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A Cenomanian/Turonian boundary succession in the northeastern Tethyan realm, Kopet-Dagh Basin in NE Iran, was studied to examine the effects of biological productivity, atmospheric CO2 concentration, and sea water temperature on the benthic foraminiferal assemblages. Our δ13Ccarb and δ13Corg chemostratigraphy of the Gharesu section reveals three positive peaks that can be correlated with carbon isotope peaks in the CTB reference sections (Eastbourne, England; Pont d'Issole, France; Rock Canyon, USA). Two intervals of suspected high sea surface temperature were distinguished according to pCO2 maxima (Δ13C; difference between δ13Ccarb and δ13Corg), low δ18O values, and high TOC bearing deposits. These intervals are followed by falling pCO2 and cooling caused by enhanced burial of organic matter into the sediments. Patterns of changes in the benthic foraminiferal assemblages are correlated with these climatic changes. Warm intervals are characterized by low diversity of benthic foraminifera, dominance of agglutinated forms, and high abundance of infaunal morphogroups or opportunistic epifauna due to intensified weathering, high primary productivity, and oxygen deficiency in the bottom water. The cold intervals coincide with higher diversity of benthic foraminifera and dominance of calcareous benthic taxa.

In this study, quantitative climate information for central Japan for the past 158 ka is reconstructed on the basis of pollen composition data of NJ88 core from Lake Nojiri and those of TKN-2004 core from the lacustrine Takano Formation using a modern analogue technique. Reconstructed values at the sites around 36.6°N and 700 m altitude are as follows. In marine isotope stage (MIS) 6, the average annual mean temperature was about 2.1 °C, with a coldest month temperature of −11.8 °C, which suggest very cold climate conditions. The climates of MIS 4 and 2 were similarly cold, and the precipitation was low with ∼1050 mm for mean annual precipitations during these cold periods. In contrast, the annual mean temperatures of MIS 5e and MIS 1, among the warmest periods, averaged about 5.5 °C and 9.1 °C, respectively. The annual mean temperature of MIS 5e was significantly lower than that of the Holocene. We estimate that an intensely cold winter controlled the vegetation, which resulted in the lower temperature reconstruction for MIS 5e. The annual mean temperatures of intermediately warm periods such as MIS 5c and 5a were a slightly high, with averages of 4.4 °C and 5.1 °C, respectively. Annual precipitations increased up to ∼1400 mm on average in these warmer periods. Annual mean temperatures of MIS 5d and 5b were low with averages of about 3.0 °C. Annual mean temperatures reconstructed for MIS 3 fluctuated over short periodicities that correspond to Dansgaard–Oeschger cycles. For example, the annual mean temperature of the interstadial GI-8 (Greenland Interstadial 8), 38–39 cal ka BP (calendar ka before 1950 CE) was about 4.0 °C, and that of the stadial HE 4 (Heinrich event 4) in 42–43 cal ka BP was about 2.6 °C. From 14 to 12 cal ka BP, annual mean temperature increased significantly in a relatively short period, from 1.3 to 9.5 °C, and annual precipitation also increased from 1040 to 1380 mm. A cool event corresponding to the Younger Dryas was identified in this deglaciation process, but its intensity was much weaker than that in the North Atlantic region. The climate in the Holocene (MIS 1) was warm, with an average annual mean temperature of 9.0 °C with wide variation, by a maximum of about 2 °C, which suggests temporal change of the Arctic polar front situated in mid-latitude regions.

