About 20 billion tonnes of world-class, high-grade phosphorite resources occur in a small area of the eastern Mediterranean region, including Jordan, northern Negev (Palestine), northwestern Saudi Arabia, western Iraq, and southeastern Syria. Major deposits were formed during Campanian to Eocene times and contribute significantly to the economic development of these countries, particularly Jordan and Syria. The phosphorite deposits consist mainly of reworked granular material. The phosphate particles are peloids, such as pellets, intraclasts, nodules, coated grains and coprolites, and vertebrate fragments (bone and teeth). The phosphorite sequences are associated with extensive bedded chert, porcelanite, and organic-rich marls. The main phosphate mineral is francolite, a carbonate-rich variety of fluorapatite that has a relatively enhanced uranium content as a result of substitution for calcium in its crystal structure.
Two factors are deemed responsible for the deposition of the phosphorites and their associated chert, porcelanite, and marl within this relatively restricted area. The first was a compressional event associated with the initial collision of the oceanic forefront of the Afro-Arabian Plate with the subduction trench of Eurasia that began in Turonian times and continued into the Eocene. This event resulted in gentle folding that produced the Syrian Arc, the Ha’il, Rutba, and Sirhan paleohighs and the Ga’ara Dome, which were loci for the deposition of phosphorites. The second factor was the obstruction and consequent upwelling of oceanic currents by these tectonic highs, enhanced by winds blowing from east to west along the southern platform margin of the Neo-Tethys Ocean. The intense upwelling was associated with the Tethyan Circumglobal Current that flowed along the Afro-Arabian platform on the southern margin of the Neo-Tethys Ocean. In contrast, relatively minor phosphorite deposition took place to the north in southern Europe.
The upwelling spread cold, nutrient-rich oceanic water from the deep Neo-Tethys Ocean to the surface, thereby enhancing bioproductivity to produce organic-rich sediments. The subsequent authigenesis of phosphorites, their diagenesis and the reworking and winnowing of the phosphorite-rich sediments, concentrated the materials into economic deposits. Phosphorite deposition ended in the Late Eocene following the final collision of the Afro-Arabian Plate with Eurasia. The sub-aerial exposure of this formerly productive shallow-marine platform was the result of the separation of the Arabian Plate from the African Plate during the mid-Miocene.
The eastern Mediterranean region and North Africa hold more than half the world’s phosphorite resources, amounting to about 80 billion tonnes of high-grade commercial phosphorites (Jasinski, 2003, 2011; Van Kauwenbergh, 2010). These deposits form part of the Late Cretaceous to Eocene Tethyan Phosphorite Regime that extends through North and northwest Africa, and into parts of the Caribbean and Columbia and Venezuela in northern South America (Lucas and Prévôt, 1975; Bentor, 1980; Notholt, 1980; Abed, 1994; Lucas and Prévôt-Lucas, 1995; Föllmi, 1996; Soudry, et al., 2006). The Tethyan phosphorites, together with the Miocene–Holocene deposits of the USA, account for the majority of the world’s phosphorite resources and production (Notholt, 1980; Notholt et al., 1989). In the Middle East, most of the phosphorite deposits are in Iraq, Jordan, Palestine, Saudi Arabia and Syria, and their production is of primary economic importance to the development of countries with limited oil and gas production; for example, Jordan and Syria.
This paper presents an overview of the geology of the Tethyan phosphorite deposits in the Middle East (Figure 1). Its aim is threefold. Firstly, the paper describes and correlates the various phosphorite deposits of the eastern Mediterranean region; secondly, it discusses the regional plate-tectonic setting associated with the formation of the deposits; and thirdly it attempts to explain the presence of giant phosphorite deposits that were formed in a relatively small part of the eastern Mediterranean region in a relatively short period of geological time.
Resources and reserves of phosphorites deposits, as of 2010, in the eastern Mediterranean countries (Figure 1) are about 20 billion tonnes and 2.4 billion tonnes, respectively (Table 1) (Van Kauwenbergh, 2010). Both resources and reserves are dynamic and are changing continuously due to increasing exploration activities. For example, the phosphorite resources of Iraq, currently 5.7 billion tonnes, will become 10 billion tonnes when the recently discovered Swab deposits, west of Akashat, are added. Also, grade reductions can significantly increase resources; for example, Iran’s resources at about 170 million tonnes (Mt) at a grade of 20% P2O5 would be increased by 70 Mt if the grade was lowered to 12% P2O5. Iraq and Saudi Arabia have most of the region’s resources with 5.7 billion tonnes and 7.8 billion tonnes, respectively, although Jordan is the major producer with 6 Mt/year (Table 1). Iraq was producing about 2 Mt in 1989 but this declined to 100,000 tonnes in 2001 and production has now ceased due to the adverse security conditions. Saudi Arabia started production towards the end of 2010 at a rate of about 5 Mt/year. The mined rock phosphate is upgraded by various beneficiation processes usually involving washing, separation, flotation and concentration, depending on the ore. Concentrates need a P2O5 content of more than 30% in order to compete in global markets. Phosphorites, worldwide, have a much higher uranium (U) content than other sedimentary rocks. The average U in phosphorite is 120 ppm compared with 3.5, 0.5 and 2.2 ppm in shale, sandstone and limestone respectively; an enrichment factor of about 30 relative to shale. Certain phosphorite beds in Jordan have as much as 240 ppm U (Abed and Sadaqah, 2013). Uranium can be extracted from some phosphorites as a byproduct during fertilizer production, which adds to their economic importance.
Most of the Middle East phosphate production is exported; for example, Jordan exports about 80% of its mined production. Locally, there is production of phosphoric acid and fertilizers such as diammonium phosphate (DAP), monoammonium phosphate (MAP) and triple superphosphate (TSP), depending on the country. The price of the high-grade concentrates (> 70% tricalcium phosphate (TCP)) was fairly constant for many years at between US$40–50/tonne until 2007. A very sharp increase then occurred and the price increased to US$500/tonne. At this time Jordanian concentrates with 70–74% TCP sold for about US$350/tonne whereas those of North Africa reached US$500/tonne. Prices have since declined and are now at about US$100/tonne (Van Kauwenbergh, 2010; Jasinski, 2011).
GEOLOGICAL SETTING AND GLOBAL DISTRIBUTION
The major Tethyan phosphorites were laid down during the Late Cretaceous to Eocene. During this relatively short time interval the closure of the Neo-Tethys Ocean took place as the Afro-Arabian and Eurasian plates converged (Robertson and Dixon, 1984; Beydoun, 1991; Brew et al., 2001; Sharland et al., 2001; Haq and Al-Qahtani, 2005). These tectonic activities were responsible for setting the scene for the formation of the major phosphorite deposits in the eastern Mediterranean region and throughout the Tethys realm (see Belayouni and Beja-Sassi, 1987; Sheldon, 1988; Abed, 1989; Al-Bassam, 1990).
Phosphorites are poorly represented throughout geological history compared to other sedimentary rocks such as limestones, dolomites, sandstones, shales and evaporites. They are restricted in their distribution in space and time and also they show a distinct episodicity (Sheldon, 1981; Riggs, 1986; Balson, 1990). During phosphogenic episodes, phosphorite deposits were distributed on a global scale, whereas in non-phosphogenic periods only minor, local deposits were laid down. Four major depositional episodes are known (Figures 2a, b):
(1) Late Neoproterozoic–mid Cambrian deposits: these occur mainly in Australia, China, India and Russia, with minor deposits in other localities (Cook and Shergold, 1986; Brasier and Callow, 2007; Papineau, 2010).
