--> Abstract: Migration of Dynamic Subsidence Across the Late Cretaceous U.S. Western Interior Basin in Response to Farallon Plate Subduction, by Dag Nummedal, Shaofeng Liu, and Lijun Liu; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Migration of Dynamic Subsidence Across the Late Cretaceous U.S. Western Interior Basin in Response to Farallon Plate Subduction

Dag Nummedal1; Shaofeng Liu2; Lijun Liu3

(1) Colorado Energy Research Institute, Colorado School of Mines, Golden, CO.

(2) Earth Science and Resources, China University of Geosciences, Beijing, China.

(3) Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA.

The Cretaceous Western Interior Basin is generally thought of as a foreland basin because of the asymmetric westward-thickening sediment wedge and its relationship to the Sevier thrust belt along its western margin. However, flexural backstripping results document clearly that only along a narrow band, about 120 - 180 km wide, directly in front of the thrust belt, was the subsidence driven by the load of the Sevier thrust belt. Backstripped and decompacted cross sections of the Upper Cretaceous succession across central Utah and Colorado and southern Wyoming reveal a component of continuously evolving long-wavelength residual subsidence, characterized by an initial maximum subsidence in the west and transforming into a subsiding “trough” that migrated eastward over time in perfect synchrony with the west-to-east passage of the Farallon slab, as reconstructed from tomography based on quantitative inverse models. This subsidence component is additive to well-understood subsidence driven by the thrust belt and associated sediment and water loads.

The new residual subsidence data permit rigorous testing of existing geodynamic models, and reveals that the residual subsidence is of dynamic topographic nature and that the major driver behind the Western Interior Basin was subduction of the Farallon plate. The subduction created buoyancy-induced mantle flow with a downward drag on the crust. Moreover, regional variations in subsidence rates suggest a possible deficit of negative buoyancy (mantle loading) inside the slab beneath Colorado, supporting the hypothesis that a thick flat slab beneath Colorado represents a subducted oceanic plateau. Outside this plateau, as for example in Wyoming, the normal thickness of the subducted plate would cause greater subsidence.

Reconstructed subsidence profiles across Utah, Colorado and Wyoming all demonstrate variations in subsidence on a spatial scale of about 100 km after about 80 Ma. This spacing is the typical length scale of the subsequent Laramide basins and ranges. These short wavelength ‘spikes’ in the broad dynamic subsidence profiles, therefore, are thought to reflect the onset of Laramide-style uplifts at depth.

Overall, this paper documents how the Cretaceous stratigraphy records the timing, patterns and position of underlying mantle processes during Farallon slab subduction.