ORIGINAL PAPER Depositional environment and Ichnology (Nereites ichnofacies) of the Late Devonian Sahara region (SW Algeria) Mohamed Bendella & Abdelkader Ouali Mehadji Received: 23 October 2013 /Accepted: 1 September 2014 # Saudi Society for Geosciences 2014 Abstract The late Famennian strata of the Marhouma out- crop, located in the Saoura (Algerian Sahara), consist of two formations: the Argiles de Marhouma Formation and the overlying Grès de Marhouma Formation. The former is char- acterized primarily by fine-grained turbidite successions, in- tersperse with griotte limestones bearing a pelagic fauna. There is a wide variety of trace fossils in the lower part of the formation: Chondrites, Helminthopsis, Ichnyspica, Megagrapton, Neonereites, Nereites irregularis, Nereites jacksoni , Nereites missouriensis , Palaeophycus , Paleodictyon , Phycodes , Planolites beverleyensis , Protopaleodictyon submontanum, and Thalassinoides suevicus. The hydrodynamics of the depositional environment as well as the associated trace fossils indicate the Nereites ichnofacies. The depositional conditions indicate a basinal environment in a mesodistal area. The upper coarser forma- tion is composed of two members. The lower member consists of alternating turbidites, green clay and thin sandstone, with slumps, debrites, olistoliths, and synsedimentary faults. There are some visible fossil traces that may point to the Zoophycos ichnofacies. It marks the slope deposits of a submarine deep- sea fan that completes the Devonian megasequence. The upper member of the second formation starts with a transgres- sive muddy deltaic system that formed during platform con- struction. It is followed by iterative sequences of muddy and sandstones layers deposited on a storm-dominated platform that emerged at the beginning of early Tournaisian time. The distributions of fossil traces and sediments are indicative of bathymetric fluctuations. A major fluctuation, probably due to tectonic instability, is recorded as early as in the basal part of the Argiles de Marhouma Formation, which indicates the beginning of the Eovariscan phase. Keywords Ichnology . Nereites . Sahara . Algeria . Deep-sea environments . Devonian . Famennian Introduction The Upper Famennian outcrops involved in this study are found on the left bank of the Saoura Wadi, bordering the western Algerian Sahara close to the Marhouma palm grove (Fig. 1). These Frasnian–Famennian outcrops have been de- scribed as alternations of griotte limestone with monotonous, rhythmic, sandstone-pelite ensembles of a flysch-like (Menchikoff 1932; Petter 1959; Abbache 2001; Benhamou et al. 2004; Ait Ouali 2006) and turbiditic (Bendella 2004, 2012) nature. From the Frasnian to the Famennian IV, the griotte limestones evolved in basinal environment and the Saoura sedimentary basin is structured in tilted tectonic blocs arranged in horsts and graben (Elmi and Ameur 1984) that generates furrows limited by steepness and shoals. Above this facies, the existence of a deltaic environment (Maache 1987; Ait Ouali 2006) was commonly acknowledged before the presence of a turbiditic system or the ichnological data were revealed. Therefore, the works of Bendella (2004, 2012) and Ouali Mehadji et al. (2006, 2012), based on sedimentological facies and supplemented by ichnofacies data, both tend to- wards the same results. From the end of the Famennian IV to the Famennian V, the area evolved into a trough, with a deep- sea fan established in the later stages of the sea-level decrease. At the end of the Famennian, the beginning of a new phase of transgression (Famennian infra-VI), caused by the rising sea level, facilitated the evolution of a detrital platform through M. Bendella (*) Laboratoire de Géodynamique des Bassins et Bilan Sédimentaire, Université d’Oran, 1524, El M’naouer, Oran 31000, Algeria e-mail: ben_d_mohamed@yahoo.fr A. O. Mehadji Laboratoire de Paléontologie Stratigraphie et Paléoenvironnement, Université d’Oran, 1524, El M’naouer, Oran 31000, Algeria Arab J Geosci DOI 10.1007/s12517-014-1602-9