In order to evaluate Oceanic Anoxic Event 2 (OAE2) at the Cenomanian-Turonian boundary and its effects on benthic foraminifera, the Taherabad stratigraphic section in the east of Kopet-Dagh basin was studied for pattern of changes in benthic foraminiferal communities. Total Organic Carbon (TOC) concentration at the Taherabad section shows that black shale was not deposited in this succession but TOC increases up to 0.68 wt% in the three intervals of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. Also, Total Nitrogen (TN) values were measured in our study succession. High TOC/TN ratios (up to 18) occur in the intervals of TOC enrichment. Foraminiferal assemblages, TOC, TOC/TN and Detrital Index (DI, an index for detrital input) changes in the study section allowed us to divided study section into 4 intervals. Interval A and C are associated with low abundance and diversity of benthic assemblages coeval with lack of planktic foraminifera. Benthic assemblages are strongly dominated by shallow and deep infaunal agglutinated foraminifera including Lagenammina , Saccammina , Reophax and Tritaxia . The foraminiferal composition associated with higher TOC, TOC/TN and DI suggest an influx of fresh water to the basin in the warm-wet periods, which diminished hospitable conditions for planktic foraminifera and probably enhanced land-derived organic matter and/or primary productivity. The hyposaline cap led to development of salinity-stratified water and induce bottom water oxygen depletion. By contrast, the assemblages found in the interval B and D are more diverse and contain high abundance of planktic and calcareous benthic foraminifera. Common benthic taxa in these parts are praebuliminids, lenticulinids, gavelinellids and Valvulineria . These assemblages associated with lower TOC, TOC/TN and DI indicate decreased detrital input and more normal marine condition resulted in improved ventilation of sea-floor, which is favorable for planktic and benthic taxa.

We examined the vertical distributions of total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), and 21 polycyclic aromatic hydrocarbons (PAHs) in a 100-cm-long sediment core collected from Lake Kitaura, a small and shallow eutrophic freshwater lake in central Japan, to elucidate changes in its aquatic environment and the input of PAHs with respect to human activity over the last 1000 years. Using a cross-plot of TOC and TS, the aquatic environment of this lake was well classified into four stages: a marine–brackish water period (≤1321 AD), a brackish–freshwater period (1394–1646 AD), a freshwater period (1726–1958 AD), and a eutrophication period (≥1971 AD). During the current eutrophication period, both TOC and TN have increased dramatically and TOC/TN (which is a useful indicator for distinguishing between aquatic and terrestrial plant sources) has decreased because algal production has markedly increased recently due to eutrophication. The vertical distributions of PAHs (which have derived primarily from combustion over the last 1000 years) showed increases in layers corresponding to periods of volcanic activity in the 18th century, as well as dramatic increases from 1971 to the present. Thus, both the aquatic environment and the input of PAHs in Lake Kitaura have been strongly affected by recent human activity. On the other hand, among all of the PAHs, only perylene—which is known to be of biological origin—was consistently formed via first-order kinetics over the period covered by the core. Its formation was barely influenced by fluctuations in the input of the precursor of perylene or how reductive the environment in the bottom water was.

Total organic carbon (TOC) and total nitrogen (TN) concentrations are analyzed with high temporal resolution (ca. 100 years) for cores MD179-3304 and MD179-3312 taken from the Japan Sea off Joetsu City. The temporal changes in TOC and TN concentrations vary quasi-regularly in similar patterns. The age models are formed on the basis of the dates of 14C dating, marker tephra beds, TL layers, and marine isotope events with depth. TOC concentration is high in MIS 1 and 5, low in MIS 2 and 4, and slightly elevated in MIS 3 with frequent short fluctuations. This general trend is very similar to LR04 curve, except for the reduced dominance of TOC around the MIS 5.5 substage. As shown typically in MIS 3, there are many peaks of TOC in a short interval. The details of these TOC peaks can be correlated with the warm interstadials of the Greenland ice core. We can identify a sawtooth-like decreasing trend of TOC in MIS 3. In contrast, the decreasing trend of δ18O in the ice core corresponds to an increasing trend of TOC in MIS 5. The most plausible explanation for the correlation of climate changes between East Asia and the North Atlantic is oscillation of the Arctic polar front through time. The detailed correspondence of TOC concentrations of the Japan Sea sediments to other common paleoclimate proxies means that the TOC concentrations of these sediments is an excellent paleoclimate record in Far East Asia, although the genetic relationship between air temperature and biological productivity in the Japan Sea is as yet unknown.

