The Geological Structure of India

Geological structure of India tells us about the arrangement in the positions of Rock in the earth’s crust which plays a dominant role in determining the relief of land and nature of soil.

Geological structures helps us in –

• • Knowing about the worst mineral wealth deposited Beneath earth surface
  • Land use planning
  • Development of transport and communication lines
  • Increasing potential for irrigation
  • Determining the quality and quantity of groundwater resources
  • Understanding disasters like earthquake volcano landslide etc.

Geological Regions of India

Geological Structure of India is divided into three reasons –

1. The peninsular region which includes Meghalaya plateau in the North East and the kuchchh Kathiawar region in West
2. The extra peninsular region the Himalaya and their Eastern extension including Andaman and Nicobar Island
   • • The Himalayas are young, weak and flexible in their geological structure, unlike the rigid and stable Peninsular Block.
     • Consequently, they are still subjected to the interplay of exogenic and endogenic forces, resulting in the development of faults, folds and thrust plains.
     • These mountains are tectonic in origin, dissected by fast-flowing rivers which are in their youthful stage.
     • Various landforms like gorges, V-shaped valleys, rapids, waterfalls, etc. are indicative of this stage.
3. Indo Gangetic plain between Peninsula and extra Peninsular region

Geological History of India

Major events in the geological history of India:

• • Peninsular India was a part of the old landmass since the formation of the Earth’s Crust
  • The upheaval of Himalayas in the tertiary period.
  • Aggradation formation of the Indo-Gangetic plain during the Pleistocene period. It continues till today through sedimentation in the floodplains of the rivers and the lower part of the Gangetic plain.

Based on this complex and varied geological history, Geological survey of India has classified Rock systems of the country into following four major division –

1. 1. 1. 1. The Archaean Rock System
         2. The Purana Rock System
         3. The Dravidian Rock System
         4. The Aryan Rock System

1. The Archaean Rock System

1. Rock structure prior to the Cambrian system
2. Term ‘Archaean’ was first used by J.D. Dana
3. It includes –

1. Gneisses and Schists

• • Oldest rock (about 4000 million years ago).
  • Formed by cooling and solidification of upper crust of the earth’s surface in pre Cambrian era.
  • Azoic or no fossiliferous
  • Crystalline
  • Extremely contorted and faulted.
  • Have a well-defined foliated (sheet) structure.
  • These are plutonic rocks I.e. Formed by intrusion of magma.
  • They are also called ‘Basement Complex’ or ‘Fundamental Complex’

• • Gneisses – Found in 2/3rd of peninsular region. Contains minerals which can vary from granite to gabbro. Possesses a constant, foliated and banded structure.

• • Schists – They are mostly crystalline. They ranges from mica, talc, hornblende, chlorite, sillimanite and graphite schists.

• • Found in – Central and southern part of peninsula. In North East peninsula covers Odisha, Meghalaya, M.P., Chhattisgarh and Chota Nagpur plateau of Jharkhand. Also found in bundelkhand, Aravalli range in North and in Himalayan range

2. The Dharwar System

• • Includes highly metamorphosed (weathered) rocks of both sedimentary and igneous origin.
  • Formed by metamorphism of sediments of Archaean Genesis and Schists.
  • Formed between 4 million years ago to 1 billion years ago.
  • found today in metamorphic forms and do not contain fossils.
  • Major rocks includes hornblende, schists, quartzite, phyllites, slates, crystalline limestone and dolomites.
  • Found in- Karnataka, Chhattisgarh, Jharkhand, Madhya Pradesh, Odisha and Aravalli range. In extra peninsular region found in Northern and Central Himalayan region as well as Meghalaya plateau.
  • Importance – Economically the most important rocks as it contains valuable minerals like high grade iron ore, manganese, copper, lead, gold, quartzite, slates, mica etc.

