Sedimentology and palaeoecology of barnacle-dominated, Amphistegina-bearing facies from the lower Pliocene of Liguria (northwestern Italy)

The lower Pliocene deposits of Pairola (Liguria, northwestern Italy) feature the otherwise uncommon occurrence of rock-forming amounts of barnacles (mostly belonging to the Neogene Euro-Mediterranean species Concavus concavus). Three main facies are recognized in the investigated succession: a barnacle-dominated facies, which formed along a shallow (<15 m deep) nearshore environment; a foraminifera-dominated facies from relatively deeper waters (40–100 m); and an intermediate transitional facies. These facies and their mutual relationships suggest deposition in a flooded valley, i.e. a ria (a kind of setting that was common along the Mediterranean coasts after the Messinian salinity crisis). Differing from other rias, the Pairola basin was exposed to strong waves, resulting in conditions favourable to barnacles. Although sedimentological and stratigraphic observations indicate that the Pairola succession formed within a timespan covering both cold and warm phases, the sub-tropical foraminifer Amphistegina is ubiquitous throughout the succession. Amphistegina occurs in the Pliocene and lower Pleistocene (Gelasian) of northern Italy, but not in the remainder of the Pleistocene. Crucially, this genus is currently recolonizing the Mediterranean and it is projected to reach the northern coasts of this basin soon, foretelling that Anthropocene Mediterranean temperatures might be approaching those typical of the Pliocene.