Facies analysis, architectural elements, and paleoenvironmental reconstruction of alluvial deposits of the low terraces and floodplains in the Middle Sebou river (Eastern Saïss foreland basin, Morocco)

Abstract

This paper focuses on the study of the floodplain and low terrace deposits of the Middle Sebou Valley, which crosses the south-rif corridor and constitutes the eastern limit of the Saïss Basin. The study includes the identification of facies, the determination of architectural elements, the reconstruction of paleoenvironments, and the proposal of a model for deposit formation. The work is based on detailed sedimentological analysis of the deposits, focusing on lithology, grain size, primary sedimentary structures, and the types of contact between facies. Facies analysis identified 21 facies grouped into three associations corresponding to nine architectural elements whose identification was based on the study of their lateral and vertical profiles. The architectural elements identified include the channel (CH), gravel bars and bedforms (GB), sandy bedforms (SB), downstream accretion (DA), lateral accretion (LA), sediment gravity flows (SG), natural levee (LV), floodplain (FF), and abandoned channels and meanders (FF (CH)). The alluvium is organized into rhythmic and fining-up elementary sequences reflecting its deposition in different fluvial environments: alluvial fan, straight to slightly sinuous and braiding-tending fluvial environment, and meandering fluvial environment. Alluvial deposition is controlled by lithology, climate, and tectonics. Lithology and tectonics controlled the slope, the degree of valley confinement, the accommodation space, and the alluvial fan development. Climate controlled the flow regime, sediment dynamics, and the formation of paleosol and calcrete.