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 summarize the contents of this Memoir, including some of the proposed revisions of depositional models, correlations and the sequence nomenclature, 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.

Abstract This chapter includes 11 cross-sections and one well log profile to show the depositional geometry and setting in specific areas around the basin: the Saudi Arabia outcrop belt; the Rimthan Arch; and the eastern and central areas of the intrashelf basin in Saudi Arabia, Bahrain, Qatar, Abu Dhabi and Oman. These cross-sections are used to demonstrate the similarity and degree of continuity of the upper Dhruma Formation, the Tuwaiq Mountain Formation, the source rock, the Hanifa, Jubaila–Arab and Arab–Hith formations and depositional sequences in these different locations in the basin. They show the manner in which the underlying platform formed, the rim developed, the source rock was deposited and the basin progressively filled. The blanket deposition of the Arab-D anhydrite was followed by the Arab-C to Arab-A and Hith carbonate and evaporite sequences. The cross-sections provide the framework used in subsequent chapters to make a series of facies maps and other interpretative diagrams and cross-sections that summarize and, for some intervals, revise the interpretation of the settings and geological events that formed the Arabian Intrashelf Basin.

Abstract Qatar plays a key role in the understanding of the Phanerozoic petroleum geological history of the Arabian plate through the continuous influence of the Qatar High on the regional sedimentation patterns and deformation styles. This tectonic unit originated in the Late Pre-Cambrian, when it separated the Hormuz salt, as a high, into an eastern and western basin. Ever since it has functioned as a stable area in between two differently behaving halokinetic regimes and has provided a relative high at various times in the Mesozoic. Notably, in the Jurassic and Cretaceous, it formed a shallow water carbonate platform between intra-shelf basins, which later became the focus for oil and gas migration. Taking into account tectonic control, depositional systems, and climatic variations, the Phanerozoic history of Qatar can be subdivided into six tectono-sedimentary phases: 1) late Pre-Cambrian rifting with the development of the Qatar High surrounded by the Hormuz Salt Basin; 2) Paleozoic clastic-dominated, mostly shallow marine sedimentation, interrupted by a phase of erosion and non-deposition representing the local equivalent of the Hercynian orogeny–Ice age-influenced sedimentation occurred during the Silurian and early Permian; 3) Late Permian–Triassic regional carbonate-evaporite shelf deposition; 4) Jurassic to Middle Cretaceous carbonate platforms and intra-shelf basins, controlled by local subsidence patterns, eustatic sea level fluctuations, and local siliciclastic influx; 5) latest Cretaceous to Middle Miocene Foreland Basin creation and infill by siliciclastics and carbonates; and 6) Middle Miocene to recent mostly non-deposition due to both uplift caused by the Neo-Tethys closure with continued foreland basin development and glacio-eustatic sea level lows. Three known petroleum systems developed within this geological setting: the Paleozoic Khuff–Qusaibah system, the Mesozoic Arab-Hanifa, and the Middle Cretaceous–Hanifa systems. The crest of the Qatar High hosts both the Khuff gas reservoirs of North field, sourced by Silurian Qusaibah shales, and the stacked Middle Cretaceous oil reservoirs of the Al Shaheen field, sourced by the Jurassic Hanifa shales. The Jurassic oil reservoirs of the Dukhan field are located on the northern flank of the high, whereas smaller occurrences are present in Jurassic and Cretaceous strata of salt dome structures in the Rub Al Khali Basin in the east. Oil for these was sourced from the underlying Jurassic organic-rich intra-shelf basinal deposits of the Hanifa and Jubailah Formations, which matured in the oil kitchens adjacent to the Qatar High.

Abstract This volume is intended to generate ideas for the future exploration of immature and mature basins across the Tethyan Region. From the Paleozoic to the Cenozoic, the Arabian Plate, North Africa and parts of Southern Eurasia, were on the margin of a series of Tethys seaways, Proto-Tethys, Paleo-Tethys, and Neo-Tethys. These areas evolved together and as a result they have numerous similarities in their tectono-stratigraphic history and petroleum systems. These similarities could be used to extrapolate proven petroleum systems to underexplored areas and lead to hydrocarbon discoveries. The back cover illustrates the countries that evolved along the Tethyan Region in their present day location. Countries covered in this volume are outlined.