Till macro- and microfabrics of mega-scale glacial lineations of Mūša–Nemunėlis Lowland, north Lithuania

Abstract

North Lithuania was chosen for a study of the “drumlinised” morainic surface produced during the Last Glaciation, typified as well-expressed mega-scale glacial lineations (MGSLs). The goal pursued in the present study was to investigate the morphology and macro- and microfabrics of some large glacial lineations to substantiate their formation mechanism. The geological structure of Quaternary strata of an area and the erosion depression of sub-Quaternary surface suggest favourable conditions for the glacier to rapidly fluctuate into the area during deglaciation of Late Glaciation. Investigations of Pleistocene tills observed in the MSGLs of the area preserved on the eastern and western margins of the study area show that these deposits are formed from the upper part of the Baltija Subformation – Middle Lithuanian till. According to two sets of grain sizes, MSGL tills are often notable for increased values of relative entropy. Therefore, morainic material deposited during the redeposition of the Baltija Subformation till was thoroughly mixed. The data on orientation and inclination of long axes of gravel and pebbles in the tills that form MSGLs, as well as the anisotropy of magnetic susceptibility (AMS) of microclast material suggest that the formation of MSGLs may have been influenced by directions of the local glacial stress that are different from the regional direction of glacial motion (about N–S). The change of macro- and microfabric of till confirms the formation of MSGLs during glacier erosion by groove-ploughing from the Baltija Subformation till. This occurred when basal ice carried over clast material to MSGL crests from interridge areas.