How is sedimentary rock formed?

Answer 1

Methods of Sedimentary Rock Formation#1. The classic route begins with the weathering and erosion of sedimentary, igneous, or metamorphic rocks. Through these processes, larger rock is broken up into smaller particles which are transported by moving water, ice, gravity or wind, and deposited at the bottom of a lake, a river delta, an ocean, or similar location where further movement is restricted or slowed down. The rock particles can range in size from boulders to clay particles less than .002 mm in diameter. If these rock particles are covered by additional particles, eventually the weight from above will start the process of lithification. Lithification is the compaction and cementation of particles which form rock. Compaction squeezes out the fluids and space that exist between the particles, and cementation results when the fluids that are squeezed out are replaced with minerals that crystallized from the fluids. Once cementation occurs, the new sedimentary rock has been formed. Rocks formed in this manner include sandstone, shale, mudstone, breccia, and conglomerate and are called clastic sedimentary rocks.

#2. Organic sedimentary rocks like some limestones and coal are formed largely from the remains of once living organisms. Chalk and fossiliferous limestones are formed from the skeletons of marine organisms. Coal is formed from vegetation that previously existed in swampy and marshy waterlogged soils which prevented their full decay after their death. As their remains piled up and were covered by more and more deposits, they gradually underwent compaction and cementation as described in #1. above.

#3. Sedimentary rocks can also form when minerals in a body of water have so saturated the water that they precipitate out, like a cloud that is so full of moisture that it pours out rain. Some limestones are formed in this manner as the mineral calcite precipitates out of a saturated solution and undergoes the process of compaction and cementation. The supersaturated solutions can also be caused by evaporation of a body of water high in mineral content. As the water evaporates, the mineral percentage of the remaining solution becomes higher and higher, until the mineral crystallizes. Rocks such as rock salt and rock gypsum are formed in this manner. Sedimentation from precipitation and evaporation form rocks called chemical sedimentary rocks.

Answer 2

The answer is

For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away

by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

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