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New Opportunities for Advance in the Use of Geochemical Indices in the Study of Dolomitization

Peter K. Swart
University of Miami/Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL

It has been 25 years since the landmark paper of Lynton Land “The Isotopic and Trace Element Geochemistry of Dolomite: The State of the Art”. Since this paper, which described the uncertainties in using the stable oxygen and carbon isotopic composition and certain trace elements to unravel the mysteries of the formation of dolomite was published, there has been sporadic progress in using geochemical signatures to characterize the nature of the dolomitization environment. This progress has been mainly achieved in areas such as fluid inclusions and other geochemical indicators such as 87Sr/86Sr ratios, and non-conventional geochemical indicators such as sodium and sulfur. Few advances have been made in addressing the principal problems of the stable oxygen isotopic composition of dolomite, namely uncertainty in the equilibrium values, problems regarding the complex nature of the dolomite mineral itself, and disentangling the competing roles of temperature and fluid composition on the eventual isotopic composition of the dolomite. The use of fluid inclusion data, which can present information on both temperature and salinity is an important advance, but such data frequently present new problems of interpretation in that at high salinities the relationship between salinity and the oxygen isotopic composition of fluids is weak to non-existent. New methods to interpret the fluid composition are needed in order to establish definitively the importance of early dolomitization with respect to later higher temperature induced dolomitization. Opportunities arise through the use of parameters such as carbonate associated sulfur (CAS) which can reveal both salinity and the influence of organic diagenesis (δ34S) and the trapped water of crystallization, which can be analyzed for its δD.