Arabian Journal of Earth Sciences (AJES)

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1 Arabian Journal of Earth Sciences Vol. 2 (2015) - Issue 1: الدورية العربية لعلوم األرض Arabian Journal of Earth Sciences (AJES) Neoproterozoic (infracambrian) - Paleozoic Total Petroleum Systems of Arabian Peninsula; an Overview Adel AL-Johi, Abdulaziz Al-Laboun Department of Geology and Geophysics, College of Science, King Saud University, Riyadh, Saudi Arabia. KEYWORDS Neoproterozoic Paleozoic Total petroleum system Arabian Peninsula ABSTRACT The Neoproterozoic (infracambrian)-paleozoic total petroleum systems are considered as major TPS in Arabian Peninsula. The Neoproterozoic TPS located in subsiding rift basin which has been formed during the infracambrian. It is represented generally by Huqf Supergroup. The Infracambrian is consisting of two sub-tpss. The North Oman Huqf/ Q Haushi (!)(201401) TPS involving Ghaba-Makarem Combined Structural Assessment Unit (AU), has been identified for the Ghaba Salt Basin Province. Second TPS is North Oman Huqf Shu aiba (!) TPS (201601); Fahud-Huqf Combined Structural AU in Fahud Salt Basin Province. In both provinces, hydrocarbons were generated from Infracambrian buried source rocks pertaining to the Huqf Supergroup. Oil in the Ghaba Salt Basin may be linked to at least two distinct Huqf source-rock units: a general North Oman Huqf-type oil source and a more dominant questionable unidentified source or Q -type Huqf oil source. For the (201401) TPS migration is vertical and lateral into Permian-Carboniferous Haushi Group carbonate- clastic reservoir within structurally complex traps. The North Oman Huqf-Shu aiba TPS (201601) and Fahud-Huqf Combined Structural AU mostly produce gas from Middle Cambrian to Lower Ordovician clastic reservoirs of the Haima Supergroup and the traps are mainly structural. Paleozoic TPS in the Arabian Peninsula encompassed many systems that extend regionally within the Gulf Countries. The Paleozoic TPS consisted of Qusaiba-Paleozoic TPS (202101), Qusaiba/Akkas/Abba/Mudawwara TPS (202301); and the Silurian Qusaiba TPS (201903) which widely distributed within greater Rub al Khali Basin. All Paleozoic TPSs sourced in basal Qusaiba hot shale. The reservoir rocks are mainly sandstone of the Lower Permian Unayzah and Devonian Jauf Formations in center Arabia; and also Permian Unayzah sandstone in north center Arabia and Rub al Khali Basin but carbonate in Northern Qatar Arch Extension UA. The traps are mostly structural with stratigraphic and the seals are dominant anhydrite, shale, salt and tight carbonates. I. INTRODUCTION The Neoproterozoic and Paleozoic Total Petroleum Systems (TPSs) are counted among five prolific hydrocarbon producing systems in Arabian Peninsula. And both petroleum systems have potential plays in conventional and unconventional petroleum systems. This area is revealed to be rich in petroleum since it subjected through the late Neoproterozoic to complex tectonic events coincided with widespread erosion, and/or incision peneplanation on the Platform. The *Corresponding author, address : alm-1985@hotmail.com; ibnlaboun@yahoo.com 1

2 main episode is Najd strike-slip movement which accompanied by the development of rift basins within which the Hormuz and Ara salt were deposited (Haq and Qahtani, 2005). The plate comprised an extensive depositional platform along a Paleozoic passive margin of Gondwana. Extensive source-rock deposition within these basins, and major tectonic episodes of compression and extension, produced large structural closures coincident with peak oil generation and migration. Furthermore large source rocks have been regionally sealed by extensive evaporite seals. Fig. 1- Arabian Plate showing general tectonic and structural features, Infracambrian rift salt basins. Modified from Ziegler (2001). 2

3 The Neoproterozoic (Infracambrian) TPS is found within the geographic limits of most rift (Ghaba and Fahud) salt basins of Neoproterozoic age (Fig. 1, see also Fig. 6). The system is identified two Huqf petroleum subsystems in North Oman; the Ghaba Salt Basin (2014) and Fahud Salt Basin (2016) provinces. In both provinces hydrocarbon are sourced in Neoproterozoic Huqf Supergroup and migrated during range from Neoproterozoic to Cretaceous and trapped structurally into clastic-carbonate reservoirs ranging in age from Neoproterozoic to Cretaceous. The Paleozoic TPS is partitioned into subsystems in the eastern Arabian Peninsula (see fig.9). All those subsystems are sourced in basal (hot shale) of lower Qusaiba Shale Member of The Qalibah Formation. The Hercynian tectonic movement played significant roles controlling formation of reservoir rocks and traps which are mostly structural with some stratigraphic. The reservoir rocks varied from province to other of alluvial, eolian sandstones of the Permian Unayzah Formation; shallow marine shelf sandstones of the Devonian Jauf and Permo-Triassic carbonate of Khuff formation. Fig. 2- Generalized northwest-southeast cross section across northern Oman and the Ghaba Salt Basin, Central Oman Platform (Makarem High), and Fahud Salt Basin showing major oil and gas fields, proven occurrences, and potential traps. Modified from Dros (1997). II. NOMENCLATURE AND METHODS According to the U S Geological Survey World Petroleum Assessment 2000 project, the world is divided into 8 regions and 937 geologic provinces in which rank depends on the discovered oil and gas volumes. Among these divisions 76 priority provinces and 26 boutique provinces (both exclusive of the U.S.) were selected for appraisal of oil and gas resources. A geologic province is an area having characteristic dimensions of hundreds of kilometers which encompasses a natural geological entity (for example, a sedimentary basin, thrust belt, or accreted terrane) or some combination of contiguous geological entities and bounded along natural geologic boundaries (Pollastro, 1999). Originally, the term of total petroleum system (TPS) was first introduced by Dow and the first use was by Perrodon (Magoon and Dow 1994). The TPS comprised of essential elements such as source rocks, reservoir rocks, seal rocks, and overburden rocks and processes as generationmigration-accumulation and entrapment that are related to petroleum which occurring generally in seeps, shows, and accumulations, in both discovered 3

