Wajid Sandstone Fm
Type Locality and Naming
Is in Jabal al Wajid, south-west Saudi Arabia, where some 950m of sandstone are exposed beneath the Khuff Formation. M. Steineke, R.A. Bramkamp and N.J. Sander, 1958
Synonym: “Bahrain Unit B”, Milne, 1959. “Pre-Khuff Clastic”, Dominguez, 1965.
Reference Section:
Q.P.C. Well Dukhan No. 65, lat. 25°27’38”, long. 50°47’63” E, elevation 42.6 m (140 ft), completed 21.1.1960, between drilled depths 3393 and 4042 m (11132 and 13261 ft).
Lithology and Thickness
Top. 1. Quartzose sandstone, compact, dark grey, composed of medium sized angular to sub angular quartz grains, with grey-brown, micaceous shale at top and fine-grained siltstone in lower part. 8.2 m (27 ft). 2. Quartzite, very hard, light grey, medium, angular to sub angular grains in siliceous matrix. 5.5 m (18 ft). 3. Sandstone, white and grey, medium to fine grains, some streaks of green and brown siltstone. 11 m (35 ft). 4. Siltstone, purple, green, and brown, slightly micaceous. 15 m (50 ft). 5. Sandstone, white, medium grained. 10.6 m (38 ft). 6. Siltstone and fine sandstone, varicoloured with subordinate grey sandstone. 37 m (122 ft). 7. Sandstone, white, quartzose, interbedded with grey, sandy siltstone. 51 m (168 ft). 8. Sandstone, white, medium grained, interbedded with thin silty sandstone. Carbonaceous material at base, 48 m (158 ft). 9. Sandstone as above, interbedded with siltstone often brown. Slightly micaceous (muscovites) in lower half. 205 m (672 ft). 10. Grey-brown, sandy, micaceous siltstone. 13 m (43 ft). 11. Sandstone, as above, with thin, dense, dolomite beds containing some anhydrite in lower half. 67 m (219 ft). 12. Sandstone, grey to white, fine to medium grained, showing occasional flow structures and ripple marks in cores. Interbeds of siltstone normally black or grey, micaceous, but green to red towards middle of unit. 177 m (579 ft). Base. Its thickness is 649 m (2129 ft), bottom not penetrated.
Relationships and Distribution
Lower contact
The base of the Formation has not been seen in Qatar.
Upper contact
Khuff Fm, nature of contact not discernible. Placed at contact of the lowest carbonate of the Khuff, above, with grey-green to brown shale and marl of the uppermost Wajid, below.
Regional extent
Encountered in Q.P.C. Well Musaiymir No. 1, in eastern Qatar. Also, in deep wells in Bahrain and offshore Qatar.
GeoJSON
Fossils
In unit 11. Indeterminate plant and fish remains and one plate of an arthrodire fish.
Age
Depositional setting
Additional Information
Originally, informally named the “Bahrain Unit B”, this wholly clastic formation is now named after the Wajid Fm of Saudi Arabia. Both are silico-clastic units which underlie the Khuff Fm and whose minimum age range is Permian to Devonian. The wide separation of Qatar from the type section of the Wajid is no impediment to adoption of the name. The Wajid Sandstone is considered to be a useful receptacle for pre-Khuff clastic units found in southeast Arabia which cannot be fitted in any established stratigraphic scheme. The alternative is the proposal of new, local formation names for isolated subsurface discoveries, such as those in Qatar.