Paleosols of kurgans of the Early Iron Age in the Transural steppe zone

Paleosol studies of archaeological monuments of different ages have been conducted on the Transural Plateau. The morphological and physicochemical properties of paleosols under burial mounds (kurgans) of the Early Iron Age (the fifth and fourth centuries BC) were compared with the properties of background surface soils. A paleosol of the Savromat epoch (2500 BP) is characterized by high contents of gypsum and soluble salts. The presence of humus tongues in its profile attests to the aridity and continentality of the climatic conditions during that epoch. Paleosols buried under kurgans of the Late Sarmatian epoch and the Hun epoch (about 1600 BP) are characterized by a higher content of humus and greater depth of the carbonate horizon, which attests to the humidization of climatic conditions. The evolution of soils as related to climate dynamics in the first millennium BC and the first millennium AD is characterized.     

Short chronosequences of paleosols from the Skvortsovka kurgans in the Buzuluk River valley of Orenburg oblast

Paleosols buried under kurgans of the Yamnaya (the third millennium BC) and Srubnaya (the 18th–17th centuries BC) cultures within the Skvortsovka group of kurgans in the Buzuluk River valley in Orenburg oblast have been studied. This is the area of the dry steppe zone. The changes in the paleosol properties make it possible to distinguish between relatively short-term chronointervals separately for the Yamnaya and Srubnaya cultures. The paleosol data and radiocarbon dating have been used for revealing the relative order of the construction of the kurgans within these chronointervals and for the paleoclimatic reconstruction. Quite definite changes took place in the soil formation from the beginning to the end of the particular chronointervals: the contents of humus and exchangeable bases and the portion of calcium ions in the composition of the exchangeable cations increased in parallel with the enhanced leaching of carbonates and the enhanced biological activity. These changes attest to the increasing amount of precipitation. In general, the climate of the Srubnaya cultural epoch was less continental, whereas the climate of the Yamnaya cultural epoch was relatively close to the modern climate. The ¹⁴C dates of the pedogenic carbonates in the upper meter of the paleosol profiles have been used as auxiliary data to confirm the sequence of the soil’s burial during the short chronointervals corresponding to the humid stages of the paleosol’s evolution, and the 14C dates of the diagenetic carbonates have been used to determine the dates of construction of the kurgans with due account for some time gap between the construction of the kurgans and the appearance of these carbonates in the buried soil profiles.     

Reconstruction of Climate,Soils, and Vegetation in the Turan–Uyuk Basin of South Siberia at the Beginning of the Subatlantic Period of the Holocene

Four Scythian kurgans of the burial site Beloe Lake-3 were studied in the Turan–Uyuk Depression in the Republic of Tyva. They were constructed about 2565–2390 calendar years ago (calibrated with deviation 1 σ). Soil formation after 2500 yrs of the construction of the kurgans was examined in the interkurgan area. The properties of the background surface and ancient buried soils have much in common, and the difference between the soils of the four kurgans is small. This attests to the fact that the paleoclimatic conditions in the period of the necropolis construction remained stable and were similar to the modern climatic conditions. According to palynological data, the climate at the stage of the construction of the first two kurgans was a little more humid in comparison with the modern climate; it became somewhat drier after 95 years, during the construction of the third kurgan (2425 cal. BP) and again tended to humidification at the final stage of the necropolis creation. These changes in the paleoclimatic conditions are indicated by variations in the structure and composition of associations of xerophytes, mesophytes, hydrophytes, and ruderal plants. At the Uyuk stage, the area was mainly occupied by steppe phytocenoses with a predominance of xerophytes over mesophytes, and hydrophilous vegetation was allocated to moistened habitats near water reservoirs. Larch forests grew near water bodies. The variable anthropogenic impact on the landscape was stronger at the initial and final stages of the construction of the Uyuk culture necropolis.     

Comparative characterization of microbial communities in kurgans,paleosols buried under them,and background surface soils in the steppe zone of the Lower Volga region

A comparative analysis of the state of microbial communities in kurgans, paleosols buried under them, and background surface soils in the dry steppe zone of the Lower Volga region has been performed. It is shown that the population density of microorganisms of various trophic groups in the kurgans is an order of magnitude lower than that in the A1 horizon of the corresponding buried paleosols and background surface soils within the areas of chestnut, light chestnut, and solonetzic soils. The respiration activity of the microbial communities in the upper layer of the kurgans is comparable with that in the A1 horizons of the background surface soils; it decreases in the deeper layers of the kurgans. In the A1 horizon of the buried paleosols, the respiration activity is approximately the same as in the deep layers of the kurgans. In the buried paleosols, the spatial variability in the numbers of soil microorganisms is approximately the same or somewhat higher than that in the background surface soils. The spatial variability in the respiration activity of the buried paleosols is two to four times higher than that in the background surface soils.     

