Paleoclimate and Paleoenvironment Reconstructions from Middle Eocene Successions at Beni-Suef, Egypt: Foraminiferal Assemblages and Geochemical Approaches

Abstract

The Eocene deposits of Egypt provide a wide variety of shallow marine facies and fossil assemblages, allowing paleoenvironmental reconstructions in this warmhouse climate interval. Forty-three rock samples have been collected from two middle Eocene sections, exposed at southeast Beni-Suef area in northern Egypt. The studied outcrops are lithologicsally subdivided into two rock units named from base to top as follows: (1) the Qarara Formation (Lutetian) and (2) the El Fashn Formation (Bartonian). Most investigated rock samples showed richness in benthic foraminiferal assemblages and only rare occurrences of index planktonic foraminifera. They yielded 160 foraminifera species which belong to 4 suborders, 19 superfamilies, 34 families, and 59 genera. The stratigraphic distribution of the identified species allowed us to define four local benthic bio-ecozones: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone, (3) Nonion scaphum Lowest Occurrence Zone, and (4) Brizalina cookei/Nonionella insecta Concurrent-Range Zone (Bartonian). These biozones are described and discussed in detail and correlated to stratigraphic equivalents in Egypt. The rareness of index planktonic foraminifera through the studied sections does not allow a precise biostratigraphic and chronostratigraphic correlation. The shale samples show low TOC values, which may be related to low productivity, high sediment influx, and/or prevailing oxic conditions. Bulk rock geochemistry, consistent with the benthic foraminifera ecological preferences, indicated that the studied sections were deposited in moderate to high oxygen levels and warm climatic conditions in a typical shelf marine setting. The identified species showed strong similarities with nearby southern Tethys areas, reflecting migration via the trans-Sahara seaway, and minor similarities with those identified from the northwestern Tethys and the North Atlantic province attributed to the change in the environmental and climatic conditions, such as cooler, latitudinal zoned climatic conditions along the northwestern Tethys, which was unsuitable for their biological demands. The warming trend identified from Lutetian to Bartonian intervals corresponds to the onset of the Middle Eocene Climatic Optimum (MECO).

1. Introduction

The Eocene Epoch exhibited significant variations in global climate and fluctuating sea levels, with the early Eocene characterized by high temperatures, the Early Eocene Climatic Optimum, followed by a cooling trend that culminated in a cold period at the Eocene–Oligocene transition [1,2]. The middle Eocene was marked by another hyperthermal event, the Middle Eocene Climatic Optimum, that was identified by negative oxygen isotopic excursion, whereas the late Eocene (Priabonian) was distinguished by a milder warming event [3].

Geochemical features of sediments that record information about the plaeoenvironments are significantly influenced by the depositional environments [4,5,6,7]. Therefore, geochemical analyses, together with micropaleontological investigations, perform an important role in reconstructing the paleoecologic conditions and constructing models for sea-level changes in response to changing inhabited areas, climate, and sedimentary supply [7,8,9,10,11]. Many authors focused on studying the Eocene strata of Egypt concerning paleontology, lithostratigraphy, biostratigraphy, and paleoecology [12,13,14,15,16,17,18,19,20,21,22,23,24]. Along the broad North African shelf, the middle Eocene rocks of Egypt are exposed in different localities showing distinctive facies changes from carbonates to clastics, all marked by the occurrence of distinctive Southern Tethyan foraminiferal assemblages [18,19,20,21,22,23,25,26,27,28]. Here, benthic foraminifera are more abundant than planktonic foraminifera, so only they can be used for biostratigraphic purposes [19,20,29,30,31,32,33,34]. Moreover, benthic foraminifera are very sensitive to environmental conditions; thus, they can provide valuable data to constrain the sea-bottom setting. Their abundance, diversity, and morphological features are considered adequate tools for interpreting the sedimentary environment, mainly controlled by the bottom oxygenation, nutrient availability, and organic flux [35,36,37,38].

Therefore, the present study aims to investigate the benthic foraminiferal assemblages in detail and also provide a more comprehensive estimation of paleoecology, paleobiogeography, and paleoclimatic conditions that prevailed during the deposition of the Eocene sediments in the study area based on both micropaleontological and geochemical approaches. In addition, this work presents an improved lithostratigraphy and local benthic foraminiferal biozonation. Moreover, this study emphasizes studying the relation between the foraminiferal traits (shell composition and life habit) through the studied sections and paleoecological parameters (climate conditions, substrate type, and oxygen level), which are considered crucial to changes in the foraminiferal communities.

2. Geologic Setting and Stratigraphy

The study area (Figure 1) is represented by two exposed sections situated on the eastern side of the Nile Valley between Beni Suef City and Gebel Qarara (southeast Beni Suef City). The exposure of Gebel Qarara (G. Qarara on Figure 1) lies at about 48 km southeast of Beni Suef, at latitude 28°37′37.2″ N and longitude 30°55′29.1″ E, whilst that at Gebel El Heiba (G. El Hadid) is located at approximately 34 km southeast Beni Suef City, at latitude 28°46′36.9″ N and longitude 30°57′15.1″ E (Figure 1). The detailed lithostratigraphic description and field investigation of the studied exposures allowed us to recognize two rock units from base to top, the Qarara and the El Fashn formations (Figure 2), which were named after reviewing the studies that have been carried out on the Eocene rocks of northern Egypt [15,18,19,21,22,23,39,40,41,42,43,44,45,46,47,48]. These are briefly discussed and described from older to younger in the following chapter.

