Boring of various faunal elements in the Oligocene-Miocene Bluff Formation of Grand Cayman, British West Indies

Molds of corals, bivalves, and gastropods in the Oligocene-Miocene Bluff Formation of Grand Cayman Island contain casts of Entobia (9 ichnospecies including the new ichnospecies E. dendritica), Trypanites (3 ichnospecies), Gastrochaenolites (2 ichnospecies), Maeandropolydora (1 ichnospecies), Talpina (1 ichnospecies), and Caulostrepsis (1 ichnospecies), as well as the new ichnogenus Uniglobites, indeterminate ichnogenus a, and a problematical boring. Entobia accounts for approx 75% of the borings, while Uniglobites and Trypanites together account for 15% of the borings. Comparison of Uniglobites with modern borings of known affinity suggests that it was produced by adociid and/or clionid sponges while indeterminate ichnogenus A was probably formed by bivalves. The amount of boring, which ranges from 0-75%, varies from skeleton to skeleton or, in some cases, from branch to branch of the same coral colony. The branching coral Stylophora was particularly susceptible to boring, probably because of its small size and high surface area. The average boring of approx 38% compares favorably with the amount of boring found in modern corals. Analysis of the borings suggests that sponges were responsbile for most of the borings in the corals from the Bluff Formation. Comparison with bioerosion in modern reefs suggests that similar patterns of bioerosion were also occurring in Oligocene-Miocene times.