The Monte Carrubba Formation (Messinian, Sicily) and its correlatives: new light on basin-wide processes controlling sediment and biota distributions during the Palaeomediterranean-Mediterranean transition.

A little known marine Miocene (Messinian) succession in the Hyblean region of south eastern Sicily preserves a carbonate ramp sequence which developed on the tectonically stable foreland margins of the African Plate (Pelagian Block). The ramp (Monte Carrubba Formation) was distally steepened and contained a shoalwater barrier and lagoonal inner ramp complex. The outer ramp is poorly preserved though distal deep water ramp facies (Tellaro Formation) in the south Hyblean region preserve a full Globorotalia mediterranea Subzone and major part of the Globigerina multiloba Subzone succession. This ramp sequence faithfully records the subtle interplay between the global eustatic curve and internal Palaeomediterranean base-level signatures for the Late Miocene. The earliest second order Palaeomediterranean lowstand occurred in the Late Tortonian at about 7.3 Ma and a second occurred at about 6.75 Ma within the Early Messinian G. mediterranea Subzone. Although the overriding control at the time was the global eustatic curve, harmonic discrepencies between it and the Palaeomediterranean curve resulted from constriction of the Atlantic connection during the latest Tortonian. From about 6.4 Ma until about 5.96 Ma increasingly restricted conditions developed across the Monte Carrubba inner ramp. These faithfully reflect many second order, constriction-driven Palaeomediterranean sea-level oscillations which were superimposed on to the falling global signal as the connecting Atlantic seaways became constricted. These oscillations resulted in major reductions in planktonic faunal diversity within the outer ramp, followed by total emergence of the inner ramp by about 6.05 Ma. Marine deposition continued until about 5.96 Ma in the southern part of the Hyblean region. However, between 6.05 Ma and about 5.6 Ma the amplitude of successive Palaeomediterranean sealevel oscillations increased to over 100 m, causing prolonged periods of total Palaeomediterranean isolation. The Hyblean carbonate suite also contains post-Messinian Salinity Crisis (post-MSC) ‘Lago Mare’ highstand deposits which are developed unconformably above the Monte Carrubba Formation. The widespread distribution of hyposaline to near-marine Congeria faunas within the Lago Mare episode argues for high post-MSC Mediterranean water levels in the Central Mediterranean Late Messinian.