Planktonic foraminiferal biostratigraphy and quantitative analysis during the Campanian-Maastrichtian transition at the Oued Necham section (Kalaat Senan, central Tunisia)

The Oued Necham (ON) section (Kalaat Senan, central Tunisia) provides a well-exposed outcrop of a CampanianMaastrichtian series that consists essentially of chalky limestones (i. e. the Abiod Formation) grading progressively to a marly unit (i. e. the El Haria Formation). The transitional Abiod-El Haria succession comprises a rich hemipelagic-pelagic fauna in the study area, but ammonites (e. g., Pachydiscus neubergicus, the Campanian/Maastrichtian (C/M) boundary index taxon) are scarce to absent, thus preventing the recognition of the standard zones defined for the Tethyan realm. However, the rich planktonic foraminiferal taxa of the El Haria Formation allow us to establish an accurate biostratigraphical scheme. Accordingly, this work presents a high-resolution planktonic foraminiferal biostratigraphy that is characterised by distinct bioevents associated with the reported C/M boundary (i. e. lowest occurrences (LOs) of Rugoglobigerina scotti and Contusotruncana contusa) at the Global Stratotype Section and Point (GSSP) of the Tercis-les-Bains section, south-western France. Based on these zonal markers, the rugoglobigerinids and multiserial heterohelicids are used to define a subzonal scheme spanning the standard Gansserina gansseri Zone, including the Rugoglobigerina rotundata Subzone indicative of the late Campanian and the Rugoglobigerina scotti Subzone and the Planoglobulina acervulinoides Subzone, respectively, indicative of the early Maastrichtian. The abundance of foraminiferal assemblages allowed us to carry out high-resolution quantitative analyses that document a significant climate cooling during the early Maastrichtian intermittent with short-term warming episodes. Thus, opportunist taxa (r strategists, mostly heterohelicids) thrived during the earliest Maastrichtian cooling event, whereas specialist taxa (k strategists, mostly double-keeled) that had dominated the late Campanian assemblages declined gradually without any extinction. Opportunist and specialist taxa fluctuated in opposite phases throughout the early Maastrichtian (LO of Rugoglobigerina scotti -LO of Abathomphalus mayaroensis), suggesting essentially variations in water temperature. Since surface dwellers dominated the assemblages, they imply continuous sea surface optimal conditions of nutrient supply and water connectivity induced from upwelling currents.