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

International audienceGroundwaters from the Quaternary, Pliocene and Pontian layers in two adjacent basin areas of Hungary (Szeged andKörös). and from the intermediate basement high, all belonging to the central part of the Pannonian Basin, have beeninvestigated chemically and isotopically. Most of the waters are NaHCO3 type with significant quantitative and qualitativeregional differences for the Szeged and Ko¨ro¨s areas, the intermediate high, and the deepest studied lithostratigraphic zonethe 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 andintermediate areas, and during a preceding warmer period in the Körös area. Over the entire studied region, waters in thedeepest lithostratigraphic position are mixtures of paleometeoric waters and deep waters squeezed out from the thicksequence of fine-grained (Pannonian). sediments that underlie the Pontian thermal water aquifer. In the Szeged andintermediate areas, the effect of the upward seepage from the deeper (Pannonian) layers was overprinted by the recharge inthe last cold period. In the Körös area, due to the lack of infiltration during the last cold period, the mixing with Pannonianwaters is seen up to a depth of 1000 m. Based on 87Sr/86Sr ratios, water flow systems were separated. In the Szeged andintermediate areas, a shallower and a deeper flow systems were distinguished, one in the Pleistocene and Plioceneformations, and another in the Pontian layers. In the Körös area, most of the waters belong to the same flow system thatoccupies 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 87Sr/86Sr ratios