Geology March 2005 Vol 54/1 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology



Volume 54 No. 1March 2005



AntoRaukas – an encyclopaedist in Estonian Quaternary geology; 3–4

Dimitri Kaljo, Avo Miidel, Leili Saarse, and AlvarSoesoo

Chronologicaldata from Estonian Pleistocene; 5–25

Volli Kalm

Abstract. Pleistocenechronostratigraphy in Estonia is based on 60 radiocarbon (14C, 14CAMS), 63 TL/OSL, and 17 10Be datings from 57 studiedsites/sections that cover a time span from approximately200 000 yr BP to the Pleistocene–Holocene chronostratigraphicboundary. For the first time all scattered data from 40 years ofchronological study into Estonian Pleistocene are presented together andcritically analysed in regard to validity of obtained ages. Half of therelatively abundant but scattered chronological data cover only the youngest5000–6000 year part of the Late Weichselian. New OSL datings, togetherwith the results of earlier palynological, carpological, and diatom studies,have invalidated almost one-third of the available 14C dates,obtained mostly in the late 1960s and 1970s. Thermoluminescence ages fromtills, available from the early 1980s, are very inconsistent within the studiedsections and are considered to be unreliable because of questionable bleachingof the TL signal. The resultsof the 10Be method, recently applied to the study of deglaciationchronology of the Estonian territory, do not contradict the earlier ageestimations. However, due to relatively large uncertainties of the method, theresults were not able to refine the existing Late-Glacial chronology in Estonia.

Key words: geochronology, Late Weichselian, deglaciation, Estonia, dating methods.

Eskersin the periphery of their distribution in North Estonia; 26–39

Reet Karukäpp

Abstract. Eskers are frequent landforms in thepalaeo-glacial erosional zone. A channelized network ofsubglacial water conduits above the nonpermeable surface is an obligatoryprecondition for esker genesis. The currentstudy supports the results of the investigations of modern high-arctic eskerformation. The structure and stratification of the esker deposits indicate fastchanges and alternation of erosion–transport–accumulation processes. The extentof esker systems over tens or hundreds of kilometres indicates theirtime-transgressive inherited genesis.

Theterritory of Estonia lies in the periphery of the esker distribution area ofthe Scandinavian glaciation. Radial eskers inEstonia consist mainly of coarse-grained deposits of local Palaeozoicbedrock. The combination of eskers and glaciokarst kettle holes orglaciofluvial plateaus and kame fields isfrequent. The ridge-like glaciofluvial topography, morphologically similar toeskers but formed in stagnant ice is specified as crevasse fillings, andis genetically related to kames.

Key words: eskers,Scandinavian glaciation, glacial topography, lithology, Late Weichselian.

Grainsize of the bottom sediments of Lake Väike Juusa (southern Estonia) as theindicator of water-level fluctuations; 40–51

Jaan-Mati Punning, Jaanus Terasmaa, and Ene Kadastik

Abstract. Surfacesediments and sediment cores from Lake Väike Juusa were studied in order to examine the dependence of the sedimentation regime on the topographyand development of the lake. Close relationship was established between thegrain size of the surface samples and depth of water at the sampling site. Thedata obtained show that in the lake the accumulation area is situated deeperthan 4.0 m. The grain size data for three sediment cores allowedreconstruction of lake-level fluctuations andtheir amplitude.

Key words: lithology, lake sediments, lake-level fluctuations,palaeolimnology, Estonia.

Palynostratigraphyof Holocene lake sediments on the Otepää Heights, southern Estonia; 52–68

Mihkel Kangur

Abstract. The pollen diagram with acceleratormass spectrometer (AMS) radiocarbon dates coveringHolocene sediments from the Otepää Heights gives a general overview of thevegetation history of the area. The pollen assemblage zones (PAZs) defined onthe pollen diagram of the Lake Väike Juusacore in general correspond to the PAZs on the stratigraphic chart of Holocenesediments in Estonia. Comparison of thepollen profile of Lake Väike Juusa with other pollen diagrams from the same area enables us to distinguishdifferences in the vegetation history induced by local factors. The mostcharacteristic differences occur in the Picea pollen content. Picea migratedto the Otepää Heights in small patchesalready at the end of the Boreal Chronozone and started to spread at the end ofthe Atlantic Chronozone. This is about 1000 years earlier than shown in the Holocene stratigraphic chart of Estonia. Alsohuman activity and forest fires in the areas surrounding the study siteshave affected the vegetation dynamics on a local scale during the last twomillennia.

Key words: pollen, palynostratigraphy, vegetation history, forest fires,southern Estonia.

Instructionsto authors; 69–71

CopyrightTransfer Agreement; 72