Cosmogenic Research Articles

Reducing uncertainty in source area exploration of mineralized glacial erratics using terrestrial cosmogenic radionuclide dating

Mineral exploration often relies on sedimentary indicators as first signs of a potential nearby mineralization in bedrock. The transportation of sediment by glacial and fluvial processes introduces uncertainty into the tracing of potential source areas of the sediment. This is particularly challenging in areas where glacial erosion has been weak, resulting in reworking of sediments and multiple directions of transportation. In this study we explore the use of Terrestrial Cosmogenic Nuclides (TCN) alongside conventional mineral exploration methods to better link indicators with their potential source areas.The study focuses on a mineral exploration project site in northern Finland in a region with stratigraphic evidence of multiple glaciations. The project targets the source of discovered Au mineralized erratic boulders that have been deposited atop the most recent till unit. The superposition suggests transportation in the latest glacial event. However, the 10Be (35.9 ± 1.3 and 30.3 ± 1.1 ka) and 26Al TCN ages analyzed from the mineralized erratics precede the latest glacial event, suggesting the possibility of multiple stages of transportation. The local bedrock TCN inventories (48.9 ± 1.9 and 85.3 ± 2.8 ka) are well preserved, suggestive of weak glacial erosion and therefore short recent transportation distances for the mineralized erratics. By combining the TCN interpretation and historical ice flow directions derived from the till stratigraphy, we suggest a nearby source locating NNW of the dated erratics.We find that TCN dating can limit some of the transportation related uncertainties in glaciated terrain. Through the analysis of TCN inventories from bedrock and boulders it is possible to characterize glacial erosion and boulder transportation, and to identify repeated exposure events, i.e., the possibility of multi-staged transportation. The method benefits from combined use of stratigraphic investigations that can identify both the local transportation directions and local glacial coverage history. TCN sampling has a minimal environmental impact, can be used in remote areas and can provide information about the transport history already in the early stages of exploration. Although the analysis is time consuming, the survey is light to conduct and informative even with a small number of samples.

Combining geomorphological and kinematic models to analyze tectonic deformation rates: A case study of the Bayin anticline in the eastern Tian Shan Mountains

Quantitatively characterizing the geometry, kinematics, and deformation rate of fold-thrust belts in intermontane basins is the key to understanding strain partitioning within the Tian Shan range. This work focuses on the Bayin anticline in the Youludusi Basin, a typical intermontane basin located within the eastern Tian Shan. The Kaidu River cuts through the Bayin anticline and has developed three levels of terraces (T1–T3) across the structure. By using cosmogenic nuclide and optically stimulated luminescence dating methods, the formation ages of terraces T1 and T3 are constrained to 11.54 ± 0.55 ka and 42 + 7.0/−7.1 ka, respectively. When applying a listric thrust fault model to the Bayin anticline and using terraces as references, the vertical displacements are estimated to be 16.45 + 6.46/−3.19 m (T1), 32.08 + 12.85/−6.19 m (T2), and 95.93 + 38.94/−18.6 m (T3), and the shortening amounts are 10.56 + 8.33/−5.04 m (T1), 20.46 + 16.68/−9.64 m (T2), and 61.24 + 50.22/−28.93 m (T3). Based on this listric thrust fault model and terrace T1–T3 ages, the rate of fault slip controlling the growth of the Bayin anticline is determined to be 1.6 ± 1.0 mm/yr, and the crustal shortening rate of the anticline is 1.0 + 0.7/−0.6 mm/yr. The estimated crustal shortening deformation of the Bayin anticline accounts for ∼12 % of the total deformation in the Youludusi Basin. In terms of the entire orogenic belt, the crustal shortening absorbed in the southern, central, and northern parts accounts for 24 %–56 %, 46 %–71 %, and 19 %–74 %, respectively, of the total strain across the eastern Tian Shan. Therefore, we believe that the Eastern Tianshan undergoes uniform deformation.

