Chapter 20 - Triassic sedimentation and rifting in the High Atlas (Morocco)

Abstract

Abstract The Triassic rocks cover most of northern Morocco. In the Moroccan meseta, they are primarily siltstone, shale and evaporite. In the High Atlas, the Triassic comprises a thick, red clastic series that locally overlies purple coarse-grained strata that is considered Permian in age. During the Late Triassic, the extensional stress field reactivated older faults as normal and strike-slip faults, principally east-northeast, and created north-northeast neoruptures. This synsedimentary tectonic activity is recorded in the sedimentary record as planes of synsedimentary faults, variation of thickness and slumping of sediments, and angular unconformities. The large High Atlas graben, oblique to the North Atlantic graben, was invaded by the sea from two directions. Extension stopped at the end of the Triassic in the High Atlas graben which had been completely filled with clastics. Extension continued in the meseta and in the North Atlantic graben. A shallow epicontinental sea covered the area of the meseta and of the High Atlas. Evaporites precipitated in shallow and subsiding basins. In the Early Liassic, tholeiites were extruded in the meseta and High Atlas domain. They announced the initiation of continental drifting in the North Atlantic graben.