Carbon isotope chemostratigraphy of the Lower Permian Dingjiazhai Formation in the Baoshan Block,Yunnan

The present paper deals,on the basis of section measurement and borehole geological records,with the carbon and oxygen isotope study of the carbonate rocks and gravel-bearing calcareous greywacke from the Lower Permian Dingjiazhai Formation in the Baoshan Block,Yunnan. The δ¹³C values of the carbonate rocks both in the overlying and underlying horizons of the Lower Permian Dingjiazhai Formation are positive values while those within the Dingjiazhai Formation display one or several negative excursions. The coral and bryozoan fossils found separately in the Pumenqian and Dingjiazhai Formations have provided the new evidence for the age dating of the Formatioms mentioned above. The correlation between the carbon and oxygen isotope values for the Dingjiazhai Formation and other places in the world suggests a highly linear correlation of the carbon and oxygen isotope data during the Carboniferous-Permian. The negative excursions of δ¹³C values may well be related to the surface exposure during the deposition and diagenesis of the glacial lowstand deposits. Numerous factors such as the increase of CO₂ contents,global warming,strengthening of weathering,and the increase of terrigenous supply caused by the large-scale eruption of the Woniusi basalts as well as the glaciation have exerted the combined effects on the variations in marine inorganic carbon isotope values for the Dingjiazhai Formation.