Amino Acid Geochronology is a relative, and sometimes absolute, dating method that relates the diagenesis of fossil protein preserved in carbonate materials with time (geologic age of the sample) and temperature (long term chemical temperature of the enclosing sediment). Stratigraphic applications of the method have been demonstrated from both marine and non-marine sequences all over the world using a variety of carbonate fossil materials including mollusks, foraminifera, bone, ostrich egg shells, ostracodes, and tooth enamel. Of limited usefulness are studies on pedogenic soil carbonates and tufas.
The stratigraphic resolution of the method and the age range for which it is useful is highly dependent upon mean annual soil temperatures and the amplitude of the temperature difference between winter and summer extremes at the depth of burial. The rate of chemical reactions concerned are directly related to temperature. Consequently, amino acid diagenesis will proceed more slowly at cooler sites than at warmer sites. Samples from some mid-latitude regions, for example, provide resolution of 20 - 30 ka with a useful range of ~ 2 Ma; Arctic samples provide a resolution of ~ 100 ka with a useful range of 5 to 6 Ma.
The Amino Acid Geochronology Laboratory housed in the Department of Geosciences at the University of Massachusetts is set up to routinely analyze carbonate fossils using automated high pressure liquid chromatography (HPLC). This analytical technique is fine tuned to optimize the resolution of L-isoleucine (Ile) and its diastereomer D-alloisoleucine (alle). The ration of all/Ile has been shown to be a reliable index of age and has been widely used for stratigraphic studies. Most of our experience at Umass is with the analysis of foraminifera and of marine and terrestrial mollusks.