Research

Project overview

Over geologic time, sediment flux to coastlines may depend on large-scale drainage capture events. Capture events are an under-studied potential source of temporal variability in supply of sediment to coastlines. A poor understanding of supply controls may lead to misinterpretation of controls on deltaic avulsion or shoreline transgression. This project advances our understanding of

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Introduction

Exogenic forcings such as climate, tectonics, eustasy and dynamic topography define the boundary conditions for a drainage network, and collectively determine the topographic gradients, drainage area, and hydrology of the system. Both in response to and independent of exogenic forcing, the internal autogenic processes of the linked hillslope-channel network, such as landslides, sapping, and avulsions drive system dynamism which further modifies the channel network configuration and evolution (Hajek & Straub, 2017). Continental divides, and their mobility, are an integrated expression of those responses and feedbacks between exogenic forcing and autogenic processes at a range of spatiotemporal scales, rendering the interaction of these forcings complex and thus poorly understood.

Figure 1: Appalachian 150 km filter overlain with contours of calculated total rock deformation (thick gray lines) since 3.5 Ma, resulting from the combined effects of mantle induced dynamic topography and the flexural response of the lithosphere to unloading and loading of sediments across the surface. The Roanoke River (R) will eventually capture the headwaters of the New River (N), causing the actual divide to jump farther west, ultimately approaching or reaching the synthetic divide. Inset shows the record of sediment flux off the Appalachians into the Atlantic passive margin Baltimore Canyon Trough basin (Pazzaglia & Brandon, 1996). The unsteady flux is characterized by pulses in increased sediment deposition that are interpreted to result from large-scale drainage captures that rapidly incise an enlarged Atlantic slope drainage area.

Methods

My research utilizes isolated long-wavelength topography synthesized by a low-pass filter (Figure 1), and complemented by the channel metric \(\chi\), provides a novel framework for predicting the direction of divide movement, as well as an estimate of the ultimate divide location. The methodology has been applied in two tectonically diverse settings to evaluate divide migration under the lens of geomorphic evidence that has generated 1) recent controversy over the geodynamic evolution of the Gibraltar Arc and Alboran Sea, and 2) over a century of speculation on the cause and timing of the Eastern North America (Appalachian) drainage divide migration.

Insights

The result is compelling evidence that argues for the unsteady migration of drainage divides, through basin integration and drainage capture, that organizes major rivers to broad regional-scale landscape gradients.

Publications generated by this research

1. Moodie, A. J., Pazzaglia, F. J., & Berti, C. (2017). Exogenic forcing and autogenic processes on continental divide location and mobility. Basin Research. doi: 10.1111/bre.12256

References

1. Hajek, E. A., & Straub, K. M. (2017). Autogenic Sedimentation in Clastic Stratigraphy. Annual Review of Earth and Planetary Sciences, 45(1), 681–709. doi: 10.1146/annurev-earth-063016-015935

2. Pazzaglia, F. J., & Brandon, M. T. (1996). Macrogeomorphic evolution of the post-Triassic Appalachian mountains determined by deconvolution of the offshore basin sedimentary record. Basin Research, 8(3), 255–278. doi: 10.1046/j.1365-2117.1996.00274.x