Research 50 (2014) 38e51

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Cretaceous Research

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Palaeoecological and post-depositional changes recorded in CampanianeMaastrichtian black shales, Abu Tartur plateau, Egypt

Moataz El-Shafeiy a,b,*, Daniel Birgel c, Ahmed El-Kammar a, Ahmed El-Barkooky a, Michael Wagreich c, Omar Mohamed d, Jörn Peckmann c a Geology Department, Faculty of Science, Cairo University, Egypt b MARUM e Center for Marine and Environmental Sciences, University of Bremen, Germany c Department of Geodynamics and Sedimentology, University of Vienna, Austria d Minia University, Faculty of Sciences, Geology Department, El-Minia, Egypt article info abstract

Article history: The Upper Cretaceous black shales of Egypt are part of the worldwide belt of Late Cretaceous organic-rich Received 20 November 2013 shales. Black shales are particularly prominent in North Africa and the Middle East. In Egypt, these shales Accepted in revised form 30 March 2014 occur in an east-west trending belt extending from the Quseir-Safaga district along the Red Sea to the Available online Kharga-Dakhla land-stretch passing through the Nile Valley. The black shales are hosted mainly in the to Duwi and Dakhla formations. In order to reconstruct palaeoenvironmental Keywords: conditions, the present work focuses on the distribution of organic matter including lipid biomarkers Biomarkers within the Abu Tartur borehole section, which was drilled in 2007 in the Maghrabi-Liffya area. The Rock-Eval Mineral composition kerogen in the Abu Tartur section is of type III with the exception of sedimentary deposits at the Duwi/ CampanianeMaastrichtian Dakhla transition. Low Tmax, odd-over-even predominance of n-alkanes with a commonly high Carbon Black shales Preference Index, good preservation of carboxylic acids and abundant 17b,21b-hopanes and -hopanoic Abu Tartur acids indicate immaturity of the organic constituents in the bitumen. Although thermal maturation was Egypt only low, the preponderance of rearranged steranes (diasterenes) over regular steranes indicates enhanced clay catalysis. Significant allochthonous input typifies the Abu Tartur section deposits, which are characterized by high contents of long-chain n-alkanes and low carbonate contents. The high content of desmethyl steranes and diasterenes suggests that marine algae were the main marine primary pro- ducers. The presence of different isomers of hopanes (C27,C29eC31) and hopanoic acids (C31eC33) reveals input from various bacteria. The observed variation in the abundance of biomarkers corresponds to changes in planktic algal assemblages associated with sea level change and episodic photic zone anoxia, which are indicated by the occurrence of aryl isoprenoids, biomarkers of green sulphur bacteria. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction current speeds and low oxygen levels (Killops and Killops, 2005; Takashima et al., 2006), favouring the preservation of organic Black shales are dark, finely laminated, fine-grained argillaceous, matter. On the other hand, high-energy systems can be considered calcareous and sometimes siliceous deposits that formed under as alternative settings for black shale deposition (Alexandre et al., anoxic conditions. They are rich in organic matter, mainly preserved 2012). The main environments of black shale deposition are clas- as kerogen, and contain abundant sulphide minerals (e.g., pyrite). sified according to Tourtelot (1979) into three categories, (1) the Black shales commonly have high contents of redox-sensitive trace restricted circulation type, (2) the open ocean type and (3) the elements such as V, Cu, Cd, Ni, Co, Mo, U and rare earth elements continental shelf type. (Brumsack, 2006; Loukola-Ruskeeniemi and Lahtinen, 2013). The CampanianeMaastrichtian was characterized by increased Black shales are deposited predominantly in oxygen minimum pCO2 from prominent global igneous activity and is known as a zones, where depositional environments are characterized by low typical greenhouse period (Takashima et al., 2006) with moderate to high pCO2 levels from the Late Cretaceous until the early Eocene (Kent and Muttoni, 2013). Increased burial was accompanied by changes in the composition of the phytoplankton community * Corresponding author. fl E-mail address: [email protected] (M. El-Shafeiy). (coccolithophores, dino agellates and diatoms), associated with http://dx.doi.org/10.1016/j.cretres.2014.03.022 0195-6671/Ó 2014 Elsevier Ltd. All rights reserved. M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 39 increased storage capacities caused by the opening of the Atlantic marine transgression conducive for the formation of organic Ocean basin (Katz, 2005). Phytoplankton diversity was rapidly de- carbon-rich shales and massive phosphorites; (2) high energy tached from the long-term sea-level trends at the Cretaceouse deposition, representing regressive stages with advancing deltas, Palaeogene boundary (Falkowski et al., 2004). seawards reworked glauconites and prograding brackish oyster In northern Africa and the Middle East, deposition of organic- banks in the Red Sea area. rich black shales was widespread in the Late Cretaceous to Palae- According to Baioumy and Tada (2005), the Duwi Formation in ocene. During this period, the sedimentation processes were the Red Sea, Nile Valley and Abu-Tartur areas can be subdivided influenced by greenhouse climate, favouring the establishment of into four subunits: lower, middle, upper and uppermost members. anoxic conditions in many marine basins along a broad marine The Duwi Formation ranges in age from late Campanianelate continental shelf across northeast Africa (Robinson and Engel, Maastrichtian, in the Red Sea (Zalat et al., 2008) to late Campanian 1993). Apart from organic-rich shales, phosphorites, carbonates, in the Kharga-Dakhla area. The Duwi Formation has been suggested glauconitic deposits and cherts dominate the shelf sequences (Bein to be unconformably overlain by the Dakhla Formation, which is and Amit, 1982; Tröger, 1984; Germann et al., 1985; Mikbel and early Maastrichtian to early Thanetian in age in the Dakhla-Kharga Abed, 1985; Notholt, 1985; Ganz et al., 1987; Abed and Al-Agha, region (El-Azabi and Farouk, 2010). The inferred unconformity was 1989; Glenn and Arthur, 1990; El-Kammar 1993). Black shales and believed to have been caused by a tectonic movement coupled to a marls reflect periods of high primary productivity on the shallow regression that took place during the latest Campanian, resulting in shelves, favouring the preservation of organic matter. As a conse- a hiatus in the Kharga-Abu Tartur district (Barthel and Herrmann- quence of the absence of a pronounced catagenesis, massive black Degen, 1981). This area was probably a palaeohigh at that time. shale successions have been preserved in Egypt and elsewhere in Sedimentation has been suggested to commence again in the early North Africa. late Maastrichtian, resulting in the deposition of Dakhla shales Some work on organic geochemical proxies in the Egyptian overlying the Duwi Formation (Mansour et al., 1982; Hendriks et al., sequences of the Red Sea area has been conducted by Ganz (1987) 1984; El-Azabi and Farouk, 2010). and Ganz et al. (1990). Samples from the Abu Tartur mine were The Dakhla Formation in the Dakhla-Kharga area has been previously studied by El-Kammar (1993), who did some biomarker subdivided by Awad and Ghobrial (1965) into Mawhoob, Baris and work, pointing to deposition in saline to hypersaline waters under Kharga members in ascending order. The Kharga shale member has anoxic conditions with high primary productivity. This interpreta- been further subdivided by Luger (1985) into two subunits, the tion was based on the presence of abundant acyclic isoprenoids, lower and upper Kharga shales. These subunits are separated by an gammacerane, hopane/sterane and pristane/phytane ratios <1, as unconformity representing the Cretaceous/Palaeocene boundary. well as C27/C29 steranes ratios >1. In addition, El-Kammar (1993) On the Abu Tartur plateau, the lower part of the upper Kharga shale found that the largest part of the extracts consisted of hetero- is replaced laterally by limestones with shale interbeds named the compounds and asphaltenes with the presence of naphthenes Kurkur Formation (Issawi, 1968). (C25 and C30). The present work focuses on the organic matter distribution 3. Material and methods within the Abu Tartur black shale sequence, analysing a complete core that was drilled in 2007 in the Maghrabi-Liffya area. We put Black shales weather readily and weathering may have a sig- particular emphasis on the lipid biomarker inventory of the strata nificant effect on chemical composition, introducing artefacts in at the transition from the Duwi to the Dakhla Formation, covering samples collected in outcrops (e.g., El-Kammar and El-Kammar the transition from the Campanian to the Maastrichtian. At this 1996). Accordingly, the black shales studied here were taken from transition, changes in sedimentation, primary productivity and a drilled core that was not affected by surficial weathering. The preservation of organic matter are observed based on the quanti- borehole was drilled by the Egyptian Mineral Resources Authority fication of biomarkers including n-alkanes, n-fatty acids, steroids, (EMRA). Ten cores were drilled in the course of a project aiming to hopanoids and isoprenoids. The overall palaeoenvironmental con- evaluate the potential of Egyptian black shales as unconventional ditions during the deposition of the studied strata are finally source rocks. Among these cores, only one core was drilled in the reconstructed, combining the interpretation of lipid biomarker Western Desert of Egypt. This study focuses on this drill core taken patterns and organic and inorganic bulk parameters. on the Abu Tartur plateau (Maghrabi-Liffiya sector) in the Western Desert (Fig. 1). Drilling was done in cooperation of the Ministry of Ó 2. Geologic setting Petroleum and DanaGas Egypt.

