LATE PALEOZOIC DEFORMATION OF INTERIOR NORTH-AMERICA - THE GREATER ANCESTRAL ROCKY-MOUNTAINS

Late Paleozoic deformation within interior North America has produced a series of north-northwest-to northwest-trending elongate basins that cover much of Oklahoma, Texas, New Mexico, Colorado, and Utah. Each b asin thickens asymmetrically toward an adjacent region of coeval basem ent uplift from which it is separated by synsedimentary faults with gr eat vertical relief. The remarkable coincidence in timing, geometry, a nd apparent structural style throughout the region of late Paleozoic d eformation strongly suggests that these paired regions of basin subsid ence and basement uplift form a unified system of regional deformation , the greater Ancestral Rocky Mountains, Over this region, basin subsi dence and basement uplift were approximately synchronous, beginning in the Chesterian-Morrowan, continuing through the Pennsylvanian, and en ding in the Wolfcampian (although minor post-Wolfcampian deformation o ccurs locally), The basement uplifts show evidence for folding and fau lting in the Pennsylvanian and Early Permian, Reverse faults and thrus t faults have been drilled over many of the uplifts, but only in the A nadarko region has thrusting of the basement uplifts over the adjacent basin been clearly documented, Extensive basement-involved thrusting also occurs along the margins of the Delaware and Midland basins, and suggests that the entire greater Ancestral Rocky Mountains region prob ably formed as the result of northeast-southwest-directed-intraplate s hortening. Deformation within the greater Ancestral Rocky Mountains wa s coeval with late Paleozoic subduction along much of the North Americ an plate margin, and has traditionally been related to emplacement of thrust sheets within the Ouachita-Marathon orogenic belt; The nature, timing, and orientation of events along the Ouachita-Marathon belt mak e it difficult to drive the deformation of the greater Ancestral Rocky Mountains by emplacement of the Ouachita-Marathon belt along the sout hern margin of North America. We speculate the deformation was driven instead by events within a late Paleozoic Andean margin along the sout hwestern margin of North America, Evidence for the existence of this p reviously unrecognized Andean margin comes from east-central Mexico, w here a Pennsylvanian and Permian volcanic are indicates that a northea st-dipping subduction boundary lay to the south and west, The interpre tation that deformation throughout the greater Ancestral Rocky Mountai ns occurs by basement-involved overthrusting on gently to moderately d ipping thrust faults suggests that potential hydrocarbon reserves bene ath crystalline thrust sheets may be much greater than is generally su pposed.