Print this pageA Depositional Model and Sequence Stratigraphy of the Trias Argilo-Greseux Inferieur (T.A.G.I.) in the Ghadames Basin, Algeria
FORD, GARY W. and ALAN J. SCOTT
Early development and use of fundamental geologic models has been a primary key to Anadarko Algeria's successful exploration program in the Ghadames Basin, Algeria. A detailed stratigraphic analysis of the Trias Argilo-Greseux Inferieur (T.A.G.I.) strata in the Ghadames Basin documented temporal and lateral facies relationships of the various T.A.G.I. reservoir intervals. Importance of this model is not only for future exploration, but as the primary building block for T.A.G.I. reservoir characterization and reservoir management.
A sequence stratigraphic approach was successful in providing a viable basis for subdivision of the TAGI into broad regional chronostratigraphic intervals. The deposition of the T.A.G.I. occurred in an overall transgressive episode. Depositional cycles are well developed and represented by a basal fluvial sandstone interval overlain by a regional shale interval. Delineation of the distribution of these cycles forms a basis for defining the T.A.G.I. stratigraphic framework and the sequence stratigraphic interpretation. The Hercynian Unconformity is the lowstand surface of erosion and the sequence boundary of the Lower T.A.G.I. third-order sequence. All strata of this sequence are components of a transgressive systems tract and represents a progressive filling of a pre-T.A.G.I. incised valley system. A second younger sequence is also a transgressive systems tract and includes all Middle and Upper T.A.G.I. intervals. The younger cycle is considered a fourth-order sequence associated with a rejuvenation of T.A.G.I. fluvial systems.