1 INTRODUCTION

The stratigraphy, palaeontology, and palaeoecology of the Eocene successions in Fayoum area have been examined by many authors (Abdallah, Helal, & Abd El-Aziz, 2002; Abdel-Fattah, 2016; Abu El Ghar, 2005; Anan & El Shahat, 2014; Ansary, 1955; Bassiouni, Boukhary, Shama, & Blondeau, 1984; Beadnell, 1905; Boukhary et al., 1993; Elewa, Omar, & Dakrory, 1998; El-Fawal, El-Asmar, & Sarhan, 2013; El-Younsy & Salman, 2021; Helal, 2002; King, Underwood, & Steurbaut, 2014; Marzouk, El Shishtawy, & Kasem, 2014; Morsi & Speijer, 2003; Said, 1962; Strougo, Faris, Haggag, Abul-Nasr, & Gingerich, 2013).

The study by Said (1962), on the Middle–Upper Eocene succession in Fayoum area, recognized three formations (from base to top, Gehannam, Birket Qarun and Qasr El Sagha). Bassiouni et al. (1984) identified four new species from the Middle Eocene rocks of Fayoum, involving Loxoconcha vetustopunctatella, Carinocythereis (Reticulina) ismaili, Costa crassireticulata, and C. ducassae. Elewa et al. (1998) established three ostracod biozones from the Middle Eocene sediments of Fayoum area, comprising Leguminocythereis sadeki–Loxoconcha vetustopunctatella Zone, Costa praetricostata Zone, and Costa humboldti Zone. Helal (2002) identified 37 foraminiferal species and 21 ostracod species from the Eocene successions exposed at Fayoum depression. He also established two foraminiferal biozones and three ostracod biozones. Morsi and Speijer (2003) identified 4 species belonging to the genus Nummulites and 21 ostracod species from the Middle–Upper Eocene succession from Gebel Na'alun, southeastern Fayoum. Moreover, Abu El Ghar (2005) subdivided the Upper Eocene rocks of Fayoum into two formations, Birket Qarun and Qasr El Sagha. Strougo et al. (2013) subdivided the Middle-Upper Eocene rocks in Wadi Hitan, Fayoum, into four formations (El Gharaq, Gehannam, Birket Qarun, and Qasr El Sagha). They documented three planktonic foraminiferal biozones, including Truncorotaloides rohri Zone, Turborotalia pseudoampliapertura Zone, and Globigerinatheka semiinvoluta Zone. El-Fawal et al. (2013) constructed the depositional evolution of the Middle-Upper Eocene rocks in Fayoum area. The study of Anan and El Shahat (2014) focused on the sedimentological characteristics of the Gehannam and Birket Qarun formations to detect their depositional environments. Abdel-Fattah (2016) focused on the depositional models of the Upper Eocene deposits along the northern coast of Birket Qarun.

Also, many investigations have been done on the Eocene ostracods from other countries such as Nigeria (Okosun, 1989), Togo (Carbonnel & Johnson, 1989), Libya (El Waer, 1992), Algeria (Faid, 1999), Israel (Honigstein, Rosenfeld, & Benjamini, 2002), and Tunisia (Amami-Hamdi, Dhahri, Jomaa-Salmounaa, Ben Ismail-Lattrachea, & Ben Chaabane, 2016). In Nigeria, Okosun (1989) studied the Early–Middle Eocene ostracods and identified the following species, Costa dahomeyi, Togoina attitogonensis, Cytherella sylvesterbradleyi, Bythocypris olaredodui, Leguminocythereis bopaensis, Loxoconcha lagosensis, Buntonia (Buntonia) attitogonensis, Quadracythere (Hornibrookella) lagaghiroboensis, and Ruggeria? harpa. He concluded that, there are common species between Nigeria and Togo, including Costa dahomeyi, Togoina attitogonensis, Loxoconcha lagosensis and Buntonia (Buntonia) attitogonensis. In Libya, El Waer (1992) subdivided the Middle–Upper Eocene rocks into five ostracod biozones, involving: Heptaloculites harshae, Heptaloculites semirugosa, Heptaloculites minuta, Heptaloculites cavernosa, and Heptaloculites aff. gortanii. In Algeria, Faid (1999) identified 50 ostracod species from the Early-Middle Eocene interval. She stated that most of the Algerian ostracods have strong similarities to those from the southern Tethys. In Israel, Honigstein et al. (2002) subdivided the Eocene succession into three biozones, Soudanella laciniosa triangulata, Costa capsella, and Mauritsina jordanica israeliana. They stated that, most of their species were found in Egypt, Jordan, Libya, Algeria, and west Africa. In Tunisia, Amami-Hamdi et al. (2016) subdivided the Middle–Upper Eocene succession into the following biozones, Loculicytheretta semipunctata, Loculicytheretta semirugosa, Loculicytheretta minuta, Loculicytheretta cavernosa and Loculicytheretta aff. gortanii.

Regrettably, few examinations used multivariate analyses to detect the palaeobiogeography of the Eocene ostracods of Egypt. The main goals of this work are to (a) identify the collected ostracod fauna, (b) establish their biostratigraphic zones, (c) detect their palaeoenvironment, and (d) construct their palaeobiogeographic provinces with the aid of multivariate analyses (principle component analysis, cluster analysis, and similarity index).