Total organic carbon (TOC) and total nitrogen (TN) analyses have been performed for three core samples obtained recently from Lake Biwa, which include BIW07-5, BIW07-6, and BIW08-B cores. The TOC and TN data from these cores show similar stratigraphic changes and can be regarded as reliable records of biological productivity occurring in the lake during the past 52 ka. Pollen analysis data are also used to determine climate change during the past 40 ka by reconstructing meteorological parameters such as annual temperature and precipitation. Temporal changes in TOC concentration show detailed climate changes in tens-year intervals. Climate change of orbital scale are well recognized, demonstrating the change from MIS 3 to 1 associated with severe cold periods known as Heinrich events 1 to 5 and warm periods known as Greenland interstadials (GIS 1–13). These climate events in millennial time scale are also well supported by pollen characteristics and by modern analogue analysis. The good concordance of climate change between North Atlantic region and Japan is explained by a hypothesis that the intensity of the Arctic air mass controls the climate in both the North Atlantic and East Asia regions through the migration of the Arctic polar front. Although the average annual mean temperature in MIS 3 was 8.2 ± 0.8 (2σ) °C, it varied largely and frequently among its substages. For example, 9.4 ± 2.0 °C was detected in a warm interstadial (GIS 8), and 6.3 ± 1.5 °C indicated in a cold stadial (Heinrich event 4). The average annual temperature was 4.5 ± 0.3 °C in MIS 2, when the average temperature of the coldest month was −7.3 ± 0.2 °C and that of the warmest month was 16.8 ± 0.2 °C. Through Termination 1, the annual mean temperature suddenly increased more than 5 °C, and the annual mean temperature became 11.2 ± 0.8 °C in early MIS 1, which is much lower than that of the present temperature. This low temperature estimation is attributed to the delay in expansion of evergreen broadleaf trees. The annual mean temperature in the late MIS 1 was as same as that of present meteorological observation.

The pattern of latest Pleistocene climate changes reconstructed on the basis of sediment cores from Lake Nojiri is one of the most detailed and reliable reconstructions in Japan. The climate changes over the last 72 ka can be compared directly with those recorded at Upper Paleolithic and Incipient Jomon sites on the basis of a revised age model for the Lake Nojiri sediment cores and the revised 14C dates, calibrated after IntCal09. Fossil bones of megafauna from the Tategahana site beside the lake have been placed ca. 53–37 ka cal BP, in the relatively warm, temperate climate of the early MIS 3. Part of the Tategahana site was interpreted as a kill and butchery site, although the presence of the “big game hunters” is still uncertain, as so far there is no reliable archaeological evidence in the Japanese archipelago dating back to the Middle Paleolithic. The number of Paleolithic sites increased suddenly after 38 ka cal BP around Lake Nojiri. This seems to coincide with the timing of the migration of Homo sapiens into the Japanese archipelago. The climate had been gradually cooling toward the Last Glacial Maximum (LGM). However, the area around Lake Nojiri in the late MIS 3 seems to have been a suitable place for the subsistence of hunter-gatherers. Backed blade industries (ca. 29–20 ka cal BP), point-tool industries (ca. 22–19 ka cal BP), and microblade industries (20–16 ka cal BP) were characteristic of the Late Upper Paleolithic. The number of sites around Lake Nojiri decreased significantly during the LGM. At the end of the LGM, an abrupt change of vegetation, from subarctic conifer forest to deciduous broadleaf forest, had occurred around 14 ka, and human activities became prominent around Lake Nojiri, as shown by the linear-relief pottery group (ca. 15–13 ka cal BP). The number of sites seems to have decreased slightly during the Younger Dyras cooling event. Patterns of human occupation around Lake Nojiri show the influence of global and local climate changes.

No pre-1977 quantitative data exist that describe phytoplankton biomass in the water column of Lake Suwa, a Japanese eutrophic lake, although several studies have been conducted since. To assess recent environmental changes with time in the lake, phytoplankton composition was determined from analysis of photosynthetic pigments in the sediment core. Specifically, the total chlorophyll a (TCh-a) concentration in the water column before 1977 was estimated for comparison with that of the water column and sediment deposited since 1977. The depth profile of zeaxanthin, a potential indicator of cyanobacteria activity, substantially increased from 1960 to 1973 (from 9.53 to 76.7 nmol g−1). Additionally, the concentration of fucoxanthin, diadinoxanthin and diatoxanthin, originating from diatoms and dinoflagellates, increased slightly during this period (from 1.64 to 4.90, 1.86 to 3.54, and 4.00 to 3.26 nmol g−1). Cyanobacteria have been the major algal species in the lake since 1949; however, the ratio of fucoxanthin versus total algal carotenoids has gradually increased since 1981 indicating diatoms have increased relative to cyanobacteria since 1979, and that organic matter inflow and nutrient concentrations have resulted in changes in the phytoplankton composition. Since 1977, the chlorophyll a concentration in water in the lake had a very similar pattern as the TCh-a concentration in the sediment. The concentration in the water column also corresponds to those in the sediment even before 1977. These results indicate that it might be possible to predict the phytoplankton biomass of the water column based on the TCh-a in the water and sediment in this lake.

