Pollen analysis, radiocarbon dating, and tephra analysis were performed on five sedimentary drilling cores obtained from Tashiro Mire (570-590 m a.s.l.), Aomori Prefecture, Northeast Japan. The local vegetation changes reconstructed since approximately 13,000 yrs BP are as follows.
Zone TA-1 (ca. 13-11.6 ka) ; Subarctic coniferous forest mixed with Betula, zone TA-2 (ca. 11.6-10.4 ka) ; Betula forest, zone TA-3 (ca. 10.4-8.9 ka) ; transitional zone from the Betula forest to cool temperate broad-leaved forest, zone TA-4 (ca. 8.9-6.6 ka) ; cool temperate broad-leaved forest composed mainly of Quercus subgen. Lepidobalanus, zone TA-5 (ca. 6.6 ka-present) ; cool temperate broad-leaved forest dominated by Fagus, zone TA-6 (present) ; cool temperate broad-leaved forest accompanied by Pinus densiflora substitution forest and Cryptomeria japonica plantation forest.
Changes in the frequencies of shrub and herbaceous pollen suggest that wet grassland expanded in ca. -8 ka and ca. 4-2 ka, and swamp forest invaded grassland in ca. 8-4 ka and ca. 2 ka-present. These changes correspond to paleo-hydrological changes marked by the sediments of the drainage area.

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A total of 49 distal tephra layers intercalated with four deep-sea sedimentary cores of MR0102-PC1, KR0215-PC2, KR0215-PC3, and KR0217-PC7 from the northwestern Pacific have been studied to establish a highly reliable chronology of the past 300 kyr. Based on the mineral composition of tephras, the shapes and major chemical compositions of volcanic glasses, and stratigraphy, six correlatable tephras are found in these analyzed cores. Further, three of these tephras are correlated with known widespread tephras : Aso-4, On-Pm1, and Ata-Th. Based on the constraint of stratigraphic levels of these tephras, continuous magnetic susceptibility records of these cores and the previously dated sedimentary core of S2612 from the Shatsky Rise are correlated. Based on this correlation, a new chronology for these cores is provided. This chronology reveals that the ages of On-Pm1 and other three tephras can be assigned as approximately 98, 159, 219, and 230 ka in descending sequence. This chronology also provides changes of the sedimentation rates for these cores during the last 300 kyr, which will contribute to future paleoceanographic study of the subarctic boundary of the northwestern Pacific.

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The Kiso river delta has been prograding since the Holocene high sea-level stand. A conspicuous fluvial system has been contemporaneously formed covering the delta system, accompanied by the formation of well-preserved fluvial landforms. This study clarified the fluvial landform evolution process of the modern Kiso river delta, based on the reconstruction of the surface fluvial system, by using 24 shallow cores obtained from the present flood plain and the delta plain area. Nine sedimentary units were identified based on sedimentary structure, grain size, and their vertical successions ; delta front (DF) and tidal flat (TF) deposits of the basal delta system ; back swamp (BS), crevasse splay (CS), natural levee (NL), channel (CH), abandoned channel fill (CF), crevasse channel (CC) deposits of the fluvial system, and gravelly channel (GC) deposits of the tributary fluvial system. The distribution of sedimentary units corresponds to the present landform pattern. Grain-size distributions of each sedimentary units show the clear separation of the bed-load of channel (CH) and crevasse channel (CC) deposits from the suspended load of back swamp (BS) deposits (Md=5.0-8.2φ). In contrast, natural levee (NL) and crevasse splay (CS) deposits show variations of grain size from the bed load to the suspended load. Stacking patterns of the sedimentary units in two cross-sections from the northen flood plain and the southern delta plain were reconstructed. Both of the sections consist of delta systems at their bottoms, and overlying fluvial systems. The fluvial system is well developed in the northern section, but limited in the southern section. The fluvial system in the northern section indicates that channel avulsion has repeatedly occurred accompanied by the relocation of a set consisting of a natural levee, crevasse splay, and back marsh. Following the relocation, the abandoned set of landforms had been buried by the suspended sediment from the newly formed active channel. Delta-front sedimentation occurred 4.5-5.0 cal ka at the northern flood plain section, and 2.5-3.0 cal ka at the southern delta plain section. Six ¹⁴C ages, taken from four cores, indicate that the evolution of fluvial landforms, and a fluvial system began around 2,000 to 2,500 cal BP after the deposition of delta front deposits.

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Fluvial-fan sediments including volcanic ashes and plant fossils are thickly accumulated in the Ozu and Uchiko Basins along the Hiji River, Ehime Prefecture, Northwest Shikoku.
These sediments, distributed inside the basins, can be divided into three formations Tomisuyama, Uchiko, and Ozu Formations of the Lower-Middle Pleistocene, and terrace deposits (Furuta, Sugeta, and Hatsukaichi Formations) unconformably underlain by these formations.
In this study, the authors discovered newly volcanic ashes and plant fossils from these strata that are usable for chronological study. According to stratigraphical observations and features of volcanic ashes, the Tomisuyama 12 ash is correlated to the Pink ash (1.0 Ma) and the Kurochibo 3 ash is correlated to the Aso-1 ash (0.25 Ma). The Tomisuyama Formation and the lower part of the Uchiko Formation contain plant fossils such as Metasequoia glyptostroboides, and Picea cf. maximowiczii. In addition, it is clear that the Shobu ash was deposited at 0.6 Ma. These results indicate that the deposits of the Lower-Middle Pleistocene were formed at least at 1.4 Ma and continued till about 0.5 Ma. Those of the Middle Pleistocene were formed about 0.3-0.2 Ma.
The Lower-Middle Pleistocene in the Ozu and Uchiko basins is correlated to the strata that are distributed along the Median Tectonic Line, such as the Lower-Middle part of the Shobudani Formation, Upper-Uppermost part of the Gunchu Formation, Middle-Uppermost part of the Dochu Formation, and Lower-Upper part of the Osaka Group.

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We found evidence of paleo-mass-movement on the Otanairi Mountain, North-central Kiso Range. The mass movement caused a debris avalanche whose volume is estimated to be over 10⁷ m³, and it dammed up branched rivers. To clarify the timing of this mass movement, we collected the age data from historical documents and geological records. No certain historical records about this mass movement were found, but a document described the natural dam of Nogaike pond bursting in AD 1661. Another small enclosed pond, Shitanoike, remains on the filltop of the debris avalanche. A hand auger and percussion drilling survey revealed that this pond is composed of lacustrine mud overlying sand and gravel. We obtained a ¹⁴C sample of humus dated to AD1520-1950 from the sand layer 3.6m beneath the pond. On the surface of the debris avalanche, a lot of rotted stumps (over 1m diameter) which were sawed for lumber 80-90 years ago have remained. Their annual rings can be estimated to over 300 years. The surface soil is relatively immature, and its base is ¹⁴C dated to AD1660-1950. These facts indicate that the deposition age of debris avalanche is pre-dated to the 17^th century. Because such a large scale event is unusual in this area, the activity of surrounding active faults was probably affected to unstabilize the slope of the Otanairi Mountain, though a specific trigger of the paleo-mass-movement cannot be specified.

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