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

Francesco Massari (*) & Iginio Dieni (*)
(*) Dipartimento di Geoscienze, Università degli Studi di Padova, Via Gradenigo, 6 - 35131 Padova. Corresponding author: francesco.massari@unipd.it

The Mid-Eocene clastic wedge with olistoliths of the Caporalino Unit and correlated units in Corsica are regarded as sedimentary mélanges emplaced at shallow structural level by means of submarine, gravity-driven mass wasting processes in fault-bounded basins of the Corsican accretionary wedge. This occurred in the frame of synorogenic sinistral strike-slip motion generated by oblique convergence between the Iberia and Adria plates. During the final, Late Eocene collisional stage the mélanges were overprinted and structurally reworked as olistostromal carpets at the base of the uppermost thrust 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 Alpine belt, as suggested by evidence of forebulge migration from Late Cretaceous onwards. However, the NE and SE sectors of Sardinia show different responses to the Mid-Eocene geodynamic event, as the related wrench faulting and transpressional deformation are well developed only in the NE part, the change being identifiable at the level 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 boundary preventing the southward prosecution of the Alpine subduction. The transpressional response of NE sector of Sardinia to the stress field was accompanied by accumulation of elongate clastic wedges by mass-wasting processes at the base of tectonic scarps. The wedges display several features comparable to those of Corsican mélanges, and, although obviously generated in different geologic contexts, both are considered to be the expression of a peculiar Mid-Eocene geodynamic event of the Alpine orogenic belt.

Corsica, Sardinia, major Mid-Eocene geodynamic episode, sedimentary mélanges, transpression, synorogenic exhumation.