オウムガイ類の遺骸漂流

抄録

Post-mortem drift of the Recent Nautilus shells by oceanic currents is exemplified by the materials collected from the west coast of the Malayan Peninsula and the Japanese Island arcs. Characteristics of habitat (H) and realm of post-mortem transport (T) in general fossil assemblages were schematically explained. T is composed of H, To and Tt, where To is the realm of postmortem transportation outer than H in usual condition, and Tt is the extended portion of To especially caused by an oriented agency of transportation such as turbidity current or strong oceanic current for instance. Thanathocoenose in H is tentatively called as quasiautochthonous assemblage being separated from the true autochthonous, i.e. orthoautochthonous one. Thus, allochthonous assemblage is defined as the dead assemblage out of H or the inner realm of post-mortem transportation. In short, there is an almost fixed relationship between H and T insofar as the areal distribution, and an inequality T>>H, where T=H+To+Tt, is given. The distributional pattern of T inclusive of To and Tt is also diagrammatically presented. Its general figure shows an asymmetry to the center of H. State of preservation, density of distribution and other g neral characteristics of a thanathocoenose should have a tendency to decrease as the realm becomes wider and wider. This tendency is named H→Tt declination.