Pakistan Stratigraphy · stratigraphy.pk
Besham Group
https://stratigraphy.pk/formation/besham-group
Besham Group
Archean to Paleoproterozoic (>1800 Ma)
Archean-Paleoproterozoic in the time scale →Stratigraphic position
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.
The ~1.9-billion-year-old crystalline basement at Besham — orthogneiss, schist and marble — beneath the Karora cover.
Exposed in the Besham-Swat area as a tectonic window through Lesser Himalayan nappes. Represents some of the oldest crystalline basement of the Indian Plate in Pakistan. Includes Lahor Complex and Besham Nappe with polyphase deformation history.
Significance. The Precambrian crystalline basement of the Indian plate exposed in the Besham Nappe; Ar–Ar amphibolite ages of about 1850–2000 Ma place it in the Late Archean(?) to Middle Proterozoic. Baig (1990) divided it into the lower Thakot Formation and the upper Pazang Formation; it is overlain unconformably by the Karora Group cover.
- Lithology
- Granitic, biotite-rich orthogneiss together with metasedimentary gneiss, schist, metapsammite, marble and amphibolite, with komatiitic metavolcanics.
- Thickness
- 3000+ m
- Type locality
- Besham, Indus valley (the Besham Nappe)
- Introduced by
- Fletcher et al. (1986)
- Economic importance
- Gemstone potential (emeralds in associated rocks)
Provinces
References
- 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.
Reviewer confidence: medium
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