Browsing by Author "Cui, Huan"

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    An authigenic response to Ediacaran surface oxidation: Remarkable micron-scale isotopic heterogeneity revealed by SIMS
    Cui, Huan; Kitajima, Kouki; Orland, Ian J.; Baele, Jean-Marc; Xiao, Shuhai; Kaufman, Alan J.; Denny, Adam; Spicuzza, Michael J.; Fournelle, John H.; Valley, John W. (Elsevier, 2022-08-01)
    The Ediacaran Shuram excursion (SE) records a global decrease in carbonate carbon isotope (δ13Ccarb) values from +6‰ down to ca. –10‰, representing the largest δ13Ccarb negative anomaly in Earth history. While the SE is widely recorded in the upper Doushantuo Formation of South China, it shows highly variable δ13Ccarb profiles among correlative sections. This inconsistent expression of the SE challenges the conventional view of a homogeneous marine dissolved inorganic carbon (DIC) reservoir. A potential process that could explain δ13Ccarb variability is local mineralization of isotopically distinct authigenic carbonates near the sediment–water interface during early diagenesis. However, a direct test of such authigenic carbonates is still limited. Here, following a recent study on the SE in an intra-shelf environment, we revisited an outer-shelf section, identified and analyzed μm-scale, syn-depositional authigenic calcite cements via integrated cathodoluminescence (CL), micro-X-ray fluorescence (μXRF), scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and secondary ion mass spectrometry (SIMS). Our new SIMS results reveal remarkable micron-scale heterogeneity of δ13Ccarb in authigenic calcite cements, including extremely negative values down to –37.5‰ (VPDB). We interpret these calcite cements as methane-derived authigenic calcite (MDAC) resulting from microbial sulfate reduction (MSR) and anaerobic oxidation of methane (AOM) during early diagenesis. Based on the new results, we propose that the heterogeneous SE in South China — manifest on micrometer, centimeter, and basinal scales — was modulated by methane oxidation under variable local redox and water depth conditions. The SE, therefore, was coupled with different degrees of methane oxidation in individual basins, and globally triggered by enhanced seawater sulfate during an atmospheric oxygenation event. In light of this study, the potential role of redox variability in methane oxidation during the SE may have been underestimated. Our study demonstrates that integrated SIMS-SEM analysis can distinguish different generations of isotopically distinct carbonates otherwise undetected by conventional analysis, and is thus an effective approach to assess the origin and diagenetic history of δ13Ccarb anomalies in the sedimentary record.
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    Deposition or diagenesis? Probing the Ediacaran Shuram excursion in South China by SIMS
    Cui, Huan; Kitajima, Kouki; Orland, Ian J.; Xiao, Shuhai; Baele, Jean-Marc; Kaufman, Alan J.; Denny, Adam; Zhou, Chuanming; Spicuzza, Michael J.; Fournelle, John H.; Valley, John W. (Elsevier, 2021-11)
    The Ediacaran Period (ca. 635–541 Ma) witnessed the earliest paleontological evidence for macroscopic animals (i.e., Ediacara biota) and geochemical observations of the largest carbon cycle anomaly in Earth history (i.e., Shuram Excursion, SE). Numerous hypotheses have been proposed for the origins of the SE, ranging from primary seawater anomaly to syn- or post-depositional diagenesis. Despite intensive geochemical and theoretical work published in the past decade, empirical evidence that is strictly based on fundamental petrographic results at the micrometer scale is still limited. To evaluate depositional compositions and diagenetic effects on samples from the SE, we investigated the EN3 interval in the Doushantuo Formation of South China via integrated cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), and scanning electron microscope (SEM). Detailed petrographic observations reveal that the EN3 limestone is dominated by calcite microspar, with minor but variable amounts of disseminated zoned dolomite crystals. The former likely formed via neomorphism of depositional micrite, while the latter was the result of progressive post-depositional dolomitization. The mean values of paired SIMS δ13Ccalcite and δ13Cdolomite compositions are indistinguishable in each sample and consistent with published micro-drilled bulk-powder δ13C values, which we interpret to represent depositional “background” signals of seawater dissolved inorganic carbon (DIC). We also observed μm-scale variability of SIMS δ13C data that may reflect a variable diagenetic overprint after deposition. Our integrated petrographic and geochemical results are consistent with a depositional origin of the SE and provide little evidence for the hypothesized isotope alteration by meteoric and mixing-zone diagenesis or late burial diagenesis. In light of this study, we propose that the SE indeed represents a marine carbon cycle anomaly that bears a close temporal link to the Ediacaran surface environment.
