| Summary: | The reconstruction of hydrogeological conditions during the Late Pleistocene and Holocene has been performed for the southern part of the Baltic Artesian Basin (BAB) situated on the slope of the Belarusian-Masurian crystalline basement. The reconstruction was accomplished modelling the freezing-and-thawing of the subsurface and migration of unfrozen water under the permafrost, which covered the whole 250-270 m thick fresh water zone before the Nemunas (Late Weichselian) glacier advance (22 000-23 000 BP). Due to anomalous high gradients (0.003-0.004) caused by glacier loading (in the north) and draining periglacial lake (in the south), the unfrozen mineralised water could fill a 10-35 km wide strip in the lower beds of the sedimentary cover at the BAB’s southern margin. This can explain the current small thickness of the fresh water zone, as well as the older age of water in deeper beds and water mineralisation in the southern part of the BAB as compared to the northern part of the basin, which is in a similar geological setting.
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