Print this pageAbstract: Leonardian Strata in Northern Midland Basin of West Texas
The study area includes Hockley, Lubbock, Crosby, Terry, Lynn, and Garza Counties, Texas. The Leonard Series, second of four series in the Permian System, is composed of a regressive sequence of prograding, shelf-edge barrier reefs which separate a shelf facies from a basin facies. The shelf facies is bedded carbonate rocks intercalated with light-colored shales and anhydrite. The basin facies is dark shales and argillaceous limestones. The reefs usually are massive dolomite. The oldest Leonardian deposit is the Wichita (Abo) Formation. There is an upper and a lower reef cycle within the Wichita Formation. The Wichita is overlain by the lower Clear Fork Formation which has no mappable basinal facies. The lower Clear Fork is overlain by the Tubb sandstone on the shelf and ts basinal equivalent, the Dean sandstone. The Dean sandstone is the basinal equivalent of both the lower Clear Fork and the Tubb sandstone. This relation is apparent at the north end of the Midland basin where the shelf edges are separated horizontally by progradation, and depositional topography is minimized. The Tubb and Dean sandstones are overlain by the middle Clear Fork Formation, the upper Clear Fork, and the Glorieta sandstone. The basinal equivalent of these is the Spraberry formation. The Glorieta and upper Spraberry sandstones are overlain by the San Andres Formation which may be in part or all Leonardian. The upper boundary of the Leonard Series is problematic.
AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma