake from the Sea of Okhotsk. All are Middle Pleistocene marine terraces one level above the last-interglacial marine terrace, with former shorelines at elevations of 10–30 m. Around Lake Saroma, the last-interglacial marine terrace identified by Kussharo pyroclastic-flow deposits IV (KP IV) occurs only locally along the northern and western margins of the Gifu Plateau (Okumura, 1996). This outcrop exposes the reference tephra succession of this area from the Middle Pleistocene to the last interglacial (Sakaguchi and Okumura, 1986; Okumura, 1991). Mombetsu volcanic ash-1 (Mb-1) and Toetoko volcanic ash (TT), contained in the upper marine deposits, are both rich in K₂O (approximately 4 wt%) and share petrographic characteristics with tephras originating in central Hokkaido. The intervening Horoiwa volcanic ash consists of glass with major-element compositions matching KP VII and is considered tephra erupted from Kussharo volcano contemporaneously with KP VII. Similar tephra has also been found above the terrace-forming deposits of the Gifu Plateau. Glass resembling KP VI has been found in the ash overlying humic silt above the Horoiwa ash. KP IV and its co-ignimbrite ash, the Kussharo–Haboro volcanic ash, are widely distributed in central and eastern Hokkaido and identify last-interglacial terrace surfaces (see WS-16). This outcrop is at the northern limit of the pyroclastic-flow deposits. Pollen analysis of the peat and humic-silt beds indicates that a period somewhat warmer than the present followed marine deposition, after which a cooler-than-present climate persisted. However, since no pronounced warm or cold period is recognized below KP IV, this section apparently lacks deposits of the cold interval of oxygen-isotope stage 6 and the warm interval of stage 5e (Sakaguchi and Okumura, 1986).

References: Okumura (1991); Okumura (1996); Sakaguchi and Okumura (1986).

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1:50,000 “Lake Saroma” (Mombetsu 4). Horoiwa, Horoiwa Farm; elevations 3.1, 24.0, 3.3, 9.7. Factory name at left edge is cropped.

Original Japanese lettering

5万分の1「サロマ湖」（紋別4号）。幌岩，幌岩牧場；標高3.1，24.0，3.3，9.7。左縁の工場名は切れている。

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Scale 0, 1, 2 m. From top: Kussharo pyroclastic-flow deposits (KP) IV; Pink; peat; humic silt; Toetoko volcanic ash; peat; humic silt; Horoiwa volcanic ash; Mombetsu volcanic ash-1 [deposited under water]; sand and silt containing trace fossils.

Original Japanese lettering

尺度0，1，2m。上から：屈斜路火砕流堆積物(KP)IV；Pink；泥炭；腐植質シルト；登栄床火山灰；泥炭；腐植質シルト；幌岩火山灰；紋別火山灰-1［水中堆積］；生痕を含む砂・シルト。

HK-4 Stratigraphy of Akan pyroclastic-flow deposits north of Akan caldera

Koji Okumura

Locality: Kaisei, Kitami City, Hokkaido. Coordinates: N43°44′15″ E143°53′04″. Elevation: 120 m. Outcrop type and condition: artificial exposure; condition unknown. Deposits and age: pyroclastic-flow deposits; Middle Pleistocene. Date described: September 1984. Keywords: Akan Upper Pyroclastic-flow Deposits; Akan Welded Tuff; Akan Lower Pyroclastic-flow Deposits; Kussharo pyroclastic-flow deposits; eastern Hokkaido; Kitami Basin.

Large-volume pyroclastic flows erupted from Akan caldera on three occasions during the Middle Pleistocene are divided into the Akan Lower Pyroclastic-flow Deposits (ALP), Akan Welded Tuff (AWT), and Akan Upper Pyroclastic-flow Deposits (AUP) (Yamaguchi and Sato, 1966; Okumura, 1991). ALP is thickly deposited around Kitami-Aioi north of Akan caldera, but its distribution elsewhere has not yet been confirmed. AWT is distributed widely as welded tuff chiefly around the Kushiro Wetland south of the caldera. One distal occurrence has been found within sand and gravel below the deposits forming the Kushiro terrace (Matsui et al., 1987; see HK-13). At this outcrop at Kaisei, Kitami, an approximately 20-m-thick dark brown nonwelded part of AWT can be observed overlying pumiceous sand and gravel. AWT consists of blackish-brown volcanic glass with highly vesicular bubble-wall forms and contains orthopyroxene, clinopyroxene, and quartz phenocrysts. White nonwelded AUP overlies AWT, separated by a weathered zone in the upper AWT and less than 1 m of volcanic-ash soil. AUP is characterized by a basal fine volcanic-ash bed containing abundant accretionary lapilli. It is exposed north of the caldera from the Tsubetsu River basin to the southern margin of the Kitami Basin, with a distal occurrence also found north of Kussharo caldera (Okumura, 1991; HK-8). Kussharo pyroclastic-flow deposits V and IV (KP V, KP IV) successively overlie AUP. A thin pink volcanic-ash bed occurs in the uppermost volcanic-ash soil immediately below KP IV. This ash is recognized widely throughout the distribution of KP IV and provides a clue for its correlation.

