REPRODUCING THE CRETACEOUS WESTERN INTERIOR SEAWAY USING COUPLED MANTLE-LANDSCAPE EVOLUTION MODELING

The tectonic origin of the Western Interior Seaway (WIS) has evolved from the earlier attribution to the Sevier foreland basin to later introduction of dynamic subsidence due to abnormal mantle processes. This conceptual transition results from a combination of stratigraphic analysis for residual subsidence and geodynamic modeling of past mantle evolution. One outstanding question is whether the WIS represents a laterally stationary depression feature or the result from geographically migrating surface subsidence. Answering this question is important for further understanding the underlying tectonics, with candidate driving mechanisms including uplift above and subsidence next to a flat slab, subsidence due to a gradual reduction of slab dip angle, and westward motion of North America over a stationary mantle downwelling.

One way to address the above question is to quantitatively reproduce the seaway using different scenarios of vertical motion history. We use a new landscape evolution code BadLands to model WIS formation. We systematically tested the dependence of model results on grid resolution, coefficients of erosion and deposition, as well as climate forcing. The differences in the resulting basin-scale stratigraphy due to different tectonic scenarios are largely independent of these model parameters. Our preliminary results demonstrate that the migrating subsidence history inferred from our inverse mantle convection models can properly reproduce the main characters of WIS stratigraphy, including its overall age range within Late Cretaceous, largest sediment thickness inside the westernmost flexural depression, and eastward shifting deposition centers across the rest of the seaway. We will also discuss results using other vertical motion scenarios.