Correlation between C-14 ages and aspartic acid racemization at the upper Palaeolithic site of the Abri Pataud (Dordogne, France)

The Upper Palaeolithic site of the Abri Pataud (Dordogne, France) has been the subject of numerous C-14 age determinations which cover the period from 20,400 +/- 450 years BP (OXA-373) to 34,250 +/- 675 years BP (Grn-4507). The racemization ratios of aspartic acid have been determined in 26 fossil bones. The bones are present in two different sedimentary surroundings: levels (fine deposits with numerous artefacts and fossil bones) and ''eboulis'' (coarse deposits derived from the neighbouring limestone cliff). Racemization ratios for total aspartic acid have a poor correlation with C-14 ages (respectively r(2) = 0.59 and 0.82 for the two environments) but apparent racemization rates are clearly dependent on the type of deposits (levels: k = 4.4 x 10(-6) year(-1); eboulis: k = 9 x 10(-6) year(-1)). Racemization ratios of aspartic acid in a high molecular weight protein fraction (>10,000 Da) correlate much better with C-14 ages (r(2) = 0.999) for the samples from the levels (k = 2.1 x 10(-5) year(-1)). From this regression line we estimate ages for two Aurignacian levels: level 6 approximate to 29,560 years BP and level 9 approximate to 30,440 years sp. It is noteworthy that none of the regression lines intercepts the origin. Racemization of aspartic acid appears to occur only after a delay of many thousands of years. This phenomenon could be the result of a coupling between the degradation of proteins and the racemization of amino acids. (C) 1996 Academic Press Limited