Vindhyan system

Topic: Minerals, Rocks and the Rock Cycle · NCERT: Beyond NCERT

Meaning

The Vindhyan system is a very thick pile of sandstones, shales and limestones laid down in the Proterozoic, after the Cuddapah rocks. These rocks have barely been changed by heat or pressure, and they stretch from Sasaram (Bihar) to Chittorgarh (Rajasthan).

It matters because it is the youngest of India's Precambrian (Purana) rock systems. It supplies red sandstone for building and limestone for cement, it holds the Panna diamond belt, and its stromatolites are among India's best records of early life.

Explanation

Where it fits in India's rock order

• Indian rock systems are groups of rocks that formed in the same long period of Earth's history.
• Order from oldest to youngest: Archaean → Dharwar → Cuddapah → Vindhyan → Gondwana → Deccan Traps → Tertiary → Quaternary.
• The first four are the Precambrian or Purana rocks. "Precambrian" means older than about 541 million years.
• Proterozoic is the part of the Precambrian from about 2.5 billion to 542 million years ago. The Cuddapah rocks were laid down in this time, and the Vindhyan rocks were laid down later in it, on top of the older basement rock [3].
• The Cuddapah and Vindhyan basins are less deformed basins inside the old cratons (the old, stable cores of a continent). They formed in the Mesoproterozoic (the middle part of the Proterozoic), along the edges of ancient plates [4].

How the rocks formed

• Cause: older rocks of the Peninsular shield were worn down by weather, rivers and wind.
• Process:
• Sand, mud and lime settled layer upon layer in large, shallow basins of water.

• Over time, the layers were pressed together into rock: sand became sandstone, mud became shale, and lime became limestone.

• Result: a very thick pile of flat or gently tilted layers.

• They are largely unmetamorphosed. Metamorphism means rock is changed by heat and pressure. The Vindhyan rocks escaped strong heat and pressure, so they still look much as they did when they were laid down.

Key features

• Rock types: sandstone, shale and limestone. They are sedimentary, not crystalline.
• Metamorphism: almost none. They are the least changed of the Precambrian systems.
• Fossils: rare. The main traces of early life are stromatolites.

• Stromatolite means a layered mound built up over time by mats of blue-green algae (cyanobacteria) in shallow water. It is one of the oldest signs of life on Earth.

• Minerals and materials:

• Red sandstone is a building stone.
• Limestone is a raw material for cement.

• Diamonds are found in the Panna belt. They are carried up through kimberlite pipes.

• Kimberlite means a volcanic rock that rises from deep in the mantle through narrow, pipe-shaped vents. It carries diamonds up to the surface.

Where it occurs

• Extent: from Sasaram (Bihar) in the east to Chittorgarh (Rajasthan) in the west.
• Regions crossed: the Son valley and the Malwa plateau.
• Panna diamond belt, Madhya Pradesh:
• The diamonds come from the Majhgawan pipe. Its kimberlite nature was recognised in 1930 [5].

• Majhgawan is a fully mechanised mine run by NMDC (National Mineral Development Corporation) [5].

• Stromatolite Park, Bhojunda (Chittorgarh district, Rajasthan): the Geological Survey of India (GSI) declared it a National Geological Monument so that it is protected and maintained [1].

• World context: the Indian Platform is a Precambrian shield. It is one of the four shields around which the Asian continent was built up [3]. The Vindhyan rocks are a younger sedimentary cover lying on this shield.

Don't confuse with

• Vindhya Range: this is a mountain range, a landform. The Vindhyan system is a group of rocks of a certain age. The rock system also covers areas such as Sasaram and Chittorgarh.
• Cuddapah system: it is older than the Vindhyan and shows a little more metamorphism. It sits in the crescent-shaped Cuddapah basin in Andhra Pradesh and holds uranium at Tummalapalle [2]. The Vindhyan system holds diamonds (Panna) [5].
• Dharwar system: these rocks are also sedimentary in origin, but they are highly metamorphosed and give metallic ores (iron, manganese, gold). The Vindhyan rocks are barely changed and mainly give non-metallic materials (sandstone, limestone).
• Gondwana system: it is younger and comes right after the Vindhyan. It is India's main coal system, while the Vindhyan system has no coal.

Prelims Hooks

• Vindhyan extent: Sasaram (Bihar) to Chittorgarh (Rajasthan), across the Son valley and the Malwa plateau.
• Least to most metamorphosed: Vindhyan < Cuddapah < Dharwar.
• Panna (Madhya Pradesh): diamonds come from the Majhgawan kimberlite pipe, recognised in 1930 and run by NMDC [5].
• Bhojunda Stromatolite Park (Chittorgarh, Rajasthan) is a GSI National Geological Monument [1].
• Trap: Vindhyan fossils are rare and are mainly stromatolites (made by cyanobacteria). They are not shells or bones.
• Order trap: Cuddapah comes before Vindhyan. Both are Proterozoic, and Vindhyan is the youngest Purana system.

Mains Points

• Rock type decides the resource (GS-I/III):
• The barely changed Vindhyan sediments give non-metallic materials: red sandstone for building and limestone for cement.
• This supports cement and stone-quarrying industries across the Son valley–Malwa–Rajasthan belt.

• The kimberlite pipes in the Vindhyan rocks make Panna (Majhgawan, NMDC) India's diamond-mining centre [5].

• Geo-heritage conservation (GS-I/III):

• Precambrian sites hold the record of early life, for example the Bhojunda stromatolites [1].

• Quarrying is common in the Vindhyan and Aravalli belts, so these sites need legal protection, such as the GSI's National Geological Monument status.

• Contrast with the metal-rich shield: the Dharwar rocks were heated and squeezed for billions of years, which concentrated metals into ores. The Vindhyan layers escaped this, so the Vindhyan belt is a store of building materials, cement material and diamonds rather than metal ores.

Related concepts

• Indian rock systems
• Archaean system
• Dharwar system
• Cuddapah system

Read more

• India's rock systems I: Archaean to Vindhyan (the Precambrian shield)