Ichnoassociations, facies and depositional environments of a modern barrier-island: Ilha da Tavira (Ria Formosa, Portugal)

The distribution of modern ichnoassociations in the Tavira barrier-island system (Ria Formosa, Algarve, Portugal) is mapped using a GPS-equipped camera. 36 ichnites are identified, including modern analogues of the trace fossils Archaeonassa, Avipeda, Diopatrichnus, Diplocraterion, Entobia, Laterigradus, Lockeia, Lumbricaria, Monocraterion, Oichnus, Polykladichnus, Protovirgularia, Psilonichnus, Rusophycus, Skolithos and Haplotichnus. These traces form 15 ichnoassociations, each of which is linked with a well-constrained depositional setting. Ichnoassociations of the wave-swept fore-barrier foreshore are characterized by low diversity and bioturbation intensity, whereas those of the back-barrier (protected) tidal flats display high diversity and bioturbation intensity. This asymmetrical distribution is primarily explained by hydrodynamics, deriving from the sheltering role of the barrier. Emersion time and substrate cohesiveness also play an important structuring role in the distribution of the Tavira Island ichnoassociations. Ichnoassociation mapping allows to define a predictive model of ichnoassociation distribution, providing an immediately applicable tool for palaeoenvironmental reconstitutions of barrier-island systems. •Each ichnoassociation is linked to a specific facies and depositional environment.•Intense bioturbation, deep tiering and Psilonichnus characterize the back-barrier.•The fore-barrier displays low bioturbation intensity and shallow tiering.•Hydrodynamics, substrate firmness and exposure structure the ichnoassociations.•A model relating ichnoassociations to depositional environments is proposed.