Departmental Bulletin Paper 大阪府南部の和泉山脈北麓に点在する時代未詳堆積岩の有機物熟成指標による地史の検討

清家, 一馬

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大阪府南部の和泉山脈北麓の父鬼川、牛滝川、および槇尾川に小規模に露出する3つの堆積岩 について,ロックエバル分析とビトリナイト反射率の2種類の方法で有機物熟成度を測定した.2つ の地質単元の熟成段階は明確に区別される.牛滝川砕屑岩の有機物熟成段階は和泉層群と同程度の カタジェネシス帯・過熟成であり,深部への埋積による被熱があったと考えられる.甘南備層の有 機物熟成段階はダイアジェネシス帯・未熟成ではあるが,地下数 km の埋積が推定される.甘南備層 の有機物熟成段階は従来の層序・地史の解釈と矛盾しない.側川礫岩層はこの手法で熟成段階が評 価できないほどの熱変成をうけた可能性が高い.
Three blocks of sedimentary rock, which were poorly exposed along the Chichioni River, the Ushitaki River and the Makio River in the north Izumi Mountains of southern Osaka Prefecture, were studied by using Rock-Eval pyrolysis and vitrinite reflectance. The results revealed that two rocks are clearly distinguished by the degree of organic maturation level. The Ushitakigawa Clastic Rock had reached the stage of catagenesis / post mature parity with the Izumi Group, and its high maturity was probably caused by the influence of deep burial diagenesis. The Kannabi Formation had reached the stage of diagenesis / immature but is assumed to be weekly baked at a few km burial depth. The thermal maturation levels of the Kannabi Formation are compatible with stratigraphy and geologic history shown by previous studies. The Sobagawa Conglomerate must have been thermally metamorphosed at high temperature as maturation level can not determined by Rock-Eval pyrolysis and vitrinite reflectance.
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