The sediments, the origin of the sedimentary rocks, are in the terrestrial surface resulting from fenomena of weathering and erosion of pre-existing rocks as well as organic remains.
Water and wind are rhe main sediement transport agents. When this agents lose their ability to carry, due to a slowing down, sedimentation occurs. As sedimentation continues, the sediemnts arranged in the lower strata arecompacted (reduced volume) and cemented (precipitation of new minerals around the deposited particules, gluing them). The set of processes that transform the sediments into consolidated sediementary rocks is called diagenesis.
Sediments and sediemntary rocks are characterized by the presence of strstification, which results from the formation of parallel and horizontal layers by the continuous deposition of particules on the botton of an ocean, lake, river or continental surface. In a sequence of strata that have not been modified fromtheir original position, a stratum is older than the one that overlaps it, and more recent than that wich underlies it.
It is when the deposition of sediements takes place that the burial of organisms that can originate fossils takes place.