3D gravity interpretation of the pre-Tertiary basement in the intramontane depressions of the Western Carpathians: a case study from the Turiec Basin

Abstract

Abstract New results related to the thickness and density of the sedimentary fill of the Turiec Basin allowed us to construct the first original stripped gravity map for this typical intramontane Neogene depression of the Western Carpathians. The stripped gravity map of the Turiec Basin represents the Bouguer gravity anomalies corrected for the gravity effect of the density contrast of its Quaternary-Tertiary sedimentary basin fill. It means that the map reflects the gravity effects of the density inhomogeneities which are located beneath the sedimentary basin fill. This map is therefore suitable for the interpretation of the structure and composition of the pre-Tertiary basement. Based on the new data analysis, two different density models of the sedimentary fill were constructed. The 3D density modelling was used to calculate the gravity effect of the density models. The stripped gravity maps were produced by subtracting the density model gravity effects from Bouguer anomalies. The regional trend was also removed from the stripped gravity maps. The residual stripped gravity maps were consequently used for geological interpretation of the pre-Tertiary basement of the Turiec Basin. The pre-Tertiary basement of the Turiec Basin can be divided into northern and southern parts due to its gravity characteristics. Furthermore the northern part can be split into two domains: western and eastern. The crystalline basement of the western domain is probably formed by the Hercynian crystalline basement of the Tatric Unit. In the eastern domain the basement could consist mostly of the Mesozoic complexes of the Fatric Unit. The southern part of the pre-Tertiary basement of the Turiec Basin is built predominantly by Mesozoic complexes of the Hronic Unit. It is suggested that the Hronic Unit also forms the bedrock of the volcano-sedimentary complex of the Kremnické vrchy Mts. The resultant stripped gravity maps and the map of total horizontal gravity gradients have also proven to be very useful for the interpretation of faults or fault systems in the study area. Various faults, particularly of NNE-SSW and NW-SE directions were discovered. The analysis of the faults indicates clearly that the contact of the Turiec Basin with the Malá Fatra Mts and the Veľká Fatra Mts is tectonic.