The carbonate mass transport deposits of the Paleogene Friuli Basin (Italy/Slovenia): internal anatomy and inferred genetic processes

The Paleogene carbonate "megabreccia" units of the Friuli Basin are composite deposits produced by catastrophic shallow-water carbonate platform collapses re-deposited in relatively deep-water inner foredeep settings developed at the front of the advancing Dinaric thrust system. These thick, basin-wide mass transport deposits (MTDs) record the catastrophic emplacement of bipartite slide masses, comprising a lower coherent/cohesive blocky flow and an upper grain/turbulent flow. We here present the results of micro- to outcrop-scale structural analyses, constrained by stratigraphic and sedimentologic observations, performed to identify the internal deformation mechanisms and the emplacement processes of four of the largest MTDs exposed in two large three-dimensional outcrops: the Vernasso (NE Italy) and Anhovo (W Slovenia) open-pit quarries. Our results reveal a variety of primary (sedimentary) soft sediment deformation structures testifying fluid overpressure conditions within the brecciated, fine-grained matrix that sustain, intrude and surround slide blocks and clasts. Meso-scale structural analyses unraveled paleo-transport directions toward the N for the Vernasso quarry and toward the S for the Anhovo quarry. This suggests a forced propagation of the mass transport events controlled by the shape of basin, and reinforces the interpretation of different source areas related to multiple collapses from a carbonate platform rimming the southeastern tip of the basin. These units are thought to represent exhumed fossil examples of the MTDs extensively mapped in the present-day, carbonate-dominated continental margins, and thus, considered as reliable analogues for integrated studies