A PALEOENVIRONMENTAL ANALYSIS OF THE EUTAW FORMATION, AT OCHILLEE CREEK, CHATAHOOCHEE COUNTY, GEORGIA

The Eutaw Formation is a Santonian age coastal deposit with exposures ranging from northeastern Mississippi to western Georgia, with the type section in western Alabama. It ranges in thickness from 75 to 50m, and is largely composed of argillaceous and glauconitic silty sands, including the massive Tombigbee Sand facies within the upper portions of the Alabama exposures. The marine glauconitic sands thin towards the east, becoming absent within the Upatoi Creek and Ochillee Creek Valley outcrops in Fort Benning, Chatahoochee County,western Georgia. Within this region, they are instead replaced by diagenetic marl, subdivided into cyclical subfacies of highly fossiliferous beds interspersed amongst non-fossiliferous beds composed of carbonate cemented micaceous glauconite sands and silts.

These fossiliferous subfacies serve as valuable paleoenvironmental indicators, featuring abundant mollusks dominated by bivalves, along with diverse gastropods and ammonites. Rare, but well preserved vertebrate material includes teeth and jaw elements from lamniform sharks and osteicthyes, and phalanges and a metacarpal of a pterosaur. The sediment also includes abundant carbonaceous material, presumably from terrestrial plants. The assembled taxa and the state of their preservation, when matched with the lithology of the formation itself, points to this section of the Eutaw typifying a mostly quiet, back barrier marine deposit, with one exception. One of these fossiliferous layers, characterized by a large abundance of unidentified neogastropods of variable size, represents a range of energy environments, and is likely indicative of a catastrophic event.