The Paleogene sedimentation in Amakusa-Shimoshima, Kyushu, was examined from a standpoint of organic and inorganic diagenesis. The degree of the diagenetic alteration of the studied sequences is higher than that of the Paleogene rocks in the surrounding areas of Kyushu. The progressive diagenetic process might primarily have been caused by a great amount of accumulation of sediments, namely by an intensive subsidence of the basin which originated from a successive tectonic movement from upper Cretaceous to Miocene age as already mentioned (MIKI, 1975).
Diagenesis of the sediments are, in consequence, intimately related to the tectonic movement in Amakusa-Shimoshima, but not to the tectonic pressure as has been regarded.
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