Sedimentary facies and radiocarbon dates of GS-AHH-1 core obtained from Hirano District, Adachi-ku, Tokyo Metropolitan

Abstract

    The GS-AHH-1 core, obtained from the buried terrace under Adachi-ku in the Tokyo Lowland, consists of facies BR (braided river sediments), TM (tide-influenced shallow marine sediments), TF (tidal fl at sediments), SM (shallow marine sediments), PD-DF (prodelta to deltafront sediments), MT (modern tidal fl at sediments) and AS (artifi cial soil) in ascending order. The Alluvium (latest Pleistocene to Holocene incised valley fi lls), which consists of facies TF, SM, PD-DF, MT and AS, unconformably overlie Shimosa Group (middle to late Pleistocene deposits) of facies BR and TM. The facies TF and SM and facies PD-DF, MT and AS can be correlated to estuary and delta systems, respectively. The Maximum Flooding Surface at the estuary-delta system boundary is dated at 6.9-7.3 cal kyr BP. The facies TF, which consists of bluish gray mud, overlies the facies TM, which consists of greenish gray mud, with sharp boundary. The difference in the color of mud can be a good indicator to identify the Shimosa Group–Alluvium boundary in this region.