SEDIMENTARY STRATAL DISRUPTION AND LITHOLOGICAL MIXING IN POLYGENETIC MÉLANGES

Mass transport processes are efficient mechanisms in the production of intense stratal disruption and lithological mixing. The vast spectrum of products recording the ideal downslope evolution from sediment failures to gravity flows may be preserved within polygenic mélanges exhumed in orogenic belts, even though usually overprinted by polyphased tectonics and associated metamorphism. In an ideal evolutionary transect, sedimentary units spans from relatively proximal slump-type facies, sharing the same characteristics of the tectonic broken formations, to relatively distal debris flow-type facies, showing the classical attributes of ascribed to block-in-matrix mélanges. Here we provide an overview on these primary structures identified in different case studies preserved in various geodynamic contexts, focussing on the mechanisms responsible for the entrainment of intra- (native) and extra- basinal (exotic) sedimentary material and its progressive deformation. Important informations , such as the coherent vs. flow-type behavior or the kinematics of processes, can be reconstructed from the study of these primary features, providing crucial constraints on the paleography and physiography of the depositional environment. In this framework, the correct recognition and understanding of these preserved sedimentary imprints will provide the terms for an updated and tuned up reappraisal of classic mélange worldwide.