Abstract In order to define the diagenetic processes occurring in the sabkhas along the south shore of the Persian Gulf, it is necessary to understand the direction and rate of movement and the origin of the highly saline groundwaters and surface waters in the sabkha environment. Two possible origins or sources, marine or continental, exist for the brines in the coastal sabkha. To determine the origin of the brines, ion ratios have been used. The Na + /CI and CI 7K + ionic ratios are not satisfactory indices, but the Cl /Br and K + /Br ratios are reliable indicators of brine origin. Brines with CI 7Br™ ratios less than 1,000 are predominantly of marine origin, those with ratios between 1,000 and 5,000 are of mixed continental and marine origin, and those with ratios greater than 5,000 are predominantly of continental derivation. Brines with K + /Br ratios less than 25 are of marine origin, those with ratios between 25 and 150 are of mixed continental and marine origin, and those with ratios greater than 150 are of continental derivation. The seaward movement of the zone of mixed continental and marine brines over the past 5,000 years indicates an approximate groundwater flow rate in the central sabkha of 0.3 to 1 m/yr.