[H-CG23] Earth surface processes related to deposition, erosion and sediment transport

[HCG23-P05] Forced regression deposits during MIS 5c and 5a observed in the Iioka marine terrace (the Pleistocene Katori Formation, central Japan)

*Hiroko Okazaki¹, Hiroomi Nakazato², Toru Tamura³, Kazumi Ito³, Masakazu Nara⁴ (1.Division of Earth Science, Natural History and Institute, Chiba, 2.Institute for Rural Engineering, NARO, 3.Institute of Geology and Geoinformation Geological Survey of Japan, AIST, 4.Sciences Unit, Natural Sciences Cluster, Research and Education Faculty, Kochi University)

Keywords:Forced regression, marine terrace, shallow marine

The Kanto Plain, eastern Japan, is known to be the largest Quaternary sedimentary basin characterized by the extensive presence of the raised Last Interglacial marine terrace. The Iioka marine terrace, which exposes a marginal terrace section at the eastern end of the Kanto Plain, consists of the Katori Formation. This report presents that the Katori Formation potentially contains the deposits formed during the MIS 5c and 5a with K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating, tephra correlation, etc. The depositional sequence of the Katori Formation consists of inner shelf, lower shoreface, upper shoreface, beach, and fluvial facies upward above the sequence boundary. The contact between the lower shoreface and the upper shoreface indicates a sharp erosional surface, and the upper shoreface is characterized by tabular-bed sets that may originate from alongshore or oblique shore dunes. The beach and fluvial facies level lower northeastwards (offshore) along with the marine terraces that descend stepwise, which is indicative of a forced regression succession.