GEOLOGICAL STRUCTURE OF INDIA

SOURCE: D.R. KHULLAR &  MASJID HUSSAIN

1.THE ARCHAEAN ROCK SYSTEM :

(i). THE ARCHAEAN SYSTEM –GNEISSES AND SCHISTS.

(ii). DHARWAR SYSTEM.

(i). THE ARCHAEAN SYSTEM –GNEISSES AND SCHISTS :

PERIOD :  PRE-CAMBRIAN

• The Archaean Era is also known as the Precambrian Period.

• The division of 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).

• The Precambrian time constitutes about 86.7% of the Earth's history.

• The term 'Archaean', introduced by J.D. Dana in 1782, refers to the oldest rocks of the Earth's crust.

• The oldest known rocks of the Earth, the evolutionary atmosphere, the first chemosynthesis, the first photosynthesis, the life-supporting atmosphere and the Earth's modem atmosphere, were developed during the Precambrian Era (Archaean and Protozoic).

• Rocks of the Archaean System are devoid of any form of life (No Life, no tree = no fossil & no coal).

• The Archaean rocks are all azoic or unfossiliferous.

• They are thoroughly crystalline, extremely contorted and faulted, and practically devoid of any sediment.

• They are largely intruded by plutonic intrusions and generally have a well-defined foliated structure.

• These rocks are known as the basement complex or fundamental gneisses.

• Cover two-thirds of Peninsular India.

• In the Peninsular region, the Archaean rocks are known to be of three well-defined types:

The Bengal Gneiss:

• Occurs in the Eastern Ghats, Orissa (known as Khodoliles after Khond tribes in Koraput and Bolangir districts), stretching over Manbhum and Hazaribagh districts of Jharkhand, Nellore district of Andhra Pradesh and Salem district of Tamil Nadu.

• For the first time these rocks were identified in the Midnapur district of West Bengal.

The Bundelkhand Gneiss:

• Forms the second group of fundamental gneiss of the Archaean age.

• Occurs in Bundelkhand (U.P.), Baghelkhand (M.P.), Maharashtra, Rajasthan, Andhra Pradesh and Tamil Nadu.

• A coarse grained gneiss which looks like granite.

• Conspicuously criss-crossed and characterised by quartz veins.

The Nilgiri Gneiss:

• The name being given in honour of job Charnock whose tombstone in Kolkata was made of this rock.

• Bluish-grey to dark coloured rock, medium to coarse grained in texture.

• This is plutonic gneiss intruding into the other Archaean rock masses.

• Nilgiri gneiss is popularly recognised as belonging to the Chamockite series.

• widely found in South Arcot, Palni Hills, Shevaroy Hills and NiJgiri in Tamil Nadu, Nellore in Andhra Pradesh, Balasore in Orissa, Kamataka, Kerala, Malabar,Jharkhand, Chhattisgarh and Aravallis (Rajasthan).

ECONOMICAL IMPORTANT:

• The Archaean rocks are the repositories of the mineral wealth of lndia.

• These rocks are rich in ferrous and non-ferrous minerals like iron ore, copper, manganese, mica, dolomite, lead, zinc, silver and gold.

(ii). DHARWAR SYSTEM (PROTEROZOIC FORMATIONS) :

PERIOD :  This geologic time extends from 2500 million years ago to 1800 million years ago.

• The first metamorphosed sedimentary rock systems known as the Dhatwar System in the Indian Geological Time Scale.

• In India, these rocks were studied for the first time in the Dharwar district of Karnataka.

• Composed largely of igneous debris, schists and gneisses.

Distribution:

• Dharwar and Bellary districts of Kamataka and extend up to the Nilgiris and Madurai districts of Tamil Nadu,  Central and eastern parts of the Chotanagpur Plateau, Meghalaya Plateau and Mikir Hills, and the Aravallis, Rialo (Delhi series), from Delhi to the south of Alwar and the Himalayan region Nilgiris and Madurai districts of Tamil Nadu,.

ECONOMICAL IMPORTANT:

• Dharwar rocks are highly metalliferous.

• Rich in iron ore, manganese, lead, zinc, gold, silver, dolomite, mica, copper, tungsten, nickel, precious stones and building materials.

2.THE PURANA ROCK SYSTEM :

PERIOD :  1400 – 600 MILLION YEARS

(i).THE CUDDAPAH SYSTEM.

(ii). THE VINDHYAN SYSTEM.

(i).THE CUDDAPAH SYSTEM

• named after the district of Cuddapah in Andhra Pradesh,

• sedimentary & metamorphic formations.

Distribution :

• The Cuddapah System occurs in the (i) Cuddapah and Kumool districts of Andhra Pradesh, (ii) Chhattisgarh, (iii) Rajasthan-Delhi to the south of Alwar, and (iv) the Lesser Himalayas in the extra-Peninsular region.

