Subsurface data show that in the northern Mississippi Embayment Cretaceous, Paleocene, and lower Eocene deposition occurred in a single sedimentary cycle.

The cycle began with Cretaceous deposition of nonmarine Tuscaloosa gravel, restricted in area. Marine advance and depositional limits reached a maximum in the Paleocene with the deposition of Porters Creek Clay, which once generally extended beyond the embayment limits. Deposition ended in the early Eocene with nonmarine Wilcox beds, now restricted to the subsurface near the embayment axis. Uplift and erosion resulting in marked truncation followed to complete the cycle.

Overlying middle Eocene Claiborne Group beds overlap all the lower Eocene Wilcox Group and part of the Paleocene Midway Group, all around the northern end of the embayment north of the Tennessee-Mississippi border.

Within the cycle five advances and regressions of the sea, which are illustrated by stratigraphic cross sections and a series of paleogeographic maps, are recorded.

The pattern of contemporary subsidence of the embayment is shown on four isopach maps, which indicate that the present trough shape of the embayment appeared during latest Cretaceous and persisted through the Paleocene and early Eocene.

Subsidence of the embayment trough strongly influenced geography from late Paleocene through early Eocene. During this time the sea occupied bays that followed the embayment axis. A delta was prominent in western Kentucky and northwestern Tennessee during Late Cretaceous and late Paleocene.

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