Possible tsunami signatures from an integrated study in the Augusta Bay offshore

Abstract

Twelve anomalous layers, marked by a high concentration of displaced epiphytic foraminifera (species growing in vegetated substrates like the Posidonia oceanica) and subtle grain-size changes were found in a 6.7 mlong, fine sediment core (MS-06), sampled 2 kmoff the shore of the Augusta Harbor (Eastern Sicily) at a depth of 72 m, recording the past 4500 yrs of deposition. Because concentrations of epiphytic foraminifera are quite common in infralittoral zones, but not expected at −72 m, we believe that these anomalous layers might be related to the occurrence of tsunamis causing substantial uprooting and seaward displacement of P. oceanica blades with their benthic biota. Our approach involved the study of geophysical data (morphobathymetry, seismic reflection, and seafloor reflectivity) and sediment samples, including X-ray imaging, physical properties, isotopic dating, tephrochronology, grain-size and micropaleontology. Correlations between anomalous layers and tsunami events have been supported by a multivariate analysis on benthic foraminifera assemblage and dates of historical tsunami records. We found that four out of the eleven layers were embedded in age intervals encompassing the dates of major tsunamis that hit eastern Sicily (1908, 1693, and 1169) and the broader Eastern Mediterranean (Santorini at about BP 3600). One more layer, even if less distinct than the others, was also defined and may be the evidence for the AD 365 Crete tsunami.