Theory suggests that the response time of alluvial-channel systems to perturbations in climate can be related to the magnitude and direction of the forcing, and the length of the system; shorter systems may record a higher frequency of forcing compared to longer systems. The Toro Basin in the Eastern Cordillera of NW Argentina has preserved a suite of eight alluvial-fan deposits along the western flanks of the Sierra de Pascha. Farther downstream, a flight of cut-and-fill terraces have been linked to eccentricity-driven (100-kyr) climate cycles since ca. 500 ka. We applied cosmogenic radionuclide (¹⁰Be) exposure dating to the fan surfaces to explore (1) how channel responses to external perturbations may or may not propagate downstream, and (2) the differences in landscape response to forcing frequency as a function of channel length when comparing the upper basin alluvial fan deposits with the lower basin terrace sequence. Our new Toro ¹⁰Be dataset consisted of 30 boulder samples from the fan surfaces and five pebble samples from a fan depth profile. We identified two generations of fan surface; the first (G1) and second (G2) generations record surface activity and abandonment between ca. 800 and 500 ka, and within the last 100 kyr, respectively. G1 fans record a prolonged phase of net incision, which has been recognised throughout the Central Andes, and was likely triggered by prolonged and enhanced global glacial cycles following the Mid-Pleistocene Transition. Relative fan surface stability followed, while 100-kyr cut-and-fill cycles recorded by the fluvial terraces persisted downstream, suggesting a disconnect in behaviour between the two reaches. G2 fans record higher frequency climate forcing, possibly the result of precessional forcing of climate (ca. 21/40-kyr timescales). The lack of a high-frequency signal farther downstream provides field support for theoretical predictions of a filtering of high-frequency climate forcing with increasing channel length. We show that multiple climate periodicities can be preserved within the sedimentary record of a single basin. Differences in the timing of alluvial fan and fluvial terrace development in the Toro Basin appear to be associated with how channel length affects fluvial response times to climate forcing as well as local controls on net incision, such as tectonic deformation.

How to cite: Orr, E., Schildgen, T., Tofelde, S., and Wittmann-Oelze, H.: Landscape response to tectonic deformation and cyclic climate change since ca. 800 ka in the southern Central Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1456, https://doi.org/10.5194/egusphere-egu24-1456, 2024.

Cosmogenic nuclide burial dating exploits the differential decay rate of a nuclide pair, typically ²⁶Al and ¹⁰Be. There are three basic approaches; simple burial dating, the isochron method and P-PINI (Particle Pathway Inversion of Nuclide Inventories). The simple burial age is based on deviation from the surface production ratio assuming quick and deep burial. The isochron method incorporates multiple samples from a single stratigraphic layer and assumes steady erosion in the sediment source area. P-PINI accommodates more complicated situations, such as landscapes undergoing non-steady erosion and an eroding or accumulating sink zone. This source-to-sink model uses a Monte Carlo simulator to create a library of plausible erosional and depositional histories and then compares those histories against measured nuclide data to derive a burial age estimate. In cases involving multiple dated layers in a section or when an independent age estimate is available, a Bayesian tool further constrains the burial age.

With the aim of constraining the timing of the Eurasian Ice Sheet at its largest known extent, we applied P-PINI at Wapenveld in the Netherlands and at Szczerców in central Poland. From a drill-core at Wapenveld we collected three sand samples from the Early Pleistocene ‘Hattem’ beds, and derived the P-PINI burial age bracketed by simple burial ages calculated from the units above and below. Szczerców is an open-cast mine exposing multiple Middle Pleistocene till units rich in cobble-sized clasts. Here, P-PINI burial ages show sensitivity to the thickness of the dated layer, a problem we resolve by including feldspar infrared-simulated luminescence dates higher up the sequence.

We discuss the pros and cons of our approach at Wapenveld and Szczerców. Burial dating multiple units in section requires considerably more lab effort but also offers important advantages that can be boosted by carefully considering which grain-size to sample, and by incorporating independent age constraints.

How to cite: Ylä-Mella, L., Wagner, K., Margold, M., Knudsen, M. F., Busschers, F., Bakker, M., Wachecka-Kotkowska, L., Krzyszkowski, D., Wieczorek, D., Szuman-Kalita, I., Eriksen, B. L., Andersen, J. L., Olsen, J., Perić, Z., Alexanderson, H., and Jansen, J. D.: Unveiling the early Eurasian glaciations with new advances of 10Be-26Al burial dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11574, https://doi.org/10.5194/egusphere-egu24-11574, 2024.

