Oil shales are immature source rocks that have significant energy resources. They are considered as a potential deposit for hydrocarbon generation upon thermal maturation. Shale oil and gas can be generated by organic matter artificial thermal maturation [1] . Oil shales formed as early as Cambrian and continued to form in a variety of depositional environments [2] . The oil shale (OS) organic matter ( OM ) is mixed with varied amounts of mineral matter. The major OM fraction in the OS is the kerogen that could decompose to yield oil, gas and residual carbon through the pyrolysis process [3] .

In Jordan , oil shale deposits are the main fossil fuel resource. They have widespread occurrence and good quality [4] . The most important deposits are those of the Late Cretaceous-Palaeocene. About 26 known deposits of OS are present. Some of them, such as El-Lajjun OS, are large and relatively high-grade [5] . Alqudah et al. [6] reported that Jordanian oil shales were formed since Palaeozoic till Eocene, and they were deposited in various sub-basins such that of El-Lajjun in central Jordan.

Jordanian OS is typically brown, gray, or black, and consists of two parts: The first one is the inorganic part that is known as the mineral matter, this part forms the bulk of the OS rock material; The second one is the organic material (OM) which forms a minor fraction from OS rock material [7] . The sulphur content of Jordanian OS is up to 4.3% [5] [8] . El-Lajjun OS deposit has the highest average oil content at average oil yield of about 9% [9] . Several exploration and feasibility studies have been carried out on the Jordanian OS by the Natural Resources Authority (NRA). More attention has given to those deposits in central Jordan . This paper shows the results of characterization analyses for selected oil shale samples from El-Lajjun OS deposit in central Jordan . The results presented in this paper are part of a research project on Jordanian oil shales.

El-Lajjun oil shale is part of South Tethyan oil shale-phosphorite giant belt [10] . During the formation of oil shale, Jordan was located in an epicontinental sea [11] . Bioproductivity was enhanced by deep cold water rich in nutritants brought to the surface by upwelling currents [12] [13] . The deposition was influenced by syn-sedi- mentary tectonics [14] resulted in the formation of internal shelf basins structured by shallow swells [15] . The paleotopography of the depositional shelf during the OS formation became an important factor [16] . Syngenetic concentrations of OM in these restricted basins on the continental shelf resulted in OS formation [17] . The deposition oil shales have influenced by other controlling factors such as high rates of sedimentation (e.g. [8] [18] ) and the influx of terrigenous material [19] (Figure 1).

The stratigraphic column of carbonate rocks of upper cretaceous to early tertiary is shown in Figure 2. Oil shale in Jordan is part of Muwaqqar Chalk Marl (MCM) formation [7] . The MCM formation consists of thick bedded chalky marl and marly limestones and locally microcrystalline limestones [20] .

Three selected OS samples were collected from surface outcrop at El-Lajjun OS deposit (Figure 3, Table 1). The oil shales are typically brown, or black. Weathered surfaces are bluish gray. The selected fresh samples cover different rock qualities and loci within the same outcrop. Full and detailed sampling and sample preparation is reported in Alnawafleh and Fraige [4] . Sample preparation includes sample cleaning, crushing and grinding, and thin rock chips for thin section preparation.

The methodology and experimental work performed in this study is reported in Alnawafleh and Fraige [4] . For petrographic study, three thin sections were prepared and studied via the polarizing microscope and photomicrographs of each OS sample were taken using digital camera type Canon Power Shot S70. Total Organic Carbon (TOC) was determined using carbon determinator available at the Natural Resources Authority (NRA). Oil shale samples were acidified to remove inorganic carbon as CO₂, and then the organic carbon combustion products of the combusted sample were catalytically converted to CO₂ and measured by the carbon determinator. Around 3 grams of finely ground (<100 µ) OS were accurately weighed. About 30 ml of HCl (20% wt) were slowly added to the sample and then allowed to react with boiling acid for several minutes then left to cool for room temperature. After cooling, the sample then filtered and rinsed with distilled water to remove the acid solution then allowed to dry. The weight of the dried digested sample divided by the weight of the original sample before digestion is a factor used to calculate the percentage of organic carbon (OC) after analysed by the carbon determinator as follows:.

For OS mineralogical composition, the OS samples were analyzed using the XRD PHILIPS (XPERT MPD) X-ray power diffraction set with Sietronics “siehilt” automation software and Hiltonbrooks HXB data collection. Mineral identification was performed using PC-APD Diffraction software and published data. Operation and experimentation conditions are as follows: radiation: Co Kα., wave length 1.78896 angstrom, generation voltage is 40 kV, current 45 mA, scanning speed 1.2˚/min, step size 0.02˚.

Fisher assay analysis carried out via the Fisher assay apparatus available at the NRA. About 100 grams of OS powder which dried at 70˚C for 24 hours were transferred to the retorter after cooling to the room temperature in the desiccator. After setting up the instrument, the thermal program starts up After 10 minutes. Within 60 mi- nutes, the temperature raises up to 520˚C. The volatile organic gases that resulted from the thermal destruction of kerogen are converted to liquid by the action of the cooling unit. After cooling, the weight of the burnt sample (spent shale) is recorded. Water then separated from the liquid organic matter by addition of 100 ml of xyelene, and upon heating water condensed and separated from oil. The weight of oil and water then recorded. Accordingly,

the weight of volatile loss can then be determined.

El-Lajjun oil shale in central Jordan is organic rich carbonate. The dominant carbonate mineral is calcite. Some OS bands are silicified. The rock contains traces of phosphate clay and iron oxides and is rich in foraminifera bioclasts that are partly invaded by organic matter. Clay minerals are primary smectite. EL-Lajjun OS has high average oil content and good oil yield capacity. Such high yield characteristic indicates that El-Lajjun OS is of good quality. This OS deposit is considered as one of the Jordanian OS potential deposits for future utilization.

This research project is funded by the Al-Hussein Bin Talal University (Research Fund # 6/2009) and the Scientific Research Support Fund-Ministry of Higher Education and Scientific Research (Research Fund # E/2/23/ 2008), Jordan. The authors are also thankful for the NRA, Jordan, for their assistance during the lab work.

Hani M.Alnawafleh,Feras Y.Fraige,11,11, (2015) Analysis of Selected Oil Shale Samples from El-Lajjun, Central Jordan. Geomaterials,05,77-84. doi: 10.4236/gm.2015.53008