ABSTRACT

Four reference sections through the calcareous-siliciclastic rocks of the Lower Cretaceous Kurnub Group and the Amman and Muwaqqar formations of the Upper Cretaceous to Paleogene Belqa Group in Jordan document the various processes of accumulation and alteration of organic matter (OM). Sections at Jerash, Sultani, Wadi Isal, and in the Kharazeh area were investigated by means of sedimentary petrography/mineralogy, organic petrography, and organic chemistry, and correlated with equivalent deposits in Syria and Egypt. The impacts of oxidation potential (Eh), acidity/basicity (pH) and temperature variations during the post-depositional alteration of these organic concentrations were assessed using x-y plots. Syngenetic Aptian-Albian coaly and organic-rich amber beds near Jerash developed in a tide-dominated delta under marginally alkaline conditions and were altered under slightly acidic conditions at temperatures of less than 100°C. Environmental analysis focused on Maastrichtian-Paleocene (?), oil shales in the Sultani area that were deposited in a small restricted basin on the continental shelf of the Neo-Tethys Ocean. Abnormally high contents of vanadium (V), phosphorus (P), zinc (Zn), and uranium (U) gave rise to yellow uranium ore minerals, phosphates and zinc sulfides and so bridge the gap between OM concentrations and those of uranium. The western part of the Arabian Peninsula is known for its uraniferous phosphorites and U-bearing calcretes. Reducing conditions during deposition of syngenetic OM in the oil shales may have shifted, in places, toward more oxidizing conditions in the course of post-depositional alteration at temperatures well below 200°C. Epigenetic fault-related concentration of OM was responsible for the Wadi Isal Aptian-Albian tar sand deposit and the oil seepage system in calcareous wall rocks of the Kharazeh Fault. The alteration of the tar sands (fluvial sandstones) is designated a high-sulfidation type (introduced aluminum sulfate minerals), whereas the oil seepage in Campanian shallow-marine carbonates is a low-sulfidation type (removal of aluminum sulfate minerals). Both alteration patterns may have implications for structure-bound base- and precious-metal deposits whose emplacement involves hydrocarbons as a carrier of metals in the mineralizing fluids. The Jordanian oil shales, tar sands, and uranium mineralization are possible sources of energy. Recent economic deals on the recovery and use of oil shales and uranium in Jordan are reviewed.

ENERGY RESOURCES AT THE WESTERN MARGIN OF THE ARABIAN PLATE

The Arabian Plate (Figure 1a) is bounded to the west by the well-known strike-slip Dead Sea Transform Fault whose morphological expression is the Jordan Valley and the Gulf of Aqaba (Sharland et al., 2001). Whereas the northeastern boundary of the Arabian Plate (Gulf Region) is marked by a cluster of world-class gas and oil deposits elongated northwest, there are no energy deposits of similar size along its western boundary. The energy resources of the Gulf Region have sparked numerous studies; for example, Alsharhan and Nairn (1995), Al-Aswad (1997), Al-Siddiqi and Dawe (1999), Sadooni and Alsharhan (2004), and Al-Jallal and Alsharhan, (2005).

In Jordan, the number and size of energy resources is manifestly less than those of the Arabian Gulf region, but the diversity of potential energy resources is high and includes coaly material, hydrocarbons, and uranium mineralization. A small fraction of domestic energy requirements is met by the Hamzah oil field near Azraq east of Amman, and the Risha gas field near the Jordan-Iraq border (Figure 1b) (Abu-Ajamieh et al., 1988). Various aspects of the domestic oil shales have been studied, but the depositional environment is still poorly known (Hufnagel et al., 1980; Abed and Amireh, 1983; Jaber and Probert, 1997, 1999; and Hamarneh, 1998). The emphasis on the oil shales has eclipsed other carbonaceous rocks as potential fossil fuels.

This paper presents the results of the investigation of a stratigraphic interval from the Upper Cretaceous through the Paleogene that hosts hydrocarbon deposits, lignite seams and uranium mineralization (Figures 1b, c). The organic-rich sedimentary rocks, locally containing uranium, are related to a variety of paleoenvironments that have been studied geologically, mineralogically and petrographically, and their organic and inorganic chemical composition investigated.

This study provides an overview of four sites that are rich in organic matter but differ in the types of organic matter present. They are the Jerash amber-bearing coaly and organic-rich beds (Kurnub Group), the Sultani oil shales (Muwaqqar Formation), the Wadi Isal tar sands (Kurnub Group), and the oil seepage in the Kharazeh area (Amman Formation) (Figure 1b; Table 1). The types of organic matter are typical of the western edge of the Arabian Plate and can be correlated with deposits in Syria and Egypt. The main focus is placed on diagenetic and epigenetic alteration and the constraining physico-chemical regime, an approach that had not been taken in Jordan although it had been used elsewhere on the Arabian Plate (Dill et al., 2007). Papers published by, for example, Al-Rifaiy et al. (1993) and Schulze et al. (2005) on the western parts of Jordan were based on common microfacies analysis and exclusively centered on the calcareous platform sediments with no attention paid to the chemical and mineralogical inventory.

GEOLOGICAL SETTING DURING THE CRETACEOUS AND PALEOGENE IN NORTHWESTERN JORDAN

Cretaceous and Paleogene strata in Jordan are subdivided into three groups. From bottom to top they are the Kurnub, Ajlun, and Belqa groups. Table 1 summarizes the groups and provides a stratigraphic subdivision into formations and accompanying lithology.

Kurnub Group

The Kurnub Group is of Early Cretaceous (Aptian-Albian) age. During this time, the area that is now Jordan was emergent and the locus for fluvial deposition (Abed, 1968; Amireh, 1993, 1997). The Group is up to 300 m thick and consists of fluvial deposits dominated by varicolored quartz arenitic sandstones with minor mud rocks arranged in fining-upward cycles (Abed, 1982; Amireh, 1997). Terrestrial plants, especially ferns were widespread. Although there has been some attempt to divide the Group into formations (for example, Amireh, 1999), Jordanian geologists prefer to keep it as a group because of difficulties in identifying formations in the field. In northern Jordan, some marine transgressions occurred during this time and marine deposits of dolomite and glauconitic sandstone with some body and trace fossils are present, alternating with fluvial material.

Ajlun Group

This Late Cretaceous (Cenomanian-Turonian) Ajlun Group consists of five formations; from base to top they are the Naur, Fuhais, Hummar, Shuaib, and Wadi Es Sir formations (Masri, 1963). Its thickness increases from about 100 m in the south to more than 600 m in the north of the country. The group consists exclusively of carbonate rocks, except in the extreme south where clastic rocks make up a great part of the sequence. The group is rich in well-preserved body fossils, such as, cephalopods, bivalves, gastropods, and echinoderms. The microfossils foraminifera, ostracodes, and serpulids are also common. Lithologically, it consists of alternating limestones and dolostones and some soft, interbedded yellowish-greenish marls to marly limestones. These intercalations are used for subdividing the group into formations (Table 1).

In the Early Cenomanian, a major rise in sea level occurred and the Neo-Tethys Ocean transgressed over large parts of the Eastern Mediterranean region, including present-day Jordan (Bender, 1974). Jordan then became part of the southern epicontinental shelf. This paleogeographic setting favored deposition of the carbonate series of the Ajlun Group. The group pinches out southward, and the content of clastic rocks increases toward the Arabian-Nubian continent. During Turonian and Senonian times, a compressional event known as the Syrian Arc Folding, affected the area (Bowen and Jux, 1987). The northward movement of the African Plate triggered the event and the resulting basin and swells account for the variations in thickness of the Turonian Wadi Es Sir Formation.

Belqa Group

The Coniacian-Santonian to Eocene Belqa Group consists of six formations; from the base upward they are the Ghudran, Amman, Al-Hisa, Muwaqqar, Rijam, and Shallaleh formations (Table 1). As with the Ajlun Group, the thickness of the Belqa Group decreases southward along with a relative increase in clastic rocks. During deposition of the Belqa Group, the African Plate moved northward and the basin-and-swell topography of the Syrian Arc became more pronounced. The resulting paleotopography of the epicontinental shelf became an important factor in the depositional pattern (Abed and Sadaqah, 1998).

During the Eocene, the Rijam and Shallaleh formations were deposited. The Rijam is composed of chalk with alternating bedded chert and minor phosphorite horizons, indicative of strong upwelling. There are nummulite buildups at certain places within the shallower parts of the platform.

By the end of the Eocene, the Neo-Tethys Ocean had completely receded from Jordan and most of the Eastern Mediterranean interior, leaving Jordan emergent. Tectonic activity occurred during the Oligocene and, as a result, conglomerates and sandstones were deposited in intermontane basins to form the locally developed Dana Formation near the Dead Sea. During the Middle Miocene, movement along the Dead Sea Transform Fault began and has continued into the present.

METHODOLOGY

For this overview, the four sites in northwestern Jordan (Jerash, Sultani, Wadi Isal, and the Kharazeh area), each with different lithologies and organic matter type were sampled. The rock properties were described visually and under the petrographic microscope using common schemes and comparison charts: rock strength (Selby, 1987); grain morphology (Illenberger, 1991); sorting (Jerram, 2001); fabric variations (Collinson and Thompson, 1982); and chemical data based on conventional X-ray fluorescence analysis.

