The Cenomanian–Turonian boundary in the northwestern part of the Adriatic Carbonate Platform (Ćićarija Mtn., Istria, Croatia): characteristics and implications

Change from rimmed to ramp platform forced by regional and global events in the Cretaceous of the Friuli-Adriatic Platform (Southern Alps, Italy)

“…This facies is very similar and probably correlates with the coeval Sveti Duh Fm, outcropping some 80 km to the southeast in Istria and Dalmatia (e.g. Brčić et al, 2017, see Fig. 1).…”

“…In fact, toward the east in Istria and south of it (see Fig. 1), the east-dipping Cenomanian ramp was characterized by partial drowning, with pelagic limestones rich in open-sea organisms (Gušić and Jelaska, 1993;Korbar et al, 2012;Brčić et al, 2017). These facies, started around the early-middle Cenomanian, reached the maximum diffusion at the Cenomanian/Turonian boundary, which may be seen as the effect of OAE 2 and related sea-level rise on the platform margin.…”

“…More detailed data from this region (e.g. Tišljar et al, 1998;Otoničar, 2007) indicate that the flexural subsidence was creating a westward prograding subsidence pulse, with final flexure toward the east (Gušić and Jelaska, 1993;Brčić et al, 2017).…”

“…1. From the end Albian to Cenomanian, associated to the passive margin to foreland transition, the subsidence in the southern and western sector of the Friuli -Adriatic Platform abruptly stopped, as it is demonstrated by the persistent post Albian gap in the subsurface (wells Nervesa, Cesarolo) and outcrops in western Istria (Otoničar, 2007;Brčić et al, 2017), whereas other wells to the north and east show a more continuous Upper Cretaceous succession (Cargnacco and Grado, see ViDEPI and Cimolino et al, 2010). Underlying a prominent unconformity, covered by upper Oligocene to Lower Miocene glauconitic carbonates (Cavanella Group of the subsurface, e.g.…”

“…The OAE 2 (latest Cenomanian) in the AdCP was more effective in decreasing the carbonate productivity, with drowned intervals persisting for most of the Turonian, like the Sveti Duh Fm (e.g. Jenkyns, 1991;Korbar et al, 2012;Brčić et al, 2017).…”