Geologic Map of the Parts of the Judayyidat ‘Ar’Ar Quadrangle, Sheet 31E, and Fadyat al Adyan Quadrangle, Sheet 31F, with Explanatory Notes, Kingdom of Saudi Arabia
Saleh M. Dini, Abdullah F. Al-Khatabbi, Chester A. Wallace, Ahmed S. Bankhar,
Mohammed H. Al-Kaff, and Saad M. Al-Garni
The mapped area consists of part of the Judayyidat ‘Ar‘Ar quadrangle (sheet 31E) and a small part of the Faydat al Adyan quadrangle (sheet 31F) in northwestern Saudi Arabia adjacent to Iraq. The exposed rocks are Late Cretaceous and Tertiary in age, and Triassic, Permian, and Carboniferous sedimentary rocks occur in the subsurface. Nonconsolidated gravel, sand, and silt occupy most wadis and depressions. The main structural element is the northeast-trending ‘Ar‘Ar arch in the central part of the map area. Our geologic mapping discovered phosphate deposits in the Badanah Formation (Aruma Group) in the western part of the map area. Carbonate mounds in the Badanah Formation occur in the west and they may be related to seabed methane seeps. In addition, we recognized for the first time the extensive Aba al Qur dissolution-collapse structure in the eastern part of the map area, and identified the ‘Ar‘Ar arch in the central part of the map area. The exposed sedimentary rocks are the Zallum and Badanah Formations of the Aruma Group (Late Cretaceous age) and the Miocene to Pliocene? Ajfar Formation, in ascending order. The Zallum Formation (Kaz) is composed of shale, mudstone, and fine-grained dolomitic limestone, and the upper part of this unit contains prominent shell banks of the giant foraminifer Loftusia sp. The Badanah Formation (Kab) is divided into two parts by the ‘Ar‘Ar arch. West of the arch the Badanah Formation consists of informal lower and upper members. The lower member (Kabl) is a dolomitic limestone that contains Loftusia sp. at the base, overlain by interbedded gypsiferous, chalky limestone and dense dolomitic limestone that grades laterally into carbonate mounds composed of fine-grained, microcrystalline, bioturbated dolomitic limestone, and thin beds of algal laminated limestone. The upper member (Kabu) is composed of crossbedded, pisolitic oolite overlain by phosphatic, bioclastic, dense or chalky dolomitic limestone. East of Wadi ‘Ar‘Ar, this Formation consists of bioturbated, sparsely fossiliferous, fine-grained dolomitic limestone, limestone, silicified limestone, and interbedded gypsum. Locally layers and concretions of chert and geodes occur in limestone. West of Wadi ‘Ar‘Ar, the Badanah Formation was deposited on a tropical, open, shallow-marine carbonate shelf at, and below, wave base; to the east, circulation on the tropical shelf was periodically restricted to form an evaporite basin. Rocks previously mapped as the Umm er Radhuma Formation in the eastern part of the map area were recognized as breccia of dolomitic limestone and limestone of the Badanah Formation that collapsed into the Aba al Qur dissolution-collapse depression. The Ajfar Formation (Taj) (Miocene to Pliocene?) is composed of coarse-grained quartz sandstone, limestone, and gypsum deposited in a fluvial and lacustrine environment on the floor of the Aba al Qur dissolution-collapse depression. Alluvial deposits fill wadis throughout the area, and gravel deposits mantle the bedrock in the extreme east. Eolian deposits form isolated patches of dunes and thin layers of sand in the central area. Khabras are common in the eastern part of the map area in dissolution depressions and evaporite karst; khabra deposits consist of silt and clay cemented by evaporite minerals. Quaternary calcareous and gypsiferous duricrust occur in alluvial deposits and in breccia and gravel deposits in the eastern part of the area. The principal structure is the northeast-trending ‘Ar‘Ar arch in the central part of the map area. The arch extends into Iraq from the city of ‘Ar‘Ar directly south of the map boundary. The crest of the arch exposes the Zallum Formation and the Badanah Formation dips gently away from the crest on the flanks of the fold. A conjugate set of linear features, most likely a joint system, trends at about N.45E. and N.45W. Other linear features are aligned north-south, east-west, and N.30°W. Wadi courses follow some of the linear features. The Aba al Qur dissolution-collapse structure occupies the eastern part of the map area. This structure resulted from interstratal dissolution of evaporite beds and collapse of interbedded limestone of the Badanah Formation. The western limit of the structure is marked by a zone of sinkholes, east of which is a terrain of extreme drainage disruption, sinkholes, caves, and dissolution-collapse breccia. These two zones form the upland region of the dissolution-collapse structure. A prominent east-facing escarpment marks the eastern edge of the upland region. The escarpment is 30 to 50 m high. Sheets of carbonate-dissolution breccia in the escarpment generally dip toward the east into the dissolution-collapse depression. On the floor of the depression are large masses of collapse breccia, isolated hills of dissolution breccia, and abundant sinkholes. The main period of dissolution-induced subsidence may have occurred during Oligocene or Miocene time. Potential resources include phosphate, limestone and dolomitic limestone, evaporite minerals, silica sand, and possibly oil or gas. The upper member of the Badanah Formation contains phosphorite. Gypsum is the most common evaporite mineral exposed in the Aba al Qur dissolution-collapse depression, but minerals that are more soluble, such as halite and sylvite, might occur at depth. No systematic evaluation was made of the oil and gas potential, although possible source rocks exist at depth. Sand, gravel, and limestone are quarried for aggregate in Wadi Badanah.
Dini, S.M., Al-Khattabi A.F., Wallace, C.A., Banakhar, A.S., Al-Kaf, M.H., and Al-Garni, S.M., 2007, Geologic Map of Parts of the Judayyidat ‘AR ‘Ar quadrangle, Sheet 31E, and Faydat Al Adyan quadrangle, Sheet 31F, with Explanatory Notes, Kingdom of Saudi Arabia: Saudi Geological Survey Geoscience Map GM-140, scale 1:250,000, 45, p., 43, figs., 2 tables, 1 pl.