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A Novel Plate Tectonic Scenario for the Genesis and Sealing of Some Major Mesozoic Oil Fields It’s Time—Renew Your GSA Membership and Save 15% DECEMBER | VOL. 26, 2016 12 NO. A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA® IRAQ A Novel Plate Tectonic Scenario for the Genesis KUWAIT and Sealing of Some Major PERSIAN GULF Mesozoic Oil Fields IRAN BAHRAIN Ghawar Field QATAR SAUDI ARABIA OMAN U.A.E. DECEMBER 2016 | VOLUME 26, NUMBER 12 GSA TODAY (ISSN 1052-5173 USPS 0456-530) prints news Featured Articles and information for more than 26,000 GSA member readers and subscribing libraries, with 11 monthly issues (March/ April is a combined issue). GSA TODAY is published by The Geological Society of America® Inc. (GSA) with offices at SCIENCE 3300 Penrose Place, Boulder, Colorado, USA, and a mail- ing address of P.O. Box 9140, Boulder, CO 80301-9140, USA. 4 A Novel Plate Tectonic Scenario for the Genesis GSA provides this and other forums for the presentation and Sealing of Some Major Mesozoic Oil Fields of diverse opinions and positions by scientists worldwide, Giovanni Muttoni and Dennis V. Kent regardless of race, citizenship, gender, sexual orientation, religion, or political viewpoint. Opinions presented in this Cover: NASA satellite photo of the Persian Gulf area publication do not reflect official positions of the Society. with the Ghawar Oil Field in the lower left of the picture. © 2016 The Geological Society of America Inc. All rights See related article, p. 4–10. reserved. Copyright not claimed on content prepared wholly by U.S. government employees within the scope of their employment. 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Kent, Earth and Persian Gulf (Al-Awwad and Collins, 2013). However, carbonate Planetary Sciences, Rutgers University, Piscataway, New Jersey sands for a reservoir and especially an anhydritic seal are more 08854, USA, and Lamont-Doherty Earth Observatory of Columbia likely formed at tropical latitudes (~5–30°) where evaporation University, Palisades, New York 10964, USA exceeds precipitation even under highly variable atmospheric pCO2 levels (Manabe and Bryan, 1985). So it seems that to form a ABSTRACT winning temporal sequence of source-reservoir-seal rock units, Recent research reveals evidence of a major event of global plate Arabia (= Persian Gulf region) needs to cross the ITCZ (deposi- motion during the Jurassic, with a magnitude and tempo hitherto tion of Callovian-Oxfordian source rocks) and into the tropical not fully appreciated. Yet, its legacy persists today as the potent arid belt (deposition of Kimmeridgian reservoir and especially Jurassic source-reservoir-seal oil systems in the Persian Gulf region. Tithonian seal) in less than 15 m.y. within the Late Jurassic. We suggest that these formed as a consequence of a sweeping Recent research shows the existence of a major event of global tectonic movement whereby Arabia drifted rapidly from the oil- plate (or even whole-mantle) motion during the Jurassic that was forming Intertropical Convergence Zone along the equator to the hitherto unknown to the earth science community and can be arid tropics of the southern hemisphere with rapid deposition of referred to as the Jurassic polar shift (Kent and Irving, 2010; relatively uncemented carbonate reservoirs and anhydrite seals, all Muttoni et al., 2013; Kent et al., 2015). When the Jurassic polar during as little as 15 m.y. in the Late Jurassic. The Ghawar super- shift is taken into account to describe global paleogeography, the giant oil field of Saudi Arabia was one of the results. Rapid latitu- rapid trans-zonal plate motion that produced the source-reser- dinal change may have influenced the development of some voir-seal sequence at Ghawar and elsewhere in the world can be source-reservoir-seal oil systems elsewhere as well. adequately explained. INTRODUCTION JURASSIC POLAR SHIFT Ghawar is the world’s largest oil field, a supergiant that accounts The recent discovery of the Jurassic polar shift was made from for ~60% of Saudi Arabia’s crude production (Al-Anazi, 2007). paleomagnetic studies that provide a means to track the motion The source rocks at Ghawar are marine muds and carbonates of the of tectonic plates relative to Earth’s spin axis. Under favorable Tuwaiq Mountain and Hanifa formations (Alsharhan and Nairn, conditions, the remanent magnetization of rocks records ancient 1997) deposited in the Callovian-Oxfordian stages of the Late geomagnetic field directions, which when averaged over several Jurassic (Al-Husseini, 2009) between 166 and 157 Ma (time scale of thousands of years, closely correspond to those of a geocentric Cohen et al., 2013). The reservoirs are located in overlying bioclastic axial dipole (GAD). According to the GAD hypothesis, paleomag- limestones of the Kimmeridgian (Late Jurassic; 157–151 Ma) Arab netic directions of similar age from localities on a rigid tectonic Formation that are sealed by anhydrites of the Tithonian (Late plate should give the same paleomagnetic pole and hence the loca- Jurassic; 152–145 Ma) Hith Formation (Alsharhan and Nairn, 1997; tion of that plate with respect to the geographic axis or, equiva- Al-Husseini, 2009). lently, parallels of latitude. A temporal sequence of paleopoles or This closely packed layercake stratigraphy with source and an apparent polar wander (APW) path is a convenient way to reservoir rocks sealed upsection with anhydrites makes Ghawar represent the motion of a tectonic plate with respect to the rota- and similar supergiant oil fields of the Persian Gulf a dreamland tion axis (e.g., Creer and Irving, 2012). Relative motions between for oil exploitation essentially because it minimizes the variables tectonic plates (usually their continental proxies) are detected by associated with oil maturation and migration that are by far the systematic differences in their respective APW paths (e.g., Van der most difficult to forecast in oil assessment protocols. At the same Voo, 1990). It is also possible that Earth’s entire crust and mantle time, these hydrocarbon provinces constitute a paleogeographic rotated with respect to the spin axis, a still poorly understood 2016 conundrum. Organic matter that eventually transforms into oil phenomenon referred to as True Polar Wander (TPW) (e.g., and gas with burial and maturation can originate in abundance Goldreich and Toomre, 1969). In either case—APW or TPW— in sedimentary basins along the Intertropical Convergence Zone the included continents experience an effective rotation about a (ITCZ), which straddles about ±5° from the equator (Manabe and Euler pole that involves a systematic change in latitude according Bryan, 1985; Kent and Muttoni, 2013; McGee et al., 2014) due to to the GAD hypothesis. high levels of nutrients upwelled from deep waters or in run-off The Jurassic polar shift largely derives from the recognition of a from adjoining continents onto shelf areas.
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