Henry Lickorish - Structural Geology
Calgary, Canada
tel: +1 250 213 2643
Tectonics and sequence stratigraphy in Messinian basins, Sicily: constraints on the initiation and termination of the Mediterranean salinity crisis
Butler R.W.H., Lickorish W.H., Grasso M., Pedley H.M. and Ramberti L. 1995
Geological Society of America Bulletin, 107, 425-439.

Deposits within the Caltanissetta basin of central Sicily have been important for developing the dessicating deep basin model for the Messinian salinity crisis in the Mediterranean. Linked structural and stratigraphic studies show that the Sicilian depocentres are synclines related to underlying thrust publications of the frontal part of the Maghrebian chain. Prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the Mediterranean. The precursor sediments (Terravecchia Formation) formed a delta, sourced from the north. Early Messinian regression acted on a range of palaeobathymetries, shallow in the north and progressively deeper in the south, locally complicated by active thrust publications. Initian draw-down of the Mediterranean base-level is marked across the thrust belt by first-cycle carbonates and evaporites on the structural highs and lows respectively. Vast accumulations of halite and potassium salts (up to 1200m) are restricted to growing thrust synclines. The different evaporite signitures may be related to different water conditions reflecting various meteoric and marine circulations across various sub-basins, with cyclicity reflecting high frequency variations in sea-level. A sequence stratigraphic model is developed to explain fractionation of evaporite facies between different palaeobathymetric settings and to predict the temporal evolution of the successions in different sub-basins. Thrusting provides accommodation space for evaporites and also controls the water pathways into the desicating basins. The intra-Messinian unconformity separating first and second-cycle evaporites is a 'type 1 sequence boundary' related to the forced regression associated with the acme of Mediterranean dessication, an interpretation supported by local ravinement and incised valley fills. The overlying second-cycle evaporites are a combination of detrital, reworked first-cycle material and primary gypsum formed under brackish water. Regional on-lap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base-level. These interpretations have several implications for Messinian correlations in the Mediterranean: The deep basin evaporites correlate with an intra-Messinian unconformity that separates the two cycles on Sicily and post-date the first-cycle deposits; regional base-level was largely restored before the end of the salinity crisis.