Paleoredox Conditions, Paleoproductivity, and Terrigenous Sediment Influx of the lLower-Middle Cenomanian Strata in the Abu Gharadig Basin, Northern Egypt

: During the Late Cretaceous (Cenomanian), significant disruptions in the carbon cycle, global warming, and episodes of oceanic anoxia occurred, leading to the deposition of organic carbon-rich sediments. In well BED2-3, located in the BED2 gas field within the Abu Gharadig Basin (north Western Desert, Egypt), the lower-to-middle Cenomanian Bahariya Formation displays thick alternating layers of sandstones, siltstones, and shales. Detailed geochemical analyses were conducted on thirty-three cutting samples from the Bahariya Formation, focusing on total organic carbon (TOC), whole-rock elemental geochemistry, and carbonate content. These geochemical measurements provided valuable information regarding paleoredox conditions, marine biological productivity, terrigenous sediment influx, weathering and paleoclimate conditions, and mechanisms influencing organic matter accumulation. The enrichment factors (EF) of redox-sensitive trace elements were utilized to infer oxygenation conditions and marine biological productivity during the deposition of the Bahariya Formation. The stratigraphic distribution of redox-sensitive elements allowed for the Bahariya Formation to be categorized into lower and middle-upper intervals. The results revealed that the lower interval exhibited strong-to-enriched EF values of redox-sensitive elements and fair-to-rich TOC content, indicating a prevalent anoxic setting during deposition. In contrast, the middle-upper interval displayed weakly-to-slightly enriched EF values with poor-to-fair TOC content, suggesting deposition under oxic-suboxic redox conditions. By examining Al-normalized redox-sensitive ratios and their correlations with TOC content, significant relationships were observed in the lower interval, indicating a coupling between the enrichment of redox-sensitive elements and organic matter. This suggests enhanced biological productivity during deposition of the lower interval compared to the relatively low productivity during deposition of the middle-upper interval of the formation. These conditions controlled the production and preservation of organic matter in the lower interval, while the middle-upper interval suffered from organic matter dilution and destruction due to an increased influx of terrigenous material and lower biological productivity. Geochemical proxies related to detrital materials provided evidence of alternating terrigenous sediment flux, consistent with shifts between coarse-and fine-grained fractions and related facies of sandstones, siltstones, and shales. These findings align with active continental weathering in the source terrane and deposition under enhanced warm-humid climatic conditions, with intermittent arid-to-semi-arid phases. These conclusions are further supported by the palynomorph assemblages and clay mineralogy within the Bahariya Formation.


Introduction
During the Cenomanian transgression, thick sequences of siliciclastic and carbonate sediment were deposited in the southern Tethys, such as in the north Western Desert of Egypt [1,2].The north Western Desert was a major shelf area attested to the deposition of a complete petroleum system during the Late Cretaceous.It is considered one of the major oil and gas provinces in Egypt.In the past few decades, optimal hydrocarbon exploration activities in the north Western Desert have led to successful production from the Upper Cretaceous strata of the Abu Roash Formation [1].
Recently, there has been significant focus on investigating the characteristics, quantities, and qualities of organic matter for hydrocarbon exploration.This attention aims to enhance our understanding of source rock exploration, which can be more effectively used in regions having high hydrocarbon potential, thereby mitigating production risks.The organic carbon content in sediments is influenced by several controlling factors, including paleoredox conditions in bottom and pore waters, marine biological productivity, terrigenous sediment influx, paleoclimate and associated hydrological processes, continental weathering, and the rate of sedimentation [3][4][5].Furthermore, organic carbon in sediments can be influenced by positive mechanisms, such as the production and preservation of organic matter, two processes that are facilitated by enhanced biological productivity and reduced oxygenation conditions.Conversely, the negative influences include organic matter dilution resulting from sediment fluxes into the basin and/or destruction through increased oxidation in bottom and pore waters.Thus, to gain insights into these environmental variables, quantifying the organic carbon content and conducting bulk-rock geochemical analyses are crucial.
The Abu Gharadig Basin in northern Egypt (Figure 1) has emerged as a prominent area of focus for hydrocarbon exploration and production because it contains a complete petroleum system developed by a complex tectonic evolution.Extensive research efforts have been directed toward this basin, aiming to enhance our understanding of its geology and potential for hydrocarbon resources [1].The Late Cretaceous (Cenomanian) of the Abu Gharadig Basin attested to the thick deposition of siliciclastic sediments of the Bahariya Formation (Figure 2).Numerous studies have been conducted to investigate various aspects of the Bahariya Formation, including palynostratigraphy, palynofacies analysis, as well as paleoenvironmental and sequence stratigraphic reconstructions [6][7][8], source rock evaluation, and paleoclimatic conditions based on geochemical and palynological analyses [9].However, despite these research efforts, there is still a gap in our understanding of certain aspects of the Bahariya Formation.Studies of redox conditions and paleoproductivity, terrigenous sediment influx, and weathering conditions of the Bahariya Formation are still lacking.
Recent investigations of the Bahariya Formation in well BED2-3 (Figure 1) have delved into various aspects such as palynological analysis, sequence stratigraphic reconstruction, and source rock assessment [8,9].Building upon these previous studies, this research aims to provide a comprehensive understanding of the Bahariya Formation through detailed geochemical analyses.Specifically, the study focuses on analyzing total organic carbon (TOC), whole-rock major and trace elements, and carbonate content.The primary objectives of this study are as follows: (1) reconstruct the paleo-redox conditions and marine biological productivity prevalent during deposition of the lower-middle Cenomanian Bahariya Formation; (2) investigate the role of terrigenous sediment flux, weathering intensity, and paleoclimate conditions that were prevalent during the early-middle Cenomanian in this part of the southern Tethys; and (3) interpret the mechanisms governing the quantity of the organic matter in terms of abundance and distribution within the Bahariya Formation, such as the factors controlling production and preservation potential versus dilution and decomposition of labile organic matter.Illustrating a location map of the Abu Gharadig Basin, along with other sedimentary basins, major highs, and structural features that have a significant influence on northern Egypt.The map also highlights the specific location of the BED2 gas field and the location of the studied BED2-3 well (modified after EGPC [1]).Recent investigations of the Bahariya Formation in well BED2-3 (Figure 1) have delved into various aspects such as palynological analysis, sequence stratigraphic reconstruction, and source rock assessment [8,9].Building upon these previous studies, this research aims to provide a comprehensive understanding of the Bahariya Formation through detailed geochemical analyses.Specifically, the study focuses on analyzing total

