Hydrogeochemistry in two adjacent areas in the Pannonian Basin (Southeast-Hungary)

Abstract

Groundwaters from the Quaternary, Pliocene and Pontian layers in two adjacent basin areas of Hungary (Szeged and Körös) and from the intermediate basement high, all belonging to the central part of the Pannonian Basin, have been investigated chemically and isotopically. Most of the waters are NaHCO 3 type with significant quantitative and qualitative regional differences for the Szeged and Körös areas, the intermediate high, and the deepest studied lithostratigraphic zone (the base of the Pontian stage). Hydrogen and oxygen isotopes indicate that most of the waters have a paleometeoric origin. The period of infiltration for the entire studied depth interval (75–2500 m) was within the last cold period in the Szeged and intermediate areas, and during a preceding warmer period in the Körös area. Over the entire studied region, waters in the deepest lithostratigraphic position are mixtures of paleometeoric waters and deep waters squeezed out from the thick sequence of fine-grained (Pannonian) sediments that underlie the Pontian thermal water aquifer. In the Szeged and intermediate areas, the effect of the upward seepage from the deeper (Pannonian) layers was overprinted by the recharge in the last cold period. In the Körös area, due to the lack of infiltration during the last cold period, the mixing with Pannonian waters is seen up to a depth of 1000 m. Based on 87 Sr/ 86 Sr ratios, water flow systems were separated. In the Szeged and intermediate areas, a shallower and a deeper flow systems were distinguished, one in the Pleistocene and Pliocene formations, and another in the Pontian layers. In the Körös area, most of the waters belong to the same flow system that occupies the depth interval from the base of the Pontian (about 2500 m) up to 1000 m. The two shallowest samples studied (above a depth of 1000 m) show lower 87 Sr/ 86 Sr ratios.