Geological structure and development of the continental margin of northwest Africa

Abstract The continental margin of northwest Africa has developed through the Mesozoic and Tertiary by prograding sedimentation on a subsiding basement. Eocene phosphorites were deposited in offshore continuations of shallow Early Tertiary gulfs in the region of A1 Jadida and of Essaouira. These phosphorites now crop out on the outer shelf seaward of outcropping Cretaceous strata. Oligocene earth movements gave rise more or less to the present shelf-slope configuration. Subsequent subsidence notably continued only in the northern part of the Aaiun Basin and the Souss Trough. The major locus of post-Oligocene deposition has been the continental slope and probably the continental rise. Parts of the uppermost slope off the southern Spanish Sahara and the High Atlas Chain are tectonically oversteepened and essentially non-depositional environments. A transgressive phosphatic Miocene deposit thinly mantles parts of the Moroccan shelf although much appears to have been removed by Pleistocene erosion. Restricted subsidence in the northern Aaiun Basin is represented by the development of Lower Pliocene phosphorites. The existence of salt diapirs within the continental margin is inferred locally.