Do you know about Geological Structure of India ?

Geological Aspects of India

The Geological Structure of India started with the geological evolution of rest of the earth. India entirely falls under the Indian plate that was formed when it split off from the major tectonic plate of ancient continent Gondwanaland (Ancient landmass, consisting of the southern part of the supper continent of Pangaea.

Geological Structure of India

Geologically, India represents a monumental assemblage of rocks of different character belonging to different ages, ranging from Precambrian to the recent times. The Geological Survey of India (Sir T Holland) divides geological formation of India into four groups.

  1. The Archaean Rock System First half of the Precambrian era (about 4000 million years ago).
  2. The Purana Rock System Second Half of the Precambrian era (1400-600 million years).
  3. The Dravidian Rock System Cambrian to middle carboniferous (600-700million years old)
  4. The Aryan Rock System Upper Carboniferous to the Pleistocene ( 300 million years old)

1.The Archaean Rock System

The word Archaean was first used by JD Dana for rock structure prior to the Cambrian system. It includes the following two rock groups.

a) Gneisses and Schist:

This system contains the first formed rocks of the Earth. These rocks in the peninsula are found primarily in Tamil Nadu, Andhra Pradesh, Karnataka, Odisha, Meghalaya, Madhya Pradesh and Chhattisgarh and Chhotanagpur Plateau of Jharkhand.

They also cover the whole of Bhundelkhand in the North and to the North-west, they are formed in the number of isolated outcrops, extending from north of Vadodara to a long distance along the Aravallis.

b)The Dharwad System:

This System derives its name from the rocks, first studied in the Dharwad district of Karnataka. These are the earliest formed sedimentary rocks, found today in metamorphic forms. These rocks were deposited in three major cycles; the earliest one is over 3100 million years old and the latest one about 2300 million years old.

They were metamorphosed around 1000 million years ago. These rocks do not contain fossils and are found in Karnataka, Madhya Pradesh, Jharkhand, Chhattisgarh, Odisha, Meghalaya, and Rajasthan. They occur also in the central and Northern Himalayas.

Schist, slates quartzite and conglomerates are some of the rocks. This system carries minerals like gold, manganese ore, iron ore, chromium, copper, and Uranium, thorium and mica and building materials like granites, marbles, quartite and slate.

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The Purana Rock System

In India, the word purana has been used in place of proterozoic and includes two divisions.

a)The Chuddapah System:

A long interval of time elapsed before the rock system next to the Dharwads and peninsular gneisses began to be deposited. A great thickness of unfossiliferous clay, Slates, quartzite, sandstones and limestone was deposited presumably in great synclinal basins.

This formation is known as the Chuddapah System, from the occurrence of the most typical and first studied outcrops of these rocks in chuddapah districts of Andhra Pradesh.

b)The vindhyan System

This system of ancient sedimentary rocks stands over the Chuddapah rocks. Except a few traces of animal and vegetable life, this group is devoid of any recognizable fossils. It covers a large area in Madhya Pradesh, Chhattisgarh, Utter Pradesh, Bihar, Rajasthan, Karnataka and Andhra Pradesh. This System contains rocks like limestone, Sandstones, shale and Slates which are useful as building materials often over 4000 m thick.

3. The Dravidian Rock System

These rocks do not occur in the peninsular plateau as it was above the sea level at that time, but are found in continuous sequences in the Himalayas. Most Rocks of this system are found in the extra peninsular region and in one or two patches of lower Permian age, near Umaria.

The rocks belonging to the Dravidian System contains abundant fossils, which help in finding the inclusions of rocks of different periods like the rocks of Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods.

a)The Cambrian Rocks

These are best developed in the North-West Himalayan region. It includes slates, clays, quartzite, and limestone.

b)The Ordovician Rocks

These rocks overlie the Haimanta System and are also present in the Lidar Valley of Kashmir and in the Kumaon region. It includes quartzite, grits, sandstone and limestone.

c)The Silurian Rocks

In this Spiti valley, the Silurian rocks are in continuation with the Ordovician. Round the core of the Lidar anticline, there runs a thin, but continuous band of Silurian strata. The Lahul and Kullu Valleys of Himachal Pradesh also have some Silurian deposits. The lime and shale of the kumaon region belongs to the Silurian period.

 d)The Devonian Rocks:

These Rocks have been identified in the muth quartzite of Spiti and Kumaon, on the flanks of Lidar anticline and in the Haridwar district of Uttarakhand.

e)The Carboniferous System

These rocks are generally divided into Upper Carboniferous, middle Carboniferous and lower Carboniferous types. The upper Carboniferous rocks are made of limestone and dolomite. Mount Everest is composed of upper Carboniferous limestone. The middle Carboniferous has been the age of great upheavals.

The Aryan Rock System

The marine sedimentary rocks belonging to late Paleozoic to tertiary periods are exposed today in the northern part of the Central Himalayan axis extending from Kashmir to Sikkim. These rocks in the peninsula occur in several places in Gujarat, Rajasthan, Tamil Nadu and North-Eastern India.

a)The Gondwana System

The peninsula during the Upper Carboniferous period experienced crustal movements, which led to the formation of basin shaped depressions. These depressions had countless terrestrial plants and animals, which were buried to from coal deposits in India known as the Gondwana Rocks.

These rocks have also marks of climatic changes from arctic cold to tropical and desert conditions. These Rocks are found mainly in the Damodar, the Mahanadi and the Godavari valleys of the peninsula.

b)The Triassic System 

This system is almost unknown in the peninsula, but is found over extensive areas from Hazara to Nepal. The trias are generally divided into lower, middle and upper divisions.

c)The Jurassic System 

Rocks of the Jurassic system covered with area of 190 km length and 64 km width found in the Kutch. The area of jaisalmer of Rajasthan also has some Jurassic rocks. Coral limestone, oolitic limestone, sandstone, conglomerates and shale occur in Kutch.

d)The Cretaceous System

No other system is widely distributed in India as the cretaceous system both in the peninsular and extra-peninsular regions. They are found in the Spiti area, in the Kumaon region, in the Rupshu and Brazil areas of Kashmir and in the plateau of Meghalaya. The upper cretaceous system occurs in the Pondicherry, Tiruchchirappalli belt.

e)The Deccan Trap 

Towards the end of the Mesozoic era, intensive volcanic activity took place, which flooded with lava vast areas of Maharashtra and other parts of the Deccan known as the Deccan traps. The volcanic rocks contain some thin fossiliferous sedimentary layers found between the lava flows. This indicates that the lava flows was not continuous. The volcanic activity led to two great events

  • 1.    Breakup of the Gondwanaland masses
  • 2.    Uplift of the Himalayas out of the Tethys Sea.

f)The Shiwalik System:

The Shiwalik strata are found all along the length of Shiwalik hills. Sandstone, grit, conglometer clays and slits comprise the rocks of this system. They have been deposited in lagoons and fresh water lakes by the rivers of that time. The great bulk of the Shiwalik formation is non-fossiliferous, but in certain areas, some formations are highly fossiliferous.

The fauna records the sedimentation from middle Miocene to lower Pleistocene and has yielded a variety of fossils showing wide range of environment from humid forests to aridity.

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