Sedimentary rock
Sedimentary rocks record Earth's history and provide vital resources.
Sedimentary rocks are types of rock formed by the cementation of sediments—particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. They cover 73% of the Earth's current land surface but constitute only 8% of the crust's volume, forming a thin veneer over a crust mainly composed of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers called strata, often in large structures known as sedimentary basins, and have also been found on Mars.
- formation_process
- Cementation of sediments from geological or biological detritus
- land_surface_coverage
- 73% of Earth's land surface
- crust_volume
- 8% of Earth's crust volume
- primary_classifications
- Clastic, biochemical, chemical, and other sedimentary rocks
- key_discipline
- Sedimentology
- notable_occurrence
- Also found on Mars
Lore & Background
Sedimentary rocks originate from the accumulation and cementation of sediments. Geological detritus comes from weathering and erosion of existing rocks or from solidification of molten lava blobs erupted by volcanoes, transported by water, wind, ice, or mass movement. Biological detritus consists of bodies, shells, and fecal mass of dead aquatic organisms, slowly piling up on the floor of water bodies as marine snow. Sedimentation can also occur when dissolved minerals precipitate from water solution.
Reader's Guide
The study of sedimentary rocks and rock strata provides information useful for civil engineering, such as constructing roads, houses, tunnels, and canals. They are important sources of natural resources including coal, fossil fuels, drinking water, and ores. The sequence of sedimentary rock strata is the main source for understanding Earth's history, including palaeogeography, paleoclimatology, and the history of life. Sedimentology, the scientific discipline studying these rocks, is part of both geology and physical geography and overlaps with pedology, geomorphology, geochemistry, and structural geology. Sedimentary rocks are classified by origin into clastic, biochemical, chemical, and other types (e.g., volcanic tuff, impact breccias). Clastic rocks are subdivided by grain size into conglomerates/breccias, sandstones, and mudrocks. Biochemical rocks include limestone from calcareous skeletons, coal from compressed vegetation, and chert from siliceous organisms. Chemical rocks form by inorganic precipitation, such as evaporites like halite and gypsum. Compositionally, they are grouped into siliciclastic, carbonate, evaporite, organic-rich, and siliceous types.
Did You Know?
- Sedimentary rocks cover 73% of Earth's land surface but only 8% of the crust's volume.
- Sedimentary rocks have been found on Mars.
- The study of sedimentary rock strata is the main source for understanding Earth's history, including paleoclimatology and the history of life.
- Clastic sedimentary rocks are subdivided by grain size into gravel, sand, and mud fractions using the Udden-Wentworth scale.
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