Cosmogenic 10Be Research Articles

Denudation systematics inferred from in situ cosmogenic 10Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (<250 µm) than typically analyzed in 10Be studies, and few studies have measured 10Be concentrations in quartz grains smaller than 100 µm or assessed the impacts of mixing, grain size, and interannual variability on the 10Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic 10Be concentrations of quartz grains in the 50–100 and 100–250 µm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from 10Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed 10Be concentrations. Both analyzed size fractions returned similar 10Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02±0.78)×104 to (4.40±0.64)×104 atoms g−1 of quartz. By comparing expected and observed 10Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual 10Be concentrations were in agreement within uncertainties, except for one upper subbasin. The 10Be-derived denudation rates of Var subbasins range from 0.10±0.01 to 0.57±0.09 mm yr−1, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24±0.04 mm yr−1, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) may return accurate denudation rates and are thus potentially suitable targets for future 10Be applications, such as studies of paleo-denudation rates using offshore sediments.

MnO2 fiber as a sorbent for radionuclides in oceanographic investigations

The paper presents the results of a study of the physical, chemical and sorption properties of a fibrous sorbent—polyacrylonitrile modified with a mixed phase of manganese oxide, in relation to the natural isotopes of radium in seawater. The paper contains methodical guidelines for synthesizing the material the most efficiency and hydromechanical stability. It is described using structural (diffractometry, IR spectroscopy) and physicochemical methods of analysis (thermal analysis, gas adsorption). The possibility of using this sorbent for the concentration of cosmogenic (7Be) and natural (226Ra, 228Ra, 234Th) radionuclides from seawater samples under field conditions was studied. The results of determination of the concentration of dissolved 226Ra, 228Ra, 234Th in seawater samples using this sorbent were compared with the published data. Evidence of sorption 7Be from seawater samples using this fiber was obtained by γ-spectrometric analysis.

26Al/10Be ratios reveal the source of river sediments in the Kimberley, NW Australia

AbstractWe use cosmogenic 10Be and 26Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr‐1, with a mean value of 1.0 ± 0.6 m.Myr‐1 (n=15), whilst two bedrock samples collected directly within river‐beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr‐1, respectively). Bedrock 26Al/10Be ratios are all compatible with simple, continuous sub‐aerial exposure histories. Modern river sediment yield lower 10Be and 26Al concentrations, apparent 10Be basin‐wide denudation rates ranging between 1.8 and 7.7 m.Myr‐1, with a median value of 2.6 m.Myr‐1, more than double the magnitude of bedrock erosion rates. 26Al/10Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted 26Al/10Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass‐balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock‐walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin‐scale studies using cosmogenic nuclides, especially in slowly eroding post‐orogenic settings. © 2019 John Wiley & Sons, Ltd.

Negative correlation between the number of sunspots and the occurrence of 7Be and 22Na in the surface air and their contribution to radiation doses.

This article presents yearly mean concentrations of cosmogenic radionuclides 7Be and 22Na occurring in dry and wet depositions (fallout) and aerosols. Time dependencies negatively correlated with the yearly mean number of sunspots. Activity concentrations of 7Be and 22Na in aerosols in the surface air had a correlation of near-unity. 7Be in aerosols exhibited a smoother time dependence than 22Na, implying that the production of 22Na is more sensitive to the solar activity than the production of 7Be. The effect of the measured doses on the general population through internal and external exposure to radiation from cosmogenic radionuclides was small.

