HYDROGEOLOGICAL DATA FROM SE TRANSDANUBIA AS A PART OF MARGINAL AREA OF THE GREAT HUNGARIAN PLAIN AND DRAVA BASIN DE. M. KASSAI*-Â. LOBBBBEB**—L. R6NAKI***-DB. T. SZEDERKÉNYI* * Hungarian Geological Institute, Regional Geological Service, Pecs, Hungary. ** Research Institute for Water Resources Development, Budapest, Hungary. *** Mecsek Ore Mining Company, Pecs, Hungary. Geological review of SE Transdanubia The area of SB Transdanubia is geologically divided into four parts according to the structure of the pre-Tertiary basement and thickness of covering Neogene deposits. On the pre-Tertiary basement contour map (Fig. 1) —which can be regarded as a Neogene isopach map—the following distinct parts are recorded : a) The Neogene Depression of Drava Basin. Thickness of the Neogene sequence increases from 1000 m up to 3500 m showed a fairly uniform SW trend. The basement of this area is generally composed of Precambrian meta- morphic rocks. This depression—as a great basin—is the subject of our detailed investigation. b) The area of Mecsek — Villâny Anticline. Thickness of the Neogene de­ posits on the highland areas goes from 0 m to 500 m but on the southeastern and northwestern flanks of the anticline they enlarge from 500 to 1000 m thickness. This situation of the anticline is motivated by the trench of the "Mecsekalja Tectonic Belt" filled up by more than 500 m thick Neogene deposits. The core of the anticline consists of Precambrian metamorphic rocks, granites and Late Paleozoic sedimentary formations. The bottom part of the flanks consists of Mesozoic cavernous carbonate rocks (see Fig. 2). c) Neogene trench-like area between Liget- and Ellend Basin. Thickness of the Neogene sequences of both basins surpasses at least 1000 m. The bottom part is generally composed of karstic carbonate rocks. This Neogene tectonic zone is located to the area of so-called "Villâny —Szalatnak Paleozoic Deep Fracture Zone" and it is regarded as a Neogene renewal of the Late Paleozoic movements. This area is isolated from the great basin, therefore further details are omitted. d) The area located to the east from the Villâny—Szalatnak Paleozoic Deep Fracture Zone where some strips of the rocks can be found with particular geological structures, bordered by fractures striking NE —SW direction. This area is also separated from the great basin. Concluded from the mean-thickness distribution of the Neogene deposits 26 MAFI Évkonyv s. V + V 9, \ + + ^à\ \v+ + \ v"i'\ N. + + sH\ \> MÈ2 404 as well as tectonic inference, the main tectonic zones of the investigated region are the following ones : 1. NW —SE striking fracture zone at the eastern border of Drava basin, which is a notable water-flow zone too. This gives a possibility for fundamental inferences related to the investigation of great basins. 2. Tectonic zones with NE — SW trend represented in the area of Mecsek — Villâny anticline (Villâny Mts. and northern side of Mecsek Mts) as [well as trench-depression of "Mecsekalja Tectonic Belt". 3. NW—SE striking Neogene tectonic zone coinciding with "Villâny — Szalatnak Paleozoic Deep Fracture Zone" having some tectonic elements which are deeply wedged into pre-Tertiary basement. 4. Tectonic zones having a NE—SW trend which are located to the eastern part of the area. Hydrodynamie investigations of the deposits j)f Drava "great basin" Neogene deposits of the young depressions of the examined area are rather uniform. The basement is overlying by predominantly impermeable Middle Miocene clayey-marls, clayey-calcareous sandstones, tuffs and lavas, as well as a Lower Pannonian sequence; and all these at several localities have some separated sandstone lenses with concentrated salty-water content. The oil-prospecting boreholes explored Badenian "Leitha limestone" lenses above the uplifted basement frequently containing waters of extremely high pressure. In loose and porous sandstones Of the Upper Pannonian complexes there are utilizable thermal waters as reservoir fluids with low salinity. In the investigated area such an aquifer is drained by the well of Pettend, village supplying artesian water of 39.5 °C temperature. Similar water quality has the thermal water of Sellye, with 48 °C temperature. According to many signs near to the surface, the Upper Pliocene and Pleistocene formation waters and phreatic ones form a single, continuous porous water-bearing formation. Salt content of the Upper Pannonian layers is the same as the sea-water, however, in the lower part of the Upper Pannonian stage brackish-water can be found, during the upflow it changes gradually into fresh-water (B. KLEB 1973). According to the geoelectric soundings carried out on the area, the "regionally impermeable floor" of the coarse-grained complexes near the surface is more or less on the level of the lignite beds of Upper Pannonian complex, which at the same time is the boundary between salty and