Carbon and strontium isotopes and global correlation of Cambrian Series 2-Series 3 carbonate rocks in the Keping area of the northwestern Tarim Basin, NW China

Abstract

One hundred and ten carbon and nineteen strontium isotopic values of outcropping Cambrian Series 2 and Series 3 carbonate rocks in the Penglaiba section of the Keping area were analyzed. Effective isotopic data with little influence of diagenesis were used to address the global correlation. The δ 13C values exhibit two major positive excursions (peaking at 3.1‰ and 3.3‰) and three major negative excursions (peaking at −3.0‰, −4.2‰ and −3.2‰). The carbon isotope excursions (peaking at −3.0‰ and −4.2‰) across the Cambrian Series 2-Series 3 boundary show good correlations with similar variations reported in Siberia, Laurentia, North China and South China. In contrast, the other three carbon isotope excursions (peaking at 3.1‰, 3.3‰ and −3.2‰) do not have a fairly good global correlation because of the lack of biostratigraphic data. With respect to the 87Sr/ 86Sr ratios, they show good correlation with those reported for Laurentia, and further support the global δ 13C comparison. On the basis of these new data, it is showed that the combination of δ 13C curves and 87Sr/ 86Sr variations serves as a powerful tool for correlation and subdivision of Cambrian strata in the Tarim Basin of northwest China, and provides new data for global correlation.