Sulphur and oxygen isotopic compositions of groundwater and sabkha - sulphate in the Middle East

The climate and topography of landward margins around the southern Mediterranean and the Arabian Gulf have given rise to areas of recent evaporite formation known as 'sabkhas'. These supratidal evaporitic flats have developed as a result of a relative fall in sea level after the last marine transgression (about 4000 years B.P.) which deposited carbonate sediments over coastal areas. Inland sabkhas may also develop in low lying areas and the desert 'soils' often have a 'getch' (duricrust) layer of gypsum or calcite near the surface. Published sulphur isotope studies of the sabkhas in the Gulf of Sirte (Libyan Arab Jamahiriya), Al Khiran (Kuwait) and Abu Dhabi (United Arab Emirates) indicate a sea water influence (δ34S ≅ +21 per mille; δ18O ≅ +10 per mille) only in the outer sabkha. At Al Khiran, Gulf of Sirte and Bardawil (Egypt) the δ34S values decrease to +14 per mille on the landward side. Continental sabkhas in the United Arab Emirates have δ34S values between +13 and +16 per mille and the continental getch in Kuwait has δ34S=+15.6 per mille. Sulphate minerals from the Al Khiran sabkha have δ34S and δ18O values up to +17 and +16 per mille respectively, much lower than at Abu Dhabi, where sea water sulphate and bacterial activity are more prevalent. At Al Khiran the δ34S mineral values drop to +12 per mille and the spread is connected with mineral transformations. In the Libyan Arab Jamahiriya and the United Arab Emirates the continental sulphate was thought to be derived from Cretaceous sediments. However, in Kuwait, an aquiclude, the Rus Formation (L. Eocene), prevents older water and sulphate from entering the sabkhas. This widespread sulphate source with δ34S=+14 per mille may be derived from continental getch and surface evaporites which are transported and homogenized by dust storms. (author). 10 refs, 4 figs