T228 Critical Earth-Life Transitions: The Marine Perspective (Posters)

Tuesday, 21 October 2014
9:00 AM - 6:30 PM
Exhibition Hall C

TEMPERATURE CHANGES AND GREAT PLAINS ECOSYSTEM EVOLUTION DURING THE MIOCENE TO THE HOLOCENE IN MEADE BASIN, KANSAS

Paper number: T228-10
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Over the last 4.5 m.y., the Great Plains region transitioned into the modern grassland ecosystem, which is now composed dominantly of C4 grasses. It remains unclear; however, what drove the expansion of C4 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 C4 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 δ18O values of paleosol carbonate decreased and δ13C 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 C4 biomass. However, making robust estimates of temperature from terrestrial δ18O values of carbonate (δ18Ocarb) is limited by the role of δ18O values of water (δ18Ow) on δ18Ocarb, and vice versa for estimating δ18Ow from terrestrial δ18Ocarb. Therefore, we applied carbonate clumped isotope (Δ47) thermometry to paleosol carbonates from Meade Basin to develop a detailed and better-constrained temperature and δ18Ow 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).