Bioerosion and encrustation as paleoenvironmental indicators in Upper Cretaceous corals, Aruma Formation, Saudi Arabia

Abstract This study documents and interprets bioerosion and encrustation traces on Upper Cretaceous scleractinian corals from the Hajajah Member of the Aruma Formation in northern Khashm Buwaibiyat, central Saudi Arabia. Fieldwork in 2023 and 2024 involved detailed bed-by-bed stratigraphic logging, ichnological assessment, and fossil collection across marl and limestone units. A total of 213 coral specimens with bioerosional features were analyzed, leading to the identification of 10 ichnospecies across 5 ichnogenera, including Gastrochaenolites, Entobia, Caulostrepsis, Rogerella, and Labyrintichnus. These traces reflect a range of ethological categories, primarily domichnia, indicating permanent dwelling structures by polychaetes, sponges, bivalves, barnacles, and crustaceans. The Hajajah Member records a shallow marine back reef to shoal environment, periodically interrupted by high-energy events. Bioerosional features suggest ecologically complex settings with abundant hard substrates, frequent colonization, and biologically mediated sediment modification. This work contributes to the ichnological record of the region. It underscores the importance of bioerosion as a tool for reconstructing paleoenvironmental conditions in the Late Cretaceous carbonate settings of the Arabian Plate.