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Article

Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt

by
Safaa Abu Bakr
1,
Ibrahim M. Abd El-Gaied
2,
Mostafa M. Sayed
3,4,5,
Petra Heinz
5,*,
Michael Wagreich
4 and
Abdelaziz Mahmoud
1
1
Department of Geology, Faculty of Science, Helwan University, Cairo 11795, Egypt
2
Faculty of Earth Science, Beni-Suef University, Beni-Suef 62511, Egypt
3
Geology Department, Faculty of Science, Beni-Suef University, Beni-Suef 62511, Egypt
4
Department of Geology, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna, 1090 Vienna, Austria
5
Department of Palaeontology, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna, 1090 Vienna, Austria
*
Author to whom correspondence should be addressed.
Diversity 2025, 17(4), 293; https://doi.org/10.3390/d17040293
Submission received: 28 February 2025 / Revised: 13 April 2025 / Accepted: 17 April 2025 / Published: 19 April 2025
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Abstract

:
The middle and upper Eocene sedimentary successions exposed along the northwestern and northeastern portions of the Nile Valley, Egypt, have been thoroughly examined for their ostracod assemblages. This study enhances the understanding of biostratigraphic zonations and evaluates the paleobiogeographic distribution and paleoenvironmental conditions that prevailed during the deposition of this sedimentary record. Lithostratigraphically, the studied successions are subdivided into four stratigraphic units, arranged in ascending order as follows: the Qarara, the El Fashn, the Gehannam, and the Beni Suef formations. A total of 125 rock samples were selected and well analyzed, resulting in the identification of sixty-five ostracod species and subspecies belonging to thirty-three genera, fifteen families, and three superfamilies. The stratigraphic distribution of the recorded ostracod taxa contributed to the construction of four local biozones, spanning the interval from the upper Lutetian to lower Priabonian: Schizocythere fadlensis Zone (upper Lutetian–lower Bartonian), Loxoconcha pseudopunctatella Zone, Dygmocythere ismaili Zone (Bartonian), and Asymmetricythere hiltermanni Zone (Bartonian–Priabonian). These biozones are well described, discussed, and correlated with those previously documented in different areas of Egypt and neighboring countries. The statistical analysis, supported by ternary plot diagrams, indicates that the depositional environments of the studied rock units fluctuated between shallow inner neritic and deeper outer neritic marine environments. The identified taxa display a wide geographic distribution and show a significant similarity with those identified in the southern, northern, and eastern Tethyan provinces, suggesting a direct marine connection during the Eocene.

1. Introduction

The Eocene spans a vast region in Egypt, encompassing the Eastern Desert, Nile Valley, Western Desert, and Sinai Peninsula [1]. These sedimentary deposits are rich in ostracods and benthic foraminifera, both of which play a crucial role in stratigraphic and paleoecological studies. Research on the Eocene ostracods in the Nile Valley has been comprehensive, beginning with the work of Khalifa and Cronin [2], followed by contributions from Bassiouni [3,4,5], Boukhary et al. [6], Elewa [7,8,9], Abdallah et al. [10], Abd El-Aziz and Abd El-Gaied [11], Shahin et al. [12], and Helal and El Baz [13]. Additionally, studies on ostracods from the Fayoum area have primarily concentrated on their paleoecological and systematic paleontological aspects [10,14,15,16,17,18,19,20,21,22].
Recently, Helal and El Baz [13] investigated the paleobathymetry and paleobiogeography of middle Eocene ostracods from the southeast Fayoum area, Egypt. They proposed a potential marine connection between the southern and northern Tethys provinces. In addition, Adebambo et al. [23] explored the paleobiogeographic distribution of ostracods during the Paleogene in West–Central Africa. Their study identified two primary ostracod bioprovinces during this period: the Southern Tethys province and the West African province, which were connected during the Paleocene–Eocene interval through the Trans-Saharan Seaway, as evidenced by the significant similarities between the ostracod assemblages of North and West Africa. These findings align well with the results of Bassiouni and Luger [24], Keen et al. [25], Elewa [26], Speijer and Morsi [27], Morsi et al. [28], Youssef et al. [29], and Sayed et al. [30]. Furthermore, El Baz et al. [22] reported a marked similarity between the ostracod assemblages of North Africa and the Middle East during the middle Eocene. Shahin et al. [12] identified fifty-one ostracod species from the middle Eocene of the northwestern Eastern Desert, Egypt, and recognized three local ostracod zones. They examined the paleoecology of each assemblage zone and discussed the paleobiogeographic distribution of the species, revealing a direct connection between the Southern Tethyan province and the Western Europe Tethyan province, through which the ostracod assemblages migrated. Abd El-Aziz and Abd El-Gaied [11] studied middle and upper Eocene ostracods in three rock units (El Fashn, Beni Suef, and Maadi formations) in the northeastern Beni Suef area, Egypt. They recorded sixty-one species and subspecies and identified two ostracod biozones: the Trachyleberis nodosus nodosus Zone (upper middle Eocene) and the Uromuellerina saidi Zone (upper Eocene). Numerous studies have been conducted on Eocene ostracods in the southern Tethyan province, including research in Libya [31,32], Algeria [33], and Tunisia [34,35,36]. Similarly, several studies have focused on ostracod fauna in the northern Tethyan province [37,38,39,40,41,42,43,44,45].
The planktonic foraminifera along the investigated sections were recently studied by Abu Bakr et al. [46]. They identified four planktonic biozones: the Morozovelloides lehneri Zone, Orbulinoides beckmanni Zone, Morozovelloides crassatus Zone (upper Lutetian–Bartonian), and Globigerinatheka semiinvoluta Zone (upper Bartonian–lower Priabonian). Despite thorough studies conducted in nearby areas, none of these works have provided a detailed analysis of the ostracod assemblages. Therefore, the present study aims to offer more comprehensive biostratigraphic zonations for the middle and upper Eocene ostracods and to correlate the identified biozones with those found in the Tethyan provinces. Additionally, it integrates the lithological characteristics and statistical analysis of the recorded ostracod fauna with their known ecological preferences to better constrain the paleoenvironmental evolution of this region. Moreover, it highlights the paleobiogeographic distribution of the recorded species within the Tethyan province, tracking their spatial and temporal occurrences during the middle and late Eocene.

2. Geologic Setting and Lithostratigraphy

To achieve the objectives of the present study, three stratigraphic surface sections were selected, measured, and described in detail. The first section is located at 29°15′ N, 30°58′ E, near the Beni Suef–El Fayoum new asphalt road, at El Garabaa Village. The Fayoum area is situated on the western side of the Nile Valley, between latitudes 28°60′ N and 29°45′ N, and longitudes 30°00′ E and 31°15′ E, approximately 100 km southwest of Cairo City. The Fayoum basin has been significantly influenced by tectonic interactions between the African and Eurasian plates [47]. The area is predominantly characterized by sedimentary sequences from the middle Eocene and Miocene, which are unconformably overlain by Pliocene and Pleistocene deposits [48,49,50]. The second section is located at 29°02′ N, 31°17′ E, in Wadi Bayad El Arab, east of Beni Suef City, while the third section, known as the Gabal Abyiad exposure, is located at 28°45′ N, 31°14′ E, east of El Fashn City (Figure 1).
The lithological features of the middle and upper Eocene sections allowed for the identification of four lithostratigraphic units: the Qarara, El Fashn, Gehannam, and Beni Suef formations (Figure 2 and Figure 3). Recently, Abu Bakr et al. [46] conducted a detailed study on the stratigraphy and planktonic foraminiferal contents of these rock units in the study area. A brief description of these rock units is provided below.

