Montoya-Pino, Carolina; Weyer, Stefan; Anbar, Ariel D.; Pross, Joerg; Oschmann, Wolfgang; van de Schootbrugge, Bas; Arz, Helge W. (2010): Global enhancement of ocean anoxia during Oceanic Anoxic Event 2; a quantitative approach using U isotopes. Geological Society of America (GSA), Boulder, CO, United States, Geology (Boulder), 38 (4), 315-318, georefid:2010-039395
Abstract:
During the Mesozoic greenhouse world, the oceans underwent several oceanic anoxic events (OAEs) characterized by intervals during which organic-rich black shales were deposited, indicating strong oxygen depletion in the marine realm. The Cenomanian-Turonian OAE2 (ca. 93 Ma) represents one of the most prominent events of the Cretaceous, with significant perturbations of the global carbon cycle. Although OAE2 likely reached a global scale, the spatial extent of seawater anoxia during this OAE is poorly constrained. Here we demonstrate that variations in the (super 238) U/ (super 235) U isotope ratio (delta (super 238) U), a newly developed paleoredox proxy, can be used to quantify the extent of marine anoxia. For black shales from the mid-Cretaceous OAE2 we find a systematic shift toward lighter delta (super 238) U and lower U concentrations as compared to modern equivalent organic-rich sediments from the Black Sea. This shift translates to a global increase of oceanic anoxia during OAE2 by at least a factor of three as compared to the present day or to periods before and after OAE2. The constant offset in U concentrations and isotope compositions of black shales throughout OAE2 compared to modern Black Sea sediments indicates an enhancement of oceanic anoxic conditions already prior to the onset of OAE2.
Coverage:
West: -54.1900 East: -54.1900 North: 9.0300 South: 9.0300
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Supplemental Information:
With GSA Data Repository Item 2010085
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