HR: 0800h
AN: PP41A-0585    [Abstracts]
TI: The Toarcian Oceanic Anoxic Event (T-OAE): Global v Local Causes
AU: * Schootbrugge, B v
EM: vandesch@imcs.rutgers.edu
AF: IMCS Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901 United States
AU: * Schootbrugge, B v
EM: vandesch@imcs.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 United States
AU: Bailey, T R
AF: National Museum and Galleries of Wales, Cathays Park, Cardiff, CF10 3NP United Kingdom
AU: Rosenthal, Y
EM: rosentha@imcs.rutgers.edu
AF: IMCS Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901 United States
AU: Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 United States
AU: Miller, K G
EM: kgm@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854 United States
AU: McArthur, J M
EM: j.mcarthur@ucl.ac.uk
AF: University College of London, Gower Street, London, WC1E 6BT United Kingdom
AB: The rapid and massive dissociation of methane from gas-hydrates has been proposed as a trigger for the Toarcian Oceanic Anoxic Event (T-OAE) and potentially could explain simultaneous large negative excursions (up to 7$\permil$ PDB) in bulk carbonate ($\delta$$^{13}$C$_{carb}$) and organic carbon isotope records ($\delta$$^{13}$C$_{org}$) from across sections in NW Europe. After oxidation of the released methane, raised atmospheric carbon dioxide levels are thought to have caused global greenhouse climate conditions. Acceleration of the hydrological cycle and persistently high rates of weathering and run-off fuelled increased primary production, which aided by salinity stratification, led to the deposition of widespread black shales with TOC up to 18%. We present C-isotope records from belemnites ($\delta$$^{13}$C$_{bel}$) sampled from two localities, calibrated with high-resolution ammonite biostratigraphy, in Yorkshire (England) and Dotternhausen (Germany), that do not show such rapid and large negative C-isotope excursions when compared with coeval ($\delta$$^{13}$C$_{org}$) and ($\delta$$^{13}$C$_{carb}$) records. Therefore light carbon can not have dominated the entire carbon system, as would be expected in the case of methane dissociation. Based on a critical evaluation of all carbon isotope records, including our ($\delta$$^{13}$C$_{bel}$), we support a model in which the recycling of DIC from the deeper levels of a stratified water body and shallowing of anoxic conditions into the photic zone play a central role. A compilation and comparison of ($\Delta$$\delta$$^{13}$C$_{carb-org}$) records from sections across an inshore-offshore transect further illustrates that belemnites recorded a more open ocean (positive) carbon isotope signal, while (bulk) carbonate and organic carbon tracked the degree of stratification and related carbon dioxide pressure.
DE: 4870 Stable isotopes
DE: 3030 Micropaleontology
DE: 1045 Low-temperature geochemistry
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting