Introduction

Benthic foraminifera were broadly used for reconstruction of paleoecological parameters, comprising depth, salinity, temperature, and oxygen content (van der Zwaan et al. 1999; Gooday 2003; Murray, 2006; Boscolo Galazzo et al. 2013; Ostad-Ali-Askari et al. 2020). Several investigations were done on the paleoenvironment, taxonomy, and biostratigraphy of the Middle Eocene foraminifera from Egypt (e.g., El Dawy, 1997; Shahin, 2000; Elewa, 2004; Nassif and Korin, 2018; Abd El-Gaied, 2019; Farouk et al. 2020).

El Dawy (1997) subdivided the Middle Eocene outcrops in the Nile Valley into three biozones Uvigerina nakkadyi-Anomalinoides fayoumensis Zone, Brizaline cookie Zone, and Nonion scaphum-Pararotalia audouini Zone. Shahin (2000) subdivided the Middle Eocene rocks in western Sinai into Norcottia danvillensis-Alistoma aegyptiaca Zone and Uvigerina rippensis-Uvigerina churchi Zone. Ali et al. (2011) dealt with the taxonomy of Eocene foraminifera from the Nile Valley and identified 128 species. Nassif and Korin (2018) subdivided the outcrops in the North Eastern Desert into three subzones, Quinqueloculina carinata, Uvigerina rippensis, and Textularia adalta. Moreover, Abd El-Gaied et al. (2019) subdivided the sequences at Cairo-Helwan area into five biozones. Farouk et al. (2020) concentrated on the evaluation of the Middle Eocene foraminifera at Wadi Nukhul, Sinai, to detect the fluctuations in paleoproductivity and paleobathymetry.

This paper concentrated on the Middle Eocene small benthic foraminifera from Qattamiya area, Cairo–Suez district, Egypt. It represents an attempt to identify the relationship between the Egyptian benthic foraminifera and those from the southern Tethys (Libya, Tunisia) from one side, and those from the western Tethys (Spain, Italy, and France) from the other side. Recently, multivariate analyses represent an essential tool in detecting the paleobiogeographical provinces of the microfossils (e.g., Elewa and Mohamed, 2014; Elewa, 2018; El Baz, 2019; Shahin and El Baz, 2021). Therefore, this work is carried out using multivariate analyses (principal component analysis, Q-mode cluster analysis and Jaccard index). The examined foraminifera include Lagena sulcata, L. striata, Nuttalides truempyi, Marginulinopsis tuberculata, Gaudryina pyramidata, Cibicidoides beadnelli, C. eocaenus, C. libycus, Bulimina jacksonensis, Orthokarstenia nakkadyi, Uvigerina mexicana, Cancris subconicus, Bolivina carinata, Spiroplectammina carinata, Globulina gibba, Cibicides lobatulus, Oridorsalis umbonatus, and Lenticulina cultrata. Also, this work aims to establish the benthic foraminiferal biozones and to detect the paleoenvironment.

Geological setting

The considered outcrop occurs in the Qattamiya area (Fig. 1), Cairo-Suez district (latitude 29° 53′ 56″ N and longitude 31° 24′ 13″ E). This district is covered by relatively thick Eocene sequences composed of limestones intercalated with shales and marl. The study area was subjected to the stresses resulted from the collision between European and African plates during Lutetian time (Issawi et al. 1999). This tectonic event produced variable sedimentary environments, each with characteristic rock units and benthic foraminiferal assemblages.

Fig. 1
figure 1

Location and geologic maps (modified after the Geological Survey of Egypt, 2014)

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Material and methods

Thirty-two rock samples were collected to examine their foraminiferal content. Approximately 100 g of dry rock sample was saturated with a 5% H2O2 solution, washed through a 63-μm mesh sieve, and then dried and sieved. About 1 g of each washed residue was examined. The picked individuals were identified and classified following Loeblich and Tappan (1988). Some selected foraminiferal species were photographed by the scanning electronic microscope (Fig. 2). The proposed biozones are correlated with their equivalents in Egypt. Furthermore, the paleoecological conditions that prevailed during the Middle Eocene depended mainly on the characters of the recorded assemblage, such as abundance, richness, and percentages of Rotaliina, Textulariina, and Miliolina. Also, the percentages of epifaunal and infaunal species were calculated to deduce the oxygen content. In this work, multivariate analyses were used to detect the paleobiogeographic provinces. The principal component analysis and Q-mode cluster analysis (based on Ward’s method) were applied on a matrix composed of 19 foraminiferal species from six countries (Tunisia, Egypt, Libya, France, Spain, and Italy). Furthermore, the similarity index (Jaccard index) was calculated to identify the relation between these regions.

Fig. 2
figure 2

Vertical distribution of the identified species

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Results and discussion

Lithostratigraphy

The whole Middle Eocene succession is subdivided into the Observatory Formation (at the base) and the Qurn Formation (at the top).

