Paleogeographical development and correlation of Continental Strata (former Nubian Sandstone) in northeast Africa

Abstract

The main result of geological work of our group in Egypt and Sudan was the subdivision of the so-called Nubian Sandstone in its type-area Nubia and in the surroundings of Nubia. More than 20 formations have been identified, ranging in age from Cambrian to Paleocene and comprising an impressive number of facies variations. The only characteristic these strata have in common is their position near the northern edge of the African craton. This position caused similiarities within the continental facies and it also influenced marine sedimention, which in general took place in shallow to very shallow seas. The former Nubian Sandstone is strata deposited on both sides of shallow transgressions or in shallow, purely continental basins. Variations of facies were mainly influenced by changes of climate. Except for shallow marine carbonates of Early Tertiary age present in a larger area in northwestern Sudan, all sediments formenly called Nubian Sandstone are of clastic nature including thick sequences of paleosols.Based on the stratigraphical and the sedimentological results, an analysis is now possible on the paleogeographical and the structural development of large parts of NE Africa. At the same time, the results are used as a basis for hydrogeological studies (including a hydrogeological model for the whole Nubian Aquifer System) and for interpretations of the potential of sedimentary mineral deposits.The structural development is dominated by two major elements: pre-existing structural trends (Precambrian developments) and their activation in response to major events of global tectonics. Internal orientation of structural units and related distribution of sediments in this cratonal area of NE Africa was mainly controlled by the major structural pattern formed during cratonization before the Cambrian and by reactivation of selected older elements during plate motion. Preference of reactivation changed several times, depending on differences in the plate situation at the different global events.