Hith Anhydrite Fm
Type Locality and Naming
In Saudi Arabia
Synonym:
Reference Section:
Q.P.C. Well Dukhan No. 25, lat. 25°22’52” N, long. 50°45’50” E, elevation 23 ft., completed 30.12.1951, between drilled depths 1178 [in fact, 1787m] and 1928 m (5862 and 6324 ft).
Lithology and Thickness
Top. 1. Limestone, brown and grey-brown, dense, dolomitic, with abundant nodules of anhydrite. 12 m (40 ft). 2. Limestone, brown, oolitic, dolomitized. 4 m (13 ft). 3. White, nodular anhydrite with abundant streaks and stringers of dense or compact brown dolomite. 35 m (117 ft). 4. Anhydrite, white, massive, rarely with stringers of dolomite. 30 m (98 ft). 5. White nodular anhydrite with numerous stringers of brown dolomite. Several thin beds of porous, oolitic or pellety, brown, dolomitized limestone. 20 m (66 ft). 6. Anhydrite, white to light brown, massive, partly with stringers of brown dolomite. 29 m (94 ft). 7. Anhydrite, white, nodular, with numerous stringers of dark brown dolomite changing downwards to dolomite, grey-brown, with abundant nodules of anhydrite. A six-foot bed of dolomitized oolitic limestone near the base. 10 m (35 ft). Base. Its thickness is 141 m (462 ft)
Relationships and Distribution
Lower contact
Qatar Fm, contact conformable. The contact is taken at the top of the purely carbonate upper member of the Qatar Fm. Beds showing gradational change to massive anhydrite are included in the Hith, contrary to practice in Saudi Arabia (H. Steineke et al., loc. Cit.). ARAMCO practice has publication priority but the alternative, long established in Qatar records, is retained as a matter of convenience.
Upper contact
Sulaiy Fm, contact conformable. At the highest occurrence of limestones with abundant nodular anhydrite typical of the upper unit of the Hith Fm.
Regional extent
Throughout the oilfield areas of Saudi Arabia, Bahrain and Qatar. The formation can be traced eastwards into Abu Dhabi but disappears in the eastern part of that State as the result of erosion or facies change. It is absent from Oman
GeoJSON
Fossils
Undeterminable vestiges
Age
Depositional setting
Additional Information
The top of the Hith Anhydrite is commonly accepted as a convenient time boundary between the Jurassic and Cretaceous Systems in many parts of Arabia. This position is maintained in Saudi Arabia in spite of suggestions based on palynological studies that the Hith and upper Arab Formation could be of Lower Cretaceous age (O.D. Hemer, 1965).
Evidence for a lower Cretaceous age assigned to a similar anhydrite unit occurring in Umm Shaif, Abu Dhabi (F.E. Banner and G. Wood, 1964) was refuted by H.V. Dunnington (1967).
A Jurassic (probably Tithonian) age is applied to the Hith Fm in Qatar in conformity with majority practice.
The mode of origin of this widespread (Iraq to Abu Dhabi and south Rub-al-Khali) anhydrite unit is open to conjecture. Originally supposed to result from evaporation in a silled basin, the Hith Anhydrite could have formed in a shallow, hypersaline sea (W. Sugden, 1963). Some, at least, of the sequence may result from diagenesis in supratidal sediments resulting from processes similar to those recorded from present-day coastal sabkhas in Abu Dhabi.
The Hith Anhydrite marks the final shallowing and infilling of the long-established Jurassic Sea in which vast thicknesses of limestone were deposited over much of Arabia.
An equivalent of the Hith Anhydrite can be traced northwards into Iraq, as the Gotnia Fm. It can also be recognized in south-west Iran. The halite deposits recorded from the south-west Rub-al-Khali extend southwards to form the Sabatayn Fm which is found in the salt-domes of the Shabwa area of western Hadhramaut.