Effects of sediment mixing on 10Be concentrations in the Zielbach catchment,central-eastern Italian Alps |
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| Institution: | 1. University of Bern, Institute of Geology, Baltzersstrasse 1+3, CH-3012 Bern, Switzerland;2. Victoria University of Wellington, School of Geography, Environment and Earth Science, PO Box 600, 6140 Wellington, New Zealand;3. University of Bologna, Department of Earth Science, Geology and Environment, Via Zamboni 67, 40127 Bologna, Italy;4. University of Milano-Bicocca, Department of Geological Sciences and Geotechnologies, Piazza della Scienza 4, 20126 Milano, Italy;5. ETH Zürich, Labor f. Ionenstrahlphysik (LIP), Schafmattstrasse 20, 8093 Zürich, Switzerland;1. Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France;2. Laboratoire de Géographie Physique Environnements quaternaires et actuels (UMR 8591, CNRS-Universités Paris I & Paris XII), 1 place Aristide Briand, F-92195 Meudon cedex, France;3. Service Régional de l’Archéologie / DRAC Nord-pas-de-Calais-Picardie, 1 rue Henri Daussy, F-80000 Amiens, France;4. INRAP Canal Seine-Nord Europe, 16 rue du Général Leclerc, F-80400, Croix-Moligneaux and UMR 7194 CNRS, Institut de Paléontologie Humaine, 1 rue René Panhard, F-75013, Paris, France;5. GéoArchÉon SARL, 30, rue de la Victoire, F-55210 Viéville-sous-les-Côtes, France;6. College of Geography Science, Nanjing Normal University, Nanjing 210023, China;7. Laboratoire de Mathématiques Jean Leray Université de Nantes. 2, rue de la Houssinière, Po Box 92208, F-44322 Nantes, France;8. Département de Préhistoire du Muséum national d’Histoire naturelle, UMR 7194 CNRS, Institut de Paléontologie Humaine, 1 rue René Panhard, F-75013 Paris, France;1. Department of Physics, University of Helsinki, P.O. Box 48, 00014 University of Helsinki, Finland;2. Natural Resources Institute Finland, P.O. Box 18, 01301 Vantaa, Finland;3. Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland;4. Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland;5. School of Forest Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland;1. Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China;2. Wuhan Base of Institute of Crustal Dynamics, China Earthquake Administration, Wuhan 430071, China;1. Université Côte d’Azur, CNRS, OCA, IRD, Géoazur, France;2. Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer-Sheva, Israel;3. Aix-Marseille Univ., CNRS, IRD, Coll. France, UM 34 CEREGE, Technopôle de l’Environnement Arbois-Méditerranée, BP80, 13545, Aix-en-Provence, France;1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;2. College of Geographical Sciences, Nanjing Normal University, Nanjing 210023, China;3. Site Museum of Maba Hominin, Qujiang District, Shaoguan 512100, China;4. Guangdong Provincial Institute of Cultural Relics and Archaeology, Guangzhou 510075, China;5. Radiogenic Isotope Facility, School of Earth Sciences, the University of Queensland, Brisbane, QLD 4072, Australia |
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| Abstract: | 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. |
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