About the Indian Rock System

As a geological unit, India comprises a series of rock systems belonging to different ages and periods. The rock system of India has been classified under the following four categories:

1. Archaean Rock System

Refers to a rock system before the Cambrian system, considered the oldest rock system in the world. Further classification:

The Archaean System – Gneisses & Schists

• Period of Formation: About 4 billion years ago.
• Features:
  • Azoic (unfossiliferous)
  • Crystalline (volcanic origin)
  • Foliated (thin sheets)
  • Extremely contorted and faulted
  • Often formed as plutonic intrusions
• Major Rocks:
  • Gneiss: Covers two-thirds of peninsular India.
  • Schists: Mostly crystalline.
• Location: Himalayas, central and southern parts of the Peninsula, Orissa, Meghalaya, Madhya Pradesh, Chhattisgarh, Jharkhand, Bundelkhand.
• Significance: Rich in mineral resources like mica, talc, hornblende, chlorite, etc.

2. The Dharwar System

• Period of Formation: 3,100 to 1,000 million years ago.
• Features: Most ancient metamorphosed sedimentary rock system formed due to the metamorphosis of sediments of Archaean gneisses and schists.
• Major Rocks: Hornblende, Schists, Quartzites, Phyllites, Slates, Crystalline Limestones and Dolomites.
• Location: Dharwar-Bellary-Mysore belt of Karnataka, Jharkhand, Madhya Pradesh, Chhattisgarh, Odisha, Himalayan region.
• Significance: Important rocks in an economic sense with valuable minerals.

3. The Purana Rock System

Period of Formation: Formed during the Proterozoic period (1400-600 million years ago). The term “Purana” is used instead of Proterozoic in the Indian context.

Features: Sedimentary metamorphic formations and are unfossiliferous.

Major Rocks: Clay, Slates, Sandstones, limestones, durable stones, etc.

Location: Cuddapah system in Andhra Pradesh, southern part of Chhattisgarh, along the main axis of the Aravalli range, Vindhyan Rock system from Sasaram to Chittorgarh.

Significance: Cuddapah Rock system has rich deposits of iron, manganese, copper, cobalt, nickel. Vindhyan Rock System has deposits of limestone, ornamental stones, and pure glass-making sand.

Classification of Purana Rock System

1. Cuddapah System:

• Called Cuddapah system as rock outcrops were first observed in Cuddapah district of Andhra Pradesh.
• Deposited in synclinal basins.
• Unfossiliferous rocks.
• Rocks include clay, slates, sandstones, and limestones.
• Contain ores of iron, manganese, copper, cobalt, nickel, etc.

2. Vindhyan System:

• Named after the Vindhyan mountains.
• Ancient sedimentary rocks superimposed on the Archaean base.
• Mostly unfossiliferous.
• Occupies an area of 1,00,000 sq. km.
• Found in Chhattisgarh, Karnataka, Andhra Pradesh, etc.
• Diamond-bearing regions (Panna and Golconda).
• Provide durable stones, ornamental stones, limestone, pure glass-making sand, etc.

4. The Dravidian Rock System (Palaeozoic)

Period of formation: 600-300 million years.

Features: Dravidian period marked the onset of coal formation, particularly the high-quality Carboniferous coal. Abundant in fossils.

Major Rocks: Shales, sandstones, clays, quartzites, slates, salts, etc.

Location: Found in the Extra Peninsular region and rarely in the Peninsular region.

Significance: Includes mineral resources like shale, sandstones, clays, quartzites, salts, talc, dolomite, marble, coal, etc.

Classification of Dravidian Rock System

• The Cambrian Rocks: Best developed in the northwest Himalayan region.
• The Ordovician Rocks: Include quartzites, grits, sandstones, etc.
• The Silurian Rocks: Found in the Lahoul and Spiti Valley in the form of limes and shales.
• The Devonian Rocks: Devoid of any fossil fuel remains.
• The Carboniferous Rocks:
  • Upper Carboniferous: Made up of limestone and dolomite.
  • Middle Carboniferous: Found in Spiti Valley, Kashmir, Shimla, etc.
  • Lower Carboniferous: Comprises various types of slates.

5. The Aryan Rock System

Period of formation: Upper Carboniferous period to Recent.

Location: Found in the Peninsular and Himalayan regions.

Classification of Aryan Rock System

• The Gondwana System:
  • Period of formation: Permian period (250 million years ago).
  • Features: Continental origin, fluviatile, and lacustrine deposits laid down in synclinal troughs on ancient plateau surfaces.
  • Location: Damodar Valley in Jharkhand, Mahanadi River Valley in Chhattisgarh and Odisha, parts of Madhya Pradesh, etc.
  • Major Rocks: Rich deposits of iron ore, copper, uranium, and antimony. Sandstones, slates, and conglomerates are used as building materials.
  • Significance: Important as they contain nearly 98 percent of India’s coal reserves.
• Jurassic System:
  • Period of Formation: Formed between 201.3 million to 145 million years ago.
  • Features: Marine transgression in the latter part of the Jurassic gave rise to a thick series of shallow water deposits in Rajasthan and Kuchchh.
  • Location: Overlay the Triassic system and cover wide areas in Tibet, South Ladakh, Spiti, Nepal, and Bhutan.
  • Major Rocks: Coral limestone, sandstone, conglomerates, and shales.
  • Significance: Rock strata laid down during the Jurassic Period have yielded gold, coal, petroleum, and other natural resources.
• The Deccan Trap:
  • Period of formation: During the transition from the end of the Cretaceous to the beginning of the Eocene.
  • Features: Extensive volcanic upheaval leading to the formation of the Deccan Traps, covering an expansive region with basaltic lava.
  • Major Rocks: Basalt type rocks, weathering of these rocks gave birth to black cotton soil known as ‘regur’.
  • Location: Spans across regions like Kuchchh, Saurashtra, Maharashtra, the Malwa plateau, and northern Karnataka.
  • Significance: Regur (black soil) ideal for cotton in the Peninsular region.
• The Tertiary System:
  • Period of formation: 60 to 7 million years.
  • Features: Marks an era during which the Himalayan mountain range came into existence. Called the “Age of Mammals” due to fossil remains.
  • Major Rocks: Found in India’s northern plains, Kashmir’s karewas, and the Great Plains’ Bhangar and Khadar.
  • Location: Significant locations are in India’s northern plains, Kashmir’s Karewas, the Great Plain, and along the coasts of Kachchh, Kathiawar, Konkan, Malabar, Nilgiri, and the Eastern Ghats.
  • Significance: Rocks of this period have revealed a wealth of petroleum and coal deposits.
• Shivalik System:
  • Takes its name from the Shiwalik hills between the Ganga and Yamuna rivers.
  • Major Rocks: Sandstones, grits, conglomerates, clays, and silts.
  • Significance: Famous for its oil resources, lignite, bauxite, and clays of different varieties.
• The Pleistocene and Recent (Quaternary):
  • Quaternary is a brief period of nearly one million years.
  • Types: Older Pleistocene and younger Recent.
  • Deposits: Fossiliferous clays, sands, and gravels of the Upper Satluj and alluvial deposits in the river valleys of Tapi, Godavari, and Krishna.
  • Recent deposits: Alluviums in the Indo-Gangetic region, categorized as Bhangar and Khadar.