Submarine landslide deposits in orogenic belts: Olistostromes and sedimentary mélanges

Olistostrome and sedimentary mélange are two synonymous genetic terms referring to the “fossil” products of ancient submarine mass‐transport processes exhumed in orogenic belts. Lithology, stratigraphy, lithification degree, and structural anatomy of these units reflect the synergic and combined action of different mass‐transport processes leading to composite deposits developed through multistage deformation phases. The general depositional physiography, tectonic setting, and the type, scale, and rate of slide mass transformation mechanisms during the downslope motion and emplacement and postdepositional processes are the main factors controlling the final internal anatomy of olistostromes and sedimentary mélanges. These features are commonly progressively reworked by subsequent burial, diapiric, and tectonic processes and may be eventually almost completely obliterated by metamorphic processes during orogenic belt and/or subduction complex evolution. The correct recognition of olistostromal units and their intrinsic features in different orogenic belts needs extensive and careful fieldwork and ultimately provides excellent proxies for the timing of various tectonic‐sedimentary events interacting during the Wilson cycle. The basic concepts of structural geology, sedimentology, stratigraphy, and basin analysis should be jointly applied in studying the internal structure, lithological arrangement, and formation-deformation mechanisms of olistostromes and sedimentary mélanges.