Abstract

Along the Mediterranean coast of Israel, calcareous sands and sandstones have been accumulating since the Pleistocene. These sediments are generally a mixture of quartz grains and marine biofragments which have undergone marine or continental, or both, processes of cementation and diagenesis. The mineralogical composition of the cements is generally a good indication of the environment of lithification, but that environment can be best determined by the oxygen and carbon isotopic composition of the cement. In the Recent beachrocks, cementation is not only by Mg-calcite and aragonite precipitation with typical marine isotopes but also by Mg-bearing calcite (with 4-10 mole % MgCO 3 ), which has isotopic compositions lighter than a marine origin alone would indicate. A similar Mg-bearing calcite cement occurs in submerged sediments which were cemented earlier by calcite originating from meteoric water. The isotopic composition of this cement indicates that it might have formed by submarine growth of Mg-calcite with < 10 mole % MgCO 3 over calcitic seeds. In Holocene to Pleistocene calcareous quartz arenite the cement is uniformly composed of calcite, but its carbon isotopic composition indicates progressive stages of diagenesis in which the heavier isotopes originating from dissolution of the marine grains are replaced by the lighter isotopes of continental origin.

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