Analyzing Spatial Patterns in Modern Carbonate Sand Bodies From Great Bahama Bank

Three carbonate sand bodies on Great Bahama Bank, which show a range of depositional facies patterns typifying modern deposits as well as their ancient counterparts, are quantitatively interrogated to broaden our perspective of the types of information that can be derived from studies of modern environments. Rimming the southern end of Tongue of the Ocean (TOTO) is the broadest expanse of “high-energy” sands found in the Bahamas, characterized by narrow sandbars separated by wide, deep channels and a lack of islands. A variation of the tidal-bar motif with broader and more irregular sandbars, relatively narrow channels, and few small islands occurs at the northern end of Exuma Sound (Schooners). Sands associated with tidal channels and the numerous islands of the Exumas chain along the western edge of Exuma Sound occur primarily as flood tidal deltas. The geometry of sandbars that inhabit the three sand bodies is quantified using Landsat remote sensing and assembled, along with optically derived bathymetric surfaces, into a GIS. This database is quantitatively examined using a suite of morphometric tools to compare and contrast geometric character of sandbars within and between the three sand bodies. Considered are properties such as the size, shape, complexity, distribution, orientation, and topography of the individual sandbars. Profiles and spatial analysis tools enable sandbar and channel spacing, position relative to the platform margin, connectedness, separation distances, and density to be characterized. As has been previously reported for reef-dominated environments, certain aspects of the geometry of the three systems are found to behave in a systematic and hence predictable manner, though important mathematical differences are revealed between the scaling of reefal landscapes and the grainy geobodies considered by this study. Because the three sand bodies are disparate in their overall extent and depositional settings (e.g., orientation, prevalence of islands), this predictable behavior has the potential to impart considerable insight to the characterization of grainstone systems