Trace fossil assemblages from the Lower Devonian (Lochkovian-Emsian) of the Touat area (Reggane Basin, Algerian Sahara) and their palaeoenvironmental significance

Mixed siliciclastic-carbonate deposits of Lower Devonian (Lochkovian-Emsian) age are exposed in the northeastern part of the Reggane Basin (Touat region). Based on lithological, sedimentological and palaeontological data, these deposits are subdivided into four distinct lithological units: Unit A characterises the Silurian-Devonian transitional zone; Unit B consists of a thick succession of Lochkovian-Pragian age, whereas Units C and D both document Emsian deposits. The studied section exhibits low to moderate ichnodiversity consisting of 14 ichnotaxa: Arenicolites isp., Chondrites isp., Curvolithus multiplex, Lockeia siliquaria, Monomorphichnus isp., Neonereites bisserialis, Neonereites uniserialis, Ophiomorpha isp., Palaeophycus isp., Planolites isp., Psilonichnus upsilon, Skolithos linearis, S. verticalis, and Thalassinoides isp. Both Curvolithus multiplex and Psilonichnus upsilon are documented for the first time from Palaeozoic deposits of the Saharan platform. These ichnofaunas are commonly ascribed to the Skolithos and Cruziana ichnofacies. Five distinct ichnoassemblages (Ichnoassemblages A to E) were defined, reflecting palaeoenvironmental changes from the foreshore to upper offshore zones, with frequent storm influence. Ichnofabric analysis of the section studied reveals six levels with different bioturbation intensities showing different palaeoecological conditions in various environmental settings (Monospecific Planolites, Lower combined Skolithos-Arenicolites, Combined Skolithos-Thalassinoides, Monospecific Skolithos, and Upper combined Skolithos-Arenicolites and Reburrowed Chondrites ichnofabrics). The vertical evolution of these deposits displays the successive deepening and shallowing trends recorded during the Lower Devonian in this area.