Cenozoic tectono-sedimentary evolution of the Upper Moulouya continental basins (Moroccan Atlas system): Insights from lithostratigraphy, structural analysis and paleostress reconstruction

Abstract

The Upper Moulouya massif (UMM) is located at the junction between the Middle and the High Atlas mountain ranges where outcrop a segment of the Moroccan Variscan belt and its unconformably overlying Meso-Cenozoic cover. In this paper, we propose the Cenozoic tectono-sedimentary evolution of the continental series filling the intramontane basins of the UMM using a multidisciplinary approach with multiscale geological-structural and paleostress analyses. The lithostratigraphic study shows that these series correspond to Oligo-Neogene fluvio-lacustrine sequences, alluvial fans deposits, and alluvial outwash plains, associated with volcanic rocks. Structural and paleostress analyses provide a complex tectono-sedimentary evolution marked by the superposition of four tectonic phases with changes in paleostress orientations. These tectonic phases are consistent with strike-slip tectonic regimes associated with compressional, transpressional, transtensional and extensional episodes: (i) the first tectonic phase is characterized by NW-SE trending σ1 axis, and NE-SW trending σ3 axis, with NNW-SSE to N–S sinistral strike-slip faults, ENE-WSW to E-W dextral strike-slip faults, and NE-SW reverse faults cross cutting the Mesozoic and Oligo-Miocene series; (ii) the second tectonic phase is characterized by ENE-WSW to E-W σ1 axis, and NNW-SSE to N–S σ3 axis where the subsidence of Pliocene lake basins is probably controlled by ENE-WSW to E-W extensional faults and NE-SW transtensional faults; (iii) the third phase is marked by NNE-SSW to NE-SW trending σ1 axis, and WNW-ESE to NW-SE trending σ3 axis, with submeridian dextral strike-slip faults, subequatorial sinistral strike-slip faults, NE-SW normal faults, and NW-SE reverse faults; (iv) the last tectonic phase is characterized by NNW-SSE to N–S σ1 axis, and ENE-WSW to E-W σ3 axis responsible for subequatorial reverse faults, submeridian normal faults, NE-SW sinistral strike-slip faults, and NW-SE dextral strike-slip faults.