This paper presents the geochemical and petro-graphical analyses of the Qarat Jahanam Member of Maradah Formation (Aquitanian-Burdigalian). This member consists mainly of siliciclastic deposits from which vertebrates (mammalian and reptilian) are excavated, with carbonates intercalations. Only the clayey horizons are analyzed at the locality Z100 in Jabal Zaltan area, in order to determine the depositional environment and searching for any possible dating minerals. The common clay minerals are montmorillonite, illite, margrite, chlorite, and glauconite. In addition, the nonclay minerals are quartz, hematite, gypsum, anhydrite, halite, and ferroan dolomite. The chemical composition indicates an excess of Ca2+ (Ca/Mg/Fe ratio is 45:30:25). The dolomites in rock record are associated with sulfate suggesting that both minerals originated from hypersaline brines. Petrographic study shows that dolomite is common in varying amounts; euhedral rhomb-shaped crystals are distinctly zoned and locally contain inclusions of sulfate minerals and are thus cloudy. It occurs both as a fabric-selective replacement of the carbonate mud matrix and as cement. The rocks show dolomitic limestone ranging from 35 to 48 %. Accordingly, the depositional environment of Qarat Jahanam Member is dominated by very hypersaline lagoons of arid to semi-arid conditions with a restricted shallow platform to intertidal pulses. A comparative approach with member "U1" clays of As Sahabi Formation is also performed. Economically, impurities may have effect on the quality of products manufactured from the clay.