MIDJURASSIC EVENTS IN THE WESTERN HIGH ATLAS (MOROCCO)

Angular unconformities, time gaps, and progressive increase of thickne ss in the Mesozoic sedimentary pile of the Western High Atlas, Morocco , point to mid-Jurassic tectonic pulses in this area. Red beds, Middle Jurassic in age, were deposited in the nearshore Agadir-Essaouira bas in in contrast to transgressive tendencies of the eustatic curve. Thes e phenomena are easily explained by uplift and erosion in the central part of the mountain belt even in the Middle Jurassic. Thus, a rift st age (Permian to Early Jurassic) in the tectonic history of the Western High Atlas was followed by a gulf stage (Late Jurassic to Middle Cret aceous) until later the high mountain range generated by inversion in Late Cretaceous and Neogene to recent times. Tensional forces that cre ated the mobile rift belt were superimposed by vertical uplift during the Middle Jurassic that gave rise to a NNE-SSW stretching high. Even in the present-day high mountain range this area, called the >>ancient massif<<, is strongly elevated. Thus, the evaluation of the geologica l history of the Western High Atlas seems much complicated.