Cross-calibration of the racemization rates of leucine and phenylalanine and epimerization rates of isoleucine between ostracodes and gastropods over the Pleistocene in southern Spain

Abstract

Cross-calibration of the racemization rates of leucine and phenylalanine and the epimerization rates of isoleucine between Middle and Lower Pleistocene ostracodes and gastropods from southern Spain is presented. Using these two relationships, along with previously-calculated age estimation algorithms, it is possible to estimate the age of samples from southern and central Spain because of the shared thermal history of these regions. They can also be used to establish the aminostratigraphy of Quaternary deposits from the areas. However, for d/ l ratios below those in the ostracodes and gastropods of the Cortijo del Negro-1 site, the cross-calibration equations may not be satisfactorily applied. The racemization/epimerization ratios in ostracode shells can be measured precisely because of the excellent preservation of amino acids within an valves and an abundance that makes the standard error or variance smaller. It has been observed that in modern samples the racemization in ostracodes is slower than in gastropods but the d/ l ratios become similar in older samples.