For X-ray diffraction, a Philips diffractometer PW 3710 (40 kV, 30 mA) with CuKa radiation and equipped with a fixed divergence slit and a secondary graphite monochromator was used. Random powder samples were scanned with a step size of 0.02° 2 theta and counting time of 1 second per step over a measuring range of 2° to 65° 2 theta. Additional scans were performed from 17° to 28° with a counting time of 30 seconds per step to evaluate the disordering of the kaolin group minerals.

An FEI QUANTA 600 FEG scanning electron microscope with an energy-dispersive system (SEM-EDS), was used to assist in mineral identification and image analysis for morphological studies.

Dried samples of sedimentary rocks were crushed to minus 1 mm and placed in a 3-cm-diameter mold and vacuum-impregnated with epoxy resin. Following impregnation, particulate blocks were subjected to dry grinding and polishing. For huminite/vitrinite reflectance (Glossary), 50 huminite/vitrinite particles were measured from each polished particulate block in accordance with German Standard Guidelines (DIN 22020, Part 5). A Leica DMRX microscope system was used for incident and fluorescent light microscopy using x 20, x 50, and x 100 oil immersion objectives and an MPV-2 photometer system. Digital images were captured using Leica DC 300F and Image Manager (Leica, IM50) software.

The total carbon (TC), total organic carbon (TOC) and the total sulfur contents (TS) of the samples were determined with a LECO CS 200 carbon-sulfur-analyzer by combustion in a high-frequency furnace at between 1,800°C to 2,200°C. The carbon dioxide and sulfur dioxide contents generated were measured with infrared detectors. For the TC and TS analysis, untreated rocks were used. The TOC was determined after removal of carbonates with 2N HCl at 80°C.

Rock-Eval Pyrolysis was performed with a Rock-Eval 6 instrument according to standard methods (Espitalié et al., 1977). About 100 mg of sample was pyrolized using nitrogen as a carrier gas. Pyrolysis products were measured with a Flame Ionization Detector (FID), and the concurrent released carbon dioxide was determined by infrared detection. The temperature program started with an isothermal step for 3 minutes at 300°C followed by a heating step up to 650°C at a rate of 25°C/minute. Hydrocarbons released during the isothermal and heating steps are quantified as S1 and S2 peaks, respectively (both in milligram hydrocarbons per gram rock). Carbon dioxide generated to 400°C is summed as S3 (in milligram carbon dioxide per gram rock).

Hydrogen and oxygen indices (HI and OI) were S2 and S3 normalized to the TOC content. Tmax is the temperature of the maximum generation of cracking products. About 6 g of the fine-grained samples were extracted in a Dionex Accelerated Solvent Extractor 200 at 80°C and 1,200 psi with dichloromethane/methanol (DCM/MeOH) 95:5 as the solvent. Sulfur was removed with activated copper granulate. After a clean-up procedure using silicagel and hexane, the aliphatic fraction of the extract was injected into a Hewlett Packard 5890 gas chromatograph, coupled to a 5972 Hewlett Packard Mass Selective Detector. A 30-m-long nonpolar fused silica capillary column was used, operated at a temperature program of between 50°C and 300°C. In the Selected Ion Monitoring Mode, mass fragments m/z 71 (n-alkanes), 191 (triterpanes), 217 (5α, 14α, 17α-steranes) and 218 (5α, 14β, 17β-steranes) were recorded. Total ion current traces and full spectra of selected compounds were recorded using a 95 S Finnigan gas chromatograph/mass spectrometer system.

All samples containing organic matter were double-checked by coal petrographic and mineralogical methods, for example, SEM-EDX (scanning electron microscope-energy dispersive using X-rays), to ensure that subaerial processes had no impact on the samples taken. Degradation of organic matter at outcrop can therefore be ruled out.

COALY AND ORGANIC-RICH AMBER DEPOSITS

An Overview of Coal on the Western Margin of the Arabian Plate

(See Glossary for coal/organic matter terminology.)

The western margin of the Arabian Plate is barren of economic coal accumulations. Coalified matter is only of importance in this region in association with amber, a commodity that has brought Lebanon to the attention of gemologists. Lower Cretaceous amber sites in Lebanon, Palestine and Jordan are commonly considered to be of great scientific and jewelry interest (Azar, 2000; Poinar and Milki, 2001; Kaddumi, 2005).

Egypt is the only Middle Eastern country to have viable deposits of coal. The Middle Jurassic Safa Formation contains workable coal seams in the Maghara area of northern Sinai (Hassaan et al., 1992; Mostafa and Younes, 2001). The extracts of the coal have an atypical n-alkane distribution whereby the gas chromatograms are dominated by unusual compounds eluting between n-C19 and n-C21. These compounds suggest significant conifer contributions to the coal. Carbonaceous shales and coal samples from these seams are characterized by organic material that could have been derived from non-microbial organisms such as ferns. The Maghara coal was formed in a wet forest–swamp environment situated in a marine-influenced lower delta plain (Mostafa and Younes, 2001). No workable coal seams occur anywhere higher in the stratigraphic sequence; however, concentrations of organic matter occur similar to those investigated in Jordan.

Organic matter is also found in Late Aptian to Early Cenomanian (mid-Cretaceous) sediments on the paleoshelf of northern Sinai. The organic facies is dominated by hydrogen-depleted OM of either terrestrial or degraded marine origin (kerogen types III and IV) (Kim et al., 1999). The organic facies of mid-Cretaceous deposits from northern Sinai indicates a proximal fluvio-deltaic or oxic shelf environment. Random vitrinite reflectance values range from 0.6% to 0.7% Rr, equivalent to high volatile bituminous coalification stages.

Coaly and Organic-rich Amber Beds near Jerash

Stratigraphy and Geology

Near Jerash in northwestern Jordan, the Aptian–Albian Kurnub Group that is approximately 200 m thick, rests unconformably on the Kimmeridgian Mugha Formation and is overlain by the Cenomanian Naur Formation of the Ajlun Group (Amireh, 1997) (Figures 2 and 3). In our study area, the Kurnub Group consists of three regressive-transgressive depositional sequences, whereas continental clastics predominate in central and southern Jordan.

The lowermost part of the sequence in the Jerash area is composed of sandstones and conglomerates containing abundant plant debris that was deposited in a unidirectional stream system with a paleocurrent directed toward the north-northwest (Amireh, 1997). The upper half of the section contains abundant coaly and organic-rich beds centimeters to decimeters thick, alternating with calcareous sandstone units and oolitic ironstones. Organic-rich shales with leaf imprints, charcoal accumulations and amber pebbles occur frequently (Figure 2; location indicated by the wide vertical bar between 120 and 150 m). Underlying the Cenomanian Naur Formation, glauconite beds and iron-bearing sandstones are interbedded with arenaceous and argillaceous bedsets (Figure 3). The glauconite occurs in an arenaceous dolomite unit, referred to as the glauconite marker unit (GMU), in the upper part of the Kurnub Group that persists throughout Jordan (Figures 3a, c) (Amireh et al., 1998). The stratigraphic age of the Early Cretaceous Kurnub Group is based on the K-Ar dating of the glauconite. The apparent age, constrained within the analytical uncertainty limits and derived from the most evolved glauconite, is 96.1 ± 1.1 Ma; this suggests that the GMU is of Early Cenomanian age (Figure 3c).

Petrography and Mineralogy

Bandel and Haddadin (1979) recorded seams of low-quality, high-ash coal (lignite) and associated amber along the Zarqa River northeast of Amman. The sequence shown in Figure 4 hosts a decimeter-thick bed of organic and coaly matter with pebbles of amber. The sedimentary section consists of centimeter-thick, thinly laminated layers of whitish-gray sand, and dark-gray organic and coaly matter that are stained with sulfate. The coaly and organic-rich amber bed passes upward through bedded sandstones into massive amalgamated sandstone, and below into gray organic-rich mudstones. Varicolored sandstones containing abundant in goethite, hematite and gypsum replace the coaly–sandstone couplet laterally. The fining-upward cyclicity proposed for a major part of the Kurnub Group (see above) may locally turn into regressive cycles as shown in Figure 4.

The host rocks of the coaly and organic-rich sedimentary beds are mudshales with silty intercalations composed of quartz, illite, kaolinite, and anatase, together with minor amounts of alkaline feldspar and organic matter (Figure 5a, Table 2). The detrital grains are well sorted and subrounded to rounded. The roundness parameter, however, is strongly affected by the replacement processes along with cementation that has caused deterioration of the roundness of quartz clasts and destroyed almost all labile constituents; for example, alkaline feldspar. Grains are freely floating within the fine-grained argillaceous matrix and sulfide cement. The clean and mature sandstones are infiltrated by goethite substituting for the argillaceous matrix of illite and kaolinite (Figure 5b). The sequence of mineralization in the pore space of the sandstones is as follows: quartz-illite-OM ⇒ kaolinite-pyrite-marcasite ⇒ goethite ⇒ Fe sulfate (Figure 5d). Eventually, the entire pore space of the sandstones and mudshales is occluded by marcasite and pyrite and minor amounts of sphalerite (Figures 5c and d).