Observatory Formation

This rock unit was firstly described by Farag and Ismail (1959). It was subdivided into (from base to top) the Upper Building Stone and Guishi members. In this study, it is overlain conformably by the Qurn Formation. The base of this rock unit is unexposed. It is composed of hard fossiliferous limestone and marly limestone. The thickness reaches 32 m. The identified benthic foraminiferal assemblage includes Eponides ellisorae, Neoeponides schreibersi, Cancris subconicus, Lobatula lobatulus, Baggina brady, Textularia agglutinans, Nonionella spissa, Nonionella auris, Nonion scaphum, Idalina cuvillieri, Triloculina gibba, Triloculina trigonula, Pyrgo elongata, Bolivina carinata, Brizalina cookei, Uvigerina jacksonensis, Uvigerina rippensis, Uvigerina multistriata, and Uvigerina mediterranea. The occurrence of larger benthic (Nummulites spp.) is restricted to some levels.

The documented macrofossils include small branched corals, Vulsella sp., and gastropod moulds. Based on the studies of Shahin et al. (2007), Nassif and Korin (2018), Sallam et al. (2018), and Abd El-Gaied et al. (2019), the Observatory Formation is assigned to the Middle Eocene (Lutetian).

Qurn Formation

This rock unit was originally described by Farag and Ismail (1959). The upper part of this formation is unexposed. The exposed part is 20 m thick, consisting mainly of hard limestone and dolomitic limestone. Benthic foraminiferal assemblages of this unit are relatively low and include Quinqueloculina ludwigi Zone, lobatula lobatulus, Elphidium trompi, Triloculina gibba, Triloculina trigonula, Pyrgo elongata, and Textularia agglutinans. In some intervals, some moulds of bivalves and gastropods occur. Based on the studies of Shahin et al. (2007), Nassif and Korin (2018), Sallam et al. (2018), and Abd El-Gaied et al. (2019), the Qurn Formation is assigned to the Middle Eocene (Bartonian).

Systematic of foraminifera

According to the classification of Loeblich and Tappan (1988), 27 benthic foraminiferal species are identified. Also, the stratigraphic distribution of each species is briefly discussed.

Order: Foraminiferida Eichwald, 1830

Suborder: Textulariina Delage et Herouard, 1896

Superfamily: Textulariacea Ehrenberg, 1838

Family: Textulariidae Ehrenberg, 1838

Subfamily: Textulariinae Ehrenberg, 1838

Genus: Textularia Defrance, 1824

Textularia agglutinans d’Orbigny, 1839

(Pl. 1, Fig. 1 )

1839 Textularia agglutinans d’Orbigny, pl. 1, figs. 17, 18, 32–34.

1963 Textularia agglutinans d’Orbigny-Said and Metwalli, pl. 1, Fig. 13.

Occurrence: Obervatory Formation.

Stratigraphic distribution: Eocene of Belgium (Kaasschieter, 1961) and Middle Eocene of Egypt (e.g., Shahin et al. 2007).

Suborder: Miliolina Delage et Hérouard, 1896

Superfamily: Miliolacea Ehrenberg, 1839

Family: Hauerinidae Schwager, 1876

Subfamily: Hauerininae Schwager, 1876

Genus: Quinqueloculina d’Orbigny, 1826

Quinqueloculina carinata d’Orbigny, 1850

(Pl. 1, Fig. 2)

1990 Quinqueloculina carinata d’Orbigny-Helal, pl. 1, figs. 9–13.

2019 Quinqueloculina carinata d’Orbigny-Abd El-Gaied et al., Fig. 4.11.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of France (Le Clavez, 1949) and Egypt (Shahin et al. 2007; Nassif and Korin, 2018), Middle to Late Eocene of Egypt (Abu Ellil. 2004; Abd El-Gaied et al. 2019; Hassan and Korin, 2019), and Late Eocene of Egypt (Helal, 1990).

Quinqueloculina ludwigi Reuss, 1866

(Pl. 1, Fig. 3)

1866 Quinqueloculina ludwigi Reuss, p. 126, pl. 1, Fig. 12.

1970 Quinqueloculina ludwigi Reuss-Boukhary, pl. 15, Fig. 3.

2019 Quinqueloculina ludwigi Reuss-Abd El-Gaied et al., Fig. 4.14.

2021 Quinqueloculina ludwigi Reuss-Ramadan et al., Fig. 6.26.

Occurrence: Qurn Formation.

Stratigraphic distribution: In Egypt, it was reported from the Middle Eocene (Boukhary, 1970; Nassif and Korin, 2018), the Early Eocene (Shamah and Helal, 1993), the Middle-Late Eocene (Abd El-Gaied et al. 2019; Hassan and Korin, 2019), and Late Eocene (Ramadan et al. 2021). In Italy, it was reported from the Late Eocene (Barbin and Keller-Grünig, 1991).

