Sedimentology and Paleo-environment of Phosphate Facies of the High Atlas of Marrakech (Morocco)

Abstract

The poorly studied phosphate assemblages of the eastern part of the High Atlas of Marrakech were the subject of a sedimentological, petrographic, granulometric, and mineralogical study, coupled with a description of macro- and microfacies of the geologic section surveyed in the field. Indeed, the results of the petrographic study revealed very similar compositions to those of the phosphates of central Morocco with a greater richness in detrital elements and faunal content: benthic foraminifera, ostracods, and algae. These facies testify for a marine sedimentation at the Amezmiz golf bottom, which is highly influenced by detrial inputs. The grain size analysis of phosphate facies reflects the characteristics of a very well-classified phosphate, dominated by a spherical shape to ovoid phosphate grains of different origins. There are also vertebrate bioclasts, benthic foraminifera, echinoids radioles, internal ostracods molds, and most often an abundant exogangue rich in detrital quartz. This composition suggests a closed, very shallow marine deposition environment with a strong continental influence. The first results relating to mineralogy provide valuable information on the mineral paragenesis, quality and quantity of these residual phosphate deposits. The results of these combined made it possible to assess the importance of phosphate sedimentation in this region.