The occurrence of warm-water planktonic foraminifera, the δ¹⁸O of both benthic and planktonic foraminifera, and the total organic carbon content were measured for a sediment core (KH94-3, LM-8) collected from the continental slope off Sanriku area, on the east coast of Japan. The occurrence of warm-water planktonic foraminifera increased during the interglacial periods of the oxygen isotopic substage 5₁ and stage 1 and decreased during the glacial periods from the oxygen isotopic stage 4 to stage 2. This indicates that the core site was affected by the warm-water mass derived from the Kuroshio Current during the oxygen isotopic substage 5₁ and stage 1. The δ¹⁸O curve of benthic foraminifera shows a very similar pattern to the standard δ¹⁸O curve, but the δ¹⁸O curves of planktonic foraminifera are quite different from the standard curve. This suggests that the surface water condition at the core site has been changing over the last 90, 000 years. The total organic carbon content increased during oxygen isotopic stages 5₁, 2, and 1, suggesting possible increases in surface productivity during these periods. Based on comparison of the paleotemperatures calculated from the oxygen isotopic values in three piston cores which were retrieved off the east coast of Japan, it is suggested that the surface temperatures off Kashimanada and Sanriku decreased by 7.6°C and 4.4°C, respectively, during the last glacial maximum (LGM). Such large temperature drops are believed to be caused by the southward migration of the mixed water mass and the Oyashio Current into these area during the LGM.

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The Boso Peninsula of South Kanto, central Japan, is a seismotectonically active region which has experienced two historical large earthquakes, the 1703 Genroku earthquake (M=8.2) and the 1923 Kanto earthquake (Taisho earthquake; M=7.9), due to the complex convergence of three plates: the Pacific, North American, and Philippine Sea plates.
The Hota lowland in the southern part of the Boso Peninsula developed Holocene marine terraces which are classified into four levels, here named Hota I, Hota II, Hota III, and Hota IV terraces. The Hota IV terrace has been considered to have been created by crustal uplift that accompanied the 1703 Genroku earthquake. However, the ¹⁴C age of peat (830yrs BP) and historical remains indicate that the Hota IV terrace emerged before 1703. Further, historical documents and old maps showing the coastline between before and after Genroku earthquake show that the Hota lowland was subsided at the time of the 1703 seismic event. The amount of subsidence was inferred to be about 0-0.9m on the basis of geomorphic data.
Hota I and Hota II terraces were formed before 4, 350yrs BP, and Hota III was formed before 2, 200yrs BP, as dated by ¹⁴C ages from peat and tree roots. These terraces are not correlated to a series of Numa terraces in the southernmost part of the Peninsula that were generated by Genroku-type earthquakes (Nakata et al., 1980). This fact indicates that the Hota lowland has subsided whenever Genroku-type earthquakes occurred. Therefore, it is considered that a series of Hota terraces have been formed by crustal uplift accompanying Taisho-type earthquakes. The mean recurrence time of Taisho-type earthquakes is deduced to be less than 670 years based on the height of the former shoreline of Hota I (14m asl.).

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Middle and Upper Pleistocene deposits successively crop out at a sea cliff near Anden at the northern coast of the Oga Peninsula, Akita Prefecture, Northeast Japan. The deposits have been historically classified into the Shibikawa, Anden, and Katanishi formations in ascending order. The type localities of the Shibikawa and Anden formations are located in this sea cliff, and that of the Katanishi formation is placed in the Katanishi area, in the easternmost part of the Peninsula. The aim of this report is to stratigraphically re-examine these formations.
The Katanishi formation is subdivided into the following four members: the Tarusawa Sand, Kakumazaki Mud, Matsukizawa Sand and Gravel, and Honnai Sand. The Kakumazaki Mud member conformably overlies the Tarusawa Sand member, the lowermost of the formation, and interfingers with the Matsukizawa Sand and Gravel member. The Honnai Sand member lies upon the Matsukizawa Sand and Gravel member with conformity.
Recently, volcanic ash intercalated both in the Anden formation and in the Kakumazaki Mud member was identified as Toya ash, which erupted from the Toya Caldera, Hokkaido, and which is one of the prominent marker tephras in Japan. Consequently the Anden formation is regarded as a part of the Katanishi type formation tephrostratigraphically. Furthermore, faunal, floral, and lithological evidence shows that the Anden formation consists of offshore deposits correlatable with the Kakumazaki Mud and Matsukizawa Sand and Gravel members of the Katanishi type formation. Thus, the Anden formation is here called the Anden Sand member of the Katanishi formation.
The lower boundary of the Katanishi formation coincides with the basal unconformity of the Anden facies at Anden, where submarine sedimentation continues over the emergence horizon in the type area of the formation. The Tarusawa Sand member yields pollen and cold water molluscan fossils. The pollen assemblage of the member is characterized by dominance of coniferous tree pollen, which resembles that of the uppermost Shibikawa formation. These facts indicate that the definition of the upper and lower boundaries of the Katanishi formation is still questionable.

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Sandy and/or gravelly reworked deposits are intercalated in the Holocene bay-floor muds around the southern Kanto region of central Japan. These deposits consist of poorty sorted muddy sand and sandy gravel beds in increasingly fine upward sequences, with abundant transported shells and rip-up clasts, unconformably covering bioturbated bay-floor muds yielding in situ and indigenous molluscs.
These deposits are observed in six drilling cores at three alluvial plains and can be combined into seven isochronal layers, denoted T1 to T7 in ascending order, based on 79 radiocarbon ages of shell and wood samples dated by AMS.
Molluscan and ostracode assemblages in normal sediments above and below layers T3 to T7 indicate that the depositional environment was a muddy floor which occupied the central part of the bay at a depth of 10-20m. However, layers T3 to T7 include molluscs which inhabited the rocky coast or shore platforms, mixed with muddy bay-floor assemblages. Molluscan shells in these layers have reversed radiocarbon ages with respect to the underlying muds.
Layers T1 and T2 show sedimentary structures and fossil contents similar to the preceding anomalous deposits. In particular, they include ostracode assemblages indicating the invasion of open marine water into the brackish embayment.
The sedimentary facies, sedimentary structures, fossil assemblages, and radiocarbon ages of these layers indicate that submarine and coastal erosion and transportation of reworked sediments into the bay floor were accomplished by strong water currents.
Moreover, layers T3 to T7 show ages for that match the rapid emergence of five Holocene marine terraces in this region caused by great earthquakes centered around the Sagami Trough (trench) south of Kanto. The age agreements strongly suggest that the anomalous reworked layers are earthquake-induced tsunami deposits. The tsunamis occurred at intervals of 400 to 2, 000 years during the past 10, 000 years.

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[in Japanese]

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The Upper Pliocene Nakatsu Group along the Sagami River, in Sagamihara and Atsugi Cities and Aikawa Town in Kanagawa Prefecture, has been mainly studied by some palaeontologists as part of their research on molluscan fossils. The Nakatsu Group has been lithologically divided into the Kosawa, Kanzawa, Shimizu, Otsuka, and Shiota Formations in ascending order. The Otsuka and Shiota Formations intercalate many tephra layers; however, detailed stratigraphic study using these tephra layers has never been done. The Mk 19 tephra layer, interbedded in the Otsuka Formation, is composed of Ta, Tb type glass shards, plagioclase, quartz, garnet, amphibole, biotite, and opaque minerals. The garnet is an almandine-spessartine solid solution. The combination of Mk 19 and the Mk 20, abundant in quartz, is useful for correlation in this region.

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