Vindhyan Rock System

1.1 What is it?

It is a huge stack of sedimentary rock in central India. Sediment is sand, mud and lime that settles and hardens. The stack is mostly sandstone, shale and limestone. Geologists call it the Vindhyan Supergroup. Most of it is undeformed and unmetamorphosed.

That means it was never folded hard or baked by heat.

1.2 Where does it lie?

It stretches from Chittorgarh in Rajasthan to Sasaram in Bihar. The rocks show at the surface in three sectors: the Son valley, Bundelkhand and Rajasthan. The Bundelkhand Massif splits the basin into the Son Valley part and the Chambal Valley part. The Chambal part runs from Agra to Chittorgarh.

1.3 How big and how thick is it?

It covers about 162,000 sq km. About half of that, near 80,000 sq km, lies buried under the Ganga plain.

Thickness depends on who measures and where. The DGH gives a maximum of around 3 km for the Supergroup. It also describes a pile of more than 5000 m. The INSA review says about 5 km. So say “3 to 5 km” and note the source.

2.1 What age do the rocks give?

They are around 1.7 to 1.0 billion years old. The Lower Vindhyans were laid down between about 1750 and 1600 million years ago. Tuff layers, which are hardened volcanic ash, give 1602, 1593 and 1628 Ma. Ma means million years ago.

Ages from the INSA review and the Shanti Swarup Bhatnagar Prize profile, listed under the cards.

2.2 Why does that rule out fossils?

The rocks predate the Cambrian period. So the Lower Vindhyans cannot hold Cambrian or younger fossils. If a textbook shows trilobites in them, the textbook is wrong.

2.3 When did the basin end?

Carbonates in the Bhander Formation suggest closure around 900 Ma. Older studies gave 1400 to 600 Ma. Those dates were questioned because they carried large errors.

3.1 Which groups make up the Supergroup?

There are four. From bottom to top they are Semri, Kaimur, Rewa and Bhander. Semri is the Lower Vindhyan. The other three are the Upper Vindhyan.

3.2 What lies inside the Rewa Group?

Rewa has four formations. They are the Panna Shale, the Itwa Sandstone, the Jhiri Shale and the Gahadra Sandstone.

It holds sandstone, shale and conglomerate. A conglomerate is a rock made of rounded pebbles cemented together. Rewa was laid down under lagoonal conditions, in calm shallow water cut off from the open sea.

Facts from the DGH, INSA, NMET and BSIP pages listed under the cards.

3.3 How did the setting change upward?

The Kaimur sandstones came from rivers and shallow seas. The Upper Vindhyan is mostly sandstone and shale, with carbonate at the top. So the rock type tells you how the water changed.

4.1 What happened between Semri and Kaimur?

Almost nothing was laid down. The Kaimur Group is about 400 Ma younger than the Semri Group below it. Geologists call such a long break a depositional hiatus. A hiatus is a missing slice of time in the rock record.

4.2 What marks the break?

A rock called the Dulchipur Conglomerate. It sits at the base of the Kaimur Group. After that break the Upper Vindhyan began to build up.

4.3 How do we know the Kaimur age?

A direct date came from the Bijaigarh Shale of the Kaimur Group. The Re-Os method gave 1210 Ma, plus or minus 52. The Majhgawan Kimberlite, dated to about 1073 Ma, suggests the Bhander-Rewa groups are younger than about 1075 Ma.

5.1 What are the three sources?

The Panna belt in Madhya Pradesh gives diamonds from three places. First, the Majhgawan and Hinota kimberlite pipes. A kimberlite is a volcanic rock pipe that brings diamonds up from deep in the Earth.

Second, diamond-bearing conglomerates in the Rewa Group, near the top of the Lower Rewa Sandstone and the base of the Jhiri Shale. Third, Quaternary alluvium in streams that drain the belt.

5.2 Who mines them?

Majhgawan is the only hard rock diamond mine in India. It has been worked since the early 19th century.

In the 2015 national inventory it was the only commercial-scale diamond mine in the country, run by NMDC. Small operators in Panna district also recover stones from conglomerate and gravel beds. They work on annual permits from the Diamond Officer of the Madhya Pradesh government.

5.3 Did Golconda diamonds come from here?

No. Golconda was the great trading centre, not a source. The IBM lists river Krishna gravel in Andhra Pradesh and the Panna belt as producing centres. Do not write that Golconda diamonds are Vindhyan.

The kimberlite nature of the Majhgawan and Wajrakarur pipes was recognised only in 1930.

6.1 Are the range and the rock system the same?

No. The Vindhya Range is a line of hills. The Vindhyan Supergroup is a stack of rock layers. The two names mean different things. An exam may test exactly this.

6.2 Where does it sit among India's old basins?

The Vindhyan is the largest of the Purana basins. Purana means ancient, here the great basins of Proterozoic age. The Cuddapah Basin is the oldest of them. It started around 1.9 Ga ago. Ga means billion years. The Vindhyan began later, about 1.7 Ga ago.

7.1 What does the Vindhyan hold besides diamonds?

Limestone is a big one. The Rohtas Limestone is in the Semri Group and is explored as a limestone resource.

The Bhander Limestone, high in the Upper Vindhyan, carries stromatolites. Stromatolites are layered mounds built by microbes. A 2026 BSIP report also describes trail-like structures in the basin that strongly resemble biological traces.

7.2 What was the latest Panna find?

In August 2026 workers found a 17.96-carat gem diamond at a shallow mine in Sarkoha village, Panna. It lay on top of an old mine after heavy rain. A government auction was expected in the first half of October. Seven workers will share the net amount equally.

8.1 What do exams ask?

They test the order of the groups and the age gap. Know Semri, Kaimur, Rewa, Bhander from the bottom. Know the Chittorgarh to Sasaram span. Know that Panna diamonds are tied to the Rewa Group and kimberlite pipes.

8.2 What are the traps?

Three. Do not call the hills and the rocks the same thing. Do not say Golconda was a source. Do not say the whole basin is exposed.