Phytolith analysis of soils interstratified with tephras in Tengutai section near Hachinohe, northeastern Japan, revealed a record of climate fluctuations since the Last Interglacial. The Holocene soils have phytolith assemblages in which Panicoid dominates over Festucoid, suggesting a warm climate period. In addition, they are characterized by dominant non-Bambusoideae phytoliths, suggesting the existence of a grassland composed of non-Bambusoideae taxa. Such a grassland was thought to be the result of human impact through deforestation. The Last Glacial soils have phytolith assemblages which are characterized by dominant Pooideae, suggesting a cold climate period. In soils between Hachinohe Pumice (HP) and Biscuit-1 Pumice (BP-1), corresponding to δ¹⁸O stage 2, coniferous phytoliths generally occurred with relatively high frequency, indicating that boreal coniferous forest spread throughout this region. Soils between Biscuit-1 Pumice and Kibidango Pumice (KbP), corresponding to δ¹⁸O stage 3 to 4, were characterized by relatively high frequency of Bambusoideae phytoliths. The Last Interglacial soils generally have phytolith assemblages characterized by dominant Bambusoideae phytoliths. In the lowest layers of the soils over Madara Pumice (MP), which correlates to δ¹⁸O stage 5e, Bambusoideae phytoliths from Pleioblastus were dominant. This assemblage indicates a warmer climate condition than the present because Pleioblastus is a dominant taxon in warmer climate zones than the study region. In the uppermost layers of the soils, which correlate to δ¹⁸O stage 5a, Bambusoideae phytoliths from Sasa were dominant, indicating a warm to cool climate condition similar to the present. The lower part of these soils, which are interbedded with Okoshi Pumice (OP), had a relatively higher frequency of a broadleaved deciduous tree phytolith such as elliptical multifaceted phytolith from Magnolia, suggesting the existence of a broadleaved deciduous forest. The soils interbedded with Aosuji Pumice (AP), which correlate to δ¹⁸O stage 5b, had assemblages characterized by relatively higher frequency of Pooideae phytoliths, suggesting a cold period in the Last Interglacial. The soils which correlate to δ¹⁸O stage 5d, probably with an assemblage characterized by a relatively higher frequency of Pooideae phytolith, are yet to be recognized.

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There is a large degraded area of about 350ha on the ridge portion of the Kitakami mountains, especially on the windward, west-facing slope. The area has volcanic ash overlying an angular gravel layer. The soils in the area are formed of Holocene tephras, Iwate-b from Iwate volcano and Chuseri pumice from Towada volcano and Pleistocene tephras, Akita-Komagatake-g and Yanagisawa pumice, from Akita-Komagatake volcano. The degradation phenomenon is believed to have been triggered by the felling of the native beech (Fagus crenata) forest to create grassland initially for the breeding of horses and later on cattle followed by bad pasture management or mere abandonment of the land. Removal of the native forest exposes the unprotected soil to the severe periglacial environment. The exposed soil is then subjected to repeated freezing and thawing during winter which promotes wind erosion and rain out-wash. The degradation process is also enhanced by the unique properties of weathered tephric materials such as high allophane content. The ¹⁴C dating of the buried A horizon shows that degradation phenomenon started from around the Edo (270±80yrs BP) to the Meiji (100±70yrs BP) eras. Development of the degradation phenomenon in the Kitakami mountains is a result of a chain of events. After the felling of the native forest to create grasslands, the severe environmental conditions coupled with mismanagement, gave rise to the formation of the bare lands. The degradation phenomenon in the Kitakami mountains also shows the influence of the interaction between climate, topography and human activity.

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A paleomagnetic secular variation record of geomagnetic field direction for the time span from 25 to 16ka was obtained from oriented bog sediment samples in a coastal area of the eastern Inland Sea, Japan. The plot of this secular variation record, combined with Holocene secular variation data, shows that a long-term westerly declination feature began after 16ka and ended at 7.5ka. This feature lasted more than 4, 000 years and less than 8, 500 years. The declinations at 25-16ka are dominated by easterly values, and no westerly declination was observed in the time span of 24-19.5ka. The inclinations at 25-16ka are characterized by slightly shallow values with small amplitude changes, compared to those in the Holocene. Prior to 18ka a large clockwise looping was dominant in the motion of the geomagnetic vector, while counter-clockwise rotations were dominant after it. Many features of secular variation in the last glacial period have the potential to yield good age constraints for use in paleomagnetic dating.

