Microfaunas from Late Devensian glaciomarine deposits in the Irish Sea Basin

Abstract

Abstract:Fine-grained, Late Devensian glaciomarine sediments from 26 sites in the Irish Sea Basin contain an almost exclusively foraminiferal fauna dominated by Elphidium clavatum, Haynesina orbiculare, Cibicides lobatulus and Cibicides fletcheri. This biofacies is typical of shallow-water, Arctic environments where glaciers are in retreat. The relatively well-preserved, cold-water species are accompanied by poorly preserved temperate species, considered to have been reworked from earlier deposits on the sea floor. These include Ammonia batava, Ammonia falsobeccarii, Elphidium crispum and Elphidium species A. Although ice transport and ice marginal reworking occurred during rapid ice withdrawal and produced a mixed fauna basin-wide, subsidiary species show marked geographical variation in distribution. E. nitida is restricted to the south-eastern Ireland stations and E. asklundi is much less numerous on the east side of the basin. The derived temperate element is also much stronger at sites in south-eastern Ireland. Species derived from beds older than the Pleistocene are rare. The largely in situ, cold-water faunal elements provide evidence for extensive glaciomarine conditions during the decay cycle of the Late Devensian Irish Sea glacier. The dominance of Elphidium clavatum assemblages is a signature for a major meltwater event which may be linked to catastrophic release of meltwater to tidewater ice margins when rising sea-level broke the seals around meltwater reservoirs within the main glacier.