Inherited terrestrial cosmogenic nuclides in landscapes of selective glacial erosion: lessons from Lochnagar, Eastern Grampian Mountains, Scotland

ABSTRACTInheritance from prior exposure often complicates the interpretation of terrestrial cosmogenic nuclide (TCN) inventories in glaciated terrain. Lochnagar, a mountain in eastern Scotland, holds a clear geomorphological record of corrie glaciation and the thinning of the last Scottish ice sheet over the last ~15 ka. Yet attempts to date the main stages in deglaciation after sampling of 21 granite boulders for 10Be, 26Al and 14C from corrie moraines, an ice sheet lateral moraine and boulder spreads revealed widespread, but variable, TCN inheritance. Only the youngest boulder ages fit within the range of expected deglaciation ages. To identify the sources of geological uncertainty, we provide simple models of ice cover duration and erosion histories for plateau, corrie and strath landscape domains, identify the variable nuclide inheritance that derives from different sources for boulders in these domains, and outline the effects of rotation, splitting and erosion of boulders during glacial transport. The combined effects increase clustering around arbitrary mean TCN values that exceed deglaciation ages. A further implication is that boulders have survived beneath overriding ice sheets. Such boulder trapping at Lochnagar may have resulted from topographic controls on katabatic winds and surface ablation acting on a thinning, cold‐based ice sheet.

Quantifying denudation rates and sediment recycling of low-relief, high-elevation landscapes using in-situ and meteoric cosmogenic nuclides

Quantifying Earth’s surface denudation rates is crucial for estimating sediment flux and its role in regulating global climate change. The inability of in-situ cosmogenic 10Bein to quantify denudation rates in quartz–free environment has prompted the need for a new proxy–the ratio of meteoric 10Bemet to mineral-weathered 9Be in reactive phase (precipitated in or adsorbed onto secondary minerals). This study utilized 10Bein–26Alin, 10Bemet/9Be, and major element analyses of reactive and mineral phases of bedload sediments to infer basin-wide denudation rates and sediment recycling (reworking of deeply buried sediments) in the Three River Source Region (TRSR) of the central Tibetan Plateau. Results from 10Bein-26Alin analysis of bedload sediments and bedrock samples (quartz grain, 250–500 μm) suggest that the sediments underwent burial events since at least 0.54 ± 0.16 million years ago. Combining paleoclimate records in the central Tibetan Plateau, we interpret the “Great Burial” as most likely the result of climate-controlled deglaciation and denudation at the termination of Naynayxungla glaciation during the MIS 13–15 period. This event marks the first widespread deglaciation on the Tibetan Plateau. The 10Bein-26Alin derived paleo–denudation rates range from 4.2-0.8+0.9 to 151-32+37 mm/kyr, consistent with previous 10Bein–derived modern denudation rates of 10–117 mm/kyr in TRSR. These rates show a moderate positive correlation with regional topography, particularly channel steepness, indicating a decrease in both relief and denudation rates from lower to upper streams. This spatial discrepancy is likely due to enhanced river headward incision and active neotectonic activities in the southeast. Denudation rates derived from the 10Bemet/9Be proxy range from 13 to 248 mm/kyr, alongside a chemical weathering intensity ranging from 43 % to 67 %. These denudation rates are strongly correlated with, but about 1.5 times higher than, the 10Bein–26Alin derived paleo–denudation rates from the same watershed. This suggests that the 10Bemet/9Be extracted from fine grains (<64 μm) may reflect a different sediment recycling pattern compared to 10Bein–26Alin in quartz sediments. Alternatively, the 10Bemet/9Be ratio could indicate a mixture of carbonate rock with a high denudation rate and silicate rock with a lower denudation rate, whereas 10Bein–26Alin reflects a single silicate denudation signal.

