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Chapter 1

Introduction to the Jurassic Arabian Intrashelf Basin

A. O. Wilson Independent Consultant, London, UK 0000-0001-6685-5501 Correspondence: [email protected]

Abstract: The Jurassic Arabian Intrashelf Basin provides the setting for the world’s greatest conventional oil reserves, including the world’s largest oilfield, the supergiant Ghawar field. The stratigraphic interval corresponding to the development and infill of the Arabian Intrashelf Basin is from the uppermost Dhruma Formation to the top of the Hith Anhydrite Formation, spanning the late Bathonian–early Callovian to Tithonian. Many areas of the intrashelf basin have been well described in recent years and the stratigraphic succession has been defined in sequence concepts, but the regional development of the intrashelf basin has not been well synthesized. This Memoir builds on published data to give a regional interpretation of the geological evolution of the Arabian Intrashelf Basin. This introductory chapter reviews some of the earlier work, summarizes the key events and elements in the geological history of the Arabian Intrashelf Basin and gives a brief review of the history of petroleum exploration in this region. It is intended to serve as an extended abstract to introduce the general setting and sum- marize the contents of this Memoir, including some of the proposed revisions of depositional models, correlations and the sequence nomen- clature, providing a context for considering and evaluating each subsequent chapter. The themes summarized in this chapter are documented and discussed in much greater detail in the subsequent chapters of this Memoir.

This Memoir is organized as follows: Chapter 2 (Wilson indicates in green or red the fields with oil or gas sourced 2020a) summarizes the structural history of the basin. Chapter from the Jurassic Arabian Intrashelf Basin (the fields in 3(Wilson 2020b) summarizes the lithostratigraphy, biostrati- Kuwait with some Jurassic-sourced oil in the Gotnia–Mesopo- graphy,87Sr/86Sr dating and sequence stratigraphy. Chapter 4 tamian Basin are not coloured green). Figure 1.4 shows the (Wilson 2020c) illustrates the depositional geometry around locations of the lines of published cross-sections used to inter- and across the basin. Chapters 5 (Wilson 2020d) and 6 (Wil- pret the depositional geometry within the Arabian Intrashelf son 2020e) further discuss, evaluate, integrate and interpret Basin. Figure 1.5 presents the lithostratigraphic nomenclature the data presented in Chapters 2–4(Wilson 2020a, b, c) inter- across the area. The age dating used in this Memoir is shown val by interval. The themes include the influence of changes on the left. The ages and stratigraphy together form a complex in sea-level and the global climate and the effects of subtle issue, which is covered extensively in subsequent chapters. tectonics during each phase of basin formation and on the These five figures are included to orient those new to the intrashelf basin rim. The illustrations include a regional sum- area to the important features and terminology of this region. mary cross-section, cross-sections illustrating the depositional geometry of specific areas and facies maps at different phases of the development and infill of the intrashelf basin. The facies maps presented here are more regionally detailed than earlier General setting of the Arabian Intrashelf Basin published versions. Chapter 7 (Wilson 2020f) is a discussion of the implications for exploration. Chapter 8 (Wilson 2020g) Figure 1.2 summarizes the extent and key elements of the Ara- summarizes this Memoir, including comparisons with the bian Intrashelf Basin as interpreted in this Memoir. It is based global eustatic sea-level curve. Each chapter is written to on the many references cited, discussed and illustrated in this stand alone and the subdivisions are geological and not segre- Memoir. The basin is largely defined by the area of source rock gated by geography. deposition shown in olive brown. It may have extended further Figure 1.1 is a Google Earth image of the Arabian region into the Rub’ al-Khali area. Note that this map shows the general with the country borders and major tectonic features labelled. setting early in the basin’s history. The proportion of shallow The general area of the Arabian Intrashelf Basin is shown, as subtidal facies to basin centre deeper water facies expanded well as the southern portion of the generally coeval, but very and contracted within each subsequent depositional sequence. different, Gotnia–Mesopotamian Basin to the north, which is (Fig. 1.4 indicates some important sources of published data known as the Lurestan Basin in Iran (Murris 1980). The Ara- used in this Memoir to define the features shown in Fig. 1.2). bian Intrashelf Basin may extend southwards into the Rub’ The setting is one of an intrashelf basin surrounded by a shal- al-Khali area. Major present day geographical features include low rim. The western rim includes the Saudi Arabia outcrop, the huge Rub’ al-Khali sand dune region, the Precambrian but the edge of the rim is in the subsurface. A broad shelf rim Arabian Shield, the Zagros fold belt and the thrust sheets adja- in the east and south separated it from the Neotethys Ocean. cent to the Arabian plate boundary in Oman. Paleozoic to Cre- In the north, a much narrower belt of shallow water carbonate, taceous outcrops border the Arabian Shield in Saudi Arabia, the Rimthan Arch, separated the Arabian Intrashelf Basin and variably onlapping one another and dipping to the east. The the Gotnia–Mesopotamian Basin. Both early- and very late- Jurassic outcrop is c. 800 km long in Saudi Arabia. Other stage dolomitization occurred along the Rimthan Arch. The Jurassic outcrops are found in the Zagros folds and the Musan- very late dolomitization is facies-destructive and discordant dam thrust sheets. The Jurassic outcrops in Oman are in Tethys and is associated with subsurface dissolution and breaching shelf to ocean floor facies. Erosional outliers of the intrashelf of the anhydrite seals (Broomhall and Allan 1985), which com- basin rim facies occur in Ras Al-Fujairah, in the eastern United plicates stratigraphic correlation across the arch. The name Arab Emirates (UAE). Jurassic outcrops and rift basins also Rimthan Arch was initially used only along this narrow belt, occur in Yemen, but are not covered in this Memoir. but some researchers (e.g. McGuire et al. 1993; Al-Nazghah Figure 1.2 shows the general setting of the Arabian Intra- 2011) later also applied this name to the intrashelf basin rim shelf Basin. Figure 1.3 gives the names of oilfields and further SE in the Berri and Qatif field areas, which is where

From: Wilson, A. O. 2020. The Middle and Late Jurassic Intrashelf Basin of the Eastern Arabian Peninsula. Geological Society, London, Memoirs, 53,1–19, https://doi.org/10.1144/M53.1 © 2020 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

2 A. O. Wilson

Fig. 1.1. Google Earth image illustrating the Google Earth Image, copyright 2017 Google: Data SIO, NOAA,US Navy, NGA,GEBCO main geographical and geological features of Image Landsat/Copernicus, copyright 2017 Orion-ME the Arabian Intrashelf Basin region. the Rimthan Arch merges with the inner edge of the broad shelf (1995, Abu Dhabi), regionally expanded using the Galloway bordering the Neotethys Ocean. In this Memoir, the term Rim- system of maximum flooding surfaces in Sharland et al. than Arch is used only where it separates the Gotnia Basin from (2001) and later modified in many papers, most recently by the Arabian Intrashelf Basin. The Jurassic intervals in the west Tang et al. (2016). A sequence stratigraphy of the important onlapped older strata, and possibly even the Precambrian Arab-D reservoir has been proposed by Handford et al. shield, but have been eroded. The present day outcrop belt in (2002) and Lindsay et al. (2006). Al-Husseini (1997, 2009) Saudi Arabia is largely in inner ramp facies. Late in the Jurassic and Al-Husseini and Matthews (2005), Al-Husseini et al. a land barrier, a very low angle unconformity, developed in (2006) evaluated the revisions and provided modifications to Oman and the eastern UAE (Rousseau et al. 2006; Grelaud the 2001 concepts, including tying events to orbital forcing et al. 2012) and in Iran, as evidenced by an unconformity cycles, in a proposed Arabian orbital stratigraphy. Enay noted by Gollesstaneh (1965, 1974), Setudehnia (1978) and et al. (1987, 2009) remapped the outcrop belt, revising earlier Motaharian et al. (2014). age dating of Arkell (1952). Hughes (2004a, b) has provided extensive documentation and revision of the micropalaeontol- ogy within Saudi Arabia. De Matos and Hulstrand (1995), de Matos (1994, 1997) and de Matos and Walkden (2000) docu- Previous studies in this region mented micro- and other fossils within Abu Dhabi. Regarding broader issues of relevance that impact this Facies maps for selected intervals were presented by Grabow- study, and using a new geological timescale, McArthur ski and Norton (1995). Hughes-Clarke (1988) and Rousseau et al. (2012) and Gradstein et al. (2012) made significant revi- et al. (2006) synthesized the Jurassic of Oman and Forbes sions to the time spans of the Mid and Upper Jurassic stages, et al. (2010) wrote a lexicon for Oman. Summaries of the petro- which have not been changed to date. Dromart et al. (2003) leum geology of the region include Cantrell et al. (2014, Saudi proposed the late Callovian–early Oxfordian glacial lowstand, Arabia), Chaube and Al-Samahiji (1995, Bahrain), van which occurred during a crucial time in the origin of the intra- Buchem et al. (2014, Qatar), Alsharhan et al. (2014a, Abu shelf basin and the deposition of the main source rock interval. Dhabi), Bordenave (2014, Iran), Droste (2014, Oman) and Donnadieu et al. (2011) proposed a model for the end- Alsharhan et al. (2014b, Kuwait). Broader regional summaries Callovian break in shallow water carbonate production, the include Alsharhan and Kendall (1986), Alsharhan and Magara resulting glacial lowstand and a change in seawater chemistry (1994) and Ziegler (2001). De Keyser and Kendall (2014) facilitating source rock deposition. showed depositional models for the development and infill of Ayres et al. (1982) is a summary of the 1973–77 major joint the Arabian Intrashelf Basin that are similar to those presented Aramco-Chevron evaluation of source rocks in Saudi Arabia, in this Memoir, but differ in some details. which was the first study to identify and map source rocks in Recent studies of the Saudi Arabia outcrops have added that country. In that project, L.W. Slentz of Chevron Research considerable detail to the outcrop section. These include isoto- and this author sampled from TD (total depth) to surface every pic studies by Al-Mojel et al. (2018) and Eltom et al. (2018), wildcat well, every stratigraphic test well (36 wells) and all the Hanifa sequences by Fallatah and Kerans (2018) and the deeper field wells drilled up to that time in Saudi Arabia. Jubaila outcrop by El-Asmar et al. (2015). The samples were screened for total organic carbon, followed The sequence stratigraphy for the region was proposed ini- by further analyses of the potential source rock intervals. The tially by Le Nindre et al. (1990) and de Matos and Hulstrand main source rock associated with the Tuwaiq Mountain and Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 3

5 56 60 2 o o o

Late Jurassic N N E L Exposure, Erosion Tethys imits Hith Anh ydrite Se o al Palaeonorth Ocean 32 Dashtak-1 Oman: Present-day structurally Margin ? Includecomplex sparse mountain outcrops

Gotnia-Mesopotamian Basin edge Jurassic outrops. Tethys shelf & shelf cordant Post-Jurassic Late Jurassic o South Facies-Dis Exposure, Erosion 10

Rimthan Arch ? Arabian Intrashelf Basin Butabul-1

o 28 Southeast ? Palaeotradewinds ? ? Qatar arch Jurassic ? Arabian Intrashelf facies continuity Basin Jurassic across Bro sourced oil, gas ad sync lin Oil, gas from a l tr zoic Intrashelf basin other source Palaeo-Edge o u Extended West g extension ? intervals & basins, h Outcr Palaeo ? oil & gas Source rock? or uncertain of outcrop in deeper traps. ? Hughes et al. 2008 op 200 km

o Arabian Intrashelf Basin 24 General Regional Bajocian to early Tithonian, then southward Setting

44 o 48 o o 20

Fig. 1.2. General setting of the Arabian Intrashelf Basin. Fields sourced from the Arabian Intrashelf Basin Jurassic are coloured green (oil) or red (gas). The main source rock facies (olive brown) defines the extent of the basinal portion. A main premise in this Memoir is that the intrashelf basin is continuous as shown, with a shallow rim. It may have extended further SW in the Rub’ al-Khali (e.g. Hughes et al. 2008), but that area has not been well documented. Palaeolatitudes and the location within the SE palaeotradewind belt are important factors. The northeastern limits of the Late Jurassic Hith Anhydrite seal are shown: it extends south and west to the outcrops, across the Rimthan Arch into the Gotnia–Mesopotamian Basin and into the Rub’ al-Khali. The outcrop in Saudi Arabia was initially a broad synclinal low (Enay et al. 1987) largely filled by end-Callovian deposits. This map is compiled and drawn from information contained in the many sources cited in this Memoir.

Hanifa intervals was first identified by Slentz and Chevron lab- More recent papers and abstracts describing the source rock oratory manager R.W. Jones’ analyses and interpretation. The in the various areas are discussed and used to supplement previous interpretation had been that the oil was sourced by this early work in the relevant chapters. These include Frei lateral migration from within the Jubaila and Arab-D (reser- (1984), Lehner et al. (1984), Wilson (1984), Droste (1990), voir) intervals (Arabian American Oil Company Staff 1959). Cole et al. (1994), Carrigan et al. (1995), Al-Suwaidi et al. The actual analyses had shown only very low (<1%) total (2000), Al-Ibrahim (2014), Al-Ibrahim et al. (2017), Alansari organic carbon in the Jubaila–Arab-D interval, except for et al. (2016) and Lindsay et al. (2015, 2016). Many other ref- thin beds of moderate richness in some wells at the base of erences are cited in this Memoir and the data and interpretations the Jubaila Formation in the intrashelf basin. in all of these are used to document, evaluate and interpret the Slentz continued with the geochemical evaluation and this events that created the Arabian Intrashelf Basin and its vast author regionally correlated and mapped the thickness and hydrocarbon resources. richness of the main source facies using well logs and thin sec- tions of cores and cuttings. R.M. Christensen used Lopatin techniques to model maturation and also evaluated the chro- Wireline logs matographic data. The resulting net source rock by this author and later published in Ayres et al. (1982), first defined the areal Despite the many references available for this area spanning extent of the intrashelf basin in the Eastern Province of Saudi more than 600 × 1000 km, remarkably few wireline logs Arabia, which was Aramco’s main operating area at that have been published for the entire upper Dhruma to top Hith time. In this Memoir, this isopach is combined with source interval. Of those that have been published, many are only rock data for the intrashelf basin to the east to provide a frame- gamma ray logs. Wilson (1985) published an FDC-CNL log work for the regional interpretation of the intrashelf basin. and gamma ray log for the interval in the Qatif field in Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

4 A. O. Wilson

52 56 60

o o o Arabian Intrashelf Basin Jurassic N sourced oil, gas

o Oil, gas from 32 Dashtak-1 other source intervals & basins, or uncertain Exploratory wells

Al - Complex structures, with some Marjan W Ferdowsi Hamoon Bu assmi Alpha Zuluf Hazbah ’amama South Pars Reshalat Burgan Ferousan Balal Tethys shelf and shelf edge Harqus Ras Resalat Ribyan Nasr Karan Qirtas Jurassic outcrops Minagish Jurayd Zakum Kurayn Jarn Japhour Safaniya Jana Abu North Field Wafra Manifa Berri Sa'fah Al-Rayyan Umm Shaif Jauf Sharar Rimthan Jarim Sahil Niyashin Dibdibah Abu Hadriya Khursaniyah Awali Mender Lekhwair Juraybi'at Fadhili Damman Murban Samin Ghasha Asab -Bab Jaladi Qusahwira Suban Watban Bakr Dukhan Waríah Fazran Abqaiq Bu Hasa ? Shah Shaybah EL-Haba Dhib Ghawar Faridah ‘Ain Dar Butabul-1 Oil in some reservoirs Uthamaniyah Kidan N Jafurah Marzouk Ramlah o from Jaham 28 Hawiyah Maghrib Gotnia Basin Khurais Harmaliyah Lughfah Haradh Kidan S Jurassic source rocks Tinat Qirdi Jawb Abu Jifan Niban Mazalij Jurassic Tukhman Sources Al-Husseini 1997 Al-Saad & Sadooni 2001 Al- Silwadi et al. 1996 Beydoun 1987 Gas, oil in Paleozoic Grötsch et al. 2003 reservoirs Outcrop Cantrell et al. 2014 Esrafili-Dizaji & 200 km Rahimpour-Bonab 2019 ? o 24 ? Oil and Gas Fields Dashed lines approximate borders, and Names not all shown Al-Husseini, 1997

44 o 48 o o 20

Fig. 1.3. Names of oil and gas fields in the region. Fields coloured green and red are sourced from the Arabian Intrashelf Basin. Where the Upper Jurassic anhydrite seals thin and become ineffective in eastern Abu Dhabi, some of the oil and gas in Lower Cretaceous reservoirs is interpreted as sourced from the Jurassic (Yin et al. 2018).

Saudi Arabia. Handford et al. (2002) published five well logs The lack of well logs does make a regional interpretation from almost the complete interval in Saudi Arabia. Hohman and summary more difficult, but not impossible. There are et al. (2005) published four Saudi Arabia and seven Qatar many published pieces of data, variably documented, that gamma ray and porosity logs for the Tuwaiq Mountain and can be assembled as pieces of the puzzle posed by the Arabian Hanifa formations. Saner and Abdulghani (1995) published Intrashelf Basin, although important details are often missing. several Arab–Hith gamma ray and porosity well logs from Mattner and Al-Husseini (2006) discuss some of these diffi- the Abqaiq field. Magara et al. (1993) published seven culties in the context of an Aptian geology question. Arab–Hith well logs in a cross-section across NE Saudi Arabia. For Qatar, van Buchem et al. (2014) published, at a very General terminology small scale, three complete and one partial log for the entire Mesozoic. For the Tuwaiq Mountain to lower Jubaila equiva- In older lithic descriptions, the Brankamp and Powers (1958) lent interval in Abu Dhabi, de Matos and Hulstrand (1995) and Powers (1962) terms calcarenite and calcarenitic lime- published eight onshore gamma ray logs. Al-Suwaidi and stone are used, which roughly correspond to the now com- Aziz (2002) published nine offshore gamma ray, density and monly used Dunham (1962) terms of grainstone and porosity logs and Al-Silwadi et al. (1996) published a similar wackestone to packstone, respectively. set of 13 well logs on- and offshore for the Arab–Hith interval. The edge of the intrashelf basin shallow water facies is Other papers with partial well logs include Langdon and Mal- referred to as the intrashelf basin rim or simply as the rim. acek (1987), showing two Tuwaiq Mountain and Hanifa well This is not to be confused with the ramp model term rimmed logs from the Rimthan Arch area. Chaube and Al-Samahiji ramp, which implies a steep margin, possibly with reefs at the (1995) published six Hanifa interval well logs from Bahrain. edge. Deposition in the sequences that formed the Arabian By contrast, good well log coverage for the Jurassic of Intrashelf Basin was largely in ramp settings, but generally Oman is available in Rousseau et al. (2006), with 18 Jurassic with low depositional gradients. There is some variation in porosity and gamma ray well logs. Very good coverage is also the nature of the edge of the shallow water ramp. These vari- available for Kuwait (e.g. Kadar et al. 2015). ations are described in their appropriate context in this Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 5

52 56 60

o o o N

o MostlyOil Iran Gas 32

5.3 de Matos, 1997 3.7 4.64.7 A Hanifa-Tuwaiq Mtn North Field 3.8,3.37.4.12, 5.2 4.8 outcrop 4.3 Q 3.19 Kuwait, oil 4.2 4.10, 4.11 in some 5.2 4.13 reservoirs 4.4 from 3.19, 5.17 Butabul-1 Gotnia Basin 4.5 4.13 o Jurassic 28 source rocks 6.2 6.8

Jurassic 5.2 Figure numbers and references 3.3, 3.7, 4.1, 5.2 3.7, Al-Moraikhi1 ,Al-Moraikhil et al. etal.2014;2014 Kadar et al. 2015 4.13, Hughes-Clarke 1988 et al 3.3, 3.7,8, 1 4.1,0, 20, 5.2, 32 Enay etalet al.,.19871987 Rousseau . 2006 3.8, 3.37,11,19, 4.12, 32 5.2,Al-Suwaidi Al-Suwaidi & Aziz, & 2002Aziz, Al-Silwadi2002 et al. 1996 Arabian Intrashelf Oil 3.19, 5.17, Al-Ibrahim et al. 2017; Al-Saad & Sadooni 2001 12, Al-Ibrahim, 2014, Al-Saad & Sadooni,2001 Basin Jurassic Outcrop 4.2, Langdon and Malacek 1987 sourced fields Gas 21, Langdon &Malacek 1987 31, Hughes=Clarke, 1988 4.3, McGuire et al.1993; Handford et al. 2002 6.2, RousseauMagara et etal.,al. 1993 2006 22,23, McGuire et. al., 1993, Handford etal. 2002 Fields, oil, gas 4.4, Ayres et al. 1982 6.8, Mitchell et al. 1988 from other sources 24, Ayres etal. 1982 38 Hohman etal2005 4.5, Carrigan et al. 1995 5.4, Razin et al. 2014 4.6, 4.8,25 Carrigan Chaube etal.& Al-Samahiji 1994 1995 40, Magara etal. 1992 o Q,41, Qatif Mitchell field, etal. Wilson 1988 1985 24 Data Sources 4.7, 26,van ChaubeBuchem & et Samahiji, al. 2014 1994 et al For Some of Figures 4.8, 27,Frei van1984 Buchem etal., 2014 A. Hohman49A, Razin etal.. 2005 2012 Qatar, Q, Qatif Saudi well, Wilson,Arabia 1985 With Cross Sections 4.10,29,30. 4.11, dede MatosMatos ,1997; 1995, de & Hulstrand,Matos & Hulstrand 1994. 1995 Not marked: Al-Silwadi et al. 1996, Abu Dhabi Arab-Hith 6.4, 6.5.

