Hodgson, J.A. and Ture, M.D. (2016)
During 2015 the Tellus programme collected new airborne data within the counties of Dublin,
Meath, Kildare, Wicklow, Offaly and Laois in the Republic of Ireland (ROI) and is collectively
referred to as block A1. An earlier survey (2014-2015) was carried out across counties
Roscommon, Longford and Westmeath as part of the Tellus North Midlands project (Hodgson &
Ture 2015). All surveys measured magnetic field, electrical conductivity and gamma-ray
spectrometer data (primarily potassium, thorium and uranium). The two surveys were completed
in 2015 and this report looks at the interpretation of the geophysical data of the merged data from
Numerous new features have been observed through the magnetic data, often lying beneath the
existing bedrock. Buried volcanic bodies are interpreted particularly in north county Roscommon,
central Kildare and along the border of counties Offaly and Westmeath. Some of these features
have been previously mapped while others haven’t. However, the new geophysical data allows
their extent to be mapped in greater detail and helps in our understanding of the geological
structure of Ireland. The data allows direct and indirect mapping of faults, as well as high gradient
features close to the edge of the Leinster Granite to be resolved. The anthropogenic signal from
wind farms and pipe lines are also evident.
The radiometric data clearly maps chemical variations in quaternary deposits and shows that the
underlying bedrock is the main control on the soil composition. Interesting variations in uranium
concentration across similar till and bedrock units suggest a remapping of till units may be
required or that other controlling variables may exist and should be further investigated.
The EM data allows geological units to be remapped based on their conductive signature, with
more conductive shale units apparent within limestone formations. The data can also be
manipulated to show how conductivities vary with depth creating cross sections and depth slices.
These can be used to map dipping layer and the variation of different units with depth.