ABSTRACT

Upper Wilcox deposits (Late Paleocene to Early Eocene) at Katy Field in southeastern Texas, consist of terrigenous clastic facies which are stratigraphic equivalents to the uppermost beds of the outcropping Wilcox Formation. Wilcox sediments extend basinward to a known total subsurface thickness of 9100 feet at Katy Field. The Upper Wilcox is 1800 feet thick at Katy; however, only the upper 800 feet were included in the study. Analysis of the regional stratigraphy, structural trends and paleobathymetric relationships indicate that sediments were deposited by high-constructive and destructional delta systems marginal to the subsiding Gulf of Mexico basin; resultant deltaic and interdeltaic facies were ultimately transgressed by open shelf environments.

The interpreted depositional sequence begins with prodelta silty clay at the base and coarsens upward to very fine- and fine-grained sands in a typical progradational delta-front sequence. Progradation was repeated after abandonment and subsidence, yielding a second series of delta-front and overlying fluvial facies. The next vertical sequence consists of thinly laminated and burrowed silty clay and thin sand beds, which are locally slumped and micro-faulted, and sand units containing shale clasts. These thin units represent a period of minor sediment influx and comprise interdeltaic marsh to offshore silty clay and destructional delta-front sand facies environments; local distributary channels cut into the bay-marsh transition facies. The third vertical sequence is largely offshore silty clay, thin glauconite beds, and thin silty sand units, which onlapped the area as a result of increased subsidence and marine transgression. Local relict shoreline sand units were deposited during temporary stillstands as the shoreline shifted landward.