Smykiv – the new key section of the upper pleistocene of the Volyn Upland

Abstract

Formulation the problem. The new section at Smykiv in the Volyn Upland has an informative stratigraphic record, showing details of climatic phases in the Late Pleistocene. The site is located in the Rivne Oblast, 40 km south of Lutsk, on slope of the River Dezha (the tributary of the River Styr). Review of previous publications and studies. The loess-palaeosol sequence of the Volyn’ Upland has been intensively studied by Ukrainian, Russian and Polish researchers such as A. Bogucki, M. Lanczont, P. Voloshyn, A. Tsatskin, V. Nechaev, T. Morozova, L. Bezusko, J. Kusiak, S. Fedorowicz, J. Nawrocki, R. Dmytruk and many others. Methods. The section has been studied using lithostratigraphic, palaeopedological, palaeocryological, grain size, micromorphological and partial chemical methods, which enable the reconstruction of past climate and environment. The stratigraphy is applied follows the Quaternary Framework of Ukraine (Veklitch et al., 1993). All the stratigraphical units of the Upper Pleistocene are represented in the section; and, herein, these divided into smaller parts characterized by distinct environmental histories. The purpose of the article is to study the detailed stratified sequence at Smykiv by various methods in order to clarify the regional Quaternary palaeogeographical scheme. Results. The periglacial alluvium of the Dnipro unit, at the base of the sequence, and the analysis of the position of the site in the relief indicate the interpretation that it is located on the Dezha river’s terrace. The alluvium bed is distorted by syngenetic involutions. The overlying Kaydaky unit truncates the alluvium, and is inclined parallel to the present valley slope. Three pedogenetic phases during the Kaydaky times are identifiable: pedosediments formed in the first phase (kda), pedosediments of forest soil formed in the early optimum (kdb1) and a Retisol formed in the late optimum (kdb2). During the Tyasmyn cold event, a network of small soil veins formed. Renewed, but less intense than in the Kaydaky unit, erosion processes started in Pryluky times. It can be demonstrated that the Pryluky polygenetic soil was formed in three phases, divided by a cold event in mid Pryluky times (pl2). A Chernozem with signs of slight podzolisation and biogenic aggregation was formed during the first phase (pl1b2). The soil is disturbed by cryogenic features formed during pl2. An incipient Cambisol was enriched with a fine organic matter during the phase pl3b1. An incipient Calcic Cambisol (pl3b2), aggregated and slightly gleyed, formed at the end of the Pryluky time. Erosion processes were not strongly developed during Pleniglacial. At the beginning of the stadials (in Uday and Bug times), solifluction processes occurred. At the beginning of these stadials, other cryogenic features, such as soil veins, frost fissures and ice-wedges, were also formed. Upper Pleistocene loess beds show slight pedogenesis, particularly very weak humus accumulation and biogenic aggregation. Furthermore, all Pleniglacial units are enriched in carbonates in diverse forms: however, the most common is disperse powdery lime. These last are frequently interpreted as being the result of calcite crystallization under cryogenic processes. During Vytachiv and Dofinivka interstadial times, boreal soils were formed – Gleyic Cambisol and Calcic Gleyic Cambisol, respectively. The first is mostly represented by pedosediments (indicating intense erosion), whereas the second soil is preserved in situ and it is enriched in fine organic matter and is well-microaggregated. The last loess unit of the Upper Pleistocene, the Prychornomorsk loess unit, is subdivided into two loess subunits (pc1 and pc3) which are connected with cryogenic events, and a Gleysol (pc2), indicating a relatively warm period.