Saudi Geological Survey

The awţat Ban Tamm quadrangle (sheet 23 I) is located in the east-central part of the Kingdom of Saudi Arabia about 100 km south of Ar Riy, and the rock units consist of Mesozoic to Cenozoic sedimentary rocks and nonconsolidated Quaternary deposits.  The main structure is the east-dipping Interior Homocline, which is bounded on the west by the prominent north-south-trending uwayq escarpment.  Superposed on the homocline is the Ad Dilam depression, which is a large dissolution-collapse morphostructure in the east-central part of the map area.  The east margin of the Ad Dilam depression is defined by a sinuous escarpment underlain by the Sulaiy Formation.  The escarpment is an asymmetric anticline in which beds dip steeply to the west toward the Ad Dilam depression along the west face of the escarpment, and beds dip gently eastward on the east flank of the fold.  This flexure corresponds to a gravitational drape-fold that formed over the dissolution front developed in underlying evaporite beds of the ‘Arab and Ht(?) Formations.  The Phanerozoic strata that underlie most of the awţat Ban Tamm quadrangle form part of the west edge of the Arabian sedimentary basin, and the formations range in age from late Paleozoic to Neogene.  These Phanerozoic units were deposited in deltaic, strandline, supratidal, lagoonal, and shallow-marine environments, and the Neogene and Quaternary units were of continental and lacustrine origin.  These rock units were deposited unconformably over the east flank of the Proterozoic Arabian Shield.  The Dir‘yah supergroup is Permian to Cretaceous in age, and the Shaqr’ group (Early Jurassic to Late Jurassic) forms the middle part of the supergroup.  In ascending order, the Shaqr’ group exposed in the map area contains the Dhrum, uwaiq, anfah, Jubailah, ‘Arab, and Ht(?) Formations.  The Dhrum Formation is composed of bioclastic limestone.  The uwaiq Formation consists of fossiliferous limestone, calcareous sandstone, and shale.  The anfah Formation is a sequence of nodular limestone, limestone, and shale.  Strata of the Jubailah Formation are interbedded bioclastic and argillaceous limestone.  The ‘Arab and Ht(?) Formations form a cyclic sequence of limestone and anhydrite.  Locally, anhydrite has been transformed into gypsum by hydration near the surface.  Above the Shaqr’ group, the Thammah Group (Late Jurassic? to Early Cretaceous) contains the Sulaiy, Yammah, Buwaib, and Biyadh Formations, in ascending order.  The Sulaiy Formation is composed of argillaceous and bioclastic limestone.  The Yammah Formation is a sequence of bioclastic and argillaceous limestone.  The Buwaib Formation consists of interbedded sandstone, limestone, and siltstone.  The Biyadh Formation is a crossbedded, medium-grained sandstone interbedded with minor siltstone and shale.  Above the Thammah Group is the Wasa‘ Formation (Early to Late Cretaceous), which is composed of crossbedded, conglomeratic, medium- and coarse-grained sandstone.  The ‘Aruma Formation above is a richly fossiliferous Upper Cretaceous rock unit composed of bioclastic limestone and calcareous shale.  Paleogene rocks disconformably overlie the older sedimentary units, and these are fossiliferous, nodular limestone of the Umm Radhamah Formation (early Paleocene(?) to early Eocene(?)).  The youngest strata in the quadrangle are Neogene and Quaternary conglomerate, sandstone, and limestone of the terrestrial Umm ash Sha‘l formation (Pliocene(?) to Pleistocene(?)).  Paleozoic and Mesozoic rock units are part of the gently eastward dipping Interior Homocline, which includes, in the western part of the map area, the prominent west-facing uwaiq escarpment.  The escarpment has a local relief of 180 to 218 m.  The uwaiq Formation forms the cap rock on the escarpment and an extensive east-facing dip slope, above which are mesas composed of the overlying anfah and Jubailah Formations.  The ‘Arab, Ht(?), and Sulaiy Formations underlie the north-south-trending Ad Dilam depression, which is about 25 km wide.  This morphostructure resulted from subsidence caused by interstratal karstification of evaporite beds in the ‘Arab and Ht(?) Formations, and the depression consists of a hummocky terrain characterized by dissolution-collapse features.  The Sulaiy Formation, and to a lesser extent the Yammah and Buwaib Formations, are affected by gravitational subsidence and deformation related to dissolution of underlying evaporite beds in the ‘Arab and Ht(?) Formations.  The Biyadh and Wasa‘ Formations form a northeast-trending band of low hills and a flat, poorly dissected plain that developed an eastward drainage pattern.  The ‘Aruma and Umm Radhamah Formations form a flat plain marked by low outcrops that rarely exceed 2 to 3 m in local relief.  The Umm ash Sha‘l formation (Pliocene(?) to Pleistocene(?)) forms prominent buttes along the east edge of the Ad Dilam depression.  Quaternary deposits overlie parts of all rock units in the quadrangle and mantle a broad area to cover Jurassic and Cretaceous Formations east of the uwaiq escarpment.  Three generations of alluvial gravel mantle bedrock in the eastern part of the map area and in the Ad Dilam depression.  Alluvium occurs in modern drainages, and khabras of two different ages were separated in the western part of the quadrangle.  Extensive dune systems, both active and inactive, occupy the north-central part of the map area.  Active and inactive sand sheets cover extensive tracts of the gravel plain in the east. The Wd Miraqah Fault trends to the northwest and cuts the Sulaiy escarpment.  Slip on this fault rotated the southwest block down on the northeast side, which caused the southwest block to dip northeastward toward the fault.  This structure, which is located in the Ad Dilam depression, could be related to dissolution-induced subsidence.  On the rotated block, integrated drainage systems developed on the oldest alluvial gravel, and these drained toward the northeast, toward the hanging wall of the Wd Miraqah Fault.  An elongate anticlinorium-synclinorium pair occurs in the south-central part of the quadrangle that deformed the Yammah and Buwaib Formations.  These folds, located near the east edge of the Ad Dilam depression, may be related to sagging caused by differential interstratal karstification of evaporite in the ‘Arab and Ht(?) Formations.  Folds of smaller dimension occur in the irjat al ‘Aqlah area of the Ad Dilam depression, and these folds, too, may be related to ductile subsidence of limestone caused by dissolution of underlying evaporite beds.  Mineral resources in the map area consist of industrial minerals and hydrocarbons.  Limestone and dolomitic limestone suitable for manufacture of cement or use as fluxing agents, lime production, aggregate, and building stone occur extensively in the quadrangle.  Gypsum is common in the map area and can be used for wallboard, plaster, roof tile, or fillers in paper or paint.  Silica sand can be used for manufacture of glass, bricks, glass, concrete production, or foundry sand.  Oil and gas reservoirs are exploited in the awţat Ban Tamm quadrangle, and exploration has been active in the map area.

Abdullah M. Memesh, Saleh M. Dini, Saeed A. Al-Amoudi, C.A. Wallace, Saleh A. Sobhi, and Abdulrahman J. Al-Juaid, 2010, Geologic map of Hawtat Bani Tamim quadrangle, with Explanatory Notes, Kingdom of Saudi Arabia: Saudi Geological Survey Geoscience Map GM-143C, 64 p., 41 figs., 1 pl.