The black shales of the Upper Cretaceous to lower Palaeocene in 3.1. Sampling Egypt occur in an east-west trending belt from Quseir-Safaga in the east along the Red Sea to the Kharga-Dakhla land-stretch toward Two sampling strategies were applied during the present study. the west, passing through the Nile Valley (Fig. 1; see also Baioumy First, down-core samples were collected every 10 cm and subse- and Tada, 2005; El-Azabi and Farouk, 2010 for detailed maps). The quently 10 successive samples were mixed and homogenized to organic-rich shales are hosted in two formations. The Duwi For- obtain representative bulk samples for homogeneous 1 m transects mation is a phosphorite-bearing formation with intercalations of for routine analyses. However, additional samples were taken in marls, chert-rich deposits along the Red Sea, and glauconite- case of lithology changes in the transects. The obtained rock pieces bearing horizons in the Kharga-Dakhla area including the Abu were ground to a suitable mesh size for bulk analyses (TOC% and Tartur plateau. The Duwi Formation is well known for its numerous Rock Eval). Secondly, lower resolution sampling (every 2e6m)was phosphorite mines, which have been active since the beginning of made to monitor lithology or facies changes. These samples were the last century. The superjacent Dakhla Formation is characterized used for biomarker and XRD analyses. by abundant foraminifera-rich shales and marls with limestone and rare siltstone intercalations. 3.2. X-ray diffraction According to Glenn and Arthur (1990), two major modes pre- vailed during the deposition of these Upper Cretaceous strata: (1) About 35 X-ray diffraction (XRD) analyses were performed on shallow hemipelagic deposition, representing the initial stages of bitumen-free samples to determine the bulk mineralogy. The X-ray 40 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51

Fig. 1. Satellite image showing the study area on the Abu Tartur Plateau with the Maghrabi-Liffiya region (red box) enlarged below. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) diffraction was done on a Bruker D8 Advance diffractometer resulting carbon dioxide was quantitatively measured using an equipped with a Cu-tube (ka1 1.541, 45 kV, 40 mA), a fixed diver- infrared detector. For the Rock Eval measurements, approximately gence slit of 0.2,a8 15 samples changer, a receiving slit of 60e100 mg of the ground rock material was weighed and placed 0.1 mm, a secondary graphite monochromator and the Lyxneye into an auto-sampler crucible. During isothermal heating (300C), detector system. The measurements were made at the Geosciences S1 hydrocarbons (free hydrocarbons) were volatilized and detec- Department of Bremen University, Germany. Mineral identification ted by a flame ionization detector (FID), and were quantified as was done by means of the Philips software X’Pert HighScoreÔ, and milligrammes of hydrocarbon per gram of rock (mg/g). A tem- quantification has been performed using the full-pattern software perature increase to 600C caused the release of additional hy- package QUAX (cf. Vogt et al., 2002). drocarbons (S2) and simulated the pyrolytic degradation (i.e. cracking) of kerogen in the rock. This is roughly equivalent to the 3.3. Total organic carbon and Rock Eval analysis hydrocarbon potential of the rock. The carbon dioxide that was released up to approximately 400C is reported in milligrammes Aliquots of about 130 representative homogenized samples per gram of sediments (S3). The amount of S3 is a measure of the were measured for total organic carbon (TOC) contents (wt %) and amount of oxygen in the kerogen. Ó Rock Eval pyrolysis in the laboratories of StratoChem in Egypt. For the TOC contents, rock material was ground and sieved 3.4. Lipid biomarker analysis through a 40 mesh. 200 mg of the ground rock was weighed into a Pyrex beaker and reacted with hydrochloric acid to dissolve any Thirty-five biomarker samples were selected for extraction of inorganic carbon that may have been present in the samples. easily soluble organic matter (bitumen). All samples were Thereafter, the samples are transferred to a microfiber filter paper measured by coupled gas chromatographyemass spectrometry using a Millipore filter apparatus. The samples were combusted in (GCeMS) as well as gas chromatography with a flame ionization a LECO C230 or LECO EC-12 combustion furnace, where the detector (GCeFID) following the extraction procedures below: M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 41