Geologic and Stratigraphic Settings
The tectonic history of the Abu Gharadig Basin can be traced back to the late Paleozoic.During this time, the north Western Desert, including the Abu Gharadig Basin, began to take shape as the Hercynian tectonics became activated [10].It experienced several tectonic activities from the Paleozoic to the Cenozoic and is considered an active tectonic province because of its location on the unstable shelf (Figure 1) [11,12].The main phase of basin development, however, occurred during the Jurassic and Cretaceous periods [12,13].In the Middle Jurassic, the central Atlantic Ocean started to spread, causing a left-lateral drifting of the African continent relative to Europe [11,14,15].This was accompanied by the activation of the major mountain-building Alpine Orogeny.The combined effects of these tectonic processes led to the deepening of the Neo-Tethys Ocean, which, in turn, facilitated the deposition of thick sequences of siliciclastic and carbonate sediments across northern Egypt, including the Abu Gharadig Basin.
This was followed by successive tectonic events from the Early-to-Late Cretaceous that further shaped the Abu Gharadig Basin (Supplementary Figure S1).At this time, the region experienced the development of NW-SE trending tensile stresses and active rifting, and a sinistral (left-lateral) drift of North Africa, which resulted in homoclinal rotation of the Abu Gharadig Basin [12,15,16].Additionally, the formation of E-W listric growth faults played a crucial role in controlling the subsidence of the basin (Supplementary Figure S1).In Turonian, a significant uplift and basin inversion in north Western Desert took place in response to the dextral (right-lateral) drift of Africa-Europe [16].Further right-lateral displacement of Africa against Laurasia controlled NW compressive forces and the development of the Syrian Arc System in northern Egypt and the Middle East [17].The tectonic history, which involved the development of major structural highs, rifting, and basin inversions, led to the formation of a complete petroleum system within the Abu Gharadig Basin.
The Abu Gharadig Basin is an E-W elliptical basin that covers a large area (18,000 km 2 ) between longitudes 29 • 15 ′ and 27 • 15 ′ E and latitudes 30 • 15 ′ and 29 • 00 ′ N (Figure 1).The studied well BED2-3 is in the Bedr El Din-2 field, which is located in the Mid-Basin Arch of the major subsiding depocenter of the basin (Figure 2).The central part of the basin contains several NE-SW plunging anticlines, representing the major style of hydrocarbon entrapment (Figure 1) [14].
The Bahariya Formation was first introduced based on a thick interval from the surface outcrop sections in the Gebel El Dist, Bahariya Oasis [6].In the BED2-3 well, the Bahariya Formation shows a thick stratigraphic succession (208 m in thickness) of siliciclastic sediments (Figure 2).It consists of dark-gray-to-greenish-gray fissile shale and siltstone interbedded with white medium-to-coarse-grained subangular sandstones with high porosity and permeability (Figure 2).In parts, the sandstones are partly glauconitic with calcareous and ferruginous cements, and patchy oil saturates at several intervals.The sandstones of the Bahariya Formation in the Abu Gharadig Basin are considered a high-quality reservoir [1].The Bahariya Formation rests conformably above the Kharita Formation and underlies the Abu Roash Formation (Figure 2).Recent palynological achievements erected four interval zones within the Bahariya Formation from the Gindi Basin, including the lowermost Cenomanian Trilobosporites laevigatus, lower Cenomanian Cretacaeiporites densimurus and Elaterosporites klaszii zones, and lower-middle Cenomanian Afropollis jardinus zone [2].Similar age constraints were reported for the same interval from the BED2-3 well in the Abu Gharadig Basin [8].Palynofacies analysis of the Bahariya Formation in the BED2-3 well revealed a phytoclast-dominated assemblage for the lower part and phytoclast and amorphous organic matter-dominated assemblage within the middle-upper part [8].These two assemblages indicated the deposition of the lower Bahariya in fluvial to fluvio-deltaic and marginal marine settings, whereas the middle-upper Bahariya was deposited in an inner neritic shelf.Interestingly, in the adjacent Gindi Basin (North Qarun-1x well), the Bahariya Formation was categorized into three palynofacies assemblages suggesting the deposition from fluvio-deltaic-to-shallow marine similar environments [2].In the Shushan Basin (Salam-17 well), palynofacies and palynomorph analyses of the lower Bahariya Formation indicated a predominantly regressive phase of relative sea level, characterized by distributary and tidal channels, and deltaic settings [7].

Materials and Methods
A total of thirty-three cutting rock samples were collected from the Bahariya Formation in the BED2-3 well at depth intervals from 2238 m to 2446 m (6-12 m sample spacing) (Figure 2).The study well BED2-3 is located at a latitude 29 • 53 ′ 13.23 ′′ N and a longitude 27 • 42 ′ 11.27 ′′ E, and was drilled by Badr-El Din Petroleum Company (in 2000) at the horst block of the northwestern part of the Mid-Basin Arch in the Abu Gharadig Basin (Figure 1).

Whole-Rock Geochemical Composition
All samples were analyzed for bulk-rock quantitative composition of major and trace elements using an energy-dispersive X-ray fluorescence (model hand-held ED-XRF) equipped with an Rh X-ray tube.An aliquot of 10 g of each sample was milled into fine particles (ca. 100 µm) using a digitally operated crushing machine.Each powdered sample was placed on a thin plastic wrap in a 25 mm diameter plastic sample cup and put on top of the Bruker AXS "TRACER IV-SD" (Billerica, MA, USA).The dual mode analysis was used to measure bulk geochemical composition of samples under two different excitation energies.Low-and high-excitation energies worked at 15 kV (to detect major elements along with V, Ni, and Cr) and 40 kV (to measure other trace elements), respectively.Measured major elements include Si, Al, Ca, Mg, Fe, Mn, Ti, K, and P, whereas trace elements include Cr, Co, Ni, V, Sr, Zn, Zr, Ba, Cu, Pb, Ce, and Mo.Spectra (model SPECTRA EDX S2 CONFIGURATION) were loaded in the calibration software of the proprietary Bruker AXS.Internal standards and related calibrations measured by ICP-MS were applied for hand-held ED-XRF software (version 1.1) to provide reliable measurements of major and trace elements.The analytical errors were about ±5% and trace elements detection limits are ±3 ppm.Triplicate measurements were conducted to calculate the reproducibility index and the precision was about ±1.5%.Milling of samples into powder and whole-rock geochemical measurements was carried out at the Department of Geology, University of Vienna.
Redox proxies were calculated for trace elements based on their relative enrichment with respect to the average shale.The formula of enrichment factor (EF) was applied as follows: X EF = (X/Al) sample /(X/Al) average shale [18], where X is the concentration of redox-sensitive trace elements.Redox-sensitive elements can be interpreted in terms of strongly enriched, significantly enriched, enriched, weakly enriched, depleted, and significantly depleted, for the EF values in the range of >10, 10 − 5, 5 − 2, 2 − 1, 1 − 0.5, <0.5, respectively [19,20].

