CONTENTS & ABSTRACTS
In English. Summaries in Estonian
Proceedings of theEstonian Academy of Sciences.
Geology
Volume 53 No. 2June 2004
Effect of the GRACE satellite mission on gravityfield studies in Fennoscandia and the Baltic Sea region; 67–93
ArtuEllmann
Abstract. It is customary to utilize the Earth’s artificial satellites fordetecting long-wavelength componentsof the Earth’s gravity field. The tracking data of the GRACE twin-satellitesare the basis of the new geopotential model GGM01, released by the Centre forSpace Research at the University of Texas in July
2003. The present paperassesses the quality of the GGM01 model through comparisons with an earlier geopotential model (EGM96). Themethod of spherical harmonic expansions is used in numerical investigations.The results of evaluation in Fennoscandia and the Baltic Sea region illuminate the discrepancies between thelong-wavelength contributions of the models,which may reach several decimetres in the geoidal heights. Thus, even in thegravimetrically well studied arealike the Baltic Sea region, the new satellite gravity missions may improve the gravity data significantly. Tests withhigh-precision GPS-levelling data indicate the offsets between global geoidmodels and national vertical datums in the Baltic Sea region. The gravityanomaly grid and the GGM01 model are utilized in the computation of theEstonian gravimetric geoid model by theleast squares modification of Stokes’ formula. The new model EST-03 is fittedto a set of 26 high-precision GPS-levelling points, yielding a root meansquare error of 3 cm for the post-fitting residuals. This order ofdiscrepancies is sufficient formany practical and scientific applications.
Redox changes in the deep shelf of the East BalticBasin in the Aeronian and early Telychian (early Silurian); 94–124
EnliKiipli
Abstract. Aeronianblack shales and overlying Telychian greenish-grey and red claystones of thedeep shelf of the East Baltic Basin indicate different synsedimentary redoxconditions of the bottom water of the sea. In the Aeronian, the primarybioproductivity rise caused accumulation of organic-rich black shale in deepshelf and formation of microcrystalline limestone with chertification, chert nodules, and barite in shoreward areas. In theearly Telychian, the bioproductivity decreased, as concluded from theabsence of indicators of high primary bioproductivity in the Aeronian. The suggested mechanism regulating primarybioproductivity and oxygen content of bottom waters of deep shelf was a change from wind-inducedupwelling in the Aeronian to downwelling in the Telychian. The sedimentation rate did not influence the change in theredox regime of the deep shelf sediment, as it was low for both theAeronian and Telychian.
Revision of the Ordovician cheirurid trilobite genusReraspis with the description of theearliest representative; 125–138
Helje Pärnaste
Abstract. Themorphology of Reraspis Öpik, 1937 isreviewed and compared with other cyrtometopinines. Species previously referredto Reraspis are discussed and thegeneric composition is revised. Reraspis ranges from the Kunda (lower MiddleOrdovician) to the Oandu (middle Upper Ordovician) Stage. It occurs in northernEstonia, Russia, and central Sweden (Dalarna). The earliest representative ofthe genus is the new species Reraspisorvikui from the Pakri Sandstone of Väike-Pakri Island, NW Estonia. Thegenus also includes the type species R. plautini(Schmidt, 1881), R. latifrons (Warburg,1925), and possibly R. kaljoi Männil,
1958. Specimensfrom the Keila Stage of Estonia, originally referred to as Ceraurinella? cf. latifrons,are rather similar to R. latifrons andmay either prove conspecific or closely related. Hemisphaerocoryphe? rosenthali(Schmidt, 1881) and Reraspis? kaljoi Männil,1958 share several characters with Reraspisand Cyrtometopella Nikolaisen, 1961, but a safe generic assignmentrequires better knowledge of the latter genus, especially concerning thepygidia. Reraspis? sexermis Öpik, 1937 is better assigned to Xylabion Lane,
1971. The closely similar X. helgoeyense (Nikolaisen, 1961) may constitute a juniorsynonym. Remipyga? sp. sensu Männil, 1958, [ = Xylabion sp.(Männil)] is also very closely related to Xylabionglaber. All three may in turn provejunior synonyms of Xylabion glaber(Angelin, 1854).
