The effects of salt diapirs on the thermal maturity of surrounding sediments in the western Pyrenees, Spain

Salt diapirs have been modeled as having a large effect on the thermal maturity of surrounding sediments as a result of the high thermal conductivity contrast between halite and other lithologies. The goal of this study was to confirm these and other theoretical predictions through sampling of three salt structures in the western Pyrenees, Spain. Stratigraphic units around these three diapirs were targeted based on their lithologies and positions relative to the diapirs. Samples were analyzed for vitrinite reflectance and quartz cementation to determine their levels of thermal maturity. Remote sensing instruments were used to attempt to measure present day heat flow above the diapirs, and available well logs and seismic data were analyzed to determine the subsurface extent and orientation of the diapirs. Vitrinite reflectance revealed that sediments closest to the Ribera Alta and Orduna diapirs were undermature compared to regional values. The extent of the thermal anomalies around the Ribera Alta and Orduna diapirs extended to approximately 1.5 times the radii of the diapirs. Samples located above the Gernika salt weld were generally more mature than samples located below the weld, and samples closest to the root of the weld were less mature than samples further from the root. Remote sensing proved ineffective in this locality due to the high moisture content in surface vegetation. Determining the effects of salt on the thermal maturity of surrounding sediments is important because it allows a more comprehensive understanding of source rock maturity and reservoir porosity preservation within the context of petroleum systems in basins that contain salt.