Two-dimensional computer modeling of the development of the Andean-type Idaho-Wyoming thrust belt shows that formation of the foreland basin was controlled by the isostatic subsidence of an elastic crust due to thrust loading. The palinspastic shape of the sedimentary wedge on the west side of the Cretaceous Western Interior seaway corresponds best to predicted crustal downwarping by thrust plate loads as computed from cross section with a flexural rigidity of 10²³ Nm. Material eroded from the uplifted thrust plates and deposited in the basin effectively redistributed the load, causing subsidence over a much wider area than could have been accomplished only by loading in the thrust belt.

After three major Cretaceous thrust events, paleotopography was reconstructed from load and subsidence. The resulting mountains, gentle alluvial plain, and flat sea floor correspond well to local paleogeographic data and to topography of the modern Andean foreland system. The predicted sea floor level rose through time, as did reported eustatic sea level. In the thrust belt, topography was controlled by the subsurface geometry of thrusts (particularly positions of ramp zones) and by isotatic subsidence.

This quantified mechanical model and data from only thrust belt or basin may allow prediction of the geometry of the other part of the foreland couplet. Furthermore, with this mechanical model and future models of other foreland systems (e.g., Himalayan-type), exploration models in foreland basins in frontier regions may be developed from a knowledge of regional plate-margin tectonics.

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