Freshwater carbonate deposit, as a special phenomenon in the Danube-Tisza Interfluve, located in the centre of Hungary, is a significant geological heritage in the Carpathian Basin. At present there is not any applicable method to investigate the presence of carbonate layers in an undisturbed way, as neither vegetation nor morphological characteristics indicate unambiguously these formations. Ground-penetrating radar technology is widely used in various earth science related researches, and the number of applications is steadily increasing. The aim of the study was to determine the spatial extension of freshwater limestone using geophysical methods near Lake Kolon, Hungary. The lake, which is now a protected wetland area with opened water surfaces, was formed in the paleo-channel of the River Danube. Measurements were performed with the help of ground-penetrating radar, the results were calibrated by high spatial resolution drillings. Investigations have been made since 2012, and freshwater limestone was detected at several locations determining the more exact extension of the formation. Ground-penetrating radar proved to be an appropriate method to detect the compact and fragmented freshwater limestone layers in such an environment. However, based on the results the method can be best applied under dry soil or sediment conditions while the uncertainty of the results increases significantly as a matter of higher soil moisture. Further control measurements are necessary verified by several drillings in order to give an exact method to determine freshwater limestone.
Freshwater carbonates are unique depositions in the centre of the Carpathian Basin, with debated origin and age. Their formation on the sand covered area of the Danube-Tisza Interfluve is mainly related to lakes appearing in low lying interdune areas from time-totime. Carbonate deposition is governed by various processes, but in general it can be traced back to climatic and concomitant surface and subsurface hydrological variations. Therefore marl, limestone and dolomite layers can be a marker of environmental change. To identify the type of environmental change they may indicate absolute or numerical ages are needed. In previous studies this issue has been addressed by the means of radiocarbon dating. In the present study we attempted to bracket the age of freshwater carbonate formation with the help of optically stimulated luminescence dating and compared our results to radiocarbon data from the literature. In general, the luminescence properties of the investigated samples proved to be suitable for determining the age of the bedding and covering sediments. OSL dates confirmed previous interpretations that freshwater carbonate formation in the area could have a peak around 10,5 ka. However, the termination of the deposition could not be unambiguously determined at the present stage of the analysis. The compound geomorphology and sedimentology of the study area call for further investigations.