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GEOPHYSICAL INVESTIGATION OF THE NEAR SURFACE GROUNDWATER FLOW IN THE AREA OF MELEDIC PLATEAU (BUZAU COUNTY, ROMANIA): PRELIMINARY RESULTS

I. Fikos

Abstract

In the East Carpathians Bend region (Romania), a salt formation was deposited during the lowermost Miocene (Aquitanian-Burdigalian). Subsequently, the salt reached present-day structural positions by diapiric piercing of the overlying sedimentary deposits. As a result, a multitude of isolated ? although quite large - outcrops of salt diapirs are encountered nowadays. In this complex geological setting, a great number of salt karst phenomena occur, generating dolines, sinkholes and salt caves. The surface topography is highly affected by the underground rapid salt dissolution (subrosion), leading to depression or sudden collapse. The particular setting of this area is given by the presence of quite extended freshwater ponds (up to 10,000 m2) accumulated on the detritic cap rock of several salt diapirs, while salt springs and caves formed by salt dissolution are known in nearby locations. In an attempt to acquire information on the shallow groundwater preferential flow paths and the effect of the salt massif dominating the area, the survey was focused on the Meledic Plateau. Here, 47 karst cavities generated by salt dissolution are listed. Among them, one of the biggest salt caves currently explored worldwide is located not far north of the freshwater accumulation known as Meledic Lake (maximum reported depth 5.4-6.9m). The geophysical survey of the area consisted of electrical measurements by means of Electrical Resistivity Tomography (ERT) method, Induced Polarization (IP) and Self Potential (SP), performed in the area of Castle and Meledic Lakes. Digital Elevation Model was created from available data to have an enhanced model of the surface drainage. Finally, water samples were collected from 5 locations in order to identify the liquids characteristics in terms of salinity, as depicted from electrical conductivity measurements. The underground resistivity distribution, calculated from the ERT, was correlated with water conductivity data from water samples (measured in situ), while the SP variations were interpreted taking into consideration the topography of the area and the observed surface water bodies. The results reveal preferential paths of the shallow unconfined aquifer towards areas with lapies and karstic depressions. The water conductivity observations suggest that fresh water infiltrating from the lakes and ponds dissolves the salt formations and becomes rapidly brackish.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s05.104

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