India's rock systems II: Gondwana, Deccan Traps, Tertiary and Quaternary

Detail

The four younger systems at a glance

System	Age	Main rocks and where they are	Resources and meaning
Gondwana	about 300–150 million years ago (Carboniferous to Jurassic). NCERT: "a little over 200 million years"	River and lake sediments in rift basins of the Peninsula	Most of India's coal
Deccan Traps	about 66 million years ago (66–60 million years; end-Cretaceous to early Palaeogene)	Flood basalt over the Maharashtra plateau and parts of Gujarat, MP, Karnataka and Telangana	Black (regur) soil, building stone, few metals
Tertiary	about 66–2.6 million years ago	Siwalik sediments laid down as the Himalaya rose; coastal and north-east basins	Petroleum, lignite, north-east coal
Quaternary	last 2.6 million years	Indo-Gangetic–Brahmaputra alluvium, deltas, Thar sands, Kashmir karewas	Almost no economic minerals; groundwater and fertile soil

Gondwana system: India's coal store

What it is

• Gondwana system: a thick pile of sedimentary rocks (sandstone, shale and coal seams) laid down by rivers and lakes about 300–150 million years ago.
• The name comes from the Gond region of central India, the land of the Gond people (Madhya Pradesh–Chhattisgarh area).
• Gondwana (Gondwanaland) is also the name of the old southern supercontinent. It joined India, Africa, South America, Australia and Antarctica.

How the coal formed (cause → process → result)

• Cause: the crust of the Peninsula cracked and some blocks sank between parallel faults. These sunken strips are rift basins or grabens (a graben is a long block of land that has dropped down between two faults).
• Process: rivers flowed along these troughs. Thick forests grew in the swamps. Dead plants were buried under sand and mud again and again. Pressure and heat slowly turned them into coal.
• Result: coal seams lie in long belts that follow today's river valleys. These rivers still flow along the old rift lines.

Coal valleys (learn these pairs)

Valley	State	Key coalfields
Damodar	Jharkhand–West Bengal	Jharia (largest coking coal field), Raniganj (oldest, mined from the 18th century), Bokaro, Karanpura, Giridih
Son	Madhya Pradesh–Chhattisgarh	Singrauli, Sohagpur
Mahanadi	Odisha–Chhattisgarh	Talcher, Ib river, Korba
Godavari	Telangana	Singareni
Wardha	Maharashtra	Chandrapur and the Wardha valley fields

How much coal

• Gondwana rocks hold most of India's coal. The figure usually quoted is about 98% of reserves.
• Total geological coal resources were 361.411 billion tonnes down to 1,200 m depth as on 1 April 2022. Of this, 187.105 billion tonnes were "Proved" resources [2].
• Most Gondwana coal lies in the eastern and central Peninsula. Small Gondwana deposits also occur in Assam and Sikkim [2].
• Of India's resources (1 April 2022), prime-coking coal (coal good for making steel) was only 5.318 billion tonnes. Most of the rest is non-coking coal, about 326.306 billion tonnes [2].
• Raw coal despatches in 2021-22 ranked by state were Odisha (24%) > Chhattisgarh (20.31%) > Jharkhand (16.91%) > Madhya Pradesh (14%) > Telangana (8.26%) > Maharashtra (7.66%). All of these are Gondwana states [2].
• About 86% of raw coal despatched in 2021-22 went to the electricity sector [2].

Evidence for continental drift

• Talchir tillite: a tillite is hard rock made from old glacier debris (mixed boulders, pebbles and clay). The Talchir tillite at the base of the Gondwana pile is named after Talcher in Odisha. It shows that India was once covered by ice near the South Pole.
• Glossopteris: a fossil seed-fern with tongue-shaped leaves. The same plant is found in India, Africa, South America, Australia and Antarctica.
• Meaning: today these lands are separated by oceans, so the plants and ice sheets could not have spread between them. The lands must once have been joined as Gondwanaland. This is key evidence for continental drift (the idea that continents move slowly over the Earth's surface).

Deccan Traps: the great lava plateau

What it is

• Deccan Traps: a huge flood basalt province (a region where very fluid basalt lava poured out again and again from long cracks and spread in flat sheets over a vast area).
• Age: about 66 million years ago (66–60 million years), at the end of the Cretaceous and the start of the Palaeogene.
• Extent: most of the Maharashtra plateau, plus parts of Gujarat (Saurashtra, Kachchh), Madhya Pradesh (Malwa plateau), Karnataka and Telangana.

