The Mass-Transport Deposits of the Paleogene Julian Basin (Italy/Slovenia): observations on the dynamic of emplacement and tsunamigenic potential

The External Dinarides between Italy and Slovenia feature some exceptional exposures of Paleocene-Eocene Mass-Transport Deposits (MTDs) formed by repeated catastrophic events, in which large sectors of the Adriatic Carbonate Platform collapsed and redeposited in a foredeep basin system, the Julian Basin. The sedimentary succession of the basin contains at least 25 major MTDs. The largest can be up to 260 m thick and can be traced laterally for at least 100 km. The mechanism of emplacement of these “megabeds” consists of a bipartite flow of material with a cohesive blocky/debris flow at the base, and a grain to turbulent flow on top. Each MTD features basal units of calcareous breccias embedding carbonate, siliciclastic-carbonate and marly slide blocks, topped by graded calcirudite, calcarenite and marlstone deposits. Here we discuss new interpretations of some representative megabeds, exposed in the area’s main open-pit quarries, based on X-ray fluorescence spectrometry (XRF), Powder X-ray diffraction (Powder XRD) and Total Organic Carbon (TOC) data, together with outcrop analysis carried out in the field and on Virtual Outcrop Models (VOMs). Results provide new insights into the emplacement dynamics and tsunamigenic potential of the MTDs in the Julian Basin. The inferred shape of the basin, the dimensions of the main "megabeds" and the data analysis from the above outcrops suggest that some of these submarine landslides may have triggered tsunami waves, with possible subsequent rebound deposits on top of them, traces of which are possibly recorded by multiple geological-geochemical proxies.