2.1. Qarara Formation (Lutetian-Bartonian)

The Qarara Formation was first recognized by Bishay [52] in Gabal Qarara, east of Maghagha City, and is composed of limestone successions, reaching a thickness of about 170 m. In the present study, the Qarara Formation is recorded in the Gabal Abyiad section, represented by its upper part, which measures 48 m in thickness. The lower part of this rock unit primarily consists of intercalations of egg-yellow, fossiliferous marls (rich in ostracods and both benthic and planktonic foraminifera), and yellowish to grayish-white limestones with yellowish-green gypsiferous shales, measuring 18 m thick. The middle part has a thickness of about 8 m and is composed of yellowish-gray argillaceous limestones with a thin marly bed (50 cm thick) filled with ostracods, planktonic, and benthic foraminifera. The upper part of this formation is approximately 12 m thick, consisting of grayish to snow-white chalky limestones (with rare to common ostracod assemblages) and hard ledges of limestone with nodules of flint and thin bands of chert (Figure 3). The Qarara Formation is dominated by ostracod assemblages, including smoothed and ornamented carapace specimens of genera such as Cytherella, Bairdia, Loxoconcha, Paracypris, Schizocythere, Grinioneis, Bradleya, Semicytherura, Xestolebris, Uroleberis, Novocypris, Leguminocythere, Paracosta, Cativella, Soudanella, Asymmetricythere, and Cytheropteron. It is also characterized by high occurrences of marker planktonic foraminiferal species, such as Orbulinoides beckmanni, Morozovelloides lehneri, Morozovelloides bandyi, Turborotalia boweri, Turborotalia possagnoensis, Acarinina bullbrooki, Acarinina praetopilensis, Acarinina rohri, Acarinina spinuloinflata, and Igorina broedermani, along with associations of large benthic foraminifera, such as Nummulites gizehensis. This rock unit is assigned a late Lutetian–Bartonian age based on the recorded ostracod species, as well as the index planktonic and large benthic foraminifera [46,52,53,54,55,56].

2.2. El Fashn Formation (Bartonian)

The El Fashn Formation was first introduced by Bishay [52] for the sedimentary succession exposed at Wadi El Sheikh, southeast of El Fashn City. This formation is fully exposed in the Gabal Abyiad section, with a thickness of 86 m, while its upper part is only exposed in the Wadi Bayad El Arab section, where it attains a thickness of about 22 m. In the Gabal Abyiad section, this rock unit overlies the Qarara Formation, and its lower part, measuring 26 m, mainly consists of greenish-gray shales with thin intercalations of egg-yellow marls and yellowish-white limestones (Figure 2C). The middle part consists of intercalations of yellowish-gray marls, snow-white chalky limestones, and yellowish-white limestones, with a thickness of 27 m. The upper part, which is 33 m thick, is composed of scarp-forming light-gray to snow-white limestones, with a yellowish-gray marly bed in the middle (Figure 3). The El Fashn Formation in the Gabal Abyiad section is dominated by well-preserved and highly diversified ostracod assemblages, represented by 42 species belonging to different genera, such as Paracosta, Leguminocythere, Cativella, Reticulina, Xestolebris, Asymmetricythere, Digmocythere, Loxoconcha, Bairdia, Cytheropteron, Cytherella, Schizocythere, Paracypris, and Paracytheridea. It is also characterized by the rare presence of species from genera such as Buntonia, Hornibrookella, Semicytherura, Eucytherura, Martinicythere, Bradleya, Grinioneis, Novocypris, Krithe, Uroleberis, Actinocythereis, and Acanthocythereis. In the Wadi Bayad El Arab section, this formation is overlain by the Beni Suef Formation and consists of yellowish-gray shales and light-gray marls in the lower part, followed upward by yellowish-white, scarp-forming marly to argillaceous limestones (Figure 2E). The exposed portion of this rock unit is characterized by less diversified, but abundant, ostracod assemblages, including the following species: Loxoconcha vetustopunctata, Loxoconcha pseudopunctata, Bairdia gleberti, Paracosta ducassae, Paracosta ansaryi, and Reticulina scitula. The high abundance of marker planktonic foraminiferal species, such as Orbulinoides beckmanni, and species related to the genera Morozovelloides, Turborotalia, Acarinina, Globigerinatheka, and Streptochilus, along with the presence of small and large benthic foraminifera, supports a Bartonian age for this rock unit [30,46,54,56,57,58,59].

2.3. Gehannam Formation (Bartonian-Priabonian)

The term for the present formation was first defined by Said [49] at Qaret Gehannam in the Fayoum area. It was previously referred to as “Ravine beds” for a sedimentary succession belonging to the middle Eocene that underlies the alluvial deposits of ravines in the Fayoum area [48]. In the current study, this formation is exposed only in the El Garabaa section, where it measures 48 m in thickness (Figure 2A,B). It is primarily composed of light-gray marls, capped by grayish-white argillaceous to dolomitic limestone in the lower part (23 m thick), followed by grayish-white argillaceous limestone and yellowish-white to yellowish-gray limestone with thin marly beds in the upper part (25 m thick) (Figure 3). The ostracod assemblages recorded in this rock unit are well-preserved and highly diversified (41 species), distributed throughout the entire succession. The most abundant species include Paracosta ducassae, Paracosta rogeri, Leguminocythereis sadeki, Cytherella triestina, Cytherella tarabulusensis, Cytherella palanaensis, Xestoleberis subglobosa, Bairdia gleberti, Cativella qurnensis, Reticulina heluanensis, Reticulina ismaili, Novocypris eocenana, Digmocythere ismaili, Loxoconcha vetustopunctatella, Loxoconcha pseudopunctatella, and Pterygocythereis minor. The presence of index planktonic foraminiferal species, such as Morozovelloides crassatus, Acarinina bullbrooki, Acarinina rohri, Acarinina spinuloinflata, and Acarinina medizzai, particularly in the lower part of this formation (beds 1–5), along with the first appearance of the ostracod species Asymmetricythere hiltermanni in the upper part, suggests a late middle to late Eocene (Bartonian–Priabonian) age for this portion of the Gehannam Formation [10,20,46,60,61,62].

2.4. Beni Suef Formation (Bartonian-Priabonian)

First recognized by Bishay [52] as a sedimentary sequence (100 m thick) at Gebel Homret Shaibon, in the northeast Beni Suef area, this formation was further subdivided by Mansour et al. [63] into the Qurn Member at the base and the Tarbul Member at the top. It conformably overlies the El Fashn Formation (Bartonian) and underlies the Maadi Formation (Priabonian) (Figure 2E). In the studied area, the Beni Suef Formation is exposed in the Gabal Abyiad section and is represented only by the Qurn Member, which has a thickness of 26 m. It is also exposed at the Wadi Bayad El Arab section, where it has a thickness of 77 m and is represented by both the Qurn and Tarbul members (Figure 3).

2.4.1. Qurn Member (Bartonian–Priabonian)

In the Gabal Abyiad section, the Qurn Member of the Beni Suef Formation overlies the El Fashn Formation and is primarily composed of yellowish-gray, slope-forming shales and marls, capped by hard, grayish-white limestones. It is characterized by abundant and highly diversified ostracod assemblages (40 species). The most abundant and characteristic species include Loxoconcha vetustopunctatella, Bairdia gleberti, Bairdia crolifai, Bairdia crebra, Paracosta ducassae, Paracosta rogeri, Paracosta cf. parakefensis, Paracosta ansaryi, Paracosta praetricostata praetricostata, Reticulina scitula, Reticulina ismaili, Reticulina heluanensis, Asymmetricythere youssefi, Asymmetricythere hiltermanni, Cytheropteron boukharyi, Cytheropteron tarabulusensis, Cytherella triestina, Cytherella palanaensis, Cytherella tarabulusensis, Cativella qurnensis, Soudanella ghalilae, Digmocythere ismaili, Xestolebris ghalilae, Acanthocythereis projecta, and Ordoniya burmaensis. In the Wadi Bayad El Arab section, this member is completely exposed, overlying the El Fashn Formation and underlies the Tarbul Member of the Beni Suef Formation, measuring 37 m thick (Figure 2E,F). It consists of repeated light-gray shales, capped by yellowish-gray argillaceous and marly limestones. The ostracod assemblages in this member are less abundant and consist of eleven species, including Loxoconcha vetustopunctatella, Loxoconcha pseudopunctatella, Bairdia gleberti, Paracosta ducassae, Leguminocythereis sadeki, Asymmetricythere youssefi, Digmocythere ismaili, Digmocythere sp., Cytherella triestina, Paracosta ansaryi, and Reticulina ismaili.

2.4.2. Tarbul Member (Priabonian)

In the studied region, the Tarbul Member is exposed in the Wadi Bayad El Arab section, overlying the Qurn Member. It has a thickness of 40 m and consists of repeated beds of egg-yellow, fossiliferous marls, topped by light-gray argillaceous and marly limestones (Figure 2E,G). This member is characterized by rare occurrences of ostracod assemblages (10 species), including Loxoconcha vetustopunctatella, Loxoconcha pseudopunctatella, Paracosta ducassae, Asymmetricythere hiltermanni, Digmocythere ismaili, Cytherella triestina, Reticulina ismaili, Paracosta praetricostata praetricostata, Semicytherura africana, and Grinioneis moosi. The presence of spinose planktonic foraminifera (Morozovelloides and Acarinina) in the lower part of the Qurn Member, which later disappear and are replaced by smoothed planktonic species in the upper part of the Qurn Member and the Tarbul Member, along with the appearance of the ostracod species Asymmetricythere hiltermanni, as well as other ostracod assemblages and both small and large benthic foraminifera (Nummulites spp.), assigns a late middle to late Eocene (Bartonian–Priabonian) age to the Beni Suef Formation [30,46,58].

