Palaeoenvironmental interpretation of the Tramore Limestone Formation (Llandeilo, Ordovician) based on bryozoan colony form

The Tramore Limestone Formation (Llandeilo, Ordovician), exposed in southeast Ireland, contains ■well-preserved colonies of the trepostome bryozoan Diplotrypa petropolitana . Two palaeoenvironmental settings – a deep water carbonate basina! facies, and a shallow water carbonate shelf facies – are represented. Shape, size and attitude to bedding of Diplotrypa colonies were measured in the field. These data were compared with results gathered from experiments carried out to test the behaviour in a wave tank of representative models of bryozoan colonies. Results have demonstrated a clear environmental partitioning of colonies, and suggest that dome-shaped colonies are more dominant in deep water facies than bell-shaped colonies, which occur more abundantly in the shallow water facies. Morphological analysis of bryozoan colonies can be a useful tool for palaeoenvironmental interpretation.