Abstract The Southern Tethys Margin region combines the Arabian, North Africa, and Southern Eurasia plates. For much of geologic history the Phanerozoic sedimentary fill over these plates had a common history with similar tectonic, depositional settings, and a stratigraphy that often can be correlated across many parts of the region. This same sedimentary fill has prolific proven accumulations of hydrocarbons and many more remain to be found. Historically the focus of exploration has been confined to the giants and super-giants of the Middle East and North Africa. These proven petroleum systems contain numerous new plays that can be expected to evolve to new hydrocarbon discoveries. Similarly, regions paralleling the Southern Tethys may contain other large hydrocarbon accumulations matching those of the traditional Middle East regions, but as yet are underexplored in these exploration frontiers. This chapter highlights the stratigraphy and depositional settings of the Southern Tethyan region and its numerous petroleum systems. The intent of this chapter and AAPG Memoir 106 is to spark future exploration in the region.

Abstract The United Arab Emirates is located on the stable Arabian foreland of the Arabian plate and is separated from the unstable Iranian fold belt by the Arabian Gulf. During the Late Paleozoic (Upper Permian) to the Cenozoic (Tertiary) Eras the vast Arabian platform lay along the southern margin of the Tethys Ocean. During this period epeiric shelf carbonates associated with only minor clastics and evaporites were deposited. Sedimentation patterns were controlled by many factors such as epeirogenic vertical movements due to basement tectonism, halokinesis, climatic variations, and, most importantly, sea-level variations. The Late Paleozoic to Cenozoic stratigraphic sequence shows lateral variations in formation thicknesses as well as in the distribution and continuity of lithofacies characteristics. Abundant giant oil and gas reservoirs have been found in Jurassic (Araej and Arab) and Cretaceous (Habshan, Lekhwair, Kharaib, Shuaiba, Mishrif, and Simsima) formations. Gas was discovered in the Upper Permian (Khuff Formation) carbonates in offshore and Upper Jurassic (Arab Formation) carabonates in onshore Abu Dhabi. Most hydrocarbon accumulations are related to structural traps, although combined stratigraphic-structural or stratigraphic traps exist in some areas. In western Abu Dhabi, most of the oil and gas are in Jurassic reservoirs, whereas in the central areas most of the oil is in Lower Cretaceous reservoirs. In the eastern offshore areas (Abu Dhabi and Dubai), oil and gas reservoirs are of Permian and Middle Cretaceous with minor production from Lower Cretaceous intervals. In western Abu Dhabi, structural traps started developing in the Upper Jurassic, getting progressively younger toward the east. The main (peak) tectonic event that shaped most of the structures occurred at the end of the Middle Cretaceous and was related to the obduction of the Oman Ophiolite and the formation of the Oman Mountains. The Tithonian Hith anhydrite and the Albian Nahr Umr shale are the two principal sealing formations of the oil and gas accumulations in the Jurassic and Cretaceous reservoirs. However, secondary seals and barriers also exist throughout the stratigraphic sequence. The Silurian Qusaiba Formation is the main source rock for the Permian gas reservoirs. The Upper Jurassic Diyab/Hanifa Formation and the Middle Cretaceous Shilaif/Khatiyah Formation are the main source rocks for the giant Jurassic and Cretaceous carbonate reservoirs, respectively. Other potential source rocks are also identified within the Lekhwair and Shuaiba (Bab Member) formations.

