Accepted Manuscript Integrated palaeo-environmental proxies of the Campanian to Danian organic-rich Quseir section, Egypt Moataz El-Shafeiy, Daniel Birgel, Ahmed El-Kammar, Ahmed El-Barkooky, Michael Wagreich, Sameh Tahoun, Jörn Peckmann PII:
S0264-8172(17)30232-5
DOI:
10.1016/j.marpetgeo.2017.06.025
Reference:
JMPG 2959
To appear in:
Marine and Petroleum Geology
Received Date: 1 October 2016 Revised Date:
12 June 2017
Accepted Date: 16 June 2017
Please cite this article as: El-Shafeiy, M., Birgel, D., El-Kammar, A., El-Barkooky, A., Wagreich, M., Tahoun, S., Peckmann, Jö., Integrated palaeo-environmental proxies of the Campanian to Danian organic-rich Quseir section, Egypt, Marine and Petroleum Geology (2017), doi: 10.1016/ j.marpetgeo.2017.06.025. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Integrated palaeo-environmental proxies of the Campanian to Danian
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organic-rich Quseir section, Egypt
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Moataz El-Shafeiya,b*, Daniel Birgelc, Ahmed El-Kammara, Ahmed El-Barkookya, Michael Wagreichd, Sameh
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Tahouna, Jörn Peckmannc,d a
Geology Department, Faculty of Science, Cairo University, Egypt
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b
MARUM – Center for Marine and Environmental Sciences, University of Bremen, Germany
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c
Institute for Geology, Universität Hamburg, Germany
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d
Department of Geodynamics and Sedimentology, University of Vienna, Austria
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[email protected]
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ABSTRACT
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The Cretaceous-Palaeogene sequence of Egypt is a part of a giant belt of organic-rich
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deposits in North Africa and the Middle East. The present work focuses on changes in trace
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element, bulk organic, and lipid biomarker inventories archived in sediments of the Duwi and
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Dakhla formations of the Quseir section in the Red Sea area. The studied section can be
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divided into 6 geochemically constrained units: the lower, middle, upper and uppermost
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members of the Duwi Formation (Fm) and the Hamama and Beida members of the Dakhla
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Fm. The composition of kerogen is found to vary significantly among these units. The lower
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and upper members of Duwi Fm are typified as land-derived type-III kerogen. The middle and
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uppermost members contain type-II kerogen. Most of the Dakhla Fm is typified by type-II
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kerogen with the exception at the lowermost and middle Hamama member and middle part of
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the Beida member that contain type-I kerogen. The repeated occurrence of photic zone anoxia
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as indicated by the presence of aryl isoprenoids was accompanied by strongly reducing
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conditions in the bottom waters and in sediments. This led to strong enrichments of some
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redox sensitive elements like molybdenum. Photic zone anoxia preferentially occurred during
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marine transgressions, in accord with high hydrogen indices typifying marine organic matter.
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However, such periods were interrupted by periods of increased input of terrigenous material,
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reflected by high aluminium contents and type-III kerogen. Overall, low temperature of
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maximum generation (Tmax), odd-over-even predominance of n-alkanes, the preservation of
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carboxylic acids, and a predominance of biological 17β,21β(H) hopanoids over their
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geological 17α,21β(H) stereoisomers reveal that the organic material of the Quseir section is
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immature to at best moderately mature. The observed dominance of rearranged steranes
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(diasterenes) is consequently best explained by enhanced clay catalysis, rather than by
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thermochemical alteration. Additionally, the biomarker inventory of the Quseir section
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corroborates that eukaryotic algae were affected by the extinction event at the Cretaceous-
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Palaeogene boundary to a much greater extent than bacteria including bacterial primary
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producers.
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Keywords: Cretaceous-Palaeogene, Egypt, Quseir, Black shale, Rock-Eval, Trace metals,
Biomarkers.
