Tracing the geochemical imprints of Maastrichtian black shales in southern Tethys, Egypt: Assessing hydrocarbon source potential and environmental signatures

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS International Journal of Coal Geology Pub Date : 2024-01-20 DOI:10.1016/j.coal.2024.104457
Douaa Fathy , Alireza Baniasad , Ralf Littke , Mabrouk Sami
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Abstract

This study conducted comprehensive bulk and molecular geochemical analyses, as well as elemental investigations, on seventeen black shale samples collected from the Upper Cretaceous sediments on the western margin of the Red Sea. The primary objective is to assess the hydrocarbon generation potential, maturity, source input, biodegradation levels, and depositional environment characteristics within the Lower Maastrichtian interval near the Safaga area. Lower Maastrichtian black shales demonstrate very good to excellent source rock generative potential based on pyrolysis data. The prevalent kerogen type in the older black shale at the Heweitat mine is Type II, whereas within the younger units at the Queih mine, it predominantly exhibits Type II/III kerogen. These Maastrichtian black shales remain thermally immature, as evidenced by vitrinite reflectance (VRr < 0.5%), pyrolysis data, and biomarker proxies.

The studied black shales show that the organic matter input comprises bacterial and algal biomass with minor terrigenous contributions. Additionally, there is no evidence of significant biodegradation in the studied samples based on molecular fossils data. Microscopic analysis and various bulk and molecular characteristics, in conjunction with major and trace element profiles, collectively indicate a marine depositional environment with oxygen-deficient bottom water conditions during source rock deposition. The presence of isorenieratene and aryl isoprenoids suggests persistent and episodic photic zone anoxia during the Maastrichtian period. Elevated nutrient inputs and paleobioproductivity were recorded in the older black shale at the Heweitat mine compared to the younger one at the Queih mine. Paleoproductivity and oxygen depletion emerge as pivotal factors influencing the accumulation and preservation of organic matter within the black shales. These findings provide valuable insights into the environmental conditions prevailing during the deposition of Maastrichtian sediments in the Eastern Desert.

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追踪埃及特提斯南部马斯特里赫特黑页岩的地球化学印记:评估烃源潜力和环境特征
这项研究对从红海西缘上白垩统沉积物中采集的十七个黑色页岩样本进行了全面的块状和分子地球化学分析以及元素调查。主要目的是评估萨法加地区附近的下马斯特里赫特统区间的碳氢化合物生成潜力、成熟度、源输入、生物降解水平和沉积环境特征。根据热解数据,下马斯特里赫特黑页岩显示出非常好到极好的源岩生成潜力。Heweitat 矿区较老的黑色页岩的主要角质类型为第二类,而在 Queih 矿区较年轻的单元中,主要表现为第二/三类角质。这些马斯特里赫特黑页岩仍然处于热不成熟状态,这一点可以从玻璃光泽反射率(VRr < 0.5%)、热解数据和生物标志物代用指标中得到证明。此外,根据分子化石数据,研究样本中没有明显的生物降解迹象。显微分析、各种块状和分子特征以及主要和微量元素剖面共同表明,在源岩沉积期间,海洋沉积环境的底层水缺氧。异烯烃和芳基异戊烯类化合物的存在表明,在马斯特里赫特时期,光照区缺氧现象持续存在并时有发生。与 Queih 矿区较年轻的黑色页岩相比,Heweitat 矿区较古老的黑色页岩中记录到了较高的营养输入和古生物生产率。古生物生产率和氧气耗竭是影响黑页岩中有机物积累和保存的关键因素。这些发现为了解东部沙漠马斯特里赫特沉积物沉积期间的环境条件提供了宝贵的见解。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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