Samples were homogenized by pestle and mortar avoiding zone CC25be26 of Sissingh (1977) and Perch-Nielsen (1985), and contamination. 40 ml dichloromethane (DCM):methanol (3:1 v/v) UC20 of Burnett (1998) in the studied samples (Fig. 2). The was added prior each extraction step. The extraction was done by remaining samples of the well of the Abu Tartur section were found microwave extraction with a CEM MARS X for 15 min at 80C and to be barren of fossils. 600 W. Internal standards of various polarities (squalane, behenic Additional data for the Campanian/Maastrichtian boundary in- acid methylester, 1-nonadecanol and 2-methyl-octadecanoic acid) terval at the Duwi/Dakhla transition were obtained using organic- were added to the samples prior to extraction. The samples were walled dinoflagellate cysts (dinocysts; for sample preparation see extracted several times until they became colourless (at least three Mohamed and Wagreich, 2013). The diversity of the dinocyst times). The extracted organic phases were collected and dried with assemblage (species per sample) was found to be very low (8 sodium sulphate. The combined total lipid extracts (TLE) were species). The Duwi Formation samples are characterized by a evaporated under a stream of nitrogen. Subsequently, separation of moderate abundance of dinocysts, mainly Andalusiella polymorpha the DCM-soluble asphaltenes from the n-hexane soluble maltenes (see Appendix I). This species has a stratigraphic range from the late was achieved. This procedure was applied as a clean-up procedure Santonian to the Maastrichtian (Williams and Bujak, 1985). using 150 mm pasteur pipettes filled with glass wool and sodium The first occurrence of Cerodinium diebelii and Palae- sulphate. The maltenes were fractionated into four fractions with ocystodinium golzowense are recorded in the lowermost sample of increasing polarity (1: hydrocarbons, 2: esters/ketones, 3: alcohols the Dakhla Formation, continuing above. Schiøler and Wilson and 4: carboxylic acids) by means of a solid phase extraction col- (2001) documented that the first occurrence of C. diebelii is an umn (Supelco DSC-NH2; 500 mg). The reagents used were (1) 4 ml important biostratigraphic marker situated close to, but below the n-hexane, (2) 6 ml n-hexane:DCM (3:1, v/v), (3) 7 ml DCM:acetone Campanian/Maastrichtian boundary. The first occurrence of (9:1, v/v) and (4) 8 ml 2% formic acid in DCM, respectively. Car- P. golzowense was recorded in the Maastrichtian by Brinkhuis and boxylic acids were transformed to methyl esters by adding 1 ml of Zachariasse (1988) among others. The co-occurrence and rela- boron trifluoride (BF3) in methanol to the dried fatty acid fraction. tively high abundance of Palaeocystodinium golzowense and Cer- The reaction time was 1 h at 70C. The hydrocarbon and fatty acid odinium diebelii in the sample at depth 155.5 with some differences fractions were examined in all samples, whereas the alcohol frac- in the dinocyst assemblage between these samples (155.5e130.5 m tions were found to lack pristine biomarker signatures. depth) and the lower samples (156.7 and 157.4 m depth) suggests Aliquots of the hydrocarbon and fatty acid fractions of each that the Campanian/Maastrichtian boundary interval is situated sample were injected into the GCeFID for quantification and a se- around sample 155.5 m. lection of samples was injected on the GCeMS for identification of Most abundant among the dinocysts are peridinioids (>90%), compounds. The samples were measured on a Thermo Electron which indicates an overall high palaeoproductivity. The particularly Trace GCeMS equipped with a 30 m Rxi-5MS fused silica capillary high abundance of peridinioid taxa such as Andalusiella, Cerodinium column (0.32 mm i.d., 0.25 mm film thickness) using helium as a and Palaeocystodinium in the lowermost Dakhla Formation in- carrier gas. The GC temperature program was 60C (1 min) to 150C dicates a very high productivity and efficient nutrient cycling in at 15C min 1, then to 320Cat4C min 1. The final temperature Abu Tartur region. Integrating the available biostratigraphic data, was held for 37 min. The analysed samples represent different li- the boundary between the Duwi Formation and the Dakhla For- thologies including black shale, mudstone, marl, limestone (wacke- mation is regarded to represent roughly the Campanian/Maas- to packstone) and phosphorite in order to identify possible varia- trichtian boundary in the study area as already suggested by tion of biomarker patterns with different lithologies. Tantawy et al. (2001).

4. Results 4.2. Bulk rock analysis

4.1. Stratigraphy and micropalaeontology The TOC content varies between 0.2 and 3.5%; the highest contents are recognized at the Duwi/Dakhla transition including A multistratigraphic framework for the Upper Cretaceous in the the uppermost member of the Duwi Formation and the lowermost Western Desert, including the Abu Tartur-Dakhla area, was given by part of the Mawhoob member of the Dakhla Formation (Fig. 2). In Tantawy et al. (2001). These authors assigned the top part of the general, the samples of the Duwi Formation have lower TOC con- Duwi Formation to the late Campanian CF8a planktonic forami- tents (0.95% on average) compared to those of the Dakhla Forma- nifera zone as well as nannofossil zones CC23a and the base of tion (1.33% on average). The highest TOC contents, reflecting two CC23b. The Duwi/Dakhla boundary corresponds to the base of CF8b peaks, coincide with the maximum hydrogen index (HI) values, planktonic foraminifera zone and was interpreted to represent the reaching 575 mg HC/g TOC, indicating good preservation of marine Campanian/Maastrichtian boundary, followed by CF7, which in- organic matter. Elsewhere, the HI mostly varies between 30 and cludes a thick interval barren of fossils, then CF6, CF4 and CF3 up to 200, but reaches approximately 300 mg HC/g TOC in places. The an unconformity around the Cretaceous/Palaeogene boundary overall low Tmax values (less than 435 C) confirm that organic (Tantawy et al., 2001). matter is characterized by low to intermediate maturity with re- Our investigation of calcareous nannofossil assemblages using gard to hydrocarbon generation. standard smear slide techniques (e.g., Bown and Young, 1998)of With respect to the oxygen index (OI) to HI, the Tmax to HI and well samples revealed two stratigraphic levels: (1) one sample (at TOC% to S2 ratios, the majority of samples from both the Duwi and depth 156.7 m) from the topmost part of the Duwi Formation Dakhla formations are located in the field of kerogen type III (Fig. 3), contained an assemblage including Ceratolithoides aculeus. The whereas the samples from the Duwi/Dakhla transition are in the coccolith indicates a late Campanian age; CC20e23 of the Sissingh field of kerogen type II. Additionally, two argillaceous limestone (1977) and Perch-Nielsen (1985) zonations and UC15be16 of the samples from the Baris member also plot in the kerogen type II field Burnett (1978) zonation. After an interval almost barren of fossils at 121 and 124 m depth with a HI of 293 and 299 mg HC/g TOC, from 155 to 130 m, rich and diverse nannofossil assemblages from respectively (Figs. 2 and 3). It can be inferred that the majority of sample 125.5 m onwards indicate a late Maastrichtian age based on the Duwi and Dakhla shales contains organic matter that is chiefly the presence of the zonal markers Lithraphidites quadratus and derived from land plants, whereas at the boundary between the Arkhangelskiella maastrichtiana. This indicates nannofossil standard two formations the rocks contain organic matter apparently 42 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51