Age of the Berlin moraine complex, New Hampshire, USA, and implications for ice sheet dynamics and climate during Termination 1

AbstractAt its late Pleistocene maximum, the Laurentide Ice Sheet was the largest ice mass on Earth and a key player in the modulation of global climate and sea level. At the same time, this temperate ice sheet was itself sensitive to climate, and high-magnitude fluctuations in ice extent, reconstructed from relict glacial deposits, reflect past changes in atmospheric temperature. Here, we present a cosmogenic 10Be surface-exposure chronology for the Berlin moraines in the White Mountains of northern New Hampshire, USA, which supports the model that deglaciation of New England was interrupted by a pronounced advance of ice during the Bølling-Allerød. Together with recalculated 10Be ages from the southern New England coast, the expanded White Mountains moraine chronology also brackets the timing of ice sheet retreat in this sector of the Laurentide. In conjunction with existing chronological data, the moraine ages presented here suggest that deglaciation was widespread during Heinrich Stadial 1 event (~18–14.7 ka) despite apparently cold marine conditions in the adjacent North Atlantic. As part of the White Mountains moraine system, the Berlin chronology also places a new terrestrial constraint on the former glacial configuration during the marine incursion of the St. Lawrence River valley north of the White Mountains.

Cosmogenic 10Be exposure dating of glacial erratics on Horseshoe Island in western Antarctic Peninsula confirms rapid deglaciation in the Early Holocene

AbstractThe rapid warming observed in the western Antarctic Peninsula gives rise to a fast disintegration of ice shelves and thinning and retreat of marine-terminating continental glaciers, which is likely to raise global sea levels in the near future. In order to understand the contemporary changes in context and to provide constraints for hindcasting models, it is important to understand the Late Quaternary history of the region. Here, we build on previous work on the deglacial history of the western Antarctic Peninsula and we present four new cosmogenic 10Be exposure ages from Horseshoe Island in Marguerite Bay, which has been suggested as a former location of very fast ice stream retreat. Four samples collected from erratic pink granite boulders at an altitude of ~80 m above sea level yielded ages that range between 12.9 ± 1.1 ka and 9.4 ± 0.8 ka. As in other studies on Antarctic erratics, we have chosen to report the youngest erratic age (9.4 ± 0.8 ka) as the true age of deglaciation, which confirms a rapid thinning of the Marguerite Trough Ice Stream at the onset of Holocene. This result is consistent with other cosmogenic age data and other proxies (marine and lacustrine 14C and optically stimulated luminescence) reported from nearby areas.

A Mediterranean perspective on 10Be, sedimentation and climate around the Matuyama/Brunhes boundary: les liaisons dangereuses?

The 10Be/9Be ratio is commonly employed as a tool for establishing the stratigraphic position of paleomagnetic excursions and reversals whenever the traditional paleomagnetic approach fails to provide conclusive results. In particular, it is held that 10Be production rates in the atmosphere depend on the strength of the Earth’s magnetic field, and the fallout and deposition of cosmogenic beryllium at the surface happen on a very short time scale. However, investigations performed on terrestrial and marine successions demonstrate that the 10Be record and the paleomagnetic signal are often asynchronous. Mechanisms that control the conveyance and deposition of cosmogenic 10Be to the seafloor are still ambiguous and poorly documented. Here, we discuss the dynamics of 10Be in a central Mediterranean marginal marine depositional scenario characterized by a pervasive terrigenous influx. Our data show that a very close correlation exists between 10Be concentrations and the local proxy of rainfall rates and regimes (pollen), indicating that a considerable 10Be transport from the mainland may occur in response to the remobilization of terrestrial reservoirs during periods of increased runoff. Superimposed is a dynamic oceanographic setting that further controls the preservation potential of 10Be at the bottom, in terms of changing water chemistry and/or composition of the sedimentary flux to the seafloor. Results of our investigation suggest that, in particular environmental and depositional settings, the interplay between climate, terrigenous yield and oceanography may jeopardize the sedimentary depiction of the meteoric 10Be contribution, thus challenging the use of 10Be for tracking the stratigraphic position of geomagnetic reversals.