High-resolution pollen records from Taiwan, Japan and Sakhalin document regional vegetation changes during Dansgaard-Oeschger (D-O) cycles during the last glacial. During the period from the cold phase (GS 18/19) to warm phase (D-O 19), the biome shift from temperate conifer forest to cold/cool conifer forest in Japan and from subtropical forest to temperate deciduous/conifer forest in Taiwan. The vegetation in D-O 17, cool mixed forest in central Japan, temperate deciduous broadleaf forest in western Japan and subtropical forest in Taiwan, indicates warm condition but not wet in all area. These vegetation changes lead to biome shift from MIS (Marine Isotope Stage) 4 to MIS 3. The abundance of Cryptomeria japonica and Fagus crenata in D-O 12 and D-O 8 indicates wet conditions brought by the strong summer monsoon through the Islands and high snowfall brought by the inflow of the Tsushima Warm Current into the Sea of Japan. The registration of other D-O warming events in MIS 3, although reflected by shifts in the abundance of key species, is not sufficient to produce changes in biomes. Development of cold deciduous forest in HS (Heinrich events) 1 in Sakhalin, Hokkaido and central Japan was conspicuous and was much larger than that in YD. Vegetation response in YD was small scale and within the same biome in the East Asian Islands. In D-O 1 at the termination of the last glacial, the same taxa that developed in the early Holocene, cold evergreen needleleaf trees in northern region, temperate deciduous broadleaf trees in central and western Japan, and warm-temperate evergreen trees in Taiwan, increased.

長野市信更町に分布する高野層のボーリングコア（TKN-2004）について，14～4万年前までの化学組成に基づく珪藻生産量の変動を検討した．高野層のSiO2/Al2O3比は，生物源シリカ量と相関を持つので，珪藻生産量の指標となる．珪藻生産量と花粉に基づく環境指標を比較した結果，珪藻生産量はおもに気温に支配された可能性が高い．珪藻生産は，深水層の栄養塩が有光層まで回帰する時に高まることから，気温が表層水温を規制し，湖沼の循環機構に影響を及ぼしたと考えられる．スペクトル解析では2万年周期が検出されるので，この現象は歳差運動に支配されているといえる．しかし，気温上昇よりも珪藻生産の増加が遅れる時期がある．これは気温上昇により形成される土壌起源の栄養塩が，湖内に蓄積する時間を反映する可能性がある．土壌起源の栄養塩を運搬するのは河川なので，土壌形成を促す気温のみならず，降水量も影響しているのであろう．しかし，高野盆地のような閉鎖的で集水域の小さな場所にできた湖沼では，降水量の影響よりも気温に影響を受けることが指摘できる．

In Al Qasim Province, Saudi Arabia, calcareous pedogenic duricrust overlies the Upper Permian carbonates and clays of the Khuff Formation, and ranges in thickness from 60 cm to 2 m. It consists of white sandy duricrust capped by brown, nodular porous duricrust. Petrographic investigation led to recognition of three lithofacies that show spatial distribution: 1- structureless sandy calcareous mudstone, 2- brecciated-nodular calcareous mudstone, and 3- pisolitic calcareous mudstone. The diagenetic changes in duricrust are aggrading neomorphism and formation of calcite rims around quartz grains. Microprobe chemical analysis was performed on the diagenetically altered material. The development of the duricrust is controlled by four factors: the climate changes, the type of underlying rocks, source of carbonate and biological effects. The repeated changes from semi-arid climate with alternating wet and dry seasons are the main controlling factor, in generation of duricrust development. During humid periods, descending water carries the dissolved carbonates downward as bicarbonates, whereas dry and interpluvial period, the carbonate-rich solutions are carried upwards by capillary or evaporation. The claystone and sandstone interbeds possibly affect the development of calcareous duricrust, more than the sandstones and dolostones, because the former have the ability to attach calcium carbonate to form the duricrust. The development of calcareous duricrust is mainly attributed to the Pleistocene and Early Holocene alternating humid and arid periods that prevailed over the Arabian Peninsula during this time.