2.1. Qarara Formation

Bishay [41] proposed this term to describe the succession of limestone attaining a thickness of about 170 m at Gebel Qarara, east Maghagha area. Said [49] stated that the limestone succession of the Qarara Formation was unconformably overlying the Maghagha Formation, which was composed of intercalated nummulitic limestone and marls with reddish clays. In the present work, the exposed part of the Qarara Formation has a thickness of about 46 m at Gebel Qarara. The lower and middle parts of this rock unit are about 16 m, composed of yellowish-grey and dark grey to black shales with gypsum capped by pinkish siltstones (Figure 2 and Figure 3A). The 30 m thick upper part consists of fossiliferous, hardly lithified, and burrowed yellowish-grey limestone, marl, and marly limestone with oysters and bivalves (Figure 2 and Figure 3B). The limestone is characterized by Thalassinoides horizons and Nummulites gizehensis accumulation. Based on the previous studies, the index planktonic and benthic foraminifera, besides the occurrence of large benthic foraminifera represented by Nummulites gizehensis, assigned this rock unit to upper Lutetian [18,24,41,50,51,52,53,54,55].

2.2. El Fashn Formation

This rock unit was first named by Bishay [41], who described it as a succession exposed at the Wadi El Sheikh area, southeast El Fashn City, consisting of 88 m thick, chalky limestone, shale, and sandy shales. The El Fashn Formation is exposed in both Qarara and El Heiba sections. At Gebel Qarara, it occupies the upper part of the section with an exposed thickness of about 25 m, consisting of yellow-green marls and hard, burrowed (Thalassinoides) and fossiliferous marly limestone (Figure 2 and Figure 3C). The uppermost part of this rock unit at Qarara section is characterized by high abundance and richness of Nummulites spp. (e.g., Nummulites beaumonti) (Figure 2 and Figure 3D). At the El Heiba section, the El Fashn Formation represents the whole exposed section with a thickness of about 83 m. The lower part attains a thickness of 16 m, comprising greenish-gray shale with interbeds of gypsum, grayish-yellow marly limestone, and yellow friable marls (Figure 2 and Figure 3E). The middle part is about 37 m thick, consisting of interbedded white to yellow marly limestone, white and hard fossiliferous limestone, and yellow marls. The upper part has a thickness of about 30 m of white to grayish-white and hard limestone intercalated with yellow marls and yellow marly limestone. The El Fashn Formation is highly fossiliferous and marked by high a abundance of well-preserved micro-fauna. The occurrence of index benthic foraminifers (Bulimina jacksonensis, Nummulites beaumonti), besides small-sized and spinose planktonic foraminiferal species (Acarinina spp., Morozovelloides spp.), assign this rock unit to upper middle Eocene (Bartonian) [18,19,21,22,23].

3. Materials and Methods

The present work is based on the investigation of forty-three rock samples collected from two sections with sampling intervals ranging from 50 cm to 2 m. About 200 g of each sample (shale, marl, marly limestone, and limestone) were soaked in water for 24 h in order to accelerate the disintegration process, then washed under flowing water using a sieve of size 63 μm. The hard samples were gently crushed, then soaked in hydrogen peroxide for a minimum of two days. The residue was dried and separated into several fractions by using sieves with sizes greater than 63, 90, 125, and 250 μm in order to facilitate the picking of the foraminiferal content. About 20 g from each size fraction were checked carefully under a binocular microscope. The foraminiferal specimens were picked and mounted on graduated slides. The picked benthic species were identified and classified following the scheme of Loeblich and Tappan [56]. Counts were normalized to 1 g sediment.

The prevailed ecological conditions were estimated depending on counting the total number of the foraminifers in each sample, then we calculated the percentages of the benthic species (B%), Calcareous species (Ca%), Arenaceous species (Ar%), Epifaunal species (Ep%), and Infaunal species (In%), see Table S1. In our study, some samples recorded only a relatively small number of foraminiferal specimens, which was in line with previous works in nearby areas. Therefore, we relied on the findings of Fatela and Taborda [57], who stated that counts as low as 100 specimens are sufficient, and the work of Abd El-Gaied et al. [57]. The Shannon Index and Dominance were used to characterize the diversity and carried out using PAST, v. 2.17 [58]. The relative abundance of the identified species has been calculated, and species with ratios more than 5% are considered. The ternary diagram of Murray [59] has been applied to estimate the salinity and the settings of the depositional environments based on calculating the percentages of the following suborders: Miliolina (M%), Lagenina (L%), and Rotaliina (R%) for each sample (Table S1).

The Benthic Foraminiferal Oxygen Index (BFOI) was calculated for each sample to determine the oxygen level of bottom waters (Table S1). This index is mainly dependent on the classification of Kaiho [60], who categorized the benthic foraminifers into three groups, Oxic (O), Suboxic (S), and Dysoxic (D), based on the morphological features of the shells (Table S1). The BFOI formula is defined as [O/(O + D) × 100], where O represents the number of oxic species and D refers to the number of dysoxic species. If oxic species (O) = 0 and D + S > 0, the BFOI formula will be as follows: [(S/(S + D) − 1] × 100 (the ecological preferences of each used species can be found in Table S1). For evaluating paleobiogeographic relationships, Q-mode cluster analysis has been performed on a dataset consisting of 41 species identified from the present work and published surveys [61,62,63,64,65,66] from the southern and northwestern Tethys and the North Atlantic (i.e., Libya, Spain, Italy, Belgium, England, and France).

All the collected samples have been subjected to carbonate content measurements using a FOG II Digital Soil Calcimeter. Approximately 1 mg powder of each sample was carefully introduced into a reaction bottle containing 6 N HCl; the bottle was tightly closed with the cuvette cap, then shaken to mix all sample powder with the acid in order to ensure accurate measurement. The results were obtained immediately within a few seconds (Table S2). These measurements were carried out at the Department of Geology, University of Vienna. For TOC analyses, about 100 mg of shale samples only were measured by using an LECO carbon analyzer (RC 612) with an analytical error of less than ±1%, at a temperature of 1100 °C through an induction furnace. TOC analyses were completed at the Microbiology and Environmental Systems Science Center, University of Vienna. Bulk geochemical analyses have been completed for all samples to measure major oxides and trace elements by using an X-ray fluorescence spectrometer Philips PW 2400; fused pellets were used to detect major elements and powder pellets for trace elements following the procedure of Sami et al. [67], see Table S2. XRF analyses were performed at the Department of Lithospheric Research, University of Vienna.

