Geography Ch02 – Geological Structure of India

🌍 Origin — Pangaea Theory

🌐 Division of Pangaea

Pangaea → divided into Angaraland (North) and Gondwanaland (South)
Indian subcontinent was part of Gondwanaland

📊 4 Groups of Indian Rocks

1️⃣

Archaean Group

2️⃣

Purana Group

3️⃣

Dravidian Group

4️⃣

Aryan Group

⏳ Geological Timeline

Era-wise Classification

Oldest

Archaean / Pre-Cambrian Era

Gneiss & Schist — ancient Precambrian basement; generally unfossiliferous

Purana Group

Cuddapah + Vindhyan Systems

Proterozoic sedimentary systems — Cuddapah and Vindhyan

Paleozoic Era

Dravidian Group

Fossiliferous Paleozoic strata; mainly extra-peninsular, with limited occurrence near Umaria (MP)

Late Paleozoic → Recent

Aryan Group

Gondwana (coal), Deccan Trap (basalt/black soil), Tertiary (Himalayas), Quaternary (alluvial)

⚡ QUICK RECALL — Fossil Memory

Archaean → No fossils (Earth cooling)
Dharwar → No fossils
Cuddapah → generally fossil-poor or unfossiliferous
Vindhyan → General absence of fossils
Dravidian → fossiliferous Paleozoic strata ✅
Gondwana → Fossils present ✅

⛏️ Group 1 — Archaean

🌏 Archaean System — Most Ancient Rocks

Ancient Precambrian crystalline basement; commonly gneiss and schist
Formed during cooling of the Earth
Generally unfossiliferous; recognizable fossils are usually not preserved
Rock types: Gneiss and Schist

Bundelkhand Gneiss (most ancient)

Bengal Gneiss

Found In:

Karnataka

Tamil Nadu

Andhra Pradesh

Madhya Pradesh

Odisha

Chotanagpur Plateau (Jharkhand)

🏔️ Dharwar System of Rocks

Formed by erosion & deposition of Archaean rocks
Most developed in Dharwar region, Karnataka
No Fossils
Aravalli mountain range — formed from these rocks

⚡ QUICK RECALL

Dharwar rocks → Aravalli mountainsformed | Most developed inKarnataka (Dharwar district)

🚨 EXAM TRAP

Bundelkhand Gneiss = most ancient rocks of India
Archaean rocks form very ancient crystalline basement, commonly represented by gneiss and schist.
The Aravalli system is associated with Dharwar rocks rather than the older Archaean system in this classification.

📦 Group 2 — Purana

🔵 Cuddapah System

Formed by erosion of Archaean + Dharwar rocks
Layered rocks (sedimentary)
Generally fossil-poor or unfossiliferous
Named after Cuddapah district, Andhra Pradesh
Eastern Ghats — formed from these rocks

🟣 Vindhyan System

Plateau — divides Ganga Plain from Deccan
Layered, formed by water deposition
General absence of fossils
Minerals: sandstone, shale, limestone and glass-making sand

📊 Cuddapah vs Vindhyan — Comparison

Feature	Cuddapah System	Vindhyan System
Formation	Archaean + Dharwar erosion	Water deposition
Fossils	Generally fossil-poor	Generally absent
Landform	Eastern Ghats	Vindhya Plateau
Named After	Cuddapah district (AP)	Vindhya mountains
Minerals	—	Sandstone, Limestone, Shale/Clay, Glass-making Sand

🚨 EXAM TRAP

The Eastern Ghats are associated with the Cuddapah rock system.
The Vindhyan range forms an important divide between the Ganga Plain and the Deccan region.
The Cuddapah system is named after the Cuddapah region of Andhra Pradesh, where these rocks are extensively found.

🦕 Group 3 — Dravidian

🦴 Paleozoic Era Rocks

Rocks of Paleozoic Era
Fossiliferous Paleozoic strata
This rock system is especially rich in fossils.
Mainly developed in extra-peninsular regions, especially the Himalaya
Limited Peninsular occurrence: Umaria area, Madhya Pradesh

🚨 EXAM TRAP — Most Asked!

Dravidian = Paleozoic, fossiliferous; mainly extra-peninsular, especially the Himalaya; limited Peninsular occurrence near Umaria (MP).

⚡ QUICK RECALL

Dravidian = Paleozoic | Fossil-rich strata | Mainly extra-peninsular; Umaria (MP) is a limited Peninsular occurrence

🔥 Group 4 — Aryan (4 Sub-Systems)

🪨 1. Gondwana System — Coal Treasure

Construction of basin landforms
Fossils present
~98% of India's coal reserves found here!

