Late Quaternary denudation of the Alps,valley and lake fillings and modern river loads |
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| Institution: | 1. Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso 35, I-10125 Torino, Italy;2. IPHES, Institut Català de Paleoecologia Humana i Evolució Social, Zona Educacional 4, Campus Sescelades (Edifici W3), E-43007 Tarragona, Spain;3. Àrea de Prehistòria, Universitat Rovira i Virgili (URV), Avinguda de Catalunya 35, E-43002 Tarragona, Spain;4. Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Edifici Z (ICTA-ICP), Carrer de les Columnes s/n, Campus de la UAB, E-08193, Cerdanyola del Valles, Barcelona, Spain;1. Institute of Crop Science and Resource Conservation (INRES), Soil Science and Soil Ecology, University of Bonn, Nussallee 13, 53115 Bonn, Germany;2. Institute of Geoscience, Organic Geochemistry, University of Kiel, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany;1. University Lumière Lyon 2, UMR 5133 CNRS Archéorient, 69365 Lyon, France;2. Department of Archaeology, University of Southampton, Avenue Campus, Southampton SO17 1BF, United Kingdom;3. University of Strasbourg, UMR LIVE 7362 CNRS-ENGEES, 67083 Strasbourg, France;4. University Lumière Lyon 2, CNRS UMR 5600, 69676 Bron, France;5. University of Freiburg, Institute of Earth and Environmental Sciences, Albertstr. 23b, 79104 Freiburg, Germany |
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| Abstract: | Erosional denudation of the Alps and their role as sediment source underwent major changes throughout the Quaternary, by repeated glaciation and deglaciation. The sediment fluxes of 16 major Alpine drainage basins were quantified by determining the sediment volumes which have been trapped in valleys and lake basins. These became sedimentologically closed after the last glacier retreat around 17 000 cal. BP. The sediment volumes distributed over their provenance areas yield mean mechanical denudation rates between 250 to 1060 mm ka–1. In contrast, modern denudation rates, derived from river loads and delta surveys, range from 30 to 360 mm ka–1. Relief, such as mean elevation and slope, turned out to be the primary control of both modern and Late Glacial mechanical denudation. Rock types seem to be responsible for some scatter of the data, but their role is masked by other factors. Modern denudation rates increase with higher proportions of bare rocks and glaciated area, but decrease with forest cover. An area-weighted extrapolation of the studied drainage basins to the entire Alps on the basis of major morphotectonic zones yields a mean denudation rate of 620 mm ka–1 over the last 17 000 years. This rate clearly exceeds the modern rate of 125 mm ka–1. Lake sediments and palaeoclimatic reconstructions confirm that the sediment yield of the Alps reached a maximum during deglaciation when large masses of unconsolidated materials were available, vegetation was scarse, and transport capacities were high. During the early Holocene sediment yield declined to a minimum before some climate deterioration and human activities again accelerated erosional processes. Assuming a denudation rate in the early Holocene half of the modern one, the Late Glacial denudation rates must have been in the order of 1100 to 2900 mm ka–1. Consequently, denudation rates during a glacial/interglacial cycle probably varied by a factor of 14, which lies well within the range of other studies in central Europe, Scandinavia and North America. From large scale sediment budgets of perialpine sedimentary basins the overall denudation rate of the Alps during the Quaternary has been c. 400 mm ka–1, i.e. about one third lower than the estimate for the last 17000 years. This can be well explained by the outstanding role which deglaciation played in the time span studied here. |
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