Zmiany gęstości w spągu trzeciorzędu i ich wpływ na możliwości poszukiwań złóż węgla brunatnego metodami geofizycznymi
Abstract
DENSITY CHANGES AT THE BASE OF THE TERTIARY AND THEIR SIGNIFICANCE FOR SEARCH OF BROWN COALS BY GEOPHYSICAL METHODS
Summary
The search for brown coal deposits in banded negative gravity anomalies is conducted assuming that Tertiary rocks are characterized by lower density than the older ones. However, analyses of density data showed that the opposite situation is fairly common in NW Poland, where density of Tertiary rocks may be higher than. that of the underlaying ones. Compilation of borehole data gave the enclosed map of differences in density of Tertiary and older rocks. The map shows distribution of zones of positive density anomalies, in which densities of Tertiary rocks are greater than those of the underlaying ones, and zones of negative density anomalies, in which the ration is opposite. At the same time the map fails to show areas which would be more or less perspective from the point of view of search for brown coal deposits. However, coal deposits may be expected in the case of banded negative gravity anomalies in the zones of positive density differences. In tum, possibilities of occurrence of coal deposits in the zones of negative density differences (i.e. zones with anomalies the nature of which remains unclear) are still to be established.
Attention should be paid to gravitational effects of the known tectonic troughs at the background of the above discussed map. The effects usually disappear at the boundary of zones of negative density differences. This may be due to disappearance of either such trough or its gravity effects in result of density inversion.
Summary
The search for brown coal deposits in banded negative gravity anomalies is conducted assuming that Tertiary rocks are characterized by lower density than the older ones. However, analyses of density data showed that the opposite situation is fairly common in NW Poland, where density of Tertiary rocks may be higher than. that of the underlaying ones. Compilation of borehole data gave the enclosed map of differences in density of Tertiary and older rocks. The map shows distribution of zones of positive density anomalies, in which densities of Tertiary rocks are greater than those of the underlaying ones, and zones of negative density anomalies, in which the ration is opposite. At the same time the map fails to show areas which would be more or less perspective from the point of view of search for brown coal deposits. However, coal deposits may be expected in the case of banded negative gravity anomalies in the zones of positive density differences. In tum, possibilities of occurrence of coal deposits in the zones of negative density differences (i.e. zones with anomalies the nature of which remains unclear) are still to be established.
Attention should be paid to gravitational effects of the known tectonic troughs at the background of the above discussed map. The effects usually disappear at the boundary of zones of negative density differences. This may be due to disappearance of either such trough or its gravity effects in result of density inversion.