New insights on the benthic Foraminifera at the Cenomanian-Turonian boundary (OAE2) aftermath and the role of the genus Rotorbinella Bandy through the Late Cretaceous

The Late Cretaceous was characterized by extremely high temperatures. The modeled CO2 concentration in the atmosphere is among the highest of the entire Phanerozoic and it has been considered the main driver of such trend. The gradual warming started in the Albian and culminated during the Cretaceous Thermal Maximum (KTM) across the Late Cenomanian and early Turonian where sea-surface temperatures reached >=30 °C in the tropics and >=20 °C in the southern mid- to high latitudes. This has produced the flooding of large portions of continents and created shallow water environments suitable for the development of carbonate platforms and their associated benthic biota. Data at our disposal on rotaloidean Foraminifera place their very first appearance in shallow-water platforms shortly before the KTM, in the early Cenomanian, or during the late Albian. They were represented by small r-strategist Rotorbinella and Pararotalia, thought later extinct at the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2), along with all the Cenomanian larger foraminifera. The KTM was followed by a long-term gradual cooling which lasted until the Maastrichtian, where Tethys benthic foraminifera experienced a striking diversification. Rotaloideans evolved and diversified independently, following biprovincial and/or endemic patterns. The genus Rotorbinella is known in the Santonian-Campanian of the central-western Atlantic Tethys (Pyrenean gulf) and central Tethys (e.i. isolated platforms of the Apennines and Adriatic area) occurring along with other several rotaloideans. In the eastern Tethys (Arabian platforms) and westernmost Tethys (Caribbean) an apparently hybrid association with endemic species is recorded in the Santonian-Campanian timespan. Several species are also described from the uppermost Cretaceous of the Caribbean, southern Spain and the Arabian platform. Such an outstanding richness of rotaloideans was poorly known, and several of these morphotypes have been systematically described in recent decades only. The high diversity roots on the possible survival of some small Cenomanian r-strategist across the OAE2 with capability to survive or stay in quiescence. It is thus of a key aspect to understand what was the evolutionary history of the group nearby the Cenomanian-Turonian boundary (OAE2) and how really this event impacted or boosted on its evolution. To do so we have sampled a Cenomanian-Turonian shallowwater succession cropping out in the Friuli region (Adriatic Carbonate Platform), and performed a detailed temperature trends with absolute estimations at a very high temporal resolution. Furthermore, we have also collected inedited data from the very poorly known "Rotalia skourensis" assemblage of the Coniacian-Santonian of Iran (Arabian platform). Results show that i) in the Adriatic, Rotorbinella occurs in the late early Turonian, along with several Late Cretaceous 'newcomers', including the genus Rotalispira, once temperatures started dropping; ii) in the Arabian platform, Rotorbinella thrived along with a species closely related to the genus Orbitokathina, which represents a further Late Cretaceous 'newcomer'. The pervasive occurrence of Rotorbinella in the Cenomanian, late early Turonian, as well as in the rest of Late Cretaceous represents a key aspect that highlight the fundamental role of such a basic morphotype as a pioneer for the recovery and diversification of benthic foraminifera after the most impactful global events, such as the Cenomanian- Turonian. A pattern comparable with that here observed is also displayed through the end-Cretaceous and Paleogene (KPg) times.