Using in situ-produced 10Be to constrain the age of the latest surface-rupturing earthquake along the Middle Kedrovaya fault (Baikal rift)

Abstract The 30-km-long Middle Kedrovaya (MK) fault, on the northwestern flank of Lake Baikal, is one of the most impressive late Quaternary seismogenic structures in the Baikal rift. In places, surface fault scarps expose striated bedrock fault planes and offer some opportunities to examine the faulting history. Using cosmogenic 10Be exposure dating, we measured the exposure ages of one of the MK scarps (54.44630°N, 108.51524°E, elevation 985 m). This ~12-m-high normal fault scarp is composed of cataclasites in early Proterozoic granitoids of the Irel complex. We analyzed 12 of 18 samples, collected every 0.5 m, from 0.45 m above the toe of the exposed fault plane, which dips 55° in its lower half (samples 1–6) and 45° in upper half (samples 7–12). Exposure ages are the following from the toe upward: sample 1, 2.26 ± 0.53 ka; 2, 1.54 ± 0.55 ka; 3, 0.80 ± 0.55 ka; 5, 1.44 ± 0.55 ka; 6, 2.13 ± 0.62 ka; 8, 1.45 ± 0.48 ka; and 9, 1.40 ± 0.52 ka. The relationship between the oldest calculated ages (samples 1 and 6) and the relative sampling height along the scarp suggests that a recent surface-rupture event with a vertical component of 2.05 m (i.e. net slip of 2.5 m) occurred on the cliff ~2.2 ± 0.6 ka. Striations on the fault plane in the sampling points 1 and 6, as well a close date of 2145–2463 cal years BP calculated from radiocarbon age of a paleoseismic rupture within the Cape Shartly, ~62 km further southwestward, support this interpretation. The close ages assume that the dated deformations were related to a single Mw = 7.4 earthquake, the coseismic effects of which extended at least 82 km (the rupture length between the Cape Shartly and the NNE termination of the MK paleoseismic rupture zone). A more concentrated age mode of about 1.46 ± 0.53 ka (samples 2, 5, 8 and 9), which is in an incorrect stratigraphic order in reference to the older ages, is assumed to result from local erosion or partial shielding. Cosmogenic dating of fault scarps and seismogenic landslide scarps in bedrock potentially offers an independent method of reconstructing the late Quaternary paleoseismology of the northwestern flank of Lake Baikal.

Development of a steep erosional gradient over a short distance in the hyperarid core of the Atacama Desert, northern Chile

Abstract Although generally considered to exist under hyperarid conditions over the long term, landscapes in many parts of the Coastal Cordillera of northern Chile have undergone fluvial erosion. Small-scale drainage systems in this mountain range are mostly isolated from river networks and associated processes originating in the Precordillera or the High Andes to the east, thus providing natural laboratories to investigate the interplay between erosion, atmospheric deposition, tectonics and local (micro-) climatic conditions. In this study, we present a set of cosmogenic 10Be and 26Al derived, catchment-wide erosion rates along a short (2.5 km) E-W transect on the northern rim of the Rio Loa Canyon in the Coastal Cordillera of northern Chile (latitude 21.4°S). Here, a flat sedimentary gravel surface, which was deposited before the Middle Miocene, becomes increasingly dissected and changes into a badland-like topography to the west. The 10Be erosion rates increase by approximately an order of magnitude from east to west, reflecting (1) localised tectonic movements, (2) geologically recent base level lowering, (3) time-integrated (micro-) climatic gradients and (4) the presence/absence of gypcrete. These findings are corroborated by analysis of geomorphologic parameters, which point towards the presence of two fundamentally different erosional regimes in this small study area. These regimes are sharply delineated along a topographically modest tectonic ridge. To the west, a detachment-limited erosion regime prevails, while in the east a transport-limited regime is dominant. The presence or absence of gypcrete, whose prevalence is governed by (micro-) climatic conditions, generally appears to reflect the respective erosional regimes. The erosion rates we infer point to a long-term process of differential drainage evolution in the study area, likely on timescales of millions of years.

