Two episodes of 13C-depletion in organic carbon in the latest Permian: Evidence from the terrestrial sequences in northern Xinjiang, China

• Published in: Earth and planetary science letters 2008-06, Vol.270 (3), p.251-257
• Main Authors: Cao, Changqun, Wang, Wei, Liu, Lujun, Shen, Shuzhong, Summons, Roger E.
• Format: Article
• Language: English
• Subjects: carbon isotope; China; Permian; terrestrial; Triassic; Xinjiang
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2008.03.043

New analyses reveal two intervals of distinctly lower δ 13C values in the terrestrial organic matter of Permian–Triassic sequences in northern Xinjiang, China. The younger negative δ 13C org spike can be correlated to the conspicuous and sharp δ 13C drops both in carbonate carbon and organic carbon near the Permian–Triassic event boundary (PTEB) in the marine section at Meishan. The geochemical correlation criteria are accompanied by a magnetic susceptibility pulse and higher abundances of distinctive, chain-like organic fossil remains of Reduviasporonites. The older negative δ 13C org spike originates within a latest Permian regression. Significant changes in organic geochemical proxies are recorded in the equivalent interval of the marine section at Meishan. These include relatively higher concentrations of total organic carbon, isorenieratane, C 14–C 30 aryl isoprenoids and lower ratios of pristane/phytane that, together, indicate the onset of anoxic, euxinic and restricted environments within the photic zone. The massive and widespread oxidation of buried organic matter that induced these euxinic conditions in the ocean would also result in increased concentrations of 13C-depleted atmospheric CO 2. The latest Permian environmental stress marked by the older negative δ 13C org episode can be correlated with the distinct changeover of ostracod assemblages and the occurrences of morphological abnormalities of pollen grains. These observations imply that biogeochemical disturbance was manifested on the land at the end of the Permian and that terrestrial organisms responded to it before the main extinction of the marine fauna.