Carbonate Content and Total Organic Carbon (TOC)
Thirty-three samples were measured for the carbonate content by treating an aliquot of each powdered sample in HCl (25%) using the Müller-Gastner Bomb [21] at the Department of Geology, University of Vienna.
Because of sample contamination with oil-based mud, thirty-three samples were extracted by a mixture of chloroform-methanol (89:11 v:v) for one day, followed by washing the samples with distilled water and drying in an oven at 50 • C for 4 h.A 60 mg aliquot of each powdered sample was analyzed for the TOC content using the Rock-Eval ® 6 Turbo analyzer (Austin, TX, USA) [22].The TOC analysis was conducted at the Advanced Technology Center of Core Laboratories facilities in Houston (Texas, USA).

Elemental Proxies
Assessing the paleo-redox conditions is conducted based on enrichment factor (EF) values of redox-sensitive trace metals.Stratigraphic trends of EF of certain elements within the Bahariya Formation, such as V, Cr, Ni, Zn, and Cu, show generally similar patterns to each other and to the TOC content (Figure 3).The EF values of V are the highest compared to other redox-sensitive elements such as Cr, Ni, Zn, and Cu.The V EF values are in the range of 34.2-2.6 (13.9 on average), whereas Cr EF and Zn EF are in the range of 8.8-1.0 (2.9 on average) and 6.1-0.2 (2.2 on average), respectively.Ni EF (6.4-0.4) and Cu EF (3.8-0.7)show the lowest average values of 1.3 and 1.8, respectively (Figure 3).

Elemental Proxies
Assessing the paleo-redox conditions is conducted based on enrichment factor (EF) values of redox-sensitive trace metals.Stratigraphic trends of EF of certain elements within the Bahariya Formation, such as V, Cr, Ni, Zn, and Cu, show generally similar patterns to each other and to the TOC content (Figure 3).The EF values of V are the highest compared to other redox-sensitive elements such as Cr, Ni, Zn, and Cu.The VEF values are in the range of 34.2-2.6 (13.9 on average), whereas CrEF and ZnEF are in the range of 8.8-1.0 (2.9 on average) and 6.1-0.2 (2.2 on average), respectively.NiEF (6.4-0.4) and CuEF (3.8-0.7)show the lowest average values of 1.3 and 1.8, respectively (Figure 3).The evaluation of terrigenous sediment flux into the basin is typically carried out through the use of geochemical ratios, such as Si/Al, Zr/Al, and Ti/Al.The stratigraphic patterns of Si/Al and Zr/Al show overall similar trends.In contrast, the Ti/Al ratio exhibits a long-term similar pattern but with short-term smoother peak and trough features.The Si/Al and Zr/Al ratios are in the range of 10.2-2.0 (4.5 on average) and 20.3-1.2 (8.2 on average), respectively (Figure 4).The highest values for both Si/Al and Zr/Al occur in the lower part of the Bahariya Formation.The Si/Al ratio shows a relatively stable pattern, interrupted by two minor peaks in the middle part of the formation.This is followed by a significant increase with a plateau shape in the upper part of the Bahariya Formation.The Ti/Al ratio ranges from 0.51 to 0.01, with an average of 0.13 (Figure 4).The highest abundance of Ti/Al was reported at a depth of 2442 m.The Ti/Al ratio exhibits a long-term The evaluation of terrigenous sediment flux into the basin is typically carried out through the use of geochemical ratios, such as Si/Al, Zr/Al, and Ti/Al.The stratigraphic patterns of Si/Al and Zr/Al show overall similar trends.In contrast, the Ti/Al ratio exhibits a long-term similar pattern but with short-term smoother peak and trough features.The Si/Al and Zr/Al ratios are in the range of 10.2-2.0 (4.5 on average) and 20.3-1.2 (8.2 on average), respectively (Figure 4).The highest values for both Si/Al and Zr/Al occur in the lower part of the Bahariya Formation.The Si/Al ratio shows a relatively stable pattern, interrupted by two minor peaks in the middle part of the formation.This is followed by a significant increase with a plateau shape in the upper part of the Bahariya Formation.The Ti/Al ratio ranges from 0.51 to 0.01, with an average of 0.13 (Figure 4).The highest abundance of Ti/Al was reported at a depth of 2442 m.The Ti/Al ratio exhibits a long-term decreasing trend upward, interrupted by three distinct peaks at depths of 2364 m, 2316 m, and 2286 m (Figure 4).
The weathering conditions during the deposition of the Bahariya Formation are interpreted using geochemical detrital proxies, including the K 2 O/Rb, Rb/Sr, and Al/K ratios.The Rb/Sr and Al/K ratios exhibit slightly similar patterns and range from 0.34 to 0.04 (0.16 on average) and from 6.2 to 0.5 (2.1 on average), respectively (Supplementary Materials, Figure 4).In contrast, the K 2 O/Rb ratio ranges from 525 to 97 (200 on average) and shows a long-term falling trend, punctuated by minor peaks.The weathering conditions during the deposition of the Bahariya Formation are interpreted using geochemical detrital proxies, including the K2O/Rb, Rb/Sr, and Al/K ratios.The Rb/Sr and Al/K ratios exhibit slightly similar patterns and range from 0.34 to 0.04 (0.16 on average) and from 6.2 to 0.5 (2.1 on average), respectively (Supplementary Materials, Figure 4).In contrast, the K2O/Rb ratio ranges from 525 to 97 (200 on average) and shows a long-term falling trend, punctuated by minor peaks.

Carbonate Content
The carbonate content of the Bahariya Formation is relatively low and ranges between 19.5% and 13.2%, with an average of 16.4% (Figure 4).The sample at 2256 m is characterized by the highest carbonate content of 29.2% throughout the studied succession (Supplementary Materials, Figure 4).

