A. O. Alekseev

Magnetic mineralogy of soils across the Russian Steppe: climatic dependence of pedogenic magnetite formation.

Formation of ferrimagnets in well-drained, buffered, unpolluted soils appears to be related to climate, and especially rainfall. If robust, this magnetism/rainfall couple can be used to estimate past rainfall from buried soils, particularly the multiple soils of the Quaternary loess/soil sequences of Central Asia. However, dispute exists regarding the role of climate vs. dust flux for the magnetic properties of modern loessic soils. Here, we examine the mineralogical basis of the magnetism/rainfall link for a climate transect across the loess-mantled Russian steppe, where, critically, dust accumulation is minimal at the present day. Magnetic and independent mineralogical analyses identify in situ formation of ferrimagnets in these grassland soils; increased ferrimagnetic concentrations are associated with higher annual rainfall. XRD and electron microscopy show the soil-formed ferrimagnets are ultrafine-grained (<50 nm) and pure. Ferrimagnetic contributions to MA¶ssbauer spectra range from 17% in the parent loess to 42% for a subsoil sample from the highest rainfall area. Total iron content varies little but the systematic magnetic increases are accompanied by decreased Fe2+ content, reflecting increased silicate weathering. For this region, parent materials are loessial deposits, topography is rolling to flat and duration of soil formation effectively constant. The variations in soil magnetic properties thus predominantly reflect climate (and its co-variant, organic activity) â�� statistical analysis identifies strongest relationships between rainfall and magnetic susceptibility and anhysteretic remanence. This magnetic response correlates with that of the modern soils across the Chinese Loess Plateau. Such correlation suggests that the rainfall component of the climate system, not dust flux, is a key influence on soil magnetic properties in both these regions.

Geochemical Characterization of Loess-Soil Complexes on the Terek-Kuma Plain and the Azov-Kuban' Lowland

The changes in the material composition of the buried soils and loesses in relation to the dynamics of the climate and sediment accumulation were studied for revealing the pedogenetic features and assessing the natural conditions in the steppe zone of the southern Russian Plain. A comparative analysis of the chemical compositions of the different-aged Pleistocene loess-soil complexes (the Otkaznoe, Port-Katon, and Shabel’skoe profiles) on the Terek-Kuma Plain and the Azov-Kuban’ Lowland was performed. An increase in the concentrations of Fe and Mn, which are intensively involved in the biological cycle, and Rb, which is accumulated due to the activation of weathering processes, was observed in the paleosols that developed in interglacial periods of activation of pedogenesis. Increased coefficients of weathering (chemical index of alteration (CIA)) = [Al/(Al + Ca + Na + K)] 100, Al/(Al + Ca + Na + Mg), Rb/Sr, and Mn/Sr), leaching (Ba/Sr), and biological activity and bioproductivity (Mn/Fe, Mn/Al) were also noted for the paleosol horizons as compared with the loess horizons. It is argued that geochemical coefficients can be used as an efficient tool in the soil and paleogeographic studies aimed at the reconstruction and refinement of the schemes of changes in the bioclimatic conditions during the Pleistocene.

Serpukhovian Stage (Carboniferous) in type area: Sedimentology, mineralogy, geochemistry, and section correlation

This paper delivers bed by bed descriptions and detailed correlation of the sections Novogurovskii, Dashkovka, and Zaborie of the type area of Serpukhovian Stage of the International Stratigraphic Chart. Above a weakly expressed Forino Unconformity discovered in the lower Tarussian, no subaerial unconcormities can be confirmed up to the top of Steshevian. The basinal character of the Steshevian lobata montmorillonite shale unit is demonstrated. Oxygen minimum and perhaps greatest Early Serpukhovian highstand is revealed by geochemistry and trace fossil association in the lower part of the lobata shale. The paleogeographic model of the “Steshevian basin” outlined in this paper involves suppression of photozoan carbonate production in front of a low-energy delta causing development of a shallow depression in the surrounding carbonate platform. In the Steshevian black shale unit, upward change from lobata montmorillonites to shallower marine palygorskites is explained by evaporative pumping of magnesium and silica in basinal water under progressive climatic aridization.

