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Abstract

Study of Mississippi an cores in the Palo Duro and Hardeman Basins of the Texas Panhandle reveals that the Chappel Formation (lowermost Mississippi an) comprises an offlap sequence of lithofacies that documents the development of a carbonate skeletal sand shoal. In core from the eastern Palo Duro Basin, the lower Chappel contains interlayered (1) dark gray, spiculitic wackestone, (2) brown, laminated, skeletal wackestone, (3) skeletal, lime-silt grainstone, and (4) skeletal, lime-sand grainstone. Spiculitic wackestone represents quiet, relatively deep water marine deposition in an outer platform setting. Laminated wackestone, lime-silt grainstone, and lime-sand grainstone represent allochthonous sediments that were deposited by turbidity currents and mass sediment transport. The upper Chappel Formation comprises (1) echinoderm-bryozoan, lime-sand grainstone, and (2) minor laminated, skeletal wackestone. These lithofacies represent winnowed, skeletal sands and associated slack-water carbonate muds deposited in a shoaling environment.

Synthesis of regional data suggests that the Chappel upward-shoaling sequence formed by aggradation and eastward progradation of a carbonate ramp. Conodont faunas indicate that, contrary to previous interpretations, the Chappel Formation contains no rocks older than Meramecian age. This suggests that the entire sequence of depositional events represented by the Chappel—inundation of the area, development of outer platform conditions, and formation of a carbonate shoal complex—occurred in Meramecian time.

Adequate porosities for hydrocarbon accumulation are present in the lower Chappel in the eastern Palo Duro Basin. Paleoenvironmental reconstructions suggest that this area may also contain isolated carbonate buildups similar to those that are productive in the Hardeman Basin to the east.

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