Acta Geologica 44. (2001)
1. szám - M. Kovác - A. Nagymarosy - K. Holcová - N. Hudácková - A. Zlinská: Paleogeography, paleoecology and eustacy: Miocene 3rd order cycles of relative sea-level changes in the Western Carpathian - North Pannonian basins
2 M. Kovác et al. Pronounced late Early Badenian transgression (NN5 zone) followed by highstand was observed in all Western Carpathian - North Pannonian Basins during the extensional synrift stage of the development. The late Early Badenian to Middle Badenian relative sea-level cycle, which can be correlated with the ТВ 2.4 global eustatic cycle (Haq et al. 1988) is known only from the East Slovakian Basin, where the late highstand characterized the evaporite sedimentation. The next sea level change, which can be correlated with the ТВ 2.5 global cycle (Haq et al. 1988) is proved by transgression followed by deepening of the sedimentary environment during the Late Badenian (NN6 zone). In the Vienna and Danube Basins the late Early Badenian transgression was followed by highstand conditions, which lasted until the Late Badenian. The last well-observed relative sea-level cycle, which can be correlated with the ТВ 2.6 global eustatic cycle (Haq et al. 1988; Haq 1991) was associated with the Sarmatian transgression (NN7 zone), highstand and gradual shallowing in the Early Pannonian. The Late Miocene global sea-level changes cannot be satisfyingly interpreted by means of paleoecology in the Western Carpathian basins due to their isolation and lack of relevant chrono- and biostratigraphic data in the Pannonian and Pontian deposits. Key words: Early and Middle Miocene, Central Paratethys, biostratigraphy, paleoecology, sequence stratigraphy Introduction The Neogene paleogeography of the Western Carpathian - North Pannonian region (Fig. 1), as a combination of aquatic and continental environments in the Central Paratethys, was influenced not only by geodynamic factors but also by the regional manifestations of global sea-level changes (sensu Haq et al. 1988; Haq 1991; Hardenbol et al. 1998). The proper determination of depositional systems tracts was carried out by detection of relative eustatic changes using geophysical methods and sedimentology, but the study of relative sea-level cycles based on paleoecology also played an important role (Kovác and Hudácková 1997; Kovác and Zlinská 1998; Kovác et al. 1999). Along with the estimation of onlap curves, the paleobathymetric reconstruction of sedimentary environment was carried out as well. The correlation of cycles in the respective time intervals was enabled by new bio- and chronostratigraphic data. Simultaneously, the principal rule of sequence stratigraphy was taken into account in that the reflection of a sea-level change can be strengthened, weakened or it may disappear completely, depending on the value of tectonic subsidence and the rate of sediment input (Brown and Fischer 1977; Vail et al. 1984; Posamentier and Vail 1988; Van Steen and Winkler 1988). Therefore the study of the relative sea-level cycles manifestations in the Western Carpathian - North Pannonian Basins (Figs 5, 6, 7, 8) also took into consideration, beside the global sea-level changes (Haq et al. 1988; Haq 1991), data on the tectonic subsidence and detrital input rates proved by analysis of the subsidence history (Lankreijer et al. 1995; Baráth et al. 1997; Lankreijer 1998) In the paleogeography of the Western Carpathian - North Pannonian Basins representing individual bays of the Paratethys sea during the Miocene, Acta Geologien Hungarica 44, 2001