Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights |
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| Institution: | 1. Departamento de Geología, Universidad de Jaén, 23071 Jaén, Spain;2. Laboratoire de Géologie de Lyon, UMR 5276 CNRS, Université Lyon 1, ENS Lyon, 69622 Villeurbanne, France;3. Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain;1. Instituto de Ciencias de la Tierra, Universidad Central de Venezuela, 3895, Caracas 1010-A, Venezuela;2. Institut des sciences de la mer de Rimouski, Université du Québec, à Rimouski, 310 allée des Ursulines, Rimouski, Quebec G5L 3A1, Canada;3. GEOTOP Research Center, C.P. 8888, succursale centre-ville, Montreal, Quebec H3C 3P8, Canada;4. DTP Laboratorios SRL, Condarco 1136, Buenos Aires, Argentina |
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| Abstract: | Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. Tmax values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents. |
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