Type: Prelims Only

The Ministry of Science & Technology has inaugurated India’s first open rock museum displaying different types of rocks gathered from different States of ages ranging from 3.3 billion years to around 55 million years.

Rock System in India

Based on this complex and varied geological history, the Geological Survey of India has classified rock systems of the country into 4 major divisions:

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

[I] Archaean Rock System:

The Archaean group of rocks consists of two systems-(a) Achaean granites and gneisses, and (b) Dharwarian sedimentary:

Archaean Gneisses and Schists (pre-2500 million years)

• The Archean System contains the first formed rocks of the earth.
• The rocks are primarily gneisses and granites, having no marks of fossils.
• They often underlie the strata formed subsequently and the system is generally known as the basement complex or fundamental gneisses.
• The Archaean rocks cover two-thirds of peninsular India. They also occur in the roots of the mountain peaks all along the Greater Himalayas, trans-Himalayan ranges of Zaskar, Ladakh and Karakoram.

Dharwar System (2500-1800 million years ago)

• The weathering of the Archaean rocks yielded the earliest sediments and formed the oldest sedimentary strata, the Dharwar system.
• These are found today in metamorphic forms and do not contain fossils.
• These rocks occur in scattered patches in parts of Karnataka, Tamil Nadu, central and eastern parts of Chotanagpur plateau, Meghalaya plateau, Aravalis, Himalayan region etc

Mineral contents:

• They contain gneisses (which range from granite to gabbro) and schists (crystalline rocks such as mica, talc etc.).
• These rocks have metallic and non-metallic minerals like copper, tin, graphite, lead, zinc, etc.

[II] Dravidian Rock System:

• This is also known as carboniferous rock system and formed during the Paleozoic era, i.e., from 600- 300 million years ago.
• They are not much abundant in India.
• They have plentiful fossils and beginning of coal formation can be seen in this period. The quality of carboniferous coal is high.
• They are found in extra- Peninsular regions of the Himalayas and the Gangetic plains.

Mineral content

• This type of rock system comprises of limestones, shale and quartzite and Mount Everest is formed of upper Carboniferous limestones.
• Most of the coal is not of the Carboniferous period, which is found in India.
• The meaning of Carboniferous in geology is coal-bearing.

[III] Purana Rock System:

The Purana rock system has two divisions: Cuddapah system and Vindhyan system. The word ‘Purana’ was used in place of a Proterozoic era in India.

Cuddapah Rock system:

• They are observed in Cuddapah districts of Andhra Pradesh.
• The non-fossiliferous clay, slates, sandstones and limestones were accumulated in the depression between two-fold mountains which is known as synclinal basins.
• They also have a large accumulation of building purpose cement grade limestones and quartzites.
• This type of rock contains ore of iron, cobalt, nickel, manganese etc.

Vindhya Rock System:

• This type of rock system is also ancient or old sedimentary rocks which are superimposed on the Archaean rock base and derived its name from Vindhya mountains.
• The recognition of fossils is negligible, only traces of few animal and plant life were found.
• This rock system has diamond-bearing regions from which Golconda and Panna diamond mined.

[IV] Aryan Rock System

The Aryan rock system in India has the following four subsystems:

1. Gondwana rock system
2. Jurassic Rock System
3. Cretaceous system/ Deccan Trap
4. Tertiary rock system

(1) Gondwana Rock System:

• These are found mainly in Raniganj, Jharia regions of Jharkhand, Damodar valley, Pench valley in Chhattisgarh and Madhya Pradesh.
• They are called so after the name of Gondwana tribe (indigenous people especially residing in Telangana and Andhra Pradesh region).
• In this type of rock system, you found metallic minerals like iron, manganese, uranium etc. other than coal.
• They have low carbon content as it is much younger than Carboniferous coal. These rocks have nearly 98% of India’s coal reserve.

(2) Jurassic Rock System

• During the latter part of Jurrasic when sea level rises as compared to land and shoreline moves towards ground or land which result in a flood. In geology, this phenomenon is called marine transgression.
• This gives rise to a thick series of shallow-water deposits kin Rajasthan and Kutch. Between the Guntur and Rajamundry, another transgression in the east coast of Peninsula.
• In Kuchchh, coral limestone, shales and conglomerates are found.

(3) Deccan traps

• These are formed by the flow of magma over the solidified rock system in layers.
• Deccan trap gets rise due to volcanic outburst over a major area of Peninsular India from the end of Cretaceous till the beginning of Eocene.
• The meaning of trap is “stair” or “step” in Swedish and called due to deposition of the volcanic outburst which has a flat top and steep sides.
• It is mainly found in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau and Northern Karnataka and presently cover near 5 lakh sq. Km.
• Regur, which is black soil, is formed due to the weathering of these rocks for a long time.

(4) Tertiary rock system

• The formation of this type of rock system occurs from 60 to 7 million years ago.
• It is the most noteworthy period in India’s geological history as the Himalayas were born and recent form came in this period.

Also read:

The Geological Structure of India

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Under the influence of two consecutive western disturbances, New Delhi is in for a wet spell.

Western Disturbances

• A western disturbance is an extratropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent.
• It is a non-monsoonal precipitation pattern driven by the westerlies.
• The moisture in these storms usually originates over the Mediterranean Sea, the Caspian Sea and the Black Sea.
• Extratropical storms are global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
• In the case of the Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
• Western disturbances are more frequent and strong in the winter season.

Impact: Winter Rainfall and Extreme Cold

• Western disturbances, specifically the ones in winter, bring moderate to heavy rain in low-lying areas and heavy snow to mountainous areas of the Indian Subcontinent.
• They are the cause of most winter and pre-monsoon season rainfall across northwest India.
• An average of four to five western disturbances forms during the winter season.

Its significance

• Precipitation during the winter season has great importance in agriculture, particularly for the rabi crops.
• Wheat among them is one of the most important crops, which helps to meet India’s food security.

Try this PYQ:

Q. Consider the following statements:

1. The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.
2. The moist air masses that cause winter rains in the North-Western region of India are part of westerlies.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

 

 

Post your answers here.

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