Depositional cycles and evolution of the Paleogene Wilcox strata, Gulf of Mexico Basin, Texas

The Wilcox Group is one of the major thick elastic successions of the Tertiary Gulf Coast. The Wilcox is conventionally subdivided into lower, middle, and upper parts. Detailed correlation of more than 700 well logs has identified two depositional cycles of the Wilcox strata, each of which is represented by four parasequence sets or high-frequency genetic stratigraphic sequences. Two depositional cycles bounded by maximum flooding events were characterized by depocenter shifting, shelf-margin progradation, and depositional system evolution, and lasted several million years. The sedimentary record of two depositional cycles documents two aspects of these cycles. One aspect is that the shelf margin alternated between periods of active outbuilding and periods of relative stability or minor retrogradation. Another aspect of the cycle is that depositional system evolution displays a progression from progradation to aggradation to retrogressive transgression. The time spans of these two cycles are 3.6 m.y. and 7.5 m.y., respectively, based on the Haq time scale. Each of the two depositional cycles generally corresponds to a pulse of Laramide tectonism. Deposition of two cycles may also reflect a eustatic sea level overprint.