Calcareous nannofossil and planktonic foraminifera biostratigraphy through the Middle to Late Eocene transition of Fayum area, Western Desert, Egypt Akmal Mohamed Marzouk a,⇑ , Ahmed Moustafa El Shishtawy a , Atef Masoud Kasem b a Geology Department, Tanta University, Tanta, Egypt b Geology Department, Damanhour University, Damanhour, Egypt article info Article history: Received 13 February 2014 Received in revised form 5 July 2014 Accepted 8 July 2014 Available online 22 July 2014 Keywords: Eocene Calcareous nannofossils Planktonic foraminifera Biostratigraphy Middle/Upper Eocene boundary Egypt abstract The Eocene sequence exposed at Gebel Naalun (Fayum-Nile divide), Guta section-I (West of Birket Qarun near Guta Village) and Guta section-II (Northwest of Birket Qarun near Guta Village) is differentiated, from base to top, into two formations; Gehannam Formation (Middle–Late Eocene) and Birket Qarun Formation (Late Eocene), respectively. Two calcareous nannofossil zones were recognized from the Eocene succession at Gebel Naalun; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones as well as one planktonic fora- miniferal zone; Truncorotaloides (Acaranina) rohri (P14) zone. However, at Guta section-I, two nannofossil zones were defined; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones; the preservation of planktonic foraminiferal assemblage is too poor to enable us to recognize marker species as a result of many diagenetic processes. At Guta section-II, two nannofossil zones; Chiasmolitus oamaruensis (NP18) and Isthmolithus recurvus (NP19) and two planktonic foraminiferal zones; T. pseudoampliapertura zone and G. semiinvoluta zone are recorded. Several authors found that the lowest occurrence of Chiasmolithus oamaruensis is a poor criterion for defining the base of NP18 Zone, which is confirmed here. The same criticism has been applied to the lowest occurrence of Isthmolithus recurvus which defines the NP18/NP19 zonal boundary. It is generally agreed that NP19 Zone falls in the Priabonian (Late Eocene). As a result of the occurrence of the nannofossil marker species; Isthmolithus recurvus only in side views below and above the first appearance of Chiasmolithus oamaruensis at both Naalun and Guta section-I, this species is not reliable to define the NP18/NP19 zonal boundary. At Guta section-II, the Middle/Upper Eocene boundary can be delineated by the first appearance of Globigerinatheka semiinvoluta above the first occurrence of Isthmolithus recurvus in both plane and side views. Ó 2014 Published by Elsevier Ltd. 1. Introduction The Fayum depression is roughly triangular to circular in shape and occupies approximately 17,000 km 2 . It is located in the northern part of the Western Desert of Egypt immediately to the west of the Nile Valley, about 95 km south–southwest of Cairo and 15 km north-west of Beni Suef. It lies between latitudes 28°60 0 and 29°50 0 N and longitudes 30°00 0 and 31°15 0 E(Fig. 1). Sev- eral geological, stratigraphical, sedimentological and paleontologi- cal studies were carried out in the Fayum depression. A voluminous literature containing a great deal of new information has been gathered on the vertebrate fauna of Fayum during the past thirty years. Surprisingly, calcareous plankton (planktonic foraminifera and calcareous nannofossils) and larger foraminifera, the most widely used biostratigraphic tools for age calibration, have seldom been studied, and then only in very localized sections (Strougo and Haggag, 1984; Haggag, 1990; Faris and Strougo, 1992; Haggag and Bolli, 1995, 1996; Bouhkary et al., 2003; Bouhkary and Kamal, 2003). Saber (1998) studied in detail the stratigraphy and facies asso- ciation of Eocene rocks; Gehannam Formation (Middle Eocene) and Birket Qarun Formation (Late Eocene) in the area between Fayum and Nile Valley (Gebel Naalun and Monqar El Lahun). He concluded that, the lower part of Gehannam Formation at Gebel Naalun was deposited mainly in subtidal lagoons under calm conditions with open circulation while its upper part was accumulated in shallow http://dx.doi.org/10.1016/j.jafrearsci.2014.07.003 1464-343X/Ó 2014 Published by Elsevier Ltd. ⇑ Corresponding author. Tel.: +20 01223284932. E-mail address: akmal_marzouk@live.com (A.M. Marzouk). Journal of African Earth Sciences 100 (2014) 303–323 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci