Learn about the geological history of India by exploring its diverse rock systems from the ancient Archaean to the modern Quaternary. Discover formations, significance, and locations of each significant rock era shaping India’s landscape.
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 system of India has been classified under the following four categories:
- Archaean Rock System
- The Purana Rock System
- The Dravidian Rock System
- The Aryan Rock System
Archaean Rock System
It refers to a rock system before the Cambrian system. They are considered the oldest rock system in the world. The further classification of the Archaean Rock System is as follows:
- The Archaean System – Gneisses & Schists
- Period of Formation: These are considered the oldest rocks, formed about 4 billion years ago at the time of the cooling and solidification of molten magma in the upper crust of the earth’s surface.
- Features:
- Azoic (unfossiliferous)
- Crystalline (because of volcanic origin)
- Foliated (consisting of thin sheets)
- Extremely contorted and faulted
- Often formed as plutonic intrusions (volcanic rocks found deep inside)
- Major Rocks:
- Gneiss: These cover two-thirds of peninsular India. Their mineral composition varies from granite to gabbro. They possess foliated or banded structures.
- Schists: These are mostly crystalline.
- Location:
- Himalayas
- Central and southern parts of the Peninsula
- Orissa, Meghalaya, Madhya Pradesh, Chhattisgarh, and Chotanagpur Plateau of Jharkhand
- Bundelkhand
- Significance:
These rocks consist of mineral resources like mica, talc, hornblende, chlorite, etc.
- The Dharwar System
This rock system derives its name from the rocks identified and studied in the Dharwar district of Karnataka. They are found in abundance in the Dharwar district of Karnataka.
- Period of formation:
- These rocks were formed and deposited in 3 major cycles, the period of which ranges from 3,100 million years ago to 1,000 million years ago.
- Features:
- They are the most ancient metamorphosed sedimentary rock system in the world formed due to the metamorphosis of sediments of Archaean gneisses and schists
- Major Rocks:
- Hornblede, Schists, Quartzites, Phyllites, Slates, Crystalline Limestones and Dolomites.
- Location:
- Dharwar-Bellary-Mysore belt of Karnataka
- Jharkhand, Madhya Pradesh, Chhattisgarh, Odisha etc.
- Himalayan region
- Significance: These are the most important rocks in an economic sense as they possess valuable minerals like high-grade iron-ore, manganese, copper, lead, gold, etc.
The Purana Rock System
Period of Formation: These rocks were formed during the Proterozoic period (1400-600 million years ago). But, in the Indian context, the word Purana has been used instead of Proterozoic, so they are named the Purana Rock system.
Features: These are sedimentary metamorphic formations and are unfossiliferous.
Major Rocks: Clay, Slates, Sandstones, limestones, durable stones, etc.
Location: The Cuddapah system is found in the Cuddapah and Kurnool districts of Andhra Pradesh. They are also found in the southern part of Chhattisgarh and along the main axis of the Aravalli range. The Vindhyan Rock system is found in a stretch extending between Sasaram and Rohtas in Bihar to Chittorgarh in Rajasthan.
Significance: The Cuddapah Rock system has rich deposits of iron, manganese, copper, cobalt, nickel, etc. The Vindhyan Rock System has deposits of limestone, ornamental stones, and pure glass-making sand.
Classification of Purana Rock System: This rock system is further subdivided into two systems – the Cuddapah System and the Vindhyan System.
1. Cuddapah System:
- It is called the Cuddapah system because the rock outcrops were first observed in the Cuddapah district of Andhra Pradesh.
- These were deposited in the synclinal basins.
- These are unfossiliferous rocks.
- Some of the rocks in this category are clay, slates, sandstones, and limestones.
- These rocks contain ores of iron, manganese, copper, cobalt, nickel, etc.
2. Vindhyan System:
- This rock system derives its name from the great Vindhyan mountains.
- These are ancient sedimentary rocks superimposed on the Archaean base with a thickness of 4000 m thick.
- These are mostly unfossiliferous devoid of any recognisable fossils.
- They occupy an area of 1,00,000 sq. km.
- They are found in Chhattisgarh, Karnataka, Andhra Pradesh etc.
- Vindhayan system has diamond-bearing regions from which Panna and Golconda diamonds have been mined. They are devoid of any kind of metalliferous minerals but provide large quantities of durable stones, ornamental stones, limestone, pure glass-making sand, etc.
The Dravidian Rock System (Palaeozoic)
- Period of formation: 600-300 million years.
- Features: The Dravidian period marked the onset of coal formation, particularly the high-quality Carboniferous coal. However, abundant deposits of these coals are not found in India. These are abundant in fossils and the beginning of coal can be seen in this period.
- Major Rocks: Shales, sandstones, clays, quartzites, slates, salts, etc.
- Location: These are found in the Extra Peninsular region and are rarely found in the Peninsular region. The regions of Anantnag of Kashmir, Spiti, Kangra & Shimla region of Himachal Pradesh, Handwara, Lider Valley, Gharwal & Kumayun of Uttarakhand, and Pir Panjal are the major regions of Dravidian rocks.
- Significance:
These include mineral resources like shale, sandstones, clays, quartzites, salts, talk, dolomite, marble, coal etc.
