Nine present-day structural basins occur along the leading edge of the Ouachita thrust belt, a 1,400 mi (2,250 km) Paleozoic overthrust trend that extends from the Appalachians to Mexico. These basins, now separated by either subtle arches or pronounced basement uplifts, are components of a widespread late Paleozoic foredeep that formed in front of the Ouachita orogenic belt as a result of tectonic loading. This elongate depression filled during Pennsylvanian and Permian times with up to 15,000 ft (4,590 m) of sediment ranging in origin from alluvial to deep marine.

An estimated 10 tcf of commercially recoverable natural gas has been discovered to date in the clastics of this foredeep basin trend. Four basins contain the bulk of these known reserves.

The major conclusions of a study of late Paleozoic paleogeography, the structural style, and the habitat of hydrocarbons in this foredeep trend are:

1. The clastics were derived from cratonic or Appalachian sources, not from the rising Ouachita orogene. There appear to be a least 4 major entry points along the northern margin of the foredeep.

2. The facies range from coal-bearing deposits to deep-water turbidities. Fluvial and shallow-marine facies are found in the more stable areas; several turbidite depocenters occur in the areas of rapid, early subsidence.

3. The vast majority of the discovered hydrocarbons (gas) occurs in gas-saturated deep-basin traps. These very large fields occur in turbidites (Val Verde and Arkoma basins) and fluvial to shallow-marine deposits (Fort Worth basin).

4. Large undeveloped reserves can be documented in several basins in low-permeability reservoirs. In addition, there has been only rank wildcat exploration in 3 of the basins--Desha, Kerr, and Marfa.

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