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The erosion of cold bedrock hillslopes in alpine environments depends not only on rates of frost weathering and accumulated rock damage, but additionally on the removal of the weathered material from the bedrock surface. In the Mont Blanc massif, steep bedrock faces with exposure ages sometimes much older than 50,000 years sit in close proximity to actively-eroding rockwalls, suggesting a more complex relationship between temperature and erosion rates than encompassed by the proposed “frost-cracking window.” Stochastic events like rockfalls and rock avalanches, despite their rarity, contribute a non-trivial proportion of the total sediment budget in alpine permafrost regions, adding to the contribution from background “steady-state” erosion. Employing a methodology based on the combination of in-situ cosmogenic nuclides 3He -10Be-14C, we test the temperature-dependence of high-alpine erosion while taking into account erosional stochasticity.From cosmogenic 10Be concentrations of amalgamated samples collected on the Aiguille du Midi (3842 m a.s.l.) in the Mont Blanc massif, we find an order of magnitude difference in erosion rate across the peak’s surface. Our preliminary measured erosion rates, ranging between appx. 0.03 mm yr-1 and 1.0 mm yr-1, correlate neither with modern temperature measurements from borehole thermistors, nor with our current estimates of bedrock cosmogenic 3He-derived paleotemperatures. The corresponding cosmogenic 14C/10Be ratios (between 1.70 and 4.0) for these erosion rates indicate that our measurements are not biased by recent stochastic rockfall events. Our current results therefore suggest that on geomorphic timescales, bedrock hillslope erosion rates are not set solely by rates of frost-cracking, but rather by the combined effects of frost-cracking and permafrost thaw-induced rockfalls. These insights are relevant both for short-term monitoring of alpine permafrost and associated geohazards under a warming climate, as well as studies of proposed “buzzsaws” operating on glacial-interglacial timescales.

River terraces provide insight into the spatial-temporal patterns of transient tectonic and climatic forcings. The Tropoja Basin is located at the junction of the Dinaride-Albanide-Hellenide belt in north-eastern Albania and is part of the hanging wall of the Shkoder Peja Normal Fault (SPNF) system, which accommodated orogen-parallel extension since Early- to Mid-Miocene times. The basin features Plio-Pleistocene fill comprising lacustrine deposits (Pliocene) overlain by sub-horizontal layers of carbonate-rich conglomerates and marl that are interlayered by reddish clay. We found that this fill was incised by at least three generations of river terraces (T1-T3). The controls on river terrace formation within the area, i.e. faulting, climate events and drainage evolution, have been unclear so far. In this study, we date the river terraces within the Tropoja Basin with 36Cl-cosmogenic-nuclide depth-profiles dating and combine these results with further fluvial geomorphic analysis of digital elevation models (DEM) to assess the process of terrace formation in the light of region-wide drainage basin reorganization.36Cl-depth-profiles dating yield ages of ~ 8.8 ka for the youngest terrace (T1) and ~ 15.4 ka for the intermediate terrace level (T2), indicating that both terraces formed after the Last Glacial Maximum (LGM). Imbrication of conglomeratic clasts in terrace T2 suggests that the paleo flow was southwest directed at the time of deposition followed by a high incision rate of ~7 mm/yr. Also, we checked for activity of the SPNF and its potential impact on terrace formation in the basin by calculating normalised channel steepness index (Ksn) for streams crossing the fault. We found that Ksn-values do not change across that part of SPNF, thus indicating inactivity of the fault in the late Pleistocene to Holocene times. Instead, Ksn-values correlate well with the upper limit of the ice sheet of the LGM of the Valbona Valley. Despite the recent inactivity of the SPNF, the fault might have controlled the spatial fluvial bedrock competence by emplacing carbonates in the footwall adjacent to ophiolites and mélange in the hanging wall forming the floor of the Tropoja Basin. Chi-values of the regional river network in the Tropoja Basin (includes the Valbona and Gashit Rivers, parts of the Drin River system) reveals that the basin was internally drained.We conclude that the Pleistocene fill of the Tropoje Basin post-dates most, if not all normal faulting. The time difference between Mio-Pliocene normal faulting and Pleistocene filling of the basin suggests that sedimentation and incision were controlled directly by climate and basin connectivity through the river network to the regional base-level of the Adriatic Sea. Internally drained, the basin led to lake formation prior the LGM where at times reconnected with regional base-level of the Adriatic Sea after via the Drin River system. This transient evolution of the river network was characterised by basin filling and potential river over-spilling leading to drainage integration events with increased headward erosion and river entrenchment.

