ABSTRACT

Correlation via fossil vertebrates from exposures of the Castor Creek Member of the Fleming Formation within Fort Polk supports an early late Barstovian Land Mammal age for the sites and relies mainly on the presence of the rodent Copemys, a gomphothere (Proboscidea), and the artiodactyl Prosynthetoceras francisi. Copemys marks the beginning of the Barstovian, which has previously been reported to range from 16.8 to 11.5 Ma, and the first appearances of proboscidea coming as immigrants to North America are reported to fall between 16.2 Ma and 14.8 Ma. Prosynthetoceras francisi is currently the best animal for comparison of stage-of-evolution in a Gulf Coast lineage. It is similar to animals from the Barstovian Cold Spring Local Fauna of the Texas coastal plain, larger than those from the earlier Burkeville Local Fauna, previously reported as possibly 14.5-13 Ma in age. The Fort Polk sites are older than 11.5 and probably younger than 13 Ma.

Invertebrate fossils of the Potamides matsoni zone, previously reported in the Castor Creek Member in Louisiana and associated with the Burkeville local fauna in Texas, have not been recovered from Fort Polk. Carbon isotope study confirms that carbonate nodules associated with the Fort Polk faunas are older than the worldwide 7.0-7.4 Ma positive shift. A single pollen sample from a level slightly below the most prolific vertebrate site, suggests an age for its level no older than approximately 10-12 Ma.