GEOCHEMICAL EVIDENCE OF POSSIBLE HORSE DOMESTICATION AT THE COPPER AGE BOTAI SETTLEMENT OF KRASNYI YAR, KAZAKHSTAN

The eneolithic (3600-2300 B.C.) Botai culture of the Eurasian Steppe region in northern Kazakhstan was heavily dependent on the horse for subsistence; no evidence exists that domestic crops were raised.  At the Krasnyi Yar site, remote sensing using electrical resistivity and magnetic field gradient imaging revealed a large number of possible pit houses and post moulds.  Many of the post moulds are found in near-circular and semicircular arrangements, suggesting horse corrals or stockades.  To further investigate this possibility, twenty-two soil samples were taken along N-S and E-W transects (two meter spacing) from a depth of 15-25 cm within one of the semicircular sites near several pit house sites.  For comparison, two additional background samples were taken from outside the site. Sequential ammonium acetate (NH₄OAc) and hydrochloric acid (HCl) leaches of the <2 mm fraction were analyzed by ICP-AES for major and trace elements (using the method of Homsey and Capo, 2006, Geoarcheology, 21:237).  Modern horse manure is enriched in nitrogen (N), phosphorous (P), and potassium (K) relative to undisturbed soils, with the greatest enrichment in N.  However, N is relatively mobile and can be lost to groundwater or the atmosphere by organic and inorganic processes.  In contrast, phosphorus can be fixed in calcium and iron phosphates, and is more likely to be preserved in archeological environments.  Phosphorous concentrations in the NH₄OAc leaches for all samples inside the Krasnyi Yar transect area were elevated relative to that in the background soils (113-740 mg/kg vs. 40-80 mg/kg); a similar trend for the HCl leachates was observed, although several perimeter samples were similar to background.  High P can also reflect human occupation, but hearth activity tends to significantly elevate K/P ratios in the HCl-leachable portions of soil samples.  Nearly all of the transect samples had K/P ratios <0.2 in the HCl leachate, in contrast to values of 0.7-0.8 in soil samples from outside the circular area defined by the posts.  Sodium concentrations were also significantly higher in the transect samples (range: 80-90 ppm in the background soils; 120-1300 ppm in the circular site, with an average of 520 ppm).  These results are consistent with, but do not prove, the interpretation that the Krasnyi Yar site was a locus for early horse domestication.