3. Materials and Methods

Three middle–upper Eocene sedimentary exposures along the northwestern and northeastern parts of the Nile Valley province were carefully selected, measured, and described. A total of 125 rock samples were collected from the studied sections, with sampling intervals ranging from 1 to 2 m for the hard limestones, and 30 cm for the shales and marls. Approximately 250 g from each sample were soaked in normal water for three days and then washed under running water multiple times using a 63 μm sieve. The residue from the washing process was dried and separated into several fractions using sieves with mesh sizes of 63, 90, 125, and 250 µm. About 10 g from each size fraction was used as a standard weight and examined under a stereo-binocular microscope (OPTIKA, Via Rigla, 30, Bergamo, Italy). The identified species were mounted on holders and photographed using the Scanning Electron Microscope (SEM), JSM 5400 LD (JEOL, Tokyo, Japan), at Beni Suef University, and then illustrated in Figure 4, Figure 5 and Figure 6. The ostracod species were systematically classified following the schemes of Moore [64] and Horne et al. [65] (sub-orders, superfamilies, families, genera, and species), as shown in Figure 7. The stratigraphic distribution of the identified ostracods and the recorded ostracod biozones in the studied sections are shown in Figure 8, Figure 9 and Figure 10. For paleoecological estimation, the total number of ostracod specimens (articulated carapaces were counted as one, and single valves as 0.5 [66,67,68]) and the percentage of ostracod groups (Cytherellidae %, Cypridacea & Bairdiacea %, and Cytheracea %) were calculated. The ternary plot diagram of Dingle [69] was also applied to determine the paleobathymetry of each rock unit. The paleobiogeographic evaluation was conducted through multivariate analyses, including Q-mode clustering and principal component analysis (PCA) on a dataset of thirty-five ostracod species from the present study and those previously recorded in eight countries related to the northern, southern, and eastern Tethys provinces (Table 1) [11,12,13,21,30,36], using PAST software, version 4.13 [70]. The obtained dendrogram was reconstructed using the paired group method and the Euclidean similarity index.

4. Results

4.1. Ostracod Data

The investigation of 125 samples led to the identification of sixty-five ostracod species and subspecies, belonging to thirty-three genera, fifteen families, and three superfamilies. These species belong to the order Podocopida and are classified into two main suborders. The first suborder is the Platycopina, which includes only one family, the Cytherellidae, represented by the genus Cytherella. This group is characterized by smoothed carapace specimens and comprises four species: Cytherella triestina, Cytherella kozialis, Cytherella tarabulusensis, and Cytherella palanaensis (Figure 7). The other suborder is the Podocopina, which includes three superfamilies: (1) Bairdiacea, represented by the smoothed carapace specimens of the family Bairdiidae and the genus Bairdia; (2) Cypridacea, represented by smoothed carapace specimens of the genera Novocypris, Paracypris, and Pontocyprella from the families Cyprididae, Paracyprididae, and Pontocyprididae; (3) Cytheracea, which includes both smoothed and ornamented carapace specimens, and is represented by the families Brachycytheridae, Leguminocythereidae, Cytherideidae, Cytheridae, Loxoconchidae, Trachyleberididae, Hemicytheridae, Paracytheridae, Cytheruridae, and Xestoleberididae (Figure 8a,b). These assemblages are well-preserved and distributed across all four studied rock units and the recognized biozones. The highest abundance and richness were observed in the Gabal Abyiad and Garabaa sections, whereas the Wadi Bayad El Arab section exhibited the lowest. The Podocopina assemblages were significantly more abundant and diverse, comprising thirty-two genera and sixty-one species and subspecies, and they display a broader geographic distribution compared to those of the Platycopina suborder.

4.2. Biostratigraphy

The vertical distribution of the identified ostracod species in the studied sections allowed for the recognition of four local biozones, spanning the interval from the middle to the upper Eocene (upper Lutetian–Priabonian). The stratigraphic distribution charts of the recorded and recognized biozones are presented in Figure 8, Figure 9 and Figure 10. The correlation of these zones with those in Egypt and neighboring countries is shown in Figure 11. A brief discussion of these zones follows.

4.2.1. Schizocythere fadlensis Lowest-Occurrence Zone

  • Definition: This local zone is defined by the biostratigraphic interval between the lowest occurrence (LO) of Schizocythere fadlensis and the lowest occurrence (LO) of Loxoconcha pseudopunctatella.
  • Age: middle Eocene (late Lutetian–early Bartonian).
  • Main taxa: Twenty-seven ostracod species and subspecies are recorded in this zone, and most of them have a stratigraphic distribution that extends into the overlying zone, except for one subspecies (Martinicythere samalutensis dorsocostata), which disappears within this zone (Figure 8a). The most characteristic species, in addition to the nominate species, include: Leguminocythereis africana, Cytherella kozialis, Cytherella triestina, Schizocythere distincta, Martinicythere samalutensis dorsocostata, Asymmetricythere youssefi, Cytheropteron boukharyi, Urolebris striatopunctatella, Paracosta praetricostata praetricostata, Loxoconcha vetustopunctatella, and Soudanella ghalilae.
  • Remarks and correlation: The recorded zone can be correlated with the Qarara Formation in the Gabal Abyiad section, which measures about 42 m. It is equivalent to the standard middle Eocene planktonic foraminiferal Morozovelloides lehneri Zone and the lower part of the Orbulinoides beckmanni Zone [46,71,74]. It also correlates with the upper Lutetian ostracod Loculicytheretta (Heptaloculites) minuta Zone and the basal part of the Bartonian Loculicytheretta (Heptaloculites) cavernosa Zone in Libya [31] and Tunisia [36] (Figure 11). In Egypt, this zone is correlated with the Loxoconcha vetustopunctatella/Trachyleberis nodosus nodosus Zone from the upper Lutetian of the northwest region of the Eastern Desert [12], and the Xestoleberis subglobosa Zone recorded from the same stratigraphic interval in the Gabal Mokattam area [75]. It is also equivalent to the upper Lutetian Brachycythere ismaili/Bairdia tarabulusensis Zone [10], and the Costa praetricostata praetricostata Zone [19] from the Fayoum area. Furthermore, this zone could be correlated with the upper part of the Reticulina saitoi/Trachyleberis nodosus nodosus Zone from southwest Sinai [72], as shown in Figure 11.

4.2.2. Loxoconcha pseudopunctatella Lowest-Occurrence Zone

  • Definition: This zone is defined by the biostratigraphic interval between the lowest occurrence (LO) of Loxoconcha pseudopunctatella and the lowest occurrence (LO) of Digmocythere ismaili.
  • Age: middle Eocene (Bartonian).
  • Main taxa: Forty-eight ostracod species and subspecies are recorded in this zone. Five species have their first occurrence in this zone and are restricted to it: Paracypris buisae, Digmocythere omari, Buntonia bassiounni, Hornibroolella cf. macropora, Eucytherura dentata, and Uroleberis curta. Additionally, four species extend from the underlying zone and disappear in this zone: Schizocythere fadlensis, Schizocythere distincta, Bradleya boukharyi, and Urolebris striatopunctata. Meanwhile, sixteen species that occur in this zone have a stratigraphic distribution extending into the overlying zone, and the remaining ostracod species are transitional, i.e., they occur in this zone and extend from the underlying to the overlying zones (Figure 8a,b).
  • Remarks and correlation: This zone can be correlated with the El Fashn Formation at the Gabal El Abyiad section, which measures 69 m. It is the stratigraphic equivalent of the standard middle Eocene planktonic foraminiferal Orbulinoides beckmanni Zone and the lower part of the Morozovelloides crassatus Zone [46,71,74]. It also correlates with the ostracod Loculicytheretta (Heptaloculites) cavernosa Zone, which was defined from the middle Eocene (Bartonian) of Libya [31] and Tunisia [36] (Figure 11). In Egypt, this zone is equivalent to the middle Eocene (Bartonian) Asymmetricythere youssefi-Loxoconcha pseudopunctatella Zone from the northwest Fayoum area [22] and the Xestoleberis subglobosa/Asymmetricythere asymmetrella Zone from the Gabal Mokattam area [9]. It is also correlated with the lower part of the Bartonian Asymmetricythere youssefi-Loxoconcha pseudopunctatella Zone from the northwest Fayoum area [20], the Loxoconcha pseudopunctatella/Asymmetricythere asymmetrella Zone from the northwest region of the Eastern Desert [12], the Asymmetricythere youssefi/Cytherella piacabucoensis Zone from southwest Sinai [72], and the lower part of the Costa humboldti Zone and Costa crassireticulata/Costa ducassae Zone, as defined by Elewa et al. [19] and Abdallah et al. [10] from the Fayoum Depression (Figure 11).

