Gondwana system

Geography glossary

Also called: Gondwana rocks · Topic: Minerals, Rocks and the Rock Cycle · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"

Meaning

The Gondwana system is a thick sequence of sedimentary rocks (sandstone, shale and coal seams) laid down by rivers and lakes in sunken rift basins of Peninsular India. It formed about 300–150 million years ago, from the Carboniferous to the Jurassic period. NCERT describes it as "a little over 200 million years" old.

It matters for two reasons:

  • It holds about 98% of India's coal reserves, so it is the base of India's power and steel industry.
  • Matching Gondwana rocks and fossils on the southern continents are key evidence for continental drift.

Explanation

Name and meaning

  • Gondwana system: the name comes from the Gond region of central India, the land of the Gond people (the Madhya Pradesh–Chhattisgarh area).
  • Gondwana (Gondwanaland) is also the name of the old southern supercontinent. It joined India, Africa, South America, Australia and Antarctica.
  • Main rocks: sandstone, shale and coal seams. These are all sedimentary rocks, formed from layers of sand, mud and buried plant matter.
  • Coal type: mostly bituminous coal. Jharia also has coking coal (coal good for making steel).

How the coal formed (cause → process → result)

  • Cause: the crust cracked and sank
  • The crust of the Peninsula cracked along parallel faults (breaks in the crust along which rocks move).

  • Some long blocks dropped down between these faults. These sunken strips are called rift basins or grabens. A graben is a long block of land that has dropped down between two faults.

  • Process: forests were buried again and again

  • Rivers flowed along these troughs.
  • Thick forests grew in the swamps.
  • Dead plants were buried under sand and mud, layer after layer.

  • Over a long time, pressure and heat slowly turned the plant matter into coal.

  • Result: coal lies in long belts along rivers

  • The coal seams lie in long belts that follow today's river valleys.
  • These rivers still flow along the old rift lines.

Conditions needed

  • Sinking basins: troughs that kept slowly sinking, so new sediment could keep piling up on top.
  • Swampy forests: a lot of plant growth in wet, low-lying land.
  • Quick burial: plants were covered by sand and mud before they could rot fully.
  • Time, pressure and heat: these slowly turned buried plants into coal.

Gondwana rocks as evidence for continental drift

  • Talchir tillite:
  • A tillite is hard rock made from old glacier debris (mixed boulders, pebbles and clay).
  • It lies at the base of the Gondwana pile and is named after Talcher in Odisha.

  • It shows that ice once covered India when India lay 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.

  • What this shows:

  • Today oceans separate these lands, so the plants and ice sheets could not have spread across 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).

Where it occurs

India: the coal valleys

Valley State Key coalfields
Damodar Jharkhand–West Bengal Jharia (largest coking coal field), Raniganj (oldest, mined since 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
  • Main region: most Gondwana coal lies in the eastern and central Peninsula. Small Gondwana deposits also occur in Assam and Sikkim [2].
  • Resources (1 April 2022): India's total geological coal resources were 361.411 billion tonnes, counted down to a depth of 1,200 m. Of this, 187.105 billion tonnes were "Proved" resources [2].
  • Coal types: prime-coking coal was only 5.318 billion tonnes. Most of the rest is non-coking coal, about 326.306 billion tonnes [2].
  • Despatches by state (2021-22): Odisha (24%) > Chhattisgarh (20.31%) > Jharkhand (16.91%) > Madhya Pradesh (14%) > Telangana (8.26%) > Maharashtra (7.66%). All of these are Gondwana states [2].

World

  • Matching Gondwana-type rocks and Glossopteris fossils occur in Africa, South America, Australia and Antarctica. These are the other parts of the old Gondwanaland.

Don't confuse with

  • Gondwanaland: this is the old southern supercontinent (a landmass). The Gondwana system is a sequence of rocks in India named after the Gond region. They share a name, but one is a landmass and the other is a rock sequence.
  • Deccan Traps: these are flood basalt (igneous rock from lava), about 66 million years old, and they hold almost no coal. Gondwana rocks are sedimentary and much older, and they hold most of India's coal.
  • Tertiary coal: this is younger coal, about 55 million years old, found in Assam, Arunachal Pradesh, Nagaland and Meghalaya. It is high in sulphur [2] and makes up only a very small share of reserves. Gondwana coal is about 300–150 million years old and makes up about 98% of reserves.
  • Lignite: this is low-grade brown coal from Tertiary sediments. About 79.3% of it is in Tamil Nadu (Neyveli) [2]. It is not Gondwana coal.

Prelims Hooks

  • Coalfield–valley pairs: Jharia, Raniganj and Bokaro are in the Damodar valley. Talcher and Ib are in the Mahanadi valley. Singareni is in the Godavari valley. Singrauli is in the Son valley.
  • Jharia is the largest coking coal field. Raniganj is the oldest coalfield, mined since the 18th century.
  • Talchir tillite (glacier debris rock, named after Talcher in Odisha) and Glossopteris fossils are Gondwana evidence for continental drift.
  • Coal despatch ranking (2021-22): Odisha > Chhattisgarh > Jharkhand > Madhya Pradesh > Telangana > Maharashtra [2].
  • Trap: small Gondwana coal deposits also occur in Assam and Sikkim [2]. Not all north-east coal is Tertiary coal.
  • Order from oldest to youngest: Gondwana → Deccan Traps → Tertiary → Quaternary. The Deccan Traps are not Gondwana rocks.

Mains Points

  • Geology decides where industry is located (GS-I, GS-III):
  • Gondwana coal lies in old rift basins of the eastern and central Peninsula.
  • So coal-based power plants and steel plants are concentrated in Odisha, Chhattisgarh and Jharkhand. These three states made up over 60% of coal despatches in 2021-22 [2].

  • India has very little prime-coking coal (5.318 billion tonnes) [2]. This limits steel-making from Indian coal alone.

  • Energy security (GS-III):

  • About 86% of raw coal despatched in 2021-22 went to the electricity sector [2].

  • Proved 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].

  • Gondwana as a record of plate movement (GS-I):

  • The Talchir tillite shows that ice once covered India near the South Pole.
  • Glossopteris fossils shared with Africa, South America, Australia and Antarctica show that these lands were once joined as Gondwanaland.
  • Together, these support continental drift and help explain how India broke away and drifted north.

Related concepts

Read more

Sources

  1. 1Class 11, Ch 4 "Distribution of Oceans and Continents" (primary)
  2. 2Indian Minerals Yearbook 2022, "Coal and Lignite", Indian Bureau of Minesibm.gov.in · tier 1