Gastrochaenolites ichnofacies from intertidal seashells, Al-Khobar coastline, Saudi Arabia

Abstract

Bioerosional structures and encrusters on a total of 349 bivalves and 209 gastropod shells were studied from Al-Khobar coastline along the Arabian Gulf, Saudi Arabia. Nine ichnospecies belonging to five ichnogenera were identified, namely: Entobia geometrica, Entobia isp., Oichnus paraboloides, Oichnus simplex, Gastrochaenolites dijugus, Gastrochaenolites isp., Caulostrepsis taeniola and Maeandropolydora isp. Barnacles, serpulids, bryozoans and bivalves were recoded as encrusters on the internal and external surfaces of the investigated seashells. The studied bioerosional structures were defined as Gastrochaenolites-dominated ichnoassemblage, which is composed of Gastrochaenolites, Oichnus and borings of polychaete annelids and clionid sponges. It reflects marine conditions, in a shallow water depth and low rates of sedimentation. A postmortem colonization has been confirmed on the basis of the presence of different encrusters on the internal surfaces of many seashells, while those on the external surfaces indicated a colonization process mostly took place during the lifetime of the seashells.