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  • 1
    Publication Date: 2019-05-02
    Description: Concentrations of in-situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers covers a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone are potentially biased. To date, knowledge about catchment attributes that may induce grain-size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain-size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology, and abrasion. We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=73 catchments) – comprising catchments with contrasting hillslope angles, climate, lithology, and catchment size – revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as “negative grain size dependency”) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth interval. These catchments include steep (〉 25∘) and humid catchments (〉 2000 mm yr−1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with weak lithologies and long sediment travel distances (〉 2300–7000 m, depending on lithology) where abrasion may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.
    Print ISSN: 2196-6311
    Electronic ISSN: 2196-632X
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
    Publication Date: 2018-12-03
    Description: Concentrations of in situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers cover a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone could potentially be biased. To date, knowledge about catchment attributes that may induce grain size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology and abrasion. We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate-gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=62 catchments), comprising catchments with contrasting hillslope angles, climate, lithology and catchment size revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as negative grain size dependency) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth-interval. These catchments include steep (〉25°), arid (〈100 mm yr−1) and humid catchments (〉2000 mm yr−1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with long sediment travel distances (〉2300–7000 m, depending on lithology) where abrasion and sediment provenance may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.
    Electronic ISSN: 2196-6338
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
    Publication Date: 2021-11-30
    Description: Abstract
    Description: Concentrations of in-situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers covers a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone are potentially biased. To date, knowledge about catchment attributes that may induce grain-size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain-size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology, and abrasion. We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=73 catchments) – comprising catchments with contrasting hillslope angles, climate, lithology, and catchment size – revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as “negative grain size dependency”) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth interval. These catchments include steep (〉 25°) and humid catchments (〉 2000mm yr-1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with weak lithologies and long sediment travel distances (〉 2300–7000 m, depending on lithology) where abrasion may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.Samples from the Chilean Coastal Cordillera were processed in the Helmholtz Laboratory for the Geochemistry of the Earth Surface (HELGES). 10Be/9Be ratios were measured at the University of Cologne and normalized to the KN01-6-2 and KN01-5-3 standards. Denudation rates were calculated using a time-independent scaling scheme according to Lal (1991) and Stone (2002) (St scaling scheme) and the SLHL production rate of 4.01 at g-1 yr-1 as reported by Phillips et al. (2016)The global compilation exists of studies that measured 10Be concentrations in different grain sizes from the same sample location. We only included river basins of 〈5000 km2 which measured 10Be concentrations in at least one sand-sized fraction 〈2 mm and at least one coarser fraction 〉2 mm. Catchment parameters have been recalculated using a 90-m SRTM DEM.The data are presented in Excel and csv tables. Table S1 describes the characteristics of the samples catchments, Table S2 includes the grain size dependent 10Be-concentrations measured during this study and Table 3 the global compilation of grain size dependent 10Be-concentrations. All samples of this study (the Chilean Coastal Cordillera) are assigned with International Geo Sample Numbers (IGSN). The IGSN links are included in Table S2 and in the Related References Section on the DOI Landing Page. The data are described in detail in the data description file and in van Dongen et al. (2018) to which they are supplementary material to.
    Keywords: Denudation ; Grain size dependent 10Be-concentrations ; Chile ; Coastal Cordillera ; Global compilation ; Cosmogenic 10Be ; Cosmogenic nuclides ; chemical element 〉 element of group II (alkaline earth metals) 〉 beryllium ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEOMORPHIC LANDFORMS/PROCESSES 〉 FLUVIAL PROCESSES 〉 ABRASION ; EARTH SCIENCE 〉 SOLID EARTH 〉 ROCKS/MINERALS/CRYSTALS 〉 BEDROCK LITHOLOGY ; EARTH SCIENCE 〉 LAND SURFACE 〉 EROSION/SEDIMENTATION 〉 LANDSLIDES ; EARTH SCIENCE 〉 LAND SURFACE 〉 EROSION/SEDIMENTATION 〉 WEATHERING ; EARTH SCIENCE 〉 LAND SURFACE 〉 EROSION/SEDIMENTATION 〉 SEDIMENT TRANSPORT ; EARTH SCIENCE 〉 LAND SURFACE 〉 EROSION/SEDIMENTATION 〉 EROSION
    Type: Dataset
    Format: 4 Files
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  • 4
    Publication Date: 2023-03-27
    Description: Abstract
    Description: This data publication is supplementary to a study on the effect of large boulders and bedrock fracture patterns on hillslope denudation rates in the Chilean Coastal Cordillera, by Lodes et al. (submitted). Hillslope denudation rates are primarily determined by tectonic uplift rates, but landscape morphology is also controlled by climate and lithological properties such as bedrock fractures. Fracture patterns can influence the locations of ridges and valleys in landscapes through lowering surface grain sizes in fractured areas, and therefore the residence time of fractured hillslope material, dictating differential denudation rates. In this project, we used 10Be cosmogenic nuclide analysis to quantify the denudation rates of fractured bedrock, boulders, and soil on hillslopes, and compared the orientations of surrounding streams and faults, to understand the effects of fracturing and faulting on denudation rates, fluvial incision, and grain size in three field sites along a climate gradient in the Chilean Coastal Cordillera. In the humid and semi-arid climate zones, we found that denudation rates for unfractured bedrock and large hillslope boulders (10 to 15 m Myr-1) are lower than for soil (15 to 20 m Myr-1), indicating that exposed bedrock and boulders retard hillslope denudation rates. In the mediterranean climate zone, hillslope denudation rates are higher (40-140 m Myr-1) and show a less consistent pattern, likely due to steeper slopes. LiDAR-derived stream orientations support a fracture-control on landscape denudation in the three field sites, which we link with fracture density. Together, our results thus provide new insights into how fracture patterns can dictate topographic highs and valleys through grain size reduction. The main objective of this data publication is to provide our 10Be dataset which we used to calculate denudation rates for bedrock, boulders, and soils.
    Description: Methods
    Description: We conducted fieldwork in Chile in February 2019 and March 2020. We collected 32 samples from bedrock, boulders, and topsoil in three field areas (Nahuelbuta National Park, La Campana National Park, and Private Reserve Santa Gracia) for cosmogenic 10Be analysis. A detailed description of the field areas can be found in Lodes et al. (submitted). We collected bedrock samples by chipping off and amalgamating 10-15 pieces (~25 cm2 and 〈2cm thick) of bedrock in an area of ~20 m x 20 m. Boulder samples consist of similarly-size chips from 10-15 different boulders of similar size, from an area of ~40 m x 40 m, depending on the abundance of boulders. We collected soil samples from the area surrounding the sampled boulders. The samples are assigned with IGSNs, which are listed in the accompanying data table 2022-004_Lodes-et-al_Data.
    Keywords: 10Be ; cosmogenic radionuclides ; geomorphology ; fractures ; landscape morphology ; tectonic geomorphology ; erosion ; denudation ; boulders ; hillslopes ; EARTH SCIENCE 〉 LAND SURFACE 〉 GEOMORPHOLOGY 〉 FLUVIAL LANDFORMS/PROCESSES ; EARTH SCIENCE 〉 LAND SURFACE 〉 GEOMORPHOLOGY 〉 TECTONIC LANDFORMS/PROCESSES ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEOMORPHIC LANDFORMS/PROCESSES ; land 〉 geomorphic process 〉 erosion ; science 〉 geography 〉 geomorphology
    Type: Dataset , Dataset
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