Facies architecture of the Plio-Quaternary alluvial fan deposits from south-eastern margin of the Saïss foreland basin (Morocco): Paleoclimatic and neotectonic implications

• Published in: Journal of African earth sciences (1994) 2023-03, Vol.199, p.104818, Article 104818
• Main Authors: El Asmi, Hicham, Gourari, Lahcen, Benabbou, Mohamed, El Yakouti, Imad, Hayati, Aziz, Chellai, El Hassane, Theilen-Willige, Barbara
• Format: Article
• Language: English
• Subjects: Alluvial fans; Neotectonic and climate controls; Plio-Quaternary; Saïss foreland basin; Sedimentary facies
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2022.104818

Eight Plio-Quaternary alluvial fans from south-eastern margin of the Saïss foreland basin were the subject of a thorough sedimentological study based upon detailed facies analysis. This study allowed distinguishing 16 sedimentary facies. The typology of the latter, their spatial distribution and sedimentary organization afforded the classification of the studied fans into three groups. Group 1 is dominated by non-cohesive debris flow and cohesive to very poorly-sorted blocky conglomerate deposits that are associated with silt-clayey and calcrete. The setting up of the deposits of this group occurred in a tectono-karstic depression whereby a WNW progradation of the deposits and an important incision into the previous consolidated deposits would have been controlled. Group 2 is characterized by a predominance of the muddy fraction, presumably linked to the large surface area of the watershed and the river activity. Group 3 is dominated by coarse deposits with rare mudflows interpreted to be the direct consequence of an important neotectonic activity which is expressed by localized incremental pulses of the Agourai-El Hajeb-Ain Cheggag faults system and Middle Atlas directional faults (i.e., NE-SW) along toe fan during the Plio-Quaternary period. Groups 2 and 3 are also characterized by deposits whose the related processes are dominated by cohesive and non-cohesive debris flows, mud-rich debris, channelized debris flows and non-cohesive flows, hyper-concentrated flows and sheet-flood flows. The morphogenesis of these alluvial fans and the emplacement of their deposits are neotectonic- and climate-controlled. Tectonics have played a major role in the rejuvenation of the Middle Atlas relief and, through controlling the base-level, created the space available for the establishment and development of alluvial fans onto the south-eastern margin of the Saïss basin. This extensive tectonics has resulted in normal faultings and layer tiltings. The climate played an important role in the formation of facies by controlling (i) the mechanical properties of paleoflows, (ii) sedimentary dynamics and (iii) the formation of paleosols and calcrete. •Lithology and neotectonic activity afforded considerable conglomerates-rich fan accumulation.•Fan facies variation was climate-paced during the Plio-Quaternary.•Arid (humid) climate would have enhanced debris-flows and calcrete development. (fine-grained accumulation).