Sulfides are the dominant minerals (other than quartz) in some of the siliciclastic rocks (see TSC, Table 2). Figure 5e shows the youngest generation of pyrite lining the pore spaces and infilling to some extent the interstices. These pyrite crystals consist exclusively of octahedral crystals {111} with their edges beveled and smoothed by dissolution. They are poor in trace elements such as Ni, Co and As that may substitute for Fe in the pyrite structure (Vaughan and Craig, 1978; Duchesne et al., 1983; Dill et al., 1993, 1997). The most recent sulfide precipitation involved pyrite oxidation into Fe-Mg-sulfates that coat the coaly and organic-rich amber beds (Figure 5f). Globular aggregates of botryogen (an Mg-Fe hydrated sulfate) are responsible for the brown coatings visible with the naked eye, and needles of ferroan epsomite have also been detected. Rhombs of native sulfur occur along the boundary between quartz clasts and pyrite where kaolinite was almost totally destroyed and pyrite shows solutions pits (Figure 5d inset).

Coal/Organic Petrography and Organic Chemistry of Amber and Coal

At the Jerash site, distinct amber fragments several centimeters in size were recovered. These are most probably terpene-derived wound resins exuded at the plant surface (Taylor et al., 1998). Within large amber fragments, plant remains and other small-sized inclusions were recognizable in fluorescence mode.

Some amber nodules have inclusions of subparallel-aligned siliciclastic debris and the host nodules are fractured and the resultant fissures filled with illite (Figure 6a). Figure 6b shows elongated dark-yellow to dark-brown fluorescing streaks of possible plant origin embedded in a pale-green fluorescent resinitic mass. In addition, small inclusions of variable fluorescence, color, and intensity are detectable, but are of unknown origin. Similarly, numerous, vague and circular dark-brown fluorescent bodies were observed (Figure 6c) that resemble, to some degree, well-developed funginite. In Figure 6d, other elongated bright-yellow and dark-brown fluorescent bodies from 5 to 25 μm length are of unknown origin, but their shape indicates a layered deposition.

In fine-grained sandstone to siltstone, collotelinite is porous and fissured (Figures 6e, f). Where the fine-grained sandstone to siltstone is extremely rich in massive pyrite (grain size 100–400 μm), organic matter occurs in both the pore spaces and within clayey laminas. Porous collotelinite as well as telovitrinite were observed. Liptinite macerals are represented by thin-walled cutinite, microspores and isolated suberinites with a dark-yellow organic fluorescence (Figures 7a, b). In Figures 7c and d, fissured huminitic tissue (ulminite) and suberinite (Figures 7e, f) are shown in polished section in incident-light white-field mode and under blue-light excitation.

Collotelinite also occurs in medium-grained sandstone but is poorly preserved. It is porous, dissected by fissures and strongly corroded giving an impression of naturally weathered telovitrinite. In addition, suberinite and silty intercalations with liptodetrinite were also observed. Liptinite macerals are represented by fine alginite, dinoflagellates(?), and isolated cutinite as well as numerous microspores (Figures 8a, b) in samples from the Jerash section.

Coarse-grained sandstones are extremely rich in massive pyrite and frequently contain coaly particles. The organic matter in these coarse siliciclastics shows mostly intensive yellow organic fluorescence (vitrinite). The samples contain mainly ungelified to slightly gelified textinite.

In samples from the Jerash section, random vitrinite reflectance values range from 0.40% to 0.49% Rr (Table 3) suggesting that the coaly material is sub-bituminous A coal (“Mattbraunkohle” according to the German coal classification). The δ13C isotopic signature of huminite from Jerash is homogeneous at about –23‰ (Table 2). The relatively heavy carbon isotopes probably reflect a high contribution of gymnosperms to the biomass (see Bechtel et al., 2002, 2008, and references therein).

Four samples were analyzed using organic geochemical techniques. The total organic content (TOC) ranges from 0.5 to 2.3 percent. Three samples are very rich in sulphur (15–30%). The hydrogen index (HI) is about 40 to 50 mgHC/gTOC indicating a prevalence of type III kerogen. The content of liptinite, including resinite (amber), in these samples is low. Tmax values ranging from 396°C to 411°C indicate that the organic matter is thermally immature. The amount of soluble organic matter is low (30–70 mg/gTOC), which agrees well with the low maturity and low HI values. Gas chromatograms show a dominance of long-chain n-alkanes (see Figure 9). Pristane/phytane ratios range from 1.2 to 3.1. Figure 9 also shows high values of C29 steranes that are typical for coaly samples.

Depositional Environment

Amireh (1997) provided the first overview of the depositional environment of the Kurnub Group. A more detailed interpretation is given in this paper for the Jerash area (see vertical bar between 120 m and 150 m in Figure 2). The Kurnub Group consists of a 200-m-thick upward-fining succession that is a transition from fluvial to tide-modified sedimentation and reflects an overall deepening of the basin (Figures 2 and 3). Full marine sub-tidal conditions with glauconitic beds were attained during deposition of the Cenomanian Naur Formation (Figure 3). This glauconite horizon dated at 96.1 ± 1.1 Ma has been correlated with the Maximum Flooding Surface (MFS) K120 (98 Ma) of Sharland et al. (2001), in the Furais Shale of the lower Aijun Group in the Azraq basin, Jordan.

The conglomeratic lag deposits and coarse-grained siliciclastic sediments in the lower half of the Kurnub Group record braided-alluvial processes with a limited preservation potential for organic matter. The top strata of the various cycles within the Kurnub Group are best expressed in terms of sequence stratigraphy by the MFS K100 and MFS K110 (Figure 2), which allow for a correlation with the Burgan delta sediments in Kuwait and Iraq on a plate-wide scale (Al-Fares et al., 1998; Sharland et al., 2001). Leaf imprints predominate over well-developed seams of coaly material. Within the section studied, mudstone drapes, and vertically stacked sandstone-siltstone and mudstone laminations or tidal bundles typical of tidal flats, were not observed. However, some large-scale coarsening-upward cycles can be recognized within this overall fining-upward trend (Figure 4). The stacked cycles are attributed to a fluvial drainage system changing from alluvial-braided into meandering to anastomosing drainage patterns that, from time to time, were interrupted by marine inundation, probably related to absolute sea level fluctuations in a tidal-dominated system. Point-source tide-dominated delta systems gradually became replaced by linear shoreline-dominated tidal-flat systems toward younger series.

Estuarine series with peat-forming mangroves occur in the modern Fly River Delta of Papua New Guinea and are recorded from Permian through Eocene beds (Coleman et al., 1970; Petersen and Andsbjerg, 1996; Holz et al., 2002; Holz and Kalkreuth, 2003; Takano and Waseda, 2003). The coaly amber site studied in the Aptian-Albian Kurnub Group is almost identical in terms of age and depositional environment with the lignite-amber (“Burmite”) site from the Hukawng Valley of Myanmar (Cruickshank and Ko, 2003). In conclusion, the most appropriate site to concentrate organic matter in the form of coaly and organic-rich sediments together with amber, is in a tide-dominated delta overlying braided/meandering river deposits (Figure 2). The amber resin surrounded the siliciclastic debris during or subsequent to the compaction of the host sediment when associated sheet silicates were already parallel oriented {001}. Aging of the resin provoked shrinkage cracks that became filled with phyllosilicates (Figure 6a).

The coaly and organic-rich sediments are characterized by porous and fissured collotelinite. Deterioration of dispersed organic matter in siliciclastic sediments resulted from long-distance transport leading to the mechanical rupture of organic particles (Taylor et al., 1998). Other causes of corrosion of organic matter may include weathering associated with oxidation. These can generate changes in texture and color, respectively, causing microfractures, “dirty” and inhomogeneous surfaces, as well as dark oxidation rims, as detected in the examined samples. Such features can, however, also result from recrystallisation by the influx of late-stage hydrothermal fluids. Minerals at outcrop (green fields, Figure 10) are identical with those established from thermodynamic calculations at 25°C. Therefore, hydrothermal alteration of organic matter associated with these minerals is excluded. Mineral assemblages in the Jerash region are stable under near-ambient conditions and need no temperature increase. Random vitrinite reflectance as well as dark-yellow organic fluorescence of land-derived liptinite point toward the immature stage of the examined sediments in terms of thermal maturation of hydrocarbons. In some samples, the organic matter appears to be purely terrestrial. In others, the presence of lamalginite (phytoplankton), with dinoflagellates among the humic matter of land plants indicate, at least in part, deposition within a marine environment. These coal petrographic results corroborate the interpretation of the depositional environment.

The data obtained from organic chemistry also contribute to the environment analysis. According to Didyk et al. (1978), high pristane/phytane ratios (>3.0) indicated aerobic conditions during diagenesis, and values between 1.0 and 3.0 were interpreted as dysaerobic and values <1 as anaerobic environments. However, pristane/phytane ratios are affected by maturation (Tissot and Welte, 1984) and by differences in the precursors for acyclic isoprenoids (bacterial) origin (Goossens et al., 1984; Volkman and Maxwell, 1986; and ten Haven et al., 1987). Sterane patterns dominated by C29 steranes (80-86%) indicate a dominance of land plants (Volkman, 1986), whereas very low 20S/(20S+20R) sterane isomer ratios of the 5a(H),14a(H),17a(H)-C29 steranes (<0.04) result from low maturity (Mackenzie and Maxwell, 1981). Thus, the Jerash pristane/phytane ratios and C29 sterane values suggest slightly oxygen-reduced conditions and a dominance of land plants.

