what is alluvial gravels
Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit.ost, if not all, alluvium is very young (Quaternary in age), and is often referred to as cover because these sediments obscure the underlying bedrock. Most sedimentary material that fills a basin (basin fill) that is not lithified is typically lumped together as alluvial.