TOC Content
Within the BED2-3 well, the TOC values of the Bahariya Formation are in the range of 0.3-4 wt% (0.9 wt% on average) (Supplementary Materials, Figure 3).Moderate-to-high TOC values are reported within the lower part of the Bahariya Formation at depths of 2349

Carbonate Content
The carbonate content of the Bahariya Formation is relatively low and ranges between 19.5% and 13.2%, with an average of 16.4% (Figure 4).The sample at 2256 m is characterized by the highest carbonate content of 29.2% throughout the studied succession (Supplementary Materials, Figure 4).

TOC Content
Within the BED2-3 well, the TOC values of the Bahariya Formation are in the range of 0.3-4 wt% (0.9 wt% on average) (Supplementary Materials, Figure 3).Moderate-to-high TOC values are reported within the lower part of the Bahariya Formation at depths of 2349 to 2444 m (1.4 wt% on average).This resulted in separating the lower interval while interpreting the redox conditions during deposition of the studied interval, especially when correlating EF values of redox-sensitive elements and TOC.

Redox Conditions and Role of Biological Productivity
Reconstructing the paleoredox conditions during the deposition of the Bahariya Formation can be conducted by examining the changes in the enrichment of redox-sensitive elements and their relationship to organic matter.The concentration of redox-sensitive elements increases under enhanced oxygen depletion at bottom and pore water settings, and/or in association with available organic matter and sulfides from abiotic or biotic processes [23].Under severe anoxic conditions, trace elements, such as Mo, U, Cr, V, and Co, are efficiently adsorbed from seawater onto bottom water sediments due to their low solubility [19,24].Other trace elements, such as Zn, Ni, Cu, and Cd, are associated with labile organic matter under enhanced bioproductivity and increased oxygen-deprived conditions [19,24].They also occur in association with pyrite after severe organic matter decomposition under active sulfate-reducing bacteria [3,4,25].The accumulation of labile organic matter in sediments can be driven by enhanced surface water biological productivity.The assessment of the biological productivity in the Bahariya Formation is conducted based on the evaluation of the enrichment factor (EF) values of Zn, Ni, and Cu (Figure 3), and the relationship between their Al-normalized ratios and the TOC content (Figure 5A-E).Additionally, the P/Al ratio (Figure 3) and its relationship to TOC content can provide further insights into the role of marine primary productivity (Figure 5F).coupling relationship between the enrichment of these trace metals and organic matt content.The correlations observed provide evidence that the deposition of the lower Bahari Formation was driven by an accelerated input of organic matter under prevailing anox conditions [19,24,26].The strong-to-moderate correlations between the Al-normalized va ues of V, Cr, Zn, Cu, and Ni and the TOC content (Figure 5A-E) indicate a coupling rel tionship between the enrichment of these redox-sensitive elements and the availability organic matter.This suggests that these redox-sensitive elements behaved as micro-nut ents [19].These findings reveal that the lower Bahariya Formation was deposited und enhanced biological productivity and organic matter export, facilitated by increased pr duction and burial under oxygen-deficient settings [3,4].The presence of high abundanc Understanding the provenance and dynamics of these trace elements is for deducing past redox conditions.Before reconstructing the redox conditions of the Bahariya Formation, the EF values of redox-sensitive elements and lithology-related elements, such as Minerals 2024, 14, 632 9 of 17 Si, Al, and Ca, were obtained to evaluate the impact of lithology on the excess enrichment of these elements [26].Notably, strong negative correlations are observed between Al and the EF values of redox-sensitive elements of V EF (r = −0.77,p < 0.001, n = 33), Cr EF (r = −0.81,p < 0.001, n = 33), Zn EF (r = −0.80,p < 0.001, n = 33), Cu EF (r = −0.87,p < 0.001, n = 33), and Ni EF (r = −0.62,p = 0.001, n = 33).Similarly, moderate negative correlations to a lack of correlation are observed between Si and the redox-sensitive elements V EF (r = −0.20,p = 0.26, n = 33), Cr EF (r = −0.55,p < 0.001, n = 33), Zn EF (r = −0.26,p = 0.14, n = 33), Cu EF (r = −0.60,p < 0.001, n = 33), and Ni EF (r = −0.57,p < 0.001, n = 33).Additionally, no correlation is observed between the carbonate content and the EF values of redox-sensitive trace elements (Supplementary Materials).These findings indicate that the specific enrichment of the redox-sensitive trace metals was driven by their authigenic behavior under the prevailing redox conditions at the time of deposition.
Based on the stratigraphic distribution and EF values of redox-sensitive elements and the TOC content, the Bahariya Formation can be distinguished into a lower interval (2444-2394 m) and a middle-upper interval (2394-2238 m) (Figure 3).The lower interval of the Bahariya Formation is characterized by fair-to-rich organic carbon content.These deposits exhibit high to moderate values of V EF , Cr EF , Zn EF , Ni EF , and Cu EF that reach up to 35.2, 8.8, 6.1, 6.4, and 3.8, with an average of 17, 3.9, 3.0, 1.9, and 2.1, respectively (Figure 3).The elevated enrichment values indicate a strong enrichment of V EF compared to significant-to-enriched enrichment levels of Cr EF , Zn EF , Ni EF , and Cu EF .Such enrichment patterns of these redox-sensitive elements suggest that the lower part of the Bahariya Formation was deposited under conditions of enhanced oxygen deprivation in the bottom and pore waters [19].These observations are supported by strong-to-moderate correlations between the redox-sensitive trace elements normalized to Al and the TOC content (V/Al: r = 0.85, p = 0.002, n = 10; Cr/Al: r = 0.60, p = 0.07, n = 10; Zn/Al: r = 0.71, p = 0.02, n = 10; Cu/Al: r = 0.49, p = 0.15, n = 10; and Ni/Al: r = 0.40, p = 0.25, n = 10) (Figure 5A-E).This indicates a coupling relationship between the enrichment of these trace metals and organic matter content.
The correlations observed provide evidence that the deposition of the lower Bahariya Formation was driven by an accelerated input of organic matter under prevailing anoxic conditions [19,24,26].The strong-to-moderate correlations between the Al-normalized values of V, Cr, Zn, Cu, and Ni and the TOC content (Figure 5A-E) indicate a coupling relationship between the enrichment of these redox-sensitive elements and the availability of organic matter.This suggests that these redox-sensitive elements behaved as micronutrients [19].These findings reveal that the lower Bahariya Formation was deposited under enhanced biological productivity and organic matter export, facilitated by increased production and burial under oxygen-deficient settings [3,4].The presence of high abundances of terrestrial palynomorphs, such as spores and pollen, within the lower Bahariya Formation further supports the evidence of enhanced organic matter runoff [8].Additionally, the high concentration of plant-derived material, including phytoclasts, and the presence of Type III kerogen of gas-prone hydrocarbon suggest the deposition of lower Bahariya occurred in proximity to fluvio-deltaic and marginal shallow marine environments [9].
Phosphorous (P) plays a crucial role in various metabolic processes within marine ecosystems.Under conditions of bottom water oxygen depletion, remobilization and diffusion of P from seafloor sediments can occur, leading to the release of this essential nutrient into the water column [27,28].P regeneration into the bottom waters may, in turn, enhance marine biological productivity through a positive feedback mechanism [27].In this context, the relationship between the P/Al ratio and TOC content provides valuable insights into the role of biological productivity during deposition.The lower interval of the Bahariya Formation shows a strong linear correlation between the P/Al ratio and TOC content (r = 0.75, p = 0.01, n = 10), suggesting enhanced biological productivity likely occurred during deposition (Figure 5F).This positive correlation further suggests that periods of enhanced marine primary productivity led to increased organic matter accumulation and preservation within the lower Bahariya Formation.
In contrast to the lower interval, the middle-upper interval of the Bahariya Formation (spanning 2394-2238 m) is characterized by poor-to-fair TOC content, ranging from 0.3 to 0.9 wt%, with an average of 0.7 wt% (Figure 3).This part of the formation exhibits moderate-to-low values of Cr EF , Zn EF , Ni EF , and Cu EF that are in the range of 5.1-1.4(average 2.5), 3.5-0.9(average 1.8), 2.7-0.4 (average 1.0), and 3.0-1.0(average 1.7), respectively (Figure 3).These diminished enrichment levels indicate only weakly-to-slightly enriched conditions for these redox-sensitive elements.The overall enrichment patterns imply a slightly higher oxygenation level in this part of the Bahariya Formation compared to the lower interval, indicating oxic to suboxic redox conditions in the bottom and pore waters [19,20,26].This interpretation is consistent with the moderate-to-weak correlations observed between the Al-normalized redox-sensitive elements and the TOC content (Cu/Al: r = 0.36, p = 0.09, n = 23; Cr/Al: r = 0.28, p = 0.19, n = 23; Zn/Al and Ni/Al: r = 0.26, p = 0.23, n = 23; and V/Al: r = 0.24, p = 0.27, n = 23) (Figure 5A-F).These relationships suggest a weakly coupled relationship between the enrichment patterns of redox-sensitive metals and concentrations of organic matter, indicating that the organic carbon export was partially controlled by the redox conditions.Additionally, the weak correlations imply relatively low surface water biological productivity, which may have hindered increased organic matter production and burial due to enhanced respiration [3,4].Similarly, a moderate correlation between the P/Al ratio and TOC content is observed for the middle-upper interval of the Bahariya Formation (r = 0.33, p = 0.12, n = 23), suggesting limited P regeneration and diffusion under the oxic-suboxic conditions, and thus a relatively low biological marine productivity during the deposition of this part of the Bahariya Formation (Figures 3 and 5F).In contrast, the V EF and Cr EF show strong enrichment to enriched values with remarkable peaks at depths of 2304-2268 m, ranging from 32.0 to 5.7 (average 18.9) and 5.1 to 1.4 (average 3.1), respectively (Figure 3).However, no correlations are observed between TOC content and V EF (r = 0.02) and Cr EF (r = −0.03)at these depths, suggesting a decoupling relationship.The elevated EF values of these redox-sensitive elements are likely controlled more by lithologic composition, as indicated by the strong negative correlations with carbonate (V EF : r = −0.68;Cr EF : r = −0.69)and silica contents (V EF : r = −0.69;Cr EF : r = −0.61)(not shown) [4,5].

Assessing the Terrigenous Sediment Flux
Evaluating the role of detrital sediment fluxes and paleo-weathering conditions is crucial to understanding basin infilling processes and their impact on the sedimentary environment and organic matter availability and preservation in the sedimentary rock record.Terrigenous material can introduce variations in the bulk geochemical composition and mineral-associated facies of sedimentary rocks.This is because several factors control the pathways of sediment transport, such as changes in the energy of riverine runoff, wave and storm action, and wind action.These factors can result in shifts in the grain size distribution of siliciclastic mineral components, including elements such as titanium (Ti), zirconium (Zr), silicon (Si), aluminum (Al), potassium (K), and iron (Fe).Si is predominantly found in quartz and clay minerals, while Al is more common in clay mineral fractions.The Si/Al ratio is widely used to track changes in sediment grain size and the relative abundance of sand, silt, and clay [29].Ti typically occurs in sand-and silt-sized sediment fractions, as well as in heavy minerals like augite, ilmenite, titanite, and rutile, and tends to accumulate earlier than Al-bearing minerals [30].Zr is concentrated in heavy mineral fractions such as detrital zircon grains in the sand-and silt-size range.In this context, analyzing proxies like Si/Al, Zr/Al, and Ti/Al ratios can provide insights into changes in terrigenous sediment flux, grain size variations, proximity to detrital sources, and sea/lake level fluctuations [30][31][32][33][34].
The lower part of the Bahariya Formation (spanning 2444-2394 m) exhibits distinct characteristics in terms of geochemical ratios.At a depth of 2442 m, there is a significant peak in the Si/Al ratio, followed by a sustained rise and plateau between depths of 2430 m and 2406 m (Figure 4).These ratios exceed the average values of the Post-Archaean Australian Shale (PAAS, 3.32) and the Upper Continental Crust (UCC, 4.33), indicating an increased influx of terrigenous sediment and a shift toward larger grain size fractions [30], potentially transitioning from shale to siltstone and/or coarse sandstone [32,34].Similarly, the Zr/Al and Ti/Al ratios show similar trends to the Si/Al ratios, suggesting increased inputs of siliciclastic and coarser detrital materials, likely from nearby sources.The lithological composition of the lower Bahariya Formation aligns with these variations in detrital sediment proxies, with a transition from organic matter-rich shales to siltstone and organic matter-lean coarse-grained sandstones, accompanied by a decrease in carbonate content (Figure 4).However, the subsequent changes in the ratios, including the peaks and plateau patterns, likely indicate shifts in the sediment provenance, transport mechanisms, and depositional environments within the basin.The minor plateau observed in the Ti/Al ratio, compared to the more distinct plateaus in Si/Al and Zr/Al, may be attributed to variations in the mineralogy of the source terrane, influenced by provenance and weathering intensity [33,35].Furthermore, the geochemical composition changes observed in the clastic facies of the lower Bahariya Formation align with its mineralogical composition.The SiO 2 -Al 2 O 3 -CaO ternary plot (Figure 6), commonly used to illustrate lithological and mineralogical differences in sediments [18], indicates that the lower Bahariya samples mostly fall below the line of average shale composition.This suggests a slightly higher contribution of quartz-grained size fractions compared to clay-size particles, consistent with the peaks observed in Si/Al, Zr/Al, and Ti/Al ratios in this interval.The findings from geochemical proxies are supported by the analysis of palynomorph and palynofacies compositions, which reveal the dominance of pteridophyte spores (averaging 47.5%) and pollen (averaging 29.8%), as well as an abundant content of total phytoclasts, while marine phytoplankton, such as dinoflagellate cysts (averaging 13.3%) and foraminiferal test linings (averaging 9.4%), are relatively diminished [8].
Minerals 2024, 14, x FOR PEER REVIEW 12 of 18 Subsequently, the three proxy indicators show stable patterns with moderate average values, aligning with the lithological composition of shales and siltstones and indicating an enhanced input of fine-grained sediment fractions [32,34].Another notable pattern emerges from the Si/Al, Ti/Al, and Zr/Al ratios in the upper part of the Bahariya Formation, which corresponds to a gradual coarsening of sediment fractions and a facies transition from shale to silt-and sand-sized particles [30].Furthermore, the samples from the middle-upper interval of the Bahariya Formation plot within the SiO2-Al2O3-CaO ternary diagram (Figure 6) primarily align with the average shale composition [18].Only a few samples exhibit a slight increase in quartz content, which is consistent with the presence of sandstone interbeds in this interval (Figure 6).