Subfamily: Miliolinellinae Vella, 1957

Genus: Pyrgo Defrance, 1824

Pyrgo elongata (d’Orbigny, 1850)

(Pl. 1, Fig. 4)

1850 Biloculina elongata d’Orbigny, p. 298, pl. 16, figs. 5,6 and 7.

2019 Pyrgo elongata (d’Orbigny) -Abd El-Gaied et al., Fig. 4.17.

Occurrence: Observatory and Qurn formations.

Stratigraphic distribution: Eocene of Belgium (Kaasschieter, 1961), Middle Eocene of Egypt (Abu Ellil, 2004; Shahin et al. 2007; Nassif and Korin, 2018), and Late Eocene of Egypt (Helal, 1990; Shamah and Helal, 1993).

Genus: Idalina Schlumberger and Munier-Chalmas, 1884

Idalina cuvillieri Bignot, 1992

2004 Idalina cuvillieri Bignot-Abu Ellil, p. 60, pl. 6, figs. 5, 6, 8; pl. 14, figs. 1–8; pl. 18, Fig. 8.

2019 Idalina cuvillieri Bignot-Hassan and Korin, Fig. 11.9.

Occurrence: Observatory and Qurn Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Strougo et al.1992; Abu Ellil, 2004; Hassan and Korin, 2019).

Genus: Triloculina d’Orbigny, 1826

Triloculina gibba d’Orbigny, 1846

1846 Triloculina gibba d’Orbigny, p. 274, pl. 16, figs. 22–24.

1993 Triloculina gibba d’Orbigny-Shamah & Helal, p. 253, pl. 2, Fig. 15.

Occurrence: Observatory and Qurn formations.

Stratigraphic distribution: Middle Eocene of France (Le Calvez, 1949) and Egypt (Helal, 1990), and the Middle-Upper Eocene of Egypt (Abu Ellil, 2004).

Triloculina trigonula (Lamarck, 1804)

(Pl. 1, Fig. 5 )

1961 Triloculina trigonula (Lamarck)-Kaasschieter, p. 165, pl. 5, figs. 8 -11.

2019 Triloculina trigonula (Lamarck)-Abd El-Gaied, et al., Fig. 4.20.

Occurrence: Observatory and Qurn formations.

Stratigraphic distribution: Eocene of Belgium (Kaasschieter, 1961) and Middle Eocene of Egypt (El Dawy, 1997; Shahin et al. 2007).

Suborder: Rotaliina Delage et Hérouard, 1896

Superfamily: Bolivinacea Glaessner, 1937

Family: Bolivinidae Glaessner, 1937

Genus: Bolivina d’Orbigny, 1839

Bolivina carinata Terquem, 1882

(Pl. 1, Fig. 6)

1882 Bolivina carinata Terquem, p. 149, pl. 15, Fig. 19.

1970 Bolivina carinata Terquem-Boukhary, p. 142, pl. 19, Fig. 15.

2019 Bolivina carinata Terquem-Abd El-Gaied et al., Fig. 4.38.

2021 Bolivina carinata Terquem-Ramadan et al., Fig. 7.20.

Occurrence: Observatory Formation.

Stratigraphic distribution: Eocene of France (Terquem, 1882) and south Atlantic Ocean (Müller-Merz and Oberhänsli, 1991), Middle-Late Eocene of Egypt (Boukhary, 1970), the Middle Eocene of Egypt (El Dawy, 1997) and Early-Middle Eocene of Libya (Abd El-Gaied and Abd El-Aziz, 2020) and Spain (Ortiz and Thomas, 2006), and Late Eocene of Egypt (Ramadan et al. 2021).

Genuus: Brizalina Costa, 1826

Brizalina cookei (Cushman, 1922)

1922 Bolivina cookei Cushman, p. 126, pl. 8, figs. 25–26.

1997 Brizalina cookei (Cushman)-El Dawy, pl. 2, figs. 7–8.

2002 Brizalina cookei (Cushman)-Helal, pl. 2, Fig. 10.

2019 Brizalina cookei (Cushman)-Abd El-Gaied, et al., figs. 4.36–4.37.

2021 Brizalina cookei (Cushman) -Ramadan et al., Fig. 7.22.

Occurrence: Observatory Formation.

Stratigraphic distribution: Eocene of Belgium (Kaasschieter, 1961), Middle Eocene of Egypt (Helal, 2002; Hassan and Korin, 2019), and Late Eocene of Egypt (Shahin, 2000; Ramadan et al. 2021).

Superfamily: Buliminacea Jones, 1875

Family: Buliminidae Jones, 1875

Genus: Bulimina d’Orbigny, 1826

Bulimina elongata d’Orbigny, 1826

(Pl. 1, Fig. 7)

1826. Bulimina elongata d’Orbigny, p. 269.

2019 Bulimina elongata d’Orbigny-Hassan and Korin, Fig. 11.5.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Hassan and Korin, 2019).