Improving our understanding of the timing, rates and distribution of erosion across mountains and valleys plays a key part in resolving longstanding debates on how landscape dynamics are influenced by the interactions between climate, tectonics and erosion. In particular, the onset of glaciations and more variable climate in the Pliocene-Quaternary have been invoked to explain the observed global increase in erosion rates, arguing that glaciers are more efficient at eroding bedrock than rivers. But questions about the temporal and spatial impact of glacial erosion and potential feedback remain. To contribute to resolving this debate, we conducted a local-scale thermochronological study in the Tauern Window, Eastern European Alps, with the aim to compare our findings to patterns in the wider region and the Western Alps. The Tauern Window presents an ideal natural laboratory to isolate these interdependent effects due to its well constrained tectonic history of rapid uplift until ∼8 Ma. Comparatively, the western Alps have experienced similar glaciation but a different tectonic history, and show significantly higher geodetic uplift rates and millennial-timescale erosion rates. Thus, an East-West comparison could help shed light on the dominant controls on the laterally variable Alpine morphology.

Here, we present new apatite (U-Th)/He (AHe) data distributed along elevation profiles through several glacial valleys: the Italian Ahrntal and the Austrian Floitental, Krimmler Achental and Windbachtal. The low closure temperature of the AHe system is sufficiently sensitive to enable correlating recorded exhumation/denudation to surface processes and landscape-shaping dynamics, and allows us to examine the late-Cenozoic thermal history of the area. AHe dates range from ~3.4 to 12.5 Ma; the youngest dates are thus time congruent with the onset of glaciation.

Our data indicate variations in erosion rates with elevation down these valleys, which we suggest can be attributed to altitude-dependent glacial erosion intensity. These patterns are compared to a hypsometric analysis of the Eastern Alps, to determine possible links between observed denudation over the last few million years and present-day markers of glacially reshaped topography. This study also provides initial insight into the best suited locations for a future higher-resolution investigation using ⁴He/³He thermochronometry, which promises to be able to resolve the area’s denudation history into the Quaternary and allow for a more direct comparison to modern hypsometry. These findings will also inform a future focused investigation into landscape-shaping couplings discernible from thermochronological data used alongside landscape analysis via thermal-kinematic modelling in PecubeGUI.

How to cite: Wapenhans, I., van der Beek, P., Bernard, M., Colleps, C., and Amalberti, J.: Reconciling late Cenozoic spatio-temporal patterns of Alpine topographic changes from low-temperature thermochronology and glacial morphometric signatures , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16703, https://doi.org/10.5194/egusphere-egu24-16703, 2024.

Burial dating with two cosmogenic nuclides (e.g. ²⁶Al and ¹⁰Be) is unveiling the last 5 million years of the sedimentary record. There is no dating method of comparable reliability for the fragmentary records typical of terrestrial settings. For the first time, we can explore events on the same timescale as mountain-building, we can reconstruct landscapes that predate the initiation of the northern hemisphere glaciations, and we can explore milestones in the evolution of our species. Here we focus on illustrating the latter: two field sites in which ¹⁰Be-²⁶Al burial dating has reshaped our understanding of early human dispersal in Eurasia. Both are well known Palaeolithic sites hosting Mode-1-type stone tools that despite being intensively studied have not been dated conclusively by other methods.

At Korolevo on the Tysa River in western Ukraine, alluvium containing stone tools is dated to 1.42 ± 0.10 Ma using the burial dating model, P-PINI (Particle-Pathway Inversion of Nuclide Inventories). Korolevo stands as the earliest securely dated hominin presence in Europe and bridges the spatial and temporal gap between the Caucasus (~1.85–1.78 Ma)and southwestern Europe (~1.2–1.1 Ma). Our findings advance the hypothesis of colonisation of Europe from the east well before the Middle Pleistocene Transition.