ECONOMICAL IMPORTANT :

• The principle rocks of the Cuddapah System are sandstones, shales, limestone, quartzites slates, inferior quality of iron-ore, manganese ore, asbestos, copper, nickel, cobalt (Delhi System), marble, jasper, building material and stones for interior decoration.

• The metallic contents in the ores of Cuddapah rocks are, however, low and at places uneconomical for extraction.

(ii). THE VINDHYAN SYSTEM:

• Derives its name from the Vindhyan Mountain.

• This mountain forms a dividing line between the Ganga Plain and the Deccan Plateau.

• The system covers an extensive area of 103,600 sq km from Chittorgarh in Rajasthan to Sasaram in Bihar.

• Has enormous sedimentary deposits and at places their depth is more than 4000 metres.

• In some tracts, the Vindhyan rocks are buried under Deccan lava.

• The Great Boundary Fault (GBF) separates the Vindhyan System from the Aravallis for a distance of about eight hundred km.

ECONOMICAL IMPORTANT:

• Well known for red-sandstone, sandstone, building material, ornamental stone, conglomerates, diamondiferous and raw materials for cement, lime, glass and chemical industries.

• In certain places these rocks yield inferior, quality of iron ore and manganese.

• 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, Birla Mandir, the Buddhist Stupa of Sanchi, etc. have been constructed from the red-sandstone obtained from the Vindhyan Ranges.

• Coarser sandstones have been used as grindstones and millstones.

3.THE DRAVIDIAN ROCK SYSTEM:(THE PALAEOZOIC GROUP)

PERIOD :  CAMBRIAN TO CARBONIFEROUS PERIOD.

• The Palaeozoic Era includes the Ordovician, Silurian, Devonian, Carboniferous and the Permian periods of the Standard Geological Time Scale. known as the Dravidian Era in the Indian Geological Time Scale.

• The Palaeozoic Era extends from 570 million years ago to 24.5 million years ago.

• It marks the beginning of life on the Earth's surface.

• The formations of this period are almost absent in the Peninsular India except near Umaria in Rewa.

• These formations exist in the Pir-Panjal, Handwara, Lidder-Valley, AnantnagofKashmir Uammu & Kashmir), Spiti, Kangra, Shimla region (Himachal Pradesh), and Garhwal and Kumaun (Uttarakhand).

• It was during this period that the Pangaea was broken and the Tethys Sea came into existence.

• The Cambrian rocks include shales, sandstones, clays, quartzites slates, salts, marble, etc.

• Palaeozoic System in the Indian Geologic Time Scale The Gondwana formations are fluviatile and lacustrine in character.

• They were deposited in the river basins and lakes during the Upper Carboniferous Period.

• These basins later subsided along the trough faults amidst ancient rocks of the great southern continent called the Gondwanaland.

• These rocks were formed during the Upper Carboniferous and the Jurassic Periods (Mesozoic Era).

4.THE ARYAN ROCK SYSTEM:

PERIOD : Upper Carboniferous

• The beginning of the Upper Carboniferous Period is known as the Aryan period.

The salient features of the Aryan formations are:

• During the Upper Carboniferous Period, the Himalayan region was occupied by a vast geosyncline which was connected to the Pacific Ocean in the east through China and the Atlantic Ocean in the west through Afghanistan, Iran, Asia Minor and the present Mediterranean Sea. This was called the Tethys Sea.

• The area of the Kashmir Himalayas (from Pir Panjallo Hazara in the north-west and Ladakh in the north-east) witnessed violent volcanic activity.

• The Upper continent of Gondwanaland developed fissures and its broken parts started drifting away from each other.

• The Subcontinent of India drifted towards north and northeast to collide with the Asian land mass (Eurasian Plate).

• There was large scale eruption of lava in the Deccan Trap.

• The development and expansion of the Arabian Sea and the Bay of Bengal.

• The Tertiary mountain building gave birth to Himalayas.

• The Subcontinent of India assumed its present shape.

• The beginning of ice Age, belonging to the Pleistocene Period, covering large parts of the earth under ice-sheet.

• Evolution and spread of man in different parts of the world.

(i).THE GONDWANA ROCK SYSTEM.

(ii). THE DECCAN TRAP.

(iii). THE TERTIARY SYSTEM.

(iv).THE QUATERNARY.

(i).THE GONDWANA. SYSTEM:

PERIOD:THE MESOZOIC ERA 

• 'Mesozoic' means middle life.

• The term is used for a period of geologic time in which the presence of fossil invertebrates dominated the rocks.

• includes three periods: Triassic, Jurassic, and Cretaceous.

• In the Indian Geological Time Scale, these periods extend from the Upper Carboniferous up to the beginning of the Cenozoic Era or the Aryan Era.

• The Gondwana group begins with the Permo-Carboniferous period which, in the Standard Geologic Time Scale, is known as a period of coal formation.

ECONOMICAL IMPORTANT :

• The Lower Gondwana rocks are found in the Talcher, Panchet and Damuda series.

