Jakościowa korelacja wyników badań sejsmicznych i grawimetrycznych w strefie Lutomiersk-Mogilno

Abstract

QUALITATIVE CORRELATION OF THE RESULTS OF SEISMIC AND GRAVIMETRIC SURVEYS IN THE ZONE LUTOMIERSK-MOGILNOSummaryThe correlation of seismic and gravimetric surveys has been made in order to obtain new information on the geological structure of the Lutomiersk-Mogilno zone, as well as to explain methodical possibilities of a better interpretation of data obtained by means of both methods. An analysis of the bulk density measurements made on drilling samples has demonstrated that, regarding the selected zone of the Mogilno-Łódź trough, relations should be expected to occur between the structure of the Zechstein-Mesozoic complex and the gravity anomalies. They result from density contrasts between the heavy Jurassic, Lower Cretaceous and early Upper Cretaceous formations and the lighter, Maestrichtian, Campanian, and Zechstein deposits.The seismic and gravimetric materials have been compiled in the form of a sketch that presents the position of the Zechstein-Mesozoic beds against the background of gravimetric residual anomalies. The qualitative analyses has been supplemented by estimated value calculations for the individual structures ascertained by seismic methods, and for the corresponding gravimetric anomalies. The analysis has demonstrated that the Mesozoic structures and the Zechstein salt structures are the main source of the local gravity anomalies considered. It has been demonstrated that in the northern part of the area, where the anomaly is more disturbed, are found anomalies characterized by greater amplitudes, the positive anomalies corresponding to anticlines, and the negative anomalies – to the adjacent synclines. There is observed here a partial compensation of positive effect, caused by the elevation of the Jurassic-Triassic rock mass, by a negative effect of the salt mass elevation found within the cores of sub-Mesozoic anticlines. The Łódź portion of the synclinorium is characterized by a phenomenon of the inversion of results obtained using both methods.It has been shown that the gravimetric interpretation in the areas distinguished by such gavimetric effects and such a complex density model, cannot give – without the knowledge of seismic data – any univocal information on the origin of local anomalies. A precise explanation of these problems is seems to be posible only due to the complex interpretation which has been presented in this paper. This attempt allowed the author to determine and to explain the main relations between the structure of the Zechstein-Mesozoic complex and the gravity anomalies.