Fig. 2. Whole-rock organic geochemical data of the Abu Tartur section (TOC%; Hydrogen Index; and total sulphur). The grey zone represents the strata with the highest TOC contents at the Duwi/Dakhla transition (Nanno zone CC20e23 at 156.7 m). derived from marine sources, which was deposited under anoxic (0.10%) are observed in the Mawhoob member of the Dakhla For- conditions as indicated by high TOC contents, high HI, the absence mation, whereas the highest values are observed in the Baris of bioturbation, as well as lipid biomarkers (see Section 5.2). member of the Dakhla Formation (Fig. 2). Interestingly, the samples The majority of total sulphur (Stot) contents range from 0.22 to with the highest TOC and HI contents at the Duwi/Dakhla transition 10.00%, not correlating with TOC (Fig. 2). The lowest Stot contents do not show particularly high Stot contents (0.57e2.14). The

Fig. 3. Plots of the samples of the Abu Tartur section on (A) a van Krevelen diagram, (B) a Tmax versus hydrogen index diagram and (C) a Langford and Blanc-Valleron (1990) diagram. M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 43 majority of the sulphur is most likely present as pyrite and not significant input of terrigenous organic matter. This is also associated with the organic matter, as suggested by XRD data, confirmed by the positive relation between the CPI and the where pyrite was found to average 1.2% (0.2e4.2%) in the Duwi Terrestrial/Aquatic Ratio (TAR; R2 ¼ 0.31). The TAR for n-alkanes is Formation and 1.7% (0.3e5.3%) at the Duwi/Dakhla transition, and used as an indicator for vascular land plant input into marine en- reaches its highest abundance in the Baris member averaging 2.3% vironments (cf. Bourbonniere and Meyers, 1996). The determined (0.2e10.4%) from the total mineralogical composition. TAR is variable but generally 1 with the exception of phosphorite and limestone samples of the Duwi Formation and the limestone 4.3. Lipid biomarkers intervals in the Dakhla Formation where the TAR is 0.5 (Fig. 5). Both the TAR and CPI values are not correlating with TOC (R2 ¼ 0.01 4.3.1. Hydrocarbons and 0.001, respectively). The most prominent acyclic isoprenoids The n-alkanes range from n-C14 to n-C32 (Fig. 4) with quite are phytane (Ph), pristane (Pr) and in some samples farnesane variable distributions through the entire section. In general, there is (Fig. 4). The Pr/Ph ratio of the majority of samples is 1, most likely an odd over even n-alkane preponderance in all samples. Long indicating anoxic conditions during deposition. Samples of the > chain n-alkanes are usually maximizing at n-C27, n-C29 and n-C31, lower and middle Duwi Formation have ratios 1, whereas the whereas short chains maximize at n-C15, n-C17 and n-C19. The short samples from the upper and uppermost members have relatively chain n-alkanes are typically derived from aquatic algae and micro- low Pr/Ph ratios (up to 1.7; Fig. 5). The Dakhla Formation shows organisms (Blumer et al., 1971; Cranwell et al., 1987), whereas long significantly lower Pr/Ph ratios, especially the Baris member and chain n-alkanes derive from epicuticular waxes of vascular land lower Kharga members (<0.5). plants (e.g., Eglinton and Hamilton, 1967). The Carbon Preference In contrast to the desmethyl steranes, rearranged C27e29 diaster- Index (CPI), calculated after Marzi et al. (1993),is>3 on average for 13(17)-enes (characterized by m/z 257) were observed in nearly all all samples (Table 1). The CPI values are variable but generally samples (see Appendix II for structures). Only in the middle and significantly higher than 1, except for the limestone interbeds of the upper members of the Duwi Formation, diasterenes occur in lower Dakhla Formation (Baris member), where the CPI is around 1 abundance than elsewhere (Fig. 6). Diasterenes are predominantly (Table 1). The CPI typifies the organic matter and its maturity present as 5a,14a,17a(H) 20R isomers, whereas the 5a,14b,17b(H) (Tissot and Welte, 1984). The obtained high CPIs indicate a 20R isomers are only present in minor amounts (Fig. 4). Diasterenes

Fig. 4. Gas chromatograms of a sample from the Baris member as an example for the hydrocarbon fraction, showing the distribution of n-alkanes (m/z 71), regular steranes (m/z 217), diasterenes (m/z 257), triterpenoids (m/z 191) and aryl isoprenoids (m/z 132e134). TIC: total ion chromatogram, Pr: pristane, Ph: phytane, Fa: farnesane, IS: internal standard, solid square: unidentified compounds. 44 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51

Table 1

Maturity parameters for Abu Tartur section including Carbon Preference Indices (CPI) for hydrocarbons (HC) and fatty acids (FA), bb/ab ratio for C30e31 hopane (H.) and C32e33 hopanoic acid (H.A.); n.d.: not determined.

Rock unit Depth CPIodd HC CPIeven FA bb/ab C31 H. bb/ab C30 H. bb/ab C32 H.A. bb/ab C33 H.A. Dakhla Formation 63.75 4.84 6.12 2.11 10.57 6.33 2.55 71.30 2.90 1.84 1.95 8.57 5.28 2.28 74.40 3.33 3.80 3.62 6.38 5.56 2.23 80.15 3.38 3.51 2.36 5.43 4.55 2.90 84.80 3.82 2.59 1.46 4.70 1.94 2.48 88.40 3.15 3.84 1.30 5.42 3.96 2.74 90.70 3.23 7.01 1.53 6.62 4.30 2.60 96.70 4.22 5.36 1.60 6.22 5.75 3.29 101.35 1.80 1.65 2.44 4.28 7.83 2.63 104.70 2.27 n.d. 2.17 3.33 n.d. n.d. 108.50 3.23 6.09 1.73 6.06 6.34 4.00 116.20 3.32 6.86 2.54 3.82 4.97 2.33 120.70 3.28 8.62 2.08 2.78 3.44 2.95 121.20 1.49 1.10 3.10 4.11 6.95 3.78 123.50 1.77 0.92 3.30 3.91 5.34 2.39 125.50 3.38 6.28 2.78 3.41 4.86 2.17 130.50 1.09 4.01 1.84 3.76 3.03 2.05 132.40 2.70 n.d. n.d. n.d. n.d. n.d. 137.50 4.52 n.d. 1.50 6.60 n.d. n.d. 141.50 4.41 4.94 1.47 6.58 3.38 4.08 145.50 3.88 5.50 1.66 6.37 3.24 4.63 149.50 3.94 3.87 1.52 5.70 3.64 3.64 154.35 3.35 8.13 2.09 3.77 4.93 6.57 155.50 2.74 3.49 2.13 2.42 5.33 5.50 156.70 3.83 5.90 2.12 2.60 4.03 8.84 157.45 1.48 0.81 2.05 3.84 4.13 n.d.

