Proterozoic Sedimentary Basins (Purana Basins)
A number of nearly flat-lying, virtually un-metamorphosed, and partly deformed Proterozoic cratonic basins form a significant part of the Precambrian shield of India. These sub-horizontal Proterozoic basins predominantly contain orthoquartzite shale-carbonate suites varying in thickness from 100 to 10,000 meters and were deposited episodically, with frequent breaks in sedimentation, over some time of about 1000 Ma. These are called “Purana” basins in Indian stratigraphy after Holland, akin to the Riphean of Russia due to their great similarities. The Hindi word ‘Purana’ means ‘ancient’ and is “necessarily a somewhat vague though most convenient term.”
Characteristics of Purana Basins
The Purana basins are mainly intra-continental basins, often called cratonic or epicratonic basins. They are mostly situated close to the periphery of cratons (pericratonic basin), some are located in the cratonic interior (intra-cratonic basins like Kaladgi and Bhima), and rarely between cratons (inter-cratonic basins like the Pranhita-Godavari basin lying between Dharwar and Bastar cratons). They are also described as platform basins and witness the story of early crustal evolution. These basins are useful for global comparison with similar basins in Canada, Australia, Africa, etc., and importantly, they unveil the prelude to the Cambrian explosion of life. They occupy 20% of the area of the Precambrian of Peninsular India. The common depositional environments are fluvial to shallow marine (deltaic, beach, inshore, lagoonal, tidal flat, etc.) grading into shelf-slope-basin settings. Aeolian and evaporitic (sabkha) environments are locally developed. Glacial and glacio-fluvial successions, recorded from other comparable global basins, are not yet established on an all-India basis from the Purana basins.
Division
| Palaeo-Proterozoic Basins | |
| Basin | Craton |
| Bijawar and Sonrai Basins and Harda Inlier | Bundelkhand Craton |
| Gwalior Basin | Bundelkhand Craton |
| Abhujmar Basin | Bastar Craton |
| Papaghni Sub-basin (Cuddapah basin) | Dharwar Craton |
| Meso-Neo Proterozoic Basins | |
| Basin | Craton |
| 1. Vindhyan basin | Bundelkhand Craton |
| 2. Chhattisgarh basin | Bastar Craton |
| 3. Khariar basin | Bastar Craton |
| 4a. Ampani basin | Bastar Craton |
| 4b. Keskal, Singanpur, and Chedrapal outliers | Bastar Craton |
| 5. Indravati basin | Bastar Craton |
| 6. Sabari (Sukma) basin | Between Bastar and Dharwar Cratons |
| 7. Pranhita-Godavari basin | Between Bastar and Dharwar Cratons |
| 8. Cuddapah basin | Dharwar Craton |
| 9. Kaladgi basin | Dharwar Craton |
| 10. Bhima basin | Dharwar Craton |
Palaeoproterozoic Basins
1. Bijawar Basin (1700-1800 Ma)
- Location: Bundelkhand Craton
- Extent: Trends ENE-WSW for about 100 km with a width of 4 to 20 km from Ken River in the east to Sonari in the west.
- Geological Setting: Sandwiched between Bundelkhand granite and Vindhyan sediments.
| Bijawar Group | |
| Karri Sandstone | Gangau Subgroup |
| Hirapur Phosphorite | Gangau Subgroup |
| Malehra Chert Breccia | Moli Subgroup |
| Pukhra Sandstone | Moli Subgroup |
| Dargawan Sill | Moli Subgroup |
| Bajno Dolomite | Moli Subgroup |
| Bhusor Basalt | Moli Subgroup |
| Kawar Conglomerate | Moli Subgroup |
2. Sonari Basin
- Location: Bundelkhand Craton
- Extent: 28 km long and 5 km wide, EW trending, situated to the west of the ‘type’ Bijawar basin.
3. Harda Inlier
- Location: Bundelkhand
- Exposure: Exposed at Harda within the Vindhyan succession and Deccan Trap of Narmada valley.
4. Gwalior Basin
- Location: Extends E-W for 80 km with a width of 25 km, near Gwalior to the north of Bundelkhand granite, almost 200 km NW of Bijawar basin.
5. Abujhmar Basin
- Location: Named for ‘abujh mar’ or ‘unknown hills’ in the remote Bansal region.
- Extent: Covers an area of 3000 sq. km.
| Abujhmar Group | Maspur Basalt (with gabbro/dolerite sills and dykes) |
| Gundul Formation | |
| Unconformity | |
| Nandgaon, Bailadila, and Sukma Groups with surrounding gneisses/granites |
Vindhyan Basin
The Vindhyan Basin is the largest single Purana basin, spectacularly sickle-shaped, and ENE trending. It is situated on the Bundelkhand craton and is named after the Vindhya Mountains. The basin is bounded by the Great Boundary Fault (GBF) in the northwest and the Son Narmada Lineament in the south. The Vindhyan Basin is well known for its diamonds, dolomite limestone, building stones, and glass sands.
Stratigraphy
The basin includes four groups in succession:
- Semri Group: Marine slope-shelf environment (3000-4000m)
- Kaimur Group: Lagoonal environment (400m)
- Rewa Group: Fluvial-deltaic environment (100-300m)
- Bhander Group: Fluvial-deltaic environment (1300-1500m)
Major Structure
The major structure of the basin is a synclinorium with the axis curving along the middle of the sickle-shaped basin.
Dating
Recent robust dating has fixed the beginning of Vindhyan sedimentation around 1600-1720 Ma. It is also known as the upper Purana.
Life
Stromatolites are abundant in the Vindhyan record, but they have a long time range and hence have only limited correlative value. Stromatolites are found in formations like Fawn Limestone, Khajrat Limestone, Rohtas (Semri), and Lakheri Limestone (Bhander).
Rock Types and Sedimentation
Chief rock types are shales, limestone, and sandstone, predominantly of shallow water origin. The upper Vindhyan sequences are fluvial in origin, whereas the lower Vindhyan sequences are marine and thicker.