(2) Permian deposits: these are primarily the Phosphoria Formation that crops out in the western USA, principally in Idaho and Wyoming (Sheldon, 1981, 1989; Hiatt and Budd, 2001; Piper and Link, 2002).
(3) Late Cretaceous–Eocene deposits: these belong to the Tethyan Phosphorite Regime, represented by the deposits of the eastern Mediterranean (Figure 1, Table 2), North and northwestern Africa, and northern South America and parts of the Caribbean (Jarvis, 1992; Lucas and Prévôt-Lucas, 1995; Föllmi, 1996; Soudry et al., 2006).
(4) Miocene–Holocene deposits: these occur in California and the southeast USA, Mexico, the Peruvian-Chilean shelf, Namibian-South African shelf, and the eastern shelf of Australia (Birch, 1980; Riggs and Sheldon, 1990; Heggie et al., 1990; Burnett, 1990; Wigley and Compton, 2007).
The episodic nature of phosphorite deposition is related to the fact that they do not form or precipitate directly from seawater, as is the case of limestones, evaporites or other chemical, biological and biochemical sedimentary rocks. Instead, several regional and local factors must be present in the depositional environment to ensure the formation of a high-grade phosphorite deposit (Glenn et al., 1994; Föllmi, 1996). The abundant occurrence of phosphorus (P) and silicon (Si) in seawater is a requirement for enhanced bioproductivity in the photic zone of the ocean. In turn, the high bioproductivity increases the deposition of organic matter in the bottom-water sediments. One mechanism that enhances this process is oceanic upwelling that brings P and Si from the deep ocean, which is rich in these and other elements, to the surface (Figure 3). Organic matter preserved in shallow-marine sediments and containing P and Si is then released and enriched in the pore water of the sediments through microbial mediation and diagenesis, leading to the precipitation of francolite and siliceous deposits (Lucas and Prévôt, 1975; Abed and Fakhouri, 1990; O’Brien et al., 1990; Lucas and Prévôt-Lucas, 1995; Föllmi, 1996; Slomp and Van Capellen, 2007; Powell and Moh’d, 2012).
PHOSPHORITE DEPOSITS OF THE EASTERN MEDITERRANEAN
Lithology and Mineralogy of the Phosphorite Deposits
The phosphorite deposits of the eastern Mediterranean region are almost always associated with bedded chert (Figure 4), porcelanite, and oyster-bearing limestones (Figures 5a, b), in addition to minor marl, chalk and sandstone (Powell, 1989; Almogi-Labin et al., 1993). Glauconite is comparatively rare as it contains abundant iron that is not freely available in oceanic water. Phosphorites containing abundant glauconite, such as those of Abu Tartur of Egypt, are thought to be sourced from terrestrial chemically weathered deposits rather than from the deep oceanic phosphorus cycle (Glenn and Arthur, 1990).
Phosphorites almost always have a granular grainstone/packstone texture and minor calcite cement (Figure 6). The grains consist of phosphate peloids (intraclasts, nodules, coated grains, and coprolites) and vertebrate fragments such as bone and teeth. Laminated phosphorites, sometimes called pristine phosphorites, are not uncommon. The dominance of granular phosphorites may indicate reworking of the original phosphorite mudstones to form the intraclasts and other peloids (Abed and Al-Agha, 1989), or the reworking and winnowing of the original phosphate nodules (Burnett, 1990). Furthermore, the low percentage of fines may be due to winnowing that concentrated the granules by removing the fines (Riggs, 1980; Soudry and Nathan, 1980). The quartz sand content of the phosphorites increases in the southernmost deposits, especially in Jordan and northwest Saudi Arabia. This is because of the proximity to the sedimentary basin of a hinterland represented by the granitoid Nubian-Arabian Shield and its overlying cover of Paleozoic to Lower Cretaceous siliciclastic rocks.
Francolite (carbonate fluorapatite, Ca5(PO4,CO3)3(F,OH)) is the apatite mineral species present throughout all of the Middle Eastern marine phosphorites (Axelrod and Rohrlich, 1982; Abed and Fakhouri, 1996). In this, they are similar in their mineralogy to marine phosphorites worldwide (Bentor, 1980). Substitution commonly takes place within the crystal structure of francolite; for example, CO3 substitutes for PO4; U, Sr, and REE for Ca; and F for OH (the F and CO3 content can be as much as 4% each). A generalized chemical formula for the Jordanian phosphorites for hand-picked phosphate particles (Abed and Fakhouri, 1996) is [Ca 9.86Mg 0.005 Na 0.14] [PO4 4.93CO31.07F 2.06].
The major Tethyan phosphorite deposits are Late Cretaceous to Eocene in age; however, the age of each individual deposit differs according to its geological and paleoenvironmental setting (Lucas and Prévôt-Lucas, 1995) (Table 2). In the following discussion, the Middle Eastern Tethyan deposits are described starting in Jordan, the Negev and Saudi Arabia, and then clockwise into Syria, Turkey, Iraq and Iran. (see Figure 1).
Substantial phosphorite deposits are present in the Al-Kora area of northwestern Jordan, Ruseifa near Amman, in central Jordan (Al-Abiyad and Al-Hisa), Eshidiyya in the south, and Wadi Sirhan in the southeast (Figures 7 and 8). The Sirhan deposits are an extension of major deposits in Saudi Arabia. The phosphorites are assigned an Early Maastrichtian age by authors such as Burdon (1959), Hamam (1977), Abed and Ashour (1987), and Capetta et al. (1996), whereas others interpret their age as Late Campanian (Bender, 1974; Pufahl et al., 2003; Powell and Moh’d, 2011). The Late Campanian age is accepted here due to similarities with deposits in the Negev and Syria. The phosphorites occur in the Al-Hisa Phosphorite (AHP) Formation (El-Hiyari, 1985; Powell, 1989; Powell and Moh’d, 2011), which consists of three members in the type area in central Jordan. From the base up they are: (1) the Sultani Member consisting of alternating limestone and bedded chert with minor silicified phosphorites; (2) the Bahiyya Coquina Member formed of oyster shells and shell fragments of Lopha villi; and (3) the Qatrana Member. The Qatrana Member is the main high-grade phosphorite-bearing unit; in addition, it contains minor limestone, marl and organic-rich marl.
Due to the paleotopographic configuration of the shelf floor, the phosphorites were deposited in basins (Abed and Sadaqah, 1998; Powell and Moh’d, 2011) that vary in size from a few kilometers in central Jordan to tens of kilometers in the north (Al-Kora and Ruseifa basins and the Eshidiyya Basin in the south (Figure 7). On the highs that separate the basins, particularly in central and south Jordan, oyster buildups predominate with a general absence of phosphorites. Within the buildups, the oyster shells at the base are in their growth position and become more fragmentary up-section. They are displayed as conspicuous clinoforms (Abed and Sadaqah, 1998; Powell and Moh’d, 2011) that generally dip southeast toward the centers of basins (Figures 5a, b). The oyster buildups acted as baffles behind which thick phosphorite deposits could be generated during rises in sea level (see Abed et al. (2007) for Eshidiyya and Powell and Moh’d (2011) for central Jordan).