No direct age evidence is available for these pyroclastic-flow eruptions. However, no marine transgression is recognized between AWT and last-interglacial marine deposits in urban Kushiro (Matsui, 1987), and some last-interglacial marine terraces near Memanbetsu consist solely of reworked AUP and KP V deposits overlain by terrestrially deposited KP IV. These observations indicate that AWT, AUP, and KP V certainly erupted successively during the interval from oxygen-isotope stage 7 to stage 5 (Okumura, 1991). The photograph shows AUP (lower right) overlain by KP V.

References: Matsui (1987); Okumura (1991); Yamaguchi and Sato (1966).

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1:50,000 “Kitami” (Kitami 2). Kaisei, サントンエイ [original map lettering]; elevations 210.8, 215, 189.

Original Japanese lettering

5万分の1「北見」（北見2号）。開成，サントンエイ〔地図原表記〕；標高210.8，215，189。

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Scale 0, 10 m. From top: Kussharo pyroclastic-flow deposits (KP) IV; Pink ash; volcanic-ash soil; Kussharo pyroclastic-flow deposits (KP) V; weathered part of AUP; Akan Upper Pyroclastic-flow Deposits (AUP); volcanic ash containing accretionary lapilli; Akan Welded Tuff (AWT: nonwelded); sand. Embedded prose and references are included in the main text.

Original Japanese lettering

尺度0，10m。上から：屈斜路火砕流堆積物(KP)IV；Pink ash；火山灰土；屈斜路火砕流堆積物(KP)V；AUPの風化部；阿寒上部火砕流堆積物(AUP)；火山豆石を含む火山灰；阿寒溶結凝灰岩（AWT：非溶結）；砂。画像内本文と文献は本文に収録済。

HK-5 Tokoro volcanic ash along the Sea of Okhotsk coast, eastern Hokkaido

Kunihiko Endo, Mari Sumita, and 星住リベカ

Locality: Tokoro Town, Tokoro District, Abashiri Subprefecture, Hokkaido. Coordinates: N44°7′38″ E144°1′3″. Elevation: 5–20 m.

Outcrop type and condition: boreholes and artificial exposures; partly extant. Deposits and age: fallout tephra and coastal-dune deposits; Late Holocene.

Dates described: 1970–1988. Keywords: Tokoro volcanic ash; Tarumae-a tephra; Komagatake-c₂ tephra; Mashu-b tephra; Tarumae-c tephra.

Several thin beds of white to pale brownish-grey fine volcanic ash occur in surficial deposits and soils along the Sea of Okhotsk coast of Hokkaido. They were named Tokoro volcanic ashes I, II, III, and IV in ascending order (Endo et al., 1972; Endo et al., 1984). They were used to classify and correlate Holocene terrace I of the Jomon transgression (5–6 m elevation) and Holocene terrace II (3 m elevation) on the Tokoro Plain, and, within the coastal dune belt, the older dunes covering older sandbars corresponding to the former terrace and the younger dunes covering younger sandbars corresponding to the latter. All four ashes, I–IV, are found together in peat in low-lying wetlands; a borehole column is shown at the lower right. Tokoro ashes I and II are intercalated in soil layers at Late Jomon, Epi-Jomon, and Satsumon horizons. Tokoro ashes III and IV are widely recognized in the younger kurosuna (black-sand) layer and younger dunes, and near the surface of peat in valleys dissecting the plateau. Similar thin white fine-ash beds in the Konsen region were called Me-a₁ and Me-a₂ and attributed to Meakan-dake (Hokkaido Volcanic Ash Nomenclature Committee, 1972). In recent years, however, their thickness distributions and other features had suggested more distant source volcanoes. These surficial tephras were re-examined in the late 1980s. Endo et al. (1988, 1989) and Sumita (1990), working mainly from Konsen through Shari, Abashiri, and Tokoro, based their conclusions on distribution and glass refractive indices; Tokui (1988, 1989, 1993) used glass chemical compositions. They reached essentially the same conclusions. Thus, the surficial tephras of eastern Hokkaido comprise Tarumae-a (Ta-a; 1739), Komagatake-c₁ (Ko-c₁; 1856), Komagatake-c₂ (Ko-c₂; 1694), and other tephras. Somewhat lower lie Tarumae-b (Ta-b), Komagatake-d (Ko-d), Mashu-b (Ma-b), Baitoushan–Tomakomai (白頭山苫小牧, B-Tm), and the Yausubetsu bed, correlated with Tarumae-c (Ta-c) by Tokui (1988), among others. Tokoro ashes III and IV in the younger dunes are Ko-c₂ and Ta-a. Numerous archaeological remains of the Okhotsk, Satsumon, Epi-Jomon, and other cultures occur in the Tokoro area, and these tephras are intercalated in their fill. Tokoro ash II is Ma-b. B-Tm becomes indistinct in this region. Tokoro ash I may be the Yausubetsu bed (Ta-c).

