Last Glacial aeolian landforms and deposits in the Rhône Valley (SE France)Spatial distribution and grain-size characterization

Authors Organisations
  • Mathieu Bosq(Author)
    University of Bordeaux
  • Pascal Bertran(Author)
    University of Bordeaux
  • Jean-Philippe Degeai(Author)
    Université de Montpellier III
  • Sebastian Kreutzer(Author)
    Université Bordeaux Montaigne
  • Alain Queffelec(Author)
    University of Bordeaux
  • Olivier Moine(Author)
    Université Paris 1 Panthéon Sorbonne-CNRS
  • Eymeric Morin(Author)
    Université Lumière - Lyon II
Type Article
Original languageEnglish
Pages (from-to)250-269
Number of pages20
JournalGeomorphology
Volume318
Early online date22 Jun 2018
DOI
Publication statusPublished - 01 Oct 2018
Externally publishedYes
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Abstract

In the Rhône Valley, a north-south oriented Cenozoic rift in southeast France, thick Pleistocene loess deposits have been recognized since the beginning of the last century. These loess records, which are disconnected from the North European Loess Belt (NELB), are of significant interest to document the evolution of perimediterranean landscapes and environments during the Last Glacial. To overcome the poor precision of available aeolian distribution maps, aeolian deposits were mapped using the topsoil textural database provided by the Land Use and Cover Area frame Statistical Survey project (LUCAS). The grain-size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops. Then, the areas showing a similar grain-size composition were extracted from the LUCAS rasters. The resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess, in better agreement with the known distribution of outcrops. The map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits. The deflation-related landforms, i.e., yardangs, closed depressions (pans), and desert pavements, are widespread south of narrowings of the Rhône Valley between latitudes 44°N and 45°N. They indicate palaeowinds blowing from the north/northwest. Aeolian sand, loessic sand, sandy loess, and loess deposits successively spread on both sides of the Rhône River. The loess is characterized by a coarse texture (main mode around 60 μm), strong local thickness (>5 m), limited extension, and abundant bioturbation. This preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the Last Glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources

Keywords

  • aeolian deposits, cartography, grain-size distribution, last glacial, LUCAS topsoil database, yardangs