Electrical Resistivity of Coastal Back-Barrier Sediments from South Devon, South-West England, United Kingdom

Abstract

Electrical resistivity surveying is a commonly used geophysical method in civil engineering, but few examples of this application exist in palaeoenvironmental reconstructions. Here, we provide an example of the application of the method to the two-dimensional distribution of lithofacies from coastal back-barrier sites of south-west England. The region is particularly important in coastal studies because of the current paucity of stratigraphic data and its position along the fastest subsiding coastline in Britain. Surveys were carried out at four sites along the south Devon coastline with the ABEM LUND Imaging System. Ranges of electrical resistivity of subsurface sediments were interpreted by ground-truthing from boreholes placed along the survey runs. Electrical resistivity surveys carried out at coastal locations can be affected by a range of phenomena—in particular, saltwater intrusion from rising tides and storm-induced overwash events. Conductive groundwater can cause temporal variations in the electrical profiles measured at the surface. This has not been witnessed to any significant degree at our sites. Despite anthropogenic and environmental noise (e.g., fences, tracks, drainage ditches, streams, and the possibility of salt water intrusion), the system has produced encouraging results and demonstrated that the technique has a future in coastal research. In particular, it readily identified the depth of gravel barriers and depth to basal strata. Given the speed and efficiency of data collection and interpretation available in the field, such systems should prove valuable in future research. Integration of the resistivity profiles with borehole information and radiocarbon dates of selected samples show that back-barrier basins began to fill with fine minerogenic sediments and shells ca. 9000 to 8000 Cal BP, and the majority of sites became terrestrialised by ca. 4500 Cal BP.