The studied Sinian strata are distributed in Hunan, Guizhou and Sichuan Provnces, and include the Early Siruan Chumnu, Minle, and Nantuo, and the Late Siuan houshantuo and Uengying Formations. They are underlain unconformably by slightly metamorphosed nx:ks and orerlain confurmahly by the Early Cambrian siliceous rock,phosphorus nodule-bearing black shale and muddy limestone. Chunmu Formation is composed of pebbly sandstone, sandstone and silty mudstone. Minle Formation is composed of manganese carbonate ore, black shale, dolostone and dray shale. Nantuo Formation is the tillite horizon widely distributed in south China. Toushantuo Formation consists or dolostone, black shale, gray shale and siltstonc. Dcngying Formation is composed of limestone. The estimated age of the boundary between tire Sinian and Prc-Sinian strata is 74b Ma, and the Rb-Sr isochronic age of the manganese carbonate ore beds at the bottom of Minle Formation is (728±27) Ma.The Early Sioian strata have an anomalous heavy sulphur isotopic composition in pyrite The δ34S values are around+24‰ at the bottom increase upwards, and can reach up to+60‰-64‰ in the manganese carbonate ore and the adjacent black shales. The very positmc δ34S values of the Early Sinian strata are in accordance with the isotopic composition feature of the world-wide late Proterozoic black shales that, probably, reflects a global supercontinent tectonic setting. It seems that the Yangtze block had already joined the aurercontinent R odinia in the Early Sinian time.A marked variation in the sulphur isotopic composition of pyrite is observed in the Late Sinian strata. The negative δ34S values occur at the bottom,decrease upwards, and maintain-22‰-30‰ which are typical of the normal marine sedimentary rocks. This variation in sulphur isotopic composition of the Sinian strata indicates great changes from close to open marine basin conditions. It is in accordancc with the suggestion that the breakup of the Rodinia around 0.7Ga scparatcd Yangtzc (plus Cathaysia) blocks from the other continents.
Li Renwei,Zhang Shukun,Lei Jiajin et al. TEMPDRAL AND SPACIAI, VARiAT10N IN δ34S VALUES OF PYRITE FROM S1N1AN STRATA DISCUSSION ON RELATIONSHIP BETWEEN YANGTZE BLDCK AND THE LATE PROTEROZOIC SUPERCONTINENT[J]. Chinese Journal of Geology, 1996, (3): 209-217.