Quantitative Meso-/Cenozoic development of the eastern Central Atlantic continental shelf, western High Atlas, Morocco

Abstract

The well exposed Late Paleozoic to Cenozoic succession in the western High Atlas (Morocco) documents the early rift to mature drift development of the eastern Central Atlantic continental shelf basin. Vertical sections, depositional geometries and unconformities have been used to reconstruct the basin architecture prior to Atlasian inversion. Two-dimensional reverse basin modeling has been performed to quantitatively analyze the development of the continental shelf between the latest Paleozoic to Early Cenozoic. Basin evolution stages include (i) early rift, Late Permian to Anisian; (ii) rift climax, Ladinian to Carnian; (iii) sag, Norian to Early Pliensbachian; (iv) early drift, Late Pliensbachian to Tithonian; (v) mature drift, Berriasian to Cenomanian; (vi) mature drift with initial Atlasian deformation, Turonian to Late Eocene; (vii) Atlasian deformation; Late Eocene to Early Miocene; (viii) Atlasian uplift and basin inversion, Early Miocene to Recent. The Late Permian to Late Cretaceous basin development comprises eight subsidence trends of 10–35 Myr duration. Trends were initiated by changes in thermo-tectonic subsidence, which in turn triggered positive and negative feedback processes between sediment flux, flexural and compaction-induced subsidence. Plate-tectonic reconfigurations in the Atlantic domain controlled the thermo-tectonic subsidence history and the basin development of the Agadir segment of the northwest African passive continental margin: (1) major shifts in the sea-floor spreading axis; (2) significant decreases in sea-floor spreading rates; (3) the stepwise migration of crustal separation and sea-floor spreading in and beyond the Central Atlantic; (4) African–Eurasian relative plate motions and convergence rates. During the Early Pliensbachian/Toarcian to Cenomanian the first three plate-tectonic reconfigurations triggered changes in ridge-push forces and modulated the extensional stress field of Central Atlantic plate drifting. Since the Turonian, African–Eurasian relative plate motions and convergence rates represented the dominant control on the thermo-tectonic subsidence history in the Agadir Basin. Major variations in sediment flux and total subsidence characterize the development of the northwest African passive continental margin. The explanation of typical stratigraphic sequences as caused predominantly by sea-level fluctuations, and rough assumptions on sediment input/production and subsidence, is not necessarily applicable to passive continental margins. The methodology applied in this study, including the newly developed tool of ‘Compositional Accommodation Analysis’, allows to develop more rigorous genetic models for the development of continental shelf basins.