What is the name given to the sediment deposited by rivers, also known as silt?

The name given to the sediment deposited by rivers, commonly referred to as silt, is alluvium. This term encompasses a variety of materials, including clay, silt, sand, and gravel, that are transported by flowing water and eventually settle in riverbeds, floodplains, and deltas. Alluvium is particularly significant in shaping landscapes and ecosystems because it plays a crucial role in soil fertility and agricultural productivity.

The other choices refer to specific types of sediment or rock. Clay is a fine-grained material that is often a component of alluvium but does not describe the sediment as a whole. Siltstone is a type of sedimentary rock formed from compacted silt and, while it can originate from alluvial deposits, it is not the term utilized for the unconsolidated sediment deposited by rivers. Sand, while sometimes found in alluvial deposits, is coarser than the silt that specifically characterizes alluvium. Thus, the correct term for the sediment in question is alluvium, highlighting its broader classification.