Hydrothermal dolomitization of basinal deposits controlled by a synsedimentary fault system in Triassic extensional setting, Hungary

Dolomitization of relatively thick carbonate successions occurs via an effective fluid circulation mechanism, since the replacement process requires a large amount of Mg-rich fluid interacting with the CaCO3 precursor. In the western end of the Neotethys, fault-controlled extensional basins developed during the Late Triassic spreading stage. In the Buda Hills and Danube-East blocks, distinct parts of silica and organic matter-rich slope and basinal deposits are dolomitized. Petrographic, geochemical, and fluid inclusion data distinguished two dolomite types: (1) finely to medium crystalline and (2) medium to coarsely crystalline. They commonly co-occur and show a gradual transition. Both exhibit breccia fabric under microscope. Dolomite texture reveals that the breccia fabric is not inherited from the precursor carbonates but was formed during the dolomitization process and under the influence of repeated seismic shocks. Dolomitization within the slope and basinal succession as well as within the breccia zones of the underlying basement block is interpreted as being related to fluid originated from the detachment zone and channelled along synsedimentary normal faults. The proposed conceptual model of dolomitization suggests that pervasive dolomitization occurred not only within and near the fault zones. Permeable beds have channelled the fluid towards the basin centre where the fluid was capable of partial dolomitization. The fluid inclusion data, compared with vitrinite reflectance and maturation data of organic matter, suggest that the ascending fluid was likely hydrothermal which cooled down via mixing with marine-derived pore fluid. Thermal gradient is considered as a potential driving force for fluid flow

Hydraulic evaluation of the hypogenic karst area in Budapest (Hungary)

The Buda Thermal Karst area, in central Hungary, is in the focus of research interest because of its thermal water resources and the on-going hypogenic karstification processes at the boundary of unconfined and confined carbonates. Understanding of the discharge phenomena and the karstification processes requires clarification of the groundwater flow conditions in the area. Consequently, the aim of the present study was to present a hydraulic evaluation of the flow systems based on analyzes of the archival measured hydraulic data of wells. Pressure vs. elevation profiles, tomographic fluid-potential maps and hydraulic cross sections were constructed, based on the data distribution. As a result, gravitational flow systems, hydraulic continuity, and the modifying effects of aquitard units and faults were identified in the karst area. The location of natural discharge areas could be explained and the hydraulic behavior of the Northeastern Margin Fault of the Buda Hills could be determined. The flow pattern determines the differences in the discharge distribution (one- and two-component) and related cave-forming processes between the Central System (Rózsadomb area) and Southern System (Gellért Hill area) natural discharge areas. Among the premises of hypogenic karstification, regional upward flow conditions were confirmed along the main discharge zone of the River Danube. The flow pattern determines the differences in the discharge distribution (one- and two-component) and related cave-forming processes between the Central System (Rózsadomb area) and Southern System (Gellért Hill area) natural discharge areas. Among the premises of hypogenic karstification, regional upward flow conditions were confirmed along the main discharge zone of the River Danube. The flow pattern determines the differences in the discharge distribution (one- and two-component) and related cave-forming processes between the Central System (Rózsadomb area) and Southern System (Gellért Hill area) natural discharge areas. Among the premises of hy