Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology

Volume 51 No. 3 September 2002

New species of Estlandia (Clitambonitidina, Brachiopoda) in the Upper Ordovician of the East Baltic; 135–142

Michael Zuykov and Linda Hints

Abstract. A new species of the gonambonitid genus Estlandia, E. hispida, is described from the lower part of the Upper Ordovician in Estonia and northwestern Russia (Ingria). The new species differs clearly from the most similar species E. marginata (Pahlen) in the external sculpture, in having less convex valves, and in the stratigraphical distribution.

Key words: Brachiopoda, Rhynchonelliformea, Gonambonitidae, Upper Ordovician, Estonia, northwestern Russia.

Correlation of Telychian sections from shallow to deep sea facies in Estonia and Latvia based on the sanidine composition of bentonites; 143–156

Tarmo Kiipli and Toivo Kallaste

Abstract. Sanidine composition of 130 samples of bentonites from 12 sections of Telychian (some possibly Sheinwoodian) age was analysed by X-ray diffractometry for correlation purposes. Solid solution of magmatic sanidine contained 20–47% NaAlSi₃O₈ molecules. The sanidine composition is very individual for many beds and can be used successfully for correlations.

Key words: sanidine, bentonites, correlation, Silurian.

Geological history of Lake Võrtsjärv; 157–179

Tanel Moora, Anto Raukas, and Elvi Tavast

Abstract. Lake Võrtsjärv, with a surface area of 270 km², has a very complicated geological history. Proglacial lakes of different shape and size were formed in the Võrtsjärv Lowland. Due to the tectonic uplift outflows to the west closed in the Early Holocene. At the beginning of the Middle Holocene, about 7500 BP, an outflow to the east developed and little by little the lake acquired its present contours. Like many lakes in Europe, Võrtsjärv has an open eastern (leeward) and a more swampy and overgrown western (windward) bank. The bottom sediments consist mostly of sapropel (gyttja), fine sand and silt. The sediments are thicker in the southern part of the elongated lake basin where the up to 9 m thick layer of sapropel is usually underlain by 8 m of lacustrine lime. Gradual rise of water level in the southern portion of the basin is caused by land uplift, the rate of which increases towards the northwest.

Key words: glacial lakes, neotectonic uplift, outflows, sapropel, lake marl, floods.

Stable isotope and pollen stratigraphy in marl sediments from Lake Ilmjärv (central Estonia); 180–192

Jaan-Mati Punning, Tiiu Koff, Tõnu Martma, and Göran Possnert

Abstract. The aim of the present research was to reconstruct trends in the environmental changes and estimate the importance of the rapid change of d¹³C in the Boreal as a stratigraphic marker by comprehensive study of stable carbon and oxygen isotopes and pollen from the lake marl section of Lake Ilmjärv (c. 2.5 ha closed lake situated in the Vooremaa drumlin area). The d¹³C and the d¹⁸O values reached their maxima near the end of the Boreal, then dropped and were practically constant up to the top of the marl sequence c. 3000 BP. These changes were accompanied by a remarkable improvement of climatic conditions and shifts in the vegetation.

Key words: lake marl, carbon and oxygen isotopes, pollen analysis, isotope stratigraphy, Estonia.

Instructions to authors; 193–195