Benthic foraminiferal assemblage turnover during intensification of the Northern Hemisphere glaciation in the Piacenzian Punta Piccola section (Southern Italy)

Abstract

We present the results of a high-resolution analysis of the benthic foraminiferal assemblages at the Punta Piccola section (Stratotype for the Piacenzian Stage), which spans the gradual climate transition of the intensification of the Northern Hemisphere glaciation (3.6–2.6Ma). This study highlighted a major benthic foraminiferal fauna turnover, which started at about 3.05Ma with LO of Cibicidoides italicus, registered the gradual decline of Stilostomella spp. and culminated at about 2.7–2.75Ma, when the dominant Siphonina reticulata was replaced by Cibicidoides pachyderma, costate Bulimine, spinose Bulimine, spinose Uvigerine and the Bolivina dilatata group. Four compositional zones, identified by constrained cluster analysis, are indicative of palaeoenvironmental changes and document the transition from stable and mainly oligotrophic conditions to unstable, mesotrophic and more fluctuating bottom conditions.Two intervals of deposition of sapropelite clusters coded as O and A, investigated using both benthic and planktic assemblages, reveal that anoxia conditions were never reached. Planktic foraminifera in the sapropelite layers of cluster O indicate deep mixing and benthic foraminifera suggest an increase in export productivity to the sea floor. By contrast, planktic foraminifera in the uppermost sapropelite layers of cluster A indicate oligotrophic surface water conditions, stratification and more eutrophic subsurface water conditions, without deep mixing. The benthic foraminifera indicate hypoxic and eutrophic bottom conditions, and evidence the first episode of down-slope transport, which testifies to a strengthening of runoff and stratification of superficial waters, but not true stagnation.