Soil-archaeological studies of Koy-Gunzhar Scythian tumuli (Kazakhstan): building materials and techniques, diagenetic transformations of buried paleosols

The tumuli of the Koy-Gunzhar burial ground (2400-2000 cal years BP) in the North Kazakhstan are monumental earthen mounds, built in honour of the Scythian elite. The tumuli, besides representing the diversity of the building techniques for such earth burial mounds, also provide a unique opportunity to study the direction and character of the paleosol diagenesis for nearly 2400 years. This soil-archaeological study aimed to reveal mound building techniques, the characteristics of materials used for construction, and diagenetic changes of the buried paleosols. The comparative analysis of tumulus embankments and buried soils (their genesis and diagenetic transformations) provided the opportunity to establish the source of the building material and to reconstruct some details of the building technologies. For instance, the Calcic Someric Kastanozem (Arenic, Protosodic), buried by loam-sandy and sandy substrate of the tumulus 3, corresponds to dry steppe conditions and has no considerable signs of diagenetic transformations, whereas the paleosol under the tumulus 1 was affected by strong diagenetic transformation supposedly due to acid drainage from the embankment which originally contained sulfidic material being subjected to oxidation and acidification after the tumulus construction. Diagenesis was manifested in the redistribution of pedogenic carbonates and enrichment in iron, magnesium, manganese, and aluminum compounds in the upper 32 cm of the buried soil. These elements were partially accumulated at the carbonate geochemical barrier (over Bk horizon of the buried soil). This soil was transformed by diagenesis from Kasrtanozem to Mollic Cambic Umbrisol (Epiloamic, Katoarenic). The builders of the tumulus 1 used a loamier substrate to construct the mound, different from the parent material for adjacent soils (loamy sands and sands). The loamier substrate ensured the firmness of the mound construction. The builders employed an uncommon technique to produce a mound with defined properties and used foreign building materials brought from the distance.