Considerable data exist on the isotopic composition of ancient sedimentary sulfates. Interpretation of these data has been hampered by the absence of a base line for comparison from a modern evaporite environment.

Isotopic analyses (258 total determinations) of pore brines [^dgrO¹⁸(H₂O), ^dgrS³⁴(SO₄⁼)] and coexisting diagenetic gypsum and anhydrite [^dgrS³⁴(SO₄⁼)] in the Abu Dhabi sabkha indicate: (1) that the regional distribution of ^dgrO¹⁸ and ^dgrS³⁴ in brines reflect the climatic regime and possible favorable fractionation of O¹⁸ into H₂O of precipitated gypsum (^dgrO¹⁸); (2) that the source (marine versus continental) of fluid input into the sabkha is reflected in the brine ^dgrO¹⁸ and ^dgrS³⁴ values; (3) that ^dgrS³⁴ in diagenetic sulfate minerals reflects the favorable fractionation of S³⁴ into the prec pitating sulfates from pore fluids and (4) ^dgrS³⁴ values of anhydrites permit the identification of anhydrites formed under a marine versus continental-derived fluid regime.

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