BENGTSON ANALYSIS OF FOLDS IN THE CENTRAL REGION OF THE OUACHITA FOLD-THRUST BELT

Initial structural analysis of folds in the central region of the Ouachita Fold-Thrust Belt is presented in this poster. Tangent diagrams (Bengtson, 1980) were automated with Mathematica to help understand fold geometry in the area. The fold geometries may explain the kinematics of the Ouachita Fold-Thrust Belt.

The program constructs the tangent diagram as a background. Then it plots bedding attitudes as points on the diagram. Next, it constructs a grid over area of the diagram. At each grid node, a function counts all points within a defined search radius and assigns to the value to the node. Once all grid nodes have a point count value, the data is contoured. Finally, the contour plot and bedding attitude points are superimposed on the tangent diagram. A function for rotating a parametric parabola for the least-squares analysis is currently under development.

Bedding attitudes from several folds in the central region were analyzed to evaluate this program. These folds were Boktukola Syncline, Big One Anticline, and Nunihchito Anticline. The results show gradual changes in fold geometry from east to west across the study area. The best-fit curve for Nunihchito Anticline is a tight parabola, for Boktukola Syncline is an open parabola, and for Big One anticline is linear. This suggests folds become less conical and more cylindrical toward the west. Mechanisms creating this effect may be the reactivation of ancient strike-slip faults along the Laurentian continental margin or may be due to oroclinal bending of this portion of the Ouachita Salient.

Bengtson, C., 1980, Structural uses of tangent diagrams: Geology, v. 8, no. 12, p. 599-602.