THE CHEMICAL EVOLUTION OF KURNUB GROUP PALEOWATER IN THE SINAI-NEGEV PROVINCE - A MASS-BALANCE APPROACH

The chemical evolution of the Kurnub Group paleowater was studied star ting from rainwater in recharge areas of the Sinai and along groundwat er flowpaths leading to the natural outlets of this regional aquifer. This was achieved by investigating the chemical composition of groundw ater, ionic ratios, degrees of saturation with common mineral species, normative analysis of dissolved salts and by modeling of rock/water i nteraction and mixing processes occurring along groundwater flow paths . The initial groundwater composition used is from the Nakhel well in Sinai. It evolves from desert rainwater percolating through typical Ku rnub Group lithology in Sinai. This rainwater dissolves mainly gypsum, halite and dolomite together with smaller amounts of marine aerosol a nd K-feldspar. At the same time it precipitates calcite, SiO2, smectit e and degasses CO2. Between the area of Nakhel and the northern Negev the chemistry of Kurnub Group waters is influenced by dissolution of h alite and lesser amounts of gypsum of surficial origin in recharge are as, small amounts of feldspars and of dolomite cement in sandstones er oded from the Arabo-Nubian igneous massif of Sinai and organic degrada tion-derived CO2. Concomitantly, there is precipitation of calcite, sm ectite, SiO2 and probably analcime characteristic of sediments in cont inental closed basins. North of the Negev, the Kurnub Group fluids are diluted and altered by mixing with Judea Group aquifer groundwaters. On the E there is mixing with residual brines from the water body ance stral to the Dead Sea, prior to discharge into the Arava valley. Rock/ water interaction indicated by NETPATH and PHREEQC modeling is in agre ement with lithology and facies changes previously observed in the Kur nub Group sequence. (C) 1998 Elsevier Science Ltd. All rights reserved .