Production of CO<Subscript>2</Subscript> by Paleosol Samples Taken in the Steppe Zone under Kurgans Constructed in the Periods of Relative Aridization and Optimum of the Climate

The studies of recent soils and paleosols buried under kurgans created in the periods of long-term aridization (3000–2000 BC) and climatic optimum (13th–14th centuries AD) were performed in steppes of the southeastern part of the East European Plain (Privolzhskaya Upland and Caspian Lowland) in order to determine the rate of carbon dioxide production by the soil samples at the natural moisture and after moistening up to 60% of the total moisture capacity. The CO₂ emission from the samples of paleosols corresponding to the period of climatic aridization in the Lower Volga River at their natural moisture status was lower than that from the samples of background surface soils, whereas the CO₂ emission from the samples of paleosols buried under optimum climatic conditions was higher than that from the samples of background surface soils. After moistening of the samples, the increase in the CO₂ emission from the paleosol samples depended on the actual humidity of the climate in the corresponding period.     

Buried vertic paleosols of the North Caucasus in the third millennia BC

Paleosols buried under kurgans dating back to the Yamnaya, Catacomb, and Post-Catacomb cultural epochs of the Bronze Age (4600–3900 BP) on the territory of the Stavropol Upland (the North Caucasus) in the area occupied by vertic chernozems were studied. It was found that solonchakous and deeply solonchakous and solonetzic chestnut soils and solonetzes proper predominated in the study area during the Bronze Age. The solonetzic process was the leading pedogenetic process in the automorphic paleosols of the second half of the third millennium BC. The vertic features were weakly developed in the automorphic paleosols; they were better manifested in the paleosols developed on the floodplains. The paleosol data were used to reconstruct the environmental conditions in the region during the Bronze Age. The climatic conditions of that period were more arid and with less sharp contrasts between wet and dry seasons in comparison with the modern climate.     

Changes in the Structural State of Soils in the Lower Volga Region during the Past 3500 Years as Related to Climate Fluctuations

The structural state of modern and buried chestnut soils on the Privolzhskaya Upland (Volgograd oblast) was studied in order to determine changes in the soil structure in dependence on the time of soil burying. The soils buried 3500, 1700, and 700 years ago and modern background chestnut soils were examined. The structural state of soils was determined via their fractionation on a set of sieves (10–0.25 mm) in the air-dry state. We determined the contents of coarse aggregates, total aggregates, disperse soil matter, aggregation coefficient, and the degree of differentiation of the soil profiles. It was found that the structure of buried soils is preserved for 3500 years after the soil burying. The structural state of the studied soils changed with time depending on the climatic conditions that existed at the moment of soil burying. In humid periods, the amount of coarse aggregates (lumps) decreased, and the content of aggregated fractions increased; the reverse processes took place in arid epochs. Thus, it was shown that the aggregate composition of soils is specific for each period of soil formation and depends on the degree of climatic humidity. It is preserved in the buried soils independently on the duration of their existence in the buried state. We determined the impact of aggregate size on the C_org tolerance toward mineralization processes. It was shown that the content of organic carbon and its physical protection from mineralization are determined by different mechanisms of its fixing in aggregates of different sizes and depend on the conditions for the development of soil structure before burying and on the duration of the soil existence in the buried state. The results obtained in this study can be used as a retrospective basis for predicting changes in the physical properties of soils under conditions of changing climate.     

Paleosols from the groups of burial mounds provide paleoclimatic records of centennial to intercentennial time scale: A case study from the Early Alan cemeteries in the Northern Caucasus (Russia)

Buried soil chronosequences under a series of Early Alan kurgans (burial mounds) in the Vladikavkazkaya depression of the Northern Caucasus, Russia, were studied to derive a high-resolution paleoclimatic record from the variations of the selected paleosol properties. Haplic Chernozems occur under kurgans and on the actual land surface. Three kurgan cemeteries, Brut 1, Brut 2 and Beslan, dated from the end of the second to the beginning of the seventh centuries AD have been studied. The cemeteries are situated close to each other under similar lithological and geomorphological conditions but differed in the paleosols' preservation. The Brut 2 site has been recently altered due to annual ploughing and intensive irrigation for more than 30 years. The background soils and paleosols of the Brut 2 site have been compared with synchronous soils of non-irrigated Brut 1 and Beslan sites to detect pedogenic properties that are less changed by irrigation and thus comprise the “soil memory”. Stronger black color of humus horizon, increase of humus content and decrease of humus δ¹³C values; clear signs of biological activity, absence of morphological and analytical signs of solonetz properties; diffused carbonate white soft spots in the Bca horizon and decreasing carbonate content are thought to be related to the comparatively humid climatic conditions in the region. On the contrary, relatively low humus content, tongue-like lower boundary of humus horizon, increase of humus δ¹³C values, morphological signs of solonetz properties together with high content of exchangeable Na, relatively large and clearly shaped carbonate white soft spots in the paleosols of the Brut 2 site, as well as increase of density, thickness of the carbonate pseudomicellium and high carbonate content in the upper part of profiles in the paleosols of the non-irrigated Brut 1 site are assumed to be xeromorphic features, indicating comparatively drier climatic conditions. The paleosols of the earliest chronointerval of burial (the end of the second to the beginning of the third centuries AD) demonstrate clear xeromorphic properties which indicate a relatively dry climate with a mean annual precipitation 50–100 mm less than today. The estimated duration of the period with such climatic conditions is thought to be not less than 100 years. In addition, those paleosols have some weak signs of humid conditions indicating that between the end of the first and the middle of the second centuries AD the climate was getting more moist, mean annual precipitation became equal or slightly higher than today. The paleosols buried in the first half of the fifth century AD again demonstrate the gradual enhancement of xeromorphic properties reflecting the next stage of droughts. Thus, the period with favourable humid climate when the Early Alan culture flourished in the Northern Caucasus was relatively short (about 400 years). Studying the detailed chronosequence in the non-irrigated Brut 1 site the records of intercentennial time scale soil properties variability produced by comparatively “fast” pedogenic processes typical for the steppe zone i.e., humus formation and accumulation, bioturbation, carbonate accumulation and transformation and solonetzization, have been provided.     

Soil-archaeological studies of the bronze-age settlement on the Urshak River floodplain, Bashkortostan

Soil-archaeological studies were performed on the territory of the Muradym ancient settlement, which dates back to the Srubnaya cultural epoch of the Bronze Age (the 15th–14th centuries BC) and is located on the Urshak River floodplain in Bashkortostan. The morphological, chemical, and some biological properties of the habitation layer and the underlying meadow-chernozemic soil were studied. It was shown that the habitation layer differs from the buried soil in color and in the increased contents of humus, total nitrogen and phosphorus, and available potassium. The enzymatic activity in the habitation layer was also higher than that in the buried natural soil, which can be explained by the properties of the sediments composing the habitation layer, the anthropogenic activity of ancient humans, and by the involvement of the habitation layer into the sphere of modern pedogenesis.     

Paleosols buried under kurgans of the Pit-grave culture in the steppe zone of the Cis-Ural region

The analysis of soil chronosequences developed from loamy and loamy sandy substrates and buried under kurgans dating back to the Pit-grave archaeological culture in the steppe zone of the Cis-Ural region demonstrated that it is possible to trace the dynamics of the soil properties and to perform paleoclimatic reconstructions for different intervals within the studied period. The properties of sandy soils changed more rapidly than the properties of loamy soils. For sandy soils, notable changes in their properties were revealed in the soil chronosequences dating back to the particular stages of the Pit-grave culture; for loamy soils, such changes could only be traced for the soils buried under the kurgans dating back to different stages of the Pit-grave culture.     

Paleosol and paleoenvironmental conditions in the Lower Volga steppes during the Golden Horde period (13th–14th centuries AD)

Paleosols buried under steppe kurgans of the Golden Horde period (13th–14th centuries AD) in the Lower Volga basin are characterized by an increased humus content, lower salinity and gypsum content, and higher magnetic susceptibility of the soil material in comparison with the paleosols buried in the preceding period and the background surface soils. A comparative analysis of the morphological, chemical, and magnetic properties of the buried and surface soils allows us to conclude that an increase in climatic humidity within this dry region took place in the period of the high Middle Ages, with a peak in the 13th–14th centuries AD. The climatic change was manifested in the soil evolution at the taxonomic levels of soil genera and soil subtypes (in the ecotone zones). On the basis of measured magnetic susceptibility values, the mean annual precipitation levels in the Golden Horde period have been reconstructed. According to our estimates, the mean annual precipitation in the Lower Volga basin in that time was 30–80 mm higher than at present. The favorable paleoenvironmental and paleosol conditions of the Golden Horde period were important factors that affected the ethnic and political situation in the Lower Volga region.     

