Editing Bitumen (section)

== Occurrence ==
[[File:Puy de Poix, gisement bitumeux.JPG|thumb|right|upright|Bituminous outcrop of the Puy de la Poix, [[Clermont-Ferrand]], France]]
The majority of bitumen used commercially is obtained from petroleum.<ref>{{cite book|last=Speight|first=James G.|title=Asphalt Materials Science and Technology|url=https://books.google.com/books?id=PtMVBQAAQBAJ&pg=PA82|year=2015|publisher=Elsevier Science|isbn=978-0-12-800501-9|page=82}}</ref> Nonetheless, large amounts of bitumen occur in concentrated form in nature. Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic [[algae]] ([[diatom]]s) and other once-living things. These natural deposits of bitumen have been formed during the Carboniferous period, when giant swamp forests dominated many parts of the Earth.<ref>{{Cite web|date=5 January 2021|title=What is Bitumen?|url=https://highways.today/2021/01/05/what-bitumen/|access-date=4 January 2022|website=Highways Today|language=en-GB}}</ref> They were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat (above 50{{nbs}}°C) and [[pressure]] of burial deep in the earth, the remains were transformed into materials such as bitumen, [[kerogen]], or petroleum.

Natural deposits of bitumen include lakes such as the [[Pitch Lake]] in Trinidad and Tobago and [[Lake Bermudez]] in [[Venezuela]]. Natural [[petroleum seep|seeps]] occur in the [[La Brea Tar Pits]] and the [[McKittrick Tar Pits]] in [[California]], as well as in the [[Dead Sea]].

Bitumen also occurs in unconsolidated sandstones known as "oil sands" in [[Alberta]], Canada, and the similar "tar sands" in [[Utah]], US.
The Canadian province of [[Alberta]] has most of the world's reserves, in three huge deposits covering {{convert|142000|km2}}, an area larger than [[England]] or [[New York state]]. These bituminous sands contain {{convert|166|Goilbbl}} of commercially established oil reserves, giving Canada the third largest [[oil reserves]] in the world. Although historically it was used without refining to pave roads, nearly all of the output is now used as [[raw material]] for [[Oil refinery|oil refineries]] in Canada and the United States.<ref name="ST98"/>

The world's largest deposit of natural bitumen, known as the [[Athabasca oil sands]], is located in the [[McMurray Formation]] of Northern Alberta. This formation is from the early [[Cretaceous]], and is composed of numerous [[lens (geology)|lenses]] of oil-bearing sand with up to 20% oil.<ref name=bunger>{{cite journal | last1 = Bunger | first1 = J. | last2 = Thomas | first2 = K. | last3 = Dorrence | first3 = S. | year = 1979 | title = Compound types and properties of Utah and Athabasca tar sand bitumens | journal = Fuel | volume = 58 | issue = 3| pages = 183–195 | doi=10.1016/0016-2361(79)90116-9| bibcode = 1979Fuel...58..183B }}</ref> Isotopic studies show the oil deposits to be about 110 million years old.<ref>{{cite journal | last1 = Selby | first1 = D. | last2 = Creaser | first2 = R. | year = 2005 | title = Direct radiometric dating of hydrocarbon deposits using rhenium-osmium isotopes | journal = Science | volume = 308 | issue = 5726| pages = 1293–1295 | doi=10.1126/science.1111081 | pmid=15919988| bibcode = 2005Sci...308.1293S | s2cid = 41419594 }}</ref> Two smaller but still very large formations occur in the [[Peace River oil sands]] and the [[Cold Lake oil sands]], to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80% has to be produced by oil wells using [[enhanced oil recovery]] techniques like [[steam-assisted gravity drainage]].<ref name=oilsandfacts>{{cite web|title=Facts about Alberta's oil sands and its industry |publisher=Oil Sands Discovery Centre |url=http://history.alberta.ca/oilsands/resources/docs/facts_sheets09.pdf |access-date=19 January 2015 |archive-url=https://web.archive.org/web/20151123024928/http://history.alberta.ca/oilsands/resources/docs/facts_sheets09.pdf |archive-date=23 November 2015 }}</ref>

Much smaller heavy oil or bitumen deposits also occur in the [[Uinta Basin]] in Utah, US. The [[Utah oil sands#Tar Sand Triangle|Tar Sand Triangle]] deposit, for example, is roughly 6% bitumen.<ref name=bunger />

Bitumen may occur in [[hydrothermal vein]]s. An example of this is within the [[Uinta Basin]] of [[Utah]], in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed [[Gilsonite]]. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the [[Green River Formation]] during burial and [[diagenesis]].<ref>{{cite book |author=T. Boden and B. Tripp |title=Gilsonite veins of the Uinta Basin, Utah |publisher=Utah Geological Survey, Special Study 141 |location=Utah, US |year=2012}}</ref>

Bitumen is similar to the organic matter in carbonaceous [[meteorite]]s.<ref>{{cite journal |author=R Hayatsu |author2=RG Scott |author3=RE Winans |title=Comparative structural study of meteoritic polymer with terrestrial geopolymers coal and kerogen (abstract) | journal = Meteoritics | volume = 18 | page = 310 }}</ref> However, detailed studies have shown these materials to be distinct.<ref>{{cite journal | last1 = Kim | last2 = Yang | title = Carbon Isotope Analyses of Individual Hydrocarbon Molecules in Bituminous Coal, Oil Shale and Murchison Meteorite | journal = Journal of Astronomy and Space Sciences | year = 1998 | volume = 15 | issue = 1| pages = 163–174 | bibcode = 1998JASS...15..163K }}</ref> The vast Alberta bitumen resources are considered to have started out as living material from marine plants and animals, mainly [[algae]], that died millions of years ago when an ancient ocean covered Alberta. They were covered by mud, buried deeply over time, and gently cooked into oil by geothermal heat at a temperature of {{convert|50|to|150|C|sigfig=2}}. Due to pressure from the rising of the [[Rocky Mountains]] in southwestern Alberta, 80 to 55 million years ago, the oil was driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands.<ref name=oilsandfacts/>