TY - JOUR A1 - Tofelde, Stefanie A1 - Schildgen, Taylor F. A1 - Savi, Sara A1 - Pingel, Heiko A1 - Wickert, Andrew D. A1 - Bookhagen, Bodo A1 - Wittmann, Hella A1 - Alonso, Ricardo N. A1 - Cottle, John A1 - Strecker, Manfred T1 - 100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina JF - Earth & planetary science letters N2 - Fluvial fill terraces in intermontane basins are valuable geomorphic archives that can record tectonically and/or climatically driven changes of the Earth-surface process system. However, often the preservation of fill terrace sequences is incomplete and/or they may form far away from their source areas, complicating the identification of causal links between forcing mechanisms and landscape response, especially over multi-millennial timescales. The intermontane Toro Basin in the southern Central Andes exhibits at least five generations of fluvial terraces that have been sculpted into several-hundred-meter-thick Quaternary valley-fill conglomerates. New surface-exposure dating using nine cosmogenic Be-10 depth profiles reveals the successive abandonment of these terraces with a 100 kyr cyclicity between 75 +/- 7 and 487 +/- 34 ka. Depositional ages of the conglomerates, determined by four Al-26/Be-10 burial samples and U-Pb zircon ages of three intercalated volcanic ash beds, range from 18 +/- 141 to 936 +/- 170 ka, indicating that there were multiple cut-and-fill episodes. Although the initial onset of aggradation at similar to 1 Ma and the overall net incision since ca. 500 ka can be linked to tectonic processes at the narrow basin outlet, the superimposed 100 kyr cycles of aggradation and incision are best explained by eccentricity-driven climate change. Within these cycles, the onset of river incision can be correlated with global cold periods and enhanced humid phases recorded in paleoclimate archives on the adjacent Bolivian Altiplano, whereas deposition occurred mainly during more arid phases on the Altiplano and global interglacial periods. We suggest that enhanced runoff during global cold phases - due to increased regional precipitation rates, reduced evapotranspiration, or both - resulted in an increased sediment-transport capacity in the Toro Basin, which outweighed any possible increases in upstream sediment supply and thus triggered incision. Compared with two nearby basins that record precessional (21-kyr) and long-eccentricity (400-kyr) forcing within sedimentary and geomorphic archives, the recorded cyclicity scales with the square of the drainage basin length. (C) 2017 Elsevier B.V. All rights reserved. KW - Be-10 depth-profiles KW - surface inflation KW - aggradation-incision cycles KW - glacial-interglacial cycles KW - landscape response to climate change KW - Eastern Cordillera Y1 - 2017 U6 - https://doi.org/10.1016/j.epsl.2017.06.001 SN - 0012-821X SN - 1385-013X VL - 473 SP - 141 EP - 153 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Dey, Saptarshi A1 - Thiede, Rasmus Christoph A1 - Schildgen, Taylor F. A1 - Wittmann, Hella A1 - Bookhagen, Bodo A1 - Scherler, Dirk A1 - Jain, Vikrant A1 - Strecker, Manfred T1 - Climate-driven sediment aggradation and incision since the late Pleistocene in the NW Himalaya, India JF - Earth & planetary science letters N2 - Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 10(3) to 10(5) yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives. New surface-exposure dating of six terrace levels with in-situ cosmogenic Be-10 indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4 +/- 3.2 ka and 43.0 +/- 2.7 ka (1 sigma). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6 +/- 1.2 ka and 15.3 +/- 0.9 ka, while terraces sculpted into the upper Pleistocene-Holocene fan (AF2) provide ages of 9.3 +/- 0.4 ka (T3), 7.1 +/- 0.4 ka (T4), 5.2 +/- 0.4 ka (T5) and 3.6 +/- 0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision. (C) 2016 Elsevier B.V. All rights reserved. KW - alluvial-fan sedimentation KW - terrestrial cosmogenic nuclides KW - Indian Summer Monsoon KW - Last Glacial Maximum KW - paleo-erosion rate Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.05.050 SN - 0012-821X SN - 1385-013X VL - 449 SP - 321 EP - 331 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Savi, Sara A1 - Schildgen, Taylor F. A1 - Tofelde, Stefanie A1 - Wittmann, Hella A1 - Scherler, Dirk A1 - Mey, Jürgen A1 - Alonso, Ricardo N. A1 - Strecker, Manfred T1 - Climatic controls on