Situ-produced Cosmogenic Nuclides Research Articles

In situ-produced 10Be and 26Al indirect dating of Elarmékora Earlier Stone Age artefacts: first attempt in a savannah forest mosaic in the middle Ogooué valley, Gabon.

Discovered in 1988 by R. Oslisly and B. Peyrot, Elarmékora is a high terrace that, today, is situated 175 m above the Ogooué River in the historical complex of Elarmékora, attached to the Lopé National Park in Gabon, a World Heritage site since 2007. The site yielded a small lithic assemblage, including mainly cobble artefacts embedded within the 1 m thick alluvial material. Based on geomorphological and palaeoclimatological criteria, the preliminary dating suggested an age of 400 ka. However, Elarmékora could be a key site for Atlantic Central Africa if this lithic industry can be dated absolutely. In 2018 and 2019, two field trips were organized to collect surface samples as well as samples in vertical depth profiles with the aim of measuring their in situ-produced cosmogenic nuclide (10Be and 26Al) content. Results suggest a surface abandonment between 730 and 620 ka ago representing a minimum age for the cobble artefacts. Concurrently, technological reappraisal of the artefacts suggests an atypical lithic industry that should, for the moment, be considered as ‘undiagnostic’ Earlier Stone Age. This age bracketing may be compared with a similar age range obtained for prehistoric occupations in Angola using the same approach. This age will place Elarmékora among the oldest evidence for the presence of hominins in western Central Africa and raises the question of a ‘West Side Story’ to early human dispersals in Africa.This article is part of the theme issue ‘Tropical forests in the deep human past’.

Culturing Ancient Bacteria Carrying Resistance Genes from Permafrost and Comparative Genomics with Modern Isolates.

Long considered to be a consequence of human antibiotics use by deduction, antibiotic resistance mechanisms appear to be in fact a much older phenomenon as antibiotic resistance genes have previously been detected from millions of year-old permafrost samples. As these specimens guarantee the viability of archaic bacteria, we herein propose to apply the culturomics approach to recover the bacterial content of a Siberian permafrost sample dated, using the in situ-produced cosmogenic nuclide chlorine36 (36Cl), at 2.7 million years to study the dynamics of bacterial evolution in an evolutionary perspective. As a result, we cultured and sequenced the genomes of 28 ancient bacterial species including one new species. To perform genome comparison between permafrost strains and modern isolates we selected 7 of these species (i.e., Achromobacter insolitus, Bacillus idriensis, Brevundimonas aurantiaca, Janibacter melonis, Kocuria rhizophila, Microbacterium hydrocarbonoxydans and Paracoccus yeei). We observed a high level of variability in genomic content with a percentage of shared genes in the core genomes ranging from 21.23% to 55.59%. In addition, the Single Nucleotide Polymorphism (SNP) comparison between permafrost and modern strains for the same species did not allow a dating of ancient strains based on genomic content. There were no significant differences in antibiotic resistance profiles between modern and ancient isolates of each species. Acquired resistance to antibiotics was phenotypically detected in all gram-negative bacterial species recovered from permafrost, with a significant number of genes coding for antibiotic resistance detected. Taken together, these findings confirm previously obtained data that antibiotic resistance predates humanity as most of antimicrobial agents are natural weapons used in inter-microbial conflicts within the biosphere.

Inferring the timing of abandonment of aggraded alluvial surfaces dated with cosmogenic nuclides

Abstract. Information about past climate, tectonics, and landscape evolution is often obtained by dating geomorphic surfaces comprising deposited or aggraded material, e.g. fluvial fill terraces, alluvial fans, volcanic flows, or glacial till. Although surface ages can provide valuable information about these landforms, they can only constrain the period of active deposition of surface material, which may span a significant period of time in the case of alluvial landforms. In contrast, surface abandonment often occurs abruptly and coincides with important events like drainage reorganization, climate change, or landscape uplift. However, abandonment cannot be directly dated because it represents a cessation in the deposition of dateable material. In this study, we present a new approach to inferring when a surface was likely abandoned using exposure ages derived from in situ-produced cosmogenic nuclides. We use artificial data to measure the discrepancy between the youngest age randomly obtained from a surface and the true timing of surface abandonment. Our analyses simulate surface dating scenarios with variable durations of surface formation and variable numbers of exposure ages from sampled boulders. From our artificial data, we derive a set of probabilistic equations and a MATLAB tool that can be applied to a set of real sampled surface ages to estimate the probable period of time within which abandonment is likely to have occurred. Our new approach to constraining surface abandonment has applications for geomorphological studies that relate surface ages to tectonic deformation, past climate, or the rates of surface processes.

