Most exploration concepts for the Wilcox Group are based on paleogeographic reconstructions derived from maps of net sand or sand percent. Coarsening-upward tidal sequences exposed in the highwalls of two lignite mines in east Texas show the shortcomings of these reconstructions. In the past, the coarsening-upward sequences have been interpreted as prograding floodplain splays because they occur in an area of supposed fluvial sedimentation (conventional paleogeographic reconstructions show a large river system occupying the East Texas embayment during the deposition of the Wilcox Group). Recognition of the tidal origin of the coarsening-upward sequences suggests an embayed coast or a shoreline within the East Texas embayment at the time the coarsening-upward sequences wer deposited--information which has exploration implications. Paleogeographic reconstructions based on maps of net sand or sand percent show time-averaged conditions. The search for the subtle trap requires paleogeographic maps based on smaller stratigraphic intervals than present reconstructions provide. These intervals can be defined by using the principles of sequence stratigraphy and tracing unconformities in the subsurface.

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