This paper presents a study of the usefulness of flood layers as a time marker in sediments and a report of a case study of Lake Kizaki in central Japan. A flood layer can be identified as a layer having a higher density, coarser grain size, lower TN content, and higher C/N ratio than those of the upper and lower horizons. It can also be characterized by a hyperpycnal sequence composed of a basal coarsening-upward unit and a top fining-upward unit. When flood layers can be correlated with heavy rains in meteorological records, detailed age markers are well established in the sediment. Five flood layers were identified in the surface sediment of Lake Kizaki, and they could be attributed to the historical heavy rainfalls that took place on July 12, 1995; September 28, 1983; August 25, 1974; September 26, 1959; and September 1, 1949 under the constraint of an age model. A precise age model is essential to clarify the environmental changes such as the pollutant history in detail.

野尻湖底堆積物および後期更新世高野層のTOC含有率を指標として，過去16万年間の中部山岳地域における気候変動の復元を試みた．まず，TOC含有率の増減が花粉組成の示す寒暖変動で裏付けられており，気候変動の指標として有効であることをそれぞれで確認した．次に，それぞれで標準化したTOC変動曲線を広域テフラDKPを鍵としてつなぎ合わせて，過去16万年間の詳細な変動を復元した．TOCの経年変動は，グリーンランドの氷床が記録する気候変動に匹敵する時間分解能を持ち，その大局的な変動は，海洋酸素同位体比曲線とも対応しており，汎世界的な気候変動を反映している．それを基に陸域の指標テフラを気候編年上に位置づけることができた．解明された詳細な気候変動と指標テフラの枠組みは，列島内の各地の気候変動の対比のみならず，堆積盆の形成や埋積過程，海水準変動の影響などを高精度で解析する上で重要な土台を提供する．

更新世後期の最終間氷期を中心に，日本列島陸域および周辺海域の古気候・古環境変動について研究の現状を紹介し，今後の課題を提起した．海洋域では海底コアの多面的な解析が，海洋環境と古気候変動の解明に大きく貢献している．陸域の研究では，長期間に及ぶ連続堆積物を用いた花粉分析や珪藻分析，有機炭素分析によって高精度の古気候復元が試みられている．海域と陸域を繋ぐ鍵として広域テフラの有用性は高く，琵琶湖堆積物や高野層に挟まれた指標テフラは古気候を時間・空間的に結合させて復元する鍵となる．特に指標テフラ密度の高い9～10万年前の日本列島とその周辺は，有望な研究対象である．このように，テフラを介して海域と陸域の古気候・古環境情報を比較・統合して，高時間分解能で総合的な古気候復元を行うことは，日本列島の地域性を明らかにするとともに，汎世界的な気候変動のシステムを理解する上でも必要な貢献となる．

The Takano Formation of late Pleistocene lacustrine sediment is distributed at the southern Nagano City. The TKN-2004 core, 53.88 m long, was taken at the central part of the basin, and is composed mostly of homogenous clayey silt. Age of the sediment was estimated from the relationship between radiometric ages and calibrated depths of DKP, Aso-4, K-Tz, Ata and Aso-2 tephras, postulating that the sedimentation rate is constant.Paleoclimate from 169 ka to 37 ka was reconstructed on the basis of TOC content variation. The long-term TOC fluctuations are concordant with the SPECMAP curve. This result is supported by pollen composition. The short-term variations are similar to stadial-interstadial cycles in the Greenland ice cores, and most of warm peaks can be correlated with IS 9 to 25.