Preliminary results of CoQtz-N: A quartz reference material for terrestrial in-situ cosmogenic 10Be and 26Al measurements

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

Design and performance of an automated chemical extraction bench for the preparation of 10Be and 26Al targets to be analyzed by accelerator mass spectrometry

The growing number of studies based on data provided by the accelerator mass spectrometry (AMS) technique from increasingly diverse matrices implies that developing very effective and reproducible sample processing techniques is crucial to meet the demand generated.After being dissolved, the isolation of the cosmogenic nuclide to be measured and its chemical purification imply complex processes throughout successive stages The presented automatic system was designed to perform the final steps of the 10Be and 26Al chemical extraction protocol from natural matrices (sediments, pure mineral phases,…), previously purified, decontaminated and dissolved in the case of in situ-produced cosmogenic nuclides, or leached or dissolved in the case of meteoric cosmogenic nuclides. Driven by Labview software, the developed automatic system, in addition to freeing the operator from tedious tasks, allows reproducibly processing simultaneously up to eight samples of different volumes in roughly 40 min. This article presents the design of the automated extraction bench and its performance based on the recovery efficiency of the stable element and the reproducibility of the measurements of the cosmogenic nuclide concentrations by AMS.

Revisiting the age of the Jumento volcano, Chichinautzin Volcanic Field (Central Mexico), using in situ-produced cosmogenic 10Be

Previous studies on Jumento volcano, based on radiocarbon dating and comparative morphometric analysis, suggest that it could be the youngest volcano of the Sierra Chichinautzin. Here we establish a new chronology of the emplacement of the Late Holocene lava flows of Jumento volcano using in situ-produced 10Be cosmic ray exposure (CRE) dating of quartz xenocrysts to test this hypothesis. Depending on the choice of the cosmogenic nuclide production parameters in the exposure age calculators used, the mean 10Be CRE ages ranges between 1.86 ± 0.68 ka and 2.41 ± 0.97 ka for the inner lava flow and between 1.90 ± 0.29 ka and 2.49 ± 0.41 ka for the breakout lava flow. These preliminary mean 10Be CRE ages confirm that the Jumento volcano is one of the youngest volcanoes of the Sierra Chichinautzin although slightly older than the Xitle volcano. This first 10Be eruption chronology of the Sierra Chichinautzin shows that 10Be CRE dating represents an alternative approach to date volcanic rocks, not only for the Sierra Chichinautzin but also for other volcanic fields, especially when no charcoal or paleosoils are available for radiocarbon dating. Furthermore, it suggests that in situ-produced cosmogenic nuclide dating has considerable potential to throw light on the volcanic history and eruption recurrence of this volcanic field, in order to provide enough data for the mitigation of the hazards and related risks in Mexico City, the city of Cuernavaca and the small towns around the volcanic field.

Timing of European fluvial terrace formation and incision rates constrained by cosmogenic nuclide dating

Age constraints of late Cenozoic fluvial terraces are important for addressing surface process questions related to the incision rates of rivers, or tectonic and climate controls on denudation and sedimentation. Unfortunately, absolute age constraints of fluvial terraces are not always possible, and many previous studies have often dated terraces with relative age constraints that do not allow for robust interpretations of incision rates and timing of terrace formation. However, in situ-produced cosmogenic nuclides allow absolute age determination, and hence incision rates, of fluvial deposits back to 5 Ma. Here we present, cosmogenic depth profile dating and isochron burial dating of four different river systems in Europe spanning 12° of latitude. We do this to determine river incision rates and spatial variations in the timing of terrace formation. Isochron burial age constraints of four selected terraces from the Vltava river (Czech Republic) range between 1.00±0.21 to 1.99±0.45Ma. An isochron burial age derived for the Allier river (Central France) is 2.00±0.17Ma. Five terrace levels from the Esla river (NW Spain) were dated between 0.08+0.04/−0.01Ma and 0.59+0.13/−0.20Ma with depth profile dating. The latter age agrees with an isochron burial age of 0.52±0.20Ma. Two terrace levels from the Guadalquivir river (SW Spain) were dated by depth profile dating to 0.09+0.03/−0.02Ma and 0.09+0.04/−0.03Ma. The one terrace level from the Guadalquivir river dated by isochron burial dating resulted in an age of 1.79±0.18Ma. Results indicate that the cosmogenic nuclide-based ages are generally older than ages derived from previous relative age constraints leading to a factor 2–3 lower incision rates than previous work. Furthermore, the timing of terrace formation over this latitudinal range is somewhat obscured by uncertainties associated with dating older terraces and not clearly synchronous with global climate variations.

