Depositional model of the Eocene El Kohol Formation (Central Saharan Atlas, Algeria): integration of facies analysis, palaeontology and petrography

Abstract The present study documents the lithostratigraphy, biostratigraphy, facies evolution and depositional environments of the Eocene El Kohol Formation exposed on the southern flank of the Central Saharan Atlas (Algeria), through the integration of lithological characteristics, fossil and ichnofossil assemblages, and microfacies analysis. The succession is subdivided into two formal members: the Marly El Kohol Member, comprising a lower marlstone-dominated interval, and the Siliciclastic Kheneg ed Dis Member, representing an upper sandstone-dominated succession. The boundary between these members is marked by a transition from pale, carbonate-rich deposits to darker clastic sediments. Field observations and microscopic analyses have enabled the recognition of sixteen facies types (Ft1–Ft16), which are interpreted in terms of depositional environment and grouped into four main facies associations (FA1–FA4): (FA1) an inland lake environment; (FA2) a palustrine environment, characterized by carbonate deposition in freshwater to brackish conditions with subaerial exposure and paedogenic modification; and alluvial settings comprising (FA3) fluvial channel and (FA4) floodplain deposits. Palaeontological analyses have produced new micropalaeontological data for the region, including charophytes ( Sphaerochara parvula , Nodosochara [ Turbochara ] sp., Gyrogona sp ., Harrisichara cf. leptocera , Lamprothamnium papulosum , Peckichara torulosa var. varians , Raskyella cf. sahariana and Nitellopsis cf. [ Tectochara ] dutempleii ), ostracods ( Neocyprideis meguerchiensis , Paracypris ? sp. 1, Paracypris ? sp. 2 and Thalassocypria ? sp. 1) and actinopterygian fish microremains (primarily from polypterids and alestids). Additionally, fragmentary remains of the terrestrial proboscidean Numidotherium koholense have been recovered. Ichnological analysis of the succession identified five ichnotaxa: Ophiomorpha isp., Palaeophycus isp., Skolithos annulatus , Skolithos linearis and Thalassinoides horizontalis . This study contributes to refining the regional and North African understanding of the spatial extent and palaeoenvironmental evolution of the Eocene succession and helps to complete the ichnological and palaeontological records of the Eocene in the area.