debris-flow activity and sediment aggradation: The Del Medio fan, NW Argentina JF - Journal of geophysical research : Earth surface N2 - In the Central Andes, several studies on alluvial terraces and valley fills have linked sediment aggradation to periods of enhanced sediment supply. However, debate continues over whether tectonic or climatic factors are most important in triggering the enhanced supply. The Del Medio catchment in the Humahuaca Basin (Eastern Cordillera, NW Argentina) is located within a transition zone between subhumid and arid climates and hosts the only active debris-flow fan within this intermontane valley. By combining Be-10 analyses of boulder and sediment samples within the Del Medio catchment, with regional morphometric measurements of nearby catchments, we identify the surface processes responsible for aggradation in the Del Medio fan and their likely triggers. We find that the fan surface has been shaped by debris flows and channel avulsions during the last 400 years. Among potential tectonic, climatic, and autogenic factors that might influence deposition, our analyses point to a combination of several favorable factors that drive aggradation. These are in particular the impact of occasional abundant rainfall on steep slopes in rock types prone to failure, located in a region characterized by relatively low rainfall amounts and limited transport capacity. These characteristics are primarily associated with the climatic transition zone between the humid foreland and the arid orogen interior, which creates an imbalance between sediment supply and sediment transfer. The conditions and processes that drive aggradation in the Del Medio catchment today may provide a modern analog for the conditions and processes that drove aggradation in other nearby tributaries in the past. Y1 - 2016 U6 - https://doi.org/10.1002/2016JF003912 SN - 2169-9003 SN - 2169-9011 VL - 121 SP - 2424 EP - 2445 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Rosenkranz, Ruben A1 - Schildgen, Taylor F. A1 - Wittmann, Hella A1 - Spiegel, Cornelia T1 - Coupling erosion and topographic development in the rainiest place on Earth BT - Reconstructing the Shillong Plateau uplift history with in-situ cosmogenic Be-10 JF - Earth & planetary science letters N2 - The uplift of the Shillong Plateau, in northeast India between the Bengal floodplain and the Himalaya Mountains, has had a significant impact on regional precipitation patterns, strain partitioning, and the path of the Brahmaputra River. Today, the plateau receives the highest measured yearly rainfall in the world and is tectonically active, having hosted one of the strongest intra-plate earthquakes ever recorded. Despite the unique tectonic and climatic setting of this prominent landscape feature, its exhumation and surface uplift history are poorly constrained. We collected 14 detrital river sand and 3 bedrock samples from the southern margin of the Shillong Plateau to measure erosion rates using the terrestrial cosmogenic nuclide 10Be. The calculated bedrock erosion rates range from 2.0 to 5.6 m My−1, whereas catchment average erosion rates from detrital river sands range from 48 to 214 m My−1. These rates are surprisingly low in the context of steep, tectonically active slopes and extreme rainfall. Moreover, the highest among these rates, which occur on the low-relief plateau surface, appear to have been affected by anthropogenic land-use change. To determine the onset of surface uplift, we coupled the catchment averaged erosion rates with topographic analyses of the plateau's southern margin. We interpolated an inclined, pre-incision surface from minimally eroded remnants along the valley interfluves and calculated the eroded volume of the valleys carved beneath the surface. The missing volume was then divided by the volume flux derived from the erosion rates to obtain the onset of uplift. The results of this calculation, ranging from 3.0 to 5.0 Ma for individual valleys, are in agreement with several lines of stratigraphic evidence from the Brahmaputra and Bengal basin that constrain the onset of topographic uplift, specifically the onset of flexural loading and the transgression from deltaic to marine deposition. Ultimately, our data corroborate the hypothesis that surface uplift was decoupled from the onset of rapid exhumation, which occurred several millions of years earlier. KW - river profile analysis