PRELIMINARY BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF CENOMANIAN-TURONIAN TUSCALOOSA GROUP SEDIMENTS FROM SOUTHEASTERN MISSISSIPPI TO SOUTHWESTERN ALABAMA, USA

Calcareous nannofossils were recovered from cored intervals of the Tuscaloosa Group in five wells along a cross section from southeastern Mississippi to southwestern Alabama: Mississippi Power Company (MPC; 8589-8534 ft, 7933-7906 ft), International Paper Company (IPC; 6872-6806 ft), T.R. Miller Mill 26-16 #1 (TRM; 5750-5730 ft), Ann Jones et al., Trustees #1 (AJ; 5451-5259 ft), and J.H. Wall Estate et al., #4 (WE; 5419-5414 ft, 5289-5250 ft, 4593-4573 ft). The biostratigraphy, combined with geophysical log data, allows provisional interpretation of parasequences, parasequence sets that define partial systems tracts, and notably a sequence boundary.

Detailed biostratigraphy of the “Lower Tuscaloosa Sandstone” (LTS) places it in middle to upper Cenomanian zones UC3-UC5 (equivalent to Zone CC10a). A shift in geophysical signatures of the top of the LTS show that this unit is capped by the informal “Pilot Sand,” which can be traced across the study area. The thickness of the LTS decreases from west to east. Recent workers have identified the presence of three parasequences within it. Contact with the overlying “Tuscaloosa Marine Sand” (TMS) is unconformable in IPC and TRM, where a hiatus between 0.13-0.35 my is identified. Thus, the contact most likely indicates a sequence boundary. This contact was not cored in AJ and WE, and the interval was barren of calcareous nannofossils in MPC.

The TMS is lower Turonian spanning calcareous nannofossil zones UC6-UC7 (CC10b-CC11) in the study area. Species richness peaks at the base of the TMS, suggesting a surface of maximum flooding. Three parasequences are provisionally identified and possibly correlate to parasequences identified from the Spinks Core in Pike County, Mississippi.

Samples of the “Upper Tuscaloosa Sandstone” (UTS) were only available from 4593-4573 ft in the WE well. They are assigned a middle Turonian age (UC8a; CC12) based on the presence of Eiffellithus eximiusand the absence of Lithastrinus septenarius. The UTS thickens to the east in the study area and consists of alternating sands and clays, possibly representative of as many as eleven parasequences.