"Thrust belt" structures with "foreland" influence; The interaction of tectonic styles

The Rocky Mountain foreland and adjacent thrust belt have long been considered as separate tectonic entities, with primary consideration of interaction limited to a narrow frontal zone. Basement in the thrust belt has usually been interpreted as a passive floor, but we question that view. Models are presented in which cover folds, caused by basement faulting, initiate thrust ramp development, and where basement faulting causes folding of preexisting thrust sheets. The structures so created would generally be interpreted as purely thrust features, given the usual exposure or subsurface penetration. Typically, the transported hanging-wall geometry is identical in the two modes of formation. The models illustrate how basement faulting can participate in the development of geometries typical of thrust belts, and that a number of classical thrustbelt geometries could have a foreland element in their genesis. The models are geometric, but they incorporate the concept of mechanical stratigraphy and are illustrated by means of schematic cross sections and maps.