CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology

Volume 52 No. 2 June 2003

Glauconitic rocks in the Baltic area: estimation of specific surface; 69–86

Alla Shogenova, Ida L. Fabricius, Uffe Korsbech, Vita Rasteniene, and Saulius Šliaupa

Abstract. We studied 97 samples from the Baltic area, having varying lithology (limestone, dolomite, dolomitic and calcareous marlstones, and siliciclastics), geological age (Cambrian, Ordovician, Cretaceous, Palaeogene, and Neogene), and thermal history (weakly heated Estonian and Russian samples, more heated Lithuanian samples, and most heated Danish and Polish samples). It was found that the specific surface of glauconite-bearing reservoir rocks could be estimated indirectly from the potassium content as measured by gamma spectrometry, and from magnetic susceptibility. The relationship between the potassium content and specific surface is best defined for a given geological age and thermal history, but is largely independent of lithology. The relationship between magnetic susceptibility and specific surface is best defined for specific lithologies and geological age, but is largely unaffected by thermal history. The thorium and uranium contents as measured by gamma spectrometry gave no clear indication of specific surface.

Key words: specific surface area, specific magnetic susceptibility, U, Th, K, glauconite-bearing rocks, Baltic area, thermal history.

Early Cambrian tubular fossils of the genus Onuphionella from Estonia; 87–97

Kaisa Mens

Abstract. Two forms of agglutinated tubes referable to the genus Onuphionella Kirjanov, 1968, occur in the Lower Cambrian of Estonia. The older, Onuphionella agglutinata Kirjanov, 1968, whose tubes are coated with muscovite flakes, is found in the sandy-clayey deposits of the Lontova Stage (pretrilobite Early Cambrian). The other specimen, assigned to the Onuphionella cf. durhami Signor & McMenamin, 1988, occurs in the lowermost part of the trilobite-bearing Early Cambrian, defined as the Sõru Formation in Estonia. This form differs from O. agglutinata in the occurrence of organic matter in the tube wall and in flexible tube construction. Except Estonia, the genus Onuphionella has been reported from the Lower Cambrian of the Ukraine, Poland, and the USA.

Key words: Lower Cambrian, Estonia, body fossils, Onuphionella.

Paralogania from the Rootsiküla (Wenlock) and Paadla (Ludlow) stages of Estonia; 98–112

Tiiu Märss

Abstract. Paralogania species in the Rootsiküla (Wenlock) and Paadla (Ludlow) stages from Saaremaa Island, Estonia, were re-studied. Extremely well preserved scales of P. martinssoni (Gross) were described from Silma Cliff (Himmiste Beds of the Paadla Stage) and compared with the scales from Vesiku Brook (Vesiku Beds of the Rootsiküla Stage), the type locality of the species. Paralogania kaarmisensis sp. nov. was established on the basis of relatively large, strongly elongate scales carrying a row of very fine spines laterally of the crown; the scales have one to two fine oblique ridges above the row of spines. The new species has a short range in the Phlebolepis elegans Biozone (Ludlow, Upper Silurian).

Key words: Paralogania, Thelodonti, Agnatha, Wenlock, Ludlow, Silurian, Estonia.

Comparative study of dolomites of different genesis (Raikküla Formation, Silurian; Estonia); 113–127

Aada Teedumäe, Toivo Kallaste, and Tarmo Kiipli

Abstract. Dolomites of the Upper Subformation of the Raikküla Formation (middle Llandovery), representing the deposits of the northern marginal part of carbonate shelf consisting of cyclically laminated limestone and lagoonal dolomite were studied. The formation of dolomite was investigated using X-ray diffraction, X-ray fluorescence, and titration analyses of the rocks of the same primary origin in nondolomitized sections and those affected by massive pervasive dolomitization. The CaCO₃/MgCO₃ ratio and lattice parameters of dolomites are in good agreement with the genesis. The primary lagoonal dolomite near the contact with limestone and dolomite in limestone have the most expanded lattice; the primary dolomite near the contact with pervasively dolomitized limestone has the parameters equal to the minimal for primary dolomites, registered in the centre of the layer; the most altered secondary dolomite is close to stoichiometric. The bimodal frequency distribution of the Ca content in dolomites of different genesis reflects the preferred levels of Ca uptake. The highest stoichiometry of the secondary (replacive) dolomite points to the role of recrystallization and crystallization rate. Compared to limestones dolomites are depleted in Sr and enriched in Mn. Major, minor, and trace element concentrations suggest that seawater (or modified seawater) was the dominant dolomitizing fluid. No evidence of hypersalinity or inflow of outside fluids has been observed. The direct relationship of dolomitization to the migrating inner shelf facies and regressive stages of the evolution of the Silurian Baltic Palaeobasin suggests early dolomitization.

Key words: Silurian, dolomitization, lithology, Palaeozoic dolomite, X-ray diffraction, Estonia.

Instructions to authors; 128–130