Paleoclimate and Weathering Conditions
Changes in paleoclimatic conditions and related factors, such as precipitation, temperature, and vegetation cover, can have a significant impact on the weathering intensity of the provenance terrane.During periods of more humid and warm climates, increased precipitation and higher temperatures can enhance continental weathering processes and vice versa [36,37].This leads to the breakdown of minerals, increased dissolution, and alteration of rock compositions [30].Changes in continental weathering can be assessed by integrating detrital geochemical proxies, such as Rubidium (Rb), Al, and K. Rb is a large alkali metal cation that tends to be retained in clay-rich layers and is preferentially adsorbed onto clay mineral surfaces during the weathering process [38].Unlike the smaller strontium ion (Sr 2+ ), Rb is more enriched in carbonate mineral fractions, and can be more easily leached out of the weathered material and transported through water pathways [39].The contrasting behavior of Rb and Sr during weathering and their different sedimentological affinities make them useful geochemical proxies.For example, the Rb/Sr ratio (Figure 4) can provide insights into the weathering conditions at the source area.The middle-upper interval of the Bahariya Formation (2394-2238 m) displays cyclic trends in Si/Al, Zr/Al, and Ti/Al ratios, reflecting the influence of sedimentary processes (e.g., sediment sources, provenance terrane, sediment sorting, and/or grain size distribution) and environmental conditions (e.g., sea level change, terrestrial/riverine influx, and hydrological cycle) during that time (Figure 4) [30].Specifically, at depths ranging from 2376 to 2340 m, the Zr/Al ratio exhibits a distinct plateau, which differs from the single peak observed in the Si/Al and Ti/Al ratios (Figure 4).This pattern suggests fluctuations in sediment sources and depositional environments, particularly indicating an increase in Zr-associated heavy minerals.These minerals, originate from granitic and/or metamorphic rocks and are highly resistant to weathering [30].In agreement with this interpretation, the lithological composition of this interval is dominated by a thick sandstone layer, which implies the accumulation of coarse-grained episodic sediment input [30].Subsequently, the three proxy indicators show stable patterns with moderate average values, aligning with the lithological composition of shales and siltstones and indicating an enhanced input of fine-grained sediment fractions [32,34].Another notable pattern emerges from the Si/Al, Ti/Al, and Zr/Al ratios in the upper part of the Bahariya Formation, which corresponds to a gradual coarsening of sediment fractions and a facies transition from shale to silt-and sand-sized particles [30].Furthermore, the samples from the middle-upper interval of the Bahariya Formation plot within the SiO 2 -Al 2 O 3 -CaO ternary diagram (Figure 6) primarily align with the average shale composition [18].Only a few samples exhibit a slight increase in quartz content, which is consistent with the presence of sandstone interbeds in this interval (Figure 6).

