Jordan has huge oil shale (OS) resource and considered one of the world leading countries in its OS potential deposits. More than 24 deposits are recorded [1] . The well-known Jordanian OS belongs to the upper cretaceous and lower tertiary formations [2] . The Jordanian OS is generally not exposed. Previous work conducted on Jordanian OS is based mainly upon shallow boreholes and limited OS outcrops. Previous work and OS exploration in Jordan have focused on Upper Cretaceous OS from Muwaqqar Chalk Marl formation (MCM) (e.g. [3] - [8] ). The OS from MCM formation is bituminous limestone [8] . At Wadi Al-Bustan, south-western corner of Jordan (Figure 1 and Figure 2), the OS is found in two stratigraphical levels. The upper (younger) level is that of MCM formation (Figure 2(a)) from Maastrchtian-Paleocene [2] . Full Petrographic and geochemical characterization of this OS type is found in Alnawafleh [8] and later papers by the same author (e.g. [9] [10] ). The lower level (older) (Figure 2(b)), which is bituminous dolomitic limestone, is a part of upper Campanian Amman Silicified Limestone (ASL) Formation [2] .

The ASL formation is related to the Late Cretaceous Belqa Group. Jordan was flooded during the Late Cretaceous and the shallow marine sediments of the Belqa Group were deposited [11] . The age of the ASL Formation is latest Cretaceous (Campanian-early Maastrichtian) [12] . Its thickness varies from 30 to 100 m [13] [14] . The base of this formation is defined below the first massive thick-bedded chert and above the marly chalks or silts/sands of the Wadi Umm Ghudran/Fassua Formation [15] .

Dolomite is generally associated with sedimentary limestone. As a mineral, dolomite is common in ancient marine and terrestrial deposits [16] . Dolomite is found in wide range of formational setting [17] . Theories re-

lated to dolomite formation are continued to evolve and many modes of dolomite origins are proposed. Based on their mode of formation, dolomites can be broadly divided into primary and secondary dolomites [18] . In Jordan, dolomite can be found in the Burj Dolomite-Shale Formation of Cambrian age and in upper cretaceous Naur, Hummar and Wadi Es-sir formations [19] .

Literature deals with dolomitization in OS are quite limited. It is the purpose of this paper to understand the geologic characteristics and the genesis of dolomitized OS rocks from Jordan. The geochemical parameters discussed here are based on the various analyses results on OS surface outcrop samples from the bituminous dolomitic limestone section of the upper Campanian ASL Formation.

Jordan’s OS from Campanian age is rarely referred to in literature. More attention has been given to that OS of the Muwaqqar Chalk Marl Formation. The OS from Campanian age is related to Amman Silicified Limestone Formation (ASL). These OS beds can easily be traced in the field as they are exposed in some wadis like Wadi Al-Bustan in Ash-Shoubak area. Amman Silicified Limestone Formation is easily traced across the country. This formation is characterized by cliff forming, massive chert beds overlaying the Wadi Umm Ghudran/Fassua Formation [15] . In South and Southeast Jordan, the deposition took place under marginal marine conditions with increased content of siliciclastic deposits [15] . Shallow near-shore environment for chert beds of this formation was concluded by Abed and Kraishan [20] . More information about the genesis of this formation is found in Abu Jaber et al. [13] . They reported that the ASL Formation was deposited on a shallow carbonate platform along the fringes of the Tethyan seaway. The stratigraphic column of ASL Formation within the studied area is shown in Figure 3.

