Acta Geologica 40. (1997)

1. szám - R. Kemenci - M. Canović: Geologic setting of the Pre-Tertiary basement in Vojvodina (Yugoslavia) Part I.: The Tisza Mega-unit of North Vojvodina

Geology of the Tisza Mega-unit of Vojvodina 3 as far back as the last century. The results obtained to date are presented in publications given in the list of references. The crystalline schists, magmatites and the Mesozoic formations in the buried portion of the Tertiary basement have become accessible to investigation thanks to the deep wells drilled for hydrocarbon exploration. The crystalline basement and the Mesozoic deposits lie at varying depths beneath the Tertiary formations. Their burial depths range from several hundreds meters to more than 3300 m. The maximum burial depths of the Mesozoic series occur in Central and North Banat (Fig. 1). The crystalline basement was penetrated by drilling at apparent thicknesses ranging from 3 to maximum 86 m. There are no available data on actual thicknesses of most Mesozoic and of Pre-Mesozoic units. Some of the wells only reached the coarse clastic sequences of metamorphic material produced by erosion. The thickness of penetrated Mesozoic series is usually expressed in terms of several tens and less frequently of several hundreds of meters. Only five wells drilled through 1000 to 2000 m of Mesozoic. Six wells penetrated into the crystalline schists in the base of the Mesozoic. Generally, the objectives of petroleum exploration projects were the accumulations in Tertiary pools and the interest in the underlying formations was rather academic. This partially explains the lack of cores. To aggravate the situation, only a small number of cores recovered during early explorations were preserved and saved. The lack of core material set certain limitations to our investigations. More samples than available would be necessary to define the series poor in paleontological evidence or without sufficiently indicative fossil content. This statement applies principally to the basinal series which have often been drilled in survey area. Much of the core material was recovered from tectonically disturbed (crushed) series and biostratigTaphical data were difficult to acquire. The infrequent cores did not provide sufficiently reliable paleontological and isotopic geochronological data, which resulted in the lack of accurate stratigraphic interpretations. There is a certain limitation for isotopic analysis application due to the low number of cores and to the intense changes occurring <- Fig. l Geologic map of the Pre-Tertiary basement of the Pannonian Basin in Vojvodina (according to well data). From Canovic, M. and Kernend, R. (1988). 1. Upper Cretaceous, basinal facies (clastic-carbonate and flysch); 2. Lower Cretaceous, shallow-water and reef facies (Urgonian); 3-6. Lower Cretaceous, Upper and Middle Jurassic basin, pelagic and deep-water facies; 7. Lower Jurassic, basin facies; 8. Upper and Middle Triassic, various basin limestones recrystallized, partly marbled, calcschists, silificied, brecciated; 9. Upper Triassic, shallow-water fades (carbonate platform); 10. Middle Triassic, shallow-water and partly semipelagic facies; 11. Lower Triassic, shallow-water facies (clastic-carbonate and evaporite); 12. Permian-Carboniferous, shallow-water facies; 13. serpentinites; 14. gabbros; 15. diabases, spilites; 16. rhyolites; 17. granites, granodiorites; 18. migmatites; 19. crystalline schists (generally); 20. megastructural unit boundary; 21. isobaths, approximated from well data Acta Geologica Hugarica 40, 1997

Next