Pleistocene glaciations in Ireland

Abstract

A literature survey and data from recent investigations are used to reconstruct ice limits in Ireland during the last (Midlandian) and penultimate (Munsterian) cold periods which are correlated with Marine Isotope Stages (MIS) 2-5d (Weichselian) and 6-8 (Saalian) respectively. Evidence for Munsterian ice limits and flow directions is equivocal and based mainly on erratic carriage and the presence of striae and subdued glacial landforms found outside well-marked Midlandian end moraines. Ice extent and flow direction is known only from the late Midlandian (MIS 2; 24-10 kyr BP) although ice may well have been present in the early Midlandian (MIS 3-5d; 24-117 kyr BP). Six late Midlandian glacial stages are identified on the basis of morphosedimentary and dating evidence, and patterns of subglacial bedforms including drumlins and Rogen moraines. Previous late Midlandian glacial models are well-established but are generally based on incomplete and/or erroneous datasets, are not age-constrained, and do not consider time-transgressive sedimentation and landform-shaping events. Recent work shows that repeated ice advance-retreat cycles (oscillations) occurred during the late Midlandian. Oscillations resulted in stratigraphically superimposed, overprinted and cross-cut landform and sediment patterns that record ice activity throughout the glacial cycle. Additionally, subglacial bedforms previously unrecorded in the British Isles, such as flow-transverse ridges (Rogen moraines), are also present. Late Midlandian ice oscillations in Ireland occurred in tempo with millennial-scale changes in North Atlantic climate, suggesting connection to hemispheric shifts of the ice-ocean-atmosphere system.