Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology

Volume 52 No. 1 March 2003

Correlation of lower–middle Llandovery sections in central and southern Estonia and sedimentation cycles of lime muds; 3–27

Heldur Nestor, Rein Einasto, Peep Männik, and Viiu Nestor

Abstract. Stratigraphical units of the Juuru and Raikküla regional stages (lower to middle Llandovery) are described and correlated in the Põltsamaa, Heimtali, and Ikla drill cores. A new unit, the Heinaste Member, is established at the base of the Saarde Formation. The Distomodus kentuckyensis, Aspelundia expansa, and A. fluegeli conodont biozones, as well as the Ancyrochitina laevaensis, Belonechitina postrobusta, Euconochitina electa, Ancyrochitina convexa, Conochitina alargada, and C. malleus chitinozoan biozones are recognized, the last two zones in both groups for the first time in Estonian sections. Biostratigraphical correlation by means of chitinozoans and conodonts proves synchroneity of extensive strata of micritic limestones recurring three times in the sequence of the Raikküla Stage. The pure, micritic limestones, almost barren of benthic shelly fossils, alternate with more argillaceous, nodular, biomicritic limestones (skeletal packstones and wackestones) in the Nurmekund Formation, and with marlstones or argillaceous limestones in the Saarde Formation. Alternation of micritic deposits, very poor in benthic fauna, with argillaceous, biomicritic deposits rich in shelly fauna, suggests that such cyclicity was not directly controlled by changes in water depth, but more likely by cyclic changes in certain biogeochemical conditions. Alternation of arid and humid climate states supposedly induced lime mud accumulation cycles: during humid periods terrigenous input and freshwater runoff from the adjacent continent produced more argillaceous sediments, whereas during the arid periods terrigenous input decreased but salinity increased, causing accumulation of pure lime muds. Cyclic accumulation of lime muds in low-latitude shallow seas was characteristic of the supposed latest Ordovician–earliest Silurian icehouse period.

Key words: Estonia, Llandovery, conodonts, chitinozoans, biostratigraphy, correlation, sedimentation cycles.

Current primary pedogenesis on Devonian sandstone in southern Estonia; 28–41

Loit Reintam

Abstract. A profile of Eutric Cambisol, formed during 50–55 years on the cross-bedded whitish-grey Devonian sandstone of the Burtnieki Stage, was studied on the excavated outcrop on the bank of the Helme River at Helme, southern Estonia. The topsoil of 10 cm, being the A–Bw subsection, represents the result of humus accumulation, pedogenetic weathering of the sand fractions, and the accumulation in situ of silt and clay in the initial sand column of 6.18 cm. Considerable loosening, accompanied with the upward expansion of the solum, has taken place at an annual rate of 0.7–0.8 mm. As a consequence of interfraction changes, 260–290 g m^–2 yr^–1 of fine textural particles and 100–120 g m^–2 yr^–1 of chemical constituents have accumulated in the thin solum, while some air deposition and surface lateral inflow cannot be excluded. The annual input of organic carbon at a rate of 25–28 g m^–2 has operated as the driving force for rapid and intensive soil formation of accumulative origin. Fulvic acids have played a great role in the progress of initial pedogenesis, while the formed fulvates bound with alkaline earths favour the development of accumulative phenomena. Increase in base exchange capacity of the solum several times is the direct result of accumulation of humus, silt, and clay.

Key words: primary pedogenesis, Devonian sandstone, accumulative soil processes, Cambisol.

Sea floor deposits in Keibu Bay and Nõva Bay (northwestern Estonia) and the adjacent offshore area; 42–62

Jüri Kask, Tuuli Kalberg, Aado Talpas, Klaus Schwarzer, and

Carolyn Wegner

Abstract. Grain-size distribution of sea floor deposits of Nõva Bay and Keibu Bay, northwestern Estonia, is discussed. Based on grain-size statistics, the lateral and vertical distribution of different types of bottom sediments is shown and compared for the two bays. The bottom deposits consist mostly of sand (80–100%). The proportion of silt and gravel is considerably smaller: up to 3% in Nõva Bay and up to 7% in Keibu Bay. In Nõva Bay medium sand predominates. Grain-size distribution of deposits is rather uniform and an obvious correlation exists between the occurrence of different fractions and the water depth. In Keibu Bay sand of different grain size prevails. Along the boundary between the mouths of the bays and the open sea, a belt of coarse sand runs parallel with the shoreline. Beyond this belt silt and clay are predominant.

Key words: Estonia, nearshore environment, Quaternary deposits, grain-size distribution, bottom deposits.

Instructions to authors; 63–65