Phosphorites were deposited at the onset and throughout marine transgressions. They represent the transgressive systems tracts (TST) in sequence stratigraphy (Abed et al., 2007). For example, in the Al-Hisa Phosphorite Formation at Eshidiyya in southern Jordan, the lower member represents the TST of a lower sequence that is overlain by the middle member of oyster buildups, that represent the highstand systems tracts (HST) (Figure 8). The oyster-buildup HST is terminated by a sequence boundary (SB) associated with an unconformity and subaerial exposure at the base of the second sequence. The upper phosphorite member was deposited as the TST of the second sequence with overlying marls as its HST (Figure 8). The unconformity at the top of the oyster buildups in the Eshidiyya area may not be present in other areas such as Al-Hisa in central Jordan (Powell and Moh’d, 2011). Reworking and winnowing during the transgression is thought to have concentrated the phosphorites in this upper unit into high-grade deposits (Abed and Sadaqah, 2013).
Commercial-grade phosphorites associated with sandy facies become increasingly important to the south and southeast due to the proximity of these areas to a paleoshoreline and the re-working of Lower Cretaceous and Paleozoic sandstones. This is the case for the lower member of the Al-Hisa Phosphorite Formation in Eshidiyya in the south of Jordan (Figure 8). The sandy facies continues eastward and is well developed in the Thaniyat area of northwestern Saudi Arabia (Berge and Jack, 1989).
The Ruseifa mines, located east of Amman, were closed in 1988 due to their proximity to a large urban area despite the presence of several tens of millions of tonnes of commercial-grade phosphorite reserves. The central Jordan deposits of Al-Abiyad and Al-Hisa are nearly depleted with more than 250 Mt having been extracted since 1965. The Al-Kora deposits in the northwest of the country, with tentative deposits of several hundred million tonnes of commercial phosphorites occur in a folded belt located in a highly urbanized area and adjacent to some of the best forests in Jordan (Mikbel and Abed, 1985; Abed and Al-Agha, 1989). The Sirhan deposits are buried beneath as much as 200 m of overburden in places, and no estimates of their reserves are available (Abed and Amireh, 1999). They are overlain by the Maastrichtian–Eocene Muwaqqar, Rijam and Shallaleh formations, and are assigned a Coniacian–Campanian age based on lithological field correlation (Abed and Amireh, 1999; Abed, 2000; Powell and Moh’d, 2011). Production is now moving to the Eshidiyya Basin that has more than 1 billion tonnes of estimated reserves (Soframines, 1987; Sadaqah, 2000).
High-grade phosphorites are present in the northern Negev region of Palestine (Figure 9) in the upper part of the Campanian Mishash Formation (Bartov and Steinitz, 1977; Bartov et al., 1980; Soudry et al., 2006) (Figure 10). They are also present in the uppermost part of the Sayyarim Formation in the southern part of the Negev. Minor amounts of phosphorites were deposited until the Eocene. Commercial phosphorite deposits increase in quantity toward the centers of the synclines (basins) associated with the Syrian Arc Fold system, whereas bedded cherts are more abundant towards paleohighs where the phosphorites clearly thin out (Kolodny and Garrison, 1994). The sedimentological features of the phosphorites are similar to those of the Jordanian deposits discussed above, which continue as an arcuate belt through northern Sinai and the Eastern Desert of Egypt (Glenn and Arthur, 1990).
The Saudi Arabian phosphorite deposits occur in the northwestern part of Saudi Arabia between the Iraqi deposits in the north and the Eshidiyya and Sirhan phosphorites of Jordan (Abed and Amireh, 1999). The high-grade phosphorites occur in the uppermost Campanian–Eocene Turayf Group, which is divided from the base up into the Jalamid, Mira and Umm Wu’al formations (Figure 11). Each formation has an important phosphorite member at its base; these are the Thaniyat, Ghinah and Arqah members, respectively (Riddler and Van Eck, 1984; Riddler et al., 1989; Berge and Jack, 1989; Jacobs International, 1992).
The Campanian–Maastrichtian and Lower Paleocene Thaniyat Member (Jalamid Formation) has a lower unit of sandy phosphorites, overlain by a silicified biomicrite, above which friable to partially silicified phosphorites alternate with various lithologies including bedded chert. The thickness of the phosphorite beds varies from 10 cm to 4.5 m in the Thaniyat area in the southern part of the region. The phosphorites consist of peloids, intraclasts and fine-grained shell and bone debris. They become less phosphatic to the northwest, but increase in grade considerably to the north-northeast, where, near the town of Jalamid the phosphorite beds contain between 15% and 32% P2O5. The Jalamid deposits are as much as 13 m thick; an overburden thickness of from 4.5 to 22 m gives a stripping ratio of 0.5 to 8.4 (Jacobs International, 1992). In the Jalamid area, the Thaniyat Member overlies the Late Cretaceous Aruma Formation and is of Early Paleocene age, as are the Akashat phosphorite deposits in western Iraq.
The Ghinah Member phosphorite units at the base of the Paleocene to Lower Eocene Mira Formation are siliceous, calcareous to semi-friable, 20 to 80 cm thick, and interbedded with micrite, claystone and chert that are weakly phosphatized. The uppermost phosphate bed is sandy and conglomeratic. The phosphorites consist of peloids, fossil fragments and teeth within a hard, siliceous matrix. The Ghinah phosphorites are too thin to have an economic potential. The overlying members of the Mira Formation mainly consist of carbonates with chert nodules and bedded chert toward the top of the formation and several nummulitic limestone beds. They contain some low-grade phosphorites of no economic importance.
The Arqah Member occurs in the lower part of the Middle Eocene Umm Wu’al Formation. The phosphorites at the base are 10 cm to 8.5 m thick, carbonate-cemented, semi-friable and interbedded with limestone and chert. This unit is overlain by silicified, phosphatic limestone. As with the Mira Formation, the overlying members of the Umm Wu’al Formation generally consist of carbonates, with chert nodules and several nummulitic limestone beds. The Arqah Member phosphorites may prove to be commercial in the future. Both the Ghinah and Arqah members are correlated with the Ratga phosphorites of western Iraq.
Figure 11 shows the cyclic nature of deposition throughout the Turayf Group in northwestern Saudi Arabia. The coarse-grained, granular phosphorites at the base of each cycle were deposited in high-energy transgressions as reworked lag deposits within depressions. Carbonate banks of nummulites and other fossils may have formed by similar processes in near-shore environments (Riddler et al., 1989).
Commercial phosphate production started in late 2010. Further exploration is directed toward the Thaniyat Member of the Jalamid Formation where the most potentially commercial deposits are present, especially near Al-Jalamid in the northernmost part of the area. Here, two friable to semi-friable phosphorite units are present with bedded chert and carbonates. P2O5 contents are between 15% and 32%. A relatively thin overburden ranging from 4.5 to 22 m thick provides a stripping ratio of between 0.5 and 8.4 (Jacobs International, 1992). The reserves at the Al-Jalamid site alone at a grade of 19.3% P2O5, is in excess of 4 billion tonnes (Jacobs International, 1992).
High-grade phosphorites are restricted to the Palmyride mountains in southeastern Syria (see Figure 1). Minor deposits are present in the Kurdagh region in the northwest (Al-Maleh, 1974). The Palmyride phosphorites belong to the Coniacian–Late Campanian Sukhneh Group, which consists of two formations (Figure 12):
(1) Rmah Formation of Coniacian–Early Campanian age is composed of fossiliferous interbedded marl, limestone, dolomite and some chert nodules, overlain by alternations of bedded chert, limestone and thin phosphorite units. Its thickness is 60 m increasing northward to 280 m where it consists of deep-water facies. It also changes into more calcareous facies to the southwest.
