Abstract:

Extremely ¹³C-depleted isotope is the key evidence to identify ancient cold seepage and methane release event in Earth history. There has been no report of direct evidence of cold seepage in Early Permian period so far. Here we unprecedentedly present the carbonate carbon and oxygen isotopes with extreme 13C depletion in Early Permian of Lasha Block, Tibet. The negative correlation of carbon and oxygen isotopes is pronounced and the lowest carbon isotope is to -34.69‰(VPDB), exclusively indicating anaerobic oxidation of methane. These carbonates occur in the upper member of the Lanfjie Formation in Xainza, Tibet as carbonate lens and carbonate-cemented concretion, and calcite crystal fans are more depleted in 13C than carbonate cements in the concretions. We infer the occurrence of ancient cold seepage in Early Permian in the study area and attribute this event to the postglacial destabilization of gas hydrate reservoir. This study is significant to investigate glacioeustatic change, oceanographic geochemistry, paleoecology and climate change.

Key words: Xainza,Tibet, Early Permian, carbonate, extremely ¹³C-depleted isotop