Finite strain analysis of deformed elastic sedimentary rocks below and above the Acadian unconforinity oil the Dingle Peninsula, SW Ireland, reveals that this boundary represents a significant bulk strain discontinuity. The Late Emsian Acadian event is primarily responsible for penetrative cleavage development and high strain in rocks below the unconformity and not, as previously held, the later Variscan event, which overprinted the peninsula with a weak and localized disjunctive cleavage. The presence of apparent anticlockwise transecting cleavage and implied dextral Closure of the Dingle Basin during the Acadian event is compatible with northward convergence of Armorica with respect to Eastern Avalonia.