References: Endo et al. (1972, 1984, 1988, 1989); Hokkaido Volcanic Ash Nomenclature Committee (1972); Sumita (1990); Tokui (1988, 1989, 1993).

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Both maps: 1:25,000 “Tokoro” (Abashiri 16-3). Upper map: Lake Saroma, Tokoro archaeological site, Tofutsu; elevations 1.8, 1.6. Lower map: Gifu; elevation and other figures 5, 5, 6. North–south cross-section of the Tokoro coastal dune belt and column at locality C (Endo and Uesugi, 1972; Endo, 1984). Key: I, Tokoro volcanic ash I; II, ash II; III, ash III; IV, ash IV. Left inset: III, IV. Central inset, from top: kurosuna (black-sand) layer (older); III; II; I; kurosuna layer (younger). Section: younger dunes; older dunes; younger sandbar; older sandbar. Elevation 0, 10, 20 m; horizontal scale 0, 100, 200 m. Right column: IV; III; peat; II; I. Depth 0, 0.5, 2 m (break symbol in between). Embedded prose and references above have been restored in the main text.

Original Japanese lettering

二地図とも2.5万分の1「常呂」（網走16号-3）。上図：サロマ湖，常呂遺跡，鐺沸；標高1.8，1.6。下図：岐阜；標高等5，5，6。 トコロ海岸砂丘列の南北断面図とC地点の柱状図（遠藤・上杉,1972；遠藤,1984）。凡例I：トコロ火山灰I；II：同II；III：同III；IV：同IV。左挿図：III，IV。中央挿図上から：クロスナ層（旧期）；III；II；I；クロスナ層（新期）。断面：新砂丘；旧砂丘；新期砂州；旧期砂州。標高0，10，20m；水平尺度0，100，200m。右柱：IV；III；泥炭層；II；I。深度0，0.5，2m（中間省略記号）。画像上部の本文・文献は本文に復元済。

HK-6 Late Pleistocene tephra beds in the Kiyosato–Shari area—Kussharo- and Mashu-derived tephras and widespread tephras

Mari Sumita

Locality: Konan, Kiyosato Town, Hokkaido (South No. 26, Line 5). Coordinates: N43°46′44″ E144°34′59″ (locality A); N43°46′57″ E144°35′17″ (locality B). Elevation: 80–110 m. Outcrop type and condition: artificial exposures; extant in 1992. Deposits and age: fallout tephra and pyroclastic-flow deposits; Late Pleistocene. Date described: September 1986. Keywords: Kussharo volcano; Mashu volcano; Shikotsu-1 tephra; Daisetsu–Ohachidaira tephra.

