Origin,distribution, and evolution of salt-fresh groundwater in North Jiangsu Basin,China

Connate saltwaters are contained within the upper Pleistocene and overlying sediments. The high salinity of phreatic water and subsoil has significant effects on the development of industry and agriculture in the area. This articie is a report on conditions of the salt-fresh ground-water in the North Jiangsu Basin (NJB), China. Connate saltwaters in the western part and within old dunes in the eastern part of the area have been flushed out by infiltrating meteoric water, since regression happened about 1,000 years ago. A broad transition zone of saltwater-freshwater exists due to repeatedly eustatic sea-level fluctuation during the Quaternary period, through analyzing relationships between marine beds and the distribution of salt-fresh groundwater. In the coastal plain, the distribution of salt-fresh water is quite complex. There are four types of vertical distribution represented by chloride and/or Total Dissolved Solids (TDS) profiles: (1) salt-fresh water inversion, (2) salt-brackish water inversion, (3) salt-fresh-brackish water superimposition, and (4) salt-fresh-salt-fresh water superimposition. Groundwater in the middle-layered aquifer system is replenished in some places in the west, and flows slowly eastward. Chemical characters of water result from halite dissolution and incongruent dissolution of some aluminosilicate minerals, ion exchange and adsorption, mixture of salt-fresh water, and others. Hydrochemical types evolve from HCO₃ type to HCO₃ Cl type, lacking the sulfate type due to the mixture of salt and freshwater. The Chebotarev hydrochemical evolution sequence is, therefore, not relevant.