Editing Sedimentary rock (section)

==Stratigraphy==
{{main|Stratigraphy}}
Sedimentary rock are laid down in layers called beds or strata, each layer is horizontally laid down over the older ones and new layers are above older layers as stated in the [[Law of superposition|principle of superposition]]. There are usually some gaps in the sequence called [[unconformity|unconformities]] which represent periods where no new sediments were laid down, or when earlier sedimentary layers were raised above sea level and eroded away.<ref name=dkp>{{cite book|chapter=geology, geography, and meteorology|title=The Ultimate Visual Family Dictionary|publisher=[[DK (publisher)|DK Pub.]]|year=2012|language=en|page=276-280|location=New Delhi}}</ref><ref name=los>{{cite web|title=Law of superposition - Definition & Facts - Britannica|website=Britannica|url=https://www.britannica.com/science/law-of-superposition|access-date=29 December 2024}}</ref>

Unconformities can be classified based on the orientation of the strata on either sides of the unconformity:<ref name=dkp/><ref name=mjs>{{cite book|title=Physical geology: exploring the Earth|publisher=[[Cengage Group|Cengage Learning]]|year=2007|first1=Monroe|last1=J.S.|first2=Wicander|last2=R.|first3=Hazlett|last3=R.W.|isbn=9780495011484|language=en}}</ref>
* Angular unconformity when the earlier layers are tilted and eroded while the later layers are horizontally laid.
* Nonconformity if the early layers have no bedding in contrast to the later layers, ie. they are igneous or metamorphic rocks.
* Disconformity if both the early beds and the later beds are parallel to each other.

Sedimentary rocks contain important information about the [[history of the Earth]]. They contain fossils, the preserved remains of ancient [[plant]]s and [[animal]]s. Coal is considered a type of sedimentary rock. The composition of sediments provides us with clues as to the original rock. Differences between successive layers indicate changes to the environment over time. Sedimentary rocks can contain fossils because, unlike most igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossil remains.