Browsing by Author "Bao, Huiming"

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    Transient marine euxinia at the end of the terminal Cryogenian glaciation
    Lang, Xianguo; Shen, Bing; Peng, Yongbo; Xiao, Shuhai; Zhou, Chuanming; Bao, Huiming; Kaufman, Alan J.; Huang, Kangjun; Crockford, Peter W.; Liu, Yonggang; Tang, Wenbo; Ma, Haoran (Springer Nature, 2018-08-01)
    Termination of the terminal Cryogenian Marinoan snowball Earth glaciation (similar to 650-635 Ma) is associated with the worldwide deposition of a cap carbonate. Modeling studies suggest that, during and immediately following deglaciation, the ocean may have experienced a rapid rise in pH and physical stratification followed by oceanic overturn. Testing these predictions requires the establishment of a high-resolution sequence of events within sedimentary records. Here we report the conspicuous occurrence of pyrite concretions in the topmost Nantuo Formation ( South China) that was deposited in the Marinoan glacial deposits. Sedimentary facies and sulfur isotope data indicate pyrite precipitation in the sediments with H2S diffusing from the overlying sulfidic/euxinic seawater and Fe (II) from diamictite sediments. These observations suggest a transient but widespread presence of marine euxinia in an ocean characterized by redox stratification, high bioproductivity, and high-fluxes of sulfate from chemical weathering before the deposition of the cap carbonate.
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    A transient peak in marine sulfate after the 635-Ma snowball Earth
    Peng, Yongbo; Bao, Huiming; Jiang, Ganqing; Crockford, Peter; Feng, Dong; Xiao, Shuhai; Kaufman, Alan Jay; Wang, Jiasheng (National Academy of Sciences, 2022-05-10)
    A series of dramatic oceanic and atmospheric events occurred in the immediate aftermath of the Marinoan “snowball Earth” meltdown ∼635 My ago. However, at the 10-to 100-ky timescale, the order, rate, duration, and causal-feedback relationships of these individual events remain nebulous. Nonetheless, rapid swings in regional marine sulfate concentrations are predicted to have occurred in the aftermath of a snowball Earth, due to the nonlinear responses of its two major controlling fluxes: oxidative weathering on the continents and pyrite burial in marine sediments. Here, through the application of multiple isotope systems on various carbon and sulfur compounds, we determined extremely 13C-depleted calcite cements in the basal Ediacaran in South China to be the result of microbial sulfate reduction coupled to anaerobic oxidation of methane, which indicates an interval of high sulfate concentrations in some part of the postmeltdown ocean. Regional chemostratigraphy places the 13C-depleted cements at the equivalent of the earliest Ediacaran 17O-depletion episode, thus confining the timing of this peak in sulfate concentrations within ∼50 ky since the onset of the deglaciation. The dearth of similarly 13C-depleted cements in other Proterozoic successions implies that the earliest Ediacaran peak in marine sulfate concentration is a regional and likely transient event.