SEDIMENTOLOGICAL, PETROGRAPHICALAND GEOCHEMICAL CHARACTERIZATION OF THE OLIGOCENE “GABALAHMAR FORMATION” AT MAADI-QATTAMIYA AREA, EGYPT

An integrated mechanical, mineralogical, petrographical and geochemical studies were carried out on the sand and sand- stone samples from the Gabal Ahmar Formation in Maadi- El Qattamiya area. Twenty-nine samples were collected from two sections. Grain size analysis of the studied sediment has been carried to evaluate its textural parameters and statistical mea- sures to depict the depositional pattern of sediments in the study area.
The samples are medium to very coarse-grained (1.007 to -0.54 φ), poorly to very well-sorted (-0.040 to 1.32φ), very fine to coarse skewed (-0.11 to 1.72φ) and mesokurtic to very leptokurtic (-1.59-2.82φ) in nature. The grain size distribution reveals that the transporting medium must have undergone series of rise and fall in its velocity. The studied samples could be classified into three types gravelly and slightly gravel sand, gravel and sand class.
Petrographically, the Gabal Ahmar sandstones are mainly ferruginous arenite, ferruginous and calcareous greywackes, generally, moderately/poorly sorted, sub-angular, sub-rounded with silica, carbonate and sericite cement. The main mineral- ogical constituents are quartz, montmorillonite, calcite, microcline and hematite. The detected heavy minerals are magnetite, hematite, limonite, zircon, and glauconite. All the identified grains of heavy minerals show different shapes.
The geochemistry of the studied sandstones supports the petrographic results. The sandstone is therefore highly siliceous, with exception of three calcareous sandstone samples which recorded a major amount of CaO up to 30.35%. The Gabal Ahmar sandstones can be classified chemically into arenite and greywacke.