(2) Sawwaneh Formation of Late Campanian age contains the major Syrian phosphorite deposits, particularly near its base. The formation consists of marly limestone interbedded with phosphorites that are as much as 10 to 12 m thick in the central-southern part of the Palmyrides. The upper part of the formation is dominated by marl and marly limestone overlain by a glauconitic-phosphatic marl. Its thickness is 17 m and increases considerably northward to 317 m in a deep basinal setting.
The phosphorites disappear almost completely toward the western boundary of the Palmyrides (Al-Maleh and Mouty, 1994; Bardet et al., 2000). The phosphorites are predominantly granular in texture and the grains are typically made of phosphate pellets, coated grains, vertebrate skeletal fragments, and coprolites. The lack of oyster buildups make the Sawwaneh phosphorite similar to those of Al-Kora deposits in northwest Jordan, but differ from those of central and southern Jordan where the buildups are conspicuous. Phosphate mines are present in the Khneifiss and Sawwaneh areas in the central part of the southern Palmyrides.
From the foregoing discussion, the age of the high-grade phosphorites in Jordan, the Negev and the Palmyrides is Late Campanian (Al-Maleh and Mouty, 1994; Kolodny and Garrison, 1994). They are all associated with the Syrian Arc Fold Belt (see below).
Eocene-age phosphorites occur at Habari and Sirji in the southeast of the country. A sequence 5.5 to 10.5 m thick contains up to seven beds that contain between 16% and 24.8% P2O5 with up to 56% SiO2 (Atfeh, 1966).
In Turkey, phosphorites and phosphatic sediments are present in the southeast of the country in the Mardin-Diyarbakir area near the border with Syria (see Figure 1) (Lucas et al., 1980; Ozguner, 1993). The major producer is the Mazidagi deposit. The phosphorites are found in the Tasit, Karababa, Kasrik, Semikan, Karabogaz and Akras formations that range in age from Turonian–Coniacian (Tasit Formation) to Maastrichtian–Paleocene. These formations consist predominantly of carbonate lithologies with widely separated, relatively thin phosphorite and phosphatic sediments. The phosphorites occur as pelletal, nodular and fossiliferous (fish remains and bones), bedded, oolitic, limonitic and glauconitic phosphatic limestone. For example, the Tasit deposit is pelletal, nodular and fossiliferous; the Karik deposit is pelletal and oolitic associated with red clay and cherty rock; and the Akras consists of limonitic and glauconitic phosphatic limestone (Berker, 1989; Chernoff and Orris, 2002). Bedded chert and chert nodules are present throughout the section and glauconite becomes more abundant up section. Their ages range from Turonian–Coniacian (Tasit Formation) to the Maastrichtian–Paleocene for the younger formations. The Tasit deposits of minor commercial importance are some of the oldest in the eastern Mediterranean. Total reserves are estimated as 136 Mt, of which 45 Mt are proved reserves (Lucas et al., 1980; Ozguner, 1993).
The main phosphorite deposits of Iraq are located in the west within the Ga’ara Basin about 40 km and 100 km from the borders with Syria and Jordan, respectively (see Figure 1). The deposits are present in the Jeed, Akashat and Ratga formations, with the main commercial deposits being in the Paleocene Akashat Formation (Figure 13). The following account is taken from Jassim et al. (1986), Al-Bassam (1990, 2007) and Al-Bassam and Al-Allak (1985).
The Maastrichtian–Danian Jeed Formation contains several intraclastic phosphorite units, especially in the middle and upper part of the formation, associated with oyster beds and bedded chert. The rest of the formation is predominantly composed of limestones containing shallow-water benthic fossils such as oysters, corals and rudists (hippuritids). Planktonic foraminifera are present in minor shale units. The phosphorites thin out and disappear in the Tayarat Formation, a lateral time-equivalent of the Jeed Formation. Deposition is interpreted as having taken place in shallow-marine back-reef, fore-reef and deeper basinal environments. The lithology of this type of phosphorite deposit is similar to that of central Jordan in having oyster buildups and bedded chert.
The Paleocene Akashat Formation contains the main phosphorite deposit in western Iraq. The phosphorite beds occur mainly in the middle part of the formation and have a maximum thickness of 11 m (Figure 12). They thin southward to about 7 m south of the Rutba-Amman Highway and there is a lateral change to marl and marly limestone. The uppermost 4 m of the formation are composed of shelly limestone with chert nodules. Beds of coquina limestone and shale are also present. The phosphorites are pelletal (granular) in texture and consist of phosphate pellets and oolites (Al-Bassam, 1990) with carbonate and silica cements. The present author believes that the oolites are not true oolites (that is, they are not formed through direct chemical precipitation from sea water), but represent phosphatic mud coatings that have resulted from several phases of reworking and deposition. This is supported by the fact that the Akashat deposits are well sorted and of much higher grade than other Iraqi deposits. The depositional environment is predominantly shallow-marine but the presence of planktonic foraminifera indicates connections to a more open-marine circulation.
The Eocene Ratga Formation has an apparent conformable contact with the underlying Akashat Formation in the Rutba area (Jassim and Goff, 2006). It consists essentially of repeated beds of nummulitic limestone that are commonly silicified. Chert beds and chalk are common, particularly in the middle part of the formation. Nummulites, bivalves, gastropods, corals and operculina are present in the lower part of the formation. Phosphorites mostly overlie the nummulitic beds, but may also occur below them. They consist of coarse-grained phosphatic peloids, intraclasts, skeletal vertebrate fragments, and coprolites. The phosphorite deposits are of limited commercial importance. The depositional environments of the Ratga Formation are interpreted as nummulitic/bivalve shoals that grade into basinal marl and chalk. The formation can be correlated with the Eocene Umm Rijam Formation in the Risha area of eastern Jordan, located immediately west of the Iraqi border, which also contains minor phosphorites.
Recent estimates of the high-grade phosphate resources of Iraq put them at about 10 billion tonnes (Al-Bassam, 2007). Phosphorites in western Iraq have been mined since 1983 with more than 2 Mt being exported annually.
In Iran, the Tethyan phosphorites are restricted to the Eocene–Oligocene Pabdeh Formation (Figure 14) located in southwestern Iran (see Figure 1). The formation consists predominantly of shale and minor amounts of limestone and marl deposited in a deep-marine environment. The phosphorites are present in two units at the middle and top of the formation, the lower one being shaly and the upper glauconitic. The P2O5 content is as much as 11% (Salehi, 1989; Bahrami and Shirazi, 2010). The most economically important deposits belong to the Neoproterozoic–Lower Cambrian Soltanieh Formation and the Upper Devonian–Lower Carboniferous Geirud Formation, both located in the Elburz Mountains in the north of the country (Salehi, 1989). The Late Proterozoic Esfordi deposits are also economically important (Salehi, 1989).
TECTONIC SETTING OF THE NEO-TETHYS OCEAN
Almost all the phosphorites of the eastern Mediterranean were formed on the southern margin of the Neo-Tethys Ocean. The following is a brief discussion on the evolution of the Neo-Tethys.