Late Quaternary slip rate of the Central Sierra Madre fault, southern California: Implications for slip partitioning and earthquake hazard

The Sierra Madre fault system accommodates contraction within a large restraining bend area of the San Andreas fault along the northern margin of the Los Angeles metropolitan area in southern California. Reverse slip along this fault system during earthquakes controls growth of the San Gabriel Mountains and poses a significant seismic hazard to the region. Here, we measure the late Quaternary slip rate of the Central Sierra Madre fault (CSMF) using analysis of high-resolution topography combined with cosmogenic 10Be surface exposure dating and post-IR IRSL geochronology. We mapped terrace and fan surfaces from three drainages that cross the CSMF and correlate them based on deposit character and geomorphic position. Cosmogenic nuclide and luminescence ages are consistent amongst the three prominent surfaces offset ∼5 to 28 m across the fault zone. Age estimates for these surfaces are 53 +21/−15 ka, 35 ± 9 ka, and 12±5 ka based on data from two dating methods at three locations, refined by inset age relationships. Estimated slip for these geomorphic markers is more uncertain than the measured vertical separation due to uncertainties in fault dip and ranges from 7.5 +5.4/−3.1 m to 58.5 +46.3/−14.4 m. Incremental dip-slip rate estimates from different age surfaces and locations overlap within uncertainty, with median values ranging from 0.6 to 1.1 mm/yr. The average slip rate for all three generations of markers is 1.1 +1.1/−0.4 mm/yr. This late Quaternary slip rate for the CSMF is slower than estimates based on interseismic geodetic data, and emphasizes the importance of contraction distributed across multiple structures south of the Sierra Madre fault when assessed against the geodetic shortening budget. Despite being the central portion of the broader Sierra Madre fault system, the CSMF has a slip rate similar to or lower than neighboring sections, suggesting that slip transfer onto other nearby faults control the along-strike pattern of deformation rate. Paleoseismic evidence indicates that the last earthquake on the CSMF was in the early Holocene, and the slip rate we estimate suggests that the accumulated elastic strain could produce many meters of slip in future earthquakes.

Millennial-scale denudation rates in the Himalaya of Far Western Nepal

Abstract. The Himalayas stretch ∼3000 km along the Indo-Eurasian plate boundary. Along-strike variations in the fault geometry of the Main Himalayan Thrust (MHT) have given rise to significant variations in the topographic steepness, exhumation rate, and orographic precipitation along the Himalayan front. Over the past 2 decades, the rates and patterns of Himalayan denudation have been documented through numerous cosmogenic nuclide measurements in central and eastern Nepal, Bhutan, and northern India. To date, however, few denudation rates have been measured in Far Western Nepal, a ∼300 km wide region near the center of the Himalayan arc, which presents a significant gap in our understanding of Himalayan denudation. Here we report new catchment-averaged millennial-scale denudation rates inferred from cosmogenic 10Be in fluvial quartz at seven sites in Far Western Nepal. The inferred denudation rates range from 385±31 t km−2 yr−1 (0.15±0.01 mm yr−1) to 8737±2908 t km−2 yr−1 (3.3±1.1 mm yr−1) and, in combination with our analyses of channel topography, are broadly consistent with previously published relationships between catchment-averaged denudation rates and normalized channel steepness across the Himalaya. These data show that the denudation rate patterns in Far Western Nepal are consistent with those observed in central and eastern Nepal. The denudation rate estimates from Far Western Nepal show a weak correlation with catchment-averaged specific stream power, consistent with a Himalaya-wide compilation of previously published stream power values. Together, these observations are consistent with a dependence of denudation rate on both tectonic and climatic forcings, and they represent a first step toward filling an important gap in denudation rate measurements in Far Western Nepal.

A NW-striking dextral strike-slip fault at the eastern end of the Altyn Tagh fault and its tectonic implications for northeastward growth of the Tibetan Plateau

