ABSTRACT

The Lower Tuscaloosa and Dantzler formations of east-central Louisiana and southeastern Mississippi are excellent examples of fluvial-deltaic sediments deposited in a semiarid climate. This deltaic deposition was subsequently slowly transgressed by the sea and deposition of the Middle Marine Tuscaloosa occurred.

The Lower Cretaceous Dantzler sediments were deposited in a downdip stranded (dry) basin (Perry Basin) contemporaneous to uplift and erosion of the land to the north. Deposition continued in this manner throughout the Lower Tuscaloosa. By this means the basins were filled with sediment and deltas were built seaward of the older Edwards shelf edge. As the sea continued to transgress during the Middle Tuscaloosa time, all fluvial-deltaic deposition was restricted to the far up-dip areas. The result of this marine transgression and sediment deposition has been a tripartite relationship of depositional environments. Observations from electric logs, cores, and cuttings indicate a typical depositional sequence consists of a basal braided channel complex overlain by meanderbelt point bars and topped by overlapping, shallow-marine, nearshore bars. Facies and depositional interpretations indicate that the Lower Tuscaloosa and Dantzler are facies equivalents of one another and, as such, form a time-transgressive unit which spans the Upper-Lower Cretaceous boundary.