4 and undiscovered that generated by a pod or by closely related pods of mature source rock (Magoon and Schmoker, 2000). An assessment unit has been informally used by petroleum explorationists to describe present-day structural or stratigraphic features that could be mapped and drilled. The assessment unit (AU) is a volume of rock within the TPS that encompasses fields, discovered and undiscovered, homogeneous in terms of geology, exploration strategy and risk characteristics to constitute a single population of field characteristics with respect to criteria used for resource assessment. If the AU is contained more than 13 discovered fields then it is called established AU and frontier if they contain 1-13 discovered fields and hypothetical if they contain no discovered fields (Magoon and Schmoker, 2000). A TPS may be subdivided into two or more AU based on exploration considerations, and risk to assess individually. A numeric code identifies each region, province, TPS, and AU. For example, number 2 refers to the region (Middle East and North Africa; MENA), three digits to the right of region code refer to province 2021 (Greater Ghawar Uplift), TPS (Central Arabia Qusaiba-Paleozoic) assigned by adding two digits to the right of province code, and AU also, by add two digits to the right of TPS (North Gulf Salt Basin Structural Gas). The elements of the TPS are provided in the form of an events chart which include the major rock-unit names(see fig. 7,8,10,15), the temporal extent of source-rock deposition, reservoir-rock deposition, seal rock deposition, overburden-rock deposition, trap formation, generation-migration-accumulation of petroleum, and preservation of petroleum; and the critical moment, which is defined as the time that best depicts the generation-migration-accumulation of hydrocarbons in a petroleum system (Magoon and Schmoker, 2000). Fig. 3- An east-west structural cross-section across Arabia showing the major structures of Ghawar (Saudi Arabia) and Dukhan (Qatar). Formations are shown in color along with major bounding faults in solid lines and an approximate depth scale in meters (modified after Konert et al., 2001). III. TECTONIC EVOLUTION AND MAIN STRUCTURES SETTING The Arabian plate is bounded by the southern and western Oligocene-Miocene rift margins where spreading and rotation modeled the Red Sea and the Gulf of Aden as well as the eastern and northern margins characterized by compressional tectonic settings that formed the Zagros Fold Belt of southwestern Iran, the Simple Fold Belt of 4

5 southwestern Turkey, and the Makran Fold Belt where subduction occurs in the Gulf of Oman (Fig. 1). Fig. 4- Stratigraphic section of Oman showing source rocks and producing reservoirs for Ghaba and Fahud Salt Basins. Modified from (Loosveld et al., (1996) and (Droste 1997). The Arabian plate has been subjected to a complex tectonic history which is reflected by influences of eustastic sea level changes. These event changes being represented by either subsidence that led to form sedimentary accommodations and/or significant erosional hiatuses. The late Precambrian saw the onset 5

6 of the northwest-southeast Najd strike-slip movement, which is evidenced from Egypt to Oman, with possible continuation into the then contiguous Indian Plate (Haq and Qahtani, 2005). Tectonically, Oman is bounded on the south by the Gulf of Aden spreading zone, to the east by the Masirah Transform Fault and the Owen Fracture Zone Trough, and to the north by the complex Zagros-Makran convergent plate margin, compression along which produced the Oman Mountains (Loosveld et al., 1996). During Early Cambrian (570 and 530), The Ghaba and the Fahud Salt Basins were formed as subsiding rift basins from left-lateral, strike-slip movement of the Najd transform fault system which ultimately dislocated the Arabian plate some 300 km to the east. In Oman, the Hugf Supergroup interpreted as syn-rift sequences (Ahlbrandt et al., 2000). The Huqf Supergroup consisted of a Neoproterozoic to Early Cambrian succession of continental to marine clastics, evaporites and carbonates, that overlying metamorphic basement and unconformably overlain by the Haima Supergroup (Fig. 2; Forbes et al., 2010). Fig. 5- the lithostratigraphic succession and Total Paleozoic petroleum system of Saudi Arabia. Modified after Laboun (2012). 6

7 On the Arabian Peninsula and Arabian Gulf, the oil fields trend N-S. Folds occur above oriented horst structures which formed along normal faults in the Precambrian basement of the Arabian Shield. In the eastern Persian-Arabian Gulf oil fields formed above salt diapirs that were formed by the rise of Early Paleozoic salt deposits (Frisch et al., 2011). Early Cambrian uplift led to widespread erosion and the subsequent Cambrian-Devonian sequences were mostly deposited on a peneplaned platform continental platform (Konert et al., 2001). During the Early Silurian deglaciation period the sea level rose resulting in the deposition of the organic-rich Qusaiba shale Formation proven as source rock directly overlying the Ordovician glaciogenic and periglacial rocks (Husseini, 1991). During the Late Devonian to mid-permian time interval the Arabian plate was located in a general back-arc setting in moderate southern latitudes and partly coeval with the Hercynian Orogeny. This phase characterized by extensional stresses, separated by a period of compression where the fluvial-dominated Unayzah Formation was deposited during Carboniferous to Permian. Alternatively, during the Mesozoic known as a large extensional phase (from 255 to 92 Ma), the plate was located in an equatorial setting and progressive continental rifting occurred around the plate, that lead to north- and southeast-facing passive margins. Late Permian, Triassic, and Jurassic sedimentation was dominated by carbonate-evaporite deposition, and Early Cretaceous was dominated by open-marine mixed clastic-carbonate deposits (Pollastro, 2003). Fig. 6- Map showing Fahud Salt Basin Province (2016), North Oman Huqf -- Shu aiba (!) Total Petroleum System (201601), and Fahud-Huqf Combined Structural Assessment Unit ( ) and showing Ghaba Salt Basin Province (2014), North Oman Huqf/ Q -- Haushi (!)Total Petroleum System (201401) and Ghaba-Makarem Combined Structural Assessment Unit ( ). Oil and gas field centerpoints (Petroconsultants, 1996) and boundaries for pod of active source rock and minimum petroleum system are also shown. Modified by Pollastro (1999). Scale = 1:2,750,000. A thick sequence of Phanerozoic sediments (up to 12,000 m) accumulated along the eastern Arabian Peninsula. In this area, a pre-mesozoic depositional basin, the Greater Arabian basin, was of extent thousands of kilometers. It was quite flat, thus providing an ideal setting for deposition on a large geographic extent of source, reservoir, and seal rocks (Alsharhan and Nairn, 2003). Progressive burial of the 7