4.2.3. Digmocythere ismaili Lowest-Occurrence Zone

  • Definition: The present zone is defined by the biostratigraphic interval between the lowest occurrence (LO) of Digmocythere ismaili and the lowest occurrence (LO) of Asymmetricythere hiltermanni.
  • Age: middle Eocene (Bartonian).
  • Main taxa: Forty-six ostracod species and subspecies are identified in this zone (Figure 8, Figure 9 and Figure 10). Three species have their first occurrence (FO) in this zone and are restricted to it (Neocypredeis boukharyi, Paracosta crassireticulata, and Soudanella ghalilae), and five species have their first occurrence in this zone, but their stratigraphic distribution is extended to the overlying zone (Bairdia buisae, Acanthocythereis salahii, Digmocythere ismaili, Leguminocythereis sadeki, Reticulina scitula, Paracosta cf. parakefensis, and Paracosta ducassae). In addition, seven species occur in this zone and have a stratigraphic distribution extended from the underlying zone (Leguminocythereis africana, Leguminocythereis numidica, Schizocythere antiquimicronesiana, Loxoconcha matainensis, Loxoconcha tarabulusensis, Paracosta mokattamensis, and Paracytheridea pseudotuberosa), while the other species have wider stratigraphic range.
  • Remarks and correlation: This zone is recorded in three studied sections. It correlates with the upper part of the El Fashn Formation and the lower part of the Qurn Member of the Beni Suef Formation at Gabal Abyiad section, measuring 38 m, and with the Wadi Bayad El Arab section, approximately 29 m thick, and also with the lower part of the Gehannam Formation at Garabaa sections (23 m thick). It is the stratigraphic equivalent of the standard middle Eocene planktonic foraminiferal Morozovelloides crassatus Zone [46,65,66]. It is equivalent to the upper part of the ostracod Loculicytheretta (Heptaloculites) cavernosa Zone that was recorded from the Bartonian of Libya [31] and Tunisia [36], as shown in Figure 11. In Egypt, the present zone is correlated with the upper middle Eocene (Bartonian) ostracod Reticulina heluanensis–Leguminocythereis sadeki Zone recorded from northwest Fayoum area [22], Cativella qurnensis Zone from northeast Beni Suef area [30], Cytherella alii Zone from Gabal Mokattam area [9], and Trachyleberis nodosus nodosus Zone defined from the Fayoum area [14,17], Abd El-Gaied and Abd El-Aziz [73], Gabal Mokattam area [76], and northeast Beni Suef area [11]. Moreover, this zone can be correlated with the upper part of the late middle–early late Eocene Asymmetricythere yousefi-Loxoconcha pseudopunctatella Zone recorded from the northwest Fayoum area [20], and to the upper middle Eocene Loxoconcha pseudopunctatella/Asymmetricythere asymmetrella Zone defined from the northwest region of the Eastern Desert [12], Asymmetricythere yousefi/Cytherella piacabucuensis Zone from southwest Sinai [68], and also the upper parts of the Costa humboldti Zone and the Costa Crassireticulata/Costa ducassae Zone that were defined from the Fayoum Depression [8,10] (Figure 11).

4.2.4. Asymmetricyther hiltermanni Total-Range Zone

  • Definition: This local zone is defined by the bio-stratigraphic interval of the total range of Asymmetricythere hiltermanni.
  • Age: late Eocene (Priabonian).
  • Main taxa: Forty-three ostracod species and subspecies occur within this zone (Figure 8, Figure 9 and Figure 10). Five species have their FO in this zone and are restricted to it (Pterygocythere minor, Acanthocythereis tarabulusensis, Trachyleberis nodosus nodosus, Ordoniya burmaensis, and Buntonia ghalilae), whereas the other species have wider stratigraphic range.
  • Remarks and correlation: This zone is recorded in the three studied sections. It correlates to the upper part of the Qurn Member of the Beni Suef Formation at Gabal Abyiad section, and the Qurn and the Tarbul members of Beni Suef Formation at Wadi Bayad El Arab section. It also correlates to the upper part of the Gehannam Formation at Garabaa sections. It is the stratigraphic equivalent of the standard upper Eocene planktonic foraminiferal Globigerinatheka semiinvoluta Zone [46,65,66]. It is matched stratigraphically with the topmost part of the Bartonian Loculicytheretta (Heptaloculites) cavernosa Zone and the Priabonian Loculicytheretta (Heptaloculites) aff. gortanii Zone that were recorded from Libya [31] and Tunisia [34,36,77,78,79], as shown in Figure 11. In Egypt, this zone is correlated to the upper middle–upper Eocene Loxoconcha bassiounni Zone from northeast Beni Suef area [30]. It is also correlative with the upper Eocene Trachylebris nodosus nodosulcatus-Ruggeria (Keijella) glabella Zone recorded from the northwest Fayoum area [22], Asymmetricythere hiltermanni Zone from the Fayoum area [18,69], Uromuellerina saidi Zone from north-east Beni Suef area [11], Acanthocythereis projecta/Asymmetricythere hiltermanni Zone from Gabal Mokattam area [70], and also correlates with the Loxoconcha bassiounii and Asymmetricythere hiltermanni zones recorded from the same stratigraphic interval in the Fayoum area [20].

5. Discussion

5.1. Paleoenvironment

The ostracod assemblages are used to identify the paleodepths and environmental conditions that prevailed during the deposition of the studied rock units, as these faunas occur in various aquatic environments at different depths. Furthermore, the dominance, scarcity, or disappearance of ostracod species with known ecological preferences provides insights into changes in the depositional settings. For this purpose, the abundance and diversity of the ostracod assemblages in the studied samples are calculated and presented in the prepared histogram (Figure 12). Additionally, the percentages of the different ostracod groups (Cytherellidae %, Cypridacea %, Bairdiacea %, and Cytheracea %) are calculated, as shown in Figure 13. The Ternary Diagram of Dingle [69], which is subdivided into seven fields, was also applied to estimate the water depths for each rock unit (Figure 14).

5.1.1. Qarara Formation

This rock unit is only present in the Gabal El Abyiad section and is primarily composed of carbonate rocks in its upper part, with intercalations of limestone, shale, and marls in its lower part. It is rich in both ostracods and benthic foraminifera and shows sporadic occurrences of planktonic foraminifera at certain levels (samples 9, 19). The abundance of the recorded ostracod assemblages in this rock unit is lower than in the overlying formations. The highest diversity is observed in sample 9 (40 specimens), sample 11 (35 specimens), and sample 19 (33 specimens), represented by rare to common occurrences of species from the following genera: Cytherella, Loxoconcha, Paracosta, Leguminocythere, Cytheropteron, Schizocythere, Bairdia, Soudanella, Paracypris, Xestolebris, Urolebris, Grinioneis, Bradleya, Martinicythere, and Semicytherura. For the ostracod groups, the average ratio of Cytherellidae is 20.5%, while Cypridacea and Bairdiacea reach 28%, and the ratio of Cytheracea is 62.6%. The plots of the ostracod assemblages from this formation on the ternary diagram are concentrated in the 1–3 field, near the Cytheracea corner, with a few plots in the 4a field (Figure 14), indicating shallow marine environments, with a water depth not exceeding 200 m.
The high diversity of ornamented ostracods, such as Schizocythere, Paracosta, Loxoconcha, Leguminocythere, Grinioneis, Bradleya, and Martinicythere, characterizes the shallow marine inner to middle neritic environment, while the occurrence of smoothed and thin-shelled ostracods, represented by Cytherella and Paracypris, distinguishes the open marine, deeper outer neritic environment [13,14,31,35,80]. Babinot et al. [81] mentioned that species of Bairdia reflect open sea environments but also occur in the inner shelf platform, albeit as a minor element. The analysis above, in conjunction with the lithological characteristics and previous studies, suggests that the Qarara Formation in this study was deposited in an inner to middle neritic environment with high to moderate oxygen conditions and in an outer neritic environment under low oxygen water levels during certain periods. The ostracod assemblages recorded in this rock unit, which characterize the neritic depositional environment, are highly similar to those ostracods that distinguish the depositional environment of the middle Eocene Upper Building Stone Member of the Observatory Formation in the Qattamiya area, the north region of the Eastern Desert, Egypt [12], and the Lutetian–Bartonian Midawara Formation in the Fayoum area [13].