2. The Purana Rock System

• 1400-1600 million years ago.
• The Archaean gneiss and the Dharwar rocks underwent further erosion leading to the formation of the Purana Rock system.
• Comprises of Proterozoic era.
• It includes two divisions :

1. 1. 1. 1. The Cuddapah system
         2. The Vindhyan System

1. The Cuddapah System

• • These are composed of unfossiliferous clay, slates, quartzite, sandstone and limestones.
  • The metallic content in ores of Cuddapah rocks is low and at places uneconomical for extraction.
  • Found in – Andhra Pradesh (Kurnool, Cuddapah), Chhattisgarh (Dantewara, Baster, Kanker, Raipur, Durg), Jharkhand (Singhbhoomi), Odisha (Kalahandi, Keonjhar) and Aravalli Range etc.
  • Importance – Rocks contains ores of Iron, Manganese, Copper, Cobalt, Nickel, barites, jasper, Asbestos etc. Also contains building purpose quartzite and limestones.

2. The Vindhyan System

• • 1300- 600 million years ago
  • Comprises of ancient sedimentary rocks superimposed on the Archaean base.
  • Vast stratified formation of limestones, shales, and sandstones.
  • Over 4000 m thick.
  • Comprises of two distinct but unequal sets of deposits –

a. The lower vindhyan

• • • 1300-1100 million years ago
    • Marine in origin, mostly calcareous in nature and shows tectonic deformation.
    • Found in son valley in Chhattisgarh, Mewar.

b. The upper vindhyan

• • • 1000-600 million years ago
    • Fluviatile In origin i.e. formed by river.
    • Generally lie in horizontal undisturbed strata.
    • Two famous Diamond Mines Panna and Golconda are found in upper vindhyan rocks.
    • Found in – Deccan trap covering Bihar to Rajasthan except Bundelkhand. Also found in Chhattisgarh, Karnataka and Andhra Pradesh.
    • Importance – Devoid of metallic minerals. But provides large quantities of excellent and durable stones, limestones, ornamental stones, flagstones, pure glass making sand and some coal.

3. The Dravidian Rock System

• 600-300 million years ago
• Found in extra peninsular region. These formations do not occur in the peninsular plateau as it was above the sea level at that time but are found in continuous sequence in the Himalayas.
• Contains abundant fossils which helps in determining the age of rocks.
• Coal formation started from this period, hence, named Carboniferous age.
• It includes following –

a. The Cambrian Rocks

• • • 600 million years
    • Includes slates, clays, quartzite and limestones.
    • Found in North West Himalaya.

b. The Ordovician Rocks

• • • 500 million years
    • Includes quartzite, grits, limestones and sandstones.
    • Found in spiti valley and Lidar valley of Kashmir and in the Kumaon region.

c. The Silurian Rocks

• • • 440 million years
    • Found in Spiti valley, Lahul and Kullu valley and to some extent in Kumaon region.

d. The Devonian Region

• • • 400 million years
    • Devoid of any fossils.
    • These rocks are identified in Muth quartzite of Spiti and Kumaon and in Haridwar.

e. The Carboniferous Rocks

• • • 350 million years
    • Comprises mainly of limestones, shales and quartzite.
    • Coal formation started in the Carboniferous age.
    • These rocks are divided into –
      • • Upper Carboniferous – Made of limestone and dolomites. Mount Everest is composed of this type of rocks.
        • Middle Carboniferous – Mainly found in Spiti valley, Kashmir, Shimla and eastern Himalaya.
        • Lower Carboniferous – Includes slates of different types. Found in Pir panjal trap and some parts of Kumaon region.

4. The Aryan Rock System

• From Upper Carboniferous to the recent.
• Fairly preserved in peninsular region and in Himalayan region along the north border.
• It comprises of the following –

a. The Gondwana System

• • Consists of sandstones with some shales and clays.
  • They are of continental origin, fluviatile and lacustrine deposits deposited in geosynclinals troughs on ancient plateau surface.
  • The peninsula during the Upper Carboniferous period experienced crustal movements, which led to the formation of basin-shaped depressions.
  • The sediments are accumulated in the troughs and loaded troughs subsided.
  • Fresh water and sediment accumulated in these troughs resulting in terrestrial plants and animals.
  • These rocks have also marks of climatic changes from arctic cold to tropical and desert conditions.
  • This system occurs around Permian period (250 million years ago)
  • Found in – Along the Damodar valley in Jharkhand, along the Mahanadi river valley in Chhattisgarh and Orissa, Madhya Pradesh, Along the Godavari River.
  • In extra Peninsular region found in Kashmir, Darjeeling and Sikkim.
  • Importance – Gondwana rocks contains 98% of Indian coal reserves. They also have rich deposits of iron ore, copper, Uranium and Antimony. Sandstone, Slates and Conglomerates are used as building materials.