The last maximum ice extent and subsequent deglaciation of the Pyrenees: an overview of recent research

This paper reviews data currently available on the glacial fluctuations that occurred in the Pyrenees between the Würmian Maximum Ice Extent (MIE) and the beginning of the Holocene. It puts the studies published since the end of the 19th century in a historical perspective and focuses on how the methods of investigation used by successive generations of authors led them to paleogeographic and chronologic conclusions that for a time were antagonistic and later became complementary. The inventory and mapping of the ice-marginal deposits has allowed several glacial stades to be identified, and the successive ice boundaries to be outlined. Meanwhile, the weathering grade of moraines and glaciofluvial deposits has allowed Würmian glacial deposits to be distinguished from pre-Würmian ones, and has thus allowed the Würmian Maximum Ice Extent (MIE) –i.e. the starting point of the last deglaciation– to be clearly located. During the 1980s, 14C dating of glaciolacustrine sequences began to indirectly document the timing of the glacial stades responsible for the adjacent frontal or lateral moraines. Over the last decade, in situ-produced cosmogenic nuclides (10Be and 36Cl) have been documenting the deglaciation process more directly because the data are obtained from glacial landforms or deposits such as boulders embedded in frontal or lateral moraines, or ice-polished rock surfaces. On that basis, it is now accepted that (i) the Würmian MIE occurred in the Pyrenees during MIS 4 and not the Global LGM; and that (ii) a major glacial readvance took place during the Global LGM. This ice readvance reached a position close to the MIS 4 icefield boundary in the Eastern part of the range, but apparently not in the west. (iii) Soon after the Global LGM, the Pyrenean ice margin went into major and rapid recession. Even before the beginning of the Lateglacial, the main trunk glaciers had already retreated to the upper parts of the valleys. (iv) The paleogeography of the Pyrenean icefield during the Last Glacial-Interglacial Transition (LGIT) is still partially unknown but all available data indicate that glaciers during the Oldest Dryas (GS-2a) were substantially smaller than during the Global LGM. During the Bølling-Allerød interstadial, the Pyrenean ice margins retreated substantially, and glaciers locally vanished definitively. The Younger Dryas cooling event generated either a short readvance of existing cirque glaciers or the development of rock glaciers.

Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka

Silicate weathering – initiated by major mineralogical transformations at the base of ten meters of clay-rich saprolite – generates the exceptionally low weathering flux found in streams draining the crystalline rocks of the mountainous and humid tropical Highlands of Sri Lanka. This conclusion is reached from a thorough investigation of the mineralogical, chemical, and Sr isotope compositions of samples within a regolith profile extending >10m from surface soil through the weathering front in charnockite bedrock (a high-grade metamorphic rock), corestones formed at the weathering front, as well as from the chemical composition of the dissolved loads in nearby streams. Weatherable minerals and soluble elements are fully depleted at the top of the profile, showing that the system is supply-limited, such that weathering fluxes are controlled directly by the supply of fresh minerals. We determine the weathering rates using two independent means: (1) in situ-produced cosmogenic nuclides in surface soil and creek sediments in the close vicinity of the regolith combined with immobile element mass balance across the regolith and (2) river dissolved loads. Silicate weathering rates determined from both approaches range from 16 to 36tkm−2y−1, corresponding to a weathering front advance rate of 6–14mmky−1. These rates agree across the 101 to 104ytime scales over which our rate metrics integrate, suggesting that the weathering system operates at steady state. Within error these rates are furthermore compatible with those obtained by modeling the advance rate of the weathering front from chemical gradients and mineral dissolution rates. The silicate weathering flux out of the weathering profile, measured on small creeks, amounts to 84% of the profile’s export flux; the remaining 16% is contributed by non-silicate, atmospheric-derived input. The silicate weathering flux, as measured by dissolved loads in large catchments, amounts to ca. 50% of the total dissolved flux; the remainder being contributed by dust, rain, and weathering of local marble bands. Spheroidal weathering is the key processes of converting the fresh bedrock into saprolite at the weathering front. The mineralogical composition of weathering rinds shows that the sequence of mineral decomposition is: pyroxene; plagioclase; biotite; K-feldspar. Observable biotite alteration does not appear to initiate spheroidal weathering within corestones; therefore, we infer that other processes than biotite oxidation, like pyroxene oxidation, clay formation from pyroxene and plagioclase decomposition, the development of secondary porosity by plagioclase dissolution, or even microbiologic processes at depth enable the coupling between slow advance of the weathering front and slow erosion at the surface. The comparison to tectonically more active tropical landscapes lets us conclude that the combination of hard rock with tightly interlocked mineral grains and slow erosion in the absence of tectonically-induced landscape rejuvenation lead to these exceptionally low weathering rates.

Effects of sediment mixing on 10Be concentrations in the Zielbach catchment, central-eastern Italian Alps

Basin-wide erosion rates can be determined through the analysis of in situ-produced cosmogenic nuclides. In transient landscapes, and particularly in mountain catchments, erosion and transport processes are often highly variable and consequently the calculated erosion rates can be biased. This can be due to sediment pulses and poor mixing of sediment in the stream channels. The mixing of alluvial sediment is one of the principle conditions that need to be verified in order to have reliable results. In this paper we perform a field-based test of the extent of sediment mixing for a ∼42 km2 catchment in the Alps using concentrations of river-born 10Be. We use this technique to assess the mechanisms and the spatio-temporal scales for the mixing of sediment derived from hillslopes and tributary channels. The results show that sediment provenance and transport, and mixing processes have a substantial impact on the 10Be concentrations downstream of the confluence between streams and tributary channels. We also illustrate that the extent of mixing significantly depends on: the sizes of the catchments involved, the magnitude of the sediment delivery processes, the downstream distance of a sample site after a confluence, and the time since the event occurred. In particular, continuous soil creep and shallow landsliding supply high 10Be concentration material from the hillslope, congruently increasing the 10Be concentrations in the alluvial sediment. Contrariwise, a high frequency of mass-wasting processes or the occurrence of sporadic but large-magnitude events results in the supply of low-concentration sediment that lowers the cosmogenic nuclide concentration in the channels. The predominance of mass-wasting processes in a catchment can cause a strong bias in detrital cosmogenic nuclide concentrations, and therefore calculated erosion rates may be significantly over- or underestimated. Accordingly, it is important to sample as close as possible to the return-period of large-size sediment input events. This will lead to an erosion rate representative of the “mass-wasting signal” in case of generally high-frequency events, or the “background signal” when the event is sporadic. Our results suggest that a careful consideration of the extent of mixing of alluvial sediment is of primary importance for the correct estimation of 10Be-based erosion rates in mountain catchments, and likewise, that erosion rates have to be interpreted cautiously when the mixing conditions are unknown or mixing has not been achieved.

Coupling cosmogenic dating and magnetostratigraphy to constrain the chronological evolution of peri-Mediterranean karsts during the Messinian and the Pliocene: Example of Ardèche Valley, Southern France

