2.2.2. Vigla Formation

This pelagic formation can be described as sub-lithographic thin-bedded to platy deposits, rich in plaktonic organisms (*Calpionelles*, *Radiolaires*, and *Globotruncanes*) of Cretaceous age. Their continuity is usually interrupted by thin intercalations, chert lenses, or even thin chert layers. Its dominant lithology consists of light grey to yellowish micrites and radiolarian biomicrites (wackestones to packstones). More explicitly, the calcareous beds (Vigla Limestones) of the lower part consist of mudstones-wackestones, biomicrites with foraminifera and radiolaria, and siliceous wackestones and packstones [42]. In the upper part, this formation consists of the Vigla Shale member (also known as "Upper siliceous zone"; [66]) composed by yellow marly or shaly limestones and shales with chert intercalations, and red to green or locally black clay layers. The latter contains the equivalent of the anoxic events of Selli (OAE1a) during the Aptian-Albian, Paquier Evet (OAE1b) of Early Albian age and Bonarelli (OAE2) at the Cenomanian-Turonian boundary in the Ionian zone [12,14,73,74], and extends to Italy and Albania. Vigla Limestones generally feature considerable lateral variations in thickness, mainly in the basin borders where its thickness may reach the double of its average, which is indicative of persistent differential subsidence [34,58,59]. In the internal sub-basin, the Vigla Limestones consist of compact, thick-bedded, often bituminous, dolomitic limestones, with lenses of slightly dolomitized microbreccia and thin cherty intercalated layers or nodules. It is also characterized by the presence of several aptychus in its lower part [59,64]. In Epirus, along the eastern border of the central Ionian zone, phosphatic horizons are intercalated with the uppermost horizons of the Vigla Limestone formation, stratigraphically above the Vigla Shale member. Overall, this formation corresponds to the first post-rift sediments of the Ionian zone [58,59,64].
