CONTENTS &
ABSTRACTS
In English. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Geology
Volume 50 No. 1
March 2001
Editorial; 3–4
Facies and stratigraphy of the middle Caradoc
mixed siliciclastic-carbonate sediments in eastern Baltoscandia; 5–23
Leho AINSAAR and Tõnu MEIDLA
Abstract. The middle Caradoc sedimentary facies transitions and dynamics in southern Estonia and the Gotland area in the Keila, Oandu, and Rakvere stages are described. Grain size analysis of the noncarbonate component demonstrates differences between the major confacies belts. A new name, the Variku Formation, is proposed for a rock unit of intercalating quartzose siltstones, claystones, and marls in southern Estonia, and the late Keila to Rakvere age of this unit is suggested by ostracode data. The change of the deposition type in the Caradoc Baltic Basin lasted for a considerable time and can be characterized by a sequence of successive climatic, isotopic, and eustatic events and change in sedimentary material input. Complex reasons related to the continental drift and continental glaciation are proposed for the Caradoc turnover.
Key words: Ordovician, Caradoc, lithofacies zones, mixed
siliciclastic-carbonate sediments, Estonia, Sweden.
Lithostratigraphy
and distribution of tills in the Saadjärve Drumlin Field, east-central Estonia;
24–42
Maris RATTAS and Volli KALM
Abstract. Middle and Upper Pleistocene till beds with stratified glaciofluvial and glaciolacustrine deposits constitute the structure of the drumlins in the Saadjärve Drumlin Field. The only interglacial deposits of the area belong to the Karuküla Formation (Holsteinian) at the distal end of the drumlin field. The differences in grain-size distribution, mineralogical and chemical composition are regarded as confirmation of the crucial role of compositional characteristics in determining the stratigraphy of these tills. Analysis shows that the Upper Sangaste (Elsterian) till, the oldest in the area, as well as the Valgjärve (Lower Weichselian) and Võrtsjärve (Upper Weichselian) tills have distinct compositional characteristics. The Lower and Upper Ugandi (Saale glaciation) tills have no lithological differences; thus there may be only one Saalian till in the area. The stratigraphy and distribution of tills in the Saadjärve Drumlin Field proves an accretionary origin of these drumlins. They started to form during Saale glaciation and the formation process lasted for several glacial advances.
Key words: till, lithology, stratigraphy, drumlin, Saadjärve Drumlin Field, Estonia.
The shell structure and mineralogy of Mickwitzia (Lingulata: Brachiopoda) from the Lower Cambrian Kakumäe
Beds of Estonia; 43–50
Jüri NEMLIHER
Abstract. XRD analysis shows that phosphatic pebbles and Mickwitzia valves from the Kakumäe Beds consist of apatite, pyrite, and quartz. The apatite of valves is well crystallized F-apatite with a moderate carbonate content (0.2–3.4%). The lattice parameter a of F-apatite ranges from 9.345 to 9.367 Å and c from 6.881 to 6.887 Å. Pebbles contain the same apatite variety. Although the valve sculpture is variously preserved, the shell structures appeared to be lost. Shells consist of apatite-cemented quartzose silt and sand. The observed structure and mineral composition have formed via phosphatization of a primarily organic-rich shell.
Key words: Lingulata, shell apatite, shell structure, Lower Cambrian.
Spread of
broad-leaved trees in Estonia; 51–65
Leili SAARSE and Siim VESKI
Abstract. The spread of broad-leaved trees (Ulmus, Tilia, Quercus, Fraxinus, Carpinus, and Fagus) is reviewed on the basis of 46 radiocarbon dated pollen diagrams from lake and mire sediments from Estonia. Ulmus immigrated into Estonia in the second half of the Pre-Boreal, expanded between 9000 and 7800 BP, and reached its maximum values 7900–4200 BP. The immigration of Tilia began between 8800 and 6200 BP; it expanded at 8200–5200 BP, and culminated between 7200 and 4000 BP. Quercus was the next tree to arrive in Estonia, about 7900–7500 BP. Oak spread between 6800 and 4000 BP, with a maximum intermittent between 4200 and 3100 BP. Fraxinus was first recorded about 6500 BP from East Estonia. Carpinus is a late immigrant which reached Estonia in the Sub-Boreal. Comparison of the immigration and expansion of elm, lime, and oak manifests their different response to climate, with elm forest being most broadly distributed between 9000 and 7000 BP, lime between 7000 and 4000 BP (forming then up to 30% of the total forest area), and oak between 4000 and 3500 BP. Elm showed a very rapid colonization from the south; the immigration of lime was more time-transgressive and took place from the south and east. Oak immigrated from the southwest and, in contrast to elm, spread very slowly. The broad-leaved forest reached its maximum density in the second half of the Atlantic and at the beginning of the Sub-Boreal. A gradual retreat of thermophilous trees started with the elm decline at about 5500–5000 BP, which was quite asynchronous, being caused by the combination of climate deterioration, anthropogenic forest clearances, and fungal diseases.
Key words: Ulmus, Tilia, Quercus, Fraxinus, Carpinus, Fagus, pollen, immigration, Holocene, Estonia.
CHRONICLE
Estonian Academy of Sciences:
Meeting the challenges for 2000–2004.
Framework of activities; 66–67