2 GEOLOGICAL SETTING AND STRATIGRAPHY

The Fayoum depression lies between the Nile valley and the Western Desert (Figure 1), occupying about 1,700 km² (Zalat, Khalil, Fathy, & Tarek, 2017). It represents one of the main oases in the Western Desert. It is placed in the unstable shelf of Egypt (Said, 1990). Bahr Yousif canal connects Fayoum area with the Nile Valley. The exposed rock units in this basin consist mainly of Eocene and Oligocene deposits. In this study, two sections were carefully chosen to examine the late Middle Eocene–early Late Eocene sediments in the northwestern portion of Fayoum area (Figure 1). The first section is placed at Garet Umm Rigl, while the second section is placed at Qasr El Sagha. Lithostratigraphically, the studied Eocene sediments are subdivided into three formations; Gehannam, Birket Qarun, and Qasr El Sagha (Temple Member). The type section of the Gehannam Formation was formally designated by Said (1962) as Garret Gehannam section. In this study, the base of Gehannam Formation is unexposed, while the exposed upper part consists of marl, argillaceous limestone, calcareous mudstone, siltstones and ended with dolomitic concretions (Figure 2). The thickness of the exposed part reaches about 48 m. The recorded ostracod assemblage from this unit includes: Asymmetricythere yousefi, Cytherella compressa, C. parallela, C. tarabulusensis, Leguminocythereis sadeki, L. oertli, Loxoconcha pseudopunctatella, L. vetustopunctatella, Cativella qurnensis, Paracosta crassireticulata, P. crassireticulata fayoumensis, P. ducassae, Digmocythere ismaili, Nigeroloxoconcha sp, Reticulina ismaili, Xestoleberis subglobosa, Trachyleberis nodosus nodosulcatus, T. nodosus reticulatus, Bairdia gliberti, Acanthocythereis salahii, Novocypris eocenana, Parakrithe crolifa, Reticulina heluanensis, and Grinioneis moosi. Some authors assigned the Gehannam Formation a Middle–Late Eocene age (Haggag, 1990; Marzouk et al., 2014). In contrast, it was given a Middle Eocene age by others (Abdel-Fattah, 2016; Strougo et al., 2013; Zalat, 1995). The latter is followed in the present study.

The Birket Qarun Formation was firstly introduced as Birket el Qurun Series by Beadnell (1905), whereas it was termed as Birket Qarun Formation by Said (1962). In this study, it overlies the Gehannam Formation at Umm Rigl section and attains a thickness of about 62 m. It consists of layers of brown clays, siltstones, shale, argillaceous limestone, and sandstone (Figure 2). Stratigraphically, this unit may be comparable to both the Qurn and Wadi Garawi formations that were recognized at Helwan area by Farag and Ismail (1959). The recorded ostracod assemblage includes: Cytherella compressa, Bairdia gliberti, Krithe bartonensis, Loxoconcha bassionii, L. vetustopunctatella, Trachyleberis nodosus reticulatus, Grinioneis haidingeri, G. moosi, Ruggeria (Keijella) glabella, Paracosta humboldti, Pterygocythereis minor, Asymmetrycythere hiltermanni, A. yousefi, Leguminocythereis oertli, and Xestoleberis subglobosa. Some previous studies dated Birket Qarun Formation as a Middle Eocene age (Elewa et al., 1998; Shamah, 1981; Strougo, 1977). On the contrary, others dated it as Late Eocene age (Abdel-Fattah, 2016; Abu El Ghar, 2005; Gingerich, 1992; Haggag & Bolli, 1995; Helal, 2002; Marzouk et al., 2014; Morsi & Speijer, 2003; Said, 1962; Strougo, 1992; Strougo et al., 2013; Zalat, 1995). This deduction is followed here.

Finally, the Qasr El Sagha Formation was firstly described by Said (1962). It is differentiated from Birket Qarun Formation by having higher ratios of sandstone, sandy mudstone, and shale (Issawi, El-Hinnawi, Francis, & Mazhar, 1999). Stratigraphically, it may be comparable to Tayiba Formation that was described by Hume, Madgwick, Moon, and Sadek (1920), Wadi Hof Formation of Farag and Ismail (1959) and Maadi Formation of Said (1962). Qasr El Sagha Formation was subdivided into two members, from base to top, as the Temple and Dir Abu Lifa members (Bown & Kraus, 1988). In this study, the only recorded unit in Qasr El Sagha section is the Temple Member, which attains a thickness of about 65 m. It consists of mudstone, gypsiferous claystone, sandstone, glauconitic sandstone, and sandy fossiliferous limestone interbeds (Figure 3). The recorded ostracod association contains Cytherella compressa, C. tarabulusensis, Krithe bartonensis, Loxoconcha punctatella, Nigeroloxoconcha sp., Paracosta crassireticulata fayoumensis, Ruggeria (Keijella) glabella, Trachyleberis nodosus nodosulcatus, Xestoleberis subglobosa, Digmocythere ismaili, and Novocypris eocenana. Macrofossils include gastropod and bivalve banks. The age of this unit is assigned as Late Eocene (Abu El Ghar, 2005; Vondra, 1974; Zalat, 1995; and this study). Strougo et al. (2013) stated that the first appearance of Carolia placunoides represents the base of Qasr El Sagha Formation.

3 MATERIALS AND METHODS

The material of this work contains 77 samples from two sections, (49 samples from Umm Rigl and 28 from Qasr El Sagha), located at Fayoun area. To extract the ostracod assemblage, 150 g of dried sample were immersed with a solution of 10% H₂O₂ and then washed over a 63 μm sieve. One gram of washed residue was tested under a binocular microscope. The ostracod carapaces were picked and identified. To detect the palaeoecology, some ostracod parameters were calculated (total abundance, abundance of common species, total richness, common families). The reconstruction of palaeobiogeography was based on multivariate analysis (principle component analysis, cluster analysis, and similarity index), using the program of PAST 3.2 (Hammer, Harper, & Ryan, 2001). The PCA was applied on a matrix containing 19 ostracod species (from this study and previous studies) and 10 regions (Egypt, Libya, Tunisia, Algeria, Jordan, Israel, Senegal, Togo, Ivory Coast and Nigeria). Also, Q-mode cluster analysis (established on Ward's method) was applied on the same matrix to distinguish the palaeobiogeographical provinces of the selected ostracods during Eocene age. Finally, the similarities between the Egyptian ostracods and those from other Tethyan regions were calculated using the similarity index.