Abstract This volume is the product of the international conference on “Jurassic/Cretaceous Carbonate Platform-Basin Systems, Middle East Models” that was convened in December 1997 jointly by SEPM (Society for Sedimentary Geology) and the United Arab Emirates University in the oasis city of Al Ain, United Arab Emirates (U.A.E.). The concept of this meeting had its roots in the Carbonate Platform Working Group of the Cretaceous Resources, Events and Rhythms Project (CRER), which first convened in 1988 ( Ginsburg and Beaudoin, 1990 ). In order to pursue the CRER goals, the 1997 conference objectives were: (1) to promote and disseminate research on geological and geophysical studies of carbonate platforms in the Tethyan Realm; (2) to provide access to the superb outcrops of the famous Jurassic-Cretaceous platforms and the classic Holocene coastal sabkha of the Arabian Gulf; (3) to promote the interaction between research and exploration/production geoscientists in the region and worldwide; and (4) to demonstrate the interaction of SEPM, academia, and industry personnel as a global community of geoscientists.

Abstract Plate-tectonic movements made the Cretaceous a time of major change in the area of the modern Oman and Zagros Mountains. Neo-Tethys 1 had been created in the Late Permian by the calving of a microcontinent (Anatolia, Sanandaj–Sirjan/Central Iran) along the NE margin of Arabia. In the Late Triassic, a second spreading axis, Neo-Tethys 2 (more readily recognizable in Iran than in Oman) replaced that of Neo-Tethys 1 by the separation of the Central Iran and Sanandaj–Sirjan–Kawr microcontinents. Neo-Tethys 1 had a passive continental margin during the Triassic and Jurassic as the Afro–Arabian portion of Gondwana moved westward away from the actively spreading oceanic ridge of Neo-Tethys 2. Shallow-marine sediments along the continental margin were the source of carbonate turbidity currents that flowed basinward to the abyssal plain of Neo-Tethys 1 until the early Late Cretaceous, whereas the floor of Neo-Tethys 2 seems to have been starved of coarse sediment in its Oman sector. Early in the Cretaceous, the South American and Afro–Arabian portions of Gondwana began to separate to create the South Atlantic Ocean. South America continued to move to the west, but Afro-Arabia reversed its sense of motion. The ensuing buildup of horizontal compressional stresses led to an eastward-dipping subduction zone within the Oman sector of Neo-Tethys 2, leading to obduction of the Late Permian to mid-Cretaceous Hawasina Series (deposited in Neo-Tethys 1) and the Semail Nappe, which was generated by back-arc spreading. North of the Dibba Line, subduction also took place within Neo-Tethys 1. The latest Cretaceous was a time of tectonic adjustment and shallow-marine carbonate sedimentation across the area of the present Oman Mountains and southern Zagros, but the effects of late Maastrichtian subduction in Neo-Tethys 2 are visible in the Inner Makran. Evidence of subduction beneath the northern half of the Gulf of Oman suggests that this process has been more or less continuous over the Makran area until today. Uplift of the Oman Mountains began in the Mio–Pliocene, about the same time as the Zagros Mountains began to form.

Abstract Wadi Naqab, SE of Ras Al Khaimah in the U.A.E., exposes an 800 m thick, shallow-water, Middle Jurassic succession. The base of the Bajocian is placed at a sequence boundary a t ca. 460 m above the top Triassic and 45 m beneath the horizon that yielded the ammonite Poecilomorphus sp. The Bajocian/Bathonian contact is marked by the highest occurrence of Haurania deserta . The questionable Bathonian/Callovian boundary either coincides with the last occurrence of Alzonella cuvillieri or is near the base of the Trocholina palastiniensis zone. The last occurrence of Kilianina bianchiti indicates the top of the Callovian. A new Bajocian foraminifer, Pseudodictyopsella jurassica , has been identified. In Wadi Naqab, the Middle Jurassic corresponds to a broadly shallowing succession comprising multiple, meter-scale, fifth-order cycles. The Bajocian is predominantly subtidal, and cycles are commonly terminated by thick, massive oncoidal/peloidal packstones or grainstones. Most of the Bathonian and Callovian cycles start with spicular wackestones and end with cross-bedded peloidal/oolithic grainstones and/or stromatoporoid/coral rudstones. A direct comparison is established between the Middle Jurassic of Wadi Naqab and the subsurface of the Emirates. In the subsurface of Abu Dhabi, the Bajocian Izhara and Bathonian–Callovian Araej formations are the rock units that make up the Middle Jurassic. As a result of regional comparisons performed in this study, the Izhara Formation is redefined and a new type section proposed.

