The Marfa, Marathon, Val Verde, and Delaware basins and related uplifts formed the major structural elements of the southwestern continental margin of North America during the Paleozoic. In contrast with the relatively simple relationships where the southern Oklahoma aulacogen intersects the Ouachita orogenic belt, structural relationships in the area of these basins are very complex. Various geologic evidence points to an allochthonous Marathon basin. However, a prominent gravity anomaly is associated with the Ouachita system as it extends from western Arkansas through Oklahoma and Texas into northern Mexico. If this anomaly is the signature of the early Paleozoic continental margin, then the location of the Marathon basin with respect to this anomaly suggests lateral di placements have been only on the scale of tens of kilometers. The Delaware basin seems clearly analogous to the Anadarko basin in that it formed as a result of reactivation of a major crustal flaw (not necessarily a rift). This reactivation was a result of the Ouachita orogeny. The Marfa basin is also flanked by a linear gravity high and basement uplift. The relationship of this anomaly to the gravity high associated with the Ouachita system suggests that the Marfa basin may be more analogous to the Delaware basin than foreland basins such as the Ft. Worth and Arkoma. A prominent gravity high that extends into northern Mexico is associated with the Devil's River uplift, and the relationships between this feature, the Val Verde basin, and adjacent structures suggest major deformation on a crustal scale.

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