Decker, Steve¹
(1) ChevronTexaco, Houston, TX

ABSTRACT: A Detailed New Look at Structures in the Ardmore Basin, Southern Oklahoma, USA

This is a detailed, highly constrained example of the relationship between mechanical stratigraphy, pre-existing fold geometry, and subsequent fold initiation. It also illustrates potentially surprising opportunities that may hide in the core of some compressional structures.
The Milroy and Velma structures in the Ardmore Basin of Oklahoma are disharmonic with three scales of structuring. First order morphology is from basement thrusting that verges northeasterly ahead of the Wichita Mountain Front, a major tectonic feature in the basin. Second order morphology is from backthrusting in the 4500’ thick Arbuckle Lime above the basement, and synchronous forelimb rabbit ears in the shale-rich Simpson as it accommodated stain within the core of the structure. Third order is from detachments in the shallower Caney-Goddard shales which carried rock up both limbs, inducing folding above convex inflections below. Later Arbuckle orogenic reactivation further deformed the structures, and produced breakthrough of faulting from the Arbuckle Lime.
Mechanical stratigraphy influenced fold morphology. Thick shales focused fault-fold initiation in the Simpson and Goddard. Thick limestone constrained faulting in the Simpson shales below the Viola Lime. Simpson rabbit ears form map-scale substructures causing the main structures to commonly have two or more Simpson closures their core.
The fold morphologies at Velma and Milroy are inconsistent with a strike-slip origin. The causal fault and the resulting fold are coincident rather than oblique. Divergent and convergent bend related features are missing. The only observed translation is where ~ 2500 ft of translation occurs at a localized tear zone at Velma.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.