Features indicative of prolonged and severe periglacial activity in Ireland, with particular reference to the South-West

Abstract

lce wedge casts, once thought to be largely restricted to the area south of the South lreland End Moraine, are, in fact, widespread, both areally and within the Quatemary stratigraphic sequence. Although such features occur through the Quaternary sequence from the Courtmacsherry raised beach (6-8 m m.s.l.) upwards through the deposits of the last glaciation, this does not imply permafrost or periglacial conditions any earlier than early Vistulian times, for there is no basis for the old stratigraphic subdivision of the Quatemary deposits in Ireland, and current interpretation, relying on standard stratigraphic procedures, places all of the glacial and periglacial deposits postdating the Courtmacsherry raised beach and the Gortian interglacial sediments in the last glaciation. A consideration of the stratigraphic distribution of ice wedge casts indicates at least three major phases of permafrost activity, a prolonged period (probably extending intermittently through the whole glacial period) of periglacial conditions conducive to frost shattering and gelifluction on a large scale. Studies in south-west Ireland indicate that cryoturbation features are best developed in the zone of the end moraine of the last glaciation and outside this moraine, but do not seem to occur inside it. In areas where the end moraine zone of the Kerry-Cork (south-west lreland) ice cap of the last glaciation can be identified the occurrence of well developed ice wedge casts both within and outside it indicates that it will be extremely difficult, if not impossible, to map the permafrost zone associated with this moraine and its correlatives unless criteria can be identified which will isolate the permafrost features of this period. An intensive programme aimed at dating the deposits in which the permafrost features occur is therefore essential to such a project.