Abstract

Middle–late Campanian strata of the Book Cliffs, Utah, USA, archive three clastic wedges of the North American Cordilleran foreland basin east of the Sevier fold and thrust belt. Variations in wedge geometries provide an opportunity to evaluate controls on foreland basin stratigraphic architecture. There is a significant increase in eastward progradation rate from the Lower to Upper Castlegate Sandstone, followed by a decreased progradation rate in the overlying Bluecastle Tongue and Price River Formation. Rapid progradation during deposition of the Upper Castlegate Sandstone has been attributed to increased sediment supply due to either rapid exhumation of the Sevier fold and thrust belt or introduction of a new sediment source. Rapid progradation has also been attributed to a reduction in basin subsidence due to intraforeland Laramide uplifts or a change in the locus of dynamic subsidence. We test these hypotheses by documenting temporal and spatial changes in the detrital zircon U-Pb age spectra attributable to changes in sediment dispersal patterns, changes in orogenic belt configuration, and/or major tectonic episodes. Mixture modeling of relative contributions from potential source areas indicates a mixed contribution of thrust-belt, northern, and southern sources during rapid progradation. The introduction of multiple sources is likely due to a northward propagation of exhumation in the thrust belt coeval with introduction of axially-sourced detritus in the medial–distal foreland basin. The northward propagation of exhumation culminated with exhumation in the Charleston-Nebo Salient and Uinta Uplift north of the Book Cliffs and may point to a common cause for these phenomena. Mixture modeling points to a change to a dominant southern source during slower progradation in the overlying strata. The return to slower progradation is coeval with a decrease in thrust-belt derived detritus and transition to a dominant southern-source contribution. Transition to a dominantly axial fluvial system during this interval is consistent with a northeastward migration of the regional depocenter. Migration of subsidence and exhumation can be attributed to dynamic subsidence and uplift associated with the northeastward subduction of the Conjugate Shatsky Rise oceanic plateau beneath the Book Cliffs area. Rapid progradation observed during deposition of the Upper Castlegate Sandstone was controlled by a combination of increased sediment supply due to increased exhumation in the Sevier thrust belt and introduction of multiple sources.

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