Bulimina jacksonensis Cushman, 1925

(Pl. 1, Fig. 8)

1925 Bulimina jacksonensis Cushman, p. 6, pl. 1, figs. 6 and 7.

1970 Bulimina jacksonensis Cushman-Boukhary, pl. 18, Fig. 17.

1992 Bulimina jacksonensis Cushman-Hussein, figs. 2.10–2.11.

2021 Bulimina jacksonensis Cushmans-Ramadan et al., figs. 7.23–7.24.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Libya (Barr and Berggren, 1980), Tunisia (Amami-Hamdi et al. 2014) and Egypt (Elewa, 2004; Farouk et al. 2020), the Middle-Late Eocene of Egypt (Fahmy, 1975; Hassan and Korin, 2019), and the Late Eocene of Egypt (Shahin, 2000; Ramadan et al. 2021).

Family: Uvigerinidae Haeckel, 1894

Subfamily: Uvigerininae Haeckel, 1894

Genus: Uvigerina d’Orbigny, 1826

Uvigerina compressa Ansary, 1955

1955 Uvigerina mediterranea Hofker var. compressa Ansary-Ansary, p. 96,

pl. 3, Fig. 17.

1994 Uvigerina compressa Ansary-Anan, Fig. 9.1.

Occurrence: Observatory Formation.

Stratigraphic distribution: Late Eocene of Egypt (Ansary, 1955) and Middle-Late Eocene of Egypt (Anan, 1994).

Uvigerina jacksonensis Cushman, 1925

(Pl. 1, Fig. 9)

1925 Uvigerina jacksonensis Cushman, pl. 10, Fig. 13.

2000 Uvigerina jacksonensis Cushman-Abul Nasr, Fig. 12.6.

2019 Uvigerina jacksonensis Cushman-Hassan and Korin, Fig. 11.22.

2021 Uvigerina jacksonensis Cushman-Ramadan et al., Fig. 7.28.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Elewa, 2004; Hassan and Korin, 2019) and Late Eocene of Egypt (Abul Nasr, 2000; Ramadan et al. 2021).

Uvigerina mediterranea Hofker, 1932

1932 Uvigerina mediterranea Hofker, p. 119, tf. 32.

1970 Uvigerina mediterranea Hofker-Boukhary, pl. 19, Fig. 16.

2021 Uvigerina mediterranea Hofker-Ramadan et al., Fig. 7.29.

Occurrence: Observatory Formation.

Stratigraphic distribution: Late Eocene of Egypt (Ansary, 1955; Ramadan et al. 2021), Middle Eocene of Egypt (Boukhary, 1970).

Uvigerina multistriata Hantken, 1871

1983 Uvigerina multistriata Hantken-Sztrakos, pl. 1, figs. 7–13.

2000 Uvigerina multistriata Hantken-Abul Nasr, figs. 12.1–12.3.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Abul Nasr, 2000; Shahin et al. 2007).

Uvigerina rippensis Cole, 1927

1927 Uvigerina rippensis Cole, pl. 2, Fig. 16.

2004 Uvigerina rippensis Cole-Elewa, pl. 1, Fig. 2.

2019 Uvigerina rippensis Cole-Hassan and Korin, Fig. 11.23.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Libya (Barr and Berggren, 1980) and Egypt (Hussein, 1994; Elewa, 2004; Nassif and Korin, 2018), and Middle-Late Eocene of Egypt (Anan, 1994), Late Eocene of Egypt (Shahin, 2000).

Superfamily: Discorbacea Ehrenberg, 1838

Family: Bagginidae Cushman, 1927

Subfamily: Baggininae Cushman, 1927

Genus: Baggina Cushman, 1926

Baggina bradyi (Brotzen, 1936)

1936 Valvulineria bradyi Brotzen, p. 154.

2019 Baggina bradyi (Brotzen)-Abd El-Gaied, et al., Fig. 5.6.

Occurrence: Observatory Formation.

Stratigraphic distribution: In Egypt, it was recorded from the Late Eocene (Ansary, 1955), Middle Eocene (Abd El-Gaied, et al. 2019), and Middle-Late Eocene (Anan, 1994).

Genus: Cancris De Montfort, 1808

Cancris subconicus (Terquem, 1882)

(Pl. 1, Fig. 10)

1882 Rotalina subconicus Terquem, pl. 4, Fig. 5.

2002 Cancris subconicus (Terquem)-Helal, pl. 3, Fig. 11.

2019 Cancris subconicus (Terquem)-Abd El-Gaied, et al., Fig. 5.9.

Occurrence: Observatory Formation.

Stratigraphic distribution: Eocene of France (Terquem, 1882), the Middle Eocene of Egypt (Boukhary, 1970; Abdel Ghany, 1990), the Late Eocene of Italy (Barbin and Keller-Grünig, 1991), and the Middle-Late Eocene of Egypt (Anan, 1994; Abd El-Gaied, et al. 2019).

Family: Eponididae Hofker, 1951

Subfamily: Eponidinae Hofker, 1951

Genus: Eponides De Montfort, 1808

Eponides ellisorae Garrett, 1939

1939 Eponides ellisorae Garrett, pl. 66, figs. 6–8.

1997 Eponides ellisorae Garrett-El Dawy, p. 435.

Occurrence: Observatory Formation.

