Integrated micropaleontological study of the Messinian diatomaceous deposits of the Monferrato Arc (Piedmont basin, NW Italy): New insights into the paleoceanographic evolution of the northernmost Mediterranean region

The upper Miocene diatom-bearing section of Pecetto di Valenza (Piedmont, NW Italy) represents a unique site for reconstructing the paleoceanographic processes that occurred before the onset of the Messinian salinity crisis in the northernmost Mediterranean basin. The combined analysis of foraminifera, calcareous nannofossils, diatoms and other siliceous microfossils observed in the marly and diatomaceous sediments allowed us to define four main evolutionary stages of the biogenic sedimentation. Each stage was typified by specific water column and seafloor conditions, tentatively correlated to the precession/insolation variability. In particular, the variation of the benthic assemblages allowed us to distinguish two stages in the evolution of the diatomaceous deposition, which would be otherwise impossible from the lithology. The accumulation of the diatomaceous sediments was likely controlled by the interplay between riverine runoff, water column stratification and convective mixing, rather than with upwelling and seafloor anoxia as inferred for the Western and Eastern sectors of the Mediterranean.