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1. Introduction The Late Cretaceous to early Cenozoic was characterized by increased carbon dioxide
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levels triggered by prominent global igneous activity and is among the best studied
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greenhouse periods (e.g., Takashima et al., 2006), where the phytoplankton community
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(coccolithophores, dinoflagellates, and diatoms) was modified significantly. Phytoplankton
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diversity was rapidly detached from the long-term sea-level trends at the Cretaceous-
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Palaeogene boundary, when mass extinction removed much of the diversity that had
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developed over the preceding millions years, especially among coccolithophores and
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dinoflagellates (Falkowski et al., 2004). In northeast Africa, marine continental shelves
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prevailed across the Upper Cretaceous-Palaeogene boundary. Sedimentation at that time was
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influenced by global warming, which consequently led to the development of anoxia in the
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oceans, leading to the deposition of organic-rich shales (Robinson and Engel, 1993). These
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continental shelf environments were characterized by high sedimentation rates (Tourtelot,
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1979). Due to the consumption of oxygen in the upper water column by bacterial degradation
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of organic matter in these settings, sediments became anoxic. The resulting black shales are
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excellent oil source rocks, which sourced some of the giant and supergiant oil fields in the
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Middle East (cf. Robinson and Engel, 1993). In Egypt, the time-equivalent deposits are
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preserved as laterally extensive black shale successions that are represented by the Duwi and
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Dakhla formations in ascending order. They are rich in organic matter, mainly preserved as
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kerogen, and contain abundant sulphide minerals (e.g., pyrite). The black shales commonly
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contain high concentrations of redox-sensitive trace elements such as V, Cu, Cd, Ni, Mo, and
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U (Brumsack, 2006; Loukola-Ruskeeniemi and Lahtinen, 2013). Under anoxic conditions, the
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export of redox-sensitive trace metals to the seafloor is high, resulting in a significant
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drawdown of trace metals concentrations in seawater (Ross and Bustin, 2009). Organic-rich
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sediments are consequently commonly enriched in Cu and Ni, and the sulphide mineral-
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forming elements Mo, V, Cd, Zn, U, and rarely Co (Brumsack, 2006; März, 2007; Hetzel et
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al., 2009). In the easily extractable fraction of black shales from phosphate mines within the Duwi
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Formation (Fm) along the Red Sea coast of Egypt, cyclic terpenoids (steranes) have been
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found and the sterane C27/28 ratio was used as an indicator for increased marine organic matter
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input (Ganz, 1987). Further, Ganz et al. (1990) used Rb (whole rock) and sterane
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C27/(C27+C29) ratios to better characterize the terrestrial input to the sites Abu Shegela and
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Younis north mines in the Red Sea area. Sterane C27/(C27+C29) ratios were 0.2-0.7 and 0.4-0.6
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for Abu Shigaila and Younis mines, respectively. Ganz et al. (1990) suggested that carbonate
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and phosphorite intervals are dominated by marine organic matter. The C29-sterane/C30-
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hopane ratio reported by El-Kammar (1993) increased upwards in the Quseir section with
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increasing marine affinity. Robinson and Engel (1993) recorded variations in the organic
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matter within the Duwi and Dakhla formations based on samples from six phosphorite mines
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in the Red Sea area. The lower Duwi Fm is organic matter-rich and this organic matter shows
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a low hydrogen index, whereas the upper Duwi Fm is poor in organic matter, but
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characterized by a high hydrogen index. The lowermost Dakhla Fm is oil-prone and reflects
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the highest hydrocarbon source rock potential in the wider study area (e.g., El-Shafeiy et al.,
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2014). The high Cr, V, and Zn contents with high Ni/Co, V/Cr, and U/Al ratios reported by
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Baioumy and Ismael (2010) of shale samples from the Duwi Fm suggest a more reducing
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depositional palaeoenvironment for shales of the Red Sea area compared to their time-
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equivalent shales of the Western Desert.
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This work focuses on chemostratigraphic changes in the Quseir black shale sequence,
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using a core drilled in 2008 in the Duwi mountain area (Fig. 1). The emphasis of this study is
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put on trace element patterns and bulk organic and lipid biomarker inventories of the Duwi
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and Dakhla formations. These two formations cover the transition from the Upper Cretaceous ~6~
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organic matter sources, and preservation efficiency are inferred from the variations of the
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different geochemical parameters to finally evolve a scenario for the deposition of organic
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black shales. Thermal maturity assessed from Rock Eval data and diagenetic modifications of
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some lipid biomarkers allow for a better understanding of the transformation of the not deeply
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buried black shales.
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2. Geological Setting
During the Late Cretaceous to early Palaeocene, sedimentation in northeastern Egypt was
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controlled by a pronounced erosion related to active uplift during the late Campanian to early
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Maastrichtian. Deposition of the Upper Cretaceous to Lower Palaeocene rocks of Egypt was
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controlled by tectonically induced and global eustatic sea level fluctuations (e.g., Hendriks
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and Luger, 1987; Hendriks et al., 1987; Philobbos, 1996). Broad continental shelves
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developed in North Africa and the Middle East, including Egypt, as a result of Late
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Cretaceous transgressions (Baioumy and Tada, 2005). This resulted in a high productivity
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upwelling regime that existed during Late Cretaceous time along the south-eastern margins of
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the Tethys associated with the Syrian Arc system (Ashckenazi-Polivoda et al., 2011;
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Schneider-Mor et al., 2012) and is recorded by phosphate-rich sediment sequences (Fig. 1A).
