Palaeogeography of South Lithuania during the last ice age

Abstract

The palaeogeographical development of South Lithuania during the last ice age (Nemunas = Weichselian) was reconstructed by various methods. The recurring permafrost and cryogenic structures in the ground were an important phenomenon of the southeastern periglacial zone. The 3–4 lithocomplexes of the extraglacial cover correlate with the Lithuanian and Mid-European Late Pleistocene Weichselian (Nemunas) biostratigraphic divisions. In the northwest, the palaeogeography is influenced by the deglaciation during the Žiogeliai (Frankfurt) Phase and the Baltija (Pomeranian) Stage of the last ice age. The deglatiation process is shown in a series of palaeogeography maps. During the Weichselian, the SW–NE oriented middle part of the area, commonly regarded as part of the Vilnius-Warsaw-Berlin Urstromtal (ice-marginal streamway), underwent intensive interstadial fluvial erosion and accumulation, glacial erosion and sedimentation, followed by subsequent glaciofluvial accumulation on sandurs and glaciolacustrine sedimentation in a series of small basins.

Introduction

Results of theoretical and practical investigations of the Late Pleistocene palaeogeography in Lithuania have been presented by, among others, Micas (1964), Basalykas (1965), Vaitiekūnas (1968), Gaigalas, 1979, Gaigalas, 1995, Kudaba (1983), Kabailienė (1990), Dvareckas (1993), and Kondratienė (1996). Spores and pollen from the last interglacial (Eemian), Late Glacial and Holocene in South Lithuania and adjacent regions have been investigated by Seibutis (1974), Kunskas (1977), Kondratienė, 1979, Kondratienė, 1996, Satkūnas et al. (1998), Seibutis and Savukynienė (1998), Satkūnas (1999), Kabailienė (2001), and others; geochemical, lithological, petrographic and textural research has been carried out by Mikalauskas (1985), Baltrūnas, 1995, Baltrûnas, 2002, Stančikaitė et al. (1998), Švedas (2001) and others, whereas geomorphological and structural investigations of Quaternary sediments have been performed by, among others, Voznyachuk and Valczyk (1978), Ber, 1981, Ber, 2000, Basalykas et al. (1984), Dvareckas and Dicevičienė (1987), Karabanov (1987), Komarovsky (1996), and Marks (2002).

Valuable information on the geomorphology and palaeogeography was obtained from a study carried out in the framework of the programme “The Stone Age in South Lithuania”, supported by the Lithuanian State Science and Studies Foundation, the results of which have been presented by Baltrūnas (2001), Gaigalas (2001), Kabailienė (2001) and others; they identified and described the Quaternary glacial sediments (till) of South Lithuania according to their genesis and time of formation by means of carbon dating (¹⁴C), and by analysis of the granulometric and mineral characteristics (in the 0.25–0.1 and 0.1–0.05 mm fractions), petrography (the 30–10, 10–5, and 5–2 mm fractions), and geochemistry (in the fraction < 1 mm). These data were supplemented with the results of pollen and diatom analysis of interglacial and post-glacial sediments. Neither was a comprehensive evaluation of the palaeogeographical conditions carried out in the above works, however, nor were the Pleistocene stratigraphical events related to the changing periglacial conditions. A first attempt to summarise these events was made recently by Švedas et al. (2004).

Permafrost-induced structures of the soil, and a systematic classification of (glacial and) periglacial environments, facies and deposits have been dealt with in special works (e.g. Washburn, 1979, Brodzikowski and Van Loon, 1987, Brodzikowski and Van Loon, 1991, Murton and French, 1994). Kopp and Jäger (1972) called the surficial sediments in the periglacial environment a series of periglacial perstruction, composed of different layers. Polish research (by, among others, Goździk and Pazdur, 1987, Kozarski, 1993, Jary, 1996, Issmer, 1999, Jary et al., 2002) and investigations in Belarus (Karabanov, 1987, Sanko, 1987, Komarovsky, 1996; and others) contributed a wealth of new data on the periglacial zone, allowing a more reliable reconstruction of the palaeogeographical events in the whole area. These areas have experienced comparable extraglacial conditions, i.e. central Poland and the Medininkai (Ašmena) Upland in Lithuania were not glaciated in the Weichselian.

The ‘cover deposits’ are regarded in these works as loess-like sediments. They are interbedded with or occur in close proximity to “typical” loesses. They are, like the ‘typical’ loesses, composed of fine-grained material that was derived from older sediments under the influence of physical and chemical weathering, eolian, cryogenic, slope, and other processes. In Lithuania, these sediments form part of the European belt of loesses and loess-like sediments, extending from Russia and Belarus to the Ukraine, Poland, Germany, North France, The Netherlands, Belgium and Great Britain. The present study of these sediments in Lithuania thus provides additional information on the maximum extent of the Pleistocene glaciations.

The main purpose of the present contribution is to summarise the previous investigations on the geology and palaeogeography of the last glaciation, which is called ‘Nemunas’ in Lithuania and ‘Wisconsinan’ in Northern America. In the following text, the NW European term ‘Weichselian’ will be used. A second objective is an inventory of the permafrost structures in the previously periglacial areas of southern Lithuania, in order to obtain a comprehensive model of the evolution of the area.