Taphonomy and Sedimentological Significance of Oyster Shell Beds within Cretaceous Transgressive Sediments in Japan

Abstract

Through taphonomical analyses of Crassostrea shell beds included in several Japanese Cretaceous strata, paleoecological and sedimentological significance of intertidal muddy and sandy bottom dwelling oysters are examined. The Upper Cretaceous Crassostrea shell beds show a variety of modes of occurrence, lithological changes and sedimentary structure, suggesting composite formative, paleoecological and sedimentary processes. Crassostrea seems to have adapted from muddy substratum during early Cretaceous to coarser sandier substratum often influenced by physical turbulence such as tidal currents and waves during the mid-Cretaceous time, associated with increasing in shell size and thickness, and colony dimension.