Complex erosional response to uplift and rock strength contrasts in transient river systems crossing an active normal fault revealed by 10Be and 26Al cosmogenic nuclide analyses

AbstractUnderstanding the influence of bedrock lithology on the catchment‐averaged erosion rates of normal fault‐bounded catchments and the effect that different bedrock erodibilties have on the evolution of transient fluvial geomorphology remain major challenges. To investigate this problem, we collected 18 samples for 10Be and 26Al cosmogenic nuclide analysis to determine catchment‐averaged erosion rates along the well‐constrained Gediz Fault system in western Türkiye, which is experiencing fault‐driven river incision owing to a linkage event ~0.8 Ma and has weak rocks overlying strong rocks in the footwall. Combined with existing cosmogenic data, we show that the background rate of erosion of the pre‐incision landscape can be constrained as &lt;92 mMyr−1, and erosion rates within the transient reach vary from 16 to 1330 mMyr−1. Erosion rates weakly scale with unit stream power, steepness index and slip rate on the bounding fault, although erosion rates are an order of magnitude lower than slip rates. However, there are no clear relationships between erosion rate and relief or catchment slope. Bedrock strength is assessed using Schmidt hammer rebound and Selby Rock Mass Strength Assessments; despite a 30‐fold difference in erodibility, there is no difference in the erosion rate between strong and weak rocks. We argue that, for the Gediz Graben, the strong lithological contrast affects the ability of the river to erode the bed, resulting in a complex erosional response to uplift along the graben boundary fault. Weak covariant trends between erosion rates and various topographic factors potentially result from incomplete sediment mixing or pre‐existing topographic inheritance. These findings indicate that the erosional response to uplift along an active normal fault is a complex response to multiple drivers that vary spatially and temporally.

Multi-tracer approach to constrain groundwater flow and geochemical baseline assessments for CO2 sequestration in deep sedimentary basins

Geological storage of gases will be necessary in the push to net zero and the energy transition to reduce carbon emissions to atmosphere. These include CO2 geological storage in suitable sandstone reservoirs. Understanding groundwater flow, connectivity and hydrogeochemical processes in aquifer and storage systems is vital to prevent risk and protect important water resources, such as the Great Artesian Basin. Here, we provide a ‘tool-box’ of geochemical assessment methods to provide information on flow patterns through the basin's aquifers (changes in chemistry along flow path), stagnant versus flowing conditions (cosmogenic isotopes and noble gases), inter-aquifer connectivity and seal properties (major ions, Sr and stable isotopes), water quality (major ions and metals) and general assessments on residence times of groundwater (cosmogenic isotopes and noble gases). This information can be used with reservoir and groundwater models to inform on possible changes in the above-mentioned processes and serve as input parameters for CO2 injection impact modelling. We demonstrate the use and interpretation on an example of a potential CO2 storage geological sequestration site in the Surat Basin, part of the Great Artesian Basin, and the aquifers that overly the reservoir. The stable water isotopes are depleted compared to average rainfall and most likely indicate greater contributions from monsoonal rain events from the northern monsoonal troughs, where amount and rainout effects lead to the depletion rather than colder recharge climates. This is supported by the modern recharge temperatures from noble gases. Inter-aquifer mixing between the Precipice Sandstone reservoir and the Hutton Sandstone aquifer seems unlikely as the Sr isotope ratios are distinctly different suggesting that the Evergreen Formation is a seal in the locations sampled. Mixing, however, occurs on the edges of the basin, especially in the south-east and east where the Surat Basin transitions into the Clarence-Moreton Basin. Groundwater flow appears to be to the south in the Precipice Sandstone, with a component of flow east to the Clarence-Morton Basin. The cosmogenic isotopes and noble gases strongly indicate very long residence times of groundwater in the central south Precipice Sandstone around a proposed storage site. 14C values below analytical uncertainty, R36Cl ratios at secular equilibrium as well as high He concentrations and high 40Ar/36Ar ratios support the argument that groundwater flow in this area is extremely slow or groundwater is stagnant. The results of this study reflect the geological and hydrogeological complexities of sedimentary basins and that baseline studies, such as this one, are paramount for management strategies.

Modeling of Cosmogenic Cr Isotopes Produced in Lunar Rocks Compared With Existing Calculations and Measurements

AbstractThe nucleosynthetic Cr isotope anomalies provides useful information to trace the source and origin of extraterrestrial samples, but it is usually influenced by high‐energy cosmic rays, and evaluating such effect of cosmic rays in lunar samples is especially important. Those cosmic radiation particles (primary particles) can react with lunar materials, creating many secondary particles. Both primary and secondary particles can produce cosmogenic nuclides on the Moon. Radiation Environment and Dose at the Moon (REDMoon) is a novel GEANT4 Monte‐Carlo model built to simulate the interactions of space particles with the lunar surface and subsurface content. Using this model, we simulate the production of cosmogenic Cr isotopes (50Cr, 52Cr, 53Cr, 54Cr) at different depths of lunar surface, and compare the contribution of different reactions generating these nuclides. The results suggest that spallation reactions are the most important process producing cosmogenic Cr isotopes. We also analyze the relationship between 53Cr/52Cr and 54Cr/52Cr predicted by our model and compare it with different Apollo samples. As previously studied, we also find an approximate linear relationship between ɛ53Cr and ɛ54Cr, where ɛ53Cr (or ɛ54Cr) is the relative deviation from the standard 53Cr/52Cr ratio (or 54Cr/52Cr ratio), normalized to 1/10,000. Furthermore, we reveal a change of this linear relationship in different depths of lunar surface. Besides, we investigate how the slopes can be influenced by exposure age and the Fe/Cr ratio. With these additional factors carefully considered, the comparison between our modeled results and the measurements is better than previous studies.

Cosmogenic Isotopes in Lunar Soil: Solar Activity and the Exploding of Nearby Supernova

Cosmogenic Isotopes in Lunar Soil: Solar Activity and the Exploding of Nearby Supernova

Coupled luminescence and cosmogenic nuclide dating of postglacial deflation surfaces and sand drift on a raised ice-contact delta at Veinge, SW Sweden

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.

Exploring the potential of rock surface luminescence from glacial sediments: dating and transport history

The dating of moraine deposits can present challenges to standard geochronological methods; terrestrial cosmogenic nuclide (TCN), sediment luminescence and radiocarbon dating may suffer from problems of incomplete resetting (by inheritance, intermittent cover/exposure, transport under unfavourable conditions) and/or a lack of suitable (organic) material. Rock surface luminescence burial dating (RSLBD) offers an alternative approach with considerable potential in dating moraines. In RSLBD, large cobbles/boulders are targeted, rather than smaller grains usually used in luminescence dating. The age limit of RSLBD is much higher than that of radiocarbon dating, and rocks are much more readily available than organic material. In contrast to TCN dating, the effect of exposure prior to deposition can be measured. In this study, we sampled a broad selection of primarily granitic boulders of various sizes and shapes (e.g. different degrees of roundness and sphericity) from the Vimmerby Moraine, a prominent and accessible feature in southern Sweden dated using TCN to 14.4±0.9 ka. Our study was designed to test whether morphological characteristics can be used to discriminate in favour of the most light‐exposed boulders and minimize measurements of non‐exposed boulders. As expected, not all RSLBD ages can be attributed to the same depositional event, but the majority of the resulting ages provide a mean age of 13.0±1.5 ka, consistent with the cosmogenic nuclide dating of the Vimmerby Moraine. Despite the apparently successful TCN study, the luminescence–depth profiles measured in the buried surfaces of the sampled clasts indicate that &gt;50% of these moraine boulders were exposed to light (and cosmic radiation) before final deposition, implying some (presumably small) TCN inheritance; seven of the 16 boulders identified as light exposed were sufficiently bleached to be useful for RSLBD. These results and their implications in regard to transport and deposition of the sampled cobbles are critically discussed and evaluated.

