Clastic Wedge Development in the Cordilleran Foreland Basin, USA: Implications for Basin Dynamics during the Cretaceous Sevier-Laramide Transition
A new high-resolution regional correlation and isopach maps (1) provide evidence that Laramide deformation began as early as ca. 77 Ma in central Utah, and (2) suggest that rapid and extensive progradation of an unusual clastic wedge was caused by interference of a Laramide-style uplift with flexural subsidence in the foredeep, and may have been enhanced by reduced dynamic subsidence during this time. Three Campanian, alluvial-to-marine clastic wedges that traversed 250-400 km eastwards across the Cordilleran foreland basin are present in the basin fill. Wedges A and C are high-volume successions with a rising-trajectory shoreline stacking pattern (Blackhawk Formation and lower Castlegate Sandstone; Bluecastle Tongue and Rollins Sandstone) that reflect relatively slow progradation of narrow (10-20 km wide), wave-dominated shorelines. In contrast, Wedge B consists of lower-volume successions with a flat-to-falling shoreline stacking pattern (middle Castlegate Sandstone, Sego Sandstone, Neslen Formation, Corcoran and Cozzette Members of the Iles Formation) that reflects rapid progradation of embayed (60-80 km wide), tide-influenced shorelines. Wedges A and C prograded 200-250 km in more than ca. 5 Ma, whereas Wedge B prograded 340-400 km in just ca. 2 Ma (~170 km m.y.-1). Stratigraphic relations and growth strata analysis indicate development of Wedge B coeval with both Sevier- and Laramide-style deformation in this part of the foreland basin. Basin-wide accommodation space was reduced during this overlap, or transition in structural styles. We postulate that tectonic transitions such as Sevier-Laramide can fundamentally alter the dynamics of foreland basins, and may influence the type of clastic wedges and the facies assemblages that develop during this time.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009