Geologically, the subcontinent of India was a part of the Gondwanaland which itself was a part of the
supercontinent of Pangaea. At that time, Indian landmass was attached to Madagascar and southern Africa on
the south west coast, and Australia along the east coast.
During Jurassic period, the supercontinent Pangea break apart into two super-continents namely, Gondwana (to the south) and Angaraland or Laurasia (to the north). The Gondwana Land includes India, Australia, South Africa, South America, and Antarctica.
According to Geological point of view:
- Peninsular India was a part of the old landmass since the formation of the Earth’s Crust
- In the tertiary period, the upheaval of Himalayas happened.
- During the Pleistocene period, aggradational formation of the Indo-Gangetic plain started which continues till today through sedimentation in the floodplains of the rivers and the lower part of the Gangetic plain.
The Indian geological eras are:
• The Archean or Early Pre-Cambrian
• The Purana or Late Pre-Cambrian
• The Dravidian or Paleozoic (Cambrian to Middle Carboniferous period)
• The Aryan (400 million years old to the present)
The Archean era or Early Pre-Cambrian
The geologic time scale from the formation of the Earth (about 4.6 billion years ago) to the beginning of the Cambrian Period of the Paleozoic Era (about 570 million years ago) constitutes the Archean era. The term Archaean refers to the oldest rocks of the Earth’s crust. Rocks of the Archaean System are devoid of any form of life. The group of these rocks consists of two systems:
1. Archaean gneiss
2. Dharwarian sedimentary
1. Archaean gneiss
The Archean gneiss includes the Aravalli, Dharwar, Cuddapah, Vindhyan, Meghalaya Plateau and Mikir Hills. The constituent minerals are orthoclase, oligoclase, quartz, muscovite, biotite and hornblends.
• The Archaen rocks cover two-thirds of Peninsular India and also occur in the roots of the mountain peaks all along the Greater Himalayas as well as in the Trans-Himalayan ranges of Zaskar, Ladakh and the Karakoram ranges.
In the Peninsular region, the Archaean rocks can be divided into three types:
(i) The Bengal Gneiss: It occurs in the Eastern Ghats, Odisha stretching over Manbhum and Hazaribagh districts of Jharkhand, Nellore district of Andhra Pradesh and Salem district of Tamil Nadu. They also occur in the Son Valley, Meghalaya Plateau and Mikir Hills. These formations are very thinly foliated (in thin layers that can be separated).
(ii) The Bundelkhand Gneiss: It occurs in Bundelkhand (Uttar Pradesh), Baghelkhand (MadhyaPradesh), Maharashtra, Rajasthan, Andhra Pradesh and Tamil Nadu. It is a coarse grained gneiss which looks like granite.
(iii) The Nilgiri Gneiss: It is widely found in South Arcot, Palni Hills, Shevaroy Hills and Nilgiri in Tamil Nadu, Nellore in Andhra Pradesh, Balasore in Odisha, Karnataka, Kerala, Malabar, Jharkhand, Chhattisgarh and Aravallis (Rajasthan). It is is bluish-grey to dark coloured rock, medium to coarse grained in texture.
2. Dharwarian sedimentary
This geologic time extends from 2500 million years ago to 1800 million years ago. These are the first metamorphosed sedimentary rock systems. They got their name from the place Dharwar district of Karnataka where they were first studied. They are composed largely of igneous debris, schists and gneisses. These rocks occur in Dharwar and Bellary districts of Karnataka, Nilgiris and Madurai districts of Tamil Nadu, central and eastern parts of Chotanagpur plateau, Meghalaya plateau, Aravalis, Himalayan region. They are rich in iron ore, manganese, lead, zinc, gold, silver, dolomite, mica, copper, tungsten, nickel, precious stones and building materials.
The Purana or Late Pre-Cambrian
The Archaean gneiss and the Dharwar rocks underwent further erosion leading to the formation of the Purana Rock system. It is further subdivided into:
1. The Cuddapah
2. The Vindhyan
1. The Cuddapah
These formations, named after the Cuddapah district in Andhra Pradesh are sedimentary metamorphic formations. These rocks are generally without fossils. It is made of shales, slates, limestone and quartzite. The Cuddapah System occurs in the Cuddapah and Kurnool districts of Andhra Pradesh, Chhattisgarh, Rajasthan-Delhi to the south of Alwar, and the Lesser Himalayas in the extra-Peninsular region. These rocks contain ores of iron, manganese, copper, cobalt and nickel, and deposits of barytes, asbestos.
