Abstract

New biostratigraphic (ammonoids and conodonts) and geochemical data (carbonate carbon and oxygen stable isotopes, and organic carbon stable isotopes) are presented for the Carnian (Upper Triassic) marine succession of Ma'antang, Jiangyou County, in Upper Yangtze Block (NW margin of Sichuan Basin, China). In this locality, the Ma’antang Formation lies on top of the Tianjingshan Formation and contains at least four intervals of terrigenous deposits. A lithological change from mainly carbonates to terrigenous clastic rocks occurs between Units 3 and 4. This interval is biostratigraphically well constrained by the occurrence of ammonoids from the clayey siltstone of Unit 4 suggesting a Julian 2 age (Early Carnian), while conodont associations allow also to place the Julian/Tuvalian boundary in the upper part of Unit 4. A wide negative carbon isotope oscillation of about 2 ‰ occurs in Units 1 and 2, attributed to the onset of the Carnian Pluvial Episode (CPE). The present isotopic data show that the CPE began roughly isochronally with the first terrigenous input at Ma'antang. So far, Ma'antang is the only locality of the Sichuan Basin where the carbon isotopic perturbation related to the Carnian Pluvial Episode has been documented.

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