The Taylor Marl unconformably overlies the Austin Chalk on the western margin of the East Texas basin. Along this contact, up to 275 ft (84 m) of upper Austin is missing in the Waco area and up to 450 ft (137 m) in Bell County. However, the Austin Chalk appears to have been more-or-less uniformly deposited throughout the study area. Apparently regional uplift caused a regression that terminated Austin deposition and was related to the erosion of the upper Chalk. While the unconformity is areally extensive, slightly angular, and accounts for a relatively long period of time, the mechanism of erosion that caused the unconformity is still uncertain. Erosion was terminated by the deposition of the lower Taylor Marl. Taylor "A", the lowermost subdivision of the lower Taylor, w s deposited in a near-shore environment that was highly variable.

Of particular interest is the relationship of this unconformity to structure and probably to oil occurrence in the Austin Chalk in McLennan and Falls Counties. Major Austin fracturing, which apparently does not extend into the Taylor in Falls County, clearly indicates that structure in the Chalk, at least in part, antedates Taylor deposition.

Oil occurrence in the Chalk is clearly related to fracturing and probably is localized by post-Austin-pre-Taylor fracture systems.

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