8 large distributed source, reservoir, and seal rocks on a gentle structural setting allowed the efficient horizontal migration that could drain large, mature petroleum-generating source areas into extraordinarily large gentle structural closure (Fig. 3; Pollastro, 2003). Fig. 7- Petroleum system events chart for North Oman Huqf/ Q -- Haushi (!) Total Petroleum System (201401), Ghaba Salt Basin Province (2014), Oman, modified by Pollastro, IV. Stratigraphy The Neoproterozoic rocks crop out in the north (Jabal Alkdar and Saih Hatat), center (Huqf area) and the south (Mirbat area) of Oman (Cozzi and Al-Siyabi, 2004) (Fig. 6). They are comprised within Hugf Supergroup (Fig. 4). The Huqf Supergroup consisted of marine clastics, carbonates and evaporites, overlying metamorphic basement and overlain unconformably by the Haima Supergroup (Forbes et al., 2010). The Huqf contains several clastic and carbonate source rocks of exceptional quality; Huqf source rocks form the basis of the primary petroleum systems for hydrocarbons produced throughout Oman. The Cambrian Ara Formation is a carbonate /evaporite sequence (Pollastro, 1999). Along the southern Arabian platform rim, the lower Paleozoic section consists of mainly continental clastics, with some marine intercalations, which form important hydrocarbon reservoirs in the Ghaba and Fahud Salt Basins. A thick sequence rift-fill terrigenous and shallow-marine siliciclastics of the Haima Supergroup overlies the Ara Formation (Droste, 1997). The Haima Supergroup is a major composite siliciclastic succession, locally with minor limestone development. It was deposited in both continental and marine environments. The basal part (Mahatta Humaid Group) was deposited in arid to semi-arid, continental settings and marine, marginal marine and marine-influenced depositions of Andam and Safiq groups which represent the upper part of the Haima Supergroup (Forbes et al., 2010). In the Ghaba Salt Basin, sediments of the Haima Supergroup fill and cover the margins of the basin reaching thicknesses in excess of 6 km along the central axis. In eastern Oman, Silurian, Early Devonian through Late Carboniferous most of the Safiq Group and overlying rocks are not preserved resulting in broad uplift and erosional events. 2003). The erosional events have been recognized in deep wells from the main producing fields in the Ghaba and Fahud Salt Basins (Pollastro, 1999). Late Carboniferous time is represented in Oman by glacial clastics of the Al Khlata Formation and shallow marine and fluvial clastics of the Gharif Formation, both of which compose the Haushi Group which are important hydrocarbon reservoirs throughout Oman. Lower Khuff Formation shallow carbonate rocks is formed during a middle Permian marine transgression that forms a major regional seal above the clastic reservoirs of the Gharif Formation. In northern Oman, the carbonate rocks of the Jurassic Sahtan, and the Cretaceous Kahmah (Thamama) and Wasia Groups deposited as result of Sub-sequent transgressions of shelf cycles and changes in sedimentation during the Jurassic and most of the Cretaceous have been controlled mostly by eustatic fluctuations rather than 8

9 tectonics (Pollastro, 1999). Extension and/or reactivation of normal faulting along a northwestsoutheast trend, such as those associated with Natih and Fahud fields. In late Cretaceous, the salt movement in the Ghaba and Fahud Salt Basins have been pronounced. A significant unconformity is present between the Wasia Group and the overlying, shale and carbonate facies of the Fiqa Formation (Aruma Group), (Pollastro, 1999). Early Tertiary Hadhramaut carbonates and clastics rocks of Fars group are unconformably overlying the Aruma Group. Fig. 8- Petroleum system events chart for North Oman Huqf -- Shu aiba (!) Total Petroleum System (201601), Fahud Salt Basin Province (2016), Oman. Modified by Pollastro, (1998). In the center of the Arabia, the first sedimentary rocks covering the Arabian Shield are the alternating Infracambrian carbonates, clastics, and evaporites deposited within the rift salt basins in Oman. Thick and well-preserved Paleozoic rocks is exposed and penetrated in the greater Arabian Basin where oil and gas have been discovered in sandstone and limestone reservoirs in these rocks (Laboun, 2011). The post- Najd Rift sediments compose of sandstone and siltstones of the Middle Cambrian to Early Ordovician Saq Formation (Fig. 5). In northern Arabia, increased clastic influx in the Late Cambrian generally terminated by carbonate deposition (Saq Formation). During the Middle Ordovician, the Arabian Plate was covered by a major marine prograding clastic sequence (Konert et al., 2001). Thus, shallow marine sandstone and shale of the Middle to Late Ordovician Qasim Formation overlies the Saq Formation. During Late Ordovician times the Plate occupied southern latitudinal location, so the western part of the plate was affected by a glacial episode leaving behind evidence of glaciation on the Arabian Shield and broad and deeply cut subglacial valleys (Haq and Qahtani, 2005). This glaciation episode is recorded by Zarqa and the Sarah Formations which consist of complex glacial, periglacial sequences, tillite, boulder-clay, and finegrained, micaceous sandstone lithofacies. Sarah Formation was deposited in more confined paleovalleys reaching more than 300 m thick in outcrop and striated pavements occur in the lower parts of the formation, extending almost parallel to the paleovalley axis (Laboun, 2010). The Early Silurian Deglaciation caused a rise in sea level, which resulted in the widespread deposition of Qalibah Formation source rock. The Qalibah Formation consists of a lower Qusaiba Member and an upper Sharawra Member (Fig. 5). Lower Silurian organic-rich shale show a distinctive high gamma-ray on logs at the base of the Qusaiba Member. This basal, high-gamma unit is considered as the highest quality Paleozoic source rock for hydrocarbons in Saudi Arabia and referred to as the hot shale (Abu Ali et al., 1999, 2005). The overlying Sharawra Member consists of deltaic sandstones, siltstones, and shallow marine shale; however, formation log analysis indicates that these are poor quality reservoirs. Late Silurian-Early Devonian Tawil Formation disconformably overlies the Sharawra Member, which composed of fluvial to marginal marine sandstones. Due to extensive cementation by silica and kaolinite, the Formation is 9