4. Results

4.1. Systematic Paleontology and Foraminiferal Biostratigraphy

The investigated rock samples yielded 160 foraminifera species and subspecies which belonging to 4 suborders, 19 superfamilies, 34 families, and 59 genera (Figure 4, Figure 5 and Figure 6).

The stratigraphic distribution of the identified species through the studied sections enabled us to construct four local benthic foraminiferal biozones of the middle Eocene age (see distribution chats in Table S1). These local biozones are described in detail and correlated to equivalents in different areas in Egypt (

Table 1. Correlation of the benthic foraminiferal zones identified herein and their counterparts.

Age/Locality	Fayoum Area			Nile Valley			North Eastern Desert			Helwan Area	Present Study
	Elewa et al. [46]	Helal [68]	Abd EL Azeam [69]	Mansour et al. [70]	El Dawy [71]	Abd El-Aziz [72]	El Dawy and Dakrory [73]	Aly et al. [17]	Abd El-Gaied et al. [19]	Abd El-Gaied et al. [20]
late Middle Eocene (Bartonian)	Lenticulina alatolimbata	Bulimina jacksonensis/Uvigerina jacksonensis	Lenticulina cosata	Nummulites beaumonti	Nonion scaphum/ Pararotalia audouini	Palmula ansaryi	Bolivina jacksonensis/ Pararotalia audouini	Palmula ansaryi	Palmula ansaryi	Nonion scaphum	Brizalina cookei/ Nonionella insecta
										Brizalina cookei	Nonion scaphum
					Brizalina cookei		Brizalina cookei
	Cibicidoides truncanus			Orbitolites complanatus		Uvigerina coaensis/ Uvigerina continusa				Nonionella africana	Cibicides mabahethi/Cancris a. primitivus
Middle Eocene (Lutetian)					Uvigerina nakadyi/Anomalinoides fayoumensis	Haplophragmoides emaclatus/ Ammobaculites cubensis	Anomalinoides fayoumensis			Quinqueloculina seminula	Bolivina carinata
	Bulimina jacksonensis/Uvigerina jacksonensis			Nummulites gizehensis

).

4.1.1. Bolivina carinata Lowest Occurrence Zone

• Age: middle Eocene (Lutetian)
• Definition: Interval from the lowest occurrence (LO) of Bolivina carinata to the LO of Brizalina cookei.
• Occurrence: This zone represents the exposed part of the Qarara Formation corresponding to the lower and middle parts of the Qarara section (samples 1 to 9) with a thickness of about 46 m.
• Assemblages: Forty-six species and subspecies are recorded from this zone; the most dominant species are: Bolivina alazanensis venezulana, B. jacksonensis striatella, B. carinata, Nonionella spissa, Cibicides mabahethi, Cibicidoides westi, C. laurisae, Cibicidina carinatus, Eponides ellisorae, Fursenkoina dibolensis, F. squamosa, Lobatula lobatulus, and Uvigerina seriata.
• Correlation: The recorded zone is equivalent to the Quinqueloculina seminula and Haplophragmoides emaclatus/Ammobaculites cubensis zones that were previously recorded from the middle Eocene rocks of the Helwan area and the Nile Valley [20,72]. The interval also correlates to the upper part of the Anomalinoides fayoumensis and Uvigerina nakkadyi/Anomalinoides fayoumensis zones that were defined from the Eastern Desert and Nile Valley, respectively [71,73], as shown in Table 1. On the other hand, it is matched with the lower part of the Bulimina jacksonensis/Uvigerina jacksonensis Zone that was defined by Helal [68] and the upper part of the same zone in addition to the lower part of Cibicidoides truncanus Zone of Elewa et al. [46] in the Fayoum area (Table 1). Regarding the large benthic foraminiferal zonation, this zone could be correlated to the upper part of Nummulites gizehensis Zone and also matches with the lower part of Orbitolites complanatus Zone from the middle Eocene of the Nile valley [70]. Furthermore, it is equivalent to the upper part of Nummulites aff. puchellas Zone, which was recorded from the middle Eocene of Helwan area by Boukhary et al. [74].
• Age: Based on the above-mentioned data and previous studies which have been completed on the studied section, besides the occurrence of the index large benthic foraminifera (Nummulites gizehensis), this zone is assigned to a Middle Eocene (Lutetian) age [18,24,41,50,51,52,53,54,55].

4.1.2. Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone

• Age: middle Eocene (Bartonian)
• Definition: Interval from the LO of Brizalina cookei to the highest occurrence (HO) of Cancris auriculus primitivus.
• Occurrence: This zone corresponds to the whole thickness of the El Fashn Formation exposed in the upper part of the Qarara section (25 m, samples 10 to 20).
• Assemblages: One hundred and forty-three species and subspecies are identified from this zone. The most important and abundant species are: Bolivina alazanensis venezulana, Bolivina carinata, B. jacksonensis, B. jacksonensis striatella, Nonionella insecta, N. spissa, Cancris auriculus primitivus, C. turgidus, Cibicides mabahethi, Cibicidoides laurisae, C. westi, C. yankaulensis, Eponides ellisorae, E. jacksonensis, Neoeponides schreibersi, Fursenkoina dibolensis, F. squamosa, Nonion scaphum,, lenticulina alabamensis, L. alatolimbata, L. costata, L. politus, Pleurostomella cubensis, textularia adamsi, T. arenacea, and T. recta.
• Correlation: The identified zone correlates to the Nonionella africana and Uvigerina coaensis/Uvigerina continusa zones that were reported from the middle Eocene (Bartonian) of the Helwan area [20] and the Nile Valley [72]; see Table 1. It is also coeval to the lower part of the Palmula ansaryi Zone the from north Eastern Desert [17,19] (Table 1). Moreover, this zone is correlated to the middle part of the middle Eocene Bulimina jacksonensis/Uvigerina jacksonensis Zone from Fayoum [68] and the middle to upper part of the Brizalina cookei and Cibicidoides carinatus zones that was identified, respectively, from the north Eastern Desert [73], Nile Valley [71], and Fayoum [46] (Table 1). In addition, it is equivalent to the middle and upper parts of the larger benthic foraminifera Orbitolites complanatus Zone recorded from the Bartonian of the Nile Valley by Mansour et al. [70].
• Age: This zone is correlated to the lower part of the planktonic zone E13 based on the occurrence of the index small and spinose planktonic species Acarinina rohri and Morozovelloides spp., coupled with the coexistence of the large benthic foraminifera Nummulites beaumonti attributing late middle Eocene (Bartonian) age [18,21,23].