Paleoclimate and Weathering Conditions
Changes in paleoclimatic conditions and related factors, such as precipitation, temperature, and vegetation cover, can have a significant impact on the weathering intensity of the provenance terrane.During periods of more humid and warm climates, increased precipitation and higher temperatures can enhance continental weathering processes and vice versa [36,37].This leads to the breakdown of minerals, increased dissolution, and alteration of rock compositions [30].Changes in continental weathering can be assessed by integrating detrital geochemical proxies, such as Rubidium (Rb), Al, and K. Rb is a large alkali metal cation that tends to be retained in clay-rich layers and is preferentially adsorbed onto clay mineral surfaces during the weathering process [38].Unlike the smaller strontium ion (Sr 2+ ), Rb is more enriched in carbonate mineral fractions, and can be more easily leached out of the weathered material and transported through water pathways [39].The contrasting behavior of Rb and Sr during weathering and their different sedimentological affinities make them useful geochemical proxies.For example, the Rb/Sr ratio (Figure 4) can provide insights into the weathering conditions at the source area.Additionally, K 2 O/Rb and Al/K ratios can also be used to trace paleoclimatic variations (Figure 4) [29,40,41].
During phases of increased weathering conditions, it is commonly observed that the Rb/Sr ratios tend to increase, while the K 2 O/Rb ratios decrease relative to the average values of the UCC, which are >1 and 252, respectively [30,38].The detrital Al/K ratio can provide additional insights into the continental weathering of the source terrane.Higher Al/K values indicate a greater clay content, predominantly kaolinite, resulting from intense weathering [41].Conversely, low Al/K values suggest an enrichment of potassium-rich clay fractions due to continental weathering [41].Within the lower part of the Bahariya Formation, moderate K 2 O/Rb ratios are observed, with average values around 231, close to the UCC average values (Figure 4).This suggests intensified hydrological cycle and continental weathering.However, the Rb/Sr ratios in this interval exhibit a gradual increase but remain relatively low with average values of 0.16, compared to the UCC average of 0.32 (Figure 4).A negative correlation (r = −0.61,p = 0.06, n = 10) is observed between the Al/K versus Si/Al ratios, indicating an increasing trend in weathering conditions (Figure 7).The middle-upper interval of the Bahariya Formation shows a long-term decrease in the K 2 O/Rb ratio.In contrast, the Al/K and Rb/Sr ratios display relatively stable patterns, but with higher values compared to the lower interval.Additionally, a strong negative correlation (r = −0.70,p < 0.001, n = 23) is observed between the Al/K and Si/Al ratios, indicating that the increase in continental weathering coincided with abundant clay fractions relative to coarse-grained quartz grains (Figure 7).These findings suggest prolonged warm and humid climatic conditions, indicative of enhanced continental weathering during the deposition of the Bahariya Formation.
(Figure 7).The middle-upper interval of the Bahariya Formation shows a long-term decrease in the K2O/Rb ratio.In contrast, the Al/K and Rb/Sr ratios display relatively stable patterns, but with higher values compared to the lower interval.Additionally, a strong negative correlation (r = −0.70,p < 0.001, n = 23) is observed between the Al/K and Si/Al ratios, indicating that the increase in continental weathering coincided with abundant clay fractions relative to coarse-grained quartz grains (Figure 7).These findings suggest prolonged warm and humid climatic conditions, indicative of enhanced continental weathering during the deposition of the Bahariya Formation.The interpretation of the aforementioned geochemical detrital poxy data is supported by paleoclimate reconstructions during the deposition of the Bahariya Formation as documented in the study of well BED2-3 by Mansour et al. [9].The studied interval yielded a diverse palynomorph assemblage consisting of spores, pollen, and dinoflagellate cysts.The dominant spore types include ferns such as Cyathidites and Deltoidospora (comprising 8.6 to 62.5% with an average 22.1%), Dictyophyllidites (5.8% on average), Cicatricosisporites (ranging from 0.9 to 15.5% with an average 5.6%), and Crybelosporites (0.8%-12.9%, 3.4% The interpretation of the aforementioned geochemical detrital poxy data is supported by paleoclimate reconstructions during the deposition of the Bahariya Formation as documented in the study of well BED2-3 by Mansour et al. [9].The studied interval yielded a diverse palynomorph assemblage consisting of spores, pollen, and dinoflagellate cysts.The dominant spore types include ferns such as Cyathidites and Deltoidospora (comprising 8.6 to 62.5% with an average 22.1%), Dictyophyllidites (5.8% on average), Cicatricosisporites (ranging from 0.9 to 15.5% with an average 5.6%), and Crybelosporites (0.8%-12.9%, 3.4% on average).These spore assemblages indicate the presence of herbaceous, hygrophilous vegetation that thrived in wetland environments under warm-humid climatic conditions [42], including freshwater marshes [43].Although humidity indicators increase, the middle part of the Bahariya Formation is characterized by abundant records of Elaterate pollen within the Elaterosporites klaszii Interval Zone [9], indicating the presence of Gnetalean plants [44].This suggests a shift toward a more arid-to-semi-arid climate in the middle part of the formation (samples at depths of 2368-2352 m) [9].Therefore, the composition of the palynomorph assemblage, together with moderate-to-high concentrations of kaolinite and smectite, and lesser amounts of illite and chlorite, corroborates warm and humid climates interrupted by a shift toward a more arid-to-semi-arid climate during the deposition of the Bahariya Formation, [9].

Factors Controlling Organic Carbon Accumulation
The factors influencing efficient organic carbon burial have been extensively studied to provide insights into the mechanisms governing its abundance.Some of the key factors include the lithological composition and sedimentological processes within carbonate and siliciclastic facies in relation to the export of organic carbon [5,45], sedimentation rate, changes in relative sea level, redox conditions, role of biological productivity [3,19], paleoclimate and related weathering intensity, hydrological cycles, and terrestrial/riverine runoff, as well as the type of water column, such as upwelling, downwelling, stratified, and high-energy water column [4].Understanding these factors and their interactions provides valuable information into the local to regional processes governing organic carbon preservation potential and its significance within the global carbon cycle.
Generally, the organic matter of the Bahariya Formation is characterized by hydrogen index (HI) values (78 mg HC/g TOC on average) that reflect kerogen Type III of gasprone hydrocarbon and low generation potential due to depleted Rock-Eval S 2 values (0.5 mg HC/g rock), except for the lower interval that shows slightly higher S 2 values of 4.5-1.4mg HC/g rock [9].The deposition of the lower Bahariya interval occurred during prevalent conditions of enhanced surface water biological productivity under deficient, anoxic settings, and increased terrestrial/riverine input [8,9].These conditions likely led to a well-stratified water column and the preservation of moderate-to-high amounts of organic carbon [4,8], with the dominance of active rifting and spreading in the north Western Desert basins [11].This active tectonic setting likely caused a relatively low relief fluvio-deltaic belt intermittent by marginal marine inundation from the Tethys Ocean in the southern part of the Western Desert [2,6].Consequently, there was limited water mass exchange and restricted settings with a stagnant water column during deposition, which aligns with the adsorption of high amounts of redox-sensitive elements into the shales and siltstones of the lower Bahariya Formation.Therefore, oxygen-deprived and enhanced water column stratification conditions controlled organic matter production and the enhanced preservation and burial of organic carbon.Furthermore, the lower part of the Bahariya Formation exhibited low carbonate production in the water column, which is consistent with the efficiency of coarse clastics and detrital clay mineral accumulation.A moderate negative correlation between the TOC and carbonate contents (r = −0.48,p = 0.16, n = 10), compared to a weak negative correlation with Si (r = −0.18,p = 0.62, n = 10), indicates enhanced carbon sequestration and preservation through clay mineral fractions such as smectite [46].This suggests that the increased production via enhanced biological productivity and riverine runoff and preservation potential of organic matter in the sediments outweighed the effects of dilution and decomposition of siliciclastic and carbonate components.
The middle-upper interval of the Bahariya Formation appears to be subjected to different paleoenvironmental and ecological conditions during deposition, resulting in organic carbon-lean sediments.Although terrestrial/riverine runoff was predominant during the deposition of this interval, based on the high proportions of spores and pollen versus a minor contribution of marine phytoplankton [8], such a runoff could not contribute to high levels of organic matter production and preservation.This is evident from relatively low TOC values and the predominance of kerogen Type III of terrestrial origin (HI values reached up to 119 mg HC/g TOC, with an average of 77 mg HC/g TOC [9]).This reflects the negative impact of enhanced bottom and water column oxidation of available organic matter during deposition [5].Oxygen-respiring bacteria can easily oxidize high proportions of the labile organic matter under ventilated settings and/or low sedimentation rates [47].This is evidenced by the almost equal average values of translucent (31%) and opaque phytoclasts (25%) of the middle-upper Bahariya Formation samples [9], where the opaque phytoclasts originated from the significant oxidation of the translucent phytoclasts.Furthermore, the lithological composition of this middle-upper part shows successive alternations between shales, siltstones, and sandstones, compared to carbonate interbeds (Figure 4).Notably, the deposition of the former facies occurred during a relatively low surface water biological productivity and increased siliciclastic/terrigenous sediment supply.Therefore, a weak correlation between the TOC content and CaCO 3 of this interval (r = 0.29, p = 0.18, n = 23) is observed, compared to moderate negative correlations between the TOC and SiO 2 (r = −0.64,p = 0.001, n = 23), Al 2 O 3 (r = −0.31,p = 0.15, n = 23), and TiO 2 (r = −0.54,p = 0.008, n = 23).This indicates that the available siliciclastic sediment fractions have a dilution effect and decomposition of the available organic matter, which ultimately controlled the organic carbon-lean deposition in the middle-upper Bahariya interval [4,5,45].