The eastern end of the Altyn Tagh fault connects the western Qilian Shan thrust belt and its foreland basin, the Hexi Corridor, which contains numerous active faults with various strikes and kinematics. Although understanding of the geometry and kinematics of these active faults is increasing, the deformation pattern since the late Quaternary in the western end of the Hexi Corridor remains controversial. Studying the geometry and kinematics of these faults provides great benefit for understanding regional deformation patterns. The North Kuantan Shan fault (NKTSF) is located at the eastern end of the Altyn Tagh fault and the western end of the Hexi Corridor. Remote sensing images and field investigations suggest that the NKTSF strikes NW and acts as a right-lateral strike-slip fault with a reverse component. Optically stimulated luminescence (OSL) data combined with vertical offsets of the fault scarp imply a range of vertical slip rates of 0.015–0.093 mm/a, and cosmogenic 10Be ages and displacements of river terrace risers suggest a range of horizontal slip rates of 0.25–0.71 mm/a. The geometry and kinematics of the NKTSF enable us to estimate the deformation pattern in the western Hexi Corridor, which indicates that this area is undergoing northeastward compression related to the northern Tibetan Plateau (Qilian Shan). Active faults in the region are driven by the northeastward push of the Tibetan Plateau rather than the eastward extension of the Altyn Tagh fault.

Spatial patterns of erosion and landscape evolution in a bivergent metamorphic core complex revealed by cosmogenic 10Be: The central Menderes Massif (western Turkey)

AbstractIn extensional provinces with low-angle normal faulting (such as the Aegean region), both tectonic processes and erosion induce landscape change, but their interaction during the evolution of topography and relief accompanying continental extension has rarely been addressed. Here we present local and catchment-wide 10Be erosion rates that document the spatial pattern of erosion in the central Menderes Massif, a metamorphic core complex consisting of two asymmetric mountain ranges (Bozdağ and Aydın) bound by detachment faults and active grabens. Catchment-wide erosion rates on the northern flank of the Bozdağ Range are rather low (40–110 mm/k.y.) but reach values of >300 mm/k.y. on the steep southern escarpment—a pattern that reflects both topography and bedrock lithology. In the Aydın Range, erosion rates are generally higher, with mean erosion rates of ∼190 and ∼260 mm/k.y. on the northern and southern flank, respectively, and more variable along strike. In both ranges, erosion rates of ridge crests derived from amalgamated clasts are 30–90 mm/k.y. The difference between local and catchment-wide erosion rates indicates that topographic relief increases in most parts of the massif in response to ongoing fault-related uplift and concomitant river incision. Our findings document that tectonic processes exert a significant control on landscape evolution during active continental extension and are reflected in both the topographic signature and the spatial pattern of erosion. In the Menderes Massif, rock susceptibility to weathering and erosion is a dominant factor that controls the erosional contribution to rock exhumation, which varies spatially between ∼10% and ∼50%.

The SPICE project: Production rates of cosmogenic 21Ne, 10Be, and 14C in quartz from the 72 ka SP basalt flow, Arizona, USAu

The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40 Ar/ 39 Ar age of 72 ± 4 ka (2σ). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic 21 Ne, 10 Be, and 14 C have been determined from SP flow quartz. Production rate ratios for 21 Ne/ 10 Be, 21 Ne/ 14 C, and 14 C/ 10 Be are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2σ uncertainty) of 4.44 ± 0.32, 1.43 ± 0.10, and 2.85 ± 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 21 Ne, 10 Be, and 14 C are 17.0 ± 1.1, 3.84 ± 0.27, and 11.2 ± 0.6 at/g/yr (2σ), respectively, using time-independent Lal (1991)/Stone (2000) ( St ) scaling factors. St scaled spallogenic 10 Be and 14 C rates are 3.73 ± 0.26 and 9.2 ± 0.6 at/g/yr, respectively. 21 Ne and 10 Be production rates are integrated over the past 72 ka, whereas 14 C production rates are integrated over 25 ka, the time at which SP flow quartz has reached saturation with respect to 14 C. These rates overlap within 2σ uncertainty with other St -scaled production rates in the literature, including the total reference SLHL 21 Ne production rate of Niedermann (2000), which is revised in this paper to 16.8 ± 3.3 at/g/yr (2σ; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SLHL production rates are lower if time- dependent Sf , Sa , and Lm scaling factors are used. For example, error-weighted mean, sea-level, high latitude (SLHL) total reference production rates for 10 Be as calculated in the CREp online calculator range from 3.49 ± 0.23 to 3.74 ± 0.25 at/g/yr (2σ), using time-dependent Lm scaling factors. Commonly used SLHL 10 Be and 14 C production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field is proposed to have been weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. However, our study finds no measureable difference between St -scaled production rates of cosmogenic 21 Ne and 10 Be over the past 20 ka and St -scaled 21 Ne and 10 Be production rates over the past 72 ka. As such, the study suggests that 21 Ne and 10 Be production rates in quartz were not significantly greater during the proposed period of decreased magnetic strength from 20 to 50 ka. • Total reference production rates at SLHL are calculated in 72 ka quartz. • Cosmogenic 21 Ne, 10 Be, and 14 C rates ( St ): 17.0 ± 1.1, 3.84 ± 0.27, and 11.2 ± 0.6 at/g/yr. • These rates agree with St scaled production rates over past 20 ka in literature. • There is a proposed period of decreased geomagnetic field strength from 20 to 50 ka. • SPICE rates do not record increased cosmogenic nuclide production over past 72 ka.

