Deep-water sandstones in tectonically complex systems: the Numidian of Sicily as an example

The turbidite systems of the central Mediterranean-Alpine region are widely used as analogues for a variety of deepwater hydrocarbons reservoirs. Understanding whether the system is unconfined and deposited on relatively unstructured basin floor or confined by actively deforming basin-floor is important for the prediction of sand distribution and therefore the applicability of analogues. This case of study consider the Numidian turbidite system (Oligocene-Miocene) of Sicily - for many the type example of thick massive submarine sandstones. The tectonostratigraphic setting of the Numidian is analogous to the Angostura (Trinidad) - Scotland (Barbados) sand systems of the Caribbean and associated ultra-deep water exploration. New mapping and detailed sedimentology in the Nebrodi and Madonie Mountains (northern Sicily), allied to existing and new biostratigraphy data, challenge conventional ideas on the Numidian turbidite system as a whole. Rather than having being deposited within an unstructured foredeep by relatively unconfined flows, we show that Numidian deposition was strongly confined by active structures. The system was controlled by thrust related folds and their intrabasin submarine slopes, together with basin-floor architecture inherited from the under-filled passive continental margin. Thrust-top basins filled diachronously implying a large scale tectonic control both on sand fairways and facies variations along their margins. Existing models wrongly suggest that facies variations between adjacent outcrops on Sicily (and elsewhere) result from long-range stratigraphic variations being juxtaposed by later large-displacement thrusts. Our research reveals a much simpler tectonic structure but a more complex stratigraphic arrangement for the Numidian on Sicily - a characteristic of confined turbidite systems.