Abstract

The tectonic mechanism(s) that caused subsidence of the Delaware and Midland basins during late Paleozoic time are enigmatic. Previous interpretations about subsidence mechanisms for the Delaware basin are based on characteristics of boundary faults between the basin and adjacent uplifted areas and on the form of poorly constrained subsidence curves. In this study, restoration of synorogenic strata in the Delaware and Midland basins, structural cross-sections through deformed lower Paleozoic strata and Precambrian basement of the Central Basin Platform (CBP), and two-dimensional flexural analyses suggest that the CBP acted as a topographic load and affected subsidence in the adjacent basins.

The Central Basin Platform is composed of two, or possibly three, segmented blocks that are arranged in a dextral en echelon pattern. Seismic sections across the SW and NE corners of the Fort Stockton Block (the southern most block of the CBP) are characterized by over thrust faults that dip toward the interior of the block. East-west profiles of restored Mississippian to lower Permian synorogenic strata in the Delaware basin are asymmetric (i.e., thicker) towards the CBP at the SW corner of the Fort Stockton Block. On the other side of the CBP, equivalent synorogenic strata in the Midland basin are thinner and east-west basin profiles are nearly symmetrical.

A structural cross-section of lower Paleozoic strata across the Delaware basin, the southern part of the CBP, and into the Midland basin indicates an excess of material beneath the CBP, In this study, 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, a loading geometry was determined from the excess material measured from the structural cross-section. This loading geometry then was used to calculate a static profile of the deflected lithosphere across the area, based on flexural models for elastic lithosphere. The model profiles are asymmetric (i.e., deeper toward the CBP) across the Delaware basin and shallower, but nearly symmetric across the Midland basin. These results might explain the observed synorogenic profiles of the basins. Discrepancies between the calculated and observed basin profiles increase away from the CBP. This suggests that part of the synorogenic subsidence in the basins might have been produced by additional topographic loads that bordered the basins.