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Variations in Geochemistry and Crystallography of Fossil Bioapatite vs. Aragonite in Carbonate Paleoenvironments


Rare Earth Element (REE) signatures in bioapatite are acquired during fossilization and record the composition of early diagenetic fluids. In addition to changing the chemical composition of bioapatite, substitution of REE, fluoride and other species cause alterations of Unit Cell Dimensions (UCD) within the mineral. REE signatures and UCD for vertebrate fossils may be distinctly different among lithostratigraphic units reflecting the changes in depositional environment. My previous researches with Pierre Shale vertebrates confirmed that the REE signatures and UCD differ among lithologic units but were statistically identical within the unit. These “markers” from individual units of the Pierre Shale were laterally constant over many km. REE and UCD proves to be potentially a powerful method for stratigraphic correlation in predominantly siliclastic marine environments. This research in stratigraphic variations of REE and UCD has been expanded to include Carbonate paleoenvironments. REE signatures and UCD for bioapatite from different carbonate environments are successfully used to shed light on diagenetic processes, reconstruct paleoenvironmental conditions, and accomplish stratigraphic correlation. Stratigraphic variations in REE and UCD in two distinct Carbonate paleoenvironments were explored. Florida Pleistocene vertebrate fossils of the Anastasia Formation and the Fort Thompson Formation were collected to represent near shore, shallow carbonate environments. Both collections were analyzed for REE signature (ICP-MS) and UCD (XRD) variations. REE signatures and UCD variations were found to be consistent within individual lithostratigraphic units but are significantly different between these units. Therefore, REE signatures and UCD act as markers for their units and may be used to discriminate between units for purposes of stratigraphic correlation. A combination of REE analysis and UCD analysis can better identify specific units that correlate to a specific original depositional environment. Results of the research indicate that this combination of methods may provide for a finer scale of resolution for stratigraphic correlation in carbonates and shed more light on the fossilization process of Bioapatite in carbonate environments.