| Two deep continuous core-borings, Clino (677.3 m) and Unda (442 m), located on the leeward margin of the Great Bahama Bank, consist of an offlapping succession, from a skeletal, non-reefal slope--to reefal--to shallow-water platform top (from Pliocene to Pleistocene). The platform expanded not as a simple migration of facies outward, but rather with several sedimentologic and morphologic transformations in response to changing sea levels. Fluctuations in sea level resulted in: (1) a flattening of the platform slope; (2) the development of numerous meter-scale alternations of shallow-marine carbonates and subaerial exposure horizons (or parasequences); and (3) major compositional changes in the sediment.;Based on sequence stratigraphic interpretation a hierarchical stratigraphic pattern composed of two, third-order sequences with 11 superimposed parasequences in Clino and 15 in Unda (excluding the Holocene) is proposed. The lithologic sequence boundary does not coincide with the seismically described sequence boundary. Parasequences are the building blocks of the platform and "typical" platform interior and platform margin parasequences are described. Within parasequences, systems tracts are designated, however, applying the strict definitions of systems tracts is problematic.;The depositional and sea level history of the leeward platform, over a 60 km distance, is described. The rise and fall of sea level in the core borings is inferred from the parasequences which consist of alternations of shallow marine sediments (transgressive and high stand deposits) and subaerial exposure horizons (low stand deposits). During the Pliocene, the platform margin was pushed back by overall higher sea levels. Regional subaerial exposure was rare. As a result of frequent (100,000 yr period), high-amplitude sea level oscillations, the platform flattened beginning in the late Pliocene. During the late Pleistocene, the entire platform was exposed at least nine times. This number is consistent with the number of oxygen isotope stages inferred from deep sea cores.;Until the latest Pleistocene, corals were instrumental in building the margins upwards. Pliocene and Pleistocene marginal reefs developed during the initial rise in sea level. During the high stands, corals were often smothered by platform-derived sediment, whereas, during low stands they became subaerially exposed. |
