Detailed field mapping and imagery analysis (Landsat, SIR-A radar, and black-and-white air photos) facilitate a structural and tectonic interpretation of the Parras basin. Parras basin is the erosional remnant of a Maestrichtian-Paleocene foreland basin with over 4,000 m of interfingered deltaic and marine deposits that accumulated during the early development of the Sierra Madre Oriental. The deformation sequence in Parras basin began with a main phase of north-northwest-directed thrusting accompanied by layer-parallel shortening, producing a weak solution cleavage. Thrusting was followed by formation of east-northeast-trending, symmetric to slightly asymmetric, north-northwest-verging, gently west-plunging, parallel folds with minor limb thrusting and thinning. The earl cleavage was rotated in the limbs of the folds and a moderate axial surface-parallel solution cleavage was formed in the hinge zones. A well-defined 20-km wide zone of north-northwest-trending high-angle strike-slip and normal faults cuts all previously developed structures. Mesoscopic folds, slickenfibers, syntectonic vein fibers, and striae document a dominant north-northwest transport direction and a poorly developed secondary west-northwest transport direction. Parras basin rocks and structures reflect Laramide orogenic activity and the development of the Sierra Madre Oriental. Early thrusting of the thick Mesozoic carbonate sequence and flexure of the foreland generated an asymmetric, longitudinal depression parallel with the advancing sheet. The thickest accumulations of detritus hed from the rising hinterland are preserved along the Sierra Madre Oriental structural front. Continued northward migration of this front along a basal decollement culminated with local overthrusting and the incorporation of the Parras basin rocks in the fold-thrust belt. The present transverse and salient geometry of the fold-thrust belt reflects the influence of irregular basement structures related to the late Paleozoic configuration of northeastern Mexico.

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