Lacustrine Sedimentation in an Evaporitic Environment: The Ludian (Palaeogene) of the Mormoiron Basin, Southeastern France

  1. Albert Matter and
  2. Maurice E. Tucker
  1. Georges Truc

Published Online: 29 JUN 2009

DOI: 10.1002/9781444303698.ch10

Modern and Ancient Lake Sediments

Modern and Ancient Lake Sediments

How to Cite

Truc, G. (1978) Lacustrine Sedimentation in an Evaporitic Environment: The Ludian (Palaeogene) of the Mormoiron Basin, Southeastern France, in Modern and Ancient Lake Sediments (eds A. Matter and M. E. Tucker), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303698.ch10

Author Information

  1. Département des Sciences de la Terre, 15–43 Bd du 11 Novembre 1918, Université Lyon 1, 69621 Villeurbanne, France et Lab. associé au C.N.R.S. No. 11 “Paléontologie stratigraphique et Paléoécologie”, France

Publication History

  1. Published Online: 29 JUN 2009
  2. Published Print: 24 NOV 1978

ISBN Information

Print ISBN: 9780632002344

Online ISBN: 9781444303698



  • rifting affected the ‘pyreneo-provenc,ale’ folds;
  • Evaporite mineralogy;
  • dissolution and/or dehydration of gypsum;
  • crystallization of gypsum as lenticular, twinned (swallow-tail) and ‘grass-like’ crystals;
  • increasing aridity leading to desiccation


The Palaeogene basin of Mormoiron is one of many sedimentary basins and grabens developed along the Rhône—Saône axis of southeastern France. During the Palaeogene the Rhodanian trough, between the Massif Central and the Alps, consisted of several subsiding grabens separated by stable platforms. From west to east small grabens were located at Alès, Nîmes and at Manosque, bordering the Durance fault, and basins at Mormoiron and Apt-Forcalquier. The graben structures in the Ludian were formed as a result of an east—west extensional tectonic phase following the Lutetian and Bartonian compression of the ‘pyrénéo—provençale’ phase. The structural regime produced a palaeogeography of isolated lake basins in which evaporites were formed. In the basin of Mormoiron, a thin sequence of evaporites developed on the platform areas, and a much thicker sequence was deposited in the more rapidly subsiding basin centre. In the Lower Ludian, terrigenous clastics were deposited around the margins of the basin, with finer material reaching the basin centre where organic-rich clay accumulated. In the eastern part of the basin, near the Monts-de-Vaucluse, limestones with brackish-water molluscs (Potamides, Tympanotonus and Melanopsis), ostracoda and foraminifera were deposited. Elements of a marine fauna indicate adaptation of certain species derived from a nearby marine area. Evaporites also formed in the basin centre during the Lower Ludian so that lenticular gypsum crystals are scattered in the organic-rich clay. During the Upper Ludian, a decrease in supply of terrigenous material led to desiccation and the Mormoiron lake basin became part of a much larger evaporitic area. Dolomite, sepiolite and magnesian smectites formed in the basin centre together with gypsum. At the basin margins limestones became more dolomitic. A fauna persisted in this evaporitic situation through ground-water springs from the Monts-de-Vaucluse. Periodically, desiccation of the basin produced mud-cracked horizons, locally with bird and mammal footprints. At the end of this arid period, an extensive development of algal mats covered the whole area of the basin. This was followed by a renewed phase of terrigenous clastic sedimentation indicating a return to a more humid climate. Diagenetic phenomena in the sulphate deposits include anhydrite after gypsum and secondary gypsum (alabastrine-type) after anhydrite.