Paleoseismological investigation offshore eastern Sicily and Calabria (Ionian Sea) and possible origin of megaturbidites

Abstract:

E Sicily and Calabria have been repeatedly struck by destructive historical earthquakes and tsunamis (1693 Catania M7.4, 1908 Messina 7.2). The latter triggered a submarine landslide and turbidity current that ruptured submarine cables. We present the preliminary results of a paleoseismological investigation on a set of deep marine sediment cores from the Ionian Sea acquired during the CIRCEE survey (R/V Le Suroit in Oct. 2013). The objective is to improve our understanding of the chronology and origin of large catastrophic events, which have affected the area. One of the thickest and well known deposits is the up to 10-12 m thick Augias “homogenite” (or megaturbidite) which covers the entire floor of the Ionian abyssal plain and represents a volume of ~100km³. The origin of this deposit once thought to be associated to the Santorini collapse event dated at 3.5 ka (Cita et al., 1996) is enigmatic and more recent work suggests it may have been caused by the 365 AD Crete mega-thrust earthquake (Polonia et al., 2013)

In order to better understand the extreme events that led to such deposits in the Ionian abyssal plain and along the Sicily/ Malta slope, our study aims to correlate the megaturbidites observed in the slope and in the deep Ionian basin by CHIRP echosounder profiles and sedimentary facies analysis. Seismic profiles show several superposed acoustically transparent units identified as megaturbidites. The Augias megaturbidite was completely sampled in 6 new cores. An older megaturbidite, possibly the Deeper Transparent Layer (DTL), is also sampled in 3 new cores. Geochemical signatures, thicknesses and grain sizes show wide variability for the same deposit among the cores. For example, the thickness of the Augias deposit varies between 70 cm and 605 cm, and the lithology and sedimentary structures of the base of the deposit is also highly variable, ranging from massive and laminated medium sand to silty-clay. For the two megaturbidites described in the cores, we establish a preliminary stratigraphy based in part on correlations to data described by Polonia et al. (2013). Radiocarbon dating and other work in progress should help to better characterize the megaturbidites, in terms of areal extent, thickness, chemical composition and grain size distribution, and provide new constraints on their origin and transport.