Paper No. 210-10
Presentation Time: 11:15 AM
TEMPERATURE CHANGES AND GREAT PLAINS ECOSYSTEM EVOLUTION DURING THE MIOCENE TO THE HOLOCENE IN MEADE BASIN, KANSAS
FETROW, Anne, Department of Geology, University of Puget Sound, 1500 N. Warner Street, Tacoma, WA 98416, SNELL, Kathryn E., Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, MC 100-23, Pasadena, CA 91125, FOX-DOBBS, Kena, Department of Geology, University of Puget Sound, 1500 N. Warner St, CMB 1048, Tacoma, WA 98416-1048, FOX, David L., Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, POLISSAR, Pratigya J., Biology and Paleo Environment, Lamont Doherty Earth Observatory, Palisades, NY 10964-8000, UNO, Kevin T., Biology and Paleoenvironment, Lamont Doherty Earth Observatory, 61 Route 9W, PO Box 1000, Palisades, NY 10964-8000, MARTIN, Robert A., Department of Biology, Murray State University, Murray, KY 42071 and FEINBERG, Joshua, Institute for Rock Magnetism, University of Minnesota, Department of Earth Sciences, 310 Pillsbury Drive SE, Minneapolis, MN 55455
Over the last 4.5 m.y., the Great Plains region transitioned into the modern grassland ecosystem, which is now composed dominantly of C
4 grasses. It remains unclear; however, what drove the expansion of C
4 grasses and what effect these overall environmental changes had on the regional fauna. The Meade Basin, a depositional basin located in southwest Kansas, provides a unique opportunity to determine how paleoenvironmental conditions changed during C
4 grassland expansion, because of its well-exposed late Miocene to Holocene fossils and paleosols. To evaluate paleoenvironmental change, we need to develop a detailed paleoclimate record during this time. Previous work
(1, 2) showed that δ
18O values of paleosol carbonate decreased and δ
13C values increased during Miocene-Holocene time in Meade Basin. These trends were interpreted as a decrease in temperature and/or an increase in available moisture, coincident with an increase of C
4 biomass. However, making robust estimates of temperature from terrestrial δ
18O values of carbonate (δ
18O
carb) is limited by the role of δ
18O values of water (δ
18O
w) on δ
18O
carb, and vice versa for estimating δ
18O
w from terrestrial δ
18O
carb. Therefore, we applied carbonate clumped isotope (Δ
47) thermometry to paleosol carbonates from Meade Basin to develop a detailed and better-constrained temperature and δ
18O
w record.
Preliminary temperature estimates from six sections in the Meade Basin average 21.4°C ± 5.5°C; the modern mean annual temperature for Meade, KS, is ~14°C while modern warm season temperature is ~24°C (1). These temperature estimates show little average change from ~9 to 2 Ma. In contrast, δ18Owater and δ18Ocarbonate values shift to more positive values upsection. There is a complex interplay of factors that may cause these patterns, including differences in depositional environment, soil type and depth, and possible aridity changes. We will discuss further work addressing the role of these factors, which will include additional samples and replicates.
(1) Fox et al., GSA Bulletin, 124, 431-443 (2012a).
(2) Fox et al., GSA Bulletin, 124, 444-462 (2012b).
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