SOURCES AND DISTRIBUTION OF TRACE AND MINOR ELEMENTS IN THE WESTERN DEAD-SEA SURFACE SEDIMENTS

Twenty Dead Sea surface sediment samples were analyzed for their major , minor and trace element compositions. The samples represent muddy se diments along the western parts of the lake, from water depths of 8-25 0 m. These sediments were deposited after 1983, under oxic conditions, following the overturn of the water column in 1979, which ended about 300 years of meromictic stratification with an anoxic lower water mas s. The changes in their metal concentrations are discussed in view of the different brine oxidation state. The sediments consist of detrital minerals-carbonates, quartz and clays and authigenic minerals-aragoni te, halite and traces of gypsum. Calculations indicate that all mud sa mples contain more than 3.6% authigenic aragonite, which was found to precipitate preferentially in near shore sediments. An increase in Ca and a decrease in Al concentrations with decreasing water depths and i n a transect from N to S were observed. These are attributed to differ ential settling of detritus and authigenic carbonates close to the sho re and fine Al-silicates in the deep waters, and to the southward decr ease in the contribution of clay minerals, I mostly derived from the J ordan river. Fe, Ce, Be and Eu were found to exhibit conservative beha vior with respect to Al during the transition from stream sediments in the drainage basin to lake sediments. When compared to normal marine sediments, the Dead Sea sediments have similar Cu, Ni, Zn, Be, Ce and Eu concentrations, whereas Cd is enriched by nearly 1 order of magnitu de. A good correlation exists between Cd and P, suggesting that the Cd enrichment arises from outcrops of Cd-rich phosphate rocks that are f ound in the Dead Sea basin. The somewhat depleted Pb concentrations in the lake muddy sediments might be explained by the somewhat high Pb c oncentrations (normalized to salinity) in the Dead Sea water column, a s compared to seawater and by its removal, mainly through halite preci pitation. The unusual distribution of Mn concentrations in the surface sediments and its association with authigenic aragonite imply, as has already been suggested, that Mn co-precipitates with aragonite. (C) 1 997 Elsevier Science Ltd.