Eugenija Rudnickaitė

Peculiarities of sedimentation conditions in the oxbow lakes of Dubysa River (Lithuania)

Abundant wood remains and buried trees have been found in the western part of Lithuania near Zakeliškiai and Lyduvėnai on Dubysa River (a tributary of Nemunas River) where deposits are rich in organic remnants and buried soils. In Zakeliškiai and Skiručiai sections of Dubysa River oxbow sediments were investigated by various methods (dendrochronological, carbonate, granulometric, pollen and mollusc fauna analysis). In addition, these sections were dated using the radiocarbon method. Samples were collected from deposits of Dubysa River outcrops. The studied oxbow lakes have existed for more than 5 thousand years (from ca. 4300 BC to 1000 AD). During this period organic rich deposits with trees and branches were formed in the oxbow lake. This indicates that at the end of Atlantic, during Subboreal and in the early Subatlantic periods there was a forest growing that contained mainly oaks which were falling down into an oxbow lake and later were covered by sandy and silty deposits. The granulometry of alluvial deposits, as well as the mixture of medium-grained sand and silt show different stages of Dubysa River palaeochannel formation: riverbed and oxbow lakes. Three climate warming cycles were revealed according to carbonate analysis data in all investigated sections. The rheophile thermophilous Holocene age molluscs species Bithynia tentaculata L., Unio cf. crassus Philipsson, Pisidium amnicum (Müller), Theodoxus fluviatilis (Linnaeus) have been found. The pollen composition and sequences have been divided into five local pollen assemblage zones (LPAZ) and described according to pollen spectra in each zone. In this way it is possible restore palaeoclimatic coherent evolution, trends and cyclical change.

Geochemical records of paleocontamination in late pleistocene lake sediments in West Flanders (Belgium)

ABSTRACT Concentrations of trace elements in Late Pleistocene lake sediments from two localities in West Flanders (Belgium) were studied using inductively coupled plasma-mass spectrometry. The studied sediments were deposited during the transition of the Allerød to the Younger Dryas. Trace elements enter lake environments from a variety of sources, but mostly from bedrock weathering in catchments and as wind-blown dust particles. These sources create a natural trace element background in lake sediment records. The concentration and distribution of trace elements across the studied lake sediment sequences display features consistent with inputs of materials other than those from soil or bedrock. Input from volcanic eruptions, biomass burning and meteorite impacts should be considered among the main sources of non-anthropogenic contamination of lake environments.