4.1.3. Nonion scaphum Lowest Occurrence Zone

• Age: middle Eocene (Bartonian)
• Definition: The present zone is defined from the LO of Nonion scaphum to the LO of Lenticulina alabamensis.
• Occurrence: It represents the lower and middle parts of the El Fashn Formation at the El Heiba section, attaining a thickness of about 34 m (samples 1 to 11).
• Assemblages: Eighty species and subspecies are recorded from this zone. The most common species are: Bolivina carinata, Bulimina jacksonensis, Cibicidoides laurisae, C. westi, Cibicides mabahethi, Eponides jacksonensis, E. cocoaensis, Neoeponides schreibersi, Fursenkoina dibolensis, Uvigerina seriata, Cancris auriculus primitivus, C. danvillensis, Baggina bradyi, Asterigerina brenci, Cibicidina carinatus, Cibicidoides pharoaensis, Halkyardia minima, Lobatula lobatulus, Planulina cocoaensis, Uvigerina batjesi, U. jacksonensis, U. mediterranea, U. peregrina, and U. rippensis.
• Correlation: The present zone is correlated with the Brizalina cookei Zone as proposed by Abd El-Gaied et al. [20] from the middle Eocene sediments in the Helwan area (Table 1). It is matched to the middle part of the Palmula ansaryi Zone in the north Eastern Desert [17,19] and to the lower part of the same zone in the Nile Valley [72]. On the other hand, it is equivalent to the upper part of the Brizalina cookei Zone and the lower part of the Bolivina jacksonensis/Pararotalia audouini Zone recorded from the north Eastern Desert [73], and to the upper part of Brizalina cookei Zone and the lower part of the Nonion scaphum/Pararotalia audouini Zone in the Nile Valley [71], as indicated in Table 1. In the Fayoum area, it is equated to the middle part of the middle Eocene Bulimina jacksonensis/Uvigerina jacksonensis Zone [68], the middle part of Lenticulina costata Zone [69], and the lower part of the Lenticulina alatolimbata Zone [46]. The identified zone could be matched to the lower and middle part of the Nummulites beaumonti Zone, which was identified by Mansour et al. [70] from the Bartonian of the Nile Valley.
• Age: This zone corresponds to the lower and middle parts of the planktonic zone E13 based on the presence of the index planktonic foraminifers Acarinina rohri and Morozovelloides spp., also assigning a late middle Eocene (Bartonian) age to this zone [18,21,23].

4.1.4. Brizalina cookei/Nonionella insecta Concurrent-Range Zone

• Age: middle Eocene (Bartonian)
• Definition: Interval from the LO of Lenticulina alabamensis to the HO of Cibicides mabahethi.
• Occurrence: The present zone is defined from the upper part of the El Fashn Formation, occupying the uppermost part of the El Heiba section with a thickness of about 42 m (samples 12 to 22).
• Assemblages: Seventy-nine species and subspecies are identified from this zone. The most dominant species are: Bolivina carinata, B. jacksonensis striatella, Cibicidoides westi, Cibicides mabahethi, Cibicidina carinatus, Lobatula lobatulus, Eponides ellisorae, Neoeponides schreibersi, Nonionella insecta, Uvigerina peregrine, and U. seriata.
• Correlation: The present zone is equivalent to the Nonion scaphum Zone recorded by Abd El-Gaied et al. [20]) from the Helwan area. It is matched to the upper part of the following zones: the Palmula ansaryi Zone from the north Eastern Desert [17,19] and Lenticulina costata Zone that is recorded from the Fayoum area [69]. It also correlates to the middle and upper parts of the Palmula ansaryi Zone in the Nile Valley [72], Lenticulina alatolimbata Zone defined in the Fayoum area [46], the Bolivina jacksonensis/Pararotalia audouini Zone recorded from north Eastern Desert [73], and the Nonion scaphum/Pararotalia audouini Zone from the Nile Valley [71] (Table 1). In addition, it is equated to the upper middle part of the Bulimina jacksonensis/Uvigerina jacksonensis Zone from Fayoum [68] and to the middle and upper part of the Nummulites beaumonti Zone recognized in the Nile Valley [70].
• Age: Depending on the stratigraphic position, this zone is correlated to the upper part of the planktonic foraminifera zone E13, which witnessed the occurrence of the index small and spinose planktonic species (Acarinina spp., Morozovelloides spp.). Therefore, the recorded zone is assigned to the late middle Eocene (Bartonian) age [18,21,23].

4.2. Geochemistry

The values of the major oxides and trace elements of the analyzed samples by XRF are shown in Table S2. Here, we report results for paleoenvironmental proxies used in this study. TOC values of the shale samples are shown in

Table 2. TOC values of shale samples in the studied sections.

Sample No.	Weight (g)	Organic Carbon TOC (%)	Inorganic Carbon %	Total Carbon %
0 Q	0.1000	0.3800	0.5098	0.8898
1Q	0.1002	0.3724	0.5267	0.8991
2Q	0.1001	0.2179	0.1101	0.3281
3Q	0.1001	0.1969	0.1821	0.3789
4Q	0.1000	0.1407	0.1599	0.3007
5Q	0.1000	0.3625	3.6795	4.0420

.

