Bow-shaped, concentrically laminated polychaete burrows: A Cylindrichnus concentricus ichnofabric from the Miocene of Tarragona, NE Spain

Bow-shaped, concentrically laminated burrows from the Miocene of the El Camp de Tarragona Basin in northeastern Spain are described. Although the ichnotaxonomic assignment of these traces is controversial, they are here designated as Cylindrichnus concentricus. A detailed analysis of the overall architecture of the burrows and the constructional features of their characteristic linings allows direct comparison with structures produced today by terebellid polychaetes. Similar trace fossils have been described in the literature from shallow marine environments as old as the Jurassic, which highlights the recurrence of this ichnotaxon and its importance in these settings. C. concentricus occurs in Tarragona as an elite trace fossil in intensely bioturbated ichnofabrics formed in offshore settings with low sedimentation rates, a comparable depositional setting to that of similar Neogene ichnofabrics.