Which sediment type is most consistent with lake bed deposits given significant fines and plasticity?

• A. Marine sandstone
• B. Lake bed deposits
• C. Weathered granite
• D. Alluvial gravel

Answer: (B)

Fine-grained, plastic sediments point to deposition in a quiet, low-energy environment where tiny particles can settle out of suspension and later develop cohesive, clay-rich characteristics. Lakes provide precisely that setting: calm waters allow silt and clay to accumulate over time, creating lacustrine deposits with significant fines and plasticity due to the clay minerals and moisture present.

In contrast, marine sandstone implies a coastal or shelf environment where water movement is strong enough to transport and deposit sand-sized grains, yielding coarser, non-plastic material. Weathered granite represents weathered rock fragments rather than cohesive sedimentary deposits. Alluvial gravel forms in high-energy river settings, where coarse gravel dominates and plasticity is minimal.

Therefore, the sediment type most consistent with lake bed deposits given significant fines and plasticity is lake bed deposits.