4.2.1. Paleo-Redox Proxies

The studied samples of Gebel Qarara are rich in some major oxides, such as CaO (mean 20.7 wt%) and SiO₂ (mean 25.8 wt%), and have low contents of TiO₂ (0.68 wt%), Al₂O₃ (7.6 wt%), Fe₂O₃ (5.8 wt%), MnO (0.09 wt%), MgO (1.8 wt%), and P₂O₅ (0.1 wt%) (S 2). The samples of Gebel El Heiba are dominated by carbonate sediments reflected in high amounts of CaO (30.5 wt%) and contain relatively lower values of SiO₂ (4.9 wt%), TiO₂ (0.004 wt%), Al₂O₃ (1.85 wt%), Fe₂O₃ (1.47 wt%), MnO (0.026 wt%), MgO (0.88 wt%), and P₂O₅ (0.05 wt%). Trace elements, such as U (with an average of 5–8 ppm), Co (4–9 ppm), Cr (35–100 ppm), Cu (10–14 ppm), Mo (2–4 ppm), Ni (9–14 ppm), and V (23–60 ppm), can be used to unravel and estimate the paleoenvironment and paleoclimatic conditions (see Table S2).

Oxidizing environments are characterized by low values of Uranium (U), whereas oxygen-depleted environments are rich in U content [75,76,77,78]. In addition, trace elemental ratios (Cu/Zn, Ni/Co, V/Ni, and V/Cr) have been used to interpret the paleo-redox conditions [79,80,81,82,83,84,85]. Jones and Manning [82] stated that oxic depositional settings are enriched in Cobalt (Co) relative to Nickel (Ni), reflected by low values of Ni/Co ratios, while high values suggest anoxic conditions. According to Xiong and Xiao [86], reducing environments are characterized by a high value of Ni/Co (>7), oxidizing conditions showed low values (<5), and values between 5 and 7 reflect anaerobic and sub-reducing environments.

Dill [81] and Mir [85] reported that sediments that accumulated in reducing environments are commonly associated with vanadium (V) versus chromium (Cr) which is not directly related to the redox conditions. High values of V/Cr ratio (>2) reflect sediment deposition in anoxic conditions, and low values (<2) indicate oxic conditions [82]. Additionally, high ratios of Cu/Zn support a reducing environment, while low ratios indicate oxic conditions [79,87]. Furthermore, vanadium (V) and nickel (Ni) are considered crucial tools for paleo-redox conditions [88,89,90].

In the present work, the measured samples showed low values of U (on average 5–8 ppm) in addition to low trace elemental ratios of Cu/Zn (an average of 0.24 and 0.48), Ni/Co (an average of 1.8 and 3.7), and V/Cr (an average of 0.068 and 0.58). In addition, bivariate diagrams, which are mainly based on the relation between the following trace elemental ratios: Mo-Ni/Co, V/V + Ni-Ni/Co, and V/Cr-Ni/Co, have been applied for all the measured samples to reconstruct the redox conditions (Figure 7 and Figure 8). Results from these bivariate diagrams indicate that most samples fall into the oxic fields.

4.2.2. Paleoclimate and Salinity Proxies

Trace elements and major oxides can be used to reconstruct paleoclimate trends and water salinity [91]. The C-value for paleoclimate can be calculated from the following equation: [C-value = Σ (Fe + Mn + Cr + Ni + V + Co)/Σ (Ca + Mg + Sr + Ba + Na)] (Table S2). High C-values (>0.6) reflect humid climate conditions, whilst low values (<0.4) indicate a more arid climate [92]. Furthermore, the ratio of Sr/Cu is a valuable tool for paleoclimate evaluation, where high values of Sr/Cu (>5) refer to hot and arid conditions, and low values of Sr/Cu (<5) reflect a warm and more humid climate.

The analyzed samples showed high values of Sr/Cu ratios (>5, see Table S2), suggesting hot arid conditions. The lower part of the Qarara Formation (samples 0–5) record Sr/Cu ratios much lower (mean 35.2) than the upper part of the same rock unit (mean 63.2) and all samples of the El Fashn Formation at Gebel Qarara (mean 92.83, see Table S2). However, the samples of the El Fashn Formation at El Heiba show very high Sr/Cu values (mean 172.3). Concerning C-values, the lower part of the Qarara Formation shows relatively high, more humid values (ranges from 0.4 to 0.9, see Table S2), while the upper part of this rock unit and the El Fashn Formation exhibit generally lower, more arid values (ranges from 0.007 to 0.6 with an average of 0.18, Table S2). At the El Heiba section, the El Fashn Formation also has low C-values with an average of about 0.07 (Table S2).

Concerning paleosalinity, Deng and Qian [93] showed that the Sr/Ba ratio can be used as a paleosalinity indicator, and Xu et al. [94] classified high values of Sr/Ba ratio (>1) as more saline water (marine), while low values (<0.6) reflect freshwater environment. In the present study, the estimated Sr/Ba ratios show persistent high values (>1) representing fully marine conditions (Table S2).

4.3. Foraminiferal Data

The total number of the recorded species, infaunal/epifaunal ratio, arenaceous/calcareous percentage, and BFOI were calculated for each sample (Table S1; Figure 9 and Figure 10). In the present work, the lower part of the Qarara Formation at Gebel Qarara is characterized by very low diversity and high dominance of the foraminiferal assemblages, while the upper part shows a remarkable increase in diversity and decrease in dominance (Table S1) compared to the lower part. The lower part of the Qarara Formation is distinguished by the occurrence of infaunal species (Bolivina sp.), which is reflected by the high values of infaunal/epifaunal ratios (with a mean of about 77%). Due to the low values of foraminiferal specimens in samples 1 to 7, extra caution was taken at this level. Our interpretation was not only reliant on the foraminiferal data but was also corroborated by the use of geochemical techniques. In contrast, the upper part of the Qarara Formation showed a distinct increase in the epifaunal species, where the infaunal/epifaunal ratio decreased (mean of 64%, see Table S1; Figure 9), coupled with the appearance of macrofauna (gastropods and bivalves) and trace fossils of Thalassinoides sp. (samples 8–9). Additionally, this rock unit shows few representatives of arenaceous species, where the calculated values of the arenaceous/calcareous (A/C) ratio ranges from 2% to 3% and reach its maximum value in sample 2 (23%). Most of the species recorded within this rock unit belong to the suborder Rotaliina (98–100%), which is why all samples are plotted at or near the Roataliina corner of the ternary diagram of Murray [59] (Figure 11).

