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The Origin of Surface Sediments
 
large product photo   Early Sediment Maps

The Great Bahama Bank has served as an inspiration for geologists in understanding modern process of carbonate sedimentation since the pioneering work of Field (1931) and Illing (1954). In fact most of our knowledge of the spatial distribution of sediments on the Great Bahama Bank is based on work of Illing (1954), Ginsburg et al. (1958), Newell et al. (1959), and Purdy (1963a,b) (Map of Ginsburg shown to left). Valuable as these early descriptions are, it is the aim of this study to re-evaluate the distribution of the surface sediments of the Bahamas using samples collected from well defined points (established using GPS) and to quantify not only the types of sediments present but also the mineralogy, grain-size distribution and skeletal and non-skeletal content.

New Facies
 
  New Samples

Approximately 300 samples were obtained from using a Shipek sampler during four cruises aboard the RV Bellows between 2001 and 2004 (Fig. 1B). The construction of this sampler prevents muds from escaping from the sample taken when retrieving the sample from the sea-bottom It thus differs from the Van-Veen sampler applied during earlier studies (Purdy, 1963a,b) in that it better retains the mud fraction.Immediately after collection, samples were assigned to a modified Dunham scheme (Dunham, 1962).  In order to compliment the classification we added divisions between wackestone (facies-no. 2) and mudstone (mud-rich wackestone; facies-no. 1.5), between a packstone (facies-no. 3) and wackestone (mud-rich packstone, facies–no. 2.5), and finally between packstone and grainstone (facies-no. 4) (mud-lean packstone or poorly-washed grainstone; facies-no. 3.5) (Fig. 2A).  Samples from all cruises were preserved in cold storage and after the 2004 cruise all samples were re-examined to ensure consistency between cruises.

 
 
Geochemistry
 
large product photo   Isotopes

The d13C and d18O of the carbonate materials was determined using dissolution in phosphoric acid using the common acid bath method (Swart et al. 1991) at 90oC.  The gas produced was analyzed using a Finnigan-MAT 251.  Later some samples were also analyzed using a Kiel III device attached to a Finnigan Delta plus.  Data produced in both methods were corrected for isobaric interferences using the procedures (Craig 1957) modified for a triple collector mass spectrometer.  Data are reported relative to V-PDB using the conventional notation.  Average standard deviation based on replicate analyses of internal standards is < 0.1‰.