Qahash Fm
Period:
Cretaceous
Age Interval:
Berriasian-Barremian
Province:
Cyrenaica Basin
Type Locality and Naming
Synonym: Kahash Fm
References: El Oshebi and Fares (2026). and Google Gemina (Aug’26)
Lithology and Thickness
Coal and shale (diagram of El Oshebi and Fares, 2026). Or “High-thickness, continental fluvio-lacustrine red and white quartzitic sandstones interspersed with carbonaceous shales and streaks of black coal.” (Google Gemini overview)
Lithology Pattern:
Coal
Relationships and Distribution
Lower contact
Unconformable onto Jurassic of the Sirual Fm (south and central Cyrenaica Basin) or its equivalent Malieg Fm (coastal and offshore Cyrenaica Basin) (El Oshebi and Fares, 2026)
Upper contact
Conformable overlain by the Daryanah Fm.
Regional extent
subsurface of the Cyrenaica Basin and eastern Sirt Basin.
GeoJSON
{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[24.38,28.97],[24.44,29.45],[23.6,29.81],[21.28,29.89],[20.27,32.06],[20.25,33.14],[20.67,33],[23.31,33.18],[24.38,32.55],[24.99,32.54],[25.2,31.39],[26.18,29.37],[24.38,28.97]]]}}
Fossils
“Well cuttings and core samples yield distinct Early Cretaceous palynomorph assemblages. The presence of key spores such as Crybelosporites striatus, Afropollis species, and early monosulcate pollen (e.g., Afropollis jardinus) marks the Neocomian–Aptian transition. Dinoflagellate Cysts: Marine-influenced interbeds toward the top of the formation contain Aptian-aged microplankton (dinoflagellates), confirming that the top of the unit reaches into the Early Aptian before grading into the fully marine Bir Hacheim Fm shales.:
Age
Spans the Berriasian through Barremian according to the stratigraphic diagram in El Oshebi and Fares (2026). However, the Google-Gemini review of logic for the age assignment concludes it is “Barremian to early Aptian”. Therefore, as a compromise, a Hauterivian to earliest Aptian span is adopted here.
Age Span:
Beginning stage:
Hauterivian
Fraction up in beginning stage:
0.0
Beginning date (Ma):
132.60
Ending stage:
Aptian
Fraction up in the ending stage:
0.2
Ending date (Ma):
119.76
Depositional setting
“Records a continental to marginal-marine transgressive sequence. Deposition occurred in high-energy fluvial, delta-plain, and estuarine environments before the regional marine transgression that deposited the overlying Bir Hacheim Fm shales took over.” (Google Gemini overview)
Depositional pattern:
Additional Information
:
Compiler:
s:Shaltami, O.R., et al. (2020). Petroleum system of the Cyrenaica Basin – A review. In: 1st 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, 32nd International Geological Congress. 36 pp.