Paleosol complex in the uppermost Mikhailovian Horizon (Viséan, Lower Carboniferous) in the southern flank of the Moscow Syneclise

The beds composing an unconformity at the boundary of the Mikhailovian and Venevian horizons in the Polotnyanyi Zavod quarry (Kaluga Region) are investigated. A detailed study has shown that, at the base of black “rhizoid” limestone, a pedocomplex of two paleosols of different genesis is formed. From below upwards, rocks of subaerial (Paleosol 1 of the rendzina type), subaerial–subaquatic (Paleosol 2 on bog marl), and palustrine genesis replace each other. Both paleosols display a horizontal structure of profiles; the presence of the root systems, imprints of plants, and traces of animal’s activity; the presence of soil new formations (micritic calcite with a light isotopic composition of C, Fe-concretions ). In paleosols, some geochemical indices (PWI, CIA, CIA-K), the ratios Ba/Sr, Rb/Sr, and concentration of Ga increase. The soil complex was formed under conditions of a warm subhumid climate. In the structure and lateral scale of distribution, the object investigated is comparable to the Everglades marsh landscape of Florida (United States).

Biogeochemical Processes in Steppe Landscapes of the Ergeni Upland in the Holocene

A soil catena was studied on the Ergeni Upland; the soils and plants were sampled in five dependent points. The contents of macro- and microelements in them were determined. It was found that the radial (vertical) geochemical migration predominates in the eluvial positions of the catena, and the lateral geochemical migration predominates in the transeluvial and transeluvial–accumulative positions. Plants of the Poa L. genus intensely accumulated elements within the eluvial part of the catena, whereas plants of the Artemisia genus were element accumulators within the trans-superaquatic position. Plants of the Artemisia genus were generally characterized by a higher coefficient of the biological uptake of elements in all parts of the catena, except for the eluvial position, where this parameter was higher for plants from the Poa L genus. A rise in the magnetic susceptibility of the soil profile relative to the parent material was the highest in the eluvial position and the lowest in the trans-superaquatic position. A comparative analysis of geochemical ratios for modern soils showed that they are determined by the topographic position of the given point. However, the gradient of variations for surface soils is much smaller in comparison with that for buried soils indicative of the climatic fluctuations. The obtained geochemical indicators can be used for comparative analysis of buried soils found not only on the divides but also in the subordinate landscape positions.

The Mississippian Paleosols in the Brontsy Quarry, Kaluga region

A chronosequence of five Visean (Aleksinian–Venevian interval, C1v, 326–336 Mya) paleosols on the territory of Moscow calcareous sedimentary basin (Brontsy quarry, Kaluga region) was studied in detail. Two lowermost paleosols are coastal peat-bearing paleosols developed under mangrove vegetation. Three upper paleosols develop pedocomplexes, in which the lower part is the marine limestone altered to different degrees by weathering/pedogenesis with the formation of eroded Rendzina-type soil. It is overlain by paleosols developed from terrigenous sediments of playa origin. They are characterized by elevated concentrations of Fe, Mg, Ti, Ga, and some other elements; the formation of secondary micritic carbonates, iron oxides, and smectites; and increased values of geochemical indexes (such as CIA-K). Smectite (low-charged beidellite) predominates in these paleosols. Iron oxides are represented by goethite and lepidocrocite attesting to the predominance of oxygenic environments. Pedocomplex at the Mikhaylovian/Venevian boundary is overlain by non-marine palustrine deposits known as “black rhizoidal limestone.” The paleoclimate reconstruction based on the chemical composition data attests to its polycyclic character. The Mikhaylovian time was most humid was (~1000 mm/yr). Later, starting from Venevian, gradual aridization of the climate began and annual precipitation decreased to 750 mm/yr and less.

Biogeochemical Technology for Disturbed Tundra Soils Recultivation by Peat and Potassium Humate Application

The biogeochemical technology of recultivation of disturbed tundra soils includes the joint application of local peat and its potassium humate from the Taz peninsula (the Yamalo-Nenets Autonomous Okrug). At the same time the potassium humate is produced from humic acids of local peat by consecutive decalcifying, extraction, sedimentation and clarification. Efficiency of application of peat and potassium humate to the disturbed soils in doses depending from their granulometric composition is estimated on a basis of biomass of grown grass-cereals plants. The given technology is forwarded to increasing the efficiency of recultivation of the disturbed soils.