Miocene unconformities in the central Apennines: Geodynamic significance and sedimentary basin evolution

This paper shows the results obtained from an integrated study (geology, biostratigraphy and geochemistry) carried out on the Miocene sedimentary deposits in Central Italy in order to define the timing of the sedimentary basin evolution. This paper deals also with the causes of the unconformities recorded in these basins. In the Miocene deposits of the Latina Valley and the Ernici-Simbruini Mts. several unconformities which distinguish different stratigraphic sequences have been recognized (D-0, D-1, D-2, D-3 and D-4). For each unconformity a general description together with a geodynamical significance is provided. In particular, D-0 unconformity appears to be related to a regional tectonic event (Adria-Europe collision). As a consequence, the Adria lithosphere folded and the area underwent a regional erosive event. D-1, D-2 and D-3 unconformities have had a more local tectonic control since they represent the stratigraphic record of the migration of the Apennines thrust belt/foredeep system. D-1 and D-2 unconformities are related to the late Tortonian foredeep stage, whereas D-3 is linked to the early Messinian piggy-back stage. Moreover, the D-4 unconformity, which took place during the Messinian piggy-back stage, is strictly linked to the sea-level drop of the Messinian salinity crisis. In this paper the genesis and evolution of a late Tortonian foreland basin is also stressed (Latina Valley foredeep basin). Finally, taking into account sequence boundaries, nannofossil biostratigraphy and geochemistry isotopic data, a comparison with the curve of the 3rd order of the relative coastal onlap (Haq et al., 1988) has been attempted in order to distinguish the unconformities controlled either by tectonic or eustatic processes.