The Ardèche River entrenches a deep canyon in the Saint Remèze plateau from Vallon-Pont-d'Arc to its confluence with the Rhône. This plateau is part of the Ardèche Cretaceous limestone plateau located at the edge of the Mid Rhône valley. It is characterized by dense multi-level cave systems, such as Saint-Marcel Cave (50km of mapped passages) and Chauvet Cave, famous for its paleolithic paintings. Until now, and despite the absence of absolute dating, stepping of the Saint Remèze cave levels has been interpreted as the result of the Messinian salinity crisis. To clarify this interpretation, fluvial sediments of cave systems have been absolutely dated, while cave sediments have been demonstrated to be ideal for “burial dating” based on the different radioactive decay rates of the in situ-produced cosmogenic nuclides 10Be and 26Al. Combined with magnetostratigraphy and constrained by the Lower Ardèche base-level curve, this contribution provides an absolute dating for each cave level. The obtained results are consistent with the stepping per ascensum model of both surface landforms and caves for the Messinian–Pliocene eustatic cycle. Finally, this study provides evidence for a rise of the Ardèche river level to 40m above the Pliocene abandonment surface. The second active period of the Chauvet Cave is evidenced between 2.96 and 2.18Ma (cave filling). An absolute dating for the Pliocene abandonment surface between 1.94 and 1.77Ma is also obtained, which brings new understandings to the geodynamic evolution of the area. The Lower Ardèche has been uplifted after the Pliocene, with a rate of 0.03mm/year since 1.77Ma.

Sediment production and delivery in the Amazon River basin quantified by in situ-produced cosmogenic nuclides and recent river loads

Research Article| May 01, 2011 Sediment production and delivery in the Amazon River basin quantified by in situ–produced cosmogenic nuclides and recent river loads Hella Wittmann; Hella Wittmann * † 1Institut für Mineralogie, Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany *Present address: GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Friedhelm von Blanckenburg; Friedhelm von Blanckenburg * 1Institut für Mineralogie, Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany *Present address: GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Laurence Maurice; Laurence Maurice 2Université de Toulouse, Université Paul Sabatier (UPS), Observatoire Midi-Pyrénées (OMP) and Laboratoire Mécanismes et Transferts en Géologie (LMTG), 14 Av. E. Belin, 31400 Toulouse, France3Institut de recherche pour le développement (IRD), Laboratoire Mécanismes et Transferts en Géologie (LMTG), 14 Av. E. Belin, 31400 Toulouse, France Search for other works by this author on: GSW Google Scholar Jean-Loup Guyot; Jean-Loup Guyot 4Instituto de Pesquisa para o Desenvolvimento (Institut de recherche pour le développement [IRD]), CP 7091 Lago Sul, 71619-970 Brasília, Brazil Search for other works by this author on: GSW Google Scholar Naziano Filizola; Naziano Filizola 5The Federal University of Amazonas, Av. Darcy Vargas, 1200 s/C-28, 69050-020 Manaus, Brazil Search for other works by this author on: GSW Google Scholar Peter W. Kubik Peter W. Kubik 6Laboratory of Ion Beam Physics, Eidgenössische Technische Hochschule Zürich (ETH), 8093 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (5-6): 934–950. https://doi.org/10.1130/B30317.1 Article history received: 31 May 2010 rev-recd: 31 Aug 2010 accepted: 02 Sep 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hella Wittmann, Friedhelm von Blanckenburg, Laurence Maurice, Jean-Loup Guyot, Naziano Filizola, Peter W. Kubik; Sediment production and delivery in the Amazon River basin quantified by in situ–produced cosmogenic nuclides and recent river loads. GSA Bulletin 2011;; 123 (5-6): 934–950. doi: https://doi.org/10.1130/B30317.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We use cosmogenic nuclide-derived denudation rates from in situ–produced 10Be in river sediment to determine sediment production rates for the central Amazon River and its major tributaries. Recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage, with the result that fluxes of the sediment-producing hinterland can now be linked to those discharged at the basins’ outlet. In rivers of the central Amazonian plain, sediment of finer grain sizes (125–500 μm) yields a weighted cosmogenic nuclide-derived denudation rate of 0.24 ± 0.02 mm/yr that is comparable to the integrated rate of all main Andean-draining rivers (0.37 ± 0.06 mm/yr), which are the Beni, Napo, Mamoré, Ucayali, and Marañón rivers. Coarser-grained sediment (>500 μm) of central Amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the Guyana and Brazilian shields, for which the denudation rate is 0.01–0.02 mm/yr. Respective sediment loads can be calculated by converting these cosmogenic nuclide-derived rates using their sediment-producing areas. For the Amazon River at Óbidos, a sediment production rate of ∼610 Mt/yr results; non-Andean source areas contribute only ∼45 Mt/yr. A comparison with published modern sediment fluxes shows similarities within a factor of ∼2 with an average gauging-derived sediment load of ∼1000 Mt/yr at Óbidos, for example. We attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long-term deposition within the basin and second to the buffering capability of the large Amazon floodplain. The buffering capability dampens short-term, high-amplitude fluctuations (climatic variability in source areas and anthropogenic soil erosion) by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Erosion rates in an active orogen (NE-Taiwan): A confrontation of cosmogenic measurements with river suspended loads

