Sedimentary rocks are formed through the process of sedimentation, in which sediment is deposited in layers over time, and then lithified, or turned into rock, through the process of compaction and cementation. The process of sedimentation begins with the weathering and erosion of preexisting rocks, which breaks the rocks down into smaller fragments. These fragments, or sediment, can be transported by water, wind, ice, or gravity to a location where they are deposited.
Once the sediment is deposited, it can be compacted and cemented together by the weight of overlying layers, or by the precipitation of minerals from solution. The process of compaction involves the squeezing together of the sediment particles, which reduces the volume of the sediment and increases its density. The process of cementation involves the bonding of the sediment particles together through the precipitation of minerals, such as quartz or calcite, from solution.
The type of sedimentary rock that forms depends on the size and type of sediment that is deposited, as well as the conditions under which it is deposited. For example, sandstone is a clastic sedimentary rock that forms from the consolidation of sand-sized particles, while limestone is a chemical sedimentary rock that forms from the precipitation of calcite from solution.
Sedimentary rocks are often found in layers or strata, and these layers can be used to infer the relative ages