The Siluro-Devonian of Illizi Basin (Algeria): An Example of Cratonic Clastic Sedimentation Systems

By

Henniche Messaouda¹, Eschard Remi², Hamel Aîcha³, Proust Jean-Noël⁴

(1) SONATRACH, Boumerdès, Algeria (2) Institut Français du Pétrole, Rueil-Malmaison, France (3) SONATRACH, Algiers, Algeria (4) Géoscience-Rennes-1, Rennes, France

 The Illizi basin (Algeria) is one of the most prolific basin in North Africa which was a part of the Gondwana super continent during the Paleozoic times.

The sedimentary architecture of the Siluro-Devonian series reservoir correspond to cratonic sedimentation and constitute two long term cycles.

The first one correspond to a long-term progradation from the Llandoverian to Pridoli. This cycle is subdivided to six third-order sequences (S1 to S6). The second cycle corresponds to transgression from the Lochkovian to Emsian and is made by two third order sequences (D1, D2). The limit between the two cycles corresponds to Caledonian unconformity.

Sedimentary facies are various: the marine facies correspond to wave and tide progradational ramps deposited in an continental sea and tide dominated estuaries. The fluvial facies include proximal braided systems passing to meandering and straight systems to North of the basin.

The sedimentation of this cratonic area is principally characterised by:

-         A very low subsidence rate during Silurian and Devonian which is specific to cratonic basin during the Paleozoic.

-         A high sediment supply rate with thick fluvial units of regional extension and systematic Northwest direction of paleocurrents.

-         Evidence of tectonic activity during Siluro-Devonian sedimentation with the differentiation of sub-basin.