Reconstructing Sunspot Number by Forward-Modelling Open Solar Flux

The open solar flux (OSF) is the integrated unsigned magnetic flux leaving the top of the solar atmosphere to form the heliospheric magnetic field. As the OSF modulates the intensity of galactic cosmic rays at Earth, the production rate of cosmogenic isotopes – such as 14C and 10Be stored in tree rings and ice sheets – is closely related to the OSF. Thus on the basis of cosmogenic isotope data, OSF can be reconstructed over millennia. As sunspots are related to the production of OSF, this provides the possibility of reconstructing sunspot number (SSN) and hence properties of the solar cycles prior to the first sunspot telescopic observations in 1610. However, while models exist for estimating OSF on the basis of SSN, the hysteresis present in OSF and the lack of a priori knowledge of the start/end dates of individual solar cycles means that directly inverting these models is not possible. We here describe a new method that uses a forward model of OSF to estimate SSN and solar cycle start/end dates through a Monte Carlo approach. The method is tested by application to geomagnetic reconstructions of OSF over the period 1845-present, and compared to the known SSN record for this period. There is a substantial improvement in reconstruction of both the SSN time series and the solar cycle start/end dates compared with existing OSF-SSN regression methods. This suggests that more accurate solar-cycle information can be extracted from cosmogenic isotope records by forward modelling, and also provides a means to assess the level of agreement between independent SSN and OSF reconstructions. We find the geomagnetic OSF and observed SSN agree very well after 1875, but do differ during the early part of the geomagnetic record, though still agree within the larger observational uncertainties.

Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

AbstractHow tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic 10Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.

Dating the late Miocene marine sediments around the southern middle Durance valley (Provence, SE France): new evidences for a Tortonian age

The present study aims dating the topmost 50 m of a 115 m-long core retrieved from a valley located in the Cadarache Area (Upper Provence, South East France). Based on burial dating by in situ produced cosmogenic nuclides (10Be, 26Al and 21Ne), and paleomagnetic analyses, a Tortonian age was determined for the sedimentary succession exhibited in the core. In addition, thin sections, grain size analyses and quartz morphoscopy were used to characterize a shallow marine environment and to correlate the sediment core to the surrounding exposed sections. When comparing the studied sedimentary record to global sea level estimates, we establish that the local Tortonian transgression was not synchronous with the global scale sea level high-stand, but happened more likely later, during a global regressive trend. The timing of the Tortonian flooding in Upper Provence was therefore most probably driven by regional tectonic forcing. Finally, the Tortonian shallow marine sediments are topped by lacustrine tight carbonates. These carbonates protect the marine sediments from the following major erosional events resulting from the Messinian sea level drop and from interglacial-glacial fluctuations that both yielded to the present-day valley topography.

Lower Palaeolithic in Korolevo I (Transcarpathia, Ukraine, East-Central Europe): the earliest in Europe?

A recently published article in “Nature” (Garba et al., 2024) claims that lithic finds in the lowermost artefact-bearing sediments of lithological unit 26 at the Korolevo I site (Transcarpathia, Ukraine) are the oldest in Europe, dated to ca. 1.42 Ma with cosmogenic nuclides of gravel pebbles. These surprisingly old dates were then used to build hypotheses on the geochronology and routes of the initial Homo erectus colonization of Europe from the east. The present author reviews all published and unpublished Lower Palaeolithic (LP) data of the Korolevo I site, the field investigations of which he also participated in the 1980s, and came to the following negative results. The dated pebbles in Korolevo I unit 26 are of “intrusive” character, they do not date unit 26 and its lithic finds. Also, the proposed Early Pleistocene interglacial MIS 47, 45 and 43 periods for the LP colonization of Europe either via Asia Minor and the Danube River valley or the Caucasus and the southern part of Eastern Europe do not correspond to the known palaeogeographic and archaeological data from Western Eurasia. Besides, our review of LP contexts in Korolevo I suggests that the so-called lowermost LP lithic artefacts found in situ in archaeological horizon VII within lithological unit 26 in Korolevo I in 1984-1986 are distributed randomly horizontally and vertically. Moreover, they are mostly unworked hyalodacite and siliceous sandstone pieces together with several artefacts redeposited from the sediments above. Accordingly, the only certainly LP material in Korolevo I we know so far is situated in archaeological horizon VI, which is geochronologically associated with the Middle Pleistocene inter-Mindel period or MIS 14, dated to ca. 550 ka BP. However, the Korolevo I site still appears to represent the oldest LP human occupation in both Eastern Central Europe and Ukraine.

