HR: 0800h
AN: PP41A-0579    [Abstracts]
TI: Lower Mississippian Positive Carbon Isotope Excursion in Shallow Water Carbonates, Wyoming and Montana
AU: * Katz, D A
EM: dkatz@rsmas.miami.edu
AF: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Swart, P K
EM: pswart@rsmas.miami.edu
AF: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Buoniconti, M R
EM: mbuoniconti@rsmas.miami.edu
AF: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Eberli, G P
EM: geberli@rsmas.miami.edu
AF: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Smith, L B
EM: lsmith@mail.nysed.gov
AF: Reservoir Characterization Group, New York State Museum, Room 3140 CEC, Albany, NY 12193 United States
AB: Lower Mississippian carbonates from Wyoming and Montana show a positive carbon isotope excursion (maximum \delta$^{13}$C values range from +5 to +7.5 \permil PDB) within North American-Lower Mississippian/Kinderhookian to Osagean (Tournasian to Lower Visean) intervals, indicating a fluctuation in the global carbon cycle at that time. This carbon isotope excursion is found along the entire Madison ramp in cores (Elk and Bighorn Basins) and in measured sections in Wyoming and Montana. The excursion is independent of facies and occurrs in pervasively dolomitized up dip locations as well as basinward locations composed entirely of limestone. Positive carbon values are intimately associated with sequence stratigraphy previously determined in the measured sections. The onset of the transgression in Sequence II coincides with the most depleted carbon values (ca. 1 \permil PDB) and a progressive increase of enrichment during the transgression. It reaches a maximum enrichment (ca. 7 \permil PDB) at the turnaround to the regression, followed by a gradual trend from maximum values at the turnaround to minimum values (ca. 2 \permil PDB) at the top of the sequence. On the Madison ramp, the positive carbon excursion can be used to correlate third order sequence boundaries across the 1100 km ramp system, providing a time line within otherwise undatable sections. On a larger scheme, these enriched values also correlate to time-equivalent strata discovered in previous studies from Utah, Nevada, Idaho, Wyoming, Iowa, and Western Europe, indicating its potential use as a global chronostratigraphic tool. The timing of this event probably coincides with low atmospheric CO$_{2}$ levels and the initiation of conditions that lead to the Icehouse Earth in the Upper Mississippian. In order to confirm this interpretation we are measuring the \delta$^{13}$C of coexisting organic material to compare the difference between \delta$^{13}$C of the inorganic and organic components and assess pCO$_{2}$ levels and associated changes within the marine organic and inorganic carbon pools.
DE: 4267 Paleoceanography
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 0325 Evolution of the atmosphere
DE: 0400 Biogeosciences
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting