Assessment of Mineralogical and Geochemical Composition of Oligocene/Eocene Black Shale Deposits in Beni Suef Area, Egypt

Black shale deposits are widespread in the Paleogene successions in the Beni Suef area, Egypt. In this work, the mineralogical composition, total organic carbon (TOC), and total sulfur (TS) contents of black shales were determined. ­e organic matter (OM), thermal maturation, and kerogen type can be determined using Rock-Eval pyrolysis. ­e results show that smectite and kaolinite are the dominant clay minerals in the analyzed samples. Al2O3 and SiO2 as major elements and Zr as a trace element are dominant constituents of terrigenous origin of the Dabaa and El Fashn formations.­e total organic carbon content reaches 2.27 wt % at the El Fashn Formation in the Ghaida Al-Sharqia quarry but 0.36wt% in the Oligocene Dabaa Formation in the Maydoum quarry. However, the total sulfur content reaches 0.58wt% in the Dabaa Formation but 1.52wt% in the El Fashn Formation. ­ese results conrm that (1) the Dabaa Formation was formed in oxidizing environments and oxidized the high volume of OM and (2) the El Fashn Formation accumulated in reducing environments of mostly suboxic conditions. ­e Rock-Eval pyrolysis results of the black shale deposits reected a kerogen type III of terrestrial origin of the El Fashn Formation due to the high OM content preservation in suboxic shallow marine environments. ­e Tmax and production index parameters of Rock-Eval pyrolysis reected that the black shale deposits in the El Fashn Formation are immature, but with surface retorting, it can generate natural gas.


Introduction
Recently, unconventional oil and gas resources, such as oil shale and shale gas, have received more attention due to uctuating global oil shale prices. Oil shale has good prospects for use in elds, such as chemical and building material industries, medicine, agriculture, and environmental protection [1,2]. Oil shale is a potential source for critical energy, hydrocarbons, and other products that should be fully exploited in the future as it produces substantial gas and oil quantities upon destructive distillation [3][4][5]. e global interest in oil shale relates to the widespread appreciation of its value as an essential unconventional source rock or natural resource of future fuel.
Although the cost is high, the energy produced through the retorting process and direct combustion of oil shale is viable [6]. e dark color is associated with the total organic carbon (TOC) content and various kerogen types and their sources [7].
In Egypt, many studies have focused on the speci c stratigraphy and geology of oil shale deposits [6,[8][9][10][11]. In the depositional marine environment, biological productivity regulates the speci c quality and high OM content [9]. Preserving OM depends on the sedimentation rate and oxygen level. X-ray powder di raction (XRD) results of the black shale samples in the Maydoum quarry (west Nile Valley) revealed that montmorillonite and kaolinite are the major clay phases, whereas Ca and Qz are mostly nonclay minor phases [11]. e amorphous noise in the XRD pattern indicated the high OM content in the black shale samples [11]. In Egypt, black shale has not been well evaluated in the study area. erefore, this work aims to define the geochemical and mineralogical compositions of Eocene/Oligocene black shale deposits using XRD, X-ray fluorescence (XRF), TOC, and total sulfur (TS) analyses for the collected black shale samples. Moreover, seven shale samples were selected and analyzed to evaluate the significant OM content, thermal maturation, and kerogen type using the Rock-Eval pyrolysis instrument.

Geologic Setting and Stratigraphy
Paleogene black shale deposits were distributed along the Nile Valley in the Beni Suef area, south Cairo of Egypt. e study area is marked by excellent successions of shale deposits at two large quarries (Ghaida Al-Sharqia and Maydoum quarries). e Ghaida Al-Sharqia quarry is at latitude 28°55ʹN and longitude 31°2ʹE (east River Nile). e Maydoum quarry is at latitude 29°22ʹN and longitude 31°9ʹE (west River Nile; Figure 1). e successions were measured, sampled, and described in the field for their lithological characteristics and sedimentary structures. Macrofossils were also observed from well-defined fossiliferous beds. e shale deposits of the Ghaida Al-Sharqia quarry occurred in the El Fashn Formation (Middle Eocene; Figure 2). Typically, the El Fashn Formation comprises limestone, shale, and marl intercalations exposed at the Gabal Abiayd east El Fashn area in the Beni Suef area [12]. Stratigraphically, the El Fashn Formation unconformably overlies the Qarara Formation (Middle Eocene) and underlies the Beni Suef Formation (Late Eocene; Saber and Salama, 2017). e presence of planktonic foraminiferal species (Truncorotaloides rohri, Morozovella spp., Truncorotaloides spp., and Acarinina spp.) supports the Late-Middle Eocene (Bartonian) age of the El Fashn Formation [10,13,14].
In the Maydoum quarry, shale deposits occurred in the Dabaa Formation (Oligocene). e Dabaa Formation typically comprises argillaceous and carbonaceous shales, with some glauconitic and sandy limestone interbeds with oysters and benthic foraminifera of the shallow marine environment ( Figure 2). It rests conformably on the Apollonia Formation in the study area, and its age is Oligocene [15,16].

