This paper describes the Holocene stratigraphy and depositional environment at Kuninaka Plain on Sado Island, off Niigata, on the Japan Sea side of central Japan, using stratigraphy, ¹⁴C dates, and diatom analysis of cores, and it discusses the upper limit of Holocene marine deposits and paleogeographical changes during the Holocene. Kuninaka Plain is the largest plain on Sado Island, and is located between two active tilted blocks, Osado to the northwest and Kosado to the southeast. The northeast-trending Kuninaka-minami fault is an approximate boundary between the plain and the Kosado mountains. Kuninaka Plain is divided into two parts by the last interglacial marine terrace (T3): the northeastern part, facing Ryotsu Bay, includes Kamo Lake, filled with brackish water. The southwestern part is a large alluvial plain facing Mano Bay. Diatom analysis and facies observation of Holocene deposits at the southwestern part of the Kuninaka Plain indicate that the upper Holocene marine limit is 1 to 2m above sea level and that the emergence took place ca. 4, 000-5, 000yrs BP. Since that time, no transgression has occurred. In contrast, deposits of nearly the same age occur below the present sea level in the northwestern Ryotsu Bay area, suggesting the relative subsidence of that area, where minor transgressions and regressions have recurred since that time. This may not be caused eustatically, but rather may have originated from the opening and closing of the barrier. The marine limit is rather high, ca. 3-4m on the Holocene terrace along Ryotsu Bay. This is probably a result of the uplifting of the upthrown side of Kuninaka-minami fault. Holocene paleo-geographical changes are reconstructed for three stages.

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Kutcharo-Haboro tephra (Kc-Hb), Sinsei tephra (Sns: in this paper), and Azuma-4 tephra (Aafa4) are intercalated in the lower part of the fluvial-peaty sediments which were deposited succeeding the Last Interglacial (Oxygen Isotope Stage 5e) in the southern part of the Tokachi Plain. These three tephras are identified on the basis of petrographic properties such as mineral compositions and refractive indices of volcanic glass, orthopyroxene, and hornblende. The sea level was already at least 25m lower than that of the Last Interglacial maximum transgression when Aafa4, Sns, and Kc-Hb erupted. This stage probably coincided with Oxygen Isotope Stage 5d. The petrographic properties suggest that Sns was derived as a product of the Kutcharo caldera formation, prior to the eruption of Kc-Hb.
Toyoni tephra (Tyn, in this paper) is intercalated as a drift pumice in the marine terrace sediment of Oxygen Isotope Stage 7. Bansei tephra (Bns, in this paper) is intercalated in the lower part of the marine sediment of Oxygen Isotope Stage 9. Although the distribution and the source volcanoes of these two tephras are still unknown, they should be key tephras for examining some Quaternary geologic issues during Oxygen Isotope Stage 7 and 9.

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Loess samples from the 22-m-thick Shajinping section on the second-lowest terrace of the Yellow River in Lanzhou, Gansu Province, China, were dated by infrared stimulated luminescence (IRSL) and by thermoluminescence (TL).
Isothermal preheating tests for IRSL dating were made at two different temperatures, 120 and 160°C, to determine the preheating condition most appropriate for isolating the stable IRSL signal. The irradiated/non-irradiated IRSL ratio reaches a plateau after preheating for 24 to 144 hours at 120°C, or for 1.5 to 5 hours at 160°C. The IRSL signal with preheating at 120°C was enhanced by increasing the artificial gamma irradiation, but the IRSL signal with preheating at 160°C was saturated at a low dose, so it was difficult to use the dose-response curve to calculate an equivalent dose (D_E). The 120°C preheating was determined to be most appropriate; therefore, all samples were preheated at 120°C for 96 hours before IRSL measurement.
Except for one sample, the IRSL and TL dates for samples from the upper 12m of the section agreed with each other, within the error range, but the IRSL dates for samples from the lower 9m of the section were younger than the TL dates. This discrepancy between IRSL and TL dates might have been caused by underestimation of the IRSL dates, due to the samples' low saturation value of IRSL D_Es at about 200Gy. The IRSL and TL dates indicate that the loess deposition rate during the last 60ka has changed several times. A very high loess deposition rate was obtained for the late marine isotope stage (MIS) 3, whereas the deposition rate seems to have been lower during MIS 2.

