--- title: "Discontinuities; Siwalik and Higher Himalaya lithology" subject: "Engineering Geology I" chapter: 7 key: "semester_3/engineering_geology_i:discontinuities-siwalik-and-higher-himalaya" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/discontinuities-siwalik-and-higher-himalaya site: BCT Engineering --- # Discontinuities; Siwalik and Higher Himalaya lithology Engineering Geology I · Chapter 7: Geology of Nepal - Asked in: 2080 Bhadra, 4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/discontinuities-siwalik-and-higher-himalaya - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7 ## Question What are the major discontinuities of the Nepal Himalaya? Describe the lithological characteristics of the Siwaliks and Higher Himalayan zone. ## Short answer The major discontinuities are the Main Frontal Thrust (MFT/HFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT), and South Tibetan Detachment System (STDS). The Siwalik zone comprises Miocene-Pleistocene sandstone, mudstone, and conglomerate in lower, middle and upper divisions. The Higher Himalaya is composed of high-grade metamorphic rocks: kyanite-sillimanite schist/gneiss, calc-silicate gneiss and marble, and augen gneiss with leucogranite. ## Answer #### Major discontinuities of the Nepal Himalaya | Thrust | Between | Tentative location | Age of last movement | |---|---|---|---| | MFT / HFT | Terai and Siwalik | Along the southern foot of the Churiya hills | Active (Holocene) | | MBT | Siwalik and Lesser Himalaya | Along the northern edge of the Siwaliks / foot of the Mahabharat range | Late Pleistocene, reactivated | | MCT | Lesser and Higher Himalaya | Along the foot of the Higher Himalaya, mostly north of Kathmandu | Miocene, partly active | | STDS | Higher Himalaya and Tethys | Along the northern slopes of the Great Himalaya | Normal fault, Miocene | #### Siwalik zone **Lithology (three divisions)** - **Lower Siwalik:** alternation of fine-grained sandstone, mudstone and siltstone; red, purple and grey colours (Miocene). - **Middle Siwalik:** thick, massive, coarse "salt and pepper" sandstone with some mudstone and conglomerate lenses (Mio-Pliocene). - **Upper Siwalik:** poorly cemented boulder-pebble conglomerate with sandstone and clay (Plio-Pleistocene). **Structure:** the strata are folded into anticlines and synclines with strike roughly parallel to the Himalaya (WNW-ESE), often steeply dipping or overturned in the north near the MBT, and cut by thrust faults such as the MBT and MFT. #### Higher Himalaya **Lithology (three formations)** - **Formation I (lower):** kyanite-sillimanite schist and gneiss, with migmatite. - **Formation II (middle):** calc-silicate gneiss, marble and diopside bearing rocks. - **Formation III (upper):** augen gneiss, quartzite, and Manaslu and other leucogranite intrusions. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which pair of discontinuity and the zones it separates is correct? A. MBT: Terai and Siwalik B. MCT: Lesser and Higher Himalaya C. STDS: Siwalik and Lesser Himalaya D. MFT: Lesser and Higher Himalaya Answer: B. MCT separates the Lesser and Higher Himalaya; MFT is Terai-Siwalik, MBT is Siwalik-Lesser, STDS is Higher Himalaya-Tethys. (Key point: Discontinuities) 2. What kind of fault is the STDS? A. Active thrust of Holocene age B. Normal fault of Miocene age C. Strike-slip fault D. Blind thrust Answer: B. The South Tibetan Detachment System is a normal fault, Miocene in age. (Key point: Nature of STDS) 3. How is the Middle Siwalik characterised? A. Fine red and purple siltstone B. Thick, massive coarse salt-and-pepper sandstone C. Boulder conglomerate D. Marble and calc-silicate gneiss Answer: B. Middle Siwalik is thick coarse salt-and-pepper sandstone with some mudstone and conglomerate lenses. (Key point: Middle Siwalik) ## Related in Engineering Geology I - [Lithology of Higher Himalaya and Tethys zone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alithology-of-higher-himalaya-and) — Engineering Geology I, chapter 7, asked 3× - [Lithology of Lesser and Tethys Himalaya; Siwalik difference](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alithology-of-lesser-and-tethys) — Engineering Geology I, chapter 7 - [Physiographic division; Siwalik and Higher Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aphysiographic-division-siwalik-and-higher) — Engineering Geology I, chapter 7 - [Discontinuities and engineering problems in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-and-engineering-problems-in) — Engineering Geology I, chapter 7 - [Siwalik zone in detail](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asiwalik-zone-in-detail) — Engineering Geology I, chapter 7, asked 2× - [Tectonic zones and major discontinuities](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atectonic-zones-and-major-discontinuities) — Engineering Geology I, chapter 7, asked 2× ## Related in other subjects - [Problems of Siwalik and Higher Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asiwalik-higher-himalaya-problems) — Engineering Geology II, chapter 2, asked 2× - [Major discontinuity systems of Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Anepal-discontinuity-systems) — Engineering Geology II, chapter 2, asked 12× - [Geological hazards of Higher Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ahigher-himalaya-hazards) — Engineering Geology II, chapter 2 - [Engineering geological problems of Siwalik zone](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asiwalik-problems) — Engineering Geology II, chapter 2, asked 4×