A long-lasting question in glacial geology is how and how fast glaciers were able to shape the distinctive landscapes of the Alps. This study contributes to the understanding on the formation of overdeepened basins, especially the processes and the amount of time involved. We examine the remarkably high (150 m) cross-valley bedrock riegel and the associated overdeepening located in front of the Trift glacier in the central Swiss Alps. A combined approach of field survey with measurements of two cosmogenic nuclides, 10Be and in-situ 14C, and a numerical model was used to determine the spatial glacial erosion patterns on the bedrock riegel. Ten samples were taken along two transects; one perpendicular to the glacier flow direction, from outside of the Little Ice Age (LIA) extent down to the centre of the riegel, and the other following the former ice-flow direction across the riegel. Analysis of measured nuclide concentrations shows that the sample outside of the LIA was constantly exposed since the retreat of the Egesen stadial Trift glacier (~11.5 ka). The samples inside the LIA extent indicate a distinct trend of increasing glacial erosion rates from 0 mm/a near the LIA ice margin to high erosion all across the top of the riegel. The resulting minimum glacial erosion rates from samples on the riegel are 0.5–1.1 mm/a (10Be) and 0.6–>1.8 mm/a (in-situ 14C) which correspond to minimum erosion depths of 1.6–>3 m (10Be) and 1–>5 m (14C). The extremely low nuclide concentrations measured at the riegel highlight the substantial erosion (predominantly abrasion) of the bedrock surface during late Holocene glacier coverage. Field observations suggest that the formation of the overdeepening and, as a consequence, the riegel is due to a combination of valley shape, bedrock structures, glacier confluence and hydrology. We further hypothesise that the gorge is a key factor responsible for this impressive overdeepening, by lowering the threshold for the subglacial meltwater, effectively decoupling the height of the riegel from the depth of the overdeepening., Geomorphology, 375, ISSN:0169-555x, ISSN:1872-695X

The Säntis nappe is a complex fold-and-thrust structure in eastern Switzerland, consist-ing of numerous tectonic discontinuities and a range of hillslopes prone to landsliding and large slope failures that modify the topography irreversibly. A slope failure, namely the Sennwald rock avalanche, occurred in the southeast wall of this fold-and-thrust structure due to the rock failure of Lower Cretaceous Helvetic limestones along the Rhine River valley. In this research, this palaeo-landslide is examined in a multidisciplinary approach for the first time with detection and mapping of avalanche deposits, dynamic run-out modelling and cosmogenic nuclide dating. During the rock failure, the avalanche deposits were transported down the hillslope in a spreading-deck fashion, roughly preserving the original stratigraphic sequence. The distribution of landslide deposits and surface exposure age of the rock failure support the hypothesis that the landslide was a single catastrophic event. The36Cl surface exposure age of avalanche deposits indicates an age of 4.3 ± 0.5 ka. This time coincides with a notably wet climate period, noted as a conditioning factor for landslides across the Alps in the mid-Holocene. The contemporaneity of our event at its location in the Eastern Alps provide additional support for the contention of increased regional seismic activity in mid-Holocene., Geosciences, 11 (8), ISSN:2076-3263

We compile detrital 10Be concentrations of Alpine rivers, representing the denudation rates pattern for 375 catchments across the entire European Alps. Using a homogeneized framework, we employ state-of-the-art techniques for inverting in-situ 10Be concentrations into denudation rates. From our compilation, we find that (i) while lithologic properties and precipitation/runoff do influence erosion mechanisms and rates at the scale of individual catchments and in some specific Alpine regions, such controls do not directly stand for the entire Alps, (ii) as also previously suggested, catchment-wide denudation rates across the entire European Alps closely follow first-order Alpine topographic metrics at the scale of individual catchments or selected Alpine sub-regions. However, in addition to previous local-scale studies conducted in the European Alps, our large-scale compilation highlights a functional relationship between catchment-wide denudation and mean catchment slope angle. Catchment-wide denudation positively correlates with mean catchment slope up to a threshold angle (25–30°). Above this threshold, any correlation between catchment-wide denudation and slope as well as other catchment metrics breaks apart. We can reconcile these systematic patterns by proposing a regional erosion model based on diffusive-transport laws for catchments located below the slope threshold angle. In oversteepened catchments situated above-threshold slopes, erosion is stochastic in nature, as glacial carving likely caused a partial decoupling between hillslope and fluvial domains with complex topographic relationships and sediment connectivity patterns. Finally, we identify a first-order positive relationship between modern geodetic rock uplift and catchment-wide denudation for the European Alps. The observed spatial pattern is highly variable and possibly reflects the surface response to deep geodynamic mechanisms prevailing in the different Alpine regions. We conclude that today's topography and geomorphic features of the entire Alps are the result of a millenial-scale geomorphic response to past glacial processes and active rock uplift, highlighting a link between external and internal drivers for mountain erosion. ISSN:0012-8252 ISSN:1872-6828

