IMPROVING AMINOSTRATIGRAPHIC RESOLUTION USING BALANUS SPP. IN LOWER MIOCENE TO UPPER PLEISTOCENE FOSSILIFEROUS SEDIMENTS IN FLORIDA

Amino acid stereochemistry provides a valuable tool for relative age assessment across discrete geologic formations. In this investigation we established a preparation protocol to study the relative concentrations of several amino acids in calcite shells of the barnacle Balanus spp. in order to characterize geologic formations ranging from Lower Miocene to Upper Pleistocene, in Florida. Barnacle shells were chosen because previous studies indicated that amino acid concentrations in barnacles far exceed those of the more commonly studied bivalve shells, and racemization occurs more slowly, offering the potential for extending the temporal range of the method.

Preparatory studies were performed on modern and Late Pleistocene Balanus shells in order to develop a protocol that would minimize intrashell variability in amino acid concentrations and D/L ratios. We hypothesize that amino acids internally sequestered in the crystal lattice of calcite shell would be less susceptible to contamination, leaching, and other diagenetic effects in the natural environmental and therefore yield more consistent racemization and concentration measurements. Experiments were designed to (1) determine whether the concentration of any amino acid varies among the wall or basal plates of the barnacle shell; and (2) determine whether intra-crystralline amino acids could be isolated from the barnacle shells and analyzed separately from bulk amino acids. For this second experiment, shells of modern Balanus spp. were pulverized, and different size fractions soaked in a solution of 10% NaOCl for between 2 and 36 hours. We determined that 12 hours bleaching of 250-500 μm particles reduced total amino acids in Balanus particles significantly, while further exposure was found not to impact the remaining, presumably intracrystalline amino acids.

The outcome from these two experiments resulted in a preparation protocol that is being applied in the temporal analysis of samples from five sampling sites across Florida. An amino acid profile for each site (D/L ratios and absolute concentrations of both free and hydrolyzed amino acids) is underway. This will allow us to test the aminostratigraphic utility of Balanus spp. in resolving different sea-level highstands in Florida from the Early Miocene through the Late Pleistocene.