The Pennsylvanian Collier limestone in Hansford County, Texas, is found at depths of 4,500 to 4,700 ft at Hitchland field, along the shelf edge in the western portion of the Anadarko basin. Lithology and geometry of the limestone can be compared with Bahamian oolite shoals.

The four major carbonate rock types or facies present within the Pennsylvanian Collier limestone are: (1) oolite grainstone, (2) fusulinid pelletal mudstone, (3) bioclastic wackestone, and (4) bioclastic grainstone. Discontinuous, thin lime mudstones and shales are found above and below the Collier limestone.

A Collier isopach map indicates a northeast-southwest depositional strike. The Collier shoal complex extends approximately 20 mi in length and 5 mi in width with a maximum thickness of 45 ft. Paleogeographic slice maps reveal that three isolated shoals, adjacent and parallel to the shelf-slope margin, prograded shelfward, coalescing to form one large oolite shoal complex. The Amarillo-Wichita uplift and basin subsidence caused a rapid rise in sea level and a northward influx of clastic sediment toward the shelf. These events finally drowned and destroyed the carbonate environment that formed the Collier limestone.

Diagenetic alteration occurred in eogenetic and mesogenetic stages. During eogenetic diagenesis, five events occurred: (1) cementation of allochems by bladed isopachous calcite and coarse, equant, spar calcite in the freshwater phreatic zone; (2) dissolution of allochems in the freshwater, phreatic zone; (3) development of micrite envelopes in the marine phreatic zone; (4) fracturing of the oolite grainstone facies; and (5) Dorag dolomitization. Mesogenetic diagenesis included: (1) partial infilling by saddle dolomite in vuggy and moldic porosity; (2) fracturing of the oolite grainstone facies; and (3) stylolitization of the fusulinid pelletal mudstone facies.

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