Adaffa Fm
Type Locality and Naming
"Type Section: Aynunah graben in southeast Midyan (28°05'45"N; 35°16'3.4"E) (Clark, 1986). . . . Clark (1986) named his Adaffa formation after Al Adaffa village in Wadi ash-Sharmah in the Aynunah area of southeast Midyan. The formation now described corresponds to the lower part of Clark’s formation as much of his outcrop, including the fossiliferous calcarenite, has been reassigned to the Miocene Maqna group. Prior to the recent study, the sequence was assigned to the ‘Un-named Clastic Unit’ unit by Hughes and Filatoff (1995) " (Hughest et al, 1999). Column: Red Sea Saudi Arabia. Lowermost formation in Siqaj Gr
Synonym:
Lithology and Thickness
Sandstone. Clark estimated the Adaffa to be possibly 200 meters (m) thick (see Figure 8). The section is made up of a thin basal conglomerate overlain by approximately 300 feet (ft) of yellow to reddish-brown cross-bedded sandstone and gray-green shale. The conglomerate contains granite cobbles and pebbles, phosphatic nodules, dinosaur and turtle bones, and petrified wood fragments. The sandstone is a well-sorted quartz arenite (Afifi et al., 1993; Milner et al., 1993). (Hughes et al., 1999)
Relationships and Distribution
Lower contact
Regionally, the next older unit is Basement. " Clark stated that the siliciclastics in the lower part of his Adaffa Fm had a faulted contact with the Proterozoic basement.
The Proterozoic basement borders the Midyan region to the north and northeast and also crops out in the core of the Maqna massif to the west of the Ifal plain. It consists of ultramafic, metavolcanic, and metasedimentary rocks and granitic plutons, that have been intruded by basalt, rhyolite, and dolerite dikes (Figure 7). The basement has been dated at about 600 to 700 million years old (Gardner et al., 1996) and is considered to have been formed along an accreting Proterozoic volcanic arc. Exploration drilling in the Ifal basin shows that the basement rocks are fractured and leached. The granitic character of the basement indicates a continental rift origin for the proto-Red Sea, rather than spreading and the generation of oceanic crust (Bosworth, 1993; Sultan et al., 1993)." (Hughes et al., 1999)
Upper contact
Unconformably overlain by the Usfan Fm. In the type section, Clark (1986), although the upper contact was not clearly defined, suggested that it was conformably overlain by the Oligocene Sharik Fm (equivalent to Al Wagh Fm in current scheme?)
Regional extent
"The distribution of the formation is not known in detail but it is present in outcrop in Midyan and at depth in the Jiddah area. Similar rocks crop out in the Wadi Azlam basin on the Red Sea coast between Duba and Al Wajh. . . . The group is the siliciclastic age equivalent of various carbonate units in the Gulf of Suez, such as the Duwi Fm (Lower Campanian) and Sudr Fm (Upper Campanian-Maastrichtian) " (Hughes et al., 1999)
GeoJSON
Fossils
"Clark (1986) cites microfossil evidence of Andrieff (Le Nindre et al., 1981; Redmond and Teixido, 1980) to support a Late Cretaceous to Eocene age. In addition, in the Aynunah region, a thin bed of limonitic sandstone at the top of the sandstone succession contains bones of a sauropod (Titanosaurid) dinosaur and turtle plates (Ref: 28°05'45"N; 35°16'3.4"E) (Milner et al., 1993). The co-existence of Albian-Maastrichtian dinosaur bones and Cretaceous to Recent turtle plates provides an Albian to Maastrichtian age for the Adaffa formation. A similar assemblage of dinosaur and turtle remains, together with crocodiles, lungfishes and theropods, has been found in Sudan and given a Late Cretaceous age (Buffetaut et al., 1990). A Late Cretaceous microflora has been found in similar rocks approximately 290 km to the south at Wadi Azlam (Clark, 1986; Giot et al., 1980)." (Hughes et al., 1999)
Age
Depositional setting
"A fluvial depositional environment has been suggested for the formation by Afifi et al. (1993). In Sudan, the fossil assemblages similar to those of the Adaffa formation have been interpreted as indicative of a lacustrine to braided-river environment (Buffetaut et al., 1990). The significance of the phosphatic nodules is unclear, but their presence within conglomerates suggests high energy derivation from a possible bone bed source." (Hughes et al., 1999)
Additional Information