Miklós Kozák

EUSTATIC AND TECTONIC/VOLCANIC CONTROL IN SEDIMENTARY BENTONITE FORMATION – A CASE STUDY OF MIOCENE BENTONITE DEPOSITS FROM THE PANNONIAN BASIN

Seven sedimentary bentonite deposits were investigated in theMiocene series of the Pannonian Basin. The following stratigraphic and genetic characteristics were significant: (1) all deposits were formed within a transgressive series of a given Miocene sequence; and (2) it is possible that the source material of the bentonites is rhyolitic, confirmed by radiometric data proving simultaneous rhyolite tuff volcanism.A detailed investigation on three lithologically different bentonite horizons within the same transgressive series was made at Sajoábaábony to determine the source material and to determine the causes of the differences. X-ray diffraction, differential thermal analysis and geochemical data of the different lithological types show that they all have rhyolitic source material, although in the case of the lowermost horizon the existence of reworked material from an underlying andesite tuff series is also presumed. The main difference is the degree of weathering. Considering the ratio between the amorphous phase and the montmorillonite, the amorphous volcanic glass can be regarded as the main source of the montmorillonite formation. The differences in the degree of alteration can be related to the changing characteristics of the tuff accumulation and the sedimentation. Transgression decreases the sedimentation rate allowing the optimal alteration of the amorphous phase. The increasing intensity of the tuff accumulation can also limit the bentonite formation because rapid deposition and burial present too little time for the optimal alteration of the amorphous phase.Summarizing the results from the stratigraphic interpretation of the bentonite deposits and from the comparative analyses of the different bentonite horizons within the same transgressive systems tract, we can state that the relationship of the tectonic-related tuff accumulation and the eustasy-related sedimentation rate can affect both the possibility of bentonite formation in macro-scale and the degree of bentonitization in micro-scale.

GEOCHEMICAL RECORDS OF A BENTONITIC ACID-TUFF SUCCESSION RELATED TO A TRANSGRESSIVE SYSTEMS TRACT – INDICATION OF CHANGES IN THE VOLCANIC SEDIMENTATION RATE

A detailed stratigraphic and facies reconstruction of a bentonitized acid-tuff succession, deposited within the transgressive systems tract of the Upper Miocene-Sarmatian Ser-3 eustatic cycle, at Sajóbábony, northern Hungary, was performed via petrographic, mineralogical and geochemical analyses. The purpose of the work was to analyze the degree of alteration of the volcanogenic sediments, as an indicator of the relative volcanic sedimentation rate. This may have an important role in indicating volcanic periods synchronous with sedimentation or reconstructing the volcanosedimentary paleoconditions. Sample pairs were collected from each bentonite and tuff layer, and, to facilitiate microstratigraphic relations, samples were collected every 10 cm within bentonite layers. Mineralogical analyses were performed by X-ray diffraction and geochemical analyses by inductively coupled plasma-mass spectroscopy.The CaO/K2O and Eu/La ratios correlate with each other and with a montmorillonite/X-ray-amorphous phase ratio, reflecting Ca and Eu incorporation associated with devitrification and smectite formation. In accordance with the current literature, these mineralogical and geochemical proxies can be related primarily to the weathering processes. Considering vertical distributions in a sequence-stratigraphic context, the Ca content and Eu/La values show that local peaks and Eu anomalies characteristic of acid tuffs show minima at flooding surfaces (FS). Within a bentonite layer, representing a single transgressive period, the repeated events of dust-tuff accumulations have been determined by K2O/CaO and La/Eu peaks, confirmed also by the Eu anomalies in the rare earth element (REE) patterns, thus leading to the conclusion that the level of alteration is closely correlated with the elimination of terrigenous input and a minimum in volcanic sedimentation rate allowing more intensive alteration of the deposited volcanic material. In the case of fine tuff beds, Eu anomalies on REE patterns reflect limited alteration at the bottom and more intensive alteration in the upper parts of the beds, reflecting the effect of infiltration of sea water into the pores.

Sustainability aspects of thermal water production in the region of Hajdúszoboszló-Debrecen, Hungary

Abstract As geothermal energy usage becomes more conspicuous the long-term effects of thermal water extraction become more significant. The greatest extent of exploitation in East Hungary occurs in the area of Hajdúszoboszló and Debrecen. The extracted thermal water is utilized mainly by their baths. In this paper, the sustainability of this system was examined with a steady state hydrodynamic model. The solid model is based on sequence stratigraphic interpretation while the hydraulic conductivity values were estimated based on the values of geophysical well-logs. The closely spaced wells cause a great subregional decrease of hydraulic head, particularly in the most intensively extracted layer, i.e. the layer of the delta front facies. The effects of extraction by the two spatial groups of wells intersect resulting in decreased profitability of subsequent wells. However, rationalizing thermal water utilization using water from shallower zones simultaneously may have beneficial effects on the yield distribution among the different layers.

Environmental Geological Examination of Chromium-Contamination in Eastern Hungary

Industrialisation in Hungary in recent decades was not accompanied by appropriate environmental regulation. The government orders protecting the geological environment were only formulated in the year 2000. After the regime change in 1989 the government undertook the rehabilitation of the contaminated areas. The regional environment protection authorities have surveyed the significant pollution sources nationally since 1995 and the remediation of 17 of the registered sites started in 1997. One of these pollution sources was the dangerous waste disposal site, operating since the 1960’s on the southwestern edge of Hungary’s second largest city, Debrecen. Our paper presents the investigations carried out on the waste disposal site. 2. Behaviour of chrome in the geological environment Amphoteric metals can be readily transported in alkaline, oxidising waters, but two geochemical processes can inhibit this movement. The first results from the presence of reducing or sulfide-rich conditions in the receiving medium, which results in the fixation of ions in, for example, relatively insoluble sulfides. A second is associated with adsorption of the ions on solid phases. According to laboratory experiments (Fule, 1995) the chromatic reduction effect of humic soil layers on chromate can reduce the impact of chromium contamination on an area. The Cr 3+ ion remains in solution under acidic conditions, while it is precipitated in the presence of CaCO3. Thus, the sorption of Cr 3+ changes with the infiltration coefficient and the carbonate content. The CrO4 2− ion reduces in the presence of organic material (e.g. soil humic substance, etc.) and

Geoinformatic background of geothermal energy utilisation and its applications in East Hungary

Powerful geothermal energy utilisation requires geoinformatic tools from potential surveying through the designing and setting of geothermal systems to certain operational tasks. However, practical data processing strongly depends on the elaboration of basic data and information, the type of the geothermal energy harvesting system and the character of the calculation demonstrated by case studies from East Hungary, in addition the usability of the resulted maps are also presented. Besides their usability for investors these maps could be refined in the location of the development before hydraulic/heat transport modelling.