2. The Vindhyan
The Vindhyan System derives its name from the Vindhyan Mountain. This mountain forms a dividing line between the Ganga Plain and the Deccan Plateau. It stretches from Sasaram in Bihar to Chittorgarh in Rajasthan with the exception of the central tract of Bundelkhand gneiss. It consists of enormous sedimentary deposits of great thickness. The Vindhyan system is well known for red-sandstone, sandstone, building material, ornamental stone and raw materials for cement, lime, glass and chemical industries. The well known diamond mines of Panna and Golconda lie in the Vindhyan System. The historical buildings of Qutab Minar, Humayun’s Tomb, Fatehpur Sikri, Agra Fort, Red Fort, Jama Masjid etc. have been constructed from the red-sandstone obtained from the Vindhyan Ranges.
The Dravidian or Paleozoic (Cambrian to Middle Carboniferous period)
The rocks of the Dravidian system are about 600-300 million years old. These are found in the extra-Peninsular regions of the Himalayas and the Gangetic plain.
The Dravidian rocks includes Cambarian, Ordovician, Silurian, Devorian and Carboniferous periods.
They are found in the north western region. It consists of slates, quartizites and dolomities.
They overlie the Haimanta system in all parts of the Spiti in the form of a thick series underlain by conglomerates. They are also present in the Lidar valley of Kashmir and in the Kumaon region.
The Silurian Rocks
In the Spiti valley, the Silurian rocks are in continuation with the Ordovicians. Lime and shales of the Kumaon region belong to the Silurian period.
The Devonian Rocks
These rocks are found in the Muth quarzite of Spiti and Kumaon, on the flanks of Lidar anticline and in the Haridwar district of Uttarakhand.
Carboniferous in geology means coal bearing. Coal formation started in the Carboniferous age. Carboniferous coal is of a higher quality, though it is not found abundantly in India.
The Aryan (Upper Carboniferous to Recent)
These rocks began to be formed since the Carboniferous period. This rock system is made up of diverse kinds of rocks, from the Gondwana rock system, Jurassic system, Deccan trap and Tertiary period. These are found in the Peninsular India and in the Himalayan region along the entire northern border.
The Gondwana System
The Gondwana group begins with the Permo-Carboniferous period, a period of coal formation. This system has huge carbon deposits contained within them which makes them the largest source of coal in India, containing up to 98 percent of our coal deposits. The rocks are found in the Talcher, Damuda and Panchet series. Talcher Series is named after Talcher in Dhankenal District of Odisha. It is rich in good quality coal used for smelting and in thermal power plants. The important coal areas of Damuda Series are Raniganj, Jharaia, Karanpura and Bokaro of the Damodar basin, Singrauli, Korba, and Pench valley in Chhattigarh and Madhya Pradesh, Talcher in Mahanadi Basin in Odisha, and Singareni of Satpura Basin in Madhya Pradesh. Panchet series consists of greenish-sandstone and shales. These are particularly well developed in the Raniganj coalfield of West Bengal. However, they contain inferior quality iron ore.
Gondwana coal is much younger than the Carboniferous coal thus its carbon content is low. They have rich deposits of iron ore, copper, uranium and antimony also.
This system has marine transgressions on both west and east coasts. This led to shallow water deposits in Rajasthan and the Kutchch region on the west and Guntur and Rajahmundry areas of Andhra Pradesh. This system includes Coral limestone, sandstone, conglomerates and shales.
Towards the end of the Cretaceous period, intensive volcanic activity took place in the Peninsula. The lava got flooded over vast areas of Maharashtra and other parts of the Deccan known as the Deccan traps. These are formed by the flow of magma over the solidified rock systems in layers. The Deccan lava covers about five lakh sq km of area in Gujarat (Kachchh, Kathiawad), Maharashtra, Madhya Pradesh (Malwa Plateau), Chhattisgarh, Jharkhand, northern Andhra Pradesh and north-western Karnataka. The Deccan Tra.p has a maximum thickness of about 3000 m along the coast of Mumbai from where it decreases towards south and east. It is about 800 m in Kachchh, 150 m at Amarkantak and 60 m at Belgaum (Karnataka).
The rocks of the Tertiary System were formed from Eocene to Foliocene about 60 to 7 million years ago. Fossils in these rocks include mammals, plants and invertebrates. Important rock systems of this system are Karewas of Kashmir, Bhangra and Khadar of the Gangetic plains.
Quarternary rock system (The Pleistocene and recent formations)
These are very recent deposits, which contains fossils of species with living representatives. The area include Satluj-Ganga-Brahmaputra plains and Karewa formations of the Kashmir valley.