Paleoenvironments reconstructed from formation processes of recent and fossil oyster reefs, and the paleoecological evolution of oysters

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Several representative, well-preserved Cretaceous to Recent oyster beds and reefs around Japan are extensively studied for reconstructing their formation processes and considering their formative factors on the basis of taphonomy and sedimentary structures of shell beds, and morphology and ecology of the oyster shells. We reconstructed the Holocene sedimentary history and sea-level changes of the Akkeshi Lake area (east Hokkaido) with large Crassostrea gigas reefs lived until 1980s. We found the alternated autochthonous/allochthonous Crassostrea shell beds affected by some large earthquake-induced tsunamis during the early Holocene Jomon transgression in Pashikuru estuary. Furthermore, we surveyed the geomorphology and ecology of Parahyotissa imbricata reef mounds on the subtidal sea floor in the Yatsushiro Inland Sea.