THE DETERMINATION OF LATE QUATERNARY PALEOENVIRONMENTS AT EQUUS CAVE,SOUTH-AFRICA, USING STABLE ISOTOPES AND AMINO-ACID RACEMIZATION IN OSTRICH EGGSHELL

The stable carbon and nitrogen isotopes from organic compounds, and st able oxygen and carbon isotopes from inorganic carbonate in modern and fossil ostrich eggshell (OES) at Equus Cave, South Africa, were used to determine relative changes in C-3 and C-4 vegetation, rainfall, and temperature throughout the last 17 ka. Amino acid racemization and th ree new radiocarbon dates were used to assign ages to the individual O ES fragments analyzed for stable isotopes, and to evaluate the stratig raphic integrity of the samples. The amino acid racemization and radio carbon data indicate that most of the OES fragments are not in correct stratigraphic context, and may have been upwardly and downwardly mixe d; thus, each fragment was placed in chronological sequence using radi ocarbon-calibrated amino acid racemization. The stable carbon isotope data from the fossil OES do not change systematically through the last 17 ka. The ostriches primarily consumed C-3 plants (between 70% and 9 0%), and smaller quantities of C-4 plants (between 30% and 10%), indic ating that a mixture of C-3 and C-4 plants has been in the vicinity of Equus Cave for the last 17 ka. Stable nitrogen isotope data from OES indicate that at 17 ka, mean annual precipitation (MAP) was at a minim um (190 +/- 50 mm/yr), increased steadily to modern values by 6 ka (60 0 +/- 150 mm/yr), and remained relatively unchanged until present. Sta ble oxygen isotope data coupled with nitrogen isotope data indicate th at paleotemperatures were at a minimum between 14 and 17 ka, and reach ed their maximum in the latest Holocene. This study demonstrates the p lethora of paleoenvironmental information that can be derived from ana lysis of three different stable isotopes (carbon, nitrogen, and oxygen ) in the same sample-type (OES), and presents a new tool with wide app licability for reconstructing paleoenvironments in semi-arid and arid regions of Africa. (C) 1997 Elsevier Science B.V.