Geology December 2004 Vol 53/4 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology



Volume 53 No. 4December 2004



Diversity of late Ordovician rugose corals in Baltoscandia: role ofenvironmental changes and comparison with other areas; 233–245

DimitriKaljo

Abstract. Regional biodiversity curves are controlled environmentallyand reveal details that can be correlated with stable isotope data, sea levelcurves, etc. This paper uses such ties for better under­standing of the environmental background of certain palaeobiologicalevents. The first appearance of rugose corals in the shelf seas ofBaltica in the Middle Caradoc seems to be linked to the warming of sea waterand climate due to the drift of the continent closer to the equator. The samefactor also favoured a further biodiversity rise in which both biology andecology should be considered. The generaldiversity rise was slowed down by repeated coolings in the late Caradoc andearly Ashgill and caused a diversitylow within the early Ashgill. Along with a favourable temperature regime,changes in oceaniccirculation, nutrient flow, and availability of suitable habitats were of greatimportance. The Hirnantian glaciation,accompanied by a pronounced sea level fall, brought about favourable conditions for coral evolution on manysubequatorial cratonic shelves, which helped corals to survive the severeconditions of the end-Ordovician glacial time. The Baltoscandian rugosecoral assemblage is the most diverse by comparison with those of Australasiaand Laurentia thanks to the abundance of old lambelasmatids living inrelatively cooler and deeper habitats.

Key words: rugose corals, biodiversity, carbon isotopes, Ordovician,Baltoscandia.



Apatite varieties in the shell of the Cambrian lingulate brachiopod Obolus apollinis Eichwald;246–256

Jüri Nemliher,Tiia Kurvits, Toivo Kallaste, and Ivar Puura


Abstract. An XRD study of heat-treatedshell samples of the lingulate brachiopod Obolusapollinis Eichwald from the upper Cambrian (Furongian) of NW Russia (basalTosna Formation, Lava River section)revealed the presence of two phases of apatite persisting the temperatures from200 to 700 °C. At higher temperatures, 900 and 1000 °C, only onephase was detected. The lattice parameters of the two phases suggestpossible preservation of carbonate-hydroxylapatite within the compact laminaeof initially organo-phosphatic lingulate shells. The formation of anotherphase, carbonate-fluorapatite, is attributed to the precipitation of apatite tothe free space available after disintegration of organic tissues of the shelland to partial recrystallization of initial shell apatite.

Keywords: brachiopods, XRD, apatite, taphonomy,Cambrian, NW Russia.

The earliest known Trypanites borings in the shells of articulate brachiopodsfrom the Arenig (Ordovician) of Baltica; 257–266

Olev Vinn

Abstract. Several specimens of the Arenig (VolkhovStage) brachiopod Antigonambonitesfrom Northwest Russia and North Estonia bear the earliest known Trypanites borings in articulate brachiopod shells. Two basic types ofborings are recorded: rare large rounded borings that penetrate the shell of the brachiopod, and abundant borings that follow theshell, almost never intersecting it. Rare shell repair marks are associatedwith some Trypanites borings.Presumably some shell-boring worms inhabited also the living Antigonambonites brachiopods, suggestingthat diverse shell boring strategies had evidently evolved by the Arenig.

Key words: Trypanites, shell borings, brachiopods,palaeoecology, Arenig, Northwest Russia, North Estonia.

Application of OSL and 10Betechniques to the establishment of deglaciation chronology in Estonia; 267–287

Anto Raukas

Abstract. The deglaciation history of Estonia has been under researchfor about a century. Despite the great numberof publications devoted to this subject and marked improvements in studymethods, many problems of topical interest have not been solved yet, especiallydue to the lack of good direct dating methods. In this paper the suitability ofOSL and 10Be dating techniques for establishing accuratedeglaciation chronology for Estonia is assessed. Turbidity and water depth, velocityof outwash streams and transport length, possible fast sedimentation at nighthours or below the ice, incorporation ofolder, unbleached particles, and other factors affected the extent of thebleaching of the TL signal in different ways, causing great variability ofdates. Surface inclination, height ofthe surface over ground, snow and vegetation cover, and evolution of waterbodies influenced the calculation ofreliable exposure ages of objects dated using the 10Be method. Itmeans that age determinations of bothglaciofluvial deposits with the OSL method and erratic boulders with the10Be method are highly problematic, especially for glaciofluvialintertill sediments where the exact genesisof deposits is unknown and for boulders, which have been in the forest, underthe waters of proglacial lakes and/or the Baltic Sea, or under snow cover for along time.

Key words: ice-marginal formations, glaciofluvial deposits, OSL dating,deglaciation chronology, erratic boulders, cosmogenic 10Be.



CHRONICLE



The Eighth Marine Geological Conference “The Baltic – 8th” (23–28September 2004); 288–290

Igor Tuuling



CopyrightTransfer Agreement; 291

Contents ofvolume 53; 292–293