Mesozoic • Cretaceous

Humai Formation

Late Cretaceous (Maastrichtian)

Stratigraphic position

In the Chagai Hills column

SandstoneIgneousConglomerateFossils 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.

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.

Significance. 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.

Lithology: Basal conglomerate, then intercalated shale, sandstone, siltstone and limestone (including the 'Hippuritic limestone' of Vredenburg), with thick volcanic beds.
Thickness: 200-400 m
Type locality: Koh-i-Humai, Koh-i-Sultan
Environment: marine, volcanic-arc
Introduced by: HSC (1961)

Fossils

Hippurites (rudist bivalves)OrbitoidesLepidorbitoidesGastropods

Provinces

Chagai Hills

References

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.

Reviewer confidence: medium

Related units

Below · older

Sinjrani Volcanic Group

Cretaceous

Above · younger

Nisai Limestone

Cretaceous–Paleogene