Article, Enviromental Pollution. 138(3): 529-537 (2005)

Article, The Journal of the Geological Society of Japan. 110(1): 1-10 (2004)

1988年に野尻湖湖底から採取されたオールコア試料の上部について,30～50年間隔の精度で有機炭素(TOC)・全窒素(TN)の測定と花粉分析を行った.4点の14C年代測定,鬼界アカホヤ(K-Ah)および姶良Tn(AT)の指標火山灰年代に基づいて推定した堆積年代と,TOC・TNおよび花粉の分析結果に基づくと,遅くとも14C年代で1.4～1.5万年前より前には落葉広葉樹花粉の増加で示されるような温暖化が始まり,以後,「寒の戻り」を伴いながら約1万年前まで温暖化が進行した.約1.3万年(較正年代1.5万年前)前後には,「寒の戻り」を示す亜寒帯針葉樹花粉の明瞭な増加が認められる.約1,2万年前(較正年代1.4万年前)には,広葉樹花粉の急増と針葉樹花粉の激減があり,同時に全有機炭素・窒素量の激増も認められ,短期間のうちに急激に温暖化が進行したと推定される.なお,14C年代で約1.45万年前にも微弱な広葉樹花粉の減少が認められる.これらの気候変動のパターンは,北大西洋地域の気候イベント(新旧ドリアス期など)とよく似ているが,本稿における編年に基づけば,北大西洋地域よりもそれぞれ2,000～3,000年ほど古いようにみえる.較正年代で約1.3万年前と9千年前においても,軽微な気候変動が認められ,そのうちの後者はボレアル期に対比できる.

ln order to understand the climate ｖariability of the Holocene period, two sediment cores were extracted at the northeastern part of Lake Aoki,an intermontane freshwater body located near the northern Japanese Alps, Central Japan. The sediments are mainly composed of silty clay with some interealation of event sediments, including a tephra known as the Kikai-Akahoya (K-Ah) that dates 7,250cal BP. The sediment chronology yields the sedimentation rate of ca. 0.16 and 0.37 mm yr⁻¹ above and below the tephra, respectively. The sediments were investigated at 0.5cm interval, providing a time resolution of 13-29 years, for total organic carbon (TOC) and total nitrogen (TN) contents. The record of the organic contents along with the diatom abundance at 50 horizons is used as limnological monitors and climate proxies. The diatom record suggests that the lake has been oligotrophic and alkaline. TOC content and diatom abundance yield close correspondence with both short- and long-term fluctuations, shifting between low-and high-values. Climate, which control surface-water temperature, appears to be the main factor to affect the variability in the proxy records in Lake Aoki. The climate is dynamic, abruptly switching from various degrees of cool to warm Conditions in centennial to millennial scale. Warm conditions prevail from ca. 750-1300, 1750-3050, 4000-5250, 6150-7250, and 8800-10000calBP, and cooling occurs during 150-750, 1300-1750, 3050-4000, 5250-6150, and 8350-8800cal BP. The period between 7250-8350cal BP is rather Auctuating.Climatic events such as the Little Ice Age (LIA), the Medieval Warm Period (MWP), the Kofun cold stage, and the Holocene Optimum (HOP) are evident, and some other warm and cool events not well recorded before in Japan and abroad are also recognized. The lake also provides a valuable window into the recent climate change and the modern hydraulic changes in the lake system., 青木湖は北アルプスの山麓,標高822mにある貧栄養湖である.表層堆積物の粒度分布を検討し, 1954年以降の電源開発のための人為的水利用が堆積物の性質と堆積速度に大きな影響を与えていることを明らかにした.青木湖の北東部から採取した2.2m長のコア試料は,おもに粘土質シルトから構成されており,年代的には約1万年間をカバーしていた.この柱状試料中の有機炭素･窒素含有率と珪藻殻含有数の増減はよく一致しており,湖の生物生産性の増減が有機炭素･窒素含有率の増減に反映している. 1954年以前の青木湖の生物生産性は,気温と連動した水温の変化に支配されていた可能性が高いので,有機炭素含有率の時代的変遷を基にして完新世の気候変動を復元することができた.完新世にはそれぞれ5つの温暖･冷涼期と1つの変動期が認められた.それらの多くは,小氷期,中世温暖期,完新世最温暖期などの汎世界的な寒暖変動とはぼ一致する., climatic variability, Holocene Optimum, Article, 地質学雑誌 108(4): 249-265(2002)

Limnological features and sediment characteristics were studied in Lake Nakatsuna, a mesotrophic lake in central Japan. The lake is dimictic, and is anoxic in the hypolimnion during thermal stratification from May to September. In an attempt to reconstruct paleoclimatic changes around the lake, a sediment core taken from the lake center spanning the past 1300 years was analyzed for its organic and inorganic contents. Climatic influences were examined on the variation of total organic carbon (TOC), total nitrogen (TN), and sand contents. Short- and long-term fluctuations in TOC, TN, and sand contents are evident, and variation in atmospheric temperature appears to be important for their long-term variability. The sediment record from AD 900 to 1200 indicates hot summers and warm winters with less snow accumulation, whereas the record from AD 1200 to 1950 is characterized by high variation of temperature, with three cool phases from AD 1300 to 1470, 1700 to 1760, and 1850 to 1950. The warm period from AD 900 to 1200 corresponds well to the Medieval Warm Period, and the second and third cool phases are related to the Little Ice Age.