44 o 48 0 o o 2

Fig. 1.4. Map showing the trends of some of the published cross-sections used to construct the maps and much of the interpretation in this Memoir. The numbers refer to the figure numbers in this Memoir and to the references in the yellow box. Not all of the sources used are shown in this figure; these are credited where they are used in the figures in other chapters.

Memoir. Similarly, the term shelf has been used in some of the other anticlinal structures. The fields in northern Saudi papers with reference to the intrashelf basin rim. In this Mem- Arabia and in Kuwait have oil largely in Mid Cretaceous res- oir, unless otherwise noted, shelf refers to the broad Tethys ervoirs, possibly sourced from Kazhdumi Mid Cretaceous margin shelf. source rocks (Ayres et al. 1982; Lehner et al. 1984). The fields shown near the south ends of the Ghawar and Khurais fields and near and under the Saudi Jurassic outcrop have Silurian fi sourced oil and gas in Paleozoic reservoirs. The oil and gas Field names and elds probably sourced from the in Iran may have been sourced from Jurassic and Cretaceous Arabian Intrashelf Basin facies source rocks. The fields in the western UAE and Oman (the Fahud–Lekhwair area) have oil in Mid Cretaceous reservoirs The fields shown in green or red in Figure 1.2 contain oil or gas derived from Cretaceous source rocks. The smaller fields in that is likely to have been sourced from the Arabian Intrashelf the central Oman Ghaba salt basin have oil in Upper Paleozoic Basin source rock. The oil in Jurassic reservoirs below the and Mesozoic reservoirs. In south Oman, there is Paleozoic oil upper Dhruma reservoir includes Marrat oil in Kuwait (Yousif in glacial sediments, partly(?) sourced from Infracambrian and Nouman 1997), which is not coloured green because most source rocks (Beydoun 1987). This summary is extracted Jurassic reservoirs in Kuwait have oil sourced from the Juras- from Beydoun (1987), Alsharhan and Nairn (1997), Cantrell sic in the Gotnia Basin. The oil in the Faridah and Sharar res- et al. (2014), Bordenave (2014) and other references listed ervoirs in the Dhruma of Saudi Arabia are from pre-Lower on Figure 1.2 Fadhili–Uwainat Dhruma source rocks (Ayres et al. 1982; Tang et al. 2016). The oil in these reservoirs has only been reported for the Faridah and Sharar fields, but there may be Introduction to the stratigraphic nomenclature other locations. Other fields coloured yellow in Figure 1.2 have oil or gas A major goal of this Memoir is to clarify the various strati- from other source rocks, such as deeper Paleozoic oil and graphic relationships within the area of the Arabian Intrashelf gas in western Saudi Arabia. The North field offshore Qatar Basin, which is confined to Saudi Arabia, Bahrain, Qatar, the and Iran has Permian Khuff gas, as do the Ghawar and some UAE and Oman. Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

6 A. O. Wilson

As used in this memoir

Maximum Bahrain Qatar UAE Oman Iran (Fars) Kuwait Ages by Flooding Saudi Outcrop Saudi Subsurface South Iraq Ages from Enay et al.1987 (De Matos & Hulstrand 1995) (Hughes-Clark (Setudehnia 1987) Surfaces 1988, Powers 1968 et al. (Various terms have Lexique Al-Husseini1997 Sharland Rousseau (Lurestan See below Formation Reservoir been used) Onshore Offshore Stratigraphique GTS 2012 2001 2006) same as Iraq) Lower (Yamana Detrital) Oolite Same as Minagish Onshore Karimia- Makhul Berriasian Ratawi Oolite Berriasian (Sulaiy in South) 145 my MFS Sulaiy Sulaiy Sulaiy Sulaiy Fahliyan HabshanSalil Rayda Makhul Tithonian J110 ManifaManifa Rayda Chia Gara Hith Hith Hith Hith Hith Asab, Mender (Portlandian) Rimthan ? See comments below Hith S (J105) imilar t Tithonian Anhydrite

152 my Gotnia s (Portlandian Precise correlations in Kuwait uncertain and S. Iraq to section ) r Gotnia

J100 n Salt

i a

Arab A A Arab A A Arab A A Arab A A Arab A A o

F Salt h

l Rayda? J90 Arab B B B B B B B B B B e

Qatar or Arab I to III, at

m s C C C C C C Arab IV or Fahahil CC CC ruS J80 aoc D D D D D D D D D D Eroded later Kimmeridgian in some areas? (thin)

Jubaila Erod Jubaila Jubaila Jubaila Jubaila Jubaila or Darb Jubaila or J70 Jubaila Jubaila e 157 my Diyab? d Kimmeridgian Lowstand? ? Hanifa (LowerrewoL( Jubaila) aliabuJ ) (Thin) J60 (Ulayyah hayyalU( Mbr) .rbM ) Najmah Hanifa Hanifa Hanifa ? Limestone Hanifa Hanifa Hanifa Hanifa-Diyab-DukhannahkuD-bayiD-afinaH HanifaDiyabayiD b Hanifa Oxfordian (Hawtah Mbr) Hanifa Local Gap Najmah J50 Delta Member Upper Najmah Glacial Lowstand? Lower Hanifa Source Rock In Basin ? Gap ? ? ? 164 my End Callovian Gap? organic-rich Naokelekan Oxfordian ? (laminite) Hadriya Hadriya Hadriya Tuwaiq Tuwaiq Surmeh Upper Araej Upper Araej ? Lower Mountain Tuwaiq Tuwaiq Mountain Callovian U.Fadhili Mountain Mountain Najmah ? Callovian J40 Sargelu HisyannaysiH Mbr Lower .rbM FadhiliUwainat Uwainat or Uwainat Uwainat Mand / 166 my Atash Mbr Mbr.Fadhili Uwainat Mbr ? Sargelu Sharar Bathonian Bathonian J30 Lower Araej Araej Araej ? ? Dhruma Dhruma 168 my Dhruma Dhruma ? Dhibi Mbr Bajocian Dhruma Faridah Dhruma Fm. Dhruma Bajocian Izhara Izhara Izhara 170 my J20 ? ? ? Aalenian ? ? ?? ? ?? ? "Lithiotis" Alan hiatus ? Mus Toarcian Local gaps?, U 174 my Marrat or Marrat or naicraoT variable tarraMtarraMtarraMtarraM tarraM ro halmaH reppU qarfaM Neyriz Marrat M Adaiyah <183 my J10 Hamlah Hamlah ? L Upper Butmah ???? Several Butmah my time gap? Early Jurassic Minjur Rhaetian hiatus Minjur Minjur Minjur Minjur Hamlah or Gulailah Minjur Lower Mafraq Rhaetian or Minjur UAE & Oman. Rayda, Mender Glauconite, Asab interpreted as Kimmeridgian --Tithonian (de Matos & Hulstrand 1995, Kuwait: Marrat=lower Sinemurian to Aalenian. Alsharhan et al. 2014) or younger than Hith-Arab Minjur; Rhaetian to lower Sinemurian. by Razin et al. 2012. Part of Jurassic in Oman and UAE eroded Yousif and Nouman 1997 et al. eastward (Rousseau et al. 2006, de Matos1997, de Matos & Al-Moraikhil 2014 et al. Hulstrand 1995) Kadar 2015 Similar facies in coastal Fars, Iran

Lithostratigraphic Nomenclature, Also Maximum Flooding Surfaces, Sharland et al. 2001 as modified in this memoir.

Fig. 1.5. Lithostratigraphic nomenclature. The left-hand side shows both the early age dating of the section in Saudi Arabia, which was adopted in other country areas, and the more recent dating in Enay et al. (1987) and Al-Husseini (2009) used in this Memoir. In this Memoir, the main interval of the source rock is interpreted to be a lowstand deposit. Modified Sharland et al. (2001) maximum flooding surfaces are also included on the left-hand side. This chart is repeated in Wilson (2020b, Fig. 3.1, Chapter 3, this Memoir). The intervals in Kuwait have been dated using nannofossils, but comparable data are not known to be available for the interval in Saudi Arabia, hence precise age correlations to Kuwait are not shown in this chart. A general consensus of the correlations is shown in Figure 3.7 in Wilson (2020b, Chapter 3, this Memoir).

It is important to understand the different nomenclatures Arabian Intrashelf Basin and adjacent and different interpretations used in the Gulf countries. Gotnia–Mesopotamian Intrashelf Basin Nomenclatures were first established early in the exploration of this region and vary from country to country; in some The Arabian Intrashelf Basin section is located stratigraphi- cases they even vary within a given country. Despite this com- cally between the Jurassic Upper Dhruma Atash–Lower plexity in nomenclature, there is remarkable lithostratigraphic Fadhili–Uwainat interval and the top of the Hith (Anhydrite) continuity, especially around the basin rim, in the underlying Formation. A separate intrashelf basin of similar age in Kuwait Dhruma Atash–Lower Fadhili–Uwainat reservoir facies and in and Iraq is the Gotnia–Mesopotamian Intrashelf Basin, but its the Jubaila and Arab–Hith formations at the top. The strati- lithofacies are very different even where similar stratigraphic graphic interval within the deeper basin itself is more complex. names are used, with deeper water facies followed by thick Another issue has been the initial use of layer cake lithostrati- salt intervals (Kadar et al. 2015). The portion of the Gotnia– graphic terminology, which tends to obscure lateral facies Mesopotamian Basin in Iran is known as the Lurestan changes between the intrashelf basin centre and its rim. Basin. The name Gotnia Basin by itself is used to refer to Figure 1.5 shows the Jurassic stratigraphic nomenclature. the area of the basin in Kuwait, the southern edge of Iraq On the left-hand side are the ages in the older literature as and at the NE edge of Saudi Arabia. The section in Iran in given in Powers (1968) and the dating used in this Memoir. areas close to the Arabian Intrashelf Basin is included in the Sugden et al. (1975), in their Lexique Stratigraphique for Surmeh Group (Setudehnia 1978). Qatar, observed that the conflicting nomenclatures evolved in early exploration as a result of physical isolation and a lack of communication between the petroleum geologists Age dating working for different companies in different countries. More recently, as can be seen for Qatar in van Buchem et al. The age dating used in this Memoir is strongly based on the (2014) and other papers discussed in this Memoir, the Saudi extensive remapping and palaeontology of the Saudi Arabia Arabian formation names have increasingly become inter- Jurassic outcrop by Enay et al. (1987), who modified the ear- mixed with the earlier company and country nomenclatures, lier ages summarized in Powers (1968) and revised the making the basic lithostratigraphy even more confusing, espe- ammonite zones of Arkell (1952). Microfossils in the outcrop cially when comparing older literature with newer papers. and subsurface are strongly controlled by the facies. Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 7