4 RESULTS AND DISCUSSION

4.1 Biostratigraphy

The ostracod community contains 33 species belonging to 20 genera and 9 families. The classification of Moore (1961) and that of Horne, Cohen, and Martens (2002) are adopted in this study, and later documented genera are treated according to their authors. The distribution of the examined species is drawn in Figures 2 and 3. Some selected ostracods were photographed under binocular microscope (Figure 4). Based on the stratigraphic distribution of ostacods, three local biozones are distinguished. The correlation between the suggested biozones and previously documented biozones is displayed in Table 1.

TABLE 1. Comparison between the proposed ostracod biozones and their equivalents in Egypt, Libya and Tunisia

			Libya	Tunisia	Egypt
Age			El Waer (1992)	Amami-Hamdi et al. (2016)	Shahin (2000)	Helal (2002)	Abd-Elshafy et al. (2007)	Shahin et al. (2008)	Korin and Hassan (2021)	Present study
Eocene	Upper	Priabonian	Heptaloculites aff. gortanii	Loculicytheretta aff. gortanii	Leguminocythereis africana–Buntonia faresi	Loxoconcha bassounii	Uromuellerina saidi–Asymmetricythere yousefi		Xestoleberis subglobosa–Uromuellerina saidi	Trachyleberis nodosus nodosulcatus–Ruggeria (Keijella) glabella
										Reticulina heluanensis–Leguminocythereis sadeki
	Middle	Bartonian	Heptaloculites cavernosa	Loculicytheretta cavernosa	Asymmetricythere yousefi–Loxoconcha pseudopunctatella	Asymmetricythere yousefi–Loxoconcha pseudopunctatella	Cativella qurnensis–Cytheropteron boukharyi	Loxoconcha pseudopunctatella–Asymmetricythere asymmetrella	Loxoconcha vetustopunctatella	Asymmetricythere yousefi–Loxoconcha pseudopunctatella

4.1.1 Asymmetricythere yousefi–Loxoconcha pseudopunctatella assemblage zone

Definition: It is defined as the interval from the first appearance of the nominate taxa to the first appearance of Reticulina heluanensis.

Thickness and stratigraphic level: about 43 m, it represents most of the Gehannam Formation.

Characteristic species: Asymmetricythere yousefi, Loxoconcha pseudopunctatella, Cytherella compressa, Leguminocythereis sadeki, Loxoconcha vetustopunctatella, Cativella qurnensis, Paracosta ducassae, Cytherella tarabulusensis, Digmocythere ismaili, Leguminocythereis oertli, Nigeroloxoconcha sp., Paracosta crassireticulata, Reticulina ismaili, Xestoleberis subglobosa, Trachyleberis nodosus nodosulcatus, Bairdia gliberti, Paracosta crassireticulata fayoumensis, Acanthocythereis salahii, Cytherella parallela, and Novocypris eocenana.

Equivalents and age: In Egypt, this zone is comparable to the Asymmetricythere yousefi–Cytherella piacabucuensis Zone of Shahin (2000), the Asymmetricythere yousefi–Loxoconcha pseudopunctatella Zone of Helal (2002), the Cativella qurnensis–Cytheropteron boukharyi Zone of Abd-Elshafy, El-Fawal, Ismail, and Mattar (2007) and the Loxoconcha pseudopunctatella–Asymmetricythere asymmetrella Zone of Shahin, El Halaby, and El Baz (2008). Outside Egypt, this zone is equivalent to the Heptaloculites cavernosa Zone of El Waer (1992) from Libya and the Loculicytheretta cavernosa Zone of Amami-Hamdi et al. (2016) from Tunisia. Thus, this zone is dated as a late Middle Eocene age (Bartonian).

4.1.2 Reticulina heluanensis–Leguminocythereis sadeki interval zone

Definition: It is defined as the interval from the first appearance of Reticulina heluanensis to the last appearance of Leguminocythereis sadeki.

Thickness and stratigraphic level: about 49 m, it includes the most upper part of the Gehannam Formation and most of the Birket Qarun Formation.

Characteristic species: Besides the above-mentioned species in the preceding biozone, the most distinctive species include Reticulina heluanensis, Leguminocythereis sadeki, Parakrithe crolifa, Trachyleberis nodosus reticulatus, Grinioneis moosi, Ruggeria (Keijella) glabella, Loxoconcha bassionii, Pterygocythereis minor, Asymmetricythere asymmetrella, Krithe bartonensis, Paracosta humboldti, Asymmetrycythere hiltermanni, and Grinioneis haidingeri.

Equivalents and age: In Egypt, this zone is comparable to the lower parts of Uromuellerina saidi Zone of Bassiouni, Hamza, and Morsi (1994), the Leguminocythereis africana–Buntonia faresi Zone of Shahin (2000), the Loxoconcha bassounii Zone of Helal (2002), Leguminocythereis sadeki–Loxoconcha bassionii–Costa humboldti Zone of Ismail and Abd El-Azeam (2008), the Uromuellerina saidi–Asymmetricythere yousefi Zone of Abd-Elshafy et al. (2007) and the lower part of Xestoleberis subglobosa–Uromuellerina saidi of Korin and Hassan (2021). Outside Egypt, this zone is correlated with the lower parts of Heptaloculites aff. gortanii Zone of El Waer (1992) from Libya, and Loculicytheretta aff. gortanii Zone of Amami-Hamdi et al. (2016) from Tunisia. Consequently, this zone is dated as early Late Eocene age (Priabonian).

4.1.3 Trachyleberis nodosus nodosulcatus–Ruggeria (Keijella) glabella assemblage zone

Definition: The base of this zone is unexposed, while the upper boundary coincides with the last occurrence of Ruggeria (Keijella) glabella.

Thickness and stratigraphic level: about 32 m, it includes the lower part of the Temple Member.

