Continental‐Scale Landscape Evolution: A History of North American Topography

Abstract

The generation and evolution of continental topography are fundamental geologic and geomorphic concerns. In particular, the history of landscape development might contain useful information about the spatiotemporal evolution of deep Earth processes, such as mantle convection. A significant challenge is to generate observations and theoretical predictions of sufficient fidelity to enable landscape evolution to be constrained at scales of interest. Here, we combine substantial inventories of stratigraphic and geomorphic observations with inverse and forward modeling approaches to determine how the North American landscape evolved. First, stratigraphic markers are used to estimate postdepositional regional uplift. Present‐day elevations of these deposits demonstrate that >2 km of long‐wavelength surface uplift centered on the Colorado‐Rocky‐Mountain plateaus occurred in Cenozoic times. Second, to bridge the gaps between these measurements, an inverse modeling scheme is used to calculate the smoothest spatiotemporal pattern of rock uplift rate that yields the smallest misfit between 4,161 observed and calculated longitudinal river profiles. Our results suggest that Cenozoic regional uplift occurred in a series of stages, in agreement with independent stratigraphic observations. Finally, a landscape evolution model driven by this calculated rock uplift history is used to determine drainage patterns, denudation, and sedimentary flux from Late Cretaceous times until the present day. These patterns are broadly consistent with stratigraphic and thermochronologic observations. We conclude that a calibrated inverse modeling strategy can be used to reliably extract the temporal and spatial evolution of the North American landscape at geodynamically useful scales.

Scale‐Dependent Flow Directions of Rivers and the Importance of Subplate Support

“…The long wavelength flow directions of large western North American rivers are therefore likely to be no older than the ongoing mantle support. This result is consistent with geomorphic and provenance studies, which indicate that the present day planform of rivers draining western North America has been broadly stable during the last few tens of millions of years (Blum & Pecha, 2014;Fernandes et al, 2019;Galloway et al, 2011).…”

“…Second, calculated dynamic topography was added to this surface by converting long wavelength free‐air gravity anomalies using an admittance of 25 mGal/km (Figure 1b). We note that this surface is similar to cumulative post‐Cretaceous uplift mapped using the distribution of marine rocks in western North America, and its crest coincides with loci of Cenozoic basaltic magmatism (Fernandes et al., 2019; Klocking et al., 2018). Simulations of North American landscape evolution parameterized in a similar way have yielded broadly stable Cenozoic drainage planforms (Fernandes et al., 2019).…”

“…We note that this surface is similar to cumulative post‐Cretaceous uplift mapped using the distribution of marine rocks in western North America, and its crest coincides with loci of Cenozoic basaltic magmatism (Fernandes et al., 2019; Klocking et al., 2018). Simulations of North American landscape evolution parameterized in a similar way have yielded broadly stable Cenozoic drainage planforms (Fernandes et al., 2019). In the third step, the resultant surface is eroded so that channels form using the well‐known stream power formulation of fluvial erosion, which has the form of a nonlinear advective equation where z is elevation, t is time, and A is upstream drainage area (Howard & Kerby, 1983; Rosenbloom & Anderson, 1994; Tinkler & Wohl, 1998; Whipple & Tucker, 1999).…”

“…Gravity anomalies, tomographic models, magmatism and isostatic calculations, which include crustal thickness estimates, indicate that western North American topography is principally a consequence of subcrustal support moderated by tectonic and erosional processes (Atwater, 1970; Fernandes et al., 2019; Wernicke, 1985). A guide to the amplitude and wavelength of subplate support is the transfer function (admittance) between long wavelength free‐air gravity and topography (McKenzie, 2010).…”

Spatiotemporal evolution of the global species diversity of Rhododendron

“…In the middle to late Miocene, active mountain building in East Asia, the Himalayas, and Southeast Asia to Oceania produced highly heterogeneous habitats represented by a wide altitudinal range 26,27,29 , which, together with high precipitation caused mainly by the intensi cation of Asian monsoons, greatly promoted the rapid rediversi cation of subgenera Tsutsusi and Hymenanthes and section Vireya of the subgenus Rhododendron and the evolution of new lineages, leading to the highest diversi cation rate of this genus. Although mountain building also occurred in southern Europe and western North America in the Neogene 29,30 , it was not active as in Asia, and the relatively dry habitats limited the rediversi cation of Rhododendron. This also explains why only a few intercontinental dispersals occurred within subgenera of this genus, except the deciduous subgenus Pentanthera, which grows in very low altitudes.…”