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    Extensive marine anoxia during the terminal Ediacaran Period
    Zhang, Feifei; Xiao, Shuhai; Kendall, Brian; Romaniello, Stephen J.; Cui, Huan; Meyer, Mike; Gilleaudeau, Geoffrey J.; Kaufman, Alan J.; Anbar, Ariel D. (AAAS, 2018-06-20)
    The terminal Ediacaran Period witnessed the decline of the Ediacara biota (which may have included many stem-group animals). To test whether oceanic anoxia might have played a role in this evolutionary event, we measured U isotope compositions (δ238U) in sedimentary carbonates from the Dengying Formation of South China to obtain new constraints on the extent of global redox change during the terminal Ediacaran. We found the most negative carbonate δ238U values yet reported (−0.95 per mil), which were reproduced in two widely spaced coeval sections spanning the terminal Ediacaran Period (551 to 541 million years ago). Mass balance modeling indicates an episode of extensive oceanic anoxia, during which anoxia covered >21% of the seafloor and most U entering the oceans was removed into sediments below anoxic waters. The results suggest that an expansion of oceanic anoxia and temporal-spatial redox heterogeneity, independent of other environmental and ecological factors, may have contributed to the decline of the Ediacara biota and may have also stimulated animal motility.
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    The Sedimentary Geochemistry and Paleoenvironments Project
    Farrell, Una C.; Samawi, Rifaat; Anjanappa, Savitha; Klykov, Roman; Adeboye, Oyeleye O.; Agic, Heda; Ahm, Anne-Sofie C.; Boag, Thomas H.; Bowyer, Fred; Brocks, Jochen J.; Brunoir, Tessa N.; Canfield, Donald E.; Chen, Xiaoyan; Cheng, Meng; Clarkson, Matthew O.; Cole, Devon B.; Cordie, David R.; Crockford, Peter W.; Cui, Huan; Dahl, Tais W.; Mouro, Lucas D.; Dewing, Keith; Dornbos, Stephen Q.; Drabon, Nadja; Dumoulin, Julie A.; Emmings, Joseph F.; Endriga, Cecilia R.; Fraser, Tiffani A.; Gaines, Robert R.; Gaschnig, Richard M.; Gibson, Timothy M.; Gilleaudeau, Geoffrey J.; Gill, Benjamin C.; Goldberg, Karin; Guilbaud, Romain; Halverson, Galen P.; Hammarlund, Emma U.; Hantsoo, Kalev G.; Henderson, Miles A.; Hodgskiss, Malcolm SW W.; Horner, Tristan J.; Husson, Jon M.; Johnson, Benjamin; Kabanov, Pavel; Brenhin Keller, C.; Kimmig, Julien; Kipp, Michael A.; Knoll, Andrew H.; Kreitsmann, Timmu; Kunzmann, Marcus; Kurzweil, Florian; LeRoy, Matthew A.; Li, Chao; Lipp, Alex G.; Loydell, David K.; Lu, Xinze; Macdonald, Francis A.; Magnall, Joseph M.; Mand, Kaarel; Mehra, Akshay; Melchin, Michael J.; Miller, Austin J.; Mills, N. Tanner; Mwinde, Chiza N.; O'Connell, Brennan; Och, Lawrence M.; Ossa Ossa, Frantz; Pages, Anais; Paiste, Kart; Partin, Camille A.; Peters, Shanan E.; Petrov, Peter; Playter, Tiffany L.; Plaza-Torres, Stephanie; Porter, Susannah M.; Poulton, Simon W.; Pruss, Sara B.; Richoz, Sylvain; Ritzer, Samantha R.; Rooney, Alan D.; Sahoo, Swapan K.; Schoepfer, Shane D.; Sclafani, Judith A.; Shen, Yanan; Shorttle, Oliver; Slotznick, Sarah P.; Smith, Emily F.; Spinks, Sam; Stockey, Richard G.; Strauss, Justin V.; Stueken, Eva E.; Tecklenburg, Sabrina; Thomson, Danielle; Tosca, Nicholas J.; Uhlein, Gabriel J.; Vizcaino, Maoli N.; Wang, Huajian; White, Tristan; Wilby, Philip R.; Woltz, Christina R.; Wood, Rachel A.; Xiang, Lei; Yurchenko, Inessa A.; Zhang, Tianran; Planavsky, Noah J.; Lau, Kimberly V.; Johnston, David T.; Sperling, Erik A. (Wiley, 2021-07-05)
