KINDERHOOKIAN-OSAGEAN CARBON ISOTOPE EXCURSION (A MARINE OR TERRESTRIAL ORGANIC MATTER BURIAL EVENT?) AND ITS RELATIONSHIP TO CLIMATE AND LAND PLANT EVOLUTION

The Kinderhookian-Osagean (Tournaisian) carbon isotope excursion is one of the largest in the Phanerozoic (~7 per mil) and has been previously interpreted as a global marine organic matter burial event. This organic carbon burial may have drawn down atmospheric pCO2 to levels sufficiently low to favor Carboniferous glaciation. Parallel, high-resolution sulfur isotope records from sections in the Great Basin are invariant before, during and after the carbon excursion. These records, derived from carbonate-associated sulfate, differ from those across other carbon isotope excursions (e.g., SPICE event and Toarcian OAE), which are also attributed to enhanced marine organic matter burial. In contrast to the Carboniferous pattern of S isotope uniformity, the SPICE and Toarcian data show parallel, positive carbon and sulfur isotope excursions representing burial of marine organic matter with coupled burial of pyrite. One explanation for the observed Carboniferous relationship is a terrestrial carbon burial event coupled to only very limited pyrite burial under the sulfate-limited conditions of freshwater settings. Alternatively, the relatively invariant sulfur isotope data may reflect a large marine sulfur reservoir, as estimated from fluid inclusions within marine halites and from numerical modeling of rates of S isotope variability. Even with high rates of pyrite burial, the isotopic composition of the ocean may have been buffered by the large mass of the marine reservoir, resulting in little or no isotopic change. In order to test these two hypotheses we will present results from geochemical box modeling designed to shed light on the mechanisms behind this carbon isotope excursion as constrained by parallel sulfur isotope data. A better understanding of carbon burial as controlled by climate or land plant evolution, among other potential factors, will illuminate the primary triggers of one of earth's greatest episodes of continental glaciation.