The Messinian Salinity Crisis as a trigger for high pore pressure development in the Western Mediterranean

Abstract

AbstractEvaporites are typically described as impermeable seals that create some of the world's highest reservoir pressures beneath the salt seal. However, several laboratory studies demonstrate that evaporites can retain open pore spaces that hydraulically connect the sediments above and below them in sedimentary basins. During the Messinian Salinity Crisis (5.97–5.33 Ma), up to 2,400 m thickness of evaporites were rapidly deposited in the Western Mediterranean, which may have generated high pore fluid overpressure in the basin sediments. Here we use one‐dimensional numerical modelling to quantify the temporal evolution of overpressure at two distinct locations of the Western Mediterranean, the Liguro‐Provençal and Algero‐Balearic basins, from the Miocene to Present. We reconstruct the sedimentation history of the basin, considering disequilibrium compaction as an overpressure mechanism and constraining model parameters (such as permeability and porosity) using laboratory experiments and the literature. In the Liguro‐Provençal basin the highest overpressure of 11.2 MPa occurs within the halite during deposition of Pliocene to Quaternary sediment, while in the Algero‐Balearic basin at the base of the Emile Baudot Escarpment, the highest overpressure of 3.1 MPa also occurs within the halite but during stage 3 of the Messinian Salinity Crisis (5.55–5.33 Ma). In the Algero‐Balearic basin an overpressure of 3.1 MPa could have been sufficient to hydro fracture the sediments, which agrees with the development of fluid escape features observed on seismic reflection profiles. In general, our models with evaporite deposition rates above 20 m kyr−1 and permeabilities below 10–18 m2, suggest that high overpressure, approaching lithostatic, can be generated in salt basins.