|Historic Quaternary mapping and records dating form mid 1800’s and early 1900’s were the main source of information on Dublin’s Quaternary geology until recent reconnaissance mapping initiatives developed a more sophisticated understanding of the nature and extent of Quaternary deposits beneath our capital city. During the second half of 2005, the Quaternary section of the Geological Survey of Ireland undertook a Quaternary Geology compilation map for County Dublin derived from historical and borehole data. This was followed by a quaternary geology mapping program to the reconnaissance standard of the GSI, carried out between mid 2006 and June 2008. Two comprehensive digital datasets have derived from this exercise, Depth to Bedrock and the Quaternary Geology maps of County Dublin. A national Quaternary Geology map released in October 2013, integrating previous work and results of recent data gathering initiatives, replaces the previous mapping in the Geourban framework.
The Quaternary Geology Map displays the dominant sediment type within 1m of the surface, description of quaternary sediments at specific sites, distribution and outline of the main geomorphological features and ice direction indicators. Diamictons and glaciofluvial sediments derived from both, onshore and Irish Sea ice sheets are the main quaternary sediments occurring in the area.
South East County Dublin with Quaternary/Unconsolidated sediments layer and hillshade (courtesy of EPA) displayed.
The depth to bedrock is a prediction map resulting from an interpolation exercise by means of the kriging geostatistical method. This data assists with the interpretation of the erosive and sedimentary processes occurring in the area. The average drift thickness has been estimated at 4.65m. Drift free regions occur on higher ground on the North Dublin Uplands, Dublin Mountains and Howth peninsula. Maximum drift thickness of 45m is reached along a buried channel in the Dublin Port area.
The Depth to Bedrock layer and hillshade (courtesy of EPA) as displayed on the GeoUrban Viewer.