In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 53 No. 2 June 2004


Effect of the GRACE satellite mission on gravity field studies in Fennoscandia and the Baltic Sea region; 67–93

Artu Ellmann

Abstract. It is customary to utilize the Earth’s artificial satellites for detecting long-wavelength components of the Earth’s gravity field. The tracking data of the GRACE twin-satellites are the basis of the new geopotential model GGM01, released by the Centre for Space Research at the University of Texas in July 2003. The present paper assesses the quality of the GGM01 model through comparisons with an earlier geopotential model (EGM96). The method of spherical harmonic expansions is used in numerical investigations. The results of evaluation in Fennoscandia and the Baltic Sea region illuminate the discrepancies between the long-wavelength contributions of the models, which may reach several decimetres in the geoidal heights. Thus, even in the gravimetrically well studied area like the Baltic Sea region, the new satellite gravity missions may improve the gravity data significantly. Tests with high-precision GPS-levelling data indicate the offsets between global geoid models and national vertical datums in the Baltic Sea region. The gravity anomaly grid and the GGM01 model are utilized in the computation of the Estonian gravimetric geoid model by the least squares modification of Stokes’ formula. The new model EST-03 is fitted to a set of 26 high-precision GPS-levelling points, yielding a root mean square error of 3 cm for the post-fitting residuals. This order of discrepancies is sufficient  for many practical and scientific applications.


Redox changes in the deep shelf of the East Baltic Basin in the Aeronian and early Telychian (early Silurian); 94–124

Enli Kiipli

Abstract. Aeronian black shales and overlying Telychian greenish-grey and red claystones of the deep shelf of the East Baltic Basin indicate different synsedimentary redox conditions of the bottom water of the sea. In the Aeronian, the primary bioproductivity rise caused accumulation of organic-rich black shale in deep shelf and formation of microcrystalline limestone with chertification, chert nodules, and barite in shoreward areas. In the early Telychian, the bioproductivity decreased, as concluded from the absence of indicators of high primary bioproductivity in the Aeronian. The suggested mechanism regulating primary bioproductivity and oxygen content of bottom waters of deep shelf was a change from wind-induced upwelling in the Aeronian to downwelling in the Telychian. The sedimentation rate did not influence the change in the redox regime of the deep shelf sediment, as it was low for both the Aeronian and Telychian.


Revision of the Ordovician cheirurid trilobite genus Reraspis with the description of the earliest representative; 125–138

Helje Pärnaste

Abstract. The morphology of Reraspis Öpik, 1937 is reviewed and compared with other cyrto­metopinines. Species previously referred to Reraspis are discussed and the generic composition is revised. Reraspis ranges from the Kunda (lower Middle Ordovician) to the Oandu (middle Upper Ordovician) Stage. It occurs in northern Estonia, Russia, and central Sweden (Dalarna). The earliest representative of the genus is the new species Reraspis orvikui from the Pakri Sandstone of Väike-Pakri Island, NW Estonia. The genus also includes the type species R. plautini (Schmidt, 1881), R. latifrons (Warburg, 1925), and possibly R. kaljoi Männil, 1958. Specimens from the Keila Stage of Estonia, originally referred to as Ceraurinella? cf. latifrons, are rather similar to R. latifrons and may either prove conspecific or closely related. Hemisphaerocoryphe? rosenthali (Schmidt, 1881) and Reraspis? kaljoi Männil, 1958 share several characters with Reraspis and Cyrtometopella Nikolaisen, 1961, but a safe generic assignment requires better knowledge of the latter genus, especially concerning the pygidia. Reraspis? sexermis Öpik, 1937 is better assigned to Xylabion Lane, 1971. The closely similar X. helgoeyense (Nikolaisen, 1961) may constitute a junior synonym. Remipyga? sp. sensu Männil, 1958, [= Xylabion sp. (Männil)] is also very closely related to Xylabion glaber. All three may in turn prove junior synonyms of Xylabion glaber (Angelin, 1854).