The marine sedimentation along the margin of the southeastern Neo-Tethys during the oceanic convergence stage between the Senonian and the Eocene took place on sea-bottom topography formed by the folding of the Syrian arc deformation belt. The clay mineral assemblage within the marine rocks of the synclinal basins of the Syrian arc deformation belt in the southeast of Israel is dominated by smectitic IS (interstratified illite/smectite rich in smectite layers) accompanied by kaolinite, palygorskite and occasional sepiolite. The smectitic IS originated by conversion of the smectite transported from the open marine environment to the synclinal basins. The conversion of the precursor smectite took place due to warm water and the higher salinity resulting from the development of stratified water bodies in the marine synclinal basins. The origin of authigenic palygorskite and occasional sepiolite is related to the conditions of hypersaline bottom waters due to accumulation of residual heavy brines, enriched by Mg. Detrital kaolinite and discrete illite accompanying the smectitic IS in the marine rocks were transported to the Tethyan margin from the continent.
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