Taphonomic study of shell-concentrated bed: case studies in Kakegawa, Tohnohama, and Miyazaki Groups.

本文分析了日本本州岛中部太平洋一侧的卡克川群上新世第一组中的一个贝壳密集层，并将该层解释为滨面存款。和30厘米深的块。我鉴定了该区块中25种腹足类的1966个标本和18种双壳类的1131个标本，并将它们解释为生活在桑迪底，泥质沙质底，在浅水沃茨有一个坚硬的底部。我认为贝壳层是在高速和高速的条件下沉积的-由西北向东南流动的异重流，瞬间将贝壳和贝壳碎片堆积起来。在临岸环境中，可以假设一个地转流和一个大风暴的巨浪的瞬时组合流。它在沉积物上方产生非常强的剪切应力，可能很容易形成密度流，它的能量很快就会减少，可能导致密度流中贝壳的瞬间积累。

I analyzed a shell-concentrated bed in the upper Pliocene Dainichi Formation of the Kakegawa Group, exposed at the Pacific side of central Honshu, Japan, and interpreted the sequence including the bed as a shoreface deposit.I examined the species composition, the shell-orientation patterns, the convex-down ratio of bivalves, and the shell-size ratios, of the four horizons of the bed, using a 43cm- high, 40cm-wide, and 30cm-depth block. I identified the 1966 specimens of 25 gastropod species and the 1131 specimens of 18 bivalve species in the block, and interpreted them to be a mixed assemblage of the species that live in a sandy bottom, a muddy sand bottom, and a hard bottom in shallow waters.I interpreted the shell bed to have deposited under a condition that a high-speed and a high-density current that flowed from northwest to southeast, accumulated instantaneously the shells and the shell fragments. In a shoreface environment, it is possible to assume an instantaneous combined current of a geostrophic flow and a backwash of a huge wave of a major storm. It gives a very strong shear stress just above the sediments, probably easily making a density current, and it's energy is reduced very quickly, probably resulting instantaneous accumulation of the shells from the density current.