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 theatmosphere is among the highest of the entire Phanerozoic and it has been considered the main driver of such trend. Thegradual warming started in the Albian and culminated during the Cretaceous Thermal Maximum (KTM) across the LateCenomanian and early Turonian where sea-surface temperatures reached >=30 °C in the tropics and >=20 °C in thesouthern mid- to high latitudes. This has produced the flooding of large portions of continents and created shallow waterenvironments 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 shortlybefore the KTM, in the early Cenomanian, or during the late Albian. They were represented by small r-strategistRotorbinella and Pararotalia, thought later extinct at the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2), alongwith all the Cenomanian larger foraminifera. The KTM was followed by a long-term gradual cooling which lasted untilthe Maastrichtian, where Tethys benthic foraminifera experienced a striking diversification. Rotaloideans evolved anddiversified independently, following biprovincial and/or endemic patterns. The genus Rotorbinella is known in theSantonian-Campanian of the central-western Atlantic Tethys (Pyrenean gulf) and central Tethys (e.i. isolated platformsof the Apennines and Adriatic area) occurring along with other several rotaloideans. In the eastern Tethys (Arabianplatforms) and westernmost Tethys (Caribbean) an apparently hybrid association with endemic species is recorded inthe Santonian-Campanian timespan. Several species are also described from the uppermost Cretaceous of theCaribbean, southern Spain and the Arabian platform.Such an outstanding richness of rotaloideans was poorly known, and several of these morphotypes have beensystematically described in recent decades only. The high diversity roots on the possible survival of some smallCenomanian r-strategist across the OAE2 with capability to survive or stay in quiescence. It is thus of a key aspect tounderstand what was the evolutionary history of the group nearby the Cenomanian-Turonian boundary (OAE2) andhow really this event impacted or boosted on its evolution. To do so we have sampled a Cenomanian-Turonian shallowwatersuccession cropping out in the Friuli region (Adriatic Carbonate Platform), and performed a detailed temperaturetrends with absolute estimations at a very high temporal resolution. Furthermore, we have also collected inedited datafrom 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 LateCretaceous 'newcomers', including the genus Rotalispira, once temperatures started dropping; ii) in the Arabianplatform, Rotorbinella thrived along with a species closely related to the genus Orbitokathina, which represents afurther Late Cretaceous 'newcomer'.The pervasive occurrence of Rotorbinella in the Cenomanian, late early Turonian, as well as in the rest of LateCretaceous represents a key aspect that highlight the fundamental role of such a basic morphotype as a pioneer for therecovery 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.