Late Jurassic Entobia ichnofacies from Chilean coral carpets (35°S): insights into bioerosion and back-arc palaeoenvironments

Tithonian mixed siliciclastic–carbonate strata of the Baños del Flaco Formation, deposited in the western back-arc Neuquén Basin, central Chile, contain a 2-m-thick interval of in situ branch-dominated scleractinian coral carpets with clear evidence of bioerosion. Coral-bearing strata were analysed through an integrated ichnological and microfacies approach to evaluate the controls on substrate colonization. The ichnoassemblage is dominated by Gastrochaenolites, with subordinate Caulostrepsis, Trypanites, Rogerella, and minor Entobia, defining a mature endolithic community characteristic of the Entobia ichnofacies. Both ante- and post-mortem infestations are documented, although colonization of dead skeletons predominated. Stratigraphic evidence indicates that marine transgression promoted coral settlement and initial boring by acrothoracicans, annelids, and bivalves, whereas continued sea-level rise caused coral drowning. Dead skeletons then provided stable substrates for extensive post-mortem colonization, demonstrating that bioerosion intensified after coral mortality rather than causing it. The dominance of Gastrochaenolites and bafflestone development suggest moderately nutrient-rich shallow-marine conditions, probably linked to synchronous Andean arc volcanism. These results refine current understanding of Late Jurassic bioerosion in back-arc settings, highlight the ecological distinctiveness of coral carpets, and provide the first detailed characterization of fossil coral–endolithic communities in Chile and of bioerosion in Upper Jurassic corals from the Neuquén Basin.