Further evidence of the complexity of the racemization process in fossil shells with implications for amino acid racemization dating

Abstract

Simulated aging experiments with shells of Ostrea, Anadara and Katelysia spp from Modern, Holocene and Pleistocene marine sediments in southern South Australia give further insight into the difficulties in using D L ratios of amino acids for quantitative age determinations. Evidence is given that the progress of racemization, as monitored by changes in D L ratios with time, is not only non-linear but also may be reversed, demonstrating a decrease in the observed degree of racemization. The observed changes in D L ratio with time differ according to the age and the genus of shell, and the amino acid examined. Katelysia spp. gives less variable values than Ostrea or Anadara and similarly valine racemization and isoleucine epimerization are far less variable than aspartic acid racemization.