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The Duwi Mountain is located on the eastern Egyptian margin of the Red Sea. This area was
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strongly influenced by the Red Sea tectonics. Uplift associated with this rift event and related
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Red Sea faulting caused the faulted block geometry of the Duwi Mountain and exposure of
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the organic black shales.
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The Cretaceous-Palaeogene black shale deposits of Egypt are part of the Duwi and Dakhla
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formations. Their depositional environment are mainly inner (Duwi Fm) to middle and rarely
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outer (Dakhla Fm) shelf (e.g., Tantawy et al., 2001; Zalat et al., 2008; El-Azabi and Farouk, ~7~
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phosphogenic belt (Baioumy and Tada, 2005), composed mainly of phosphates but
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accompanied by organic-rich shales, glauconites, oyster limestones, cherts, and silt- to
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sandstones (Bein and Amit, 1982; Tröger, 1984; Germann et al., 1985; Mikbel and Abed,
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1985; Notholt; 1985; Ganz et al., 1987; Abed and Al-Agha, 1989; Glenn and Arthur, 1990;
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El-Kammar 1993 and references therein). The presence of organic-rich intervals indicates a
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period of high primary productivity on the shallow shelves that favoured the preservation of
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organic matter (Glenn and Arthur, 1990). The Dakhla Fm is characterized mainly by
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foraminifera-rich shales and marls with limestones and rare siltstone intercalations.
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The deposition of the Duwi Fm represents the initial stage of the Late Cretaceous marine
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transgression in Egypt. The Duwi Fm in the Red Sea, Nile Valley, and Abu Tartur areas was
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subdivided by Baioumy and Tada (2005) into lower, middle, upper, and uppermost members.
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The Dakhla Fm is subdivided into Hamama and Beida members in ascending order in the Red
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Sea area according to Abdel Razik (1972), Luger (1988), Awad et al. (1992), and Zalat et al.
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(2008). These subunits are separated by the unconformity that represents the Cretaceous-
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Palaeogene boundary. Zalat et al. (2008) subdivided the Dakhla Fm into two deepening
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upward cycles in the Safaga-Quseir area, corresponding to the Hamama and Beida members.
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The Dakhla Fm is unconformably overlain by chalky limestone of the Upper Palaeocene
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Tarawan Fm (Awad and Ghobrial, 1965).
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3. Material and methods
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The organic-rich sediments were collected from a core drilled by the Egyptian Mineral
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Resources Authority (EMRA) in cooperation with the Ministry of Petroleum and sponsored
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by DanaGas© Egypt. The drilling site was located in the Quseir area (Duwi Mountain) in the
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Eastern Desert of Egypt (Fig. 1). ~8~
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According to El-Shafeiy et al. (2014), two sampling strategies were applied during the
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present study. Downcore samples were collected every 10 cm and subsequently 10 successive
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samples were mixed and homogenized to obtain representative bulk samples for 1 m of
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profile for routine analyses after grinding (TOC, Rock Eval, and trace metals). Secondly,
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lower resolution samples (every 2 to 6 m) were collected to monitor lithology or facies
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changes. These samples were also used for the lipid biomarker analyses.
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3.2. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
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Homogenized samples
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were analysed using Inductively Coupled Plasma-Mass
Spectrometry in ACME Laboratories (Vancouver, Canada; El-Shafeiy et al., 2016). The
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analytical procedure included the dissolution of the samples, which is achieved by the
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sequential addition of 4 ml HNO3, 3 ml HClO4 and finally 5 ml HF, and then evaporated to
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dryness at 200°C. The residue was first dissolved with 5 ml HNO3 by heating, then 5 ml of 4
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ppm indium solution was added to the sample as internal standard. Prior each measurement,
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the nebulizer and spray chambers were washed by introducing the solution for 3 min. with 0.5
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rpm and 30 seconds with 0.18 rpm.
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3.3. Total Organic Carbon and Rock Eval analysis
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For the analyses of Total Organic Carbon (TOC) contents and Rock Eval, the methods
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described in El-Shafeiy et al. (2014; 2016) were used. In brief, the homogenized routine
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samples were measured for their TOC contents (wt%) and Rock Eval pyrolysis analyses in the
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laboratories of StratoChem in Egypt. For TOC contents, 200 mg of the homogenized rock was
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weighed into a Pyrex beaker and reacted with hydrochloric acid (HCl), then transferred to a
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microfiber filter paper using a Millipore filter apparatus. The samples were combusted in a
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LECO C230 or LECO EC-12 combustion furnace, where the resulted carbon dioxide (CO2)
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was quantitatively measured by using an infrared detector.