Abstract Meter-scale cyclicity is developed on a number of Lower Jurassic peri-Tethyan carbonate platforms, and comparable cyclicity is known from basinal successions in parts of Europe. Analysis of the 234-m-thick Hettangian to Early Pliensbachian section of a recently constructed reference section through inner- to mid-shelf Jurassic carbonates in Wadi Naqab, U.A.E./Oman border, shows that facies patterns alone give an inaccurate and even misleading record of this cyclicity. Omission surfaces, however, can provide far more reliable evidence for sea-level change and enable the “tuning” of cyclicity data derived from facies studies. Clear distinctions need to be made, in the field, between a number of different marine and subaerial omission surfaces, including firmgrounds, hardgrounds, karsts, corrosion surfaces, and paleosols. Some of these surfaces display similar or ambiguous characteristics in the field, and difficulties can be compounded by the re-texruring and remodeling effects of burial diagenesis. High-resolution data, incorporating systematically observed and logged omission surfaces, have potentially high value in correlation and greatly improve the reliability of interpretations. In the Wadi Naqab succession the incorporation of carefully observed cycle-boundary data more than doubles the number of cycles seen. The data show that average duration of the high-frequency cycles was ca. 90,000 years, well within the range of Milankovitch forcing factors but outside the 40,000 years obtained from basinal Milankovitch successions of the same age in Europe. The difference reflects the incompleteness of the shallow-water succession, and it is likely that both types of cyclic successions in the Lower Jurassic share the same climatic and/or eusta tic causes. Fischer-plot analysis of the 149 cycles reveals the additional operation of two strong third-order sea-level fluctuations, and possibly two further smaller ones, between late Hettangian and early Pliensbachian. Subaerial omission surfaces are best developed and most numerous on the falling limbs of these, where cycles are thin. These points would correspond to the falling stage of third-order sea-level change when there was limited creation of new accommodation and maximum subaerial exposure. Omission surface data therefore support the case for both fifth-order and third-order sea-level change in the Jurassic. A particular characteristic of this and other shallow-water Milankovitch successions is their thin-bedded nature. This is likely to impart a strong flow anisotropy in reservoir settings, enhanced by stratiform weathering and diagenetic features, but many of the definitive features are likely to be missed in seismic sections and well logs. Actual omission surfaces can be hard to detect even in core.

Abstract Central Lebanon provides some of the best exposed and most readily accessible Upper Jurassic (Kimmeridgian-Tithonian) sections in the Middle East, and is one of the few places where lateral equivalents of the prolific Arab Formation (Kimmeridgian-Tithonian) reservoirs of Peninsular Arabia can be studied at outcrop. At the Bikfaya outcrop section (35 km ENE of Beirut), the uppermost Jurassic comprises at least two disconformity-bounded third-order depositional sequences. Sequence 1 (“Falaise de Bikfaya”) is 61 m+ thick and comprises a progradational succession (highstand systems tract) of foreshoal micropeloid packstones, shoal-crest stromatoporoid floatstones, back-shoal Permocalculus wackestones, and (?attached mainland-) shoreface facies culminating in tidal-flat deposits. This interval is of Early to Middle Tithonian age. Sequence 2 (“Calcaire de Salima”) is ca. 63 m thick, and commences with an abrupt transgressive surface and an associated influx of calcareous dinocysts. The lower part of this sequence comprises strongly argillaceous micropeloidal packstones and occasional peloid-intraclast packstones, interpreted as an offshore transition zone facies association. The initial marine flooding event is of late Middle Tithonian (upper fallauxi-ponti Zone) age. A candidate maximum flooding surface (MFS) is recognized within the late Middle Tithonian ponti Zone, coincident with calcareous dinocyst species and abundance maximum. (A ponti Zone MFS has also been identified elsewhere in the Middle East.) The recessive middle part of Sequence 2 is largely unexposed, whereas the upper cliff-forming part comprises ca. 22 m of Upper Tithonian ooid-skeletal grainstones that coarsen and thicken up-section. These grainstones are characterized by pronounced planar cross-stratification with set heights of up to 3.6 m, and are interpreted as a wave-dominated shoal complex culminating in emergent foreshore facies. Sequence 2 is terminated by a prominent paleo-karst (Type 1 sequence boundary) corresponding to the Jurassic-Cretaceous boundary, and is overlain by basal Cretaceous wacke-ironstones that form the lower part of the Chouf Sandstone Formation. The lower part of the Chouf Sandstone Formation lacks age-diagnostic fossils. The timing of initial Cretaceous onlap is thus only poorly constrained by the presence of Late Tithonian taxa in the underlying “Calcaire de Salima” and the presence of Barremian spores in the upper part of the Chouf Sandstone Formation.

