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Selected Observations on Wilcox Stratigraphy and Sandstone Petrography in South Texas in the Context of Regional Gulf of Mexico Paleocene-Eocene Exploration

Marc B. Edwards
Marc B Edwards Consulting Geologists Inc, Houston, TX

Published regional petrographic studies of the Paleocene-Eocene Wilcox tend to lump all samples into a single Wilcox Group stratigraphic unit, suggesting that while there may be geographic variations in sandstone composition, there are only minimal significant stratigraphic variations in sandstone composition within the Wilcox. A regional stratigraphic framework extending from the US-Mexican border to Mississippi has been constructed to more closely resolve detailed provenance-related petrographic variations within the trend.

In South Texas, The Lower Wilcox is structural and depositional complex, while the Upper Wilcox expands in thickness and complexity, adding to diversity of stratigraphic units and sandstone provenance assemblages. Well log correlation reveals details about the timing and extent of episodes of shelf margin progradation and retrogradation, and the modification of the shelf margin by salt/raft tectonics.

Integration of petrographic information with this stratigraphic/tectonic framework illustrates significant shifts in composition between and within the component stratigraphic units. These variations have implications for reservoir prediction in the Wilcox trend, between the onshore deltaic gas play and the deep water submarine fan oil play.