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was weighed and placed into an auto-sampler crucible for isothermal heating. S1
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hydrocarbons (free hydrocarbons) were volatilized (at 300°C) and detected by a Flame
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Ionization Detector (FID). At 600°C, the release of additional hydrocarbons (S2) was
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achieved, simulating the pyrolytic degradation (i.e., cracking) of kerogen in the rock. Then,
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the CO2 was released after cooling to approximately 400oC. The released CO2 is reported as
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milligrams of S3 per gram of sediments. The amount of S3 represents the amount of oxygen
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in each sample.
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Sixty-two samples were selected for the extraction of easy soluble organic matter
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(bitumen), and were treated as follows: Samples were homogenized by pestel and mortar
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avoiding contamination. The homogenized samples were extracted by adding 40 ml
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dicholoromethane (DCM):methanol (3:1 v/v) prior each extraction step. The extraction was
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done by microwave extraction with a CEM MARS X for 15 min at 80°C and 600 W. Internal
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standards of various polarities (squalane, behenic acid methylester, 1-nonadecanol, and 2-
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methyl-octadecanoic acid) were added to the sediments prior extraction. The samples were
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extracted several times until they became colourless (at least three times). The resulting
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extracted organic phases were collected after each single extraction step and dried with
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sodium sulphate. The combined total lipid extracts (TLE) were evaporated under a stream of
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nitrogen. Subsequently, separation of the DCM-soluble asphaltenes from the n-hexane soluble
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maltenes was achieved. This procedure was applied as a clean-up procedure using 150 mm
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pasteur pipettes filled with glass wool and sodium sulphate. The maltenes were fractionated
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into four fractions with increasing polarity (1: hydrocarbons, 2: esters/ketones, 3: alcohols and
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4: carboxylic acids) by means of a solid phase extraction column (Supelco DSC-NH2; 500
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mg). The reagent used were (1) 4 ml n-hexane, (2) 6 ml n-hexane:DCM (3:1, v/v), (3) 7 ml
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were transferred to methyl esters by adding 1 ml of boron trifluoride (BF3) in methanol to the
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dried fatty acid fraction. The reaction time was 1 hour at 70°C. The hydrocarbon and fatty
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acid fractions were examined in all samples, whereas the ester/ketone and alcohol fractions
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were found to lack pristine biomarker signatures.
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Aliquots of the hydrocarbon and fatty acid fractions of each sample were injected to a gas
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chromatograph with a flame ionization detector GC-FID for quantification, and a selection of
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samples was measured by coupled gas chromatography-mass spectrometry (GC-MS) for
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identification of compounds. The samples were measured on a Thermo Electron Trace GC-
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MS equipped with a 30 m Rxi-5MS fused silica capillary column (0.32 mm i.d., 0.25 µm film
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thickness) using helium as a carrier gas. The GC temperature program was 60°C (1 min) to
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150°C at 15°C min-1, then to 320°C at 4°C min-1. The final temperature was held for 37 min.
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The analysed samples represent different lithologies including black shale, mudstone, marl,
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limestone (wacke- to packstone), and phosphorite in order to identify possible variation of
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biomarker patterns with different lithologies.
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4. Results
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4.1.
Stratigraphy
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The thickness of the Duwi Fm varies significantly from a maximum (150-170m) at the
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Duwi Mountain in Red Sea area, which considered being the type locality, to a minimum (20-
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70m) in the Kharga-Dakhla landscape (Youssef, 1957; Said, 1962; Baioumy and Tada, 2005).
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The Dakhla Fm varies in an opposite manner and its type locality is in Dakhla Oasis (Said,
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1961). The Dakhla Fm reaches its largest thickness (within Red Sea area) in the Duwi
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Mountain and it is highly reduced toward the north in Safaga area.
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(Baioumy and Tada, 2005) and is composed of grey laminated silty claystone, green medium
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to coarse-grained glauconitic sandstone, grey laminated shale, intercalated with thin beds of
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sandy phosphorites 5% TOC). The depositional regime in the Quseir area witnessed a high degree of lithofacies
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variation, which in turn indicates different sources of sediments and consequently organic
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matter inventories. The average chemical composition for each lithofacies was reported by El-
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Shafeiy et al. (2016).
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4.2.
