Abstract

Backstripped cross sections of the Late Cretaceous succession across central Utah, Colorado, and southern Wyoming in the Western Interior Basin, United States, reveal a component of continuously evolving long-wavelength residual subsidence, in addition to subsidence driven by the Sevier thrust belt and associated sediment loads. The loci of maximum rates of this residual subsidence moved eastward from ca. 98 to 74 Ma in phase with the west to east passage of the Farallon slab, as reconstructed from tomography based on quantitative inverse models. These new subsidence data allow testing of existing subduction models and confirm the dynamic subsidence origin of the Western Interior Basin. Furthermore, regional variations in subsidence rates suggest a possible deficit of negative buoyancy (mantle loading) inside the slab beneath Colorado, supporting the hypothesis that the thickened slab represents a subducted oceanic plateau. This paper documents how the Cretaceous stratigraphy records the timing, patterns, and position of underlying mantle processes during Farallon slab subduction. The new data also reveal patterns indicative of the commencement of the Laramide orogeny in the western United States.

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