美濃-丹波-足尾テレーンの石灰 : ジュラ系海洋性岩石(構成岩石の起源)(ジュラ紀付加体の起源と形成過程)  [in Japanese] Carboniferous to Jurassic oceanic rocks of Mino-Tamba-Ashio terrane, southwest Japan(Origin of sedimentary rocks)(Origin and evolution of Jurassic accretionary complexes in Japan)  [in Japanese]

美濃-丹波-足尾テレーンの石灰〜ジュラ系浅海成および深海成海洋性岩石群の分布・層序・年代をレビューした.浅海成海洋性岩石は下部ペルム系中部〜上部ペルム系下部生砕性石灰岩で代表され, 玄武岩類からなる地形的高まりの頂部で浅海成炭酸塩堆積体として形成された.ペルム紀新世後期の世界的海退で形成された炭酸塩堆積体内の洞窟はトリアス紀コノドント混合群集を含む砕屑性石灰岩で充填された.深海成海洋性岩石群は下部ペルム系中部〜上部ジュラ系上部層状チャート・珪質泥岩で代表され, 浅海成炭酸塩で覆われた玄武岩質高まりの下部斜面から周囲の大洋底で堆積した.浅海起源の砕屑性炭酸塩岩・砕屑粒子を多くの層準に含む.浅海成および深海成海洋性岩石は玄武岩質高まりの頂部から下部斜面にかけて堆積した, 同時異相関係にある堆積物として復元出来る.両者をリンクするのは, 化石年代と層状チャート中の浅海起源の砕屑性炭酸塩岩・砕屑粒子である.

Distribution, lithostratigraphy, and age of the Carboniferous to Jurassic oceanic rocks of the Mino-Tamba-Ashio terrane were reviewed. On the basis of facies interpretation of these oceanic rocks, we discuss their sedimentary evolution.The oceanic rocks comprise two lithologically different assemblages. One is a shallow-marine assemblage chiefly of the middle Lower to lower Upper Permian bioclastic limestone having local cyanobacterial boundstone. Mixed Triassic conodont elements-bearing clastic limestone in places occurs filling caves in the Permian limestone. The other is a deep-marine assemblage predominantly of the middle Lower Permian to upper Upper Jurassic bedded radiolarian chert and related siliceous rocks. The siliceous rock succession includes the claystone across the Permo-Triassic boundary and at several levels the shallow-marine clastic carbonates and detrital grains. Both the Permian carbonates and bedded chert overlie a basaltic succession. Biostratigraphic examination reveals that the Permian carbonates and siliceous rocks are time-equivalent, and the cave-filling Triassic carbonates and Triassic bedded chert are also coeval.We consider that the Permian shallow-marine carbonates accumulated to form a buildup at the top of a basaltic topographic high, presumably of a seamount, during mid-Early to early Late Permian. The carbonate sedimentation was interrupted by the late Late Permian global regression, which resulted in submarine cave formation. On the foot of carbonate-capped seamounts and their surrounding ocean floor, the radiolarian chert and related siliceous rocks accumulated during mid-Early Permian to late Late Jurassic with intermittent influxes of shallow-marine clastic carbonates and related detrital grains.All lines of evidence lead the authors to a sedimentary model emphasizing that these coeval shallow-marine and deep-marine oceanic rocks primarily pass laterally into each other. Their lateral link is represented by the clastic carbonates and related detrital grains in the bedded chert. The contemporaneity of the shallow-marine and deep-marine oceanic rocks plays an important role for understanding their sedimentary evolution.