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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-66
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
11 May 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).
Latest Permian carbonate-carbon isotope variability traces heterogeneous organic carbon accumulation and authigenic carbonate formation
Martin Schobben1,2, Sebastiaan van de Velde3, Jana Suchocka2, Lucyna Leda2, Dieter Korn2, Ulrich Struck2, Clemens Vinzenz Ullmann4, Vachik Hairapetian5, Abbas Ghaderi6, Christoph Korte7, Robert J. Newton1, Simon W. Poulton1, and Paul B. Wignall1 1School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
2Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstr. 43, D-10115 Berlin, Germany
3Analytical, Environmental and Geochemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium
4College of Engineering, Mathematics and Physical Sciences, Camborne School of Mines, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, United Kingdom
5Department of Geology, Khorasgan (Esfahan) Branch, Islamic Azad University, P.O. Box 81595-158, Esfahan, Iran
6Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
7Department of Geosciences and Natural Resource Management, University of Copenhagen, ØsterVoldgade 10, DK-1350 Copenhagen, Denmark
Abstract. Bulk-carbonate carbon isotope measurements are a widely applied proxy for investigating the ancient biogeochemical carbon cycle. Temporal carbon isotope trends serve as a prime stratigraphic tool, with the inherent assumption that bulk micritic carbonate rock is a faithful geochemical recorder of the isotopic composition of seawater dissolved inorganic carbon. However, bulk-carbonate rock is also prone to incorporate diagenetic signals. The aim of the present study is to disentangle primary trends from diagenetic signals in carbon isotope records which traverse the Permian–Triassic boundary in marine carbonate-bearing sequences of Iran and South China. By pooling newly produced and published carbon isotope data we confirm that a global first-order trend towards depleted values exists. However, a large amount of scatter is superimposed on this geochemical record. In addition, we observe a temporal trend in the amplitude of this residual δ13C variability, which is reproducible for the two studied regions. We suggest that (sub)seafloor microbial communities and their control on calcite nucleation as well as on ambient porewater dissolved inorganic carbon-δ13C pose a viable mechanism to induce bulk-rock δ13C variability. Numerical model calculations highlight that early diagenetic carbonate rock stabilization, and linked carbon isotope alteration, can be controlled by organic matter supply and subsequent microbial remineralization. Low marine sulfate and a major biotic decline among late Permian bottom-dwelling organisms facilitated a spatial increase in heterogeneous organic carbon accumulation, causing varying degrees of carbon isotope overprint. A simulated time series suggests that a 50 % increase in the spatial scatter of organic carbon relative to the average, in addition to an imposed increase in the likelihood of sampling cements formed by microbial calcite nucleation to one out of 10 samples, is sufficient to induce the observed signal of carbon isotope variability. These findings put constraints on the application of Permian–Triassic carbon isotope chemostratigraphy based on whole-rock samples, which appears less refined than classical biozonation dating schemes. On the other hand, this signal of increased carbon isotope variability concurrent with the largest mass extinction of the Phanerozoic may inform about local carbon cycling mediated by spatially heterogeneous (sub)-seafloor microbial communities under suppressed bioturbation.

Citation: Schobben, M., van de Velde, S., Suchocka, J., Leda, L., Korn, D., Struck, U., Ullmann, C. V., Hairapetian, V., Ghaderi, A., Korte, C., Newton, R. J., Poulton, S. W., and Wignall, P. B.: Latest Permian carbonate-carbon isotope variability traces heterogeneous organic carbon accumulation and authigenic carbonate formation, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-66, in review, 2017.
Martin Schobben et al.
Martin Schobben et al.

Data sets

carbonate project
M. Schobben
http://doi.org/10.5281/zenodo.496086

Model code and software

carbonate project
M. Schobben
http://doi.org/10.5281/zenodo.496086
Martin Schobben et al.

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Short summary
Stratigraphic trends in carbon isotope composition of calcium carbonate rock can be used as a stratigraphic tool. An important assumption when using isotope chemical records is that they record a globally universal signal of marine water chemistry. In this study we show that carbon isotope scatter at confined centimeter stratigraphic scale appears to represent a signal of microbial activity. However, long-term carbon isotope trends are still compatible with a primary isotope imprint.
Stratigraphic trends in carbon isotope composition of calcium carbonate rock can be used as a...
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