KW - land-use change KW - Be-10 KW - orographic rainfall KW - erosion Y1 - 2017 U6 - https://doi.org/10.1016/j.epsl.2017.11.047 SN - 0012-821X SN - 1385-013X VL - 483 SP - 39 EP - 51 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Acosta, Veronica Torres A1 - Schildgen, Taylor F. A1 - Clarke, Brian A. A1 - Scherler, Dirk A1 - Bookhagen, Bodo A1 - Wittmann, Hella A1 - von Blanckenburg, Friedhelm A1 - Strecker, Manfred T1 - Effect of vegetation cover on millennial-scale landscape denudation rates in East Africa JF - Lithosphere N2 - The mechanisms by which climate and vegetation affect erosion rates over various time scales lie at the heart of understanding landscape response to climate change. Plot-scale field experiments show that increased vegetation cover slows erosion, implying that faster erosion should occur under low to moderate vegetation cover. However, demonstrating this concept over long time scales and across landscapes has proven to be difficult, especially in settings complicated by tectonic forcing and variable slopes. We investigate this problem by measuring cosmogenic Be-10-derived catchment-mean denudation rates across a range of climate zones and hillslope gradients in the Kenya Rift, and by comparing our results with those published from the Rwenzori Mountains of Uganda. We find that denudation rates from sparsely vegetated parts of the Kenya Rift are up to 0.13 mm/yr, while those from humid and more densely vegetated parts of the Kenya Rift flanks and the Rwenzori Mountains reach a maximum of 0.08 mm/yr, despite higher median hillslope gradients. While differences in lithology and recent land-use changes likely affect the denudation rates and vegetation cover values in some of our studied catchments, hillslope gradient and vegetation cover appear to explain most of the variation in denudation rates across the study area. Our results support the idea that changing vegetation cover can contribute to complex erosional responses to climate or land-use change and that vegetation cover can play an important role in determining the steady-state slopes of mountain belts through its stabilizing effects on the land surface. Y1 - 2015 U6 - https://doi.org/10.1130/L402.1 SN - 1941-8264 SN - 1947-4253 VL - 7 IS - 4 SP - 408 EP - 420 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Tofelde, Stefanie A1 - Duesing, Walter A1 - Schildgen, Taylor F. A1 - Wickert, Andrew D. A1 - Wittmann, Hella A1 - Alonso, Ricardo N. A1 - Strecker, Manfred T1 - Effects of deep-seated versus shallow hillslope processes on cosmogenic Be-10 concentrations in fluvial sand and gravel JF - Earth surface processes and landforms : the journal of the British Geomorphological Research Group N2 - Terrestrial cosmogenic nuclide (TCN) concentrations in fluvial sediment, from which denudation rates are commonly inferred, can be affected by hillslope processes. TCN concentrations in gravel and sand may differ if localized, deep-excavation processes (e.g. landslides, debris flows) affect the contributing catchment, whereas the TCN concentrations of sand and gravel tend to be more similar when diffusional processes like soil creep and sheetwash are dominant. To date, however, no study has systematically compared TCN concentrations in different detrital grain-size fractions with a detailed inventory of hillslope processes from the entire catchment. Here we compare concentrations of the TCN Be-10 in 20 detrital sand samples from the Quebrada del Toro (southern Central Andes, Argentina) to a hillslope-process inventory from each contributing catchment. Our comparison reveals a shift from low-slope gullying and scree production in slowly denuding, low-slope areas to steep-slope gullying and landsliding in fast-denuding, steep areas. To investigate whether the nature of hillslope processes (locally excavating or more uniformly denuding) may be reflected in a comparison of the Be-10 concentrations of sand and gravel, we define the normalized sand-gravel index (NSGI) as the Be-10-concentration difference between sand and gravel divided by their summed concentrations. We find a positive, linear relationship between the NSGI and median slope, such that our NSGI values broadly reflect the shift in hillslope processes from low-slope gullying and scree production to steep-slope gullying and landsliding. Higher NSGI values characterize regions affected by steep-slope gullying or