Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial

	Become an AGU Member Subscribe to AGU Journals



Read Full Article (file size: 922937 bytes) Cited by PALEOCEANOGRAPHY, VOL. 20, PA1006, doi:10.1029/2003PA000950, 2005 Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial Sadat Kolonic Faculty of Geosciences, University of Bremen, Bremen, Germany Thomas Wagner Faculty of Geosciences, University of Bremen, Bremen, Germany Astrid Forster Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Den Burg, Netherlands Jaap S. Sinninghe Damsté Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Den Burg, Netherlands Ben Walsworth-Bell Ardito Desio Department of Earth Sciences, University of Milan, Milan, Italy Elisabetta Erba Ardito Desio Department of Earth Sciences, University of Milan, Milan, Italy Steven Turgeon Institute for the Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany Hans-Jürgen Brumsack Institute for the Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany El Hassane Chellai Faculté des Sciences Semlalia, Départment de Géologie, Cadi Ayyad University, Marrakech, Morocco Harilaos Tsikos Department of Earth Sciences, University of Oxford, Oxford, UK Wolfgang Kuhnt Department of Geosciences, Christian-Albrechts University of Kiel, Kiel, Germany Marcel M. M. Kuypers Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany Abstract High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from ∼2 g/m² · yr prior to the OAE2 to ∼12 g/m² · yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that ∼2% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only ∼0.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Received 9 July 2003; accepted 20 August 2004; published 4 February 2005. Keywords: Cretaceous black shale; oceanic anoxic event; orbital forcing; biomarkers; trace metals; photic zone euxinia. Index Terms: 1055 Geochemistry: Organic and biogenic geochemistry; 4802 Oceanography: Biological and Chemical: Anoxic environments (0404, 1803, 4834, 4902); 4875 Oceanography: Biological and Chemical: Trace elements (0489); 9305 Geographic Location: Africa; 9610 Information Related to Geologic Time: Cretaceous. Read Full Article (file size: 922937 bytes) Cited by Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006, doi:10.1029/2003PA000950. Copyright 2005 by the American Geophysical Union.

Abstract