b. The Triassic System

• • 280-225 million years
  • Found in- in the south of Greater Himalaya from Kashmir to Byans in Eastern Kumaon.

c. The Jurassic System

• • Marine Transgression in later part of Jurassic gave rise to thick series of shallow water deposits in Rajasthan and Kuchchh.
  • Coral limestone, Shales, Sandstone and Conglomerates occurs in Kuchchh.
  • Found in- Covers wide areas in Tibet, South Ladakh, Spiti, Nepal and Bhutan.

d. The Cretaceous System

• • 135-70 million years ago
  • Rocks includes sandstones, quartzite, limestones and shales.
  • In central parts of the peninsula occurs estuarine and lacustrine deposits called ‘Lemetas’.

e. The Deccan Trap

• • The period between the Cretaceous period till the beginning of Eocene, saw major volcanic outburst and eruptions in vast area of peninsular India.
  • Basaltic lava covered the area as large as 10 lakh sq. km.
  • These volcanic deposits have flat top and steep sides and hence called ‘trap’ which means stairs in Swedish.
  • The volcanic activity led to two great events –

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

• • Denudation over a long period of time has reduced the Deccan trap to almost half of its original size which is now only 5 lakh sq. km.
  • Thickness varies from 3000 m along the west which toward south gets reduced to 600 – 800 m, 800 m in Kuchchh and only 150 m towards east in Amarkantak.
  • The weathering of these rocks for a long time has given birth to black cotton soil known as ‘regur’.
  • Found in- Parts of Kuchchh, Saurashtra, Maharashtra, Malwa plateau and northern Karnataka. Parts of Telangana, Tamil Nadu, Jharkhand and Uttar Pradesh also have some outliners.
  • Importance- Great source of quartz, agate, calcite, building stones and roads building materials.
  • The Deccan Trap is divided into following –

The Upper Trap – 

• • • • • Found in Maharashtra and Saurashtra.
        • Thickness – 450 m
        • Contains inter trappean beds and layers of volcanic ash.

The Middle Trap –

• • • • • Found in Central India and Malwa.
        • Thickness – 1200 m
        • Has numerous ash beds and devoid of inter trappean.

The Lower Trap

• • • • • Found in Central India and Tamil Nadu.
        • Thickness – 150 m

f. The Tertiary System

• • Rocks were formed from Eocene to Pliocene (60 to 7 million years ago).
  • Quaternary is the name proposed for very recent deposits, which contains fossils of species with living representatives
  • These include Sutlej-Ganga-Brahmaputra plains and Karewa formations of the Kashmir valley.
  • Himalayas were born during this period and India came into its present form in this period only.
  • It is generally divided into following –

The Eocene System

• • • • 60 million years ago
      • Found in Jammu and Kashmir, Himachal Pradesh, Rajasthan, and Gujarat and in North-eastern part of India.

Oligocene and Lower Miocene System

• • • • 40-25 million years ago
      • Found in some parts of Assam, Kashmir (between Indus and Chenab), Shimla area etc.

The Shiwalik System – Middle Miocene to Lower Pleistocene

• • • • 14-0.2 million years ago
      • It is divided into three divisions –

Upper shiwaliks – 1800 – 2750 m

Consists of boulders, Conglomerates beds, sandstones, clays.

Richly fossiliferous in Shiwalik hills

Middle Shiwaliks – 1800-2500 m

Consists of Gravels, Sandstones, shales and clays.

Lower Shiwaliks – 1200-1500 m

Consists of Shales and sandstones.

The Pleistocene and the Recent (Quaternary)

• • • This is the period of nearly 1 million years.
    • This is the recent period and has just began.

So, this is all about the Geology of India or Geological Structure of India.

In the next post (Click here), we would study about the Physiographic Regions of India.