Radar facies of paraglacial barrier systems: coastal New England, USA

Abstract

Analysis of a large data base of ground‐penetrating‐radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid‐ to high‐latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment‐source areas are characterized by chaotic, parallel, and tangential‐oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection‐free, and bounding‐surface configurations. Back‐barrier sediments may yield basin‐fill configurations, but generally include abundant signal‐attenuating units. The GPR data, calibrated with information from cores, were collected across swash‐aligned and drift‐aligned barriers in a variety of wave‐ and tidal‐energy settings. Application of a 120‐MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m. The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt‐marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.