THE SEDIMENTARY COVER OF THE ALPINE, CORSICAN, AND APENNINE OPHIOLITES: A CLUE TO THE PRE- AND SYN-CONVERGENCE HISTORY OF THE LIGURIAN-PIEDMONT OCEAN BASIN

Abstract

Remnants of the Ligurian-Piedmont Ocean Basin are preserved within ophiolite successions of the Western Alps, Northern Apennines, and Alpine Corsica. By integrating sedimentological, structural, and metamorphic data from selected ophiolite sequences, we refine the stratigraphic architecture of the ophiolite sedimentary cover and reconstruct the basin evolution from the Middle Jurassic onward. Three major deposit types are recognized. (i) Pre-convergence pelagic deposits (Bajocian - Santonian), represented by the Monte Alpe Chert, Calpionella Limestone, and Palombini Shale Formations, are characterized by low sedimentation rates and basin-wide facies homogeneity, reflecting a long-lived period of tectonic quiescence. (ii) Syn-convergence basin-plain turbidites abruptly appeared during the Campanian stage, marking the onset of eastward subduction. (iii) Trench-related deposits of Maastrichtian-early Paleocene age consists of high-rate turbidites interbedded with mass-transport deposits, formed by interaction with the unstable slope of the accretionary wedge. Comparisons between units experiencing different metamorphic conditions reveal that the thickness and rheology of the sedimentary cover exert a first-order control on subduction processes. Variations between high- and low-grade metamorphic units reflect the influence of subducted bathymetric reliefs on the downward migration of the active décollement. Our findings outline the importance of integrated multidisciplinary approaches for reconstructing the evolution of ancient ocean basins worldwide.