Characteristic species: Cytherella tarabulusensis, C. compressa, Krithe bartonensis, Loxoconcha punctatella, Nigeroloxoconcha sp., Paracosta crassireticulata fayoumensis, Ruggeria (Keijella) glabella, Trachyleberis nodosus nodosulcatus, Xestoleberis subglobosa, Digmocythere ismaili, and Novocypris eocenana.

Equivalents and age: In Egypt, this zone is comparable to the upper parts of Uromuellerina saidi Zone of Bassiouni et al. (1994), the Leguminocythereis africana–Buntonia faresi Zone of Shahin (2000), the Loxoconcha bassounii Zone of Helal (2002), Leguminocythereis sadeki–Loxoconcha bassionii–Costa humboldti Zone of Abd El-Azeam (2008), the upper part of Uromuellerina saidi–Asymmetricythere yousefi Zone of Abd-Elshafy et al. (2007), the upper part of Xestoleberis subglobosa–Uromuellerina saidi of Korin and Hassan (2021). Outside Egypt, this zone is correlated with the upper parts of Heptaloculites aff. gortanii Zone of El Waer (1992) from Libya, the Loculicytheretta aff. gortanii Zone of Amami-Hamdi et al. (2016) from Tunisia. Consequently, this zone is dated as early Late Eocene age (Priabonian).

4.2 Palaeoecology

The deduction of palaeoecological conditions during the Middle and Late Eocene is based mainly on some parameters of ostracod assemblage such as, total number of ostracods, abundance of common species, total richness, and richness of families. However, the presence of benthic foraminifera and some macrofossils groups are also helpful to detect the palaeoecology.

4.2.1 Ecozone 1

It represents the Gehannam Formation, and it attains a thickness of about 50 m. The collected samples that yielded ostracods include 12 samples (Gh2, Gh3, Gh4, Gh5, Gh6, Gh9, Gh10, Gh11, Gh12, Gh13, Gh15, and Gh17), whereas only seven samples are barren of ostracods (Gh1, Gh7, Gh8, Gh14, Gh16, Gh18, and Gh19). The ostracod community is characterized by a low abundance, where the total number of ostracod tests is 163 tests. The highest number of ostracod tests is 30 tests/g in sample Gh3, whereas the lowest number is 2 tests/g in sample Gh13 (Table 2 and Figure 5). Moreover, the richness of this community is not high, where the total number of species reaches 24. The lowest number of species is recorded in sample Gh13 (one species), while the highest number is recorded in sample Gh3 (13 species) as shown in Table 3 and Figure 5. The documented ostracodes are represented by the families Cytherellidae (Cytherella compressa, C. parallela, C. tarabulusensis), Bairdiidae (Bairdia gliberti), Cyprididae (Novocypris eocenana), Krithidae (Parakrithe crolifa), Loxoconchidae (Loxoconcha pseudopunctatella, L. vetustopunctatella, Nigeroloxoconcha), Trachyleberididae (Cativella qurnensis, Paracosta ducassae, Digmocythere ismaili, Paracosta crassireticulata, Trachyleberis nodosus nodosulcatus, Trachyleberis nodosus reticulatus, Paracosta crassireticulata fayoumensis, Acanthocythereis salahii, Reticulina heluanensis, Grinioneis moosi), Cytheridae (Asymmetricythere yousefi), Leguminocythereididae (Leguminocythereis oertli, L. sadeki) and Xestoleberididae (Xestoleberis subglobosa). It is clear that, the most diverse family is Trachyleberididae, followed by Loxoconchidae, Cytherellidae and Leguminocythereididae. Also, the most common species are Leguminocythereis spp. (31 tests), Loxoconcha spp. (29 tests), Asymmetricythere yousefi (26 tests), Cytherella spp. (21 tests), and Paracosta spp. (21 tests).

TABLE 2. The total abundance of ostracods per sample and abundance of the most common ostracods in the Gehannam and Birket Qarun formations

Sample no.	Ecozone	Abundance of ostracods/g	Asymmetricythere spp.	Cytherella spp.	Leguminocythereis spp.	Loxoconcha spp.	Cativella qurnensis	Paracosta spp.	Trachyleberis spp.	Bairdia gliberti
BQ30	Barren	0	0	0	0	0	0	0	0	0
BQ29		0	0	0	0	0	0	0	0	0
BQ28		0	0	0	0	0	0	0	0	0
BQ27		0	0	0	0	0	0	0	0	0
BQ26		0	0	0	0	0	0	0	0	0
BQ25		0	0	0	0	0	0	0	0	0
BQ24		0	0	0	0	0	0	0	0	0
BQ23		0	0	0	0	0	0	0	0	0
BQ22	Ecozone 2 (Birket Qarun Formation)	3	1	0	1	0	0	0	1	0
BQ21		0	0	0	0	0	0	0	0	0
BQ20		1	0	0	0	0	0	0	1	0
BQ19		3	1	0	1	0	0	0	0	1
BQ18		6	1	0	3	0	0	0	0	1
BQ17		0	0	0	0	0	0	0	0	0
BQ16		6	0	0	2	0	0	1	0	2
BQ15		0	0	0	0	0	0	0	0	0
BQ14		0	0	0	0	0	0	0	0	0
BQ13		0	0	0	0	0	0	0	0	0
BQ12		0	0	0	0	0	0	0	0	0
BQ11		0	0	0	0	0	0	0	0	0
BQ10		12	1	0	0	5	0	0	0	2
BQ9		0	0	0	0	0	0	0	0	0
BQ8		0	0	0	0	0	0	0	0	0
BQ7		0	0	0	0	0	0	0	0	0
BQ6		0	0	0	0	0	0	0	0	0
BQ5		0	0	0	0	0	0	0	0	0
BQ4		0	0	0	0	0	0	0	0	0
BQ3		0	0	0	0	0	0	0	0	0
BQ2		3	0	1	0	0	0	0	0	1
BQ1		7	0	1	0	2	0	0	1	1
Gh19	Ecozone 1 (Gehannam Formation)	0	0	0	0	0	0	0	0	0
Gh18		0	0	0	0	0	0	0	0	0
Gh17		10	0	1	2	0	2	3	0	0
Gh16		0	0	0	0	0	0	0	0	0
Gh15		11	0	1	0	3	0	2	3	0
Gh14		0	0	0	0	0	0	0	0	0
Gh13		2	0	2	0	0	0	0	0	0
Gh12		22	2	3	5	4	2	3	0	0
Gh11		7	0	2	0	3	0	0	0	0
Gh10		16	1	1	4	5	0	2	0	1
Gh9		19	0	2	5	6	0	4	0	1
Gh8		0	0	0	0	0	0	0	0	0
Gh7		0	0	0	0	0	0	0	0	0
Gh6		10	6	0	3	0	0	0	0	1
Gh5		20	8	0	0	3	3	2	3	0
Gh4		7	2	1	3	0	0	0	0	0
Gh3		30	3	6	7	4	1	5	0	0
Gh2		9	4	2	2	1	0	0	0	0
Gh1		0	0	0	0	0	0	0	0	0

