Sedimentary rocks are found in many locations across the globe, often in areas where sediment has accumulated over time. These rocks form from the buildup and compression of mineral and organic particles that have settled and accumulated. The particles come from the weathering and erosion of pre-existing rocks. Sedimentary rocks can be found on every continent and make up around 75% of all the rocks exposed on the earth's surface. Here are some of the main places sedimentary rocks are found:
- Oceans – Much of the sedimentary rock on Earth accumulated on the floors of oceans. This can include sandstone formed from sand grains, shale formed from mud and clay, and limestone formed from mineral deposits of calcite. Ocean sedimentary rock often contains fossils of marine organisms.
- Lakes and Rivers – Lake beds and river deltas also provide environments where sediment can build up in layers over time. Sediments carried in rivers and streams accumulate in lakes, forming shale, siltstone and sandstone. Delta regions near river mouths contain lots of sedimentary deposition.
- Deserts – Deserts may seem barren, but they contain significant sedimentary rocks such as sandstone. Winds blow sand and silt into dunes and dry lake beds. Over time, these sediments compress into sedimentary layers of sandstone and shale. The layered red rocks of deserts like the American Southwest are often sedimentary.
- Floodplains – Floodplains along rivers and streams also accumulate sedimentary rocks gradually. Regular flooding brings new deposits of sediments along low-lying areas. These build up into sedimentary layers consisting of conglomerate, shale, limestone and sandstone.
- Coastlines – The coastlines of continents and large islands are prone to sediment accumulation. Erosion of adjacent land areas leads to offshore transport of sediment. Beaches, bays and continental shelves contain sedimentary rock like sandstone and limestone made from this coastal sediment buildup.
- Caves – Caves formed from the dissolution of rock contain unique sedimentary rock deposits like stalactites, stalagmites and flowstones that gradually accumulate from mineralized water dripping inside the cave. These contain calcite and other minerals precipitated from groundwater.
In general, any area where sediment accumulation exceeds sediment removal over time provides an environment suitable for sedimentary rock origins. Sedimentary basins within continents provide large-scale locations for sedimentary rock buildup that can be many kilometers thick. The particles accumulated to form these widespread sedimentary rocks derive from erosion of highland areas transported to lower continental regions.
