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Bedrock Unit Groups

There are more than 1,200 geological Formations and Members defined within the Republic. Their delineation is based on a variety of factors, many of which are of no relevance to the hydrogeological properties of the aquifer (for example, type of fossil). GSI’s Groundwater Section have, therefore, evaluated these Formations and Members and reduced them to 27 'Rock Unit Groups' that have hydrogeological significance.
The Rock Unit Groups are defined within a stratigraphic framework on the basis of what we understand to be important differences between rock units/ rock unit groups in terms of groundwater flow properties. For example,
• limestone purity and susceptibility to karstification;
• bedding presence or absence and it's influence on the prevalence of jointing;
• degree of deformation and its impact on flow properties (e.g., older rocks have been deformed many times since their formation, so lack pore spaces and connected fracture networks).
The way in which the aquifer classification has been undertaken is on the basis of ‘Rock Unit Groups’ rather than the individual ‘rock units’ (Formations). Note that a particular Rock Unit Group can, and often does have, a different aquifer classification in different parts of the country (for example, the Dinantian Pure Unbedded Limestones aquifer classification ranges from Ll to Rkc and Rkd, depending upon location).

Geological Survey of Ireland

2015-06-23 12:54:05

Geological Survey of Ireland

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