5.1.2. El Fashn Formation

The present formation is fully exposed in the Gabal Abyiad section, while its upper part is only exposed in the Bayad El Arab section. It is composed of shale in its lower part, followed upward by limestone and thin marls in the middle part, and mainly limestone in the upper part. Both ornamented and smoothed ostracod specimens, as well as benthic and planktonic foraminifera, dominate this rock unit. The abundance and diversity of the ostracod assemblages in this rock unit are higher than those in the underlying formations, with the highest occurrences of specimens reported in sample 43 (95 specimens), sample 32 (89 specimens), and sample 32 (55 specimens), as shown in Figure 12. This formation is dominated by species related to the genera Cytherella, Bairdia, Loxoconcha, Cativella, Reticulina, Paracosta, Leguminocythere, Digmocythere, Krithe, Novocypris, Cytheropteron, Paracypris, Xestolebris, and Urolebris. The analysis of the ostracod groups in Gabal Abyiad revealed that the average ratio of Cytherellidae is 11.7%, while Cypridacea and Bairdiacea account for 13.8%, and the ratio of Cytheracea reaches 73.4%. In the Bayad El Arab section, these ratios are 12.5% for Cypridacea and Bairdiacea, and 87.5% for Cytheracea, while Cytherellidae is completely absent. The plots of these ostracod assemblages on the ternary diagram fall within the 1–3 field near the Cytheracea corner and in the 4a field. On the other hand, a few plots are scattered in the 5a and 7 fields (Figure 14), reflecting a deeper marine setting, with water depths exceeding 200 m at some levels. The occurrence of Reticulina, Paracosta, Krithe, Bairdia, and Leguminocythere distinguishes the deeper neritic environment (middle to outer shelf), as mentioned by Jorgenson [82] and El Waer [31]. The presence of planktonic foraminifera such as Morozovelloides, Acarinina, and Truncorotaloides, along with the ostracod assemblages, characterizes the deep shelf environments [83]. Moreover, the occurrence of Paracypris indicates a middle shelf to middle slope environment [84,85]. The above-mentioned data, in addition to the observed sedimentological features and previous studies carried out on the same rock unit, indicate that deposition took place in a middle to outer neritic marine environment, with slightly upper bathyal conditions and moderate-to-low oxygenated water levels. The ostracod assemblages characterizing this formation reflect environmental conditions that are very similar to those documented for the deposition of the middle Eocene Giushi Member of the Observatory Formation in the Qattamiya area [12] and the Bartonian El Fashn Formation in the northeastern region of the Eastern Desert, Egypt [30].

5.1.3. Gehannam Formation

The present formation is only exposed in the Garabaa section and is composed of marls in the lower part, which are abundant in ostracods, benthic, and planktonic foraminifera. The limestones in the upper part are flooded with ostracods and only benthic foraminifera. The basal part of the section is marked by a high abundance of ostracod assemblages, reaching 275 specimens, and this number gradually decreases upwards to 203 specimens in sample 3, 125 specimens in sample 7, and then to 20 specimens in samples 10 and 11, as shown in Figure 12. The most abundant species are related to the following genera: Leguminocythereis, Cytherella, Bairdia, Pterygocythereis, Loxoconcha, Digmocythere, Paracosta, Cativella, Reticulina, Asymmetricythere, Novocypris, Xestolebris, Soudanella, Paracypris, and Acanthocythereis. On the other hand, the less dominant species belong to the following genera: Krithe, Trachyleberis, Buntonia, Pontocyprella, Neocyprideis, and Cytheropteron. The analysis of the ostracod groups in this formation revealed that the average ratio of Cytherellidae is 12%, while Cypridacea and Bairdiacea account for 22.3%, and Cytheracea makes up 65.5%. Furthermore, the plots of these assemblages on the ternary diagram are restricted to fields 1–3 and 4a (Figure 14), indicating shallow water depths, not exceeding 200 m. The occurrence of smoothed ostracods related to the genera Krithe, Pontocyprella, Paracypris, and Bairdia indicates deep marine environments and/or open normal sea waters [31,85,86,87]. Additionally, the predominance of Cytherella, Bairdia, Cytheropteron, and Krithe reflects low-energy, deep, open marine environments [88]. The ecological preferences of these ostracods, along with the lithological characteristics and previous studies, suggest that the Gehannam Formation in the present section was deposited in an outer neritic environment with low oxygen levels in the lower part, transitioning to a middle neritic marine setting under warm, moderate oxygenated conditions in the upper part. This interpretation is consistent with the conditions previously reported for the Gehannam Formation in the Fayoum area [20,73] and the Qurn Formation at the Qattamiya area, the north region of the Eastern Desert, Egypt [12].

5.1.4. Beni Suef Formation

This rock unit in the present study is subdivided into two members: the Qurn Member at the base, composed of shale capped by limestone, and the Tarbul Member at the top, consisting of marls topped by thin limestone. The entire exposed part of the Qurn Member and the lower part of the Tarbul Member are dominated by ostracods and both planktonic and benthic foraminifera, while the upper part of the Tarbul Member is barren of planktonic foraminifera but abundant in both ostracods and benthic foraminifera. The statistical analysis of the ostracod assemblages within this rock unit shows the highest numbers of specimens in the Qurn Member in the Gabal Abyiad section, reaching more than 130 specimens in sample 79 and decreasing upwards in the Tarbul Member in the Wadi Bayad El Arab section, where fewer than 5 specimens are recorded (samples 29, 30), as shown in Figure 12. Moreover, the most dominant species in this formation belong to the genera Loxoconcha, Cytherella, Bairdia, Reticulina, Paracosta, Asymmetricythere, Digmocythere, Xestolebris, Cytheropteron, and Leguminocythereis. Rare occurrences are observed in the genera Pontocyprella, Ordoniya, Pterygocythere, Krithe, Paracypris, and Neocyprideis. The analysis of the ostracod groups in the Qurn Member in the Gabal Abyiad section revealed that the average ratio of Cytherellidae is 15%, while Cypridacea and Bairdiacea account for 11.5%, and the percentage of Cytheracea is 73.5%. Meanwhile, in the Wadi Bayad El Arab section, the ostracod groups in the Qurn and Tarbul members showed that the average ratio of Cytherellidae is 10.3%, Cypridacea and Bairdiacea account for 7.9%, and the ratio of Cytheracea reaches 81.8%. The plots of these assemblages on the ternary diagram fall within fields 1–3 and field 4a (Figure 14), suggesting a water depth reaching 200 m. The high diversity of ornamented ostracods such as Asymmetricythere, Leguminocythereis, Loxoconcha, and Reticulina marks the shallow inner neritic environment, while the occurrence of smoothed carapace species like Pontocyprella, Paracypris, and Neocyprideis indicates a partial connection with open water environments [20,31]. Additionally, the number of ostracod individuals increases along the continental shelf and decreases with greater water depth in the bathyal environment [89]. The above data suggest that the Qurn Member of the Beni Suef Formation was deposited in a deeper outer neritic environment with low oxygen levels, while the Tarbul Member accumulated in a middle-to-inner neritic marine environment under moderate-to-high oxygenated, warm water conditions. These findings show a great similarity to the conditions responsible for the deposition of the Qurn and Tarbul members of the Beni Suef Formation in the northeastern region of the Eastern Desert of Egypt [30].

