AMINOSTRATIGRAPHY OF THE LAST GLACIAL CYCLE LOESS OF EUROPE

The loess - paleosol sequences in Europe provide an extensive and continuous record of climate change during the last glacial-interglacial cycle. However, numerous problems exist in providing a reliable chronology for these loess deposits. Amino acid racemization ratios measured in fossil gastropod shells obtained from loess units provide an important stratigraphic correlation tool for sediments deposited during that critical time interval.

Fossil gastropods were collected from previously described loess - paleosol sequences at Harmignies, Belgium; Nussloch, Toenchesberg, and Koblenz-Metternich, Germany; and Kutna Hora, Czech Republic. D/L racemization ratios measured in the total acid hydrolysate (HYD) and free amino acid fraction (FREE) of aspartic acid, glutamic acid, alanine, valine, and the alloisoleucine/isoleucine (A/I) diastereomers demonstrate that aspartic acid D/L values provide the best temporal resolution for the last interglacial – glacial cycle.

Preliminary results show HYD aspartic acid D/L racemization ratios for the gastropod genus Pupilla to be 0.440 ± 0.006 (loess correlated with oxygen-isotope stage 6), 0.370 ± 0.031 (loess of OIS-5), 0.349 ± 0.016 (loess of OIS-4), 0.325 ± 0.014 (loess of OIS 3 and 2). FREE aspartic acid D/L values measured in Pupilla were 0.572 ± 0.013 (OIS-6), 0.480 ± 0.031 (OIS-5), 0.430 ± 0.027 (OIS-4), and 0.381 ± 0.030 (OIS 3 and 2). Among the amino acids analyzed, the coefficient of variability for D/L values measured in multiple gastropod shells from the same stratigraphic interval ranged from about 4% for aspartic acid to 25% for A/I.

Previous studies in the region measured only A/I values, which were unable to distinguish stratigraphic units deposited during the last glacial cycle. Because it is a faster racemizing amino acid, aspartic acid D/L values are able to resolve differences within that time interval. The inability of aspartic acid to distinguish between loess deposited during OIS 3 and OIS 2 may indicate that temperatures did not increase significantly in Europe during the oxygen-isotope stage 3 interstadial period.