Abstract: Paleoenvironments of the Tombigbee Sand Member of the Eutaw Formation (Upper Cretaceous) of Eastern Mississippi and Western Alabama

Ernest A. Mancini, David D. Soens

The Tombigbee Sand Member of the Eutaw Formation and Mooreville Chalk of eastern Mississippi and western Alabama accumulated during a marine transgression in the late Cretaceous (Santonian-Campanian). The Tombigbee includes up to 80 ft of very fine- to fine-grained, glauconitic, calcareous, fossiliferous, micaceous, bioturbated, massive-bedded, marine shelf quartzose sand. The inner to middle neritic sands of the Tombigbee disconformably overlie thinly laminated to cross-bedded shoreface and tidal fine-grained sands of the Eutaw Formation. Although Ophiomorpha burrows are common in the Eutaw, no calcareous microfossils were recovered from the Eutaw. The Eutaw-Tombigbee contact is marked by a 1- to 2-in. sand bed containing phosphatic pebbles, shark teeth, and sideritic mollus molds. The Tombigbee contains a diverse macrofauna, including gastropods, scaphopods, cephalopods, and bivalves (Exogyra, Ostrea, Pycnodonte, Anomia, and Inoceramus) and a rich microfauna, including foraminifera, ostracodes, and calcareous nannoplankton. The foraminiferal assemblage consists of globotruncanids, heterohelicids, nodosariids, anomalinids, discorbids, polymorphinids, and textulariids.

Nodosariids are more abundant in the lower Tombigbee beds, while anomalinids and planktonic species are more abundant in the upper Tombigbee beds. The middle neritic, glauconitic, chalky marls of the Mooreville conformably overlie the Tombigbee. These lower Mooreville marls have diverse macrofaunal and microfaunal assemblages similar to the upper Tombigbee beds.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994