Editing Kerogen (section)

==Formation==
Formation is a rock with unique lithogical characteristics that makes it mappable and recognizable within the earth surface. Kerogen is a type of rock formed during sedimentary [[diagenesis]] from the degradation of living or dead organic matter called fossil.The original organic matter can comprise lacustrine and marine [[algae]] and [[plankton]] and terrestrial higher-order plants. During diagenesis, large [[biopolymers]] from, e.g., [[proteins]], [[lipids]], and [[carbohydrates]] in the original organic matter, decompose partially or completely. This breakdown process can be viewed as the reverse of [[photosynthesis]].<ref>[[Tucker M.E.]] (1988) ''Sedimentary Petrology, An Introduction'', Blackwell, London. p197. {{ISBN|0-632-00074-0}}</ref> These resulting units can then [[Condensation reaction|polycondense]] to form [[geopolymers]]. The formation of geopolymers in this way accounts for the large [[molecular weight]]s and diverse chemical compositions associated with kerogen. The smallest units are the [[fulvic acid]]s, the medium units are the [[humic acid]]s, and the largest units are the [[humins]]. This polymerization usually happens alongside the formation and/or sedimentation of one or more mineral components resulting in a sedimentary rock like [[oil shale]].

When kerogen is contemporaneously deposited with geologic material, subsequent [[sedimentation]] and progressive [[burial]] or [[overburden]] provide elevated pressure and temperature owing to lithostatic and geothermal gradients in Earth's crust. Resulting changes in the burial temperatures and pressures lead to further changes in kerogen composition including loss of [[hydrogen]], [[oxygen]], [[nitrogen]], [[sulfur]], and their associated [[functional groups]], and subsequent [[isomerization]] and [[aromatization]] Such changes are indicative of the thermal maturity state of kerogen. Aromatization allows for molecular [[Stacking (chemistry)|stacking]] in sheets, which in turn drives changes in physical characteristics of kerogen, such as increasing molecular density, ''[[vitrinite]] reflectance'', and spore coloration (yellow to orange to brown to black with increasing depth/thermal maturity).

During the process of [[maturity (geology)|thermal maturation]], kerogen breaks down in high-temperature pyrolysis reactions to form lower-molecular-weight products including bitumen, oil, and gas.  The extent of thermal maturation controls the nature of the product, with lower thermal maturities yielding mainly bitumen/oil and higher thermal maturities yielding gas. These generated species are partially expelled from the kerogen-rich source rock and in some cases can charge into a reservoir rock. Kerogen takes on additional importance in [[unconventional resources]], particularly shale.  In these formations, oil and gas are produced directly from the kerogen-rich source rock (i.e. the source rock is also the reservoir rock). Much of the porosity in these shales is found to be hosted within the kerogen, rather than between mineral grains as occurs in conventional reservoir rocks.<ref name=":0">{{Cite journal |last1=Richardson |first1=E.J. |last2=Montenari |first2=M. |date=2020 |title=Assessing shale gas reservoir potential using multi-scaled SEM pore network characterizations and quantifications: The Ciñera-Matallana pull-apart basin, NW Spain |url=https://www.sciencedirect.com/science/article/abs/pii/S2468517820300010 |journal=Stratigraphy & Timescales |volume=5 |pages=677–755 |doi=10.1016/bs.sats.2020.07.001 |isbn=9780128209912 |s2cid=229217907 |via=Elsevier Science Direct|url-access=subscription }}</ref><ref>{{cite journal |last1=Loucks |first1=R. |display-authors=etal|title=Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale |journal=Journal of Sedimentary Research |volume=79 |issue=12 |pages=848–861 |doi=10.2110/jsr.2009.092|year=2009 |bibcode=2009JSedR..79..848L |s2cid=59400824 }}</ref> Thus, kerogen controls much of the storage and transport of oil and gas in shale.<ref name=":0" />

Another possible method of formation is that [[vanabin]]-containing organisms cleave the core out of [[chlorin]]-based compounds such as the magnesium in [[chlorophyll]] and replace it with their vanadium center in order to attach and harvest energy via [[light-harvesting complex]]es. It is theorized that the bacteria contained in worm castings, ''[[Rhodopseudomonas palustris]]'', do this during its [[photoautotrophism]] mode of metabolism. Over time colonies of light harvesting bacteria solidify, forming kerogen {{Citation needed|date=January 2023}} .