Abstract

OUAJHAIN, Brahim; DAOUDI, Lahcen; MEDINA, Fida  and  ROCHA, Fernando. Palaeogeographic control of the Jurassic clay sedimentation of the Essaouira atlasic basin (Western High Atlas, Morocco). Comunicações Geológicas [online]. 2009, n.96, pp.51-66. ISSN 1647-581X.

Jurassic clay mineral assemblage variations of sediments outcropping in the Essaouira field (North of Western High Atlas Basin) permit to identify three mineralogical zones. As the effects of burial diagenesis seem weak, the vertical evolution of clays depends mainly from various combinations of palaeogeographic factors. The input of illite and sometimes of chlorite throughout the series results from tectonic movements of the continental edges in relation with the subsidence of the basin. This tectonic activity is intersected by phases with deceleration of subsidence which allow the installation, under a hot climate, of pedological covers responsible for the input in the basin of kaolinite, mixed-layers and, later smectites. The variations of sea level are also expressed in the Callovian succession, where the generalized transgression permits the development in the basin of a detrital clay sedimentation instead of a chemical sedimentation.

Keywords : Essaouira; Jurassic; Clays; Diagenesis; Tectonic; Climate; Eustatisme.

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