The glacial landforms at Wangen an der Aare provide a footprint of the extent of the Valais (Rhone) glacier during the Last Glacial Maximum. The early studies of the region played a key role in development of the glacial theory during the early nineteenth century. The Valais glacier advanced into the region several times leaving evidence of its presence in deposits of moraines and outwash. The former are recognized as the broad band of hills that extends from Oberbipp to Butzberg and around to the south at Steinhof–Steinenberg. Direct dating of erratic boulders with cosmogenic 10Be suggests withdrawal of the Valais glacier from the area starting at about 24,000 years ago. Coarse gravels carried by meltwater streams emanating from the glacier were deposited as outwash plains to the northeast of the moraines. As the glacier withdrew stepwise incision into the plains left a flight of terraces extending down to the present flood plain and path of the Aare River.

River terraces located in the Tropoja Basin in northern Albania are characterized by high elevation (c. 600 m) and by multiple incision events that highlight the interaction between tectonically induced surface uplift, glaciation, and erosion. The Tropoja Basin is located in the hanging wall of the Shkoder-Peja Normal Fault (SPNF) a crustal-scale normal fault trending orthogonal to the strike of the Dinarides Belt. Neo-tectonic activity along the SPNF is indicated by several recent earthquakes. Glaciated valleys drain into the upper reaches of the Valbona River draining the basin. The processes regulating the evolution of the basin infill and the incision of the river terraces remain unclear.Our mapping reveals that the Pliocene basin fill is overlain by two sub-horizontal layers of Pleistocene-Holocene sediment: porous conglomerate below and red clay above. The conglomeratic layer contains components derived mostly from Mesozoic limestones in Dinaric nappes in the glacial Valbona and Gashi Valleys. The drainage direction in the basin inferred from paleo flow indicators in both layers was to the SW, i.e., in the direction of present-day flow into the Drini Gorge that cuts down to the Adriatic coast. In addition, we recognize three terrace levels in these sediments, the top two of which are carved by abandoned river channels. The terraces and channels cut across the Pleistocene-Holocene layer contacts and are therefore younger than the layers’ deposition. The layers themselves thicken away from the SPNF, and show no preferred dip toward or away from the SPNF. Work is underway to date these terraces with cosmogenic nuclides.Initial relief leading to the Pliocene infill of the Tropoja Basin is interpreted to be a by-product of SPNF activity, which began already in mid-Miocene time. However, this activity is insufficient to explain post-Pliocene sedimentation in the Tropoja Basin because the thickness and dip of the Pleistocene-Holocene layers do not vary systematically with proximity to the SPNF. We, therefore, interpret the Pleistocene-Holocene basin fill to be glacial, with the basal porous conglomerates deposited during sudden out washing of the glacial valleys due to release of melting water behind moraine dams. The overlying red clay layer is interpreted to be a lacustrine deposit due to damming further down the Drini Valley. The preservation of abandoned stream channels in the terraces may reflect episodic uplift and fluvial down-cutting events. The down-cutting may be attributed either to isostatic uplift of the upper plate of the retreating Hellenic subduction and/or to interglacial unloading.

Determining sediment transfer times is key to understanding source‐to‐sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic 14C‐10Be‐chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady‐state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the 14C‐10Be steady‐state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic 10Be‐26Al isochron burial dating, and 10Be‐26Al depth‐profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the 14C‐10Be disequilibrium measured in the channel. Instead we propose that the 14C‐10Be offset results from: (i) non‐uniform erosion whereby deep gullies supply hillslope‐derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the 14C‐10Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape.

