Basement-Influenced Deformation in the Marathon Fold-Thrust Belt, West Texas

Abstract

The Marathon Basin of West Texas is a window into the southwestern end of the Ouachita system and formed as a response to north-to-northwest-directed late Paleozoic thrust faulting. Folds in the basin are elongate, trend northeast, and are highly non-cylindrical. Thickness and facies changes within the flysch sediments of the basin are coincident with the plunge of major anticlinoria. These features are superimposed on a pre-existing structural framework inherited from earlier deformation and modified by pre-, syn-, and post-tectonic sedimentation. Field, seismic, aeromagnetic, and deep well data indicate the presence of both northeast-trending frontal ramps and northwest-trending transverse ramps beneath the allochthonous rocks of the Marathon Basin. Evidence for reactivated northwest-trending features includes: (1) changes in plunge of first- and second-order folds; (2) large offsets in Devonian carbonate/top of basement seismic reflectors; (3) structure contours on Cretaceous rocks surrounding the basin; (4) dramatic changes in elevation of top of Ellenburger along strike; (5) variable tectonic stratigraphy and flysch thickness along strike; (6) a northwest-trending magnetic low through the middle of the basin; and (7) outcrop and well data for large-scale vertical movements along colinear northwest-trending features both north and south of the basin proper. These basement structural features (high-angle faults?) were inherited from Late Precambrian rifting and reactivated during Ouachita, Laramide, and Basin and Range events. Basement-influenced transverse structures affect the sedimentological and subsequent deformational histories of this and other fold-thrust belts around the world.