The Hazm al Jalamid quadrangle (31D) and Markaz ‘Anazah quadrangle (32D), which are in the northwestern part of Saudi Arabia adjacent to Jordan and Iraq, are underlain by Late Cretaceous rocks of the Aruma Group, early Tertiary sedimentary rocks of the Turayf group, and Tertiary and Quaternary basalt and sedimentary deposits. Devonian, Silurian, Ordovician, and possibly Cambrian sedimentary rock occur in the subsurface. Basalt of Harrat al Harrah overlies older Tertiary units in the southwestern part of the map area, and nonconsolidated gravel, sand, and silt occupy most wadis and depressions. The Khawr Umm Wu’al graben trends northwest in the western part of the map area, and this extensional structure is bounded by the principal set of faults in the quadrangle. Sedimentary rocks exposed at the surface in the map area consist of the Badanah formation of the Aruma Group, the Jalamid, Mira, and Umm Wu’al formations of the Turayf group (Paleocene and Eocene), and the Sirhan Formation (Miocene to Pliocene?), in ascending order. The Badanah formation, the oldest unit exposed at the surface in the map area, is composed of fine-grained dolostone that contains some lenses and beds of pelletal phosphate. The Badanah formation was deposited in a shallow-marine environment on a carbonate shelf below wave base. The Jalamid formation, at the base of the Turayf group, is divided into two members, the Thaniyat phosphorite member at the base and the Kuwaykabah member at the top. These members are composed of phosphorite; shale; dolostone; and rare, cherty limestone; and dolomitic limestone. The Jalamid formation was deposited in a shallow-marine environment. In this region the Mira formation is divided into the Ghinah phosphorite member at the base, and the Hawsa, Mindassah, and Sib members, in ascending order. The Hawsa member, however, has thinned in the subsurface and is absent at the surface in the Hazm al Jalamid quadrangle. This sequence is composed mostly of pelletal phosphorite, dolomitic limestone, limestone, argillaceous silicified limestone, and some dolostone. The Mira was deposited in shallow-marine conditions. The Umm Wu’al formation is divided into the Arqah phosphorite member at the base, and the Amud, Hamad, Tarbah, and Shihiyah members, in ascending order. This sequence is composed mostly of phosphorite, limestone, coquinoid limestone, cherty limestone, argillaceous limestone, claystone, and calcareous shale (marl). The Umm Wu’al formation was deposited in an open-water marine environment. At the top of the sedimentary sequence, the Sirhan Formation is mostly a fine-grained limestone that contains lesser amounts of interbedded sandy and argillaceous limestone, marl, and rare beds of chert and claystone. The Sirhan Formation occurs only in the western part of the map area in the Khawr Umm Wu’al graben. The Sirhan Formation was deposited in a restricted marine and lacustrine environment. Harrat al Harrah, an extensive basalt field of Tertiary and Quaternary age in the Sirhan-Turayf basin, is exposed in the southwestern part of the map area where lava flows and pyroclastic material are composed of alkali-olivine basalt. Volcanic cones form the highest peaks in the map area. Quaternary calcareous and gypsiferous duricrust forms discontinuous mantles on bedrock in much of the map area. Duricrust was probably much more widespread, and it may have mantled most rocks exposed at the surface earlier in Quaternary time. The occurrence of duricrust suggests that a wetter environment existed earlier in Quaternary time than at the present time in northern Saudi Arabia. Alluvial deposits form nonconsolidated gravel mantles over bedrock and fill wadis. Khabras and sabkhas consist of silt and clay and commonly are cemented by evaporite minerals. Khabras occur mainly in the Khawr Umm Wu’al graben in the western part of the map area. The principal structure in the map area is the northwest-trending Khawr Umm Wu’al graben in the western part of the map area. The Khawr Umm Wu’al graben extends northwestward into the adjoining Turayf quadrangle. Bounding faults of this graben are not precisely located because younger sedimentary deposits cover the faults. Dip slip on bounding faults of the graben may have been initiated during late Paleocene(?) to early Eocene time during an extensional tectonic regime that predated the actual rifting of the Arabian plate to the northwest as the Red Sea rift opened. In the eastern part of the map area rocks dip gently toward the west by less than one degree. A conjugate set of northwest- and northeast-striking linear features are common and a few northwest-striking faults and linear features occur in the map area, both of which may be related to the Miocene and younger extensional regime that accompanied rifting of the Arabian plate. Potential resources in the Hazm al Jalamid and Markaz ‘Anazah quadrangles (31D and 32D) include phosphorite, uranium, limestone, lignite, and oil and gas. Phosphorite resources occur in the Thaniyat phosphorite member of the Jalamid formation, in the Ghinah and Sib members of the Mira formation, and in the Arqah phosphorite member of the Umm Wu’al formation. The Al Jalamid phosphorite deposit, which occurs in the Thaniyat phosphorite member, contains 400 million metric tons of measured and inferred resources of phosphate in two ore zones. The lower ore zone has a P2O5 concentration of less than 20 percent, and the upper ore zone has a P2O5 concentration of 16 to 22 percent. The phosphorite resources in the Ghinah member of the Mira formation are not regarded as economic under present conditions because the phosphorite beds are thin and lenticular. Phosphorite occurrences in the Sib member occur locally in beds 3 m thick, and these beds have an average P2O5 concentration of 19 percent. In the northwestern part of the map area, phosphorite beds are near the surface, and the Arqah phosphorite member is estimated to contain 200 million metric tons of friable phosphate in several beds that range between 1 and 4 m thick. The average P2O5 concentration in the Arqah phosphorite beds is 15 percent, and some beds contain 33 percent P2O5. Uranium (U3O8) occurs as a trace element in phosphorite deposits of the Arqah phosphorite member, but the economic potential for uranium oxide recovery as a by-product of phosphorite production has not been evaluated. High-purity limestone occurs in the western part of the quadrangle, where the Tarbah member of the Umm Wu’al formation is exposed. Lignite has been identified from drill cores in nearby quadrangles, but because of the great depth at which lignite might occur, this potential resource is unlikely to be exploited. Oil and gas were generated during Paleozoic time in northwestern Saudi Arabia, and probably during Mesozoic time in the Wadi as Sirhan graben, which is located west, southwest, and west of this map area, so an unknown potential exists for the occurrence of oil and gas in structural and stratigraphic traps in this map area. Oil shows have been reported in Cretaceous rocks of the Wadi as Sirhan graben, and oil has been discovered recently in the northern extension of the Wadi as Sirhan graben in adjacent Jordan, but the potential for oil or gas east and north of the Wadi as Sirhan graben is not known.
Wallace, C.A., Dini, S.M., and Al-Farasani, A.A., 2001, Geologic Map of the Hazm al Jalamid quadrangle, sheet 31D, and part of the Markaz ‘Anazah quadrangle, sheet 32D with Explanatory Notes, Kingdom of Saudi Arabia: Saudi Geological Survey Geologic Map GM-124C, 34 p., 33 figs., 1 table, 1 pl.