10Be surface exposure dating of glacier fluctuations on the eastern slope of Mount Geladandong, central Tibetan Plateau

Moraine complexes formed by multiple glaciations are well-preserved in the Mount Geladandong area, the largest center of current glaciation in the Tanggula Mountains in western China. Studies of these glacial landforms provide insights into past glacier changes and contribute to understanding palaeoclimate and palaeoenvironment in the central Tibetan Plateau (TP). Here we report on 10Be surface exposure dating of thirteen rock samples collected from a sequence of glacial landforms associated with the Gangjiaquba Glacier. Based on the dating results, historical records (topographical maps) and morphological relationships, clear Little Ice Age (LIA) landforms are identified, and other landforms are tentatively assigned Neoglacial and global Last Glacial Maximum (LGMG) ages. Dating results for samples from modern glacial landforms demonstrate that the boulders were not affected by nuclide inheritance, and that 10Be surface exposure dating may be used to constrain glacier fluctuations during the past century in high-altitude areas that have high 10Be production rates. A comparison of the ages of a glacially polished surface and adjacent glacial deposits indicates that subglacial erosion by abrasion of the rock surface was insufficient to remove cosmogenic nuclide inventories. Thus the apparent exposure age on the polished surface includes inheritance and over-estimates the actual age for the exposure of this surface. Samples from hummocky moraine have wide age spreads, indicating long-lasting surface instability after deposition of this landform. Successive reduction in glacial extent in the Mount Geladandong area since the LGMG reflects temperature and precipitation changes over this timeframe in the central TP, with climate forcing for glacial advances correlated with cooling signals in the North Atlantic that may have been transmitted to this area by the westerlies.

Erosion rates and morphogenesis of the El Peñol de Guatapé inselberg, northern Andes (Colombia), inferred from geomorphic analyses and cosmogenic 10Be measurements

Inselbergs are isolated rock bodies that develop as a result of differential weathering and erosion advances during topographic etchplain formation. The timing and rate of inselberg growth are key for constraining external controls on landscape evolution, particularly in etching terrains associated with elevated plateaus carved on granitic lithologies, and in tectonically active provinces in tropical climate zones (e.g., Antioqueño Plateau, AP). We applied new morphostratigraphic and geomorphometric analyses, along with 10Be terrestrial cosmogenic nuclide (TCN) measurements, to in situ rock samples from the Peñol de Guatapé Inselberg (PGI), in the AP of the Colombian Andes to address the chronological framework of bornhardt formation in this tropical setting. The PGI is located in a rejuvenated landscape between middle Miocene to late Mio-Pliocene erosion surfaces. Erosion rates inferred from 10Be analyses ranged between ∼0.0024 ± 0.0001 and 0.24 ± 0.0283 mm/yr. This broad range is consistent with the long-term erosion rate of ∼0.04 mm/yr and mid-term erosion rates of 0.01–0.08 mm/yr previously documented for the region using low-temperature thermochronology. Our findings indicate that the PGI emerged as an important landscape feature over a period of ∼0.5–2.0 Myr and has protruded high above the average AP surface since the Pliocene. The new TCN-derived erosion-rate estimates for the AP Inselberg enable us to better understand the role of weathering and erosional processes that controlled the evolution of landscape surfaces during Andean orogenic cycles documented in the region.

Late Neogene terrestrial climate reconstruction of the central Namib Desert derived by the combination of U–Pb silcrete and terrestrial cosmogenic nuclide exposure dating

