A new turbidite facies tract scheme including supercritical and transitional sand-mud flows; an outcrop perspective from Mediterranean-type foreland basins

The studies carried out on tectonically-confined turbidite systems in Mediterranean-type foreland basins have shown that these deposits can be dominated by supercritical flows and by their transformation into subcritical and/or transitional (mud-sand) flows. In these confined turbidite systems, flow deceleration is favoured especially by morphologies transversal to paleocurrents, e.g., slope breaks or adverse slopes that can vary in scale from regional tectonic structures to depositional features such as thick mass-transport complexes and lobes. Based on data of more than fifty years of outcrop studies in foreland and wedge top basins, a new facies tract scheme is presented that includes the occurrence of supercritical flow deposits and hybrid event beds in turbidite successions. A review of the main turbidite facies schemes available in the literature is given, and detailed field examples of the Apennine and Alpine (Peira Cava) foreland basins are given that demonstrate the effect of basin morphology on the type of facies tracts. The concept of flow efficiency is revisited as sediment transport depends not only on flow behaviour but also on basin size and basin-floor morphology (e.g., large foredeeps are characterised by facies that reflect high-efficiency, whereas small piggy back basins are characterised by facies related to low-efficiency transport).