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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2020-15
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-15
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Mar 2020

Submitted as: research article | 04 Mar 2020

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This preprint is currently under review for the journal CP.

Driving mechanisms of organic carbon burial in the Early Cretaceous South Atlantic Cape Basin (DSDP Site 361)

Wolf Dummann1,a, Sebastian Steinig2,b, Peter Hofmann1, Matthias Lenz1, Stephanie Kusch1, Sascha Flögel2, Jens Olaf Herrle3, Christian Hallmann4,5, Janet Rethemeyer1, Haino Uwe Kasper1, and Thomas Wagner6 Wolf Dummann et al.
  • 1Institute of Geology and Mineralogy, University of Cologne, Cologne, 50674, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24148 Kiel, Germany
  • 3Institute of Geosciences, Goethe-University Frankfurt, Frankfurt am Main, 60438, Germany
  • 4Max Planck Institute for Biogeochemistry, Jena, 07745, Germany
  • 5MARUM, University of Bremen, Bremen, 28359, Germany
  • 6Lyell Centre, School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University, Edinburgh, EH14 4AS, UK
  • anow at: Institute of Geosciences, Goethe-University Frankfurt, Frankfurt am Main, 60438, Germany
  • bnow at: School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK

Abstract. Extensive black shale deposits formed in the Early Cretaceous South Atlantic, supporting the notion that this emerging ocean basin was a globally important site of organic carbon burial. The magnitude of organic carbon burial in marine basins is known to be controlled by various tectonic, oceanographic, hydrological, and climatic processes acting on different temporal and spatial scales, the nature and relative importance of which are poorly understood for the young South Atlantic. Here we present new bulk and molecular geochemical data from an Aptian–Albian sediment record recovered from the deep Cape Basin at Deep Sea Drilling Project (DSDP) Site 361, which we combine with general circulation model results to identify driving mechanisms of organic carbon burial. A multi-million year decrease (i.e. Early Aptian–Albian) in organic carbon burial, reflected in a lithological succession of black shale, gray shale, and red beds, was caused by increasing bottom water oxygenation due to abating tectonic restriction via South Atlantic-Southern Ocean gateways. These results emphasize basin evolution and ocean gateway development as a decisive primary control on enhanced organic carbon preservation in the Cape Basin at geological time scales (> 1 Myr). The Early Aptian black shale sequence comprises alternations of shales with high (> 5 %) and relatively low (∼ 3 %) organic carbon content of marine sources, the former being deposited during the global Oceanic Anoxic Event (OAE) 1a, as well as during repetitive events before and after OAE 1a. In all cases, these short-term events of enhanced organic carbon burial coincided with strong influxes of sediments derived from the proximal African continent, indicating closely coupled climate–land–ocean interactions. Supported by our model results, we propose that fluctuations in weathering-derived nutrient input from the southern African continent, linked to fluctuations in pCO2 and/or orbitally driven humidity/aridity, were the underlying drivers of short-term organic carbon burial in the deep Cape Basin. These results suggest that deep marine environments of emerging ocean basins responded sensitively and directly to short-term fluctuations in riverine nutrient fluxes. We explain this relationship by the lack of wide and mature continental shelf seas that could have acted as a barrier or filter for nutrient transfer from the continent into the deep ocean.

Wolf Dummann et al.

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Wolf Dummann et al.

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Short summary
This study uses geochemical and climate modeling data to evaluate the impact of basin evolution and climate variability on organic carbon burial in the Early Cretaceous S-Atlantic Cape Basin. Our results identify the opening of ocean gateways and fluctuations in riverine nutrient supply as drivers of long- and short-term carbon burial dynamics, respectively. We conclude that specific bathymetric features (tectonic restriction/narrow shelves) conditioned the Cape Basin for enhanced carbon burial.
This study uses geochemical and climate modeling data to evaluate the impact of basin evolution...
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