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Evolution of the Oman Tethyan Continental Margin |
Amoco Production Company, P.O. Box 3385, Tulsa, OK 74102, USA
Carbonate deposits dominated the southeastern part of the Arabian Shelf from Berriasian to Santonian time, approximately 60 Ma. Deposition was terminated by the development of the Oman Foredeep in Coniacian-Santonian following the initial emplacement of the Hawasina and Semail nappes in the Turonian. The Lower and middle Cretaceous units in Arabia correlate with European reference sections and the current ages of the stage boundaries can be used to form a quantitative scale.
The Thamama-Kahmah Group to the Ilam-Halul Limestone consists of four major unconformity-bounded, shoaling-up depositional sequences that range in duration from 3 to 22 Ma. These sequences represent significant transgressive events on the shelf. The Rayda-Salil-Habshan sequence represents drowning and extensive incursion of the deep shelf landward; it lasted about 13 Ma. Small-scale, possibly climatic cycles comprise the Salil and Rayda formations. The contact with the overlying Lekhwair-Kharaib-Shuaiba sequence is normally sharp with no evidence of erosion. This sequence lasted about 18 Ma and consists of numerous shoaling-up cycles and local disconformities. The unconformity between the Shuaiba and Nahr Umr is a regional disconformity with evidence of local exposure. The hiatus spans most of the Late Aptian in the Oman Mountains, and in Abu Dhabi it spans the youngest part of the Late Aptian.
The Nahr Umr-Natih sequence in Oman spanned about 22 Ma and consists of four shoaling-up cycles. An important drowning event in the Oman Mountains occurred during the earliest Middle Cenomanian and is represented by the submarine hardground at the top of the ‘E’ member. The youngest sequence consists of the Laffan-Ilam formations in the Khatiyah Basin and lasted about 3 Ma. These depositional sequences correspond to transgressive events on other plates and represent eustatic sea level changes. The onlapping unconformities in the Oman Mountains represent times when the peripheral swell was active.
Restricted, intraplatform basins, in which organic-rich muds were deposited, developed four times. These units are best developed in the Bab-Khatiyah Basin and locally extended eastward into Oman. The Bab Member of the Shuaiba Formation is mainly Late Aptian. The Khatiyah Formation is coeval with the Early Cenomanian, lower ‘E’ member of the Natih in Oman. The ‘B’ member of the Natih is Late Cenomanian in age. The Laffan Formation is mainly Coniacian in age and represents the final restricted basin upon the southeastern Arabian Shelf.
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