Sirual Gr

Period:

Jurassic

Age Interval:

Aalenian-Oxfordian

Province:
Cyrenaica Basin

Type Locality and Naming

The Sirual Fm “takes its name from the Sirual Trough (a regional east-west structural depression that opens westward toward the Antelat Trough along the southern/western margins of the Cyrenaica Platform). “Shaltami et al. (2020a) raised the Sirual Fm to group status and divided into the lower Ghurab Fm and the upper Mallegh Fm based on 207Pb/ 235U isotope analysis that referred to the Middle Jurassic (the upper Bathonian is not present; lost time = 1 Ma).” (Shaltami et al., 2022).

Synonym: Maybe equivalent is (and transitions into) the Chameau Mort Fm in the coastal-to-shallow platform marine deposits, although the Chameau Mort Fm begins earlier (Google Gemini overview).

References: El Oshebi and Fares (2026). Shaltami et al., 2022, and Google Gemina (Aug’26)

Lithology and Thickness

Shallow-marine limestone (diagram of El Oshebi and Fares, 2026). However, the upper unit -- the Mallegh Fm -- is “characterized by marlstone with strikes of calcareous sandstones” (Shaltami et al., 2022). The lower unit – the Ghurab Fm – is also “marls and limestones with minor clastic components” (Google Gemini overview). Both are deep-water

Lithology Pattern:

Pelagic marl

Relationships and Distribution

Lower contact

Unconformity (entire upper Permian through early Jurassic is absent) onto the lower-Permian Al Watyah Fm. [However, there may be some Triassic units – unclear.]

Upper contact

Overlain (unconformably?) by the Qahash Fm,

Regional extent

“It forms part of the deep Mesozoic syn-rift and post-rift succession in subsurface well sections (such as offshore well B1-120 and onshore wells like A1-152 on the Al-Jabal al-Akhdar uplift).” (Google Gemini overview). [Probably equivalences, nomenclature and age spans of the Middle and Late Jurassic (and earliest Cretaceous) depends upon the local troughs and highs, which is not clarified in the publications or online tools that have been consulted for this Lexicon entry.]

GeoJSON

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Fossils

The upper unit of the Mallegh Fm is “contains pelecypods, echinoderms, fossil fragments, and planktonic foraminifera (Shaltami et al., 2022). The lower unit of Ghurab Fm “contains a predominantly planktonic fauna” (GeoGPT overview).

Age

Spans the Middle through Late Jurassic according to the stratigraphic diagram in El Oshebi and Fares (2026). The upper Mallegh Fm is latest Bathonian through late Oxfordian (the upper Bathonian is not present; lost time = 1 myr) (implied in Shaltami et al., 2022). Therefore, tentatively, the lower Ghurab Fm is Bajocian(?) through middle Bathonian.

Age Span:

Beginning stage:

Bajocian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

170.90

Ending stage:

Kimmeridgian

Fraction up in the ending stage:

1.0

Ending date (Ma):

149.24

Depositional setting

It represents the deeper syn-rift, graben-fill facies deposited simultaneously in subsiding structural depressions (such as the Sirual Trough).” (Google Gemini overview)

Depositional pattern:

Additional Information

Compiler:

Shaltami, O.R., et al. (2020). Petroleum system of the Cyrenaica Basin – A review. In: 1^st International Symposium on Geosciences (ISG2020), 21th March 2020, Proceeding Book: published by BR Petrobras. P. 64-71.

Shaltami, O. R., F. F. Fares, R. B. Elojaly, A. E. Algomati, O. A. Geniber, F. M. El Oshebi, M. Abioui, A. A. Rhouma, andB. El Abedi (2022), Mallegh Formation in wells A1–152 and B1–120, source rock evaluation for hydrocarbon generation withinthe Cyrenaica Basin, northeastern Libya: SAGE Record 098, 11 p., <https://sagetech.org/sage_record_098_shaltami_et_al/>.Oral presentation at SAGE/ESSL BIGEC 2022, 30 Aug.–01 Sept. 2022, Benghazi, Libya, and Online.

Tawadros, E.E. (2011). Geology of North Africa. CRC Press (Taylor & Francis Group), 931 pp.

Google Gemini (Aug 2026) – assembled synthesis of Cyrenaica Basin units from various web-accessible publications.

El Oshebi, F.M., Fares, F.F. (2026). Stratigraphy, facies, and depositional environments of the Eocene sequence in the Ras Al Hilal area, Cyrenaica, Libya. Arabian Jour. Geosciences, 19:79. https://doi.org/10.1007/s12517-026-12488-2.

El-Hawat, A.S., Abdulsamad, E.O. (2004) Geology and Archeology of Cyrenaica, Northeastern Libya. Field trip guide B01, 32^nd International Geological Congress. 36 pp.