AAPG Geoscience Technology Workshop

Datapages, Inc.Print this page

Halite Crystallization on Submerged Density Interfaces (Pycnoclines) Within the Deep Mediterranean Depressions

Abstract

The successful recovery of Messinian-age sediment from directly below the massive halite in the Levant Basin of the Eastern Mediterranean confirms a synchronous onset of calcium sulfate (gypsum) on the Mediterranean margins and halite in enclosed depressions (Meiilijson et al., 2018). The halite observed as a thick acoustically transparent layer in reflection profiles is present at elevations below today’s sea surface from <1 km to > 4 km. Alternating sulfate and marls without halite extend to depths of more than 1.2 km on the margin of Spain (Oacha, 2015), yet halite without sulfate can be found even higher in enclosed depressions in the Aegean and on the Balearic promontory (Maillard et al., 2014). Thus, there is strong evidence that during the Messinian Salinity Crisis the brine in the Mediterranean became stratified and denser brines accumulated in depressions where they concentrated to NaCl saturation below a sharp density interface. We propose that halite hopper-type crystals with their brine inclusions grew not at the water/air interface as observed today in salina, but on submerged density interfaces (pycnoclines) within the depressions, much like the evaporites that crystalized and incorporated Holocene foraminifera along the edges of pycnoclines in eastern Mediterranean brine deeps (Corselli & Aghib, 1987). Brine concentration first starts by evaporation at the air/sea surface. To account for the magnitude of halite eventually precipitated in <0.5 my, evaporation had to have occurred over an extensive surface area. Yet thick halite is only present in depressions or in such thin deposits on slopes as not to be imaged in reflection profiles. Concentrating brine cascaded into the depressions much like turbidity currents driven by the weight of their suspended sediment. Cascading brine is analogous to Antarctic bottom-water as it descends today into the ocean abyss due to its colder temperature. Cold temperatures at the bottom water-body of the Mediterranean depressions enhanced halite crystallization. References: Corselli & Aghib, 1987; Maillard et al., 2014; Meiilijson et al., 2018; Oacha, 2015