10 considered poor reservoirs; whereas the overlying early to middle Devonian shallow marine sandstones of the Jauf Formation are of good reservoir quality (Pollastro, 2003). This sedimentary sequence overlain unconformably by poor reservoir quality sandstones of the middle to late Devonian Jubah Formation. The Carboniferous is mostly missing due to generalized uplift and erosion related to the Hercynian Orogeny (pre-unayzah Unconformity) particularly in the Greater Ghawar Uplift Province. During middle Carboniferous to Early Permian fluvial and coldclimate dune sands of the Unayzah Formation were deposited. Fig. 9- Petroleum system events chart for North Oman Huqf -- Shu aiba (!) Total Petroleum System (201601), Fahud Salt Basin Province (2016), Oman. Modified by Pollastro, (1998). The basal Unayzah Formation is composed of fineto coarse-grained sandstones that filled relict, erosional topography (Al-Laboun, 1987; and Laboun, 2010). Glacial sediments, including cold-climate dune fields of the Lower Unayzah are also recognized in the south half of the eastern Arabian Peninsula from the southern part of the Greater Ghawar Uplift Province, into the Rub al Khali Basin Province where Deposition in glacial environments in Oman continued during the early Permian represented by glaciallyinfluenced sediments of the Al Khlata formation (Forbes et al., 2010; Konert et al., 2001; and Pollastro, 2003). The Unayzah Formation forms the principal of Paleozoic hydrocarbon reservoir in the south half of the Greater Ghawar area; whereas, the Unayzah is absent due to Hercynian erosion in the northern part of the Arabian sub-basin (Pollastro, 1999, 2003). During the late Permian, a major marine transgression took place throughout the eastern Arabian Peninsula coinciding with Late Permian rifting along the Zagros, opening of the Neo-Tethys Ocean after the Iranian terranes had split and drifted away, and deposition of the cyclic, dominantly shallow water carbonates sedimentation on the Platform over a breakup unconformity and evaporites of the Late Permian to Lower Triassic Khuff Formation (Haq and Qahtani, 2005). The evaporites form seal intervals for the different Khuff reservoirs in the Ghawar area. In Central and eastern Arabia, the Khuff ranges in thickness from 365 to 490 m whereas thickens reaches more than 900 m in the Rub al Khali Basin (Al-Jallal, 1995). The Basal Khuff Formation clastics were deposited as channel and valley fill sediments on an incised Unayzah surface and forms important 10

11 reservoirs whereas, Shales and tight carbonates within the basal Khuff clastics form a regional seal for all the pre-khuff reservoirs in Central and Eastern Arabia. Within the Khuff formation, Late Permian dolomites form major gas reservoirs, particularly along the offshore North Gulf north and west of Qatar. Shales of the Nahr Umr Formation provide a good regional seal, and locally a hydrocarbon source rock, from Oman to Qatar. Farther to the west and northwest in Saudi Arabia, clastic units become more pronounced in the Wasia Group and are divided into the Safaniya and Khajfi Members (Alsharhan and Nairn, 2003). Fig. 10- Total petroleum system events chart for Central Arabia Qusaiba-Paleozoic Total Petroleum System(202101) of the Greater Ghawar Uplift Province (2021) and surrounding geologic provinces of central Saudi Arabia, showing total petroleum system element and timing of trap formation and Hydrocarbon generation. Modified from Pollastro (2003). V. NEOPROTEROZOIC AND PALEOZOIC TPS 5.1. Neoproterozoic (~infracambrian) TPS The infracambrian TPS within Arabian Peninsula restricted in some (USGS) provinces of Oman which sourced in Huqf Supergroup. The Neoproterozoic Huqf Supergroup contains of multiple carbonate and shale units and most associated with Ara Salt. The Ara Group (Latest Ediacaran earliest Cambrian) is a carbonate-evaporite sequence with salt as thick as 1,000 m (Ahlbrandt, 2000; and Forbes et al., 2010). The carbonates often float isolated in the salt (stringers), they can attain considerable thickness ( m) (Forbes et al., 2010). In the South Oman Salt Basin the Ara Group consists of salt diapirs, which enclose several isolated carbonate bodies at a depth of 3 5 km, known as the intra-salt Ara carbonate stringer play. The Ara carbonate reservoirs pores and vugs are filled by solid bitumen that derived from pre-ara carbonate/evaporite source rocks and represents a major exploration risk decreasing reservoir quality (Schoenherr, et al., 2007). Pollastro (1999) identified two Huqf petroleum subsystems in North Oman for the assessment of the Ghaba Salt (2014) and Fahud Salt Basins (2016) provinces (fig 6). In the North Oman, Huqf / Q -Haushi (201401) TPS and the assessment unit Ghaba-Makarem Combined Structural ( ) lies entirely in Oman and defined by the underlying the Cambrian Ara Salt and southern migration path of the Infracambrian Q-type oils over the Central Oman High and into the South Oman Salt Basin province (fig. 6) (Pollastro, 1999, 2003). The unit is structurally bounded to the north by the Makarem-Mabrouk high and Oman Mountains, to the east-southeast by the Huqf-Haushi Uplift, to the south by the Central Oman High, and to the west by the Rub al Khali Basin. The primary source of Huqf oils in Haushi reservoirs of North Oman is Shuram Formation which consisted of interbedded red-brown shales, carbonates, and dark grey organic-rich shales (Forbes et al., 2010; and Pollastro, 2003). Oil-type (light) shows that more than 90% of the oil-in-place is derived from the Infracambrian Q source rock unit near the top of the Ara Salt and in the Shahabad source rock interval (Pollastro, 1999).The Huqf/ Q-type source rocks contain structureless, type I and type II oil-prone organic matter (Tab. 1). Oil generation from Huqf/ Q source rocks in both basins to reservoirs 11

12 aged in range from Precambrian to Cretaceous (Ahlbrandt et al., 2000). Migration is both vertical and lateral into multiple reservoirs that range in age from Infracambrian to Cretaceous (Pollastro, 2000). Migration of Q-type oils occurred in a southward pathway along the regional Permian Khuff seal and into Sharif reservoirs far into the South Oman Salt Basin. Gas generated during ( Ma) was sourced on the west flank of the Ghaba Salt Basin and migrated mainly east into Haima structures along the western margin of the basin. Reservoirs include clastics and carbonates ranging in age from Infracambrian to Cretaceous. The main oil reservoirs are clastics of the Permian-Carboniferous Haushi Group (Gharif and Al-Khlata Formations). In most fields, the Al-Khlata Formation and laterally continuous, porous deltaic sands of the Lower Gharif form one continuous reservoir and are sealed by the Haushi Limestone member (Pollastro, 1999) (Fig. 4). Regionally deposited Rahab Shale member at the top of the Al Khlata and between the Al Khlata and Gharif Formations commonly forms a seal for Al Khlata reservoirs. Some production is from the overlying Permian Khuff Formation (Pollastro, 1999). Traps vary and are structurally complex (combined structural), salt-induced anticlines and domes. Specific common trap styles are faulted closures, dip closures, and faulted-dip closures (Ahlbrandt et al., 2000; and Pollastro, 1999). Primary regional seals are: (1) the Cambrian Ordovician Mabrouk shale; (2) the Permian Khuff Formation carbonates; and (3) thick shales of the Cretaceous Nahr Umr and Fiqa Formations. The North Oman, Huqf / Q -Haushi (201401) TPS is summarized in the events chart of Figure 7. Fig. 11- Hydrocarbon expulsion history from the Qusaiba source rock as modeled in Udaynan well and in hypothetical Model wells about 30 Km to the south-east of the kitchen. Modified from (Abu-Ali and et al., 1999). A North Oman, Huqf-Shu aiba TPS (201601) and Fahud-Huqf Combined Structural AU ( ) were defined for the Fahud Salt Basin Province. The North Oman Huqf Shu aiba (!) TPS is interpreted extend beyond the Fahud Salt Basin Province boundary and onto the central portion of the Makarem- Mabrouk high of the Central Oman Platform Province (2015) and include A small portion of the eastern flank portion of the Rub al Khali Province (2019) (Fig. 6).The TPS can be divided into two TPSs based on stratigraphy and geochemical data. The first one of the TPS name implies a combination of all source beds of 12

13 the Huqf Supergroup in the Fahud Salt Basin Province that generate the oils, referred as North Oman Huqf -type, and the second system name refers to the carbonate reservoirs (porous rudist buildups and fractured chalk) of the Cretaceous Shu aiba Formation, for example, Yibal field. The reserve of Yibal field is estimated at about 3 billion barrels of stocktank oil (Pollastro, 1999). Fig. 12- Center Arabia and Greeter Ghawar area showing expulsion of oil and gas from Qusaiba hot shale. A, Area of basin that has expelled oil from Qusaiba hot shale. Darker green indicates the most mature area that expelled the greatest amount of oil. B, area of basin that expelled gas from Qusaiba hot shale. Darker red indicates the most mature area that expelled the greatest amount of gas. Modified from (Abu Ali et al., 1999; 2000). Here, the Lower Cretaceous Shu aiba (grainstones and chalky carbonates) and Middle Cretaceous Natih limestones account for most of the production. In both the Shu aiba and Natih Formations, shallow water, shelf-margin carbonate buildups (mainly rudistid reefs) and associated grainstones (debris shoals) formed on and around low-relief structural highs (mostly formed by salt pillows and tilted, up-thrown fault blocks) comprise the best reservoirs. Sandstones of the Haushi Group (Gharif and Al Khlata Formations Khuff limestone seal) form reservoirs in some fields. In both Huqf TPS and AU units, deep gas is produced mainly from Middle Cambrian to Lower Ordovician clastic reservoirs of the Haima Supergroup (Ahlbrandt, 2000). Traps in nearly all hydrocarbon accumulations of these TPS are mainly structural complex, salt-induced anticlines and domes that have been broken up into several fault blocks (Pollastro, 1999). Source rock/ oil type OMt TOC (%) 13C ( ) Sterane % (C27, C28, C29) API %S X-c North Oman Huqf I/II 3 33 to 35 20,20, yes Huqf Q I/II N.D. 30 to 31 63,22, yes Natih I/II ,38, no Tab. 1- Common characteristics of source rocks and oils of Ghaba and Fahud Salt Basin Provinces, north-central Oman. [TOC, total organic carbon in weight percent: OMt, organic-matter type; %S, percent sulfur in oil; Xc, presence/absence of X-branched compounds; N.D., no data]. 13

14 Visser (1991) suggests that an early minor stage of oil generation occurred in Middle and Lower Huqf source rocks during the Early Silurian whereas Peak oil generation occurred during Late Permian/Early Triassic (~250 Ma); gas generation began during the Cretaceous (~110 Ma). Amthor and others (1998) suggests that gas expelled from Huqf source rocks in the Fahud Salt Basin and reached the Makarem high during a period ranging from 80 Ma to present day (Pollastro, 1999). North Oman, Huqf-Shu aiba TPS (201601) is summarized in the event chart of the Figure 8. Fig. 13- Burial history and hydrocarbon generation model for base of the Silurian Qusaiba Member source rock in Udaynan well, Saudi Arabia. Modified from Wender et al., 1998) Paleozoic Total Petroleum System Paleozoic TPS in the Arabian Peninsula encompassed many systems that extend regionally especially within some of the Arabian Gulf Countries. The Paleozoic TPS is comprised of a regionally extensive, Silurian source facies that can be locally partitioned into subsystems along a north-south trend across the eastern Arabian subcontinent (Husseini, 1991). Deglaciation in the Early Silurian resulted in a major sea level change and the widespread deposition 14

15 of the upward-coarsening, progradational Qalibah Formation (Ahlbrandt et al., 2000). The Qalibah Formation consists of a lower Qusaiba Shale Member and upper sandstones, siltstones, and shale of the Sharawra Member (the formation is upgraded to group and member to formation (Laboun, 2012)). The base of the Qusaiba Member contains regionally correlative, organic-rich shale with a distinctive high gamma-ray signal on geophysical logs; this high gamma-ray interval is generally referred to as the hot shale (Abu-Ali et al., 1999). The organic-rich hot shale was deposited in a broad, anoxic, marine shelf environment of Gondwana, which included the greater part of present Arabia and North Africa (Husseini, 1991). The Lower Silurian, basal hot shale is a darkgray to black, with about 75 m and with as much as 8 weight percent TOC (Ahlbrandt et al., 2000). The Silurian base Qusaiba source rock contains type II organic matter with a hot shale thickness ranging from 3-70m and averages 3 to 4 weight percent TOC in Saudi Arabia (Abu-Ali et al., 1999; and Abu-Ali, 2005) and 6 weight percent in Iraq and is considered the principal source rock for hydrocarbons of the Silurian-Paleozoic petroleum system throughout the Arabian Platform and Zagros Fold Belt (Ahlbrandt et al., 2000). Fig. 14- Paleozoic Qusaiba/Akkas/Abba/Mudawwara Total Petroleum System (202301) and adjecent Total Petroleum Systems. Modified after Pollastro, (2003). According to current USGS assessment of the Arabian subcontinent portion, there are three separate Paleozoic subsystems which are described to more accurately represent local variations in the more regional Paleozoic TPS. The first one, The Central Arabia Qusaiba-Paleozoic TPS (202101) encompasses an area mostly within Saudi Arabia, Bahrain, and western Qatar. The TPS includes all of the Greater Ghawar Uplift Province and extends into the central part of the Interior Homocline Central Arch Province (2020), the northern edge of the Rub al Khali Basin Province (2019), the Southeastern most parts of the Widyan Basin Interior Platform Province (2023), the Mesopotamian Foredeep Basin (2024) Province, and the western flank of the Qatar Arch Province (2022) (Pollastro, 2003) (Fig. 9). 15

16 Fig. 15- Timing of events critical to petroleum accumulation in the Paleozoic Qusaiba/Akkas/Abba/Mudawwara Total Petroleum System of the Widyan Basin Interior Platform Province modified after (Wender et al., 1998). The geographic boundaries of the Paleozoic TPS are assigned on the base of several features, as limitation of the geographic extent of the source rock, or closely coincide with the geologic boundaries forming the Central Arabian intraplatform sub-basin (Pollastro, 2003). The western boundary of the Central Arabia Qusaiba-Paleozoic TPS (202101) is defined by the absence of the Qusaiba hot shale source facies along the Central Arabian Arch and Arabian Shield due to Hercynian uplift and erosion (Abu-Ali et al., 1999). The TPS boundary is also limited to the north and west by the geographic extent of the Qusaiba hot shale. The Central Arabia Qusaiba-Paleozoic TPS is divided into two assessment units, the southern onshore unit is called the Central Arch Horst-Block Anticlinal Oil and Gas AU ( ); and the North Gulf Salt Basin Structural Gas AU ( ) encompasses the northeast half of the TPS that is underlain by the Hormuz Salt (Pollastro et al., 1998). In the Central Arch Horst-Block Anticlinal Oil and Gas Assessment Unit, hydrocarbons are sourced by the organic-rich basal shale of the Qusaiba Formation and produced from sandstone reservoirs including eolian and fluvial sandstones of the Lower Permian Unayzah Formation and shallow marine shelf sandstones of the Devonian Jauf Formation and some production comes from Ordovician sandstones in the northern and western portion of the AU (Ahlbrandt et al., 2000). Light sweet oils with high (44 53 ) API gravities and non-associated gas are produced in the central Arabian fields along the western portion of the AU (Pollastro, 2003). The primary regional seal is the Permian Khuff Formation which consists of a combination of shale, tight carbonate rocks, and anhydrite. Generation and expulsion of oil and gas from the Qusaiba Member hot shale studied by (Abu-Ali et al., 1999; and Abu-Ali, 2005) using actual wells as Udaynan well and hypothetical wells located in deepest part of the kitchen (fig. 12). They provided expulsion of oil and gas is limited to a small region in the southeastern part of the Central Arabian sub-basin. In the deepest part of the Central Arabian sub-basin, the source rock was thermally mature by the Late Jurassic, but hydrocarbon expulsion was not initiated until the Early Cretaceous (Pollastro, 2003) (Fig. 11). Oil and gas are expelled simultaneously, but gas expulsion continued for a longer time period. Most of the gas was expelled during the Late Cretaceous; whereas expulsion of oil nearly ceased after the Late Cretaceous. The expulsion profile shows three events: the first episode of expulsion about 120 Ma caused by primary kerogen cracking; secondary cracking of 16

17 heavy components (nitrogen, sulfur, and oxygen) and oils, causing a second episode of expulsion at about 100 Ma; and third episode of expulsion occurred at about Ma as result of later uplift and erosional event, where the gas was separated from the oil, causing re-migration (Abu-Ali et at., 1999) (Fig. 11). The burial history of hydrocarbon generation for Lower Silurian Qusaiba member source rock (hot shale) in Udaynan well in Saudi Arabia shown in (Fig. 13). Migration path is westward and updip from a more thermally mature eastern source area. The types of trap from the north-south are structural where anticlines formed by sediments draping over basement horst blocks, in the central Arabian fields, wrench faulting and stratigraphic pinch-out traps in Unayzah Formation. Through the last discovery reported in the Petro-consultants (1996) database to 1995, 14 oil fields and 4 gas fields of minimum size (>20 MMBO and 120 BCFG, respectively) constitute the total known discoveries within the AU (Pollastro, 2003). Fig. 16- Paleozoic, Jurassic and cretaceous total petroleum systems and centerpoints of oil and gas field in the Rub al Khali province. Modified from Pollastro, (2003). The The second AU is North Gulf Salt Basin Structural Gas which is mostly in the northern Gulf offshore and within USGS Province 2023 (Mesopotamian Foredeep) (Pollastro, 2000). In the North Gulf Salt Basin Structural Gas AU, hydrocarbons entrapped mainly in domes over salt diapirs and salt-assistedenhanced horst-block anticlines.many of the traps forming the fields of this AU were created during post- Hercynian tectonic events. In the Gas AU, the Qusaiba basal hot shale is primarily in the main zone of gas generation. Reservoirs composed mostly of grainstones and dolomitic shelf carbonate rocks of the Upper Permian Khuff Formation. Many of fields are produce gas. The undiscovered gas fields, the following sizes of grown fields were assigned at a minimum field size of 120 BCFG (20 MMBOE) and; a maximum field size of 60 TCF (Pollastro, 2003). The total petroleum system of Central Arabia Qusaiba- Paleozoic (202101) of the Greater Ghawar Uplift 17

18 Province (2021) and surrounding geologic provinces of central Saudi Arabia is summarized in events chart (Fig. 10). The second Paleozoic TPS is the Qusaiba/Akkas/Abba/Mudawwara Total Petroleum System (202301) of the Widyan Basin Interior Platform Province (2023) has two assessment units. The AUs are the Horst/Graben-Related Oil and Gas Assessment Unit ( ) and (second) assessed undiscovered resources (Fig. 14). Here petroleum systems of Iraq and Jordan are out of studying area (Fox and Ahlbrandt, 2002). The hot shale source rock in the Tabuk Basin area separately assessed as the Jafr-Tabuk Basin Province (2026). Total organic carbon content (TOC) of the source rock exceeds 3 (%wt) and contains mixed oil/gas-prone to oil-prone potential (Alsharhan and Nairn, 2003). Silurian sourced oils from Saudi Arabia are isotopically light. The Silurian hot shale source rocks began generating hydrocarbons possibly during the late Paleozoic in the region of northern Arabia into Iraq, and during the Triassic in the region of the present-day Arabian Gulf (Fox and Ahlbrandt, 2002). Peak generation, migration, and entrapment occurred through the Jurassic and ended in early Cretaceous. The direction of migration in Saudi Arabia is toward the west (Abu-Ali, 2005). In north-central Saudi Arabia, the primary Paleozoic reservoirs are the correlative Unayzah and Ga ara Formations of Early Permian Carboniferous age, which are bounded by two regional unconformities the underlying pre- Unayzah (Hercynian) and the overlying pre-khuff unconformity(fig. 5) (Fox and Ahlbrandt, 2002). Thickness of the Unayzah Formation is variable, ranging from less than 2 m on the west end of the Central Arabian Arch to more than 400 m in the Widyan Basin (Al-Laboun, 1987). The Unayzah Reservoir mostly composed of fluvial and alluvial quartz sandstone, with siltstone, and playa claystone. Reservoir continuity may exist in dipping strata such as the Sarah formation. Paleozoic traps are prominent high-angle reverse faulting, updip pinch-outs and gentle drape folds. The most effective cap is the regional salt and evaporate seal within the Permian Khuff reservoir of Saudi Arabia (Fox and Ahlbrandt, 2002). The summary of Paleozoic Qusaiba/Akkas/Abba/Mudawwara Total Petroleum System (202301) in event chart (Fig. 15). The third Paleozoic TPS is defined by the greater Rub al Khali Basin Province (2019) and is designated the Silurian Qusaiba TPS (201903). The TPS contains two AUs the Khuff Carbonates in Salt Structures AU ( ), and The Paleozoic Reservoirs AU ( ) (Ahlbrandt et al., 2000). The Khuff Paleozoic Reservoirs AU ( ) includes most of the Rub al Khali Basin in Saudi Arabia, Oman, and Yemen where structures are related to extensive regional wrench fault systems and faults related to salt structures (Fig. 16). Source rocks are hot shales of the basal Qusaiba Member with 75 m thickness, which occurs throughout the Rub al Khali Basin. The basal Qusaiba contains TOC values as high as to 20 percent, averaging 4 percent (Schenk, 2000a). The Qusaiba mudstones are in the dry gas window over much of the central part of the basin, but are in the oil and wet gas windows along the basin margins to the west, south, and east (Schenk, 2000a). Hydrocarbons Migration phase is mainly vertical in basement, and moderate to long distance lateral migration is inferred along the basin margins with Unayzah sandstones. The Reservoir rocks are mainly alluvial, fluvial, and eolian sandstones of the Permian Unayzah Formation (Porosity as much as 30 percent, and permeabilities as high as 4 Darcy) and the basal Khuff Formation (Schenk, 2000a). Potential reservoirs may be fluvial and deltaic sandstones of the Cambro-Ordovician section. The traps along basin margins are stratigraphic and structural and structural traps in the center of basin that mainly sealed by the anhydrites of Khuff Formation (Schenk, 2000a). Whereas Khuff Carbonates in Salt Structures AU ( ) comprises of the northeastern Rub al Khali Basin where reservoirs is the Upper Permian shelf carbonate Khuff Formation which is dominant reservoirs in saltrelated structures of the Infracambrian Hormuz Salt Basin (Schenk, 2000b). The Qusaiba mudstones in this AU have passed through the zone of oil generation and are in the zone of dry gas generation throughout much of the area the Migration phase of Qusaiba hydrocarbons was mainly from the east up regional dip into the crustal portion of the Qatar Arch, forming the supergiant North- South Pars fields. Also a Vertical migration occurred along the flanks of the numerous salt structures (Ahlbrandt et al., 2000). Most reservoirs are mainly shelf carbonate grainstones and reef carbonates of the Upper Permian Khuff Formation that sealed (anhydrites within the 18

19 Permian Khuff interval) by mainly structural, and are related to salt domes and other Infracambrian structures of Hormuz Salt Basin(Schenk, 2000b). VI. CONCLUSION The total petroleum system TPS concept allows to evaluate and assess an area within geographic and geologic units based on some standard conditions such as pod of active source rocks and existence within limited mappable geologic space along other geologic elements as reservoir, seal, and overburden rocks that control the fundamental processes of generation, expulsion, migration, entrapment, and preservation of petroleum. The U.S. Geological Survey World Petroleum Assessment 2000 projects divided the world into eight regions and 937 geologic provinces based on characteristics of natural geologic entities and ranked by known volume of petroleum in barrels of oil equivalent. During the Neoproterozoic (Infracambrian) Paleozoic age, the Arabian plate subjected to major tectonic events which contributed forming sedimentary accommodation or /and hiatus. Tow Total Petroleum Systems defined in the Ghaba and Fahud Salt Basin Provinces of north-central Oman. In both Basins, hydrocarbons were generated from deeply buried source-rock units of the Infracambrian Huqf Supergroup. Oils in the Ghaba Salt Basin May be linked to distinct Huqf source-rock units, the general North Oman Huqf type oil source and a more dominant Q -type Huqf oil source. Whereas general North Oman Huqf type oil is dominant in the Fahud Salt Basin. In the Ghaba Salt Basin Province, dominate oil production from Clastic reservoirs of the Gharif and Al Khlata Formations, Haushi Group (middle Carboniferous to Late Permian). In contrast, the most production in the Fahud Salt Basin is from Cretaceous carbonates of the Shu aiba and Natih limestones. However, deep gas is produced mainly from Middle Cambrian to Lower Ordovician clastic reservoirs of the Haima Supergroup. Traps are mainly structural were formed mechanisms during periodic halokinesis of the thick Infracambrian-Cambrian Ara Salt, consequent folding, faulting, basin loading, rifting, and tectonics forming the Oman Mountains. The Paleozoic total petroleum system is regionally sourced in extensive Lower Silurian Qusaiba hot shale and locally divided into The Central Arabia Qusaiba-Paleozoic TPS, the Qusaiba/Akkas/Abba/Mudawwara TPS of the Widyan Basin Interior Platform Province, and the Silurian Qusaiba TPS Greater Rub al Khali Basin Province. Most of the gas was expelled during the Late Cretaceous; whereas expulsion of oil nearly ceased after the Late Cretaceous. In the Central Arabia TPS, hydrocarbon produced from fluvial sandstone of the Lower Permian Unayzah Formation and shallow marine shelf sandstones of the Devonian Jauf and carbonate of Khuff Formation in the north salt AU. However, the reservoirs are fluvial sandstone of the Lower Permian Unayzah Formation and basal of Khuff Formation in greater Rub al Khali Basin Province and the correlative Unayzah and Ga ara Formations of Early Permian Carboniferous age in the Widyan Basin Interior Platform Province. The seal rocks are dominantly regional evaporite with tight carbonate of Khuff Formation. The trap types are mainly structural where growth occurred during the Late Devonian to Carboniferous Hercynian Orogeny and stratigraphic (pinch out as in Unayzah Formation). ACKNOWLEDGMENT We acknowledge the US geological survey World Energy for providing publication of petroleum system online. The authors thank the Editor-in-chief Abdelouahed Lagnaoui, the associate editors Mohamed Saoua and Mohamed Hail Hakimi for their constructive remarks. This is report has been reviewed under the standard code of US geological survey World Energy project. REFERENCES Abu-Ali, M.A., Rudkiewicz, J.L.L., McGillivray, J.G., and Behar, F., 1999, Paleozoic petroleum system of Central Saudi Arabia: GeoArabia, v. 4, p Abu-Ali. M.A., 2005, Organic Petrology, Maturation, Thermal and Burial History Analysis, and Hydrocarbon Generation and Migration Modeling of the Saudi Arabian Paleozoic Petroleum Systems: Approved master thesis. Ahlbrandt, T.S., 2000, Northern Qatar Arch Extension Assessment Unit , U.S. Geological Survey World Energy Assessment Team: U.S. Geological Survey World Petroleum Assessment Ahlbrandt, T.S., Pollastro, R.M., Klett, T.R., Schenk, C.J., Lindquist, S., and Fox, J.E., 2000, Region 2 Assessment Summary Middle East and North Africa, U.S. Geological Survey World Energy Assessment Team, U.S. Geological Survey World Petroleum Assessment 2000 Description and 19

20 results: U.S. Geological Survey Digital Data Series 60. Al-Jallal, A.I., 1995, The Khuff Formation Its reservoir potential in Saudi Arabia and other Gulf countries, in AlHusseini, M.I., ed., Geo-94, Middle East Petroleum Geosciences Conference: Gulf Petrolink, Manama, Bahrain, v. 1, p Al-Laboun, A. A., 1987, Unayzah Formation: A new Permian Carboniferous unit in Saudi Arabia: Am. Assoc.Petrol. Geol. Bull., v. 71, p Alsharhan, A.S., and Nairn, A.E.M., 2003, Sedimentary Basins and Petroleum Geology of the Middle East. Amsterdam, the Netherlands: Elsevier. Amthor, J.E., Smits, W., Nederlof, P. and Lake, S., 1998, Prolific oil production from a source rock The Athel silicilyte source rock play in south Oman: Abstracts, AAPG Annual Convention and Exhibition, Salt Lake City, Utah Cozzi, A., and Al-Siyabi, H. A., 2004, Sedimentology and Play Potential of Late Infracambrian Buah Carbonate of Oman: GeoArabia Vo. 9, No. 4, p Droste, H.H.J., 1997, Stratigraphy of the Lower Paleozoic Haima Supergroup of Oman: GeoArabia, v. 2, p Forbes, G.A., Jansen, H.S.M., and Schreurs J., 2010, Lexicon of Oman Subsurface Stratigraphy: GeoArabia Special Publication 5, Gulf PetroLink. Fox, J. E., and Ahlbrandt, T. S., 2002, Petroleum Geology and Total Petroleum Systems of the Widyan Basin and Interior Platform of Saudi Arabia and Iraq: U.S. Geological Survey Bulletin 2202 E, version 1.0. Frisch, W., Meschede, M., Blakey, R., 2011, Plate Tectonics, Continental D rift and Mountain Building: Springer-Verlag Berlin Heidelberg. Haq, B. U., and Al-Qahtani, A., 2005, Phanerozoic Cycles of Sea-level Change on the Arabian Platform: GeoArabia, Vol. 10, No. 2, p Husseini, M.I., 1991, Tectonic and depositional model of the Silurian-Devonian Arabian and adjoining plates: American Association of Petroleum Geologists Bulletin, v. 75, p Konert, G., A.M. Al-Afifi., and S.A. Al-Hajri., 2001, Paleozoic stratigraphy and hydrocarbon habitat of the Arabian Plate: GeoArabia, v. 6, no. 3, p Laboun, A.A., 2010, Paleozoic Tectono-Stratigraphic Framework of the Arabian Peninsula: Journal of King Saud University (Science). P Laboun, A.A., 2011, Regional Tectonic and Megadepositional Cycles of the Paleozoic of Northwestern and Central Saudi Arabia: Arab Journal Geoscience, DOI /s Laboun, A. A., 2012, Lithostratigraphic succession of Saudi Arabia: Saudi Society for Earth Sciences, King Saud University, Riyadh, Saudi Arabia. Loosveld, R.J.H., Bell, A., and Terken, J.J.M., 1996, the tectonic evolution of Oman: GeoArabia, v. 1, p Magoon, L.B., and Schmoker, J.W., 2000, the total petroleum system the natural fluid network that constrains the assessment unit. Chapter PS in U.S. Geological Survey World Energy Assessment Team, U.S. Geological Survey World Petroleum Assessment 2000 Description and results: U.S. Geological Survey Digital Data Series 60, 31 p. Magoon, L.B., and Dow, W.G., 1994, the petroleum system, in Magoon, L.B., and Dow, W.G., eds., The Petroleum System from source to trap: American Association of Petroleum Geologists Memoir 60, p Pollastro, R. M., 1999, Ghaba Salt Basin Province and Fahud Salt Basin Province, Oman Geological Overview and Total Petroleum Systems: U.S. Geological Survey Bulletin Pollastro, R.M., Karshbaum, A.S., and Viger, R.J., 1998, Map showing geology, oil and gas fields, and geologic provinces of the Arabian Peninsula: U.S. Geological Survey Open File Report B, Version 2. Pollastro, R.M., 2000, North Gulf Salt Basin Structural Gas Assessment Unit , U.S. Geological Survey World Energy Assessment Team: U.S. Geological Survey World Petroleum Assessment Pollastro, R. M., 2003, Total Petroleum Systems of the Paleozoic and Jurassic, Greater Ghawar Uplift and Adjoining Provinces of Central Saudi Arabia and Northern Arabian-Persian Gulf: U.S. Geological Survey Bulletin 2202-H: Version 1.0, Schenk, C.J., 2000, Khuff Carbonates in Salt Structures Assessment Unit , U.S. Geological Survey World Energy Assessment Team: U.S. Geological Survey World Petroleum Assessment Schenk, C.J., 2000, Paleozoic Reservoirs Assessment Unit , U.S. Geological Survey World Energy Assessment Team: U.S. Geological Survey World Petroleum Assessment Schoenherr, J., Littke, R., Urai, J., Kukla, P., and Rawahi, Z., 2007, Polyphase thermal evolution in the Infra-Cambrian Ara Group (South Oman Salt Basin) as deduced by maturity of solid reservoir bitumen: Organic Geochemistry 38, p Visser, W., 1991, Burial and thermal history of Proterozoic source rocks in Oman: Precambrian Research, v. 54, p Wender, L.E., Bryant, J.W., Dickens, M.F., Neville, A.S., and Al-Moqbel, A.M., 1998, Paleozoic (Pre- 20