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Micropalaeontology
The Cretaceous-Palaeogene boundary was identified at 185 m depth, based on calcareous
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nannoplankton species (Fig. 2). The precise location of the Cretaceous-Palaeogene boundary
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in the core itself was not identified due to the friability of the shales during core recovery. The
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same is true for the Campanian-Maastrichtian boundary, where nannoplankton species are
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barren. Further, some drilling gaps within the oyster limestone intervals led to a shortage of
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samples from these horizons. Palynomorphs, however, allowed localisation of the boundary
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between the Campanian and the Maastrichtian, tentatively placed between 267 and 280 m
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depth (Fig. 2). However, a well-defined boundary was not assigned, because of the scarcity of
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samples in this interval caused by numerous drilling gaps.
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CC25b, CC26, and NP2-NP4 (Fig. 2), according to Sissingh (1977) and Perch-Nielsen
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(1985). The CC23 biozone is characterized by the occurrence of Uniplanarius trifidus as a
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main marker, characterizing the late Campanian age. Following upsection, the CC25b biozone
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is characterized by the occurrence of both Lithraphidites quadratus and Arkhangelskiella
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maastrichtiana as the main characteristic markers with ~72 m of thickness of Upper
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Maastrichtian strata. The biozone CC26 is characterized by the occurrence of Nephrolithus
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frequens as the main marker. The rest of the Dakhla Fm corresponds to NP2-NP4 biozones.
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They are, in turn, characterized by the occurrence of Cruciplacolithus tenuis, Cruciplacolithus
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cf. edwardsii, and Chiasmolithus cf. danicus as main markers for the Lower Palaeocene age.
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The missing record of the biozones CC24 and CC25a is most probably due to the limited
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number of samples around this interval caused by the above mentioned drilling gaps. A
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similar biozonal succession was recorded by Tantawy et al. (2001).
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The identified palynomorph assemblage is completely composed of marine species. The
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most conspicuous element of the palyniferous samples located at 233, 240.6 and 244.7 m
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depth is a high abundance and low diversity peridinioid association, which reflects a local
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African aspect. The common dinocyst species Cerodinium granulostriatum is recorded from
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the uppermost Duwi Fm. Other typical dinocysts are Palaeocystdinium australinum recorded
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from the Maastrichtian and different species of Andalusiella originally described from the
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pre-Maastrichtian (Campanian) or early Maastrichtian of Egypt (Schrank, 1984; 1987). From
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a palaeoecological point of view, high peridinioid contents in a dinoflagellate community may
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indicate low palaeosalinities (Hultberg, 1986; Schrank, 1987), but the abundant foraminiferal
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tests recorded herein together with the presence of exceedingly abundant dinoflagellate cysts
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provides evidence for a marine influence. The weakly diversified dinocyst assemblage with its
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few but common species indicates an epicontinental, neritic environment (Schrank, 1984).
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Deep-sea assemblages would be expected to be richer in species and more stable in
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composition (Wall, 1967).
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4.3. TOC, Rock-Eval pyrolysis and trace metals In order to assign the benthic palaeoenvironmental conditions as well as to identify photic
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zone anoxia, we integrated different types of proxies, including trace metal and organic-
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geochemical bulk parameters (Fig. 2). Aluminium is used as indicator of detrital terrigenous
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components. The Ce-anomaly can be used as a recorder of eustatic sea-level change (Wilde et
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al., 1996; Chen et al., 2012), but is more commonly used as palaeo-redox indicator (e.g., Hu
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et al., 2014). Similarly, the Ni/Co ratio can be used as proxy for varying palaeoredox
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conditions (e.g., Jones and Manning, 1994; Johnson et al., 2010). Total organic carbon (TOC)
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is a primary indicator on palaeoproductivity, the depositional environment, and the chances
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for preservation (e.g., Hunt, 1995). The hydrogen index (HI) is of great value to characterize
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the sources and maturity of sedimentary organic matter (e.g., Hakimi et al., 2014).
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The chosen trace metals allow a separation of oxic, dysoxic, and sub- to anoxic
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environments in the Quseir section at the time of deposition (Fig. 2; cf. Rimmer, 2004). All
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Ce values are normalized to chondrite data of McDonough and Sun (1995). The Ce-anomaly
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is calculated after Wilde et al. (1996). Molybdenum (Mo) has been widely used as a redox-
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sensitive proxy for benthic environments (Algeo and Lyons, 2006). It can be removed from
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solution via metal sulphides and organic matter under sulphidic conditions, and remains in a
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dissolved state in anoxic, non-sulphidic environments (cf. März, 2007). The U/Mo ratio was
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applied to distinguish between anoxic non-sulfidic and anoxic sulfidic conditions (Fig. 3; cf.
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Arning et al., 2009).
