Influence of pre-existing plate-margin structures on foredeep filling: Insights from the Taconian (Blountian) clastic wedge, Southeastern USA

Break up of continents gives rise to conjugate margins with irregular shapes, and with thermal histories and sedimentary records that differ along strike. These elements need to be considered in the integrated study of a foreland-basin/orogenic-belt pair that formed during subsequent contractional events. This paper relates the promontory and embayment configuration of southeastern Laurentia (North American craton) to: (1) along-strike variations in width of the initial depositional profile of the Middle to Upper Ordovician Taconian (Blountian) foredeep; (2) northeastward (toward the embayment) along-strike thickening and migration of siliciclastic depocenters in the foredeep, that favored the resumption of carbonate-ramp deposition on the promontory during the Late Ordovician; and (3) variation in intensity of deformation of intrabasinal structures as recorded by reactivation of across-strike structures located on the transition zone between the promontory and embayment. Geometry and composition of the Blountian foreland strata indicate that the foredeep slope was narrower and steeper on the Alabama promontory than on the southwestern flank of the Tennessee embayment. Differential slope geometries were accommodated by reactivation of transverse basement faults, which controlled local conglomerate deposition in deep-water settings on the transition zone between the promontory and embayment. In contrast, conglomerate beds at the top of coarsening-upward successions on the southwestern flank of the Tennessee embayment record the cratonward progradation of deltaic depositional systems. The results presented here may have relevance to other peripheral foreland basins formed over rifted continental margins or retro-arc foreland basins formed adjacent to inverted intracratonic rifts.