Throughout the Paleozoic, what became Africa-Arabia was part of the Gondwana Supercontinent on whose eastern margin was located the Paleo-Tethys Ocean. Most of Arabia formed part of the margin of the Paleo-Tethys where an extensive siliciclastic sequence was deposited with virtually no phosphorites and only thin carbonates (Sharland et al., 2001). This is possibly due to its location within high, cold southern latitudes. For example, during the latest Ordovician and Early Silurian, Arabia was situated at about latitude 66°S and regional glaciations were widespread in Arabia and North Africa (Vaslet, 1990; Abed et al., 1993; Powell et al., 1994; Sharland et al., 2001). By the Late Permian to Triassic, the Neo-Tethys Ocean started to open, first approximately along the Zagros lineament and then westward as shown by the presence of widespread carbonate and evaporite deposits of the Late Permian Khuff Formation in Arabia (Robertson and Dixon, 1984; Sharland et al., 2001; Haq and Al-Qahtani, 2005). Closing of the Paleo-Tethys by subduction beneath Eurasia farther north was completed during the Middle to Late Triassic (Robertson and Dixon, 1984; Dercourt et al., 1986).
At about the same time, Triassic–Jurassic sea-floor spreading occurred during a phase of extensional tectonics. The Cimmerian superterrane, that included central and northern Iran, rifted from the Afro-Arabian Plate and moved northwestward. Spreading accelerated in the eastern Mediterranean basin until the Campanian–Maastrichtian when the oceanic forefront of Afro-Arabian Plate collided with the Neo-Tethys intra-oceanic subduction trench to the north and east. As a result, widespread ophiolite obduction took place in Oman, northwest Syria and Turkey. It was also a time of a major compressional pulse that formed structural features in Arabia, such as the Syrian Arc Fold Belt and the Ha’il, Rutba, and Sirhan paleohighs, discussed below. Conversely, subsidence on the northern Arabia platform is shown by the widespread deposition throughout Maastrichtian–Paleocene times of pelagic marl rich in organic matter.
During the Late Eocene to Miocene the continent-continent collision of the Afro-Arabian Plate with Eurasia occurred. The Gulf of Aden-Red Sea-Dead Sea transform fault system formed during the Miocene, and it is still active today (Robertson and Dixon, 1984; Dercourt et al., 1986; Brew et al., 2001; Sharland et al., 2001).
Several compressional features formed during the Campanian–Eocene throughout the eastern Mediterranean when the Afro-Arabian Plate collided with the intra-oceanic trench to the north and east. Almost all of the major phosphorite deposits of the eastern Mediterranean are associated with these features.
Syrian Arc Fold Belt
The Syrian Arc is an S-shape structure that extends from northern Egypt through Sinai, the Negev, western Jordan and into the Palmyride tectonic zone in southeastern Syria (Krenkel, 1924; Chaimov et al., 1992). It consists of asymmetric folds (anticlines and synclines of varying lengths), trending east in northern Egypt, northeast in the Negev and the Palmyrides and almost north-south in northern Palestine (Figure 15) together with major faults (Bowen and Jux, 1987). In Jordan, at least two structures are interpreted as belonging to the Syrian Arc, namely the Wadi Shueib and Amman-Hallabat fold structures, both are about 80 km long and trend northeast (Mikbel and Zacher, 1981; Abed, 1989). Elsewhere in Jordan, the compression associated with the Syrian Arc led to the formation of basins and swells of varying sizes, with no folding, especially in central Jordan (Abed and Sadaqah, 1998).
There is general agreement that the major tectonic pulse of the Syrian Arc took place during the Campanian–Maastrichtian (Bowen and Jux, 1987; Guiraud and Bosworth, 1997; Walley, 2001). According to Brew et al. (2001), the compression in the Palmyrides was pre-Maastrichtian from dating the Sawwaneh Formation as Campanian in age. Abed (1989) demonstrated from sedimentological evidence that the Amman-Hallabat fold structure was active during the timeframe of the phosphorite deposition in the Ruseifa area, in the Late Campanian. A similar conclusion was arrived at for the Negev segment of the Syrian Arc (Soudry et al., 2006).
The major phosphorite deposits in Jordan and the Negev are associated with the Syrian Arc. In the Negev, they were laid down in synclines of the Syrian Arc, whereas the anticlines are less phosphatic and more cherty (Nathan and Shiloni, 1990; Kolodny and Garrison, 1994; Soudry et al., 2006). Similarly, the Jordanian phosphorites are present in basins and little or no phosphorite deposition took place on the highs (Moh’d, 1985; Abed, 1989; Abed and Sadaqah, 1998; Powell and Moh’d, 2011).
Palmyride Fold Belt
This fold belt forms the northernmost part of the Syrian Arc. It consists of asymmetric anticlines and synclines, as in the Negev, that extend from the junction with the Dead Sea Transform Fault in the southwest, through the Damascus area, to end near the Euphrates Basin (Figure 15). The major phosphorite deposits, including the producing Khneifiss and Sawwaneh mines, are located within the central part of the southwestern Palmyrides. It is questionable whether these deposits are in association with the Syrian Arc or are connected with the Hamad paleohigh, a northwestern extension of the Rutba paleohigh (see below and Figure 16). Al-Maleh and Mouty (1994) are of the opinion that the phosphorites of the Sawwaneh Formation were influenced in their deposition by the Hamad paleohigh. However, careful examination of the geology of these deposits showed the presence of both paleohighs and lows, and it seems likely that the phosphorites were laid down on the flanks of a major anticline (Atfeh, 1989), a situation similar to the deposition of the Negev and north Jordan phosphorites. Thus, it is probable that the phosphorite deposition was tectonically controlled by the Palmyride Fold Belt.
Ha’il, Rutba and Sirhan Paleohighs
The Ha’il, Rutba and Sirhan paleohighs are major tectonic features in western Arabia (Figure 16). Geophysical investigations reveal that they are not internally deformed (M.I. Al-Husseini, written communication, 2012), but represent uplifted linear highs caused by the initial collision between the Afro-Arabian Plate and an intraplate subduction zone located farther north. This interpretation is supported by surface geological investigations. For example, Powers et al. (1966) observed that the initial uplift of the Ha’il paleohigh began in the mid-Cretaceous as non-marine sediments of the upper Wasia Formation were deposited on top of the paleohigh, whereas the lower Wasia marine sediments were deposited on its flanks. Also, Abed and Amireh (1999) found that the more than 600 m-thick Ajlun Group of carbonate marine sediments is reduced to 20 m of carbonates, sandstones and sandy phosphorites along the Sirhan paleohigh. None of these paleohighs existed before the Late Cretaceous (Campanian). They were active during the Campanian–Eocene, a period of tectonic activity that, as noted above, included ophiolite obduction (Robertson and Dixon, 1984).
The Ha’il paleohigh is about 1,000 km long and 800 km wide. It extends north-northwest from the Rub’ al-Khali desert in the southeast of Saudi Arabia to the Nafud desert in the north. It was formed during Campanian to Eocene times (Sheldon, 1993), or in the Late Cretaceous to Eocene (Riddler et al., 1989).
The Rutba paleohigh extends from western Iraq through northwestern Saudi Arabia. The Hamad paleohigh in southeastern Syria is considered by Brew et al. (2001) to be the northwestern continuation of the Rutba high. The Rutba makes an angle with the Ha’il paleohigh north of the Nafud desert. Its timing of formation is considered here to be similar to that of the Ha’il. In the Ga’ara area in western Iraq and the Al-Jalamid area in northwestern Saudi Arabia, the Rutba paleohigh forms a broad anticlinorium dipping at about 0.5° to the west and east (Riddler et al., 1989).
The Sirhan paleohigh is about 400 km long. It is located slightly to the east of the eastern Jordan-Saudi Arabia border. It is a NNW-trending feature that is not exactly aligned with the Ha’il high (Figure 16). In the north it joins the Syrian Arc and its southern end is formed by the Bayer-Kilwa swell.
