THE ANCESTRAL ROCKY MOUNTAIN OROGENY AND EVOLUTION OF THE PERMIAN BASIN.

The Permian Basin is a mosaic of basins and platforms that formed in the late Paleozoic associated with compressional deformation of the Ancestral Rocky Mountains or "ARM" Orogeny. This event partitions the predecessor broad/shallow early Paleozoic Tobosa Basin. The timing of late Paleozoic basin formation is evaluated using calibrated basin models to analyze total subsidence. Two subsidence phases are interpreted--an initial period of Late Pennsylvanian to early Permian (~305-285 Ma) rapid subsidence of the basins, contrasted with very slow subsidence or uplift of the platforms. The first phase of subsidence is coeval with the flexural foreland basin subsidence in the Val Verde Basin, which is related to the thin-skinned Marathon Orogeny. While this may indicate a kinematic linkage, structural styles are very different. The most important tectonic unconformity occurs near the end of this phase, in the early Permian (Wolfcampian). The lower Wolfcampian Unconformity erodes deeply on the Central Basin Platform, Diablo Platform, and Pedernal Uplift. The interval below the unconformity is commonly significantly deformed, while the interval above is only gently folded. The second phase of subsidence is characterized by rapid and relatively uniform subsidence of the entire area, both platforms and basins, from Leonardian to Ochoan (~285-250 Ma) time. The drivers of the second phase of subsidence are less clear. Also, the timing of the onset in the Permian Basin is younger than other portions of the ARM and Ouachita orogenic belts; this may imply later collisional tectonics in the southwestern part of the system. [ABSTRACT FROM AUTHOR]