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Erosion and tectonic uplift are widely thought to be coupled through feedbacks involving orographic precipitation, relief development, and crustal weakening. In many orogenic systems, it can be difficult to distinguish whether true feedbacks exist, or whether observed features are a consequence of tectonic forcing. To help elucidate these interactions, we examine Gongga Shan, a 7556 m peak on the eastern margin of the Tibetan Plateau where cosmogenic 10 Be basin-wide erosion rates reach >5 mm/yr, defining a region of localized rapid erosion associated with a restraining bend in the left-lateral Xianshuihe Fault. Erosion rates are consistent with topography, thermochronometry, and geodetic data, suggesting a stable pattern of uplift and exhumation over at least the past 2–3 My. Transpression along the Xianshuihe Fault, orographically enhanced precipitation, thermally weakened crust, and substantial local relief all developed independently in the Gongga region and existed there prior to the uplift of Gongga Shan. However, only where all of these conditions are present do the observed topographic and erosional extremes exist, and their relative timing indicates that these conditions are not a consequence of rapid uplift. We conclude that their collocation at 3–4 Ma set into motion a series of feedbacks between erosion and uplift that has resulted in the exceptionally high topography and rapid erosion rates observed today. [ABSTRACT FROM AUTHOR]

We analyze the source-to-sink variations of in situ 10 Be, 26 Al and 21 Ne concentrations in modern sediment of the Po river catchment, from Alpine, Apennine, floodplain, and delta samples, in order to investigate how the cosmogenic record of orogenic erosion is transmitted across a fast-subsiding foreland basin. The in situ 10 Be concentrations in the analyzed samples range from ∼ 0.8 × 10 4 at / g QTZ to ∼ 6.5 × 10 4 at / g QTZ . The 10 Be-derived denudation rates range from 0.1 to 1.5 mm/yr in the Alpine source areas and from 0.3 to 0.5 mm/yr in the Apenninic source areas. The highest 10 Be-derived denudation rates are found in the western Central Alps (1.5 mm/yr). From these data, we constrain a sediment flux leaving the Alpine and the Apenninic source areas (>27 Mt/yr and ca. 5 Mt/yr, respectively) that is notably higher than the estimates of sediment export provided by gauging (∼10 Mt/yr at the Po delta). We observe a high variability in 10 Be concentrations and 10 Be-derived denudation rates in the source areas. In the Po Plain, little variability is observed, and at the same time, the area-weighed 10 Be concentration of ( 2.29 ± 1.57 ) × 10 4 at / g QTZ (±1 SD of the dataset) from both the Alps and the Apennines is poorly modified (by tributary input) in sediment of the Po Plain ( ( 2.68 ± 0.78 , ± 1 SD ) × 10 4 at / g QTZ ). The buffering effect of the Po floodplain largely removes scatter in 10 Be signals. We test for several potential perturbations of the cosmogenic nuclide record during source to sink transfer in the Po basin. We find that sediment trapping in deep glacial lakes or behind dams does not significantly change the 10 Be-mountain record. For example, similar 10 Be concentrations are measured upstream and downstream of the postglacial Lake Maggiore, suggesting that denudation rates prior to lake formation were similar to today's. On the scale of the entire basin, the 10 Be concentration of basins with major dams is similar to those without major dams. A potential modification of the 10 Be-mountain record during sediment storage in the subsiding Po Plain can be excluded as measured 26 Al/ 10 Be ratios do not show the addition of deeply buried material. A barely resolvable excess 21 Ne signal in the Po plain indicates recycling of previously eroded sediment rather than accumulation of cosmogenic nuclides during surficial floodplain transport. Our results demonstrate that the cosmogenic record of mountain erosion is effectively transmitted from the source areas to the sediment sink, even across a strongly subsiding foreland basin. We show that this record is poorly influenced by a range of potential geological and anthropogenic sources of bias, and is largely independent from upstream sediment interception and sediment storage in the floodplain. [ABSTRACT FROM AUTHOR]

