Geology December 2002 Vol 51/4 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Geology



Volume 51 No. 4December 2002



An improvedgravity anomaly grid and a geoid model for Estonia; 199–214

ArtuEllmann

Abstract. A The regular1.5’ x 3’ grid of free-air gravity anomalies over Estonia iscomputed. Significant The studycomprises the improvedmentof  gravity data coverage in the Baltic Searegion induring the lapast few years.The estimated precision of the predicted anomalies is as 2.4 mGalin Estonia. The gravity anomaly grid and the geopotential model EGM96 are utilized in thecomputation of the Estonian gravimetric geoid model EST-01 by theleast squares modification of Stokes’ formula. The EST-01 geoid modelis fitted to a set of 26 high-precision GPS-levelling points, yielding anaccuracy of 3.0 cm for the post-fitting residuals, which indicates thesuitability of the EST-01 geoid modelfor many practical applications.

Key words: gravity anomaly, prediction,geopotential model, gravimetric geoid, Stokes’ formula, least squaresmodification, GPS-levelling.



Chitinozoan biostratigraphy and lithological characteristics of theLower and Upper Visby boundary beds in the Ireviken 3 section, NorthwestGotland; 215–226

Viiu Nestor, Rein Einasto, and David K.Loydell

Abstract. The lithology of the middle part of the cliffsection at Ireviken 3 is described and the succession of chitinozoans throughthe Lower and Upper Visby formations is documented. Tenchitinozoan event levels are identified, based upon appearances ordisappearances 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 sequencesis possible: level 1 may correlate with the base of the Margachitina margaritana Biozone and level 8 approximately with thebase 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 Muszyński, Kevin Klimm, andManfred Schliestedt

Abstract. This paper presents the results of geomorphological investigations ofbowl-shaped hollows in “Rezerwat Meteoryt Morasko” –Morasko Meteorite Nature Reserve – of Poland and of mineralogical studies ofrecently found meteorites and micrometeorites. The meteorite shower fellbetween 5000 and 3500 BP, forming craters in the Morasko area. The age intervalfor this event was estimated by earlier palynological and 14Cstudies. The Morasko meteorite is an iron type octahedrite (IAB group) whichshows strong reheating effects. The investigated area is unique, because thematerial from space and the geomorphological effects of its fall can beidentified there.

Key words: meteorite craters,iron meteorite, micrometeorites, Morasko, Poland.

Vegetation history and human impact in the Parika area, CentralEstonia; 241–258

Eve Niinemets, Leili Saarse, and Anneli Poska

Abstract. In order to reconstructthe Holocene vegetation history of the northern part of the Võrtsjärv Lowland,a sediment sequence was collected from the Parika bog and analysed for fossilpollen. Peat started to accumulate at the beginning of the Holocene. Peatincrement has been more intensive since 1400 uncalibrated 14C BP(peat increment 1.47–1.60 mm yr–1) and slowest between6600 and 5000 BP (0.40 mm yr–1). Recorded vegetationdevelopment started with open birch–pine woodland. Temperate mixed forest wasestablished before 7600 BP. The proportion of broad-leaved forest wasmodest throughout the Holocene. Specific to the Parika diagram is the highfrequency of spruce since 4800 BP. Palynological and archaeologicalrecords indicate that the Võrtsjärv Lowland was inhabited during theMesolithic. 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) startedat the end of the Pre-Roman Iron Age. The Parika bog is considered to be a newbiostratigraphic 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