Stratigraphic and structural features of the Bas-Ostriconi Unit (Corsica): paleogeographic implications

The palaeogeographic origin of the Bas Ostriconi Unit (Balagne area, Alpine Corsica) has long been a matter of debate. This unit is actually detached from its original basement. It is made of Late Cretaceous carbonatic turbidites with lenses of coarse-grained polymict conglomerates (Narbinco Flysch). The turbidites have a mixed siliciclastic-carbonatic composition and are affected by a polyphasic deformation. Here, based on field observations and sampling, we analyse the sedimentary, petrographic, and structural features of the Narbinco Flysch. From these analyses, we derive that the Narbinco Flysch belongs to the sedimentary cover of the Balagne ophiolite Nappe. We also show that the carbonatic turbidites are associated with mixed siliciclastic-carbonatic coarse-grained debris, which is typical of the turbidite sediments deposited during the Late Cretaceous in the Ligure-Piemontese oceanic basin close to the European Margin. Our results thus suggest that, the Bas Ostriconi Unit originally formed on the Ligure-Piemontese oceanic crust, then was integrated to the accretionary wedge that was thrusted on the European margin of Corsica during the Eocene collisional events.