Sampling.
To achieve the study's target, many field trips have been undertaken to collect samples from the Ghaida Al-Sharqia and Maydoum quarries, where variations in the facies exist throughout (Figure 3). e samples were collected from the fresh rocks exposed inside and outside the mines. XRD and XRF analyses determined the mineralogical composition of the shale samples. Twenty-two samples were sent to the StatoChem Services Company to determine the TOC and TS contents. Moreover, seven shale samples were selected and analyzed to determine the quantity, kerogen type, and thermal maturation using Rock-Eval pyrolysis.

Analytical
Methods. Some mineralogical and geochemical analyses (XRD, XRF, TOC, TS, and Rock-Eval pyrolysis) were conducted for the shale samples from Figure 1: Satellite image of the study area (Beni Suef area), Egypt.

Advances in Materials Science and Engineering
Maydoum and Ghaida Al-Sharqia quarries to determine the major and trace elements, OM contents, kerogen types, and thermal maturation. We can summarize the methodology of these geochemical analyses as follows.  Advances in Materials Science and Engineering were generated using a handheld energy-dispersive XRF. e shale samples were strongly crushed to minimize the amount of rock aggregate to <0.063 µm grain size. e crushed samples were analyzed using XRF to define the significant major element composition. Analyses were conducted on a Philips PW 1404WD-XRF using the program POWDER hosted at the National Research Center, Egypt. A mixture of 6 g of the powder sample and 1.5 g of HOECHST C-Wax were homogenized in a vibrating device and pressed into Al-cups (40 mm diameter) at 20 t-pressure.   Advances in Materials Science and Engineering

TOC and TS.
e TOC for twenty-two shale samples of the Maydoum and Ghaida Al-Sharqia quarries was conducted at the StratoChem services lab (Cairo, Egypt) using the LECO C230 carbon analyzer. Before analysis, approximately 0.15 g of the bulk sample was pulverized into a fine powder and weighed in a labeled conical flask. HCL acid was added to remove the inorganic carbon, and the sample was filtered. e filtered sample was placed within a LECO crucible and dried and analyzed. Twenty-two shale samples of the Maydoum and Ghaida Al-Sharqia quarries were also analyzed using the LECO analyzer model SC632 hosted at the StratoChem Services Company, Egypt, to determine TS content. e technique involved removing any obvious contaminant material from the sample, pulverizing it, and weighed in the combustion boat. Add one scoop of the accelerator and mix thoroughly and analyze samples according to the instruction manual.

Rock-Eval Pyrolysis.
e Rock-Eval pyrolysis analysis was conducted on shale samples of the Maydoum and Ghaida Al-Sharqia quarries using Rock-Eval 6 (RE-6). Pyrolysis is degrading OM by heating the sample where oxygen is absent. Before the analysis, obvious contaminants from the sample are removed. Approximately 0.15 g of each sample was pulverized and weighed. Pour the sample into the RE-6 crucible. Place the crucible in the RE-6 carousel and analyze samples according to the instrument manual. S1, S2, S3, and Tmax parameters were obtained.

XRD and XRF Data.
Across the Ghaida Al-Sharqia and Maydoum quarries, XRD was used to determine the mineralogy of shale samples.

