High δ13C Carbonates from the Songpan-Garzê Orogenic Belt: Implications for Correlation of Neoproterozoic Carbon Isotope Anomalies Across the Yangtze Platform, China

A detailed stable isotopic profile measured systematically across a thick Upper Neoproterozoic (Sinian) carbonate succession at Danba, western Yangtze Platform, China, records an overall positive δ13CCarb excursion. Even having experienced amphibolite facies metamorphism, most of carbonates in the interior of the marble layer preserve pre-metamorphic δ13C and δ18O values, which vary with stratigraphic level. The marbles can be divided into lower and upper units. The lower and upper units have distinctive isotopic composition ranges, δ13CCarb=∼+5 to +7.3% and δ18OCarb=∼20 to 25%, and δ13CCarb=∼+1.5 to +3% and δ18OCarb=∼28 to 30%, respectively. This pattern of variation, especially in δ13C, is similar to that reported for the unmetamorphosed upper Sinian Doushantuo and Dengying Formations in the eastern Yangtze Platform. This suggests that the positive Neoproterozoic δ13CCarb excursion can be correlated on a basinal scale within the Yangtze Platform. The data presented here establish that high δ13C values of carbonates from the upper Sinian Doushantuo Formation are a regional feature across the Yangtze Platform.