Sirte Shale Formation

Sirte Shale Fm

Period:

Cretaceous

Age Interval:

Campanian

Province:
Sirte Basin

Type Locality and Naming

The Sirte Shale is considered the main source rock in the Sirt Basin. It is the upper unit of the Rakb Gr is the Sirte Fm.

Synonym: Sirte Fm, Sirt Fm, Sirte Shale, Sirte Shales, Sirt Shale, or Sirt Shales. It is coeval to the Tagrifet Limestone elsewhere in the Sirte Basin.

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

Lithology and Thickness

It consists of a dark-grey to brown organic-rich shale succession with minor limestone interbeds. Occasionally, the shale is calcareous, silty, sandy and glauconitic or pyritic with small phosphatic nodules in the lower part (Abugares, 2007). The Sirte Shale attains an average thickness of about 270 ft (Selley, 1997), increasing towards the troughs in the Sirt Basin and thinning towards palaeohighs of the Sirt Basin. The marine shales are interbedded with limestones.

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

It conformably overlies the Rachmat Fm.

Upper contact

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

Regional extent

It is widely distributed throughout the grabens of the Sirt Basin.

GeoJSON

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Fossils

Foraminifera

Age

entire Campanian (Abdalla et al., 2026), but may also range to lower Maastrichtian.

Age Span:

Beginning stage:

Campanian

Fraction up in beginning stage:

0.00

Beginning date (Ma):

83.65

Ending stage:

Campanian

Fraction up in the ending stage:

1.0

Ending date (Ma):

72.17

Depositional setting

Deep marine shales (Abdalla et al., 2026); but “this formation was initially deposited in a shallow restricted marine environment, rapidly subjected to deepening” (Abugares, 2007).

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.