TABLE 3. Total richness per sample and richness of ostracod families in Gehannam and Birket Qarun formations

Sample no.	Ecozone	Richness	Cytherellidae	Bairdiidae	Cyprididae	Krithidae	Loxoconchidae	Trachyleberididae	Cytheridae	Leguminocythereididae	Xestoleberididae
BQ30	Ecozone 2	0	0	0	0	0	0	0	0	0	0
BQ29		0	0	0	0	0	0	0	0	0	0
BQ28		0	0	0	0	0	0	0	0	0	0
BQ27		0	0	0	0	0	0	0	0	0	0
BQ26		0	0	0	0	0	0	0	0	0	0
BQ25		0	0	0	0	0	0	0	0	0	0
BQ24		0	0	0	0	0	0	0	0	0	0
BQ23		0	0	0	0	0	0	0	0	0	0
BQ22		4	0	1	0	0	0	1	1	1	0
BQ21		0	0	0	0	0	0	0	0	0	0
BQ20		1	0	0	0	0	0	1	0	0	0
BQ19		4	0	1	0	0	0	1	1	1	0
BQ18		4	0	1	0	0	0	1	1	1	0
BQ17		0	0	0	0	0	0	0	0	0	0
BQ16		4	0	1	0	0	0	2	0	1	0
BQ15		0	0	0	0	0	0	0	0	0	0
BQ14		0	0	0	0	0	0	0	0	0	0
BQ13		0	0	0	0	0	0	0	0	0	0
BQ12		0	0	0	0	0	0	0	0	0	0
BQ11		0	0	0	0	0	0	0	0	0	0
BQ10		8	0	1	0	1	2	3	1	0	0
BQ9		0	0	0	0	0	0	0	0	0	0
BQ8		0	0	0	0	0	0	0	0	0	0
BQ7		0	0	0	0	0	0	0	0	0	0
BQ6		0	0	0	0	0	0	0	0	0	0
BQ5		0	0	0	0	0	0	0	0	0	0
BQ4		0	0	0	0	0	0	0	0	0	0
BQ3		0	0	0	0	0	0	0	0	0	0
BQ2		3	1	0	0	0	0	1	0	0	1
BQ1		6	1	1	0	0	1	3	0	0	0
Gh19	Ecozone 1	0	0	0	0	0	0	0	0	0	0
Gh18		0	0	0	0	0	0	0	0	0	0
Gh17		7	1	0	0	0	0	4	0	2	0
Gh16		0	0	0	0	0	0	0	0	0	0
Gh15		6	1	0	1	1	1	2	0	0	0
Gh14		0	0	0	0	0	0	0	0	0	0
Gh13		1	1	0	0	0	0	0	0	0	0
Gh12		8	1	0	1	0	1	2	1	1	1
Gh11		3	1	0	1	0	1	0	0	0	0
Gh10		10	1	1	0	0	2	3	1	2	0
Gh9		11	2	1	0	0	2	3	0	2	1
Gh8		0	0	0	0	0	0	0	0	0	0
Gh7		0	0	0	0	0	0	0	0	0	0
Gh6		3	0	1	0	0	0	0	1	1	0
Gh5		6	0	0	0	0	1	3	1	1	0
Gh4		4	0	0	0	0	0	1	1	1	1
Gh3		13	2	0	0	0	3	5	1	2	0
Gh2		4	1	0	0	0	1	0	1	1	0
Gh1		0	0	0	0	0	0	0	0	0	0

The presence of Asymmetricythere yousefi, Leguminocythereis sadeki, Loxoconcha vetustopunctatella, Paracosta ducassae, Paracosta crassireticulata, Reticulina ismaili, and Trachyleberis nodosus nodosulcatus indicate an open platform environment (Bassiouni et al., 1984; Hewaidy, Morsi, & Samir, 2015). According to Elewa et al. (1998), the presence of Novocypris eocenana, Asymmetricythere yousefi, Paracosta ducassae, and Digmocythere ismaili indicates deep marine conditions. Also, the scarcity of Bairdiidae, Xestoleberididae and Krithidae indicate middle–outer shelf conditions (Helal, 2002). Also, Abd-Elshafy et al. (2007) suggested middle neritic conditions to a similar assemblage from west central Sinai. The dominance of Cytherella tarabulusensis in some intervals indicates inner neritic conditions (Amami-Hamdi et al., 2016).

In addition, the abundance of some benthic foraminifera, such as Bolivina, Bulimina, and Uvigerina indicates middle–outer neritic environment (Helal, 2002). On the contrary, the occurrence of glauconite in some intervals indicates shallow marine conditions (Amorosi, 1997; Anan & El Shahat, 2014). Therefore, the Gehannam Formation was deposited under inner–outer neritic conditions.

