Stratigraphy of Late Mid-Pleistocene in Lithuania: the current status and issues

The principal aim of this paper is to present a critical overview of the stratigraphical subdivision and correlation of the Late Mid-Pleistocene (LMP) sediments in Lithuania. In recent decades, a number of studies of LMP sediments have been carried out, allowing clarification of the stratigraphical position of individual sedimentary sections. Particular efforts have been made to determine the age of sediments using a variety of absolute age determination methods. However, there are still several outstanding questions. It is still unclear how many warm periods occurred during the Saalian in Lithuania and of what magnitude. The least problematic issue is identification of the Butėnai (Holsteinian) Interglacial as it correlates well biostratigraphically with the contemporaneous sections of adjacent areas. The most controversial unit is the Snaigupėlė Interglacial, the age of which continues to be a subject of debate. Recently, more evidence has emerged that the sediments considered to be of the Snaigupėlė Interglacial are contemporaneous with the Merkinė (Eemian) Interglacial. The chronological placement of these sediments closely hinges on the unresolved stratigraphical classification of the Medininkai deposits (MIS 6 or MIS 8?) and the Žemaitija tills (MIS 8 or MIS 10?). The debate is centred on whether these two tills were formed during two entirely different glaciations or represent different phases of a single major glaciation event. Traditionally, these two tills were attributed to distinct glaciation events separated by the Snaigupėlė Interglacial. However, no sedimentary sections have been discovered that contain both these tills and the interglacial sediments that separate them. Given the similar lithological, geochemical and petrographic composition of the Medininkai and Žemaitija tills some research has supported their possible stadial rank. The clarification of these stratigraphical issues in the future may be facilitated by the application of new proxies and re-examination of the existing LMP key sections.