Major Physiographic Divisions of India

On the basis of geological studies, major physiographic divisions of INDIA are described here, with reference to its structure and stratigraphy.

1. MAJOR PHYSIOGRAPHIC DIVISIONS OF INDIA

2. Introduction India is divided into 3 main divisions based on physiography,structure and stratigraphy They are Peninsular India Indo G angetic plain Extra Peninsular I ndia

3. PHYSIOGRAPHIC DIVISIONS Peninsular India Extra Peninsular India Indo Gangetic Plain

4. Peninsular India

5. Peninsular India Lies to the south of the plains of INDUS and GANGA river system

6. Physiography Variable physiography Contains :Plateaus, ancient fold mountains, massifs, valleys and coastal plains Western Ghats – prominent physiographic feature on western margin Mountains – Relict type Rivers – mostly attained base level erosion

7. S tructure Stable plateau remained unaffected by orogenic movements Narmada ,Son , Damodhar river valleys trend in E-W direction. Mahanadhi and G odhavari valleys trend in NW-SE direction.

8. Structure(contd..) Four distinct geomorphic and structural trends, NNW-SSE trend of the south part of Western Ghats NE-SW trend of E astern G hats E-W trend of S atpura in Central India NE-SW trend of Aravallis in Rajasthan

9. Stratigraphy Made up of rocks of Archaean and Precambrian age Archaean rocks – metamorphosed to varying degree Exists – Deccan and R ajmahal traps (Jurassic to Eocene age) Post C ambrian sedimentary rocks in Gondwana basin and coastal tracts

10. Indo- G angetic plain

11. Indo Gangetic plain Extend from Assam in east t hrough Bengal ,Bihar and U.P u pto Punjab in the west

12. Indo G angetic plain Deep crustal trough filled with quaternary sediments Origin and structure gave birth to the great HIMALAYAS

13. Physiography Very extensive alluvial plain Sloping with a very small gradient towards the sea

14. Structure Bottom is asymmetrical Northern margin of PI dips northwards gently Thickness increases towards north Maximum thickness at outer Himalayas Bottom of the trough is not stable, still changes takes place; causing earthquakes

15. Stratigraphy Made up of sands and clays of P leistocene and recent age Punjab shelf – Precambrian rocks U.P(e/w) shelf – P recambrian and V indyan rocks Bengal shelf – rocks of Gondwana Age and R ajmahal traps

16. Extra Peninsular India

17. Extra Peninsular India It lies in north extremity of India with upper r eaches of Indus and Brahmaputra rivers in the north and Arakan-yoma ranges in east.

18. Physiography Made of tectonic mountains and frontal foredeep folded belt ( SIWALIK RANGE ) The Himalayan belt extends in E-W direction of about 2400 kms Western end of belt has sharp arcuate turn called syntaxial bend Similar belt in eastern end, where NE-SW trend changes to NNE-SSW trend

19. Structure & Stratigraphy It is a rock formation disturbed by folding , faulting and overthrusting It is subdivided into A. Tethyan H imalayan zone B . Central crystalline zone of higher Himalayan C . Lesser H imalayan zone D . Foredeep folded zone

20. A. Tethyan H imalayan zone Located at north extreme Average altitude : 6000 mts Marine rocks of Palaeozoic and M esozoic ages This rest uncomfortably over the Precambrian basement

21. B. Central zone of higher H imalayas Average height : 6000 mts Mostly made up of the Precambrian basement and the granitic plutons of T ertiary age

22. C. Lesser Himalayan zone Average height : 2000-3000 mts Rock formations are less metamorphosed Unfossiliferous – correlation can’t be done Structure is very complex ,affected by thrust faults Stratigraphic succesion is reversed in many places

23. Contd.. Lower part of rocks – P recambrian age Overlain by formations of Gondwana age Above these rocks of tertiary age RIVERS : many antecedent rivers originated in T ethyan H imalayan zone flow across L esser H imalayan ranges ,cutting deep gorges

24. D. Foredeep Folded B elt Lies in Southern margin of Extra Peninsular India Also called as SIWALIK RANGE Made of sediments of Mio- P liocene age Southern boundary is marked by “Main boundary faults”.

25. MAJOR PHYSIOGRAPHIC DIVISIONS OF INDIA

26. PRESENTED BY POONTHENDRAL T K 3 rd YEAR MSC GEOLOGY (INTG) BHARATHIDASAN UNIVERSITY