The direct and feedback relationships between tectonics, climate and denudation are a matter of debate. A better understanding of these relationships requires quantifying rates of denudation in a wide range of climate and tectonic settings, as well as at various time and space scales. Because of an ongoing active collision implying high uplift rates and a climate prone to extreme rainfall events and frequent tropical typhoons facilitating strong erosion dominated by mass movements and high degree of fluvial transport, the Taiwan environment is highly dynamic. In this work, spatially-averaged denudation rates determined along the network of one of the major rivers in Taiwan (Lanyang River) from in situ-produced cosmogenic nuclides ( 10Be) measured in river-borne quartz minerals are compared to the erosion rates determined from the statistical analysis of modern sediment load data. Integrated over the last several hundreds of years, the denudation rate derived from in situ-produced 10Be concentrations averages 2 ± 1 mm/yr within the Lanyang watershed. Integrated over the last 50 years, the erosion rate given by modern sediment load data is 5–7 mm/yr within the same catchment area. The studied catchment being characterized by a relatively low-level of human activity, the discrepancy between the two rates is most probably due different sensibilities to high-frequency, stochastic erosional events (typhoons and earthquakes). The cosmogenic-derived denudation rates can thus be regarded as more representatives for quantifying erosion processes on the short-time scale, and be strictly compared to the long-term exhumation rates derived from low-temperature chronological data.

An improved experimental determination of cosmogenic 10Be/ 21Ne and 26Al/ 21Ne production ratios in quartz

The confidence in surface exposure dating and related research, such as erosion rate studies or burial dating, strongly depends on the accuracy and precision of the currently used production rates of in situ-produced cosmogenic nuclides. Reducing the uncertainties of nuclide production rates by more accurate calibrations with independently dated natural rock surfaces is crucial for further improving the quantification of earth surface processes. Here we use surface samples from the 760 ± 2 ka old Bishop Tuff in eastern California to quantify the 10Be/ 21Ne and 26Al/ 21Ne production rate ratios in quartz. Our determination is based on (1) measured nuclide concentrations of cosmogenic 10Be, 21Ne, and 26Al, (2) a conservative estimate for the erosion of the tuff in the Volcanic Tableland area, which we base on our previously published 21Ne concentrations [Goethals, M.M., Niedermann, S., Hetzel, R., Fenton, C.R., 2009. Determining the impact of faulting on the rate of erosion in a low-relief landscape: A case study using in situ produced 21Ne on active normal faults in the Bishop Tuff, California. Geomorphology 103, 401–413] and a conservative estimate for the uncertainty of the 21Ne production rate, and (3) the assumption of steady-state erosion. Other assumptions, such as the applied scaling procedure, the muon contribution to nuclide production, or the attenuation lengths of neutrons and muons in rock, do not substantially affect the results. Based on 13 samples, the following average production rate ratios and conservative uncertainty estimates are obtained for sea level, high latitude, open sky, and rock surface: 0.249 ± 0.009 or 0.232 ± 0.009 for 10Be/ 21Ne using 10Be half-lives of 1.51 and 1.39 Ma, respectively, and 1.80 ± 0.09 for 26Al/ 21Ne (for an 26Al half-life of 0.72 Ma). The 10Be/ 21Ne and the 26Al/ 21Ne production ratios are consistent with currently used production rates but the ratios are much more precise than previous determinations. The resulting 26Al/ 10Be production ratio of 7.23 ± 0.45 (for a 10Be half-life of 1.51 Ma) or 7.76 ± 0.49 (for a 10Be half-life of 1.39 Ma) is high when compared to previously published values. We discuss reasons for this difference, amongst them the possibility that 26Al analyses in general might be compromised by artefacts affecting the stable Al concentration measurements. When combined with a 10Be production rate of 5.01 at g − 1 a − 1 for the 1.51 Ma half-life (or 4.61 at g − 1 a − 1 for the 1.39 Ma half-life), our production ratios convert to 21Ne and 26Al production rates of 20.1 and 36.2 at g − 1 a − 1 (or 19.9 and 35.7 at g − 1 a − 1 ), respectively.

