Rwh. Butler et al., TECTONICS AND SEQUENCE STRATIGRAPHY IN MESSINIAN BASINS, SICILY - CONSTRAINTS ON THE INITIATION AND TERMINATION OF THE MEDITERRANEAN SALINITY CRISIS, Geological Society of America bulletin, 107(4), 1995, pp. 425-439
Deposits within the Caltanissetta basin of central Sicily have been im
portant for developing the desiccating deep basin model for the Messin
ian salinity crisis in the Mediterranean. Linked structural and strati
graphic studies show that the Sicilian depocenters are synclines relat
ed to underlying thrust structures of the frontal part of the Maghrebi
an chain, Prior to the salinity crisis these basins were hydrodynamica
lly linked through the foredeep to the Mediterranean, The precursor se
diments (Terravecchia Formation) formed a delta, sourced from the nort
h, Early Messinian regression acted on a range of paleobathymetries, s
hallow in the north and progressively deeper in the south, locally com
plicated by active thrust structures, Initial draw-down of Mediterrane
an base level is marked across the thrust belt by first cycle carbonat
es and evaporites on the structural highs and lows, respectively. Vast
accumulations of halite and potassium salts (up to 1200 m) are restri
cted to growing thrust synclines. The different evaporite signatures m
ay be related to different water conditions reflecting various meteori
c and marine circulations across various subbasins, with cyclicity ref
lecting high-frequency variations in sealevel. A sequence stratigraphi
c model is developed to explain fractionation of evaporite facies betw
een different paleobathymetric settings and to predict the temporal ev
olution of the successions in different subbasins. Thrusting provides
accommodation space for evaporites and also controls the water pathway
s into the desiccating basins. The intra-Messinian unconformity separa
ting first and second cycle evaporites is a ''type 1 sequence boundary
'' related to the forced regression associated with the acme of Medite
rranean desiccation, an interpretation supported by local ravinement a
nd incised valley fills. The overlying second cycle evaporites are a c
ombination of detrital, reworked first cycle material and primary gyps
um formed under brackish water. Regional onlap relationships and bed c
ontinuity suggest that this water body was of regional extent with a s
ystematically rising base level. These interpretations have several im
plications for Messinian correlations in the Mediterranean: The deep b
asin evaporites correlate with an intra-Messinian unconformity that se
parates the two cycles on Sicily and postdate the first cycle deposits
; regional base level was largely restored before the end of the salin
ity crisis.