This outcrop is along an agricultural road cutting the pyroclastic-flow plateau at the northern foot of Mt. Etombi, north of Mashu caldera. It is a valuable exposure where the Late Pleistocene pyroclastic succession can be observed continuously from K.P. flow IV, erupted from Kussharo volcano approximately 120 ka (Katsui and Sato, 1963), onward. In practice, combining ridge-top outcrop A and valley-facing outcrop B reveals the tephra succession from approximately 120 ka to the present. The basic tephra stratigraphy of this area is described in detail by Sumita (1988) (the columns for these outcrops are No. 1 [outcrop A] and No. 2 [outcrop B] in her Fig. 2). Sumita (1990) classified the source volcanoes from tephra thickness distributions and whole-rock chemical compositions, re-examined the regional stratigraphy from the perspective of volcanic activity, and reconstructed the volcanic histories of Kussharo and Mashu. Furthermore, ICP analyses of volcanic glass undertaken to identify sources revealed widespread tephras in addition to those from these two volcanoes, including tephra from Daisetsu volcano (Daisetsu–Ohachidaira pumice fall) and Shikotsu pumice fall-2 (Spfa-2) (Sumita et al., 1989; Yoshikawa, 1990). The Aso-4 tephra, Shikotsu pumice fall-1 (Spfa-1), and Toya tephra, discovered by Okumura (1985), Okumura et al. (1985), and others and important as time-equivalent horizons in Hokkaido, can also be seen here (see WS-9-4, WS-7-3). The interleaved activity of Kussharo and Mashu, elucidated through these widespread-tephra identifications and source classifications, is shown in the figure at right. It indicates that Mashu activity began at least as early as Kiyosato pumice-2 (KyP-2), preceding the fallout of Spfa-2, whose age is considered approximately 32 ka (Sumita et al., 1989; Yoshikawa, 1990).

Regional stratigraphy often uses breaks in landform development as stratigraphic boundaries. From the perspective of volcanic activity, however, these breaks frequently do not coincide with boundaries in the eruption history. Particularly around caldera volcanoes producing large-volume pyroclastic flows, volcanic influences and climate-driven landform development are intricately interwoven. This outcrop contains scarcely any of the dune deposits derived from pyroclastic-flow material, river-terrace deposits, or alluvial-fan deposits common in this area. It therefore has good continuity and fresh pyroclastic material, making it a good exposure for observing the process of constructing a volcanic history from regional stratigraphy.

References: Endo and Uesugi (1977); Katsui and Sato (1963); Katsui et al. (1988); Yoshikawa (1990); Okumura (1985); Okumura et al. (1985); Sato (1968, 1969); Sone (1985, 1988); Sone et al. (1991); Sumita (1988, 1990, 1993); Sumita et al. (1989).

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A; B; 500 m; 1:25,000 “Sattsuru” (Shari 6-3). Contour figures 120, 100, 80.

Original Japanese lettering

A；B；500m；2.5万分の1「札弦」（斜里6号-3）。等高線数字120，100，80。

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Kussharo-derived tephras / Mashu-derived tephras. In descending order, right=Mashu-derived and left=Kussharo-derived:

Order	Side	Original name, code, and age
1	Right	Mashu-b5 (Ma-b5)
2	Right	Mashu-f, i, j (Ma-f, i, j)
3	Right	Mashu-l (Ma-l)
4	Right	Konan pumice (Ko-P)
5	Right	Nakashari pumice (Na-P)
6	Left	WTfl-2
7	Right	Kurogoma scoria (KgSc), approximately 23 ka (Sone et al., 1991)
8	Left	WTfl-1
9	Right	Kuroppu (KuSc)
10	Left	Toyozumi pumice (TyP)
11	Right	東カヤノ pumice (HKP)
12	Left	Koshikawa pumice-4 (KwP-4)
13	Left	Koshikawa pumice-3 (KwP-3)
14	Right, ★	Daisetsu–Ohachidaira pumice fall, approximately 28 ka (Katsui et al., 1988)
15	Left	Koshikawa pumice-1 (KwP-1)
16	Left	Kussharo pyroclastic flow 1 (Kpfl-I), approximately 30 ka (Sato, 1969; Endo and Uesugi, 1977; Sone, 1988, and others)
17	Right	Yambetsu pumice (YmP)
18	Right	Tarako pumice (Tr-P)
19	Left, ★	Shikotsu pumice fall-1 (Spfa-I)
20	Left, ★	Shikotsu pumice fall-2 (Spfa-II)
21	Right	Izumi scoria (IzSc)
22	Right	Kiyosato pumice-3 (KyP-3)
23	Right	Kiyosato pumice-2 (KyP-2)
24	Left	Kiyosato pumice (KyP-1)
25	Left	Lithic-fragment pumice (LfPm)
★ denotes widespread tephra. Note: the tephra nomenclature partly follows Sato (1968) and Sone (1985). Tephras of this region, part of the composite stratigraphic column, and their respective source volcanoes. For details, see Sumita (1991) or Sumita (1993). Tephras marked ★ are widespread tephras. (Simplified from Sumita, 1990.) Text fragments at the left edge are included in the main text.

