ABSTRACT

In eastern Mississippi and western Alabama, the Tombigbee Sand Member of the Eutaw Formation accumulated as part of a marine transgression during the Late Cretaceous (Santonian Stage). The Tombigbee includes glauconitic, fossiliferous, micaceous, bioturbated, massive-bedded, quartzose sandstone and siltstone deposited on a marine shelf. The inner to middle shelf sandstone and siltstone of the Tombigbee disconformably overlie thinly laminated to cross-bedded, tidally influenced, fine- to medium-grained, nearshore sandstone of the Eutaw Formation. Ophiomorpha burrows are common in the lower member of the Eutaw, and no calcareous microfossils were recovered from this member. In eastern Mississippi, the disconformable Eutaw-Tombigbee contact is marked by a 1- to 2-in (2.54- to 5.08-cm) sandstone bed containing phosphatic pebbles, shark teeth, and reworked fossils. The Tombigbee contains a diverse macrofauna, including echinoderms, gastropods, cephalopods, and bivalves, and a rich microfauna and microflora, including foraminifera, ostracodes, and calcareous nannoplankton. The foraminiferal assemblage consists of globotruncanids, heterohelicids, nodosariids, anomalinids, verneuilinids, globotextulariids, and textulariids. The middle shelf marls of the Mooreville Chalk conformably overlie the Tombigbee. These lower Mooreville marlstone beds have a diverse microfossil assemblage similar to the upper Tombigbee beds.