Numerous papers by Hughes on Saudi Arabia since the year unique. Although this applies to the concepts presented in 2000 (e.g. Hughes 2000, 2004a, b, 2008; Hughes et al. this Memoir, some of the proposed explanations as to how 2008) have extended the stratigraphic ranges of many of the these all fit together are new. The main premises put forth in microfossils used for dating the Mid- and Late Jurassic ages this Memoir are as follows. of the section across the region. De Matos (1997) and de Matos and Hulstrand (1995) are the most thorough biostrati- • The Arabian Intrashelf Basin is a unique, complete hydro- graphic studies of Abu Dhabi (as noted by Al-Suwaidi and carbon system. Aziz 2002). However, the microfossils they cite for age deter- • The Arabian Intrashelf Basin formed within Abu Dhabi, mination in parts of the section are among those whose age Qatar, Bahrain, the edge of Oman, and Saudi Arabia as ranges have been extended or otherwise altered by more recent one single basin in the Callovian, within the relatively work. The apparent discordant ages between Abu Dhabi and open marine Tethyan shelf but 200–300 km from its outer Saudi Arabia of the Tuwaiq Mountain and Hanifa intervals edge. It was initiated by a major transgression coupled are therefore not supported by more recent data and require with minor subsidence. The subsidence was associated revision and re-assessment. In other areas, such as in Qatar with Tethys passive margin drift and rifting. (Sugden et al. 1975) and Oman (Hughes-Clarke 1988), the • There are two areas in the single intrashelf basin where the dating of the section was originally based on correlation Mid and Upper Jurassic section is slightly thicker, which with Powers (1968), but has been revised to some degree, as have been termed the Rub’ al-Khali Basin in the east and in Droste (1990). the Arabian Basin in the west (Ayres et al. 1982; Ziegler 87Sr/86Sr dating has also been used and is reviewed and eval- 2001). However, despite many references to the Qatar uated in Chapter 3 (Wilson 2020b), including adjustment, Arch separating the two (e.g. Cole et al. 1994; Ziegler where possible, to the revised geological timescale (McArthur 2001; Lindsay et al. 2006), at most there was only a slight et al. 2012). Unfortunately, most of the published 87Sr/86Sr ridging with subtle thinning between the two areas during data cannot be reliably used for age dating as a result of the this time period and any depositional effect is subtle. Van types of sample and lack of analytical detail. In many cases, Buchem et al. (2014) stated that the Qatar Arch was not the actual 87Sr/86Sr ratios are not given, so they cannot be com- an active structural high and therefore not a major factor pared to revised versions of the global 87Sr/86Sr curve. during the Mid- and Upper Jurassic. De Keyser and Kendall (2014) also showed the Arabian Intrashelf Basin as a single basin. Carbonate intrashelf basins • Within and around the rim of the single intrashelf basin, there are identifiable coeval depositional and tectonic events An important concept essential to understanding the both around the margins and in the basin. Because many of sequences and history of carbonate-dominated intrashelf these events, which formed the Arabian Intrashelf Basin basins is that the rapid aggradation of shallow water facies depositional sequences, have previously been assigned to around the rim and local tectonics can separate the deposition different ages in different areas around the basin, much of within a basin from more regional or global influences. This this Memoir consists of documentation, discussion and revi- may result in a basin becoming cut-off and slightly restricted sions as to how these events are either coeval and/or of dif- during highstands of sea-level, and even more restricted dur- ferent ages than were generally documented in the earlier ing lowstands. Two coeval intrashelf basins in the same region literature on the area. may show drastically different depositional patterns. The late • Biostratigraphic and 87Sr/86Sr dating provide a very gene- Bathonian to Tithonian intervals in the Arabian Intrashelf ral idea of the ages, but in most cases are not precise enough Basin and the Gotnia–Mesopotamian Basin are comprised of for definitive age dating. These general ages are used in con- lithofacies sequences that are very different, as shown by com- junction with the interpretation and correlation of the coeval paring the depositional facies in the stratigraphic section of depositional events to define sequences and the evolution of the Arabian Basin with the Gotnia Basin section shown in the intrashelf basin. The depositional sequences as defined Yousif and Nouman (1997), Al-Moraikhi et al. (2014) and in earlier work are reviewed and correlated with the basin- Kadar et al. (2015). These facies–stratigraphic differences wide events and, in some cases, suggested modifications are discussed in Chapter 3 (Wilson 2020b). An enclosed are presented. basin may also have a less diverse fossil assemblage and a sal- • On the relatively open marine Tethyan shelf, with rising inity and water chemistry significantly different from those of sea-levels and a greenhouse climate, a very productive shal- the global ocean. low water carbonate factory built the Tuwaiq Mountain For- Carbonate intrashelf basins form by a mixture of tectonics mation carbonate rim (Hadriya reservoir), forming the and differential carbonate deposition. The Bajocian– intrashelf basin. An end-Callovian–early Oxfordian low- Bathonian Dhruma Formation below the strata of the Arabian stand ended the shallow water carbonate progradation, leav- Intrashelf Basin is an example of deposition in an intrashelf ing a huge basinal area surrounded by the subaerially basin formed largely by tectonics, with significant develop- exposed Tuwaiq Mountain Formation rim. ment of relief beginning in the Triassic and continuing into • The global end-Callovian into early Oxfordian lowstand the Early Jurassic, illustrated by de Matos (1997,hisfig. brought restricted conditions favouring cyanobacteria– 2.11) and Fig. 2.6 (Wilson 2020a, Chapter 2, this Memoir). microbial carbonate intrabasinal deposition, which resulted The lower Dhruma intervals filled the tectonic relief with in an exceptionally organic-rich, petrographically unique upwards-shallowing sequences, each of which filled the avail- laminated carbonate source rock within the intrashelf able accommodation space without forming a distinct rim basin. By contrast, other published interpretations ascribe around the basin. Once the accommodation space had been the onset of source rock deposition to anoxic conditions filled, the middle to upper Dhruma units blanketed the area. developed with rising sea-levels. A model (Dromart et al. 2003; Donnadieu et al. 2011) for the lowstand having a gla- cial origin is discussed in the context of source rock Main premises and new interpretations deposition. • Late in the Jurassic, the deposition of the Arab–Hith carbon- In the Arabian Intrashelf Basin region, as is so often the case in ate–evaporite sequences was controlled by a balance other regions, few ideas and interpretations are truly new or between eustatic sea-level fluctuations, the development Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

8 A. O. Wilson

of a land barrier on the broad Tethys shelf and a subtle west- Upper Dhruma Formation–Dhruma Atash Sequence: the wards tilt. Previous interpretations have not fully acknowl- foundation for the formation of the intrashelf basin edged the importance of the land barrier. The following sections briefly summarize these main premises Prior to the development of the intrashelf basin, the Upper – – in the context of the depositional sequences. Dhruma Atash Lower Fadhili Uwainat shallow water car- bonates blanketed the area, forming a very broad, low-relief platform (de Matos 1997; Murris 1980; Rousseau et al. 2006; Tang et al. 2012; De Keyser and Kendall 2014). Arabian Intrashelf Basin intervals and sequences Tuwaiq Sequence: development of the intrashelf basin Schematic cross-section showing stratigraphic relationships Sea-level rise and some subsidence began the deposition of the Tuwaiq Mountain Formation depositional sequence (MFS Figure 1.6 is a schematic, roughly to scale, cross-section J40), which begins at the base of the uppermost Dhruma across the basin from the northern offshore waters of Bahrain Hisyan Member. Slightly greater subsidence in what became and Qatar to the outcrop in Saudi Arabia. This summarizes the basin centre created enough relief for aggradation and pro- the general interpretation of the intrashelf basin interval doc- gradation to form the shallow intrashelf basin rim. The subsi- umented and discussed in this Memoir, interpreted from dence was probably due to both earlier sediment loading and many sources, including: Enay et al. (1987, 2009) (Saudi subtle tectonic processes. The tectonic contribution was prob- outcrops); Ayres et al. (1982) (within the basin, east–west, ably associated with westward drift as the Tethys Ocean con- Saudi Arabia); McGuire et al. 1993 (eastern rim); Chaube tinued to develop. In the basin, deeper water facies with and Al-Samahiji (1995) (Bahrain, also this author, unpub- benthic forams and the tiny bivalve Bositra buchi accumu- lished Bahrain offshore reports 1985–86, cited in Chaube lated, as documented in Hughes (2004a, b; Hughes et al. and Al-Samahiji); van Buchem et al. (2014) (Qatar); and 2008). The deeper water facies are occasionally slightly de Matos (1994, 1997); de Matos and Hulstrand (1995); organic-rich. The Tuwaiq Mountain rim facies in the Saudi Al-Silwadi et al. (1996), Al-Suwaidi and Aziz (2002) (Abu outcrop include build-ups rich in stromatoporoids with corals Dhabi). The original cross-sections are shown in Chapter 4 and coralline algae. On the basin rim in the subsurface, the (Wilson 2020c). This schematic cross-section shows a transit shallow water facies comprise the Hadriya reservoir with where the intrashelf basin symmetry is well preserved. Else- grainstone facies (e.g. Powers 1968; Ayres et al. 1982; where, the rim facies of the eastern margin (UAE, Oman) McGuire et al. 1993; de Matos 1997; Tang et al. 2012; Lind- were partly eroded during the Late Jurassic. say et al. 2015). The Upper Fadhili reservoir below the

“Westward” “Eastward” The Sulaiy Depositional Sequence (MFS J110) ends atop the upper Sulaiy Formation reservoir facies. Jurassic-Cretaceous contact is within the Sulaiy interval Sulaiy Formation MFS J110 Manifa reservoir

e

uenc q

th Se Hi Formation

Hith Anhydrite Hith Anhydrite MFS J105

Arab-A reservoir anhydrite Arab-A Sequence (Arab-B anhydrite) Arab-B MFS J100 reservoir e (Arab-C anhydrite) anhydrite MFS J90 Arab-B Sequenc Arab-C reservoir Arab-D reservoir Arab-C Sequence (Arab-D anhydrite) Arab-D anhydrite MFS J80 Kimmeridgian - Tithonian Kimmeridgian -

Arab Formation ? Arab-D reservoir (s) ce ila-Arab-D post-Hanifa tilt Hanifa reservoir Jubaila Formation Juba Sequen mid & Hanifa reservoir MFS J70 Ullaya Late stage Hanifa upper MFS J60 h Mbr. Hanifa anhydrite Fm. MFS J50 H ) Hadriya reservoir Oxfordian Hanifa awtah Mbr. fa s ? e( MFS J50 in basin Hadriya reservoir or ani H enc voir

noitamroF

q niat y equivalent in equ ndar ? ia Gradational bou ta S fordian lowstand nu Callovian - Early Ox Upper Fadhili reser

wu Late oun mid-

oM

T

Callovian Source Rock Lowstand Sequence Tract waiq M oir

(part of ) upper Tu Sequence eserv Hisyan Member MFS J40 Fadhili-Uwainat r Atash-Lower Fadhili-Uwainat Lower rese Dhruma A rvoir tash S equence MFS J30 Shallow water carbonate, Late stage Hanifa early Callovian Sequence boundaries Major carbonate late Bathonian - late Carbonate mud-rich reservoir to peritidal facies wackestone in basin