At Diring Yuriakh on the Lena River in eastern Siberia, stone tools are buried by aeolian sand sheets. We combine optically stimulated luminescence dating with the P-PINI burial dating model to yield an age of 417 ± 82 ka, which is at least 300 kyr earlier than the previously documented earliest human presence north of 60 degrees. This timing overlaps with exceptional warmth across the High North during the ‘super-interglacial’ MIS 11c (426–396 ka), suggesting that warm climate intervals permitted human migration well beyond widely accepted territorial bounds.

Reflecting on these advances, we evaluate the pros and cons of burial dating relative to other widely used dating approaches in archaeology and palaeoanthropology.

How to cite: Jansen, J. D., Knudsen, M. F., Garba, R., Andersen, J. L., Buylaert, J.-P., Kameník, J., Kurbanov, R. N., Lachner, J., Lukyanycheva, M., Margold, M., Murray, A. S., Nørgaard, J., Olsen, J., Rugel, G., Stübner, K., Usik, V., and Ylä-Mella, L.: Redrawing early human dispersal patterns with cosmogenic nuclides , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4168, https://doi.org/10.5194/egusphere-egu24-4168, 2024.

Turbidites are underwater land sliding events that correspond to the most distal part of the source-to-sink system. They can be triggered by a number of processes including flood events, storms, earthquakes or simply destabilization of a continental slope and are a vector of terrestrial sediments to deep depocenters. Marine sedimentary cores recording turbidites represent key sedimentary archives and can be used to track back the occurrence of such land and sea processes giving information on terrestrial paleo conditions.

Unfortunately, it is often difficult to assess which process initiated turbidites in particular because these are usually poorly dated. In most studies, turbidites are considered as instantaneous events and dated using foraminifera of the over and underlying hemipelagic layers. In this study, we bring new light on the age of the material remobilized by turbidites. To do so, we use ¹⁴C to date 20 samples of foraminifera and 38 samples of vegetal debris contained in two turbidites from two different cores of the Ogooué turbiditic system in western Africa. We have also dated foraminifera in the hemipelagic layers above and under these turbidites. The radiocarbon ages measured in the turbidites, when compared to the depositional ages of under- and overlying hemipelagic layers constrain the total transportation time from the source to the turbidite deposition, including both the duration of transport on land, and the potential storage of the sediments onshore and offshore (on the continental margin).

Our results shed new light on the transport and residence time of sediments in the Ogooué drainage system which is under 15 ka, on the residence time of sediments on the continental slopes or margins which is of about 3 ka, and on the depositional sequences and mechanisms of turbidites in said system. In a broader sense, it allows a better understanding of the mechanisms controlling turbidite deposition and its intrinsic timings. 

How to cite: Large, E., Hage, S., Dennielou, B., Charreau, J., and Blard, P.-H.: Age of deposition versus age of remobilized sediments in turbidites and implication for the duration of transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20370, https://doi.org/10.5194/egusphere-egu24-20370, 2024.

Luminescence and radiocarbon dating methods are mandatory to set up reliable chronological frameworks for sedimentary systems to reconstruct climate and environmental changes quantitatively through time. Our study area, the Basin of the Great Lakes in Western Mongolia is a key area to investigate sediment archives and sediment pathways under variable climates in this region including extreme continental climatic conditions.  Alluvial fans, beach bars and dune fields, partly interacting with each other, were sampled for luminescence dating in detail. In this study, a total of thirty-four samples were taken from a beach ridge sequence of Khyargas Nuur and tested using K-feldspar single aliquot (2.5 mm) pIRIR dating to overcome the problem of the dim signal of quartz. Furthermore, single grain dating was also conducted to address the problem of insufficient bleaching of the pIRIR signals. The preliminary established chronological framework indicates that the studied samples were mostly deposited during the Holocene and the results yielded a continuous decline of the lake level for most of the Holocene period.

How to cite: Frechen, M., Rahimzadeh, N., Wolf, D., and Lehmkuhl, F.: Sediment Dating of Fluvial, Lacustrine and Aeolian Systems in the Basin of the great Lakes, Western Mongolia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12491, https://doi.org/10.5194/egusphere-egu24-12491, 2024.

