Stratigraphical and microfacies analysis of the late Eocene - early Oligocene succession of Jabal Hafeet, U.A.E.

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Hany Farouk El-Sahn
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Saudi Digital Library
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Jabal Hafeet is the only known locality in Arabia with fossiliferous, marine, Late Eocene-Early Oligocene outcrops. This succession was studied in thin section for both its stratigraphical and microfacies analysis. A total of five distinctive microfacies have been recognized and used to interpret both the age and the paleoenvironmental conditions of deposition of the succession which is proved to be of Late Eocene-Early Oligocene age. A rich assemblage of larger benthonic foraminiferid remains (mainly Nummulitids) and sparse record of Planktonic formaniferid and other remains have been identified. The succession represents a shallowing upward carbonate cycle moving from open marine shelf to shelf edge conditions. The succession is here correlated with both the Dammam and the Asmari Formations which have long been established in the Arabian Gulf stratigraphy. Although the type section of the Dammam Formation is only of Middle Eocene age and is truncated by the post-Dammam unconformity, it is here suggested to expand the term Dammam to include Late Eocene successions of similar facies in the region. The Dammam sensu lato as here defined includes carbonate facies, of shelf conditions rich in larger benthonic forminiferid remains (e.g. Nummulitids) of Middle to Late Eocene age. It was deposited in a sedimentary cycle that followed the Paleocene - Early Eocene Umm Al-Radhuma / Umm al-Rua'us (Rus) Formations. In deeper water facies (such as the subsurface of the U.A.E. the three formations pass laterally into the more shaly and marly Pabdeh Formation. Nevertheless, the overlying Asmari Limestone is generally represented by reefal facies. This testifies for the regression of the sea off Arabia during the Late Paleocene time. Such regression can be explained by the world wide low sea stand during the Late Oligocene (Chattian) time, but it can also be connected with the deformation of the sedimentary basin during both the Omani and Zagros Orogenies. Recently introduced names for rock units in the succession such as the Hafeet, Seneyeiah and Al Jaww are believed to be superfluous and are thus here dropped.
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