A sedimentary environment is an area of the earth's surface where sediment is deposited. It can be distinguished from other areas on the basis of its physical, chemical, and biological characteristics. Before studying ancient sedimentary environments, it is helpful to consider the types of sedimentary environments present on the earth today.
Alluvial fans are fan-shaped deposits formed at the base of mountains.
Alluvial fans are most common in arid and semi-arid regions where rainfall is infrequent but torrential, and erosion is rapid. Alluvial fan sediment is typically coarse, poorly- sorted gravel and sand. Fluvial environments include braided and meandering river and stream systems. Channel deposits consist of coarse, rounded gravel, and sand. Bars are made of sand or gravel.