HR: 0800h
AN: PP51B-0592    [Abstracts]
TI: Climatic And Environmental Change Across The Eocene-Oligocene Transition In The Northern Great Plains (USA) As Inferred From Carbon And Oxygen Isotope Ratios In Fossil Tooth Enamel
AU: * Zanazzi, A
EM: azanazzi@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences, 701 Sumter St., Room EWS 617, Columbia, SC 29203 United States
AU: Kohn, M J
EM: mjk@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences, 701 Sumter St., Room EWS 617, Columbia, SC 29203 United States
AU: MacFadden, B J
EM: bmacfadd@flmnh.ufl.edu
AF: Florida Museum of Natural History, University of Florida, 218 Dickinson Hall, Museum Road & Newell Drive, Gainesville, FL 32611 United States
AB: The Eocene-Oligocene transition (EOT) at 33.5-34 Ma was one of the Cenozoic's biggest, abrupt climatic events, and is widely viewed as the global shift from `greenhouse` to `icehouse` conditions. Whereas the marine record of the transition has been extensively studied for changes in deep and surficial sea isotope compositions, temperatures, circulation patterns, and faunal trends, significantly less research has focused on the continental climate and ecosystem change across the EOT, particularly for stable isotope studies. Our carbon and oxygen isotope data from tooth enamel carbonate from late Eocene-early Oligocene outcrops of northwestern Nebraska, suggest no obvious changes to ecosystem structure (e.g., aridity and vegetation openness), but a small to moderate decrease in MAT (3-7°C). The investigated samples include the middle and rear molars of three different taxa: Mesohippus, Merycoidodon, and Leptomeryx, which are all present both before and after the transition. Enamel δ¹³C values for the late Eocene and early Oligocene samples range from -12.5 to -8.5‰ and from -11.1 to -7.8‰, respectively, i.e., a small but statistically significant ~ 1‰ increase across the EOT. These values are indicative of a diet dominated by C3 vegetation. The shift in carbon isotopes mimics a global increase in δ¹³C, rather than any obvious change in ecosystem aridity. Late Eocene and early Oligocene rear molars show similar ranges in δ¹⁸O values (from ~ -10 to ~ -3‰), suggesting no change in MART. Average late Eocene values are ~ -9‰ ( Merycoidodon), ~ -7‰ ( Leptomeryx), and ~ -6‰ ( Mesohippus). Shifts in these average δ¹⁸O values across the EOT are insignificant for Merycoidodon and Leptomeryx whereas Mesohippus exhibits a significant 2‰ decrease. Because marine δ¹⁸O values increased across the EOT, these data are consistent with a relative shift in meteoric water δ¹⁸O of -1 to -3‰. This shift could reflect either a change in moisture source and/or trajectory due to rearrangement of ocean circulation patterns, or a decrease in MAT of 2-3°C ( Merycoidodon and Leptomeryx), to perhaps 6-9°C ( Mesohippus).
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005