Guadalupian (Middle Permian) δ13Corg changes in the Lower Yangtze, South China

The Middle Permian Guadalupian witnessed significant environmental changes in the Phanerozoic such as large-scale sea-level drop, supercontinent Pangaea assembly, and transition from Early Permian glaciation to Late Permian non-glacial intervals. Carbonisotope tracers can provide insights for these environmental changes. The δ13C studies of the entire Guadalupian epoch are rare, and most of them has focused on near the end of Guadalupian and carbon isotopes of inoragnics. Here, we present carbon isotopic compositions of organic matters in the Guadalupian from two sections (Chaohu and Xiaolao) in the Lower Yangtze area, South China. Our results show that δ13Corg profiles in the Guadalupian show a peak in the Roadian and a gradual negative shift from the Roadian to the middle Capitanian. These trends can be matched by δ13C changes of carbonate rocks or organic matter in South China and other places in the world, representing a global carbon cycle signal. The Roadian positive peak was probably due to high productivity which was caused by upwelling during cooling time. The gradual negative shift of δ13C was caused mainly by a decrease of organic matter burial on land and in the ocean, resulting from global sea-level drop and anoxia-caused benthos decline, respectively. The less important causes for the gradual δ13C negative shift are volcanic-gases releasing, decreased mountain belts, and the resultant reduced silicate weathering-consumption of CO2. The gradual negative shift of δ13C coincides with the gradual extinction in the Guadalupian. Therefore, global sea-level drop and marine reducing conditions may be the main causes of the gradual extinction in the Guadalupian.