Abstract
article Sabkhat(Salt flats)are common geographic featuresof low-lyingmarinecoastalareas thatdevelopunder hyper- aridclimaticconditions.Theyare characterizedby thepresenceof highlyconcentratedsalinesolutions and evap- oritic minerals, and have been cited in the geologic literature as present-day representations of hyper-arid regional paleohydrogeology, paleoclimatology, coastal processes, and sedimentation in the geologic record. It is therefore important that a correct understanding of the origin and development of these features be achieved. Knowledge of the source of solutes is an important first step in understanding these features. Historically, two theories have been advanced as to the main source of solutes in sabkha brines: an early concept entailing seawa- ter as the obvious source, and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations. Ra-226 coulduniquely distinguish betweenthese sourcesunder certain circumstances,asitistypically present atelevat- ed activity of hundreds to thousands of Bq/m 3 (Becquerels per cubic meter) in subsurface formation brines; at exceedingly low activities in open ocean and coastal water; and not significantly supplied to water from recently formed marine sedimentary framework material. The coastal marine sabkha of the Emirate of Abu Dhabi was used to test this hypothesis. The distribution of Ra-226 in 70 samples of sabkha brine (mean: 700 Bq/m 3 ), 7 sam- ples of underlying deeper formation brine (mean: 3416 Bq/m 3
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