Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology

Volume 54 No. 4 December 2005

Slope processes at the North Estonian Klint; 209–224

Avo Miidel and Anto Raukas

Abstract. Due to the rather flat topography slope processes in Estonia are rare and fairly superficially investigated. Mass movements are often related to the North Estonian Klint – the middle part of the 1200 km long Baltic Klint. Since the basal part of the klint is dominated by Cambrian clays and Cambrian and Ordovician silt- and sandstones, which are covered with hard Ordovician carbonate rocks, different types of mass movement take place, including rock falls, rock slides, rotational slips, etc. The greatest gravitational processes occur between the Island of Osmussaar and Tiskre, and in the area extending from Kalvi to Päite. In the paper the most common types of mass movements are analysed and described.

Key words: North Estonian Klint, slope processes, mass movements, rock falls, rock slides, rotational slips, talus creep.

The Pirgu Regional Stage (Upper Ordovician) in the East Baltic: lithostratigraphy, biozonation, and correlation; 225–259

Linda Hints, Asta Oraspõld, and Jaak Nõlvak

Abstract. The Upper Ordovician Pirgu Regional Stage of the East Baltic is represented by numerous formations, which characterize the lithological variability of the rocks and are used in the geological mapping of the region. Onshore-offshore drill core profiles from northern Estonia to southern Lithuania provide data on the distribution and succession of the formations. The formations described are arranged into four groups, each comprised of units with similar and characteristic lithological composition and depositional facies. Chitinozoan biozonation and bentonite (K-bentonite) beds are used to correlate selected sections and in the facies analysis of the described formations. Special attention is paid to the age and interpretation of the Jonstorp Formation in the East Baltic and Scandinavia. Correlations of the Pirgu Stage across the East Baltic are presented, and the use of the last occurrence of the chitinozoan Acanthochitina barbata Eisenack as a marker for the lower boundary of the stage is discussed.

Key words: Upper Ordovician, Pirgu Stage, litho- and biostratigraphy, East Baltic.

The tube ultrastructure of serpulids (Annelida, Polychaeta) Pentaditrupa subtorquata, Cretaceous, and Nogrobs cf. vertebralis, Jurassic, from Germany; 260–265

Olev Vinn

Abstract. Calcitic prismatic structures occurred already in Jurassic serpulid tubes, here described in Nogrobs cf. vertebralis. In Cretaceous Pentaditrupa subtorquata (Serpulidae) the external layer of the tube has a semiregular spherulitic prismatic structure closely resembling that in the vitreous tube of recent Placostegus tridentatus but differing from the external hyaline layer of recent Ditrupa arietina (Serpulidae). The internal tube layer of P. subtorquata is presumably diagenetically altered and has a granular homogeneous structure. The prismatic structures seem to have the best preservation potential in fossil serpulid polychaetes.

Key words: serpulids, tube ultrastructure, fossilization, Jurassic, Cretaceous, Germany.

CHRONICLE

Sixth International Conference on Geomorphology in Zaragoza; 266

Anto Raukas

Contents of volume 54; 268–269