THE PERMIAN BASIN AS PENNSYLVANIAN FORELAND BASIN IN FRONT OF MARATHON OROGEN

The Permian Basin (PB) occupies about 115,000 mi² (300,000 km²) of W Texas and SE New Mexico, about the size of Arizona or the nation of Italy. PB is an important hydrocarbon-producing region with a complex Paleozoic history. Shallow Permian and Triassic beds define a broad structural bowl underlain by more complex structures of Pennsylvanian age, including, from E to W, the Midland Basin, Central Basin Platform, and Delaware Basin. These structures trend NNW, perpendicular to E-W structures of the synchronous Late Pennsylvanian Marathon fold-and-thrust belt (MFTB) to the S and parallel to Ancestral Rocky Mountain structures to the N. Pennsylvanian structural differentiation of the PB also accompanied northward emplacement of MFTB nappes. The MFTB marks the westernmost extent of the Gondwanaland - Laurussia collision zone, and coarse debris from Gondwana is preserved in the Haymond conglomerate. The development of structural complexity in the PB during Pennsylvanian time succeeded the broad gentle Tobosa Basin of Early Paleozoic age. The northern margin of the MFTB marks the southern limit of the PB. The MFTB crops out in the Marathon dome (Brewster County, TX), but elsewhere is buried and recognized only in the scattered borings which allow the MFTB to be traced eastward to the Devils River Uplift. Information on structures near the overthrust southern margin is sparse. What is the geometry of these thrusts and how did Pennsylvanian orogenesis affect basin evolution and what was the age of orogenic movements preserved in sediments and structures? Can in situ Gondwana crust be identified? We need an integrated geophysical-geological study of the MFTB-PB juncture, involving both academic and industry geoscientists. We envision first interpreting existing potential field data (gravity and magnetics) over the region (possibly supplemented by new field programs to fill in data gaps), followed by a long 2D seismic reflection and refraction study. This regional line could be utilized to locate a 3D seismic reflection study for selection of one or more scientific drill sites designed to core continuously to Precambrian basement. Such an integrated study will help train a generation of new students and involve geoscience faculty, while improving understanding of PB and N. American Paleozoic tectonics and stratigraphy.