Remi Eschard¹, F. Braik², D. Bekkouche², G. Desaubliaux¹, N. Mahache²

(1) Institut Francais du Petrole, Rueil Malmaison, France
(2) SONATRACH, Boumerdes, Algeria

ABSTRACT: Stratigraphic Architecture of the Siluro - Devonian Series in Algeria (Illizi and Berkine Basins) : a Tectonic Control of the Saharan Craton

Recent oil discoveries in the Paleozoic of Algeria have emphasized the influence of tectonic highs on the Siluro-Devonian reservoir distribution. A regional synthesis of the Illizi and Berkine basins was performed with the aim of understanding the stratigraphic architecture of these depositional systems, in order to predict the reservoir distribution and to evaluate reservoir quality. The study combined subsurface correlations and outcrop observations.

The Silurian cycle started with the deposition of the Silurian "hot shales", which acted as a source rock in the Illizi basin. These were overlain by five third order sequences of marine and deltaic sediments, organized in a long-term progradation. Sequences were characterized by a very low accommodation rate, with wave - tidal ramps forming sand sheets of regional extension.

At the Silurian - Devonian boundary, the whole Illizi basin tilted. The eroded material accumulated in fluvial systems northwards, in the Berkine basin. Transgression from the North subsequently flooded the Berkine basin, while fluvial sediments aggraded in the Illizi basin. Then, the transgression reached the Illizi basin with the deposition of the Middle Devonian offshore shales. Upper Devonian sedimentation was characterized by offshore sediments, with forced regression shoreface wedges in both basins.

This study also emphasized the role of tectonic highs during sedimentation, with the uplift of the Tihemboka arch East of the Illizi basin, and of the Ahara arch between the Illizi and Berkine basins. These arches induced major erosion and condensation of the Siluro - Devonian sediments, and controlled reservoir distribution in these areas.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado