Controls on Messinian Lower Evaporite cycles in the Mediterranean

The Messinian Salinity Crisis in the Mediterranean, 5.96-5.33 Million years ago (Ma), represents the most recent case of massive evaporite deposition throughout an ocean basin. Here we quantitatively investigate the nature of the gypsum-marl cycles within its first phase, known as Lower Evaporites (LE) or Primary Lower Gypsum (PLG) (5.96-5.59 Ma). We conclude that to precondition the basin for deposition of the LE/PLG sequence, its connection with the open Atlantic must have been reduced to about 3% of the cross-sectional area of the modern Strait of Gibraltar. Using the modern strait morphology for scale, this would imply a connection with a depth of about 50 m and a width of several kilometres. We find that the LE/PLG evaporite-marl cycles may then have resulted from sea-level fluctuations of the order of 5 to 10 m and/or fluctuations in the Mediterranean's hydrological deficit of the order of 20%. Previous work has argued that sea-level control may be excluded, because there are too many cycles to agree with orbital obliquity-related timing. However, we argue from analogy with Quaternary sea- level records that sub-orbital sea-level fluctuations may easily reach the required magnitudes, so that sea-level control remains plausible.