Incised-valley topography formed into the Last Glacial Maximum beneath the southern area of the Tokyo Lowland, central Japan

Abstract

Incised-valley topography formed into the Last Glacial Maximum (LGM) beneath the southern area of the Tokyo Lowland including the Tokyo Bay area has been clarified on the basis of 5,767 borehole logs. The incised-valley topography has been reconstructed by spatially interpolating (Kriging) the depth distribution of the base of the post-LGM incised-valley fill identified in each borehole log. The PaleoTokyo River Valley flows from north to south along the present Arakawa River in the Tokyo Lowland. Three buried terraces formed during the Marine Isotope Stage (MIS) 5a, MIS 3, and the early stage of the LGM occur on the left and right banks of the Paleo-Tokyo River Valley. The buried terraces on the left and right banks of the Paleo-Tokyo River Valley are dissected by the Gyotoku Valley and the Paleo-Kanda River Valley, respectively. Absence of the Basal Gravel bed and the cover effect in the Gyotoku and Paleo-Kanda River valleys pronounced the undulation of the incised-valley topography formed in relation to the sea-level lowering and river incision into the LGM.