An Early Ordovician age for the Annascaul Formation of the SE Dingle Peninsula, SW Ireland

Abstract

The phyllitic mudrocks, quartz wacke sandstones and mélange units of the Annascaul Formation in the SE Dingle Peninsula, SW Ireland have been previously assumed to be Silurian in age, similar to overlying fossiliferous Wenlock rocks of the Ballynane Member. The contact between the Ballynane Member and the underlying Annascaul beds is either faulted or unconformable , and the Annascaul mudrocks contain two or more cleavages not present in the Silurian Ballynane and younger strata. The Ballynane Member is therefore differentiated from the Annascaul Formation by upgrading the proven Wenlock Ballynane beds to formational status. Grey and black mudrocks in the Annascaul Formation have yielded diagnostic palynomorph assemblages indicative of an Early Ordovician age. The Annascaul Formation invites comparison with similar Early Ordovician rocks, south of the putative trace of the Iapetus Suture, in SE and eastern Ireland, in the English Lake District, and in central Newfoundland.