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Wind-abraded cobbles (ventifacts) and aeolian sand are known from the sandy-gravelly coastal areas of south-western Sweden, especially in association with raised deltas. Ventifacts are recorded on at least two different stratigraphic levels, at some sites atop glaciofluvial sediment, at other sites atop littoral deposits, and in some places at both levels, while aeolian sand usually forms a surficial cover. The formation of ventifacts has usually been coupled to abrasion due to katabatic winds from the retreating ice sheet or with periglacial climate during the Younger Dryas stadial (12.8–11.7 ka). To determine the timing of these deflation events, we have applied a combination of dating methods to ventifacts and associated sediments on top of an ice-contact delta at Veinge, south-western Sweden. Quartz and feldspar luminescence dating as well as portable luminescence profiling has been used for littoral and aeolian sediments over- and underlying deflation surfaces, while rock surface luminescence burial dating and paired 14C–10Be cosmogenic nuclide dating were conducted on ventifacts. The results show that a first deflation event occurred c. 16.5 ka, just after deglaciation and prior to a regional transgression that peaked around 15.7 ka. At 12.4–11.4 ka, during the Younger Dryas stadial, a new set of ventifacts formed on the surface of the exposed littoral sands and gravels. Some wind abrasion also occurred in the early Holocene, but at c. 8.5 ka the surface was covered by aeolian sand, up to 2.5 m thick. The combination of different dating methods have allowed us to draw more informed conclusions on the timing and duration of these wind abrasion/transport events than would have been possible from the use of only single-method dating. It has also made it possible to infer some environmental conditions during deposition. For example, both glaciofluvial and littoral deposits show evidence of incomplete bleaching of the luminescence signal. This suggests short subaerial transport and brief reworking by waves, respectively, though bleaching conditions improved during shore regression. Rock surface burial luminescence profiles reveal that some ventifacts were repeatedly exposed, but that later event(s) were shorter in duration as indicated by quartz-feldspar age comparisons. [Display omitted] • Wind-abraded clasts and aeolian sand occur on an ice-contact delta in SW Sweden. • Three erosional (deflation, abrasion) and one depositional event are recorded. • Luminescence and cosmogenic exposure dating place the events between 17 and 8.5 ka. [ABSTRACT FROM AUTHOR]

Abstract Gour de Tazenat is a maar volcano on the crystalline Plateau des Domes, the uplifted margin of the Limagne Rift of the Massif Central of France, and forms one of the northernmost volcanic centers of the Chaîne des Puys volcanic field. Although long recognized as a relatively young volcanic center in the area, age determinations have been elusive, with the only one quantitative estimate based upon radiocarbon ages of bulk sediments in the crater lake and extrapolation of sedimentation rates to account for the full thickness of the sediments; that age is ∼35 cal ka. Here we test application of cosmogenic 10Be exposure dating to quartz-bearing subvolcanic rocks exposed in the wall of the maar crater. Considering erosion rates (∼5 m/Myr) that we determined from 10Be data on a nearby tor (located outside the crater), and corroborated by inverted relief of older, dated lavas in the region, the 10Be data yield an age of 29–34 ka for the maar-forming eruption of Gour de Tazenat. This is consistent with the one previous quantitative estimate, and provides confidence in the age range of the maar. This age corresponds to a pulse of volcanic activity around 30 ka in other parts of the Chaîne des Puys. [ABSTRACT FROM AUTHOR]

Abstract: Over 30 samples from bedrock and boulders from the Veliki vrh rock avalanche have been collected for surface exposure dating. The limestone rocks have been radiochemically treated to isolate and determine long-lived 36Cl by accelerator mass spectrometry. It could be shown that the Veliki vrh rock avalanche from the Košuta Mountain (Slovenia) event can be very likely linked to one of the major historical earthquakes in Europe happening on the 25th of January 1348. Taken into account independently determined denudation rates, inherited 36Cl originating from pre-exposure at shallow depths (20–55 m) could be calculated. The high amount of inherited 36Cl, i.e. 17–46% of the total 36Cl, makes this site not suitable for a precise determination of the 36Cl production rate as it was originally anticipated. Veliki vrh is a “classic” rock avalanche of high velocity. The slope failed in the upper part with a translational slide predominantly along the bedding planes, whereas dynamic fragmentation is the cause for further crushing of the material and the long runout. [Copyright &y& Elsevier]

