Proluvial Facies

Proluvial facies are a type of terrestrial facies that commonly develop in arid or semi-arid regions. In mountainous areas, intermittent floods transport weathered materials of parent rocks to the valley mouth to form deposits. Abundant gravels, sand and silts transported by floods accumulate rapidly at the valley mouth to form a fan-shaped deposit, which is called a proluvial fan. The material is poorly sorted with unclear bedding. Particle gradation is remarkable in map view; a thick layer of coarse fragments mainly composed of gravels is located close to the fan, but towards the outer margin, the particles gradually transition to smaller sizes in the form of sand, silt and mud, and the thickness decreases gradually with the development of cross-bedding.