Understanding the geological context of ancient submarine slope failure, mud diapirism and volcanism from the geological record: Olistostromes and Argille Scagliose of the Mediterranean Region

Tectonic and sedimentary mélanges, rocks with block-in-matrix fabric often referred to as ‘chaotic’, are widespread in the circum-Mediterranean collisional orogenic belts as well as in submerged Mediterranean Arcs. These rock types have been defined originally as ‘Argille scagliose’ and ‘olistostromes’ in the outcrops of the Apennine chain (Italy). Both terminology and concepts have undergone a rather complex evolution through time owing to the gradual recognition of similar chaotic bodies in all the circum-Mediterranean orogenic belts. Submarine mud volcanoes of the Mediterranean region have a much younger history. Discovered in 1981, a growing number of sea-going geophysical and geological expeditions have allowed the recognition of a major mud volcano belt in the Eastern Mediterranean and of a number of mud diapirs and mud volcano fields from the Black Sea to the Gulf of Cadiz. Structural, textural and genetic similarities between the mud breccias of the Mediterranean mud volcanoes and the olistostromes and Argille scagliose of the Apennines were noted from the very beginning, but the matter has not been the focus of any detailed study. In a similar way, a systemic study of the olistostromes in term of their sedimentological significance is still missing, as well as their comparison with other fossil examples of mass transport deposits and the modern submarine landslides. In this paper, the distribution of these rock units in the Mediterranean region explored and the assumed genetic processes are identified in order to formulate a common genetic model that can be applied to the evolution of the circum-Mediterranean sedimentary basins.