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.
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