EVOLUTION OF THE MESSINIAN MEDITERRANEAN ENVIRONMENTS - THE TRIPOLI FORMATION AT CAPODARSO (SICILY, ITALY)

New held data have been collected from the Capodarso section (Caltanis setta basin, Sicily); 48 samples from the Tripoli Formation were analy sed for foraminifera, dinocysts, palynofacies, CaCO3, pollen grains an d clay minerals. The uppermost clays of the Terravecchia Formation are clearly the result of deeper deposition than those corresponding to t he lowermost analysed samples within the overlying Tripoli Formation. So, the general evolution of the basin was from normal marine conditio ns to confinement, during which the sedimentation of diatomite vs. cla y was mainly controlled by relative sea-level changes. Three successiv e types of processes are considered to have generated the diatomites: (1) in the lower part of the section, the sea level was relatively hig h and deposition of diatomites was aided by sealevel rises of unequal importance and variations of continental precipitations and run-off; ( 2) then, relatively minor sea-level oscillations prevailed; however, t he second part of the sequence is characterized by a generally strong shallowing trend leading to basin confinement; (3) the explanation for diatomites during the last member does not rely as much on the occurr ence of substantial sea-level rises in an increasingly desiccated basi n; on the other hand, an increased number of rivers reached the centra l area of the basin, which helped to produce the youngest diatomites. The warm (subtropical to tropical) and xeric climate predisposed to su ch an evolution, inducing continuous high salt-concentration of marine waters; so, the smallest influx of less saline (oceanic) waters and/o r continental freshwater (run-off) could produce water-mass stratifica tion and diatomite deposition. However, not all lithologic breaks are likely to correspond to recorded environmental transitions. Bio- and m agnetostratigraphy of the section allow consistent relationships betwe en the sea-level curve at Capodarso and the delta(18)O curve at Site 5 88 (southwest Pacific), attesting global eustatic control on the sedim entation of the Caltanissetta basin up to the beginning of the Messini an salinity crisis.