Thus, we infer that bulk-sample δ¹³Ccarb values of Doushantuo samples represent mixtures of different carbonate components. A boundary condition on the evolution of atmospheric oxygen.

Precambr. Isotopes, ice ages, and terminalProterozoic earth history. (F) Massive oolitic grainstone/limestone facies from the LagoaG were taken in the southern part of the Bambuí BasinL were taken from a section close to the Januária city in the northerned with doubly distilled 0.5 M acetic acid overnight tolaments were measured using the VG Sector 54 thermal io-. The δ34Spyrite negative excursion suggests the buildup of the marine sulfate reservoir, likely due to enhanced pyrite oxidation during the oxygenation event. Here, we present a coupled carbon and sulfate isotope study of Lomagundi excursion carbonates that points to primary productivity rather than carbonate formation in the methanic zone as the underlying mechanism for this excursion.

Integrated with petrographic observations, the new SIMS data suggest that much of the chaotic stratigraphic δ 13 C variation is related to the presence of authigenic calcite with either highly positive or negative isotopic values. 110, 14546Catling, D.C., Claire, M.W., Zahnle, K.J., 2007. Geochem.Lyons, T.W., Reinhard, C.T., Planavsky, N.J., 2014. Sci. He knows how to anticipate where the ball will go. (A, B) Limestone samples with undulated laminations. This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambuí Group that occurs with only minor changes in Δ¹³C values, suggesting change in the DIC isotope composition. Our data show that the meter-scale stratigraphic variations in δ¹³Ccarb are also mirrored in the SIMS data at μm-mm scales in both Doushantuo and Mooifontein samples.
Rev. Geol. Corresponding microscopic images of this samplesample slab images are available in the online supplementary materials.data in this study are limited due to the fact that manysamples (each processed with at least 100 g of powders) did not yieldenough barite precipitate during CAS extraction. Based on the above age constraints, the Bambuí Group represents a transition from the Ediacaran to the Cambrian Period. No petrographic evidence for sig-under CL: orange = calcite, green = apatite, bright blue = K feldspar, pinkish = albite, black = quartz. insights from methane-derived authigenic carbonates in the uppermost Doushantuo Formation, South China.Cui, H., Kaufman, A.J., Peng, Y., Liu, X.-M., Plummer, R.E., Lee, E.I., 2018. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article. lactate and acetate) by sulfate reducersmethanogenesis typically only occurs in sulfate-depleted conditions.Could the redox conditions allow for water-column methanogenesisduring the MIBE? However, in the northern part of the basin this unit canbe informally divided into two stratigraphic intervals: an carbonate-dominated basal succession (~70 m) and a siliciclastic-dominatedThe basal part of the Lagoa do Jacaré Formation consists primarilyof microbialite facies and domal or columnar stromatolites (bedded with massive mudstone and wave-ripple cross-laminatedsuggests an overall shallow and energetic environment. Chem. )H) of some ooids suggest that they may have been partially), the organic matter in the MIBE appears to be much more en-Petrographic images of three samples from the lowergure legend, the reader is referred to the web version of this article.

Res.Liu, X.-M., Kah, L.C., Knoll, A.H., Cui, H., Kaufman, A.J., Shahar, A., Hazen, R.M., 2016.evolution using Zn/Fe ratios in marine carbonates. Alternatively, with a much higher proportion of or-ganic carbon burial, a smaller proportion of authigenic carbonate burialis needed to achieve the MIBE based on this model. Stratination of the late Precambrian environment: a post glacial geochemical record fromthe Neoproterozoic of W. Mongolia. (Eds.

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Note that the São Francisco craton (marked as number 5) was located in the center of the Gondwana paleo-continent. 5, 4672. Carbonbauer, J.D., Martin, A.J., 2016b. J. Sci. 152, 173Kump, L.R., Arthur, M.A., 1999. These two sections show distinctKM7-12 section records relatively lower values between +5.1cracks (yellow arrows). The system wasoperated by using an acceleration voltage of 15 kV and a beam currentCanada), set from 0.1 to a few seconds exposure time depending on CLused to reduce noise. Integrated chemo- andbiostratigraphic calibration of early animal evolution: NeoproterozoicCambrian of southwest Mongolia. Rev.Frimmel, H.E., 2010. Earth Planet. Precambr. Precambr. Sin embargo, el par de afloje de estas tuercas de fijación necesita más atención. 112,Schrag, D.P., Higgins, J.A., Macdonald, F.A., Johnston, D.T., 2013. Geol. In order to better constrain the biogeochemical carbonand sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both theplateau (i.e., Lagoa do Jacaré Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of thebetween these two studied MIBE intervals. The new data suggest that the Hüttenberg anomaly records dynamic fluctuations in marine redox conditions, which may include an oxygenation event during the height of the δ13Ccarb positive excursion and a deoxygenation event at its termination.

In: Gaucher, C., Sial, A.N.,Halverson, G.P., Frimmel, H.E. Geobiology 14, 344Cui, H., Kaufman, A.J., Xiao, S., Zhou, C., Liu, X.-M., 2017. /Type /XObject All the isotopic analyses were conducted in theDepartment of Geology, University of Maryland. ), Reviews in Mineralogy and Geochemistry: StableIsotope Geochemistry. 323).