Tectono-sedimentary events during Lias-Dogger at the southern margin of the Central High-Atlas, Morocco

Abstract

The tectono-sedimentary analysis of the Jurassic sediments in the southern margin of the central High-Atlas and particularly in the Todrha-Dadès area shows the existence of a good relationship between the tectonic and the sedimentary events. The structuring of this area is controlled by a group of faults whose cartographic axes show bending paces of direction NE-SW straightening toward the NNE. The analysis of the spatial organisation of lower and middle Lias deposits shows a dominance of carbonated deposits with ammonites, algae and foraminifera, with variations of thickness and lateral facies variations. The upper Lias and the Dogger correspond to clastic deposits and carbonates interbeded with neritic fauna. The structural analysis shows that the sedimentation in the southern margin of the central High-Atlas is controlled, in addition to eustatic factors, by a paleostress field dominated by minimum main stress fields of orientations which change depending on the age. The analysis of structures and their geometry as well as the syn-sedimentary tectonics allowed to establish the directions of the tectonic stress, which controlled the structuration of the studied basin in the Jurassic. The general synthesis of the data shows variations of distensive directions in time and space. In the Sinemurian-lower Carixian the direction of the tectonic stress (σ3) is NW-SE. The middle Domerian was a relative quiet tectonic time. In the upper Domerian the distensive tectonic stress is NNW-SSE to NW-SE. In the Toarcian, the sedimentation takes place in a transtensif tectonic context. The synsedimentary structures are developed by fossilized normal faults, slope deposits and spatio-temporal variations of the facies and thickness. Geodynamic and paleogeographic reconstitution of Lias-Dogger shows an arrangement of the lithostratigraphic formations, where some evolved in the borders of the basin, while others evolved in the center of the basin within a block-tilting regime controlled by the conjugation of the sea-level changes and the tectonics events.