HIGH-RESOLUTION ANALYTICAL METHOD FOR EVENT SEDIMENTATION USING ROSSELIA-SOCIALIS

Middle to late Pleistocene shallow marine deposits in the southeastern part of the Kanto Plains, central Japan, yield well-preserved specime ns of the trace fossil Rosselia socialis Dahmer, 1937, a vertical, spi ndle-shaped mud-lined tube. Aside from such spindle-like specimens, pe culiar specimens characterized by their long, vertically stacked forms have also been observed. Detailed observations of the stacked specime ns and the sedimentary structures of the host sediment reveal that the se burrows were formed as the result of the response of the trace-make r to depositional events. The characteristic mode of occurrence of the specimens can be used as a measuring stich not only for the magnitude of erosion and subsequent deposition of the host sediment, but also f or the relative frequency of the depositional events, despite bioturba tion of the host sediment. This technique can be applied readily to fi ne-scale stratigraphic and/or paleoenvironmental analyses.