Modifications of the mineralogical composition and surface properties of soils as related to steppe climate dynamics in historical time

This work presents the results of a study of changes in the soil mineral components and the related modifications of the chemical composition and surface properties of soils in the desert-steppe zone in the southern part of the Ergeni Upland. Burial mounds dating back to the Bronze epoch have been investigated. According to radiocarbon data, their ages are estimated at 5100 ± 50, 4410 ± 100, 4260 ± 120, 4120 ± 70, and 3960 ± 40 years. The substantial transformation of the clay minerals, the molar chemical coefficients, the magnetic mineralogy, and the surface properties of the soils permits us to assess the rates of the mineralogical transformations caused by the climate change during the time interval of less than <∼100 years. The ratio between the content of the mineral phases in the buried soils of different ages testifies to the primary importance of climatic factor in comparison with the total duration of weathering or the soil existence on the land surface prior to its burial, i.e., the soil age.     

Modern and buried soils of kurgans in the forest-steppe zone of the Middle Volga region (by the example of Komintern I kurgan)

The construction of the Volga–Kama cascade of water reservoirs and hydroelectric power stations in the middle of the 20th century resulted in the inundation of vast areas and the development of abrasion along the shores that threatens many monuments of the archaeological and cultural heritage. The soils buried under northernmost kurgans of the Lugovskaya culture dating back to the 15th–14th centuries BC (kurgan Komintern I) were studied on the surface of the second terrace of the Kama River near its confluence with the Volga River. Burial sites of kurgan Komintern III were subjected to destruction in 1981, and archaeological excavations of kurgan Komintern II were performed in 2008. The danger of complete disappearance of these archaeological sites necessitated their thorough study with the use of multiple methods, including special paleosol studies. The soils buried under the kurgans ceased to be active components of the soil cover about 3500 years ago. They preserve information on the paleoenvironmental conditions before their burying. The analysis of morphological features and physical, physicochemical, and chemical properties of the buried soils attests to their chernozemic nature. Background surface soils that have passed through the entire cycle of the Holocene pedogenesis have evolved since that time into gray forest soils (Luvic Greyzemic Phaeozems) under forest vegetation. These soils are characterized by the increased acidity of the surface horizons (pH_КСl 4.3) and the development of lessivage. Data on the coefficients of mineral weathering in the buried paleosols and background surface soils attest to the identical precipitation both for the surface and buried soils in the Middle and Late Holocene.     

The microbial biomass in paleosols buried under kurgans and in recent soils in the steppe zone of the Lower Volga region

The total microbial biomass (TMB) was assessed in the chestnut and light chestnut soils and in the paleosols under burial mounds (steppe kurgans) in the Lower Volga region on the basis of data on the organic carbon content in the extracted microbial fraction supplemented with the data on the extraction completeness as a conversion coefficient. The completeness of the microbial fraction extraction was determined by direct counting of the microbial cells and colony-forming units (on plates with soil agar). The total microbial biomass varied from 400 to 6600 μg of C/soil. Its values in the buried soils were 3–5 times lower than those in the surface soils. The TMB distribution in the buried chestnut soil profile was close to that in its modern analogue (with the minimum in the B1 horizon). In the buried light chestnut paleosols, the TMB values usually increased down the profile; in the recent light chestnut soils, the maximum TMB values were found in the uppermost horizon.     

Dynamics of the properties of steppe paleosols of the Sarmatian time (2nd century BC-4th century AD) in relation to secular variations in climatic humidity

Paleosols buried under kurgans of the Early (2nd-1st centuries BC), Middle (1st-2nd centuries AD) and Late (2nd-IV centuries AD) Sarmatian epochs were studied in dry steppes and desert steppes of the Lower Volga region (the Privolzhskaya and Ergeni Uplands and the Caspian Lowland). It was found that temporal variations in the morphological, chemical, microbiological, and magnetic properties of the paleosols in the interval of 2200–1600 BP were characterized by the cyclic pattern related to secular dynamics of climatic humidity with changes in the mean annual precipitation of ±30–50 mm. These climate changes did not transform chestnut paleosols and paleosolonetzes at the type or subtype taxonomic levels. However, they led to certain changes in the humus, carbonate, and salt profiles of the soils; in the character of solonetzic horizon B1; and in the state of microbial communities. According to these data, the Sarmatian time was characterized by alternation of micropluvial and microarid stages lasting fro about 100–200 years. In particular, the stages of humidization were observed in the 1st century BC-1st century AD and in the 4th century AD; the most arid conditions were observed in the second half of the 2nd and the first half of the 3rd century AD.     

