Jeff P. Crabaugh¹, Ronald J. Steel¹

(1) University of Wyoming, Laramie, WY

ABSTRACT: Tectonics and Sediment Supply in the Generation of Clastic Wedges: Two-Phase (Antitectonic) Model Revisited

There is a common bias in recent publications toward application of the two-phase, or antitectonic, model to explain clastic-wedge development in foreland basins. This model relates the timing of active tectonism to the entrapment of coarse clastics near the thrust-loaded basinmargin. Tectonic quiescence correlates with clastic wedge progradation. An important assumption in this model is that sediment supply rarely overwhelms subsidence during the active tectonic phase.

New Early Paleogene datasets from the Green River Basin of SW Wyoming and the Ebro Basin of Spain provide evidence of progradation of coarse clastics as the response to thrust-related tectonic uplift, at least at third-order scale. These 'syntectonic' relationships are evidenced by the coincidence of clastic-wedge progradation during periods of: 1) increased basinal subsidence, or 2) thrust movement as dated by cross-cutting stratigraphic relationships at the basinmargin.

Analysis of Early Paleogene successions in the Rocky Mountain foreland and the NW Gulf of Mexico Basin reveals synchroneity in three processes recurring at 2.5-3.5m.y. intervals. These processes are: 1) structural deformation at the margin of Laramide basins, 2) clastic wedge progradation in the same Laramide basins, and 3) clastic-wedge progradation in the NW Gulf Basin. This relationship suggests that, at the time-scale of several million years, drainage-system expansion can respond quickly to episodes of rejuvenated tectonic uplift in headwater regions, and that increases in sediment supply as a response to tectonic uplift can be large and abrupt. We conclude that high sediment-supply is under-appreciated as a driving control during clastic-wedge development.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado