Stratigraphic Architecture of the Siluro-Devonian Systems in Algeria and Libya: A Synthesis

Eschard, Remi¹, Messaouda Henniche², Milad M. Ben Rahuma³, Jean-Noel Proust⁴ (1) Institut Francais du Pétrole, Rueil-Malmaison, France (2) Sonatrach, Boumerdes,Algeria (3) Petroleum Research Center, Tripoli, Libya (4) CNRS, Rennes I University, Rennes, France

The Silurian and Devonian depositional systems significantly contribute to one of the most prolific petroleum system of North Africa. The Silurian source rock had a wide-spread extension all over the Gondwana whereas the Frasnian organic shales were more confined in locally subsiding troughs. Upper Silurian prograding shoreface sequences constitute a significant reservoir in the Illizi (Algeria) and Ghadames (Libya, Acacus Formation) basins. Lower Devonian fluvio-deltaic sandstones (Gedinian / Siegenian units, Tadrart formation) produce hydrocarbons in the Regane, Ahnet, Illizi, Berkine and Ghadames basins in Algeria and Libya. The objective of this presentation is to propose a chronostratigraphic scheme for the Siluro-Devonian sequences all across the Saharan platform, from outcrop and subsur­face data. The general sequence stratigraphic interpretation of these systems was based on chitinozoans datings which have evidenced time-gaps associated to major unconformities at the scale of the Gondwana. The sequence facies architecture was then studied, marine influ­ences generally increasing in the N.W part of the Gondwana platform. However, this gener­al framework is much complicated by the sub-basins configuration which characterised the Gondwana platform during Paleozoic. Local highs separating the sub-basins were episodi­cally uplifted and eroded, inducing local unconformities and local sources of sediment sup­ply. A stratigraphic modeling approach also made possible the quantification the variations of the sediment supply through time and the discussion of the parameters controlling the sequence architecture.