The Late Pleistocene soils as indicators of the impact of environmental changes on development of pedogenic processes (the study case from the Kryva Luka site, Donetsk area)

Abstract

The aim of this paper is to reveal connections between Upper Pleistocene soil types and the vegetation, which existed during their formation. Palaeovegetation was reconstructed on the basis of pollen analysis, whereas morphological description of palaeosols and the data from their laboratory study (grain-size and bulk chemical analyses, contents of Corg., CaCO3 and dry salts) were used to reconstruct palaeopedological processes. The Kryva Luka sedimentary sequence was accumulated in a deep palaeogully (the incision of which occurred in early Kaydaky times), where, as a result of high sedimentation rates, welldeveloped Upper Pleistocene pedocomplexes formed, on one hand, and very good preservation of pollen was thus guaranteed. Several phases of soil development occurred in Kaydaky, Pryluky and Vytachiv times (the Ukrainian Quaternary framework), all represented in the section by individual palaeosols, separated by loess-like beds, or by erosional surfaces. The data collected demonstrates a cyclic pattern of short-period palaeoenvironmental changes during the Late Pleistocene. The last interglacial is related by paleopedological and pollen data to the Kaydaky unit. The pre-temperate stage of the interglacial is revealed in the gully deposits of subunit ‘kd1a’. The early-temperate stage corresponds to the Luvisol of subunit ‘kd1b’, which was formed under broad-leaved woods dominated by oak. The late-temperate stage is recorded in the Greyzemic Phaeozem of the soil ‘kd3b1’ (by the appearance of hornbeam) and the Mollisol ‘kd3b2’. The post-temperate stage of the interglacial and the transition to the early glacial occurred during formation of the uppermost bed of thelatter and the incipient soil ‘kd3c’. (pedosediments were also accumulated at this time). Both vegetational composition and the soil types reflect a warmer and wetter climate for the temperate part of the last interglacial, as compared to that existing in modern times. The soils of different phases of Pryluky and Vytachiv times were formed during interstadials, with cooler climates than at present. As recorded both in soil types and pollen assemblages, the climates during the early interstadials of Pryluky and Vytachiv times were wetter than now (particularly during the ‘pl1b1’ phase), but during their late interstadials, the climate was drier than the modern one (particularly during the phase ‘pl3b2’). On the basis of TL-dating obtained in sections in western Donetsk area and Central Ukraine, Pryluky times correspond to interstadials and stadials of the early glacial, whereas Vytachiv unit may be related to the middle pleniglacial. Types of cryostructures, connected with loess-like deposits of the stadials, indicate that the studied area in those times was under a severe continental climate, with deep seasonal freezing of the grounds. Nevertheless, the absence of ice pseudomorphs and of pollen of arctoalpine plants indicates that permafrost was not present. Changes in palaeopedogenic processes (as well as in types of sedimentation) mainly paralleled changes observed in the palaeovegetation. The extent of wooded areas, the role of broad-leaved trees in the forest composition, and the spread of xeric herbal associations had particularly notable effects on the development of pedogenic processes.