The coaly and organic-rich-amber beds near Jerash are rich in sulfur. There is a strong environmental control on the sulfur content of coal seams (Casagrande et al., 1977; Diessel, 1992; Phillips and Bustin, 1996, and Chou, 1997). Studies of modern peat subjected to marine influences document that S enrichment is attributable to sulfate-reducing bacteria promoting precipitation of pyrite in peat, and that coals having marine roof rocks have higher sulfur contents than those with fresh- or brackish-water–derived roof rocks. Similar, abnormally high S contents have also been reported from the estuary of the Paleo-Naab River system in Germany. Here, at the passage from a Miocene braided-river drainage system into a meandering fluvial system hosting coaly and organic-rich sediments, arenites are cemented with pyrite (>7 wt.% S) (Dill et al., 1993). Carbonaceous matter was concentrated in both environments under discussion in the low-gradient/low-energy near-shore fluvial drainage system, whereas sulfides were concentrated beneath in the high-gradient/high-energy more landward part of the river system. Dill et al. (1993) referred to this phenomenon of sulfur enrichment immediately beneath coal seams as a “sulfur keel”.

Post-depositional Alteration

Observations by Dill et al. (1997) on pyrites from various depositional environments show a close link between the morphology of Fe-disulfides (pyrite and marcasite) and processes related to the host environments. Pyritization and the formation of marcasite are part of the post-depositional alteration of sandstones of the Kurnub Group. Prior to the precipitation of pyrite, grain cement was leached and the resultant pore space in the arenites became much larger than the amount of mineralizing fluids available to fill the spaces. These well preserved pyrites show signs of exposure to fungal/bacterial activities. Murowchick and Barnes (1987) found during their laboratory experiments that any increase of temperature and/or degree of supersaturation sparks the formation of a sequence from cube via octahedron to pyritohedron. These effects of temperature and degree of supersaturation on morphology were investigated over a temperature range of 250°C to 500°C, which is beyond the temperature regime to be expected in the environment under consideration. Marcasite forms from aqueous solution under a restricted set of depositional conditions; for example, a pH less than 5, temperature less than 240°C, and the presence of H2S (aq) (Murowchick, 1992).

The accumulation of organic matter and muscovite in the siliciclastic depositional environment takes place under slightly alkaline conditions close to pH 8 (Figure 10a). Subsequent cementation of siliciclastic minerals by kaolinite and marcasite suggest a lowering of the pH to 5 (Figure 10a). Corrosion of sulfides and destruction of phyllosilicates attest to a hiatus between the reducing and oxidation stages as marked by the precipitation of sulfur. Sulfur was derived from organic matter concentrated in the interstices of the siliciclastics. According to the stability fields in the pH-Eh plot of Figure 10b, a strong drop in pH and an increase in Eh may be assumed. Destruction of kaolinite and formation of Fe(Mg)- sulfates are indicative of pH equal to or less than 4. An increase in the sulfur fugacity and the temperature of formation rising to as much as 100°C would cause kaolinite to break down, and alunite and diaspore to form instead. As these minerals were not observed in the samples studied, we can exclude any hydrothermal effect on this lignite mineralization on the coaly and organic matter (see previous paragraph).

Economic Considerations

Coal currently has no commercial value in Jordan. However, coaly material is a marker for amber and attention should be paid to amber as a raw material for handicrafts.

OIL SHALES

An Overview of Oil Shales along the Western Margin of the Arabian Plate

Oil shales have been discovered at various stratigraphic levels in Egypt (Troger, 1984; El Kammar, 1993; El Kammar et al., 1990). The oil shales at Al-Qusiema–Al- Kuntella and Al Thamad in East Sinai are characterized by high contents of volatiles (9.98–8.98 wt%) and fixed carbon (9.02–21.92 wt%). The evaluated reserves are 75 million tonnes per square kilometer. The oil shales are of Campanian to Maastrichtian age and are somewhat older than the oil shales from Jordan discussed below. The total volume of all organic-rich Cretaceous shale amounts to 4.5 billion barrels of oil in place in the Safaga-Qusseir area, and 1.2 billion barrels of oil in place in the Abu Tartour area (Hassaan and Ezz-Eldin, 2007).

Twenty oil shale deposits of Late Cretaceous age have been identified in Palestine with about 12 billion tonnes of oil-shale reserves identified (Minster, 1994). The average heating value of Palestinian oil shales is 1,150 kcal/kg of rock with an average oil yield of 6 wt%. The organic content of these oil shales is in the range 6 to 17 wt% with an oil yield of 60 to 71 l/t. The in-place oil shale resources are 4 billion barrels (Dyni, 2003).

Marine oil shales of Late Cretaceous to Paleogene age occur in the Wadi Yarmouk basin of southern Syria (Dyni, 2003). The Yarmouk deposit may prove to be exceptional large and to extend into Jordan where, although the thickness of the oil shales diminishes, they remain of potential economic size at several localities. As much as 90 percent of the oil shale in Jordan is amenable to opencast mining (Dyni, 2003). The composition and size of the most important oil shale deposits are listed in Table 4 and their locations shown in Figure 1c. The Sultani area has been selected for a more detailed study of the diagenetic and epigenetic alteration processes, since they may also shed light on uranium redeposition, another source of energy that has had little publicity.

Oil Shales at Sultani

Stratigraphy and Geology

Oil shales of the Muwaqqar Formation form the lower part of the Belqa Group. The Muwaqqar Formation is Maastrichtian to Paleocene in age and is well exposed in the Sultani Trench, an open pit used for test mining (Figures 11a, b). The organic carbon content is as much as 37 percent of the total volume in certain small basins such as El-Lajjun about 20 km east of Karak (Yassini, 1979) (Figure 1c). The sedimentary sequence at Sultani consists of bituminous marly limestones approximately 40 m thick, overlain by marls and marly limestones (Figure 11a). In the trench, bioclastic limestones and biolithites are underlain by oil shales and unconformably overlain by polymictic conglomeratic wadi sediments (Figure 11b). Limestone concretions with gastropods extend across the bottom of the trench (Figure 11c) and are interbedded with limestone composed of disarticulated bivalve shells forming a coquina (Figure 11d).

Petrography and Mineralogy

The oil shales at Sultani are well-laminated mudshales rich in calcite, illite, and calcareous biodetritus predominantly of planctic foraminifers and the debris of unidentified bivalves, and also forams that do not show any reworking or destruction of their tests (Figure 12a). Francolite (carbonate-fluorapatite) debris is common to these mudshales (Figure 12b) as are sulfides. Zinc sulfides are most common followed by pyrite and marcasite, as corroborated by the chemical analyses of the oil shales that average 0.16 wt% Zn. As a result of scanning electron microscopic (SEM) observations, the ZnS aggregates have been subdivided into cubic sphalerite (ZnS) and hexagonal wurtzite (Zn, Fe)S. Tiny platelets among the ZnS aggregates suggest that in addition to sphalerite, wurtzite is present in the oil shales (Figure 12c). The Fe content of sphalerite/wurtzite ranges from 1.1 to 2.2 wt.% Fe.

Relatively high quantities of uranium in the oil shales at Sultani (Table 2) prompted a closer examination of uranium minerals. The most common uranium mineral is (meta)-tyuyamunite [Ca(UO2)2(VO4)2·6(H2O)] that precipitated from U- and V-bearing fluids percolating through the oil shales (Figure 12d); the prefix (meta) has been added to indicate the effects of weathering. The mineral is widespread in calcretes and in sediments enriched in organic matter (Dall’aglio et al., 1974; Mann and Deutscher, 1978; Dill, 1983a). The presence of another yellow secondary uranium ore mineral, wyartite [Ca3U(UO2)6(CO3)2(OH)18 ·3(H2O)] that is also present as tiny plates, cannot be confirmed in this organic-rich environment by SEM analysis alone. No black uranium minerals such as pitchblende, from which wyartite is derived, have been detected.

The oil shales also have anomalously high contents of Sr, Ni, Mo and Cr (Table 2) but at too low a level to form minerals of their own. They are absorbed onto the organic matter or accommodated in the structure of iron sulfides.

Organic Petrography and Organic Chemistry

The alginite and sporomorphs in dark-brown, fine-grained bituminous and calcareous shale show a pale-yellow to intense yellow organic fluorescence. The shale is characterized by well-developed microlaminas and incompletely combusted particles of pyrolitic carbon and of amorphous bituminous matter. The organic matter is composed of partially porous telohuminitic streaks with alginite and sporomorphs (width 1–4 μm) (Figure 8e). Char particles and collotelinite are embedded into shaly laminas (Figures 8c, d).

The oil shale is characterized by high TOC (18.4) and sulfur contents (5.2%). A HI of 715 classifies the organic matter as kerogen type I (to IIS) and agrees well with the high content of liptinite macerals. A high percentage of C27 steranes (38%; Figure 9) correlates with abundant alginite macerals and large amounts of short-chain and long-chain n-alkanes. A vitrinite reflectance of 0.32% Rr (Table 3), a Tmax of 405°C and the sterane isomer ratio of 0.05 show that the organic matter is immature (Peters, 1986; Mackenzie and Maxwell, 1981).

