Sedimentary rocks form through a multi-step process involving the breakdown, transport, deposition, and lithification of sediments:
- Weathering : Preexisting rocks are broken down into smaller particles by physical and chemical processes such as wind, water, ice, heat, and biological activity
- Erosion and Transport : These sediments are then moved from their source by agents like water, wind, ice, or gravity to a new location
- Deposition : The sediments settle out of the transporting medium and accumulate in layers in environments such as riverbeds, lakes, oceans, or deserts
- Sedimentation : Over time, layers of sediment build up, with older layers at the bottom and younger layers on top, creating stratification characteristic of sedimentary rocks
- Compaction : The weight of overlying sediments compresses the deeper layers, squeezing out air and water between the particles
- Cementation : Minerals dissolved in groundwater precipitate and act as a natural cement, binding the sediment grains together into solid rock. Common cementing minerals include calcite, silica, and iron oxides
This entire process, often taking millions of years, transforms loose sediments into sedimentary rock. The resulting rocks can include clastic types like sandstone and shale formed from fragments of other rocks, as well as chemical and organic types like limestone formed from biological material or mineral precipitation
. In summary, sedimentary rocks form by weathering and erosion of existing rocks, transport and deposition of sediments, followed by compaction and cementation that lithify the sediments into rock
