Pliocene sapropels in the northern Adriatic area: chronology and paleoenvironmental significance

A detailed stratigraphic and paleoenvironmental study was carried out ona marine section from the Marecchia Valley in the Northern Apennines. The section consists predominantly of deep-water hemipelagic clays intercalated with 15 thick, laminated sapropels (M1–M15). Based on biostratigraphic (calcareous nannoplankton and planktonic foraminifera) and magnetostratigraphic results, the Marecchia Valley section is interpreted as being middle to late Pliocene in age, extending from the upper part of the Gauss Chron to the lower part of the Matuyama Chron. The high resolution stratigraphy allows us to correlate, for the first time, these northern Italian sapropels with sapropels previously described from the southern Mediterranean region. Based on this long-distance correlation, we conclude that the sapropels from throughout the Mediterranean have a common origin that is related to astronomical forcing. Specifically, these Pliocene sapropels are related to wet climatic conditions in the Mediterranean and surrounding borderlands and are linked to precission minima which are times of increased precipitation. This is consistent with our pollen data, which indicate that very wet conditions existed during sapropel formation. Additionally, the planktonic and benthic foraminiferal assemblages associated with sapropels indicate that these were periods marked by high surface productivity and low bottom water oxygen.