3D MAPPING OF RADAR FACIES IN A LATE PLEISTOCENE CARBONATE PLATFORM DEPOSIT, BAHAMAS

Two 3D ground-penetrating radar (GPR) surveys collected on northwest Andros Island, Bahamas, facilitate understanding the architecture and evolution of carbonate sedimentary environments that are often unseen in 2D outcrop and core. A 200-MHz 3D GPR dataset was collected over Late Pleistocene (isotope stage 5e) bedrock at a schoolyard in northwest Andros over an area of 61 m x 61 m. This survey reveals a ~18-m wide oolitic barform that trends southwest-northeast through the study area with foresets dipping to the northwest and a ~12-m-wide tidal channel that trends north-northwest through the northeast part of the survey. These two prominent features are surrounded and underlain by low-energy mud deposits. A deeper radar surface can be seen at ~6.4 m depth dipping gently to the west, and is interpreted to be a sequence boundary. In order to better resolve the lateral and vertical spatial interaction between the shallower features (<3.5 m), a higher resolution, 35.8 m x 29.6 m 400-MHz 3D GPR dataset was collected with the survey direction optimized to image the barform and its foresets (i.e., the profiles were collected in the direction of dip). The interpretation of these features is enhanced by modern analogs found nearby at Joulters Cays, and by three cores and 56 thin sections collected through the crest and toe of the barform, and through the channel feature. The integration of geophysical and geological data enables the recognition and reconstruction of a Pleistocene depositional environment and its associated fine-scale process sedimentology, including changing current directions, barform accumulation patterns and non-depositional and erosional events.