Sedimentological and lithostratigraphic study of the Albban Lower Paleogene, the meridional flank of Central Hight Atlas, Morocco

Abstract

This work presents a lithostratigraphic, sedimentological and paleogeographic study of the Lower Paleogene of the Albban locality, meridional flank of the Central High Atlas. The lithological description was carried out along the Albban section with bed-by-bed sampling. A microfacies analysis was performed on many thin sections to characterize the fossiliferous content and evolution, as well as to suggest a paleoenvironment. The Lower Paleogene in Albban is characterized by a sequence of marls topped by a succession of limestone bars, which are frequently separated by erosive bases. These bars showed a gradual fossiliferous evolution towards the top of the section studied, its composition mostly composed of ammonites and fragments of bivalves, such as oysters and lamellibranch. This fieldwork reinforced by microfacies analysis. This last showed that the carbonate facies began with a mudstone to wackstone texture in its basal parts with a few ostracod fragments. Towards the top, the limestone become grainstone in texture, accompanied by a faunal evolution that includes bryozoans, bivalves and a few benthic foraminifera. The correlation of all these data has enabled us to suggest the evolution of a paleoenvironment in two stages. The first corresponds to a relatively isolated, stagnant lagoon environment in which the carbonated mud settled. The second the second reflects an environment that gradually evolved into a coastal to shallow marine context favored a faunal evolution well marked at the top of the section.