Stratigraphic distribution: In Egypt, it was reported from the Late Eocene (Helal, 2002), Middle Eocene (El Dawy, 1997), and Middle-Late Eocene (Anan, 1994).

Genus: Neoeponides Reiss, 1960

Neoeponides schreibersi (d’Orbigny, 1846)

1846 Rotalina schreibersi d’Orbigny, pl. 8, figs. 4–6.

1985 Eponides schreibersi (d’Orbigny)-Abd Elshafy et al., pl. 3, Fig. 16.

2021 Neoeponides schreibersi (d’Orbigny)-Ramadan et al., figs. 8.12–8.14.

Occurrence: Observatory Formation.

Stratigraphic distribution: In Egypt, it was reported from the Middle Eocene (El Dawoody, 1971), Middle-Late Eocene (Abd El-Gaied et al. 2019), and Late Eocene (Ramadan et al. 2021).

Family: Cibicididae Cushman, 1927

Subfamily: Cibicinae Cushman, 1927

Genus: Lobatula Fleming, 1828

Lobatula lobatulus (Walther and Jacob, 1798)

1798 Nautilus lobatulus Walther and Jacob, pl. 14, Fig. 36.

1963 Cibicides lobatulus (Walther and Jacob)-Said and Metwalli, pl. 3, Fig. 5.

2019 Lobatula lobatulus (Walker and Jacob)-Abd El-Gaied et al., Fig. 5.24.

2021 Lobatula lobatulus (Walker and Jacob)-Ramadan et al., Fig. 8.22.

Occurrence: Observatory and Qurn formations.

Stratigraphic distribution: Eocene of France (Le Clavez, 1949) and Egypt (Ansary, 1955), the Late Eocene of Italy and (Barbin and Keller-Grünig, 1991) Egypt (Ramadan et al. 2021), and the Middle Eocene of Egypt (Shahin et al. 2007).

Superfamily: Nonionacea Schultze, 1854

Family: Nonionidae Schultze, 1854

Subfamily: Nonioninae Schultze, 1854

Genus: Nonion De Montfort, 1808

Nonion acutidorsatum ten Dam, 1944

1944 Nonion acutidorsatum ten Dam, p. 108, pl. 3, Fig. 19.

1994 Nonion acutidorsatum ten Dam-Anan, p. 226.

Occurrence: Observatory Formation.

Stratigraphic distribution: Late Eocene of Egypt (Ansary, 1955), Middle Eocene of Egypt (Anan, 1994; Shahin et al. 2007), and Eocene of Neatherland (Ten Dam, 1944).

Nonion scaphum (Fichtel and Moll, 1798)

(Pl. 1, Fig. 11)

1798 Nautilus scaphum Fichtel and Moll, p. 105, pl. 19, figs. e, f.

2019 Nonion scaphum (Fichtel and Moll)-Abd El-Gaied et al., Fig. 5.33.

2021 Nonion scaphum (Fichtel and Moll)-Ramadan et al., Fig. 8.25.

Occurrence: Observatory Formation.

Stratigraphic distribution: In Egypt, it was reported from the Late Eocene (Anan, 1994), Middle Eocene (Shamah and Helal, 1993), and Middle-Late Eocene (Boukhary, 1970).

Genus: Nonionella Cushman, 1926

Nonionella auris (d’Orbigny, 1839)

1839 Valvulina auris d’Orbigny, p. 47, pl. 2, figs. 15–17.

1990 Nonionella auris (d’Orbigny)-Abdel Ghany, p. 86, pl. 3, figs. 11 a, b.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Shahin et al. 2007), and Late Eocene of Egypt (Abdel Ghany, 1990).

Nonionella spissa Cushman, 1931

1961 Nonionella spissa Cushman-Kaasschieter, p. 206, pl. 11, figs. 7–8.

2019 Nonionella spissa Cushman-Abd El-Gaied et al., Fig. 5.37.

Occurrence: Observatory Formation.

Stratigraphic distribution: Eocene of Belgium (Kaasschieter, 1961), Middle Eocene of Egypt (Shamah and Helal, 1993; Abd El-Gaied et al. 2019).

Superfamily: Rotaiiacea Ehrenberg, 1839

Family: Elphidiidae Galloway, 1933

Subfamily: Elphidiinae Galloway, 1933

Genus: Elphidium De Montfort, 1808

Elphidium ancestrum Le Calvez, 1950

2019 Elphidium ancestrum Le Calvez-Abd El-Gaied et al., Fig. 6.10.

2021 Elphidium ancestrum Le Calvez-Ramadan et al., Fig. 8.34.

Occurrence: Observatory and Qurn formations.

Stratigraphic distribution: Middle Late Eocene of Egypt (Abd El-Gaied et al. 2019), and Late Eocene of Egypt (Ramadan et al. 2021).