The Lavini di Marco rock avalanche deposit (“Marocca di Marco”) is located along the left side of the middle Adige Valley, south of the town of Rovereto (NE Italy). The deposit is estimated to have a volume of ∼2 × 108 m3 and cover an area of ∼6.8 km2. It comprises Jurassic Calcari Grigi limestones that detached from the western slope of Mt. Zugna Torta. The Lavini di Marco is composed of at least two different rock avalanche bodies, the main deposit known as Lavini di Marco (the principal) and the much smaller Costa Stenda deposit. Costa Stenda deposits overlie Lavini di Marco deposits. Samples for 36Cl exposure dating were collected from boulders within the deposits, from sliding plane bedrock and from the bedrock wall at the head scarp. Exposure ages range from 800 ± 210 to 21310 ± 1000 years. The latter age stands as a notable outlier suggesting that that Costa Stenda boulder was exposed for a considerable amount of time in the pre-slide bedrock. Lavini di Marco and Costa Stenda boulder ages are 2600 ± 200, 2700 ± 200, 3100 ± 300, 3300 ± 300, 3400 ± 300, 4400 ± 290, 5300 ± 300, and 5400 ± 300 years. The latter three are Costa Stenda boulders which we also interpret to contain inherited nuclide concentrations. The five remaining boulder ages cluster around 3000 years. We calculate a mean age for the Lavini di Marco and Costa Stenda rockslides of 3000 ± 400 years. Within the uncertainties of our data the two slides were simultaneous. For the bedrock sliding plane we obtained significantly younger ages, 1600 ± 100 and 1400 ± 100 years, and for the head scarp 800 ± 200 years. The sliding plane ages record small-scale reactivation which seems to overlap in time with a catastrophic flood event of the Adige River in Verona, as reported in the Fulda Annales, in 883 AD. Only the single age of 800 ± 210 years suggests activity at Lavini di Marco coincident with the well-known Verona earthquake (1117 AD). [ABSTRACT FROM AUTHOR]

We reconstruct the timing of ice flow reconfiguration and deglaciation of the Central Alpine Gotthard Pass, Switzerland, using cosmogenic 10Be and in situ 14C 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 Bølling 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 situ 14C data are overall in good agreement with the 10Be ages and confirm continuous exposure throughout the Holocene. However, in situ 14C demonstrates that partial surface shielding, e.g. by snow, has to be incorporated in the exposure age calculations and the model of deglaciation. [ABSTRACT FROM AUTHOR]

Abstract: Precariously balanced rocks (PBRs) are freestanding boulders that are precarious or fragile in the sense that they could be toppled by relatively low-amplitude earthquake ground motion. They are important in paleoseismology because their continued existence limits the amplitude of ground motion experienced at their location during their lifetime. In order to make quantitative use of PBRs for seismic hazard studies, one must determine when they attained their present state of fragility, that is, the point in time when the contact between the rocks and the pedestals on which they rest was exhumed from surrounding soil and the rock became vulnerable to earthquake ground motions. Cosmogenic-nuclide exposure dating can be used for this purpose, but is complicated because nuclide production occurs throughout exhumation of the PBR, so the apparent exposure age of any part of the rock surface exceeds the time that the rock has actually been precariously balanced. Here we describe a method for determining the length of time that a PBR has been fragile by measuring cosmogenic-nuclide concentrations at several locations on the PBR surface, and linking them together with a forward model that accounts for nuclide production before, during, and after exhumation of the PBR. Fitting model to data yields the rate and timing of rock exhumation and thus the length of time the rock has been fragile. We use this method to show that an example PBR in southern California has been fragile for 18.7 ± 2.8 ka. [Copyright &y& Elsevier]

Abstract: 3He is among the most commonly measured terrestrial cosmogenic nuclides, but an incomplete understanding of the 3He production rate has limited robust interpretation of cosmogenic 3He concentrations. We use new measurements of cosmogenic 3He in olivine from a well-dated lava flow at Tabernacle Hill, Utah, USA, to calibrate the local 3He production rate. The new 3He measurements (n = 8) show excellent internal consistency and yield a sea level high latitude (SLHL) production rate of 123 ± 4 at g−1 yr−1 following the / scaling model [Lal, D., 1991. Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters, 104, 424–439.; . Air pressure and cosmogenic isotope production. Journal of Geophysical Research, 105, 23753–23759.]. We incorporate the new measurements from Tabernacle Hill in a compilation of all published production rate determinations, characterizing the mean global SLHL production rates (e.g. 120 ± 9.4 at g−1 yr−1 with /Stone (2000)). The internal consistency of the global 3He production rate dataset is as good as the other commonly used cosmogenic nuclides. Additionally, 3He production rates in olivine and pyroxene agree within experimental error. The 3He production rates are implemented in an age and erosion rate calculator, forming a new module of the CRONUS-Earth web-based calculator, a simple platform for cosmogenic nuclide data interpretation [Balco, G., Stone, J., Lifton, N.A., and Dunai, T.J., 2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements. Quaternary Geochronology, 3, 174–195.]. The 3He calculator is available online at http://www.cronuscalculators.nmt.edu/. [Copyright &y& Elsevier]

Abstract: We have measured 36Cl in three rock surfaces of the Yenicekale building complex in Hattusha (Boğazköy, Turkey). Hattusha was the capital of Hittite Empire which lasted from about 1650/1600 to 1200 BC. At Yenicekale, Hittite masons flattened the summit of an outcropping limestone knoll to form an artificial platform as the foundation for a building. Next they built a circuit wall along the lateral precipices of the flattened bedrock platform. We took one sample from the limestone bedrock platform and two samples from limestone building blocks of the circuit wall for cosmogenic 36Cl analysis. Calculated exposure ages are 20±1ka for the sample from the bedrock platform and 24±1ka and 52±2 ka for the circuit wall blocks. These exposure ages are significantly older than the age expected based on the estimated time of construction between 3.2ka and 3.7ka. We conclude that the sampled surfaces contain significant inherited cosmogenic 36Cl. We cannot directly determine exposure ages for the building complex based on these three samples. On the other hand we may use the measured concentrations to determine how much of the rock was removed from the platform during flattening. To this end we modeled the variation of 36Cl production with depth at Yenicekale using the results from the bedrock sample. We conclude that the Hittite masons removed only around 3m from top of the limestone block. This means that the volume of rock removed from the bedrock platform is significantly less than the volume in the circuit wall atop the platform. They did not gain enough rock from this flattening to make the building. In agreement with this, the first results of our detailed microfacies analysis indicate that many of the building blocks are not of the same facies as the underlying limestone and must have been quarried elsewhere. Although we were not able to exposure date the Yenicekale complex due to the presence of inherited 36Cl, our data suggest that Hittite masons excavated (most of) the building stones not at Yenicekale, but in quarries outside of Hattusha and then transported them to the construction site. These quarries have not yet been identified. [Copyright &y& Elsevier]

Abstract: We propose guidelines for the reporting of in situ cosmogenic nuclide data for exposure age and erosion rate determinations. This is motivated by the need to maintain the utility of such data in the future, and to delineate best scientific practice. These guidelines will allow published exposure ages and erosion rates to be recalculated with confidence by others in the future, if, as is likely, procedures to calculate cosmogenic nuclide production rates are modified in the meantime. [Copyright &y& Elsevier]

Abstract: We have used cosmogenic 3He to date pre- and post-collapse lava flows from southwestern Fogo, Cape Verdes, in order to date rift zone magmatic reorganisation following the lateral collapse of the flank of the Monte Amarelo volcano. The post-collapse flows have exposure ages ranging from 62 to 11ka. The analysis of multiple flow tops on each lava flows, often at different elevations, provides an internal check for age consistency and the exposures ages conform with stratigraphic level. The exposure ages suggest that volcanic activity along the western branch of the triple-armed rift zone was more or less continuous from before 62ka to approximately 11ka. The absence of magmatic activity for the last 11kyr reflects a structural reconfiguration of the volcano and may be related to renewed flank instability. This volcanic hiatus is similar in duration to that observed in the Canary Islands. Replicate 3He exposure ages of a pre-collapse flow (123.0±5.2ka) brackets the time of the Monte Amarelo collapse between 62ka and 123ka. Reproducible cosmogenic 3He exposure ages of less than 123ka from flows away from major erosion features demonstrates that the technique is a viable alternative to the radiocarbon, K/Ar and 40Ar/39Ar chronometers for dating recent volcanism in arid climate zones. [Copyright &y& Elsevier]

