Reevaluation of Benthic Shelf Associations of the Pleistocene in the Boso Area, with Emphasis on Low-diversity Associations in Sparsely Fossiliferous Beds

摘要

Macrobenthic shelf associations consisting mainly of bivalves of the Pleistocene in the Boso area have been analyzed in terms of water temperature and water depth in many previ- ous studies. The role of another important factor controlling the distribution of the con stituent species of the associations-that is, physical disturbance caused by excavation, rapid burial and other sedimentation processes -is examined, through comparison of the composition of benthic associations between those (1)under low (Semata, Ichihara) and high (Shuku, Kisarazu) sedimentation rate condi- tions in the Yabu Formation, and (2)in moder- ately sheltered Paleo-Tokyo Bay (Semata and Shuku) in the Yabu Formation and in an open- Coast shelf exposed to the Pacific Ocean (Ichinono, Kisarazu) in the Kongochi Forma- tion.