A diverse trace-fossil assemblage from the Middle Jurassic (Bajocian) Teniet El Klakh Formation (western Saharan Atlas, Algeria)

Abstract

The mixed siliciclastic–carbonate Teniet El Klakh Formation (Middle Jurassic, Bajocian) mainly consists of a monotonous, clay and fine-grained sandstone alternation with some intercalated carbonate beds. The trace fossil record displays moderate to high ichnological diversity with different behaviours, consisting of 28 ichnotaxa belonging to 23 ichnogenera: Arenicolites isp., Bolonia lata, Chondrites targionii, Chondrites isp., Circulichnis montanus, Curvolithus simplex, Diplocraterion paralellum, Glockerichnus isp., Gyrochorte comosa, Helminthopsis abeli, Lockeia isp., Megagrapton cf. irregulare, M. submontanum, Monomorphichnus cf. multilineatus, Neonereites cf. biserialis, Nereites isp., Ophiomorpha isp., Palaeophycus cf. striatus, P. tubularis, Palaeophycus isp., Planolites isp., Protovirgularia dichotoma, Protovirgularia isp., Rhizocorallium commune var. irregulare, Rutichnus irregularis, Skolithos linearis, Taenidium cf. serpentinum, and Thalassinoides suevicus. The distribution of these trace fossils in space and time is controlled by various environmental features, mostly referred to the accumulation of organic matter in softground substrate during short phases of low hydrodynamics in well-oxygenated environments, thus allowing the occurrence of abundant and diverse invertebrates frequently dominated by deposit-feeders. The integrated sedimentological and ichnological features suggest that the Teniet El Klakh Formation had been deposited in a storm-influenced continental shelf setting ranging from the lower offshore to the lower shoreface zones with fluctuating energy regime, corresponding to the archetypal and proximal Cruziana ichnofacies transitional to the Skolithos ichnofacies. The ichnological assemblage described herein is original and rather unique, since most of trace fossils are reported herein for the first time from the Ksour Mountains.