Vitrine Reflectance (R_o) depth profiles along three wells located in the Western Pyrénées. (a) Geological map of the Western Pyrénées with the locations of the Les Cassières-2, Orthez-102 and Bellevue-1 boreholes. (b) Log of the Les Cassières-2 well with plotted Vitrinite Reflectance data along the depth profile. (c) Log of the Bellevue-1 well with plotted Vitrinite Reflectance and dip data along the depth profile. (d) Log of the Orthez-102 well with plotted Vitrinite Reflectance data along the depth profile. Each log is associated with graph showing the evolution of the thermal maturity of organic matter by Vitrinite Reflectance (R_o) versus depth. The brown curve represents the trend of R_o values related to normal statistical and steady geothermal gradient through time (Cardott and Lambert, 1985). The orange line corresponds to a sharp shift of R_o data corresponding to a maturity break.