CONTENTS &
ABSTRACTS
In
English. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Geology
Volume 51 No. 4
December 2002
An improved
gravity anomaly grid and a geoid model for Estonia; 199–214
Artu
Ellmann
Abstract. A The regular
1.5’ x 3’ grid of free-air gravity anomalies over Estonia is
computed. Significant The study
comprises the improvedment
of gravity data coverage in the Baltic Sea
region induring the lapast few years.
The estimated precision of the predicted anomalies is as 2.4 mGal
in Estonia. The gravity anomaly grid and the geopotential model EGM96 are utilized in the
computation of the Estonian gravimetric geoid model EST-01 by the
least squares modification of Stokes’ formula. The EST-01 geoid model
is fitted to a set of 26 high-precision GPS-levelling points, yielding an
accuracy of 3.0 cm for the post-fitting residuals, which indicates the
suitability of the EST-01 geoid model
for many practical applications.
Key words: gravity anomaly, prediction,
geopotential model, gravimetric geoid, Stokes’ formula, least squares
modification, GPS-levelling.
Chitinozoan biostratigraphy and lithological characteristics of the
Lower and Upper Visby boundary beds in the Ireviken 3 section, Northwest
Gotland; 215–226
Viiu Nestor, Rein Einasto, and David K.
Loydell
Abstract. The lithology of the middle part of the cliff section at Ireviken 3 is described and the succession of chitinozoans through the Lower and Upper Visby formations is documented. Ten chitinozoan event levels are identified, based upon appearances or disappearances of chitinozoan taxa. Of these, all but two are considered to reflect local, rather than basinwide, changes in assemblages. Correlation of two chitinozoan event levels with Estonian and Latvian sequences is possible: level 1 may correlate with the base of the Margachitina margaritana Biozone and level 8 approximately with the base of Interzone IV.
Key words: Silurian, Llandovery, Wenlock, Visby formations, chitinozoans, conodonts, Ireviken Event, Gotland, Sweden.
Mineralogy of Morasko meteorite and the structure of the craters; 227–240
Wojciech Stankowski, Andrzej Muszyñski, Kevin Klimm, and
Manfred Schliestedt
Abstract. This paper presents the results of geomorphological investigations of bowl-shaped hollows in “Rezerwat Meteoryt Morasko” – Morasko Meteorite Nature Reserve – of Poland and of mineralogical studies of recently found meteorites and micrometeorites. The meteorite shower fell between 5000 and 3500 BP, forming craters in the Morasko area. The age interval for this event was estimated by earlier palynological and 14C studies. The Morasko meteorite is an iron type octahedrite (IAB group) which shows strong reheating effects. The investigated area is unique, because the material from space and the geomorphological effects of its fall can be identified there.
Key words: meteorite craters, iron meteorite, micrometeorites, Morasko, Poland.
Vegetation history and human impact in the Parika area, Central
Estonia; 241–258
Eve Niinemets, Leili Saarse, and Anneli Poska
Abstract. In order to reconstruct the Holocene vegetation history of the northern part of the Võrtsjärv Lowland, a sediment sequence was collected from the Parika bog and analysed for fossil pollen. Peat started to accumulate at the beginning of the Holocene. Peat increment has been more intensive since 1400 uncalibrated 14C BP (peat increment 1.47–1.60 mm yr–1) and slowest between 6600 and 5000 BP (0.40 mm yr–1). Recorded vegetation development started with open birch–pine woodland. Temperate mixed forest was established before 7600 BP. The proportion of broad-leaved forest was modest throughout the Holocene. Specific to the Parika diagram is the high frequency of spruce since 4800 BP. Palynological and archaeological records indicate that the Võrtsjärv Lowland was inhabited during the Mesolithic. During the Late Bronze Age the area was rather open. However, compared to North Estonia, agricultural land-use was delayed about 1000 years; it was restricted in area and discontinuous. Cereal cultivation (Hordeum and Triticum) started at the end of the Pre-Roman Iron Age. The Parika bog is considered to be a new biostratigraphic reference site in the northern part of the Võrtsjärv Lowland.
Key words: pollen analysis, cultural history, chronology, vegetation history, land-use.
Contents of volume 51; 259–260