Duwi Formation 159.50 1.54 4.65 1.47 3.00 3.76 3.49 161.50 1.66 n.d. n.d. n.d. n.d. n.d. 162.00 3.42 3.92 2.26 1.60 3.03 3.76 166.70 2.88 1.51 1.67 n.d. 5.29 4.23 169.50 4.54 2.93 1.38 3.53 4.72 2.96 172.15 3.05 n.d. 2.05 2.43 n.d. n.d. 172.70 5.37 n.d. 2.01 4.07 n.d. n.d. 178.00 3.38 n.d. 1.63 2.64 n.d. n.d. 179.95 1.72 n.d. n.d. n.d. n.d. n.d. Av. Duwi (n ¼ 9) 3.06 3.25 1.78 2.88 4.20 3.61 Av. Dakhla (n ¼ 26) 3.13 4.44 2.10 5.09 4.74 3.48

maximize at the Duwi/Dakhla transition (up to 81 mg/g TOC; Fig. 6) the Mawhoob member. Apart from the saturated hopanes, a and within the Baris member (up to 80 mg/g TOC). The C27 dia- number of hopenes was found including 29-norneohop-13(18)- sterenes show maximum contents in the phosphorite samples ene, neohop-13(18)-ene as well as hop-17(21)-ene (see Appendix II compared to the others (C28 and C29). Not all of the extracted for structures). These hopenes are present in almost all samples, bitumen contains desmethyl steranes. Desmethyl steranes were but only in minor amounts compared with saturated hopanes found with low amounts at the Duwi/Dakhla transition (up to (maximum content: 30 mg/g TOC; Fig. 6). Generally, 29-norneohop- 16.4 mg/g TOC) and in samples of the Baris member (up to 14.9 mg/g 13(18)-ene is the most abundant hopene (Fig. 4). TOC). The dominant compounds are C27e29 5a,14a,17a (H) 20R Aryl isoprenoids were observed in the free lipid extracts of the desmethyl steranes with a small contribution of the 5a,14b,17b(H) hydrocarbon fraction in some samples. Raney nickel- 20R isomers, which are eluting slightly earlier (Fig. 4). The isomer desulfurization was not applied, although aryl isoprenoids were identification was based on co-injection experiments of known found in some samples at different depths. It seems that aryl iso- standards. Further, minor amounts of C-ring monoaromatic ster- prenoids are not or at least not entirely bound to sulphurized anes (m/z 253) were observed. Unfortunately, detailed identifica- organic matter. Anyway, overall contents of aryl isoprenoids are tion was hampered by co-elution with other, more abundant low. The trace amounts of aryl isoprenoids represent contents steranes. below detection limit when measured in full scan mode (Fig. 6). The distribution of hopanoids in the Abu Tartur sequence is Only when measured in single ion monitoring (SIM; m/z 133/134) shown by m/z 191 chromatograms (Fig. 4 and Appendix II). 25,28,30 mode, the aryl isoprenoids were identified by comparison with trisnorhopane, 17a(H),21b(H) and 17b(H),21a(H) norhopanes, retention times in full scan mode. Isorenieratane (C40; Appendix II) 17a(H),21b(H) and 17b(H),21b(H) hopane, 17a(H),21b(H) and was found only in few samples, reaching its maximum abundance 17b(H),21b(H) homohopane and minor 17b(H),21b(H) bishomo- at the top of the Baris member, where the Pr/Ph ratios are very low, hopane are present in the majority of samples. Overall, the bb too. Some samples yielded diagenetic products of isorenieratane isomers predominate over ab isomers. bb/ab ratios of hopanes and and other aryl isoprenoids (cf. Summons and Powell, 1987; hopanoic acids are overall >1, increasing up-section (Table 1). The Koopmans et al., 1996; Sinninghe Damsté et al., 2001). Short- distribution of bb and ab hopanes is similar throughout the chain aryl isoprenoids (including C11,C13,C14,C16 and rarely C19 lowermost Duwi Formation. At the Duwi/Dakhla transition and chains; Figs. 4 and 6) are particularly abundant in the Abu Tartur within the Dakhla Formation, however, bb-hopanes are more section, where isorenieratane was only found in minor amounts. At abundant (Fig. 6). Highest proportions of bb-hopanes were found in the Duwi/Dakhla transition the contents of short-chain aryl M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 45

Fig. 5. Geochemical and mineralogical data of the Abu Tartur section including mutual distribution of pristane (Pr) to phytane (Ph), Terrestrial/Aquatic Ratio (TAR) for hydrocarbons

(n-C27 þ n-C29 þ n-C31)/(n-C15 þ n-C17 þ n-C19), TAR for fatty acids (n-C24 þ n-C26 þ n-C28)/(n-C12 þ n-C14 þ n-C16) and carbonate to siliciclastic detritus ratios. Note logarithmic scales.

isoprenoids are higher than elsewhere in the section (Fig. 6). C33 Farouk, 2010 and references therein). However, this study resulted aryl isoprenoid (Fig. 4) reaches its highest abundance at depths in new evidence that calls a hiatus between the Duwi and Dakhla between 125.5 and 108.5 m within the Baris member (Fig. 6). formations into question. The circumstance that the highest organic carbon content was observed at the Duwi/Dakhla transition 4.3.2. Carboxylic acids e along with the recording of a complete foraminiferal biozonation Straight-chain saturated fatty acids were observed in the ma- succession at the Campanian/Maastrichtian boundary (e.g., e jority of samples, ranging from n-C12 to n-C33 and maximizing at n- Tantawy et al., 2001) argues against a hiatus, which would C16 and n-C18. They are characterized by a preponderance of even necessarily have resulted in prolonged exposure, reworking, and over odd numbered carbon chains (Fig. 7). CPIeven average values remineralization of organic matter in proximity to the hiatal sur- calculated according to Marzi et al. (1993) fall between 3.25 and face. At the studied site, the variations in the TOC profile (Fig. 2)are 4.44 for the Duwi and Dakhla formations, respectively, indicating gradual and smooth, which is in sharp contrast to what would be immature organic constituents with significant input of terrigenous expected in case of a hiatus. The high TOC contents at the Duwi/ organic matter. No unsaturated n-fatty acids were observed. Iso-(i-) Dakhla transition, thus, reflect enhanced preservation of organic and anteiso-(ai-) fatty acids are markedly less abundant than matter, confirmed by the absence of bioturbation at the Duwi/ straight-chain fatty acids (Fig. 7); i-C14 to i-C17 as well as ai-C15 and Dakhla transition. The association of these high TOC values with ai-C17 fatty acids were recognized. Pristanoic and phytanoic acids low sulphur contents suggest anoxic rather than euxinic environ- were found in some samples only (Fig. 7). Pentacyclic triterpenoic ments. As Rock Eval pyrolysis revealed organic matter composition acids (hopanoic acids), including 17b(H),21b(H) and 17a(H),21b(H) reflecting type II kerogen (marine algal-derived), increased marine bishomohopanoic acids with 31e33 carbon chains, were found to primary production rather than input of terrestrial organic matter be abundant (Fig. 7). Like with hopanes, the bb isomers dominate typifies this transition. over the ab isomers (Fig. 7 and Table 1). 5.2. Implications of redox-sensitive isoprenoids 5. Discussion High contents of both phytane and pristane in the entire section 5.1. Implications of Rock-Eval analysis probably reflect input from oxygenic phototrophs (eukaryotic algae and cyanobacteria; cf. Didyk et al., 1978; Sepúlveda et al., 2009), It has been suggested that the Duwi Formation is separated from with possible contributions from anoxygenic phototrophs (e.g., the overlaying Dakhla Formation by an unconformity (El-Azabi and Brooks et al., 1969). Although additional input from Archaea cannot 46 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51

