CONTROLS ON THE DEVELOPMENT OF CONTRASTING CURVE GEOMETRIES IN CENTRAL SIERRA MADRE ORIENTAL FOLD-THRUST BELT, MEXICO

The Sierra Madre Oriental fold-thrust belt in central Mexico displays a concave-eastward recess in the hinterland, and a linear structural trend in the frontal portions of the fold-thrust belt. The hinterland recess is symmetrical in shape. Structural trends defined by contractional structures, trend NNE-SSW and NW-SE in its northern flank and southern flank, respectively. Geologic mapping combined with available well data indicates that evaporite deposits are not uniform. Evaporite deposits in the hinterland portion of the fold belt are present along the flanks of the recess, but absent at its apex and in most of the linear foreland portion of the fold belt. Moreover, late Triassic-Early Jurassic rift-related sedimentary sequences vary in thickness from place to place, and a very thin upper part is probably continuous across the fold belt. Thus, eastward advances of thrust sheets in the northern and southern flanks were facilitated by the underlying evaporites, and resulted in arcuate structural lines in the hinterland. Our results suggest the presence of a north-northwest trending rift basin situated beneath the hinterland portion of the Sierra Madre Oriental fold belt. We interpret that thick evaporite deposits accumulated within the basin, and that the contrasting styles of deformation expressed in the Sierra Madre Oriental fold belt was controlled by the distribution of evaporite and rift-related sedimentary sequences and rift bounding structures. In the hinterland, two detachment levels are present. The deepest detachment level lies at the base of late Triassic-early Jurassic rift-related sedimentary rocks. The higher detachment level is the evaporite sequence. In contrast, only one detachment horizon was recognized in the frontal portions of the fold belt, where linear structural trends were observed at the contact between rift-related red beds and the overlying J-K limestones.