Abstract

A study of brines and diagenetically altered minerals from the coastal sabkha of Abu Dhabi, Persian Gulf, was undertaken to test the flood recharge-evaporative pumping model for early dolomitization using strontium isotopes as a tracer. The 87Sr/86Sr ratio of the sabkha brines defines a pattern of both horizontal and vertical mixing of coastal seawater and continental ground water consistent with a previously proposed model. The 87Sr/86Sr ratio of the diagenetic dolomites indicates early dolomitization by marine recharge waters. The 87Sr/86Sr ratio of gypsum from the dolomitization area (1.4 to 4.4 km from high-tide mark) and seaward reflects precipitation from marine brines, but more landward (6 to 9 km), gypsum and anhydrite record a continental signal. The transition from a marine to a continental isotope signal in the minerals suggests a paragenetic evaporative sequence (dolomite → gypsum → anhydrite). The dolomitizing fluid is evaporated seawater that recharges the sabkha aquifer during supratidal flooding and is afterward pumped upward through the saturated zone by evaporative processes.

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