The Bajocian–Kimmeridgian Jurassic sedimentary cycle of eastern Sardinia: Stratigraphic, depositional and sequence interpretation of the new ‘Baunei Group’

In eastern Sardinia, the first Jurassic sedimentary cycle (Bajocian–Kimmeridgian) develops in response to the opening of the Alpine Tethys Ocean. Starting during the Bajocian (Middle Jurassic), over a horst-and-graben system initially drowning to the northeast, at first siliciclastic sediments take place, related to continental to transitional environments. In time, they are gradually followed by marine carbonate, assigned to inner to outer ramp deposits. Afterwards, the latter, in their turn, become shallow; they are newly covered with an inner ramp lithofacies. The Kimmeridgian–Tithonian unconformity ends the cycle. Therefore, this sedimentary cycle as a whole can be interpreted as a transgressive–regressive megasequence linked to tectono-eustatic factors. All the pertaining stratigraphic units have been included within the ‘Baunei Group’, newly described. A comparison with the neighbouring areas, with particular regards to the Jurassic series of the Corsica, has been made, attempting to improve the reconstruction of this part of the Tethyan Ocean Western margin.