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This study documents the nature of large-scale ridge-moving landslides around Aigawa, in the northern part of Nagano Prefecture, central Japan, to determine the history of the northern segment of the active fault system of the Itoigawa-Shizuoka Tectonic Line. Blocky fragments of the Omachi APm Tephra Beds deformed by landslide movement were observed in a small depression of a landslide mound underlain by the well-fractured Omine Welded Tuff, and overlain by the mantlebedding layer of the Tateyama-D Tephra. This stratigraphy and the eruption ages of these tephras indicate that the large-scale ridge-moving landslides occurred within the range 0.30-0.40 to 0.12Ma. The timing of the large-scale ridge-moving landslides suggests that the northern segment of the active fault system of the Itoigawa-Shizuoka Tectonic Line was tectonically active then, and this would account for the relative height of the fault scarp which generated the landslides.

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A new and TLCI (Thermoluminescence Color Image) and effective TLCI-CIA (Thermoluminescence Color Image-Color Image Analysis) method, using quartz grains to discriminate between eolian and volcanic ash deposits, is proposed in this paper. Experimental results indicate that the coloration of quartz particles can be basically divided into two typical color categories, red and blue, characterized by α-quartz in plutonic rock and β-quartz in ash, respectively.
The source of the clay layers which cover a vast surface of Japan's landforms has been extensively discussed by Quaternary geologists, who have disagreed about whether they come from volcanic materials of the Japan Islands or from loess deposits transported from the inland area of China. To contribute to the discussion, we have used the TLCI method and the TL color quantitative analytical method, which divided the quartz TL coloration into three basic colors (red, blue, and green) by the Nikon LS-1000 system, which is illustrated on the CIE chromaticity diagram.
Three typical kinds of samples were prepared for the TLCI-CIA experiments. The first group is from 8 standard eolian samples selected from the Japanese and Hawaiian Islands. The second and third groups are composed of 6 clay deposits and 8 volcanic ash layers which are distributed in northern Hokkaido. The TLCIs emitted by the first group of standard samples and the second group of clay deposits have been classified similarly into the three different colors 5PB, 10PB, and no-TLCI (dark color), belonging to the blue color region, on the basis of the international color manual (JIS Z 8721). Further, TLCI-CIA research has indicated that 5PB is plotted around 450-495nm and that 10PB is scattered widely in two regions, of 450-495nm and 570-600nm wavelength.
The TLCIs of the third group, tephra layers, has shown a clear 7.5R red color range in the two main grain sizes of 250-590μm or 125-250μm. TLCI-CIA investigations have also shown that the 7.5R grains emitted the wavelength of 570-620nm.
The preliminary TLCI investigation on the blue color region indicated that no-TLCI and 5PB quartz grains originated in different types of source rocks, such as sedimentary, metamorphic, and plutonic rocks.
The experimental conclusion indicates that the majority of clay layers found in the tested area, are derived from eolian deposits originating in blue and no-TL quartz particles associated with small amounts of red-TL quartz particles; however, the tephra layers are mainly composed of red-TL quartz grains. The result also shows the availability of the TLCI-CIA method to identify the sources of deposits.

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An outcrop appeared around the Hottate River Pond excavation site in the southern part of Yonezawa City, Yamagata Prefecture. This outcrop consists mainly of an alternation of sandy mud and silty mud, including many wood and plant fragments and fossil cones of Picea bicolr Mayr. The ¹⁴C age of the sediments is about 18, 000 to 15, 000cal yrs BP, indicating that these sediments were deposited in the later part of the Last Glacial period. The volcanic ash intercalated in the upper part of the sediments is identified as the Asama-Kusatsu (As-K) tephra.
Almost all of the sediments were deposited under conditions of a back marsh and in the stream of the old Mogami river which flowed through the western area of Yonezawa City at this time. From 15, 000cal yrs BP, the old Mogami river changed to its present course through the eastern area of Yonezawa City. After this time, only few eolian sediments were deposited in the uppermost part of the outcrop.

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Eastern Hokkaido is known to be the area where marker tephras for the historic ages are widely distributed. The authors analyzed the diatoms in the sediments which are intercalated between the tephras of Ma-b (Mashu-b volcanic ash erupted ca. 970) and Ko-c2 (Komagadake-c2 volcanic ash erupted in 1694), and tried to reconstruct the paleoenvironment of this area. The two peaks of marine and brackish diatoms suggest the two stages of high salinity (late 10th-11th century and late 14th-late 16th century). Such salinity changes during the period from the 10th to 17th centuries seem to be phenomena corresponding to the cycles of transgression and regression that accompanied climatic changes.

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