HOW DO CONTRACTIONAL DUPLEX STRUCTURES CHANGE ALONG STRIKE OF THE ARKOMA BASIN-OUACHITA FOLD AND THRUST BELT TRANSITION ZONE?

The Arkoma Basin is an arcuate foreland basin that formed during the Pennsylvanian Ouachita orogeny. The basin contains an Atokan flysch sequence about 18,000 feet thick that was deposited in a foreland setting. It also contains about 5,000 feet of molasse deposits Desmoinesian in age. The lower Atokan Spiro sandstone is a major natural gas producer in the basin.

Along the Arkoma Basin-Ouachita fold and thrust belt transition zone in southern Oklahoma, several north-south cross-sections demonstrate the presence of a triangle zone and a duplex structure where strain partitions from the leading edge Choctaw thrust fault to the south to the undeformed flat-lying Arkoma foreland basin sedimentary units to the north. However, there are variations along strike in the geometries of the triangle zone and duplex structure from west in the Hartshorne gas field area in Oklahoma to the east in the Waldron area, in western Arkansas.

We have constructed two west-east trending cross sections along the transition zone to show the variations in the internal geometry of the duplex structure. Our preliminary interpretation suggests that the Devonian Woodford detachment becomes structurally high towards east and the number of horse structures in the duplexes decreases. This may suggest that the intensity of deformation may lessen from west to east along strike of the transition zone. The cross sections, regional stratigraphy and sedimentology will help us to determine what the controlling factors of the west to east variations of the duplex structures are.