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With regard to the kerogen composition, type-III characterizes the lower and upper
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members of the Duwi Fm (Fig. 4), together with the strata around 150 m depth of the first
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subunit of the Beida member. Type-II kerogen characterizes the middle and uppermost ~ 15 ~
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of the middle portion of the second subunit of the Beida member plot in the type–I kerogen
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field together with the highest TOC values of this interval (Fig. 2 and 4). Generally, the
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majority of the samples are immature (Fig. 4A). The Tmax values range between minimum
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403ºC and maximum 442ºC. It is worth noting that some samples from the upper member of
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the Duwi Fm and the Beida member of the Dakhla Fm are placed in the field of mature
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organic material (Fig. 4A).
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4.3.1. Duwi Formation
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The lower member is characterized by high Al contents (average 7.6%), slightly higher
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than the average shale value (5%; Wedepohl, 1971), and low negative Ce-anomalies (average
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-0.1). Moreover, the samples are characterized by low TOC contents (average 1.1%), HI
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values of 120 mg HC/g TOC in average, indicating type-III kerogen, and plotted in the
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dysoxic field of the Ni/Co ratio (Fig. 2). The high S content (average 1.4%) are mirrored by
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increased Mo contents, consequently causing relative low U/Mo ratios (average 1.5; Fig. 3).
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The middle member has slightly lower Al contents (sometimes less than average shale) but
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noticeably higher TOC values (average 2.2%). Mo contents (average 9.6 ppm) are like those
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of the average shale (Figs. 2 and 6). HI values with 352 mg HC/g TOC in average indicate
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type-II kerogen. Up-section, the characteristic bedding of the upper member, composed of
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rhythmically laminated silt- to mudstone, is characterized by higher Al contents than the
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average shale (average 8.1%), moderate TOC values (average 3.1%), and fairly low S
344
contents (average 0.3%), as well as low Mo contents (average 0.9 ppm; Figs. 2, 3 and 6). In
345
contrast, the HI of the same layer is markedly low (average 180 mg HC/g TOC), indicating
346
type-III kerogen. The Ce-anomaly in this part of the section is the highest for the entire
347
section (average ~ −0.07). For the uppermost member of the Duwi Fm, the redox conditions
348
changed from monotonously dysoxic in the previous intervals to sub-anoxic or anoxic as
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~ 16 ~
ACCEPTED MANUSCRIPT inferred from Ni/Co ratios (Fig. 2). The Al and TOC contents are low (average 2.8% and
350
1.7%, respectively), but the HI is mostly >220 mg HC/g TOC, indicating type-II kerogen. The
351
S content is generally low (average 1.1%; Fig. 3), accompanied by Mo with more or less
352
similar contents as in the average shale (average 4.5 ppm; Fig. 6).
353
4.3.2. Dakhla Formation
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Two characteristic organic-rich cycles are observed in the Hamama member of Dakhla Fm.
355
The first is the lowermost 4-5 m of the Hamama member (grey horizon; Fig. 2) with highest
356
TOC contents (up to 14% and on average 7.8%), very high Ni/Co ratios (up to 52)
357
accompanied by very high HI values (up to 1150 mg HC/g TOC), indicating type-I kerogen.
358
Additionally, S and Mo are enriched in this interval (up to 2.8% and 253 ppm, respectively;
359
Figs. 3 and 6). The Al content is markedly decreased relative to the average shale (average
360
2.8%), and the strata are typified by highly negative Ce-anomalies (average ~ −0.5) at the
361
same time. A similar observation was made for the lowermost strata of the Mawhoob member
362
of the Dakhla Fm in the Abu Tartur area (cf. El-Shafeiy et al., 2014). Up-section, an abrupt
363
decrease in the TOC content, HI, and Ni/Co ratio together with an abrupt increase in Al
364
contents and Ce-anomalies was observed (Fig. 2).
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The second cycle typified by the high organic-matter contents occurs in the upper part of
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the Hamama member where a continuous increase of TOC (2-7.1%, averaging; 4.2%) and HI
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(480-830 mg HC/g TOC) indicates the ample presence of type-II kerogen. TOC and HI
368
maximize just below the Hamama/Beida transition (i.e., the Cretaceous-Palaeogene
369
boundary). Just above this transition a decrease of TOC is observed (Fig. 2). The majority of
370
the Hamama samples falls in the sub- to anoxic field of the Ni/Co ratio (Fig. 2). The high
371
TOC content is accompanied by a high S content (average 2.1%), and is in accordance with
372
high Mo contents (average 10 ppm; Figs. 3 and 6).
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~ 17 ~
ACCEPTED MANUSCRIPT The Beida member can be further subdivided into three subunits, according to the
374
geochemical proxies used. The first subunit is placed from the base to 150 m depth,
375
characterized by continuously higher Al contents than the average shale (average 7.5%).
