CONTENTS & ABSTRACTS
In English. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Volume 51 No. 2 June 2002
Upper Llandovery to middle Wenlock (Silurian) lithostratigraphy and chitinozoan biostratigraphy in southwestern Estonia and northernmost Latvia; 67–87
Heldur Nestor and Viiu Nestor
Abstract. The lithostratigraphy and chitinozoan biostratigraphy of the Adavere, Jaani, and Jaagarahu regional stages (upper Llandovery to middle Wenlock) in the Ikla (Estonia) and Staicele (Latvia) drill cores were studied. Most of the upper Aeronian to lower Homerian local chitinozoan biozones are represented in these cores, except Interzone III, Angochitina longicollis, Conochitina proboscifera, and Margachitina margaritana biozones, partly corresponding to barren red beds of the Velise Formation, partly to a stratigraphical gap at the Llandovery–Wenlock transition. The presence of Stricklandia laevis shows that the Rumba Formation of the Adavere Stage belongs to the Telychian. The succeeding, Velise Formation has a reduced thickness and is represented only by its lower portion. Three stratigraphical gaps were established at the boundaries of the regional stages. The hiatuses at the junctions of the Raikküla–Adavere and Adavere–Jaani stages have a considerable areal extent and stratigraphical range. Probably, they reflect global glacio-eustatic falls of sea level at the end of the Aeronian and Telychian corresponding to the glaciations in South America. A gap at the base of the Jaagarahu Stage was recognized only in the Ikla core and has local significance.
Key words: lithostratigraphy, chitinozoan biostratigraphy, stratigraphical gaps, Llandovery, Wenlock, Estonia.
New thelodont (Agnatha) and possible chondrichthyan (Gnathostomata) taxa established in the Silurian and Lower Devonian of the Canadian Arctic Archipelago; 88–120
Tiiu Märss, Mark V. H. Wilson, and Raymond Thorsteinsson
Abstract. New vertebrate taxa of Silurian and Early Devonian age from the Canadian Arctic Archipelago are established. Diagnoses, type designations, and illustrations are given for 25 new species of thelodonts and 2 new species tentatively referred to chondrichthyans. In addition, 10 new genera, 6 new families, and 1 new order of thelodonts, and 1 new family and 2 new genera of possible chondrichtyans are established. Full monographic description of all available material will be published shortly.
Key words: Canadian Arctic, Silurian, Lower Devonian, 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. Data on the jointing of sandstone outcrops located in the area from Kiidjärve to Taevaskoda along the Ahja River are presented. Joints can usually be followed along the outcrop walls up to 15–20 m in the horizontal direction. In general, due to the stratification of the sandstone complex the vertical extent of joints is considerably smaller – 1.5–3 m. Along with the dominating vertical joints, a number of dipping (35%) joints are observed, having usually a dip between 60° and 70°. The majority of joints belong to a system made up of two sets with azimuth bearings of strikes 287° and 006°. The spacing of joints along the outcrops is variable, the average distance between them being 15–20 m. The cave structures 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. Similar morphology of the caves is mostly due to the horizontally enlarging flow channel in the basal part of a joint. As a result the roof of the forming cave may collapse and give it a flat arch-shaped morphology. The research carried out in the Kiidjärve–Taevaskoda area gives a reliable basis for similar studies in other regions of Estonia.
Key words: jointing, caves, sandstone, Devonian, Estonia.
The Academician Artur Luha Prize (inside back cover)