@article{SchildgenRobinsonSavietal.2016, author = {Schildgen, Taylor F. and Robinson, Ruth A. J. and Savi, Sara and Phillips, William M. and Spencer, Joel Q. G. and Bookhagen, Bodo and Scherler, Dirk and Tofelde, Stefanie and Alonso, Ricardo N. and Kubik, Peter W. and Binnie, Steven A. and Strecker, Manfred}, title = {Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity}, series = {Journal of geophysical research : Earth surface}, volume = {121}, journal = {Journal of geophysical research : Earth surface}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9003}, doi = {10.1002/2015JF003607}, pages = {392 -- 414}, year = {2016}, abstract = {Fluvial fill terraces preserve sedimentary archives of landscape responses to climate change, typically over millennial timescales. In the Humahuaca Basin of NW Argentina (Eastern Cordillera, southern Central Andes), our 29 new optically stimulated luminescence ages of late Pleistocene fill terrace sediments demonstrate that the timing of past river aggradation occurred over different intervals on the western and eastern sides of the valley, despite their similar bedrock lithology, mean slopes, and precipitation. In the west, aggradation coincided with periods of increasing precipitation, while in the east, aggradation coincided with decreasing precipitation or more variable conditions. Erosion rates and grain size dependencies in our cosmogenic Be-10 analyses of modern and fill terrace sediments reveal an increased importance of landsliding compared to today on the west side during aggradation, but of similar importance during aggradation on the east side. Differences in the timing of aggradation and the Be-10 data likely result from differences in valley geometry, which causes sediment to be temporarily stored in perched basins on the east side. It appears as if periods of increasing precipitation triggered landslides throughout the region, which induced aggradation in the west, but blockage of the narrow bedrock gorges downstream from the perched basins in the east. As such, basin geometry and fluvial connectivity appear to strongly influence the timing of sediment movement through the system. For larger basins that integrate subbasins with differing geometries or degrees of connectivity (like Humahuaca), sedimentary responses to climate forcing are likely attenuated.}, language = {en} } @article{TofeldeSaviWickertetal.2019, author = {Tofelde, Stefanie and Savi, Sara and Wickert, Andrew D. and Bufe, Aaron and Schildgen, Taylor F.}, title = {Alluvial channel response to environmental perturbations}, series = {Earth Surface Dynamics}, volume = {7}, journal = {Earth Surface Dynamics}, publisher = {Copernicus Publ.}, address = {G{\"o}ttingen}, issn = {2196-6311}, doi = {10.5194/esurf-7-609-2019}, pages = {609 -- 631}, year = {2019}, abstract = {The sensitivity of fluvial systems to tectonic and climatic boundary conditions allows us to use the geomorphic and stratigraphic records as quantitative archives of past climatic and tectonic conditions. Thus, fluvial terraces that form on alluvial fans and floodplains as well as the rate of sediment export to oceanic and continental basins are commonly used to reconstruct paleoenvironments. However, we currently lack a systematic and quantitative understanding of the transient evolution of fluvial systems and their associated sediment storage and release in response to changes in base level, water input, and sediment input. Such knowledge is necessary to quantify past environmental change from terrace records or sedimentary deposits and to disentangle the multiple possible causes for terrace formation and sediment deposition. Here, we use a set of seven physical experiments to explore terrace formation and sediment export from a single, braided channel that is perturbed by changes in upstream water discharge or sediment supply, or through downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace cutting, and (3) the transient response of sediment export from the basin. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, thus preserving the initial channel slope on terrace surfaces, and it also produces a transient increase in sediment export from the system. In contrast, a decreased upstream sediment-supply rate may result in longer lag times before terrace cutting, leading to terrace slopes that differ from the initial channel slope, and also lagged responses in sediment export. Finally, downstream base-level fall triggers the upstream propagation of a diffuse knickzone, forming terraces with upstream-decreasing ages. The slope of terraces triggered by base-level fall mimics that of the newly adjusted active channel, whereas slopes of terraces triggered by a decrease in upstream sediment discharge or an increase in upstream water discharge are steeper compared to the new equilibrium channel. By combining fillterrace records with constraints on sediment export, we can distinguish among environmental perturbations that would otherwise remain unresolved when using just one of these records.}, language = {en} } @article{SchildgenvanderBeekD'Arcyetal.2022, author = {Schildgen, Taylor F. and van der Beek, Pieter A. and D'Arcy, Mitch and Roda-Boluda, Duna N. and Orr, Elizabeth N. and Wittmann, Hella}, title = {Quantifying drainage-divide migration from orographic rainfall over geologic timescales}, series = {Earth \& planetary science letters}, volume = {579}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2021.117345}, pages = {13}, year = {2022}, abstract = {Drainage-divide migration, controlled by rock-uplift and rainfall patterns, may play a major role in the geomorphic evolution of mountain ranges. However, divide-migration rates over geologic timescales have only been estimated by theoretical studies and remain empirically poorly constrained. Geomorphological evidence suggests that the Sierra de Aconquija, on the eastern side of the southern Central Andes, northwest Argentina, is undergoing active westward drainage-divide migration. The mountain range has been subjected to steep rock trajectories and pronounced orographic rainfall for the last several million years, presenting an ideal setting for using low-temperature thermochronometric data to explore its topographic evolution. We perform three-dimensional thermal-kinematic modeling of previously published thermochronometric data spanning the windward and leeward sides of the range to explore the most likely structural and topographic evolution of the range. We find that the data can be explained by scenarios involving drainage-divide migration alone, or by scenarios that also involve changes in the structures that have accommodated deformation through time. By combining new Be-10-derived catchment-average denudation rates with geomorphic constraints on probable fault activity, we conclude that the evolution of the range was likely dominated by west-vergent faulting on a high-angle reverse fault underlying the range, together with westward drainage-divide migration at a rate of several km per million years. Our findings place new constraints on the magnitudes and rates of drainage-divide migration in real landscapes, quantify the effects of orographic rainfall and erosion on the topographic evolution of a mountain range, and highlight the importance of considering drainage-divide migration when interpreting thermochronometer age patterns.}, language = {en} } @article{GarcinSchildgenAcostaetal.2017, author = {Garcin, Yannick and Schildgen, Taylor F. and Acosta, Veronica Torres and Melnick, Daniel and Guillemoteau, Julien and Willenbring, Jane and Strecker, Manfred}, title = {Short-lived increase in erosion during the African Humid Period}, series = {Earth \& planetary science letters}, volume = {459}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2016.11.017}, pages = {58 -- 69}, year = {2017}, abstract = {The African Humid Period (AHP) between similar to 15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (similar to 2150 km(2)), deep (similar to 300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic Be-10 in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr(-1). Be-10-derived paleo-erosion rates at similar to 11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr(-1), and were 2.7 to 6.6 times faster than at present. In contrast, at similar to 8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because Be-10-derived erosion rates integrate over several millennia; we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15-6.7 and 12-6.7 kyr) suggest erosion rates that were 25 to 300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (similar to 4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern Be-10-based erosion rate of,similar to 0.013 mm yr(-1). Our simulations also flag the two highest Be-10-derived erosion rates at 11.8 kyr BP related to nonuniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at 15 or similar to 12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.}, language = {en} }