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

Abstract

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.

The Middle Jurassic Alpine Tethyan Unconformity and the Eastern Sardinia - Corsica Jurassic High: A sedimentary and regional analysis

“…The marine carbonates of the Dorgali (Bathonian-Kimmeridgian), Genna Silana and S'Adde Fms (Callovian-Kimmeridgian) (Dieni and Massari, 1985a;Costamagna et al, 2007) form a succession that is up to 600 m in the Supramonte -Monte Tuttavista area (Jadoul et al, 2010).…”

“…2) overlies a regional unconformity (see below) and starts with continental conglomerates and sandstones before passing into marine carbonates of the Genna Selole Fm (Bajocian-Bathonian) (Del Rio, 1976Dieni et al, 1983;Dieni and Massari, 1985a;Costamagna and Barca, 2004;Costamagna et al, 2007;Costamagna, 2015). This unit is up to 80 m thick in the SE of the island, and is composed of: 1) the Laconi-Gadoni lithofacies, which is a coarse, pebbly to sandy, deposit indicating fluvial high-to middle-energy braided alluvial fan environments, followed by 2) the Nurri-Escalaplano lithofacies, which is composed of finely-laminated sandstones, siltstones and clayey siltstones sedimented in low-energy coastal-palustrine-deltaic environments.…”

“…These deposits document a transgressive-regressive megacycle, and form the Baunei Group (Costamagna et al, 2007) (Fig. 2), which is a superunit linked to the sinking of the Tethys margin (Bathonian -Oxfordian) (Abbate et al, 1986;Bernoulli and Jenkyns, 1974).…”

“…2), which is a superunit linked to the sinking of the Tethys margin (Bathonian -Oxfordian) (Abbate et al, 1986;Bernoulli and Jenkyns, 1974). This latter was followed by a depositional regression (Oxfordian-Kimmeridgian) (Costamagna et al 2007).…”

“…1) (Amadesi et al, 1960;Assorgia et al, 1974;Assorgia and Gandolfi, 1975;Dieni and Massari, 1985a;Costamagna and Barca, 2004;Costamagna et al, 2007;Jadoul et al, 2010;Casellato et al, 2012;Dieni et al, 2013). This cover tectonically undisturbed rests over an unconformity that is Bajocian in age and forms the base of the Middle Jurassic succession (Dieni et al, 1983).…”