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<\/a>- Rocks formed prior to the Cambrian system.<\/li>
- The Archaean rock system includes:<\/li><\/ul>\n\n\n\n
Archaean Gneisses and Schists [4 Billion Years]<\/h2>\n\n\n\n
Gneiss == Mineral composition varies from granite to gabbro.<\/p>\n\n\n\n
Schists == mostly crystalline, include mica, talc, hornblende, chlorite, etc.<\/p>\n\n\n\n
These rocks are:<\/p>\n\n\n\n
- Oldest rocks<\/strong> [pre-Cambrian era] [formed about 4 billion years ago].<\/li>
- Rocks formed due to solidification of molten magma \u2013 the earth\u2019s surface was very hot then.<\/li>
- Known as the \u2018Basement Complex\u2019<\/strong> [They are the oldest and forms the base for new layers]<\/li>
- Azoic or unfossiliferous,<\/li>
- Foliated (consisting of thin sheets),<\/li>
- Thoroughly crystalline (because they are volcanic in origin),<\/li>
- Plutonic intrusions (volcanic rocks found deep inside).<\/li><\/ul>\n\n\n\n
Dharwar System [4 \u2013 1 Billion Years]<\/h2>\n\n\n\n
- Formation period ranges from 4 billion years ago to \u2013 1 billion years ago.<\/li>
- Highly metamorphosed sedimentary<\/strong> rock-system. [formed due to metamorphosis of sediments of Archaean gneisses and schists].<\/li>
- They are the oldest metamorphosed rocks<\/strong>.<\/li>
- Found in abundance in the Dharwar district of Karnataka.<\/li>
- Economically the most important rocks<\/strong> because they possess valuable minerals like high grade iron-ore, manganese, copper, lead, gold, etc.<\/li><\/ul>\n\n\n\n
Purana Rock System (1400 \u2013 600 Million Years)<\/h2>\n\n\n\n
- Includes two divisions: the Cuddapah System<\/strong> and the Vindhyan System<\/strong>.<\/li><\/ul>\n\n\n\n
Cuddapah System<\/h3>\n\n\n\n
- Unfossiliferous clay, slates, sandstones and limestones was deposited in synclinal basins<\/strong> [depression between two folds {Fold mountain}].<\/li>
- Outcrops best observed in Cuddapah district of Andhra Pradesh.<\/li>
- These rocks contain ores of iron, manganese, copper, cobalt, nickel, etc.<\/li>
- They contain large deposits of cement grade limestones.<\/li><\/ul>\n\n\n\n
Vindhyan System (1300-600 million years)<\/h3>\n\n\n\n
- This system derives its name from the great Vindhyan mountains.<\/li>
- The system comprises of ancient sedimentary rocks (4000 m thick) superimposed on the Archaean base.<\/li>
- Mostly Unfossiliferous.<\/li>
- Large area of this belt is covered by the Deccan trap.<\/strong><\/li>
- The Vindhayan system have diamond bearing<\/em><\/strong> regions from which Panna<\/strong> and Golconda diamonds<\/strong> have been mined.<\/li>
- It is devoid of metalliferous minerals<\/strong> but provides large quantities of durable stones, ornamental stones, limestone, pure glass making sand etc..<\/li><\/ul>\n\n\n\n
Dravidian Rock System (Palaeozoic)<\/h1>\n\n\n\n
- Formed about 600 \u2013 300 million years ago<\/strong>.<\/li>
- Found in the Extra Peninsular region (Himalayas and Ganga plain)<\/strong> and are very rare in Peninsular India. [The name \u2018Dravidian\u2019 doesn\u2019t mean they are found in South India]<\/li>
- Abundant fossils.<\/li>
- The\n rocks of Cambrian, Ordovician, Silurian, Devonian and Carboniferous \nperiods are fall under Dravidian system. (All these are not important, \nonly Carboniferous <\/strong>is important)<\/li><\/ul>\n\n\n\n
Carboniferous rocks (350 million years)<\/h2>\n\n\n\n
- The Carboniferous rocks (350 million years) comprise mainly of limestone, shale and quartzite.<\/li>
- Mount Everest<\/strong> is composed of Upper Carboniferous limestones.<\/li>
- Coal formation<\/strong> started in the Carboniferous age.<\/li>
- Carboniferous in geology means coal bearing<\/strong>. [most of the coal found in India is not of Carboniferous period; High quality coal of Great Lakes Region-USA, U.K and Ruhr<\/strong> region is Carboniferous coal].<\/li><\/ul>\n\n\n\n
Aryan Rock System<\/h1>\n\n\n\n
- Upper Carboniferous to the Recent<\/strong>.<\/li><\/ul>\n\n\n\n
Gondwana System<\/h2>\n\n\n\n
- The Gondwana System<\/strong> [derives its name Gonds<\/strong>, the most primitive people of Telangana and Andhra Pradesh]<\/li>
- They are deposits laid down in synclinal troughs<\/strong> on ancient plateau surface.<\/li>
