High δ13C carbonates from the Songpan-Garze 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 delta C-13(Carb) excursion. Even having experienced amphibolite facies metamorphism, most of carbonates in the interior of the marble layer preserve premetamorphic delta C-13 and delta O-18 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, delta C-13(Carb)= similar to +5 to + 7.3 parts per thousand and delta O-18(Carb) = similar to 20 to 25 parts per thousand, and delta C-13(Carb) = similar to +1.5 to + 3 parts per thousand and delta O-18(Carb) = similar to 28 to 30 parts per thousand, respectively. This pattern of variation, especially in delta C-13, 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 delta C-13(Carb) excursion can be correlated on a basinal scale within the Yangtze Platform. The data presented here establish that high delta C-13 values of carbonates from the upper Sinian Doushantuo Formation are a regional feature across the Yangtze Platform.