Suwei Fm
Type Locality and Naming
Originally named from a partial section in Q.P.C. Well Kharaib No. 1, the formation was later fully penetrated in Well Dukhan No. 65. Q.P.C. Well Dukhan No. 65; lat. 25°27’38” N, long. 50°47’12” E, elevation 42.6 m (140 ft), completed 21.1.1960, between drilled depths 2695 and 2894 m (8842 and 9494 ft). The section in the latter well is designated the type section. The formation takes its name from a locality to the north of Kharaib in central Qatar. W. Sugden, 1956 (unpublished report)
Synonym: Approximate equivalent of the “Sudair Shale”, Steineke et al, 1958. “Sudair Formation”, Dominguez, 1965.
Reference Section:
Lithology and Thickness
Top. 1. Marl, khaki and brown, passing down into shale, grey-green with thin beds of dolomite, grey and compact. 4.2 m (14 ft). 2. Siltstones, red, green, purple and brown, micaceous with interbedded thin quartz sandstones, grey, fine grained, glauconitic, and shale, green and grey. Occasional thin beds of dolomite, grey to brown, anhydritic, with occasional relict pellety structures. Minor anhydrite intercalations. 58.5 m (192 ft). 3. Alternating marl, grey and dolomite, grey-brown, dense. 12,8 m (42 ft). 4. Dolomite, grey to dark grey, fine grained, dense, anhydritic, with streaks and nodules and some well-developed beds of anhydrite. Occasional shales and marls, green to grey. 66.7 m (219 ft). 5. Shale, brown, grey, micaceous, with occasional thin beds of dolomite, grey, dense or, sometimes, saccharoidal. Dolomite becomes an important part of the sequence in the lowest 13m of this unit. 52.7 m (173 ft). Base. Its thickness is 199 m (652 ft)
Relationships and Distribution
Lower contact
Upper contact
Gulailah Fm; contact believed conformable. Contact selected where dolomites of the basal Gulailah Formation are underlain by brown marls and green shales of the Suwei Fm. The latter pass down rapidly into red, green and purple siltstones which typify the upper part of the Suwei Fm.
Regional extent
Q.P.C. Well Musaiymir No. 1, and deep wells in offshore Qatar (J.K. Dominguez, 1965). Deep test wells in Bahrain. In many parts of Saudi Arabia both as outcrop and subsurface. Kuwait Oil Company’s Well Burgan 113 (R.M.S. Owen and S.N. Nasr, 1958).
GeoJSON
Fossils
In 1. Lingula tenuissima Alberti and Estheria minuta Goldfuss. In 2. L. tenuissima, E. minuta and cf. Crenilepis.
Age
Depositional setting
Additional Information
The Suwei Fm was originally defined when first encountered in Qatar in Well Kharaib No. 1. The absence of any age-diagnostic fauna from units beneath the upper Izhara Fm obscured passage from Jurassic to Triassic rocks in a continuous carbonate sequence. The Guilailah Fm was believed to be Jurassic, the underlying Suwei Fm being considered a basal Jurassic clastic development. The latter was compared with the Toarcian, Marrat Fm of Saudi Arabia, but, owing to lack of concrete evidence for this correlation, it was decided to define a new formation in Qatar. The name Suwei has become so entrenched in Qatar geological literature that the name was retained after evidence obtained from Dukhan Well No. 65 proved the equivalence of the Suwei to the Sudair Fm.
In fact, the upper limits of the Suwei Fm of Qatar and the Sudair Fm of Saudi Arabia differ slightly. The top of the latter is placed above bright, variegated siltstones, excluding the thin, green-brown marls and shales of the upper unit of the Suwei.
The Suwei and Sudair Formations are widespread in Arabia, extending from the Arabian Shield to Kuwait and Qatar. The formation has not been recognized in Oman (Morton, 1959) or the Jebel Hagab section. The presence of a considerable proportion of dolomite in the formation in Qatar is probably an indication of lateral passage to a carbonate facies further from the shield.