fresh-water. (See on the hydrogeological cross-section Pig. 3. designat­ ed with "A—B", marked by a resultant line.) Relationship among aquifers occurring in different depths was examined for the first time by method of continual approaches after E. ALMÂSSY (1962). It was established that static pressure of the Quaternary, Levantian and several Upper Pannonian beds of the area shows regular alternations which have relationship with morphology of the "impermeable floor" of the porous complex. Above the uplifted basement the static water levels of the deeper wells are lower-, and on the depression they are higher than the static water- levels of the shallow wells. The static level setting in at different points of the 405 aquifer complex, or formation pressure-values are belonging to the hydrostatic pressure state. The vector sum determined is the so-called "piezometric gradi­ ent", analogically with the hydraulic gradient, derived from the potential .theory of the seepage. When the formation pressure is measured the vertical component of the piezometric gradient is 10-Ap y, [grad uL ' y-Az yQ where Ap is the measured pressure difference in [atm], z is the difference in drainage elevation [m], v is the mean specific gravity of the water head [p/cm3], 3 y0 is equal 1.0 [p/cm ] of the specific gravity of the water on 4 °C temperature. When the specific gravity of the water is unit, then this value is directly determinable from the piezometric surfaces : Ah [grad u]2 % [grad] hz=—^ . If in some chosen horizontal planes (in the so called "drainage horizons") the values of the piezometric surfaces reduced to the water having an unit specific gravity are available (see in Fig. 4), then it can be obtained average values of the vertical components of the piezometric gradient regarding certain depth intervals as a differential quotiens of the contour lines of the suitable piezometric surface maps. Values of the horizontal components can be directly measured from the individual water level contour maps, and average values referring to the intermediate depth parts can be determined by arithmetical mean of two adjacent hjx or hjy gradient maps (I. LORBERER-SZENTES and A. LORBERER 1976). The Fig. 5. shows the differential quotiens of contour maps, namely the average values of the vertical components of the piezometric gradients between + 0 and + 50 m above Adriatic sea. On the highlands and hilly elevated areas, forming the main reproduction bases of the ground waters, the values of the gradients are negative, in the depressions they are positive, referring to the decisive horizontal flow and descendent as well as ascendent water movement. If the surface or near surface derived colder waters are descending, then the rocks which are connecting with them will be cooling down and due to the heat-extraction they will be converted into thermal waters. If ascendent water flow occurs then a heat emission will take place. Consequently, a vertical water movement is followed by local negative as well as positive geothermal anomalies due to the convective heat transport. On the map of the apparent geothermal gradients (Fig. 6) the areas of negative heat anomaly (larger than 20 m/°C value patches) generally coincide with areas of negative vertical piezometric gradients. On the area of positive heat anomalies with 10 m/°C or less values, the vertical components of the piezometric gradients are also positive. The most conspicuous common feature of the piezometric gradient and geothermal as well as water quality maps (Figs. 5—7) is the definite structural orientation. The piezometric pressure profiles (Fig. 3a and 3b) represent not only potential distribution of the investigated area, but they also give data regarding universal characteristics of the events which had taken place within the basin 406 A-A' GEOLOGICAL CROSS-SECTION - 237.5° 57.5- m .^ Drâvagârdony a.s.l. SDràvatamâsi Zador Pettend Kistamési , Szigetvâr HQ (Zsib6t) PI 9 Kastélyosdombô O.b-1 it > A M0TnY tf?' r P'--xM i _Li s_i a. ±0 -1000 —1000 -2000 - -2000 -3000 --3000 MECSEKALJA -4000 TECTONIC • -4000 BELT PIEZOMETRIC PRESSURE CROSS-SECTION a.s. 300-, «ht 200- QIX ; Dràvatamàsi 1. n.rt 100 —r ±0 - -100 -200 -300 - -400 -500 -600 -700 -800 (-2583.6) 10km Fig. 3a o CM / / /' Z z O o ZjA-ISD3d l I o CE o O ce uf ce < S 1 in o 55 -o 5 o 9F °2 H 'S3-I93ZSU3D3 \ £ ZjA'IS03d \\ m S \\ 1 i I O m N UJ \\ \0> CL v) \ \ \ \ ZIA-313X33 ,Q £ « \j >• \ \ 'S3-/.V0S2y7 / / •JLVSD-/J.r3A._ N \ "Sf » > MPtfO—- 412 deposits. Since the multiannual average value of the natural subsurface flow conditions can be regarded constant, the potential distribution represented by water level contour maps and piezometric pressure profiles, corresponds to the permanent seepage condition. With respect to the flow conditions, most decisive proofs are provided by local geothermal anomaly which can be exclu­ sively explained by convective heat-transport.