Onset of sedimentation near the Carnian/Norian boundary in the northwestern Sichuan Basin: New evidence from ammonoid biostratigraphy and zircon U Pb geochronology

Upper Triassic deposits formed at the onset of subsidence in Sichuan foreland basin South China, and may record a crisis carbonate deposition related to Carnian Pluvial Episode. However, there is no consensus yet on precise age these northwestern Sichuan. In this work, ammonoid biostratigraphy has been improved, U/Pb from detrital zircons obtained New taxa Sinotropites sichuanensis n. gen., sp. Hadrothisbites hanwangensis are described upper part Ma'antang Formation Hanwang Jushui area assigned uppermost Tuvalian (Anatropites spinosus Zone, Gonionotites italicus Subzone). Ammonoid conodont biostratigraphy, combined with concordant ages 227.2 ± 1.1 Ma youngest zircons, provide robust constrain initial sedimentation phases Sichuan, suggest that terrigenous turnover was not