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KARST ET EXTENSIONS GRAVITAIRES D'ALTITUDE : LE MASSIF DU JAOUT (PYRÉNÉES OCCIDENTALES - FRANCE)
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ABSTRACT. High altitude karst and horizontal gravity extensions: the Jaout massif (western Pyrenees, France.
The fracture network has to be well-defined to better understand the subsurface water circulation in a karstic aquifer. We therefore carried out a study of the fracture network on the Jaout massif in the Western Pyrenees (France). This karstic massif, developed in the Urgonian limestones, represents an important aquifer with an area of 40 km2. We first analyzed the fracture network by remote sensing (SPOT image and aerial photographs) to define the kilometric to hectometric scale. We also recovered field measurements to define the metric to decimetric scale. When the fault planes were striated, we have measured for each fault: strike, dip, sense of dip, pitch of striations, sense of pitch and sense of movement. By this microtectonic study, all the determined fracture families can be linked to tectonic events. Along the North Pyrenean Fault, the major Pyrenean events (Eocene-early Miocene event) erased all previous evidence of movement: we only determined on the massif Jaout this event (submeridional shortening) and the two following phases (the ENE-WSW to EW compression and the recent NW-SE shortening). We also determined at high altitudes important horizontal extensions associated with superficial gravity phenomena. Water circulation in the upper part of this karstic reservoir can be explained by this contemporaneous extension. Our data underline the relationship between karstification and recent tectonic events.
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About: Stéphanie KLARICA
UMR 5831 Imagerie Géophysique, CURS-IPRA, Av. de l'Université, 64000 PAU, FRANCE
About: Yves HERVOUET
adresse actuelle: Escuela Ingeneria de Geologia, Universidad de Los Andes, Mérida, Venezuela
About: Jacques BAUER
UMR 5831 Imagerie Géophysique, CURS-IPRA, Av. de l'Université, 64000 PAU, FRANCE, e-mail: yves.hervouet@ univ-pau.fr