Ammonites from the Carnian (Upper Triassic) Xiaowa Formation, southeast Yunnan Province

This paper describes a new ammonoid assemblage from Luxi County, southeastern Yunnan Province. The assemblage comprise of 13 species of nine genera of ammonoids of which Anasirenites is discovered for the first time in South China. The Trachyceras multituberculatum zone and the Austrotrachyceras triadicum zone are recognized from the bottom to the top based upon the characteristics of each species of the assemblage and their stratigraphic distribution. The date corresponds to Julian 1 and Julian 2 of the early Carnian (Late Triassic). The ammonoid assemblage not only records the radiative events of the Trachyceratidae in the Julian of the Carnian, but also provides a good correlation with the ammonoid assemblages in the Tethys and Panoceanic of the Carnian and new supplementary materials for the study of the palaeogeography of South China. In addition, based on analysis of lithologic and biostratigraphic characteristics of the ammonoids, it is concluded that the disappearance of the carbonate platform caused by the Carnian Pluvial Episode (CPE) in southeastern Yunnan started at the end of Julian 1, slightly earlier than the terrigenous clastic inputs in Julian 2.

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