CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology

Volume 54 No. 3 September 2005

Height of the turbulent gas flow and transport distance of glassy spherules on the example of the Kaali impact, Estonia; 145–152

Anto Raukas and Kustav-Olimar Laigna

Abstract. Impact ballistics of the Kaali impact group has been considered by a number of authors giving extremely different interpretations. The exact time of the impact is also debatable, but according to direct dates the age of the craters is at least 4000 years. Spherule studies in the mires of the islands of Saaremaa and Hiiumaa show that the impact took place some 7600 years ago. As the more or less vertical gas stream could have reached a height of 6.8–7.9 km, the small glassy particles, often hollow inside, were easily transported over long distances.

Key words: emitted gas flow, Kaali impact, crater age, spherule transportation.

Lithology and evolution of Devonian carbonate and carbonate-cemented rocks in Estonia; 153–180

Anne Kleesment and Alla Shogenova

Abstract. The Devonian sedimentary sequence of Estonia is mainly composed of terrigenous rocks, but includes also carbonate and mixed carbonate-siliciclastic rocks. The accumulation of siliciclastic sediments has recurrently alternated with carbonate sedimentation. Carbonate rocks are best represented in the Narva Regional Stage where they are fully dolomitized. In addition to pure dolostones, dolomitic marlstones, and siliciclastic sediments, mixed carbonate-siliciclastic rocks were recorded in six studied drill cores (Ruhnu (500), Taagepera, Tartu (453), Valga (10), Võru, and Värska (6)). Mixed rocks were deposited in transitional tidal flat conditions of shallow epicontinental sea during simultaneous accumulation of carbonate and siliciclastic material. They include also terrigenous rocks cemented by dolomite during diagenesis. According to mineralogical, petrographical, and geochemical data, early diagenetic dolostones and dolomitic marlstones were deposited in the shallow nearshore tidal flat environment in the sea water saturated with Mg, but changed in the next stages of diagenesis. Siliciclastic rocks were cemented during middle and late diagenesis by Mg- and Mn-enriched fluids. Sometimes cement of siliciclastic and mixed rocks is represented by gypsum and late diagenetic calcite. The porosity of Devonian rocks increases with increasing clay content, and decreases with mechanical compaction, dolomitization, and carbonate cementation. The sedimentation and diagenetic history are reflected in gamma-ray logs.

Key words: Devonian, carbonate rocks, siliciclastic rocks, mixed rocks, chemical composition, diagenesis, X-ray diffractometry, porosity, gamma-ray logs.

Thelodont Oeselia mosaica gen. et sp. nov. from the Wenlock and Ludlow of the East Baltic; 181–190

Tiiu Märss

Abstract. A thelodont Oeselia mosaica gen. et sp. nov. is described from the Upper Wenlock and Lower Ludlow (Silurian) of Estonia and Latvia. The species has very small to small scales and shows low variation in scale morphology, simple branching dentine tubules, and a specific ultrasculpture with polygons of irregular shape, separated by narrow grooves.

Key words: Thelodonti, Agnatha, Silurian, East Baltic.

Recent investigations of the peculiarities of Vilnius relief dynamics; 191–203

Regina Morkūnaitė and Algimantas Česnulevičius

Abstract. The paper presents data about landslides which occurred in 2000, 2001, and 2002 usually after autumn or spring rainfalls (for example in June 2001 after the rainfall of 19.8 mm and in August after the rainfalls of 29.8 and 37.9 mm). In terms of the surrounding relief genesis, sediments, and character of morphometry, landslides occurred in erosional relief (60%) and in sandy loam sediments (80%). Landslides were the most frequent in small high hills (height over 20 m, slope length more than 100 m, slope angle over 7°). Changes along seven levelling profiles, located in the erosional, ice-marginal formations, and glaciofluvial relief types, are considered. Erosional transformations mostly took place in the upper and lower parts of the slopes, where up to 0.35 m of sediments were eroded or accumulated in two years. According to the relief stability coefficient (4.6), the Rasos–Ribiškės area was erosionally the most active.

Key words: landslide, slope stability, suffosion.

Instructions to authors; 204–206