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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Strontium-Isotope Age Dating and Correlation of Phanerozoic Anhydrites and Unfossiliferous Limestones of Arabia

George J. Grabowski1; Chengjie Liu1

(1) ExxonMobil Exploration Company, Houston, TX.

We are dating anhydrites and limestones that lack age-diagnostic faunas using 87Sr/86Sr ratios. It has enhanced our correlation of the Miocene and Oligocene, Jurassic, and Triassic-Permian.

Deposits in Iraq that have been considered Middle Miocene are actually older. Sr-isotope ages of anhydrites from the Fat’ha Formation from many wells give consistent ages of late to middle Burdigalian (15.6-18.5 Ma). Platform carbonates of the Jeribe Formation are middle to early Burdigalian in age (18.5-19.6 Ma). The basin-filling evaporites of the Dhiban Formation were deposited from earliest Burdigalian through late Aquitanian (19.6 to 21.3 Ma). The Euphrates and Serikagni formations are older still, deposited in the early Aquitanian to late Chattian (21.8-24.3 Ma).

The Kirkuk Group is composed of shelfal, shelf-margin and basinal limestones divided into many lithostratigraphic units which are not easily correlated without an age framework. The youngest units are middle to early Chattian (24.4-33.9 Ma), with the Bajawan, Baba and Tarjil formations being late to middle Rupelian (28.5-32 Ma), and the Shurau, Sheikh Alas and Palani formations are early Rupelian (32.2-33.9 Ma).

The Hith Formation is middle to early Tithonian (147.5-150.7 Ma). Anhydrites of the underlying Arab Formation on the Southern Arabian Platform (SAP) are late to middle Kimmeridgian (150.7-153.5 Ma). Sr ages of the basinal evaporites of the Gotnia Formation in the Gotnia Basin give the same ages.

Thick shelfal limestones below the Arab Formation on the SAP are early Kimmeridgian to as old as Bajocian (168-171 Ma) in the Lower Araej Formation. Thin basinal Najmah and Naokelekan formations in the Gotnia Basin are early Kimmeridgian to middle Bathonian (153.5-166.5 Ma). The underlying Sargelu Formation is early Bathonian to Bajocian (167-168.5 Ma), equivalent to the Upper Araej and Uwainat formations of the SAP.

Anhydrites in the Alan and Adaiyah formations are middle to early Toarcian (178-183 Ma) and late to middle Pliensbachian (183-187 Ma), respectively. The Butmah Formation is late Sinemurian to late Rhaetian (187-200 Ma). The Lower Araej of the SAP is early Toarcian-late Pliensbachian.

The Kurra Chine Formation in Iraq has yielded a Rhaetian Sr age, and the underlying Geli Khana is dated Ladinian. Anhydrites of the Jilh Formation on the SAP give older ages (Carnian to Anisian), equivalent to the lower part of the Gulailah Formation (Rhaetian-Norian to Ladinian-Anisian).