During the Last Glacial Maximum (LGM) the Tagliamento glacier delivered large amounts of sediment to the Cormor alluvial megafan on the southern Alpine foreland basin. To build a chronology of Late Pleistocene glacier fluctuations and assess the timing of the transition from interstadial to glacial conditions, we have performed radiocarbon (14C) dating on peat and macrofossil samples obtained from a drilling core from the distal Cormor megafan. Our chronology records fluvial and glaciofluvial aggradation from the end of MIS 3 until the end of the LGM. It shows a rapid transmission of signals of environmental change along the Cormor megafan, so that changes in the activity of the Tagliamento glacier directly affect glaciofluvial sedimentation. Our data demonstrate that the intrinsic heterogeneity of peat is most critical for the reliability and reproducibility of the obtained 14C ages. Macrofossil subsamples give evidence for significant mixing of organic components of different ages within single peat samples. Sample heterogeneity is also underlined by the results obtained from testing of different laboratory precleaning methods. Our results suggest that a rigorous ABA pretreatment is sufficient for peat cleaning. In contrast, the chemically stronger ABOX methods appear to rapidly degrade the peat, particularly destroying older organic components.

Reconstructing Quaternary landscape evolution today frequently builds upon cosmogenic-nuclide surface exposure dating. However, the study of complex surface exposure chronologies on the 102–104 years’ timescale remains challenging with the commonly used long-lived radionuclides (10Be, 26Al, 36Cl). In glacial settings, key points are the inheritance of nuclides accumulated in a rock surface during a previous exposure episode and (partial) shielding of a rock surface after the main deglaciation event, e.g. during phases of glacier readvance. Combining the short-lived in situ cosmogenic 14C isotope with 10Be dating provides a valuable approach to resolve and quantify complex exposure histories and burial episodes within Lateglacial and Holocene timescales. The first studies applying the in situ 14C-10Be pair have demonstrated the great benefit from in situ 14C analysis for unravelling complex glacier chronologies in various glacial environments worldwide. Moreover, emerging research on in situ 14C in sedimentary systems highlights the capacity of combined in situ 14C-10Be analysis to quantify sediment transfer times in fluvial catchments or to constrain changes in surface erosion rates. Nevertheless, further methodological advances are needed to obtain truly routine and widely available in situ 14C analysis. Future development in analytical techniques has to focus on improving the analytical reproducibility, reducing the background level and determining more accurate muonic production rates. These improvements should allow extending the field of applications for combined in situ 14C-10Be analysis in Earth surface sciences and open up a number of promising applications for dating young sedimentary deposits and the quantification of recent changes in surface erosion dynamics.

The Marocche di Dro deposits in the lower Sarca Valley are some of the most distinctive rock avalanche deposits of the Alps. We use geomorphology and cosmogenic 36 Cl exposure dating of boulders to divide the Marocche di Dro deposits into two rock avalanche bodies; the Marocca Principale to the north and the Kas to the south. The deposits were previously undated and had been mapped as up to five different events. The largest event Marocca Principale, which comprises an estimated 1000 10 6 m 3 of predominantly Rotzo Formation limestones, occurred 5300 ± 860 yr ago. The release area is located mainly in the alcove between Mt. Casale and Mt. Granzoline, but likely extends all the way to Mt. Brento. The Kas event took place 1080 ± 160 yr ago with detachment below Mt. Brento. The Kas debris, with an estimated volume of 300 10 6 m 3 , buried the southern third of the Marocca Principale deposit. Kas presents a barren, stark landscape dominated by house-sized Tovel Member Rotzo Formation boulders bearing distinctive chert lenses. Both the extreme relief of the rock wall (more than 1300 m) and the tectonic setting predispose the range front to massive failure. For the two events, initially translational movement likely quickly evolved into complex failure and massive collapse. Run-out across the valley of several kilometers and run-up on the opposite slope of hundreds of meters followed. A summary of all dated and large historical landslides in the Alps underlines the periods of enhanced slope activity discussed in the literature: 10-9 kyr, 5-3 kyr, and 2-1 kyr, the latter especially for the Southern Alps. No deposits of the first temporal cluster are found at Marocche di Dro. The age of Marocca Principale at 5300 ± 860 yr suggests occurrence during the second period. Failure may have been related to the shift to wetter, colder climate at the transition from the middle to the late Holocene. Nevertheless, a seismic trigger cannot be ruled out. For the Kas rock avalanche at 1080 ± 160 yr ago we implicate the “Middle Adige Valley” (1046 CE) earthquake as trigger. Its epicentral distance is much closer to the Sarca Valley in comparison to that of the Verona earthquake (1117 CE).