Abstract. The chronology of the Cenozoic “Namib Group” of the Namib Desert is rather poorly understood and lacks direct radiometric dating. Thus, the paleoclimate and landscape evolution of the central Namib Desert remains imprecise, complicating the detailed search for global and/or local forcing factors for the aridification of the Namib. The widespread occurrence of calcretes and silcretes in the Namib Desert allows us to apply the novel application of the U–Pb laser ablation dating technique on silcretes and calcretes to date important phases of landscape stability and to retrieve critical paleoclimatic and environmental information on desertification and its paleoclimatic variability. Microscale silcrete formation (maximum of 8 mm) due to pressure solution by expanding calcrete cementation provides the opportunity to date multiple phases (multiple generations of silcrete as growing layers or shells) of silcrete formation. Groundwater silcrete and calcrete formation occurred at our study site during the Pliocene, a period of relatively stable climate and landscape conditions under semi-arid to arid conditions. Terrestrial cosmogenic nuclide (TCN) exposure ages from flat canyon rim surfaces indicate the cessation of groundwater calcrete formation due to incision during the Late Pliocene–Early Pleistocene and mark a large-scale landscape rejuvenation due to climate shifts towards more arid conditions in the Pleistocene, which can be connected to global climate patterns. This study demonstrates the feasibility of applying U–Pb laser ablation to groundwater silcrete and calcretes, discusses several important issues associated with this technique, and opens up the possibility of dating numerous sedimentary sequences containing silcretes and calcretes in arid environments. In particular, the use of silcretes (as described above) reduces potential effects of detrital components and bulk signal measurements by using massive calcretes. Our study redefines and improves the generally accepted Late Cenozoic chronostratigraphy of the Namib Desert (Miller, 2008).

Cosmogenic Nuclide Tracking of Sediment Recycling From a Frontal Siwalik Range in the Northwestern Himalaya

AbstractThe Himalayan orogen exports millions of tons of sediment annually to the Indo‐Gangetic foreland basin, derived from both hinterland and foreland fold‐thrust belts (FTB). Although erosion rates in the hinterland are well‐constrained, erosion rates in the foreland FTB and, by extension, the sediment flux have remained poorly constrained. Here, we quantified erosion rates and sediment flux from the Mohand Range in the northwestern Himalaya by modeling and measuring the cosmogenic radionuclide (CRN) 10Be and 26Al concentrations in modern fluvial sediments. Our model uses local geological and geophysical constraints and accounts for CRN inheritance and sediment recycling, which enables us to determine the relative contributions of the hinterland and foreland FTB sources to the CRN budget of the proximal foreland deposits. Our model predictions closely match measured concentrations for a crustal shortening rate across the Mohand Range of 8.0 ± 0.5 mm yr−1 (i.e., approximately 50% of the total shortening across the Himalaya at this longitude) since Ma. This shortening implies a spatial gradient in erosion rates ranging from 0.42 ± 0.03 to 4.92 ± 0.34 mm yr−1, controlled by the geometry of the underlying structure. This erosion pattern corresponds to an annual sediment recycling of ∼2.0 megatons from the Mohand Range to the downstream Yamuna foreland. Converted to sediment fluxes per unit width along the Himalaya, the foreland FTB accounts for ∼21% ± 5% of the total flux entering the foreland. Because these sediments have lower 10Be concentrations than hinterland‐derived sediment, they would lead to ∼14% overestimation of 10Be‐derived erosion rates, based on Yamuna sediments in the proximal foreland.

Antarctic permafrost processes and antiphase dynamics of cold-based glaciers in the McMurdo Dry Valleys inferred from 10Be and 26Al cosmogenic nuclides

