Calcareous Nannofossil Biostratigraphy of the Paleocene-Lower Eocene Successions in the Farafra Oasis, Western Desert, Egypt

Abstract

This work deals with a high-resolution analysis of calcareous nannofossil in four exposed Paleocene-Lower Eocene successions in the Farafra Oasis, Western Desert, Egypt in order to detect the different types of stage boundaries and hiatuses. The studied four sections were collected from five localities (Gebel North Gunna, Gebel South Gunna, Ain Ramla, El-Quss Abu Said and Bir Karawin). In the study area, the Paleocene-Lower Eocene succession is made up of four formations, namely Dakhla (at base), Tarawan, Esna and Farafra (at top) that unconformably overlie the Maastrichtian Khoman Formation. The oldest Paleocene calcareous nannofossil Zone (NP 4) is recorded in the Dakhla Formation. It unconformably overlies the latest Maastrichtian Micula prinsii (CC 26b) subzone that is recognized in the uppermost part of the Khoman Formation at North Gunna section. Although Zone NP 4 is successively overlain by the Paleocene-Lower Eocene calcareous nannofossil zones NP 5, NP 6, NP 7/8, NP 9a, NP 9b, NP 10a. These zones are not sequentially recorded in all the studied sections.The Danian/Selandian boundary is traced in the uppermost part of Zone NP 4 at North Gunna and South Gunna sections. At this boundary, a minor hiatus is observed. This is in consistence with the global drop in relative sea level during the Late Danian. A pronounced hiatus is founded slightly after the base of Selandian to the base of the Thanetian at North Gunna and South Gunna sections. In contrast, in the western part of the studied area at Ain Ramla-ElQuss Abu Said section, a conformable relation is recorded at the Selandian/Thanetian boundary where the uppermost part of Zone NP 4 is directly followed by Zones NP 5, NP 6 and NP 7/8. A hiatus between the Paleocene and the Eocene (Thanetian/Ypresian boundary) is observed in the lower part of the Esna Formation at North Gunna section. The nature of the Paleocene/Eocene boundary is not recognized in Ain Ramla-ElQuss Abu Said and South Gunna sections because they are described as composite sections. However, the Ypresian NP 9b subzone is recorded at the base of South Gunna section. Subzone NP 10a is recorded in all the studied sections, which may a response to a relative sea level rise during the Early Eocene time.