Original Japanese lettering

屈斜路系テフラ／摩周系テフラ。上から順に、右＝摩周系・左＝屈斜路系：

順序	区分	原図名・符号・年代
1	右	摩周-b5(Ma-b5)
2	右	摩周-f,i,j(Ma-f,i,j)
3	右	摩周-l(Ma-l)
4	右	江南軽石(Ko-P)
5	右	中斜里軽石(Na-P)
6	左	WTfl-2
7	右	黒ゴマスコリア(KgSc)，約23ka（曽根ほか,1991）
8	左	WTfl-1
9	右	黒ップ(KuSc)
10	左	豊住軽石(TyP)
11	右	東カヤノ軽石(HKP)
12	左	越川軽石-4(KwP-4)
13	左	越川軽石-3(KwP-3)
14	右・★	大雪御鉢平降下軽石，約28ka（勝井ほか,1988）
15	左	越川軽石-1(KwP-1)
16	左	屈斜路第1火砕流(Kpfl-I)，約30ka（佐藤,1969；遠藤・上杉,1977；曽根,1988など）
17	右	止別軽石(YmP)
18	右	タラコ軽石(Tr-P)
19	左・★	支笏降下軽石-1(Spfa-I)
20	左・★	支笏降下軽石-2(Spfa-II)
21	右	泉スコリア(IzSc)
22	右	清里軽石-3(KyP-3)
23	右	清里軽石-2(KyP-2)
24	左	清里軽石(KyP-1)
25	左	岩片パミス(LfPm)
★は広域テフラ。※テフラの名称については佐藤(1968)及び曽根(1985)を一部踏襲している。本地域のテフラと総合柱状図の一部とそれぞれの給源火山。詳細は隅田(1991)ないし隅田(1993)を参照。★のついたテフラは広域テフラ。（隅田,1990を簡略化）。画像左縁の本文断片は本文に収録済。

Reading notes

WTfl-1・WTfl-2、Kpfl-I — 末尾の細字lとIの字形が紛らわしいため原図に近い表記を保持。本文はSpfa-1/2、図はSpfa-I/II。

HK-7 Periglacial features west of Kaiyo on the Konsen Plain—earth hummocks buried in Mashu loam

Shuji Iwata

Locality: Kaiyo, Nakashibetsu Town, Shibetsu District, Hokkaido. Coordinates: N43°35′23″ E144°52′37″. Elevation: approximately 87 m.

Outcrop type and condition: wall of a roadside ditch on North No. 14 Road; present condition unknown. Deposits and age: eolian tephra; Holocene, 6.5–13 ka. Date described: August 1972. Keywords: Konsen Plain; buried earth hummocks; Mashu loam; Mashu-derived tephra.

Earth hummocks are dome-shaped rises of fine soil, several tens of centimetres high and no larger than 1 m in diameter, covered by dense, mat-like herbs or dwarf shrubs and formed by seasonal soil freezing. They develop in wetlands and similar environments in polar, subpolar, and alpine zones, and are also called toketu-bozu (frost hummocks), Tokachi-bozu, or shibazuka (turf mounds). In present-day volcanic-ash terrain in Hokkaido, they occur densely on slight rises adjacent to yachi-bozu peatlands on floodplains, where the water table is high and soils are excessively wet. They also form on terrace and plateau shoulders where groundwater readily seeps out. Many were initiated by fallout of fine volcanic ash with high water-retention capacity. Undulating volcanic ash observed in a soil section along the side of a roadside drainage ditch west of Kaiyo, approximately 7 km northwest of Nakashibetsu Town, was identified as a fossil form because its shape and size match earth hummocks on the present ground surface. The hummocks here are small, 30 cm high and slightly less than 1 m wide (in diameter). They occur in the transition from the valley bottom to the surface beside a small stream, a tributary of the Musa River, incised into an alluvial-fan surface (Churui surface; Iwata, 1977). On the slope at the left of the diagram, they appear to grade into stepped ground. The central depression is probably a small gully. The earth hummocks formed through frost heave of Mashu-k volcanic ash (Ma-k; Hokkaido Volcanic Ash Nomenclature Committee, 1972), an eruptive product of Mashu volcano, and were buried by Ma-g, h, i pumice-fall beds. From the age of Ma-k forming the buried hummocks and the age of the overlying Ma-f, these hummocks are considered to have formed approximately 7–8 ka.

References: Hokkaido Volcanic Ash Nomenclature Committee (1972); Iwata (1977); Nogami et al. (1974).

Show extracted lettering and translation

English translation of figure lettering

1:25,000 “Musa” (Shari 3-1). Kaiyo, Motokaiyo, Minamikaiyo. Elevations 95, 90, 89, 83.5, 91.

