No abstract

No abstract

The Kanto Plain, the hinterland of the Tokyo metropolitan area, is the largest plain in Japan and is characterized by marked marine and fluvial terrace levels that developed during Marine oxygen Isotope Stage （MIS） 5. Late Quaternary topographical changes to the plain have been controlled by concurrent tectonic activity and glacio-eustatic sea-level changes. The shoreline at the maximum transgression of MIS 11, 9, 7, 5 and 1 is reconstructed based on the distribution of marine sediments revealed by many geologic columnar sections and marine terrace surfaces. A comparison of the magnitudes of the last five full-interglacial transgressions above shows that magnitude decreased over the long term. This is due probably to changes in the tectonic regime in the Kanto basin, from subsidence to uplift along with the northward migration of the depositional center, probably associated with changes in the motion of the Philippine Sea Plate and the collision with the Izu peninsula. The marine transgression has also been controlled by fluvial processes, especially in the north-western part of the plain because of high sediment inputs from the Tone, Ara, and Watarase rivers. Aggradation coupled with regional uplift since MIS 5.4 limited the MIS 1 marine transgression within the incised valley formed during MIS 2. As a result, the Paleo Tokyo bay, which was connected directly with the Pacific Ocean, disappeared. Instead, a large shallow submarine area of about 10,000 km 2 emerged. The northern part of the present Tokyo bay is still subsiding and large volumes of water and sediments have been concentrated in the bay area during the Holocene. Such natural environmental conditions enable supplies of natural resources, such as fresh water, fertile soil, and flat land for the development of greater Tokyo.

No abstract

Number and depth of marine intervals in seven drillcores in central Kanto Plain, central Japan, were examined by diatom fossil analysis and lithofacies observations. The numbers of identified marine intervals in seven drillcores are as follows; 15 marine intervals (TZ-M1-TZ-M15) in Tokorozawa core, six marine intervals (WM-M1-WM-M6) in Washimiya core, three marine intervals (GD-M1-GD-M3) in Gyoda core, 12 marine intervals (KGH-M1-KGH-M12) in Koshigaya-Higashi core, 14 marine intervals (KJ-M1-KJ-M14) in Kawajima core, 18 marine intervals (KK-M1-KK-M18) in Kasukabe core and eight marine intervals (FS-M1-FS-M8) in Fukasaku A-1 core. These results present basic stratigraphic data to develop the Quaternary subsurface stratigraphy of central Kanto Plain.