Wgłębna budowa geologiczna podłoża południowego Bałtyku w świetle wyników zdjęcia grawimetrycznego z lat 1970-1972

Abstract

Przedstawiono badania grawimetryczne wykonane przez IGiK wspólnie z Instytutem Fizyki Ziemi AN ZSRR. w latach 1970-1972 na obszarze południowego Bałtyku. Omówiono metodykę stosowaną w zdjęciach grawimetrycznych na morzu. Podano charakterystykę zdjęcia grawimetrycznego Bałtyku. Zbadano zależności między anomaliami siły ciężkości a wgłębną budową geologiczną podłoża południowego Bałtyku.

DEEP GEOLOGICAL STRUCTURE OF THE SOUTHERN BALTIC BASE IN THE LIGHT OF GRAVIMETRIC SURVEYS FROM THE YEARS 1970-1972

The Institute of Geodesy and Cartography in Warsaw and the Earth Physics Institute of the USSR organized four gravimetric expeditions on the southern Baltic Sea in the years 1970-1972. The expeditions, aimed at surveying the gravity field, have covered a belt 100 km wide along the whole Polish coast.

The paper deals with the methodology of gravity surveys on sea with the use of both bottom and shipboard gravimeters. Moreover, accuracy of measurements taken using both types of gravimeter is given and the factors responsible for reducing accuracy of the measurements are listed.

The southern Baltic was surveyed using gravimeter GAE.-M and location systems Decca and Sea-fix. The whole area studied was covered by measurements with mean density 1 point per 5 Mm² and a·selected sector 1300 km² in area - by measurements with mean density 1 point per 1.4 Mm².

The studies made it possible to gather data characterizing points 1.7 Mm distant from one another at the average. After adjustment errors of gravity acceleration at a given point were equal ± 1.6 mGal and ±0.6 mGal for the whole area studied and the semidetailed map of the Łeba - Rozewie area, respectively. The materials were subsequently used for drawing sketch map of Faye gravimetric anomalies of the southern Baltic Sea (Fig. 1).

The sketch map together with geological elaborations for the area studied and the data concerning neighbouring land areas as well as the results of interpretation of Danish gravimetric survey of the area between Scania and Bornholm made the basis for drawing map of deep geological structure of the southern Baltic area (Fig. 2). On the map there are distinguished: 1 - Zechstein-Mesozoic anticlines or synclines responsible for elongated, NW-SE oriented gravimetric lows and highs, 2 - elevations and depressions in the top of Precambrian crystalline basement, responsible for lows and highs without dominating orientation, 3 - faults zones or contacts of lithological complexes · differing in density in the crystalline basement, which are reflected by zones of high horizontal gravity gradients. On the background of the Ustka high connected with the Łeba elevation there are marked bends of isoanomalies which reflect local gravity anomalies presumably related to lithological differentiation in crystalline basement.