Paleoenvironmental conditions preceding the Messinian Salinity Crisis in the Central Mediterranean: integrated data from the Upper Miocene Trave section (Italy)

Integrated data of calcareous plankton and benthic foraminifers from the pre-evaporitic interval of Travesection (Central Italy) allowed the reconstruction of surface and bottom-water conditions in the CentralMediterranean during the interval from 7.61 to 6.33 Ma, preceding the Messinian Salinity Crisis.Our data point out a three-step paleoenvironmental evolution. During the first stage (7.61–7.02 Ma) benthicforaminiferal assemblages depict stable, well-oxygenated and ventilated bottom-water conditions, while thesurface water records variable temperature and high nutrient conditions, probably associated with strongseasonality. The second stage (7.02–6.70 Ma) points to unfavourable bottom-water condition, triggered bydeep-sea stagnation. This is witnessed by a significant decrease in oxygen concentration and biotic diversity,and by the presence of stress-tolerant taxa. A general warming of the surface water and a strongly stratifiedwater column, characterized by an expanded mixed layer, are also recorded.From 6.70 Ma onwards (third stage), a prominent change to more restricted, low-oxygenated, hypersalineconditions at the sea floor is testified by the total disappearance of deep-dwelling planktonic foraminifersand the increasing abundance of stress-tolerant species. Calcareous plankton reflects high instability of thesurface water in terms of nutrients, temperature and salinity. During this stage the environmentaldeterioration reaches intermediate depths in the water column.The initial change toward a step-wise isolation of the Central Mediterranean bottom-waters is probablyrelated to a general warming, responsible for a first slowing-down of the vertical circulation, favouringstratification of surface and intermediate waters and stagnation of bottom-waters. This warming is related tothe restricted connection between the Mediterranean Sea and the Atlantic Ocean, which occurred since7.146 Ma.In the Trave section, the isolation of bottom-waters most likely occurred at the same time as in otherMediterranean sections. However, due to the presence of a hiatus it cannot be excluded that it occurred witha delay of ~100 kyr, probably related to the shallower paleodepth of the basin.