丹波帯南西部の"非丹波層群"の砂岩 : モード解析とその比較

概要

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Four formations named Ajima, Yamashita, Nagaoyama and Takatsuki, are extensively distributed in the southwestern part of the Tamba Belt and have been regarded as parts of the Tamba Group. Those are mainly composed of clastic sediments such as alternating sandstone and shale, and black shale. Detrital modes of their sandstone are rich in acidic to intermediate volcanic rock fragments, plagioclase, and poor in quartz. Multivariate analyses including regression analysis and cluster analysis reveal that these sandstones are very similar to those of the upper Permian Oi Formation in the Ultra-Tamba Zone. Those formations are differentiated them from the Tamba Group (the Type I and the Type II suites) and named the "Non-Tamba Group" b formation. Furthermore, this b formation lies on the equivalent strata of the Hikami formation, and both of them are separated the Tamba Group by fault. Incidentally, there is a little difference between the facies of the Oi Formation and that of the "Non-Tamba Group" b formation. The Oi formation is an accretionary complex in the subduction zone, On the contraly, it is concluded that the "Non-Tamba Group" b formation deposited on a forearc basin during late Permian to early Triassic time.
地学団体研究会の論文
1991-01-25