Highstand versus lowstand deposition on carbonate platform margins: insight from Quaternary foreslopes in the Bahamas

Examples of both highstand and lowstand deposition have been identified on the upper platform slopes of the Tongue of the Ocean, Bahamas. Highstand deposits consist of a thick wedge of fine-grained, skeletal and non-skeletal sands and carbonate muds derived predominantly from the platform and deposited on slopes of 25–28°. These sediments were deposited subsequent to platform flooding and may be more than 30 m thick along open leeward margins. In contrast, lowstand deposits consists of coarse skeletal sands, gravels, and boulders deposited on primary depositional slopes of 35–45°. These sediments were derived from fringing reefs along the marginal escarpment and deposited during the initial rise of sea level following the last lowstand. These variations in depositional character result in a distinctive signature of highstand versus lowstand deposition for steep-sided platforms and further elucidate the response of carbonate platforms to high magnitude, 5th order scale (20,000 yrs) fluctuations in sea level.