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Geological division of Terai and Siwalik zone

Short answer

Terai: Bhabar (coarse boulder/gravel belt) and Terai proper (sand, silt, clay with high water table). Siwalik: Lower (Miocene fine sandstone, mudstone), Middle (thick salt-and-pepper sandstone), Upper (boulder conglomerate) with Dun valleys filled with alluvium. Siwalik rocks thrust over Terai along MFT.

Explain the geological division of the Terai and Siwalik zones.

Terai zone

A flat Quaternary alluvial plain (60-300 m), divided into:

  • Bhabar: a coarse boulder and gravel belt at the foot of the Siwalik.
  • Terai proper: sand, silt and clay with a high water table.

Siwalik zone

Hills of 300-1500 m (up to 2000 m) between the MFT and MBT, divided into:

DivisionAgeLithology
Lower SiwalikMioceneFine sandstone, mudstone, siltstone, variegated
Middle SiwalikMio-PlioceneThick, coarse salt-and-pepper sandstone with mudstone
Upper SiwalikPlio-PleistoceneBoulder conglomerate, sandstone and clay

The Siwalik zone also has Dun valleys (e.g. Chitwan and Dang) filled with alluvium. The Terai deposits are the youngest; the older Siwalik rocks are thrust over the Terai along the MFT.

✓ Answer checked by Claude Opus 5.5 (high effort)

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