Seismo-turbidite layers are deposited at the foot of the steep slope of the half graben in which Lake Biwa has accumulated. Sedimentary studies, especially of grain-size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo-turbidites. Development of the two constituent sublayers (lower sandy sublayer and upper silt sublayer), lack or limited appearances of traction-indicating structures and characteristic grain-size distribution in the two constituent sublayers are most remarkable and significant. The characteristic grain-size distribution features are coarse tail grading in a relatively thick sandy sublayer, exceptionally rapid distribution grading through the thin boundary interval between the two sublayers, height increase and fluctuation of the silt mode, and high clay content. Brief discussion was made on the causes of these sedimentary features. The need and importance of further comparative studies of various turbidites known triggering forces are emphasized.

青木湖周辺には,後期更新世から完新世にかけての,おもに河成や湖成の堆積物が断片的に分布しており,下位より藪沢層,崩沢層,神城砂礫層,佐野坂崩壊堆積物,青木湖成段丘堆積物,青木湖底堆積物に分けられる.指標テフラと岩相対比によって,それらの相互関係を明らかにした.佐野坂崩壊堆積物の上位には,Dpm火山灰層がのるとされていたが,それを再堆積物と判断し,周辺の地史を次のように推定した.藪沢層は,比較的広い谷の中を南がら北へ流れる蛇行河川によって形成された.その時代は5万年前以前の寒冷な時期である.約5万年前,その河川は狭い谷の中を流れる網状河川に変化した.この堆積環境の変化は,DKP火山灰層を挾む崩沢層と神城砂礫層中部が礫を主体とすることにより示されている.約3万年前に,西方の仁科山地で大規模な地すべり崩壊が起こり,佐野坂丘陵が形成された.この崩壊堆積物は川をせき止め,丘陵の南側に深い湖(青木湖)を形成した.佐野坂丘陵の北側の凹地には支谷からの堆積物供給が多く,徐々に埋積されて,現在の神城盆地を形成するようになった.

Some 20 turbidites were collected in the uppermost 3 m of surface sediments in Lake Biwa, southwest Japan. These turbidites correlate in age to historical earthquakes that caused severe loss of lives and property near Lake Biwa. The age of each turbidite was estimated precisely, based on sedimentation rate (by weight) and the age of tephra markers below the turbidites. The magnitudes and epicentres of major historical earthquakes during the last 1300 years are available from historical documents. Empirical equations relating intensity, distance to the epicentre and magnitude enable us to calculate the ground shaking at Lake Biwa from these historical earthquakes. Earthquakes having intensity stronger than grade IV L on the Japan Meteorological Agency (JMA) earthquake scale, that is 44 gal acceleration at Lake Biwa, all coincide with the turbidite ages. This intensity is apparently the lower threshold for turbidity-current initiation in Lake Biwa.

Chert from the Shimanto Belt in Kii Peninsula, Southwest Japan is mostly red, bedded, radiolarian chert. These rocks are commonly associated with greenstone. Besides chert-greenstone, flysch units occur repeatedly in the area studied. Radiolarians date the chert as Early Cretaceous, older than the surrounding argillaceous rocks or flysch unit which are of Late Cretaceous age. Ages and field occurrences indicate a slump origin for chert and greenstone, presumably related to subduction. However, some of these rocks formed at the same sites where argillaceous units occur. Sedimentary structures in the bedded cherts suggest formation by transportation and accumulation of siliceous materials, mostly radiolarian tests, on or near a submarine volcanic seamount by low density currents something like a bottom nepheloid layer. the frequent inflow of volcanic materials is indicated by intercalated black tuffaceous partings.