Determination of both exposure time and denudation rate from an in situ-produced 10Be depth profile: A mathematical proof of uniqueness. Model sensitivity and applications to natural cases

Measurements of radioactive in situ-produced cosmogenic nuclide concentrations in surficial material exposed to cosmic rays allow either determining the long-term denudation rate assuming that the surface studied has reached steady-state (where production and losses by denudation and radioactive decay are in equilibrium) (infinite exposure time), or dating the initiation of exposure to cosmic rays, assuming that the denudation and post-depositional processes are negligible. Criteria for determining whether a surface is eroding or undergoing burial as well as quantitative information on denudation or burial rates may be obtained from cosmogenic nuclide depth profiles. With the refinement of the physical parameters involved in the production of in situ-produced cosmogenic nuclides, a unique well-constrained depth profile now permits determination of both the exposure time and the denudation rate affecting a surface. In this paper, we first mathematically demonstrate that the exponential decrease of the in situ-produced 10Be concentrations observed along a depth profile constrains a unique exposure time and denudation rate when considering both neutrons and muons. In the second part, an improved chi-square inversion model is described and tested in the third part with actual measured profiles.

Potential of in situ-produced cosmogenic nuclides for quantifying strength reduction of bedrock in soil-mantled hillslopes

This study presents a semi-empirical model for quantifying the reduction in the mechanical strength of bedrock beneath actively eroding soil-mantled hillslopes. The strength reduction of bedrock controls the rate of physical disintegration of saprolite, which supplies fresh minerals that are then exposed to intense chemical weathering in soil sections. To determine the values of parameters employed in the model requires knowledge of the denudation rate of the hillslope, the thickness of the soil and saprolite layers, the strength of fresh bedrock, and the threshold strength for physical erosion at the uppermost face of the saprolite. These parameters can be obtained from cosmogenic nuclide analyses for quartz samples from the soil–saprolite boundary and basic field- and laboratory-based investigations. Further testing of the model within a diverse range of climatic, tectonic, and lithologic environments is likely to provide clues to the mechanisms responsible for local and regional variations in the rates of soil production and chemical weathering upon hillslopes.

WebCN: A web-based computation tool for in situ-produced cosmogenic nuclides

Cosmogenic nuclide techniques are increasingly being utilized in geoscience research. For this it is critical to establish an effective, easily accessible and well defined tool for cosmogenic nuclide computations. We have been developing a web-based tool (WebCN) to calculate surface exposure ages and erosion rates based on the nuclide concentrations measured by the accelerator mass spectrometry. WebCN for 10Be and 26Al has been finished and published at http://www.physics.purdue.edu/primelab/for_users/rockage.html. WebCN for 36Cl is under construction. WebCN is designed as a three-tier client/server model and uses the open source PostgreSQL for the database management and PHP for the interface design and calculations. On the client side, an internet browser and Microsoft Access are used as application interfaces to access the system. Open Database Connectivity is used to link PostgreSQL and Microsoft Access. WebCN accounts for both spatial and temporal distributions of the cosmic ray flux to calculate the production rates of in situ-produced cosmogenic nuclides at the Earth’s surface.

Numerical simulations of in situ production of terrestrial cosmogenic nuclides

A variety of geologic and environmental events and processes can be studied with the cosmogenic nuclides accumulated in terrestrial rocks. Reliable interpretation of the measured in situ-produced cosmogenic nuclides requires a good understanding of the involved nuclear processes and factors influencing them. The production rates of nuclides depend on many parameters. In this paper, calculations are reported and discussed on the influence of the air/ground interface and snow cover on production rates of in situ produced cosmogenic nuclides.

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured 10Be concentrations has been modelled using a χ 2 inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides

Abstract In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).