Bioerosional Structures from the Late Pleistocene Coral Reef, Red Sea Coast, Northwest Saudi Arabia

Herein, 20 ichnospecies belonging to 8 ichnogenera were identified in bivalves, gastropods, and corals (n = 701) from the Late Pleistocene coral reef along the Red Sea coast, northwest Saudi Arabia. The trace fossils were produced by clionid sponges (47.39%), endolithic bivalves (42.17%), polychaete annelids (5.42%), vermetid gastropods (3.81%), and acrothoracican barnacles (1.21%). The recognized ichnotaxa were Entobia geometrica, E. ovula, E. cf. goniodes, E. cf. retiformis, E. cretacea, Entobia isp., Gastrochaenolites torpedo, G. lapidicus, G. cf. dijugus, Gastrochaenolites isp., Oichnus paraboloides, O. simplex, Oichnus isp., Caulostrepsis taeniola, Caulostrepsis isp., Maeandropolydora cf. sultans, Maeandropolydora isp., Renichnus isp., Centrichnus isp., and cf. Rogerella isp., Most bivalves and gastropods contain Entobia rather than Gastrochaenolites, which is commonly found in the larger and thicker corals. 'I he content of the trace fossils indicated an Entobia ichnofacies formed in the coral reef during transgression. 'The habitat conditions changed gradually, from well-oxygenated, shallow, high-energy back-reef and reef crest bioeroding polychaetes and bivalves, to deep, low-energy reef slope dominated by boring sponges.