Dhruma Formation source rock facies Schematic Cross Section Showing General Sedimentary Architecture In Arabian Intrashelf Basin. Anhydrite (Interpreted from cross sections in Chapters 4, 5, 6, this Memoir)

Fig. 1.6. Schematic cross-section for the intrashelf basin drawn from the eastern to western rims, illustrating the basic depositional architecture as interpreted in this Memoir. The Dhruma Atash sequence formed a relatively flat platform, above which the intrashelf basin formed in the Tuwaiq sequence. A lowstand restricted the basin and the main source rock interval was deposited. With the subsequent transgression, the Hanifa sequence facies prograded well into the basin, with progradation extending further from the west than from the east. Hanifa deposition ended with a lowstand, marked by subaqueous anhydrite in the basin. The Jubaila-Arab-D sequence(s) largely filled the intrashelf basin. The Arab-D anhydrite filled remaining depositional lows and then blanketed the region. Westward tilt and subsidence began post-Hanifa and continued into the early Tithonian. The Arab-D anhydrite blanketed the region. The Arab-Cto Arab-A evaporite–carbonate sequences were formed by transgressions, with evaporite deposition followed by shallow water carbonate deposition. The massive anhydrite interval of the Hith Anhydrite Formation covered the intrashelf basin region. The Jurassic–Cretaceous contact is in the transgressive facies above the Hith Anhydrite Formation. Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 9

Hadriya reservoir pinches out into the deeper water basin cen- In this Memoir, this is attributed to dominant wind direction tre carbonate facies (Powers 1968). The Upper Fadhili facies at the time and resulting higher energy levels in the west may represent facies of a highstand systems tract of a higher (Fig. 1.9). A late Hanifa lowstand resulted in the deposition order Tuwaiq Mountain interval sub-sequence formed in an of beds of subaqueous anhydrite in the remnants of the intra- early phase of sea-level rise, or it may simply be distal facies shelf basin centre and a disconformity on the basin rim. The of the Hadriya reservoir. The Hadriya reservoir facies pro- Hanifa sequences shown are similar to the interpretation sum- graded basinwards in the highstand regressive systems tract marized in Al-Husseini (2009), except that MFS J50 is placed phase, but do not extend as far into the basin as the Upper higher in this Memoir, in the interval where the organic rich- Fadhili. ness decreases. Two informal members are defined in the Hanifa Formation in outcrop: the lower Hawtah and the upper Ulayyah (Enay et al. 1987). Sharland et al. (2001) Source rock deposition during a major lowstand sequence also proposed a local MFS J60 within the Hanifa, which has been interpreted as representing the Ulayyah interval (e.g. (Lower Hanifa lowstand systems tract) Simmons et al. 2007). The source rock interval is shown as olive brown in Figure 1.6. Most published interpretations of the source deposition attri- Post-Hanifa westwards tilt and subsidence bute it to a deep-water facies at least partly coeval with the Tuwaiq Mountain basin rim facies and deposited during a sea- At end-deposition of the Hanifa sequence, the Hanifa shallow level highstand, with the deeper intrashelf basin centre becom- water rim facies would have been near sea-level around the ing anoxic. By contrast, the interpretation favoured in this intrashelf basin rim. Concomitant with the Jubaila transgres- Memoir is for the source rock facies to be post-Tuwaiq Moun- sion, westward structural tilt provided accommodation tain and formed when the intrashelf basin was restricted by a space. This subtle structural tilt continued into the early Titho- widely recognized global end-Callovian lowstand, which con- nian. A greater thickness of Jubaila intrashelf basin facies rich tinued into the Oxfordian. During this lowstand, the margins in lime mud was deposited to the west, whereas in the east the were exposed and shallow water carbonate deposition was deposition of shallow water carbonate facies was almost con- repressed. The intrashelf basin was restricted, but enough cir- tinuous. In the west, updip of the present day outcrop in Saudi culation from the Tethys Ocean persisted to prevent major Arabia, shallow water facies may have been more prevalent in evaporite deposition. The richest source rock deposition the Jubaila. across the Arabian Intrashelf Basin began abruptly, always showing a very pronounced and sharp basal contact, as indi- cated in core and well logs. It is event-driven and not a product Jubaila: Arab-D sequence of a gradual change. The source rock is a unique organic-rich carbonate laminite facies with minimal clay, typically charac- Sea-level rise and some subsidence again expanded intrashelf terized by micropeloidal (silt-sized) micrograinstone laminae basin deposition, with the Jubaila facies rich in lime mud grad- interlaminated with very organic-rich laminae. The micrope- fi ing upwards to the shallow water facies of the Arab-D reser- loids are interpreted as calci ed cyanobacterial cells and the voir. In the outcrop, the shallow water facies are divided organic matter as intrabasinal and microbial in origin. Kendall into two members. The top of the Jubaila Formation is taken et al. (2007) also interpreted a cyanobacterial origin for the within the lower portions of the Arab-D reservoir. Prograda- organic matter. The considerable documentation to support tion into the basin was again initially from the margins, but, this lowstand interpretation is presented in subsequent chap- as the basin filled, the directions of progradation became ters and compared with the highstand systems tract interpreta- more complex, forming shoals and variably isolated remnant tion and with global factors. Recovery from the lowstand was areas of slightly deeper water. In the latest stages, the energy characterized by a gradual, but episodic, decrease upwards in levels became low, the deposition of higher energy facies organic richness and a slow return to more normal marine ceased and only shallow lagoonal remnant basins remained. intrashelf basin facies. An upwards-shallowing transition These basins were filled by lime mud and the initial deposition from highstand deposition of source rock would be similar. of the Arab-D anhydrite. Other factors distinguishing the lowstand interpretation Handford et al. (2002), Lindsay et al. (2006) and favoured in this Memoir v. the highstand systems tract inter- Al-Husseini (2009) assigned two third-order sequences to pretation are evaluated in the following chapters. the Jubaila–Arab-D and Tang et al. (2016) described the Jubaila–Arab-D as a composite second-order sequence. This subdivision into two third-order sequences is usually difficult Hanifa sequence(s): return to normal marine deposition in the subsurface, but there is evidence for this subdivision in the western Saudi Arabia outcrops. By the mid-Oxfordian, the rise in sea-level had returned more normal marine conditions to the intrashelf basin rim and cen- tre. In outcrop, the Hanifa shallow water facies include oolitic Late Jurassic Tethys margin land barrier grainstone, with stromatoporoid facies present, but less prom- inent than in the older underlying Tuwaiq Mountain Forma- In the east, a land barrier formed adjacent to the Tethys Ocean tion. Enay et al. (1987) documented that the fossil diversity as a very low angle unconformity. The interpretation of Rous- in the outcrop is much lower in the Hanifa Formation than seau et al. (2006) is that this unconformity first began to in the Tuwaiq Mountain Formation, indicating that slight develop in the Callovian and that it was a major factor in the restriction continued throughout Hanifa deposition. Prograda- formation of the Arabian Intrashelf Basin. However, this is tion of the Hanifa facies into the basin formed the Hanifa res- an isolated interpretation made in the context of its eastern set- ervoir, which extends further basinwards than the Hadriya ting and does not take into consideration its relationship with reservoir of the upper Tuwaiq Mountain. By late Hanifa dep- the rest of the intrashelf basin area. The interpretation in this osition, the deeper water remnant of the basin was much Memoir is that the Tethys margin land barrier began later. smaller in area than in earlier Hanifa times and was shifted This is because the mid-Callovian Tuwaiq Mountain rim eastwards due to faster progradation and infill from the west. developed at the same time and in the same way in all other Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

10 A. O. Wilson areas around the entire rim, far away from where the land bar- structures. Overall, including its limited geographical and rier later formed. The Hanifa Formation is also similar around stratigraphic extent, the Arabian Intrashelf Basin formed a the basin rim. Eastwards in the UAE, Grelaud et al. (2012) and self-contained hydrocarbon system and became the most Razin et al. (2012) showed Dhruma, Tuwaiq Mountain, prolific discrete hydrocarbon system in the world. Hanifa and Jubaila(?) facies truncated at this unconformity, whereas the Kimmeridgian (Arab Formation) and Tithonian at some times onlapped and at other times were exposed and Plate tectonic setting and implications: Mid- to partially eroded. The land barrier extended further northwards around the basin into Iran (Gollesstaneh 1965, 1974; Setudeh- Late Jurassic nia 1978; Motaharian et al. 2014). Cooper et al. (2016) inter- preted the uplift as due to a mild compressive phase in the Late Figure 1.7 shows the general location of the Arabian plate as Jurassic. Torsvik and Cocks (2016) showed that the opening Pangaea separated into Gondwana and Laurasia, with the Ara- of the Atlantic Ocean, beginning late in the Jurassic, may bian Intrashelf Basin on the broad shelf adjacent to the Neote- have generated a subtle compressive force far to the east of thys Ocean (Torsvik and Cocks 2016). The Neotethys Ocean the Atlantic rift. Murris (1980, his fig. 12) also recognized a was well developed by the Mid-Jurassic, with the Arabian land barrier, but interpreted it as confined to the Oxfordian plate occupying a passive margin. Figure 1.7 shows the incip- and early Kimmeridgian. ient opening of the Atlantic Ocean and the separation of India Other interpretations (e.g. Al-Silwadi et al. 1996; Alsharhan from the Arabian plate in the Oxfordian. et al. 2014a, b) have shown the Late Jurassic eastern margin of the intrashelf basin to be open to the Tethys Ocean, but the land barrier interpretation is preferred in this Memoir Palaeolatitude (discussed in Chapters 5 (Wilson 2020d) and 6 (Wilson 2020e)). A palaeolatitude of 10° S is shown in Figure 1.2, which was This Memoir interprets this mild uplift in the east and west- plotted using a palaeolatitude calculator (Fig. 1.8). Palaeolati- wards tilt as possibly Kimmeridgian and Tithonian and as a tudes are important because the various depositional models significant factor in the deposition of the Arab–Hith evapo- proposed in the literature and used or revised in this Memoir rites. The uplift and westwards tilt episodically isolated the require a knowledge of the location within palaeowind and Arabian Intrashelf Basin and also the Gotnia–Mesopotamian storm belts and the associated wind directions, strengths and Basin from the Tethys Ocean, with additional fluctuations wave energy levels and the likelihood of hurricanes impacting superimposed by eustatic sea-level rise and fall. the area. Various sources give different palaeolatitudes and palaeowind directions. Al-Husseini (1997) showed the Berri field in Saudi Arabia to be at c. 10° S. Sharland et al. (2001, fi Arab-C to the Hith carbonate–evaporite sequences their gure 3.26, citing several sources) show the equator crossing the southern tip of the Qatar peninsula during much By the end of Arab-D deposition, the Arab-D anhydrite com- of the AP7 Jurassic megasequence. Handford et al. (2002), pleted the infill of the intrashelf basin, leaving a broad and Lindsay et al. (2006) and Cantrell et al. (2014) show the gene- fi very flat evaporite platform across the intrashelf basin area ral area of the Ghawar eld in the Kimmeridgian at c. 5° S. roughly at sea-level (Wilson 1975). The lower sequence Al-Nazghah (2011) shows that the equator during the Kim- boundaries are at the base of the evaporites. The evaporites meridgian trended slightly SW from the base of the Qatar are interpreted as formed by the influx of seawater, with the peninsula. flooding baffled by the land barrier, resulting in the deposi- Figure 1.8 shows a plot of palaeolatitudes from the Batho- tion of gypsum. As the sea-level rise progressed, the waters nian to Tithonian for a point in the Arabian Intrashelf Basin. became fresh enough to allow shallow water carbonate depo- The palaeolatitudes were determined for the present latitude sition, forming the Arab-C to Arab-A carbonate reservoirs. and longitude of (24.8978° N, 49.7321° E) in the Ghawar fi The Arab-C to Arab-A sequences show thinning of the car- eld, using the palaeolatitude calculator in van Hinsbergen bonate intervals and thickening of the anhydrites westwards et al. (2015, Figure 1.8) and Torsvik et al. (2012). The ages and/or southwards from the eastern intrashelf basin rim are based on the 2012 geological timescale (Gradstein et al. fi (e.g. Magara et al. 1993; Al-Silwadi et al. 1996). To the 2012, unchanged by 2019), including 95% con dence limits. east in Abu Dhabi and northwards into Iran (Setudehnia The reference point is near the northern end of the Ghawar fi 1978), the anhydrites pinched out or were eroded. The pro- eld. The calculator indicates little change in latitude from portion of anhydrite also decreases onto the Rimthan Arch. Bajocian into Tithonian time, followed by a drift to the The Hith Anhydrite Formation formed a thick seal, but south in the Tithonian. The orientation of the palaeolatitudes intra-Hith carbonate beds increase in frequency to the east. was also determined using the calculator by picking two pre- The carbonate intervals are shallow subtidal to lagoonal and sent day positions, which were at 10° S palaeolatitude in the peritidal. The shallow subtidal facies are often seen as thin, Bajocian to early Tithonian and drawing a line through these fi transgressive oolitic beds. points, as shown in Figure 1.2. The 95% con dence interval during this time period is c. ±3–4° (180–240 nautical miles or 333–444 km). Arabian Intrashelf Basin: a unique depositional feature

