Darb Fm
Type Locality and Naming
Q.P.C. Well Dukhan No. 51 (formerly Juh. No. 1), Lat 24°53’48” N long. 50°59’55” E, elevation 76.5 m (252 ft), completed 25.10.1952, between drilled depths 2166 and 2377 m (7107 and 7800 ft). The formation takes its name from the Ta’as al Darb, a solitary sand dune near the type locality, which marks the ancient track to Mecca. W. Sugden (unpublished report)
Synonym:
Reference Section:
Lithology and Thickness
Top 1. Limestone, grey and light grey, lime mudstone, compact to dense. Dolomite streaks and bands of pyrite-stained pellet packstone. 50 m (163 ft). 2. Limestone, dark grey lime mudstone, dense with rare streaks of pyritic pellet packstone. 53 m (174 ft). 3. Limestone, grey lime mudstone, dense, becoming argillaceous downwards: numerous thin beds contain scattered, large, pyrite-stained pellets. 40 m (131 ft). 4. Limestone, dark grey, dense, lime mudstone, becoming increasingly argillaceous towards the bottom. 68 m (225 ft). Base. Thickness is 211 m (693 ft).
Relationships and Distribution
Lower contact
Diyab Fm; contact conformable, placed at the position were dense, argillaceous lime mudstone of the basal Darb Formation rests upon fine, calcarenitic limestone with interbedded, very argillaceous lime mudstone of the uppermost Diyab Formation.
Upper contact
Fahahil Fm (Arab No. 4 Limestone); contact conformable. In type section placed at boundary between fine lime mudstone of the Upper Darb Formation and porous dolomite of the basal Fahahil Formation. At other localities in Dukhan and, more markedly, to the east, the uppermost Darb Formation becomes increasingly dolomitised. As a result, an additional porous section is added to the base of the Fahahil Formation, at the expense of the Darb Formation.
Regional extent
Well established as a separate formation only in the Qatar area, where it has been encountered in many deep wells.
The typical Darb facies can be traced into the Trucial States, where it has not, however, proved possible to separate with confidence a Darb and a Diyab Fm within the interval bounded by the Fahahil Fm and the Araej Fm. It is normally possible to distinguish an argillaceous lower unit which could be compared in general with the Diyab Fm. This facies is, however, variably developed and sometimes almost absent.
The Darb Fm must be the lateral equivalent of most, or all, of the Jubaila and Hanifa Formations of Saudi Arabia. The latter names have not been adopted in Qatar because it has not proved possible to trace their exact lithological equivalents.
GeoJSON
Fossils
In 1. Kurnubia jurassica (Henson), Kurnubia cf. wellingsi (Henson), Pseudocyclammina jaccardi (Schrodt). In 2 and 3. K. jurassica, K. cf. wellingsi, P. jaccardi, Nautiloculina oolithica Mohler, Pseudocyclammina cf. virguliania Koechlin. In 4. P. jaccardi, P. cf. virguliania, N. oolithica, K. jurassica. In the lowest two feet Exogyra nana (J. Sowerby).
Age
Depositional setting
Additional Information