Jurassic clay mineral sedimentation control factors in the Essaouira Basin (Western High Atlas, Morocco)

Variations in the Jurassic clay mineral assemblages of sediments cropping out in the Essaouira field (North of the Western High Atlas Basin) make it possible to identify three mineralogical zones. As the effects of burial diagenesis seem weak, the vertical evolution of clay minerals depends mainly on various combinations of palaeogeographic factors. The inputs of illite and sometimes of chlorite throughout the series result from tectonic movements of the continental margins connected to the basin's subsidence. This tectonic activity was interspersed with phases of deceleration of subsidence, which allowed the formation under a hot climate, of pedological covers responsible for the input of kaolinite and mixed layers into the basin. Smectites are assumed to be mainly neoformed in shallow environments under hot climates. Variations in sea-level are also expressed in the Callovian, where generalized transgression allowed the development of detrital clay sedimentation instead of chemical sedimentation in the basin.