The Benthic Foraminiferal Oxygen Index (BFOI) has low values at the lower part of the Qarara Formation (mean 23%, low oxygen levels according to Kaiho [60]), while the upper part exhibits higher values (reaching 32%, moderate oxygen levels, Table S1; Figure 9). The uppermost part of the Gebel Qarara section, represented by the El Fashn Formation, is characterized by high dominance of large benthic foraminifera (Nummulites spp. and Operculina spp.), macrofauna (bivalves, gastropods), and Thalassinoides spp. (samples 10–20), in addition to a remarkable decrease in the infaunal/epifaunal values (an average 42 %). This rock unit is also marked by a few occurrences of arenaceous foraminifera, where the A/C ratio ranges from 1% to 9% and reaches the maximum value of 33% in sample 13 (Figure 9). Many species recorded within this part belong to the suborder Rotaliina (92–100%), hence all samples are plotted at the Rotaliina–Textulariina line or at the Rotaliina corner of the diagram of Murray [59] (Figure 11). Moreover, this part has a very low planktonic ratio, not exceeding 1%. Meanwhile, it is also characterized by high values of BFOI, which report values with an average of about 58% (Table S1).

On the other hand, the El Fashn Formation at Gebel El Heiba is characterized by higher values of epifaunal species (Cibicides spp., Cibicidoides spp., Eponides spp.), with a mean value of 49% of the infaunal/epifaunal ratio (Figure 10). Some intervals showed an increase in infaunal species, such as Laevidentalina spp., Pleurostomella spp., Fursenkoina spp., Uvigerina spp., and Bolivina spp. This part is dominated by calcareous species with few arenaceous forms at some intervals. Thus, most of the samples again plot at the Rotaliina corner of the Murray [59] diagram (Figure 11). Additionally, it shows a noticeable increase in the BFOI values (an average 59%) compared to the Qarara and the El Fashn formations at Gebel Qarara.

4.4. Paleobiogeography

Some of the recognized species in the present study were previously identified from southern and northwestern Tethys areas and the North Atlantic. Q-mode clustering was carried out on a matrix consisting of 41 middle Eocene benthic species recorded previously from other parts of the Tethys [19,20,23,61,62,63,64,65,66]. The resemblance of the identified benthic species in the present work with those recorded in other occurrences is shown in

Table 3. Geographic distribution of the identified benthic foraminifers (1/0 indicate present/absent).

Species/Country	Egypt	Libya	Italy	France	Spain	England	Belgium
Bolivina anglica	1	1	0	1	0	0	0
Bolivina carinata	1	1	0	1	1	0	1
Bolivina jacksonensis	1	1	0	0	0	0	0
Brizalina cookei	1	0	0	0	0	0	1
Bulimina jacksonensis	1	1	0	0	0	0	0
Cancris auriculus primitivus	1	0	1	1	0	0	1
Cancris subconicus	1	0	1	1	0	0	1
Cibicides mabahethi	1	1	0	0	0	0	0
Cibicidoides laurisae	1	1	0	0	0	0	0
Fursenkoina dibolensis	1	0	0	1	1	0	0
Globulina gibba	1	0	1	1	0	0	1
Halkyardia minima	1	0	1	0	0	0	0
Laevidentalina soluta	1	0	0	1	0	1	1
Lagena apiculata	1	0	0	1	0	1	1
Lagena hexagona	1	0	1	1	0	1	1
Lagena laevis	1	0	0	1	0	1	1
Lagena striata	1	0	1	1	0	0	1
Lagena sulcata	1	1	0	0	0	0	0
Lenticulina alatolimbata	1	1	0	0	0	0	0
Lenticulina clericii	1	1	0	0	1	0	0
Lenticulina cultrata	1	1	0	0	1	0	0
Lenticulina isidis	1	1	0	0	0	0	0
Lenticulina limbata	1	0	1	0	0	0	0
Lenticulina williamsoni	1	1	0	0	1	0	0
Lenticulina yaguatensis	1	1	0	0	1	0	1
Lobatula lobatula	1	0	1	1	1	0	1
Neoeponides schreibersi	1	1	0	0	0	0	0
Planulina cocoaensis	1	1	0	0	0	0	0
Quinqueloculina seminula	1	0	1	1	0	1	1
Saracenaria triangularis	1	0	1	0	0	0	0
Spiroplectammina adamsi	1	0	1	0	0	0	1
Spiroplectinella carinata	1	1	1	0	1	0	1
Textularia adalta	1	0	1	0	0	0	0
Textularia adamsi	1	0	0	0	0	0	1
Textularia agglutinans	1	0	0	0	0	0	1
Uvigerina cocoaensis	1	1	0	1	0	0	0
Uvigerina cookei	1	1	0	0	0	0	0
Uvigerina hispida	1	1	0	0	1	0	0
Uvigerina mexicana	1	1	1	0	0	0	0
Uvigerina rippensis	1	1	0	0	1	0	0
Uvigerina seiata	1	0	0	0	0	0	1

