Are repetitive slumpings during sapropel S1 related to paleo-earthquakes?

The recurrence of mass-flow units within sapropel S1, an organic carbon-rich lower Holocene marker bed in the Eastern Mediterranean Sea, was used to study the interplay between earthquakes and sedimentation along the seismically active Calabrian Arc (Ionian Sea). Nine turbidite beds interrupt anoxic conditions during the deposition of sapropel S1. Each of these turbidites is associated with sharp grain size and geochemical elemental anomalies (high Al and Si, low Ca and coarse-grained basal part marked by Zr peaks), and with displaced foraminiferal species from different bathymetric ranges. We used these proxies to identify turbidite beds also above and below the sapropel, where turbidite signature is less clear due to the absence of major color changes. Turbidite structure and composition, as well as comparison with historical seismoturbidites, suggest a seismic triggering for such mass flow events. The peculiar color, well-known composition, geochemistry and age of sapropel S1, make this unit a key bed within which turbidites may be considered a sort of sedimentary “bar code” recording high-energy events within the background pelagic sedimentation; deciphering this code will reconstruct paleo-seismicity in this well-defined stratigraphic interval. The pelagic units bracketing turbidite beds were radiometrically dated, and the age of the sapropel S1, deduced through age modeling, is between 6.0 and 10.2 kyr cal BP. The emplacement age of each turbidite was estimated considering the average time-interval between successive turbidite beds (from pelagic sediment thickness and sedimentation rate). Subsequently these ages were further refined through age modeling. In this way, we compiled a catalogue of mass flow events during sapropel S1 deposition, a time span long enough to include several earthquake cycles and allow reliable seismic and tsunami hazard assessment in this area.