Age and activation of microbial communities in soils under burial mounds and in recent surface soils of steppe zone

Chestnut paleosols buried under steppe kurgans about 4800, 4000, and 2000 years ago and their background analogues were studied in the dry steppe zone on the Volga-Don interfluve. Morphological, chemical, microbiological, biochemical, and radiocarbon studies were performed. Paleoclimatic conditions in the region were reconstructed on the basis of paleosol data. The ages of microbial fractions isolated from the buried and surface soils were determined using the method of ¹⁴C atomic mass-spectrometry. It reached 2100 years in the A1 horizon of the buried paleosol, which corresponded to the archaeological age of the kurgan (1st century AD). The ages of microbial biomass isolated from the B2 horizons of the buried paleosol and the background surface soil comprised 3680 ± 35 and 3300 ± 30 years, respectively. The obtained data confirmed our assumption about preservation of microorganisms of the past epochs in the paleosols buried under archaeological monuments. It is ensured by various mechanisms of adaptation of soil microbial communities to unfavorable environmental conditions (anabiosis, transformation of bacteria into nanoforms, etc.). The possibility to stimulate germination of the ancient dormant microbial pool isolated from the buried paleosols by 2–3 orders of magnitude with the use of β-indolyl-3-acetic acid as a signal substance was demonstrated.     

The solonetzic process in surface soils and buried paleosols and its reflection in the mineralogical soil memory

The development of the solonetzic process in paleosols buried under kurgans and in the modern surface soils has been studied on the basis of the analysis of the clay (<1 μm) fraction. The revealed changes in the textural differentiation of the soils and the mineralogical composition of the clay fraction during 4500 years are assessed from the viewpoint of the “memory“ of the solid-phase soil components. The mineralogical characteristics show that the solonetzic process in the modern background soil is more developed. The mineralogical approach allows us to reveal the long-term changes in the soil status; it is less useful for studying the effect of short-term bioclimatic fluctuations. In the latter case, more labile soil characteristics should be used. The mineralogical method, combined with other methods, becomes more informative upon the study of soil chronosequences. Our studies have shown that the data on the clay minerals in the buried paleosols may contain specific information useful for paleoreconstructions that is not provided by other methods.     

Production of CO<Subscript>2</Subscript> by surface and buried soils of the steppe zone under native and moistened conditions

Modern light chestnut and chestnut soils and their analogues buried under steppe kurgans in the southeastern part of the Russian Plain were studied in order to determine the rates of the CO₂ production by these soils under the native (with the natural moisture content) and moistened (60% of the total water capacity) conditions. It was found that the rates of the CO₂ production by the soil samples in the native state are relatively close to one another and vary from 0.3 to 1.4 μg of C/100 g of soil/h. The rates of the CO₂ production in the moistened state increased by two orders of magnitude for the modern surface soils and by an order of magnitude for the buried soils.     

Soils, vegetation, and climate of the southern Transural region in the Middle Bronze Age (by the example of the Arkaim fortress)

Paleosols of the unique fortress of Arkaim located in the steppe zone of the southern Transural region (Chelyabinsk oblast) were investigated. The dating of the buried soils was performed using the radiocarbon method. The time of building this archeological monument is the Middle Bronze Age (the Sintashta culture; the calibrated dating with 1σ confidence is 3700–4000 years ago). Seven pits of paleosols and ten pits of background ordinary chernozems were studied. The soils are loamy and sandy-loamy. The morphological and chemical properties of the buried and background ordinary chernozems are similar; they differ by the lower content of readily soluble salts in the paleosols as compared to the background ones. The sporepollen spectrum of the Arkaim paleosol is transitional from the steppe to the forest-steppe type. During the existence of this settlement, pine forests with fern ground cover grew, and hygrophytic species (alder and spruce) that nowadays are not recorded in the plant cover occurred. The main feature of the paleosols is the presence of pollen of xerophytic and halophytic herbaceous plants there. The few pollen grains of broad-leaved species testify to a higher heat supply as compared to the current one. Judging by the results of the spore-pollen and microbiomorphic analyses, the climate during the time of building the walls of the settlement was somewhat moister and warmer (or less continental) than the present-day climate. The duration of this period appeared to be short; therefore, soil properties corresponding to the changed environment could not be formed. They reflect the situation of the preceding period with the climatic characteristics close to the present-day ones.