Abstract
The stratigraphy and transitions of sedimentary environments in the latest Pleistocene to Holocene incised valley fills in the Arakawa Lowland are revealed based on sedimentary facies, fossil shell assemblages, physical properties, chemical element contents and radiocarbon dating in the GS-TKT-1 core, Toda City, Saitama Prefecture.
The sedimentary successions are composed of Pleistocene Shimosa Group (Unit 1), gravelly fluvial deposits (Unit 2), sandy fluvial to salt marsh deposits (Unit 3), inner bay to delta front deposits (Unit 4) and sandy fluvial deposits (Unit 5) in ascending order. Unit 2 and upper units are the latest Pleistocene to Holocene incised valley fills, indicating a transgression (Unit 2-3) followed by a regression (Unit 4-5). Depositional ages are 10000 cal yBP or before for Unit 2, 10000-9000calyBP for Unit 3, 9000-5000calyBP for Unit 4 and 5000calyBP to present for Unit 5.
In a transverse section, the gravelly fluvial deposits and the sandy fluvial deposits fill the narrow axis of the incised valley under the Arakawa Lowland, the salt marsh deposits and lower part of the bay deposits extend over a buried terrace south of the valley axis, and upper part of the bay deposits, the delta front deposits and the fluvial deposits cover the entire lowland.
