River sorting occurs in which type of deposits?

• A. Igneous intrusive
• B. Alluvial deposits
• C. Evaporite deposits
• D. Metamorphic banded

Answer: (B)

Sorting refers to how the grain sizes within a sediment become more uniform as they are transported and deposited by a moving fluid. Rivers create this kind of sorting because the water’s energy controls which particles can be carried and where they settle. In alluvial deposits, formed by running water in river channels, floodplains, and deltas, sediment is transported, then dropped as the flow slows. Coarser grains drop out first, while finer material can be carried farther, leading to layers that are relatively well-sorted by size.

The other deposit types don’t arise from this kind of transport-based sorting. Igneous intrusive rocks form when magma cools underground and crystallizes, not from sediment laid down by water. Evaporite deposits form from the chemical precipitation of minerals as water evaporates, not from bedload transport and flow sorting. Metamorphic banded rocks develop under heat and pressure, with minerals aligning or segregating due to metamorphism, not by sorting of transported sediment.

So river sorting is characteristic of alluvial deposits, where running water organizes sediment by grain size as it deposits.