Clay as a natural isolating cover: its formation in supraglacial and proglacial subenvironments in North Lithuania

Abstract

The North Lithuanian region since long ago has been known as a zone of dominant glacial erosion. The Pleistocene bed in the central part of North Lithuania is 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 different bedding and tectonic conditions were responsible for different scale of erosion in various areas of the region. Geological and geomorphological investigations through digging of test pits and investigation of outcrops, field observation and interpretation of aerial photographs were the basis for the geological-geomorphological reconstructions. Macroscopic description, graphic fixation and photography of the quarry walls were used to examine the Pleistocene succession of the study area. Two types of clayey glaciolacustrine sediments were investigated according to data of 2 boreholes. One type was formed in supraglacial subenvironment, i.e. in glaciolacustrine kame terrace on the marginal ridge of North Lithuanian phase. Another type was in proglacial subenvironment, i.e. on the territory of ice-dammed proglacial lake bottom. Regularities of the distribution, bedding conditions and structure have been revealed for both types as well as their grain-size distribution and geochemical differences according to Al, Ag, B, Ba, Co, Cr, Cu, Ga, La, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Sc, Sn, Sr, Ti, V, Y, Yb, Zn and Zr.