Abstract

Analysis of 28.5 km 2 of three-dimensional (3-D) seismic reflection data from the triangle zone of the Ouachita fold-and-thrust belt and the foreland Arkoma basin reveals structural details not recognized previously in conventional two-dimensional (2-D) seismic data. The data indicate that the frontal Kiowa syncline in the Arkoma basin has been passively uplifted by blind thrusting at the Morrowan Wapanucka Limestone level, and that smaller wavelength folds are produced by thrusting at shallower levels in the Atoka Formation. Faulting at deeper levels in the Hunton and Arbuckle groups has been traditionally interpreted as normal, but our analysis of this data set indicates that, in this area, normal faults were reactivated during the Ouachita orogeny as reverse faults, and the changes in fault separation can be followed along strike. These faults show the same trend as the overlying thrusts and are normal or have minor inversion where the overlying thrusts have small displacement. These faults have been completely inverted where the overlying thrusts have more displacement, suggesting a genetic relation between the Wapanucka thrusts and the inversion of the Hunton and Arbuckle faults. Four reflections were chosen for analysis: one reflection in the lower Atoka Formation, two reflections repeated in the Wapanucka Limestone, and a fourth reflection in the Hunton Group. All of these surfaces exhibit the same geometry with the fold axes plunging to the southwest. Variations in bearing and plunge of fold axes in the Wapanucka Limestone can be directly correlated to changes in displacement and ramp height along strike. The similarity between surface geometries suggests that the last deformation took place at deeper levels in the Hunton and Arbuckle groups and folded the overlying thrusts. Reactivation of Atokan normal faults at deeper levels in the Arkoma basin and Ouachita subthrust play may be more widespread than previously recognized.

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