Spatial Sedimentological and Geochemical Variations on a Shallow-Water Carbonate Platform

Peter Swart¹, John J.G. Reijmer², Robert Otto¹, and Thorsten Bauch^3
1 University of Miami, Miami, FL
² Université de Provence (Aix-Marseille 1), Marseille, France
³ IFM-GEOMAR, Kiel, Germany

A new series of surface sediment maps of northern part of Great Bahama Bank have been constructed using a grid (~10 km) of over 200 GPS positioned stations. Analysis of the facies distribution reveals a considerable greater degree of heterogeneity than revealed in previous studies. In all platform-interior facies the coarse fraction (> 63 µm) is dominated by pellets with values up to 80%. Clasts and coralline algae are also frequently encountered, benthic foraminifers occur in minor amounts. Green algae (Halimeda sp.), corals, red algae, and grapestones are generally restricted to the margin of the platform. The mineralogy of the coarse and fine fraction on the platform is dominated by aragonite (up to 95%), but also contains up to 5% high-magnesium calcite and minor low-magnesium calcite (max. 1%). Surface sediments distribution shows a good correlation between the aragonite percentage and the carbon isotope composition, which values are similar to that seen in the periplatform sediments. Carbon isotopic composition of all surface sediments varies between +3 and +5 per mille with little differentiation between the individual facies types. Hence platform derived material exported into the periplatform realm will have a positive C isotopic composition regardless of grain size. Organic carbon concentrations show the highest concentrations in the mud-dominated sediments, with the C isotopic composition of the organic fraction being the most depleted near the platform margin. Data obtained from this study will have important implications for the study of ancient carbonate platforms.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005