Sedimentary environments of lower Cambrian black shale in S. China

The δSpy of sedimentary pyrite from the Lower Cambrian black shale in NW Hunan of China have been determined. Except one sample with a δSpy value of –0.97‰ from the NiMo mineralized bed at the bottom Cambrian, total other 16 pyrite samples are all in the range from +10 ‰ to +28 ‰ with an mean value +20 ‰, obviously different from those in modern oceanic sediment (-20‰ to -10‰). If δS of the seawater sulphate was identical with the world seawater at the early Cambrian, about +34‰, there was a small fractionation only 14‰ during sedimentation of the black shale. The high δSpy value in the black shale should be caused by small fractionation between seawater sulphate and biogenic sedimentary pyrite in an anoxic sulfidic ocean in which the availability of sulphate is limited. Combining the data of δCorg, δCcarb and trace elements of the black shale and related paleo-atmosphere and -ocean models, we propose a preliminary idea of paleoenvironments of the Lower Cambrian black shale in NW Hunan as follows. This study supported by NSFC (40073007 & 40232020).