The Tripoli Formation (6.96–5.98 Ma) of the Central Sicilian Basin provides a good record of the paleoceanographical changes that affected the Mediterranean during the transition from slightly restricted conditions to the onset of the Messinian Salinity Crisis. The Falconara/Gibliscemi section has been selected for an integrated approach at a high resolution scale using sedimentology, stable isotopes of the carbonates and microfossils. The sedimentary succession includes 46 precession-controlled cycles resulting from the periodical increase in biosiliceous productivity (diatomites) that followed the deposition of marls and pinkish laminites, which appear as sapropel-type deposits induced by the oceanic fertilization by terrestrial nutrients during wet periods. Higher scale environmental changes are superimposed to this precession forced rhythmicity. There is a general trend of increasing basin restriction from near marine conditions at the base of the Tripoli to semi-closed settings in its uppermost part, which are the prelude of the salinity crisis. This pattern reflects the hydrological response of the Mediterranean to the progressive decrease of the Atlantic inputs and an enhanced influence of the climate on depositional conditions. However, this evolution is not linear and shows successive phases of different duration. During the first period (until 6.71 Ma), open Atlantic–Mediterranean exchanges maintained relatively stable marine conditions. The second period (6.71–6.29 Ma), marks an important step in the basin restriction with a wider range of salinity fluctuations and an increased bottom stagnation. The 6.71-Ma event, which is correlated at a Mediterranean scale, may have resulted from shallowing of the Mediterranean gateway under a tectonic control. This shallowing reduced the oceanic inputs resulting in an increased climatic constraint of the Mediterranean hydrology. During the third period (6.29–6.03 Ma) an increase of the surface water salinity resulted in stressful conditions for the marine microfauna. The 6.29-Ma change is a major step in the restriction that may be correlated with the intensification of the glaciation recorded in the Atlantic, which could have enhanced the effects of the tectonic closure. The last two cycles (48 and 49), that underlie the ‘Calcare di Base’, witnessed the rapid transition to a semi-closed Mediterranean setting characterized by large variations of salinity from diluted to hypersaline conditions, under a dominant climatic control, and by the nearly complete disappearance of the marine organisms. Long-trend environmental changes recognized within the Tripoli Formation resulted from a complex set of interfering factors controlling the water fluxes exchanged between the Mediterranean and the world ocean. Most of the rapid changes identified in Falconara/Gibliscemi at 7.16, 6.71 and 6.29 Ma, that occurred simultaneously in the western and eastern Mediterranean, were mainly controlled by the stepwise tectonic closure of the Atlantic connections, although a glacio-eustatic overprint cannot be completely excluded.

The Lorca Basin (southeastern Spain) is part of a chain of small marginal Neogene basins located in the structurally active Betic area. The Upper Miocene (Messinian) sequence is composed of a thick diatomite-bearing series (Tripoli Unit) overlain by the Main Evaporites, analogous to the classical succession that records the main events during the Salinity Crisis in the Mediterranean region. The shallow restricted conditions of this region amplified the sedimentary responses to local and global forcings. An integrated approach using sedimentology, micropalaeontology, stable isotope geochemistry and organic geochemistry has been applied to the Tortonian/Messinian succession of the Lorca Basin, in order to obtain a continuous record of the environmental changes. The sediments record two major events which affected the whole Mediterranean: (1) high levels of productivity that led to the formation of the diatomite-bearing deposits in the early Messinian (Tripoli); and (2) the Messinian Salinity Crisis with its two major stages, represented by the Halite and Gypsum Units, both mainly precipitated from marine-derived brines. The rapid reflooding of the Mediterranean by normal marine waters at the base of the Pliocene did not reach the Lorca Basin, nor other basins of this part of the Betic area. Instead, continental sediments were deposited as a consequence of the regional uplift of SE Iberia, which started close to the Messinian/Pliocene boundary. The most prominent feature of this basin concerns the record of its restriction by the time of the deposition of the Tripoli Unit, which led to intercalations of precursor evaporitic layers, consisting of Ca-sulphate deposited in sub-aqueous and sabkha conditions, interbedded with diatomites. This alternation of evaporites and diatomites proves that the Lorca Basin was periodically restricted and reflooded by marine waters, a possible cause for this being relative sea-level fluctuations in the Mediterranean. This strengthens evidence of diachronism that suggests that the onset of the first Messinian evaporitic deposition was not synchronous, but was dependent on bathymetry and local tectonics. High productivity during the early Messinian in this basin is demonstrated by the thick deposits of diatomites. However, stagnation episodes may have occurred during this interval, as suggested by the preservation of high amounts of organic matter (organic-rich shales) and the extent of bacterial sulphate reduction which apparently occurred during early diagenesis. The formation of organo-sulphur compounds, replacement of sulphates by carbonates and the high levels of elemental sulphur are by-products of diagenetic processes occurring in a restricted hypersaline environment.