- As the sediments accumulated, the loaded troughs subsided.<\/li>
- Fresh water and sediments accumulated in these trough and terrestrial plants and animals thrived.<\/li>
- This happened since Permian period (250 million years ago).<\/li><\/ul>\n\n\n\n
Gondwana Coal<\/h3>\n\n\n\n
- Gondwana rocks contain nearly 98 per cent of India\u2019s coal reserves<\/strong>.<\/li>
- Gondwana coal is much younger<\/strong> than the Carboniferous coal and hence it\u2019s carbon content is low.<\/li>
- They have rich deposits of iron ore, copper, uranium and antimony also.<\/li>
- Sandstones, slates and conglomerates are used as building materials.<\/li><\/ul>\n\n\n\n
UPSC IAS GK- Indian Rock System: Archaean, Purana, Dravidian & Aryan Rock System<\/p>\n\n\n\n
Jurassic System<\/h2>\n\n\n\n
- The marine transgression in the latter part of the Jurassic gave rise to thick series of shallow water deposits<\/strong> in Rajasthan and in Kuchchh.<\/li>
- Coral limestone, sandstone, conglomerates and shales occur in Kuchchh.<\/li>
- Another transgression on the east coast of the Peninsula is found between Guntur and Rajahmundry.<\/strong><\/li><\/ul>\n\n\n\n
Deccan Trap<\/h2>\n\n\n\n
- Volcanic outburst over a vast area of the Peninsular India from the end of the Cretaceous <\/strong>till the beginning of the Eocene<\/strong> gave rise to Deccan Traps.<\/li>
- Basaltic lava<\/strong> flowed out of fissures covering a vast area of about ten lakh sq km.<\/strong><\/li>
- These volcanic deposits have flat top and steep sides and therefore called \u2018trap\u2019 <\/strong>meaning a \u2018stair\u2019 or \u2018step\u2019 in Swedish.<\/li>
- The process of weathering and erosion (denudation) since millions of years has reduced the Deccan Trap to almost half of its original size.<\/li>
- Present Deccan Trap covers about 5 lakh sq km<\/strong> mainly in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau and northern Karnataka.<\/li>
- Thickness of the Deccan Traps is 3,000 metres along the west which is reduced to 600-800 metres towards the south, 800 metres in Kuchchh and only 150 metres at the eastern limit.<\/li>
- The weathering of these rocks for a long time has given birth to black cotton soil<\/strong> known as \u2018regur\u2019<\/strong>.<\/li><\/ul>\n\n\n\n
UPSC IAS GK Indian Rock System Archaean, Purana, Dravidian & Aryan Rock System<\/p>\n\n\n\n
The Deccan Trap has been divided into three groups:<\/p>\n\n\n\n
Group<\/td> Found in<\/td> Inter-trappean beds<\/td> Layers of volcanic ash<\/td><\/tr> The Upper Trap<\/td> Maharashtra and Saurashtra<\/td> Present<\/td> Present<\/td><\/tr> The Middle Trap<\/td> Central India and Malwa<\/td> Very rare to absent<\/td> Present<\/td><\/tr> The Lower Trap<\/td> <\/td> Present<\/td> Very rare to absent<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n Tertiary System<\/h2>\n\n\n\n
- Eocene to Pliocene about 60 to 7 million years ago.<\/li>
- The tertiary is the most significant period in India\u2019s geological history because the Himalayas<\/strong> were born and India\u2019s present form came into being in this period.<\/li><\/ul>\n\n\n\n
- Basaltic lava<\/strong> flowed out of fissures covering a vast area of about ten lakh sq km.<\/strong><\/li>
- Gondwana coal is much younger<\/strong> than the Carboniferous coal and hence it\u2019s carbon content is low.<\/li>
- They are deposits laid down in synclinal troughs<\/strong> on ancient plateau surface.<\/li>
- The Gondwana System<\/strong> [derives its name Gonds<\/strong>, the most primitive people of Telangana and Andhra Pradesh]<\/li>
- Coal formation<\/strong> started in the Carboniferous age.<\/li>
- Found in the Extra Peninsular region (Himalayas and Ganga plain)<\/strong> and are very rare in Peninsular India. [The name \u2018Dravidian\u2019 doesn\u2019t mean they are found in South India]<\/li>
- The Vindhayan system have diamond bearing<\/em><\/strong> regions from which Panna<\/strong> and Golconda diamonds<\/strong> have been mined.<\/li>
- Unfossiliferous clay, slates, sandstones and limestones was deposited in synclinal basins<\/strong> [depression between two folds {Fold mountain}].<\/li>
- They are the oldest metamorphosed rocks<\/strong>.<\/li>
- Oldest rocks<\/strong> [pre-Cambrian era] [formed about 4 billion years ago].<\/li>