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Jurassic and Cretaceous Sedimentary Fill of Intrashelf Basins of the Eastern Margin the Arabian Plate

Abstract

Middle Eastern Mesozoic intrashelf basins (ISB) contain the world's largest oil fields, most in carbonates of the AP 7 Megatectonic cycle. Arabian Plate ISBs developed while rifting occurred in Yemen, the Indian Ocean and Tethyan margin. ISB began when a rapid sea level rise exceeded carbonate production over the platform interior. Basin fill started with an organic-rich condensed/starved section while platform carbonates aggraded surrounding a starved basin whose margin then prograded and infilled into water commonly of less than 100 m. Jurassic Arabian Plate ISBs include: Marrat, Hanifa, Najmah, and Gotnia, whose dominant fill is shallow marine arid climate limestones and dolomites with common evaporites and interbedded minor transitional marine shales and basin margin grain carbonates. Cretaceous ISBs include: Garau of Iraq, Kazhdumi of Iran and Bab of the UAE, Qatar, Saudi Arabia and Oman, that were filled by humotropic carbonate with dolomites and shales but few evaporates, while ISB margins accumulated rudistid clinoforms. Giant oil fields of both Jurassic and Cretaceous sections occur in grain carbonates while rudistid buildups are the reservoirs of Cretaceous intrashelf margins. Source rocks, include the Hanifa Fm. the Najmah Sh. the Naokelekan in Iraq, and the Aptian “tar” of the Bab Member of the Shuaiba Fm. Collectively Jurassic and Cretaceous source rocks formed the prolific petroleum systems of the ISBs. Expanding exploration now includes stratigraphic plays in the ISBs, providing new exploration opportunities. The shared geologic history of the Southern Tethys region means similar tectonic and depositional settings and a stratigraphy that can be correlated across the region.