Monitoring subsidence to relict salt mines using long-term time-lapse microgravity, Marston, Cheshire, UK

Ground Penetrating Radar (GPR) is a near-surface geophysical technique, and has been previously used to obtain 3D sedimentary architectures of both modern and ancient fluvial successions. Obtaining multiple 2D profiles behind outcrop exposures should allow 3D architectures to be extracted and then used to create high-resolution deterministic 3D numerical models. This research has collected a GPR dataset at Spireslack quarry in Glenbuck, Ayrshire, Scotland. Spireslack quarry is an ex-open case coal mine and is presently designated as SCARP (Scottish Carboniferous Research Park), a long term educational resource exposing Carboniferous geology. This preliminary study collected 2D profile behind the B1 outcrop face exposing channelized fluvial features; here the soil was thinnest, giving the best chance of good signal penetration. A Sensors&Software PulseEKKO™ 100 system was used to collect both 50 MHz and 100 MHz frequency data, to determine the optimal equipment, resolution and achievable depth. Data was then processed using REFLEXW™ v.3 software before being incorporated into Schlumberger PETREL™ software to create a 3D model. GPR results imaged a fluvial channel and point bar set that had significant di-electric permittivity contrasts. Penetration depths were ~20 m, depending upon GPR antenna frequency. A very near-surface, thick limestone bed, dominated the profiles at the very near surface. Study implications suggest GPR is promising at this location to allow the capture of 3D sedimentary architectures, although recommendations should be to collect further data using lower (25 MHz) frequency profiles and where overlying soil has been removed