Integrated calcareous nannofossil and stable isotope stratigraphy across the Danian-Selandian boundary, west central Sinai, Egypt

Abstract

The stratigraphical range of bioevents across the Danian-Selandian (D/S) boundary are analysed using calcareous nannofossils and stable isotopes (δ13C and δ18O) from the Ekma section, west central Sinai (Egypt). Three calcareous nannofossil zones are recorded (from bottom to top): NP3, NP4, and NP5. Based on this, the Ekma section is the first nearly complete section from Egypt, straddling the D/S boundary. The D/S boundary is placed at the Lowest Occurrence (LO) of Lithoptychius ulii (base NTp8B). The LOs of L. varolii, L. pileatus, L. schmatzii, and Fasciculithus involutus are delayed, either as a result of diachronous and/or environmentally-controlled conditions. Two negative δ13C excursions are recorded that are associated with falling sea levels. The first one (CIE-DS1) is observed through the latest Danian Event (LDE) and within the calcareous nannofossil subzones NTp7B and NTp8A, whereas the second one (CIE-DS2) occurs within the NP5 Zone (at the top of the Dakhla Formation). No significant changes are noted in the calcareous nannofossil species distribution patterns over the D/S boundary. However, there is a distinct change in the trophic structure and watermass properties, i.e., from cool and mesotrophic (coincident with a decrease in the relative sea-level) to warm and oligotrophic conditions. There is also a gradual increase in both species diversity and warm and oligotrophic conditions with a corresponding drop in species dominance throughout the three studied intervals, pre-LDE, LDE and post-LDE.