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    Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China
    Cui, Huan; Xiao, Shuhai; Cai, Yaoping; Peek, Sara; Plummer, Rebecca E.; Kaufman, Alan J. (2019-11)
    The terminal Ediacaran Dengying Formation (c. 551.1-538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for construction of a relatively continuous chemostratigraphic profile for the terminal Ediacaran Period. In this study, a detailed sedimentological and chemostratigraphic (delta 13C(carb), delta O-18(carb), delta C-13(org), delta S-34(pyrite), and Sr-87/Sr-86) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow-marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.
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    Was the Ediacaran Shuram Excursion a globally synchronized early diagenetic event? Insights from methane-derived authigenic carbonates in the uppermost Doushantuo Formation, South China
    Cui, Huan; Kaufman, Alan J.; Xiao, Shuhai; Zhou, Chuanming; Liu, Xiao-Ming (2017-02)
    The Ediacaran Period is characterized by the most profound negative carbon isotope (δ13C) excursion in Earth history, the ShuramExcursion. Various hypotheses – including the massive oxidation of dissolved organic carbon (DOC) in the oceans, the weathering of terrestrial organic carbon, or the release and oxidation of methane hydrates and/or expelled petroleum from the subsurface – have been proposed as sources of the 13C-depleted carbon. More recently, it has been suggested that global-scale precipitation of early authigenic carbonates, driven by anaerobicmicrobial metabolism in unconsolidated sediments, may have caused the Shuram Excursion, but empirical evidence is lacking. Here we present a comprehensive analysis of a Shuram-associated interval from the uppermost Doushantuo Formation in South China. Our study reveals petrographic evidence of methane-derived authigenic calcite (formed as early diagenetic cements and nodules) that are remarkably depleted in 13C – suggesting a buildup of alkalinity in pore fluids through the anaerobic oxidation of methane (AOM) – and systematically depleted in 18O relative to co-occurring dolomite. Early authigenesis of these minerals is likely to be driven by increased microbial sulfate reduction, triggered by enhanced continental weathering in the context of a marked rise in atmospheric oxygen levels. In light of the finding of methane-derived authigenic carbonates at Zhongling, and based on our basin-scale stratigraphic correlation, we hypothesize that the marked 13C and 18O depletion (including their co-variation noted worldwide) in the Shuram Excursion may reflect an episode of authigenesis occurring within a sulfate–methane transition zone (SMTZ). If true, the Shuram Excursion was then a global biogeochemical response to enhanced seawater sulfate concentration in the Ediacaran ocean driven by the Neoproterozoic oxidation of surface environments. This paleo-oceanographic transition may have therefore paved theway for subsequent evolution and diversification of animals. Our study highlights the significance of an integrated approach that combines petrography, mineralogy, and texture-specificmicro-drilling geochemistry in chemostratigraphic studies.