4.2.2 Ecozone 2

This interval represents most of the Birket Qarun Formation (with the exception of the upper part). It attains a thickness of about 45 m. Only eight samples (BQ1, BQ2, BQ10, BQ16, BQ18, BQ19, BQ20, BQ22) yielded ostracods. In this interval, the ostracod community is characterized by a very low abundance, where the total number of ostracod tests reaches 41 tests. The highest number of ostracod tests is 12 tests/g in sample BQ10, whereas the lowest number is one test/g in sample BQ22 (Table 2 and Figure 5). Moreover, lower richness is recorded, where the total number of species reaches 15 species. The lowest number of species is recorded in sample BQ20 (one species), while the highest number is recorded in sample BQ10 (eight species) as shown in Table 3 and Figure 4. The upper part of this interval is totally barren of ostracods. The documented ostracodes are represented by the families Cytherellidae (Cytherella compressa), Bairdiidae (Bairdia gliberti), Krithidae (Krithe bartonensis), Loxoconchidae (Loxoconcha bassionii, L. vetustopunctatella), Trachyleberididae (Trachyleberis nodosus reticulatus, Grinioneis haidingeri, G. moosi, Ruggeria (Keijella) glabella, Paracosta humboldti, Pterygocythereis minor), Cytheridae (Asymmetrycythere asymmetrella, A. hiltermanni, A. yousefi), Leguminocythereididae (Leguminocythereis oertli), and Xestoleberididae (Xestoleberis subglobosa). It is clear that, the most diverse family is Trachyleberididae, while all the other families are very rare. In addition, this assemblage is dominated by Bairdia gliberti (9 tests), Leguminocythereis spp. (seven tests), and Loxoconcha spp. (seven tests). According to the foraminiferal community, the base of this interval is rich in Bolivina, Bulimina, Uvigerina, and rare planktonic foraminifera indicating deep inner neritic—middle neritic environment (Helal, 2002). The presence of larger benthic foraminifera (Nummulites and Operculina) in some beds, reflects inner-middle neritic conditions (Barr & Berggren, 1980). Therefore, the Birket Qarun Formation was deposited under inner-middle neritic conditions.

4.2.3 Ecozone 3

This interval represents the lower part of Temple Member and attains a thickness of about 32 m. Only four samples (T1, T3, T9, and T13) yielded ostracods. The ostracod community is characterized by very low abundance, where the total number of ostracod tests is 46 tests. The highest number of ostracod tests is 28 tests/g in sample T1, whereas the lowest number is 2 tests/g in sample T9 (Table 4 and Figure 6). Moreover, the richness of this community is low, where the total number of species reaches 11. The lowest number of species is recorded in samples T3 and T9 (one species), while the highest number is recorded in sample T1 (nine species) as shown in Table 5 and Figure 6. The upper part of the Temple Member is completely devoid of ostracods. The documented ostracodes are represented by the families Cytherellidae (Cytherella compressa, C. tarabulusensis), Cyprididae (Novocypris eocenana), Krithidae (Krithe bartonensis), Loxoconchidae (Loxoconcha punctatella, Nigeroloxoconcha), Trachyleberididae (Digmocythere ismaili, Ruggeria (Keijella) glabella, Trachyleberis nodosus nodosulcatus, Paracosta crassireticulata fayoumensis), and Xestoleberididae (Xestoleberis subglobosa). It is clear that, the most diverse family is Trachyleberididae, followed by Cytherellidae and Loxoconchidae (Table 5). Also, the most common species are Cytherella spp. (19 tests), Ruggeria (Keijella) glabella (nine tests) and Loxoconcha punctatella (six tests). Trachyleberis nodosus nodosulcatus indicates open platform environment (Bassiouni et al., 1984). According to Dubarr (1958), the abundance of macrofossils such as Carolia, oyster and Turritella reflects very shallow water depth. The occurrence of glauconite in some beds mirrors deposition under marine condition of normal salinity (Amorosi, 1997). Therefore, the Temple Member was deposited under shallow water conditions (Abdallah, Aboul Ela, Shamah, & Abdel Aziz, 1997; Abu El Ghar, 2005; and this study).

TABLE 4. The abundance of ostracods per sample and abundance of the most common ostracods in the Temple Member

Sample no.	Ecozone	Abundance of ostracods/g	Cytherella spp.	Ruggeria (Keijella) glabella	Trachyleberis	Paracosta	Loxoconcha
T28	Ecozone 3	0	0	0	0	0	0
T27		0	0	0	0	0	0
T26		0	0	0	0	0	0
T25		0	0	0	0	0	0
T24		0	0	0	0	0	0
T23		0	0	0	0	0	0
T22		0	0	0	0	0	0
T21		0	0	0	0	0	0
T20		0	0	0	0	0	0
T19		0	0	0	0	0	0
T18		0	0	0	0	0	0
T17		0	0	0	0	0	0
T16		0	0	0	0	0	0
T15		0	0	0	0	0	0
T14		0	0	0	0	0	0
T13		13	6	3	0	0	2
T12		0	0	0	0	0	0
T11		0	0	0	0	0	0
T10		0	0	0	0	0	0
T9		2	0	0	2	0	0
T8		0	0	0	0	0	0
T7		0	0	0	0	0	0
T6		0	0	0	0	0	0
T5		0	0	0	0	0	0
T4		0	0	0	0	0	0
T3		3	3	0	0	0	0
T2		0	0	0	0	0	0
T1		28	10	6	3	2	4

TABLE 5. Total richness per sample and richness of ostracod families in the Temple Member