Why it is called "trap"

• Trap comes from the Swedish word trappa, meaning "stairs".
• Each lava flow cooled into a flat layer. Over time, soft and hard layers wore away at different speeds.
• Result: hill slopes look like step-like terraces. They are clearly seen in the Western Ghats of Maharashtra (Sahyadri).

How it formed (cause → process → result)

• Cause: the Indian plate moved north over the Reunion hotspot. A hotspot is a fixed spot where a plume of very hot mantle rock rises and melts the crust above it.
• Process: molten rock rose through cracks in the crust. These cracks filled with magma and hardened into dykes. A dyke is a wall-like sheet of igneous rock that cuts across the layers. The dykes acted as feeders that carried lava to the surface.
• Result: fluid basalt came out in fissure eruptions (lava flowing quietly out of long cracks, not from a cone-shaped volcano). It built a thick, flat-topped plateau, layer after layer.
• Trail of the hotspot: India kept moving north. The hotspot stayed fixed and left a line of volcanic rock across the Indian Ocean (Lakshadweep–Maldives–Chagos) down to Reunion Island, where a volcano is still active.
• Timing: these eruptions happened at the same time as the end-Cretaceous mass extinction, which wiped out the dinosaurs. They are discussed as one possible cause.

Resources

• Black soil (regur): basalt weathers into black cotton soil. It is clay-rich and holds moisture well. It is rich in iron, lime and magnesia and poor in phosphorus. It swells when wet and cracks when dry, so it "self-ploughs". It is best for cotton.
• Building stone: basalt is hard and widely quarried for buildings and roads.
• Few metallic minerals: basalt is young volcanic rock and lacks the old ore bodies found in Archaean and Dharwar rocks. Bauxite caps form on some weathered basalt plateaus in hot, wet climates.

Tertiary system: the rocks of the rising Himalaya

What it is

• Tertiary system: rocks formed about 66–2.6 million years ago. This is the time when the Indian plate hit the Eurasian plate and the Himalaya rose.
• Siwaliks: the outermost, lowest range of the Himalaya. They are made of loose sand, clay and boulder beds (conglomerate) that rivers washed down from the rising mountains.

Petroleum: how it is trapped

• Oil forms from tiny marine organisms buried in sediments. Being light, it moves upward through porous rock until something stops it.
• Anticline: an upward (arch-shaped) fold in rock layers. Oil and gas rise to the top of the arch and are held there by a cap of non-porous rock.
• Fault trap: a fault (a break along which rocks have moved) places porous rock against non-porous rock. This blocks the oil and holds it in place.

Region	Oilfields
Assam (oldest oil region)	Digboi, Naharkatiya, Moran
Gujarat	Ankleshwar (largest in Gujarat), Kalol
Offshore Arabian Sea	Mumbai High (largest producer, about 160 km off Mumbai)

Lignite

• Lignite: low-grade brown coal. It is soft and holds a lot of moisture, with low carbon content. It is younger than bituminous coal.
• Lignite occurs in Tertiary sediments in Tamil Nadu, Puducherry, Gujarat and Rajasthan, and also in J&K and Odisha [2].
• Resources: about 46.024 billion tonnes as on 1 April 2022. Tamil Nadu holds 79.3%, followed by Rajasthan (13.98%) and Gujarat (5.89%) [2].
• Production 2021-22: 47 million tonnes. By share, Tamil Nadu (about 50%) > Gujarat (about 28%) > Rajasthan (about 22%) [2].
• Of the 20 lignite mines working in 2021-22, 10 were in Gujarat, 7 in Rajasthan and 3 in Tamil Nadu. All are opencast (open-pit) mines [2].
• Neyveli (Tamil Nadu) is the largest opencast mine in India. NLC runs three opencast mines at Neyveli and one at Barsingsar (Rajasthan) [2].
• Other centres: Barmer and Palana (Bikaner) in Rajasthan, and Kutch in Gujarat.

North-east coal (Tertiary coal)

• Age: younger coal, about 55 million years old.
• States: Assam, Arunachal Pradesh, Nagaland and Meghalaya [2].
• Quality: it has high sulphur content [2]. This makes it polluting and less useful in industry.
• Examples: Makum (Assam), Garo–Khasi–Jaintia hills (Meghalaya), Namchik–Namphuk (Arunachal).

