Morphogenesis of the Closed Depressions in Middle Atlas: Case of the Causse of El Menzel, Morocco

Abstract

Closed depressions are the most typical exokarstic forms of the Moroccan Middle Atlas karst. These features present a great diversity of forms and sizes related to the multiple and often obscure conditions of morphogenesis in several karstic plateaus of the tabular Middle Atlas such as that of El Menzel. This little-known carbonate panel is characterized by an important geodiversity of closed depressions with variable shapes and reliefs: poljes, uvalas, dolines, kamenitzas, and rain pits. The results confirm the tectogenetic nature of several closed depressions of which the most important are: the polje of El Menzel and the polje of Quaçbat Beni Yazgha which are aligned along the major accidents of the Causse oriented NE-SW and NW-SE. The pre-established tectonic heritage Accident Median Moyen Atlasique and Accident Nord Moyen Atlasique, and the compressive tectonics and particularly extensive phases from the upper Miocene to Quaternary during the surrection of the Middle Atlas associated with the pluvial climatic phases have permitted the development of the good potential of karstification as well as the large closed depressions of the Causse.