Original Japanese lettering

2.5万分の1「武佐」（斜里3号-1）。開陽，元開陽，南開陽。標高95，90，89，83.5，91。

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English translation of figure lettering

SW; NE. Depth 0, 1, 2 m; horizontal distance 0, 1, 2, 3 m. From top, original lettering: Ma-f pumice; Ma-g,h,i; Ma-k; Ma-l pumice. Observed in August 1972.

Original Japanese lettering

SW；NE。深度0，1，2m；水平距離0，1，2，3m。上から：Ma-f pumice；Ma-g,h,i；Ma-k；Ma-l pumice。1972年8月観察。

HK-8 Older Kutcharo pyroclastic-flow deposits at Higashimokoto, eastern Hokkaido

奥村晃史

• Locality: Higashi-Nisen (東二線), Higashimokoto Village, Hokkaido
• Latitude and longitude: N43°50′22″ E144°18′58″
• Elevation: 60m
• Outcrop type and condition: Artificial exposure; partly lost
• Deposit types and age: Pyroclastic-flow deposits and fallout tephra; Late Pleistocene
• Date of description: June 1994
• Keywords: Kutcharo pyroclastic-flow deposits; Akan Upper Pyroclastic-flow Deposit; eastern Hokkaido; Higashimokoto

The town of Higashimokoto occupies the floor of a valley deeply incised into the Kutcharo pyroclastic-flow plateau. Important exposures showing the stratigraphy of the Kutcharo pyroclastic-flow deposits repeatedly appeared and disappeared along nearby valley walls with relative heights of 70–80m. The Higashi-Nisen exposure, one of the type outcrops described by 勝井・佐藤 (1963), who first provided a detailed account of the Kutcharo pyroclastic-flow deposits (KP), survived until the late 1980s and played an important role in re-examining their stratigraphy; most of it is now covered by retaining walls. At this outcrop, KP VIII, VII, VI, the Akan Upper Pyroclastic-flow Deposit (AUP), V, and I occur in ascending order, with intervening fallout tephra and fluvial gravel beds (tephra abbreviations follow 奥村, 1991). The lowermost KP VIII remains exposed, but outside Higashi-Nisen it has been found only at Tentozan in Abashiri City. It is distinguished from the other Kutcharo pyroclastic-flow deposits by its higher K₂O content. KP VII contains relatively abundant phenocrysts and lithic fragments, and its volcanic glass is somewhat mafic. The lithology of KP VII resembles that of the Akan Lower Pyroclastic-flow Deposit at a similar stratigraphic level (山口・佐藤, 1966; HK-4) (奥村, 1991). Fallout tephras with properties matching KP VII and KP VI, respectively, have been found on the eastern shore of Lake Saroma (HK-3). Between KP V and KP VI lie approximately 2m of AUP and a basal ash-fall deposit containing accretionary lapilli (奥村, 1991). AUP is distributed from the Tsubetsu River basin north of Akan caldera to Kitami (see HK-4) as a thin pyroclastic-flow deposit with fine ash at its base; it has the same characteristics here at Higashi-Nisen. The presence of AUP provides a key link between the eruptive histories of Akan and Kutcharo calderas. The lithic-rich pyroclastic-flow deposit overlying AUP, separated from it by less than 1m of volcanic-ash soil, is KP V. The section from KP IV through KP II, representing the first half of the Late Pleistocene, has been removed by fluvial erosion, but can be confirmed upstream along the Onnenai River (WS-16-1). Superposed KP V, IV, and I can be observed at Asahidai (旭台), south of Higashi-Nisen, and at Shintomi (新富), across the valley to the east.

References: 勝井・佐藤 (1963); 奥村 (1991); 山口・佐藤 (1966).

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English translation of figure lettering

Map: 1:50,000 ‘Koshimizu’ (Shari sheet 9); 1:50,000 ‘Mokotoyama’ (Shari sheet 10); Higashimokoto, Shintomi (新富), Kamihigashi (上東), Higashi-Ichigo (東一号), Higashi-Nigo (東二号), Higashi-Sango (東三号), Higashi-Yongo (東四号), Higashi-Kisen (東基線); 46.8, 42, 130.1. General column, from top: KP I, sand and gravel bed, A, KP V, AUP, B, KP VI, KP VII, C, KP VIII; scale 10m, 0. A, from top: KP I-KSr; alternation of airfall ash and pumice; Spfa-1; Kpfa-II; Kpfa-III; sand and gravel bed; KP V; scale 5m, 0. B, from top: KP V; AUP; basal ash with accretionary lapilli; KP VI. C, from top: KP VI; Kpfa-VI; KP VII.

