Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China

Stable isotopes of inorganic and organic carbon are commonly used in chemostratigraphy to correlatemarine andterrestrial sedimentary sequences based on the assumption that the carbon isotopic signature of the exogenic carbon pool dominates other sources of variability. Here, sediment samples fromfour Permian–Triassic boundary (PTB) sections ofwesternGuizhou and eastern Yunnan provinces in South China, representing a terrestrial tomarine transitional setting,were analyzed for δ13C of organic matter (δ13Corg). These valueswere subsequently compared to published δ13C values of carbonates (δ13Ccarb) from the Global Stratotype Section and Point at Meishan and many other marine and terrestrial sections. A similar isotopic trend evident through all four sections is characterized by a negative shift of 2–3‰ at the top of the Xuanwei Formation, where we tentatively place the PTB. This negative shift also corresponds to a turnover in the vegetation and the occurrence of fungal spores, which is generally interpreted as a proliferation of decomposers and collapse of complex ecosystems during the end-Permian mass extinction event. Moreover, the absolute values of δ13Corg are more extreme in the more distal (marine) deposits. The δ13Corg values for the studied sediments aremore variable compared to coeval δ13Ccarb records from marine records especially in the interval below the extinction horizon. We contend that the depositional environment influenced the δ13Corg values, but that the persisting geographic δ13Corg pattern through the extinction event across the four independent sections is an indication that the atmospheric δ13C signal left an indelible imprint on the geologic record related to the profound ecosystem change during the end-Permian extinction event.Additional funding:Y.C. and L.R.K. acknowledge support from NSF grant EAR-0807744. The project was also partially supported by the Penn State Astrobiology Research Center (through the NASA Astrobiology Institute, cooperative agreement #NNA09DA76A). A.B. is currently supported by a Deep Time Peter Buck Postdoctoral Fellowship from the NMNH Smithsonian Institution, part of this work was conducted under the support of the Swedish Research Council (VR) postdoctoral fellowship grant 2011- 7176. J.Y. acknowledges support from the NSFC (project nos. 40972002 and 41272024) and the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan (program GBL11302).