Sample no.	Ecozone	Richness	Cytherellidae	Bairdiidae	Cyprididae	Krithidae	Loxoconchidae	Trachyleberididae	Cytheridae	Leguminocythereididae	Xestoleberididae
T28	Ecozone 3	0	0	0	0	0	0	0	0	0	0
T27		0	0	0	0	0	0	0	0	0	0
T26		0	0	0	0	0	0	0	0	0	0
T25		0	0	0	0	0	0	0	0	0	0
T24		0	0	0	0	0	0	0	0	0	0
T23		0	0	0	0	0	0	0	0	0	0
T22		0	0	0	0	0	0	0	0	0	0
T21		0	0	0	0	0	0	0	0	0	0
T20		0	0	0	0	0	0	0	0	0	0
T19		0	0	0	0	0	0	0	0	0	0
T18		0	0	0	0	0	0	0	0	0	0
T17		0	0	0	0	0	0	0	0	0	0
T16		0	0	0	0	0	0	0	0	0	0
T15		0	0	0	0	0	0	0	0	0	0
T14		0	0	0	0	0	0	0	0	0	0
T13		6	2	0	1	0	0	3	0	0	0
T12		0	0	0	0	0	0	0	0	0	0
T11		0	0	0	0	0	0	0	0	0	0
T10		0	0	0	0	0	0	0	0	0	0
T9		1	0	0	0	0	0	1	0	0	0
T8		0	0	0	0	0	0	0	0	0	0
T7		0	0	0	0	0	0	0	0	0	0
T6		0	0	0	0	0	0	0	0	0	0
T5		0	0	0	0	0	0	0	0	0	0
T4		0	0	0	0	0	0	0	0	0	0
T3		1	1	0	0	0	0	0	0	0	0
T2		0	0	0	0	0	0	0	0	0	0
T1		9	2	0	0	1	2	3	0	0	1

It is clear that, for the examined rock units, the sea level decreases from the base (Gehannam and Birket Qarun formations) to top (Temple Member), and is regular with the global decline in sea level curve (Miller, 2009). This conclusion is confirmed by Abu El Ghar (2005), Anan and El Shahat (2014) in Fayoum area and by Farouk, Jain, Belal, Omran, and Al-Kahtany (2020) in Sinai.

4.3 Palaeobiogeography

Many of the identified species have been previously recorded from the Eocene of the southern Tethys and west Africa (Apostolescu, 1961; Barsotti, 1963; Bassiouni & Morsi, 2000; Carbonnel, Alzoma, & Dikouma, 1990; Donze et al., 1982; Elewa, 2005; Faid, 1999; Helmdach & El Khoudary, 1981; Honigstein et al., 2002; Reyment, 1981; Said-Benzarti, 1978; Shahin et al., 2008).

The present study tries to establish the palaeobiogeography of some selected Eocene ostracods by means of multivariate analyses (PCA, similarity index and Q-mode cluster analysis). The PCA is applied on the proposed data matrix that is shown in Table 6. The outcomes of PCA are based on the first and second components (respectively 32.25 and 22.43%) as exposed in Table 7. This analysis designates three different provinces (Figure 7), namely North Africa (NAP), Middle East (MEP), and West Africa (WAP). The first province, which called NAP, involves Algeria, Tunisia, Libya, and Egypt. The second, MEP, involves Israel and Jordan. Moreover, the third, WAP, involves Nigeria, Ivory Coast, Togo, and Senegal. In addition, the Q-mode cluster analysis, is applied on the same data matrix. The resulted dendrogram shows the separation of two clusters (A and B) at a distance of about 6.6 (Figure 8). Cluster A represents the West Africa Province, while cluster B represents the North Africa and Middle East provinces. According to the studied matrix, the common species in the WAP include Leguminocythereis bopaensis, L. lokossaensis, L. senegalensis, Buntonia attitogonensis, Soudanella laciniosa laciniosa, S. laciniosa triangulata, and Dahomeya alata.

TABLE 6. The proposed data matrix prepared for multivariate analyses

Species	Senegal	Ivory Coast	Nigeria	Togo	Algeria	Tunisia	Libya	Egypt	Israel	Jordan
Reticulina proteros	1	0	0	0	1	1	0	1	1	1
Asymmetricythere yousefi	0	0	0	0	1	1	0	1	0	1
Paracypris jonesi	0	1	0	0	1	0	0	1	0	0
Brachycythere (Digmocythere) ismaili	0	0	0	0	1	1	0	1	1	1
Leguminocythereis africana	0	0	0	0	0	1	1	1	0	0
Leguminocythereis bopaensis	0	0	1	1	1	0	0	1	0	0
Leguminocythereis cirtaensis	0	0	0	0	1	1	1	0	0	0
Leguminocythereis lokossaensis	0	1	0	1	1	0	1	1	0	0
Leguminocythereis senegalensis	1	1	1	1	0	0	0	1	0	0
Bairdia abundans	0	0	0	0	0	1	1	1	0	0
Ordoniya hasaensis	0	0	0	0	0	0	0	1	1	1
Soudanella laciniosa triangulata	1	0	1	0	0	1	1	1	0	1
Soudanella laciniosa laciniosa	0	1	1	1	0	0	0	0	0	0
Buntonia attitogonensis	0	0	1	1	1	0	0	1	0	0
Buntonia jordanica	0	0	0	0	0	1	0	1	1	1
Dahomeya alata	1	1	1	0	0	1	1	1	0	0
Heptaloculites aff. H. gortanii	1	0	0	0	1	1	1	0	0	0
Heptaloculites prima	0	0	0	0	1	1	1	0	0	0
Heptaloculites quinqueloculita	0	0	0	0	1	1	1	0	0	0

• Note: References: Egypt (Abd-Elshafy et al., 2007; Bassiouni, 1969; Bassiouni & Luger, 1990; Boukhary, Toumarkine, Khalifa, & Arif, 1982; Cronin & Khalifa, 1979; Hewaidy et al., 2015; Shahin et al., 2008), Libya (El Sogher, 1996; El Waer, 1992; Helmdach & El Khoudary, 1981), Algeria (Abd-Elshafy et al., 2007; Faid, 1999), Tunisia (Amami-Hamdi et al., 2016; Donze et al., 1982; Said-Benzarti, 1978), Israel (Honigstein et al., 2002; Honigstein & Rosenfeld, 1995; Honigstein, Rosenfeld, & Benjamini, 1991), Jordan (Bassiouni, 1969; Bassiouni, 1970), Togo (Apostolescu, 1961; Carbonnel & Johnson, 1989), Nigeria (Okosun, 1989), Senegal and Ivory Coast, (Abd-Elshafy et al., 2007).

