A Case for Brittle Deformation of the Basement During the Laramide Revolution in the Rocky Mountain Foreland Province

Abstract

Debate over the question of whether basement rocks folded or faulted during the Laramide orogeny in the Wyoming province of the Rocky Mountain foreland has raged for many years. Proponents of one view or the other have drawn support for their case from theoretical arguments, from experimental laboratory results, from interpretations of seismic and subsurface borehole data, and from direct observation of surface outcrops and subsurface mine exposures. An analysis of the validity and applicability of these various approaches included the generation of synthetic seismic sections and an evaluation at balanced cross sections. This analysis indicated that the notion of a folded basement is supported only by the interpretation of seismic and borehole data whereas the concept of brittle deformation of the basement is supported by all of these lines of reasoning, interpretation, and observation. The conclusion is that structural basement did not fold during the Laramide orogeny.