Assessment of sedimentary environment from PAHs and aliphatic biomarkers: The case study of Fahdene black shales in northern Tunisia. (January 2020)

• Record Type: Journal Article
• Authors: Hallek, Tahani; Akrout, Dhaou; Ahmadi, Riadh; Montacer, Mabrouk
• Is Part Of: Journal of African earth sciences. Volume 161(2020)
• Publication Date: 2020-01
• Subjects: Albian-cenomanian -- Fahdene -- Source rock -- Biomarkers -- Fracture -- Tunisia; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2019.103676
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: Polyaromatic and aliphatic biomarkers extracted from the Albian-Early Cenomanian source rock (Fahdene Formation) were evaluated by Gas Chromatography – Mass Spectrometry (GC-MS) and are compared to classic geochemical and mineralogical data. In addition to terpanes, hopanes, diasteranes and steranes, thirty-seven aromatic hydrocarbon elements were identified. The absence of the angiosperm-derived biomarker (18α(H)-Oleanane) and the low abundance of trimethylnaphthalenes isomers (1, 2, 5-TMN and 1, 2, 7-TMN) suggest that no land-plant traces were founded in the studied organic matter. In this fact, the Kerogene III identified by Rock Eval is not detected, and we can attribute these indices to the algae effect. The check of maturity by Tmax and the biomarker parameters (C27 18α-22, 29, 30-trinorneohopane (Ts), sterane isomerization ratio ββ/(αα+ββ), C32 22S/(22S + 22R) HH and the methylphenanthrene index (MPI-1)) indicates that these organic rich sediments are reached the early stage of oil window. In the other hand, aliphatic and polyaromatic biomarkers confirm classic data of X-ray diffraction and calcimetry and suggest a carbonate facies with some clayey intercalations in the middle part. The fracturing analysis of these carbonates prove the presence of high density of fractures with various sizes and directions. About filling, the fibrous calcite is the major element of mineralized veins, with the presence of bitumen traces. These fractures have two main orgin; the fluid pressure and the regional tectonic stress regime. Therefore, the Albian-Early Cenomanian fractured carbonates in the Mahjouba area were deposited, under suboxic conditions, in a marine environment affected by the eutrophication phenomenon, and have just reached the equilibrium stage of maturity. Highlights: The studied source rocks have a marine origin. The marine environment is controlled by the eutrophication phenomenon. Mineralogical analysis confirmed by molecular contents. The fracturing analysis related to the fluid overpressure phenomenon. Appreciation of the unconventional petroleum exploitation.