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Liu, Shaofeng1, Dag Nummedal2, Peigui Yin2, Hongjun Luo2 
(1) China University of Geosciences, Beijing, China 
(2) University of Wyoming, Laramie, WY

ABSTRACT: Re-evaluation of Middle Cretaceous Subsidence in the Southern Wyoming Foreland Basin

Subsidence of the western interior seaway is driven by both flexural, thrust-related mechanisms as well as long wavelength processes that took place at the same time. Middle Cretaceous filling of the southern Wyoming foreland basin can be divided into 3 unconformity-bounded phases. Airy backstripping shows 3 episodes of concave-upward subsidence in the basin. Coarse-grained clastic progradation took place during periods of slow subsidence in the first two phases. During phase 3, fluvial and coastal plain deposits prograded far out into the basin, likely due to extremely slow subsidence and/or uplift caused by post-thrusting rebound. 
Flexural backstripping using reconstructed thrust loads and associated sediment wedges clearly demonstrates that the depth and wavelength of subsidence cannot be adequately explained by flexural thrust loading alone. Sevier thrust loads only explain subsidence of the westernmost part of the basin. Sediment loading in the basin explains some, but not all, of the remaining subsidence. In addition, an extra regional load must have existed to explain the pattern of subsidence observed. Subsurface loading due to dynamic topographic effects in the mantle is consistent with the distribution and magnitudes of the remaining subsidence. Hence, the western interior seaway owes its origin to surface and subsurface load distributions associated with continued convergence along the western U.S. margin.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.