Exogenic forcing and autogenic processes on continental divide location and mobility

Abstract

The position and mobility of drainage divides is an expression of exogenic landscape forcing and autogenic channel network processes integrated across a range of scales. At the large scale, represented by major rivers and continental drainage divides, the organization of drainage patterns and divide migration reflects the long-wavelength gradients of the topography, which are exogenically influenced by tectonics, isostasy, and/or dynamic topography. This analysis utilizes long-wavelength topography synthesized by a low-pass filter, which provides a novel framework for predicting the direction of divide movement as well as an estimate of the ultimate divide location that is complementary to recent studies that have focused on the v channel metric. The Gibraltar Arc active plate boundary and Appalachian stable plate interior, two tectonically diverse settings with ongoing drainage system reorganization, are chosen to explore the length scales of exogenic forcings that influence continental drainage divide location and migration. The major watersheds draining both the active-and decay-phase orogens studied here are organized by topographic gradients that are expressed in long-wavelength low-pass filtered topography (k ≥ 100 km). In contrast, the river network and divide location is insensitive to topographic gradients measured over filtered wavelengths <100 km that are set by local crustal structures and rock type. The lag time between exogenic forcing and geomorphic response and feedbacks cause divide migration to be unsteady, and occur through pulses of drainage capture and drainage network reorganization that are recorded in sedimentological, geomorphic, or denudation data.

Post‐orogenic thermal history and exhumation of the northern Appalachian Basin: Low‐temperature thermochronologic constraints

“…This study constrains a ~2–6 times increase in exhumation rates in the NAB beginning in the Late Cenozoic (30–20 Ma), accounting for the removal of ~1 km of sedimentary overburden (Figure ), hence mechanisms other than solely flexure or dynamic topography are required to account for this. The westward shift in the Appalachian continental divide is shown to be influenced by changes in crustal structure, modified by flexural isostatic deformation and dynamic topography (Moodie et al, ). Exhumation since the Miocene is most likely due to rapid geomorphic response to the westward shift of the drainage divide causing regional base level fall, catchment drainage reorganization and river incision further west into the NAB.…”

“…Blackmer et al, ; Boettcher & Milliken, ; Pazzaglia & Brandon, ; Prince et al, ; Prince et al, ; Miller et al, ; Gallen et al, ; Naeser et al, ). This event is likely a result of westward migration of the Appalachian continental divide, which was influenced by post‐orogenic isostatic and flexural‐isostatic processes plus dynamic topography (e.g., Pazzaglia & Gardner, ; Miller et al, ; Gallen et al, ; Moucha & Ruetenik, ; Moodie et al, ). Eastward flowing rivers incised westward into the NAB as a rapid geomorphic response to regional base‐level fall (Moodie et al, ), causing the increased exhumation rates documented in this study.…”

“…This event is likely a result of westward migration of the Appalachian continental divide, which was influenced by post‐orogenic isostatic and flexural‐isostatic processes plus dynamic topography (e.g., Pazzaglia & Gardner, ; Miller et al, ; Gallen et al, ; Moucha & Ruetenik, ; Moodie et al, ). Eastward flowing rivers incised westward into the NAB as a rapid geomorphic response to regional base‐level fall (Moodie et al, ), causing the increased exhumation rates documented in this study. Late Cenozoic exhumation has not been directly documented in low‐temperature thermochronology ages (e.g.…”

Base Level and Lithologic Control of Drainage Reorganization in the Sierra de las Planchadas, NW Argentina

“…Rivers transmit boundary condition changes, or changes in the wider tectonic, climatic, and lithologic setting of a region, throughout the landscape by adjusting their longitudinal profiles and planform geometry. Such transient signals have been used to elucidate landscape evolution on a variety of spatial scales, from along continental divides (e.g., Moodie et al, 2018), to individual antiforms (e.g., Ellis & Densmore, 2006), on every continent and on several planetary bodies (e.g., Black et al, 2012).…”

“…Both of these processes are governed by differential erosion rates between adjacent catchments; therefore, any boundary condition that creates an erosional gradient could result in drainage reorganization (Bishop, 1995;. A variety of exogenic and autogenic factors contribute to large-scale erosional gradients and therefore drainage reorganization, including tectonic uplift (e.g., Clark et al, 2004;Nicholson et al, 2013), horizontal tectonic advection (e.g., Miller & Slingerland, 2006;Miller et al, 2007;Willett et al, 2001), tectonic strain (e.g., Castelltort et al, 2012), orographic gradients (e.g., Bonnet, 2009), regional slope (e.g., Babault et al, 2012;Struth et al, 2015), geodynamic processes (e.g., D'Agostino et al, 2001;Moodie et al, 2018), and erosional base level differences (e.g., Ellis & Densmore, 2006;Whitfield & Harvey, 2012).…”