Foraminifera of the Faneromeni section (Crete, Greece) reflect the palaeoenvironmental development towards the Messinian salinity crisis

Abstract

A severe phase of disturbance around 7.17 Ma initiated an ongoing development towards the Messinian salinity crisis (MSC) of the Mediterranean. We present foraminiferal data from the Faneromeni section on Crete to understand how the astronomical cyclicity and the restriction phase starting at 7.17 Ma were reflected in a succession that was deposited on the continental shelf and characterized by a precession-dominated alternation of organic-enriched grey marls and sapropels and light-coloured homogeneous marls. Benthic and planktic abundance data show that the foraminifera are closely associated with precessional cyclicity. Similar as in other Mediterranean sections, the 7.17 Ma shift in benthic assemblages is sedimentologically expressed by the occurrence of the first distinct sapropel (Faneromeni cycle F18). At this level, throughout the Mediterranean a group of open marine benthic species intolerant to oxygen stress abruptly decreased in abundance with several species disappearing at or shortly after 7.17 Ma. These species were replaced by species indicating increasing stress, implying decreasing oxygen content of the bottom waters after 7.17 Ma. The data further suggests that sapropelic sediments dominated by Bolivina dilatata/spathulata were deposited under hypoxic conditions, rather than under continuous organic flux. Our data reflects a second step in the restriction of the Mediterranean between 6.8 and 6.7 Ma, indicated by decreasing benthic diversity and increasing abundances of planktic and benthic taxa considered tolerant of hypersalinity. An increase in water salinity has been suggested before, and if true, appears to have affected the bottom waters and the surface waters around the same time.