Geologic Map of Thaniyat Turayf Quadrangle, Sheet 29C with Explanatory Notes, Kingdom of Saudi Arabia

SGS-GM-129C Chester A. Wallace, Saleh M. Dini, and Anwar A. Al-Farasani
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ABSTRACT
The Thaniyat Turayf quadrangle (29C), in the northwestern part of the Kingdom of Saudi Arabia about 900 km north of Jeddah, contains Paleozoic, upper Mesozoic, and lower Cenozoic sedimentary rocks that are offset by left-slip and dip-slip faults; nonconsolidated Quaternary deposits locally form mantles over older rock units.  The quadrangle is located between lat 2900'N. and 3000'N. and long 3730'E. and 3900'E.  Sandstone, shale, and limestone of Paleozoic age occur throughout the map area.  The southern rim of the Sirhan-Turayf basin, which contains Late Cretaceous and Tertiary sedimentary rock units, extends across the northern part of the quadrangle.  A wedge of the sand sea of An Nafud extends into the southeastern part of the map area.  The Phanerozoic sedimentary rocks range in age from Late Silurian to Miocene-Pliocene(?) and were deposited in marine, deltaic, shoreline, and continental environments.  The Late Silurian shale, siltstone, and sandstone of the Sharawra Formation (Qalibah Group) is the oldest unit exposed in the map area.  The Early Devonian Tawil Formation (Huj Group), disconformably overlies the Sharawra, and the Tawil is overlain by shale, siltstone, and limestone of the Early Devonian Jauf Formation, which in turn is overlain by sandstone of the Middle Devonian Jubah formation.  Prototaxites sp., a tree-like fungus, occurs in sandstone of the Jubah formation.  The Zallum formation, a sandstone unit in the Aruma Group, is the oldest Cretaceous unit in the Thaniyat Turayf quadrangle.  The Zallum overlies progressively older members of the Tawil Formation westward across the quadrangle on a regional unconformity.  Disconformably overlying this Cretaceous sandstone are Paleocene and Eocene limestone, shale, and phosphorite of the Turayf group, which includes in ascending order, the Jalamid and Mira formations.  Shale and limestone of the Miocene and Pliocene(?) Sirhan Formation form the youngest Tertiary unit in the quadrangle.  Alluvial deposits of Quaternary age occur in modern drainages, which cut older duricrust deposits and older chert-bearing gravel deposits.  An extensive tract of eolian sand mantles the southeastern part of the map area.  The Wadi as Sirhan graben, a regional structural feature, trends west-northwest across the central and northeastern part of the quadrangle, but this structural feature is not as prominent in the Thaniyat Turayf quadrangle as it is in the Al Jawf quadrangle to the east and the Wadi as Sirhan, Turayf, and An Nabk quadrangles to the north.  The Wadi as Sirhan fault, the northeast-bounding fault of the Wadi as Sirhan graben, is near the northeastern corner of this quadrangle, and the Al Busayta-Al Huj fault zone, the southwest-bounding fault of the graben, strikes southeastward across the central part of the quadrangle.  Orientation of folds adjacent to bounding faults and relations among folds and unconformities east of this map area suggest that faults of the graben moved in a left-slip sense during Late Cretaceous time.  An area of intense deformation in the west-central part of the map area is characterized by a local reverse fault and tight, isoclinal folds in Paleozoic rocks.  The Ja'alat as Samra fault and fold system consists of northwest-southeast-trending anticlines and synclines that are parallel to a steep thrust fault.  East of the Ja'alat as Samra deformed terrane, the Abraq al Hayq fault and fold system consists of a northeast-southwest-trending fold train that is truncated at its southwestern end by a steep left-slip fault.  The intense deformation that caused these faults and folds occurred before Late Cretaceous time.  In the southwestern part of the quadrangle, northwest-striking normal faults are common, but in the east-central part of the map area northeast-striking faults dominate.   Faults of both orientations offset Paleozoic rocks.  Less common normal faults offset Tertiary rocks north of the Thaniyat Turayf escarpment.  Some normal faults are truncated by Late Cretaceous sandstone.  Two structural domes occur in the Thaniyat Turayf quadrangle.  The Banat Baqar dome is a large, broad, gently folded structure in the center of which Late Silurian rocks of the Sharawra Formation are exposed in the southwestern part of the quadrangle.  The Ja'alat as Sawda dome is a small structure that exposes the uppermost member of the Devonian Tawil Formation below members of the Jauf Formation in the central part of the map area.   Other structures, such as linear features, may represent joints or faults that show little offset.  Phosphorite occurs in the Jalamid and Mira formations, but these deposits are unlikely to represent an exploitable commodity, even though the grade of the phosphorite is as much as 21 percent P2O5, because the phosphorite beds are sporadic, thin, and lenticular.  Uranium oxide occurs as a trace element in phosphorite beds, but uranium is not likely to be recovered because phosphorite deposits probably are not economic at this time.  The presence of the Wadi as Sirhan graben in the Thaniyat Turayf quadrangle may increase the petroleum potential in the map area because producing oil wells occur in this graben in Jordan.  Lignite occurs at depth in drill holes in northwestern Saudi Arabia, but near-surface occurrences of lignite were not located.

Wallace, C.A., Dini, S.M., and Al-Farasani, A.A., 2001, Geologic Map of Thaniyat Turayf Quadrangle, Sheet 29C with Explanatory Notes, Kingdom of Saudi Arabia: Saudi Geological Survey Geologic Map GM-129C, 32 p., 23 figs., 1 table, 1 pl.