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Abstract
To accommodate the rapid increase of population and avoid the construction on green lands, it is necessary to construct on desert areas. For that reason the area between Alexandria and EI-Alamein in the northwestern coastal plain of Egypt was the subject of detailed geological, geotechnical and geoenvironmental investigations. This area comprises four longitudinal carbonate ridges extending parallel to the Mediterranean coast with broad interdunal areas that covered by lagoonal sabkha soils. The Quaternary carbonate ridges have affinities of eolianite sediments and are deposited as coastal dunes by the action of beach waves and onshore winds. Their presence along the Mediterranean coast reflects the eustatic sea level fluctuations and the climatic changes from warm interglacial to cold glacial episodes that characterize the Quaternary periods. Mineralogically, the carbonate rocks are composed, in decreasing order of abundance, of calcite (low Mg and high Mg-calcite), aragonite and non-ferroan dolomite. Aragonite predominates the carbonate minerals of the first ridge. The non-carbonate minerals include quartz and halite. The sabkha soils are largely dominated by illite and kaolinite clay minerals. The non-clay minerals include, in decreasing order of abundance, calcite, quartz, feldspars and dolomite. Granulometric analysis of the soil samples suggests that they have been deposited in fluvial environment under relatively calm conditions. Petrographic examinations of the carbonate rocks of the present area reveal that they are composed mainly of carbonate grain~ (ooids, bioclasts, intraclasts and pellets) with scattered detrital quartz. grains; cemented together by calcite and less commonly aragonite. Several carbonate lithofacies such as oosparite, oo-intrabiosparite pel-oosparite, bio-oosparite, bio-intrasparite, Intra-biosparite, bio-intramicrite and biomecrite are recorded. Texturally, they vary from grainstones to wackestones. Several diagenetic processes were acting on these rocks, in both meteoric and marine environments, which were largely modified their original composition and textural characteristics.