TABLE 7. Results of principal component analysis

PC	Eigenvalue	% variance	Cumulative percent
1	1.55879	32.251	32.251
2	1.08411	22.43	54.681
3	0.778158	16.1	70.781
4	0.605976	12.537	83.318
5	0.313018	6.4762	89.7942
6	0.243081	5.0293	94.8235
7	0.123369	2.5525	97.376
8	0.078311	1.6202	98.9962
9	0.048518	1.0038	100

Moreover, the similarity index is calculated to detect the degree of similarity between the different countries in the proposed provinces (Table 8). Based on this index, the WAP is signified by strong affinities between Nigeria and Togo (72.7%), Togo and Ivory Coast (60%), Nigeria and both of Senegal, and Ivory Coast (54.5%). Also, the MEP is signified by strong affinity between Israel and Jordan (80%). The common species include Reticulina proteros, Brachycythere (Digmocythere) ismaili, Ordoniya hasaensis, and Buntonia jordanica. Furthermore, the NAP is signified by strong similarities between Libya and Tunisia (76%), Egypt and Tunisia (61.5%), Egypt and Algeria (56%), Libya and Algeria (50%). The common species include Reticulina proteros, Asymmetricythere yousefi, Paracypris jonesi, Brachycythere (Digmocythere) ismaili, Leguminocythereis Africana, L. bopaensis, L. cirtaensis, L. lokossaensis, Bairdia abundans, Soudanella laciniosa triangulate, Buntonia attitogonensis, Buntonia jordanica, Dahomeya alata, Heptaloculites aff. H. gortanii, H. quinqueloculita, and H. prima.

TABLE 8. The Similarity index between Egypt and other regions

	Nigeria	Senegal	Ivory Coast	Togo	Algeria	Tunisia	Libya	Egypt	Israel	Jordan
Senegal	0.545	1	0.4	0.2	0.25	0.47	0.428	0.42	0.22	0.36
Ivory Coast	0.545	0.4	1	0.6	0.25	0.117	0.285	0.42	0	0
Nigeria	1	0.545	0.545	0.727	0.235	0.22	0.266	0.5	0	0.166
Togo	0.727	0.2	0.6	1	0.375	0	0.14	0.42	0	0
Algeria	0.235	0.25	0.25	0.375	1	0.608	0.5	0.56	0.266	0.35
Tunisia	0.22	0.47	0.117	0	0.608	1	0.76	0.615	0.375	0.555
Libya	0.266	0.428	0.285	0.14	0.5	0.76	1	0.43	0	0.13
Egypt	0.5	0.42	0.42	0.42	0.56	0.615	0.43	1	0.44	0.6
Israel	0	0.22	0	0	0.266	0.375	0	0.44	1	0.8
Jordan	0.166	0.36	0	0	0.35	0.555	0.133	0.6	0.8	1

Finally, the similarity between the Egyptian ostracods and those identified from Jordan reaches 60%, whereas it reaches 44% between Egypt, and Israel. Also, the resemblance between the Egyptian assemblages and those from Nigeria reaches 50%, while it reaches 42% between Egypt and Senegal, Ivory Coast and Togo. The significant similarities between Egypt and North Africa, Middle East, and West Africa, reflect an east–west ostracod migration along the southern Tethys during Eocene age.

5 CONCLUSIONS

This study deals principally with the micropalaeontological significances of the Middle–Late Eocene sediments from Fayoum area, Egypt. Three rock units are recognized (from base to top) Gehannam, Birket Qarun, and Qasr El Sagha (Temple Member). A relatively diverse ostracod assemblage is recorded, where 33 species are identified. Based on stratigraphic distribution of these ostracods, three biozones are recognized: Asymmetricythere yousefi–Loxoconcha pseudopunctatella Zone and Reticulina heluanensis–Leguminocythereis sadeki Zone (From Gehannam and Birket Qarun formations), whereas the third zone Trachyleberis nodosus nodosulcatus–Ruggeria (Keijella) glabella Zone represents the lower part of Qasr El Sagha Formation (Temple Member). The studied ostracod assemblage is similar to those previously recorded from the Middle–Late Eocene of different localities inside Egypt. The palaeoecological outline depends mainly on the characters of studied ostracod assemblages. Therefore, three distinctive ecozones are identified. The first ecozone signifies the Gehannam Formation, which was deposited under inner–outer neritic conditions. The second ecozone signifies the Birket Qarun Formation, which was deposited under inner-middle neritic conditions. The third ecozone signifies the Temple Member, which was deposited under shallow water conditions. Moreover, this study represents an attempt to use the multivariate analyses to build up the palaeobiogeographic provinces of Eocene ostracods from the southern Tethys and western Africa. To complete this work, the suggested matrix consists of 19 species from 10 countries. The results of PCA and Q-mode cluster analysis construct three provinces, North Africa, the Middle East, and West Africa. It is clear that, the resemblance between the Egyptian ostracods and North Africa is higher than with West Africa. The considerable similarity between these provinces indicates an ostracod migration along the southern Tethys during Eocene age.

CONFLICT OF INTEREST

The authors declare that this work represents an original contribution and that none of the present data were published elsewhere.