Nahr Umr Fm
Type Locality and Naming
Is in B.P.C. Well Nahr Umr No. 2, in South Iraq. R.M.S. Owen and S.N. Nasr, 1958.
Synonym: “Nahr Umr Formation”, Dunnington et al., 1959. “Nahr Umr”, Dominguez, 1965. “Wasia Shale”, Hajash, 1967. “Nahr Umr Shale Formation”, Tschopp, 1967. “Wasia Shale and Nahr Umr”, Dunnington, 1967. “Nahr Umr”, Fox and Brown, 1968. “Nahr Umr”, Al Naqib, 1967.
Reference Section:
Q.P.C. Well Dukhan No. 26, lat 25°20’54” N, long. 50°48’47” E, elevation 24.4 m (80 ft), completed 14.1.1952, between drilled depths 999m and 1167 m (3278 and 3828 ft).
Lithology and Thickness
Top. 1. Sandstone, grey and greenish grey, glauconitic, rather marly, with numerous thin beds of blue-grey shale and marl and a few thin beds of grey limestone. 32 m (105 ft). 2. Shale, blue-grey and brownish grey, with frequent beds of blue-grey marl. Occasional thin beds of marly, glauconitic sandstone in the upper half. The marl beds commonly contain ferruginous ooliths. 71 m (233 ft). 3. Sand and sandstone, grey, rather marly and with numerous thin beds of marl and shale of various colours. Many stringers and occasional thin beds of lignite yield abundant resin fragments. The more marly parts often incorporate light brown phosphatic concretions or ferruginous ooliths. 65 m (212 ft). Base. Its thickness is 168 m (550 ft)
Relationships and Distribution
Lower contact
Shu’aiba Fm; contact believed disconformable. Placed at sharp change from limestone, below to sands and silts, above. The chronological list of current rock units indicates the next older unit as Thamama Gr
Upper contact
Mauddud Fm; contact at conformable boundary between arenaceous to argillaceous clastic sediments, below, and limestone above.
Regional extent
Occurs in the subsurface throughout Qatar. Is present in much of eastern Arabia, from Iraq to Oman, in varying lithofacies.
GeoJSON
Fossils
In 1. Trocholina lenticularis Henson, Trocholina arabica Henson, Trocholina altispira Henson, Cyclammina whitei Henson. In 2. T. lenticularis.
Age
Depositional setting
Additional Information
Qatar is close to the limit of coarse clastic deposition in the Nahr Umr Fm, which becomes almost wholly composed of shale a short distance to the east.
The application of one formation name to a widespread rock unit which varies from almost pure sand at one extreme to pure shale or shale with interbedded limestone at the other results from the nature of the type section of the Nahr Umr. This section includes sand, shale and limestone (K.M. al Naqib, 1967) and, hence, can be considered as representing all possible facies variations.
With the exception of Cyclammina whitei, the foraminiferal fauna recorded above could have resulted from contamination of well samples from the overlying Mauddud Fm.