Aruma Gr
Type Locality and Naming
R.M. Owen and S.N. Nasr, 1958. An intra-Campanian unconformity described from Kuwait and South Iraq can also be recognised in Qatar and other regions to the south-east. The type Aruma Formation, which occurs at outcrop in the scarp of the Al’ Aramah plateau of Saudi Arabia, includes Upper Campanian to Maestrichtian sediments which fall wholly above this unconformity. The application of the name Aruma to a Group or a Formation including units which are separated by an unconformity from the type Aruma is of doubtful validity (H.V. Dunnington, 1967). The practise has become accepted over so long a period that it is retained in Qatar.
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Lithology and Thickness
Four formations are currently assigned to the Aruma Group in Qatar. These are the Simsima Formation (Maestrichtian), Ruilat Formation (Campanian), Halul Formation (Campanian-Santonian), and Laffan Formation (Santonian-Coniacian). From 1940 to 1953, a predominantly limestone unit which underlies the Umm er Radhuma Formation and overlies the Laffan Shale was included, by Q.P.C., in one formation. Because the only datable section was Maestrichtian, this limestone was named the Tayarat Formation by comparison with a formation of that age in Iraq.
Relationships and Distribution
Lower contact
The Aruma Gr is separated by sedimentary breaks from the underlying Mishrif Fm. The chronological list of current rock units indicates the next older unit as Simsima Fm
Upper contact
The Aruma Gr is separated by sedimentary breaks from the overlying Umm Er Radhuma Fm
Regional extent
The Aruma Group of Owen and Nasr is similar to the Aruma Formation of Saudi Arabia, where it is most fully developed in the subsurface. The application of Group status to a thick, heterogeneous rock unit, which has retained formation rank in its country of origin, results from the fact that many of its component rock units were validly assigned formation rank at an early date.
GeoJSON
Fossils
Age
Depositional setting
Additional Information
When this sequence was subsequently subdivided into two rock units, the younger, of Maastrichtian age (truly synonymous with Tayarat) became known as the Simsima Fm to avoid local confusion. The underlying, undated, limestone was named the Ruilat Fm. Detailed structural and paleontological studies had, meanwhile, proved that a major unconformity occurs below the Laffan Shale, indicating that it is more closely related to the overlying, conformable Ruilat Fm. Recent inter-company liaison has resulted in the recognition of an unconformity within the original Ruilat Fm. The lowest part is therefore segregated from it and assigned to the Halul Fm, which was originally recognized in offshore Qatar.
At the same time, convincing evidence that the Laffan Shale Fm is no older than Coniacian was discovered, thus settling a long-standing controversy of regional importance.