Paleoecology and taphonomy of fossil rocky-shore assemblages

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Rocky-shore habitats have often been preserved in the geological record, and have a high potential for interfacing with reconstructions of paleogeography and paleoenvironmental change. I paid attention to mode of occurrences of rocky-shore molluscan assembleges from the Quaternary of Hokkaido and examined paleoecologic and taphonomic features in 2003. In addition, I analyzed faunal composition and taphonomic attributes of the molluscan death assemblages and examined a fossilization process in a high energy environments. I preliminary examined rocky-shore molluscs from the Quaternary of Okinawa and analyzed molluscan death assembleges on the beach of coral reef in 2004.The Setana Formation of southwestern Hokkaido, northern Japan, was deposited at a time of glacial sea-level change. I studied the Soebetsu section of this formation, in which intercalated concentrations of well-preserved mollusc shells date to about 1.0 to 0.8 Ma. Quantitative analysis of the molluscan assemblages was per … More formed for three ecological attributes, including water depth, substrate and life style. The frequency of rocky-substrate species in each sample is approximately 30 to 40%. The paleoecological characteristics of the molluscan assemblages in this stratigraphic section reflect changes in the sedimentary environment during a sea-level transgression.The rocky tidal platform in southwestern Hokkaido is divided into five zones, based on its benthic fauna. Taphofacies analysis of the molluscan death assemblages was performed for five taphonomic attributes. The five rocky-shore zones can be characterized by the taphonomic attributes of these shells. Taphonomic gradients among the molluscan death assemblages in this sheltered, rocky-shore habitat reflect environmental gradients based on water depth (=submergence time) and wave action. These taphonomic attributes are commonly preserved in fossil assemblages and therefore are useful for paleoenvironmental reconstruction of sheltered, rocky-shore habitats. Less