The overall intrashelf basin sequence contains a prolific source Palaeotradewind direction, wave energies and rock, several reservoir intervals, and remarkably extensive and water circulation effective gypsum–anhydrite seals. Continued Tethyan shelf subsidence and Cretaceous and Tertiary sedimentation buried Figure 1.9 compares the setting of the Arabian Intrashelf the Arabian Intrashelf Basin facies deeply enough to allow Basin with the palaeotradewinds (5–30° SE). (https://ocean maturation of the source rock. The timing of maturation was service.noaa.gov/education/tutorial_currents/04currents2. such that oil migrating from the exceptionally rich source html). The palaeolatitudes would have placed the easterly rock was available to charge the reservoirs during the Late and southern margins of the intrashelf basin on the most Cretaceous–Miocene development of the huge anticlinal sheltered side of the fringing shallow shelf rim. By contrast, Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 11

Proto-Atlantic & Gulf of Mexico 60oN EasternEaster Asia

Laurasia n Asia 30oN

10oN 5oN 0o Tethys Ocean o Ara ICTZ Plat 5 S bi o a 10 S West e n Palaeotradewinds 30oS GondwanaEastEast Oxfordian 60oS Gondwana 160 myr EasternEaster Asia 60oN n Laurasia Asia 30oN

10oN o 5 N GondwanaG Ara o Pla 0 ond bi Tethys Ocean o t ITCZ e a 5 S n 10oS w Palaeotradewinds 30oS ana

60oS Toarcian 180 myr Directions of plate 60oN movement

Palaeotethys Yellow arrows: Palaeotradewinds 30oN Strong, persistent easterly winds between 5o -30oN and S latitudes. 10oN o A P rabia

5 N l Neoteth 0o ate Intertropical Convergence Zone o n ITCZ 5 S ys o o PANGAEA 10 S (ITCZ) between between 10 N and 10o S latitudes Humid, Palaeotradewinds 30oS light winds, generally no hurricanes

Oceanic crust 60oS Hettangian Position of Arabian Plate 201 myr Continental crust Early to Late Jurassic Portions of the continental margins

Fig. 1.7. Jurassic plate tectonic setting of the Arabian Intrashelf Basin (simplified from Torsvik and Cocks 2016). The general setting is on a passive margin of the developing Tethys Ocean after the break-up of Pangea. Tethyan rifting marked by the westwards drift of Gondwana is the main mega-tectonic event affecting the Arabian Intrashelf Basin in its Callovian–Tithonian existence. Its location, exposed to palaeotradewinds and the humid ITCZ, is important (Figs 1.8–1.10).

on the western and northern margins, the trade winds blow- basin were only slightly different from normal seawater during ing across several hundred kilometres of open water within much of this time. A partial analogue is the present day Ara- the intrashelf basin would have exposed those areas to bian Gulf, with slightly increased salinities and a less diverse much higher wave energies. In addition, daily heating of fauna and flora than the Indian Ocean and Red Sea (Barnes exposed areas updip from the present day western outcrops et al. 1981). would have generated sea breezes, further enhancing the The specific location of passages through which water wave energy. The area would have been at relatively would have flowed into the Arabian Intrashelf Basin from humid latitudes until the Tithonian drift to the south, the Tethys Ocean has never been defined. The wind directions which would have placed the area on the edges of the lati- create a general flow across the shelf (as shown in Figure 1.9), tudes of present day deserts. which would provide an influx of water during times of rising The Arabian Intrashelf Basin was a huge body of water sep- sea-level and highstands. Lindsay (2014) stated that there were arated from the open Neotethys Ocean by the broad Tethyan accessways (broad channels) in Arab-D time. Some access shelf. The fossil diversity after the development of the Tuwaiq may have existed across the Rimthan Arch to the Gotnia–Mes- sequence was lower (Enay et al. 1987) throughout the rest of opotamian Basin, but wind-driven currents would have forced its history. However, as can be seen in Enay et al. (1987) and water into the Gotnia–Mesopotamian Basin rather than vice in the various papers by Hughes and others cited in this Mem- versa. The Gotnia–Mesopotamian Basin itself became oir – and except for the source rock interval – there was still a increasingly restricted during much of the Mid- and Late wide range of organisms, suggesting that the waters in the Jurassic, as indicated by the lack of fossil diversity in the Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

12 A. O. Wilson

Present-day Parameters reference point 150 (in million years) Age: Latitude 25.9800457 175 Age bounds: 125 Longitude 48.8064100 Plot Palaeomagnetic ref. frame.Torsvik et al. (2012), default

Palaeolatitude for site (25.9800, 48.8054) on plate Arabia (503) - www.paleolatitude.org (version 2.1) 5.00

0.00

-5.00

-10.00 Bajocian Bathonian Callovian Oxfordian Tithonian Berriasian Kimmeridgian -15.00 Toarcian Aalenian

Palaeolatitude (degrees) Palaeolatitude -20.00 174.1 170.3 168.3 166.1 163.5 157.3 152.1 -25.00 145.5 180.0 170.0 150.0 140.0 125.0 120.0 Fig. 1.8. Van Hinsbergen et al. (2015) Age (million years) have provided an online Computed using apparent polar wander path, 95% confidence interval palaeolatitude calculator using the palaeomagnetic reference frame of Torsvik et al. (2012). This calculator was used to plot the drift during the Toarcian–Tithonian and into the Cretaceous of the reference point located near the north end of the Ghawar field. The position of the Reference point reference point stays close to 8° S from the Bathonian through Kimmeridgian, drifts southwards by . 2–3° in early Tithonian time and continues to drift southwards into the Cretaceous. Error ranges are shown. The general latitude places the area at the northern portions of the SE This map shows the current location, reference point, palaeotradewind belt and at the margin of latitudes where hurricanes & the outline of the tectonic plate are likely. The palaeolatitude of 10° Palaeolatitude calculator: Model 2.1, van Hinsbergen et al. (2015), shown in Figures 1.2 and 1.9 was et al. estimated using this using a framework of Torsvik (2012) palaeolatitude calculator.

Sargelu, Naokelekan–Najmah and the Gotnia–Barsarin evap- which is zero close to the equator. Although the Arabian Intra- orite intervals (Dunnington et al. 1959; Kadar et al. 2015; this shelf Basin was at the margin along which the strongest storms author, in multi-client reports; PGA et al. 1988, 2003). The would have begun to form much further east, the storms would effect of tidal flow is not known. There may have been distinct have drifted to the south by the time they reached the longitude channels across the broad shelf that have not yet been detected of the Arabian Intrashelf Basin. due to the regionally sparse well control, the lack of high- resolution seismic data in the areas where these may have existed, and erosion in the Late Jurassic adjacent to the Tethys Normal latitudes of evaporite deposition Ocean. Lindsay (2014), Lindsay et al. (2006) and other workers Gordon (1975) stated that present day evaporites and those have suggested that very strong hurricanes struck the area deposited as far back as the Permian are restricted between and were important in the depositional architecture because 50° latitude and the 10° boundary of the equatorial zone, the basin is located on the western side of the almost global which extends c. 10° from the equator. The palaeolatitudes fetch of the Tethys Ocean. Unless the area was further south in Figure 1.8 are used in this Memoir. The Arabian Intrashelf than the palaeolatitude calculations indicate, storms may Basin and the Gotnia–Mesopotamian Basin to the north both have been significant, but not extraordinary. Figure 1.10 shows have extensive Late Jurassic evaporites. By most palaeolati- the tracks and intensity of all tropical storms recorded since tude estimates, these evaporites would have been deposited records were first kept (from the National Oceanic and Atmo- with continuity perpendicular to the palaeoequator. Although spheric Administration website: https://www.ncei.noaa.gov/ beyond the scope of this Memoir, by comparison with the pre- news/inventory-tropical-cyclone-tracks). Most tropical storms sent day belts of arid deposition and the statement of Gordon form along 10° latitude and track west, eventually turning and (1975), we either have to accept the distribution of evaporites strengthening away from the equator. They obtain their in the Arabian and Gotnia–Mesopotamian basins as demon- strength from the circulation enhanced by the Coriolis force, strating an exception to the rule of evaporitic conditions Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 13

52 56 60

o o o Jurassic Surmeh High o Late Jurassic Exposure,o Erosion o LIM ITS Tethys HITH AN N o HYD RI 32 TE Palaeonorth Ocean Margin

Gotnia-Mesopotamian Basin

Y G Low energy, shallow

R Wind driven water flow E N Tethys margin shelf AVE E W LO LO WEST DER WE ? MO AT GY ST o E ENE R W South ERG A 10 EN Y WAVE REFRACTION V Wind driven water flow E E Rimthan V Arch E across Tethys shelf into basin A N W E T R

