Burgan Fm
Type Locality and Naming
The name Burqan Formation is taken from the Auxerap/Tenneco exploration wells drilled in the offshore Burqan field. Column: Red Sea Saudi Arabia. Type Section and Thickness: The Burqan Formation is defined in the Auxerap/Tenneco exploration well Burqan-3 (BRQN-3: 34°04′04″N, 27°55′47″E) between 6,881–10,561 ft (3,680 ft, 1,122 m thick), offshore Midyan area, Saudi Arabian Red Sea. Column: Red Sea Saudi Arabia
Two members are recognized, the sand-dominated Nutaysh Member of the Burqan Formation (Clark, 1986) and the mudstone-dominated Subayti Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).
Synonym: The Burqan Formation was informally called the ‘Globigerina Marls’ in unpublished (non-Saudi Aramco) oil company reports.
Lithology and Thickness
Claystone. The Burqan Formation is a thick succession of deep-marine calcareous mudstones with thick sand interbeds. As in the case of other syn-rift rock units, the Burqan Formation is highly variable in lithology, depositional environment, and thickness, all of which can be related to its deposition over a very irregular, often heavily faulted, Miocene paleotopography.
Turbidites (see Figure 57), conglomerates, and sandstones of the Nutaysh Member characterize the basal part of the sequence, especially in the western part of Midyan. In most of the exposures to the southeast, however, the upper part of the Burqan Fm is exposed and consists of calcareous mudstones of the Subayti Member. Clark (1986) estimated a total thickness of 400 m (1,312 ft) for the entire Burqan Fm. The calcareous mudstones are typically soft and characterized by ramifying anhydrite veinlets. The sandstone forms thick, massive, poorly consolidated beds as much as 15 ft thick (Figure 53) and is particularly well exposed in the western area of the region in road-cuts along the 'old Maqna road' from 28°20′53.8″N, 34°46′38.5″E to 28°20′04.6″N, 34°45′26.5″E).
The older Subayti Member consists of calcareous shales and siltstones with minor limestone and is readily distinguished from the sandstone-dominated Nutaysh Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). It was named after the Subayti region of northwestern Midyan by G.S. Ferguson and M. Senalp (1993, Saudi Aramco Report). The Subayti Member characterizes much of the Burqan Formation. It is found extensively in the Midyan Basin and the onshore flanks of the Gulf of Suez in Egypt. It is also present at all subsurface localities bordering the Red Sea." (Hughes and Johnson 2005)"
The younger Nutaysh Member is sand-dominated and is readily distinguished from the mudstone-dominated Subayti Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). It was originally proposed by Clark (1986), for the sand-dominated unit. The Nutaysh Member consists of coarse- and fine-grained sandstones with minor siltstone and shale. The section contains rare allochthonous limestone and granite. The Nutaysh Member is widely distributed in the Midyan region where the thick sandstones form massive, steep cliffs in outcrop, or are present in the subsurface as thin beds that act as hydrocarbon reservoirs (Burqan field).
Relationships and Distribution
Lower contact
The deep-water turbidites of the Burqan Fm lie unconformably on the upon the Al Wajh Fm of the Tayran Gr in the type section and regionally also on the Proterozoic Basement. At Jabal ar Risha (28°17′00″N, 34°45′21″E), sandstones of the Nutaysh Member conformably overlie oyster-bearing carbonates of the Musayr Fm. Regionally, for graphic purposes, the schematic strat column indicates the next older unit as Musayr Fm.
Upper contact
" In the type section, the Burqan Fm unconformably overlain by the An Numan Member of the Jabal Kibrit Fm (Maqna Gr). The unconformity at the top of the Burqan m is based on the presence of planktonic foraminifera and calcareous nannofossils of zones N6 and NN3 respectively at variable depths, including immediately below, the An Numan Member. . . .The Burqan Fm is unconformably overlain by anhydrite of the Kial Fm of the Maqna Gr, as seen in the variable exposures in the Midyan region and also in interpretations of subsurface contacts. It is apparent that during deposition of the Burqan Formation, localized Proterozoic Basement highs were exposed, and these sites of non-deposition continued until late early Miocene times when carbonates of the Wadi Waqb Member (Jabal Kibrit Fm, Maqna Gr) were deposited on them." (Hughes and Johnson, 2005). Regionally, the schematic strat column indicates the next younger unit as Jabal Kibrit Fm (lowest in the Maqna Gr regionally).
Regional extent
The Burqan Formation is well exposed in the Midyan region west of Jabal Rughama (Raghama) flanking the Maqna Massif and along the Gulf of Aqaba coast. Nonmarine equivalents of the Burqan Formation may exist in the Jiddah Basin near Harrat Buraykah.
"Based on biostratigraphic evidence, the Burqan Formation is time-equivalent to the lower part of the Rudeis Fm (Lower Rudies Fm) of the Gulf of Suez and Egyptian Red Sea (Abdine, 1979; Hughes and Beydoun, 1992; Hughes et al., 1992; Bosworth and McClay, 2001). It is also equivalent to the Maghersum Fm of Sudan (Hughes and Beydoun, 1992; Carella and Scarpa, 1962 and Sestini, 1965) and the open-marine syn-rift tectono-sedimentary unit B of Plaziat et al. (1990). It is likely that an Upper Rudeis Fm equivalent exists in the inboard portions of the Red Sea. The data available to the authors [Hughes and Johnson, 2005), however, are located on the more marginal parts of the Saudi Arabian Red Sea and do not yet support this conclusion." (Hughes and Johnson, 2005)
GeoJSON
Fossils
Presence of age-diagnostic planktonic foraminifera and calcareous nannofossil : Planktonic Foraminifera Zone N7, Globigerina ciperoensis forma atypica; Zone N6, Globquadrina praedehiscens; Zone N5 Globigerinoides primordius, and Calcareous Nannofossil Zone NN4, Helicosphaera ampliaperta; NN3, Sphenolithus belemnos; and NN2, Triquetrorhabdulus carinatus. Although of limited age significance, numerous echinoids are present within shale.
Age
Depositional setting
" The depositional environment of the Burqan Fm varied between structural elements. Cyclical flooding and differential subsidence of fault blocks were responsible for variations in both clastic supply and water depth.
The presence of certain benthonic foraminifera, including Bathysiphon taurinensis, hispid Uvigerina spp. and Nodosaria spp., and the generally high diversity planktonic and deep-marine benthonic foraminiferal assemblages, indicate a predominantly bathyal depositional environment for the mud-dominated succession of the Nutaysh Member. Well-developed trace fossils occur at the base of many of the beds, such as those at the head of the long wide wadi south of Wadi Waqb. Sandstones interbedded with the mudstones typically contain allochthonous penecontemporaneous shallow-marine microfossils.
Exposures of the Burqan Fm in the belt of northwestern outcrops in Midyan were interpreted as deep submarine-fan deposits (G.S. Ferguson and M. Senalp, 1993, Saudi Aramco Report) with several sediment sources. In the northwest, proximal turbidites display decreasing grain size towards the southeast where they become distal fan turbidites. In the southeastern outcrop, however, flute marks on the base of beds exposed at the head of Wadi Waqb (28°12′58.4″N, 34°44′40.6″E) indicate transport of sediment from the southeast. At this locality, the beds dip northwest (N35°W) at 32°. A 15 ft thick bed of massive sandstone is also exposed near here.
Lacustrine sediments considered to be a back-basin equivalent to the Upper Rudeis Fm have been described from Egypt (Wescott et al., 2000), but similar sediments have not yet been recognized in the Saudi Arabian succession" (Hughes and Johnson, 2005)
Additional Information