5.2. Paleobiogeography

The paleobiogeographic reconstruction of the middle and late Eocene ostracods is mainly based on multivariate analysis (principal component analysis and Q-mode clustering), using a dataset comprising thirty-five ostracod species from eight countries, including Egypt, Libya, Tunisia, Jordan, India, Israel, France, and Turkey (Table 1). The PCA identified three provinces: the first is the Southern Tethys Province (STP), encompassing Egypt, Libya, and Tunisia; the second represents the Northern Tethys Province (NTP), including France and Turkey; and the third refers to the Eastern Tethys Province (ETP), comprising Jordan, Israel, and India (Figure 15). The obtained PCA bioprovinces are presented in the first two principal component axes, which account for 69.22% of the total variance (48.11% and 21.11%, respectively), as shown in Table 2.
Similarly, the Q-mode cluster analysis resulted in the same three provinces (STP, NTP, and ETP) (Figure 16). The distribution and potential migration routes of the ostracod assemblages during the middle and late Eocene, based mainly on the recorded sixty-five ostracod species from more than twenty countries related to the Tethys areas, are shown in Figure 17.
There are twenty-four species recorded from the Southern Tethys Province (Libya, Tunisia, and Algeria): C. tarabulusensis, P. buisae, P. tarabulusensis, P. eocaenica, D. ismaili, L. africana, C. qurnensis, G. moosi, S. africana, X. ghalilae, B. ghalilae, P. eskeri, L. tarabulusensis, C. tarbuluensis, A. tarabulusensis, L. mataiensis, N. eocenana, L. vetustopunctatella, A. salahii, P. mokttamensis, A. yousefi, S. distincta, S. ghalilae, and L. numidica [31,34,36,90]. This reflects high similarities between the recorded ostracods in the present work and those from the STP, which are probably linked to a migration route through the Trans-Saharan Seaway, consistent with the findings of Sayed et al. [30], Morsi and Speijer [21], Bassiouni and Luger [24], and Youssef et al. [29].
In addition, a remarkable similarity is detected between the Eocene ostracod fauna of Egypt and that of the Northern Tethys countries, where ten species were previously recorded in France, Turkey, Germany, Hungary, Ukraine, Spain, England, Yugoslavia, and Belgium. These species are Krithe bartonensis, Bairdia cerbra, Bairdia gliberti, Novocypris eocenana, Xestoleberis subglobosa, Uroleberis striaropunctata, Cytherella kozialis, Cytherella triestina, Pterygocythereis minor, and Paracosta rogeri [40,45,91,92,93,94,95,96], reflecting a great resemblance to those in the NTP [13]. Subsequently, nine species were previously reported from the Eastern Tethys Province (Jordan, Israel, Iraq, Somalia, and India), including Digmocythere ismaili, Krithe bartonensis, Ordoniya burmaensis, Paracosta ansaryi, Cytheropteron boukharyi, Cytherella palanaensis, Bairdia gliberti, Eucytherura dentata, and Trachyleberis nodosus nodosus [3,24,97,98]. This similarity is linked to tectonic activities, where the basin of the Eastern Mediterranean was uplifted and the Neo-Tethys Ocean formed a large channel between the Arabian area, Turkey, and eastern Europe (Figure 17) [13,99]. Alternatively, it could be attributed to a sea-level rise, which enhanced the migration pathways of the ostracods. Furthermore, the resemblance of the middle to late Eocene ostracod fauna with those in the Middle East is due to an exchange of ostracod species between North Africa and the Middle East [35] (Figure 17). This suggestion was further supported by the larger benthic foraminiferal assemblages documented from the middle Eocene of Egypt show high similarities with those from Turkey and the Southern Tethys [100].
Some ostracod species in the present study were recorded from the upper Paleocene–lower Eocene in many countries in the southern, eastern, and northern Tethyan Provinces, such as Bairdia buisae in Libya [31], Paracypris eskeri in Tunisia [28], Libya [31], Iraq [85], Nigeroloxoconcha aegyptiaca punctata in Egypt [21,24,101], Ordoniya burmaensis in Jordan [102] and Egypt [6,103], Paracosta parakefensis in Egypt [21,24,104], Bairdia gliberti in Iraq [85], Eucytherura dentate in Iraq [85], Tunisia [28], and Egypt [105], and Pterygocythereis minor in Belgium [106]. This indicates that these ostracod species crossed the Paleocene/Eocene boundary and extended into the middle and late Eocene, which is attributed to a direct connection between these regions during this time interval [12,72]. Accordingly, the great similarity of the recorded ostracod assemblages in the present study with those in countries related to the northern, southern, and eastern Tethyan Provinces confirms a direct marine connection between these Tethyan regions during the Eocene.

5.3. Data Limitations

The preservation of ostracod specimens from hard limestones and chalky limestones is generally poor, making species-level identification challenging. Additionally, some samples exhibit low ostracod abundance, limiting the precision of paleoecological interpretations. Given these constraints, we exercised caution in interpreting these intervals.
To address these limitations, future studies should incorporate geochemical approaches, which could provide further support and enhance the reliability of paleoenvironmental reconstructions.

6. Conclusions

This study investigates the ostracod assemblages from middle-to-upper Eocene sediments in the northwestern and northeastern parts of the Nile Valley, Egypt. Four rock units are recognized: the Qarara (Lutetian–Bartonian), the El Fashn (Bartonian), the Gehannam, and the Beni Suef formations (Bartonian–Priabonian). A total of sixty-five ostracod species, belonging to thirty-three genera, fifteen families, and three superfamilies, are identified. The stratigraphic distribution of these ostracods allowed for the definition of four local biozones: the Schizocythere fadlensis Zone (upper Lutetian–lower Bartonian), the Loxoconcha pseudopunctatella Zone, the Digmocythere ismaili Zone (Bartonian), and the Asymmetricythere hiltermanni Zone (Bartonian–Priabonian), which are correlated with those in Egypt and neighboring areas. The abundance and diversity of the ostracod taxa, along with the percentages of the different ostracod groups, are used to estimate the paleo-depths and the paleoenvironmental conditions that prevailed during the deposition of the studied rock units. The Qarara Formation was deposited in an inner to middle neritic marine environment under high to moderate oxygen conditions, and in an outer neritic environment with low oxygen water levels at some periods. The El Fashn Formation accumulated in a middle to outer neritic marine environment and slightly upper bathyal under moderate-to-low oxygenated water conditions. Moreover, the deposition of the Gehannam Formation took place in outer neritic and low oxygenated settings for the lower part, transitioning to a middle neritic marine environment under warm and moderately oxygenated conditions for the upper part. The Qurn Member of the Beni Suef Formation was deposited in a low-oxygenated deeper outer neritic environment, while the Tarbul Member was deposited in a middle to inner neritic marine environment under moderate to high oxygenated, warm water conditions. Paleobiogeographically, the identified species exhibit strong affinities with those from the southern, northern, and eastern Tethyan Provinces, indicating a direct marine connection between these regions during the Eocene.

Author Contributions

Conceptualization, A.M. and I.M.A.E.-G.; methodology, S.A.B., I.M.A.E.-G., M.W., P.H. and M.M.S.; validation, A.M., M.W., P.H., M.M.S. and I.M.A.E.-G.; formal analysis, S.A.B. and I.M.A.E.-G.; investigation, S.A.B., M.W., P.H., M.M.S., A.M. and I.M.A.E.-G.; data curation, S.A.B., M.W., P.H. and I.M.A.E.-G.; writing—original draft preparation, S.A.B. and I.M.A.E.-G.; writing—review and editing, A.M., S.A.B., M.M.S., M.W., P.H. and I.M.A.E.-G.; visualization, A.M., M.W., P.H. and I.M.A.E.-G.; supervision, A.M. and I.M.A.E.-G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no funding.

Institutional Review Board Statement

Not Applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data are available in the manuscript.

