Deep-water massive sands: facies, processes and channel geometry in the Numidian Flysch, Sicily

Abstract

The sedimentology of the Numidian Flysch in northern Sicily has been little studied in the last twenty years, with most works concentrating on the structural complexities of the area, rather than the facies characteristics. The Numidian basin was intensively deformed during its complex tectonic history and the basin deposits have become segmented into different structural units. The Oligo-Miocene aged Flysch comprises predominantly quartzarenitic sandstones and interbedded mudstones, both of turbiditic affinities and most likely derived from a NW African source. The sediments are well exposed along the coast and in dry river valleys in northern Sicily, and provide excellent examples of deep-water massive sands, i.e. very thick (4–25 m) units of structureless sandstone associated with turbidites and related facies. The overall characteristics of the examined sections indicate that the sandstones were deposited within both isolated channels and larger channel complexes that fed across a mud-dominated slope. The more proximal sections, e.g. Ponte Finale and Pollina have a high proportion of pebble conglomerates, shale-clast conglomerates and very thick-bedded structureless pebbly sandstones, deposited by high-density turbidity currents, debris flows and slumping. Other sections, either more distal or with a more uniform sand-rich source, e.g. Contrada di Romano, are dominated by very thick-bedded and amalgamated structureless sandstones with extensive zones of water-escape structures. The massive sands are thought to originate from the gradual aggradation of sediment beneath steady or near-steady flows, with rapid deposition from final-stage modified grain flows forming the water-escape features.