Abstract

Tectonic transport from different directions and convergence of separate thrust belts at structural recesses impart three-dimensional variations to the pattern of foreland-basin subsidence. Assuming approximately uniform flexural rigidity of the lithosphere, subsidence is directly controlled by the geometry and density of the separate thrust loads, and flexural deformations caused by the loads interfere within the recess. For example, the Black Warrior foreland basin, which is located in Mississippi and Alabama, within a recess in the Appalachian-Ouachita orogen, formed in response to two separate thrust loads: (1) the Ouachita accretionary prism along the southwest side of the basin, and (2) thrust-imbricated passive-margin rocks in the Appalachian thrust belt along the southeast side of the basin. The subsidence history differs along two profiles, each perpendicular to the Appalachian and Ouachita thrust fronts. Subsidence of the foreland basin began in middle Mississippian (Meramecian) time in response to northeast-directed translation of the Ouachita accretionary prism. Subsequently, northwest-directed Appalachian thrusting began in middle Early Pennsylvanian (Morrowan) time. Subsidence curves from the profile perpendicular to the Ouachita prism show a clear progression of increasing subsidence rates and amounts toward the thrust front, whereas curves from the profile perpendicular to the Appalachian belt indicate out-of-plane effects from the Ouachita thrust front and a later increase in subsidence toward the Appalachian thrust front. The major implication of this work is that the three-dimensional geometry of a foreland basin within a thrust-belt recess includes diachronous interfering elements.

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