Abstract Ten depositional shoaling-upward cycles have been identified in the Aptian Shuaiba Formation of the United Arab Emirates (U.A.E.). A similar number of cycles have been recognized in the National Petroleum Reserve of Alaska (NPRA). Similarities of these cycles with the onlapping shelf geometries of the Neogene of the Bahamas suggest that the sequence geometries of Aptian strata of the NPRA and the U.A.E. are a response to high-frequency changes in eustatic sea-level position. Because the Aptian cycles of the NPRA match similarly dated, events in the U.A.E., it is suggested that where biostratigraphic data are poor the sedimentary section can be tentatively dated by relating the geometries of the shelf margin to the character of the coastal onlap curve and its coincident sea-level chart. Thus, a sea-level chart might be used at locations for which biostratigraphic data is sparse to determine and constrain preliminary depositional models for specific time intervals. With this in mind, two biostratigraphic models for dating the Shuaiba Formation and the Bab Member were tested against the sea-level curve of Haq et al. (1987) using a sedimentary simulation. The results were ambiguous because both biostratigraphic models could not be matched. Also in both cases, the simulation suggested that just prior to the deposition of the Bab Member the basin margin was uplifted and then subsided, causing a local relative sea-level fall followed by a rise, an event not found on the sea-level chart of Haq et al. (1987) . Additionally, the sedimentary simulation supports the position that the Aptian in the U.A.E. is bounded by erosional unconformity surfaces and contains higher-frequency cycles.

Abstract The mid-Cretaceous is an informal term that, in the Middle East, includes the Cretaceous stages of Hauterivian through Cenomanian. During this 37 to 45 million years time interval twenty cycles of relative change of coastal onlap were proposed by Haq et al. (1988) , and since that time, some of these cycles have been subdivided further. The average duration of these so-called second-order cycles is 1.8 to 2.2 million years, depending upon which time scale is used. The challenge is to identify accurately depositional cycles in the stratigraphic record of the Middle East platform and to correlate them precisely with a reference section of cycles. The quantitative stratigraphic technique of graphic correlation achieves this goal. Graphic correlation is a numerical correlation technique that is simple to apply and gives precise and reproducible correlations. Graphic correlation is based on an integrated database of fossil tops and bases and other geologic events. The technique creates hypotheses of correlation that make no assumptions about the completeness of each fossil range. A composite standard database from the Aptian through the Turonian has been constructed using 42 geologic sections in the Tethyan Realm. More than 1000 bioevents of ammonites, inoceramids, planktic foraminifers, selected rudists, benthic foraminifers, nannofossils, and dinoflagellates have been integrated with nearly 100 depositional and geochemical events. Among these fossils are many of the zonal indicators. The stage boundaries are defined by key taxa in generally accepted reference sections in France, Tunisia, and Texas. The scale is calibrated to the Harland time scale. Platform exposures of the middle Cretaceous in Oman record six or more global cycle boundaries at the Habshan/Lekhwair contact, at the Shuaiba/Nahr Umr contact, several within the Nahr Umr, possibly at the base and top of the Natih “F” Member, at the top of the “E” Member, and at the contact between the “C” and “B” Members. Other cycles may be recognized as more detailed stratigraphic information is collected. Sediment accumulation rates progressively increased during deposition of the Albian-Cenomariian carbonate platform. Depositional rate of the Nahr Umr was approximately 1.00 cm/1000 years. Depositional rate of the Natih was about 5.00 cm/1000 years. Clearly, many submarine hiatuses developed during deposition of the Nahr Umr.

