Palaeoclimate and palaeoenvironments in central Mediterranean during the last 1.6 Ma before the onset of the Messinian Salinity Crisis: A case study from the Northern Apennine foredeep basin

The palynological record from late Tortonian–early Messinian sediments of the Trave section (Central Italy) allows for a floristic, vegetational, and palaeoclimatic reconstruction between 7.61 and 6.33 Ma. The sedimentary succession includes 34 precession-controlled cycles expressed by marl and organic-rich/sapropel alternations. This rhythmicity, reflecting the enhanced influence of climate, is also recorded by the pollen content of both sapropels, dominated by subtropical to warm temperate angiosperm taxa, and marly limestones dominated by Pinus and other Pinaceae saccatae. At the same time the overall percentage decreases throughout the section of Pinus and other Pinaceae saccatae, as well as the distality index values [Dinocysts/(Dinocysts + pollen)], reflect the hydrological response of the Mediterranean to the progressive decrease of the Atlantic inputs. The palynological record points out the successive steps of the reduction of Atlantic–Mediterranean exchanges, with persistent relatively stable marine conditions in the Mediterranean until 7.2 Ma, followed by a phase of restriction since 7 Ma which becomes more pronounced at 6.7 Ma. Between 7.61 to 6.33 Ma the palynological signature of climate supports prevalent subtropical to warm/temperate conditions with high humidity despite minor cooler episodes between ca 7.6 and 6.5 Ma. However, the major expansion of temperate broad-leaved deciduous taxa amongst thermophilous angiosperm taxa, could reflect a slight increase of seasonality in connection with the major shallowing of the Mediterranean gateway under a tectonic control, since 6.7 Ma. The comparison with available pollen records from both southern and western sites, where drier conditions and expanded herbaceous cover dominate, demonstrate latitudinal and longitudinal gradients within the Mediterranean area. However, neither in the moister Northern Apennines, nor in the drier southern Italian and Spanish settings, is the progression to the Messinian Salinity Crisis marked by dramatic changes towards more arid climate conditions and significant increase of C4-plants. Knowledge of the complex and composite vegetation and climate scenarios in the Mediterranean proves to be relevant for comprehensive reconstructions of the history of the Messinian salinity crisis onset.