T399 The Road to Recovery—The Nature of Biotic and Geochemical Cycles During the Early Triassic

Wednesday, 30 October 2013
1:00 PM - 5:00 PM
Room 504

DIVERSIFIED SPATHIAN CHAOHU FAUNA FROM SOUTH CHINA

Paper number: T399-8
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Abstract

Mesozoic marine reptiles firstly appeared in the Early Triassic after the P/T Mass Extinction, but the fossil records are very rare. During the excavation at Majiashan Section of Chaohu, Anhui Province from 2010 to 2012, we found many marine reptiles, including more than eighty complete skeletons of the basal ichthyopterygian Chaohusaurus and some new ichthyopterygian taxa from different layers of the Middle-Upper Member of the Nanlinghu Formation, with age of Spathian, Olenekian. We also found an articulated postcranial skeleton of sauropterygian from the layer above the typical Chaohusaurus levels, which is the first definite Early Triassic sauropterygian with exact stratigraphic data within the Spathian, and a strange 1.4-meter-long diapsid, which is different from all known marine reptiles known so far, from the bed higher than the sauropterygian. Geochemical studies have shown strong perturbations in the marine carbon cycle during the Early Triassic and a lethal warming at the end of Smithian. These new taxa suggest that the multiple clades of the marine reptiles have co-existed during the middle Spathian, earlier and more diversified than we previously believed.

Integrated facies analyses were carried out on the Early Triassic Helongshan and Nanlinghu carbonate from the Majiashan Section. Results indicate a carbonate slope for the Chaohu Fauna with a regression in the Stage Scale which may be related to the tectonic evolution of the north margin of the Yangtze Plate.

The Chaohu Fauna with exact stratigraphic control is one of the earliest records of Mesozoic marine reptile faunas showing the beginning of the recovery after the P/T Mass Extinction known so far, as well as the contemporaneous Grippia Fauna from arctic Spitsbergen, and the Utatsusaurus Fauna from Japan. There are three other diverse Triassic marine reptile faunas identified in Guizhou and Yunnan provinces (southwestern China), i.e. the Anisian Panxian-Luoping Fauna as a marker of the rapid radiation of the Triassic marine ecosystem, the Ladinian Xingyi Fauna and the Carnian Guanling Biota which marks the full recovery.