Optically stimulated luminescence (OSL) dating of sediment, based on the accumulation of trapped charge in natural crystals since their last exposure to daylight, has revolutionised our understanding of the late Quaternary period. Recently, a complementary technique called luminescence rock surface dating (RSD), which uses differential spatial eviction of trapped charges in rocks exposed to daylight, has been developed to derive exposure and burial ages, and hard-rock erosion rates. In its current form, the RSD technique suffers from labour intensive sample preparation, uncertainties in the depth and dose rate estimates, and poor resolution of the luminescence-depth profile. Here, we develop a novel, 2D luminescence imaging technique for RSD of large rock slabs (3 × 5 cm) to overcome these challenges. We utilize the recently discovered infrared photoluminescence (IRPL) signal for direct, non-destructive imaging of the luminescence-depth profile in a sub-aerially exposed granitic rock, with an unprecedented spatial resolution of ~140 µm. We further establish a correlation between luminescence and geochemistry using micro X-ray fluorescence (µXRF) spectroscopy. Our study promises a substantial advancement in luminescence imaging and paves the path towards novel applications using 2D dating, micro-dosimetry in mixed composition samples, and portable instrumentation for in-situ luminescence measurements.

There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being 10Be and 26Al in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N 10Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their 26Al targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) 10Be and that it has low concentrations of the major elements that can interfere with Be and Al extraction chemistry and AMS measurements. We derive preliminary concentrations for 10Be and 26Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit.

We present a new in-situ cosmogenic 14C extraction system developed at ETH Zürich. This system quantitatively extracts 14C produced in quartz by cosmic rays using a high temperature extraction procedure. A key improvement of the new extraction system is the implementation of largely automated sequences, CO2 transport in a He flow and the addition of a “dead” CO2 carrier gas, which ensure highly reproducible operation while limiting the required operator attendance. Intercomparison quartz samples were routinely measured over a year of operation and yield 14C concentrations of 7.27 (±0.03) · 105 at/g quartz for CRONUS-A (n = 7) and 1.24 (±0.17) · 104 at/g quartz for CRONUS-N (n = 4). The excellent performance of the new system is highlighted by low procedural blanks of ca. 3 · 104 14C atoms and coefficients of variation for the CRONUS-A and CRONUS-N analyses of only 0.4% and 14% respectively., Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 457, ISSN:0168-583X, ISSN:1872-9584

Terrestrial cosmogenic nuclides (TCN) have widely been used as proxies in determining denudation rates in catchments. Most studies were limited to samples from modern active streams, thus little is known about the magnitude and causes of TCN variability on millennial time scales. In this work we present a 6 kyrs long, high resolution record of 10Be concentrations (n = 18), which were measured in sediment cores from an alluvial fan delta at the outlet of the Fedoz Valley in the Swiss Alps. This record is paired with a three-year time series (n = 4) of 10Be measured in sediment from the active stream currently feeding this fan delta. The temporal trend in the 10Be concentrations after correction for postdepositional production of 10Be was found to be overall constant and in good agreement with the modern river 10Be concentration. The calculated mean catchment-wide denudation rate amounts to 0.73 ± 0.18 mm/yr. This fairly constant level of 10Be concentrations can be caused by a constant denudation rate over time within the catchment or alternatively by a buffered signal. In this contribution we suggest that the large alluvial floodplain in the Fedoz Valley may act as an efficient buffer on Holocene time scales in which sediments with different 10Be signatures are mixed. Therefore, presumable variations in the 10Be signals derived from changes in denudation under a fluctuating Holocene climate are only poorly transferred to the catchment outlet and not recorded in the 10Be record. However, despite the absence of high frequency signals, we propose that the buffered and averaged 10Be signal could be meaningfully and faithfully interpreted in terms of long-term catchment-averaged denudation rate. Our study suggests that alluvial buffers play an important role in regulating the 10Be signal exported by some alpine settings that needs to be taken into account and further investigated. This article is protected by copyright. All rights reserved.