The small Umm Wu’al graben lies between the Sirhan and the Rutba paleohighs. The Sirhan high rifted in the Miocene to form the Sirhan graben and its associated extensive basaltic field in Saudi Arabia, Jordan and Syria that is known as Harrat Ash Shaam.
Tethyan Circumglobal Current
The Cretaceous Period was a time of major tectonic activity during which North America and Eurasia were separated from Gondwana, the Neo-Tethys evolved into a global EW-oriented seaway, and the South Atlantic and North Atlantic basins opened (Bush, 1997; Poulsen et al., 1998, 2001, Soudry et al., 2006). The eastern Mediterranean, especially the phosphorite-bearing area shown in Figure 1, was part of the southern epicontinental shelf of the Neo-Tethys Ocean. Tectonics and sea-level changes played an important role in the depositional history of this area during the Cretaceous.
Several complex plate-tectonic configurations of the Mediterranean Neo-Tethys have been constructed (see Barron, 1987; Scotese et al., 1988; Masse et al., 1993; Camoin et al., 1993; Bush, 1997; Poulsen et al., 1998, 2001; Stampfli and Borrel, 2002). It appears that the Neo-Tethys seaway was connected westward to the Pacific Ocean via the Caribbean Tethys (Figure 17). Many researchers advocate a model in which a uniform and strong W-trending Tethyan Circumglobal Current (TCC) flowing throughout the Neo-Tethys Ocean was driven by winds blowing from the east (Sheldon, 1988; Föllmi and Delamette, 1991; Jarvis, 1992; Francis and Frakes, 1993; Price et al., 1995; Bush, 1997). This model advocates the enhancement of the TCC after the South Atlantic basin was fully open in the Late Cretaceous to Eocene. Circulation in the South Atlantic was, and still is, anticlockwise; the northerly flowing current joined the TCC in the Caribbean Tethys near the Equator and then flowed westward (Robinson and Vance, 2012) into the Pacific Ocean.
The above-described model of the Tethyan Circumglobal Current (TCC) is controversial among some oceanic circulation modelers; its position, direction and strength remain uncertain. For example, Barron (1987) and Poulsen et al. (1998, 2001) postulated that there was not a uniform and intense TCC flowing from east to west, but instead a major clockwise flow in the northern Mediterranean Tethys flowing to the east and a minor westward-flowing current following the edge of the Afro-Arabian platform on the southern margin of the Neo-Tethys Ocean. Regardless of which model is considered correct, a westerly oriented flow regime connected the Neo-Tethys with world ocean basins (Figure 17). Oceanic circulation was, and still is, of prime importance for upwelling and thus the formation of marine phosphorites (see Upwelling Model below).
During the Early Cretaceous (up to the Early Albian), the eastern Mediterranean area was almost completely emergent. Sedimentation was dominated by fluvial clastic deposits that included low-grade coal in the Kurnub Group of Jordan and Negev (Amireh, 1997; Powell and Moh’d, 2011) and its equivalents in neighboring countries (Sharland et al., 2001). This fall in relative sea level might have been due the progressive uplift and tilting of the western parts of the Arabian Plate as the South Atlantic began to open and India separated from Oman; this was the breakup of East Gondwana in Late Jurassic–Early Cretaceous times (Hendriks et al., 1990; Al-Fares et al., 1998). Minor carbonate and glauconite sediments are present in Jordan, but no Lower Cretaceous phosphorites have been reported.
In Late Albian to Turonian times, a rise in sea level of more than 100 m (Haq and Al-Qahtani, 2005) was associated with a warm mid-Cretaceous greenhouse climate. The north-northwestern parts of the eastern Mediterranean region were flooded and a predominantly carbonate regime, up to several hundred meters thick, prevailed throughout this time. The rimmed carbonate platform developed around the basin margin and the platform/slope crest approximated to the present-day Mediterranean shoreline. The carbonate platform thins toward the southeast and passes laterally to marine and terrestrial sediments in southeast Jordan, northern Saudi Arabia and western Iraq (Jassim et al., 1986; Schulze et al., 2004; Powell and Moh’d, 2011). Thus, sites for major phosphorite deposits in these three localities up to the end-Turonian were not present due to emergence or the presence of marine or terrestrial siliciclastics (Powell and Moh’d, 2011).
No phosphorites are reported in the mid-Cretaceous strata of the study area. Accordingly, it is difficult to envision a strong Tethyan Circumglobal Current (TCC) flowing along the southern part of the region, and the TCC might have been restricted to the northernmost part of the Neo-Tethys. This might be because the South Atlantic was not fully open until the Turonian, after which the TCC was enhanced in the Neo-Tethys by the presence of the South Atlantic current (Poulsen et al., 1998). The flooding event (major sequence boundary 4) postulated by Powell and Moh’d (2011) during the latest Turonian to Early Coniacian supports the hypothesis of a major change in both ocean configuration and currents, and is associated with the transition from a rimmed carbonate shelf (inimical to phosphate generation) to a pelagic ramp (potentially phosphogenic) (Powell and Moh’d, 2012).
In the Coniacian, a marine transgression deposited pelagic chalks, cherts and thin phosphate beds over large parts of the eastern Mediterranean region (Powell and Moh’d, 2012). However, these pelagic chalks were not deposited in the extreme south of Jordan, the Turayf region of northwestern Saudi Arabia, and western Iraq as these areas were located east and southeast of the shoreline. Another, but more widespread, transgression took place in the early Maastrichtian producing pelagic marly chalky deposits that contained abundant organic matter and planktonic foraminifera. These relatively deeper-marine conditions continued throughout the Paleocene and ended in the Late Eocene (Price et al., 1995; Sharland, et al., 2001; Powell and Moh’d, 2011). Accordingly, the Neo-Tethys Ocean extended several hundred kilometers southward to include western Iraq, northern Saudi Arabia, southern Jordan and the Negev. The southward widening of the Neo-Tethys shelf facilitated oceanic circulation and shallow-water winnowing of phosphate grains, especially after the complete opening of the South and North Atlantic oceans at this time.
As a result of changes in the oceanic configuration during the Late Cretaceous to Eocene, a powerful Tethyan Circumglobal Current (TCC), has been advocated by some authors, whereas others suggest that a relatively weaker current flowed along the southern margin of the Neo-Tethys platform. In both models, the TCC was flowing from east to west through the Caribbean Tethys and farther west into the Pacific. Oceanic circulation can cause the upwelling of deeper, cold, nutrient-rich currents to the ocean surface. Coastal upwelling is presently taking place in several localities; for example, along the South Atlantic coasts of South Africa and Namibia (Birch, 1980; Baturin, 2000; Wigley and Compton, 2007), and off the western coasts of South America, in the waters of Peru and Chile (Burnett, 1990; Burnett et al., 2000). Since the Miocene, phosphorites have been forming due to upwelling in these locations, as well as in upwelling areas off western California (Kolodny and Garrison, 1994), the southeastern USA (Florida-North Carolina) (Riggs et al., 2000), and in the Arabian Sea off Oman (Schenau et al., 2000). Upwelling, and thus phosphorite formation, can also take place in deep ocean basins where oceanic circulation is obstructed by seamounts, atolls, and the like in the Pacific and Atlantic oceans (Cullen and Burnett, 1986, Jones et al., 2002), as is discussed below.
