Algirdas Gaigalas

Chapter 11 – Glacial Environments

Glacial environments are subject to drastic oscillations in energy regime that rapidly modify the local environment. The impact of glacial phenomena on the distribution, abundance, and evolution of biota based on trace-fossil evidence is the focus of this chapter. Arthropod trackways, shallow horizontal burrows, and fish trails dominate the glacial and periglacial trace-fossil assemblages preserved in terrestrial and glaciolacustrine sedimentary sequences, while nonspecialized feeding burrows that are diminutive when compared to normal-marine settings comprise glaciomarine ichnofaunas. As a consequence of rapid meltwater discharge, freshwater conditions prevail in some fjord settings during deglaciation, allowing for the establishment of suites more typical of freshwater or brackish-water conditions. Despite changes in the composition of the trace making community through time, ichnofacies relationships and ecological niche occupation are similar between the Paleozoic and Cenozoic, an indication of the constancy of the interplay between the biotic community and glacial processes.

GEOCHRONOLOGICAL AND SEDIMENTOLOGICAL INTERPRETATION OF INTERGLACIAL AQUATIC SEDIMENTS BASED ON TL DATING

Geochronological and Sedimentological Interpretation of Interglacial Aquatic Sediments based on TL Dating For the first time sedimentological interpretation of absolute ages obtained by thermoluminescence method on aquatic interglacial sediments was made. The analyzed size fractions of quartz grains were 160-250, 125-160, 100-125, 80-100 and 63-80 μm. The youngest and most reliable ages from 22 analyzed samples were obtained from the following quartz grain size granulometric fractions: 160-250 μm - 3 cases, 125-160 μm - 7, 100-125 μm - 6, 80-100 μm - 3 and 63-80 μm - 2 cases. Therefore, it may be concluded that the most suitable fractions for thermoluminescence dating are 125-160 μm and 100-125 μm. While evaluating the results of thermoluminescence dating it is necessary to take into account the procedure of sampling from layers of interest, their lithological composition, first of all granulometric, sedimentary environment, including sources of material, the material getting to the load flows, transportation mode and basin differentiation. From all the granulometric fractions of a sample, age of fine-grained fraction (63-80 μm) may be explained by the input of aeolian dust to a basin and sedimentation along with clasts brought to a lake by water flows. Aeolian sand storms performed precise multigenetic sedimentation that was active during that time. Bimodality of granulometric composition is defined by input of material from various sources of different composition. Older ages were obtained in the case of positive granulometric asymmetry. After sedimentological interpretation of thermoluminescence (TL) dating we can state that formation of aquatic fine-grained sands occurred 83.6±10 - 116.1±13 and 130.2±15 - 276.4±32 thousand years (ky) ago. Those geochronological zones coincide with interg lacial periods of Merkine (75.5-114 ky) and Snaigupele (180-280 ky) in Lithuania.

Timescale for Climatic Events of Subboreal/Subatlantic Transition Recorded at the Valakupiai Site, Lithuania

Oxbow lake deposits of the Neris River at the Valakupiai site in Vilnius (Lithuania) have been studied by dif- ferent methods including radiocarbon dating. A timescale was attained for the development of the oxbow lake and climatic events recorded in the sediments. 14C dates obtained for 24 samples cover the range 990-6500 BP (AD 580 to 5600 BC). Medieval human activity was found in the upper part of the sediments. Mollusk fauna found in the basal part of the terrace indicate contact between people living in the Baltic and the Black Sea basins. Mean rates were calculated for erosion of the river and for accumulation during the formation of the first terrace.

Environmental Study of the Bronze-Iron Age Transition Period of Eastern Europe

The migration of Scythians depended on climatic changes during the Bronze/Iron Age transition, which corresponds to Subboreal/Subatlantic climate periods. Data from oxbow lake sediments were used to distinguish climatic and environmental fluctuations. Climatic cooling started and humidity increased in the Late Subboreal. In the Bronze Age Subboreal draught farming spread and in the beginning of the Iron Age Subatlantic farming declined in East Europe. About 3500 years ago all the temperatures indices were about 1° higher and the precipitation was 50 mm more than nowadays. During the succeeding cooling at about 2500 years BP, the temperature was about 1° lower and the precipitation was a little greater in comparison with the modern indices. Precipitation decreased between the warming (3500 BP) and cooling (2500 BP). The biodiversity during the Bronze/Iron Age transition had an impact on the economy of Scythian cultures.

Stable Isotopes (H, C, S) and the Origin of Baltic Amber

Stable Isotopes (H, C, S) and the Origin of Baltic Amber New results of isotope analysis of light elements (H, C and S) of a dozen Baltic amber samples are described and discussed. Carbon isotope composition was nearly constant (ca. -23‰), whereas sulphur and hydrogen varied in their isotope compositions from +4 to -28‰ and from -171 to -213‰, respectively. The formation and subsequent evolution of this material since its origin in Paleogene time until present is outlined.

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.