Question

Which one among the following is the least abundant sedimentary rock in the stratigraphic record?

• A. Sandstone
• B. Limestone
• C. Conglomerate
• D. Shale

Hint:

Remember the order of abundance in the stratigraphic record:
Shale>Sandstone>Limestone>Conglomerate (least).

Answer 1

The Correct Option is C

Step 1: Abundance of major sedimentary rocks.
On average, the distribution of sedimentary rocks in the stratigraphic record is approximately: 
- Shale (mudrocks): ~60% 
- Sandstone: ~20–25% 
- Limestone (carbonates): ~10–15% 
- Conglomerate: Usually \(<1%\)

 Step 2: Compare with options. 
- Shale is the most abundant sedimentary rock. 
- Sandstone and limestone are also common. 
- Conglomerates are coarse-grained and form only in high-energy depositional environments (e.g., alluvial fans, braided rivers), hence are rare in the overall stratigraphic record. 

Step 3: Conclusion. 
Thus, the least abundant sedimentary rock is: \[ \boxed{\text{Conglomerate}} \]