Reconstructing the Alpine orogenic wedge and its foreland basin: the petrologic transition from Cretaceous passive-margin to Eocene foreland sedimentation in northern Corsica (France)

A broad synform in the Balagne region of northern Corsica (France) comprises the most complete remnant of the southwestern Alpine foreland basin and associated orogenic wedge, which have been otherwise fragmented and mostly eroded by a late Cenozoic postcollisional episode of microplate dispersal along the southern European continental margin. The Upper Cretaceous–Eocene turbidites of the Balagne region record the opening and subsequent progressive closure of the Ligurian-Piedmont ocean, the main branch of the Alpine Tethys in the Western Mediterranean. Sandstone detrital modes (gross and heavy-mineral compositions) of the Balagne turbidites can be compared with those of age-equivalent lithostratigraphic units of the western Alps and the Northern Apennines, thus defi ning broad sediment paleo dispersal patterns and providing compelling paleogeographic constraints on the transition from preorogenic passive-margin to synorogenic foreland sedimentation. Upper Cretaceous turbidites of the Novella and Alturaia Formations were deposited along the northeastern (European) margin of the narrow Ligurian-Piedmont ocean. In contrast, the mixed carbonate/siliciclastic turbidites of the Upper Cretaceous Narbinco Formation have a distinct composition relative to the age-equivalent Novella and Alturaia Formations and cannot have been derived from the same sediment source area of the Helminthoid Flysch of the Northern Apennines and the Ligurian Alps. The Middle Eocene Balagne foreland basin fi ll represents a phase of sediment underfi lling during the progressive fl exure of the Corsican foreland in front of the advancing Alpine orogenic wedge. The basin-fi ll succession consists of, from bottom to top: (1) continentalto- transitional conglomerate and sandstone fi lling paleodepressions within the foreland basement complex; (2) thin and discontinuous nummulitic limestone capping— and partly lateral equivalent to—the basal conglomerate; (3) hemipelagic pelite; and (4) a thick turbidite section.