Question

When denser sand sinks into less dense wet mud, the bulges formed at the bottom of a sandstone bed are called:

• A. slump structures
• B. mud cracks
• C. load structures
• D. convolute lamination

Hint:

Load structures form from weight imbalance between heavy sand and soft mud.

Answer 1

The Correct Option is C

To identify the correct term for bulges formed when dense sand sinks into less dense wet mud, we analyze sedimentary deformation structures.

1. Understanding the Process:
This phenomenon occurs due to density inversion during sediment deposition, where denser sand settles into underlying softer mud.

2. Evaluating Each Option:
- Slump structures: Result from mass wasting on slopes (incorrect)
- Mud cracks: Form from drying and shrinkage (incorrect)
- Load structures: Correct answer - form from density-driven loading
- Convolute lamination: Involves folding of layers (different process)

3. Characteristics of Load Structures:
- Form when dense sand loads into water-saturated mud
- Create bulbous protrusions at sandstone base
- Include specific types like load casts and flame structures
- Preserve density contrast between layers

4. Formation Mechanism:
1. Deposition of sand over wet mud
2. Liquefaction of underlying mud
3. Density-driven sinking of sand
4. Formation of downward projections (load casts) and upward mud injections (flame structures)

5. Field Significance:
- Indicators of depositional environment
- Evidence of sediment rheology during burial
- Useful for determining way-up in deformed strata

Conclusion:
The correct term for these density-driven bulges is load structures.

Final Answer:
The correct option is: load structures.