Tulmithah Formation

Tulmithah Fm

Period:

Paleogene

Age Interval:

Ypresian

Province:
Cyrenaica Basin

Type Locality and Naming

“The Tulmithah Formation (named after the coastal town of Tulmithah or Tolmeita, the site of ancient Ptolemais in northern Cyrenaica) is an Early Eocene lithostratigraphic unit recognized in modern revisions of the Cyrenaica Basin's subsurface and surface stratigraphy. Historically, geologists lumped all deeper Eocene open-marine chalks and cherts into a broad Apollonia Fm. High-resolution biostratigraphic studies identified a distinct unconformity and missing time interval (a gap in the Middle Ypresian) within that sequence. Stratigraphers proposed the Tulmithah Fm to isolate and define the lower, older portion of the original Apollonia unit.” (from Google Gemini overview -- citing Shaltami, Fares et al., 2021. “Eocene deposits of the Cyrenaica Basin”, chapter 4 in book “Isotope Geochronology of the Exposed Rocks in the Cyrenaica Basin, NE Libya” published by Springer Briefs in Earth System Science)

Synonym:

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

Lithology and Thickness

Primarily comprised of fine-grained pelagic chalk, chalky limestones, and clayey calcilutites interbedded with dark, ribbon-like chert (flint) nodules and thin marls.

Lithology Pattern:

Chalk

Relationships and Distribution

Lower contact

Unconformable onto the Al Uwayliayah Fm according to Shaltami et al. (2020). Locally, it can “rest above Cretaceous units (such as the Upper Cretaceous Al Hilal Fm or Al Athrun Fm) across a regional tectonic boundary”

Upper contact

Unconformably overlain by the Apollonia Fm according to Shaltami et al. (2020).

Regional extent

GeoJSON

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Fossils

Age

Ypresian 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:

Ypresian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

56.00

Ending stage:

Ypresian

Fraction up in the ending stage:

1.0

Ending date (Ma):

48.07

Depositional setting

“Represents deep, open-marine slope-to-basin shelf deposition along the northern continental margin of Libya during the early Paleogene transgressive highstand.” (Google Gemini overview)

Depositional pattern:

Additional Information

“Tectonic Significance: Along the coastal exposures between Tukrah and Tulmithah, this unit frequently displays prominent slump folds, syn-depositional faulting, and submarine slide structures. These deformation features record early tectonic activity associated with the Syrian Arc compressive event and the initial uplift phase of the Al-Jabal al-Akhdar structure.” (Google Gemini overview)

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.