376
Further, the Ce-anomalies are less negative in this subunit (average ~ −0.25), and are
377
maximizing at around 150 m depth. TOC (average 2.4%) and HI (average 570 mg HC/g
378
TOC), indicating type II kerogen, are continuously decreasing up-section and are lowest at the
379
top of the subunit (Fig. 2). The top of the second subunit is at 60 m depth. This subunit is
380
characterized by continuously decreasing Al contents (0.1-10 averaging 5.9%) and highly
381
negative Ce-anomalies (down to −0.8 with average ~ −0.41). In contrast, the TOC values
382
(average 4.3%) and HI contents (average 840 mg HC/g TOC), indicating type I kerogen, are
383
continuously increasing up-section and maximize at 87 m core depth (Fig. 2). The Ni/Co ratio
384
is extremely high at 87 m depth (up to 150; Fig. 2). Finally, the third, uppermost subunit is up
385
to 40 m thick, characterized by a rise of Al contents (0.1-11 averaging 6.7%), despite some
386
scatter, and less pronounced negative Ce-anomalies (average ~ −0.2). On the other hand, the
387
TOC values (average 2.1%), HI (average 605 mg HC/g TOC), indicating type I kerogen, as
388
well as the Ni/Co ratio, decrease upsection (Fig. 2). The entire Dakhla Fm is characterized by
389
high Mo contents (0.2-30 ppm, average 21.2 ppm). These values are higher than the average
390
shale (El-Shafeiy et al., 2016). Only in the layer at around 150 m, Mo contents are lower (Fig.
391
6), accompanied by low TOC values, S values, and Ni/Co ratios (Figs. 2 and 3).
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4.4. Lipid biomarker data
393
The hydrocarbon fractions of the studied samples chiefly comprise n-alkanes and cyclic
394
terpenoids (steranes and hopanoids), accompanied by various acyclic isoprenoids, also
395
including aryl isoprenoids (Fig. 5). Overall, n-alkanes and steranes are the most abundant
396
compound classes in all samples. The n-alkanes comprise chains from n-C14 to n-C32 (Fig. 5),
397
whereas contents vary throughout the sections. Generally, n-alkanes are characterized by an ~ 18 ~
ACCEPTED MANUSCRIPT odd-over-even predominance. The Carbon Preference Index (CPI), calculated according to
399
Marzi et al. (1993), is always higher than 1 (Table 1), with an average of 2.1 and 3.0 for Duwi
400
and Dakhla formations, respectively. Noteworthy, the silt- to mudstone layers in the upper
401
member of the Duwi Fm have CPI values as high as 4.7 (Table 1). The most prominent
402
acyclic isoprenoids are phytane (Ph), pristane (Pr); farnesane is only rarely present (Fig. 5).
403
The Pr/Ph ratio is mostly 1, whereas the samples from the middle and
405
uppermost members have Pr/Ph ratios as low as 0.25 (Fig. 5). Overall, the Dakhla Fm is
406
characterized by low Pr/Ph ratios, but especially in the Beida member (~ 0.5).
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Aryl isoprenoids are found in the free lipid extracts of the hydrocarbon fraction in
408
numerous samples from various parts of the section. Isorenieratane (C40) is only identified in
409
Quseir samples in trace amounts, but its highest contents coincide with the highest TOC
410
values, as for example in the interval at around 230 m depth. Isorenieratane contents reach 33
411
µg/g TOC in the middle member of the Duwi Fm (Fig. 6). In the same horizons where
412
isorenieratane is abundant, also β-carotane is present (Fig. 6). Other aryl isoprenoids are
413
short-chain aryl isoprenoids (C13, C14, C16) and rarely C11 and C19 chains (Fig. 6).
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Steranes are the most abundant cyclic terpenoids in most of the samples. Generally, the
415
regular desmethylated steranes (up to 428 µg/g TOC) are more abundant than the rearranged
416
diasterenes (up to 70 µg/g TOC; Fig. 6). The Duwi Fm contains less steranes, with two
417
exceptions in the middle member and one sample at 267.8 m from the uppermost member,
418
where sterane contents are significantly higher than below and above (Fig. 6). In the Hamama
419
member, steranes are particularly abundant within the lower strata (Fig. 6).
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420
Among the desmethylated steranes, C27–29 5α,14α,17α(H)-20R isomers predominate, but
421
are accompanied by smaller contributions of the 5α,14β,17β (H)-20R isomers (Fig. 5). C30
422
desmethylated steranes are present in trace amounts only. The middle (up to 120 µg/g TOC) ~ 19 ~
ACCEPTED MANUSCRIPT and uppermost (up to 428 µg/g TOC) members of the Duwi Fm have obviously higher sterane
424
contents than the lower (up to 75 µg/g TOC) and upper (up to 50 µg/g TOC) members (Fig.
