COMPARATIVE ANALYSIS OF OLISTOSTROMES (SEDIMENTARY MÉLANGES) IN THE APENNINE AND APPALACHIAN OROGENIC BELTS AND THE PROCESSES OF THEIR FORMATION

In the Northern Apennines (NA) of Italy and the Central Appalachians (CA) in Pennsylvania, olistostromes (sedimentary mélanges) occur at different stratigraphic levels within the sedimentary record of the subduction-accretion complexes of these orogenic belts (middle Eocene to early Miocene in NA, and late-Middle to Late Ordovician in CA). In the NA, they are widely distributed in the exhumed outer part of the Ligurian accretionary complex over an area, ~300 km-long and 10-15 km-wide (Festa et al., 2013 GSA Bull, Festa et al., 2015 IGR). Their emplacement was diachronous, progressively younging to the SE, and their size and thickness appear to have increased in the same direction along strike of the frontal wedge. In the CA, different types of olistostromes occur along the exhumed outer part of the Taconic accretionary complex over an area of hundreds of km-long and tens of km-wide (e.g. Lash, 1987 Geology; Ganis and Wise, 2008 Am J Geosc; Wise and Ganis, 2009 Tectonophysics; Codegone et al., 2012 Tectonophysics). The internal structure and stratigraphy of these sedimentary mélanges display a complete record of various deformational phases during the subduction-accretion to continental collision stages of the orogenic belt evolution. In both the Apennines and the Appalachians, olistostromes originated form slope failures in isolated sections along the wedge front where out-of-sequence thrusting, seismic events and different pulses of overpressured and tectonically-induced fluid flows took place synchronously. We suggest that mass-transport processes were effective in reshaping the outer wedge morphologically, in order to balance the non-linear migration and segmentation of the accretionary complexes and the processes responsible for their formation. Systematic documentation of olistostromes and the spatial and temporal variations in their evolution provide an effective tool to unravel the subduction-accretion and collision stages of the development of mountain belts, particularly the NA and CA. We show in this talk that the nature and the scale of the processes responsible for the development of olistostromes in the NA and the CA were comparable.