Carbonate island formation within a Modern ooid shoal, South Joulter Cay, Great Bahama Bank

Carbonate islands are a key determinant of energy distributions on carbonate platforms and therefore play a major role in governing facies distribution, including those in ooid deposits such as the Joulters ooid sand body. Joulters covers ~400km2 of Great Bahama Bank north of Andros Island. It is famous as a site for the study of high-energy carbonate deposits due to the clearly observable interplay between vast stabilized sand flats and active ooid bars. Previous field mapping and local coring place island formation later in the overall story of the sand bodys development with island development within sand body development and established they are a very young features with radiocarbon dating the island showing ages from ~2000 ybp to present. Our ongoing examination of South Joulter Cay (SJC), the largest of the islands, targets a finer-scale delineation of the stages of island formation. High resolution imagery and a DTM constructed from a drone survey improves visualization, showing SJC is close to 2.5 km long, has a maximum width >600 m and is formed by a series of elongate ridges (>40) and their intervening lows formed from primarily oolitic sands. Major ridges diverge toward the southern end of the island, and bankward-dipping foresets indicate primarily seaward to bankward deposition. An abandoned tidal channel cutting through the southern third of the island is a key morphological element which likely controlled the distribution of sediments as the island built. Also, a key elements of island formation is the nucleation mechanism, which in this study we hypothesize that hurricanes are responsible for the accumulation of the first ridge of the island. The evolution of the island is defined by turning points which are generated by autogenic processes that resulted from the feedback between sediment production, filling accommodation space and changes in wind and tide patterns.