11 Fossil Vertebrates from the Gulf Coastal Plain

Tuesday, 22 March 2016
8:00 AM - 12:00 PM
Capitol Room

THE MIDDLE MIOCENE CLIMATE TRANSITION IN LOUISIANA: PALEOENVIRONMENTAL EVIDENCE FROM UNGULATE ENAMEL STABLE ISOTOPES

Paper number: 11-8
Program: Symposia Sessions
Time: 10:05 AM – 10:25 AM

Authors

Abstract

The Middle Miocene climate transition (MMCT; ~14.5-13.0 Ma) was a pronounced episode of cooling associated with the reestablishment and advance of the Eastern Antarctic ice cap following the warmest interval since middle Eocene times. In the interest of characterizing North American Gulf Coast environmental conditions during this interval, we analyzed the tooth enamel carbonate carbon and oxygen stable isotope composition of three ungulate taxa (Prosynthetoceras francisi, Merychippus sp., and Teleoceras sp.) from two sites in the late Barstovian Fleming Formation at Fort Polk (Vernon Parish, Louisiana).

Bulk sampling δ13C (-10.99±0.94‰ and -10.92±1.4‰) of 29 enamel samples indicates C3 diets for the three taxa, and are consistent with habitation of dry, open biomes (e.g. woodland savanna). This interpretation is consistent with published pollen and phytolith data. δ13C values from Prosynthetoceras francisi were of particular interest, as they are on average lower than those of Merychippus sp. and Teleoceras sp., suggesting preference for wetter or more heavily vegetated portions of the biome. The δ13C of thirty-two serial samples from two taxa (Merychippus sp. and Teleoceras sp.) have low variability (1.37‰ and 1.11‰, respectively), suggesting little seasonal variation in precipitation in the region during the MMCT. Mean Annual Precipitation is also resolvable when referencing the values from these taxa, indicating MAP around 300-500 mm/year, which is considerably lower than today but still consistent with habitat interpretations.

The δ18O of thirty-two serial samples from two taxa (Merychippus sp. and Teleoceras sp.) have marked variability (4.16‰ and 2.09‰, respectively), suggesting either temperature seasonality or seasonal changes in water vapor source in the region during the MMCT. If this variability is attributed only to temperature seasonality we find that Mean Annual Range of Temperature is 12.55°C, suggestive of considerably more tropical-like seasonality than today.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016SC-272242

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.