Al Bayda Gr

Period:

Paleogene

Age Interval:

Rupelian

Province:
Cyrenaica Basin

Type Locality and Naming

According to Shaltami et al. (2020), this group consists of a lower Shahhat Fm separated by a major hiatus (ca. 40% of the Rupelian) from the overlying Marawah Fm. [Neither of those formations were indicated on stratigraphic charts in other publications consulted during preparation of this lexicon.]

Synonym: Al Bayda Fm

References: Shaltami, O.R., et al. (2020), and Google Gemina (Aug’26)

Lithology and Thickness

The formation is formally split into two distinct lithological members (from Google Gemini overview):

Algal Limestone Member (Upper) (Marawah Fm): Characterized by hard, bioclastic limestones, calcarenites, and rich coralline algal (rhodolith) accumulations, alongside thick accumulations of macrofossils (such as disarticulated oysters, gastropods, and echinoids like Clypeaster).

Shahhat Marl Member (Lower) (Shahat Fm): Consists predominantly of soft greenish-gray to yellowish marls, marly limestones, and detrital beds. It is notable for containing reworked bioclasts and fossils washed in from the older underlying Eocene strata.

Lithology Pattern:

Shallow-marine marl

Relationships and Distribution

Lower contact

Unconformable onto the Salantah Fm according to Shaltami et al. (2020). The basal disconformity onto the Salantah Fm marks a widespread tectonic event and sea-level fall at the Eocene–Oligocene boundary, which initiated a new post-Eocene depositional cycle across northern Africa.

Upper contact

Unconformably overlain by the Massah Fm of the Al Abraq Gr according to Shaltami et al. (2020).

Regional extent

GeoJSON

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Fossils

See lithology descriptions -- oysters, gastropods, and echinoids like Clypeaster, etc.

Age

Rupelian according to Shaltami et al. (2020). [For graphic purposes, the extent of the upper and lower unconformities, which are equivalent to nearly the same time span of the known preserved deposits, have been omitted here.]

Age Span:

Beginning stage:

Rupelian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

33.90

Ending stage:

Rupelian

Fraction up in the ending stage:

1.0

Ending date (Ma):

27.29

Depositional setting

“The sequence records a shallowing-upward marine trend. It begins with open, lower-energy shallow-shelf marls (Shahhat Member) and transitions into high-energy shallow-water platform Shoals and algal banks (Algal Limestone Member).” (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.

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.