Abstract The diversity of rudists In the Lower Cretaceous of Arabia offers great potential both for biostratigraphical correlation (particularly of certain key levels, such as the Lower/Upper Aptian boundary) and for facies analysis. With the aim of raising awareness of this potential among geologists working on core and outcrop material, we provide here synoptic diagnoses of the seventeen species (at least) so far recognized, together with comments on their stratigraphical distributions and paleoecology, and a range chart.

Abstract : The depositional environment and the diagenetic history of the Middle Jurassic carbonate (Bir Maghara Formation), north Sinai, Egypt, have been evaluated through comprehensive petrographic and geochemical studies of oncoid grains. Petrographically theoncoids are composed of micrite and vary from subspherical to spherical bodies. The abundance of the oncoids and their close association with ooids, pellets, and shelf fauna indicate that the Middle Jurassic carbonate sequence was deposited in a shal low marine environment within the photic zone. The oncoids are characterized by relatively low Fe and Mn concentrations, normal Sr concentrations, light δ 18 O values (from –3.9 to –5.5%o PDB), and heavy δ 13 C values (from+2.2 to+3.1 %o PDB). Enhanced magnesium concentrations (3.6 mol % MgCO 3 ) in these oncoids, relative to carbonate matrix (0.6 mol% MgCO 3 ), suggest their original Mg–calcite mineralogy. The δ 18 O and δ 13 C values show a narrow range, and the oncoid grains from the same stratigraphic level do not yield any large difference in their isotopic composition. Isotopic comparison of these oncoids (mean δ 18 O = –5.4%o; mean δ 13 C =+2.1 %o PDB) with the sparry calcite cements (mean δ 18 O = –9.8%o; mean δ 13 C =+0.6%o PDB) suggests that meteoric modification was coincident with the development of subaerial exposure and meteoric influx during emergence of the carbonate platform. Such diagenetic modification is probably responsible for 18 O depletion of the oncoids and the carbonate matrix.

Abstract The deposition of the Lower Cretaceous in Saudi Arabia is interpreted within the framework of a model of a simple eastward–dipping carbonate ramp that formed as the result of the extensive flooding of the Arabian Plate during Early Berriasian time. Carbonate deposition was only slightly interrupted by a minor marine regression after the deposition of the Yamama Formation, and it was succeeding by bioclastic limestones of the Buwaib Formation. It was later terminated by a Barremian regression during which clastic deposition dominated most of Central and Eastern Arabia. The Early Cretaceous carbonates of the Sulaiy, Yamama, and Buwaib formations crop out in central Saudi Arabia. According to sedimentological and paleontological data these formations consist of twenty–two successive microfacies correlated with the published standard microfacies types and belts. The Sulaiy, Yamama, and Buwaib formations were deposited in open–platform and lagoonal settings interrupted by two breaks in sedimentation: (1) a pre–Buwaib disconformity, which is marked by an abrupt change from the fine–grained lime mudstones of the upper Yamama to the sandy wackestones containing cyclamminids of the basal Buwaib, and (2) the more pronounced unconformity between the Buwaib bioclastic wackestone and the overlying Biyadh Sandstone.