• Most of the good quality coal deposits (bituminous and anthracite) of India are found in Gondwana formations.

• Moreover, iron ore occurs in the iron-stone shales of Raniganj coal fields.

• In addition to coal and iron, kaolin, fireclay, sandstone and grits are also found in the Gondwana formations.

• The Gondwana System of rocks provides over 95% of the coal of India.

• Moreover, it provides iron-ore, limestone, sandstone and raw material for ceramic industry.

• India's best and largest coal deposits are found in the Gondwana System-mainly in the Damodar Valley of West Bengal,Jharkhand, the Mahanadi valley of Orissa and Chhattisgarh, the Godavari valley of Andhra Pradesh and the Satpura basin of Madhya Pradesh

(ii). THE DECCAN TRAP

PERIOD : THE CRETACEOUS ERA

• The Cretaceous Period extends from about 146 million years ago to 65 million years ago.

• The term 'Cretaceous' has been obtained from the Latin creta, meaning 'chalk'.

• Very widely distributed system in the country which has divergent facies of deposits in different parts of India.

• This period is marked by the transgression of the sea (Coromandal coast, Narmada valley) and outpouring of huge quantity of lava (basalt) so as to form the Deccan Trap and intrusion of plutonic rocks such as gabbro and granite.

• Towards the end of the Cretaceous period the Peninsula was affected by intense volcanic activity.

• During this period, enormous quantity of basaltic lava was poured out to the surface assuming a great thickness of over three thousand metres.

• The Lava Plateau (the Deccan Trap) is the result of that lava eruption.

• 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 lava plateau of India (Deccan Trap) 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 individual lava flows, on an average, have a thickness of about 5 m to 29 m.

• Such flows have been identified in a boring near Bhusawal (Maharashtra).

• These are inter-bedded with sedimentary beds called 'inter-trappean beds'.

ECONOMICAL IMPORTANT:

• The basalt of the Deccan Trap is used for the construction of roads and buildings.

• Moreover, quartz, bauxite, magnetite, agate and semi-precious stones are also found in the trap. It is also rich in magnesium, carbonate, potash and phosphates.

(iii). THE TERTIARY ROCK SYSTEM

PERIOD: THE CENOZOIC ERA.

• Cenozoic means recent life.

• The beginning of the Tertiary Period is about 66 million years ago.

• Fossils in these rocks include many types, closely related to modern forms, including mammals, plants and invertebrates.

• The Cenozoic Era has two periods: The Tertiary and the Quaternary.

• The two great events that occurred during the Tertiary Period include:

(i) The final breaking-up of the old Gondwana continent, and

(ii) The uplift of the Tethys geosyncline in the form of the Himalayas.

• During the early Tertiary Period, as India collided with Tibet, the sediments which had been accumulating in the Tethys basin had begun to rise by a slow rise of ocean bottom.

• The upheaval of the Himalayas altered the old topography of the subcontinent.

Three phases of the upheaval of the Himalayas have been distinguished:

• During the first upheaval (Eocene-about 65 million years ago), which culminated in the Oligocene, and resulted in the upheaval of the Greater Himalayas.

• It was followed by a more intense movement during the mid-Miocene period about 45 million years ago, which resulted in the folding of Lesser Himalayas.

• The third upheaval took place during the Post-Pliocene period, about 1.4 million years ago which resulted in the folding of Shiwaliks or the Outer Himalayas. There is enough evidence to prove that the Himalayas are still rising.

• In the Peninsular region, the Tertiary System occurred on the coast of Kachchh, Kathiawar, Konkan, Malabar, Nilgiris, and the Eastern Ghats.

(iv).THE QUATERNARY:

PERIOD: THE PLEISTOCENE AND RECENT FORMATIONS

• Quaternary is the name proposed for very recent deposits, which contain fossils of species with living representatives.

• During the Quaternary Period, the ice-sheets descended to as low as 1500 metres in altitude.

• The bottom configuration of this plain, occupies largely a synclinal basin, called foredeep, which is a down warp of the Himalayan foreland of variable depth, formed concommitantly with the rise of the Himalayas to the north.

• The Pleistocene period is marked by Ice Age and glaciation on a large scaJe in the Northern Hemisphere.

• The moraine deposits and the Karewa formations· of Kashmir Valley and the Bhadarwa (Doda District of Jammu Division) are of the Pleistocene period.

• It forms the terraces of the Jhelum, on the flanks of the Pir-Panjal. The thickness of the karewas at places is up to 1400 metres.

• The river terraces of the narmada, Tapi, Godavari, Krishna, and Kaveri, etc. are also of the Pleistocene Period.

                          

Karewas :

• The lacustrine deposits of the Pleistocene period.

• They consist of sands, clays, loams, silt and boulders.

• The karewas of Kashmir are generally found along the lower slopes of Pir-Panjal with a dip towards the Kashmir Valley.

• The Pampore and Pulwama karewas are well known for the cultivation of saffron, almond, and walnut .

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