Carbon and sulfur isotopic compositions of basal Datangpo Formation, northeastern Guizhou, South China: Implications for depositional environment

Isotopic compositions of Mn-carbonate and organic carbon from the same individual samples and sulfur isotopic compositions of pyrites in the basal Datangpo Formation were analyzed. Highly S-34-enriched pyrites (delta(34)Spyrite = 31.7-59.4 parts per thousand) were precipitated in relatively occlusive pore water under anoxic condition in sediments, which is consistent with the observation of large and scattered pyrite framboids. The sulfidic deep ocean was not ``oxidized in the early Datangpo interglacial interval, thus the level of seawater sulfate remained low and marine delta S-34(sulphate) remained high. Low delta C-13(car) (average - 7.4 parts per thousand) and abnormal relationship between delta C-13(car) and fractionation (Delta(car-org)) imply that the negative delta C-13(car) excursion may have resulted from oxidation of part of a large organic carbon reservoir. High Delta(car-org) (average 25.1%) implicates high CO2 level in the atmosphere. Small standard deviation (1.0 parts per thousand) of delta C-13(car) values indicates the Mn-carbonate was precipitated near the water-sediment interface under dysoxic conditions rather than in occlusive pore water in sediments. (C) 2007 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.