Big Boldyrevo Kurgan of the Early Bronze Age in the Southern Urals: Kurgan Structures, Paleosols, and Paleoclimate Reconstruction

The chronosequence of paleosols buried under structures of different ages in kurgan 1 of the Boldyrevo IV burial site in Orenburg oblast of Russia has been studied. The kurgan was built by representatives of the early (Repino) stage of the Yamnaya culture (about 5500 years ago) and included four successively made structures. According to archaeological data, the kurgan was built during decades, and 300-year-long interval was determined by radiocarbon dating. During that period, the morphological and physicochemical properties of buried soils changed: the lower boundary of the humus horizon became more tonguing; the degree of zooturbation of the profiles by burrowing animals increased; the organic carbon content dropped; and the contents of carbonate carbon, gypsum, and exchangeable sodium in the composition of exchangeable bases and magnetic susceptibility increased. The trend of changes in morphological properties, in the content of organic carbon and carbonates, and in magnetic susceptibility in the materials from the early to late kurgan structures correlated with that for the soils buried under them. Our study enables us to suggest that the climate during the analyzed period (the early stage of the Yamnaya culture) was more arid than the modern climate. The technological approaches used by the ancient builders for kurgan construction were revealed on the basis of data on the micromorphology and physicochemical properties of the materials of kurgan structures.