Which of the following provides evidence that the Great Indian Desert was once under the sea during the Mesozoic era?
- AOption (a)
Presence of black soil
- BOption (b)
Marine deposits and wood fossils
- COption (c)
Glacial deposits
- DOption (d)
Volcanic ash layers
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Correct answer
Marine deposits and wood fossils
Why this answer is correct
The correct answer is Marine deposits and wood fossils.
Key Points
- The Great Indian Desert, also known as the Thar Desert, has a geological history that reveals it was once submerged under the sea during the Mesozoic era, specifically during the Jurassic and Cretaceous periods.
- The presence of extensive marine deposits in the Jaisalmer and Bikaner regions serves as primary evidence of ancient marine transgressions where the Tethys Sea covered large parts of western Rajasthan.
- Evidence of this maritime past is preserved at the Akal Wood Fossil Park, located about 17 km from Jaisalmer, which contains petrified remains of gymnosperms and other trees dating back nearly 180 million years.
- The discovery of fossilized ammonites, bivalves, and other marine invertebrates within the sedimentary rock layers confirms that the region supported a diverse marine ecosystem before tectonic shifts caused the sea to retreat.
- Geologists have identified that the desert floor consists of sedimentary rocks like sandstones, limestones, and shales, which are characteristic of shallow marine environments and coastal deltas from the Mesozoic and Cenozoic eras.
Additional Information
- Other options do not serve as evidence for this specific geological phenomenon:
- Black soil:
- Also known as Regur soil, it is typically formed from the weathering of basaltic volcanic rocks.
- It is predominantly found in the Deccan Trap region, covering states like Maharashtra and Madhya Pradesh, rather than being an indicator of marine history in the Thar.
- Glacial deposits:
- These are sediments like tillites transported and deposited by glaciers.
- While found in the Himalayas or related to the Permo-Carboniferous glaciation of Gondwanaland, they are not the defining evidence for the Mesozoic sea in the Thar.
- Volcanic ash layers:
- These originate from explosive volcanic eruptions.
- While some volcanic activity occurred during the Deccan eruptions, they do not prove the existence of an ancient sea bed compared to the direct evidence of fossilized marine life.