Lithostratigraphy of the Middle Eocene Dammam Formation in Qatar, Arabian Gulf: effects of sea-level fluctuations along a tidal environment
Introduction
The Dammam Formation is a widespread and correlative rock unit in the eastern Arabian Peninsula. The formation forms part of the Hasa Group, which consists of the Umm Er Radhuma, Rus and Dammam formations (latest Paleocene/Middle Eocene). In the eastern Arabian Peninsula, the Early Middle Eocene is represented by the Rus and Dammam formations. The Rus Formation is assigned an Early Lutetian age, whereas the Dammam Formation is dated as Middle–Late Lutetian (Hasson, 1985). The thickness of the Dammam Formation increases from a few meters in the western Arabian Gulf (Saudi Arabia, Qatar and Bahrain) to hundreds of meters in areas northeast and southeast of the Arabian Gulf region. The Dammam Formation was introduced by Bramkamp in 1941 (cited in Powers et al. (1966)), who named it after the Dammam Dome in eastern Saudi Arabia (Powers et al., 1966). In its type section (32.5 m), it is mainly composed of shallow-water fossiliferous shaly limestone (Powers, 1968).
In Qatar, the exposed Dammam Formation represents about 70% of the total land surface and consists mainly of white, gray, yellow shaly to marly dolomitic limestone with thickness ranging from about 35 to 52 m (Fig. 1). The outcrop pattern of the Dammam Formation sediments is controlled by a regional gentle anticline (Qatar Arch) together with small gentle longitudinal folds such as the Dukhan anticline and the Simsima Dome (Fig. 1). These structural elements are believed to represent the northeastern extension of the central Arabian Arch (Sugden, 1962).
Section snippets
Materials of investigation
Data collected from inspections of one dry borehole and three exposed sections provide the basis for interpreting the depositional and stratigraphic dynamics of the Dammam Formation (Fig. 1, Fig. 2). Both surface and subsurface sections provide incomplete records. The core samples yield information only for the lower part of the Dammam Formation. Three outcrop sections were measured and logged in detail (localities A–C; Fig. 2). Eighty-nine representative samples from the different lithofacies
Stratigraphic setting
The litho/biostratigraphy of the Dammam Formation has been described by many workers. In 1953, Sugden (cited in Sugden and Standring (1975)) designated the Dukhan area (lat. 25°28′N, long. 50°49′E) as the reference section for this formation (Fig. 1). Cavelier (1970), was the first to stratigraphically divide the Dammam Formation into two informal subformations: the lower Dammam Subformation and the upper Dammam Subformation. He also subdivided the formation into five members (Table 1).
Lithofacies characteristics
The Dammam Formation shows significant lithofacies changes. In the southwestern region, the base consists of fissile shale. In the central area, it consists of compact claystone (Midra Shale Member) overlain by massive limestone (Dukhan Member) that passes upward into dolomitic limestone (Umm Bab Member), and finally marly dolomitic limestone (Abaruq Member). Qatar is mostly covered by dolomitic limestone of the Umm Bab Member. The typical sequence of the Dammam Formation is illustrated in Fig.
Cyclicity of the Dammam sequence in Qatar
The Eocene of Qatar is the product of two major ‘second order cycles’ in the manner described by Vail et al. (1977) (Fig. 5). Stratigraphic evidence for these transgressive cycles (HST) can be detected throughout the eastern Arabian Gulf. The first cycle, from the latest Paleocene to the Early Eocene, led to the deposition of the high-stand dolomitic-carbonate sequence of the Umm Er Radhuma Formation. This cycle ended with the formation of the evaporitic-carbonate sediments of the Rus
Depositional setting
In the Paleocene, a major transgression of the Tethyan Ocean established shallow marine conditions over a vast area on the eastern Arabian Peninsula. These conditions persisted until the Middle Eocene, before sea level started to retreat. The lithologic characters and biofacies of the Dammam Formation reflect several phases of sea-level fluctuations during the transgressive period of the Middle Eocene Tethyan Sea. The formation is believed to have been deposited in a shallow, warm marine
Conclusions
The Dammam Formation covers a major part of Qatar and has been divided into four members: the Midra Shale, the Dukhan, the Umm Bab and the Abaruq members with decreasing age. In northeastern Qatar, a local unconformity is recorded between the Dammam Formation and underlying Rus Formation. In this area, the Midra and Dukhan members are missing.
The Dammam Formation sediments represent the last phase of a Middle Eocene transgression in the eastern Arabian Peninsula. Following this, the Tethyan Sea
Acknowledgements
The author would like to thank Dr A. Fowler (UAE University) for his critically reviewing the manuscript, Dr Saif Al-Hajari for providing some thin sections and Mr Adel M. Ali for drafting some figures. Thanks also due to JASES reviewers, Dr Lee and anonymous one, for their comments.
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