| Title: | Multiple controllers on organic matter accumulation at the Mesopotamia Basin of the Chia Gara Formation shale, Central Iraq |
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| Authors: | ID Ali, Rana A. (Author)
ID Al-Ali, Iman A. (Author) |
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| Files: |  PDF - Presentation file, download (9,96 MB)
MD5: D94B0BC26D04EFC19F4E9F4448790A13
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| Language: | English |
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| Typology: | 1.01 - Original Scientific Article |
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| Organization: |  GeoZS - Geological Survey of Slovenia
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| Abstract: | The Tithonian–Berriasian Chia Gara Formation in Central Iraq represents a major breakthrough in shale oil exploration. This study investigates two continuous core sections (140m and 137m) from the East Baghdad (EB1) and Balad (Ba1) oilfields, located within the intrashelf basin along the passive margin of the Arabian Plate. Comprehensive geochemical analyses, including major and trace elements, Mo isotopes, and total organic carbon (TOC), were conducted to evaluate the mechanisms controlling organic matter enrichment. The EB1 and Ba1 cores are subdivided into five and four organic sedimentary facies (OSF), respectively. In EB1, TOC values in the lower OSF 1 and OSF2 range from 3.55 to 8.0 wt.% and 2.31 to 4.42wt.% and are higher than those of the upper OSF 3, OSF 4, and OSF 5 that range from 0.5 to 3.77wt. %. In Ba1, OSF 3 and OSF 5, which range from 0.39 to 2.7wt.%. Redox indicators such as U/Th, Ni/Co, EF(U), and EF(Mo) show a progressive shift towards more oxic bottom-water conditions. The δ98/95Mo data (–0.3 to 2.5‰) confirm the presence of euxinic conditions, particularly within OSF2 in both EB1 and Ba1, thereby resolving previous uncertainties regarding bottom-water redox conditions. Primary productivity indices (Cu/Al and Ni/Al ratios) suggest relatively low productivity in deep-water slope and basinal facies. Furthermore, the upwelling indicators (EF(Co) × EF(Mn)), varying from 0 to 0.48 for EB1 and 0.05 to 0.18 for Ba1, suggest that preservation conditions played a more significant role than productivity conditions within the deep-water slope and basin. Differential subsidence, with local uplifts and erosion within the Mesopotamian Foredeep Basin likely contributed to spatial variability in organic enrichment. Overall, this study highlights the importance of the redox environment in the development of high-quality hydrocarbon source rocks in unrestricted environments that present upwelling. |
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| Keywords: | Mo isotopes, redox conditions, organic matter, primary productivity, geochemical methods, Upper Jurassic–Early Cretaceous, Mesopotamian Basin |
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| Publication status: | Published |
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| Publication version: | Version of Record |
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| Publication date: | 07.04.2026 |
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| Year of publishing: | 2026 |
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| Number of pages: | str. 55-76 |
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| Numbering: | vol. 69, no. 1 |
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| UDC: | 55 |
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| ISSN on article: | 0016-7789 |
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| DOI: | 10.5474/geologija.2026.003  |
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| COBISS.SI-ID: | 283526915 |
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| Note: |
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| Publication date in DiRROS: | 06.07.2026 |
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| Views: | 134 |
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| Downloads: | 64 |
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