Basin Evolution and Geochemical Modeling
Palaeozoic sedimentology and sequence stratigraphy of North Africa
Research by Dr Ian Carr
Objective:
A relative sealevel curve has been generated for the Paleozoic of north Africa based upon outcrops and subsurface data.
Summary:
Published sedimentological studies of the Palaeozoic strata of North Africa have been used to create sedimentological and sequence stratigraphic models and to derive a eustatic sea-level curve. By comparing Palaeozoic basin stratigraphy from outcrop and the subsurface of Egypt, Libya, Algeria, Tunisia and Morocco, the regional sedimentary history and sequence stratigraphy of North Africa has been modelled. A relative sea-level curve for North Africa has been generated by interpreting depositional water depths, recognising continental, shoreline or deep marine deposits, periods of emergence and evidence for relative rises and falls in sea-level. Evidence used for rises in sea-level was basement onlap, landward shifts in facies tracts, and condensation of basinal sedimentary sections. Evidence used for relative falls in sea-level included basinward shifts of facies tracts, and erosion in landward areas.
A regional second order sequence stratigraphic framework, bounded by sequence boundaries and containing maximum flooding surfaces, has been constructed. Placing the strata in a sequence stratigraphic framework and mapping out facies information has enabled the location of key reservoir, source and seal horizons to be predicted in both time and space. The North African area represented a stable cratonic block for much of the Palaeozoic, with long lived source and basinal areas, facies changes took place over hundreds of kilometres.
Two chronostratigraphic correlation panels have been constructed at roughly right angles to each other across North Africa, in WNW-ESE and NNW-SSE orientations. The panels illustrate the way in which sedimentology and hydrocarbon geology vary across the continent through time. The Palaeozoic succession is divided into five second-order sequences:
NA 1, Early Cambrian to Late Ordovician;
NA 2, Late Ordovician to Late Silurian;
NA 3, Devonian; NA 4, Carboniferous;
NA 5, Permian
Sequence boundaries, maximum flooding surfaces and systems tracts have been defined for NA 1 to NA 4. Palaeogeographic reconstructions for the North African region from the Cambrian to the Carboniferous have been generated, and a sea-level curve based on the panels and palaeogeographic reconstructions compared to other published sea-level curves. The proximity of the North African region to the South Pole during the Palaeozoic and its relative tectonic stability, suggest that sea-level curves derived from the area should reflect closely Palaeozoic glacio-eustasy. This study provides a useful framework for future third-order studies.