Zircon formation and modification during magmatic crystallization and high-grade metamorphism are explored using TIMS and LA-ICP-MS U–Pb geochronology, Lu–Hf isotope chemistry, trace element analysis and textural clues on zircons from the Koraput alkaline intrusion, Eastern Ghats Belt (EGB), India. The zircon host-rock is a granulite-facies nepheline syenite gneiss with an exceptionally low Zr concentration, prohibiting early magmatic Zr saturation. With zircon formation occurring at a late stage of advanced magmatic cooling, significant amounts of Zr were incorporated into biotite, nearly the only other Zr-bearing phase in the nepheline syenite gneisses. Investigated zircons experienced a multi-stage history of magmatic and metamorphic zircon growth with repeated solid-state recrystallization and partial dissolution–precipitation. These processes are recorded by complex patterns of internal zircon structures and a wide range of apparently concordant U–Pb ages between 869 ± 7 Ma and 690 ± 1 Ma. The oldest ages are interpreted to represent the timing of the emplacement of the Koraput alkaline complex, which significantly postdates the intrusion ages of most of the alkaline intrusion in the western EGB. However, Hf model ages of TDM = 1.5 to 1.0 Ga suggest an earlier separation of the nepheline syenite magma from its depleted mantle source, overlapping with the widespread Mesoproterozoic, rift-related alkaline magmatism in the EGB. Zircons yielding ages younger than 860 Ma have most probably experienced partial resetting of their U–Pb ages during repeated and variable recrystallization events. Consistent youngest LA-ICP-MS and CA-TIMS U–Pb ages of 700–690 Ma reflect a final pulse of high-grade metamorphism in the Koraput area and underline the recurrence of considerable orogenic activity in the western EGB during the Neoproterozoic. Within the nepheline syenite gneisses this final high-grade metamorphic event caused biotite breakdown, releasing sufficient Zr for local saturation and new subsolidus zircon growth along the biotite grain boundaries.

Surface exposure dating with a single cosmogenic nuclide relies on the assumption of simple constant exposure. In contrast, the combination of nuclides with different half-lives or production rate depth profiles allows constraining complex exposure histories. Here we present the systematics of how the combination of 10Be, in situ 14C and 36Cl can be used to understand both burial and erosion in a rock surface, in addition to yielding an exposure time. Concordant ages of all three nuclides characterize simple exposure. Apparently ‘too young’ 14C ages or ‘too old’ 36Cl ages indicate burial or erosion of the rock surface, respectively. We further report a first data set from a proglacial granite bedrock ridge in a small cirque in the Central Swiss Alps. Three samples were exposed for 9.6 ± 0.3 ka during the Holocene. The use of same-sample 10Be, in situ 14C and 36Cl allowed us to quantitatively show that these rock surfaces experienced simple constant exposure with ≤500 years of ice cover and ≤6 cm of erosion. In addition, the fact that samples inside and outside the Little Ice Age (LIA) ice extent yield indistinguishable ages reinforces the hypothesis that Grueben glacier reached comparable dimensions only briefly during the Holocene. Notably, at sites just inside of the LIA extent, which do exhibit fresh glacial polish, concordant ages suggest that subglacial erosion there was minimal.

Within a project aimed at understanding past catastrophic rock slope failure in the Trentino Province of Italy, we studied the Castelpietra landslide. Castelpietra encompasses a main blocky deposit, with an area of 1.2 km2, which is buried on the upper side by more recent rockfall debris. The release area is the Cengio Rosso rock wall, which is comprised of Dolomia Principale and overlying Calcari Grigi Group dolomitized limestones. 36Cl exposure dates from two boulders in the main blocky deposit indicate that the landslide occurred at 1060 ± 270 AD (950 ± 270 yr ago). The close coincidence in time of the Castelpietra event with several events that lie within a maximum distance of 20 km, including Kas at Marroche di Dro, Pra da Lago and Varini (at Lavini di Marco) landslides, strongly suggests a seismic trigger. Based on historical seismicity compilations, we have identified the “Middle Adige Earthquake” at 1046 AD as the most likely candidate. Its epicenter lies right in the middle of the spatial distribution of the discussed landslides.

We reconstruct the timing of ice flow reconfiguration and deglaciation of the Central Alpine Gotthard Pass, Switzerland, using cosmogenic 10Be and in situ14C surface exposure dating. Combined with mapping of glacial erosional markers, exposure ages of bedrock surfaces reveal progressive glacier downwasting from the maximum LGM ice volume and a gradual reorganization of the paleoflow pattern with a southward migration of the ice divide. Exposure ages of ∼16–14 ka (snow corrected) give evidence for continuous early Lateglacial ice cover and indicate that the first deglaciation was contemporaneous with the decay of the large Gschnitz glacier system. In agreement with published ages from other Alpine passes, these data support the concept of large transection glaciers that persisted in the high Alps after the breakdown of the LGM ice masses in the foreland and possibly decayed as late as the onset of the Bolling warming. A younger group of ages around ∼12–13 ka records the timing of deglaciation following local glacier readvance during the Egesen stadial. Glacial erosional features and the distribution of exposure ages consistently imply that Egesen glaciers were of comparatively small volume and were following a topographically controlled paleoflow pattern. Dating of a boulder close to the pass elevation gives a minimum age of 11.1 ± 0.4 ka for final deglaciation by the end of the Younger Dryas. In situ14C data are overall in good agreement with the 10Be ages and confirm continuous exposure throughout the Holocene. However, in situ14C demonstrates that partial surface shielding, e.g. by snow, has to be incorporated in the exposure age calculations and the model of deglaciation.

In situ radiocarbon inorganic production and retention pathways are distinct from those of the more commonly used traditional organic/atmospheric 14C. In addition, a growing number of laboratories are extracting in situ cosmogenic 14C from quartz, using a variety of analytical techniques. As such, a flexible yet internally consistent set of procedures for data reduction that recognizes the unique nature of the in situ14C system is essential for reliable comparison of results among laboratories. This article thus presents a brief data reduction framework that can accommodate differences in both AMS and laboratory analytical techniques.

We present the improved performance of the modified in situ cosmogenic 14C extraction system at ETH Zurich. Samples are now processed faster (2 days in total) and are measured with a high analytical precision of usually

Catchment-wide denudation rates (CWDRs) obtained from cosmogenic nuclides are an efficient way to determine geomorphic processes quantitatively in alpine mountain ranges over Holocene time scales. These rate estimations assume steady geomorphic processes. Here we use a time series (3 yr) in the Aare catchment (central Swiss Alps) to test the impact of spatially heterogeneous stochastic sediment supply on CWDRs. Our results show that low-frequency, high-magnitude debris-flow events significantly perturb cosmogenic nuclide ( 10 Be, 14 C) concentrations and thus CWDRs. The 10 Be concentrations decrease by a factor of two following debris-flow events, resulting in a doubling of inferred CWDRs. The variability indicates a clear time and source dependency on sediment supply, with restricted area-weighted mixing of sediment. Accordingly, in transient environments, it is critical to have an understanding of the history of geomorphic processes to derive meaningful CWDRs. We hypothesize that the size of debris flows, their connectivity with the trunk stream, and the ability of the system to sufficiently mix sediment from low- and high-order catchments control the magnitude of CWDR perturbations. We also determined in situ 14 C in a few samples. In conjunction with 10 Be, these data suggest partial storage for colluvium of a few thousand years within the catchment prior to debris-flow initiation.

We present the new 14 C extraction line at ETH Zurich. This system is designed to extract in situ -produced cosmogenic 14 C from terrestrial quartz samples, and to obtain pure CO 2 gas for analysis with a gas ion source Accelerator Mass Spectrometry (AMS) system. Samples are degassed at 1550–1600 °C without the use of a fluxing agent. Gas purification is achieved by a series of cryogenic traps and passage through hot Ag and Cu wool/mesh. Graphitization and, thus, sample dilution is not required. Tests to determine the CO 2 recovery after gas extraction and cleaning yielded consistently good recovery rates of >99.8% ( n = 7). The 14 C blank contribution from the all-metal tubing system is negligible. Our preliminary procedural blank estimate – deriving mostly from the hot extraction furnace – is 5 14 C atoms. Extraction tests on two quartz samples by stepped-heating show a quantitative separation of atmospheric 14 C at ≤500 °C from the in situ component above 1200 °C. Based on these data, we estimate to achieve a complete 14 C extraction from a quartz sample.