Acknowledgments

We are thankful to the IOAP of Open Access Funding by the University of Vienna.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (A) Location map of Egypt; (B) geologic map showing the studied sections (modified after Conoco [51] and Abu Bakr et al. [46]).
Figure 1. (A) Location map of Egypt; (B) geologic map showing the studied sections (modified after Conoco [51] and Abu Bakr et al. [46]).
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Figure 2. (A,B) Lower and upper parts of the Gehannam Formation in Garabaa section; (C) the El Fashn Formation in Gabal Abyiad section; (D) the Qarara formation in Gabal Abyiad section (E) the El Fashn Formation, the Qurn and the Tarbul members of the Beni Suef Formation in Wadi Bayad El Arab section; (F,G) the Qurn and the Tarbul members of the Beni Suef Formation in Wadi Bayad El Arab section.
Figure 2. (A,B) Lower and upper parts of the Gehannam Formation in Garabaa section; (C) the El Fashn Formation in Gabal Abyiad section; (D) the Qarara formation in Gabal Abyiad section (E) the El Fashn Formation, the Qurn and the Tarbul members of the Beni Suef Formation in Wadi Bayad El Arab section; (F,G) the Qurn and the Tarbul members of the Beni Suef Formation in Wadi Bayad El Arab section.
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Figure 3. Lithostratigraphic units and biozones of the middle and upper Eocene succession in the studied sections.
Figure 3. Lithostratigraphic units and biozones of the middle and upper Eocene succession in the studied sections.
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Figure 4. (LC = left carapace, RC = right carapace, DV = dorsal view, VV = ventral view). (1, 2) Cytherella triestina Kollmann, 1962 (1 LC, 2DV); (3) Cytherella kozialis Sonmez-Gokcen, 1973 (LC); (4, 5) Cytherella tarabulusensis El-Waer, 1992 (4 LC, 5 DV); (6) Bairdia cerbra Deltel, 1963 (RV); (7) Bairdia crolifai Morsi, Boukhary and Strougo, 2003 (LC); (8) Bairdia gliberti Keij, 1957 (LC); (9) Paracypris tarabulusensis El-Waer, 1992 (RV); (10) Paracypris eskeri El-Waer, 1992 (RV); (11) Paracypris buisae El Waer, 1992 (RV); (12, 13) Novocypris eocenana Ducasse, 1967 (12 RC, 13 DV); (14) Digmocythere ismaili Bassiouni, 1971 (LC); (15) Digmocythere omarai Cronin and Khalifa, 1979 (LC); (16, 17) Pterygocythereis minor Bassiouni, 1971 (16 LC, 17 DV); (18) Leguminocythereis africana Bassiouni, 1969c (RC); (19) Leguminocythereis sadeki Bassiouni, 1969c (LC); (20) Krithe bartonensis Jones, 1857 (LC); (21–25) Schizocythere fadlensis Cronin and Khalifa, 1979 (21, 22, 24 RC, 23 DV, 25 VV); (26, 27) Loxoconcha pseudopunctatella Cronin and khalifa, 1979 (26 LC, 27 DC); (28) Loxoconcha vetustopunctatella Bassiouni et al. 1984 (LC); (29) Loxoconcha mataiensis Khalifa and Cronin, 1979 (RC); (30) Loxoconcha tarabulusensis El-Waer, 1992 (RC). Scale bar: 100 µm.
Figure 4. (LC = left carapace, RC = right carapace, DV = dorsal view, VV = ventral view). (1, 2) Cytherella triestina Kollmann, 1962 (1 LC, 2DV); (3) Cytherella kozialis Sonmez-Gokcen, 1973 (LC); (4, 5) Cytherella tarabulusensis El-Waer, 1992 (4 LC, 5 DV); (6) Bairdia cerbra Deltel, 1963 (RV); (7) Bairdia crolifai Morsi, Boukhary and Strougo, 2003 (LC); (8) Bairdia gliberti Keij, 1957 (LC); (9) Paracypris tarabulusensis El-Waer, 1992 (RV); (10) Paracypris eskeri El-Waer, 1992 (RV); (11) Paracypris buisae El Waer, 1992 (RV); (12, 13) Novocypris eocenana Ducasse, 1967 (12 RC, 13 DV); (14) Digmocythere ismaili Bassiouni, 1971 (LC); (15) Digmocythere omarai Cronin and Khalifa, 1979 (LC); (16, 17) Pterygocythereis minor Bassiouni, 1971 (16 LC, 17 DV); (18) Leguminocythereis africana Bassiouni, 1969c (RC); (19) Leguminocythereis sadeki Bassiouni, 1969c (LC); (20) Krithe bartonensis Jones, 1857 (LC); (21–25) Schizocythere fadlensis Cronin and Khalifa, 1979 (21, 22, 24 RC, 23 DV, 25 VV); (26, 27) Loxoconcha pseudopunctatella Cronin and khalifa, 1979 (26 LC, 27 DC); (28) Loxoconcha vetustopunctatella Bassiouni et al. 1984 (LC); (29) Loxoconcha mataiensis Khalifa and Cronin, 1979 (RC); (30) Loxoconcha tarabulusensis El-Waer, 1992 (RC). Scale bar: 100 µm.
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Figure 5. (1) Nigeroloxoconcha aegyptiaca punctata Bassiouni and Luger, 1990 (RC); (2)Trachyleberis nodosus nodosus Bassiouni, 1969b (RC); (3)Acanthocythereis projecta Bassiouni, 1969b (LC); (4) Reticulina heluanensis Bassiouni, 1969b (LC); (5, 6) Reticulina ismaili Bassiouni et al. 1984 (5 RC, 6 DV); (7) Reticulina scitula Bassiouni, 1969b (LC); (8) Cativella qurnensis Bassiouni, 1969b (LC); (9, 10) Ordoniya burmaensis Bassiouni, 1970 (9 DV, 10 LC); (11) Paracosta cf. parakefensis Bassiouni and Luger, 1990 (LC); (12) Paracosta ducassae Bassiouni et al., 1984 (RC); (13) Paracosta ansaryi Bassiouni, 1969a (LC); (14) Paracosta praetricostata praetricoststa Bassiouni, 1969b (LC); (15) Paracosta mokttamensis, Bassiouni, 1969b (LC); (16) Paracosta rogeri Sonmez-Gokcen, 1973 (RC); (17) Paracosta crassireticulata Bassiouni, 1969b (LC); (18) Asymmetricythere yousefi Bassiouni, 1971 (RC); (19, 20) Asymmetricythere hiltermanni Bassiouni, 1971 (19 LC, 20 RC); (21) Buntonia bassiounii Morsi, Hewaidy and Samir, Samir 2016 (LC); (22) Buntonia ghalilae El-Waer, 1992 (LC); (23, 24) Soudanella ghalilae El-Waer, 1992 (23 DV, 24 RC); (25, 26) Grinioneis moosi (Bassiouni, 1969d) (25 DV, 26 LC); (27) Hornibrookella cf. macropora Bosquet, 1852 (LC); (28) Martinicythere samalutensis dorsocostata Bassiouni, 1969c (LC); (29) Bradleya boukharyi Bassiouni, Hamza and Morsi, 1994 (RC); (30) Paracytheridea pseudotuberosa Boukhary et al., 1993 (RC); (31) Eucytherura dentata (Lienenklaus, 1905) (RC); (32, 33) Cytheropteron boukharyi Khalifa and Cronin, 1979 (RC). Scale bar: 100 µm.
Figure 5. (1) Nigeroloxoconcha aegyptiaca punctata Bassiouni and Luger, 1990 (RC); (2)Trachyleberis nodosus nodosus Bassiouni, 1969b (RC); (3)Acanthocythereis projecta Bassiouni, 1969b (LC); (4) Reticulina heluanensis Bassiouni, 1969b (LC); (5, 6) Reticulina ismaili Bassiouni et al. 1984 (5 RC, 6 DV); (7) Reticulina scitula Bassiouni, 1969b (LC); (8) Cativella qurnensis Bassiouni, 1969b (LC); (9, 10) Ordoniya burmaensis Bassiouni, 1970 (9 DV, 10 LC); (11) Paracosta cf. parakefensis Bassiouni and Luger, 1990 (LC); (12) Paracosta ducassae Bassiouni et al., 1984 (RC); (13) Paracosta ansaryi Bassiouni, 1969a (LC); (14) Paracosta praetricostata praetricoststa Bassiouni, 1969b (LC); (15) Paracosta mokttamensis, Bassiouni, 1969b (LC); (16) Paracosta rogeri Sonmez-Gokcen, 1973 (RC); (17) Paracosta crassireticulata Bassiouni, 1969b (LC); (18) Asymmetricythere yousefi Bassiouni, 1971 (RC); (19, 20) Asymmetricythere hiltermanni Bassiouni, 1971 (19 LC, 20 RC); (21) Buntonia bassiounii Morsi, Hewaidy and Samir, Samir 2016 (LC); (22) Buntonia ghalilae El-Waer, 1992 (LC); (23, 24) Soudanella ghalilae El-Waer, 1992 (23 DV, 24 RC); (25, 26) Grinioneis moosi (Bassiouni, 1969d) (25 DV, 26 LC); (27) Hornibrookella cf. macropora Bosquet, 1852 (LC); (28) Martinicythere samalutensis dorsocostata Bassiouni, 1969c (LC); (29) Bradleya boukharyi Bassiouni, Hamza and Morsi, 1994 (RC); (30) Paracytheridea pseudotuberosa Boukhary et al., 1993 (RC); (31) Eucytherura dentata (Lienenklaus, 1905) (RC); (32, 33) Cytheropteron boukharyi Khalifa and Cronin, 1979 (RC). Scale bar: 100 µm.
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Figure 6. (1) Cytheropteron boukharyi Khalifa and Cronin, 1979 (DV); (2, 3) Cytheropteron tarabulusensis El-Waer, 1992 (RC); (4–6) Semicytherura africana El-Waer, 1992 (4, 5 LC, 6 DV); (7) Xestoleberis ghalilae El-Waer, 1992 (LV); (8) Xestoleberis subglobosa Bosquet, 1852 (LV); (9) Uroleberis curta Boukhary et al., 1993 (RV); (10–12) Uroleberis striatopunctata Ducasse, 1967 (10, 12 RV, 11 DV). Scale bar: 100 µm.
