Abstract:A comprehensive study of a sandy aquifer of deltaic origin in southern Poland included water chemistry, isotopes, dissolved trace gases and transport modelling. Tritium, sulphur hexafluoride (SF 6 ) and freons (F-11, F-12 and F-113) showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer. The presence of older Holocene waters farther from the recharge areas was indicated by lack of 3 H, SF 6 contents Ä0Ð02 fmol l 1 and relatively low 14 C values. The discharge from the system is by upward seepage in the valley of a major river. Pre-Holocene waters of a cooler climate, identified on the basis of υ 18 O, υ 2 H, 14 C, Ne and Ar data, were found in some distant wells. Concentrations of N 2 , Ne and Ar determined by gas chromatography were used for calculating the noble gas temperatures, air excess needed for correction of SF 6 , and nitrogen content released by denitrification process. The time series of 3 H content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones. The derived 3 H age distributions turned out to be very wide, with mean values in the range of about 30 to 160 years. For each well with determined 3 H age, the SF 6 data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of SF 6 through the unsaturated zone, which most probably also resulted in different types of age distributions of these tracers. Freons appeared to be of little use for individual age determinations. A quantitative estimation of two-component mixing from SF 6 -3 H relations is not possible unless the travel time of 3 H through the unsaturated zone is comparable to that of SF 6 . The ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water. That ratio is a tracer-dependent function of time. Transport modelling of SF 6 tracer done with MT3D code yielded initially large discrepancies between calculated and measured tracer concentrations. Some discrepancies remained even after calibration of the transport model with SF 6 . Simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations, particularly in the eastern part of the aquifer. The existence of distinct hydrochemical zones is consistent with the tracer data; young waters with measurable 3 H and SF 6 contents are aerobic and of HCO 3 -Ca or HCO 3 -SO 4 -Ca types. Slightly elevated Na and Cl contents, as well as the highest concentrations of SO 4 and NO 3 within this zone are due to anthropogenic influences. Anaerobic conditions prevail in the far field, under the confining cover, where pre-bomb era Holocene waters dominate. In that zone, dissolved oxygen, NO 3 and U contents are reduced, and Fe, Mn and NH 4 contents increase. In the third zone, earl...

A theoretical approach towards predicting the carbon isotope composition of carbonate cave deposits is presented. The proposed model simulates time variations of both the chemical and isotopic composition of the carbonate solution and deposited calcite in the course of CaCO3 precipitation. Two phases of the precipitation process are distinguished and treated separately: initial outgassing of the solution until a certain degree of supersaturation of CO32- ions is reached and subsequent precipitation of CaCO3 related to further outgassing. Precipitation rates of CaCO3 predicted by the model agree fairly well with literature data. The model predicts δ13C values of deposited calcite within a range of ca −16 to +3‰ depending on temperature, chemical and isotope parameters of the initial solution and actual degree of the precipitation process.

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Then, in the Cretaceous, and primarily in the Cenozoic, tectonic discontinuities filled with neptunian dykes were penetrated by karst waters and by hydrothermal solutions, which partly silicified the carbonate material infilling the dykes. The formation of dykes is genetically related to the Late Jurassic, Pan-European stress-field reorganization caused by the opening of the Northern Atlantic and Tethys Oceans.