The Albanian Dinarides represent the central segment of the Dinarides–Hellenides orogenic belt. The Albanian sector is strategically located at the boundary between continental subduction to the north and oceanic subduction to the south, making it an ideal setting to explore the interplay between surface and deep geological processes. Furthermore, modern seismicity (e.g. 1979, Mw 7.1 Montenegro, and 2019, Mw 6.4 Durres earthquakes) and geomorphic features indicate ongoing tectonic activity at least since the late Quaternary. In this study, we explore the landscape response to tectonics and climate by 1) conducting an extensive geomorphic analysis including knickpoint extraction, ksn and chi analysis, longitudinal river profile projection, and mapping of geomorphic features such as windgaps, river terraces, pediment surfaces and uplifted relict landscapes, and 2) estimating basin-wide denudation rates using cosmogenic nuclides.

Specifically, we collected river sediment samples from more than 20 rivers draining all tectonic units and we determined denudation rates using the classic in situ 10Be technique for catchments draining quartz-bearing lithologies, and the new meteoric 10Be/9Be technique in carbonate and ophiolite settings where quartz-poor lithologies predominate. In a few cases, we used both techniques on the same catchments for inter-method comparison. 

The geomorphic analysis highlights the presence of river terraces, non-lithological knickpoints, uplifted relict landscapes and wind gaps suggesting recent tectonic activity at both regional and local scales. This led to a reshaping of the river network with changes in the hydraulic connectivity with the regional sea level that altered the sediment transport directions. Furthermore, Quaternary climatic variations appear to play a crucial role in the erosive power of rivers and in controlling cycles of aggradation and incision.

Denudation rates show spatial variability, ranging from less than 0.3 mm/yr to 0.9 mm/yr in the south, where carbonate and siliciclastic predominate, to over 1 mm/yr in the central part of Albania, where siliciclastic rocks and ophiolites are widely exposed. Although the rates present a good correlation with geomorphic metrics (e.g., ksn and hillslope), the observed variability appears to be influenced by local tectonic processes associated with active normal faults and salt diapirism. Overall, the denudation rates obtained with the two Be techniques are consistent and align with published incision rates derived from river terrace dating, suggesting coupling between fluvial incision and hillslope processes over the last few thousands of years. The consistency between the two cosmogenic Be methods validates the high future potential of the meteoric 10Be technique in quantifying denudation rates in settings dominated by non-quartz lithologies.

How to cite: Bazzucchi, C., Crosetto, S., Wittmann, H., Ballato, P., Faccenna, C., Muceku, B., and Rossetti, F.: The morphotectonic evolution of the Albanian Dinarides: new insights from the application of in situ and meteoric Be cosmogenic nuclides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-433, https://doi.org/10.5194/egusphere-egu24-433, 2024.

Meteoric ¹⁰Be is a cosmogenic nuclide produced in the atmosphere and delivered to Earth’s surface by precipitation, whereas stable ⁹Be is a trace metal released from bedrock during weathering. The ratio (¹⁰Be(meteoric)/⁹Be) is set in the critical zone, where beryllium is either adsorbed to fine-grained sediment or is dissolved in water if the pH-dependent retentivity of Be is low. A prerequisite for calculating denudation and weathering rates over millennial timescales is knowledge of the flux of ¹⁰Be deposition to Earth surface and the concentration of ⁹Be in the unweathered parent bedrock. We provide a review of applications of the ¹⁰Be/⁹Be system to Earth surface studies that covers a variety of quartz-bearing rocks, lithologies largely void of quartz like mafic rocks, mixed lithologies, and, most recently, carbonate and marble lithologies.

We show the versatility of this new approach in several case studies. These range from small creek-scale mafic basins in the European midlands, medium-sized (10²-10³ km²) catchments covered by slate and marble in the rapidly eroding Taiwan Island, pure carbonate rocks from the French Jura Mountains, to large catchments draining mixed lithologies in the Chilean Andean Cordillera and the Amazon and Ganga river basins. We find that i) across all spatial scales, the dissolved and sediment-bound ¹⁰Be/⁹Be ratios agree well, indicating equilibrium of phases. Approximately at medium-sized catchment scales, ii) the ⁹Be concentration from published databases from typical parent rocks (http://earthref.org/GERM) represents the local bedrock ⁹Be concentration, but for much smaller and carbonate catchments, a locally representative bedrock concentration has to be determined on a case-by-case basis; and iii) local measurements of the depositional ¹⁰Be flux from the ¹⁰Be inventory of independently-dated deposits like e.g. terrace profiles appear to yield the most reliable estimates. Under these constraints, derived denudation and weathering rates agree in all settings to within less than a factor of 2 with either decadal-scale denudation rates from combined suspended and dissolved river fluxes or with in situ-¹⁰Be-derived denudation rates where quartz is present. This close agreement shows that ¹⁰Be/⁹Be ratios from such rock types yield meaningful denudation rates obtained from sub gram-sized amounts of sediment, independent of the spatial scale of sampling ranging from a single soil profile to the scale of the Amazon river basin. Small sample amounts and the independence of the presence of quartz provide a benefit over the “sister” nuclide in situ ¹⁰Be that has been widely used in landscapes of felsic rocks. Now, with ¹⁰Be/⁹Be, the determination of rates of Earth surface change in quartz-poor lithologies opens up entirely new opportunities.