Abstract The Simsima Formation (lower Upper Maastrichtian) is a shallow–water carbonate that crops out in eastern United Arab Emirates along the northwestern border of the Oman Mountains. Its thickness ranges in this region from 30 to 80 m. From detailed sedimentological and petrographical analysis, various microfabric types and eight sedimentary fades are recognized in the Simsima Formation. These microfacies are arranged according to their frequency and collected into three groups as follows: packstone group (orbitoidal packstone, bioclastic packstone, algal packstone, and plank tonic foraminiferal packstone); boundstone group (milleporid, coral, and algae), and dolostone, which consists mainly of dolomitized limestone. The Simsima Formation in this study can be subdivided into two new members, called here the lower member and the upper member, each with a distinct character and considerable vertical and horizontal distribution.

Abstract Rudist associations were normally destroyed during or shortly after their development. Consequently, exact paleobiological examinations are very difficult or impossible. The in–situ associations of Central Oman are often completely preserved and enable a precise paleobiological and paleoecological description to be made. They developed during a transgression onto the Arabian platform. Microfacies analysis based on extensive field observations reveal that vigorous turbulent conditions prevailed very frequently throughout the period. The development and preservation of in–situ rudist associations are rare. As a rule episodic turbulence prevented the development of such structures. In the same way, turbulence normally destroyed rudist associations. The model of constratal growth ( Perkins 1974 ; Gili et al., 1995a ; Skelton et al., 1995 ) is discussed, including the question whether thick, extensive rudist associations should be named reefs. The absence of vast rudist reefs is believed not to be a consequence of an inherent inability of vertically growing rudists to build such structures, but can be mainly attributed to exogenous, abiotic factors. The associations investigated here inhabited restrictive, shallow–marine environments. Rapid growth of a few rudist species is verified. Vertically growing rudist associations of 5–8 successive in–situ generations represent a period of only two to three hundred years.

Abstract The Middle to Upper Jurassic shallow marine carbonate platform (Amran Group) is predominantly limestone to the west and northwest of Sana’a and limestone and dolomite to the east and northeast of Sana’a. Diagenesis of the Amran Group encompasses many processes with conspicuous effects, including cementation, dissolution, neomorphism, and compaction (both physical and chemical), producing secondary microporosity, micritization, and dolomitization. Dolomite cements are common and were precipitated mostly during later diagenesis in cavities and fractures. Replacive dolomitization occurred during shallow burial (small rhombic types) and during burial diagenesis with the formation of saddle dolomite. Integration of field, petrographic, and geochemical analysis (ICP) indicates that lithification of these carbonates occurred during synsedimentary and burial diagenesis, with much of the alteration controlled by eustatic sealevel change and regional tectonism. Four major subenvironments, in which diagenesis of the Amran Group was operative, can be recognized. (1) Synsedimentary diagenesis is characterized by the formation of isopachous and syntaxiai cements, hardgrounds (with associated borings and burrows, and shelter, fenestral, framework, interparticle, and intraparticle porosity), geopetal structures, and intraclasts, indicating deposition under marine conditions. (2) Shallow burial diagenesis shows other specific features such as leaching, recrystallization, and early dolomitization (both replacive and void–filLing) and mold–filling cements. Moldic and vuggy porosity distribution, early compaction, collapse breccia, and silt deposition indicates that the Amran Group continued to receive meteoric water following sediment stabilization, enlarging some molds and vugs by solution. (3) Deep burial diagenesis is characterized by dissolution, blocky calcite cement, late compaction (fractures and sutured grains), and saddle dolomite. (4) Uplift diagenesis is characterized by reopening of stylolites along fractures and development of dolomitization under meteoric conditions. The occurrence of nonferroari calcite and ferric oxides in rhombohedral zones in dolomite indicates that dedolomitization was driven by oxidation and alteration of ferroan dolomite zones and probably reflects alteration related to recent weathering.