The paleogeography during Early Cretaceous of the northern margin of the Ligurian Tethys is poorly constrained because of deformation and erosion during Pyrenean and Alpine orogenic phases. The present-day limit between Lower Cretaceous sediments in the SouthEast basin, located at the northwestern margin of the Ligurian Tethys, and basement rocks is the consequence of a protracted erosion history. Lower Cretaceous sediments observed today in the basin, even close to the present-day outcropping border, are characteristic of pelagic environments. A larger extent of a Lower Cretaceous cover on the basement must then be considered. This study focuses on the western part of this margin (the Causses basin), in the South of the Massif Central (France), using several thermochronometers and geothermometers to decipher the former extent of the sedimentary cover. Apatite fission track thermochronology on basement rocks surrounding the Causses basin suggests that these rocks cooled from temperatures higher than 110°C during the mid-Cretaceous. Average fluid inclusion homogenisation temperatures between 94°C and 108°C are recorded in calcite veins from outcropping Toarcian and Aalenian shales. In the shales, Tmax values, temperature obtained by Rock-Eval pyrolysis of organic matter, are in agreement with these elevated temperatures. Different explanations for these relatively high temperatures, which cannot be explained by the present-day sedimentary serie in the basin, have been tested using a 1D thermal modelling procedure (Genex). For a 95±10-mW/m 2 paleoflux, thick sedimentary deposits (2.5±0.3 km) including 1.3±0.3 km of Lower Cretaceous sediments cover the South of the Massif Central; these formations have been subsequently eroded from mid-Cretaceous time onwards. This study confirms that the South of the Massif Central was a site of marine sedimentation during the Early Cretaceous where a thick sedimentary sequence was once deposited.

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Overburden shales that overlie and seal hydrocarbon reservoirs usually exhibit polar anisotropy, also called Vertical Transverse Isotropy (VTI). This anisotropy is important for correct seismic inversion, seismic-to-well ties as well as having geomechanical implications. P-wave anisotropy cannot usually be determined from a vertical well unless a walkaway vertical seismic profile (VSP) has been obtained, however, such measurements are still rare. S-wave anisotropy though can be estimated from logs if the speed of sound in mud and the Stoneley wave velocity in the shale are known. Then, the P-wave anisotropy can be computed using theoretical models or empirical trends. The Stoneley wave velocity is nowadays routinely measured by sonic tools and, if a reliable mud velocity is known, the horizontal shear wave velocity (parallel to and polarised in the bedding plane) can be estimated. Thomsen's gamma parameter for S-wave anisotropy can then be calculated. If mud velocity is not known, the horizontal shear wave velocity can be obtained using calibration in an isotropic interval. Using this method, we analyse the VTI anisotropy in the Torosa-6 well in the Caswell Sub-basin of the Browse Basin, Australia. Torosa-6 drilled through the Jamieson and Echuca Shoals shaly formations where Vclay reaches ~75%. Elastic anisotropy of the shaly Jamieson and Echuca Shoals Formations has been analysed. Thomsen's gamma shows a good correlation with the clay fraction in each of these formations. However for the same clay fraction, anisotropy is about 20% higher in the Jamieson Formation compared to the Echuca Shoals. This Jamieson Formation contains up to 15% of smectite, and we are investigating how this may lead to higher levels of VTI anisotropy compared with illitic clays predominant in the Echuca Shoals Formation.