Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : The Latest Cretaceous/Paleocene paleokarsts from Bas-Languedoc (South of France) are characterized by : 1) exokarstic paleosurfaces (sink holes, pinnacles, canyons) which are mostly superimposed onto the Late Jurassic limestones and partly filled up with breccias and sandy clays containing Paleocene planktonic foraminifera; 2) endokarstic cavities filled up by sandy pelites and laminated mudstones with similar micropaleontological assemblage. All these cavities constitute three cut-and-filled paleokarstic systems. A general model of formation for this polyphase system is proposed. These paleosurfaces are generated by a Latest Cretaceous tectonic phase and Paleocene movements associated with eustatic rises inducing rapid floodings. During Upper Danian-Lower Selandian times three successive base levels drops, whose cumulated duration could be as long as 3 Ma, have induced several hundred metres of incisions within the exposed Jurassic carbonate series. A paleogeographic reconstruction shows three main marine gulfs which extend towards NE the EW Pyrenean thrust belt ("Pyrenean Paleocene Trough", PPT) located on the axis of the future Pyrenees. The similarity of the facies and micropaleontological content in the two domains suggests connexions between the marine Paleocene deposits of Bas-Languedoc and the PPT. It could thus explain the succession of the same tectono-eustatic events. We propose, as an hypothesis, that the rapid sea-level changes, as recorded by the imbricated karstic paleomorphologies, could be induced by the closing and the opening of a strait in the Eastern part of the PPT acting as a sill. This would be controlled by tectonic movements along the active orogenic axis of the Pyrenean Range and eustatic variations of the Paleocene World Ocean. The karstic systems developed during these low-stand episodes may have been later reactivated after the Early Selandian and more specifically during the Messinian desiccation event. This late evolution may have generated deep flooded karsts, now situated below the present sea level. Such karsts, partly inherited from Paleocene, could be important aquifers of economic interest.
ISSN: 0985-3111

hal-00407601
https://hal.archives-ouvertes.fr/hal-00407601
DOI : 10.3166/ga.20.301-326

Éditeur(s) : HAL CCSD Elsevier
Résumé : Different types of fractures and fault rocks occur within the major normal fault zones bordering the NW of the Neogene Penedes basin (NE Spain). In the southwest part of the basin, the main fault is the Baix Penedes fault that places the Upper Jurassic-Lower Cretaceous dolomicrites of the footwall in contact with the Miocene siliciclastic sediments of the hangingwall. Within the footwall damage zone, different fracture systems and their respective associated breccias and cements have been recognized. Using a combination of structural, petrologic and geochemical analyses, we show that these fracture systems evolved from mainly tectonic to mainly karstic features during the progressive development and upward propagation of the fault. The earlier fractures and associated breccias represent the initial stages of the fault propagation, when the process zone formed around the fault tip was dominated by dilatant fracturing (fractures 1 and dilatant breccias B1). The fluid involved in this early deformation precipitated the dolomite cement Cl, in equilibrium with the host-rock in a closed hydrogeological system. Localization of frictional processes generated cataclasites and ultracataclasites along distinct second-order faults (fractures 2). In these fractures, the dolomite cement C2 precipitated in relation to the incipient opening of the hydrological system to percolating meteoric waters. The later fractures and associated breccias represent the late stages of the fault propagation. These structures (fractures 3, fractures 4 and the dilatant breccias B2) were formed when the extensional deformation reached the surface, resulting in an increasingly open hydrogeological system. At these stages, deposition of the dolomitic sediment DS and precipitation of the calcite cements C3, C4 and C5 show the circulation of freshwaters in a vadose meteoric environment, i.e. in karstic conditions.
ISSN: 0375-6742

hal-00512690
https://hal.archives-ouvertes.fr/hal-00512690
DOI : 10.1016/j.gexplo.2009.11.010