Freshwater Reservoir Effect on Redating of Eurasian Steppe Cultures: First Results for Eneolithic and Early Bronze Age Northeast Kazakhstan

Abstract

Freshwater reservoir effects (FRE) can cause problems when radiocarbon dating human skeletal material from the Eurasian steppe. This article presents the first results of research into the extent of the FRE in the sites of Borly 4 (Eneolithic) and Shauke 1 and 8b (Early Bronze Age), northeastern Kazakhstan. Accelerator mass spectrometry (AMS) ¹⁴C dating and stable isotope (δ¹³C, δ¹⁵N) analysis of associated groups of samples (32 samples, 11 groups in total) demonstrate the following: (a) the diet of the humans and fauna analyzed was based on the C₃ foodchain with no evidence of a C₄ plant (such as millet) contribution; aquatic resources apparently were a continuous dietary feature for the humans; (b) the first ¹⁴C dates obtained for the Upper and Middle Irtysh River region attribute the Eneolithic period of the area to the 34th to 30th centuries BC, and the Early Bronze Age to the 25th to 20th centuries BC, with a ~450-yr hiatus between the two periods; (c) the maximum fish-herbivore freshwater reservoir offset observed equals 301 ± 47 ¹⁴C yr. As such, ¹⁴C dates from aquatic and human samples from the area need to be interpreted with caution as they are likely to be affected by the offset (i.e. appear older). The article also discusses the effect of a sodium hydroxide (NaOH) wash on δ¹³C, δ¹⁵N, C:N_atomic levels and collagen yields of the bone samples. Our results indicate a minor but significant effect of NaOH treatment only on C:N_atomic ratios of the samples.

DOI: 10.2458/azu_rc.57.18431