Coupled influence of tectonics, climate, and surface processes on landscape evolution in southwestern North America.

The Cenozoic landscape evolution in southwestern North America is ascribed to crustal isostasy, dynamic topography, or lithosphere tectonics, but their relative contributions remain controversial. Here we reconstruct landscape history since the late Eocene by investigating the interplay between mantle convection, lithosphere dynamics, climate, and surface processes using fully coupled four-dimensional numerical models. Our quantified depth-dependent strain rate and stress history within the lithosphere, under the influence of gravitational collapse and sub-lithospheric mantle flow, show that high gravitational potential energy of a mountain chain relative to a lower Colorado Plateau can explain extension directions and stress magnitudes in the belt of metamorphic core complexes during topographic collapse. Profound lithospheric weakening through heating and partial melting, following slab rollback, promoted this extensional collapse. Landscape evolution guided northeast drainage onto the Colorado Plateau during the late Eocene-late Oligocene, south-southwest drainage reversal during the late Oligocene-middle Miocene, and southwest drainage following the late Miocene.

Tectonic influence on Cenozoic mammal richness and sedimentation history of the Basin and Range, western North America.

Tectonic activity can drive speciation and sedimentation, potentially causing the fossil and rock records to share common patterns through time. The Basin and Range of western North America arose through widespread extension and collapse of topographic highlands in the Miocene, creating numerous basins with rich mammalian fossil records. We analyzed patterns of mammalian species richness from 36 to 0 million years ago in relation to the history of sediment accumulation to test whether intervals of high species richness corresponded with elevated sediment accumulation and fossil burial in response to tectonic deformation. We found that the sedimentary record of the Basin and Range tracks the tectonic evolution of landscapes, whereas species-richness trends reflect actual increased richness in the Miocene rather than increased fossil burial. The sedimentary record of the region broadly determines the preservation of the fossil record but does not drive the Miocene peak in mammalian species richness.