The δ13C isotopic signature of organic matter in the oil shales of the Sultani Trench, the tar sand in Wadi Isal, and the oil seepage near Kharazeh are almost identical and cluster around -29‰ compared with -22.9‰ for the Jerash section (Table 2). The high proportion of lipid-rich organic material in both the oil shale and the source rock of the migrated petroleum at Wadi Isal and Kharazeh explains the observed depletion in δ13C relative to the Jerash coaly material.

Depositional Environment

The first description of the lithology of the Sultani oil shales was by Abu Qudaira (1996). The inorganic and organic sedimentary features observed in the underlying and overlying rocks of the oil shales of the Muwaqqar Formation attest to a shallow-marine depositional environment at the Cretaceous-Paleogene boundary (Figure 11a). Strong productivity due to upwelling currents along the shelf edge (Figure 11a) is reflected by a bimodal n-alkane distribution in the GC-FID traces that indicates the presence of autochthonous and allochthonous organic matter (see Figure 9). A fairly high degree of physical and chemical stress as a result of stenohaline conditions is a feature of this part of the Muwaqqar Formation. The stenohaline conditions contributed to the small number of species. Bivalves are preserved disarticulated and strong reworking of fossils was widespread. The shell hash of randomly distributed bivalve shells reflects storm events that formed tempestites (Figure 11d). The storm surges caused ravining of the underlying limestones. Gastropod colonies within the “ravines” attest to local tranquil conditions that allowed mound-like built-ups to develop. The oil shale with its planctic forams was the result of a moderate energy regime and deep-water conditions. The presence of glauconite and phosphate particles indicates another upwelling event that occurred in the aftermath of the deposition of the oil shales.

The upwelling currents that took cold water from the deep Neo-Tethys Ocean in the north and west onto the epicontinental shelf were usually rich in Si, P and other elements necessary for the bloom of planktonic organisms. This explains the completely different sedimentation regime of the Belqa Group from that of the Ajlun Group. Abundant chert, phosphorite, porcellanite and oil shale deposits, none of which are found in the Ajlun Group, characterize the Belqa Group. Throughout the Belqa Group, organic-rich sediments are present in varying amounts. However, the richest and most extensive are the oil shales of the Muwaqqar Formation (Yassini, 1979). Similar, but less important oil shales, are present in the underlying Lower Maastrichtian Al-Hisa Formation (Table 1). The deposition of the phosphorite and oil shale took place in small basins created by the Syrian Arc tectonic events that were the locus of upwelling currents (Abed and Amireh, 1983; Abed et al., 2005). Within the small basins, the lower part of the water column seems to have been anoxic with an overlying O2/H2S interface, as in the present-day Black Sea. The basins had a shallow depth range of 40 to 50 m that may explain the abundance of organic matter (Abed and Sadaqah, 1998).

These sedimentologic findings are supported by organic petrography. Numerous foraminifers, bivalves, and gastropods, and the presence of alginite among partially porous telohuminitic streaks and sporomorphs, indicate short distance transportation in a proximal setting and deposition within a lagoonal environment influenced by siliciclastic input into the small, restricted Sultani basin on the continental shelf.

The organic chemistry supports the interpretation of the depositional environment. The high percentage of C27 steranes (see Figure 9) correlates with large amounts of alginite derived from algae and cyanobacteria. The rock extract is characterized by high concentrations of thiophenes. This is an indication of enhanced organic sulfur incorporation. A very low pristane/phytane ratio of 0.29 argues for anoxic conditions during deposition of the oil shale (Didyk et al., 1978).

Post-depositional Alteration

Post-depositional diagenetic to epigenetic alteration is a feature of the oil shale. Heimbach and Rösch (1982) recorded the presence of wolchonskoite (a chromium-bearing clay mineral) in the mottled zone of oil shales near Khan ez Zabid southeast of Amman (see Figure 1c). Chromium in silicified travertine in the same area is indicative of hydrothermal activity and may have been leached from the underlying oil shales.

Data collected during our petrographic examinations of the oil shales do not support high temperatures representative of sanidinite metamorphic facies. Iron values in the Zn sulfides are low and similar to low-temperature hydrothermal vein-type deposits. In the case of the oil shales, they may be explained by late diagenetic to low-temperature hydrothermal processes. Uranyl vanadates are decisive in constraining the physical and chemical conditions during post-depositional alteration of the oil shales in the Sultani area (Figure 13). Tyuyamunite (a yellow secondary calcium-uranium-vanadium mineral) is stable over a wide pH range as illustrated in Figure 13a. Its presence explains the anomalous U and V values in the oil shales. However, between 200°C and 300°C it is unstable. Why tyuyamunite developed instead of its phosphate analogue autunite is not known. It may be due to a preponderance of VO43+ over PO43+ or the presence of more acidic pore fluids that did not allow autunite to form (Figure 13b).

Economic Perspectives

Oil Shales

Oil, gas, and coal deposits are scarce in Jordan but there are large and high-grade oil shale deposits that are potential future energy resources (Knutson et al., 1987; Willmon, 1992; Hamarneh, 1998; and Jaber and Probert, 1997, 1999). Of the 18 known deposits, eight, namely El-Lajjun, Sultani, Jurf Ed-Darawish, Attarat Um El-Ghudran, Wadi Maghar, Siwaga, Khan ez Zabib and El-Thamad, have been studied most intensively. The reserves and chemical and physical properties of the five most important locations are listed in Table 4.

In the sites investigated, the high TOC content, the kerogen type, and the amount of soluble organic matter (142 mg/gTOC) characterize the oil shale as an excellent hydrocarbon source rock (Peters, 1986). According to MEES (2008a), the Jordanian government and Royal Dutch Shell were in the final stages of concluding a concession agreement that will allow Shell to explore the country’s large oil shale reserves. Shell is expected to invest more than US$20 billion in the oil shale project over a period of 20 years. The concession extends from northern Jordan to Siwaga near Karak, southeast to al-Jafr, east to Wadi Sirhan on the border with Saudi Arabia, and north to Azraq. According to the National Resource Authority (NRA), Jordan has 40 to 60 billion tonnes of proven oil reserves in oil shale in the 18 known deposits, with a potential to produce up to 4 billion tonnes/year of crude oil.

The NRA signed a memorandum of understanding on September 10, 2008 with a consortium of Petrobras from Brazil and Total from France for oil shale exploration in Wadi Maghar (see Figure 1c) (MEES 2008b). The consortium will carry out a comprehensive one-year exploration program. If successful, an additional three years would be needed before the start of commercial oil production from the shales. Jordan had previously signed agreements with Shell and Eesti Energia (Estonian Energy), and local companies to investigate oil shale development.

Uranium

The Belqa Group is not only important for its oil shales and phosphorites but, because of its primary uranium content, it also bridges the gap between hydrocarbons and nuclear energy. The presence of yellow secondary uranium minerals in the oil shales is a guide to primary uranium mineralization. The world average uranium content in phosphate rock is 50 to 200 ppm. Marine phosphorite U deposits are below average at between 6 and 120 ppm U, whereas organic phosphorite deposits contain up to 600 ppm U (Baturin, 2002) as U may substitute for Ca in the apatite lattice. Although world uranium resources in phosphate rock are uncertain, marine phosphorites are low-grade, large-tonnage deposits with millions of tonnes of uranium potentially available as a by-product of phosphate mining in Morocco: (6.9), USA (1.2), Mexico (0.15), and Jordan (0.1).

In Jordan and the northern Negev and Judean Desert of Palestine, Senonian to Paleocene phosphorites provided U that is contained in a varied mineral assemblage of gypsum, vanadate, meta-autunite, (meta)-tyuyamunite, strelkinite, and carnotite in calcretes and gypcretes of Quaternary age. Areas abundant in uranium concentrations in Jordan are shown in Figure 1c. Uranium was leached from the phosphorites and migrated toward the Dead Sea Rift Valley where it was concentrated in the soil (Ilani and Strull, 1988; Minster et al., 2004). Pedogenic layers such as gypcrete acted as lithologic traps and fixed uranium, particularly under reducing conditions. Reasonably assured resources plus inferred resources of approximately 80,000 tonnes of recoverable U (at US $130/kg U) at Wadi Araba-Dana, Dubaidel-Mudawwara, Hamra-Huasha and Wadi Al Baheyya in near-surface carbonates, place Jordan currently twelfth in terms of uranium availability worldwide. In addition, Jordanian phosphorite is a potential source of uranium. It is difficult to calculate the recoverable U from low-grade, large tonnage deposits such as the Jordanian phosphorite, but they may contain as much as 100,000 tonnes of U (OECD NEA & IAEA 2007). According to Xinhua (2008), Jordan is currently negotiating a cooperation deal with a French company to purchase a nuclear reactor to produce electricity and enriched uranium for peaceful purposes. Its civil nuclear energy program, under which a nuclear plant will be built by 2015, will enable nuclear power to make up 30 percent of its energy production by 2030. Jordan is also negotiating with Canada, the USA, and China on nuclear cooperation.

