Changes in calcareous nannofossil assemblages linked to dramatic climate change over the Paleocene–Eocene Thermal Maximum in the Taramsa Section, Central Nile Valley, Egypt

To characterize paleoenvironmental changes and examine the response of calcareous nannoplankton to climatic warming during the Paleocene-Eocene Thermal Maximum (PETM), an integrated high-resolution study of calcareous nannofossils, mineralogy, and geochemistry was carried out on PETM sediments from Taramsa, west of Qena, in the central Nile Valley of Egypt. The PETM interval in the Taramsa Section is characterized by the following: (1) an extraordinary shift in δ13Corg, δ13Ccarb, and δ18Ocarb values and carbonate contents (−28.30‰, −8.75‰, −10.43‰, and 8.60%, respectively) accompanied by an abrupt decrease in calcite contents and an increase in both detrital input (quartz and phyllosilicate) and apatite content; (2) a dominance of K-mode genera such as Ericsonia, Coccolithus, Thoracosphaera, Discoaster, Rhomboaster, and Tribrachiatus, dwarfing of bony fish, “malformed” nannoliths in Discoaster multiradiatus, and a decrease in diversity to only three taxa (Coccolithus spp., Thoracosphaera spp., and Discoaster spp.) at the peak of the carbon isotope excursion (CIE). The asymmetric species Discoaster araneus and D. anartios thrived during the PETM interval and likely took shelter from environmental changes in order to adapt to the elevated temperatures and scarcity of nutrients. Dwarfism in bony fish and malformations in Discoaster multiradiatus appear to have been a response to changes in the environment that prevailed at the beginning of the Eocene, thus reflecting increasing environmental stress during the PETM interval.