Water depth m -137 -900 failure affecting both post-glacial sediment drifts and older deposits: pressure ridges & slide blocks failure affecting only the flanks of post-glacial sediment drift deposits: thin skinned mudflows 5 km HE106 MKR18 MKR12 MKR13 MSC01-424 MSC01-301 fault P7 P4 P3 P8 affected deposits of the last sea-level fall and low stand erosive surface (ES1) Mud flow deposit (8,5 Cal. ky BP) affected post-glacial sediment drifts and drapes (unconsolidated muds) Twin Slides (Late Holocene) Northern Slide: remolding of slope deposits (pressure ridges) Southern Slide: affected oklder consolidated (and faulted) deposits of last s.l. fall generating a blocky slide Large Slide during last-glacial low stand (ca. 25ky BP) post glacial sediment drift and drapes Post Slide deposits Phase I Phase II Phase III Phase IV Sicily Gela Basin Italy 0 340 Kilometers SUBMARINE SLIDES Exposed Buried -800 -850 -200 -450 -400 -700 -750 -600 -300 -650 -350 -250 -550 -200 -250 -200 2 km 75 m SE NW profile HE 106 Northern Twin Slide Southern Twin Slide fluid-escape structures stacked mass-transport deposits basin-wide mass-transport deposit (Father Slide - last glacial) fluid-escape structures CHIRP sonar profile MKR12 S N Thick debrite accumulation Frontally-emergent MTD Frontal ramp Basal shear surface 1000 m 30 m Shallow-seated headwall Undisturbed seafloor S N CHIRP sonar proflile MKR13 Disturbed seafloor sector Buried MTD Potential “horse” Frontally-confined MTD 1000 m 30 m Distal sector with disrupted stratigraphy Central sector with folds and preserved stratigraphy Blocky area Debrites Buried MTDs CHIRP sonar profile MKR18 SE NW Shelf Deep-seated headwall Blocky area Debrites Elongated ridges Debrites Sidewall 1000 m 100 m TWIN SLIDES Where older and more consolidated units are mobilised, they result in more blocky slides, while younger and shallower units generated mudflow and plastic deformation of seafloor sediment resulting in distinctive pressure ridges in the toe region. REFERENCES MINISINI D., TRINCARDI F., ASIOLI A., CANU M., FOGLINI F. (2007) - Morphologic variability if exposed mass-transport deposits on the Eastern slope of Gela Basin (Sicily Channel). Basin Research, 19: pp. 217-240. MINISINI D. & TRINCARDI F. (2009) - Very high frequency failure of the continental slope: the Gela Basin (Sicily Channel). Journal of Geophysical Research, Vol. 114, F03014, doi:10.1029/2008JF001037. TRINCARDI F. & ARGNANI A. ( 1990) - Gela submarine slide: a major basin-wide event in the Plio-Quaternary foredeep of Sicily. Geo-Marine Letters, 10: pp. 13-21. TRINCARDI F., CATTANEO A., CORREGGIARI A., RIDENTE D. (2004) - Evidence of soft-sediment deformation, fluid escape, sediment failure and regional weak layers within the late-Quaternary mud deposits of the Adriatic Sea. Marine Geology, 213: pp. 91-119. VERDICCHIO G. & TRINCARDI F. (2008) - Mediterranean shelf-edge muddy contourites: example from Gela and South Adriatic Basins. Geo-Marine Letters, 28: pp. 137-151. DOI 10.1007/s00367-007-0096-9. FAILURE RECURRENCE Basin-wide correlation of Father Slide (generated on the onset of the Last Glacial Maximum) allows definition of at least six younger failure events (black dots) during the last 24 ky. This evidence implies a remarkable recurrence interval of ca. 4 ky (Minisini & Trincardi, 2009). Mass-transport deposits are up to 30 m thick and appear either shallowly buried or exposed at the seafloor. In both cases individual mass-transport deposits mobilize relatively small sediment volumes (typically in the order of 0.1-1 km3) and display modest run outs: - high-resolution multibeam data reveal several coalescing shallowly buried or exposed slides - CHIRP sonar profiles document recurrent failure events since the last glacial (about 20-25 ky BP). The margins of Gela basin, a 1000-m-deep slope basin in the Sicily Channel (Central Mediterranean), show evidence of widespread and recurrent sediment failure during the late Quaternary. Where exposed a