Measurements of beryllium isotopes in ice wedges in Alaska

To explore the possibility of using ground ice archives for studies of the cosmogenic radionuclide 10Be, we analyzed the beryllium isotopes in ice wedges exposed in the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel and the Barrow Permafrost Tunnel in Alaska. We determined the concentrations of 10Be and 9Be in samples pretreated following two procedures: acidification before (procedure A) and after (procedure B) removal of particles. The 10Be and 9Be concentrations spanned wide ranges. Concentrations in procedure A samples were higher than those in procedure B samples. The 10Be/9Be ratios fell within a narrow range, and values from CRREL (about 8.5 × 10−9) and Barrow (about 7 × 10−9) were of the same order of magnitude. Further studies are needed to validate our findings and assess the feasibility of using the 10Be/9Be ratio of syngenetic ice wedges for reconstruction of 10Be variations due to cosmogenic and environmental changes, and radiometric dating of ice-wedge sequences that contain very old (beyond 1 Ma) ice.

The age of Wolfe Creek meteorite crater (Kandimalal), Western Australia

AbstractWolfe Creek crater lies in northwestern Australia at the edge of the Great Sandy Desert. Together with Meteor Crater, it is one of the two largest craters on Earth from which meteorite fragments have been recovered. The age of the impact is poorly constrained and unpublished data places the event at about 300,000 years ago. In comparison, Meteor Crater is well constrained by exposure dating. In this paper, we present new ages for Wolfe Creek Crater from exposure dating using the cosmogenic nuclides 10Be and 26Al, together with optically stimulated luminescence ages (OSL) on sand from a site created by the impact. We also present a new topographic survey of the crater using photogrammetry. The exposure ages range from ~86 to 128 ka. The OSL ages indicate that the age of the impact is most likely to be ~120 ka with a maximum age of 137 ka. Considering the geomorphic setting, the most likely age of the crater is 120 ± 9 ka. Last, we review the age of Meteor Crater in Arizona. Changes in production rates and scaling factors since the original dating work revise the impact age to 61.1 ± 4.8 ka, or ~20% older than previously reported.

Differential erosion and sediment fluxes in the Landquart basin and possible relationships to lithology and tectonic controls

This paper focuses on the Landquart drainage basin, where we explore geomorphic signals related to the spatial differences in bedrock lithology and differential uplift. We use concentrations of cosmogenic 10Be to quantify the sediment flux patterns in the region. Furthermore we use the chemical composition of the fine fraction (< 63 μm) of the river sediment to determine the provenance of the material, and we quantify the landscape properties through the calculation of normalized steepness values for the tributary basins. The results show that the upstream segment of the Landquart basin is a glacially imprinted landscape and contributes to about 20–50% of the total modern sediment flux of the Landquart River. Contrariwise, the landscape of the downstream part is dominated by a V-shaped landscape where tributary basins are characterized by a generally high steepness. This downstream area has delivered about 50–80% of the total eroded material. Because this lowermost part of the Landquart basin is c. 50% smaller than the upstream region (200 km2 downstream versus 400 km2 upstream), the sediment budget points to very high erosion at work in this lowermost segment. Interestingly, the bedrock of this area comprises flysch and particularly ‘Bündnerschiefer’ deposits that have a high erodibility. In addition, apatite fission track ages are much younger (c. 5–10 Ma) than in the headwater reaches (10–30 Ma). This suggests the occurrence of ongoing yet long-term rock uplift that has occurred at higher rates in the downstream segment than in the headwaters. It appears that the landscape shape and denudation rate pattern in the Landquart basin reflect the combined effect of tectonic processes and fast surface response, where uplift has promoted the exhumation of bedrock with high erodibilities, and where the low erosional resistance of the exposed lithologies has promoted the streams to respond by fast erosion.

