Morrowan carbonates and clay of the Marble Falls Group accumulated on part of a broad structural platform, the Texas craton, that was bordered on the east by the Fort Worth basin. A myriad of carbonate facies formed on landward parts of the platform, whereas a relatively thick uniform sequence of dark-gray spiculitic carbonate mudstone accumulated at its seaward margin. As much as 6,000 ft of Mississippian and Pennsylvanian shale and sandstone fill the segment of the Fort Worth basin adjacent to the carbonate platform.

Facies patterns in the Marble Falls Group are closely related to depositional setting. Changes in setting are a consequence of transgression, regression, and accumulation during transgression and regression. The response of facies patterns to changes in setting is recorded in the composition, geometry, and distribution of the facies.

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Four distinctly different vertical and lateral progressions of facies are evident in the Marble Falls Group. This progression lends itself to recognition of 4 depositional phases.

The vertical sequence for each phase results from lateral shifts of 1 or 2 facies tracts that are unique to each phase. As a consequence each phase can be described by means of 1 or 2 generalized facies models.

In places where porosity is fabric-selective, the models should allow prediction of reservoir geometry. They also may be useful in predicting target directions, and in locating the updip limits of potential stratigraphic traps.

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