Geology March 2003 Vol 52/1 []

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of theEstonian Academy of Sciences.

Geology



Volume 52 No. 1March 2003



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

Heldur Nestor, Rein Einasto, Peep Männik, andViiu Nestor

Abstract. Stratigraphicalunits of the Juuru and Raikküla regional stages (lower to middle Llandovery) are described and correlated in the Põltsamaa, Heimtali, and Ikladrill cores. A new unit, the HeinasteMember, is established at the base of the Saarde Formation. The Distomodus kentuckyensis,Aspelundia expansa, and A. fluegeli conodont biozones, aswell as the Ancyrochitina laevaensis,Belonechitina postrobusta, Euconochitina electa, Ancyrochitina convexa, Conochitina alargada, and C. malleuschitinozoan biozones are recognized, the last two zones in both groups for thefirst time in Estonian sections. Biostratigraphical correlation by means ofchitinozoans and conodonts proves synchroneity of extensive strata of micriticlimestones recurring three times in thesequence of the Raikküla Stage. The pure, micritic limestones, almost barren ofbenthic shelly fossils, alternate with more argillaceous, nodular, biomicriticlimestones (skeletal packstones and wackestones) in the NurmekundFormation, and with marlstones or argillaceous limestones in the Saarde Formation. Alternation of micritic deposits, verypoor in benthic fauna, with argillaceous, biomicritic deposits rich inshelly fauna, suggests that such cyclicity was not directly controlled bychanges in water depth, but more likely by cyclic changes in certainbiogeochemical conditions. Alternation of arid and humid climate statessupposedly induced lime mud accumulation cycles: during humid periodsterrigenous input and freshwater runoff from the adjacent continent produced more argillaceous sediments, whereas duringthe arid periods terrigenous inputdecreased but salinity increased, causing accumulation of pure lime muds.Cyclic accumulation of lime muds inlow-latitude shallow seas was characteristic of the supposed latest Ordovician–earliestSilurian icehouse period.

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

Currentprimary pedogenesis on Devonian sandstone in southern Estonia; 28–41

Loit Reintam

Abstract. A profile of Eutric Cambisol, formedduring 50–55 years on the cross-bedded whitish-grey Devonian sandstone of theBurtnieki Stage, was studied on the excavated outcrop on the bank of the HelmeRiver at Helme, southern Estonia. The topsoil of 10 cm, being the A–Bw subsection, representsthe result of humus accumulation, pedogenetic weathering of the sand fractions,and the accumulation in situ of siltand clay in the initial sand column of 6.18 cm. Considerable loosening, accompaniedwith the upward expansion of the solum, has taken place at an annual rate of0.7–0.8 mm. As a consequence of interfraction changes,260–290 g m–2 yr–1of fine textural particles and 100–120 g m–2 yr–1 of chemical constituentshave accumulated in the thin solum, while some air deposition and surfacelateral inflow cannot be excluded. The annual input of organic carbon at a rateof 25–28 g m–2 has operated as the driving force for rapid and intensivesoil formation of accumulative origin. Fulvic acids have played a great role inthe progress of initial pedogenesis, while the formed fulvates bound withalkaline earths favour the development of accumulative phenomena. Increase inbase exchange capacity of the solum several times is the direct result ofaccumulation of humus, silt, and clay.

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

Seafloor deposits in Keibu Bay and Nõva Bay (northwestern Estonia) and theadjacent offshore area; 42–62

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

Carolyn Wegner

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

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

Instructions to authors; 63–65

Copyright Transfer Agreement; 66