Noweir阿曼山前地层和构造背景_0002.pdf

387Structural and Stratigraphic Setting, Faiyah Range, Northwestern OmanGeoArabia, Vol. 3, No. 3, 1998 Gulf PetroLink, BahrainStructural and Stratigraphical Setting of the Faiyah Range, Northwestern Oman Mountain Front, United Arab EmiratesM. Atef Noweir, Abdulrahman S. Alsharhan and Mohamed A. Boukhary United Arab Emirates UniversityABSTRACTThe Faiyah Range belongs to a group of regional ridges that formed by post-obduction folding of the Upper Cretaceous-Tertiary sedimentary rocks exposed along the western margin of the Northern Oman Mountains. The Faiyah Anticline, generally trends north- northeast to south-southwest with thrust faults striking parallel to the fold axis. The anticlinal hinge was later displaced by a dextral strike-slip fault, named here as the Faiyah Fault, into two segments. The northeastern segment includes Jebels Rumaylah, Faiyah and Mulayhah, and the southwestern segment includes Jebels Buhays and Aqabah. The anticline is interpreted to result from northeast-southwest compression during the Tertiary.In the Faiyah Range the neoautochthonous sedimentary rocks are the Maastrichtian Qahlah and Simsima formations, and the Eocene Dammam Formation. Stratigraphic evidence shows that the lower part of the Qahlah was deposited in a non-marine environment while the upper part was deposited during a marine transgression. The Simsima was deposited in a shallow-marine environment. These units unconformably overlap the allochthonous Semail Ophiolite. The microfaunal content of the so-called Muthaymimah Formation (?Tertiary), of earlier authors, indicates that it is of Maastrichtian age in the Faiyah Range. This sequence is also conformable to the Simsima and therefore it is considered to be the upper member of the Simsima in this area.INTRODUCTIONThe Faiyah Range constitutes the northernmost outcrop of the western foothills of the Oman Mountains where Maastrichtian and Tertiary sedimentary rocks are exposed in a discontinuous belt of jebels (Figure 1). The range is located between the Dibba and Hatta Zones, and trends parallel to the Northern Oman Mountains Front. It consists of an elongated anticlinal structure, extending for about 21 kilometers (km) in length and 1 to 2 km in width. The range can be subdivided into five jebels (Figure 2): Buhays, Aqabah, Rumaylah, Faiyah and Mulayhah.In the eastern United Arab Emirates region, several gas/condensate fields, such as Margham and Saja’a (Figure 1), highlight the prospective nature of this province. These fields are trapped in anticlinal structures along the thrust front which constitutes the main boundary between a nearly undeformed foredeep basin to the west, and the fold and thrust belt to the east (Dunne et al., 1990; Mount et al., 1995). The complex nature of these subsurface structures is generally difficult to image with seismic data (Mount et al., 1995; O’Donnell et al., 1995). The study of the Faiyah Range therefore contributes to our understanding of the structural and stratigraphic evolution of this hydrocarbon habitat.Many recent studies describe the geology of the Northern Oman Mountains (for example, Searle et al., 1983; Searle, 1985, 1988a, b; Dunne et al., 1990; Woodward, 1994; Warrak, 1996; Noweir and Eloutefi, 1997). In addition, several published regional maps cover the entire Oman Mountains (Glennie et al., 1974 at a scale of 1:500,000) and the Northern Oman Mountains (Geological Map of the United Arab Emirates, Sheets 2 and 4, 1979 at a scale of 1:250,000; Open University Oman-Ophiolite Project, 1983 at a scale of 1:250,000). The Upper Cretaceous stratigraphy of the area is also described in several regional studies (for example, Nolan et al., 1990; Skelton et al., 1990; Hamdan and Anan, 1993; Alsharhan and Nasr, 1996; Alsharhan et al., in press). Alsharhan and Nairn (1990, 1994) outlined the regional setting of the Upper Cretaceous deposits around the fringes of the Oman Mountains.388Noweir et al.None of the above regional studies, however, provides a detailed description of the Faiyah Range. This paper presents the results of a study which is focused on the structural and stratigraphic setting of this range. We present a geological map (Figure 2, originally constructed at a scale of 1:25,000) based on the examination of vertical aerial photographs and detailed field mapping. The study also presents paleontological results which clarify the age of the stratigraphic units in this region.GEOLOGICAL SETTINGThe Oman Mountains form a prominent arcuate range which is parallel to the Gulf of Oman in southeast Arabia (Figure 1). These mountains formed in response to two main compressional events. The first resulted from the Late Cretaceous (Coniacian-Maastrichtian) obduction of the Semail Ophiolite, and associated sedimentary and volcanic rocks (Sumeini, Hawasina and Haybi groups), onto the eastern margin of the Arabian Platform. As a result of the obduction a flexural foredeep developed along the western flank of the 。