Elphidium trompi (Ansary, 1955 )

(Pl. 1, Fig. 12)

1955 Nonion trompi Ansary, p. 73, pl. 2, Fig. 25.

1975 Elphidium trompi (Ansary)-Fahmy, p. 313, pl. 2, Fig. 14.

Occurrence: Observatory Formation.

Stratigraphic distribution: Middle Eocene of Egypt (Shahin et al. 2007), and Late Eocene of Egypt (Ansary, 1955; Fahmy, 1975).

Biostratigraphy

Based on the stratigraphical distribution of the documented foraminifera, three biozones are established and correlated with their equals in Egypt (Table 1). The proposed biozones are arranged from base to top as follows:

Table 1 Correlation chart between the suggested foraminiferal biozones with their equivalents in Egypt
Full size table

Elphidium trompi-Quinqueloculina carinata Assemblage Zone

Definition: The base of this zone is not exposed, while the upper boundary is placed at the first existence of Bulimina jacksonensis. The thickness reaches 12 m and occupies the lower part of the Observatory Formation.

Characteristic species: Besides the proposed species, this assemblage comprises Eponides ellisorae, Neoeponides schreibersi, Cancris subconicus, Lobatula lobatulus, Baggina brady, Nonionella spissa, Idalina cuvillieri Triloculina gibba, Pyrgo elongata, Nonionella auris, and Triloculina trigonula (Fig. 3).

Fig. 3 
figure 3

Statistics of the foraminiferal community in the Qattamia section

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Equivalents and age: This zone is equivalent to the Nummulites gizehensis Zone of Mansour et al. (1982), the base of the Nummulites cf. syrticus Zone of Strougo et al. (1992), the lower part of the Uvigerina nakkadyi-Anomalinoides fayoumensis Zone of El Dawy (1997), the base of the Bulimina jacksonensis-Uvigerina jacksonensis Zone of Elewa et al. (1998), the base of Nummulites aff. puchellas Zone of Boukhary et al. (2002), the base of the Globigerinatheka kugleri-Morozovella aragonensis Zone of Hassan and Korin (2019), the lower part of Dictyoconus aegyptiensis Zone of El Baz (2019), and both the Elphidium cherifi, and the base of the Quinqueloculina seminula zones of Abd El-Gaied, et al. (2019). Moreover, Uvigerina rippensis, U. jacksonensis, and Nonion scaphum are distinctive taxa for the Middle Eocene (Elewa et al. 1998; Shahin et al. 2007). Also, Strougo (1979) suggested that the top of the Upper Building Stone Member marks the end of Lutetian. Accordingly, this zone belongs to the Lutetian age.

Bulimina jacksonensis Interval Zone

Definition: It is defined as an interval from the first existence of Bulimina jacksonensis to the first existence of Quinqueloculina ludwigi. The thickness reaches 17 m and occupies the top of the Observatory Formation.

Characteristic species: Bolivina carinata, Brizalina cookei, Uvigerina jacksonensis, Uvigerina rippensis, Textularia agglutinans, Nonionella spissa, N. auris, Nonion scaphum, Uvigerina multistriata, and Uvigerina mediterranea.

Equivalents and age: This zone is equal to the Orbitolites complanatus Zone of Mansour et al. (1982), the Morozovella lehneri Zone of Allam et al. (1991), both the upper part of the Uvigerina nakkadyi-Anomalinoides fayoumensis and the Brizalina cooki zones of El Dawy (1997), the top of the Bulimina jacksonensis-Uvigerina jacksonensis Zone of Elewa et al. (1998), the upper part of Globigerinatheka kugleri-Morozovella aragonensis Zone of Hassan and Korin (2019), and the upper part of the Quinqueloculina seminula and the Nonionella africana Zones of Abd El-Gaied et al. (2019). Accordingly, this zone belongs to Late Lutetian.

Quinqueloculina ludwigi Zone

Definition: It is defined from the first occurrence of Quinqueloculina ludwigi, while the top is not exposed. It occupies the whole Qurn Formation and the thickness reaches 20 m.

Characteristic species: Besides the proposed species, this assemblage comprises lobatula lobatulus, Elphidium trompi, Triloculina gibba, Pyrgo elongata, Triloculina trigonula, and Textularia agglutinans.

Equivalents and age: This zone is equal to the Nummulites beaumonti Zone of Mansour et al. (1982), both the Fabularia schwagerinides and Idalina cuvillieri zones of Strougo et al. (1992), both the upper part of Brizalina cooki and Nonion scaphum-Pararotalia audouin zones of El Dawy (1997), the Uvigerina eocaena-Uvigerina steyeri Zone of Abul Nasr (2000), the Nummulites sp. cf. beaumonti/Nummulites aff. pulchellus Assemblage Zone of Boukhary et al. (2002), the Uvigerina mediterranea Zone of Shahin et al. (2007), the Palmula ansaryi Zone of Aly et al. (2011), the upper part of Uvigerina rippensis and the Textularia adalta subzones of Nassif and Korin (2018), and the Brizalina cooki and Nonion scaphum Zones of Abd El-Gaied et al. (2019). Moreover, Issawi et al. (1999) assigned the Qurn Formation to Bartonian age. Accordingly, this zone belongs to Bartonian.