However, not all experts are in agreement that upwelling is the source for the phosphorus required for the formation of phosphorites. Glenn and Arthur (1990) explained the formation of the major phosphorites of southern Egypt without the requirement for upwelling currents. They believe that the area was too far south to have been affected by oceanic circulation and upwelling. Instead, they postulated terrestrial chemical weathering of a landmass lying to the south as the source for phosphates, brought into the phosphorite basin by rivers. The abundance of iron represented by glauconite and pyrite in the Abu Tartur deposits in southeast Egypt was taken as evidence for the absence of upwelling. This was possibly also the mode for phosphorite formation in the Proterozoic where diversified life forms had not yet evolved and thus the oceanic phosphate cycle was not possible (Papineau, 2010). The eastern Australian shelf phosphorite formation was explained by Heggie at al. (1990) as the result of an iron-pumping mechanism that did not require extensive upwelling.
In spite of these reservations, ever since Kazakov (1937) formulated his ideas on phosphorite generation, experts in the field have championed oceanic upwelling as the cause, or at least a prerequisite, for the formation of marine phosphorites throughout the Phanerozoic (see Bentor, 1980; Baturin, 1982; Slansky, 1986; Föllmi, 1996; Soudry et al., 2006; Brookfield et al., 2009; among many others). Indicators for ancient upwelling in relation to phosphorite formation are the association of phosphorites with bedded chert, porcelanite, organic-rich sediments and abundant planktonic fossils. All eastern Mediterranean phosphorite deposits (see Figure 1) contain these lithofacies associations (see Figure 4).
Formation and Concentration of Phosphorite Deposits
In the upwelling model, the source of phosphorus (P) and silica (Si) involves both elements being recycled between the deep oceanic reservoir and the surface water by upwelling currents followed by sedimentation. Upwelling currents spread deep, cold marine water to the sea surface (see Figure 3), rich in Si and P. These elements are the basic nutrients for phytoplanktons, the lowest tier in the marine food chain, which inhabit the photic zone or the upper 100 to 200 m of the seawater column. Phytoplanktons bloom, followed by zooplanktons and other higher marine life, and thus bioproductivity is greatly enhanced.
Most of the oxygen in the water column below the photic zone, would be depleted by aerobic bacteria feeding on the rain of dead organic matter, thus creating an oxygen minimum zone (OMZ). In shallow-water epicontinental shelves, such as those of the Neo-Tethys Afro-Arabian margins, the OMZ would coincide with the sea floor, thus producing a favorable anaerobic environment for the preservation of organic matter. The continuation of this regime would maintain a high rate of sedimentation and consequently a high rate of burial and the formation of organic-rich sediments (Slansky, 1986; Föllmi, 1996; Baturin, 2000; Burnett et al., 2000).
In early diagenesis, in the upper layers of the sediments (tens of centimeters to a few meters depth), phosphorus and silica are released from the organic matter to the sediment’s pore water, thus increasing their concentrations several fold as compared with bottom seawater. Further increase in concentration of phosphorus occurs as a result of the authigenesis of magnesium-rich minerals, such as dolomite and palygorskite (Birch, 1980, Glenn et al., 1994). It is from these solutions that phosphorites are precipitated ultimately as carbonate fluorapatite (francolite) and mediated by bacteria (Soudry, 1987; Abed and Fakhouri, 1990, Lamboy, 1990). Phosphorites either precipitate from pore-water fluids (authigenesis) or are formed by reactions within pre-existing sediments (diagenesis). In this case, diagenesis includes the phosphatization of foraminiferal carbonate tests and similar fossils within the sediments. The above depositional scenario explains the facies association of phosphorite, chert, porcellanite (tripoli), and organic–rich sediments within the upwelling regimes (Glenn et al., 1994; Powell and Moh’d 2011, 2012).
Two important processes are needed in order to produce the present-day granular giant phosphorite deposits through the concentration of the diluted sediments into high-grade deposits: these are reworking and winnowing. Reworking of pre-existing phosphatic mud and pristine phosphorite produces the intraclasts, peloids and pseudo-oolites (coated grains), that are the dominant grain types in present-day phosphorites. However, phosphate nodules can also form within the pore spaces of the sediments, and may coalesce to produce large masses (Riggs, 1980; Burnett, 1990). The reworking of such nodules can also produce phosphatic peloids and intraclasts. Winnowing by current action removes the fine-grained material and so concentrates the coarser phosphatic grains to produce granular phosphorites and the accumulation of high-grade deposits (Bentor, 1980; Glenn et al., 1994).
The question remains as to why were high-grade giant phosphorite deposits concentrated in this comparatively small part of the northern Arabian Plate (see Figure 1) and deposited in a relatively short period of time from the Campanian to Eocene. The author believes the primary reason is tectonic as this prepared the area for the other required factors, such as upwelling and sedimentation. The northwestern Afro-Arabian platform (the southern continental shelf of the Neo-Tethys) was dotted with submerged structural paleohighs; these were the Ha’il, Rutba and Sirhan highs, the Ga’ara Dome and the Syrian Arc, discussed above (Guiraud and Bosworth, 1997). These structures obstructed the west-flowing Tethyan Circumglobal Current and caused obstruction upwelling. The obstructed flow led to the formation of backwater eddies in the lee of these structures, thus causing the upwelling of deep, cold, nutrient-rich oceanic water (Abed and Amireh, 1983; Almogi-Labin et al., 1993; Sheldon, 1993; Föllmi, 1996) (see Figure 16). Upwelling was probably also extenuated by easterly winds that were deflected to the south onto the southern continental margins of the Neo-Tethys (Sheldon, 1988; Jarvis, 1992; Francis and Frakes, 1993; Price et al., 1995; Bush, 1997; Poulsen et al., 1998). It is the author’s belief that the region’s large high-grade phosphorite deposits were formed as a result of intense obstruction upwelling caused by the paleohighs.
Sedimentation is an additional factor, especially in areas with no intra-plate deformation; for example, in central Jordan (Al-Hisa and Al-Abiyad) and possibly Eshidiyya in the south of Jordan, all located south of the S-shaped Syrian Arc deformation belt. The presence of constructional bed forms (oyster buildups) also acted as baffles behind which thick phosphorite could be generated during rising sea level (see Abed et al. (2007) for Eshidiyya, and Powell and Moh’d (2011) for central Jordan). The oyster buildups were up to 30 m thick and formed a shallowing structure that acted to concentrate and accumulate ore-grade phosphorites. It could also be argued that the oyster buildups had grown on undeformed tectonic highs associated with the formation of the Syrian Arc, and that their growth helped in the enhancement of the ocean-floor topography for the benefit of the subsequent phosphorite formation (Abed and Sadaqah, 1998).
The phosphorite deposits of the Negev in Palestine, the Jordanian deposits of Al-Kora, Ruseifa and central Jordan (Al-Abiyad and Al-Hisa), and those of the Palmyrides in Syria, seem to have been deposited along the highs of the Syrian Arc before being reworked to the flanks of the corresponding lows (Kolodny and Garrison, 1994; Abed and Sadaqah, 1998; Brew et al., 2001; Soudry et al., 2006). The Eshidiyya deposits in southern Jordan, the Sirhan deposits in southeastern Jordan as well as the Thaniyat deposits in the western part of the Turayf region in northwestern Saudi Arabia seem to be associated with the Sirhan High. Most of the Saudi Arabian phosphorites in the Al-Jalamid region in the north of the country and the western Iraq Akashat deposits are associated with the Rutba High (see Figure 16).
These deposits are diachronous and young toward the north-northeast (see Figure 1 and Table 2). For example, the Negev phosphorites are of Late Campanian age, the Jordanian deposits are Late Campanian to Early Maastrichtian, those of the Thaniyat area are Late Maastrichtian to Early Paleocene, the Jalamid deposits of Saudi Arabia and the Akashat deposit of western Iraq are Early to Middle Paleocene, and the Pabdeh deposits of Iran are Paleocene to Oligocene. This diachronous younging is here explained by the propagation of the formation of the paleohighs in a north-northeasterly direction, which was the direction of the movement of Arabian Plate at the time. It might also be due to the migration of phosphogenic lithofacies belts north-northeastward with time as the Tethys Ocean transgressed eastward due to rising global sea levels in the Maastrichtian to Eocene. The Iranian deposits seem to have formed in the time interval near to the final closure of the Neo-Tethys.
The phosphorite deposits of Turkey are older than those to the south. The Tasit deposits are of Middle Turonian age, whereas the Kasrik-Semikan deposits are Coniacian to Santonian. Consequently, they do not fit the NNE-younging of the eastern Mediterranean deposits, and thus need some explanation. Firstly, the Turkish deposits are of minor importance and cannot be compared with the commercial giants (see Figure 1) to the south. However, they are comparable in magnitude and age with European phosphorites. For example, in southern Europe, Greek and Albanian phosphorites are Turonian to Campanian and older (Papastavrou, 1989), those of the Paris Basin in France are Coniacian to Lower Campanian (Lucas and Prévôt-Lucas, 1995), and in southern England they are of Santonian to Lower Campanian age (Jarvis, 1992). Secondly, the Anatolian (Turkey) Plate rifted from the Afro-Arabian Plate during the Early Cretaceous to Turonian, and thus became part of the Neo-Tethys proper before the southern localities. Evidence suggests that the Tethyan Circumglobal Current (TCC) became stronger from the Turonian onward and was associated with the opening of the South Atlantic. At this time, present-day Turkey and southern Europe, were situated in an area where upwelling and the formation of phosphorite took place, albeit on a minor scale (Föllmi and Delamette, 1991). At this time, neither the TCC nor even a sluggish current was flowing through the eastern Mediterranean region; as a result, no ore-grade phosphorites were deposited. It is probable that this was because the Levant, Iraq and Saudi Arabia areas were either completely emergent, as shown by the presence of fluvial siliciclastics during the Early Cretaceous, or that the Late Albian to Turonian marine-rimmed carbonate shelf was not a favorable location for the generation of phosphate.
Furthermore, why are the Turkish and southern European phosphorites smaller in size and lower in quality than the southern Neo-Tethys deposits? It has been postulated that the atmospheric circulation regime of winds blowing westward did not have the same strength in southern Europe as on the Afro-Arabian platform farther south. The winds seem to have been deflected to the southwest along the margin of the platform to cause intense upwelling, whereas wind-generated upwelling was much reduced in what is now southern Europe, thus producing only minor phosphorite deposits (Sheldon, 1988, 1993). In this scenario, the TCC did not flow to the west in the northern Mediterranean-Tethys, but instead an anticlockwise current flowing to the east was postulated (Barron, 1987; Poulsen et al., 1998, 2001), while, at the same time, a continuous TCC, albeit relatively weak, was hugging the Afro-Arabian platform. If this model is adopted, it might explain the low level of high-grade phosphorite in southern Europe. However, this model was not accepted by some authorities (for example, Föllmi and Delamette, 1991) who advocated a strong west-flowing TCC (see Tethyan Circumglobal Current).
Compressional paleohighs and lows in the productive phosphorite areas in Figure 1 were not unique to the Tethyan Afro-Arabian platform. Other phosphoritic basins and highs are reported from northern and northwestern Africa; for example, southern Egypt (Glenn and Arthur, 1990), Tunisia (Belayouni and Beja-Sassi, 1987; Svoboda, 1989), Morocco (Office Cherifien, 1989), and Senegal (Pascal et al., 1989). It is not the intention of this paper to study these deposits, but a short description of the Tunisian phosphorite deposits is an illustrative example.
Phosphorite deposits are widespread in Tunisia with a total reserves of 3 billion tonnes and annual production of about 6 Mt (Svoboda, 1989). Phosphorite deposition commenced in the Early Paleocene with most occurring in the Lower Ypresian of the Early Eocene, as represented mainly by the Metlaoui Formation (Belayouni and Beja-Sassi, 1987). The major deposits are present in the Gafsa Basin in the south, the El Kef Basin in the northwest, and the Eastern basins separated by three major highs and several smaller ones (Figure 18). It is interesting to note that the major deposits of the Gafsa and Eastern basins are situated along the flanks of the so-called Kaserine Island, a dome-like anticlinal paleohigh (Svoboda, 1989). This clearly indicates the role of these Tertiary paleohighs in the deposition of the high-grade Tunisian phosphorites and confirms the depositional scenario advocated for the eastern Mediterranean phosphorite deposits.
Nearly half of the world’s phosphorite resources were deposited in the eastern Mediterranean area and northwest Africa during the Campanian to Eocene (see Figure 1).
Modeling of oceanic circulation during the Late Cretaceous suggests that the Tethyan Circumglobal Current (TCC) flowed from east to west along the southern margin of the Afro-Arabian continental shelf. During the Turonian, the TCC may have become more powerful due to the opening of the South Atlantic basin, and in Campanian–Maastrichtian times, a compressional event occurred due to the initial collision of the Afro-Arabian Plate with the intra-oceanic subduction trench of the Eurasian Plate. This compressional event produced intra-plate paleohighs in the northern to northwestern part of the Afro-Arabian platform, such as the Syrian Arc Fold structure. As a result, much of the sea floor in the eastern Mediterranean region at this time consisted of topographical highs and lows (basins and swells). These regional events continued throughout the Late Eocene until the continent-continent collision finally took place between Afro-Arabia and Eurasia.
Obstruction upwelling along these paleohighs, enhanced by winds blowing in the same westerly direction, brought deep, cold, nutrient-rich oceanic water to the ocean surface. These circumstances caused high biodiversity that led to the deposition of organic-rich sediments and to the authigenic formation of the phosphate mineral francolite (carbonate fluorapatite). Reworking and winnowing of phosphate grains resulted in the concentration of the phosphorite deposits to produce thick, high-grade granular phosphorite giants. Constructional oyster banks that formed baffles during Campanian to Maastrichtian times, seemed to have influenced these processes in certain parts of the region.
The author would like to thank the two anonymous reviewers for their valuable comments, that greatly improved the original manuscript. Ghaleb Jarrar provided some of the literature used in the manuscript. The author would also like to thank David Grainger for editing the manuscript, Kathy Breining for proof-reading, and Moujahed Al-Husseini, for his valuable comments, which helped in the reorganization and improvement of the manuscript. The drafting and design work by GeoArabia Graphic Designer Nestor ‘Nino’ Buhay IV, is greatly appreciated.
ABOUT THE AUTHOR
Abdulkader M. Abed obtained his PhD in sedimentology and sedimentary geochemistry from Southampton University, UK, in 1972. After graduation, he joined 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 Dead Sea. More recently he has become involved in the study of the paleoclimate of Jordan and adjacent areas. He is a member of SEPM, IAS, the Mineralogical Society of London, and the Jordan Society for the History of Science. He has served as a member of the scientific boards of IGCP (1989–1995) and IUGS/UNESCO.