JOTNIAN SANDSTONES IN MORAINE DEPOSITS OF SOUTH-EASTERN LITHUANIA

Abstract

The article presents the results of a comprehensive lithological and paleogeographical study of erratic fragments discovered in the Skersabaliai quarry (Vilnius district, Lithuania). The relevance of the study lies in the necessity of detailing the reconstructions of glacial stream dynamics during the last Weichselian (Nemunas) glaciation, specifically its maximum Grūda stage. The primary focus is on red Jotnian quartzite sandstones, which serve as key indicator boulders. Mineralogical and petrographic analysis identified these rocks as medium-grained quartz arenites, which are derivatives of the Mesoproterozoic Jotnian deposits from the Satakunta formation (Finland) and the Bothnian Sea basin. Diagnostic features include a regenerative structure, the presence of chloritized siliceous fragments, and specific turbidization of quartz cores. It is demonstrated that the high textural maturity of these rocks is associated with their formation within the extensive paleoriver systems of the Fennoscandian Shield. A crucial scientific confirmation of the Bothnian-Åland transport vector is the established paragenetic association of rocks in the Skersabaliai quarry. Alongside the sandstones, a complex of igneous (red granites, rhyolite porphyries) and metamorphic rocks (gneisses, amphibolites, migmatites of the Svecofennian belt) was identified. The presence of epidotized granites with garnet indicates deep glacial erosion of the Fennoscandian crystalline basement. Simultaneously, findings of Palaeozoic sedimentary rocks (Ordovician and Silurian limestones) and an intact coral testify to the incorporation of material from the Baltic region's sedimentary cover during the glacier's transit through Estonia. The totality of the described findings proves that the eastern branch of the Bothnian ice stream passed through eastern Lithuania. The authors reconstructed the full transport trajectory: from formation in the Scandinavian Mountains and the entrapment of Jotnian rocks in the Gulf of Bothnia to the accumulation of material in south-eastern Lithuania after transit through the Baltic basin. The results obtained are of significant importance for refining the stratigraphy of Quaternary deposits and the dynamics of Pleistocene glaciations in the Baltic region.