Paleoecology

To detect the paleosalinity, paleobathymetry and the oxygen conditions, some foraminiferal parameters, including foraminiferal number, richness, the percentages of Rotaliina, Miliolina, Textulariina, and epifaunal and infaunal species, were calculated. In this study, the Middle Eocene rocks are classified into three ecozones, involving the base of the Observatory Formation, the top of the Observatory Formation, and the Qurn Formation.

Ecozone 1

Ecozone 1 represents the base of the Observatory Formation. It is characterized by a low foraminiferal number (17–198 tests per gram; average 74 tests) as shown in Table 2. The foraminiferal richness is also low (2–10 species). It is noted that the foraminiferal assemblage is dominated only by calcareous and epifaunal species (Fig. 4). Planktonic foraminifera and agglutinated foraminifera are completely absent. In order to detect the paleosalinity, the percentages of Rotaliina, Miliolina and Textulariina were calculated. Rotaliina is represented by the following genera Elphidium, Eponides, Cancris, Lobatula, Baggina, and Nonionella. The average percentage of Rotaliina reaches 80%. Miliolina (Triloculina gibba, Quinqueloculina carinata, Idalina cuvillieri, and Pyrgo elongata) reaches about 18%. The foraminiferal plots of this ecozone on the ternary diagram of Murray (1973) are placed on the line of Rotaliina-Miliolina close to the Rotaliina corner (Fig. 5), indicating hyper saline lagoonal conditions. Also, the occurrence of the following foraminiferal assemblage Triloculina, Quinqueloculina, Idalina, Pyrgo, and Elphidium indicates shallow marine environment (Phleger and Parker, 1951; Kaasschieter, 1961; Haynes, 1981). Moreover, the occurrence of Lobatula lobatulus and Cancris subconicus refers to inner-middle shelf (Murray et al. 1981). Furthermore, the presence of small branched corals reflects shallow marine environment (Wells, 1956). Therefore, the deposition of this ecozone occurred in a hyper-to hyposaline, inner neritic environment.

Table 2 Statistics of the foraminiferal community in the Qattamia section
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Fig. 4
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Foraminiferal plots of the studied ecozones on the ternary diagram of Murray (1973)

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Ecozone 2

It represents the top of the Observatory Formation. It is characterized by a low foraminiferal number (16–225 tests per gram; average 71 tests). Also, the number of foraminifera species is low (2–13 species). This ecozone is dominated by calcareous species, while only one agglutinated species is recorded. Rotaliina is represented by the following genera Bolivina, Bulimina, and Uvigerina. The average percentage of Rotaliina reaches 96%. Textulariina includes only one species (Textularia agglutinans), and it represents about 3.5%. Miliolina (Triloculina and Quinqueloculina) reaches about 0.5%. The foraminiferal plots of this ecozone are placed on the Rotaliina corner (Fig. 5), indicating hyposaline lagoonal conditions. Moreover, to detect the oxygen content, the percentages of infaunal and epifaunal species are calculated. Infaunal species represents about 66.6%, while the epifaunal species represents 33.4%. Furthermore, the genera Bulimina, Bolivina, and Uvigerina indicate outer neritic environment with low oxygen conditions (e.g., Barr and Berggren, 1980; Miller and Lohmann 1982). The genus Textularia indicates deep inner shelf ((Boersma, 1984). Nonion extends from inner to outer shelf (Murray, 2006). Therefore, the deposition of this ecozone occurred in the middle shelf with low oxygen conditions.

Ecozone 3

This ecozone represents the whole the Qurn Formation. It is characterized by a low foraminiferal number (8–117 tests per gram; average 34 tests). Also, a low number foraminiferal species is recorded (2–9 species). This ecozone is dominated by calcareous species, whereas only one agglutinated species is recorded. Planktonic foraminifera are completely absent. The average percentage of epifaunal species reaches 97.8%, while the average percentage of infaunal species reaches 2.2%. Miliolina (Triloculina, Quinqueloculina and Pyrgo) reaches about 71.2%. Rotaliina reaches 26.6%, and is represented by the following genera Elphidium, Bulimina, and Cibicides. Textulariina represents 2.2% and includes only one species (Textularia agglutinans). The foraminiferal plots of this ecozone are placed on the line of Rotaliina-Miliolina near the Miliolina corner (Fig. 5), indicating hyper saline lagoonal conditions. The dominance of Miliolina indicates hypersaline environment and water depths extending from 12 to 18 m (e.g., Parker and Gischler, 2015). Also, Elphidium indicates very shallow environment (Murray, 2006). Therefore, the deposition of this ecozone occurred in a hypersaline inner neritic environment.