How to cite: Wittmann, H., Bouchez, J., Deng, K., Gaviria-Lugo, N., Bernhardt, A., and von Blanckenburg, F.: Denudation and weathering rates from meteoric 10Be/9Be: A versatile tool in mafic, carbonate or slate-dominated lithologies from the critical zone to very large catchments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11084, https://doi.org/10.5194/egusphere-egu24-11084, 2024.

The authigenic ¹⁰Be/⁹Be dating method has emerged as a novel chronometer in the last few decades. Initially introduced by Bourles et al. (1989: Geochim. Cosmochim. Acta) for dating of oceanic sediments the method has been successfully applied to date continental sediments in some recent studies. The method utilizes decay of cosmogenic radionuclide ¹⁰Be to date the deposition of sediment in the range of 0.2 to ~14 Ma. Different source of the two isotopes ⁹Be and ¹⁰Be results in changes in the authigenic ¹⁰Be/⁹Be ratio (R) as the sediment gets transported from deltaic to offshore settings through shelfal environment. Accurate determination of initial ¹⁰Be/⁹Be ratio (R₀) is of paramount importance in this dating method to calculate the correct age of the deposited sediment. It is therefore necessary to quantify the variability of authigenic initial ratio for the effective application of the method.

This study aims to describe the variability of authigenic ¹⁰Be/⁹Be ratio in temporal as well as spatial scale. We analyzed the samples for authigenic ¹⁰Be/⁹Be ratio from two different study sites, the Late Miocene to Quaternary Slanicul de Buzau section in Romania and the Holocene Po River delta plain in Italy. 109 samples were sampled from Slanicul de Buzau section with a sampling step resolution of ~20–30 ka aiming to interpret ratio variability in temporal scale. Po coastal plain yielded 50 samples from 4 different parasequnces (5,6,7 and 8) (Amorosi et al., 2017: Mar. Pet. Geol.) to cover the variability in spatial scale. The analysis of samples from these study sites allowed us to understand the variability of the ratio in terms of sediment source proximity and change in sediment provenance.

Back calculation of initial ratio R₀ in 109 samples from Slanicul de Buzau section with the help of measured authigenic R and interpolated magnetostratigraphic age of samples reveals low variability in R₀ in deltaic and shallow water sediments, while the offshore facies exhibit significantly higher variability.

Results from measured ratio R in 50 samples of Po Plain does not show a drastic variability, slightly higher R in the samples from parasequence 6 can be attributed to the different provenance of this parasequence in contrast to the sediment source of the latter parasequences (Amorosi et al., 2020: Basin res.).

This observed low variability of authigenic ¹⁰Be/⁹Be reveals the good suitability of the dating method for river dominated deltas. We have also attempted to propose a minimum number of sample count necessary to be analyzed when using this dating method. The approach aims to estimate the sample size dependency of the ratio by running 1000 simulations and bootstrapping to estimate the 95% CI for variability of ratio, taking into consideration the three statistics namely, range, IQR, and SD. Bootstrapping performed in our data, in a particular group of n samples (e.g., samples from a specific facies type), suggests that at least nearly half the sample size of n is necessary to represent the initial ratio variability and to avoid the potential bias caused by the initial ratio variability.

How to cite: Aherwar, K., Šujan, M., Braucher, R., Chyba, A., De Leeuw, A., Matoshko, A., Amorosi, A., Campo, B., Rózsová, B., Lalinská-Voleková, B., and Team, A.: Variation of authigenic 10Be/9Be in spatial and temporal scale and its implications for applicability of dating method for river dominated deltas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10959, https://doi.org/10.5194/egusphere-egu24-10959, 2024.

