Geology June 2002 Vol 51/2 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology



Volume 51 No. 2June 2002



Upper Llandovery to middleWenlock (Silurian) lithostratigraphy and chitinozoanbiostratigraphy in southwestern Estonia and northernmost Latvia; 67–87

Heldur Nestor and Viiu Nestor

Abstract. The lithostratigraphy andchitinozoan biostratigraphy of the Adavere, Jaani, and Jaaga­rahu regionalstages (upper Llandovery to middle Wenlock) in the Ikla (Estonia) and Staicele(Latvia) drill cores were studied. Most of the upper Aeronian to lower Homerianlocal chitinozoan biozones are represented in these cores, except InterzoneIII, Angochitina longicollis, Conochitina proboscifera, and Margachitinamargaritana biozones, partly corresponding to barren red beds of the VeliseFormation, partly to a stratigraphical gap at the Llandovery–Wenlocktransition. The presence of Stricklandialaevis shows that the Rumba Formation of the Adavere Stage belongs to the Telychian. The succeeding, Velise Formation hasa reduced thickness and is represented only by its lower portion. Threestratigraphical gaps were established at the boundaries of the regional stages.The hiatuses at the junctions of the Raikküla–Adavere and Adavere–Jaani stageshave a considerable areal extent and stratigraphical range. Probably,they reflect global glacio-eustatic falls of sea level at the end of theAeronian and Telychian corresponding to the glaciations in South America. A gapat the base of the Jaagarahu Stage was recognized only in the Ikla core and haslocal significance.

Key words: lithostratigraphy, chitinozoanbiostratigraphy, stratigraphical gaps, Llandovery, Wenlock, Estonia.

New thelodont (Agnatha) andpossible chondrichthyan (Gnathostomata) taxa established in the Silurian andLower Devonian of the Canadian Arctic Archipelago; 88–120

Tiiu Märss, Mark V. H. Wilson, and RaymondThorsteinsson

Abstract. New vertebrate taxa ofSilurian and Early Devonian age from the Canadian Arctic Archipelago areestablished. Diagnoses, type designations, and illustrations are given for 25new species of thelodonts and 2 new species tentatively referred tochondrichthyans. In addition, 10 new genera, 6 new families, and 1 new order ofthelodonts, and 1 new family and 2 new genera of possible chondrichtyans areestablished. Full monographic description of all available material will bepublished shortly.

Key words: Canadian Arctic, Silurian, LowerDevonian, thelodonts (Agnatha), chondrichthyans(Gnathostomata).

Joint systems in Devonian sandstones in the Kiidjärve–Taevaskoda area, south-eastern Estonia;121–132

Enn Pirrus, Anne Kleesment, and Margus Sööt

Abstract. Dataon the jointing of sandstone outcrops located in the area from Kiidjärve to Taevaskoda along the Ahja River are presented. Joints can usuallybe followed along the outcrop walls up to 15–20 m in the horizontaldirection. In general, due to the stratification of the sandstone complex thevertical extent of joints is considerably smaller – 1.5–3 m. Along withthe dominating vertical joints, a number of dipping (35%) joints are observed,having usually a dip between 60° and 70°. Themajority of joints belong to a system made up of two sets with azimuth bearingsof strikes 287° and 006°. The spacing of joints along the outcrops is variable,the average distance between them being 15–20 m. The cavestructures of suffosional origin are formed mainly at the intersections of tilted and vertical joints.Because of the limited vertical extent of joints, most caves have a low arch-shaped cross section. Similarmorphology of the caves is mostly due to the horizontally enlarging flowchannel in the basal part of a joint. As a result the roof of the forming cavemay collapse and give it a flat arch-shaped morphology. The research carriedout in the Kiidjärve–Taevaskoda area gives a reliable basis for similar studiesin other regions of Estonia.

Key words: jointing, caves, sandstone, Devonian, Estonia.



CHRONICLE



The Academician ArturLuha Prize (inside back cover)