Carbon Isotope Records Indicative of Paleoceanographical Events at the Latest Permian Dalong Formation at Shangsi,Northeast Sichuan,China

摘要

Paired organic and carbonate carbon isotope compositions of Late Permian Wujiaping (吴家坪) and Dalong (大隆) formations at Shangsi (上寺), Northeast Sichuan (四川) were analyzed by MAT 251. An abrupt negative excursion in the two isotope records was observed in the middle part of Dalong Formation, in association with a drop in the carbon isotope difference of the two records and an increase of total organic carbon (TOC) content. The negative drop of the paired carbon isotope records is suggestive of the input of 12C-enriched CO2. The molecular ratios of pristane to phytane and dibenzothiophene to phenanthrene indicate the anoxic condition in this interval. The enhanced TOC content is indicative of the elevated preservation of organic matter due to the anoxic condition. These isotopic and organic geochemical data probably infer the occurrence of the upwelling in this interval. The additional contribution of volcanism activity observed in South China cannot be excluded to the input of 12C-enriched CO2 and the negative shifts in carbon isotope composition of bulk organic matter and carbonate.