Changes in climate coupled with long-term uplift cause alluvial rivers to aggrade or incise, resulting in the formation of fluvial terrace sequences. Such terrace records provide an opportunity to investigate past interactions between climatic forcings, tectonics, and fluvial systems. Further, they allow us to infer potential channel responses to future climatic change. To accurately decipher such interactions, precise age constraints on fluvial terraces are vital. However, established dating methods such as cosmogenic exposure dating are costly, time intensive, and require direct access to terrace surfaces. Thus, their application is not always possible.

An alternative approach to dating fluvial terraces is based on the temporal evolution of the step (riser) between successive terraces. Downslope sediment transport and elevation change, commonly modelled by hillslope diffusion equations, cause a decrease in gradient with time. If the profile of a riser is obtained in high resolution via GPS or LiDAR elevation measurements, its shape can be related back to the terrace age using inverse modelling schemes.

Here, we apply this theory to a set of fluvial terraces situated along the Río Santa Cruz and Río Shehuen in Patagonia, Argentina. A set of existing ¹⁰Be terrace exposure ages of up to ca. 1 Ma from both rivers is used for age verification and model calibration. GPS elevation transects of terrace risers measured during a field campaign in 2023 are used to establish an age chronology with negligible elevation uncertainties. To explore the feasibility of this method without access to field-quality elevation data, we also test the viability of using riser profiles derived from ca. 12 m resolution TanDEM-X data for dating. Preliminary results from synthetic riser profiles with elevation uncertainties similar to those of TanDEM-X data indicate that such DEM-derived age estimates are theoretically accurate. However, application to the Patagonian river systems and comparison against independent ¹⁰Be ages shows a wide spread in absolute age estimates for single terrace generations. Therefore, in this case, the method appears to be viable only for relative age classification. Post-abandonment riser disturbances and spatially variable sediment transport rates may be key factors hindering our ability to integrate large numbers of DEM-derived profiles into a unified interpretation. Obtaining more robust absolute age estimates may require the use of landscape evolution models that incorporate more complex, non-diffusive processes. Further, the viability of this method may be reduced for very old (i.e., ca. 1 Ma) terraces. Application to younger terrace systems may yield more accurate results.

This technique provides a low-cost, spatially extendable way of dating fluvial terraces and analysing landscape dynamics in fluvial systems. We are currently preparing to release an open-source Python library containing the tools needed to perform these analyses.

How to cite: Grimm, L., McNab, F., Fernandes, V. M., and Schildgen, T.: What can DEMs tell us about the ages of fluvial terraces?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9499, https://doi.org/10.5194/egusphere-egu24-9499, 2024.

Rapidly eroding mountain ranges act as major sources for the export of clastic sediments, solutes and organic matter from the continents to the oceans, and thereby affect the global climate via the sequestration of atmospheric CO₂ into geological reservoirs. At the same time, mountainous landscapes experienced Quaternary variations in climate and vegetation – including the waxing and waning of glacial ice masses – and were therefore exposed to temporally varying erosional regimes. In the specific case of soil-mantled hillslopes, changing environmental conditions (e.g., temperature, precipitation) along with spatially variable topographic parameters (e.g., slope, aspect) are expected to modify the geomorphic processes responsible for the mobilization and downslope movement of soil material, such that soil erosion might represent a function of both space and time. Furthermore, transient soil erosion is likely coupled to alterations of the soil thickness and hence to changes in the production of soil material from the underlying bedrock. In this study, we investigate the spatio-temporal variability of soil production and erosion on different soil-covered alpine landforms within the Goms area (Switzerland), based on paired measurements of the in situ ¹⁴C and ¹⁰Be concentrations within quartz separates of saprolite (n=12) and till-derived (n=2) samples. The short half-life of ¹⁴C compared to ¹⁰Be provides this approach with a unique sensitivity for short-term changes of soil production and/or soil thickness on Lateglacial to Holocene time scales. For multiple sites, the apparent soil production rates and exposure ages calculated from the cosmogenic nuclide concentrations reveal a constant exposure of the saprolite-soil interface, without any (detectable) signs of soil production or changes to the thickness of the overlying soil column since the Early to Mid-Holocene. The absence of soil production in combination with a constant vertical extent of the soils further implies that the erosional downslope transport of soil material is inactive at these locations, despite their generally steep slope angles (10 to 38°). Remarkably, the estimated exposure ages also differentiate between relatively young samples (¹⁰Be: 5.5 to 7.8 ka; ¹⁴C: 5.4 to 7.9 ka) from tributary hillslopes and older samples (¹⁰Be: 10.2 to 12.0 ka; ¹⁴C: 9.6 to 12.7 ka) from the hillslopes of the main valley and erosional ridges, which represent important landforms within the investigated landscape. Additional results from Markov chain Monte Carlo inversion modelling indicate the potential occurrence of instantaneous losses of the soil cover (9.3 to 14.7 m at 7.6 to 8.7 ka) or the step-like decline of soil production rates (11- to 12-fold at 12.4 to 13.1 ka) for most of the remaining samples. Overall, these observations demonstrate the co-occurrence of ‘static’ sites without active soil production and erosion and more ‘dynamic’ sites characterized by transient, non-zero soil production and erosion rates, attesting to the spatial variability of hillslope soil dynamics between an active and an inactive state.