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We analyzed diatom assemblages, oxygen isotopes in foraminiferal tests, and mineral compositions in the deep sea cores from off southern Java and attempted reconstruction of ocean currents to obtain informations about Asian monsoons, thermohaline conveyer system, and crossing of Wallace's line of modern Homo sapiens. Results suggest that (1) the West Australian Current was enhanced and the boundary zone between tropic and subtropic areas moved northwards during (sub) glacial periods; (2) the Equatorial Countercurrent was enhanced and the boundary zone moved southwards during interglacials; (3) the Java Coastal Current from the north was enhanced during oxygen isotopic stages 3 to 2, when the northwestern monsoon was enhanced, and then it was weakend by stage 2 under the gradual transgression; (4) the Western Australian Current caused coastal upwelling when the thermohaline conveyer system was weakened, but the westward horizontal movement of the conveyer system interrupted vertical movement of upwellings during the Last Interglacial; and (5) modern Homo sapiens might have crossd Wallace's line during the interval from 65 to 50ka, from the period when the Java Coastal Current, running eastward under the influens of northwestern monsoonal wind, began to be enforced to the period when the flows halted.

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Terrace sediments intercalating a marine clay layer were found in the Harima district along the northeastern coast of the Seto Inland Sea, Japan. We performed diatom and volcanic ash analyses to clarify the sedimentary environments and depositional age of the sediments. The sediments are divided into four lithostratigraphical units, I, II, III and IV in ascending order. The results of the diatom analysis suggest that unit I was deposited in freshwater conditions. Units II and III are inferred to have been deposited in marine littoral and brackish-water conditions, and unit IV in terrestrial conditions. The Kakogawa volcanic ash layer intercalated in unit III is correlative with the Koshienhama-I volcanic ash layer in the marine clay bed Mall (2) underlying the Osaka plain and the BT 51 volcanic ash layer (estimated eruption age 215ka) in the Takashima-oki 200m-core from Lake Biwa. Therefore, the marine facies of unitsII and III are stratigraphically equivalent to the Mall (2) bed, and the age of the transgression that deposited these marine units corresponds to oxygen isostope stage 7.3. From the succession of diatom assemblages, the former shoreline indicating the relative sea-level position at 215ka is recognized to be the Kakogawa volcanic ash horizon at about 44m above the present sea level. On the basis of this relative sea level and the paleo-sea level during stage 7 inferred from the coral-reef terraces in Sumba Island (Indonesia), average uplift rate during the last 215ka is estimated to be 0.2 to 0.3mm/yr at the investigated site.

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The Takatsukayama Member of the Meimi Formation is distributed at the western foothills of the Rokko Mountains, western Japan, and has been known as the Middle Pleistocene deposit intercalating a marine bed. The Takatsukayama volcanic ash layer is intercalated in the terrestrial bed immediately below the marine sediment. It was dated to be 0.41±0.12Ma by the fission-track method from 30 zircon crystals, indicating the eruption age of the ash to be ca. 0.4Ma. Petrologic characteristics (such as heavy mineral composition and types of volcanic glass shards), and refractive index of glass shards and green hornblende crystals were examined for this volcanic ash layer.
On the basis of this eruption age, and of the petrologic characteristics and refractive index of glass shards, the Takatsukayama volcanic ash layer is correlated with the Minatojima II volcanic ash layer in the Ma 9 marine clay of the Osaka Group (Miyakawa et al., 1996), as was suggested by Inoue and Yoshikawa (1998). The BT 76 volcanic ash layer in the Takashima-Oki core sample from Lake Biwa (Yoshikawa and Inouchi, 1991), which erupted at ca. 0.39Ma (Yoshikawa and Inouchi, 1993), is also considered to be equivalent to the Takatsukayama volcanic ash.
The correlation and age estimation of the Takatsukayama volcanic ash layer led to the conclusion that the marine bed of the Takatsukayama Member is equivalent to the Ma 9 marine clay and was deposited during the period corresponding to the oxygen isotope stage 11.

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