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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 59 (1975)

Issue: 6. (June)

First Page: 974

Last Page: 985

Title: Evolution of Folds around Broken Bow Uplift, Ouachita Mountains, Southeastern Oklahoma

Author(s): Roger Feenstra (2), John Wickham (2)


Folds in the studied area range from a few centimeters to 3 km in wavelength and are asymmetric with sharp angular hinge zones. Anticlines are overturned southward away from the continental interior. Fold hinges trend east-west and are arched over the Broken Bow uplift which trends northeast across the fold hinges. Asymmetric minor folds are present on the limbs of larger structures, but many minor folds do not exhibit a change in symmetry from one limb of the larger fold to the other.

Slaty cleavage is common in the southern part of the Broken Bow uplift and rare in the north. Cleavage is distributed symmetrically about axial planes in many folds. However, in the southern part of the uplift, slaty cleavage cuts across axial planes of folds at angles up to 30°. This cross-cutting relation is present in both outcrop-size folds and folds with wavelengths of a kilometer or more.

The Broken Bow uplift has at least three recognizable phases of deformation. The first phase produced buckle folds that probably were generated by gravitational body forces during the rapid deepening of the basin axis in the north associated with flysch sedimentation during the Carboniferous. The second phase was associated with the principal Ouachita diastrophism in the Late Pennsylvanian or Early Permian. The northward dipping slaty cleavage was superimposed on the earlier folds and cut across their hinge surfaces. Original fold shapes were modified greatly and anticlines were overturned producing north-dipping fold axial planes. These north-dipping axial planes are inconsistent with previous suggestions that a mobile core or infrastructure is buried beneath the Mesozoic coastal pla n sediments in the south. Additional small-scale folds probably were generated during this second phase. The second phase may have contained a large regional shear-strain component produced by underthrusting the basement toward the continental interior. The last deformation phase produced the Broken Bow uplift by arching east-west-trending folds and slaty cleavage about a northeast-southwest axis. Movements were essentially vertical with little internal deformation of the rocks.

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