Rapid change in Chernozem properties during their Holocene evolution: a case study of paleosols buried under kurgans in the pre-Ural steppe, Russia

Abstract

An extensive chronosequence of Chernozem-type soils developed on loamy sands was studied in the pre-Ural steppe, Russia. Paleosols were buried under kurgans that belonged to three main periods of construction: the Early Bronze Age (forth to third millennium BC), the Early Iron Age (eighth century BC to forth century AD) and the Middle Ages, the time of the Mongols and the Golden Horde (thirteenth to fourteenth centuries AD). Several paleosol profiles of the same archaeological chronointerval were studied as a soil chronosequence. This study restricted soil chronosequences not only to the duration of one archaeological culture but to the separated chronological phases of it. This allowed the documentation of soil property changes in time with the maximal possible resolution, and to understand the time scale of those changes. In order to take into account the changes of sets of soil properties in time, all soil features under study were attributed to either “arid” or “humid” environmental conditions, and numerical grades were assigned to each of them. For each soil of the chronosequence, the sum of numerical grades for the “arid” and “humid” properties were calculated and plotted against time. Two important conclusions were made after analyzing the curves: (1) it is necessary to distinguish the direction of change of the properties under study, and (2) the short time scale (sub-centennial or centennial) over which changes of soil properties occur. The morphological and analytical properties that change in sub-centennial or centennial time scales include the character of the lowest boundary of the humus horizon, the degree of biological activity (coprolites, humus-enriched root and mesofauna channels), the morphological patterns of carbonate accumulation, and the percentages of humus, carbonate and exchangeable sodium down through the profiles.