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 lowe r, middle, and upper parts. Detailed correlation of more than 700 well logs has identified two depositional cycles of the Wilcox strata, eac h of which is represented by four parasequence sets or high-frequency genetic stratigraphic sequences. Two depositional cycles bounded by ma ximum flooding events were characterized by depocenter shifting, shelf -margin progradation, and depositional system evolution, and lasted se veral million years. The sedimentary record of two depositional cycles documents two aspects of these cycles. One aspect is that the shelf m argin alternated between periods of active outbuilding and periods of relative stability or minor retrogradation. Another aspect of the cycl e is that depositional system evolution displays a progression from pr ogradation to aggradation to retrogressive transgression. The time spa ns 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 c orresponds to a pulse of Laramide tectonism. Deposition of two cycles may also reflect a eustatic sea level overprint.