landsliding. We relate the large scatter in the relationship, which is exhibited particularly in low-slope areas, to reduced hillslope-channel connectivity and associated transient sediment storage within those catchments. While high NSGI values in well-connected catchments are a reliable signal of deep-excavation processes, hillslope excavation processes may not be reliably recorded by NSGI values where sediment experiences transient storage. (c) 2018 John Wiley & Sons, Ltd. Y1 - 2018 U6 - https://doi.org/10.1002/esp.4471 SN - 0197-9337 SN - 1096-9837 VL - 43 IS - 15 SP - 3086 EP - 3098 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Dey, Saptarshi A1 - Thiede, Rasmus Christoph A1 - Schildgen, Taylor F. A1 - Wittmann, Hella A1 - Bookhagen, Bodo A1 - Scherler, Dirk A1 - Strecker, Manfred T1 - Holocene internal shortening within the northwest Sub-Himalaya: Out-of-sequence faulting of the Jwalamukhi Thrust, India JF - Tectonics N2 - The southernmost thrust of the Himalayan orogenic wedge that separates the foreland from the orogen, the Main Frontal Thrust, is thought to accommodate most of the ongoing crustal shortening in the Sub-Himalaya. Steepened longitudinal river profile segments, terrace offsets, and back-tilted fluvial terraces within the Kangra reentrant of the NW Sub-Himalaya suggest Holocene activity of the Jwalamukhi Thrust (JMT) and other thrust faults that may be associated with strain partitioning along the toe of the Himalayan wedge. To assess the shortening accommodated by the JMT, we combine morphometric terrain analyses with in situ Be-10-based surface-exposure dating of the deformed terraces. Incision into upper Pleistocene sediments within the Kangra Basin created two late Pleistocene terrace levels (T1 and T2). Subsequent early Holocene aggradation shortly before similar to 10ka was followed by episodic reincision, which created four cut-and-fill terrace levels, the oldest of which (T3) was formed at 10.10.9ka. A vertical offset of 445m of terrace T3 across the JMT indicates a shortening rate of 5.60.8 to 7.51.1mma(-1) over the last similar to 10ka. This result suggests that thrusting along the JMT accommodates 40-60% of the total Sub-Himalayan shortening in the Kangra reentrant over the Holocene. We speculate that this out-of-sequence shortening may have been triggered or at least enhanced by late Pleistocene and Holocene erosion of sediments from the Kangra Basin. KW - fluvial terrace KW - cosmogenic nuclides KW - steepness index KW - Jwalamukhi Thrust KW - shortening KW - orogenic wedge Y1 - 2016 U6 - https://doi.org/10.1002/2015TC004002 SN - 0278-7407 SN - 1944-9194 VL - 35 SP - 2677 EP - 2697 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Scherler, Dirk A1 - Munack, Henry A1 - Mey, Jürgen A1 - Eugster, Patricia A1 - Wittmann, Hella A1 - Codilean, Alexandru T. A1 - Kubik, Peter A1 - Strecker, Manfred T1 - Ice dams, outburst floods, and glacial incision at the western margin of the Tibetan Plateau: A > 100 k.y. chronology from the Shyok Valley, Karakoram JF - Geological Society of America bulletin N2 - Some of the largest and most erosive floods on Earth result from the failure of glacial dams. While potentially cataclysmic ice dams are recognized to have repeatedly formed along ice-sheet margins, much less is known about the frequency and longevity of ice dams caused by mountain glaciers, and their impact on landscape evolution. Here we present field observations and results from cosmogenic nuclide dating that allow reconstructing a > 100-k.y.-long history of glacial damming in the Shyok Valley, eastern Karakoram (South Asia). Our field observations provide evidence that Asia's second-longest glacier, the Siachen, once extended for over 180 km and blocked the Shyok River during the penultimate glacial period, leading to upstream deposition of a more than 400-m-thick fluvio-lacustrine valley fill. Be-10-depth profile modeling indicates that glacial damming ended with the onset of the Eemian interglacial and that the Shyok River subsequently incised the valley fill at an average rate of similar to 4-7 m k.y.