Fig. 5
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1st principal component axis versus 2nd principal component axis of the studied 6 countries

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Paleobiogeograpgy and multivariate analyses

Many of the identified foraminiferal species were previously documented from the Southern and Western Tethys areas (e.g., Le Calvez, 1949; Kaasschieter, 1961; Said and Metwalli, 1963; Barbin and Keller-Grünig, 1991; Ortiz and Thomas, 2006; Shahin et al. 2007; Amami-Hamdi et al. 2014; Farouk et al. 2020; Abd El-Gaied and Abd El-Aziz, 2020). The paleobiogeography of the studied foraminifera was done with the aid of multivariate analyses (the principal component analysis and Q-mode cluster analysis). Firstly, the principal component analysis was applied on the suggested matrix (Table 3) that consists of 18 foraminiferal species from six regions, including France, Spain, Italy, Tunisia, Egypt, and Libya.

Table 3 Proposed matrix
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The results of PCA are based on the first vector (34.17%) and the second vector (21.27%) as clarified in Table 4 and Fig. 6. It is noted that the examined countries could be classified into two provinces, the first one called the Southern Tethyan Province (STP), which includes Tunisia, Libya and Egypt, while the second province called the Western Tethyan Province (WTP) and includes Spain, France and Italy.

Table 4 Summary of principal component analysis
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Fig. 6
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Dendrogram resulting from cluster analysis in Q-mode using the Ward's method 

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Furthermore, the Q-mode cluster analysis was applied on the same matrix. Therefore, the resulting dendrogram (Plate 1) shows the separation of two clusters (A and B) at a distance of about 5. Cluster A represents the STP and is characterized by a great similarity between the Egyptian foraminiferal assemblage and those from Libya (70%) and Tunisia (55%) as noted in Table 5. The common species between these regions are Lagena sulcata, Nuttalides truempyi, Marginulinopsis tuberculata, Cibicidoides libycus, Cibicidoides beadnelli, Bulimina jacksonensis, and Uvigerina mexicana.

Plate 1
figure 1

1, Textularia agglutinans d’Orbigny, Observatory Formation; 2, Quinqueloculina carinata d’Orbigny, Observatory Formation; 3, Q. ludwigi Reuss, Qurn Formation; 4, Pyrgo elongata (d’Orbigny), Observatory Formation; 5, Triloculina trigonula (Lamarck), Observatory Formation; 6, Bolivina carinata (Terquem), Observatory Formation; 7, Bulimina elongata d’Orbigny, Observatory Formation; 8, Bulimina jacksonensis Cushman, Observatory Formation; 9, U. jacksonensis Cushman, Observatory Formation; 10, Cancris subconicus (Terquem), Observatory Formation; 11, Nonion scaphum (Fichtel and Moll), Observatory Formation; 12, Elphidium trompi (Ansary), Observatory Formation. (Scale bar = 100 µm except for 2 and 3 = 200 µm)

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Table 5 The similarity (Jaccard index) of foraminiferal species between Egypt and other Tethyan regions
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On the other hand, Cluster B represents the WTP and is characterized by a considerable similarity between Italy and Spain (35%), 25% between Spain and France, and 23% between Italy and France. The common species between these regions involve Gaudryina pyramidata, Nuttalides truempyi, Cibicidoides eocaenus, Orthokarstenia nakkadyi, Bolivina carinata, Spiroplectammina carinata, Cibicides lobatulus, and Oridorsalis umbonatus. Moreover, there is a strong similarity between Egypt and Italy (50%), Spain (44%), and France (35%). These results indicate that there was a marine connection between the Southern and Western Tethyan regions through Eocene.

Conclusions

The examined Middle Eocene succession is classified into two rock units, the Observatory Formation (at the base) and Qurn Formation (at the top). The examination of the foraminiferal assemblages leads to the recognition of 27 species belonging to 3 suborders (Textulariina, Miliolina and Rotaliina), 10 families, and 17 genera. Three local biozones are suggested Elphidium trompi-Quinqueloculina carinata Assemblage Zone, Bulimina jacksonensis Zone, and Quinqueloculina ludwigi Zone. Based on the stratigraphic position of the studied two rock units, the comparison between the suggested biozones with their equivalents in Egypt and the presence of some characteristic species as Idalina cuvillieri and Nummulites spp., the age of the two rock units is supposed to the Middle Eocene. Three local paleoecologic ecozones are suggested and denoted a hyper-to hyposaline inner neritic environment for the lower part of the Observatory, the middle shelf with low oxygen conditions for the upper part of the Observatory Formation, and hypersaline inner neritic environment for the Qurn Formation.

Moreover, the paleogeographic distribution of the studied benthic foraminifera was documented. With the aid of multivariate analysis, the paleobiogeographic framework is done. The results of PCA show that there are two provinces, the Southern Tethyan Province (Tunisia, Libya and Egypt) and the Western Tethyan Province (Spain, France and Italy). Also, the results of cluster analysis support this conclusion. The similarity between the two provinces suggests a marine connection between them through Eocene.