Original Japanese lettering

位置図：5万分の1『小清水』（斜里9号）；5万分の1『藻琴山』（斜里10号）；東藻琴，新富，上東，東一号，東二号，東三号，東四号，東基線；46.8，42，130.1．全体柱状図（上から）：KP I，砂礫層，A，KP V，AUP，B，KP VI，KP VII，C，KP VIII；スケール10m，0．A（上から）：KP I-KSr；alternation of airfall ash and pumice；Spfa-1；Kpfa-II；Kpfa-III；砂礫層；KP V；スケール5m，0．B（上から）：KP V；AUP；basal ash with accretionary lapilli；KP VI．C（上から）：KP VI；Kpfa-VI；KP VII．

Reading notes

位置図の微小な一部地形図文字と標高は判読不明。本文を含む切り出し画像の本文はページ本文に清書済み。

HK-9 Last-glacial peat beds at Barasan, eastern Hokkaido

遠藤邦彦・隅田まり

• Locality: Barasan, Betsukai Town, Notsuke District, Nemuro Subprefecture, Hokkaido
• Latitude and longitude: N43°26′0″ E145°16′2″
• Elevation: 0–3m
• Outcrop type and condition: Sea cliff; partly covered
• Deposit types and age: Aeolian tephra and peat; terminal Last Glacial to Holocene
• Date of description: 1989
• Keywords: Notsuke coast; Komagatake-c₁ tephra; Komagatake-c₂ tephra; Tarumai-a tephra; Kpfl-I; Mashu-derived tephra

Some sea cliffs along the Notsuke coast, at the eastern end of the Konsen Plateau, expose deposits filling valleys incised into a plateau composed of Kutcharo pyroclastic-flow deposits and other materials. Although most exposures have been concealed by tetrapods and similar structures, approximately ten tephra beds and peat beds dating from the end of the Last Glacial can be recognized in the sea cliff at Barasan.

The upper part of this outcrop comprises the Barasan Upper Peat Bed, deposited during the last 6,000 years; the middle part consists of a series of pumice-fall and ash beds derived from Mashu volcano (Ma-g, h, i, j, k, l); and the lower part comprises the Barasan Lower Peat Bed of terminal Last Glacial age (遠藤 et al., 1988). Two to three fine ash beds, locally three to four, are intercalated in the topsoil. Formerly called Me-a₁ and -a₂ (北海道火山灰命名委員会, 1972), they were subsequently assigned to ash falls derived from Komagatake-c₁ tephra (Ko-c₁; 1856), Komagatake-c₂ tephra (Koc₂; 1694), Komagatake-d tephra (Ko-d; 1640), Tarumai-a tephra (Ta-a; 1739), and others (遠藤 et al., 1989; 徳井, 1989; 隅田, 1990). A fine ash-fall bed known as the Yausubetsu Bed, identified as Tarumai-c tephra (Ta-c) by 徳井 (1988), occurs in the upper portion of the upper peat bed, while the Mashu-d pumice bed (Ma-d) occurs in its middle portion. The lower peat bed can be confirmed to extend to at least 1m below sea level and yields ¹⁴C ages of 12–14ka. The terminal Last Glacial Barasan Lower Peat Bed yields fossil pollen of Larix, Pinus, Betula, Alnus, Ericales, and other taxa. Larix is particularly abundant, accounting for 40–80%. Abundant plant macrofossils, including leaves and seeds, indicate that subarctic forest dominated by Guimatsu larch, Larix kamtschatic (Rupr.) Carr., existed together with wetlands (遠藤 et al., 1988). Subarctic coniferous forest dominated by this larch, now distributed in Sakhalin, extended from Hokkaido to northern Honshu during the Last Glacial (小野・五十嵐, 1991).

References: 遠藤 et al. (1988, 1989); 北海道火山灰命名委員会 (1972, 1979); 小野・五十嵐 (1991); 隅田 (1990); 徳井 (1988, 1989).

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English translation of figure lettering

Map: 1:25,000 ‘Tokotan’ (Shibetsu sheets 12-3 and 16-1); Honbetsukai (本別海); 茨 [partial place label]; 8.5. Section: 0m, 1; Ko-c1, Ko-c2, Ta-a; Yausubetsu ash; Ma-d; Ma-g–j; Ma-l; Kpfl-I. Column: m, 0, 1, 2, 3; Ko-c1, Ta-a; Ko-c2; Yausubetsu; 2420±110; Ma-d; 6200±220; Ma-g; Ma-h; Ma-i; Ma-j; Ma-l; 11960±250; 12790±290; 14270±400; Upper Barasan Peat Layer; Lower Barasan Peat Layer.

Original Japanese lettering

地図：2.5万分の1『床丹』（標津12号-3，16号-1）；本別海；茨；8.5．断面図：0m，1；Ko-c1，Ko-c2，Ta-a；Yausubetsu ash；Ma-d；Ma-g～j；Ma-l；Kpfl-I．柱状図：m，0，1，2，3；Ko-c1，Ta-a；Ko-c2；Yausubetsu；2420±110；Ma-d；6200±220；Ma-g；Ma-h；Ma-i；Ma-j；Ma-l；11960±250；12790±290；14270±400；Upper Barasan Peat Layer；Lower Barasan Peat Layer．

Reading notes

地図の微小文字には判読不明箇所がある。

Kutcharo pyroclastic-flow deposits and peat beds and tephra filling an incised valley on the Barasan coast.

HK-10 Tephra of the last 1000 years in a peatland—Biruwa, Kutcharo caldera

町田 洋

• Locality: Biruwa-genya, Teshikaga Town, Hokkaido
• Latitude and longitude: N43°32′8″ E144°25′9″
• Elevation: 115m
• Outcrop type and condition: Wall of a roadside ditch; extant
• Deposit types and age: Peat beds, volcanic ash, and pumice; Holocene, last 1000 years
• Date of description: June 1994
• Keywords: Tarumai-a tephra; Oshima-Komagatake-c₂ tephra; Mashu-b tephra; Baitoushan–Tomakomai (白頭山苫小牧) tephra; Mashu pyroclastic-flow deposit; Atosanupuri pyroclastic-flow deposit; Kutcharo caldera

Several thin ash beds transported from distant volcanoes are intercalated in the peatlands of eastern Hokkaido. Such tephras can also be observed in peatlands within Kutcharo caldera. At this exposure, removing part of the vegetation reveals four tephra beds in the surficial peat bed (Fig. 2). In descending order, these are Tarumai-a tephra (Ta-a), Oshima-Komagatake-c₂ tephra (Ko-c₂), Mashu-b tephra (Ma-b), and Baitoushan–Tomakomai tephra (B-Tm). Ta-a and Ko-c₂ lie very close together and were formerly called Meakan-a or Mashu-a. Based on major-element characteristics of volcanic glass, 徳井 (1989) succeeded in distinguishing and identifying these two beds. They are considered to be eruptive products of 1739 and 1694, respectively. Ma-b is an inversely graded pumice bed erupted from Kamuinupuri, the central cone of Mashu caldera. The ash bed several millimetres thick, lying several centimetres below it, has an alkaline composition and is B-Tm. As B-Tm erupted in the tenth century, Ma-b must have erupted in the tenth century or somewhat later.

A large outcrop occurs 3km north-northwest of this locality (the ■ site in Fig. 1), where Ta-a, Ko-c₂, and Ma-b can be recognized in the black humic surface soil. The pyroclastic-flow deposit known as Mashu-f (Ma-f), associated with formation of Mashu caldera, and the Atosanupuri pyroclastic-flow deposit (Ats fl) can also be observed there (Fig. 3).

References: 町田 et al. (1994); 徳井 (1989).

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English translation of figure lettering

1:50,000 ‘Kutcharoko’ (Shari sheet 11); Ishikaribetsu (石狩別); Biruwa; Biruwa-genya; Senmo Main Line; Kushiro River; 140, 126, 124.9, 121.9, 125.2, 120; ■; arrow.

Original Japanese lettering

5万分の1『屈斜路湖』（斜里11号）；石狩別；美留和；びるわ；美留和原野；釧網本線；釧路川；140，126，124.9，121.9，125.2，120；■；矢印．

Reading notes

一部の地図内微小文字は判読不明。

Show extracted lettering and translation

English translation of figure lettering

Ta-a; Ko-c₂; Ma-b; ←B-Tm. The scale ticks on the left have no numerical labels.

Original Japanese lettering

Ta-a；Ko-c₂；Ma-b；←B-Tm．左側の目盛に数値表記なし．

Fig. 2. Tephra in the Biruwa peatland.

Show extracted lettering and translation

English translation of figure lettering

0; 5m; Ta-a, Ko-c₂; Ma-b; Ma-f (pfl); Ma-k; Ats fl.

Original Japanese lettering

0；5m；Ta-a，Ko-c₂；Ma-b；Ma-f (pfl)；Ma-k；Ats fl．

Fig. 3. Outcrop at the ■ site.