Geological guidance of speleogenesis in marble of the Dalradian Supergroup, County Donegal, Ireland

Pollnapaste is a small but complex cave developed in marble of the Dalradian Supergroup near Lettermacaward in County Donegal, at the mouth of the Gweebarra River. Speleogenesis has largely been guided by variations in marble band lithology during inception and the early stages of void formation, but as the cave developed the influence of this banding declined. Solubility contrasts, between marble and metadolerite, and the configuration of the intrusions have provided later and greater guiding effects. Phreatic development appears largely strike-related, with only minor dip tubes connecting different segments. Metadolerite or quartz aquicludes have created perched zones of saturation, in which the early stages of the caveʹs development occurred. Breaching of these aquicludes allowed progressive lowering of the phreas and development of vadose passages along fractures cutting across the strike. There is no conclusive evidence for any pre-Devensian development of the cave system and the main passage development is presumed to be entirely late-glacial to post-glacial in age, although inception may have occurred much earlier.