Lower Ordovician (Arenig) shallow-marine trace fossils of the Pochico Formation, southern Spainpalaeoenvironmental and palaeogeographic implications at the Gondwanan and peri-Gondwanan realm

Abstract

Nineteen ichnospecies belonging to thirteen ichnogenera (Archaeonassa, Catenichnus, Cochlichnus, Cruziana, Didymaulichnus, ?Di-plichnites, Gordia, Lingulichnus, Lockeia,cf. Monocraterion, Planolites, Ptychoplasma, and Rusophycus) occur in the Pochico Forma-tion (Arenigian) in the Aldeaquemada section, Sierra Morena, southern Spain, just above the Armorican Quartzite. They belong to the archetypal Cruziana ichnofacies, indicating a lower shoreface-upper offshore zone. The low degree of sediment reworking may be due to a high rate of sedimentation. The trace fossil assemblage, rich in large Cruziana, is typical of the Armorican Quartzite that developed on the margins of Gondwana and peri-Gondwanan microcontinents. The distribution of ichnofauna during the Early Ordovician was partly palaeogeographically controlled, although ichnological data from the literature point to paths of migration between Gondwana, Baltica and Laurentia. Differences between the ichnofauna of Gondwana and Baltica could be conditioned by facies (clastics in Gondwana and carbonates in Baltica) causing a taphonomic filter, because Cruziana requires diversified clastic deposits for preservation. The ichnofauna would also be influenced by trophic group amensalism between filter feeding and deposit feeding fauna, the former prevailing in Baltica and the latter in Gondwana.