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Facts about Sedimentary Rocks for Kids

Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth’s surface and within bodies of water.

  • Sedimentation is the collective name for processes that cause mineral and/or organic particles(detritus) to settle and accumulate or minerals to precipitate from a solution.
  • Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers which are called agents of denudation.
  • The sedimentary rock cover of the continents of the Earth’s crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust.
  • Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks.
  • Clastic sedimentary rocks are composed of silicate minerals and rock fragments that were transported by moving fluids (as bed load, suspended load, or by sediment gravity flows) and were deposited when these fluids came to rest.
  • Subdivision of these three broad categories is based on differences in clast shape (conglomerates and breccias), composition (sandstones), grain size and/or texture (mudrocks).
  • Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue.
  • Common chemical sedimentary rocks include oolitic limestone and rocks composed of evaporite minerals such as halite (rock salt), sylvite, barite and gypsum.
  • Precipitating minerals reduce the pore space in a rock, a process called cementation.
  • There is little water current in such environments, so oxygen from surface water is not brought down, and the deposited sediment is normally a fine dark clay.
  • Most sedimentary rocks contain either quartz (especially siliciclastic rocks) or calcite (especially carbonate rocks).
  • In contrast with igneous and metamorphic rocks, a sedimentary rocks usually contains very few different major minerals.
  • The mineralogy of a clastic rock is determined by the supplied material from the source area, the manner of transport to the place of deposition and the stability of a particular mineral.
  • Soft tissue has a much smaller chance of being preserved and fossilized and soft tissue of animals older than 40 million years is very rare.
  • Sedimentary structures can tell something about the sedimentary environment or can serve to tell which side originally faced up where tectonics have tilted or overturned sedimentary layers.
  • Shallow marine environments exist adjacent to coastlines and can extend out to the boundaries of the continental shelf.
  • When the continent is far away, the amount of such sediment brought in may be small, and biochemical processes dominate the type of rock that forms.
  • Where the lithosphere moves upward (tectonic uplift), land eventually rises above sea level, so that and erosion removes material, and the area becomes a source for new sediment.