. The dendrogram obtained from Q-mode cluster analysis showed two clusters; the first one represents the Southern Tethys province (North Africa), exhibiting strong similarity between the species recorded from Egypt with those from Libya (Figure 12). Twenty species are in common between Libya and Egypt, represented by Bulimina jacksonensis, Bolivina anglica, B. carinata, B. jacksonensis, Lenticulina alatolimbata, L. clericii, L. cultrata, L. isidis, L. yaguatensis, L. williamsoni, Uvigerina cocoaensis, U. cookei, U. hispida, U. mexicana, U. rippensis, Spiroplectinella carinata, Planulina cocoaaensis, Cibicides mabahethi, Cibicidoides laurisae, and Neoeponides schreibersi (Table 3). The second cluster represents the northwestern Tethys province and the North Atlantic province showing low similarities between the identified middle Eocene species with those recorded from Spain, Italy, England, Belgium and France (Figure 12). The most common species between these countries and Egypt are represented by: Cancris auriculus primitivus, Cancris subconicus, Globulina gibba, Lagena hexagona, Quinqueloculina seminula, Bolivina carinata, Spiroplectinella carinata, Lobatula lobatula, and Fursenkoina dibolensis.

5. Discussion

Benthic foraminifera are very sensitive to environmental changes; therefore, they can be used as crucial tools for paleoecological estimation and are considered excellent indicators for reconstructing the depositional environments and providing a better understanding of the sea bottom. Paleoenvironmental conditions of the present study were estimated depending on the recorded small benthic foraminiferal assemblages supported by macrofauna (gastropods, bivalves), large benthic foraminifera (Nummulites spp.), and trace fossils (Thalassinoides) beside the lithologic changes. The results show noticeable changes in biotic traits, such as diversity, dominance, and mode of life, which were strongly controlled by variations in abiotic factors, such as oxygen levels and sediment type.

The statistical foraminiferal analyses, besides the lithological description and the obtained geochemical data, allowed us to detect that the lower part of the Qarara Formation was deposited in deeper environments (middle to outer shelf settings) with lower to moderate oxygen levels relative to the upper part of the same rock unit and the El Fashn Formation at Gebel Qarara. The well-bedded shales are indicative of low-energy environments below the wave base [95]. This part is also characterized by the occurrence of infaunal species such as Bolivina spp. (infaunal/epifaunal ratios range from 63 to 91%), which are considered low-oxygen taxa and prefer outer shelf settings [96]. Moreover, this part is marked by the lowest Shannon diversity (range from 1.04 to 1.84) and high Dominance (from 0.17 to 0.37, see Table S1), implies stressed depositional environments and/or may be due to the high sediment input, which limited the biological demands of some species [97]. This part was not only affected by clastic flux but also may have been subject to oxidizing events, which are reflected in the low values of TOC (range from 0.14 to 0.38; see Table 2).

The upper part of the Qarara Formation is marked by distinct lithological variations to marls, marly limestone, fossiliferous (bivalves, gastropods), and bioturbated (Thalassinoides) limestones. These facies changes, coupled with the occurrence of trace fossils and macrofauna, indicate that this part accumulated in shallower settings. This upward shallowing is probably caused by a drop in the sea level. The occurrence of macro-fauna, which is mainly represented by oysters (epifaunal and suspension feeders), reflects a shallow marine environment [19,98]. This part is also characterized by an increase in epifaunal species (infaunal/epifaunal ratios reach up to 60%, see Figure 9; Table S1), indicating high oxygen levels, which are reflected in the high values of BFOI. The significantly high numbers of the foraminiferal individuals within this part, in conjunction with the occurrence of macrofossils, the high ratios of epifaunal species, and BFOI compared to the lower part of the same rock unit, indicate better and well-oxygenated conditions and low to moderate organic flux [97]. Following upward through the El Fashn Formation, there was a noticeable representation of the epifaunal species (infaunal/epifaunal ratios range from 43 to 79%), shallower taxa, and a distinct increase in BFOI (58%), suggesting that the deposition took place in more shallow, well oxygenated depositional environments compared to the Qarara Formation at Gebel Qarara. This increase in high oxygen taxa is corroborated by the higher Shannon diversity (from 2.09 to 3.4) and lower Dominance (from 0.03 to 0.1, see Table S1) compared to the Qarara Formation, supporting well-oxygenated and improved environmental conditions. In addition, the abundance of Lenticulina spp. (Lenticulina limbata with an of average 14%), Lobatula lobatula (average 10%), and Eponides spp. (Eponides ellisorae with average 11%, Table S1) indicate inner to middle shelf environments with high oxygen conditions [19,35,99]. This conclusion was supported by the dominance of large benthic foraminifera (Nummulites spp., Operculina spp., which need light for living with their symbionts), macrofauna (bivalves and gastropods), the high abundance of the epifaunal calcareous foraminifera (0–9% arenaceous/calcareous ratio), and the occurrence of trace fossils (Thalassinoides spp.), which prefer inner shelf settings for their biological activities where high oxygen levels, clear and warm conditions are predominant [18,19,20,23,32,38,99,100,101,102,103] and suggest low organic flux. The occurrence of large benthic foraminifera (Nummulites spp.), along with the presence of small benthic foraminifera, supports the conclusion that the smaller species were able to compete effectively with the larger ones [104].

