Mesozoic • Cretaceous In GSP lexicon

Humai Formation

Late Cretaceous (Maastrichtian; ~72.2-66.0 Ma)

Cretaceous in the time scale →

Cited in 7 sources Last reviewed Jul 30, 2026

Unit summary

Rank: Not recorded
Status: Published
Age: Mesozoic · Cretaceous · Late CretaceousLate Cretaceous (Maastrichtian; ~72.2-66.0 Ma)
Named by: HSC (1961)
Type locality: Koh Humai, North Chagai (Chagai-Raskoh Magmatic Province)29.1000°N, 62.8000°E
Thickness: 91-306 m
Lithology: Variable: shale with calcareous sandstone, siltstone, thin-bedded limestone and volcanic conglomerate (lower); massive reefoid limestone (upper).
Synonyms: Not recorded

A Cretaceous volcanic-and-sedimentary unit of the Chagai arc, including reefal 'Hippuritic' limestone.

Named after Koh Humai. Contains Hippuritic (rudist) limestone at top. Overlies Sinjrani volcanics unconformably.

Fossils

Hippurites loftusi Lepidorbitoides socialis Orbitoides sp.Omphalocyclus sp.

Contacts

In the Chagai Hills column

Shale / mudIgneousFossils 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

Chagai Hills

Basin: Not recorded
Region: Not recorded
Depositional environment: marine, volcanic-arc
Coordinates: 29.1000°N, 62.8000°E

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Correlation

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

Economic significance

Not recorded

Remarks

An early, Cretaceous volcaniclastic unit of the Chagai–Raskoh magmatic arc, recording the initial (tholeiitic) phase of subduction-related volcanism along Pakistan's western margin.

Sources (6)

Malkani, M.S. & Mahmood, Z. (2017). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 24.
Perelló, J., Razique, A., Schloderer, J. et al. (2008). The Chagai Porphyry Copper Belt, Baluchistan Province, Pakistan. Economic Geology, 103(8), 1583-1612.
OpenStreetMap contributors and GEOnet Names Server (public geographic gazetteers), used to geolocate named GSP type localities to approximate decimal coordinates.
Indian Plate Lexicon (indplex.geolex.org), Geological Society of India and international compilation.
Shah, S.M.I. (2009). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 22.
Kazmi, A.H. & Jan, M.Q. (1997). Geology and Tectonics of Pakistan. Graphic Publishers, Karachi.

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.

Cite this unit

APA

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

BibTeX

@misc{stratigraphypk_humaiformation,
  author    = {Qudsi, Lareb},
  title     = {{Humai 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/humai-formation (accessed August 30, 2026).

To cite the unit's original definition instead, see: HSC (1961).

Below · older

Sinjrani Volcanic Group

Cretaceous

Above · younger

Rakhshani Formation

Cretaceous–Paleogene

Referenced in other successions

Overlain by Nisai Limestone