Deep-water sand-fairway mapping as a tool for tectonic restoration: decoding Miocene central Mediterranean palaeogeography using the Numidian turbidites of southern Italy.

As turbidity currents are sensitive to the geometry of the substrate cross which they flow, the sedimentology of turbidites can chart the development of submarine structures and betray regional palaeobathymetric connections. This rationale is applied to understand the tectonic evolution of the central Mediterranean in the early Miocene, using the African-sourced, hyper-mature Numidian sandstones and their immature, orogen-derived time-equivalents. In both Sicily and the southern Apennines, the Numidian displays characteristics of confined-uncontained turbidites: grain-size breaks and coarse bedload indicative of ubiquitous flow bypass; short-range grain-size fractionation across flow, and stacked sandy bed-sets in the flow axes. We reconstruct sand-fairways for over 300 km across the region and propose that their causative flows, axially-fed from north Africa, were confined along sinuous corridors created by active submarine thrusting. In contrast, orogen-derived turbidites (e.g. Reitano flysch, confined-contained turbidites) were ponded in mini-basins higher on the thrust wedge. The composite Apennine-Calabrian-Maghrebian orogen with its submarine thrust belt had occluded deep-water Tethyan connections through the central Mediterranean by early Miocene times. Palaeobathymetry across the submarine thrust belt increased northwards into the future Apennines. This study illustrates the utility of turbidite sedimentology, especially reconstructing sand-fairways, in building palaeogeographic reconstructions of complex tectonic regimes.