Contribution of electric, electromagnetic methods and ground penetrating radar (GPR) to the survey of the lacustrine basins. The case study of Le Lautry (Jura, France)

A geophysical exploration involving several methods - de resistivity method s, Slingram conductivity mapping (EM31) and Ground Penetrating Radar (GPR) lines - was carried out on the peat bog of Le Lautrey (Jura, France). This geophysical exploration completes advantageously the punctual observations deduced from 44 bore-holes about the topography of this basin. Thanks to th e complementary investigation depth of these methods in the range 0-15 m, i t was possible to recognise the substrate morphology of this lacustrine bas in and to precisely outline the variations of the thickness of lacustrine i nfillings over an area of 10 hectares. The dip (10 degrees SE) of the limes tones relief and the topographic irregularity due to fractures generate the thickness variations of the infillings. Three lacustrine sub-basins separa ted by an uplifting of the portlandian limestones were observed. The spatia l extent of a drainage paleochannel running to the exsurgence have been det ected. The geophysical data, added to the geological information show that the post glacial lake does not directly result from the glacier advance. It is mainly due to the tectonic structure of the area and to the impervious purbeckian marl, both factors generating the development of the lacustrine sub-basins.