Calibrating the duration and timing of the Messinian salinity crisis in the Mediterranean: linked tectonoclimatic signals in thrust-top basins of Sicily

The Messinian 'salinity crisis' which affected the Mediterranean represents one of the most dramatic examples of base-level fluctuation known in the geological record: an amplitude of perhaps 2 km within a stage with a duration of less than 2 Ma. Deposits within the Caltanissetta Basin of central Sicily are used to calibrate the duration and timing of these fluctuations. Two successions of evaporites termed 'First Cycle' and 'Second Cycle', are separated by an inter-regional unconformity. The first cycle is regionally regressive while the second is transgressive. Chronostratigraphic calibration of these deposits has been provided by a linked magnetostratigraphic, structural and sedimentological study. The regression was protracted. The earliest evaporites in our study accumulated early in Chron C3Ar (pre 6.88 Ma) and the youngest accumulated late in chron C3An (post 6.0 Ma). During this interval the basinward shift in coastline was 70 km and in vertical section implies a relative fall in sea level at 0.3-0.4 m ka(-1). Lowstand probably finally occurred at 5.8-5.5 Ma. Transgression, marked by accumulation of the 'second cycle' deposits, which all record reversed magnetizations (C3r), apparently occurred far more rapidly (200 ka), prior to the return to 'normal' marine conditions in the central Mediterranean late in Chron C3r. Local rates of tectonic deformation are relatively slow within the thrust belt which underlies the Caltanissetta Basin. Therefore, it is likely that the timing and rates of the Messinian 'salinity crisis' on Sicily are generally applicable to other basins in the region and help to underpin rates of climate change within this part of the Neogene.