The calcareous nannofossil turnover across the Paleocene-Eocene Thermal Maximum event (PETM) in the southwestern Nile Valley, Egypt

Occurrences of calcareous nannofossils in marine sediments of the Paleocene-Eocene boundary interval are described from two sections of the southwestern Nile Valley (Egypt). The distribution patterns are discussed with respect to the abundance and diversity of calcareous nannofossils. The general turnover of the assemblages across the Paleocene-Eocene transition includes the first occurrence (= FO) of the genus Tribrachiatus which has been observed just above the level of the benthic foraminifera extinction event (= BEE). The genus Discoaster shows an important diversification with several FOs within the NP9/NP10 transition (e. g. D. aranus, D. binodosus). On the other hand, the diversity and abundance of the genus Fasciculithus decrease notably and progressively across the Paleocene/ Eocene boundary until its extinction in the lower part of Biochron NP10. F. tympaniformis has its LO at the level of the BEE, whereas F. involutus and F. thomasi extend upward into the lower part of Biochron NP10. The FO of Transversopontis pulcher, which is a marker taxon indicative of the top of Biochron NP9, is just above the BEE level, followed by the rare occurrence of Tribrachiatus bramlettei. Other forms which also appear above the NP9/NP10 zonal boundary include Pontosphaera plana and Campylosphaera dela/eodela. The representatives of the family Prinsiacea were found to decrease considerably across the BEE in favour of Coccolithus pelagicus. This "C. pelagicus acme" can be used to approximate the top of the Paleocene in sections where markers are very rare or absent. The calcareous nannofossils assemblages are dominated by Discoaster, Ericsonia, Fasciculithus, and Sphenolithus, indicative of warmer surface water. © 2004 E. Schweizerbart'sche Verlagsbuchhandlung.