Abstract: The Permian Basin of west Texas and southern New Mexico is located in the foreland of the late Paleozoic Marathon-Ouachita orogenic belt. This complex foreland area consists of several sub-basins that are separated by intraforeland uplifts. In an accompanying paper in this volume, regional structural and stratigraphic relationships are used to constrain the tectonic history of the Permian Basin region. A kinematic model for the origin of the Central Basin Platform (CBP), a prominent intraforeland uplift that separates the Midland and Delaware Basins, is also presented. In this paper, we show the results of two-dimensional flexural models for the Permian Basin region. The Marathon orogenic belt is generally considered to be the dominant topographic load that caused flexural subsidence in the Permian Basin region. Basement shortening and uplift associated with the CBP, however, require that the CBP is an additional topographic load that must be considered when modeling the late Paleozoic evolution of the adjacent basinal areas. The CBP was treated as a distributed tectonic load that produced lithospheric flexure of the adjacent basinal areas. To calculate the effects of this load, loading geometries were determined from the excess basement material measured on structural cross sections. These loading geometries were then used to calculate static profiles of the deflected lithosphere using flexural models for elastic lithosphere. Results from flexural analyses compare well with reconstructed synorogenic geometries of the Midland, Delaware, and Val Verde Basins, indicating that subsidence of these basins most likely was produced by the combined topographic loads of the Marathon orogenic belt, the CBP, and probably structures associated with the Diablo Platform and cryptic loads near the Eastern Shelf on the eastern side of the Midland Basin. Best-fit model profiles for the Val Verde and Delaware Basins indicate that values for the flexural rigidity of lithosphere in the Permian Basin region are lowest near the southwest corner of the CBP. The Val Verde Basin is narrowest and the Delaware Basin is deepest near this corner. The apparently low rigidities at this corner also coincide with a prominent salient in the Marathon orogenic belt and with the greatest amount of shortening measured along the boundaries of the CBP. These low calculated rigidities reflect locally weaker lithosphere that might be related to inherent lateral strength variations in the Marathon foreland. Alternatively, high bending stresses produced by the combined loads of the southwest corner of the CBP and the prominent salient of the Marathon orogenic belt may also have weakened the lithosphere in this area.

Abstract: The Permian Basin of West Texas and southern New Mexico is located in the foreland of the Marathon-Ouachita orogenic belt. This complex foreland area consists of several sub-basins that are separated by intraforeland uplifts. This study examined the tectonic, kinematic, and subsidence history of the Permian Basin in order to evaluate how intraforeland deformation affected stratigraphic development. We focused on: (1) the kinematic history of the Central Basin Platform (CBP), an intraforeland uplift that trends at high angles to the frontal thrust of the Marathons and separates the Delaware and Midland Basins; and (2) subsidence and stratigraphic analyses of the Midland, Delaware, and Val Verde Basins. Structure contour maps, seismic profiles, and balanced structural cross sections show that the CBP can be subdivided into two fault-bounded "blucks," the Fort Stockton and Andector Blocks, which are arranged in a left-stepping, en echelon pattern. The distribution of structural features associated with the CBP is best explained by clockwise rotation of these blocks plus an additional component of east-west compression. The rotation model explains: (1) the steeply dipping reverse faults at the SW and NE corners and local extensional faults at NW corners of individual crustal blocks that comprise the CBP; (2) the large structural relief observed at the SW and NE corners of individual blocks; and (3) decreasing amounts of basement shortening away from thrust-faulted corners that can be documented along both sides of the Fort Stockton Block. An additional component of shortening is required to account for imbalances between the amount of shortening versus extension observed along block boundaries. Subsidence analyses from several points in the Midland, Delaware, and Val Verde Basins indicate that the main phase of tectonic activity probably began during middle Pennsylvanian time. Rapid subsidence in each basin began at that time and continued until Early Permian time. Thereafter, subsidence slowed considerably to the end of the Permian. Late Paleozoic unconformities developed across the CBP and locally in adjacent basinal areas at the same time as rapid subsidence in the basins, suggesting that they are related to the same general episode of tectonic activity. Upper Pennsylvanian to Lower Permian stratigraphic cross sections show that synorogenic strata generally thicken toward the CBP. These stratal relationships indicate (hat the CBP acted as an intraforeland load that caused flexure of the adjacent sub-basins that comprise the Permian Basin. The thickest accumulation of upper Pennsylvanian to Lower Permian strata is developed next to the SW and NE corners of the Fort Stockton and Andector Blocks, which also corresponds to the areas where block uplift was greatest. Finally, the variable platform-to-basin relief that was produced during uplift of the CBP resulted in very different patterns of stratigraphic onlap during late Pennsylvanian to Early Permian time. Onlapping upper Pennsylvanian to Wolfcampian strata extend farthest across the top of the CBP where structural relief was least (i.e., at (he NW and SE block corners). Stratal onlap is minimal at (he SW and NE block corners because structural relief was greatest there. This study illustrates how patterns of intraforeland deformation can dramatically affect basin stratigraphy during synorogenic stages of basin development.