TAR SANDS

An Overview of Tar Sands on the Western Margin of the Arabian Plate

Currently, the largest single tar sand deposit in the world is the Athabasca deposit in northeastern Alberta, Canada. There has been little modern research on this unconventional hydrocarbon-based energy resource in the Middle East. However, in earlier times, bitumen was recovered from tar sands in Mesopotamia and shipped to Ancient Egypt. Today, the most well-known tar sand deposit is at Al-Bushri, west of Deir ez-Zour, in eastern Syria. Here, asphalt is found in Upper Cretaceous to Miocene rocks (Alsharhan and Nairn, 1997), the source of which may lie in the Euphrates Depression. Asphalt shows are recorded in the Middle and Upper Cretaceous rocks of the Palmyra Fold Belt. It is believed that they represent oil generated as a result of deep burial during the Tertiary. The Hasbaya deposit in Lebanon (Figure 1c) has been related to similar deposits along the Dead Sea Rift. Asphalt in Cretaceous rocks in Lebanon resulted from the concentration of oil released by Tertiary erosion (Alsharhan and Nairn, 1997). These processes may be relevant to Jordanian tar sands.

Tar Sands of the Kurnub Group in the Wadi Isal Area

Stratigraphy and Geology

Tar sands have been found along the north-trending Al-Kharazeh Fault in the Wadi Isal area (Figure 1b and 14). The tar sands belong to the Kurnub Group and are stratigraphically equivalent to the section shown in Figure 2. The tar sands in the Wadi Isal area are placed stratigraphically below the coaly and organic-rich amber beds in Figure 3. However, the Wadi Isal lithology is very different, particularly with regard to the amount of syngenetic organic matter. In particular, siltstones are rich in comminuted plant material and seams of coaly material. They stratigraphically underlie the tar sands. In general, the Kurnub Group is a clastic sequence made up of clean sandstones containing only minor plant debris that alternate with conglomerates. The arenaceous rocks, up to 160 m thick, show tabular cross bedding whose bedsets and foreset lamellae are highlighted by the hydrocarbons that migrated into the sandstone (Figure 14b). Limestones and marls of the Naur Formation overlie the tar sands.

Petrography and Mineralogy

The mineral grains and lithoclasts of the tar sands range from fine- to coarse-grained. In the various bedsets, the sandstones are well sorted and moderately well rounded to angular. The mature or high-silica sandstones are composed of quartz aggregates and quartz grains that are homoaxially overgrown by a younger generation of quartz (Figure 15a). The predominance of quartz is also shown by the high SiO2 contents in the chemical composition of the quartz arenites (Table 2). The only detrital accessory mineral identified by SEM was zircon. Organic matter is concentrated intergranular and intragranular. Hydrocarbons fill the pore spaces between quartz grains that show evidence of corrosion, and solid bitumen is also present along the grain boundaries between the primary quartz nuclei and their envelope of secondary quartz (Figures 15a and b). In addition to quartz and zircon, kaolinite is the third silicate present in the quartz arenites (Figures 15c, d). Booklets of kaolinite occur between the quartz grains and were transformed into organo-mineralic compounds by organic matter migrating into the kaolinite aggregates. In places, the kaolinite platelets form concertina-like structures (Figure 15d). Quartz adjacent to this intimate intergrowth is strongly corroded (Figure 15d). The SEM-EDS analyses of these mineral assemblages revealed the presence of considerable amounts of sulfur. Pyrite and alunite are responsible for the elevated S contents (Figure 15e). Due to the tiny grain size of these pseudocubic mineral aggregates, alunite can only be described as a member of the aluminum-phosphate sulfate supergroup and cannot be investigated in detail (Störr et al., 1991; Stoffregen, 1993; Stoffregen et al., 1994; Jambor, 1999; and Dill, 2001). Another sulfur compound identified by means of SEM-EDS is phosphoalunogen. The most recent post-depositional alteration, affecting these organic matter-bearing sandstones, was the formation of salcretes that seal the sandstones (Figure 15f).

Petrography and Organic Chemistry

The organic matter of the tar sand is composed of solid bitumen filling the pore spaces between quartz grains (Figure 8f). The reflectance of the solid bitumen is low (<0.3% Rr, Table 3). Two samples of tar sands have been investigated geochemically. These samples contain about 2.3 percent organic carbon and 0.4 percent sulfur. The amount of soluble organic matter is very high (>1,000 mg/gTOC). Hydrogen index values in the range of 530 to 570 mgHC/gTOC are typical for migrated bitumen (for example, Peters, 1986). The Production Index (S1/(S1+S2)) yields information on the ratio between hydrocarbons present within the rock and those that can be generated during pyrolysis. In the presence of migrated bitumen, this ratio is typically high, but very low (<<0.1) in the present case. This is probably a result of biodegradation that resulted in the total removal of n-alkanes (Figure 9). According to the gas chromatogram of the Wadi Isal tar sands, biodegradation reached stage 6 on the classification of Peters et al. (2005).

Depositional Environment

The environment of deposition in the Wadi Isal area is similar to that of the coaly amber site in the Jerash area, but more proximal to the sediment source area (Figures 2 and 14). Correlation of the two sites by means of maximum flooding surfaces is difficult. Only MFS K120 may be traced from the Jerash area through to this section (Figure 14). The tar sand was laid down in a fluvial environment (Figure 14). The presence of zircon as the only heavy mineral underscores the supermaturity of these quartz arenites. The high ZTR (zircon-tourmaline-rutile) index (Hubert, 1962) suggests strong redeposition and alteration of the primary siliciclastics. Inter- and intragranular organic matter attest to a polystage migration of hydrocarbon into very clean sandstones. It is not known whether this conspicuous depletion in labile mineral constituents observed in the tar sands is due to provenance variation, or is a product of post-depositional alteration.

Post-depositional Alteration

At Wadi Isal, solid bitumen (migrabitumen) is present in the pore spaces between quartz grains. Based on the reflectance of about 0.2% Rr and brown fluorescence, the detected solid bitumen is classified as albertite (Jacob, 1989). Because of the severe biodegradation, the significance of biomarker ratios for the reconstruction of the depositional environment of the source rock is limited.

Hydrocarbon migration has been a polystage process prior to silicification and following kaolinization (Figure 15). The presence of kaolinite and aluminum-phosphate sulfates in the Wadi Isal area indicate a rather low pH for the mineralizing fluids percolating along the north-trending Al-Kharazeh Fault. Judging by the mineral assemblage in the Jerash and Wadi Isal areas, the pH was much lower in the tar sands than in the coaly amber beds (Figures 10 and 16). An increase in sulfate activity to log a SO42- = -2 increases the stability field of alunite at the expense of kaolinite (Figures 10a and 16a). The activites (log a) are used to calculate the stability diagrams. Fluid temperatures rising to more than 100°C cause further changes to the stability field and the destruction of kaolinite to form diaspore, a mineral not seen during examination of the samples (Figure 16b). The presence of alumino-sulfates suggests an increase in temperature and another drop of the pH value toward pH 2. Such reactive fluids could well explain the clean nature of the supermature sandstones and also the provision of pore space or accommodation space to take up the hydrocarbons. However, because some kaolinite is still present, we assume fluctuating pH values of between 5 and 2.

These findings have implications not only for hydrocarbon accumulations but also for fault-bounded mineral deposits containing uranium, base metals, mercury, and antimony. Solid hydrocarbons are concentrated along fractures and quartz veins and often are associated with black uranium ore minerals (Dill, 1983b). There are many different categories of native allochthonous bituminous substances found as vein deposits and defined as mineral wax (ozocerite), asphaltite (gilsonite, glance pitch, grahamite), and asphaltitic solid bitumen and pyrobitumen (wurtzilite, albertite, impsonite) (Jacob, 1967, 1989, 1993; Cardott et al., 1989). Mercury deposits such as New Almaden, USA, formed at less than 250°C in mineralized fracture zones containing cinnabarite, native Hg, pyrite, stibnite, chalcopyrite, sphalerite, galena, and bornite, accompanied by quartz and dolomite and hydrocarbons (Studemeister, 1984). These fault-related hydrocarbon deposits may also assist in better understanding some world-class gold-(copper) deposits designated as “Carlin-” and “High-sulfidation-” or “Alunite-kaolinite” types.

Economic Considerations of Jordanian Tar Sands

Khraisha (1999) investigated the extraction and pyrolysis of tar sand from Wadi Isal. He concluded that mixing time, temperature, particle size, and alkali concentration are the important parameters for bitumen recovery. Kerosene extraction yielded a maximum bitumen recovery of about 43 percent at 80°C and 180 to 250 μm particle size, whereas hot water extraction is ineffective since only a small amount of bitumen was obtained at the same temperature. As an unconventional energy resource, tar sands may be of interest only provided there is a sufficiently large volume amenable to open-pit extraction. As a result, stratiform tar sands have eclipsed fault-related tar sands. Also, in view of the importance of Jordanian stratiform oil shale reserves, the fault-related tar sands are at present of little economic value, although the situation may change in the future. In addition to the tar sands in Wadi Isal, there are occurrences in Wadi Aheimir and Wadi Dhira (Figure 1c).

