Rakb Gr

Period:

Cretaceous

Age Interval:

Coniacian - Campanian

Province:
Sirte Basin

Type Locality and Naming

Within the Rakb Gr are the Sirte Fm (otherwise known as Sirte Shale, Sirte Shales, Sirt Shale, or Sirt Shales), the Rechmat Fm (Rachmat Fm.), and the Arguib Fm (also known as the Arguib Carbonates, Etel Fm) (Ahlbrandt, 2001).

Synonym:

References: Selley, 1997; Ahlbrandt, 2001; Abugares, 2007

Lithology and Thickness

The top of the Rakb Gr. is equivalent to the Sirt Shale (Sirte Shale, or Sirte Fm) (Ahlbrandt, 2001). The Sirte Shale attains an average thickness of about 270 ft, and is made up of dark grey to dark brown organic rich shale (Selley, 1997). The mid-section of the Rakb Gr is equivalent to the Rechmat Fm, while the base of the group is equivalent to the Arguib Fm. The Rachmat Formation consists of shales interbedded with minor limestones, sandstones and dolomites. The shales are dominantly grey, fissile to slightly blocky, to slightly non-calcareous, and glauconitic and pyritic in many locations. The Rachmat Fm has a maximum thickness of up to 600 m in the Agedabia Trough (Abugares, 2007). The Arguib Fm (The Aragub carbonate is regarded as a basin-ward equivalent of the Etel Formation) consists of thin-bedded carbonates, shale, anhydrite, siltstone and sandstone – with its thickness ranging from 660 m in the Hagfa Trough to over 700 m in the Hameimat Trough.

Lithology Pattern:

Clayey limestone

Relationships and Distribution

Lower contact

It unconformably overlies the Lidam Fm.

Upper contact

It is conformably overlain by the Kalash Limestone Member of the Satal Fm.

Regional extent

GeoJSON

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Fossils

Foraminifera

Age

mid-Turonian through Campanian (Abdalla et al., 2026)

Age Span:

Beginning stage:

Turonian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

91.65

Ending stage:

Campanian

Fraction up in the ending stage:

1.0

Ending date (Ma):

72.17

Depositional setting

Open marine (Selley, 1997).

Depositional pattern:

Additional Information

Compiler:

T. S. Ahlbrandt (2001): The Sirte Basin Province of Libya—Sirte-Zelten Total Petroleum System, U.S. Geological Survey Bulletin 2202–F

R.C. Selley (1997): The Sirte Basin of Libya. In: African Basins. Sedimentary Basins of the World, 3, edited by R.C. Selley (Series Editor: K.J. Hsu), Elsevier Science B.V., Amsterdam, pp. 27-37.

Abugares, Miloud M. (2007): Deposition, Diagenesis, and Reservoir Development of the Cretaceous Lidam Formation, SE Sirt Basin, Libya. Durham e-Theses. http://etheses.dur.ac.uk/2599/

Elkanouni, I. E. D. (2014). Sedimentology, Sequence stratigraphy and Spatial-temporal Patterns of the late Paleocene Succession, western Sirt Basin, Libya, Durham e Theses. http://etheses.dur.ac.uk/10538/

Abdalla, M, Abdelnabi, A., Zubi, H., Qaysi, S. (2026): Depositional architecture and reservoir quality evaluation of the Early Cretaceous El Abd Sandstone Member: An integrated sedimentologic and diagenetic approach, eastern Sirte Basin, Libya. Jour. Sedimentary Environments, 11:41. https://doi.org/10.1007/s43217-026-00311-7.