Tectonic control on diagenesis in a foreland basin: combined petrologic and thermochronologic approaches in the Grès d’Annot basin (Late Eocene–Early Oligocene, French–Italian external Alps)


Dr P. Labaume, Géosciences Montpellier (cc060), Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France. Tel.: +33 467 149 354; fax: +33 467 143 642; e-mail: pierre.labaume@gm.univ-montp2.fr


Combined petrographic study and apatite fission track analysis (apatite FTA) across the Grès d’Annot basin document maximum temperatures reached by this turbiditic sandstone formation, from around 60 °C at the SW basin margin up to around 200 °C below the Penninic frontal thrust, in relation to burial below the front of Alpine nappes. Increasing diagenetic grade across the basin is primarily expressed by the development of silica transfer by pressure solution and correlated porosity loss. We infer the nappe thickness profile, from the nappe front in the SW up to around 8–10 km in the NE. Apatite FTA dates exhumation of the Grès d’Annot during the Late Miocene, in relation to thrusting of the underlying Argentera and Barrot Palaeozoic massifs. This study illustrates the influence of thrust front propagation on foreland basin diagenesis and exhumation, and highlights potential implications for the evolution of sediment reservoir properties in this context.