(-1). Comparison with contemporary ice-dammed lakes in the Karakoram and elsewhere suggests recurring outburst floods during the aggradation period, while over 25 cycles of fining-upward lake deposits within the valley fill indicate impounding of floods from farther upstream. Despite prolonged damming, the net effect of this and probably earlier damming episodes by the Siachen Glacier is dominated by glacial erosion in excess of fluvial incision, as evidenced by a pronounced overdeepening that follows the glaciated valley reach. Strikingly similar overdeepened valleys at all major confluences of the Shyok and Indus Rivers with Karakoram tributaries indicate that glacial dams and subsequent outburst floods have been widespread and frequent in this region during the Quaternary. Our study suggests that the interaction of Karakoram glaciers with the Shyok and Indus Rivers promoted valley incision and headward erosion into the western margin of the Tibetan Plateau. Y1 - 2014 U6 - https://doi.org/10.1130/B30942.1 SN - 0016-7606 SN - 1943-2674 VL - 126 IS - 5-6 SP - 738 EP - 758 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Dey, Saptarshi A1 - Bookhagen, Bodo A1 - Thiede, Rasmus C. A1 - Wittmann, Hella A1 - Chauhan, Naveen A1 - Jain, Vikrant A1 - Strecker, Manfred R. T1 - Impact of Late Pleistocene climate variability on paleo-erosion rates in the western Himalaya JF - Earth and planetary science letters N2 - It has been proposed that at short timescales of 10(2)-10(5) yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained. To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya. We compare past and present Be-10-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data. Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene. We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 +/- 13 degrees) erode at lower rates of 0.1-0.4 mm/yr compared to steeper (>40 degrees) crestal regions of the Dhauladhar Range that erode at 0.8-1.3 mm/yr. In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed. Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas. (C) 2021 Elsevier B.V. All rights reserved. KW - erosion KW - cosmogenic nuclides KW - luminescence dating KW - Indian summer monsoon KW - Himalaya Y1 - 2022 U6 - https://doi.org/10.1016/j.epsl.2021.117326 SN - 0012-821X SN - 1385-013X VL - 578 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Schildgen, Taylor F. A1 - Cosentino, D. A1 - Bookhagen, Bodo A1 - Niedermann, Samuel A1 - Yildirim, C. A1 - Echtler, Helmut Peter A1 - Wittmann, Hella A1 - Strecker, Manfred T1 - Multi-phased uplift of the southern margin of the Central Anatolian plateau, Turkey a record of tectonic and upper mantle processes JF - Earth & planetary science letters N2 - Uplifted Neogene marine sediments and Quaternary fluvial terraces in the Mut Basin, southern Turkey, reveal a detailed history of surface uplift along the southern margin of the Central Anatolian plateau from the Late Miocene to the present. New surface exposure ages (Be-10, Al-26, and Ne-21) of gravels capping fluvial strath terraces located between 28 and 135 m above the Goksu River in the Mut Basin yield ages ranging from ca. 25 to 130 ka, corresponding to an average incision rate of 0.52 to 0.67 mm/yr. Published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0.25 to 0.37 mm/yr since Late Miocene time (starting between 8 and 5.45 Ma), and 0.72 to 0.74 mm/yr after 1.66 to 1.62 Ma. Together with the terrace abandonment ages, the data imply 0.6 to 0.7 mm/yr uplift rates from 1.6 Ma to the present. The different post-Late Miocene and post-1.6 Ma uplift rates can imply increasing uplift rates through time, or multi-phased uplift with slow uplift or subsidence in between. Longitudinal profiles of rivers in the upper catchment of the Mut and Ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1.2 to 1.5 km elevation, implying a transient response to a change in uplift rates. Projections of graded upper relict channel segments to the modern outlet, together with constraints from uplifted marine sediments, show that a slower incision/uplift rate of 0.1 to 0.2 mm/yr preceded the 0.7 mm/yr uplift rate. The river morphology and profile projections therefore reflect multi-phased uplift of the plateau margin, rather than steadily increasing uplift rates. Multi-phased uplift can be explained by lithospheric slab break-off and possibly also the arrival of the Eratosthenes Seamount at the collision zone south of Cyprus. KW - Central Anatolian plateau KW - uplift KW - fluvial strath terraces KW - cosmogenic nuclides KW - biostratigraphy KW - channel projection Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2011.12.003 SN - 0012-821X VL - 317 SP - 85 EP - 95 PB - Elsevier CY - Amsterdam ER -