Geochemical and petrographical analyses of Miocene Qarat Jahanam Clays of Maradah formation in Jabal Zaltan, North Centr
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ORIGINAL PAPER
Geochemical and petrographical analyses of Miocene Qarat Jahanam Clays of Maradah formation in Jabal Zaltan, North Central Sirt Basin, Libya Saad K. El Ebaidi & Ahmed M. Muftah
Received: 1 April 2014 / Accepted: 14 July 2014 # Saudi Society for Geosciences 2014
Abstract This paper presents the geochemical and petrographical 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.
S. K. El Ebaidi : A. M. Muftah (*) Faculty of Science, Department of Earth Sciences, University of Benghazi, P.O. Box 9480, Benghazi, Libya e-mail: [email protected] S. K. El Ebaidi e-mail: [email protected]
Keywords Jabal Zaltan . As Sahabi . Maradah: dolomite . Montmorillonite . Hypersaline
Introduction Jabal Zaltan area is an important paleontological site of Neogene vertebrates. The geological map of Industrial Research Center, Tripoli, by Mastera (1985) is considered as the most useful map of the area. Due to the richness of the area with respect to the vertebrate remains, Jabal Zaltan attracted the vertebrate paleontologists (Savage and White 1965; Savage and Hamilton 1973). The Paleontological International Sahabi Research Project (ISRP) of the Garyounis Research Center of Benghazi in collaboration with other international funding agencies (see Boaz 1987), conducted paleontological excavations for vertebrate remains in Jabal Zaltan and As Sahabi areas. Maradah Formation (Early– Middle Miocene) was introduced and described by Desio (1935) from 80-m-thick section at Garet al Mazzala, near Marada Oasis. It consists mainly of siliciclastics with minor carb
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