Paleoclimate reconstruction during the Messinian evaporative drawdown of the Mediterranean Basin: Insights from microthermometry on halite fluid inclusions

Abstract

[1] Data constraining the paleoenvironmental conditions during the Messinian evaporative drawdown of the Mediterranean basin are still conflicting. Here we present a comprehensive paleoclimatic reconstruction during Messinian halite deposition from several Italian sites. We performed fluid inclusion analyses to define better both the composition of the Mediterranean water body and the paleotemperatures of the Messinian brine during halite crystallization. We measured homogenization temperatures on 218 primary all-liquid fluid inclusions in Messinian halite from the Volterra, Crotone, and Caltanissetta evaporite basins. These measurements provided mean homogenization temperatures of 17-18 C, with a range between 10-11 C and 28-29 C, which should be close to the SST of the Mediterranean Sea during halite deposition. The occurrence of major elements such as Cl, Na, Mg, S, Ca, and K within the halite fluid inclusions, together with the presence of minerals such as pentahydrite, polyhalite, and Ca-, K-, and Mg-sulfates, indicates that these salt bodies originated from mainly marine water. Taking into account both the present-day annual SST of the Mediterranean Sea around the sampling sites, which ranges between 18 and 20 C, and the lower latitude of the Mediterranean Basin during the Messinian Salinity Crisis, our homogenization temperatures point to a colder climate during the Messinian halite deposition compared to the present interglacial climate stage. This conclusion is consistent with halite deposition during a Late Miocene glacial interval (TG12).

Sea level and climate forcing of the Sr isotope composition of lateMioceneMediterranean marine basins

“…Earlier, less precise constraints had linked it to two glacial intervals: TG12 and TG14 [ Krijgsman et al ., ; Rouchy and Caruso , ; Hilgen et al ., ]. Fluid inclusion homogenization temperatures from the Messinian halite support this interpretation, as the halite precipitated from marine water with mean sea‐surface temperatures of 17–18°C, which are cooler than the 18–20°C temperatures at the same locations in the present Mediterranean water body [ Speranza et al ., ].…”

Relating natural heterogeneities and rheological properties of rocksalt: New insights from microstructural observations and petrophyisical parameters on Messinian halites from the Italian Peninsula

“…Salt samples from Petralia and Racalmuto mines (Speranza et al, 2013) and from Z1 and V1 diapirs selected for comparison with Volterra series, although coming from different locations with different geological settings, appear to fit quite well in the classification scheme defined above. In particular, salt samples from Racalmuto mine and V1 diapir are very rich in primary crystal remnants and appear almost undeformed (type I); Petralia mine sample is rather comparable to the type IV salt being constituted by only secondary, slightly deformed salt crystals, although much smaller than those pertaining to Volterra series; finally, Z1 diapir salt is very highly deformed and recrystallized and so can be easily associated to the type III salt.…”

“…Primary "cloudy" crystals, from less than 1 mm to 1 cm in length, are very abundant. Some typical primary features, like chevron crystals and growth bands, are easily recognizable (Speranza et al, 2013). Some very thin (around 2 mm) clay strata, intercalated with salt, are visible.…”

“…The crystals vary in sizes from less than 1 mm to around 1 cm in length and have typical primary salt shapes like chevrons and hoppers (Lowenstein and Hardie, 1985;Speranza et al, 2013) with easily recognizable growth bands (b and d in Fig. 3; d-7 in Fig.…”

“…They appear white/gray to the naked eye and opaque when looking with a microscope in transmitted light. This is due to the countless cubic-shaped and randomly distributed primary fluid inclusions contained in primary crystals (Speranza et al, 2013). Growth bands and shapes like chevrons, cubes, and hoppers are typical primary salt features.…”