Indian and Kerala Geology
What the exam tests
Indian and Kerala Geology tests the broad stratigraphic and physiographic framework of India and the rock units, landforms and geological history of Kerala.
Core rules
- Indian stratigraphy in order: Archaean gneisses and granulites → Dharwar (iron ore, gold) → Cuddapah → Vindhyan → Palaeozoic Gondwana coal → Mesozoic (Trichinopoly, Bagh) → Deccan Traps → Tertiary (Himalaya, Warkalli, Quilon) → Quaternary.
- Physiography: Himalaya, Indo-Gangetic plain, Peninsular Shield, coastal plains and islands.
- Kerala: Precambrian charnockite–khondalite–migmatite terrain; Tertiary Warkalli beds (sandstone, clay, lignite) and Quilon beds (limestone, marl); extensive laterite capping; coastal and riverine alluvium rich in heavy minerals.
- Landforms: Western Ghats escarpment, midland laterite plateaus, backwaters and the Vembanad lagoon, coastal ridges and spits.
Worked example
Why are Deccan Trap basalts absent in Kerala? Reasoning: Deccan volcanism was centred on the northwestern Deccan around 66 Ma. Kerala's Precambrian shield lay further south and was covered instead by Tertiary sediments, laterite and coastal alluvium. Kerala's record is dominated by crystallines, Tertiary beds and laterite, not thick basalt flows.
Traps
Treating laterite as a soil type rather than a weathering profile. Placing Warkalli beds below the Archaean basement. Mixing Dharwar and Vindhyan ages. Describing the Western Ghats as a fault scarp when it is essentially an erosional escarpment.