和歌山県湯浅地域の下部白亜系西広層の河川成堆積物およびその古流向と砕屑物供給源

概要

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The Lower Cretaceous Nishihiro Formation in the Yuasa-Aridagawa Basin is characterized by quartzose and arkosic sandstones, as well as minor conglomerate and mudstone. Sedimentary facies analysis of the Lower Sandstone Member of the formation reveals the dominance of braided fluvial deposits. Paleocurrent analysis indicates the consistent southerly dispersal of coarse clastics from the source terrane located to the north of the basin. The provenance includes granitic rocks and Siluro-Devonian felsic tuffs, which are characteristic of the Kurosegawa Terrane, which presently occurs in the axial zone of the Chichibu Terrane; however, during deposition of the Nishihiro Formation, this terrane also occurred north of the Yuasa-Aridagawa Basin, possibly as a nappe that lay upon the Chichibu Terrane.