Abstract
A detailed facies and depositional analysis of the Miocene-Pliocene siliciclastic-dominated sequence (ranges from 10 to 35 m thick) of siliciclastic succession below the basalt rocks have been carried out to interpret the depositional pattern, facies and sedimentary depositional environments. This siliciclastic-dominated succession, underlying Harrat Rahat, belonging to the Miocene-Pliocene is exposed at Al-Rehaili area, North Jeddah. Three main depositional units from bottom to top: Unit I, II and III are identified and correlated. These units comprise of gravels/conglomerates, sandstones, siltstones and mudstones. Sandstones below the basaltic rocks of Harrat Rahat generally contain about 30-70% quartz, 10-50% rock fragments, 10-20% feldspar, 15-40% detrital clay, 2-8% iron oxides, and minor amounts of other components. Siltstones are distinguished from sandstones by their finer grain sizes of the quartz silt (45-70% quart and higher proportion of clay (30-55% detrital clay minerals). Mudstones contain about 25-50% quartz, 40-60 and detrital clay minerals, 2-8 iron oxides, and minor amounts of other components. Based on petrography, components, textures, fabrics, contacts nature, sedimentary structures, stratal geometry, and stratigraphic relationships, ten facies, covering the three depositional units are distinguished representing fluvial to lacustrine depositional conditions. Copyright 2015 Geological Society of India