Fig. 6. Down-core variations of biomarkers in the Abu Tartur section including desmethylated steranes, rearranged diasterenes, C30 hopanes, aryl isoprenoids and distribution of (nor-neo)-hopenes (all in mg/g TOC). be excluded, the overall biomarker patterns rather point to pho- et al., 2005; Sepúlveda et al., 2009). Such compounds are not totrophic prokaryotes and eukaryotes. In the Baris member for restricted to the Baris member. Isorenieratane, C33 and also short- example, high phytane contents are accompanied by abundant chain aryl isoprenoids were also detected close to the Duwi/ isorenieratane and C33 aryl isoprenoids, indicating that indeed Dakhla transition, suggesting the former presence of Chlorobiaceae anoxygenic phototrophs may have contributed to the phytane along with the occurrence of photic zone anoxia (cf. Summons and input. Aryl isoprenoids are robust indicators for water column Powell, 1987; Grice et al., 1997; Brocks et al., 2005; Knoll et al., anoxia within the photic zone (e.g., Kuypers et al., 2004; Kolonic 2007). Although no b-carotane was detected in the studied

Fig. 7. Representative gas chromatogram (FID) of a sample from Baris member (116 m depth), showing the distribution of fatty acids (methyl esters). FID ¼ flame ionization detector. M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 47 samples, it seems feasible that the short-chain aryl isoprenoids synthesize hopanoids with the 17b(H),21b(H)-configuration (bb were accessorily derived from sources other than isorenieratane hopanoids). However, extracts of sedimentary rock are often typi- including b-carotene (Schouten et al., 2000). fied by 17a(H),21b (H)-isomers (ab hopanoids) and 17b(H),21a(H)- It has to be noted that aryl isoprenoids were not only found in isomers (ba hopanoids), which formed by thermally induced the maximum TOC intervals, but also in other facies of the Duwi isomerization (Peters et al., 2005). The bbC32 hopanoic acid versus 2 and Dakhla formations. Highest contents of these compounds were bbC31 hopane ratio shows an intermediate correlation (R ¼ 0.5). encountered in the Baris member, where the TOC values are actu- The ratio between bbC31 hopanoic acid and bbC30 hopane shows an ally rather low compared to the Duwi/Dakhla transition. It has been even better correlation (R2 ¼ 0.8), suggesting that hopanes derive suggested that a marine incursion led to the deposition of the deep from the corresponding parent hopanoic acids and, thus, derive sub-tidal shales alternating with shallow sub-tidal wackestone and from the same source. Such a relationship is best explained by floatstone of the Baris member (El-Azabi and Farouk, 2010). The decarboxylation of hopanoic acids (cf. Bennett and Abbott, 1999). occurrence of C33 aryl isoprenoid together with isorenieratane in this member indicates an anoxic and possibly even euxinic water 5.3.2. Environmental implications derived from the distribution of column, the latter agreeing with high sulphur contents. The rather compounds low TOC contents of the Baris member are probably best explained The lowermost Duwi formation is typified by abundant phos- by lower productivity or only episodic oxygenation as indicated by phorite beds, along with C27 steroid predominance over other the presence of bioturbation in some layers among otherwise well- steroids (42.0% of diasterenes and 70.7% of desmethyl steranes). stratified beds. Apart from the Baris member, some samples of the Such a pattern can be attributed to high contributions from meta- Mawhoob and Kharga members yielded trace amounts of aryl zoans and zooplankton during phosphorite deposition. Similar isoprenoids, similarly indicating anoxic conditions. To sum up, the observations have also been made for the Duwi Formation phos- discontinuous distribution of aryl isoprenoids in the Abu Tartur phorites of the Younnis and Abu Shegela mines, for phosphorites section indicates the episodic occurrence of photic zone anoxia. along the Red Sea (Ganz et al., 1990), as well as for phosphorites from the Peruvian continental margin (Sandstorm, 1990). The 5.3. Changes in the dominance of eukaryotes versus bacteria content of all identified steroids (regular and rearranged) increases at the Duwi/Dakhla transition and reaches its maximum in the 5.3.1. Assessment of the sources of compounds Mawhoob member of the lowermost Dakhla Formation, accom- Sterols are mainly produced by eukaryotic algae, photosynthetic panied by low Terrestrial/Aquatic Ratios (TAR). At the same time protists and higher plants (e.g., Volkman et al., 1998). Principally, when steroid contents reach their maximum, hopanoids decrease sterols can be classified into groups including sterols with 27 car- dramatically at the Duwi/Dakhla transition, suggesting a major bons (e.g., cholesterol) produced by metazoans (Knoll et al., 2007) change in the input of organic matter. The biomarker patterns at the and various zooplankton (Huang and Meinschein, 1979; Killops and Duwi/Dakhla transition suggest input of marine organic matter and Killops, 2005). Sterols with 28 carbons are the main precursors of the development of anoxia in the photic zone, indicated by type II C28 steranes (ergostanes) and are predominantly found in algae and kerogen and abundant aryl isoprenoids. phytoplankton including diatoms, dinoflagellates and coccolitho- The carbonate to detritus ratio is a useful indicator for sea-level phorids (e.g., Knoll et al., 2007). Sterols with 29 carbons, including change. Increased carbonate contents are believed to reflect a more sitosterol and stigmasterol are produced by marine chlorophytes distant source of detrital material, suggesting greater water depth. (Knoll et al., 2007) and land plants (Huang and Meinschein, 1979; An increase in detritus, on the other hand, is believed to reflect a Volkman et al., 1998; Killops and Killops, 2005). more proximal source and shallower waters (e.g., Adatte et al., Under slightly acidic conditions in the presence of catalytic clay 2002). The carbonate to detritus ratio, calculated as calcite plus minerals and a high geothermal gradient, steranes can undergo other carbonate