A lithological assessment of the resistivity data acquired during the airborne geophysical survey of Anglesey, North Wales

Abstract

A recent airborne geophysical survey has provided high resolution estimates of the electrical resistivity of the near-surface and deeper (bedrock) formations found across Anglesey and a portion of the coastal area of North Wales. This single small survey provides new geophysical information on both the complex configuration of the Neoproterozoic and Cambrian bedrock units and the shallow near-surface geology and glacial features.The correlation between the specific rock lithologies (bedrock and sub-glacial) and the derived bulk resistivities are examined. The geological classification of the geophysical data provides an assessment of 16 lithological units and allows baseline resistivity maps at a range of investigation depths to be constructed at 1:250k scale. The study indicates a broad age-dependence with the Palaeozoic (Carboniferous) bedrock units being the most conductive formations. More detailed studies are performed using statistical departures from the norms. The data have been used to identify sub-zones, within the existing lithological classification, that define statistically distinct groupings. The study shows that the Anglesey Blueschists of the Aethwy Complex are dissimilar (displaying higher resistivities and greater dispersion) to the main schistose zones within the survey area.In the near-surface, the data map surprisingly continuous conductive and resistive zonations. Some of the conductive zones are shown to coincide with the mapped sub-glacial landforms (drumlins) deposited during the Devensian glaciations.

Proceedings of the Geologists’ Association (PGA) Volume 126, Issue 1

“…Ruban (2014) presents an evaluation of the use of the term 'lithodemes' that has been introduced to enable a stratigraphic approach for crystalline terrains. White and Beamish (2014) present the results of an experiment to assess the integrity of nearsurface electrical resistivity data acquired during a HiRES airborne geophysical, and Lark et al (2014) present a Confidence Index that expresses the confidence of experts in the quality of a 3-D model developed to represent the subsurface at particular locality. All these paper are of general interest and important for the development of their particular subject areas.…”