Stratigraphic and geodynamic characterization of Jurassic-Cretaceous 'red beds' on the Msemrir-Errachidia E-W transect (central High Atlas, Morocco)

摘要

The red detrital formations of the Central and Eastern High Atlas of Morocco continue to spark a large scientific debate around their age varying from the middle Jurassic to the upper Cretaceous period. Through this paper, we present the results of lithological correlations of five detailed geological sections, covering the Jurassic-Creta-ceous "red beds'' series, measured in the Central High Atlas along the Errachidia-Msemrir transect. These detrital strata are outcropped in syncline basin centres, delimited by raised ridges that are formed by lower and middle Jurassic formations. Important lateral variations of facies and thicknesses occur between the eastern and western parts of the studied transect. In the eastern part of the study area, the "red beds'' can be attributed to three lithostratigraphic formations, two formations that are generally sandstone-rich (Guettioua and Jbel Sidal Formations), separated by a third one which is clay-rich (Iouaridene Formation). In contrast, in the western part, the "red beds'' series is best allocated to the sandstone-rich of the Guettioua Formation. During the deposition of the Jurassic-Cretaceous "red beds", the Central High Atlas Basin was subjected to important tectonics and salt diapirism events. Hence, the important variation of facies and thickness in the "red beds'' series may be best explained by the geodynamic evolution of the Central High Atlas and its control of the building of differential depositional areas. Together with global sea-level and climatic fluctuation, changes in differentiated local sub-sidence rate are hence pictured as a major driving parameter for facies and age differentiations between the eastern and western parts of the Central High Atlas Basin.