Spread In:

Damodar Valley

Mahanadi Valley

Rajmahal

Satpura

98%

India's Coal Reserves in Gondwana Rocks

🌋 2. Deccan Trap System — Black Soil Origin

End of Cretaceous Era → Volcanic activity in western Peninsular India
Basalt lava flow → step-like landform (trap = step)
Mainly in Maharashtra and Malwa region
Also formed: Rajmahal Trap
Basalt erosion → Fertile Black Soil (Regur)

Deccan Trap States:

Maharashtra

Gujarat

Karnataka

Andhra Pradesh

⚡ QUICK RECALL

Deccan Trap → Basalt Lava → Black Soil (Regur/Cotton Soil) → Best for cotton cultivation

🏔️ 3. Tertiary System

Formed: Paleocene to Pliocene epoch
Petroleum and natural gas in Tertiary sedimentary basins
Formation of Himalayan mountains

🌊 4. Quaternary System

Rocks of Pleistocene + Holocene epoch
Widespread alluvial deposits of the Indo-Gangetic Plains
Also in Deltaic regions
Most recent rocks

🚨 EXAM TRAP

About 98% of India's coal resources occur in Gondwana rock formations.
Black soil developed from Deccan Trap basalt, not from Gondwana rocks.
"Trap" word comes from Swedish "trappa" = stairs/steps — step-like lava landform
The Damodar Valley is a major Gondwana coal belt extending through the Jharkhand–West Bengal region and is important for eastern India studies.

📋 Complete Master Summary Table

Group	System	Era	Fossils	Key Feature	Location/Landform
1. Archaean	Archaean System	Pre-Cambrian	Absent	Ancient Precambrian basement; Gneiss & Schist	Karnataka, TN, AP, MP, Odisha, Jharkhand
1. Archaean	Dharwar System	Pre-Cambrian	Absent	Formed from Archaean erosion	Aravalli mountains, Dharwar (Karnataka)
2. Purana	Cuddapah System	Pre-Cambrian	Absent	Proterozoic layered sedimentary rocks	Eastern Ghats, Cuddapah (AP)
2. Purana	Vindhyan System	Pre-Cambrian	Gen. Absent	Sandstone, Limestone, Shale/Clay, Glass-making Sand	Vindhya Plateau (Ganga–Deccan divide)
3. Dravidian	Paleozoic Rocks	Paleozoic	Rich Fossils	Fossiliferous; mainly extra-peninsular	Himalaya; limited occurrence near Umaria (MP)
4. Aryan	Gondwana System	Late Paleozoic–Mesozoic	Present	98% India's coal reserves	Damodar Valley, Mahanadi, Rajmahal, Satpura
	Deccan Trap	Cretaceous end	—	Basalt lava → Black Soil (Regur)	Maharashtra, MP, Gujarat, Karnataka, AP
	Tertiary System	Paleocene–Pliocene	—	Major Himalayan mountain-building phase	Himalayan region
	Quaternary System	Pleistocene–Holocene	—	Most recent rocks	Indo-Gangetic Plains, Delta regions

🎯 Key Revision Points

🚨 Top Exam Points

Coal (98%) → Gondwana rocks
Black Soil → Deccan Trap (Basalt)
Richest fossils → Dravidian Group
Dravidian rocks → mainly extra-peninsular; limited near Umaria (MP)
Aravalli → Dharwar rocks
Eastern Ghats → Cuddapah rocks
Most ancient → Bundelkhand Gneiss
IST + Tropic of Cancer meet → Chhattisgarh

⚡ Memory Tricks

A P D A = Archaean, Purana, Dravidian, Aryan (4 groups order)
No fossils → Arch, Dhar, Cudd, Vindh (4 oldest)
Gondwana = Coal = Damodar Valley (Jharkhand–West Bengal)
In Deccan Trap, the term trap refers to the step-like landform produced by successive basaltic lava flows.
Quaternary = most RECENT → alluvial soil of Ganga

⚡ BIHAR SPECIAL RECALL

The Gondwana coalfields of the Damodar Valley lie along the Jharkhand–West Bengal belt, close to Bihar.
Chotanagpur Plateau (Jharkhand) = Archaean rocks — mineral rich area
The Indo-Gangetic Plain, including the Bihar Plain, consists largely of fertile Quaternary alluvial deposits.

🪨 Indian Geography — Chapter 02