Several new non-marine vertebrate fossil sites were found recently in the Kashima and Taira areas, Koshikijima Islands, western Kagoshima Prefecture, Kyushu, Japan. In these areas, the Upper Cretaceous Campanian to Maastrichtian Himenoura Group crops out widely and is composed mainly of fl uvial, tidal fl at, shoreface, shelf, and slope deposits. Non-marine vertebrate remains such as the teeth and bones of reptiles (including dinosaurs, crocodilians, and aquatic turtles) and fi sh scales are abundant in various non-marine and marine depositional facies, though the remains are preserved in disarticulated and fragmented form (Miyake et al., 2009).

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This paper discusses relationship among depositional environments, origin of the sedimentary organic matter and diatom fossil assemblage, combined with sequence stratigraphy in an incised-valley system. Interpretation of the environments and their changes was based on sedimentary facies, total sulfur (TS) content, and diatom assemblages. The quantity and composition of organic matter were estimated for the environmental interpretation on the basis of the total organic carbon (TOC) content, reflected-light fluorescent microscopy, and stable carbon isotope ratios of the organic matter (δ¹³C_org). The Miocene to Pliocene Ishibane, Tatsunokuchi and Motohata formations in northeast Japan consist of estuarine and fluvial deposits that were formed during a rise and fall of sea level. The proportions of vitrinite and cutinite that are coarse-grained and terrestrial in origin are relatively high in fluvial deposits of the lowstand systems tract. The proportion of marine alginite, TOC content, and δ¹³C_org values increase upward in estuary deposits of the transgressive systems tract. This implies the increase in the influence of the sea and the estuarine bottom conditions becoming anoxic. The proportions of vitrinite and cutinite increase upward in the highstand systems tract, whereas the δ¹³C_org values and TOC content decrease upward. These reflect the strong influence of river discharge. Variations of diatom fossil assemblage of fresh water, brackish water, intertidal, coastal marine and open marine species indicate the same repetitions of transgression and regression in the Tatsunokuchi Formation. Therefore, the transgressive systems tract in the Tatsunokuchi Formation includes four cycles of transgression and regression, while highstand systems tract shows one cycle of transgression and regression.

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On October 2009, the typhoon No. 18 with a heavy rain passed the Ise Bay, central Japan, and caused a fluvial flooding at the Kushida River mouth. Here, drastic geomorphological changes on the coastal area by this fluvial flooding event were reported, and characteristics and depositional patterns of fluvial-flood sediments deposited on the tidal sand flat were described in detail. The geomorphological changes observed by this fluvial flooding event are following; 1) the spit on the right bank of the Kushida River was cut off by the flooding of the branched channels, 2) a large amount of terrestrial organic matters such as plant debris deposited along the shoreline, and 3) a fluvial flooding deposit which is mainly composed of muddy particles covered the sandy tidal flat. As a result of sedimentary facies analysis and SEM observation, two different sedimentary facies were distinguished from the fluvial-flood sediments. Facies 1 is composed of medium- to very coarse-grained sand layer with sharp erosional base, and interpreted as an “overbank” deposit. Facies 2 is composed of massive muddy layer showing microscopic granular structure in clay fabric, and interpreted as a fluid-mud deposit. The fluid-mud deposits (Facies 2) were thickly (>10 cm) developed in the local depressions such as troughs between sand bars, and a part of them was still observed 6 months later. Furthermore, fluid-mud deposits interpreted as deposited from historical flooding events were recognized from the subsurface sediments of the sandy tidal flat. These facts suggest that fluid-mud deposits by fluvial flooding events are potentially preserved in the subsurface sediments of the tidal sand flat without winnowing by wave or tidal activities.

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The sedimentary core GS-KSO-1 is obtained in Shimo-oibukuro, Kawagoe City in the Arakawa Lowland, central Japan, which is a part of the research project to construct a depositional model of the latest Pleistocene to Holocene incised-valley fills. The stratigraphy and sedimentary environments have been revealed based on sedimentary facies, grain-size distribution, CNS analysis, and radiocarbon dating.
The valley fills in GS-KSO-1 are subdivided as follows; gravelly river deposits, sandy channel fills, floodplain deposits (9000 cal yBP), backmarsh to salt marsh deposits, tidal flat deposits (8000 cal yBP), backmarsh deposits (7000-6000 cal yBP), channel fill deposits and floodplain deposits (6000 cal yBP to present).
The age of the maximum flooding surface in the Arakawa Lowland is determined as 8000 cal yBP, which is 1000 to 2000 years earlier than that in the neighboring Nakagawa Lowland. This gap is possibly due to relatively large amount of sediment supply into the Arakawa Lowland.

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