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UPSC Prelims 2001 · World Geography · Rocks, Quakes and Landforms
Consider the following statements made about the sedimentary rocks: Which of these statements are correct?
- Sedimentary rocks are formed at the earth's surface by the hydrological system
- The formation of sedimentary rocks involves the weathering of pre-existing rocks
- Sedimentary rocks contain fossils
- Sedimentary rocks typically occur in layers
- (a) 1 and 2
- (b) 1 and 4
- (c) 2, 3 and 4
- (d) 1, 2, 3 and 4
Show the answer and explanation
Answer: (d) 1, 2, 3 and 4
All four describe sedimentary rocks.
Statement by statement
1. ✓ CORRECT They form at the surface, laid down by water, wind and ice.
2. ✓ CORRECT They come from weathered older rocks.
3. ✓ CORRECT They are the rocks that hold fossils.
4. ✓ CORRECT They form in layers (strata).
The idea
Sedimentary rocks form when deposited material is turned into rock or dissolved substances precipitate. Repeated deposition commonly produces layers and may bury remains of organisms. Running water is a major agent, but wind, ice and biological processes also contribute.
Pre-existing rock weathers → Sediment is transported → Material settles in a basin → More deposits bury it → Compaction reduces spaces → Cement binds grains into rock
Why the others are wrong
(a) Drops fossils and layers.
(b) Drops weathering and fossils.
(c) Drops their surface formation.
Also know
Clastic rocks include sandstone and shale; chemical rocks include rock salt; organic accumulations can form coal. Not every sedimentary rock contains visible fossils. Bedding records episodes of deposition, while an unconformity marks a break involving erosion or non-deposition. Metamorphism can later alter a sedimentary rock and its fossils.
🔒 Sedimentary: sandstone, shale, limestone, coal — layered, fossils.
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