Advances in Materials Science and Engineering
Ghaida Al-Sharqia quarry of the El Fashn Formation varies from 0.10 wt% to 2.27 wt%. e TS content reaches 0.58 wt% in the Dabaa Formation but 1.52 wt% in the El Fashn Formation (Table 2). Furthermore, we conducted the Rock-Eval pyrolysis for shale samples of the El Fashn Formation with TOC equal to or above 0.5 wt%; therefore, the shale samples of the Dabaa Formation were neglected, as the TOC values are below 0.5 wt%. e Rock-Eval pyrolysis results indicate the OM, kerogen types, and thermal maturation quantities that will be discussed below.  (Figures 4(a), 4(b)). e recognized clay mineral associations of the analyzed rock samples are identified according to Anthony et al. [18]. Smectite (montmorillonite) and kaolinite are clay minerals detected in the analyzed samples, but chlorite and illite are absent (Figures 4(a), 4(b)). ese study results are similar to a historical study introduced by Zayed et al. [11]. erefore, in both quarries, the presence of smectite and kaolinite in significant quantities indicates black shale deposition in open marine environments and the detrital origin [19,20]. e presence of kaolinite and smectite in the marine environment was attributed to the effective chemical weathering and shale sample deposition in a Advances in Materials Science and Engineering warm humid climate [21].

Discussion
e identified nonclay minerals in the shale samples using XRD are quartz and calcite minerals (Figure 4(a), 4(b)). Calcite was found in most of Nile Valley samples, indicating the marine deposition for these shales [22].

Major and Trace Elements.
e high percentages of the major elements (Table 1) in the black shale deposits of the Dabaa and El Fashn Formations can be used in cement industries, ceramics, and red breaks [8,11]. e trace elements of shale samples of Dabaa and El Fashn formations are critical sources of Sr, Zr, Ba, Zn, V, and Cr used in different chemical industries. e usage of the studied shale in drilling mud industry was supported by the high percentage of Ba in the montmorillonite clay minerals.
According to Pearson's correlation coefficient (r) [22], the SiO 2 is correlated with Al 2 O 3 and Zr (r � 0.60 and 0.67, respectively; Figure 5). us, SiO 2 is terrigenous in origin. Typically, CaO is of biochemical origin, whereas SiO 2 , Al 2 O 3 , TiO 2 , and K 2 O are of terrigenous origin [22]. However, CaO correlates with both SiO 2 and Al 2 O 3 (r � 0.78 and 0.60, respectively; Figure 5) and supports the occurrence of marine shale [23]. e low CaO values as a major oxide in this area (Table 1) reflect that the black shale samples were mostly accumulated in shallow marine environments [22]. According to the trace elements, Ni correlates well with Cr and TiO 2 (r � 0.33 and 0.22, respectively; Figure 5). is correlation and the Ni content in the Dabaa Formation are lower than in the El Fashn Formation (Table 1), reflecting that the shale samples of the Dabaa Formation are mostly deposited in shallow marine environments with low TS. e high oxidation rate and/or weathering decreased the Ni content [22].
Moreover, the slightly positive correlation between Ni vs. TOC and TS reflected that the studied shale samples of Maydoum area were affected by strong weathering and oxidation more than Ghaida Al-Sharqia area. e chemical index of alteration (CIA) is an essential indicator for weathering and paleoclimatic conditions [24]. When the CIA value is 50-70, it reflects an arid and cold climate. On the other side, when it is 70-85, it indicates a humid and warm climate. Although most of CIA values in El Fashn and Dabaa formations are less than 50, the weathering line shows a semihumid climate in Ghaida area shifting to semiarid conditions in Maydoum area that indicated by cross plot of Al 2 O 3 + Na 2 O + K 2 O vs. SiO 2 [25]; Figure 6).

