Geology June 2003 Vol 52/2 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology



Volume 52 No. 2June 2003



Glauconiticrocks 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 Balticarea, having varying lithology (limestone, dolomite, dolomitic and calcareousmarlstones, and siliciclastics), geological age (Cambrian, Ordovician, Cretaceous, Palaeogene, and Neogene), and thermalhistory (weakly heated Estonian and Russiansamples, more heated Lithuanian samples, and most heated Danish and Polishsamples). It was found that the specific surface of glauconite-bearingreservoir rocks could be estimated indirectly from the potassium contentas measured by gamma spectrometry, and from magnetic susceptibility. Therelationship between the potassium content and specific surface is best definedfor a given geological age and thermal history, but is largely independent oflithology. The relationship between magnetic susceptibility and specificsurface is best defined for specific lithologiesand geological age, but is largely unaffected by thermal history. The thoriumand uranium contents as measured by gamma spectrometry gave no clearindication of specific surface.

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

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

Kaisa Mens

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

Key words: LowerCambrian, 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) andPaadla (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) andcompared with the scales from Vesiku Brook(Vesiku Beds of the Rootsiküla Stage), the type locality of the species.Paralogania kaarmisensis sp. nov. wasestablished on the basis of relatively large, strongly elongate scales carrying a row of very fine spines laterallyof the crown; the scales have one to two fine oblique ridges above the row of spines. The new species has a shortrange 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 TarmoKiipli

Abstract. Dolomites of the Upper Subformation of the Raikküla Formation(middle Llandovery), representing the deposits of the northern marginal part ofcarbonate shelf consisting of cyclically laminatedlimestone and lagoonal dolomite were studied. The formation of dolomite was investigatedusing X-ray diffraction, X-ray fluorescence, and titration analyses of therocks of the same primary origin innondolomitized sections and those affected by massive pervasivedolomitization. The CaCO3/MgCO3 ratio and latticeparameters of dolomites are in good agreement with the genesis. The primarylagoonal dolomite near the contact with limestone and dolomite in limestonehave the most expanded lattice; the primary dolomite near the contact withpervasively dolomitized limestone has the parameters equal to the minimal forprimary dolomites, registered in the centre of the layer; the most alteredsecondary dolomite is close to stoichiometric. The bimodal frequency distribution of the Ca content indolomites of different genesis reflects the preferred levels of Cauptake. The highest stoichiometry of the secondary (replacive) dolomite pointsto the role of recrystallization and crystallization rate. Compared tolimestones dolomites are depleted in Sr and enriched in Mn. Major, minor, andtrace element concentrations suggest that seawater (or modified seawater) wasthe dominant dolomitizing fluid. No evidence of hypersalinity or inflow ofoutside fluids has been observed. The direct relationship of dolomitization tothe migrating inner shelf facies and regressive stages of the evolution of theSilurian Baltic Palaeobasin suggests early dolomitization.

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

Instructions to authors; 128–130