Sea Level Changes and Tectonics Inferred from the Quaternary Deposits and Landforms of Boso Peninsula, Central Japan. Reevaluation of Benthic Shelf Associations of the Pleistocene in the Boso Area, with Emphasis on Low-diversity Associations in Sparsely F

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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 previous studies. The role of another important factor controlling the distribution of the constituent 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 conditions in the Yabu Formation, and (2) in moderately sheltered Paleo-Tokyo Bay (Semata and Shuku) in the Yabu Formation and in an opencoast shelf exposed to the Pacific Ocean (Ichinono, Kisarazu) in the Kongochi Formation. Infauna-dominated relatively sparse benthic association in the shelf and lower shoreface facies of the Yabu Formation (Shuku), and the much lower-diversity and extremely sparse benthic associations dominated by deposit-feeders in the shelf facies of the Kongochi Formation (Ichinono), are examples of such physically disturbed associations. Modern benthic associations off Western Sahara, and those off the west coast of Southern Alps of New Zealand, are interpreted to be similar examples of low-diversity associations caused by physical disturbance associated with sedimentation.
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