The topographic signature of a mountain belt depends on the interplay of tectonic, climatic and erosional processes, whose relative importance changes over times, while quantifying these processes and their rates at specific times remains a challenge. The eastern Andes of central Bolivia offer a natural laboratory in which such interplay has been debated. Here, we investigate the Rio Grande catchment which crosses orthogonally the eastern Andes orogen from the Eastern Cordillera into the Subandean Zone, exhibiting a catchment relief of up to 5000 m. Despite an enhanced tectonic activity in the Subandes, local relief, mean and modal slopes and channel steepness indices are largely similar compared to the Eastern Cordillera and the intervening Interandean Zone. Nevertheless, a dataset of 57 new cosmogenic 10Be and 26AI catchment wide denudation rates from the Rio Grande catchment reveals up to one order of magnitude higher denudation rates in the Subandean Zone (mean 0.8 mm/yr) compared to the upstream physiographic regions. We infer that tectonic activity in the thrusting dominated Subandean belt causes higher denudation rates based on cumulative rock uplift investigations and due to the absence of a pronounced climate gradient. Furthermore, the lower rock strength of the Subandean sedimentary units correlates with mean slopes similar to the ones of the Eastern Cordillera and Interandean Zone, highlighting the fact, that lithology and rock strength can control high denudation rates at low slopes. Low denudation rates measured at the outlet of the Rio Grande catchment (Abapo) are interpreted to be a result of a biased cosmogenic nuclide mixing that is dominated by headwater signals from the Eastern Cordillera and the Interandean zone and limited catchment sediment connectivity in the lower river reaches. Therefore, comparisons of short- (i.e., sediment yield) and millennial denudation rates require caution when postulating tectonic and/or climatic forcing without detailed studies. (C) 2015 The Authors. Published by Elsevier B.V.

Antarctic Science, 26 (6), ISSN:0954-1020, ISSN:1365-2079

The Chauvet-Pont d'Arc Cave is one of the most important sites for the study of the earliest manifestations and development of prehistoric art at the beginning of the Upper Paleolithic. Different dating techniques have been performed thus far (AMS 14C, U/Th TIMS, 36Cl dating) to model the chronological framework of this decorated cave. The cave yielded several large charcoal fragments, which enabled the opportunity for obtaining multiple dates; thus, a First Radiocarbon Intercomparison Program (FIP) was initiated in 2004 using three charcoal pieces. The FIP demonstrated that those cross-dated samples belonged to a time period associated with the first human occupation. One of the statistical interests of an intercomparison program is to reduce the uncertainty on the sample age; thus, to further assess the accuracy of the chronological framework, the Second Intercomparison Program (SIP) involving 10 international 14C laboratories was carried out on two pieces of charcoal found inside two hearth structures of the Galerie des Mégacéros. Each laboratory used its own pretreatment and AMS facilities. In total, 21 and 22 measurements were performed, respectively, which yielded consistent results averaging ∼32 ka BP. Two strategies have currently been developed to identify statistical outliers and to deal with them; both lead to quasi-identical calibrated combined densities. Finally, the new results were compared with those of the FIP, leading to the important conclusion that five different samples from at least three different hearth structures give really tightened temporal densities, associated with one short human occupation in the Galerie des Mégacéros.

Denudation processes and sediment transfer are investigated in a high-elevation, low-relief environment (eastern Altiplano, Bolivia) using Be-10, Al-26, and in situ C-14 analysis in fluvial sediments. Concentrations of the long-lived nuclides Be-10 and Al-26 yield consistently low catchment-wide denudation rates of similar to 3-29 mm ky(-1) (integrating over 21-194 ky), which reflect the low geomorphic gradients and the discontinuity of fluvial transport along the eastern Altiplano margin. No significant correlation is recorded between denudation rates of individual catchments and morphological basin parameters (slope, area, elevation). This is attributed to the overall little variability in morphology. The agreement between the denudation rates and published modern sediment discharge data suggests steady landscape evolution of the eastern Altiplano from the latest Pleistocene until today. While Be-10 and Al-26 provide long-term estimates on sediment production, in situ cosmogenic C-14 is used to trace short-term sediment storage. In situ C-14 concentrations are comparatively low indicating that C-14 decayed during alluvial storage over at least the past similar to 11-20 ky. We assume storage at shallow depth (2 m) and consider the influence of soil-mantled hillslopes on the in situ C-14 concentration. Our results illustrate the importance of sediment storage even over short distances and demonstrate the potential of in situ C-14 to study sediment routing and transfer times within drainage systems. However, this study also demonstrates that the long-lived Be-10 and Al-26 nuclides can provide adequate estimates on long-term denudation rates even if sediment transport is not fast but interrupted by several thousands of years of storage.