On the other side, the EL Fashn Formation at the El Heiba section was deposited in a middle shelf setting with moderate to high oxygen conditions compared to the same rock unit at the Qarara section. This suggestion is mainly based on the high values of BFOI (an average 59%), moderate to high abundance of epifaunal species (30–42% infaunal/epifaunal ratio), and complete absence of macrofauna, bioturbated carbonate beds, and large benthic foraminifera. Furthermore, our conclusion is reinforced by the high relative abundance of species that favor low oxygen levels (Uvigerina seriata with average 9%, Bolivina carinata 13%, and Bolivina jacksonensis striatella 12%, see Table S1). Similarly, we found a high abundance of species with high oxygen preference, including Cibicides westi (average 21%), Cibicides mabahethi (average 16%), and Cibicidoides laurisae (average 13%), as shown in Table S1. Additionally, this part is characterized by low Dominance and a high Shannon index (Table S1), reflecting better-oxygenated conditions and low environmental stress. The depositional environment was established based on the foraminiferal data, which showed common to moderate occurrences of species belonging to the following genera Cibicides and Lobatula, pointing to an inner to middle shelf environment [99,105], and high abundance of Bolivina spp., which inhabit the outer shelf settings [96,105]. Moreover, the dominance of non-bioturbated and well-bedded limestones (an average of CaCO₃ 76.9%) indicates low and calm energy environments, which are identical to outer shelf settings [22,106]. The common to high abundance of the calcareous epifaunal benthic species, coupled with high values of BFOI, point to moderate to high oxygen levels. During this period, some peaks of infaunal assemblages can be observed (reaching 84% infaunal/epifaunal ratio), maybe related to time-limited low levels of dissolved oxygen in bottom waters or high amount of sediment flux to the ocean floor [107,108,109,110]. This change in the depositional settings of the Fashn Formation from the Qarara to El Heiba sections may be related to changes in the paleotopography of the depositional basin, where the Qarara section could have been deposited in an elevated area compared to the El Heiba section or could be related to a local tectonic activity which resulted in changes in the accommodation space, showing a good accordance with the tectonic model presented by Saber and Salama [18]. The foraminiferal ratios of the studied sections proved that the substrate type performs an important role in shaping benthic foraminiferal assemblages, where rich benthic associations showed strong affinities to marls (highest richness, Table S1) and marly limestone followed by limestones and shales, respectively (Figure 9 and Figure 10). Finally, we can indicate that the environmental stress decreases and oxygen level increases upward from the Lutetian to the Bartonian, which can be seen from the upward increase in diversity and decrease in low-oxygen taxa. Regarding the paleosalinity, all rock units were deposited in a normal marine environment and typical shelf settings as indicated by plotting of all samples within the ternary diagram of Murray [59], as shown in Figure 11, and corroborated by high values of Sr/Ba ratios (>1).

Based on the geochemical data, the increased amount of the major oxides at Gebel Qarara may be related to the shallower settings near the shore, where a high amount of the (clastic) sediment influx brought to the sedimentary basin during the deposition of the Qarara section. Whilst the low values of these oxides and high amount of CaO (mean 30 wt%), and CaCO₃ (mean 37.5%, Table S2) of the El Fashn Formation at El Heiba section indicate deposition in deeper settings, away from the siliciclastic supply. It also exhibits that carbonates are the main source of Mn, Al, Si, and Ti. Moreover, the trace elemental ratios (Cu/Zn, Ni/Co, and V/Cr) of the studied sections revealed oxic depositional environments, supporting the prevailing paleoredox conditions obtained from the foraminiferal data. These conditions were confirmed by bivariate diagrams (Mo-Ni/Co, V/V + Ni-Ni/Co, and V/Cr-Ni/Co), where most of the measured samples plot within the oxic field (Figure 7 and Figure 8).

Regarding the paleoclimate, the low values of Sr/Cu ratios (mean 35.22%, Table S2) of the lower part of the Qarara Formation indicate that deposition took place in humid and wet climatic conditions, while the upper part of the same rock unit and the El Fashn Formation in both sections were deposited in hot and more dry climatic conditions. This conclusion is supported by C-values, where the lower part of the Qarara Formation has high values (mean 0.53%, Table S2) compared to the upper part (mean 0.24%) and the whole samples of the El Fashn Formation (mean 0.14 in Qarara −0.07 in El Heiba, Table S2). This warming upward from a humid Lutetian to an early Bartonian hot and arid warming peak probably corresponds to the Middle Eocene Climatic Optimum (MECO) showing good accordance with a global warming peak of a hyperthermal, e.g., in the Southern Atlantic, Indian Ocean, Spain, and Turkey [3,111,112,113].

Paleobiogeographically, the identified species and the applied clustering methods showed strong similarities with more nearby southern Tethys areas, such as Libya, reflecting migration via the Trans-Sahara Seaway, and minor similarities with those identified from the northwestern Tethys and the North Atlantic provinces. This distribution is attributed to the benthic nature, which limits their ability to move for a long distance and is related to environmental and climatic changes, such as cooler, latitudinal zoned climatic conditions, which were unsuitable for their biological demands in more northern latitudes.

6. Conclusions

The studied outcrops were lithologically subdivided into two middle Eocene rock units, the Qarara Formation (Lutetian) at the base and the overlying El Fashn Formation (Bartonian). The investigation of 43 rock samples yielded 160 species of benthic foraminifera and subspecies which belong to 4 suborders, 19 superfamilies, 34 families, and 59 genera. Four local benthic foraminiferal zones were identified and named as follows: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone, (3) Nonion scaphum Lowest Occurrence Zone, and (4) Brizalina cookei/Nonionella insecta Concurrent-Range Zone (Bartonian). The depositional environments and prevailing climatic conditions were estimated depending mainly on the geochemical results coupled with the small benthic foraminiferal fauna and their bio-ecological preferences, the lithologic features, and the associated macrofossils and large benthic foraminifera. The lower part of the Qarara Formation was deposited in the middle to outer shelf settings with low to moderate oxygen levels, and humid and wet climatic conditions. The upper part of the Qarara Formation and the exposed part of the El Fashn Formation at Gebel Qarara were accumulated in shallow water-depth, well-oxygenated environments, and hot and arid climatic conditions. El Fashn Formation at EL Heiba area was deposited in deeper settings compared to the same rock unit at Gebel Qarara. This change in the depositional environments may be related to changes in the paleotopography of the depositional basin or could be attributed to local tectonics. The strong similarity of the identified foraminiferal assemblages with Libya (southern Tethys) indicates migration through the Trans-Sahara Seaway, while minor similarities with the northwestern Tethys province and the North Atlantic could be correlated to their benthic nature, which limit their distribution distance or environmental and climatic changes (the cooler climatic conditions further to the north).