Model Answer
0 min readIntroduction
The Gondwana Supergroup represents a significant chapter in India’s geological history, formed during the late Paleozoic and Mesozoic eras. The Lower Gondwana Group, specifically, comprises the oldest sediments of this supergroup, deposited in rift valleys associated with the breakup of Gondwana land. These formations are crucial for understanding the paleoenvironment and paleoclimate of the Indian subcontinent and hold substantial economic importance due to their coal reserves. The Lower Gondwana Group is characterized by continental sedimentary rocks, primarily sandstones, shales, and coal seams, deposited in fluvial and lacustrine environments.
Geological Context and Time Period
The Lower Gondwana Group spans the Permian to early Jurassic periods (approximately 300-200 million years ago). Its formation is linked to the initial rifting phase of the Gondwana continent, leading to the creation of grabens and half-grabens. These rift valleys provided accommodation space for the accumulation of sediments derived from the surrounding highlands. The depositional environment was largely continental, with fluvial systems dominating the landscape.
Formations of the Lower Gondwana Group
1. Talchir Formation
The oldest formation of the Lower Gondwana Group, the Talchir Formation, is characterized by coarse-grained, poorly sorted conglomerates, sandstones, and shales. It represents alluvial fan and braided river deposits. Glacial deposits (tillites) are also found in some areas, indicating a period of glacial activity during the early Permian. Fossil content is generally sparse, but plant fossils (Glossopteris flora) are occasionally found. It is distributed in the eastern parts of India, including parts of Odisha, West Bengal, and Jharkhand.
2. Barakar Formation
Overlying the Talchir Formation, the Barakar Formation is predominantly composed of sandstones, shales, and coal seams. It represents a transition from braided river to meandering river systems. This formation is economically significant due to its substantial coal reserves. The coal seams are associated with thick shale layers and carbonaceous mudstones. Plant fossils, including Glossopteris, are abundant. It is found in the Damodar Valley region of West Bengal and Jharkhand.
3. Raniganj Formation
The Raniganj Formation is characterized by a repetition of sandstone, shale, and coal seam cycles. It represents a deltaic environment with extensive coal swamp development. The coal seams are generally thinner and more numerous than those in the Barakar Formation. This formation is famous for the Raniganj Coalfield, one of the oldest and largest coalfields in India. Plant fossils are common, and the presence of freshwater mollusks indicates a lacustrine influence.
4. Panchet Formation
The youngest formation of the Lower Gondwana Group, the Panchet Formation, consists of sandstones, shales, and conglomerates. It represents a transition to a more fluvial environment. Coal seams are present but are generally less extensive than in the Barakar and Raniganj formations. The formation is found in the eastern part of India, overlapping with the distribution of the other formations. It marks the end of the Lower Gondwana depositional phase.
Lithological Characteristics
| Formation | Dominant Lithology | Fossil Content | Economic Significance |
|---|---|---|---|
| Talchir | Conglomerates, Sandstones, Shales, Tillites | Sparse plant fossils (Glossopteris) | Limited, some building stone |
| Barakar | Sandstones, Shales, Coal Seams | Abundant plant fossils (Glossopteris) | Significant coal reserves |
| Raniganj | Sandstones, Shales, Coal Seams (thin) | Plant fossils, Freshwater Mollusks | Major coalfield, extensive coal reserves |
| Panchet | Sandstones, Shales, Conglomerates | Limited fossils | Moderate coal reserves |
Economic Importance
The Lower Gondwana Group is of immense economic importance due to its vast coal reserves. The Barakar and Raniganj formations are the primary sources of coal in eastern India, fueling power plants and industries. The coal is primarily bituminous, suitable for thermal power generation and metallurgical purposes. Besides coal, the sandstones and shales are used as building materials and in cement production. The formations also provide valuable insights into the paleogeography and paleoclimate of the region.
Conclusion
The Lower Gondwana Group represents a crucial period in the geological evolution of the Indian subcontinent, providing a window into the breakup of Gondwana land and the development of continental environments. Its formations, characterized by distinct lithological features and fossil content, are not only scientifically significant but also economically vital due to their abundant coal reserves. Further research and exploration are essential to fully understand the potential of these formations and ensure sustainable resource management.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.