After the Messinian Salinity Crisis (MSC), the Ebro Margin, like other Mediterranean deltaic margins, rebuilt through progradation and increasigly significant aggradation. The Plio-Quaternary transition from a ramp-like system to a “new” margin with large clinoforms is an opportunity to understand the processes that govern canyon initiation and evolution. We used a 3D seismic data set located from the outer shelf-upper slope of the Ebro margin. We tied major bounding surfaces to chrono-stratigraphic constraints from borehole data or, for the most recent interval, by inferring averaged accumulation rates derived from the borehole stratigraphy. The major seismic surfaces are sequence boundaries, some of which are tied to major climatic events. Along these surfaces, seismic attributes were utilized in order to characterize the fluvial/canyon connection, viewed as one of the key factors in canyon development. The first appearance of “proto-canyons” (dense networks of channels and gullies 50-100 m deep and 1-2 km wide) occurs in the late Zanclean. Their size increased progressively throughout the Pliocene and early Quaternary, in relation to the increase of clinoform heights. “True canyons” (with distinct interfluves, more than 200 m deep and 3-4 km wide) appeared during the Mid-Pleistocene Transition (MPT, 1250-700 ka BP). The first evidence of direct connection between canyon heads and fluvial systems is observed during Marine Isotope Stage 22, one of the most pronounced glacial stages of the Quaternary. Similar connections also existed during MIS 16 and MIS 12 at least, which are also stages of pronounced low sea level. Fluvial incision is not visible on the outer shelf at the resolution of our seismic data, but sinuous fluvial systems are very well imaged through amplitude and coherency attributes. Direct connection of fluvial systems during and after MIS 22 also favored the headward erosion of canyons and the formation of transgressive wedges during phases of early deglaciation, which are interpreted here to correspond with times of climatically-controlled increased fluxes of water and sediment

COST-ANR MEDSALT Symposium, 24-28 October 2016, Palermo, Italy.-- 3 pages, 1 figure

Peer Reviewed