Upper Visean trace fossils and their palaeo-environmental significance from the North Tindouf Basin, Algeria

The Lower Member of the Djebel Ouarkziz Formation deposited during the Upper Visean, is exposed in the north part of the Tindouf Basin (SW Algeria). There, mostly carbonates are prone in calcareous body fossils, especially in brachiopods of the genus, Gigantoproductus, but lack of any trace fossil. These deposits are subdivided into three distinct lithological units and subsequent ichnoassemblages, respectively: The lower part consists of the Arenicolites-Skolithos ichnoassemblage with highly fragmented shells in texture, formed in proximal tempestites with strong water energy above the fair-weather wave-base with low abundance and ichnodiversity represented only by Arenicolites isp. and Skolithos isp. The Middle part of the Lower Member is represented by the Thalassinoides-Neonereites ichnoassemblage, by disarticulated and convex-up shells with medium fragmentation in a packstone texture representing meso-distal tempestites. The trace fossils are dominated by Thalassinoides, Neonereites and Monomorphichnus cf. multilineatus. The second ichnoassemblage is typical of the proximal Cruziana ichnofacies. The upper part of the Lower Member corresponds to the Zoophycos-Thalassinoides ichnoassemblage characterised by articulated shells with low fragmentation in wackestone, rarely packstone, developed in a subtidal environment under weak hydrodynamic energy. This ichnoassemblage shows archetypical Cruziana conditions.