Campanian carbon isotope calibrated paleofertility estimates from northwestern Tunisia: Inferences from calcareous nannofossils

Abstract

Abstract The δ13C calibrated Campanian (upper part of CC17/UC13 to CC23a/UC16 zones) calcareous nannofossil assemblages were analyzed to reconstruct paleofertility, paleoenvironment, and sea–level changes from the Jebil section, north–western Tunisia. Seven globally–recognized δ13C events are noted: three positive [Santonian–Campanian Boundary Event (SCBE); Early–Campanian Event (ECE); Mid–Campanian Event (MCaE)] and four negative excursions (Pillula Event; Conica Event; Late–Campanian Event (LCE); Epsilon Event or the C1– Event). The nannofossil assemblage is dominated by Watznaueria barnesae (28%), Lucianorhabdus cayeuxii (8%), Micula decussata (6%), Cyclagelosphaera reinhardtii (5%) and Micula concava (4%). In spite of the dominance of W. barnesiae (range: 33–46.5%), the signal given by the nannofossil assemblage is primary. All species–based proxies (the percentage abundances of stressed/opportunistic taxa, high and low fertility taxa, cool and warm watermass taxa, and Nannoconus spp.) along with the inferred Paleotemperature Index, suggests a cooling trend for the Campanian. Data suggests that oligotrophy was a greater influencing factor than paleotemperature, for the observed changes within the nannofossil assemblage. As a result of this extreme oligotrophy, a distinct assemblage is recorded that is marked by the absence of Biscutum, reduced % abundances of Prediscosphaera (0.7%), Retecapsa (2.3%), and Zeugrhabdotus (1.8%), but with the dominance of W. barnesiae.