Which type of sediment is formed by the action of flowing water?

The formation of alluvium is a direct result of the action of flowing water, making it the correct choice. Alluvium consists of sediments that are transported and deposited by rivers and streams. As water flows over the land, it erodes particles from the banks and surrounding landscape, carrying them downstream. When the water slows or spreads out, these sediments settle and accumulate along riverbeds and floodplains. This characteristic is crucial because alluvium is typically fertile and conducive for agriculture due to its nutrient-rich composition.

Marine sediments, on the other hand, are formed in ocean environments and result from the deposition of materials in marine settings, rather than by flowing freshwater. Loess is wind-blown silt, which is not related to water flow, and colluvium is sediment that accumulates at the base of a slope due to gravity rather than flowing water. Understanding the distinctive processes behind each type of sediment helps clarify why alluvium is specifically associated with flowing water.