Evolution of the Messinian Mediterranean environments: the Tripoli Formation at Capodarso (Sicily, Italy)

Abstract

New field data have been collected from the Capodarso section (Caltanissetta basin, Sicily); 48 samples from the Tripoli Formation were analysed for foraminifera, dinocysts, palynofacies, CaCO 3, pollen grains and clay minerals. The uppermost clays of the Terravecchia Formation are clearly the result of deeper deposition than those corresponding to the lowermost analysed samples within the overlying Tripoli Formation. So, the general evolution of the basin was from normal marine conditions to confinement, during which the sedimentation of diatomite vs. clay was mainly controlled by relative sea-level changes. Three successive types of processes are considered to have generated the diatomites: 1. (1) in the lower part of the section, the sea level was relatively high and deposition of diatomites was aided by sea-level rises of unequal importance and variations of continental precipitations and run-off; 2. (2) then, relatively minor sea-level oscillations prevailed; however, the second part of the sequence is characterized by a generally strong shallowing trend leading to basin confinement; 3. (3) the explanation for diatomites during the last member does not rely as much on the occurrence of substantial sea-level rises in an increasingly desiccated basin; on the other hand, an increased number of rivers reached the central area of the basin, which helped to produce the youngest diatomites. The warm (subtropical to tropical) and xeric climate predisposed to such an evolution, inducing continuous high salt-concentration of marine waters; so, the smallest influx of less saline (oceanic) waters and/or continental freshwater (run-off) could produce water-mass stratification and diatomite deposition. However, not all lithologic breaks are likely to correspond to recorded environmental transitions. Bio- and magnetostratigraphy of the section allow consistent relationships between the sea-level curve at Capodarso and the δ 18O curve at Site 588 (southwest Pacific), attesting global eustatic control on the sedimentation of the Caltanissetta basin up to the beginning of the Messinian salinity crisis.