Deciphering surface environment in the late Proterozoic using Re-Os measurement.

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Global correlation of Precambrian stratigraphic successions can be conducted by the coarse resolution off biostratigraphic and chemostratigraphic records, because of the scarcity of precise U-Pb zircon dating. Re-Os isotope systems of organic matter-rich black shales became one of the reliable indicators of the depositional age, due to the recent developments in Re-Os analysis.Rock powders were prepared from drill-core collected at Three Gorge, South China. Re and Os isotopic compositions were measured by TIMS at JAMSTEC. The 187Re/188Os and 187Os/188Os ratios of the black shales show linearity in the isochron plot. The model 3 isochron ages were 578 Ma (error is 12 Ma) for the black shale at the lower Member 4 of the Doushantuo Fm, with initial 187Os/188Os ratios of 1.02 (2SD=0.09). The Re-Os isochron plot for all analyses yields an age of 512 (error is 12 Ma) for the black shale at the bottom of the Shuijingtuo Fm, with initial 187Os/188Os ratios of 1.15 (2SD=0.19).