Abstract. Soil and sediment mixing and associated permafrost processes are not widely studied or understood in the McMurdo Dry Valleys of Antarctica. In this study, we investigate the stability and depositional history of near-surface permafrost sediments to ∼ 3 m depth in the Pearse and lower Wright valleys using measured cosmogenic 10Be and 26Al depth profiles. In Pearse Valley, we estimate a minimum depositional age of ∼ 74 ka for the active layer and paleoactive-layer sediments (&lt; 0.65 m). Combined depth profile modelling of 10Be and 26Al gives a depositional age for near-surface (&lt; 1.65 m) permafrost in Pearse Valley of 180 +20/-40 ka, implying that the deposition of permafrost sediments predates MIS 5 advances of Taylor Glacier. Deeper permafrost sediments (&gt; 2.09 m) in Pearse Valley are thus inferred to have a depositional age of &gt; 180 ka. At a coastal, lower-elevation site in neighbouring lower Wright Valley, 10Be and 26Al depth profiles from a second permafrost core exhibit near-constant concentrations with depth and indicate the sediments are either vertically mixed after deposition or sufficiently young so that post-depositional nuclide production is negligible relative to inheritance. 26Al/10Be concentration ratios for both depth profiles range between 4.0 and 5.2 and are all lower than the nominal surface production rate ratio of 6.75, indicating that prior to deposition, these sediments experienced complex, yet similar, exposure–burial histories. Assuming a single-cycle exposure–burial scenario, the observed 26Al/10Be ratios are equivalent to a total minimum exposure–burial history of ∼ 1.2 Myr. In proximity to the depth profile core site, we measured cosmogenic 10Be and 26Al in three granite cobbles from thin, patchy drift (Taylor 2 Drift) in Pearse Valley to constrain the timing of retreat of Taylor Glacier. Assuming simple continuous exposure, our minimum, zero-erosion exposure ages suggest Taylor Glacier partially retreated from Pearse Valley no later than 65–74 ka. The timing of retreat after 65 ka and until the Last Glacial Maximum (LGM) when Taylor Glacier was at a minimum position remains unresolved. The surface cobble ages and permafrost processes reveal Taylor Glacier advances during MIS 5 were non-erosive or mildly erosive, preserving the underlying permafrost sediments and peppering boulders and cobbles upon an older, relict surface. Our results are consistent with U/Th ages from central Taylor Valley and suggest changes in moisture delivery over Taylor Dome during MIS 5e, 5c, and 5a appear to be associated with the extent of the Ross Ice Shelf and sea ice in the Ross Sea. These data provide further evidence of antiphase behaviour through retreat of a peripheral lobe of Taylor Glacier in Pearse Valley, a region that was glaciated during MIS 5. We suggest a causal relationship of cold-based glacier advance and retreat that is controlled by an increase in moisture availability during retreat of sea ice and perhaps the Ross Ice Shelf, as well as, conversely, a decrease during times of sea ice and Ross Ice Shelf expansion in the Ross Sea.

Pleistocene valley incision, landscape evolution and inferred tectonic uplift in the central parts of the Balkan Peninsula – Insights from the geochronology of cave deposits in the lower part of Crna Reka basin (N. Macedonia)

Although the general geomorphology is reasonably well understood, not much information is available on the incision rates of rivers and related tectonic uplift in the central parts of the Balkan Peninsula. Caves in the lower part of Crna Reka drainage (N. Macedonia) provide the possibility to reconstruct the Neogene-Quaternary evolution of this area, as previous research has identified two major cave development phases: one related to Pliocene-Early Pleistocene basin infilling and establishment of lacustrine environments, and a subsequent cave development phase related to valley incision due to draining of the lacustrine systems and tectonic uplift.Here, we present new geochronological data obtained by U-Th dating on speleothems and cosmogenic nuclide burial age determination of clastic cave sediments, that provide time constraints on the Pleistocene karst and valley evolution, and an insight into the related tectonic uplift. The obtained cosmogenic nuclide burial age (2.1 ± 0.5 Ma) of the clastic cave sediments from Temna Peštera – Dragožel, further supports previous results on placing the onset of the draining of the Pliocene lakes in Macedonia in the Early Pleistocene. The similar timing obtained for the downstream and upstream parts of Crna Reka drainage suggests that the draining was more likely initiated by regional uplift, rather than headward erosion related to subsidence in the Aegean Sea. The Middle to Late Pleistocene age of the dated speleothems agrees well with the existing conceptual model for karst and landscape evolution in the area. The cumulative valley incision rates based on these radiometric data show an increase towards the present, with values of <0.1 m/ka in Early Pleistocene, increasing to ∼0.2–0.5 m/ka in Middle Pleistocene, and up to 1 m/ka in Late Pleistocene. They are lower than the measured uplift rates in the area (1.1–1.2 m/ka), and mostly overlap with the range of GPS-based vertical deformation rates in the Hellenides. Higher Middle to Late Pleistocene uplift rate is inferred in the downstream part of Crna Reka, an area in the Vardar zone bounded by seismogenic faults, than in the upstream part, at the easternmost edge of the Pelagonian massif.