Expanding the Ichnofacies Model to Tidal Straits: Testing Predictions and Assessing Anomalies

Trace fossils are instrumental in facies analysis, but some depositional environments remain underexplored. Cenozoic deposits in Italy have been studied to evaluate the ichnology of tidal straits. These comprise four zones: (1) strait centre, (2) dune-bedded strait zone, (3) strait end and (4) strait margin. The strait centre is characterised by non-deposition and/or erosion and is host to firmground Thalassinoides of the Glossifungites Ichnofacies, whereas the coarse-grained deposits of the strait margin are unbioturbated. The dune-bedded strait zone is typified by high energy. The ichnofacies model predicts that this zone would be characterised by the Skolithos Ichnofacies. Instead, deposits are dominated by the spatangoid ichnogenus Bichordites, with subordinate occurrences of the opheliid polychaete burrow Macaronichnus. A stressed expression of the Cruziana Ichnofacies occurs in the strait end. These observations expand the ichnofacies model to tidal straits, suggesting that the ichnology of tidal environments is more complex than previously envisaged.