Abstract

Utilization of both surface and subsurface data permits a simple, yet logical synthesis of the structure and stratigraphy of the Marathon Fold Belt which, in turn, helps to delineate broad trends of prospective interest for oil and gas exploration. Three exploration trends correspond to pre-orogenic, orogenic, and post-orogenic (or simply pre-thrust, thrust, and post-thrust) movements. The large, northwest-southeast-oriented fault blocks associated with the compressional features of the Delaware Basin represent the first trend (i.e., Elsinore Field, etc.). The orogenic (thrust) trends are represented by folds of the Marathon Facies (McKay Creek, Thistle, Piñon fields). Post-orogenic trends are largely concentrated at the unconformity surface of the Middle Wolfcampian (Stockton Gap Formation). While major discoveries have yet to be made in the latter, significant indicators for future possibilities abound.

Isopach maps of the Caballos Novaculite and Dimple Formation, coupled with stratigraphic data, suggest that a reasonable interpretation can be made of the original depositional configuration of these two units. Since entire basins of deposition would not have been likely to thrust as single entities over a very great distance without losing their basic form, it is only possible to suggest a minimal thrust distance of about 30 miles, and a possible maximum of perhaps 100 miles. These figures are much less conservative than those of King (1937) from crustal shortening measurements, but even King suggested distances “probably much greater” than 15 miles (p. 131).

An area of major thinning of both the Caballos and Dimple formations, which suggests at least two separate depocenters, must represent a very early system of block-faulting extending out of the Delaware Basin foreland. The southwestern side of this feature is a depositional low of great magnitude, which is here designated The Marathon Sag. Evidence for the presence of this feature is deduced from both surface and subsurface data.