THE SILURO – DEVONIAN SUCCESSIONS IN THE TASSILI N'AJJER OUTCROPS (SE, ALGERIA): SEDIMENTOLOGY AND STRATIGRAPHY

peer reviewedThe sedimentary basins of North Africa have been accumulated a thick sedimentary succession of Palaeozoic, especially Siluro – Devonian sediments. These successions have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana. This sedimentation is mainly controlled by rapid eustatic sea-level variations and by the opening of the proto-Tethyan Ocean during the Early Palaeozoic (Beuf et al., 1971; Boot et al., 1998). During this Siluro-Devonian Period, a high subsidence occurred, allowing a high pile of sediments and organic-rich shales were deposited in many places that form important hydrocarbon reservoirs and source rocks throughout North Africa basins and Middle East (Lüning et al., 2000). In the prolific Illizi and Berkine basins (Western Ghadames, Algeria) a basin-wide approach is needed, especially with the new “shale gas and shale oil” frontier in the upcoming years, in order to capture regional trends and re-assessment the Siluro-Devonian successions. Our project focuses on the Berkine Basin and its margin, which covers nearly 102.000 km2. This basin includes a thick sedimentary series of 7000 m corresponding to complex reservoirs but also black shales of the basal Silurian and Frasnian, which are respectively major and secondary source rock systems. Complete logging of spectacular large-scale and well exposed outcrops of the Siluro-Devonian sediments was carried out at the south margin (SE, Tassili n’Ajjer) of the Illizi-Berkine basins (Djouder et al., 2012; Djouder et al., 2014). The following analysis incorporates biostratigraphic, ichnological, sedimentological, Magnetic susceptibility (MS) and high resolution stratigraphic data. It would allow providing a framework of deposits, ranging from offshore to deltaic deposits for the Silurian and from fluvial to normal-marine depositional conditions for the Devonian. References Cited: Beuf, S., Biju-Duval, B., De Charpal, O., Rognon, P., Gariel, O., Bennacef, A., 1971. Les Grès du Paléozoïque inférieur au Sahara : Sédimentation et Discontinuité, Évolution Structurale d’un Craton. Publication de l‘Institut Français du Pétrole. N° 18, Edition Technip, Paris. p. 464. Boote, D.R.D., Clark-Lowes, D.D., Traut, M.W., 1998. Palaeozoic petroleum systems of North Africa. In: Macgregor, D.S., Moo- dy, R.T.J., Clark-Lowes, D.D. (Eds.), Petroleum Geology of North Africa. Geol. Soc. London Sp. Publ., vol. 132, pp. 7–68. Lüning, S., Craig, J., Loydell, D.K., Štorch, P., Fitches, B., 2000. Lower Silurian ‘hot shales’ in North Africa and Arabia: regional distribution and depositional model. Earth-Science Reviews, vol. 49, pp. 121-200. Djouder, H., Pagel, M., Murat, B., Orsingher, M., 2012. Le Silurien du Bassin de Berkine. Projet « Shale Gas » Profond. 10éme Colloque du Groupe Français des Argiles, Présentation Orale, Limoge, France 14-18 Mai 2012. http://hdl.handle.net/2268/171556 Djouder, H., Boulvain, F., Da Silva, A-C., Cornet, P., Lüning, S., 2014. Tassili n’Ajjer (Sahara Oriental Algérien) – Résultats préliminaires sur le Silurien – Dévonien : Journée Thématique de l’Association des Sédimentologistes Français (ASF) – Diagenèse : avancées récentes et perspectives, Présentation Poster, Orsay-Paris, France 04 Juillet 2014. http://hdl.handle.net/2268/17155