Correlation BetweenC 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 numerous¹⁴C age determinations which cover the period from 20,400±450 years (OXA-373) to 34,250±675 years (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 “éboulis” (coarse deposits derived from the neighbouring limestone cliff). Racemization ratios for total aspartic acid have a poor correlation with¹⁴C ages (respectivelyr²=0·59 and 0·82 for the two environments) but apparent racemization rates are clearly dependent on the type of deposits (levels: K=4·4×10⁻⁶year⁻¹; éboulis: K=9×10⁻⁶year⁻¹).Racemization ratios of aspartic acid in a high molecular weight protein fraction (>10,000 Da) correlate much better with¹⁴C ages (r²=0·999) for the samples from the levels (k=2·1×10⁻⁵year⁻¹). From this regression line we estimate ages for two Aurignacian levels: level 6≈29,560 years and level 9≈30,440 years .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.