Laffan Shale Fm
Type Locality and Naming
Originally described from the interval 610 to 631 m (2002 and 2072 ft) in Q.P.C. Well Dukhan No. 25. The type section is here selected as Well Dukhan No. 55 lat. 25°24’0” N, long. 50°45’46” E. elevation 7 m (23 ft), completed 17.8.1956, between drilled depths 584 and 613 m (1916 and 2011 ft). The formation takes its name from Ras Laffan, on the north-east coast of Qatar. W. Sugden, 1953 (unpublished report)
Synonym: “Laffan Formation”, Dominguez, 1965. “Middle Shale”, Hajash, 1967. “Laffan Shale”, Fox and Brown, 1968.
Reference Section:
Lithology and Thickness
Shale, olive-green. Its thickness is 29 m (95 ft).
Relationships and Distribution
Lower contact
Mishrif Fm, contact unconformable. Shales of the Laffan overlie chalky, fossiliferous limestones of the Mishrif. On the Dukhan structure, crestal cut-out of beds of the Mishrif beneath the contact can be demonstrated. The chronological list of current rock units indicates the next older unit as Wasia Gr
Upper contact
The Da’asah Member of the Halul Fm overlies the Laffan with apparent conformity. The contact, of shales with argillaceous lime mudstones, is sharp.
Regional extent
Found in deep wells throughout onshore and offshore Qatar and much of Abu Dhabi. Also known from Bahrain and parts of Iraq.
GeoJSON
Fossils
The Laffan of the type section has yielded few fossils. The typical ostracod fauna of the Laffan Shale of Dukhan has been described in an unpublished thesis by Sayyab, 1956. All species are new.
Age
Depositional setting
Additional Information
The Laffan Shale Fm is typically a marine, ostracod-bearing shale which comprises the basal unit of the Aruma Gr over a wide area. Its age and affinities were in dispute until recent palynological investigation indicated a Coniacian to Santonian age placing it firmly in the Aruma Gr. This position is also indicated by its unconformable relationship to underlying components of the Wasia Gr.
When first encountered in Qatar the Laffan Shale was included with an older shale-limestone sequence in the so-called Khatiyah Fm. By 1949 it was apparent that a major unconformity occurred at the base of the Laffan in Dukhan. The unit was then removed from the Khatiyah Fm.