Extent and chronology of the Pleistocene permafrost in France : database of periglacial structures and OSL dating of sand wedges.

• Main Author: Andrieux, Eric
• Other Authors: De la Préhistoire à l'Actuel : Culture, Environnement et Anthropologie (PACEA), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux, Pascal Bertran
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2017
• Subjects: Pleistocene permafrost; Database; OSL dating; Pergélisol pléistocène; Base de données; Datation OSL; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Ice; permafrost; wedge*; pergélisol
• Online Access: https://tel.archives-ouvertes.fr/tel-02191524; https://tel.archives-ouvertes.fr/tel-02191524/document; https://tel.archives-ouvertes.fr/tel-02191524/file/ANDRIEUX_ERIC_2017.pdf

During the Mid to Late Pleistocene, the land area affected by periglacial conditions expanded and contracted repeatedly over large surfaces in mid-latitude Western Europe. In such environments, permafrost or deep seasonal freezing of the ground formed typical features, which have been the subject of abundant research by geomorphologists. In particular, researchers attempted to reconstruct the maximal extent of Pleistocene permafrost based on field evidence. Although most reconstructions suggest that permafrost spread over part of France during the coldest periods of the Pleistocene, there is no agreement regarding the land surface affected. This is mainly due to the scarcity of field data used for mapping and to the questionable palaeoclimatic significance of certain periglacial features. In addition, permafrost modelling during the Last Glacial Maximum using Global Climate Models does not seem consistent with field data. To solve these issues, a database of Pleistocene periglacial features has been compiled from a review of academic literature and unpublished reports, the analysis of aerial photographs and new field surveys. Polygons, soil stripes, ice-wedge pseudomorphs, sand wedges and composite wedge pseudomorphs were included in the database together with their geographic coordinates, geological context, description and references. The distribution of the identified features was analysed with a GIS software and clearly indicates that large areas in France were affected by periglaciation, apart from the southwesternmost part of France and the Languedoc. Ice-wedge pseudomorphs do not extend south of 47°N which indicates that widespread discontinuous permafrost did not affect the land south of the Paris basin. The exclusive presence of sand wedges with primary infill between 45 and 47°N, mainly in the periphery of coversands, suggests that thermal contraction cracking of the ground occurred together with sand drifting in a context of deep seasonal frost or sporadic discontinuous permafrost, unfavourable for ...