HR: 0830h
AN: PP41C-0847    [PDF]
TI: Non-steady state redox conditions in bottom and pore waters of the Mid-Cretaceous NW-African shelf at Tarfaya (SW-Morocco): Climate control and implications for synchrony of basin-wide oxidation of shallow waters during the CT-OAE2
AU: * Wagner, T
EM: twagner@uni-bremen.de
AF: University of Bremen, Geosciences, PO Box 330440,, Bremen, 28334 Germany
AU: Kasten, S
EM: skasten@uni-bremen.de
AF: University of Bremen, Geosciences, PO Box 330440,, Bremen, 28334 Germany
AU: Kolonic, S
EM: skolonic@uni-bremen.de
AF: University of Bremen, Geosciences, PO Box 330440,, Bremen, 28334 Germany
AB: Widespread deposition of organic-carbon-rich marine sediments during the Oceanic Anoxic Events (OAEs) is a distinct feature of the Cretaceous ocean that was intrinsically linked to periods of extreme oxygen-depletion in the water column. High-resolution geochemical and biofacial records from the southern proto-North Atlantic including the NW-African shelf have recently become available indicating that the redox state of the water column was far from stable during the OAE2. Instead it varied between anoxic/euxinic and probably suboxic/oxic conditions on Milankovitch- and maybe even shorter time scales. Despite these stimulating implications little is known about the degree of oxygenation of the water column, the dynamics of contrasting redox conditions, and whether oxidation of the water column occurred synchronous on a basin-wide scale, i.e. across the North American and NW-African shelves. We report millennial-scale geochemical records from a bathymetric transect through the Tarfaya Basin in SW-Morocco to address the nature, pacing, and synchrony of shallow marine redox cycles associated with the OAE2. The data propose that reoxidation of the water column repetitively occurred on orbital frequencies, the transition from anoxic to oxic conditions was abrupt and strong enough to result in distinct metal-rich layers (e.g. Mn) in the sedimentary column. The presence of these distinct layers propose non-steady state diagenesis with progressively downward migrating oxidation fronts. As known from more recent geological analogs, short oxic periods during the OAE2 drastically reduced the preservation potential of marine organic matter in the sediment and supported the re-colonization of the sea floor by benthic organisms. Correlation of one distinct and longer-lasting oxygenation event positioned right in the maximum of the CT global carbon isotopic excursion between the Tarfaya Basin and recently published data from the type section of the Western Interior Basin at Pueblo for the first time allow the discussion of basin-wide synchrony of this oxidation event and probable mechanism.
DE: 1620 Climate dynamics (3309)
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4808 Chemical tracers
DE: 4835 Inorganic marine chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting