A REEVALUATION OF SEDIMENTARY FACIES ON GREAT BAHAMA BANK

It has been over 50 years since the first sedimentary facies maps were published for Great Bahama Bank based on the work of Newell, Illing, Purdy, and Ginsburg. These maps have been used to train numerous generations of geologists in modern carbonates as well serving as the basis for facies interpretation in ancient carbonate platforms. As important as these desciption were, there are now many reasons why the sediments should be re-examined. For example, the original sampling was undertaken over a relatively coarse grid and without the benefits of precise location systems. In addition many types of geochemical measurements were not made. We have embarked upon a multi-year project to use modern navigational methods to collect a series of samples to reclassify the sedimentary facies and add information upon the geochemistry (trace elements, mineralogy, and stable isotopes). To date we have collected samples from over 250 stations on a 10 km by 10 km network. Analyses of these samples reveal many similarities to the old maps, but significantly greater complexity. Stable C isotopic analyses show that all the surface sediment, regardless of grain size, and position on the platform, are relatively positive, while the O isotopic composition is related to grain size. Organic C concentrations are low and the most depleted values are situated at the margins of the platform reflecting the input of oceanic derived carbon. Our studies will greatly improve the knowledge of modern depositional patterns in modern carbonate platforms.