Al Wajh Fm
Type Locality and Naming
Oldest unit of the Tayran Gr. Hughes and Filatoff (1995) published the name ‘Al Wajh Formation’ following its use by Saudi Aramco in detailed lithological and biostratigraphic studies on samples from several shallow boreholes in the Al Wajh Basin. Column: Red Sea Saudi Arabia. The Al Wajh Formation is defined in the Saudi Aramco exploration well Al Wajh South-1 (AWSO-1: 25°14′23.8″N, 37°12′28.6″E) between 12,787–13,420 ft, onshore coastal Saudi Arabian Red Sea. Lowermost formation in Tayran Gr
Synonym: Previously named the Wadi Al Hamd member of the Tayran Fm by Dullo et al. (1983) and Bayer et al. (1988). Clark (1986) provisionally assigned the succession to the Sharik Fm of Remond and Teixido (1980). . . . The Al Wajh Fm section is probably equivalent to the Bathan Fm described from the Jiddah region (Brown et al., 1989).
Lithology and Thickness
Sandstone. "It consists of red siliciclastics that are barren of fossils, although microfossils have been recovered from its subsurface equivalent. The mineralogical and lithological components of the siliciclastic rocks and their proximity to underlying and adjacent exposures of the granitic Proterozoic Basement, indicate a direct derivation from the Proterozoic Basement. The Al Wajh Fm consists of red and gray-green mudstones and poorly-sorted, often arkosic sandstones and conglomerate.
Thickness: In AWSO-1, the Al Wajh Fm has a minimum thickness of 633 ft (193 m). Dullo et al. (1983) recognized a maximum thickness of 114 m (350 ft) for what is now the Al Wajh Fm, whereas in the subsurface of the Saudi Arabian Red Sea, as much as 600 m (1,968 ft) has been measured (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). At the Ad Dubaybah locality in the Midyan area (28°27′09.9″N, 35°05′19.8″E), a total thickness of 93 ft is exposed beneath the limestone of the Musayr Fm." (Hughes and Johnson, 2005).
Relationships and Distribution
Lower contact
Regionally, the schematic strat column indicates the next older unit as Jizan Gr. However, in the type area, the basal conglomeratic sandstones unconformably overlie the Proterozoic Basement (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). It contains several rock types of granitic composition, but chert pebbles (Figure 33) are only present in the subsurface equivalent sediments.
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Yanbu Fm. "In a complete section, it is disconformably overlain by carbonates of the Musayr Fm (Figure 35) in Wadi al Hamd (28°23′55.9″N, 34°54′4.2″E) and on the east flank of Jabal Dhaylan in the Al Wajh Basin. Often, however, the Al Wajh Fm represents the only section within the Tayran Gr and is unconformable with the overlying Burqan m or even younger units. In the type section (Al Wajh South-1), the base of the Al Wajh Formation was not penetrated, but it is conformably overlain by anhydrite and anhydritic siltstones and shales of the Yanbu Formation in other areas." (Hughes and Johnson, 2005)
Regional extent
"Although widespread in the Red Sea coastal basins, the Al Wajh Fm is largely replaced by the Jizan Volcanics in the south. The Al Wajh Fm is well exposed in Midyan at several localities in the northern part of the Ifal Plain and in the Jabal as Safra region. . . . In the Al Wajh Basin, upholes U-60748 through U-60751 have recovered most of the stratigraphic section in the back-basin (Figure 34) showing that the basin fill consists of a thick sequence of alluvial plain deposits within the Al Wajh Fm. . . .
When Hughes and Filatoff (1996) named the formation, the regional equivalent of the Al Wajh Fm in the Midyan region was not defined. Its similarity to the Shoab Ali Member (basal sands and sandstones) of the Nukhul Fm of the Gulf of Suez (Saoudi and Khalil, 1984) was noted. It is possible that the Miocene lacustrine sediments described by Schmidt and Hadley (1984) as the Baid Fm represent a facies of the Al Wajh Fm, although the Baid Fm contains interbedded lava flows in the Qunfudah area, and may represent a transitional facies of the Jizan Gr. The Al Wajh Formation is considered equivalent to the Ranga, Abu Ghusun and Nakheil formations of the northwest Red Sea (Plaziat et al., 1998), the Hamamit Fm of Sudan (Hughes and Beydoun, 1992; Carella and Scarpa, 1962; Sestini, 1965) and to the Ghaydah Fm of the Yemeni Red Sea (Watchorn et al., 1989)." (Hughes and Johnson, 2005)
GeoJSON
Fossils
"No palynological evidence has been obtained for the age of the Al Wajh Formation in the Midyan region. An early Miocene age (Hughes and Filatoff, 1995), however, was established in the type section based on the presence of Acanthaceae-type pollen (origin at the beginning of the Miocene), Fenestrites spinosus (originates during the early Miocene), and the absence of charred Gramineae (not recorded in lower Miocene). Echinoids recently found within the siliciclastics at Ad Dubaybah are related to those considered typical of Miocene rocks in the Gulf of Suez (D. Hamama, Cairo University, personal communication, 1998). Similar echinoids found north of Maqna in the extreme northwest of the Midyan region have been assigned a late Eocene age based on their similarity to species from the upper Shumaysi Fm of the Jiddah region (Jado et al., 1990)." (Hughes and Johnson, 2005)
Age
Depositional setting
"The environment of the Al Wajh Formation is interpreted as fluvio-lacustrine with marginal marine (possibly estuarine) pulses. A brackish to freshwater paleoenvironment in Midyan is indicated by the presence of the freshwater alga Pediastrum spp. and the benthonic foraminifera Ammonia beccarii, together with charophytes and unornamented ostracods in the subsurface. Le Nindre et al. (1986) concluded that the sediments are of fluvial to alluvial fan in origin, and R.S. Johnson, D. Rodgers and G.R. Savage (1995, Saudi Aramco Report) similarly categorized the basal conglomeratic sandstones and red mudstones. The Al Wajh Formation was deposited during the early stages of slow subsidence and shows the first effects of a gradual marine transgression similar to the Nukhul Fm in the Gulf of Suez. The presence of freshwater fish fossils (Brown, 1970) and of the lower jaw of a hippopotamus-like Masritherium provide freshwater conditions for part of the Baid Fm (Schmidt and Hadley, 1984)." (Hughes and Johnson, 2005)
Additional Information