Investigating the Origin of Neogene Dolomites Using Non-Conventional Trace Elements

Willis, Kathleen¹, Peter K. Swart² (1) University of Miami, Rosenstiel School of Marine Science, Miami, FL (2) University of Miami/Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL

Dolomitization processes are important in the understanding of the prediction of the quality and distribution of reservoirs in carbonate systems. The use of geochemical indicators has increased our understanding of these processes and even though dolomite formation has been studied extensively, the results using these indicators are not definitive in terms of identifying methods of dolomitization. In this study we have examined five Neogene cores from the Bahamas and Florida, using non-conventional trace elements, sodium and sulfate, as well as conventional trace elements and stable Carbon and Oxygen isotopes. The geochemical results obtained using these methods will help geologists better understand and interpret the geochemical indices and geologic history of dolomite minerals from these locations.

All five cores have multiple dolomitized sections ranging from Middle Miocene to Pliocene age. Depositional facies of these cores vary from lagoonal, tidal flat to back reef, and shelf. Numerous sea level changes within the Neogene are recorded, resulting in the depositional and diagenetic imprint on the carbonate system. Although each of the cores have their own unique histories, the dolomite has concentrations of sodium and sulfur that covary with the mol% MgCO3. These concentrations are also higher than those found in the calcites. We have determined the distribution coefficients for sodium and sulfur in dolomite. Using the values of the distribution coefficients, it is then possible to determine the salinity of dolomitizing fluids in situations where the fluid composition is unknown. The sodium and sulfur concentrations in these dolomites suggest that many of the dolomites have originated from fluids elevated in salinity.