OIL SEEPS IN THE AMMAN FORMATION IN THE KHARAZEH AREA

Stratigraphy and Geology

The Campanian Amman Formation of the Belqa Group (Table 1) contains oil seepages that are structurally related to the north-trending Al-Kharazeh Fault in the Kharazeh area. The section studied is in the upper part of the Amman Formation that stratigraphically underlies the section exposed in the Sultani Trench (Figures 11a and 17a). Chalky beds of the Ghudran Formation and limestones of the Wadi Es Sir Formation (Aijun Group) underlie the Amman Formation. The Amman Formation is composed of limestones interbedded with chert. The overlying units attributed to the Muwaqqar Formation are lithologically different from those reported from the Sultani Trench as they are marly limestones about 20 m thick. In the study area, the oil seepage is located in the footwall carbonates of the Al-Kharazeh Fault, terminated above by a secondary fault dipping at a lower angle than the main fault and in the opposite direction (Figure 17b).

Petrography and Mineralogy

The gray dolomitic and calcitic limestones at Kaharazeh have been impregnated by oil along grain boundaries of the rhombohedral carbonate crystals (Figure 18a). As a result of dolomitization, calcite has been replaced by dolomite to more than 60 vol.% in some parts of the limestones. Elevated sulfur contents in samples (Table 2) are due to the presence of swallow-tail gypsum that marks the selvage of the fault and also cements fragments of the mudshales within the fault gouge (Figure 18b). In addition to the gypsum, numerous oxidized massive to framboidal pyrite grains were observed. As in the Wadi Isal tar sand, halite is the youngest mineral, forming coats of salcrete on the calcareous host rocks. A mineral species found in this oil seepage that cannot be identified precisely is a hydrated chlorine-bearing Ca-(Mg) silicate, possibly amstallite (CaAl(Si,Al)4O8(OH)4·((H2O),Cl). This mineral was first recorded from a graphite quarry in Amstall, Austria, and results from hydrothermal alteration of metamorphosed carbonaceous rocks (Quint, 1987).

Petrography and Organic Chemistry

A few sub-microscopic agglomerates of amorphous bituminous substance in pore spaces represent organic matter. Its reflectivity is high at 0.68% Rr. A few intercalations of black, most probably organic-rich laminas, were also identified.

The organic carbon content of the oil-bearing carbonate rock at Kharazeh is about 1 percent. A very high oxygen index indicates weathering of the organic matter, but the presence of n-alkanes suggests that biodegradation was not severe (Figure 9). A high 20S/(20S+20R) sterane isomer ratio (0.45) argues for a mature source rock for the oil seepage (Mackenzie and Maxwell, 1981). The presence of C27 and C28 steranes in considerable quantities suggests a high contribution of aquatic organisms to the organic matter in the source rock (Volkman, 1986). This is also supported by a low δ13C ratio (Table 2).

Interpretation

Depositional Environment

The Amman Formation provides an insight into depositional environments prevailing before oil shale deposition. It may be correlated with the Jordanian oil shales as well as other hydrocarbon sites on the Arabian Peninsula using sequence stratigraphic planar elements such as Maximum Flooding Surfaces (MFS) (Figures 11 and 17). The evolution of the oil shale basins of the Muwaqqar Formation was preceded by subsidence of shallow-marine basins (with local deeps) and succeeded by another deepening of the basin. The entire lithological section illustrated in Figure 17a reflects the depth variations on an extended shelf bordering the Neo-Tethys Ocean. With respect to the emplacement of organic matter, this hydrocarbon trap is more akin to the Wadi Isal area with its fault-bounded organic matter.

Post-depositional Alteration

Fine crystalline carbonate in the samples from the Kharazeh area display sub-microscopic agglomerates of an amorphous bituminous substance in pore spaces between sediment grains. The carbonate texture is fully intact and there are no signs of strong corrosion by any fluid prior to hydrocarbon migration. Given both the numerous massive iron oxide particles and oxidized massive to framboidal pyrite grains, the activity of sulfate-reducing bacteria may account for the incorporation of sulfur into iron-limited shallow-marine carbonates. Unlike the Wadi Isal area, this type of organic-matter mineralization is not the high-sulfidation or alunite-type of alteration that might create or at least enhance the pore spaces. Pyrite, gypsum, and an uncertain chlorine-bearing Ca-Al-silicate, do not provide evidence as to the pH-Eh regime at this site. Nevertheless, strongly alkaline or acidic conditions may be ruled out, and approximately neutral pH values are a plausible explanation for the fluids that gave rise to the Kharazeh oil seepage system.

Economic Considerations

The seepage system is ranked inferior to the fault-related tar sands with regard to the economic potential. It may, however, shed some light on deeper resources. A deep-seated hydrocarbon source rock in the form of Silurian organic-rich graptolitic shales is present in Jordan and has given rise to the Risha gas field (Lüning et al., 2005). These “hot” (radioactive) shales occur in two horizons worldwide and are renowned as “low-grade, large-tonnage uranium deposits” (Dill, 1986; Dill and Nielsen, 1986). Some of these shales also contain lenses and nodules of phosphate, pyrite, marcasite, sphalerite, and chalcopyrite (Dill, 1986; Dill and Nielsen, 1986). A closer look at the chemical composition of the mineralization in the vicinity of the Al-Kharazeh Fault (Table 2) shows Zn, Ni, Cu, and Co to be anomalously enriched, as are the oil and hot shales.

CONCLUSIONS

The Cretaceous-Paleogene series in Jordan formed under variable conditions along the passive shelf margin of the Neo-Tethys Ocean, and in various grabens and troughs in what was the northeastern margin of the African Plate. In Jordan, the marine to near-shore siliciclastic-calcareous series of the Kurnub Group (Aptian-Albian), and the Amman (Campanian) and Muwaqqar (Maastrichtian to Paleocene) formations, host various types of organic matter and related uranium mineralization. Some of the deposits are of economic interest.

The four types of energy resources that are the subject of this paper (coaly amber beds near Jerash, oil shales at Sultani, tar sands at Wadi Isal, and oil seepages near Kharazeh) are strongly facies controlled and were subjected to hypogene and supergene post-depositional alteration, as follows:

  • Syngenetic coaly and organic-rich amber-bearing beds developed in a paralic environment (tide-dominated delta) of the Kurnub Group near Jerash, under slightly alkaline conditions and were altered under marginally acidic conditions at temperatures of below 100°C.

  • Syngenetic concentrations of organic matter occurred in a small restricted basin on the continental shelf and led to the formation of the Sultani oil shales containing abnormally high contents of V, P, Zn, and U. In the course of post-depositional alteration at temperatures well below 200°C, yellow secondary uranium minerals were formed. The close relationship of oil shales and phosphorites as well as the contemporary strongly arid climatic conditions provided favorable conditions for the emplacement of syn(dia)genetic and surficial uranium accumulations.

  • Epigenetic fault-related concentrations of organic matter were responsible for the Wadi Isal tar sands that are located in a similar environment of deposition to the Jerash coaly material. Alteration of the fluvial sandstones that host the tar sands is identified as a high-sulfidation type with the introduction of alumino-sulfate minerals.

  • In contrast to the Wadi Isal alteration, epigenetic fault-related oil seepage systems in shallow-marine calcareous rocks along the Al-Kharazeh Fault are low-sulfidation types with alumino-sulfate minerals migrating out as a result of post-depositional alteration.

  • The two types of alteration (high- and low-sulfidation) may have implications for stratiform base metal and precious metal deposits whose emplacement involves hydrocarbons as a carrier of metals among the mineralizing fluids.

DEDICATION

The authors dedicate this paper to the memory of Professor Dr. Friedrich Bender who passed away on May 27, 2008. Under his supervision, the senior author started his career as an economic geologist in the German Federal Institute for Geosciences and Natural Resources (BGR). Friedrich was Head of the Geological Mission of BGR to Jordan from January 1961 to May 1966. The Mission was involved in geologic investigations and the mapping of the entire country, together with mineral exploration and the training of Jordanian geoscientists. It assisted the Jordanian Government in establishing the National Geological Survey in 1965, which in 1966 was renamed the Natural Resource Authority (NRA). After 1966, Friedrich continued as an advisor to the NRA. He wrote the seminal work, “The Geology of Jordan”, published in 1974.

ACKNOWLEDGMENTS

We are indebted to I. Bitz for her assistance during mineral separation and grain-size analysis, F. Korte for the XRF chemical analyses, D. Klosa for SEM analyses, and D. Weck who performed the XRD analyses. All investigations were carried out in the laboratories of the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover, Germany. U. Berner, C. Ostertag-Henning and G. Scheeder carried out the organic chemistry analyses. Their contribution is kindly acknowledged.

We are grateful to two anonymous reviewers for their comments and to Moujahed Al-Husseini for his encouragement to integrate the latest press releases on Jordanian energy deals into this paper. We thank David Grainger for his editorial assistance and support, and GeoArabia designer Arnold Egdane for preparing the final design.

The senior author would like to express his gratitude to the German Academic Exchange Service (DAAD) who provided financial grants for his stays at Amman, Jordan. He would like to thank all his friends from the University of Jordan Geological Department for their great support during his stay as a visiting professor both in the field and in the classroom.

We extend our gratitude to Professor Dr. K. Toukan, Chairman of the Jordan Atomic Energy Commission for his talk at the University of Jordan on October 30, 2008.

