Structural Architecture of the Frontal Ouachitas-Arkoma Basin Transition Zone of Western Arkansas: The Waldron Triangle Zone

Yezerski, Donald; Cemen, Ibrahim

The Arkoma Basin extends across eastern Oklahoma and western Arkansas north of the Ouachita fold-and-thrust belt. The basin contains 7,000 meters of Mississippian to Pennsylvanian sediments that record the transition from a passive margin to a foreland basin associated with the advancing thrust sheets of the Ouachita Orogeny. The frontal Ouachitas to Arkoma Basin transition zone of eastern Oklahoma is well-studied in the vicinity of several gas fields and is interpreted as a triangle zone, the Wilburton Triangle Zone, in the footwall of the Choctaw Fault. However, the structural geometry of frontal structures along strike in western Arkansas remains relatively unknown. Constraining the geometry and structural style of strain partitioned by frontal structures along the eastern continuation of the Wilburton Triangle Zone in western Arkansas is fundamental to understanding the nature of thrust propagation into foreland settings and is essential to continued oil and gas exploration efforts in the Arkoma Basin.

Preliminary interpretations of depth converted 2-D seismic reflection profiles of north-central Scott County, Arkansas demonstrate that the transition zone does exhibit geometric characteristics of a typical triangle zone. The footwall of the Ross Creek Fault contains the surface exposure of a passive-roof containing folded upper and lower Atoka Formation detached above the Lower Atokan Detachment (LAD). The LAD serves as the roof thrust of a foreland-vergent duplex of lower Atokan strata above the Morrowan Johns Valley Shale Detachment (JVSD). The JVSD serves as the roof thrust of a single basal duplex of Chesterian through Morrowan section detached at the base of the Stanley Group, referred to as the Stanley Detachment (SD). Displacement along the SD increases to the east and coincides with decreasing displacement and eventual absence of the overlying lower Atokan duplex. To the west, a south-dipping thrust offsets north-dipping strata of the Poteau Syncline and merges with a syncline-bounding backthrust. To the east, the SD ramps to merge with the backthrust.

Although the frontal structure of eastern Oklahoma and western Arkansas both contain triangle zones, the internal duplex style and position in the footwall of the Ross Creek Fault fundamentally differ from the geometries of the Wilburton Triangle Zone and lead us to name the western Arkansas frontal structure the Waldron Triangle Zone after nearby Waldron, Arkansas.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013