Comparative numerical surface exposure-age dating (10Be and Schmidt hammer) of an early-Holocene rock avalanche at Alstadfjellet, Valldalen, southern Norway

ABSTRACTApplication of calibrated Schmidt-hammer surface-exposure dating (SHD) to the run-out debris of a rock avalanche at Alstadfjellet, Valldalen, southern Norway, has yielded ages that are consistent within uncertainties with terrestrial cosmogenic 10Be surface-exposure ages for the debris. SHD calibration was based on young and old control sites that were, respectively, recent road cuts / rockfall boulders of known age, and Younger Dryas moraines for which 10Be ages had been obtained. Three SHD calibration equations were generated based on different correction factors for the 10Be ages from the moraines. The SHD ages (10.3 ± 0.59–11.1 ± 0.64 ka) for the run-out debris are from 1.1 ka to 1.3 ka older than the corresponding 10Be ages (9.2 ± 0.7–9.8 ± 0.7 ka). In addition, the former ages have a precision of 1.18–1.28 ka (95% confidence intervals) as opposed to 2.8 ka (2σ range) for the latter ages. This work demonstrates that calibrated SHD can be of comparable accuracy to and may have improved precision over 10Be ages, and should be given greater consideration and prominence in Quaternary dating studies.

Climatic reconstruction for the Younger Dryas/Early Holocene transition and the Little Ice Age based on paleo-extents of Argentière glacier (French Alps)

Investigation of Holocene extents of mountain glaciers along with the related naturally-driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change. Here, we present the first Holocene glacial chronology in the Mont-Blanc massif (Argentière glacier) in the French Alps, based on 25 in situ-produced cosmogenic 10Be dates of moraines and glacial bedrocks. The obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its Lateglacial extent and oscillated several times between ∼11.7 ka and ∼10.4 ka, i.e. during the Younger Dryas/Early Holocene (YD/EH) transition, before substantially retreating at ∼10.4 ka. Climate conditions corresponding to the past extents of Argentière glacier during the YD/EH transition (∼11 ka) and the Little Ice Age (LIA) were modelled with two different approaches: by determining summer temperature differences from reconstructed ELA-rises and by using a Positive Degree Day (PDD) mass-balance model. The ELA-rise reconstructions yield a possible range of temperatures for the YD/EH transition that were lower by between 3.0 and 4.8 °C compared to the year 2008, depending on the choice of the ELA sensitivity to temperature. The results from the PDD model indicate temperatures lower by ∼3.6–5.5 °C during the YD/EH transition than during the 1979–2002 period. For the LIA, our findings highlight the role of local precipitation changes, superimposed on the dominant temperature signal, in the detailed evolution of the glacier. Overall, this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents.

Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquí River Catchment, Eastern Cordillera, NW Argentina

AbstractUnraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles, 10Be‐derived catchment mean modern and paleo‐erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquí River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base‐level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo‐erosion rates, ranging from 56 +43/‐19 to 105 +60/‐33 mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic 10Be. However, punctuated abandonment of pediment and strath terraces at 43.6 +15.0/‐11.6, 91.2 +54.2/‐22.2, and 151 +92.7/‐34.1 ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long‐term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional‐scale studies which find precipitation to exert the dominant control.