Postorogenic denudation along the late Paleozoic Ouachita trend, south central United States of America: magnitude and timing constraints from apatite fission track data

Abstract

The magnitude and timing of synorogenic and postorogenic denudation along fold and thrust belts and their associated foreland basins, of interest because of both tectonic and economic implications, is generally poorly constrained. Along the late Paleozoic Ouachita trend, a thin veneer of Cretaceous strata is preserved above a low-relief erosional surface that beveled the Ouachita orogen and adjacent foreland areas. This regional erosion surface provides a valuable constraint for interpreting new and previously published apatite fission track (AFT) data obtained from exposed structural highs along the Ouachita trend (Marathon, Llano, Arbuckle, and Benton uplifts). AFT data from sampled localities within the deformation belt (Marathon and Benton uplifts) exhibit younger ages and, generally, longer mean lengths than data from localities on the foreland side of the deformation front (Llano and Arbuckle uplifts). This observation suggests that erosion of the orogen, rather than its extensional collapse, was the primary mechanism responsible for flexural isostatic unloading of the foreland crust. In addition, all samples show evidence for mild reheating following their pre-Cretaceous cooling history. Specifically, the lack of a significant population of >14.5-μm tracks in all samples appears to require residence at temperatures of ≥55°±5°C after development of the sub-Cretaceous erosional surface. This implies that ~1000 m of Cretaceous-Paleogene(?) strata were deposited across the entire Ouachita frontal trend and subsequently removed during later Tertiary time. This Tertiary denudation is interpreted to reflect the interplay between regional denudation and isostatic compensation in response to slow (~10 m/m.y.) epeirogenic uplift of the southern midcontinent and a long-term drop (~200 m) in eustatic sealevel during this time.