minerals divided by quartz plus feldspars plus clay rearrangement to diasterenes upon dehydration and carbocation minerals (smectite, kaolinite, illite and chlorite), is negatively migration (Rubinstein et al., 1975; Sieskind et al., 1979; Mackenzie correlated with the input of terrestrial organic matter for the Abu et al., 1982; ten Haven et al., 1989). Further reduction of diasterenes Tartur section. This relationship is represented by the positive generates diasteranes (Gaines et al., 2009). The occurrence of dia- correlation of TAR of hydrocarbons with those of straight chain sterenes in the studied Upper Cretaceous shales of low thermal fatty acids (R2 ¼ 0.63), and the negative correlation with carbonate maturity is probably best explained by clay catalysis rather than to detritus ratios (R2 ¼0.71). thermal maturation (cf. Brassell et al., 1980). Above the Duwi/Dakhla transition, in the Mawhoob member, Bacteriohopanepolyols (BHPs) are the precursors of hopanoids diasterenes are present only in trace amounts and the content of all and are exclusively derived from bacteria (Rohmer et al., 1984; other steranes is dramatically decreased. Based on steroid distri- Knoll et al., 2007). Most hopanoid-producing bacteria are aerobic butions, Pr/Ph ratios and the relative abundance of hopanes, the bacteria, including methanotrophs, methylotrophs and cyanobac- Mawhoob member differs from the strata below and above. The teria (e.g., Talbot and Farrimond, 2007 for a review). Only in recent high marine production and the development of photic zone anoxia years, anaerobic bacteria such as purple non-sulphur bacteria, that typified the Duwi/Dakhla transition had ceased abruptly. sulphate reducers and iron reducers have been recognized to pro- Interestingly, the decrease in steroid contents is mirrored by a duce a great variety of BHPs (e.g., Blumenberg et al., 2006; Rashby strong increase in hopanoid contents in this member, suggesting et al., 2007; Eickhoff et al., 2013). Anyway, only less than 10% of all the predominance of bacteria over algae during that time. Such a bacterial species are capable of producing hopanoids (Pearson et al., pattern may indicate that bacteria flourished at the expense of 2007). eukaryotes. This is at least not in conflict with more oxic conditions Hopanoic acids found in sediments and sedimentary rocks are (Pr/Ph ratios of around 1 and lower contents of aryl isoprenoids) believed to be degradation products of BHPs (e.g., Farrimond et al., and the preponderance of land-derived organic material, reflected 2002). With increasing maturity, the concentration of hopanoic in a very low hydrogen index, high TAR values and low carbonate to acids has been shown to decrease (Jaffé and Gardinali, 1990). Like detritus ratios in this member in comparison to the Baris member. for hopanes, the hopanoic acids identified in the Upper Cretaceous Marine primary productivity was apparently relatively low during strata are dominated by 17b(H),21b(H) 22R isomers, confirming deposition of the Mawhoob member and the majority of organic that the sequence experienced little thermal alteration. Bacteria matter was land-derived (kerogen type III). This land-derived 48 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 organic matter was then remineralised by various bacteria in the contents was characterized by an enhanced input of marine organic marine deposits of the Mawhoob member. matter, which is in concert with the Rock Eval data and the abun- In the overlying Baris member, the content of steranes increases dance of steranes, reflecting input from algae. Likewise, the decline again with a slightly higher contribution of C28 ergostane (35.4%) of TAR in the limestone horizon of the Baris member is in accord followed by C27 cholestane (33.1%) and accompanied by abundant with an increase of the Pr/Ph ratio (w1.0) and the increase of the hopanoids. Diasterenes of different carbon numbers (C27e29) show carbonate to detritus ratio (up to 2.1). Summing up, these patterns a similar distribution in the Baris and Kharga members; pro- suggest a marine incursion with little if any anoxic bottom water as portions of C28 diasterene (35.9% and 39.7% from total diasterenes evidenced by bioturbation in the foraminiferal limestone. for Baris and Kharga members, respectively) are followed by C29 Apart from hopanes and hopanoic acids, hopenes were identi- diasterene (34.6% and 35.3% for Baris and Kharga members, fied in the Abu Tartur section as well as in other Cretaceous rocks respectively). In the clay dominated Kharga member, steranes have (e.g., Rullkötter et al., 1982; Simoneit et al., 1984). The identified disappeared while diasterenes and hopanoids are still present. The compounds 29-norneohop-13(18)-ene, neohop-13(18)-ene and predominance of C28 steroids suggests a slightly higher contribu- hop-17(21)-ene have been suggested to be rearrangement products tion from phytoplankton containing chlorophyll c in the middle and of diploptene, a common biohopanoid present in a variety of bac- upper members of the Dakhla Formation (cf. Knoll et al., 2007). In terial lineages (Rohmer et al., 1984). Interestingly, a positive cor- agreement with the prevalence of kerogen type III and high TAR, relation (R2 w 0.5e0.7) between total hopenes and the TAR for both the dominant source of the C29 steroids were probably land plants n-alkanes and n-fatty acids was found for the Abu Tartur section. (i.e. allochthonous organic matter), although no biomarkers of This pattern suggests that the hopenes predominantly derived from flowering land plants such as oleananes were observed. Interest- terrestrial sources, probably soils. Accordingly, Simoneit et al. ingly, in the uppermost Kharga member the greatly increased (1984) and Saito and Suzuki (2007) attributed similar hopene dis- contents of bacterial-derived hopanes and low contents of tributions from Cretaceous and Miocene to recent sedimentary eukaryote-derived diasterenes point to similar conditions as rocks and sediments from the Moroccan continental margin and envisaged for the Mawhoob member. the Nankai Trough to input from soil bacteria.

