AMINOSTRATIGRAPHY OF PLEISTOCENE SEDIMENTS IN FLORIDA

During the Mesozoic and Cenozoic eras, shallow marine waters and tropical climates dominated the Florida Platform resulting in the production of carbonate sediments. As sea level fluctuated during the Pleistocene, the geomorphology of Florida was shaped and modified as carbonate and siliciclastic sediments were deposited, reworked and eroded. Evidence of sea level fluctuations is recorded in terraces and low-lying sedimentary deposits. Biostratigraphic and topographic studies have interpreted features such as upland terraces as relict shorelines (Scott 1992; MacNeil 1950). Despite many techniques used to date and correlate Pleistocene sediments in Florida, the numerical dating of these sediments is poorly constrained. Consequentially, further analysis is required to gain a thorough understanding of the timing of sea level change during the Pleistocene.

Dating techniques such as ¹⁴C, Uranium decay series, magnetostratigraphy and biostratigraphy have been successfully employed for many years. However, these techniques have potential problems or may not be applicable to the materials and time range of interest to this study. Amino acid geochronology offers an alternative dating technique when other techniques are inconclusive, inapplicable or otherwise have failed. This technique is based on isomeric forms of amino acids, and the development of a stratigraphic framework is based on racemization data, which is termed aminostratigraphy. Initially, amino acids are produced in the L-isomer form as new layers in the carbonate shell are secreted. Following biomineralization of the shell matrix, the amino acids slowly convert to the D-isomer form (Bradley 1999). Hence, the ratio of D/L isomers can be used as a relative estimate of time since death of the organism.

The goal of this study is to establish the aminostratigraphy for the Pleistocene of Florida by measuring e D/L ratios in carbonate fossils. Additionally, the latitudinal distribution of D/L ratios will be analyzed to gain an understanding of the latitudinal thermal gradient effect on racemization rates.