Response of calcareous nannofossils during the danian-thanetian isotopic events in the Elles Section, Central Tunisia

Abstract

A high resolution quantitative study of calcareous nannofossils from the Elles section in Central Tunisia (North Africa) was conducted to assess local phytoplankton paleocommunities and infer paleoclimatic conditions. This research introduces a refined subdivision of the conventional NP4 nannofossil zone into six finer intervals (NTp6, NTp7A-B, NTp8A-C), a first for Tunisia, enhancing the biostratigraphic resolution of Paleocene stratigraphy in the region. The assemblages within these subzones exhibit moderate to good preservation and correlate globally with established Tethyan biozonations. Three key isotopic events were identified: The Dan-C2 event, characterized by a negative δ¹³C shift at the base of the NP2 Zone, associated with a significant increase in oligotrophic and warm-water taxa; the Latest Danian Event (LDE), which is divided into Pre- and Post-LDE intervals. The Pre-LDE interval is marked by a short-lived negative δ¹³C excursion within the lowermost part of NTp7A Subzone boundary, accompanied by a notable decline in the diversity and richness of calcareous nannofossils. The third event, the Selandian-Thanetian Transition Event (STTE), occurs at the base of NP7/8 and is biostratigraphically defined by the Lowest Occurrence (LO) of Discoaster mohleri, with a replacement of R-mode taxa by species adapted to warmer, more oligotrophic conditions. The Danian-Selandian transition is clearly delineated by a glauconite-rich hard marl layer (upper NTp8C). This integrated stratigraphic study provides high-resolution biostratigraphy and critical insights into paleoenvironmental changes during this period. The paleoenvironment shifted from warm, oligotrophic conditions during the events to cooler, eutrophic waters both before and after. These findings suggest that the three bioevents may correspond to an early Paleocene hyperthermal episode.