Middle Eocene benthic foraminifera from Qattamiya area, Cairo–Suez district, Egypt: biostratigraphy, paleoecology, and their relation to the Southern and Western Tethyan Provinces

This study deals mainly with the biostratigraphy, paleoecology and paleobiogeogrphy of the Middle Eocene benthic foraminifera from an outcrop exposed at Qattamiya area, Cairo–Suez district, Egypt. This district is covered by relatively thick Eocene sequences composed of limestone intercalated with shales and marl. Stratigraphically, the oldest rock unit exposed in the study area is the Observatory Formation which is followed by the Qurn Formation. The examination of the collected samples led to the recognition of 27 species belonging to 17 genera and 10 families. Three benthic foraminiferal biozones are recognized Elphidium trompi-Quinqueloculina carinata Assemblage Zone, Bulimina jacksonensis Zone, and Quinqueloculina ludwigi Zone. These local biozones are correlated with their equivalents inside Egypt. Therefore, the age is assigned to the Middle Eocene. To detect the paleoecology of the recorded foraminiferal community, some parameters (Foraminiferal abundance, richness, and the percentages of epifaunal and infaunal species) are calculated. Three local paleoecologic ecozones are proposed signifying 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. Recently, multivariate analyses are considered as a valuable tool in establishing the paleoecology and paleobiogeographical provinces of the Paleogene microfossils. In this study, a matrix composed of 18 species from six countries (Tunisia, Egypt, Libya, France, Spain and Italy) is suggested for multivariate analyses. This matrix is subjected to the principal component analysis (PCA) and the Q-mode cluster analysis to detect the possible provinces. Consequently, two significant provinces are detected, the Southern Tethyan Province (Tunisia, Libya and Egypt) and the Western Tethyan Province (Spain, Italy, and France). Based on the similarity index, there is a strong similarity between the two provinces, which proposes a marine connection between them during Eocene.


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.

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% H 2 O 2 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.

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

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.

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:

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.
Equivalents  (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.  Mansour et al. (1982), the Morozovella lehneri Zone of Allam et al. (1991)

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.

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  (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.

Ecozone 3
This ecozone represents the whole the Qurn Formation. It is characterized by a low foraminiferal number ( (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.

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. 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.
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 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    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.