GPR CHARACTER OF BAHAMIAN CARBONATE STRANDLINE DEPOSITS: COMPARISON WITH LAKE BONNEVILLE SHORELINE ENVIRONMENTS

The Bahamas Island archipelago grows by the precipitation and secretion of calcium carbonate. The majority of this growth is by lateral accretion of shoreline sedimentary deposits. Previous research is not clear on whether the growth is largely due to eustasy, sediment input from catastrophic events, or a combination of both. The Bahamas is an ideal location for studying Holocene carbonate generation and deposition, but there is limited research on the analysis of strandlines in relation to lateral accretion. Carbonate strandline deposits are commonly classified as low-energy beach ridge deposits. Previous researchers have primarily focused on ooid shoals and subtidal regions. Understanding the mechanisms of platform and shoreline growth in the Bahamas is important for creating petroleum reservoir analogs for exploration. We use ground penetrating radar (GPR) to image and interpret the internal fine-scale stratigraphy of Bahamian carbonate strand plains and thereby constrain our understanding of the processes by which the islands grow. Although GPR has been used extensively to analyze the interior of clastic strandline deposits across the world, tropical carbonate settings have received little attention. We are the first to utilize GPR to study strand plains in Crooked Island, The Bahamas, our primary location for 2D GPR data acquisition. We integrate our interpretation of these data with a 3D GPR data volume collected on Pleistocene eolianites on San Salvador Island, The Bahamas. We used a GSSI (Geophysical Survey Systems, Inc.) bistatic 400-MHz antenna with a field frequency filter of 100–800 MHz for all datasets. GPR allowed visualization of the interior of the strand plains down to a depth of about 2 m with high resolution. Data processing was performed using state-of-the-art petroleum industry techniques (e.g., gain control, deconvolution, migration, seismic attribute computation) to better visualize the reflectivity. Our data constrains a model that the lateral accretion of carbonate sediment preserved in strandline was deposited in a combination of storm processes and gradual sediment progradation, rather than one or the other. Additionally, we integrate our Bahamian results with high-resolution 2D and 3D GPR data from two ancient Lake Bonneville shoreline environments in northwestern Utah, Pleistocene regressive-phase and transgressive-phase remnants. All datasets show prominent sea- or lake-ward dipping reflectors associated with a linear topographic ridge. The stratal reflectors in the Lake Bonneville cases show a transition from proximal offshore to foreshore deposition, while those in the Bahamas cases can be interpreted as linear dunes and swales that parallel the coastline and which represent seaward-migrating accretion into accommodation space.