--> Abstract: Positive Carbon Isotopic Excursions and Their Application to Sequence Statigraphy in Shallow Water Carbonates, Mississippian Madison Formation, Wyoming and Montana, by David Allen Katz, Matthew R. Buoniconti, Gregor P. Eberli, Peter K. Swart, and Langhorne B. Smith; #90039 (2005)

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Positive Carbon Isotopic Excursions and Their Application to Sequence Statigraphy in Shallow Water Carbonates, Mississippian Madison Formation, Wyoming and Montana

David Allen Katz1, Matthew R. Buoniconti1, Gregor P. Eberli1, Peter K. Swart1, and Langhorne B. Smith2
1 University of Miami/Rosenstiel School of Marine and Atmospheric Science, Miami, FL
2 New York State Museum, Albany, NY

Lower Mississippian carbonates from Wyoming and Montana show three positive carbon isotope excursions (δ13C values range from +3.5 to +7.5 ‰ PDB) within North American-Lower Mississippian/Kinderhookian to Osagean (Tournasian to Lower Visean) intervals, indicating fluctuations in the global carbon cycle at that time. These carbon isotope excursions are found along the entire Madison ramp in cores (Elk and Bighorn Basins) and in measured sections in Wyoming and Montana. The excursions are independent of facies and occur 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. On the Madison ramp, the positive carbon excursions 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 CO2 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 δ13C of coexisting organic material to compare the difference between δ13C of the inorganic and organic components and assess pCO2 levels and associated changes within the marine organic and inorganic carbon pools.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005