Biofacies and sediments in an emergent Late Pleistocene glaciomarine sequence, Skerries, east central Ireland

Abstract

Late Devensian sedimentation (ca. 18 ka B.P.) on the coastal margins of the Irish Sea Basin occurred in shallow-water glaciomarine environments around retreating tidewater ice margins. High relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last British ice sheet. At Skerries, in east central Ireland, ice-proximal glaciomarine diamict, mud, sand and gravel facies are selectively preserved in a bedrock depression. The coastal exposure, about 500 m long, can be divided into three lithofacies associations. (1) A diamict/gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin. (2) An overlying mud association was deposited from suspended sediment plumes, with minor ice-rafting, and records ice retreat and increasing distality of the site. Muds contain a mixed foraminiferal microfaunal assemblage typical of open-water shallow-marine shelves. Species can be grouped into reworked temperate, cosmopolitan and well-preserved boreo-arctic elements and indicate mixing of derived and retransported temperate species with an in-situ glaciomarine fauna. (3) At the top of the section a gravel association, derived from a nearshore fan delta, rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound. This and other sequences elsewhere in the Irish Sea Basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound.