Mesozoic • Cretaceous In GSP lexicon

Sembar Formation

Early Cretaceous (Berriasian-Barremian)

Cited in 12 sources Last reviewed Aug 10, 2026

Unit summary

Rank: Not recorded
Status: Published
Age: Mesozoic · Cretaceous · Early Cretaceous (Neocomian)Early Cretaceous (Berriasian-Barremian)
Named by: Williams (1959)
Type locality: Sembar Pass, Sulaiman Range29.9181°N, 68.5800°E
Thickness: 100-300 m
Lithology: Black, carbonaceous, pyritic shale with subordinate siltstone, sandstone and thin limestone; thins westward.
Synonyms: Not recorded

An Early Cretaceous black shale — the main source rock that generated the gas in Pakistan's Indus Basin fields.

Major source rock for hydrocarbons in Indus Basin. Deposited in anoxic marine conditions. Equivalent to Chichali in upper Indus.

Fossils

Ammonites Belemnites Foraminifera

Contacts

In the Sulaiman Fold Belt column

LimestoneShale / mudFossils recordedConformable

Band colour = period; texture = dominant rock type. Lines between bands mark the contact type. True scale makes height ∝ recorded thickness; hatched = thickness not recorded. Ages approximate, for ordering.

This unit (highlighted) within its province column; faded ends continue above and below. Line style marks the contact type.

Distribution & setting

Sulaiman Fold Belt Kirthar Range Sindh Province

Basin: Not recorded
Region: Not recorded
Depositional environment: marine, outer shelf
Coordinates: 29.9181°N, 68.5800°E

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Correlation

Not recorded. Compare this unit against other basins on the correlation panel →

Economic significance

Source rock Reservoir

The principal hydrocarbon SOURCE ROCK of the Lower and Central Indus Basin (Sui, Mari and other gas fields); the Sembar–Lower Goru is an active petroleum system.

Remarks

An Early Cretaceous organic-rich marine shale that is the main petroleum source rock of the Indus Basin, deposited during Gondwana rifting as the Indian plate began to separate.

Research notes (9)

Field-by-field findings drawn from the cited literature. Every statement is traced to a registered source — follow a citation for the full reference.

Lithology (1)

Hemphill & Kidwai (1973, USGS PP 716-B): the Early Cretaceous (Neocomian) Sembar Formation (named by Williams 1959, type near Sembar Pass) is soft black claystone with dark limestone concretions and ferruginous calcareous sandstone near the base, resting on a ~4-ft basal conglomerate of belemnitic-limestone clasts derived from the Sulaiman Limestone Group; ~931 ft in the gorge west of Mughal Kot; the western equivalent of the Chichali Formation.

Hemphill, W.R. & Kidwai, A.H. (1973)

Thickness (3)

USGS OFR 94-689 (after Fatmi 1977) gives the Sembar Formation a type-section thickness of ~135 m in the Marri-Bugti area (~30 km east of the map area), thinning near Quetta and Ziarat; the black silty shale is glauconitic and pyritic with phosphatic nodules in the basal part and commonly bears belemnites.

Maldonado, F., Khan, S.H. & Mengal, J.M. (1994)
Type-section thickness (Shah, 2009): 133 m at type section; 262 m in the Moghal Kot section; reduced to a few m near Quetta/Ziarat; absent in parts of the Axial Belt and Kirthar Province. Type locality: ~2 km SE of Sembar Pass, Mari-Bugti area, Sulaiman Province. Recorded from the GSP lexicon (Memoir 22); the existing thickness field is retained.

Shah, S.M.I. (2009)
Umar et al. (2024): the Sembar Formation is thin in the Quetta–Ziarat areas but reaches ~900 m in the Pab Range (Fatmi & Zeiss 1994), 877 m in the Sann well (Lower Indus Basin) and 262 m at Mughal Kot — the main depocentres. The curated thickness is retained; these figures are noted as regional maxima.

Umar, M., Kassi, A.M., Jamil, M., Kasi, A.K. & Khan, A.S. (2024)

Type locality & location (1)

Published type section near Sembar Pass, eastern Quetta Division (lat 29 deg 55' 05" N, long 68 deg 34' 48" E) — Williams (1959).

Hemphill, W.R. & Kidwai, A.H. (1973)

Stratigraphic contacts (1)

Umar et al. (2024): the Sembar Formation lies disconformably on Jurassic carbonates (Chiltan Limestone), marked by a lateritic interval, and passes transitionally upward into the Goru Formation. It is the lateral equivalent of the Chichali Formation of the Salt–Surghar–Kala Chitta–Hazara region.

Umar, M., Kassi, A.M., Jamil, M., Kasi, A.K. & Khan, A.S. (2024)

Economic significance (2)

Khalid et al. (2014): the Lower Cretaceous Sembar Formation black shales are the principal hydrocarbon source rock of the Sembar–Goru petroleum system in the Indus Basin, charging the overlying Goru shoreface-sand reservoirs.

Khalid, P., Qayyum, F. & Yasin, Q. (2014)
Mehfooz, Javaid & Hamza (2022), Lower Indus Basin: a petrophysical and geochemical gas-shale evaluation of the Cretaceous Sembar Formation - isopach-average thickness ~600 m, average TOC >2 wt.% with Type II-III kerogen, ~4% gas-filled porosity, water saturation <70%, and maturity in the condensate/wet-gas window in the study wells.

Mehfooz, Z., Javaid, S. & Hamza (2022)

Geological significance (1)

Malkani et al. (2022): in North and South Waziristan the Early-Cretaceous Sembar-equivalent is named the Ahni Tangi Formation — green and red shales carrying large olistostrome blocks (olistoliths). Recorded as a Waziristan local-name equivalent (Malkani corpus); not adopted as a separate unit here.

Malkani, M.S., Ilyas, M., Yasin, R., Abbas, A., Samiullah, K., Raza, T., Hassan, S.S.E., Fazal, R.M., Noor, A. & Malik, A. (2022)

Sources (11)

Malkani, M.S. & Mahmood, Z. (2017). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 24.
Kazmi, A.H. & Jan, M.Q. (1997). Geology and Tectonics of Pakistan. Graphic Publishers, Karachi.
Iqbal, M. et al. (2017). Hydrocarbon exploration perspective in Middle Jurassic-Early Cretaceous reservoirs in the Sulaiman Foldbelt, Pakistan. (ResearchGate).
Indian Plate Lexicon (indplex.geolex.org), Geological Society of India and international compilation.
Hemphill, W.R. & Kidwai, A.H. (1973). Stratigraphy of the Bannu and Dera Ismail Khan Areas, Pakistan. U.S. Geological Survey Professional Paper 716-B (Geological Investigations in Pakistan), 36 p.
Maldonado, F., Khan, S.H. & Mengal, J.M. (1994). Preliminary Geologic Map of Parts of Loralai, Sibi, Quetta, and Khuzdar Divisions, Balochistan Province, West-Central Pakistan. U.S. Geological Survey Open-File Report 94-689, 20 p., 1 sheet.
Shah, S.M.I. (2009). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 22.
Khalid, P., Qayyum, F. & Yasin, Q. (2014). Data-Driven Sequence Stratigraphy of the Cretaceous Depositional System, Punjab Platform, Pakistan. Surveys in Geophysics (Springer).
Malkani, M.S., Ilyas, M., Yasin, R., Abbas, A., Samiullah, K., Raza, T., Hassan, S.S.E., Fazal, R.M., Noor, A. & Malik, A. (2022). Geology of Northern Sulaiman Foldbelt, Shirani and Waziristan Regions (South Punjab, Balochistan and Khyber Pakhtunkhwa): New Tomistominae (Miocene False Gharial) from Sakhi Sarwar Area of Dera Ghazi Khan (South Punjab), Pakistan. Open Journal of Geology, 12(6), 521-564.
Kazmi, A.H. & Abbasi, I.A. (2008). Stratigraphy and Historical Geology of Pakistan. Department & National Centre of Excellence in Geology, University of Peshawar, Peshawar. 524 pp. ISBN 978-969-9119.
Umar, M., Kassi, A.M., Jamil, M., Kasi, A.K. & Khan, A.S. (2024). Cretaceous stratigraphic framework and sedimentary architecture, Pakistan: signatures of rift-drift tectonics and submarine volcanism along the western continental margin of the Indian Plate. In: Hart, M.B. et al. (eds) Cretaceous Project 200 Volume 2: Regional Studies. Geological Society, London, Special Publications, 545.

Reviewer confidence: high

Every fact on this page is source-cited. This entry is part of the peer-archived Pakistan Stratigraphy Dataset (doi.org/10.5281/zenodo.21363991, CC‑BY‑4.0).

Lexicon status: Name attested in the Shah (1977/2009) Geological Survey of Pakistan compilation — the national stratigraphic lexicon. This records where the name is documented; it is not an endorsement of the unit’s definition, age or figures.

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Cite this unit

APA

Qudsi, L. (2026). Sembar Formation. In Pakistan Stratigraphy Dataset [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21363991

BibTeX

@misc{stratigraphypk_sembarformation,
  author    = {Qudsi, Lareb},
  title     = {{Sembar Formation} --- Pakistan Stratigraphy Dataset},
  year      = {2026},
  publisher = {Zenodo},
  doi       = {10.5281/zenodo.21363991},
  url       = {https://doi.org/10.5281/zenodo.21363991}
}

Archived dataset: doi.org/10.5281/zenodo.21363991 (CC‑BY‑4.0) · Direct link to this entry: https://stratigraphy.pk/formation/sembar-formation (accessed October 7, 2026).

To cite the unit's original definition instead, see: Williams (1959).

Below · older

Chiltan Limestone

Jurassic

Above · younger

Goru Formation

Cretaceous

Referenced in other successions

Overlain by Mekhtar Formation (or Mekhtar Sandstone)

Underlain by Dilband Formation· Takatu Formation