Nuclear Track Mapping of Uranium as Tool for Study of Diagenesis in Carbonate Rocks: ABSTRACT

Abstract

Application of the nuclear track mapping technique to carbonates allows the spatial distribution and concentration of uranium to be matched directly with petrographic details of the rock. Application of this technique to the relatively young ooid and reef systems of Joulters Cay, the Bahamas (Holocene), the Miami limestone (Pleistocene), and the Key Largo Limestone (Pleistocene) has provided improved interpretations of diagenetic events in these systems. Data from these localities suggest that analysis of uranium in cements can: (1) precisely define the boundary between freshwater vadose (less that 0.5 ppm) and phreatic zones (about 2 ppm) in restricted aquifer settings, such as Joulters Cay, even where petrographic evidence is equivocal, (2) determine the nature of the freshwater phreatic environment, whether it be an open region aquifer or alternatively a more restricted island lens, and (3) delineate multiple episodes of diagenesis in the Miami and Key Largo limestones. A combined study using uranium, stable carbon and oxygen isotopes, and strontium as geochemical tracers suggests that the mappability of uranium provides substantial advantages over conventional geochemical indicators.