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How do sedimentary rocks form from deposited sediments?
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Earth sciences
Geologist using a rock hammer to sample active pahoehoe lava for geochemical analysis on the Kilauea volcano, Hawaii, June 26, 2009.
Sedimentary rocks form through a process called lithification, which converts loose, unconsolidated sediments into solid rock. This transformation is a key component of diagenesis, the set of physical, chemical, and biochemical processes that modify sediments after they are deposited.123
The primary mechanisms involved in lithification include:
- Compaction: As layers of sediment accumulate, the weight of overlying material exerts pressure, rearranging grains and reducing pore space to drive out trapped liquids.13
- Cementation: Minerals precipitate from fluids within the pore spaces, acting as a natural glue that binds individual grains together.143
- Authigenesis: Chemical reactions occur between minerals and trapped fluids, leading to the formation of new minerals or the modification of existing ones within the sediment.13
While many sedimentary rocks form from the lithification of transported detrital grains, some—such as certain limestones or evaporites—precipitate directly from solution at or near the Earth's surface, bypassing an intermediate stage as loose sediment.32
Would you like to learn more about the specific types of sedimentary rocks, such as clastic or chemical varieties?