Chemical Composition of Sabkha Carbonate Sediments from Southern Coastline of the Arabian Gulf

Abstract

The chemical composition of Recent carbonate sediments in Abu Dhabi sabkha was studied to estimate the depositional environment of the dolomites below the quartz sand layer (Fig. 3). Sabkha is supratidal coastal plain, where carbonate minerals including protodolomite have been formed. The sampling locations are shown in Figs. 1~3. Strontium, sulfate and fluoride ions are enriched in Recent sabkha carbonate sediments relative to Pleistocene Mubarras shoal carbonates which have been formed under normal marine environments. X-ray diffraction analysis reveals that these minor elements are present as sparingly soluble minerals (celestite, gypsum, anhydrite and probably fluorite). On the contrary, PO4 is depleted in the sabkha sediments relative to the shoal ones. The low PO4 concentration may be attributable to the fact that the sabkha sediments contain only small amounts of high Mg-calcite which is a main P-bearing mineral among carbonate sediments. The good correlations between PO4, and SiO2, Al or Fe in the sabkha sediments suggest that P is derived from detrital silicate minerals (Table 4 and Fig. 6). The behavior of these elements in underlying dolomites is geochemically similar to those in the Recent sabkha sediment, indicating the dolomites were formed under similar environments to the Recent sabkha. The Recent sabkha and the Pleistocene shoal dolomites are protodolomites with the (104) lattice spacings of 0.2894~0.2913 Å, whereas underlying dolomites have ordered structure and stoichiometric compositions (Table 7). The dolomites may be formed before the Middle Pleistocene. © 1991, The Chemical Society of Japan. All rights reserved.