Figure 6. (1) Cytheropteron boukharyi Khalifa and Cronin, 1979 (DV); (2, 3) Cytheropteron tarabulusensis El-Waer, 1992 (RC); (4–6) Semicytherura africana El-Waer, 1992 (4, 5 LC, 6 DV); (7) Xestoleberis ghalilae El-Waer, 1992 (LV); (8) Xestoleberis subglobosa Bosquet, 1852 (LV); (9) Uroleberis curta Boukhary et al., 1993 (RV); (10–12) Uroleberis striatopunctata Ducasse, 1967 (10, 12 RV, 11 DV). Scale bar: 100 µm.
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Diversity 17 00293 g007aDiversity 17 00293 g007b
Figure 7. Ostracods groups (superfamilies, families, genera, species) and their stratigraphic distribution in the recorded biozones.
Figure 7. Ostracods groups (superfamilies, families, genera, species) and their stratigraphic distribution in the recorded biozones.
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Diversity 17 00293 g008aDiversity 17 00293 g008b
Figure 8. (a,b) Stratigraphic distribution of the identified ostracods in Gabal Abyiad section.
Figure 8. (a,b) Stratigraphic distribution of the identified ostracods in Gabal Abyiad section.
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Figure 9. Stratigraphic distribution of the identified ostracods in Bayad El Arab section.
Figure 9. Stratigraphic distribution of the identified ostracods in Bayad El Arab section.
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Diversity 17 00293 g010
Figure 10. Stratigraphic distribution of the identified ostracods in Garabaa section.
Figure 10. Stratigraphic distribution of the identified ostracods in Garabaa section.
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Diversity 17 00293 g011
Figure 11. Correlation of the recorded ostracod biozones in the studied sections with those in different areas of Egypt and the surrounding countries and the planktonic foraminiferal biozones [9,10,11,12,19,20,22,30,31,36,46,71,72,73].
Figure 11. Correlation of the recorded ostracod biozones in the studied sections with those in different areas of Egypt and the surrounding countries and the planktonic foraminiferal biozones [9,10,11,12,19,20,22,30,31,36,46,71,72,73].
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Diversity 17 00293 g012
Figure 12. Histogram represents the abundance of the ostracod specimens ((A): Garabaa, (B): Gabal Abyiad, (C): Wadi Bayad El Arab).
Figure 12. Histogram represents the abundance of the ostracod specimens ((A): Garabaa, (B): Gabal Abyiad, (C): Wadi Bayad El Arab).
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Diversity 17 00293 g013
Figure 13. The percentage of the ostracod groups (Cytherellidae %, Cypridacea and Bairdiacea%, and Cytheracea %) in the studied sections, (A) Gabal Abyiad section; (B) Wadi Bayad El Arab section; (C) Garabaa section.
Figure 13. The percentage of the ostracod groups (Cytherellidae %, Cypridacea and Bairdiacea%, and Cytheracea %) in the studied sections, (A) Gabal Abyiad section; (B) Wadi Bayad El Arab section; (C) Garabaa section.
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Diversity 17 00293 g014
Figure 14. Ternary diagrams represent the distribution of the ostracod groups in the studied rock units (after Dingle [26]) ((A): Garabaa section, (B): Gabal Abyiad section, (C): Wadi Bayad El Arab section).
Figure 14. Ternary diagrams represent the distribution of the ostracod groups in the studied rock units (after Dingle [26]) ((A): Garabaa section, (B): Gabal Abyiad section, (C): Wadi Bayad El Arab section).
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Figure 15. The principal component analysis PCA (Component 1 and Component 2).
Figure 15. The principal component analysis PCA (Component 1 and Component 2).
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Figure 16. Q-mode cluster analysis showing the relationship between the study area in Egypt and other Tethys countries.
Figure 16. Q-mode cluster analysis showing the relationship between the study area in Egypt and other Tethys countries.
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Diversity 17 00293 g017
Figure 17. The paleobiogeographic map during the middle and late Eocene (after Shahin et al. [12]).
Figure 17. The paleobiogeographic map during the middle and late Eocene (after Shahin et al. [12]).
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Table 1. Thirty-five ostracod species and subspecies represented in eight countries and related to the northern, southern, and eastern Tethys bio-provinces (1/0 indicate present/absent).
Table 1. Thirty-five ostracod species and subspecies represented in eight countries and related to the northern, southern, and eastern Tethys bio-provinces (1/0 indicate present/absent).
SpeciesEgyptLibyaTunisiaJordanIndiaIsraelFranceTurkey
Cytherella kozialis Sonmez-Gokcen, 197310000001
Cytherella palanaensis Khosla, 197210001000
Cytherella tarabulusensis El-Waer, 199211000000
Cytherella triestina Kollmann, 196210000001
Bairdia cerbra Deltel, 196310000011
Bairdia gliberti Keij, 195710001010
Novocypris eocenana Ducasse, 196710100011
Paracypris buisae El Waer, 199211100000
Paracypris tarabulusensis El Waer, 199211000000
Pontocyprella eocaenica El Waer, 199211000000
Digmocythere ismaili Bassiouni, 197111110000
Pterygocythereis minor Bassiouni, 197110000000
Leguminocythereis africana Bassiouni, 1969c11000000
Krithe bartonensis Jones, 185710010011
Loxoconcha vetustopunctatella Bassiouni et al., 198410100000
Acanthocythereis salahii Bassiouni, 1969a10100000
Cativella qurnensis Bassiouni, 1969b11000000
Ordoniya burmaensis Bassiouni, 197010010000
Paracosta ansaryi Bassiouni, 1969a10010000
Paracosta mokttamensis Bassiouni, 1969b10100000
Paracosta rogeri Sonmez-Gokcen, 197310000001
Asymmetricythere yousefi Bassiouni, 197110100000
Grinioneis moosi (Bassiouni, 1969d)11000000
Cytheropteron boukharyi Khalifa and Cronin, 197910010000
Semicytherura africana El-Waer, 199211000000
Xestoleberis ghalilae El-Waer, 199211000000
Xestoleberis subglobosa Bosquet, 185210000011
Uroleberis striaropunctata Ducasse, 196710000011
Buntonia ghalilae El-Waer, 199211000000
Paracypris eskeri El-Waer, 199211100000
Loxoconcha tarabulusensis El-Waer, 199211100000
Leguminocythere numidica Apostolescu and Magne, 195610100000
Cytheropteron tarbuluensis El-Waer, 199211000000
Acanthocythereis tarabulusensis El-Waer, 199211000000
Loxoconcha mataiensis Khalifa and Cronin, 197911100000
Table 2. Results of principal component analysis.
Table 2. Results of principal component analysis.
PCEigenvalue% Variance
13.8744448.108
21.6998721.107
31.085313.476
40.6961688.6442
50.4202055.2176
60.2395192.9741
70.0380610.4726
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Abu Bakr, S.; El-Gaied, I.M.A.; Sayed, M.M.; Heinz, P.; Wagreich, M.; Mahmoud, A. Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt. Diversity 2025, 17, 293. https://doi.org/10.3390/d17040293

AMA Style

Abu Bakr S, El-Gaied IMA, Sayed MM, Heinz P, Wagreich M, Mahmoud A. Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt. Diversity. 2025; 17(4):293. https://doi.org/10.3390/d17040293

Chicago/Turabian Style

Abu Bakr, Safaa, Ibrahim M. Abd El-Gaied, Mostafa M. Sayed, Petra Heinz, Michael Wagreich, and Abdelaziz Mahmoud. 2025. "Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt" Diversity 17, no. 4: 293. https://doi.org/10.3390/d17040293

APA Style

Abu Bakr, S., El-Gaied, I. M. A., Sayed, M. M., Heinz, P., Wagreich, M., & Mahmoud, A. (2025). Biostratigraphy, Paleoenvironments, and Paleobiogeography of the Middle–Upper Eocene Ostracods from Northwestern and Northeastern Banks of the Nile Valley, Egypt. Diversity, 17(4), 293. https://doi.org/10.3390/d17040293

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