Regional isostatic response to Messinian Salinity Crisis events

Abstract

The salinity crisis of the Mediterranean during Messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years, resulting in the deposition of kilometer thick evaporitic sequences. A large and rapid drawdown of the Mediterranean water level caused erosion and deposition of non-marine sediments in a large ‘Lago Mare’ basin. Both the surface loading by the Lower Messinian evaporites, and the removal of the water load resulted in isostatic/flexural rebound that significantly affected river canyons and topographic slopes. We use flexure models to quantitatively predict possible signatures of these events, and verify these expectations at well-studied margins. The highly irregular shape of the reconstructed basin calls for a three-dimensional model. Near basin margins, plate-bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the Mediterranean. We focus on one specific sea level scenario for the Messinian Salinity Crisis, where most of the evaporite load was deposited during a sea level highstand, followed by a rapid desiccation. Evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins. Differential uplift may lead to significant slope angle changes and thus gravity flows. The relative scarcity of Lower Evaporite sequences along the margins may be a result of these phenomena. Normal faulting of Lower Evaporite and older sediments and rocks is expected on the margins. Desiccation enhances erosion of the freshly exposed continental shelf and slope. Subsidence and riverbed sedimentation occurs on the continental margins, and significant uplift towards the basin center. Reverse faulting is predicted at the margins. Finally, regional isostatic uplift following Zanclean flooding is predicted to destabilize margin slope deposits, and to cause marginal uplift, river down-cutting, and normal faulting.