Closed depressions and karst landforms in Rif Alpine Cordillera (Northern Morocco): The case of dolomitic Jbel Dersa Massif

Abstract

• Pliocene dismantling flattened the thrust fronts of the Dorsale Calcaire, as shown by geomorphological and structural evidences. • The formation and distribution of karst features in JDM are controlled by NW- and NE-trending structures. • The karstified dolomite in JDM is primarily marked by dissolution dolines, reflecting intense chemical weathering. The morphology, distribution, and structural control of karst closed depressions in a dolomitic karst landscape are the focus of this study. The study area is the Jbel Dersa Massif (JDM), part of the “Dorsale Calcaire” (DC) unit within the Rif Mountain range in northern Morocco. A combined analysis of geomorphological mapping and structural studies reveal that the Pliocene dismantling phase smoothed the crests of the original imbricate thrust fronts, characteristic feature of the DC unit’s structure. The flattening of the massif’s summit facilitated the dissolution of the rock surface. In addition to the massif’s ruiniform landscape, the observed karstic features include fracture lapies, closed karstic depressions at the summit, and travertine deposits along the structural contacts with the bordering non-karstic units. The 26 identified closed depressions are dissolution dolines. Morphometric analysis indicates that these dolines are primarily located in the endorheic and axial zones of the massif and are preferentially aligned along tectonic faults. Structural, geomorphological, and ERT profile analyses of two sinkholes confirm the structural control over their development and demonstrate that seepage occurs through the fractured material along fault planes. This study highlights the scientific, environmental, and water-supply significance of the JDM. Its karst depressions, serving as primary infiltration zones, play a crucial role in local hydrogeology, providing water sources for several settlements that rely on the massif’s springs.