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The age and depth of the Uppermost Alluvium in the coastal lowlands of Japan indicates that minor sea-level drop, termed the Yayoi regression , occurred at-ka; however, this Yayoi regression is not a eustatic phenomenon. Sedimentary facies analysis and radiocarbon dating in the Tokyo and Nakagawa Lowlands indicate that: () flood plain sediments of the Uppermost Alluvium are located at depths > m below the present sea level, and () the morphology of fluvial channel sediments of the Uppermost Alluvium changes from sheet-like (-m below present sea level, deposited at-ka) to anastomosing (< m below present sea level, deposited at-ka). Sheet-like and anastomosing sand bodies typically form during lowstand and transgressive fluvial systems, respectively. This suggests that relative sea level was lower than the present at-ka, before rising in the Tokyo and Nakagawa Lowlands to current levels between ka and the present day.

The forearc basin fill turbidite succession of the Pliocene Anno Formation is well exposed in Boso Peninsula, central Japan. As the turbidite succession of the Anno Formation is distributed along a couplet of anti-and syncline axes trending WNW to ESE, three-dimensional analysis of depositional system of the formation can be carried out by using many tuff beds as key markers. Lateral distribution and successive change of turbidite facies and palaeocurrent directions of turbidites were investigated, based on the detailed lithologic map of the study area.The Occurrence of two successive depositional systems, channel-levee system in the lower part and channel-lobe system in the upper part, forming a submarine fan, is suggested by the facies distributions and palaeocurrent directions. The upward retrogradation can be detected through the formation of the forearc basin fillinig. AbstractCThe Geological Society of Japan 2005 269

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"Chuseki-so", which is an incised-valley fill deposited since the last glacial maximum, is distributed under the Nakagawa Lowland, Saitama Prefecture, central Japan. In this study, sedimentary facies, radiocarbon dates and sediment properties of the GS-SK-1 cores (GS-SK-1A, GS-SK-1N and GS-SK-1T) drilled at a central part of the Nakagawa Lowland, were analyzed for clarifying stratigraphy and sedimentary environments of incised valley fills in the Nakagawa Lowland. The "Chusekiso" of the GS-SK-1A core is composed of fluvial to shallow marine sediments as follows, in ascending order: (1) fluvial channel fills of pebble to pebbly sand, (2) flood plain to salt marsh deposits of alternation of sand and mud, (3) muddy tidal flat deposits of massive mud containing molluskan fossils, (4) sandy tidal flat to sand shoal deposits of poorly-sorted silty sand containing shell fragments and granules, (5) inner bay (prodelta to delta front) deposits of massive mud intercalated by thin ripple sand and abundant burrows, and (6) fluvial channels fills to flood plain deposits of alternation of sand and mud. Nineteen radiocarbon dates, 48,350 to 1,270 yrBP in radiometric 14 C ages, indicate that the incised valley fills are formed by a set of transgression and regression. Sediment properties, i.e. N-value, mud contents, bulk densities, magnetic susceptibility, water contents, luminosity and color contrasts of these deposits, vary stratigaraphically, corresponding to sedimentary facies or at boundaries of them.