GLOSSARY

Alginite – a maceral of sapropelic coal (e.g., boghead-type) and organic-rich sediments (e.g., oil shales) within the liptinite group, derived from algal matter and particularly resistant. (Taylor et al., 1998).

Alkane – any of the series of saturated hydrocarbons including methane, ethane, propane, and higher members.

Biolitites – An inclusive category for all organic limestone. It is usually applied to rocks made up of organic structures in growth position and not to debris broken from the bioherm and forming pocket fillings or talus slopes.

Collotelinite – a maceral of the vitrinite group, subgroup telovitrinite, with a homogenous, more-or-less structurless appearance occurring in coals and organic-rich sediments. (ICCP, 1998).

Cutinite – a maceral of coal and organic-rich sediments within the liptinite group, derived from cuticular layers and cuticles, formed within the outer walls of the epidermis of leaves, stems, and other aerial parts of plants. (Taylor et al., 1998).

Detrohuminite – a subgroup of the maceral group huminite consisting of fine humic fragments (<10μm) occurring in coals and organic-rich sediments. It is composed of loosely packed cell fragments of other humic plant debris. Depending on its gelification, detrohuminite is subdivided into the macerals attrinite (not gelified) and densinite (gelified). (Sýkorová et al. 2005).

Dinoflagellate – a one-celled microscopic, flagellated organism, chiefly marine and usually solitary, with resemblances to both animal and plant kingdoms.

Funginite – a maceral of coal and organic-rich sediments within the inertinite group, consisting of the sclerotia (hard, rigid fragments) of fungi or fungal spores, hyphae and mycelia (stromata, mycorhiza). ICCP (2001).

Huminite – a group of macerals in brown coals, consisting of humic matter derived mainly from lignin and cellulose occurring also in organic-rich sediments. It is the precursor of the vitrinite group in bituminous coals. (Sýkorová et al., 2005).

Inertinite – oxidized organic material or fossilized charcoal.

Lamalginite – a maceral of the alginite type. It is derived from small, unicellular or thin-walled, colonial planktonic or benthic algae with distinct lamellar form with little recognizable structures in sections perpendicular to bedding. It occurs in coals and organic-rich sediments. (Hutton et al., 1980).

Liptinite – a coal maceral group including sporinite, cutinite, alginite, resinite, and liptodetrinite, derived from spores, cuticular matter, resins, and waxes (Taylor et al., 1998). It occurs also in organic-rich sediments.

Liptodetrinite – a maceral of coal and organic-rich sediments within the liptinite group, having no recognisable structure and low reflectance and fluorescence. Because of its finely divided condition it cannot be assigned with certainty to any of the other macerals of the group. (Taylor et al., 1998).

Mudshale – a consolidated sediment consisting of no more than 10 percent sand and having a silt/sand ratio of between 1:2 and 2:1; a fissile mudstone.

Phytane – a diterpenoid alkane.

Pristane – a natural saturated terpenoid alkane.

Resinite – a maceral of coal and organic-rich sediments within the liptinite group, consisting of resinous compounds, often in elliptical or spindle-shaped bodies representing cell-filling matter or resin rodlets. (Taylor et al., 1998).

Sporomorphs – originate from the outer cell walls of fossil pollen grains or spores. It occurs in coals and organic-rich sediments. (Taylor et al., 1998).

Stenohaline – said of a narrow range of salinity.

Suberinite – a maceral of coal and organic-rich sediments derived from corkified cell walls that occur mainly in barks, and also at the surface of roots, on stems and on fruits as a protection against desiccation. (Taylor et al., 1998).

Telohuminite – a subgroup of the maceral group huminite comprising macerals with preserved intact variably visible botanical cell structures, and isolated cells. The subgroup consists of the macerals textinite and ulminite. It occurs in coals and organic-rich sediments. (Sýkorová et al., 2005).

Terpene – a large and varied class of hydrocarbons derived from a wide variety of plants, particularly conifers. They are the main components of resins.

Textinite – a maceral of the huminite group, subgroup telohuminite, consisting of ungelified cell walls either of isolated but intact individual cells or within tissues. It consists of humic substances as well as of the remains of cellulose and lignin. Textinite derives from the cell walls of parenchymatous and woody tissues of roots, stems and barks, rarely also from leaves. It originated from both herbaceous and aborescent plants. It occurs in coals and organic-rich sediments. (Sýkorová et al., 2005).

Thiophene – a hetroclycic colorless liquid that closely resembles benzene; the simplest sulfur-containing compound.

Ulminite – a maceral of the huminite group, subgroup telohuminite that denotes the cell walls of more or less gelified tissues. It consists of humic acids, humates and traces of lignin and cellulose. It is derived from parenchymatous and woody tissues of roots, stems, barks, and leaves. (Sýkorová et al., 2005).

Vitrinite – a term introduced by Stopes (1935) to denote a microscopically recognizable constituent of medium-rank coal. Vitrinite designates a group of gray macerals. It occurs in coal as relatively pure layers or lenses ranging in thickness from several micrometers to several centimetres; as the continuous phase of the coal’s groundmass binding other coal components; or as amorphous fillings of cells, pores and fissures. It occurs in coals and organic-rich sediments (ICCP, 1998).

ABOUT THE AUTHORS

Harald G. Dill received his MSc in Geology from Würzburg University, Germany, in 1975 followed by studies in economic geology at the Technical University, Aachen. In 1978, he graduated from Erlangen University with a PhD for work on pyritiferous Pb-Cu-Zn deposits in Tuscany, Italy. Subsequently, he had a one-year research post at Bayreuth University. Since 1979 he has worked for the German Federal Institute for Geosciences and Natural Resources (BGR), mainly involved in radiometric dating and the study of uranium deposits. From 1986 through 1991 he was a member of the project management group of the Continental Deep Drilling Program of the Federal Republic of Germany, being responsible for economic geology, mineralogy and geochemistry. In 1982 he was made Assistant Professor in applied geology at Mainz University, where he obtained his Dr. rer. nat habil. degree in 1985. In 1991 he was appointed Associate Professor at Hannover University, where he lectured in economic geology, and in 2008 he was awarded an Honorary Professorship at Mainz University. Through BGR’s technical cooperation schemes, he is involved in training geologists from partner geological surveys in Asia and Africa and also teaches university courses in applied sedimentology and economic geology. His main interests lie in the chemistry and mineralogy of ancient and modern depositional systems and related fossil fuel, metallic and non-metallic deposits. His work has led to more than 220 publications and the Quintino-Sella-Prize awarded at the 32nd International Geological Congress (Florence, Italy).

dill@bgr.de

Jolanta Kus is an internationally accredited coal and organic petrographer at the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover, Germany. She recieved her BSc in Geology (emphasis palaeontology) and her MSc in Exploration Geology from Imperial College London, UK. From 1999 to 2000 Jolanta worked as an exploration geologist at CalEnergy Gas Ltd., London where she was involved in gas exploration in NW Poland. She joined BGR (Hannover) in 2000 and worked on the structural geology and hydrocarbon potential of the Chilean accretionary complex. Since 2005 she has been involved in the Sino-German Research Initiative on coal fires in China. Her research interest focuses on the evaluation of the hydrocarbon potential of sedimentary basins worldwide. She is a member of PESGB, ICCP and AKOP.

j.kus@bgr.de

Abdulkader M. Abed was awarded his PhD in sedimentology and sedimentary geochemistry by Southampton University, UK, in 1972. After graduation, he joined the King Abdul Aziz University in Jeddah, Saudi Arabia, and later moved to the University of Jordan, Amman where he became Professor of Geology in 1985. His research is concentrated on the Upper Cretaceous phosphorites of Jordan and the overlying oil shales, their mineralogy, geochemistry and source rocks. He has written more than 100 publications on various aspects of the geology of Jordan and writes in Arabic on the geology of Jordan, Palestine, and the Dead Sea. More recently he shifted interest to the paleoclimate of Jordan and adjacent areas. He is a member of the SEPM, IAS and the Mineralogical Society and has served on the scientific board of the IGCP from 1989 to 1995 and IUGS/UNESCO.

aabed@ju.edu.jo

Reinhard F. Sachsenhofer is Head of Petroleum Geology at the University of Leoben, Austria. He has a MSc in Economic Geology and a PhD in Geology from Loeben University. Previously, he was Humboldt-Fellow at the Institute of Petroleum and Organic Geochemistry Research Center, Jülich, Germany and Visiting Professor at the Donetsk National Technical University, Ukraine. His main research interests are in basin analysis, hydrocarbon systems, source rocks, coal, and organic petrology. He has won awards from the Austrian Geological Society, the Regional Government of Styria, Austria, and the AAPG. He is on the editorial board of several journals including the International Journal of Coal Geology.

reinhard.sachsenhofer@mu-leoben.at

Hani Abdul Khair was awarded a BSc in Earth and Environmental Sciences, an MSc in Sedimentary Geology, and a PhD in Petroleum Geology by the University of Jordan, Amman. He has over 12 years experience in petroleum exploration and research. He specializes in sequence stratigraphy, seismic interpretation, petrophysics, geohistory analysis, and the petroleum evaluation of sedimentary basins. Hani is a member of the Society of Economic Paleontologists and Mineralogists, the American Association of Petroleum Geologists, and the International Association of Sedimentologists.

haaabulkhair@yahoo.com