Why are recent groundwaters sea-tagged and fresh, whereas formation waters are brine-tagged and saline?

摘要

The active groundwater cycle operates within the zone of hydraulic differences, existing at the landscape relief that protrudes above the terminal base of drainage - the sea surface. Sea-spray is efficiently driven far inland and washed into the groundwater system, tagging the latter by Cl, Br, Na and a list of additional ions, in relative abundances as in seawater. The cycling water washes salts from the continent into the sea and by the constant evaporation and formation of new precipitation fresh water is common. At greater depth extends the zone of zero hydraulic difference, at which formation water is trapped in hydraulically isolated rock-compartments, as is born out by their high ages and spatial composition variability. The isotopic composition discloses that formation waters are of meteoric origin. They are tagged by brine-spray, reflecting the evaporitic paleo-landscapes at which they have been formed. These were vast flat lowlands frequented by alternations of sea invasions and retreats. Thus, formation water properties disclose that the host rocks were formed in vast subsiding basins, i.e. at landscapes formed during phases of orogenic tranquility.