- Classification of Dravidian Rock System:
- The Cambrian Rocks: They are best developed in the northwest Himalayan region.
- The Ordovician Rocks: These include quartzites, grits, sandstones, etc.
- The Silurian Rocks: These are found in the Lahoul and Spiti Valley. They exist in the form of limes and shales.
- The Devonian Rocks: These are devoid of any fossil fuel remains.
- The Carboniferous Rocks:
- The Carboniferous rocks formed around 350 million years ago comprise mainly limestone, shale, and quartzite. Carboniferous in geology means coal-bearing. It was during this period the coal formation started.
- These are divided into three types:
- Upper Carboniferous
- These are made up of limestone and dolomite.
- Mount Everest is composed of Upper Carboniferous limestones.
- Middle Carboniferous
- These rocks are found in Spiti Valley, Kashmir, Shimla etc.
- Lower Carboniferous
- These comprise slates of different types.
- Upper Carboniferous
The Aryan Rock System
- Period of formation: Upper Carboniferous period to Recent.
- Location: They are found in the Peninsular and Himalayan regions.
- Classification of Aryan Rock System:
- The Gondwana System: It derives its name from Gonds, the most primitive people of Telangana and Andhra Pradesh.
- Period of formation: Permian period (250 million years ago).
- Features: They are of continental origin, fluviatile, and lacustrine deposits laid down in synclinal troughs on ancient plateau surfaces.
- Location: The locations of the Gondwana rock system are Damodar Valley in Jharkhand, Mahanadi River Valley in Chhattisgarh and Odisha, parts of Madhya Pradesh, etc.
- Major Rocks: They have rich deposits of iron ore, copper, uranium, and antimony. Sandstones, slates, and conglomerates are used as building materials.
- Significance: They are important as they contain nearly 98 percent of India’s coal reserves.
- Jurassic System: These are named after the Jura mountains located on the borders of France and Switzerland.
- Period of Formation: They were formed between 201.3 million to 145 million years ago.
- Features: The marine transgression in the latter part of the Jurassic gave rise to a thick series of shallow water deposits in Rajasthan and Kuchchh.
- Location: They 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: The rock strata laid down during the Jurassic Period have yielded gold, coal, petroleum, and other natural resources.
- The Gondwana System: It derives its name from Gonds, the most primitive people of Telangana and Andhra Pradesh.
- The Deccan Trap:
- Period of formation: During the transition from the end of the Cretaceous to the beginning of the Eocene, an extensive volcanic upheaval occurred across Peninsular India that led to the formation of the Deccan Traps. The eruption resulted in the discharge of basaltic lava from fissures, covering an expansive region of approximately ten lakh square kilometers.
- Features: These volcanic deposits are distinct with flat tops and steep sides. They have been named ‘traps’ derived from the Swedish term which means ‘ stair’ or ‘step.’ The processes of weathering and erosion have significantly diminished the size of the Deccan Traps, shaping the present geological landscape.
- Major Rocks: The rocks in this region are of basalt type. The weathering of these rocks for a long time has given birth to black cotton soil known as ‘regur’.
- Location: The current extent of the Deccan Trap spans approximately 5 lakh square kilometers, primarily distributed across regions such as Kuchchh, Saurashtra, Maharashtra, the Malwa plateau, and northern Karnataka.
The Deccan Trap has been classified into the following groups:
- The Upper Trap – Saurashtra and Maharashtra.
- The Middle Trap – Malwa and Central India.
- The Lower Trap – Central India and Tamil Nadu.
- Significance: Regur which is black soil was formed due to the weathering of these rocks for a long time. It is an ideal soil type for cotton in the Penisnular region.
- The Tertiary System: The Tertiary period holds immense geological significance as it marks an era during which the Himalayan mountain range came into existence.
- Period of formation: 60 to 7 million years
- Features: This period played a pivotal role in shaping India’s present geographical form. It is called the “Age of Mammals” because of the abundance of the fossil remains of these animals in the deposits of this period.
- Major Rocks: The most significant rocks of this system may be found in India’s northern plains, in Kashmir’s karewas, and the Great Plains’ Bhangar, and Khadar.
- Location: Their significant locations are in India’s northern plains, in Kashmir’s Karewas and the Great Plain. These are also found along the coasts of Kachchh, Kathiawar, Konkan, Malabar, Nilgiri, and the Eastern Ghats.
- Significance: The rocks of this period have revealed a wealth of petroleum and coal deposits.
- Shivalik System
It takes its name from the Shiwalik hills between the Ganga and Yamuna rivers. Sandstones, grits, conglomerates, clays, and silts comprise the rock of this system. The Shiwalik system is famous for its oil resources, lignite, bauxite, and clays of different varieties.
- The Pleistocene and Recent (Quartnery)
Quaternary is a brief period of nearly one million years and is said to have started. It has two types – the older Pleistocene and the younger Recent. The fossiliferous clays, sands, and gravels of the Upper Satluj and the alluvial deposits in the river valleys of Tapi, Godavari, and Krishna belong to this age. The recent deposits in India are alluviums in the Indo-Gangetic region. These have been categorized as Bhangar and Khadar.
