Second and Third Order Sequences of the Phanerozoic of North Africa

By

 Ian D. Carr¹, Stefan Lubeseder¹, Jonathan Redfern¹, Ruth H. Underdown¹

(1) Oxford Brookes University, Oxford, United Kingdom

 A regional second order (10s my) sequence stratigraphic framework has been developed for the North African Phanerozoic. Six Paleozoic sequences (NA1 to 6) and three Mesozoic sequences (NA7 to 9) are recognized, generally bounded by regional unconformities. This framework, based on a synthesis of published data, has been tested using well logs in the Ghadames Basin of Libya and Algeria and outcrop studies in Morocco. Initial results suggest that second order systems tracts, recognized in the regional study, can be identified in fieldwork and subsurface well analysis. This study provides a valuable stratigraphic framework, which has implications for correlation of reservoirs, source and seal packages across the region and will prove valuable to seismic interpretation and regional facies prediction.

In the Ghadames Basin, Paleozoic Sequences NA3 to 5 (Silurian to Carboniferous) can be recognized sub-cropping beneath the Hercynian Unconformity from east to west, with erosion increasing towards the east. Sequences NA1 to 2 (Cambrian and Ordovician) are below the deepest well penetration, while Sequence NA6 (Permian) is not preserved. Mesozoic Sequences NA7 to 9 (Triassic to Cretaceous) are also recognized within the basin. SP and Resistivity logs have been used to sub-divide the succession into third order sequences, more useful for reservoir-scale studies. This third order framework is currently being used to conduct basin-modelling studies within the area.

Outcrop studies, undertaken in Morocco, have initiated the development of a regional third-order sequence stratigraphic framework for Sequences NA 3 and 4 (Silurian and Devonian).