• Geological and cosmogenic data from Corsica reveal two-stage river capture events. • Clast lithologies demonstrate a progressive reduction of the Paleo-Ostriconi basin. • River capture led to the formation of a large Pliocene-Quaternary submarine fan. • Focused erosion can affect sites of former river capture after millions of years. • Corsica is still adapting to the disequilibrium caused by uplift of Alpine Corsica. Quantitative analysis of fluvial topography and sediment yield changes are often independently used to detect major river capture events and episodes of drainage reorganization. Here we use a unique set of geological and in situ 10Be cosmogenic data from Corsica, Western Mediterranean, to provide evidence of major river capture events affecting the former Paleo-Ostriconi river catchment during the Pliocene, and to illustrate how the landscape of Corsica is still reacting to the disequilibrium caused by the late Miocene uplift of Alpine Corsica. We found that ∼1280 km2 of basin area originally draining towards the Ligurian Sea were abruptly connected to the Tyrrhenian Sea by the capturing Tavignano and Golo rivers, which led to the formation of a large Pliocene-Quaternary submarine fan offshore the Tyrrhenian coast. The increased sediment yield towards the Tyrrhenian margin after river capture in the Pliocene was three times greater than the average sediment yield in the same source-to-sink system during the Holocene (410±100 t·km−2· a −1 vs ∼131±8 t·km−2· a −1) and greater magnitude than any subsequent peaks in sediment yield during late Pleistocene glaciations. 10Be-derived denudation rates reveal that focused erosion still affects retreating knickpoints near the sites of former river capture in central Corsica, suggesting persistence of landscape disequilibrium for several millions of years. Our results demonstrate the potentially large impact of river capture on the stratigraphic record and highlight the importance of full consideration of landscape response times to onshore disturbances for any reliable interpretation of the offshore sedimentary archive. [Display omitted] [ABSTRACT FROM AUTHOR]

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 10 Be. 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. [ABSTRACT FROM AUTHOR]

While landscapes are broadly sculpted by tectonics and climate, on a catchment scale, sediment size can regulate hillslope denudation rates and thereby influence the location of topographic highs and valleys. In this work, we used in situ 10Be cosmogenic radionuclide analysis to measure the denudation rates of bedrock, boulders, and soil in three granitic landscapes with different climates in Chile. We hypothesize that bedrock and boulders affect differential denudation by denuding more slowly than the surrounding soil; the null hypothesis is that no difference exists between soil and boulder or bedrock denudation rates. To evaluate denudation rates, we present a simple model that assesses differential denudation of boulders and the surrounding soil by evaluating boulder protrusion height against a two-stage erosion model and measured 10Be concentrations of boulder tops. We found that hillslope bedrock and boulders consistently denude more slowly than soil in two out of three of our field sites, which have a humid and a semi-arid climate: denudation rates range from ∼5 to 15 m Myr -1 for bedrock and boulders and from ∼8 to 20 m Myr -1 for soil. Furthermore, across a bedrock ridge at the humid site, denudation rates increase with increasing fracture density. At our lower-sloping field sites, boulders and bedrock appear to be similarly immobile based on similar 10Be concentrations. However, in the site with a Mediterranean climate, steeper slopes allow for higher denudation rates for both soil and boulders (∼40 –140 m Myr -1), while the bedrock denudation rate remains low (∼22 m Myr -1). Our findings suggest that unfractured bedrock patches and large hillslope boulders affect landscape morphology by inducing differential denudation in lower-sloping landscapes. When occurring long enough, such differential denudation should lead to topographic highs and lows controlled by bedrock exposure and hillslope sediment size, which are both a function of fracture density. We further examined our field sites for fracture control on landscape morphology by comparing fracture, fault, and stream orientations, with the hypothesis that bedrock fracturing leaves bedrock more susceptible to denudation. Similar orientations of fractures, faults, and streams further support the idea that tectonically induced bedrock fracturing guides fluvial incision and accelerates denudation by reducing hillslope sediment size. [ABSTRACT FROM AUTHOR]

The Song Gianh is a small-sized (~3500 km2), monsoon-dominated river in northern central Vietnam that can be used to understand how topography and climate control continental erosion. We present major element concentrations, together with Sr and Nd isotopic compositions, of siliciclastic bulk sediments to define sediment provenance and chemical weathering intensity. These data indicate preferential sediment generation in the steep, wetter upper reaches of the Song Gianh. In contrast, detrital zircon U-Pb ages argue for significant flux from the drier, northern Rao Tro tributary. We propose that this mismatch represents disequilibrium in basin erosion patterns driven by changing monsoon strength and the onset of agriculture across the region. Detrital apatite fission track and 10Be data from modern sediment support slowing of regional bedrock exhumation rates through the Cenozoic. If the Song Gianh is representative of coastal Vietnam then the coastal mountains may have produced around 132 000-158 000 km3 of the sediment now preserved in the Song Hong-Yinggehai Basin (17-21% of the total), the primary depocenter of the Red River. This flux does not negate the need for drainage capture in the Red River to explain the large Cenozoic sediment volumes in that basin but does partly account for the discrepancy between preserved and eroded sediment volumes. OSL ages from terraces cluster in the Early Holocene (7.4-8.5 ka), Pre-Industrial (550-320 year BP) and in the recent past ( ca. 150 year BP). The older terraces reflect high sediment production driven by a strong monsoon, whereas the younger are the product of anthropogenic impact on the landscape caused by farming. Modern river sediment is consistently more weathered than terrace sediment consistent with reworking of old weathered soils by agricultural disruption. [ABSTRACT FROM AUTHOR]

The Indus River, one of Asia's premier rivers, drains the western Tibetan Plateau and the Nanga Parbat syntaxis. These two areas juxtapose some of the lowest and highest topographic relief and commensurate denudation rates in the Himalaya-Tibet orogen, respectively, yet the spatial pattern of denudation rates upstream of the syntaxis remains largely unclear, as does the way in which major rivers drive headward incision into the Tibetan Plateau. We report a new inventory of 10Be-based basinwide denudation rates from 33 tributaries flanking the Indus River along a 320 km reach across the western Tibetan Plateau margin. We find that denudation rates of up to 110 mm k.y.-1 in the Ladakh and Zanskar Ranges systematically decrease eastward to 10 mm k.y. -1 toward the Tibetan Plateau. Independent results from bulk petrographic and heavy mineral analyses support this denudation gradient. Assuming that incision along the Indus exerts the base-level control on tributary denudation rates, our data show a systematic eastward decrease of landscape downwearing, reaching its minimum on the Tibetan Plateau. In contrast, denudation rates increase rapidly 150-200 km downstream of a distinct knickpoint that marks the Tibetan Plateau margin in the Indus River longitudinal profile. We infer that any vigorous headward incision and any accompanying erosional waves into the interior of the plateau mostly concerned reaches well below this plateau margin. Moreover, reported long-term (>106 yr) exhumation rates from low-temperature chronometry of 0.1-0.75 mm yr-1 consistently exceed our 10Be-derived denudation rates. With averaging time scales of 10³-104 yr for our denudation data, we report postglacial rates of downwearing in a tectonically idle landscape. To counterbalance this apparent mismatch, denudation rates must have been higher in the Quaternary during glacial-interglacial intervals. [ABSTRACT FROM AUTHOR]

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 10Be-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. • Orographic rainfall has likely persisted for millions of years at S. de Aconquija. • Thermochronology constrains drainage-divide migration rates over millions of years. • 10Be-derived catchment average denudation rates support active divide migration. • West-vergent thrusting combined with westward drainage-divide migration. • Thermochronologic data interpretation should consider lateral topographic shifts. [ABSTRACT FROM AUTHOR]

It has been proposed that at short timescales of 102–105 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 10Be-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°) erode at lower rates of 0.1–0.4 mm/yr compared to steeper (>40°) 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. • Paleo-erosion rates in the Himalaya are modulated by climate forcing. • Erosion rates are higher during episodes of strong monsoon. • Topographic response to climate change is non-linear. • Rapid erosion during short-lived strong monsoon phases result in valley aggradation. [ABSTRACT FROM AUTHOR]

Terrestrial cosmogenic nuclide concentrations in fluvial deposits allow estimation of paleo-erosion rates and reconstruction of the response of landscapes to climatic perturbations. In partly ice-covered landscapes, however, incorporation of subglacially-derived sediments that were shielded by ice from cosmic can lead to erroneous erosion rate calculations. Here, we combine in situ -produced 10Be-derived erosion rates, based on sand and pebbles from a fluvial fill terrace and the modern riverbed in the upper Yamuna catchment, with numerical ice flow modelling to quantify this bias. New luminescence and surface exposure ages suggest that aggradation of the exposed deposits occurred between 29.9 ± 2.5 ka and 14.8 ± 2.8 ka. During most of the deposition, glaciers probably covered ∼19% of the catchment. 10Be concentrations of terrace sand samples differ from those of pebble samples. We obtained the lowest erosion rates from quartzite pebbles, which stem from low elevations, and the highest erosion rates from crystalline pebbles, which stem from high elevations in the Yamuna catchment. We explain these different erosion rates by differences in the steepness of the source areas, an effect that prevails throughout the entire aggradation period despite significant former ice-cover. Sand samples, which are thought to be derived from all elevation parts of the catchment, however show lower 10Be concentrations during the aggradation compared to present-day. We argue that this difference is due to a substantial subglacial origin of the sand during the aggradation period, and not necessarily related to enhanced erosion. We conclude that aggradation of the valley fill in the Yamuna catchment is most likely due to reduced discharge, and only marginally related to higher erosion rates during the late Pleistocene. • Paleo-erosion rates from a ∼135-m high river terrace in the Yamuna catchment. • New luminescence and surface exposure ages from the river terrace. • Aggradation occurred during marine isotope stage 2, when discharge was reduced. • Lower 10Be] in terrace sand compared to river sand can be explained by ice cover. [ABSTRACT FROM AUTHOR]