Halul Fm
Type Locality and Naming
S.C.Q. Well Id-al-Shargi No. 1, lat. 25°23’32.9” N, long. 52°21’55.93” E, between drilled depths 1009 and 1081 m (3310 and 3545 ft.). The formation takes its name from the island of Halul, off the east coast of Qatar. M.W. Hughes-Clarke, 1963 (unpublished report)
Synonym: “Halul Formation”, Dominguez, 1965 (first published reference). “Ilam Formation”, James and Wynd, 1965. “Middle Chalk”, Hajash, 1967. “Aruma Lower Limestone”, Fox and Brown, 1968.
Reference Section:
A widespread and persistent rock stratigraphic unit, which can be recognised by its characteristic foraminiferal assemblage.
The lower part (units 3 and 4) of the type section represent the only part of the Halul Formation to be recognised in onshore Qatar. This unit has been named the Da’asah Member after a locality south of Q.P.C. Well Dukhan No. 55, the site of the reference section, described below. Q.P.C. Well Dukhan No. 55, lat. 25°24’0” N. long. 50°43’46” E, elevation 7 m (23 ft), completed 17.8.1956, between drilled depths 570 and 584 m (1870 and 1906 ft).
Lithology and Thickness
The following description is adapted from one by W.O. Gigon, P.J.C. Hoogkamer and I.W.G. Hughes of S.C.Q. Top. 1. Limestone, light grey, chalky bioclastic lime packstone, particles consisting of larger foraminifera with some smaller foraminifera, ostracods and shell fragments. 27 m (90 ft). 2. Limestone, light grey, chalky bioclastic lime wackestones, particles consisting of spicules, small shell fragments with some smaller foraminifera and larger foraminifera, some pyrite and scattered dolomite rhombs. 21 m (68 ft). 3. Marl, grey-green, soft with some shale, blue-grey and some limestones, light grey-light brown, chalky, partly recrystallised. 8.6 m (27 ft). 4. Chalk, light grey, soft, frangible, occasionally slightly marly, with limestones, light grey and light brown, chalky, partly recrystallised, shell fragments in places. 15 m (50 ft). Base. Its thickness is 72 m (235 ft). Lithology in reference section is Top. 1. Limestone; light grey, fine, compact, partly silicified lime mudstones to wackestones. 10 m (32 ft). 2. Limestone, grey, argillaceous lime mudstone. 4 m (14 ft). Thickness in reference section is 14 m (46 ft).
Relationships and Distribution
Lower contact
Olive-green shales and marls of the Laffan Shale Fm conformably underlie the light grey, chalky wackestones of the Halul Fm. In reference section, Laffan Shale Fm, contact conformable. At sharp change from lime mudstone above, to shales of the Laffan Shale Fm below.
Upper contact
Fiqa’ Fm; the basal brown calcareous shales of the Fiqa’ overlie light grey, chalky lime-packstones of the Halul Fm. Contact believed to be unconformable. In reference section, Ruilat Fm, contact disconformable. At junction of grey lime wackestone of the Da’asah Member of the Halul Fm with glauconitic limestones of the basal Ruilat Fm. This contact represents a major hiatus within the Aruma Gr, equivalent to the pre-Hartha unconformity of south Iraq.
The Da’asah Member of onshore Qatar was originally the basal part of the Ruilat Fm. Recent comparison with offshore sections illustrated its similarity to a basal member of the Halul Fm to which formation it is now assigned.
Regional extent
Of limited development in onshore Qatar where only the lower, Da’asah Member is recognized. Well developed in offshore Qatar and in central, north and parts of eastern Abu Dhabi, whence it thins rapidly to the south and east. Apparently not present in Oman. The basal member of the Halul Formation of offshore Qatar can be correlated with a thin limestone section which overlies the Laffan Shale Formation in the Dukhan Field.
The Halul Formation probably equates with a unit containing a faunule composed chiefly of Kathina sp. and Cosinella sp. which occurs in the subsurface of eastern Saudi Arabia, (R.W. Powers, 1968). The S’adi Formation of south Iraq and the Ilam Formation of south-west Iran are equivalents of the Halul Formation.
GeoJSON
Fossils
In 1. Pseudedomia sp.(p), (P. aff. complanata-globularis), Rotalia aff. trochidiformis Lamarck, Dicyclina cf. schlumbergeri Munier Chalmas, Kathina sp. nov., Dictyokathina sp. nov., Rotalia sp. nov., ostracods, spicules, echinoid fragments, ?Oligostegina. In 2. Pseudedomia aff. complanata-globularis, Rotalia aff. trochidiformis Lamarck, Kathina sp. nov., Rotalia spp. Nov., spicules,? Oligostegina. In reference section, In 1. small indeterminable foraminifera, probably including Heterohelix sp..
Age
Depositional setting
Additional Information