How to cite: Wartenweiler, S. H., Lupker, M., Haghipour, N., Christl, M., and Eglinton, T. I.: Hillslopes in action? Combining in situ 14C- and 10Be-derived insights into the spatio-temporal variability of soil dynamics on Swiss alpine hillslopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15601, https://doi.org/10.5194/egusphere-egu24-15601, 2024.

Up until now, the cosmogenic radioisotope ³⁹Ar has not been used for surface exposure or burial dating of minerals due to its low concentration in rocks and the large sample size requirements for its detection by low-level counting. The novel analytical method Atom Trap Trace Analysis (ATTA) – already well established for gas samples from groundwater, ocean water or ice cores – can measure the isotopic ratio of ³⁹Ar to stable Ar in the range of 10^-16 on just a few ml STP of argon and therefore opens up new possibilities for applying ³⁹Ar.

This talk will report on the initial steps taken towards using ³⁹Ar as a geochronometer. Calculations of production rates of ³⁹Ar in typical continental rocks, exposed to cosmic radiation at the Earth surface, show that sample sizes of the order of 100 g of rock should yield a sufficient number of ³⁹Ar atoms (order 10³ to 10⁴) for detection by ATTA. However, the amount of ⁴⁰Ar in such samples – and therefore the total extractable Ar amount - is much lower than what is typically extracted from ice and water samples, which contain atmosphere-derived Ar. The ⁴⁰Ar content in rock stems from ⁴⁰K-decay and depends on the rock formation age and the potassium content. Dilution with ³⁹Ar-free Ar results in sufficient total argon volumes for the standard ATTA analysis.

Gas extractions from heated rock samples indeed show ³⁹Ar isotope abundances 2-3 orders of magnitude above the atmospheric ratio, well within the measurement range of ATTA after dilution. In order to check the feasibility of exposure dating of rocks, several samples were taken for comparison from boulders of glacier moraines, previously dated with ¹⁰Be, in the Jamtal valley in Austria. Additionally, ¹⁰Be-dated samples from other moraine sites are to be analysed for ³⁹Ar for further validation of ³⁹Ar as a tool for exposure dating. As of now it remains to be seen whether reliable agreement between the dating methods can be achieved. Due to its relatively short half-life of 268 years, ³⁹Ar would be a useful addition in multi-tracer studies on geologic processes within the last two millennia.  

How to cite: Neumann, F., Arck, Y., Gardner, W. P., Schaefer, J., Singhateh, M. L., Oberthaler, M., and Aeschbach, W.: Early development of Argon-39 as a new geochronometer for geologic processes on short time scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9605, https://doi.org/10.5194/egusphere-egu24-9605, 2024.

