The Dark Side of the Mediterranean Geological Record: the sapropel layers and a case study from the Ionian Sea

A peculiar feature of the Neogene Mediterranean marine and land sequences is the quasi-cyclic occurrence of organic carbon-rich layers named sapropels. Their occurrences in the sedimentary record usually correspond to periods of enhanced monsoon rainfall during precession minima and summer insolation maxima. Nevertheless, the causal factors that led to their formation are still highly debated. Integrated multi-proxy investigations document that during sapropel deposition important changes occurred in the entire water column: freshwater lenses in the surfacewaters led to stratification of the water column and to hypoxic or totally anoxic bottom waters. Sapropels offer the unique opportunity to perform studies on climatic, oceanographic and environmental changes at an extraordinary resolution allowing detailed insights into short-scale climatic fluctuations. Micropaleontological and magnetic signatures demonstrate that oceanographic conditions conducive to sapropel formation were not confined to the eastern Mediterranean sea but occurred also and possibly simultaneously in the entire Mediterranean. The differences appear a consequence of different preservation, changes in water column depth and local hydrographic conditions. Here we report the main features characterizing the youngest Mediterranean sapropel (S1) deposited during the Holocene in the Ionian basin.