Stratigraphic and Geologic Constraints on Geodynamic Models of North America Since the Cretaceous

Stratigraphic and sea level data along with plate motions and mantle tomographic images are used as constraints on inverse and forward models of mantle convection beneath North America. Using plate reconstruction with continuously closed plate polygons (developed using the GPlates program), we compute forward and inverse models of mantle convection with the finite element method (CitcomS). With plate motions, seismic tomography is used to estimate mantle initial conditions using an adjoint of the energy equation, as described by Liu and Gurnis during this meeting. For North America, we developed a set of forward and inverse regional geodynamic models for last 100 million years, with plate movements consistent with global paleogeographic models. We used sediment isopachs, paleoshorelines, and tectonic subsidence curves as the primary stratigraphic and geologic constraints. Tectonic subsidence history for North America was the main constraint for inverse models. In forward mantle convection models, we used the prediction of dynamic topography, along with published eustatic curves, to model sediment isopachs, paleoshorelines, and tectonic subsidence. Modeling results are than compared to stratigraphic and geologic observations, and models are updated iteratively. In a fixed North American frame of reference, our models indicate that a dynamic topography low moved eastward from 100 million years to the present, due to of the descent of the Farallon slab as the plate moved westward. During the Cretaceous, the dynamic topography low was located in the middle of North American continent. During this period, eustatic sea-level reached its maximum and when combined with a dynamic topography low, caused a substantial inundation of North America, creating the Western Interior Seaway. At the present time, the dynamic topography low is located in the eastern United States, and we argue that this region is experiencing tectonic subsidence. This tectonic subsidence can explain significant departure of regional sea-level curves developed for the eastern United States, in comparison with eustatic sea-level curves. This presentation focuses on the details of the stratigraphic data and their integration with geodynamic models.