Measurement of multiple cosmogenic nuclides in single samples is valuable for various applications. For exposure dating, multiple-nuclide systematics are important for correcting exposure ages for surface weathering and erosion, as well as quantifying when and how often a surface has experienced burial. Currently, such constraints from paired ²⁶Al/¹⁰Be/²¹Ne measurements in quartz are common practice and well established. However, ³⁶Cl/¹⁰Be/³He nuclide measurements in pyroxene would provide more precise constraints because the range in decay constants is greater. In Antarctica, the pyroxene-bearing Ferrar Dolerite is one of the dominant lithologies of clast exposed at the surface of many surficial deposits throughout the Transantarctic Mountains. While cosmogenic ³He measurements in Ferrar pyroxene are routine, ¹⁰Be and ³⁶Cl measurements are less common and not well established. Here we present recent advances in multiple cosmogenic nuclides measured in the Ferrar pyroxene, which includes (i) improvements in the extraction of ¹⁰Be and ³He from pyroxene grains, (i) production rate estimates of ¹⁰Be in pyroxene and ³⁶Cl from Ca spallation, and (iii) understanding and quantifying the non-cosmogenic inventories of ³He and ³⁶Cl in pyroxene for accurate exposure dating.

How to cite: Bergelin, M. and Balco, G.: Advances in Cosmogenic Nuclides measured in Ferrar Pyroxene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13590, https://doi.org/10.5194/egusphere-egu24-13590, 2024.

The western European Alps are characterised by deeply incised valleys, however the timing of their formation and the impact of Quaternary glaciation on rates of erosion remains disputed. This is mainly due to a lack of geochronological methods that cover the timespan of 10³-10⁶ years. Electron spin resonance (ESR) thermochronometry has a high potential to fill this temporal gap because of its low closure temperature (<100 °C), potentially allowing changes in erosion rates to be related to glacial advance and retreat. The Rhône Valley (Switzerland) was intensively glaciated during the Quaternary [1] while it is unclear how tributary valleys incised throughout the glaciation period. In this study, we focus on two study sites along the main valley, close to Sion and Visp and the Matter and Vispa river tributary valleys, towards Zermatt and Saas-Fee to compare their Quaternary exhumation histories.  Whilst bedrock samples from Sion yielded cooling ages between 209 and 674 ka, samples from Visp showed saturation around 2500 ka. Thermal stability varied between samples and signals, and sample measurement is ongoing. Preliminary inversion of the data shows that the low closure temperatures of the ESR signals in quartz allow the Late Quaternary exhumation of the Alpine valleys to be resolved, providing new insights into the glacial incision history during the Quaternary and especially how erosion rates varied temporally under a changing climate.

Reference:

[1] Valla, P.G., D.L. Shuster, and P.A. van der Beek. 2011. Significant increase in relief of the European Alps during mid-Pleistocene glaciations, Nature Geoscience. 4(10): p. 688-692.

How to cite: Wen, X., Bartz, M., Schmidt, C., and King, G.: ­­­­­ESR-thermochronometry in the western European Alps (Switzerland) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17371, https://doi.org/10.5194/egusphere-egu24-17371, 2024.

Multiple elevated temperature infra-red stimulated luminescence (MET-IRSL) has great potential to provide detailed information on the movement of sediment grains through time and space. MET-IRSL stimulates grains using infra-red light at a series of elevated temperatures to access multiple charge populations with different bleaching behaviours. Length of past light exposure and duration of storage events can be determined by the relative difference between multiple signals, or ages, for a single grain. With more signals, we can see deeper into the history of an individual grain.

Single-grain measurements paint a fine-resolution picture of how a system operates, often masked by multiple grain average measurements. The power of single-grain measurement is underpinned by three basic principles: 1) A single grain has a single transport-storage history (Rhodes and Leathard, 2022), 2) Populations of >200 grains per sample allows for quantitative estimation of the most likely, or ‘dominant’ history for a given sample, 3) It is possible to isolate different grain populations, with different histories or provenance within a single sample.

Using samples collected from the active channel of the Allt Dubhaig in Scotland, we present results from a bleach recovery experiment to illustrate an optimal method for quantifying most likely length of past light exposure using single grains, and a gaussian mixture model approach to isolating different grain populations within a single sample. Combined with a numerical model of single-grain bleaching and burial, we apply these approaches to elucidate past and present fluvial sediment transport information for the Allt Dubhaig, Scotland, and the Santa Clara River, southern California.

How to cite: Spano, T., Rhodes, E., and Hodge, R.: Using single-grain multiple elevated temperature luminescence to understand fluvial sediment transport at the system scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11032, https://doi.org/10.5194/egusphere-egu24-11032, 2024.