S G Southeast

o E 1000 kmm ofo wavee fetch Y

H Palaeotradewinds

G windwi 20 knots o I

28 H 2-3 m waves +/- Slower sedimentation & Sediment-starved, less progradation low progradation ? WAVE REFRACTION Y G Palaeotradewinds controlled energy ER MODERATE EN levels in the basin, affected storm ? tracks and strengths & drove waterflow across the broad Tethyan Intrashelf basin shelf into the Arabian Intrashelf extension ? Hughes et al. 2008 Basin and onward across the ? Energy levels on Rimthan Arch and shelf into the margins low to Gotnia-Mesopotamian Basin. moderate? 200 km

o 24 Minimal change in latude from Energy levels across Bajocian to early Tithonian, then dris the Arabian Intrashelf Basin south three degrees (Fig. 1.8)

444 o 484 o o 20

Fig. 1.9. Energy levels around the Arabian Intrashelf Basin on a daily basis were determined largely by the direction of the palaeotradewinds. This map shows where the highest energy levels would be and the likely directions of water flow across the broad Neotethys margin shelf. The Arabian Intrashelf Basin was a huge feature, providing a 1000+ km of wave fetch across the basin, which would drive the water flow towards the Gotnia–Mesopotamian Basin to the north. Greater progradation occurred from the higher energy portions, as indicated for the Hanifa Formation in Figure 1.6. Areas on the sheltered sides generally show both less progradation and thinner intervals in the intrashelf basinal areas, especially for the Hanifa basinal facies. paralleling the equator and/or find an alternative explanation. Arabian Intrashelf Basin has, in general, been interpreted as The website of the evaporite specialist John Warren gives a very arid, its palaeogeographical location suggests otherwise. model for isolated intracratonic evaporite basins (www.salt workconsultants.com/ancient-platform.html). Exploration history

This section focuses on the discoveries of Jurassic oil sourced Intertropical Convergence Zone in the Arabian Intrashelf Basin, beginning with Saudi Arabia. This history is important in understanding how the remarkable A latitude of 10° generally marks the entry into the Intertrop- continuity of the Arabian Intrashelf Basin geology has been ical Convergence Zone (ITCZ) (Waliser and Somerville obscured because it was initially defined in different ways in 1994). The ITCZ is the zone near the equator where easterly different countries and oil exploration companies. trade winds from both sides of the equator converge and decrease in strength. It is usually a humid zone with frequent rainfall and its location and other features fluctuate. The north- Saudi Arabia and Bahrain ern half of the Arabian Intrashelf Basin would have been in the ITCZ. Isotopic signatures (δ18O) indicating meteoric dia- This summary of exploration in Saudi Arabia is extracted from genesis were found by Al-Mojel et al. (2018) at the disconfor- Powers et al. (1966), Beydoun (1987), Alsharhan and Nairn mities on top of the Tuwaiq Mountain and Hanifa formations. (1997), the book Discovery (Stegner 2007) and accounts Bray (1997), Bray and Rankey (2002) and Lindsay et al. from geologists this author worked with in Aramco from (2006) found evidence for vadose diagenesis. This author 1973 to 1981. This is a brief history because the subject is has observed that early leaching is not uncommon in carbon- complex and is covered well in, for example, Beydoun ates in the area (e.g. Wilson 1985). Although the setting of the (1987) and Alsharhan and Nairn (1997). Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

14 A. O. Wilson

prize – the Ghawar field – was not discovered until 1948, first in the north end Ain Dar area and then far south at its southern end at Haradh. The structure was so large that only during 1951–53, after the northern Fazran tip and the middle Uthmaniyah, Shedgum and Hawiyah areas were drilled, was it determined that it really was a single structure and the world’s largest oilfield: 250 km long and later shown to be 30 km wide, with 396 m (1300 ft) of oil column (Alsharhan and Nairn 1997; Afifi 2005). Other discoveries were made over the same years and in subsequent years. The first offshore oil was found in 1951 in the supergiant Safaniya field, which has oil primarily in Creta- ceous siliciclastic reservoirs. Its northern extension in Kuwait is known as the Khafji field. The Safaniya–Khafji field is located on the north side of, but adjacent to, the Rimthan Arch and is in the separate Gotnia Basin. In 1944 the name of the company became the Arabian Fig. 1.10. This image is a track of all known tropical storms/hurricanes American Oil Company (Aramco) and in 1948 Standard Oil (also known as typhoons and cyclones) in modern times from the US of New Jersey (Exxon) and Socony Vacuum (Mobil) bought National Oceanic and Atmospheric Administration website: https://www. / / shares in Aramco. The Saudi Arabia government acquired a ncei.noaa.gov news inventory-tropical-cyclone-tracks. The greatest 25% share in 1973, increasing to 100% ownership in 1980 number of hurricanes form near 10° north or south of the equator, drift when the company became Saudi Aramco. The chronology westwards and gradually turn away from the equator. With clockwise of further discoveries before 1987 is included in Powers rotation south of the equator the strongest winds are on the south sides of those storms, where the winds blow in the direction of the westward drift. et al. (1966) and in Beydoun (1987). The Coriolis force is a major factor, generating the rotation and the general Chronology is only part of the story because the discovery movement from westwards to southerly. The Coriolis force changes from and development of the Saudi oil reserves is one of the most zero to a very low level between the equator and latitudes 10° north or compelling stories in petroleum exploration. In the early south of the equator, hence the storms form as shown. As the Coriolis force days, the teams sent to Saudi Arabia had to build their initial is unlikely to have been much different in the Jurassic, a similar setting in base in Dhahran. Those doing fieldwork had to be adventurers all likelihood existed in the Arabian Intrashelf Basin area, most of which who were willing to learn to survive and navigate in the desert, would have been on the periphery of the hurricane belt. learning to drive in the sand by adapting wide aircraft tyres with a circular tread to stay on top of the soft sand. They learned from, and their lives depended on, their Saudi Bedouin guides. Travel across the deserts was slow-going and parties Oil in the Arabian Peninsula area was first discovered in had to be self-sufficient and spend long times out in the Bahrain’s Awali field in 1932 after a concession had been field. Fieldwork was either curtailed or totally stopped in the granted in 1929 to Standard Oil of California (Chevron). hotter summer months. The entire region had to be surveyed The Awali field is in a large surface structure with topographic and often the weather conditions made establishing precise relief, forming an elongate and prominent jebel (hill). The locations difficult. Structure drilling to Tertiary horizons was reservoirs discovered were in the Cretaceous zones (Beydoun extensively used until 1961 to identify and further define pros- 1987), although the oils were later found to have migrated pects (Powers et al. 1966). A picture of the geology gradually upwards from the Jurassic along fractures. evolved. Work continued during the Second World War, On clear days, the prominent Dammam dome jebel on the although fears of invasion hung over the operation. The only Saudi Arabian coast could be seen from Bahrain, prompting actual war incident was a bombing raid targeting Bahrain by speculation of a structural trap similar to the Bahrain Awali four Italian planes from Ethiopia in an ambitious long-range field. Chevron pursued a limited concession in Saudi Arabia, attack. One plane separated from the others and bombed which was granted in 1933 for 66 years. A team was sent in Dhahran, but none of the bombs did any significant damage, and the first well in Saudi Arabia was drilled in 1935 on the as described in the Aramco World magazine (http://archive. Dammam dome. Texas Oil (Texaco) joined with Chevron in aramcoworld.com/issue/197604/air.raid.a.sequel.htm). 1937. Tests in the Cretaceous zones (which were productive So much oil had been discovered by the late 1950s that the in Bahrain) were disappointing, a result which continued as four owner companies, according to anecdotes among Aramco several more wells were drilled. At the same time, reconnais- geologists, had become concerned about the cost of develop- sance exploration teams were criss-crossing eastern Saudi ing new discoveries when the known reserves would last far Arabia. To the west, in the Jurassic outcrops, they found beyond the end of their 1999 concession agreements. As a Dahl Hith, a cavern at the contact of the Hith Anhydrite result, a programme of drilling off-structure stratigraphic test with the overlying Cretaceous Sulaiy Formation, and recog- wells was begun, ultimately resulting in 36 deep wells that nized that the anhydrite seal over shallow water carbonates provided valuable geological control. Some areas were relin- showed a potential Jurassic play. The Dammam dome drilling quished, so that by the 1970s Aramco was operating in one was just about to be abandoned when it was decided to deepen large area in the Eastern Province and another large area in the seventh well. It was drilled through the newly discovered Rub’ al-Khali adjacent to Abu Dhabi and Oman, where the Hith Anhydrite and found a gas cap and oil in the Arab Forma- Kidan Jurassic gas fields and the Shaybah Aptian Shu’aiba tion. Shortly thereafter, the Dammam-7 well was producing oil had been discovered. Other smaller areas with structures several thousand barrels of oil a day. had also been retained. After the Damman discovery, field parties mapped the As a result of the increased demand for oil and shortages in region further. Structure drilling was used to delineate some North America, a massive effort began to increase exploration, apparent surface anticlines and seismic work began. In 1939, field development and the Saudi Arabian infrastructure, with the concession was extended to cover the entire area of sedi- Aramco heavily involved in all of this. The turnaround was mentary rocks in Saudi Arabia. The Abu Hadriya field was underway when this author arrived in Dhahran in 1973, a discovered in 1939 and the Abqaiq field in 1940. The big week before the October 1973 Arab–Israeli war, the resulting Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

Introduction to the Jurassic Arabian Intrashelf Basin 15 oil embargo and the huge jump in the price of oil. At that time, from the lower Hanifa source rock. Zakum and other fields only one production geologist was assigned to the entire Gha- have oil in early Cretaceous Thamama reservoirs, which, war field, whose primary task was to document new data from above where the Jurassic anhydrite seals thin and pinch out the Arab-D cores in the field and maintain other aspects of the to become ineffective, may be sourced from the Jurassic. Cre- geological database. Soon after, the four parent companies taceous oil is also interpreted as sourced from the Bab and Shi- became deeply involved in work on the fields and Aramco’s laif Cretaceous source basins. Yin et al. (2018) provide a exploration staff was increased. The expansion continued recent summary of the UAE petroleum systems. throughout the 1970s and accelerated after the Saudi govern- ment acquired 100% ownership. Saudi Aramco was again given exploration rights to the entire country. A large, modern Oman and well-equipped research laboratory was established and the geological and geophysical staff increased. The end result was Oman probably does not have Jurassic oil, but exploration in that many more aspects of the geology were extensively doc- Oman has given additional data for understanding the intra- umented from the 1970s onwards. shelf basin, as in Rousseau et al. 2006. Initial exploration, Over this same period, universities in Saudi Arabia (and the which began in 1937, was by the IPC operating as Petroleum other Arabian Gulf countries) began to offer geology degrees. Development of Oman. Except for Shell, the IPC partners left Gulf area citizens were also sent to study in other countries. Oman in the 1950s after drilling several dry holes. Discoveries Today, most of the geologists conducting research and explo- were ultimately made in three main areas: the Fahud salt basin ration there are from the Gulf countries. More recently, Saudi in the central northern area (closer to the Abu Dhabi and Saudi Aramco has begun to evaluate non-conventional plays, includ- Arabia boundaries, with oil in Cretaceous reservoirs); the cen- ing those in the main Jurassic source rock (Lindsay et al. tral Oman Ghaba salt basin (oil in Upper Paleozoic and Meso- 2016), and possible stratigraphic traps (Tang et al. 2016; Alha- zoic reservoirs); and in parts of the south Oman salt basin (with waj et al. 2016). oil in Paleozoic reservoirs) (Beydoun 1987). Other companies have obtained areas in licensing rounds, including Elf, Japex and Occidental Petroleum, with some discoveries. Qatar