Abstract: We codify previously published means of calculating exposure ages and erosion rates from 10Be and 26Al concentrations in rock surfaces, and present a single complete and straightforward method that reflects currently accepted practices and is consistent with existing production rate calibration measurements. It is intended to enable geoscientists, who wish to use cosmogenic-nuclide exposure age or erosion rate measurements in their work to: (a) calculate exposure ages and erosion rates; (b) compare previously published exposure ages or erosion rate measurements on a common basis; (c) evaluate the sensitivity of their results to differences between published production rate scaling schemes. The method is available online at http://hess.ess.washington.edu. [Copyright &y& Elsevier]

In the high mountain rock walls of the Mont Blanc massif, changes in the granite surface colour are related to its exposure age. The light grey colour of fresh rock surfaces turns orange when is long exposed to weathering. In order to study this colour/age relationship, reflectance spectroscopy was performed on 73 samples, and Terrestrial Cosmogenic Nuclide (TCN) dating was used to obtain their surface exposure age. The standard deviation of the reflectance values was calculated for each wavelength of the visible spectrum to study the behaviour of each spectral region. The aim was to find two colour regions that showed opposite behaviour, and once they are combined, they could provide a representative index of the rock colour changes that are linked to the degree of weathering. As an adaptation of the Green Red Vegetation Index used to measure colour changes in vegetation, the GReen-Infrared GRanite Index (GRIGRI), a normalized difference between the granite 770 nm and 530 nm reflectance values, was developed. The GRIGRI value of a weathered granite surface has a close relationship with its exposure age (R2 = 0.85). The reflectance spectra of seven samples for which TCN dating failed and two samples for which the TCN age was considered to be an outlier were used to calculate their GRIGRI value to assess the colour-based ages, that were plausible according to rock wall morphology and the TCN exposure ages of the surrounding surfaces. We propose a new method of surface dating for the rock walls of the Mont Blanc massif using reflectance spectroscopy. • Mont Blanc granite surface colour is related to the time that it has been exposed to weathering. • Reflectance spectroscopy was used to quantify granite surface colour. • TCN dating was used to estimate granite surface exposure age. • We use different approaches to explore the relationship between the granite colour and its exposure age. • The ratio between the Green and Infrared reflectance values can be used to estimate granite exposure age. [ABSTRACT FROM AUTHOR]

In situ cosmogenic nuclides are widely employed to quantify topographic and geomorphic landscape evolution. However, few studies are devoted to investigating possibly unsteady denudation. In this work the denudation rates of five surface bedrock and one depth profile are measured using in situ cosmogenic 36Cl in different climate zones in China; cosmogenic 36Cl is a powerful proxy for the surface denudation processes of carbonate landscapes in different climatic gradients since carbonates are more sensitive to climate change than silicates. Compiling previous worldwide surface denudation studies in different gradients, we find that: (I) denudation rate increases systematically with mean annual precipitation (MAP) in arid climatic zones (MAP lower than ~700 mm yr−1) and is dominated by long-term climatic gradients; (II) humid climatic zone (MAP greater than ~700 mm yr−1) denudation rates are about constrained to 34.1 ± 11.7 mm kyr−1 by carbonate dissolution kinetics; and (III) denudation rate is also influenced by short-term physical erosion or abrupt erosive events. Accordingly, the reconstructed evolutionary history of the Guizhou depth profile results from either a relatively high denudation rate (55.5 –4.4 +5.6 mm kyr−1) and long duration exposure (274 –147 +120 ka), or an alternative a low denudation rate (0.8 –0.8 +13.3 mm kyr−1) and a recent abrupt erosive event (13.0 –1.6 +1.9 ka). These two possible solutions suggest that assumed long-term averaged denudation rate can conceal episodic erosion events. Given tectonic quiescence we propose that climate change might mainly control an erosive event during the last glacial termination (~14 ka), which also implies that caution should be taken when determining the denudation rate of a landscape where climate change and/or tectonic activity plays an important role. [ABSTRACT FROM AUTHOR]