S.N. Timireva

Development of the steppe zone in southern Russia based on the reconstruction from the loess-soil formation in the Don-Azov Region

Herbaceous communities in forest ecosystems on the southern part of the Russian Plain appeared in the Middle Miocene (∼10 Ma BP). In the Late Miocene (∼7 Ma BP), feather-grass steppe associations appeared among them. In the time span of 2.7 to 2.1 Ma BP (i.e., in the Early Quaternary, according to the current chronostratigraphic scale), the steppe zone arose on the southern Russian Plain in the Don-Azov Region. Seven stages of this zone development here have been distinguished throughout the Quaternary. The first one (Eopleistocene-Early Pleistocene) was characterized by savanna-like subtropic ecosystems. Then, in the Middle Pleistocene, the temperate zone ecosystems (tallgrass prairie-like steppes) developed here and were followed by steppe ecosystems close to the modern ones in Central Europe. The ecosystems of rich-species forb steppes developed in the Late Pleistocene. Finally, in the optimum of the modern interglacial (Holocene), steppes became similar to the modern ones here, but with a slightly higher precipitation. The general trend is characterized by reduction in heat and water provision and increase in aridization progressing from earlier to later stages.

Reconstruction of the paleotemperature and precipitation in the Pleistocene according to the isotope composition of humus and carbonates in loess on the Russian Plain

The isotope composition of carbon and oxygen in humus and carbonates has been studied in the Pleistocene loess and soil of the Russian Plain in order to reconstruct the paleoclimatic parameters during the time of their formation. It is established that most of the buried soils were formed upon the mean annual temperature exceeding the modern temperature by 1–2°C. The climate aridity (the portion of C4 plants in the ecosystem) varied from 0 to 25%. It is shown that the isotope composition of carbon and oxygen in the humus and carbonates may be a reliable indicator of the paleoclimate (i.e., the paleotemperature, paleoprecipitation, and aridity dynamics). An isotope procedure of culling soil samples unsuitable for paleoclimatic reconstruction is proposed.

Reconstruction of Late Pleistocene events in the periglacial area in the southern part of the East European Plain

An integrated study of the loess–soil sequence in the coastal exposure near the settlement of Beglitsa (Rostov oblast) allowed us, for the first time, to reconstruct the landscape-climatic changes that occurred in the eastern Azov region over the course of the Late Pleistocene. In the south of the periglacial zone, considerable differences between intensity of the loess accumulation in the Early and Late Valdai Cryochrons were revealed. In the Early Valdai Epoch, which corresponds roughly to the end of Marine Isotope Stage (MIS) 5 and MIS 4, loess accumulation occurred after completion of development of the Mezin pedocomplex and before the beginning of the Bryansk stage of soil development, i.e., over more than 20 000 years. In the much shorter Late Valdai Cryochron MIS 2 (10 000–12 000 years), loess accumulation reached 5 m. The data evaluation shows that the loess accumulation rates in the Early Valdai Epoch (~0.07 mm/year) and the Late Valdai Epoch (~0.5 mm/year) differ from each other by an order of magnitude.

СМЕНА ЛАНДШАФТНЫХ ОБСТАНОВОК НА ЮГЕ РУССКОЙ РАВНИНЫ В ПОЗДНЕМ ПЛЕЙСТОЦЕНЕ ПО РЕЗУЛЬТАТАМ ИССЛЕДОВАНИЯ ЛЁССОВО-ПОЧВЕННОЙ СЕРИИ ПРИАЗОВЬЯ

Based on the complex studying 10 meter thick loess-soil sequence in the Beglitsa section (47°08° N, 38°31° E), the landscape and climate changes in the north-eastern Azov Sea Region in the Late Pleistocene were reconstructed. The intensity of loess accumulation decreased in the interglacial and interstadial conditions, when the soil-forming processes prevailed, and increased in cryoarid conditions of the glacial epoch, and especially, during the Late Valdai. As indicated by topography of palaeosoil horizons, loess layers of various ages envelope in sequence the primary fluvial (erosional-accumulative) relief. Loess accumulation resulted in general rise of the terrace surface. It preserved the major features of original topography but gradually smoothed the minor ones. During the entire Late Pleistocene the studied area belonged to the steppe zone. Participation of forbs in steppe communities, as well as the grass cover density, decreased in the cryoarid periglacial conditions and increased under warmer and less continental interstadial or interglacial climate. The role of intrazonal tree communities (pine forests with steppe elements, birch and alder wet forests) remained minor even in the most favorable climate of the Mikulino Interglacial, when the broad-leaved trees (mainly Quercus) participated in the forests. During the interstadial warm phases of the Valdai glacial epoch, the trees growing at present in the severe continental climatic conditions (Larix, Pinus sibirica) occurred in the region. As in the present time, near the shore of the Azov Sea, the areas with disturbed soil cover, including those with saline soil, were widespread due to abrasion, development of slumps and landslides, and erosion.