Shallow-Marine Ostracods from the Lower Pleistocene Kazusa Group in the Tama Hills, Central Japan, with Their Biogeographical Significance in the Northwest Pacific Ocean

Abstract

Abstract. This study investigated an early Pleistocene ostracod fauna from the Kazusa Group in the Tama Hills (ca. 1.7-1.4 Ma) along the western side of Tokyo Bay, central Japan. We report for the first time an early Pleistocene ostracod fauna from the Kanto District. This fauna consists of 56 species, with three assemblages defined by Q-mode cluster analysis. The two most abundant species are Bicornucythere bisanensis and Spinileberis quadriaculeata in the assemblage BS, Pontocythere subjaponica and Buntonia hanaii in the assemblage PB, and Loxoconcha ikeyai and Pontocythere subjaponica in the assemblage LP. These assemblages indicate the following depositional environments: (1) the innermost to central area of an inner bay having relatively low salinity (assemblage BS); (2) the outer area of the inner bay and upper-shelf area influenced by open sea water with relatively high salinity (assemblage LP); and (3) the central to outer area of the inner bay having salinity intermediate between that of (1) and ...