Basin Evolution and Geochemical Modeling
Third order sequence stratigraphic framework for the Palaeozoic reservoirs of North Africa
PhD research by Dr Stefan Lubeseder and Dr Jonathan Redfern
Objective:
This study aims to develop a third-order sequence stratigraphic framework for the Silurian and Devonian of North Africa. Due to a stable Saharan Craton position, the Palaeozoic stratigraphy is relatively uniform across the area, allowing a regional study including Morocco, Algeria, Tunisia, and Libya.
Introduction:
Palaeozoic rocks form important reservoir and source rocks in North Africa, from the Cambrian to the Carboniferous. A sequence stratigraphic scheme together with the geometry of depositional systems and the key characteristics of their boundaries is a valuable tool for the prediction of reservoir units in areas beyond data control. Also, some outcrop studies can serve as analogues to reservoir units in the subsurface.
An inter-regional chronostratigraphic correlation chart is constructed and will be used to develop an intracratonic depositional model for North Africa. Practically, the study is split into three parts:
Morocco field case study:
Silurian: Silurian sections are studied in the Tafilalt area as well as in the Dra Plain of southern Morocco (Anti-Atlas). The emphasis is on Ludlowian “Orthoceras” limestones and the so-called “Scyphocrinites” limestones at the Silurian/Devonian boundary. These limestone levels are studied in terms of their biostratigraphic position, depositional system, and inter-regional sequence stratigraphic significance. Silurian “Orthoceras” limestones are known from various other parts of the world and a significant contribution to the understanding of these beds is expected from this study.
Early Devonian: The emphasis of the work lies on shallow-marine, Yordale-type Rich-cycles in the Dra Plain of SW Morocco, where thick storm-dominated deltaic complexes build out repetitively and are capped by thin transgressive shelfal limestones. The Rich-cycles offer a unique possibility to study Early Devonian sequences. The facies can be regarded as an outcrop analogue to the Early Devonian sequences of the Reggane Basin (Algeria), and the Middle Devonian of the Ghadames Basin (Algeria/Libya).
Late Devonian: Late Devonian sections are measured in outcrop with a spectro gamma-ray meter. The Late Devonian encompasses an important source rock in North Africa. Newly obtained data from the Tafilalt area (SE Morocco) will provide a better understanding of the Late Devonian black shale and limestone deposition across North Africa. The Late Devonian stratigraphy of the Ghadames Basin is especially oversimplified. It is hoped to refine this by correlating the well-log response to the GR- and lithological signature of the Tafilalt.
Ghadames basin subsurface case study:
Well-logs are correlated in various cross-sections across the Ghadames Basin (Berkine B., Algeria, Hamra B., Libya) and transgressive / regressive cycles are generated using basin-wide geometry patterns and progradation / retrogradation of facies tracts (based on lithology, faunal/floral content, well-log shape and stacking patterns).
Biostratigraphic data are included and reviewed to obtain the time-frame.
Literature review:
A major literature review is being undertaken on the Moroccan, Algerian, Tunisian and Libyan Devonian – Silurian system. The published data are plotted in composite sections for the various intracratonic basins and basin margins. From this a chronostratigraphic chart is constructed across North Africa, showing the facies and sediment distribution in time and space. Biostratigraphic literature data are placed into a modern zonation scheme and formation ages are accordingly corrected, if necessary and possible. The literature review tests the generated cycles in the case studies and forms the basis of an inter-regional depositional model for the Silurian - Devonian succession of North Africa.
Downloadable files:
Conference abstracts |
Conference posters |
Papers/Abstracts |
Saharan conference Geolsoc/NARG 2006 Poster Abstract (pdf 17Kb) |
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