425
6). The Hamama member reveals high contributions of desmethylated steranes (up to 70 µg/g
426
TOC), maximizing in the topmost interval (200-185 m depth), which is uppermost
427
Maastrichtian in age. Overall, all sterane contents decrease at the Hamama/Beida transition
428
(Maastrichtian-Danian; Fig. 6). The Beida member shows a variable distribution of steranes
429
with maxima (up to 49 µg/g TOC) at 120-100 m depth, mirrored by a significant HI peak
430
(Fig. 2).
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Rearranged C27–29 diaster-13(17)-enes (rearranged diasterenes) are observed in samples
432
from the Duwi Fm upsection up to 130 m depth in the Dakhla Fm (Fig. 6). They are
433
represented by predominantly 5α,4α,17α(H)-20R isomers, whereas the 5α,14β,17β(H)-20R
434
isomers are only present in minor amounts (Fig. 5). Similar to the desmethylated steranes, the
435
middle (up to 68 µg/g TOC) and uppermost (up to 112 µg/g TOC) members of the Duwi Fm
436
encompass higher contents of rearranged diasterenes than the lower (up to 45 µg/g TOC) and
437
upper (up to 26 µg/g TOC) members (Fig. 6). Very low contents of rearranged diasterenes
438
were detected in the silt- to mudstone layers of the Duwi Fm. Alike the desmethylated
439
steranes, also rearranged diasterenes maximize at the Hamama member (up to 119 µg/g TOC;
440
Fig. 6) and at the Duwi/Dakhla transition (up to 55 µg/g TOC; Fig. 6). The Beida member
441
contains no or only trace amounts of rearranged diasterenes probably due to its high carbonate
442
content (Fig. 6).
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443
The hopanoids present in the majority of the Quseir samples are; 25,28,30-trisnorhopane,
444
17α(H),21β(H) and 17β(H),21α(H)-norhopanes, 17α(H), 21β(H)- and 17β(H),21β(H)-hopane,
445
17α(H),21β(H) and 17β(H),21β(H)-homohopane, and in minor amounts 17β(H), 21β(H)-
446
bishomohopane (Fig. 5). Overall, hopanes are less prominent than steranes (Fig. 6). In the
447
Duwi Fm and the Duwi/Dakhla transition, hopanoid contents are higher than in the Dakhla
448
Fm (Fig. 6). Among hopanoids, the 17β(H),21β(H) stereoisomers predominate over the ~ 20 ~
ACCEPTED MANUSCRIPT 17α(H),21β(H) isomers in most samples (Table 1). Whereas in the lower member of the Duwi
450
Fm the 17α(H),21β(H) hopanoid isomers predominate, in the remaining Duwi Fm both
451
stereoisomers of C30 hopane prevail (up to 150 µg/g TOC; Fig. 6). As found for the steranes,
452
hopanes are also abundant in the Hamama member. At the Maastrichtian-Danian boundary
453
hopanes decline significantly (Fig. 6). Between 100-120 m, hopanes maximize (up to 7.1 µg/g
454
TOC; Fig. 6) in the Beida member, accompanied by a very high hydrogen index and a
455
maximum in sterane abundance (Figs. 2 and 6).
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Apart from acyclic and cyclic terpenoids and n-alkanes, straight-chain saturated fatty acids
457
are observed in the carboxylic acid fractions of most samples. They range from n-C12 to n-C33,
458
and maximize at n-C16 and n-C18; they are further characterized by a preponderance of even
459
over odd numbered fatty acids. The CPIeven (e.g., El-Shafeiy et al., 2014) for the Quseir
460
section shows average values of 4.27 and 4.31 for the Duwi and Dakhla formations,
461
respectively (Table 1). As in the hydrocarbon fractions, pentacyclic terpenoids were found,
462
including 17β(H),21β(H)- and 17α(H),21β(H)-hopanoic acid isomers with C31 to C33 carbons.
463
The 17β(H),21β(H) stereoisomers generally dominate over the 17α(H),21β(H) hopanoic acid
464
isomers (Table 1). Noteworthy, the ββ/αβ ratios for hopanoic acids are higher for the Dakhla
465
Fm (average 5.19 and 4.2 for C32 and C33 hopanoic acids, respectively) than for the Duwi Fm
466
(average 2.78 and 2.60 for C32 and C33 hopanoic acids, respectively).
468 469
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5. Discussion
5.1. Thermal Maturity
470
The samples from the Quseir section have generally low Tmax (
