Rankey, Eugene C.¹ 
(1) RSMAS/University of Miami, Miami, FL

ABSTRACT: Relations between Shallow Shelf Carbonate Facies and Water Depth, South Florida

Many studies of ancient shallow-water carbonate platforms focus interpretation on the primacy of changes in accommodation, inferred by assuming a direct link between depositional facies and water depth. The purpose of this study was to test this assumption explicitly by exploring relations between substrate type (benthic habitats) and the water depth at which they occur on the shallow South Florida shelf. GIS analysis of habitat and bathymetric maps illustrate that most substrate types occur across a range of water depths in a statistically random manner. At greater water depths, however, habitats are more constrained (more dominance of one class, more ‘deterministic’), with generally decreasing dominance (more diversity) at shallower water depths. 
At a scale of shelf-to-basin transects, habitats clearly are related to water depth. Yet, on this narrow, shallow shelf, at the scale of this study, water depth and habitats are not uniquely related or distinct from a random distribution. This general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium, a state in which habitats do not fully reflect ambient environmental conditions. Alternatively, it may reflect the impact of variables other than water depth (e.g., energy, spatial setting). These results emphasize the fact that variables other than water depth can significantly influence the ecological and sedimentologic attributes of depositional surfaces. Hence, detailed interpretations of water depth changes derived from facies changes may provide only ambiguous insights into the details of relative changes in sea level such as shallowing or deepening trends.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.