Organic geochemical characterization of Santonian to Early Campanian organic matter-rich marls (Sondage No. 1 cores) as related to OAE3 from the Tarfaya Basin,Morocco |
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| Institution: | 1. Institute for Earth Sciences, University of Graz, NAWI Graz, Heinrichstraße 26, 8010 Graz, Austria;2. Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, RI 02912, USA;3. Geological–Paleontological Department, Natural History Museum Vienna, Burgring 7, 1030 Vienna, Austria;1. Lebanese University, Doctoral School of Science and Technology, Hadath, Lebanon;2. Sorbonne Université, CNRS, UMR 7193 Institut des Sciences de la Terre de Paris (ISTeP), 4 place Jussieu, 75005 Paris, France;3. Lebanese University, Faculty of Sciences II, Fanar-Maten, P.O.box 26110217, Lebanon;4. Energy & Mineral Resources Group (EMR), Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany;5. Geosciences Division, IFP Energies nouvelles, 1&4 Avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France;6. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China |
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| Abstract: | In addition to previously analyzed sediments of Cenomanian to Santonian age in the Tarfaya Sondage No. 2 well, this study presents the results of a stratigraphically younger interval of Santonian to Early Campanian age in the adjacent well Tarfaya Sondage No. 1. This interval is part of the oceanic anoxic event 3 (OAE3), which occurred mainly in the Atlantic realm. Due to known high quality source rocks related to OAEs (i.e. Cenomanian–Turonian), the investigated sample section was tested for the quality, quantity and kind of organic matter (OM), describing also the depositional environment. The study was carried out by means of (i) elemental analysis (Corg, CaCO3, TS), (ii) Rock–Eval pyrolysis, (iii) vitrinite reflectance measurements, (iv) gas chromatography-flame ionization detection (GC-FID) and (v) GC-mass spectrometry (GC–MS). Total content of organic carbon (Corg), values for the hydrogen index (HI) (mainly in the range 500–700 mg/g Corg) and S2 values (10–40 mg/g rock), support the assumption of a high petroleum generation potential in these Upper Cretaceous sediments. TS/Corg ratios as well as pristane/phytane ratios indicate variable oxygen contents during sediment deposition, representing a typical depositional setting for the Late Cretaceous and are in good agreement with previously analyzed data in the Tarfaya Basin. Phyto- and zoo-plankton were identified as marine sourced. All of the investigated Early Campanian and Santonian samples are immature with some tendencies to early maturation. These results are based on vitrinite reflectance (0.3–0.4% VRr), Tmax values (409–425 °C), production indices (PI; S1/(S1 + S2)< 0.1) and n-alkane ratios (i.e. carbon preference index). As the deposition of these sediments is time related to OAE3, the depositional environment was characterized by oxygen-deficiency or even anoxic bottom water conditions. This situation was favored during the Cretaceous greenhouse climate by limited oxygen solubility in the then warmer ocean water. Furthermore, local factors related to nutrient supply and primary bioproductivity led to the exceptionally thick, Upper Cretaceous organic matter-rich sedimentary sequence of the Tarfaya Basin. |
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| Keywords: | Petroleum source rocks Tarfaya basin Morocco Late Cretaceous Depositional environment Thermal maturity Kerogen type Ocean anoxic event |
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