ABSTRACT

A composite reference section of exposed marine Upper Cretaceous sediments in central Alabama was generated to define its biostratigraphic framework. Sections were correlated on the basis of two excellent lithostratigraphic marker horizons, the Arcola Limestone Member of the Mooreville Chalk and the uppermost sand of the Eutaw Formation. Stratigraphic units include the Tombigbee Sand Member of the Eutaw Formation, the Mooreville Chalk, and the Demopolis Chalk. The ranges of ostracode and planktonic foraminiferal species are plotted in reference to these sections. All or part of four planktonic foraminiferal zones and five ostracode zones are delineated. The units range in age from late Santonian through early Maastrichtian.

The Tombigbee Sand and the lower 105 ft of the Mooreville Chalk are of late Santonian age (Dicarinella asymetrica Zone). The top of the D. asymetrica Zone marks the Santonian-Campanian Stage boundary. The upper 250 ft of the Mooreville Chalk and lower 265 ft of the Demopolis Chalk are of early to late Campanian age (Globotruncanita elevata Zone). An ostracode zone, the Ascetoleberis plummeri Zone, brackets the Arcola Limestone Member of the Mooreville Chalk. The Globotruncanita calcarata Zone, the top of which marks the Campanian-Maastrichtian Stage boundary, occurs in the upper third of the Demopolis Chalk, well below the Bluffport Marl Member. The upper 100 ft of the Demopolis and the lower 50 ft of the Ripley Formation are assigned to the Globotruncana "tricarinata" Zone of early Maastrichtian age.

Neither the Santonian-Campanian nor the Campanian-Maastrichtian Stage boundary occurs at any change in lithology or formational contact.