Quaternary Sediments

The Quaternary geology of Ireland – Sediments Map is a representation of the surficial geology of Ireland at a scale of 1 to 50,000. The map shows the sediments mapped within 1 metre of the surface which were laid down during the Quaternary, bedrock at or close to the surface water bodies or made ground. Quaternary sediments are categorised according to their genesis. The main types of sediment recognised are tills, (glacio)fluvio/lacustrine deposits, alluvium, lacustrine sediments and peat. Bedrock and karstified bedrock at or close to the surface are also mapped out as separate units.

The Quaternary sediments map illustrates sediments or bedrock within 1 metre of the surface. Quaternary sediments are categorised according to their genesis. The main types of sediment recognised are tills, (glacio)fluvio/lacustrine deposits, alluvium, lacustrine sediments and peat. Bedrock and Karstified bedrock at or close to the surface are also mapped out as separate units. Till or Irish Sea Till consist of over consolidated, or tightly packed, unsorted, unbedded, glacial deposits possessing many different particle sizes with commonly sharp, angular clasts. Tills are categorised according to their dominant petrologic component identified from lithological analyses of medium gravel sized pebbles (5 to 10 mm diameter). (Glacio)fluvio/lacustrine sands and gravels are indirect glacial deposits transported to their final position by melt-water during the ice sheet meltdown and sorted in this process. Lacustrine sediments and Marl are deposited during deglaciation or post-glacially in depressions left behind by the ice during ice retreat. Alluvium is a post-glacial deposit recorded along river valleys consisting of generally bedded gravel, sand, silt or clay in a variety of combinations, often with a fairly high percentage of organic carbon (10%-30%). Peat is a post-glacial deposit, consisting mostly of partially decomposed vegetation. Peat deposits accumulated as blanket bog in elevated areas with excessive rainfall and as raised bogs and fens on the low lying regions. Scree is a slope deposit that developed from periglacial action or during post-glacial times. Marine include beach and tidal marsh deposited along the coast. Wind-blown sands consist of aeolian sediments generally deposited along coastal regions. Made ground including Fill, Airfield, Causeway, Crannog, Dam, Embankment, Hardstand, Industrial, Pier, Spoil heap, Tailing pond and Urban indicates deposits associated with anthropogenic action. Bedrock at or close to (within 1 metre of) the surface is classified between karstified and non-karstified bedrock types.