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Radiolarian age of Triassic striped chert within the Jurassic accretionary complex of the Ashio terrane in the Ashikaga area, Tochigi Prefecture, central Japan

2020; Volume: 71; Issue: 4 Linguagem: Inglês

10.9795/bullgsj.71.297

2186-490X

Tsuyoshi Ito,

Paleontology and Stratigraphy of Fossils

A striped structure within a single chert bed has been observed in the Tamba–Mino and Ashio terranes, Jurassic accretionary complexes of the Inner Zone of Southwest Japan. This study reports striped chert beds in four sections of the Ashio terrane in Ashikaga and Sano cities of Tochigi Prefecture, namely, Hikoma, Oiwa, Tsukiya and Orihime sections, and their radiolarian ages, except for the Hikoma section. The striped chert comprises streaks and spacing. The streak indicates a thin part of a pin-striped structure within a chert bed and consists mainly of clay minerals. The spacings indicate a thick part between the streaks and is composed mainly of cryptocrystalline quartz. The Oiwa section, which contains numerous striped chert beds, partially corresponds to the middle Carnian–middle Norian (Upper Triassic). The Tsukiya and Orihime sections, which include a few striped chert beds, partially correspond to the middle– upper Anisian (Middle Triassic) and upper Norian–lower Rhaetian (Upper Triassic), respectively.