This Qatar summary was extracted from Beydoun (1987), Exploration history and our understanding of the Alsharhan and Nairn (1997) and Sugden et al. (1975). The Anglo–Persian oil company was given a concession in Qatar regional geology in 1935 and later became the Petroleum Development Com- pany of Qatar (PDQ). Oil was discovered in the Dukhan The varied exploration history in this region, contributed to by field in 1939. Years later, Shell made the offshore discovery so many different companies, which, among themselves, were of the Idd Al-Shargi field in 1960 and three other discoveries potential competitors for concessions and market share, is a not long after, including the supergiant North Dome Permian major reason why the stratigraphic terminology is so complex gas field. In 1953, PDQ became the Qatar Petroleum Company and regional synthesis has been so slow to develop. Since (QPC). The government company, the Qatar General Petro- 1994, many publications in GeoArabia and conferences leum Company, obtained 60% ownership of the QPC and originated by Gulf Petrolink have considerably improved geo- Shell areas. Later, in the 1980s, Wintershall and Sohio logical communication between the various countries and obtained areas to explore. Oil in the offshore region is largely companies. in the Arab-D reservoir and the onshore oil is in the Dukhan An interesting and sometimes frustrating quirk in the docu- fi mentation of the petroleum geology of the area is due to early eld. There is also a small area with Arab Formation oil in fl the North Dome field. British and American in uences: well depths, well logs and thicknesses are in feet, whereas surface measurements are met- ric. However, in some publications, metric measurements are UAE used or intermixed for the subsurface and we need to be care- ful when reading the literature to identify which measurement This UAE summary was extracted from Beydoun (1987), system is used. Scale errors are also not uncommon in pub- Alsharhan and Nairn (1997) and Yin et al. (2018). Regionally lished illustrations. in the UAE, the Trucial Coast Petroleum Development Com- pany (owned by the Iraq Petroleum Company (IPC) consor- tium) acquired a concession in 1936. The first discovery Table 1.1. 2018 estimates of remaining recoverable oil reserves in the onshore Abu Dhabi, the Bab-Murban structure, was made in Middle East region. Bold=All or most Arabian Intrashelf Basin sourced. 1954. The company became the Abu Dhabi Petroleum Com- pany and offshore exploration was conducted by the Abu Country Barrels of oil Dhabi Marine Areas company. The IPC relinquished the Tru- cial Coast areas and other companies moved in. Some discov- Bahrain 108 000 000 eries have been made in all of the emirates except Fujairah, Iran 155 600 000 000 which is on the Gulf of Oman–Arabian Sea. Iraq 147 233 000 000 Fields with Jurassic oil include Abu Al-Bukhush, Al-Bateel, Kuwait 101 500 000 000 Al-Bunduq, Arzanah, Belbazem, Bu Jufair, Bu Tini (gas and Oman 5373 000 000 condensate), Dlama, Ghasha, Hail (gas and condensate), Qatar 25 244 000 000 Mubarraz (gas), Nasr, Satah, Umm al Anbar, Umm Al-Salsal Saudi Arabia (2016, 2018) 266 260 000 000 ’ fi Syria 2 500 000 000 and Yasir. Sharjah s Sajaa eld has Late Jurassic gas and con- United Arab Emirates 97 800 000 000 densate, which is sealed by the Cretaceous Nahr Umr shales. Yemen 3 000 000 000 Most of these have hydrocarbons in the Arab zones, with some also having hydrocarbons in the Uwainat and Lower *Sources: Oil and Gas Journal (2018) and Saudi Aramco Facts and Figures, 2016 – Araej reservoirs. In general, hydrocarbons where the Arab– booklet handed out at the American Association of Petroleum Geologists ICE Hith anhydrite seals are effective are interpreted as sourced (October 2017, London, UK). Downloaded from http://mem.lyellcollection.org/ by guest on September 28, 2021

16 A. O. Wilson

Reserves platform carbonates from Saudi Arabia: implications for diagen- esis, correlations and global palaeoenvironmental changes. The latest estimates of remaining recoverable Middle East oil Palaeogeography, Palaeoclimatology, Palaeoecology, 511, reserves are published every December in the Oil and Gas 388–402, https://doi.org/10.1016/j.palaeo.2018.09.005 Journal. The countries in which a very large proportion of Al-Moraikhi, R., Verma, N., Mishral, P., Houben, A.J.P., van Hoof, their oil is sourced from the Jurassic Arabian Intrashelf T. and Verreusse, R. 2014. An updated chronostratigraphic Basin (as defined in Figs 1.2 and 1.3) are shown in bold in framework for the Jurassic of the Arabian platform: Towards a Table 1.1. regional stratigraphic standard. Extended abstract presented at The proportion of Jurassic-sourced oil in the UAE is not GEO-2014, the 11th Middle East Geosciences Conference and Exhibition, 10–12 March 2014 [Search and Discovery Article known because some of the oil in this country is from Cre- No. 30333]. taceous source rocks (Yin et al. 2018). Saudi Arabia has oil Al-Nazghah, M.H. 2011. The sedimentology and stratigraphy of the from sources in the Gotnia Basin in the north and from Cre- Arab-D reservoir, Qatif field. MSc thesis, University of Texas at taceous source rocks in the NE (Ayres et al. 1982; Lehner Austin. et al. 1984), but the largest proportion of the Saudi Arabia Al-Saad, H. and Sadooni, F.N. 2001. A new depositional model for oil is from the Jurassic Arabian Intrashelf Basin. Oil the Upper Jurassic Arab ‘D’ reservoir in Qatar. Journal of Petro- reserves in Bahrain are largely or entirely sourced from leum Geology, 24, 243–264, https://doi.org/10.1111/j. the lower Hanifa source rocks, but are largely in Cretaceous 1747-5457.2001.tb00674.x reservoirs as a result of leakage through the Jurassic anhy- Alsharhan, A.S. and Kendall, C.G.St.C. 1986. Precambrian to Juras- drite seals along faults. Gas reserves are not included in sic rocks of Arabian Gulf and adjacent areas: their facies, depo- Table 1.1 because much of the gas in countries with Ara- sitional setting, and hydrocarbon habitat. American Association bian Intrashelf Basin source rocks is found in Paleozoic of Petroleum Geologists Bulletin, 70, 977–1002, https://doi. reservoirs. org/10.1306/94886650-1704-11D7-8645000102C1865D Alsharhan, A.S. and Magara, K. 1994. The Jurassic of the Arabian Gulf Basin: facies, depositional setting and hydrocarbon habitat. Cana- – Funding This research received no specific grant from any funding dian Society of Petroleum Geologists, Memoirs, 17, 397 412. agency in the public, commercial, or not-for-profit sectors. Alsharhan, A.S. and Nairn, A.E.M. 1997. Sedimentary Basins and Petroleum Geology of the Middle East. Elsevier. Alsharhan, A.S., Strohmenger, C.J. and Al-Mansoori, A. 2014a. Mesozoic petroleum systems of Abu Dhabi. American Associa- References tion of Petroleum Geologists, Memoirs, 106, 679–711. Alsharhan, A.S., Strohmenger, C.J., Abdulla, F.H. and Al-Sahlan, G. Afifi, A.M. 2005. Ghawar, the Anatomy of the World’s Largest Oil 2014b. Mesozoic stratigraphic evolution and hydrocarbon habi- Field. American Association of Petroleum Geologists [Search tats of Kuwait. American Association of Petroleum Geologists, and Discovery Article No. 20026]. Memoirs, 106, 541–611. Alansari, Y., Fateh, A., Shehab, A., Almoulani, G., Ghosh, A., Al-Silwadi, M., Kirkham, A., Simmons, M.D. and Twombley, B.N. Ahmed, A. and Thampi, S. 2016. Hanifa-Tuwaiq mountain 1996. New insights into regional correlation and sedimentology, zone: the edge between conventional and unconventional sys- Arab Formation (Upper Jurassic), offshore Abu Dhabi. GeoAra- tems? Extended abstract presented at Geo 2016, the 12th Middle bia, 1,6–27. East Conference and Exhibition, Bahrain. Al-Suwaidi, A.S. and Aziz, S.K. 2002. Sequence stratigraphy of Alhawaj, H., Al-Sinan, A., Al-Fuhaid, T.L., Al-Hamad, J. and Man- Oxfordian and Kimmeridgian shelf carbonate reservoirs, off- sour, M.N. 2016. Callovian-aged debris flow stratigraphic play shore Abu Dhabi. GeoArabia, 7,31–43. in northeastern Saudi Arabia. Abstract, Geo 2016 12th Middle Al-Suwaidi, A.S., Taher, A.K., Alsharhan, A.S. and Salah, M.G. East Conference and Exhibition, Bahrain. 2000. Stratigraphy and geochemistry of Upper Jurassic Diyab Al-Husseini, M.I. 1997. Jurassic sequence stratigraphy of the western Formation, Abu Dhabi, U.A.E. In: Alsharhan, A.S. (ed.) Middle and southern Arabian Gulf. GeoArabia, 2, 361–382. East Models of Jurassic/Cretaceous Carbonate Systems. Soci- Al-Husseini, M.I. 2009. Update to Late Triassic-Jurassic stratigraphy ety of Economic Paleontologists and Mineralogists Special Pub- of Saudi Arabia for the Middle East geologic time scale. GeoAr- lications, 69, 249–273. abia, 14, 145–186. Arabian American Oil Company Staff, 1959. Ghawar oil field. Al-Husseini, M.I. and Matthews, R.K. 2005. Arabian orbital stratig- American Association of Petroleum Geologists Bulletin, 43, raphy: periodic second-order sequence boundaries. GeoArabia, 434–454. 10, 165–184. Arkell, W.J. 1952. Jurassic ammonites from Jebel Tuwaiq central Al-Husseini, M.I., Matthews, R.K. and Mattner, J. 2006. Strati- Arabia with stratigraphical introduction by R.A. Bramkamp graphic note: orbital-forcing calibration of the Late Jurassic and M. Steineke. 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Introduction to the Jurassic Arabian Intrashelf Basin 17

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18 A. O. Wilson

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