Organic Carbon/Sulfur
Contents. TOC represents the hydrocarbon potential of formations [26][27][28][29][30]. e richness of OM substantially depends on parameters, such as biological productivity, sedimentation rate, clay mineralogy, oxygenation levels, and sea-level change [31]. However, preservation is a significant factor in OM richness [32]. is preservation is associated with reduction and oxidation conditions [33,34]. Hakimi et al. [35] stated that a positive relationship between TOC and TS indicates the origin of shale samples. A similar relation was observed for TS and depositional environments. e low sulfur content reflects high accumulation of mostly black shale in the oxidizing   [35,36]). 8 Advances in Materials Science and Engineering environment, but high sulfur refers to shale deposition in a reducing environment [35][36][37]. e TOC values for shale samples of the Dabaa Formation are 0.13 wt% to 0.36 wt%, reflecting a poor source of OM [38]. e organic carbon richness for the black shale of the El Fashn Formation is mostly good, as TOC values were 0.10 wt% to 2.27 wt%. However, the TS reached 0.58 wt% at the Dabaa Formation but recorded 1.52 wt% at the El Fashn Formation (Table 2). e relationship between TOC and TS ( Figure 7) indicates that the Dabaa Formation was deposited in Oligocene/Miocene of very shallow marine environments (lacustrine) of warm and oxic conditions, oxidizing the OM and forming a thick amount of inert OM (black carbon) [39].
e El Fashn Formation was deposited in Middle Eocene in shallow marine environments with mostly suboxic conditions, causing slightly good preservation of OM (2.27 wt%). e presence of microfaunal, especially foraminifera, confirmed these results. All results matched well with the model (Figure 8), showing the relationship between depositional conditions, microfauna types, TOC, H/C ratio, and OM types [40].

Kerogen Type and Depositional Environments.
e hydrogen index (HI) values are used to show the kerogen types [26,35,[40][41][42][43] [44,45]. HI below 150 mg/g refers to kerogen type III and can generate gas [38,40,43]. In this study, the HI values of the Dabaa Formation did not record in the Rock-Eval pyrolysis technique due to the low TOC values (Table 2), representing a residue of black carbon. However, the HI values of the black shale samples of the El Fashn Formation are largely varied, from 18 to 45 mg/g (Table 2), indicating kerogen type III that can generate natural gas ( Figure 9). is kerogen type indicates that the El Fashn Formation in the Ghaida Al-Sharqia quarry was deposited in a marine environment.

5.5.
ermal Maturation and Generation Potential. Espitalié et al. [46] and Peters [38]    Oxygen Index (OI; mg CO 2 /g TOC) Hydrogen Index (HI; mg HC/g TOC) Type III Type II EI Fashn (black shale) Figure 9: Diagram showing relationship between HI and OI, and the type III for the organic matter from El Fashn black shale samples (modified after [28,40]). between 435°C and 465°C and PI between 0.2 and 0.4. In our study, the Tmax values of the El Fashn Formation shales were between 421°C and 430°C and PI between 0.13 and 0.31 (Table 2), indicating immature source rocks. To evaluate the maturity and kerogen type, shale data were plotted on an HI versus Tmax diagram [46]; Figure 10). e results indicated that the shales contained immature kerogen type III that, by surface retorting, can generate natural gas.
Finally, the shale deposits in the study area are none laminated with benthic foraminifera and oysters that confirmed the deposition in oxic to suboxic shallow marine environments. e Lagenids and Buliminids foraminifera in the shale deposits of the studied area suggest low oxygen level. However, the presence of these genera such as Lenticulina and Cibicidoides indicates oxic environments [47]. All results matched well with the model in Figure 8, showing a relationship between depositional conditions, microfauna types, TOC, H/C ratio, and OM types [40].

Conclusions
By the end, the main results of this work can be summarized in the following points [49,50]: (i) e higher smectite and kaolinite clay phase contents indicate detrital origin and deposition in shallow marine environments. (ii) e high percentage of SiO 2 , Fe 2 O 3 , and Al 2 O 3 of the Dabaa and El Fashn formations supported the usage of the studied shale in cement industries and red breaks. Moreover, the high percentage of Ba in montmorillonite of the studied shale will be more applicable in the drilling mud producing. (iii) e TOC results reflected that the Dabaa Formation (Oligocene) at the Maydoum quarry has poor OM content related to low preservation efficiency and oxic environments that oxidized some OM, forming black carbon. However, the El Fashn Formation (Middle Eocene) at Ghaida Al-Sharqia has good OM content due to deposition in shallow marine environments with suboxic conditions that led to good OM preservation. (iv) Rock-Eval pyrolysis results of the black shale indicated kerogen type III of terrestrial origin of the El Fashn Formation due to the good preservation of the high OM content in suboxic shallow marine environments.  (v) ermal maturation from the geochemical parameters of Tmax and PI from Rock-Eval pyrolysis reflected that the collected shale deposits in the El Fashn Formation are highly immature, as observed in the outcrop or near the surface; however, during surface retorting, it can generate natural gas.

Data Availability
e geochemical data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.