Araej Fm
Type Locality and Naming
Q.P.C. Well Kharaib No. 1, lat 25°27’09”N, long. 51°11’56” E, elevation 41.5 m (136 ft), completed 29.6.1953, between drilled depths 2137 and 2316 m (7010 and 7600 ft).
W. Sugden (unpublished report). The formation takes its name from the Jebel Araej in Southern Qatar.
Synonym: “Upper and Middle Dhruma Formation” Powers et al., 1966. “Araej Formation”, Dominguez, 1965. “Araej Formation”, Dunnington, 1967. “Araej Formation”, Fox and Brown, 1968.
Reference Section:
Lithology and Thickness
Top 1. Limestone, grey, foraminiferal, pellet-grainstone and packstone with some interbedded wackestone and lime mudstone. Pellets often black and pyritic. Some horizons argillaceous. 31 m (102 ft). 2. Limestone; buff, medium to coarse grained, bioclastic pellet-lump grainstone to packstone, porous; particles of buff colour without pyrite staining. 59 m (193 ft). 3. Limestone, light to dark grey, compact to dense, comprising interbedded pyrite-stained pellet grainstone and packstone, wackestone and lime mudstone. Occasional beds of calcite-cemented oolite 61 m (201 ft). 4. Limestone, grey wackestone to lime mudstone, with some interbedded pellet packstone and occasional grainstone; pellets rarely pyrite stained; some horizons silty. 28.6 m (94 ft). Base. Thickness is 180 m (590 ft)
The Upper Araej (Unit 1), typified in Qatar by pellet grainstone and packstones with abundant Trocholina palastiniensis, must be related to the Hisyan Member, which contains numerous limestones bearing the same foraminifera in similar facies. The Upper Araej is itself widely recognized in S.E. Arabia. In Qatar the upper limit of the Araej Fm is sharply defined, with marked lithologic and faunal difference from the overlying Diyab Fm. To the east, away from the Qatar axis, the unit thickens and passes gradationally into the Diyab by gradual reduction of coarse pellet debris and increase of fine lime mudstone and fine pellet calcarenite. In such situations it is not always possible to select a precise formation boundary. The thin Upper Araej development and its sharp contact with the Diyab, in the Qatar area, is suggestive of a sedimentary break between the two formations.
The contact of the Uwainat Member (Unit 2) with the Upper Araej is abrupt but conformable, with no evidence of erosion or non-deposition. Its lithology is pure, carbonate, grainstone to packstone with interbedded lime mudstones.
Relationships and Distribution
Lower contact
Izhara Fm. Contact conformable. At junction of impure, silty, pellety, grey limestones of the basal Araej, above, with buff, pure, wackestone and packstone of the upper Izhara, below.
Upper contact
Diyab Fm, contact probably disconformable. At sharp junction of highest, coarse, pyritic, trocholina-bearing grainstone of the Araej Formation with argillaceous lime mudstones and fine pellet limestones of the basal Diyab.
Regional extent
This formation is widespread in S.E. Arabia being known throughout Qatar, in the subsurface, in Bahrain, and Saudi Arabia, underlying much or all of the Trucial States and passing in attenuated form into Oman.
Correlation of the Araej Fm with the Upper and Middle Dhruma Fm of Saudi Arabia has been accepted for some time. The equivalence of the “Fadhili Zone” (now the Lower Fadhili Reservoir) to the Uwainat Member of the Araej (unit 2, above) was the key to this correlation. The publication of detailed descriptions by R.W. Powers et al., 1966, makes accurate correlation with the Saudi Arabian outcrop section possible.
The Atash Member of the Upper Dhruma is undoubtedly the equivalent of the Uwainat Member of the Araej Fm. Both are typified by the Pfenderina trochoidea assemblage which appears to be restricted to this unit in Arabia.
The Uwainat Member passes down gradationally into the Lower Araej. The latter is correlated with the Middle Dhruma because of its conformable position beneath the equivalent of the Upper Dhruma and above the Izhara Formation, whose upper member is believed to coincide in position and age with the Dhibi Limestone Member. Can be traced over a large part of eastern Arabia, where it forms an important oil reservoir.
GeoJSON
Fossils
In 1. Chlamys curvivarians Dietrich, Terebratula cf. superstes Douville, Trocholina palastiniensis Henson, Nautiloculina oolithica Mohler, Kurnubia sp. In 2. Cladocoropsis cf. zuffardiae Wells, Stromatoporina cf. somaliense Zuffardi-Comerci, Camptonectes sp., N. oolithica, T. palastiniensis, Pfenderina neocomiensis Pfender, P. trochoidea Smout and Sugden. In 3. N. oolithica, T. palastiniensis, Pfenderina sp. In 4. N. oolithica, Pfenderina sp. In addition to the above, there occur throughout the formation, but particularly in unit 2, a number of simple arenaceous fossils which have not been named and, also fossils referred to Paleotrix Farasin. (The fossil recorded above as P. neocomiensis is now believed to more closely relate to P. salernitana Sartoni and Crescenti).
Uwainat Member typically yields a foraminiferal assemblage including Pfenderina trochoidea Smout and Sugden.
Age
Depositional setting
Additional Information