Abstract

Placing Pennsylvanian and Permian regional paleogeographic and facies maps into their Late Paleozoic latitude and plate orientation helps explain and predict basin sedimentation patterns. Because west Texas was very near the equator during the Late Paleozoic, sedimentation would have been influenced by prevailing northeast trade winds. Facies distribution in the Late Paleozoic of west Texas strongly suggests that paleolatitude and paleogeography influenced sedimentation by controlling the regional prevailing winds. The warm tropical climate was conducive to carbonate and evaporite deposition. Basin orientation, combined with prevailing winds and tropical climate, strongly influenced the distribution of carbonate grain types and the geometry and location of carbonate sand bodies.

Wolfcampian and Guadalupian sedimentation appears to have been influenced by prevailing northeasterly winds and basin orientation. From numerous paleotectonic reconstructions of the Permian it is clear that both the Midland and Delaware basins were north of the equator and oriented 43 degrees east of present day north. On eastern-facing edges and structural highs east of the Central Basin platform, grainstones accumulated along the platform margin. Northeast prevailing winds and currents probably struck the Central Basin platform at an oblique angle during the Permian, creating southwesterly longshore currents.

The type and location of Wolfcampian lithofacies appear to have been influenced by paleogeography and prevailing winds. Thickest grainstones are found on structural highs where they are aligned with the northeasterly prevailing wind direction. Upper Permian San Andres-Grayburg lithofacies indicate that northeast prevailing winds and ocean currents winnowed and removed fine grains and mud from the grain-dominated sediments. The prevailing winds and currents produced a high-energy depositional zone along the eastern platform margin. The grainstones were deposited in shallow water in the windward or marginal belt of high-energy conditions. West of the grainstones in a leeward direction, wackestones, algal mudstones, and anhydrite were in lagoonal, tidal-flat, and supratidal environments.

Paleogeographic maps are very useful in explaining regional facies patterns. By combining such unknown or poorly understood factors as the orientation of tectonic features, ancient latitude and prevailing winds, carbonate sedimentation can be predicted. Once the paleogeography of ancient carbonate platforms is identified, modern carbonate models are directly applicable to understanding lithofacies patterns that are so important to both field development and regional exploration.