Ichnological analysis of the Kheneg el Aatène Formation (Floian-Dapingian) at its type locality (Saoura Valley, Ougarta Range, southwestern Algeria)

The Early-Mid Ordovician Kheneg el Aatène Formation of the Ougarta Range is here divided into two members: (i) the Aatène Micaceous Sandstone Member and (ii) the Aatène Quartzite Member. A low diversity trace fossil assemblage is present in the upper part of the second member with abundant Skolithos linearis, Skolithos isp. and Rosselia erecta, common Arenicolites isp. and Diplocraterion isp. and rare Palaeophycus isp. and ?Rusophycus isp. This association is characteristic to the Skolithos ichnofacies and indicates high-energy conditions and opportunistic colonisation within a siliciclastic shallow marine environment. The ichnoassemblage is dominated by vertical traces which occur in great densities forming typical Skolithos pipe-rocks. The pipe-rock ichnofabric is characterised by burrows that are closely spaced and occur at 20 distinct levels. Possible predation has been detected in the same Member due to the presence of ?Rusophycus intersecting worm burrows. High densities of Trypanites are present in two hardgrounds composed of calcareous lithified sandstones developed during transgressive pulses that can be related to the brevis event. Trypanites borings are evidenced for the first time from inorganic hard substrates of the Gondwanan Ordovician. These borings can be related to beginning of the Ordovician Bioerosion Revolution in Gondwana.