Mid-Eocene mass-wasting mélanges in the context of wrench faulting along the oblique-convergent Corsica-Sardinia margin

Abstract

The Mid-Eocene clastic wedge with olistoliths of the CaporalinoUnit and correlated units in Corsica are regarded as sedimentarymelanges emplaced at shallow structural level by means of submarine,gravity-driven mass wasting processes in fault-bounded basinsof the Corsican accretionary wedge. This occurred in the frame ofsynorogenic sinistral strike-slip motion generated by oblique convergencebetween the Iberia and Adria plates. During the final, LateEocene collisional stage the melanges were overprinted and structurallyreworked as olistostromal carpets at the base of the uppermostthrust sheets of the nappe stack (the Balagne-Nebbio Nappe).It is believed that the Corsica orogenic belt continued southwards,and that the present-day Sardinia behaved as foreland of the Alpinebelt, as suggested by evidence of forebulge migration from Late Cretaceousonwards. However, the NE and SE sectors of Sardinia showdifferent responses to the Mid-Eocene geodynamic event, as therelated wrench faulting and transpressional deformation are welldeveloped only in the NE part, the change being identifiable at thelevel of the Gulf of Orosei. We propose that the Orosei Canyon Line(OCL), an important lineament identified by SARTORI et alii (2001),could have been active in Eocene times as a transform boundarypreventing the southward prosecution of the Alpine subduction. Thetranspressional response of NE sector of Sardinia to the stress fieldwas accompanied by accumulation of elongate clastic wedges bymass-wasting processes at the base of tectonic scarps. The wedgesdisplay several features comparable to those of Corsican melanges,and, although obviously generated in different geologic contexts,both are considered to be the expression of a peculiar Mid-Eocenegeodynamic event of the Alpine orogenic belt.