The record of the Messinian salinity crisis in mobile belts: Insights from the Molise allochthonous units (southern Apennines, Italy)

Mediterranean marginal basins recorded the Messinian salinity crisis (MSC) in various structural settings, including syn-rift, thrust-top, foredeep, and foreland basins. During the MSC, the Apennines were one of the mobile belts of the peri-Mediterranean chain. Starting from more hinterland areas, allochthonous units of both the northern and southern Apennines migrated toward the Adriatic foreland, developing allochthonous-top sedimentary basins. One of these basins, on top of the Molise allochthonous units (southern Apennines), recorded almost all of the main steps of the MSC. In a gypsum quarry district, the occurrence of conduits yielding flow-mobilized sediments, which cross-cut the Lower Evaporites, testifies to a fluid-migration event responsible for the formation of a brecciated mudgrade limestone buildup. This event can be connected with the Mediterranean drawdown responsible for the Messinian erosional surface (MES). The post-evaporitic marly succession that unconformably overlies the Lower Evaporites and the “Brecciated limestones” is characterized by the presence of Paratethyan molluscs and ostracods (Loxoconcha muelleri and Loxocorniculina djafarovi zones), and small mammals, among which is recorded the occurrence of Stephanomys debruijni. A disconformity within the post-evaporitic succession divides it into lower (p-ev1) and upper (p-ev2) Lago-Mare deposits. A further erosional surface separates the Messinian Lago-Mare sediments from fully marine lower Zanclean (MPl2 Zone) deposits. Whilst the unconformity separating the Lower Evaporites and the Lago-Mare deposits (although enhanced by a tectonic event) could be related to a late Messinian base level drop (MES1), as well as the disconformity between p-ev1 and p-ev2 (MES2), the younger angular unconformities affecting both the Lago-Mare deposits (p-ev2) and the fully marine Pliocene sediments might be related to two different phases of orogenic transport. Those events affected the Molise allochthonous units during their Late Miocene-Early Pliocene forelandward migration.