Seasonal controls on deposition of Late Devensian glaciolacustrine sediments, Central ireland: Implications for the construction of a varve chronology for the British-Irish ice sheet

Delaney, CA, Hambrey, MJ, Christoffersen, P, Glasser, NF and Hubbard, B (2009) Seasonal controls on deposition of Late Devensian glaciolacustrine sediments, Central ireland: Implications for the construction of a varve chronology for the British-Irish ice sheet. In: Glacial sedimentary processes and products. Wiley-Blackwell. ISBN 9781444304442

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Abstract

Laminated pro-glacial glaciolacustrine sediments dating from the Late Devensian (22-10,000 bp) from central Ireland were examined using a combination of detailed logging and scanning electron microscope surface texture and fabric analyses. The sediments are rhythmically laminated and consist of coarser, pale silt layers which alternate with darker clay layers containing occasional thin laminae of fine sand and coarse silt. The pale silt layers contain grains with surface textures indicative of a combination of fluvial, glacial and aeolian transport and contain single or multiple normally graded laminae, erosional surfaces and soft sediment deformation structures, indicating deposition from multiple high density underflows, with occasional dumping of wind-blown sediment into the lake. The dark clay layers have sharp upper and lower contacts and an internal fabric consistent with deposition from a combination of flocculation and grain-by-grain deposition. The thin laminae of coarser material have surface textures consistent with subglacial and fluvial transport only and are interpreted as underflows from subglacial discharges. The sediments are interpreted as annually laminated (varved).