5.4. Implications of the terrigenous input 5.5. Reconstruction of water column anoxia

The Carbon Preference Index (CPI) values of the samples from The detection of isorenieratane and its diagenetic derivatives in the Abu Tartur section, ranging from 1.09 to 4.84 and from 0.92 to the Abu Tartur section indicates the former presence of Chlor- 8.62 for n-alkanes and n-fatty acids, respectively, reveal no diag- obiaceae. The presence of aryl isoprenoids in the rocks at the Duwi/ nostic trend and scatter over a wide range. Anyway, the obtained Dakhla transition and further up-section in the Mawhoob and Baris values are similar to those of extant vascular plants (cf. van Dongen members points to a stratified water column with a shallow che- et al., 2006), which are commonly >3, agreeing with significant mocline located within the photic zone for prolonged time periods. contributions of organic matter derived from higher plants. The A scenario for the deposition of organic-rich sediments in the study majority of this terrigenous organic matter was most probably area is shown in Fig. 8, suggesting the episodic establishment of derived from riverine transport. Although the overall composition photic zone anoxia. of the organic matter (mostly type III kerogen) reflects terrestrial During the Late Cretaceous, Egypt was positioned near the input, the great amounts of short-chain n-alkanes suggest addi- palaeoequator (Smith et al., 1982; Tantawy et al., 2001; Baioumy, tional contributions from marine sources. Short-chain lipids in 2013), agreeing with the high abundance of kaolinite minerals in marine deposits commonly reflect input of marine organic matter the Dakhla Formation, which suggests warm wet, tropical to sub- from photosynthetic algae and macrophytes (van Dongen et al., tropical conditions (Singer, 1984) with heavy rainfall and high 2006; Carvajal-Ortiz et al., 2009). concentrations of atmospheric carbon dioxide, resulting in deep Long-chain n-fatty acids and n-alkanes show some similarities in chemical weathering. The Duwi Formation overlies fluvial shale of their distribution, pointing to a precursor-product relationship (cf. the Quseir Formation and is overlain by deeper marine shales and Peters et al., 2005). C16 and C18 fatty acids are commonly the most marls of the Dakhla Formation, reflecting a general deepening trend. abundant n-fatty acids in deposits, partly because they are major A broad continental shelf developed in North Africa including Egypt lipids of phytoplankton, particularly diatoms and coccolithophorids as a result of Campanian to Maastrichtian transgressions (Baioumy (Uchida et al., 2005). In the Abu Tartur section long-chain n-alkanes and Tada, 2005). The initial stage of these Late Cretaceous marine display an odd-over-even predominance, which is best explained by transgressions in Egypt is represented by the deposition of the Duwi significant input of organic matter from terrestrial land plants (cf. Formation. In this formation, two transgressive cycles were identi- Eglinton and Hamilton,1967). Odd number long-chain n-alkanes are fied by Baioumy and Tada (2005); one in the lower member, another major components of plant cuticular waxes. Apart from n-alkanes, in the middle member when the maximum sea level was reached long-chain n-fatty acids are leaf wax components. Consequently, (High Stand System Tract; Fig. 8A). Importantly, a major regression parts of the odd number long-chain n-alkanes may have formed as a occurred at the boundary between the middle and upper members result of decarboxylation from an even-numbered fatty acid pre- (Low Stand System Tract; Fig. 8B). Interestingly, no steroids were cursor within the deposits (cf. Carvajal-Ortiz et al., 2009). The carbon detected in the samples of the middle and upper members. Hopa- number distribution in the n-alkanoic (fatty) acids strongly suggests noids were detected in tiny amounts only and disappeared in the that the acids may have generated some of the n-alkanes via upper part of the upper member. The middle and the upper mem- decarboxylation during diagenesis. bers have high Pr/Ph ratios, which, together with the absence of aryl The circumstance that TAR of n-alkanes and n-fatty acids are very isoprenoids, indicate poor preservation of organic matter in accord similar over the entire section agrees with a common origin of n- with very low hydrogen indices. The upper member of the Duwi alkanes and n-fatty acids. Generally, the obtained TAR of n-alkanes Formation is characterized by the deposition of glauconite and iron- (average 1.5) is higher than the TAR of n-fatty acids (average 0.82). rich, land-derived deposits (Pestitschek, 2010). The occurrence of The TAR of n-alkanes and n-fatty acids follow parallel trends through glauconite with both ferric and ferroan iron in its lattice indicates the section, declining rapidly in the strata with the highest TOC oxic to suboxic conditions, which hampered pronounced preser- levels. These patterns confirm that the interval with the highest TOC vation of organic matter. M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51 49

Fig. 8. Scenario for the environmental conditions in the water column during the deposition of the different intervals of the Duwi and Dakhla black shales; Mb: member, TST: Transgressive System Tract, HST: High Stand system tract.

The second transgressive cycle was identified at the base of the waters. The latter is characterized by an increase of steroids, a uppermost member (Transgressive System Tract; Fig. 8C) and decrease of hopanoids and a medium to high hydrogen index, indi- continued into the Mawhoob member (High Stand System Tract; cating higher marine productivity and better preservation of organic Fig. 8D). This transgression was probably a major factor that fav- matter except for some levels with bioturbation. oured high primary productivity and the deposition of increased Afterwards, low sub-tidal shale was deposited in the lower amounts of organic carbon at the CampanianeMaastrichtian tran- Kharga member (High Stand System Tract; Fig. 8F), pinpointing the sition. Additionally, the significant increase of short-chain aryl beginning of regional uplift and relative sea level fall (cf. El-Azabi and isoprenoids in these strata indicates the occurrence of photic zone Farouk, 2010) and the return to oxic water conditions reflected in the anoxia, favouring the preservation of organic matter. This enhanced absence of aryl isoprenoids. However, the preservation of marine preservation is reflected in high TOC% contents, high contents of organic matter was still favoured based on high steroid contents and steroids and relatively low contents of hopanes as well as the an intermediate to high hydrogen index. The relatively high TAR and absence of bioturbation. low carbonate to detritus ratios together with the occurrence of type According to El-Azabi and Farouk (2010), deposition of the lower III kerogen indicate high supply of land-derived organic material Mawhoob member ceased after a minor eustatic sea level fall (Fig. 8E). during the deposition of the lower Kharga member. Thereafter, marine invasion flooded the shelf and deep sub-tidal shale alternating with shallow sub-tidal wackestone and floatstone 6. Conclusions deposited (higher carbonate to detritus ratios and lower TAR; Transgressive System Tract; Fig. 8E). Notably, above its lower member, With the aid of detailed organic geochemical analyses and based the Mawhoob member and the majority of Baris member are char- on lithological and stratigraphical examinations of a core drilled on acterized by abundant aryl isoprenoids, indicating anoxia with good the Abu Tartur plateau (Maghrabi-Liffiya sector) in the Western conditions for the accumulation of organic matter. However, there are Desert of Egypt, the evolution of a shelf sea in the Late Cretaceous obvious differences between the Mawhoob and Baris members. The was reconstructed. former is characterized by an almost complete absence of marine steroids, abundant hopanoids and a very low hydrogen index, in 1. Type III kerogen, which is indicative of land-derived organic accord with substantial remineralization of organic matter in bottom matter, was found to dominate the Campanian to Maastrichtian 50 M. El-Shafeiy et al. / Cretaceous Research 50 (2014) 38e51

Abu Tartur section with the exception of the deposits at the Barthel, K.W., Herrmann-Degen, W., 1981. Late Cretaceous and Early Tertiary stra- transition between the Duwi and Dakhla formations; these de- tigraphy in the Great Sand Sea and its SE Margins (Farafra and Dakhla Oases), SW Desert, Egypt. Mitteilungen Bayerische Staatssammlung Paläontologie und posits reveal the highest TOC contents and contain type II Historische Geologie 21, 141e182. kerogen, which is indicative of marine organic matter. Bein, A., Amit, O., 1982. Depositional environment of the Senonian chert, phos- 2. The studied succession on the Abu Tartur plateau is character- phorite and oil shale sequence in Israel as deduced from their organic matter composition. Sedimentology 29, 81e90. ized by immature to marginally mature organic matter. The Bennett, B., Abbott, G.D., 1999. A natural pyrolysis experiment: hopanes from maturity is constrained by a low Tmax (<445 C), odd over even hopanoic acids? 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