Ahmadi Fm
Type Locality and Naming
K.O.C. Well Burgan No. 62, in Kuwait. R.M.S. Owen and S.N. Nasr, 1958
Synonym: “Khatiyah Formation”, Sugden, 1953. (unpublished) “Ahmadi Formation”, Dunnington et al. 1959. « Ahmadi Member », James and Wynd, 1965. « Khatian Formation », Dominguez, 1965. « Ahmadi Member », Powers et al. 1966. « Ahmadi Formation », Dunnington, 1967.
Reference Section:
Q.P.C. Well Dukhan No. 28, lat 25°17’12” N, long. 50°48’46” E, elevation 32m (106 ft), completed 1.5.1952, between drilled depths 727 and 925m (2384 and 3035 ft).
Lithology and Thickness
Top. 1. Limestone; light grey, fine grained, porous, wackestones and packstones with numerous thin beds of marl and shale, blue-grey to brown. 99 m (326 ft). 2. Shale, blue-grey and marly towards base. 54 m (176 ft). 3. Limestone; light grey, porous wackestones and packstones. 16 m (53 ft). 4. Shale, brown, and blue-grey, with thin beds of argillaceous sandstone in middle. 29 m (96 ft). Base. Its thickness is 198 m.
Relationships and Distribution
Lower contact
Mauddud Fm. The lowest shales of the Ahmadi Fm rest with apparent conformity upon light grey limestone of the Mauddud Fm.
Upper contact
Mishrif Fm. The conformable contact is well defined by rapid upward passage from shales and marls of the upper Ahmadi into continuous limestones of the Mishrif Fm. The lithologic change is normally sharp but occasionally gradational.
Regional extent
Deep wells throughout the Qatar peninsula and some offshore areas. South Iraq and Kuwait, and parts of Saudi Arabia. Also recorded as the Ahmadi Member of the Sarvak Formation of S.W. Iran.
GeoJSON
Fossils
In 1. Praealveolina cretacea (d’Archiac), Cisalveolina Fallax Reichel, Meandropsina vidali Schlumberger, Flabellammina sp. In 2. P. cretacea, M. vidali, Flabellamina sp., Orbitolinella depressa Henson, Serpula filiformis Sowerby, Trigonia crenulata Fraas, Corbula truncata Sowerby, Pecten orbicularis (Sowerby), Mitra cancellata Sowerby, Protocardium hillanum Sowerby, Cerithium albensis d’Orbigny, Turritella difficilis d’Orbigny, Aspidiscus cristatus König, Exogyra conica (Sowerby), E. luynesi Lartet, E. larteti Conquand, Fusus ornatus d’Orbigny, Cerithium vibrayeanum d’Orbigny, P. cretacea, Trocholina arabica Henson, Trocholina lenticularis Henson var. minima Henson. In 3. P. cretacea, T. arabica. In 4. P. orbicularis, P. hillanum, E. conica, E. larteti, Turritella granulata Sowerby, Alectryonia macroptera Sowerby, Gervillia rostrata Sowerby, Nucula subrecurva Philippi, Neithea quinquecostata Sowerby, Anomia laevigata Sowerby, Pteria anomala (Sowerby), Camptonectes curvatus Geinitz, T. lenticularis, P. cretacea.
Age
Depositional setting
Additional Information
At its type locality, in Kuwait, the Ahmadi Fm is a relatively thin (76 m) shale unit (the Cap Rock Shale) with a thin limestone unit near its base. In the Basrah area the name Ahmadi is applied to a sequence of shales and limestones of Cenomanian age. The succession in Dukhan is so similar to that in South Iraq that the older name Khatiyah was replaced by Ahmadi Fm in 1961.
The Ahmadi Fm of Qatar overlies the Mauddud Fm and underlies the Mishrif, occupying the position of the Ahmadi and Wara Formations of South Iraq. The top of the Mauddud Fm is believed by Dunnington (1959, 1967) to coincide with a widespread regional unconformity which marks the close of the Albian Stage. The Ahmadi is, therefore, believed to be wholly Cenomanian in age in Qatar.
Qatar lies close to the eastern limit of the typical, argillaceous facies of the Ahmadi. Progressive eastwards replacement of shales by limestones occurs until, in Abu Dhabi, the Ahmadi has been wholly replaced by thick shelf limestone assigned to the Mishrif Fm.