- 2079 Bhadra · 3+2 marks
Lithology of Lesser and Tethys Himalaya; Siwalik difference
Short answer
The Lesser Himalaya has low-grade slate, phyllite, quartzite, limestone, marble (Nawakot, Kathmandu Complexes) and granites. The Tethys Himalaya comprises Cambrian-Cretaceous fossiliferous marine limestone, shale, sandstone, weakly metamorphosed. The key difference: Siwalik is young, soft, poorly consolidated sedimentary rock; Higher Himalaya is old, hard, high-grade metamorphic and granite.
Describe the lithological characteristics of the Lesser and Tethys Himalayan zones. Highlight a major lithological difference between the Siwalik and Higher Himalaya.
Lesser Himalaya
Lithology
- Nawakot Complex: slate, phyllite, quartzite, limestone, dolomite and metasandstone. Lower Nawakot Group: Kuncha, Fagfog, Dandagaon, Nourpul and Dhading formations; Upper Nawakot Group: Benighat, Malekhu and Robang formations.
- Kathmandu Complex (nappe): the Bhimphedi Group of schist, quartzite and marble (Raduwa, Bhainsedobhan, Kalitar, Chisapani, Kulekhani and Markhu formations), overlain by the Phulchauki Group of slate, sandstone and limestone (Tistung, Sopyang, Chandragiri, Chitlang and Godavari formations).
- Granite and gneiss bodies: Palung granite and other granites, and the Ulleri augen gneiss.
Structure: intensely folded, faulted and thrust. There are synclinoria (e.g. the Mahabharat synclinorium of the Kathmandu nappe) with klippen, and anticlinoria, with many thrusts and tectonic windows. The beds mostly dip northward.
Tibetan-Tethys Himalaya
Lithology: Cambrian to Cretaceous (and Eocene) marine sedimentary rocks, rich in fossils: limestone, shale, sandstone, slate, quartzite and marl; the Thakkhola graben has Neogene sediments. The famous ammonite fossils (shaligram) of the Kali Gandaki valley come from Jurassic shale.
Structure: a thick sedimentary pile, unmetamorphosed or weakly metamorphosed, folded (open to tight folds) and thrust in places, and cut by later normal faults (Thakkhola graben).
Major lithological difference: Siwalik vs Higher Himalaya
| Point | Siwalik | Higher Himalaya |
|---|---|---|
| Rock type | Sedimentary (sandstone, mudstone, conglomerate) | High-grade metamorphic (gneiss, schist, migmatite) and granite |
| Age | Miocene to Pleistocene (young) | Precambrian to early Palaeozoic (old) |
| Consolidation | Soft, poorly consolidated | Hard, crystalline |
| Fossils | Mammal and plant fossils | None (metamorphosed) |
✓ Answer checked by Claude Opus 5.5 (high effort)
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