Which soil parent material is primarily deposited by wind?

Loess is a type of soil parent material that is primarily composed of silt-sized particles and is specifically formed through the deposition of wind-blown sediments. This process occurs in areas where fine particles, particularly silty dust, are carried by strong winds and eventually settle when the wind velocity decreases. The resulting deposits create loess, which often contains high levels of minerals and can provide fertile agricultural conditions.

In contrast, the other options refer to different processes or sources of soil parent materials. Colluvium is material that has moved down slopes due to gravity, residual soil forms directly from the underlying bedrock and weathering processes, and alluvium is sediment deposited by flowing water, typically found in river valleys and floodplains. Each of these materials has distinct formation processes that do not involve wind as the primary agent of deposition.