Feature	Gondwana coal	Tertiary coal
Age	about 300–150 million years	about 55 million years
Share	about 98% of reserves	very small
Where	Damodar, Son, Mahanadi, Godavari, Wardha valleys	Assam, Arunachal, Nagaland, Meghalaya
Quality	mostly bituminous; Jharia has coking coal	high sulphur [2]

Ophiolites: pieces of old ocean floor on land

• Ophiolite: a slice of old oceanic crust and upper mantle. It was pushed up onto land where two plates collided and the ocean between them closed.
• Indus–Tsangpo suture (Ladakh): a suture is the joint line where two plates have welded together. This line marks where the Indian plate met the Eurasian plate.
• Naga–Manipur hills: an ophiolite belt with chromite and nickel.
• Andaman Islands: ophiolites formed where the Indian plate sinks below the Burma microplate.

Quaternary system: the youngest cover

What it is

• Quaternary system: loose deposits from the last 2.6 million years. These rocks are still forming today.

Deposit	Where	Notes
Bhangar	Higher, older parts of the Indo-Gangetic plain	Older alluvium. It lies above flood level and has lime nodules called kankar
Khadar	Floodplains next to rivers	Newer alluvium. Each flood adds a fresh layer, so it is very fertile
Deltas and coastal plains	Ganga–Brahmaputra (Sundarbans), Mahanadi, Godavari, Krishna, Kaveri	River mud laid down where rivers meet the sea
Wind-blown sand	Thar Desert (Rajasthan)	Dunes formed by wind deposition
Karewas	Kashmir valley	Flat-topped terraces of lake clay and sand, left when an old lake drained. Known for saffron (Pampore)

Resources

• Alluvium: loose clay, silt, sand and gravel laid down by rivers.
• NCERT notes that the vast alluvial plains of north India are almost devoid of economic minerals. The mineral-bearing rocks lie buried deep under thick alluvium.
• Their real wealth: groundwater in thick, porous aquifers (water-bearing layers of sand and gravel) and fertile soils. This is why the plains are India's main food bowl and are densely populated.

Prelims Hooks

• Talchir tillite (glacier debris rock, Odisha) and Glossopteris fossils are Gondwana evidence for continental drift.
• Coalfield–valley pairs: Jharia, Raniganj and Bokaro are in the Damodar valley; Talcher and Ib in the Mahanadi; Singareni in the Godavari; Singrauli in the Son.
• Trap comes from Swedish trappa, "stairs". The Deccan Traps are flood basalt fed by dykes, formed over the Reunion hotspot about 66 million years ago.
• Trap: the Deccan Traps are not Gondwana rocks and hold almost no coal. Gondwana is coal; Deccan is basalt and black soil.
• Lignite shares (1 April 2022): Tamil Nadu 79.3% > Rajasthan 13.98% > Gujarat 5.89% [2]. Neyveli is India's largest opencast mine [2].
• Tertiary coal occurs in Assam, Arunachal, Nagaland and Meghalaya and is high-sulphur [2].
• Oil traps: anticlines and fault traps. Digboi and Naharkatiya are in Assam, Ankleshwar in Gujarat, and Mumbai High is offshore.
• Ophiolite belts: Indus–Tsangpo suture (Ladakh), Naga–Manipur hills (chromite, nickel) and the Andaman Islands.
• Bhangar is older alluvium with kankar; khadar is newer floodplain alluvium. Kashmir karewas are lake deposits known for saffron.
• Order from oldest to youngest: Gondwana → Deccan Traps → Tertiary (Siwalik, lignite, oil) → Quaternary (alluvium).

Mains Points

• Rock age controls where India's resources are found (GS-I and GS-III):
• Old Peninsular rift basins hold Gondwana coal, so coal-based power and steel are concentrated in Odisha, Chhattisgarh and Jharkhand. These three states made up over 60% of coal despatches in 2021-22 [2].
• Young Tertiary basins hold oil and lignite, so oil comes from Assam, Gujarat and offshore Mumbai High.

• The Quaternary plains have no minerals but hold food and water.

• Energy security: about 86% of coal despatched in 2021-22 went to power [2]. Proved coal reserves of about 187 billion tonnes (1 April 2022) may support peak output of only 1.2–1.3 billion tonnes a year until about 2037, so more exploration is needed [2]. North-east Tertiary coal is high in sulphur, which limits its use and causes pollution, such as acid mine drainage in Meghalaya.

• Deccan Traps and farming: basalt weathers into moisture-holding regur soil, the base of the cotton belt of Maharashtra, Gujarat and MP. But the hard rock stores little groundwater, so this rain-shadow region often suffers drought and farm distress (Marathwada, Vidarbha).
• Plate tectonics as a link: the Talchir tillite, Glossopteris, the Reunion hotspot trail and the Indus–Tsangpo ophiolites together record India's journey. It broke away from Gondwanaland, crossed a hotspot, and hit Eurasia to raise the Himalaya and Siwaliks. This is useful for answers on continental drift and how India's landforms evolved.