Detailed downhole geophysical profiles have been recorded at dm-scale through clastic coastal aquifers from experimental sites located in the Roussillon basin (Caballero et al., 2015). With core analyses, this extensive downhole dataset provides a dm-scale view of salt water intrusion processes in clastic sediments with the downhole determination of pore water conductivity in each of the holes. This inversion arises from the joint analysis of resistivity and porosity, obtained for the latter with a Nuclear Magnetic Resonance (NMR) sonde (Dlublac et al. 2013). Below major sea water intrusion in shallow Holocene sediments (40 000 to 55000 μS/cm), the Pliocene sands are intruded along m-thick sands layers, in a way which departs from the traditional Ghyben-Herzberg model. From 50 m depth downward, the pore fluid conductivity reaches 10 000 to 27 000 μS/cm in an otherwise fresh water environment. These salinity peaks are often related to higher permeability horizons identified from NMR data. A salinity increase in adjacent clay-rich sediments is also obtained, apparently resulting from a more diffusive salinity intrusion process at dm-scale. This resistivity-based approach provides a new description of salt water intrusion processes in coastal aquifers sand-shale structures from passive margins. In a climate change context and from resistivity profiles repeated over time (or permanent downhole geophysical observatories), this new dynamic insight provides a high resolution means to closely follow in space and time sea water intrusion processes in coastal aquifers. Caballero, Y., and Ladouche, B. (2015). Impact of climate change on groundwater in a confined Mediterranean aquifer. Hydrol. Earth Syst. Sci. Discuss., 12, 10109–10156. Dlubac, K., R. Knight, Y.-Q. Song, N. Bachman, B. Grau, J. Cannia, and J. Williams (2013), Use of NMR logging to obtain estimates of hydraulic conductivity in the High plain aquifer, Nebraska USA, Water Resour.Res.,49,1871-1886.