Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

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Geological Survey of Finland, Special Paper 46 Danguol Karmazien, Bronislavas Karmaza and Valentinas Baltrünas The North Lithuanian region has been known as a zone of dominant glacial erosion where the Quaternary sediment cover is relatively thin (up to 40 m in palaeoincisions) and has a specifi c structure (Bucevic v i0te . et al. 1992, and others). Previous research has shown that the character of glacial erosion and glacial material transportation are refl ected in the structure of Pleistocene deposits, particularly in tills. The aim of the present paper is to report new information on structural peculiarities of North Lithuanian Pleistocene strata. The new data were obtained using different methods of studying Pleistocene deposits in the adjacent dolomite quarries near the Petraši0nai and the Klovainiai boroughs in the Pakruojis District (Fig. 1). These quarries are 7–8 km away from each other. About 5–6 km north of the Petraši0nai quarry, is the boundary of the North Lithuanian Phase of the Baltic Stage and is marked by a distinct morainic Linkuva ridge. Macroscopic description, graphic fi xation and photography of the quarry walls were used to examine the Pleistocene succession the study site. Granulometric analysis of intertill silt served as a basis for stratigraphic classifi cation of the Pleistocene strata. The following fractions were determined: 5–2; 2–1; 1–0.5; 0.5–0.25; 0.25–0.1; 0.1–0.05; 0.05–0.01; 0.01–0.005; 0.005–0.002; 0.002–0.001 and
THE STRUCTURE OF THE PLEISTOCENE DEPOSITS OF THE REGION The Pleistocene sediments in the central part of northern Lithuania are overlying the Upper Devonian dolomite, marl, limestone, clay, and gypsum layers. The varying resistance of these deposits to mechanical and chemical impacts as well as the different bedding and tectonic conditions were responsible for the different scale of erosion in various areas of the region. According to the available data, the palaeorelief is characterized by uplifts, solitary closed dips and troughs, and long and narrow palaeoincisions (Šliaupa 1997, 2004). A trough-shaped meridional declension whose axis extends across Vaškai towards Panev≥ys stands out as a prominent feature. The minutely investigated sections of the Petraši0nai and Klovainiai quarries are on the western slope of the declension. The sub-latitudinal Palaeom0ša incision is situated north of the Petraši0nai and Klovainiai sections. According to the available borehole data, the Pleistocene deposits are composed of three complexes of glaciogenic sediments (Fig. 2). In Fig. 2. Cross-section of the Petraši0nai area Pleistocene deposits. Geological Survey of Finland, Special Paper 46 Structural characteristics of Pleistocene deposits in North Lithuania the stratigraphic scheme used by the Lithuanian Geological Survey, these glacial deposits are attributed to the Middle Pleistocene Medininkai and the Upper Pleistocene Upper Nemunas ice ages (subformations) (Lietuvos … 1994). The Pleistocene strata are rich in intertill deposits. The glacial deposits of the Medininkai sub-formation are spread locally in the region, overlie Upper Devonian rocks and are represented mainly by brown sandy loam. The till under consideration is very compact. Its greatest thickness (38 m) was measured in a palaeoincision 24 km NW of Pakruojis, with the prevailing thickness being 10–15 m. In some places it is only 3–5 m. The till left by the Medininkai glacier includes some blocks of Devonian rocks. The thickest block (21 m) was found in a borehole 28 km north of Pakruojis. Glacial deposits of the Upper Nemunas Formation cover the whole territory. These deposits overlie the Medininkai Formation or, in rarer cases, Upper Devonian rocks. At some places, the glacial depos- 33
Page 1: GEOLOGICAL SURVEY OF FINLAND Specia
Page 4 and 5: Johansson, P. & Sarala, P. (eds.) 2
Page 6 and 7: 4 CONTENTS Preface, Peter Johansson
Page 8 and 9: Geological Survey of Finland, Speci
Page 11 and 12: Applied Quaternary research in the
Page 13 and 14: DRUMLINS IN KUUSAMO AND RANUA In Ko
Page 15 and 16: RIBBED MORAINES IN SOUTHERN FINNISH
Page 17 and 18: ued fl owing from west to east but
Page 19: Sarala, P. 2005a. Glacial morpholog
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Page 45 and 46: Heavy minerals Medininkai Upland Ei
Page 47 and 48: The South Lithuanian phase of glaci
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Page 55 and 56: for dating. The deglaciation of nor
Page 61 and 62: In Lokka, the sheetfl ow tracks wer
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Page 73 and 74: deposited over the fi lled channel,
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Geological Survey of Finland, Speci
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