North American Landscape Evolution: Insights from Stratigraphy,
Thermochronology and Geomorphology
Abstract
Reconstructing patterns of topographic evolution is key to our
understanding of the various processes responsible for landscape
development. Suites of existing geodynamic models suggest the North
American landscape has been influenced by a history of evolving dynamic
support. This study investigates the extent to which this process has
played a role in generating the elevation and long-wavelength
topographic relief observed. Review of studies investigating
distribution of magmatism, marine sedimentary rocks, sediment flux,
thermochronology models, paleoaltimetry and geomorphic analyses all
point towards a staged uplift history of North America since the Late
Cretaceous. Another way to investigate regional uplift is to use
deposits of known age, containing paleo-water depth indicators, as a
datum against which post-depositional uplift can be measured.
Compilations of paleobathymetry from interpreted biostratigraphic and
stratigraphic markers, compared to their present-day elevations, are
therefore exploited to give detailed geologic constraints on surface
uplift. Our results indicate > 2 km of long-wavelength
differential uplift has developed in the continental interior during the
Cenozoic. In conjunction with these datasets, the uplift history of
North America can be calculated by considering the geomorphic evolution
of continental drainage. Results of a calibrated inverse stream-power
model are presented, where > 4000 river longitudinal
profiles are used to calculate best-fitting smooth spatio-temporal
histories of uplift rate. The resulting model also points towards a
staged uplift history in most regions of high elevation. Evaluation of
results using the biostratigraphic and stratigraphic databases shows the
model is broadly consistent with the geological record. As a further
validation of the inversion we present a continental landscape evolution
model, fed with the uplift history and erosional parameters from the
inversion. This outputs elevation, discharge, denudation and sedimentary
flux histories that are consistent with our inverse modeling schemes and
compiled datasets of sediment flux and low temperature thermochronology.
Data and modeling results are in agreement with geodynamic models
predicting > 1 km dynamic support of the North American
continent.