Conclusions
The Bahariya Formation in the BED2-3 well of the Abu Gharadig Basin, north Western Desert of Egypt, was investigated for TOC, major and trace element composition bulk rock geochemistry, and carbonate content.The obtained dataset led to significant conclusions regarding paleo-redox conditions, marine biological productivity, terrigenous sediment influx, continental weathering, and factors influencing the organic matter regime.Enrichment factors of redox-sensitive metals provided insights into the depositional environment of the Bahariya Formation.The results indicated high-to-moderate enrichment levels within the lower interval of the Bahariya Formation, suggesting the prevalence of anoxic conditions during deposition.In contrast, the middle-upper intervals exhibited weakly-to-slightly enriched redox-sensitive elements, indicating prevalent oxic-to-suboxic redox conditions.Significant correlations were observed between the Al-normalized V, Cr, Zn, Cu, and Ni and the TOC content in the lower interval.These findings suggest a coupling relationship between the enrichment of these elements and organic matter, pointing to enhanced marine biological productivity during the deposition of the lower interval.This resulted in increased organic matter production and preservation compared to the middle-upper interval, which experienced the dilution and destruction of organic matter due to the enhanced influx of siliciclastic and carbonate sediments.Geochemical detrital proxies such as Si/Al, Ti/Al, and Zr/Al ratios indicated enhanced terrigenous influx and continuous shifts between fine-and coarse-grain size fractions, corresponding to alternating layers of shale, siltstone, and coarse sandstone.The ratios of K 2 O/Rb, Rb/Sr, and Al/K indicated active continental weathering and deposition of the Bahariya Formation under warm and humid climates interrupted by minor phases of arid-to-semi-arid conditions, which are further supported by recovered palynomorph assemblages and clay mineralogy.

Figure 1 .
Figure1.Illustrating a location map of the Abu Gharadig Basin, along with other sedimentary basins, major highs, and structural features that have a significant influence on northern Egypt.The map also highlights the specific location of the BED2 gas field and the location of the studied BED2-3 well (modified after EGPC[1]).

Figure 2 .Figure 1 .
Figure 2. A depiction of the lithostratigraphic drilling carried out in the BED2-3 well spanning the Albian-lower Miocene interval (expanded to the left) as well as the current study succession and

19 Figure 2 .
Figure 2. A depiction of the lithostratigraphic drilling carried out in the BED2-3 well spanning the Albian-lower Miocene interval (expanded to the left) as well as the current study succession and thirty-two representative samples of the Bahariya Formation, to the right.The predominant lithologies and alternations between sandstones, siltstones, and shales observed within the Bahariya Formation are included to the right.

Figure 2 .
Figure 2. A depiction of the lithostratigraphic drilling carried out in the BED2-3 well spanning the Albian-lower Miocene interval (expanded to the left) as well as the current study succession and thirty-two representative samples of the Bahariya Formation, to the right.The predominant lithologies and alternations between sandstones, siltstones, and shales observed within the Bahariya Formation are included to the right.

Figure 3 .
Figure 3. Stratigraphic distribution of TOC content as well as enrichment factor (EF) values of redoxsensitive elements and P/Al ratio in the Bahariya Formation.

Figure 3 .
Figure 3. Stratigraphic distribution of TOC content as well as enrichment factor (EF) values of redox-sensitive elements and P/Al ratio in the Bahariya Formation.
decreasing trend upward, interrupted by three distinct peaks at depths of 2364 m, 2316 m, and 2286 m (Figure4).

Figure 4 .
Figure 4. Stratigraphic distribution chart of the carbonate content as well as geochemical detrital proxies used to reconstruct the role of terrigenous sediment flux and weathering conditions during deposition of the Bahariya Formation.

Figure 4 .
Figure 4. Stratigraphic distribution chart of the carbonate content as well as geochemical detrital proxies used to reconstruct the role of terrigenous sediment flux and weathering conditions during deposition of the Bahariya Formation.

Minerals 2024 ,
14, x FOR PEER REVIEW 9 of

Figure 5 .
Figure 5. (A-F) Cross-plots of Al-normalized trace elements and their correlations with the TO content of the Bahariya Formation samples.

Figure 5 .
Figure 5. (A-F) Cross-plots of Al-normalized trace elements and their correlations with the TOC content of the Bahariya Formation samples.

Figure 6 .
Figure 6.Ternary diagram between the three endmembers SiO2, Al2O3, and CaO used to reveal different lithological characteristics of the Bahariya Formation samples in the BED2-3 well.Most samples scatter around and below the line of average shales [18].

Figure 6 .
Figure 6.Ternary diagram between the three endmembers SiO 2 , Al 2 O 3 , and CaO used to reveal different lithological characteristics of the Bahariya Formation samples in the BED2-3 well.Most samples scatter around and below the line of average shales [18].

Figure 7 .
Figure 7. Cross plot between the Al/K and Si/Al ratios used to reveal the weathering activity and grain size of terrigenous material input during deposition of the Bahariya Formation [40,41].

Figure 7 .
Figure 7. Cross plot between the Al/K and Si/Al ratios used to reveal the weathering activity and grain size of terrigenous material input during deposition of the Bahariya Formation [40,41].