The formational framework of the Jordanian OS has been investigated by many researchers over the last four decades (e.g. [3] [4] [6] [8] [21] - [26] ).There are several scenarios about the formation of Jordanian oil shales. These scenarios are combination of paleoclimatic, paleogeographic and paleotectonic factors. Recent biostratigraphic and petrographic studies on Upper Cretaceous-Eocene OS from Jordan have reached to similar results on the formational and controlling factors that have been reported and discussed previously by Alnawafleh [8] (e.g. [27] - [31] ). In central Jordan, oil shale deposited in synclinal basins [3] . During the late Cretaceous period, the eastern Mediterranean formed part of the southern broad shallow epeiric shelf of the Tethys Ocean [15] . The sea-floor of the eastern Mediterranean was not topographically smooth but consisted of basins and swells [12] . These structures are believed to be resulted from the late cretaceous major tectonic pulse of the Syrian Arc fold belt [32] . With the areas covered by the Syrian Arc, the basins and swells are folded whereas in Jordan such structures are not folded [33] indicates the importance of the sea-floor bathymetry as a controlling factor of the upper cretaceous sedimentation in the region including Jordan’s OS. Regional sea-level fluctuations of Late Cretaceous have played a major role in the deposition of OS in Jordan [8] [29] . The high productivity due to upwelling currents along the shelf edge and the anoxic bottom water conditions are major controlling factors in OS formation [4] [8] [34] . It is important to mention that some parts of OS in central Jordan have been pyrometamorphosed to marble [35] .

Twelve samples were collected from the OS section that exposed at the base of Wadi Al-Bustan north of Ash-Shoubak area in south-western part of Jordan (Figure 1). The field observations show that this OS section is made of irregular rhythmic repetition of pale and dark bands of fine-grained mudstone. Nearly 5.5 meters were recorded and sampled. Oil shale section varies in hardness and occasionally fractured. The lower part is almost rich in shell fragments and fossil debris and biogenic material and contains some coarse concretion particles (biogenic debris or dolomitic lumps) and reveals sugary texture. Some bands in this section have distinguished bituminous smell. The OS in this section is overlain by marl and chert bands and underlain by phosphorite beds at the bottom.

Each sample was divided into three parts. One is saved as archive sample. The second was cut to prepare thin section for microscopic inspection. Twelve oil shale thin sections were prepared at the laboratories of Natural Resources Authority (NRA), Jordan. Half of each thin section was stained using staining test solution (Alizarin Red S) and then studied using the polarizing microscope. Photomicrographs of each OS type were taken using digital camera type Canon Power Shot S70. The third part of each sample was crushed by a crushing machine then further reduced down to monomineralic particles by vibrating agate ball mills. All samples were analyzed by carbon determinator (thermal conductivity detector) to indirectly estimate the quantity of organic matter in each sample. Total sulfur content (S wt%) in four selected samples was determined using the multi EA®200 element analyzer available at NRA. Those samples have been tested for their oil shale retorting properties via Fischer Assay apparatus available at the NRA that determines oil, water, spent shale and gas loss in OS samples according to ISO 647 by thermal cracking method. Quantitative analysis of major oxides and trace elements was performed using X-Ray Fluorescence Spectrometer (XRF).

Unlike oil shale from Maastrichtian to early Tertiary, this OS horizon is highly dolomitized. This OS type contains considerable content of OM. One economic potential for this types of OS is that the sulfur content is quite low compared with that of Maastrichtian OS types. This type of OS shows textural variations in both TOC-rich and TOC-depleted bands. The major rock component is dolomite with variable amounts of OM, calcite, quartz, and other minor minerals. Productivity indicators are positively distributed with OM. There is a negative correlation of organic matter content with carbonate content. The dolomite is diagenetic in origin and reveals complex diagenetic history and illustrates the importance of diagenetic alteration in the formation of this type of OS. The results of this study suggest that the formation of dolomite in this OS type appears to be limited by the rate of organic matter oxidation.

The authors are thankful for the NRA staff for their assistance during the lab work.

Hani M.Alnawafleh,Khalid E.Tarawneh,Hani N.Khoury,Nafeth A.Abdelhadi,Osama Y.Shakkoury,Reyad A.Dwairi,Mazen N.Amaireh, (2015) Dolomitization in Campanian Oil Shale Rocks from South-Western Jordan. Open Journal of Geology,05,689-700. doi: 10.4236/ojg.2015.510061