Synrift sedimentation on the northern Tethys margin: an example from the Ligurian Alps (Upper Triassic to Lower Cretaceous, Prepiedmont domain, Italy)

The Prepiedmont domain succession of the Ligurian Alps is formed by a thick Mesozoic sedimentary cover tectonically detached from its substratum. The Arnasco-Castelbianco unit preserves the most complete record of the Ligurian Prepiedmont, although completely overturned and deformed due to Alpine tectonics. It is composed of carbonate and clastics rocks deposited during the Upper Triassic-to-Lower Cretaceous interval. This paper is focused on the stratigraphy of the Jurassic series and its relationships to the Tethyan rifting. Each term of the sedimentary record is seen as a witness of the several phases through which the rifting took place. An early-rifting phase (Late Hettangian-Early Sinemurian) brought to the formation of a normal fault system affecting the carbonate platform, and favoured the development of condensed sedimentation on pelagic highs. The rapid transition from open-platform carbonate to slope-basin cherty limestones, testifies the increased subsidence of the margin in the Late Sinemurian, during which moderate fault activity is recorded (intraformational breccia horizons). Until the Early Pliensbachian, a tectonic pause brought to the sedimentation of a succession of pelagic carbonates, occasionally interrupted by clastic flows. During the Late Pliensbachian (?)-Toarcian, it followed the rifting phase, evidenced by the large amount of clastics generated by the renewed fault activity. Clastics flowed down into the basin as fluxoturbidites at first, and then they passed to breccias during the maximum tectonic pulse. In the Late Toarcian-Aalenian?, the thermal uplift of the Briançonnais shoulder generated a basinal infill of fine clastics. The following thermal subsidence (Aalenian-Tithonian) favoured the restoration of quiet basinal conditions evidenced by the deposition of radiolarites.