Editing Laramide orogeny

{{Short description|Period of mountain building in North America}}

The '''Laramide orogeny''' was a time period of [[mountain building]] in western [[North America]], which started in the [[Late Cretaceous]], 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this [[orogeny]] was deep-seated, [[thick-skinned deformation]], with evidence of this orogeny found from [[Canada]] to northern [[Mexico]], with the easternmost extent of the mountain-building represented by the [[Black Hills]] of [[South Dakota]]. The phenomenon is named for the [[Laramie Mountains]] of eastern [[Wyoming]]. The Laramide orogeny is sometimes confused with the [[Sevier orogeny]], which partially overlapped in time and space.<ref>{{harvnb|Willis|2000}}</ref>
[[File:Shallow subduction Laramide orogeny.gif|thumb|right|upright=1.333|The Laramide orogeny was caused by subduction of a plate at a shallow angle.]]
The orogeny is commonly attributed to events off the west coast of North America, where the [[Kula Plate|Kula]] and [[Farallon Plate]]s were sliding under the [[North American Plate]]. Most hypotheses propose that oceanic crust was undergoing [[flat-slab subduction]], that is, [[subduction]] at a shallow angle. As a consequence, no [[magmatism]] occurred in the central west of the continent, and the underlying oceanic [[lithosphere]] actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust.

Magmatism associated with subduction occurred not near the plate edges (as in the [[volcanic arc]] of the [[Andes]], for example), but far to the east, along the [[Colorado Mineral Belt]].<ref name="JonesEtal2012">{{cite journal |last1=Jones |first1=Craig |last2=Farmer |first2=Lang |last3=Sageman |first3=Brad |last4=Zhong |first4=Shijie |title=Hydrodynamic mechanism for the Laramide orogeny |journal=Geosphere |date=2012 |volume=7 |issue=1 |pages=183 |doi=10.1130/GES00575.1|doi-access=free }}</ref> Geologists call such a lack of volcanic activity near a [[subduction zone]] a [[magmatic gap]]. This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter [[asthenosphere]].<ref>{{harvnb|Dumitru|Gans|Foster|Miller|1991}}</ref> One result of shallow angle of subduction and the drag that it caused was a broad belt of mountains, some of which were the progenitors of the [[Rocky Mountains]]. Part of the proto-Rocky Mountains would be later modified by extension to become the [[Basin and Range Province]].

==Basins and mountains==
The Laramide orogeny produced intermontane [[structural basin]]s and adjacent [[Horst (geology)|mountain blocks]] by means of deformation. This style of deformation is typical of [[continental plate]]s adjacent to [[convergent boundary|convergent margin]]s of long duration that have not sustained continent/continent collisions. This tectonic setting produces a pattern of compressive uplifts and basins, with most of the deformation confined to block edges. Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon. The basins contain several thousand meters of [[Paleozoic]] and [[Mesozoic]] [[sedimentary rock]]s that predate the Laramide orogeny. As much as {{convert|5000|m|sp=us}} of [[Cretaceous]] and [[Cenozoic]] sediments filled these orogenically-defined basins. Deformed [[Paleocene]] and [[Eocene]] deposits record continuing orogenic activity.<ref name=nasa>{{Include-NASA|title=Wyoming Intermontane Basins|url=http://daac.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-8.shtml|archive-url=https://web.archive.org/web/20110617012733/http://daac.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-8.shtml/|archive-date=2011-06-17|url-status=dead|first=M|last=Hegde}}</ref>

During the Laramide orogeny, basin floors and mountain summits were much closer to sea level than today. After the seas retreated from the Rocky Mountain region, [[floodplain]]s, [[swamp]]s, and vast lakes developed in the basins. Drainage systems imposed at that time persist today. Since the [[Oligocene]], episodic [[epeirogenic movement|epeirogenic uplift]] gradually raised the entire region, including the Great Plains, to present elevations. Most of the modern topography is the result of [[Pliocene]] and [[Pleistocene]] events, including additional uplift, glaciation of the high country, and denudation and dissection of older Cenozoic surfaces in the basin by fluvial processes.<ref name=nasa />
[[File:Wpdms nasa topo bighorn basin.jpg|thumb|right|Topographic map of the western United States (and part of Canada) showing the Bighorn Basin (highlighted in orange), formed by the Laramide Orogeny]]
In the United States, these distinctive intermontane basins occur principally in the central Rocky Mountains from [[Colorado]] and [[Utah]] ([[Uintah Basin|Uinta Basin]]) to [[Montana]] and are best developed in [[Wyoming]], with the [[Bighorn Basin|Bighorn]], [[Powder River Basin|Powder River]], and [[Wind River Basin|Wind River]] being the largest. Topographically, the basin floors resemble the surface of the western Great Plains, except for vistas of surrounding mountains.<ref name=nasa/>

At most boundaries, Paleozoic through [[Paleogene]] units dip steeply into the basins off uplifted blocks cored by [[Precambrian]] rocks. The eroded steeply dipping units form [[hogback (geology)|hogback]]s and [[flatiron (geomorphology)|flatiron]]s. Many of the boundaries are [[thrust fault|thrust]] or [[reverse fault]]s. Although other boundaries appear to be [[homocline|monoclinal flexure]]s, faulting is suspected at depth. Most bounding faults show evidence of at least two episodes of Laramide ([[Late Cretaceous]] and [[Eocene]]) movement, suggesting both thrust and [[strike-slip]] types of displacement.<ref name=nasa/>

==Ecological consequences==
According to paleontologist Thomas M. Lehman, the Laramide orogeny triggered "the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction."<ref>{{harvnb|Lehman|2001|p=310}}</ref> This turnover event saw the replacement of specialized and highly ornamented [[centrosaurine]] and [[lambeosaurines]] by more [[basal (phylogenetics)|basal]] upland dinosaurs in the south, while northern [[biomes]] became dominated by ''[[Triceratops]]'' with a greatly reduced [[hadrosaur]] community.<ref>{{harvnb|Lehman|2001|p=324}}</ref>

==See also==
{{Portal|Earth sciences|Paleontology}}
*[[North American Cordillera#Laramide Belt|Laramide Belt]]
*[[Sevier orogeny]], earlier than the Laramide orogeny, in the Cretaceous era
*[[Nevadan orogeny]], still earlier, in the late Jurassic—early Cretaceous era
*[[Geology of the Rocky Mountains]]
*[[Geology of the Pacific Northwest]]

==Footnotes==
{{Reflist}}

==References==
{{refbegin}}
*{{cite journal|last1=Dumitru|first1=T.A. |last2=Gans |first2=P.B. | last3=Foster |first3=D.A. |last4=Miller |first4=E.L. |title=Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction|journal=Geology|year=1991|volume=19|issue=11|pages=1145–1148|doi=10.1130/0091-7613(1991)019<1145:ROTWCL>2.3.CO;2|bibcode = 1991Geo....19.1145D }}
*{{cite journal|first1=Joseph M.|last1=English|first2=Stephen T.|last2=Johnston|title=The Laramide Orogeny: What Were the Driving Forces?
 | journal=International Geology Review|volume=46|pages=833–838|year=2004|issue=9|doi=10.2747/0020-6814.46.9.833
 | url=https://www.researchgate.net/publication/242170712|bibcode=2004IGRv...46..833E|s2cid=129901811}}
*{{cite book|last=Lehman|first=T. M.|year=2001|chapter=Late Cretaceous dinosaur provinciality|title=Mesozoic Vertebrate Life|editor1-last=Tanke|editor1-first=D. H.|editor2-last=Carpenter|editor2-first=K.|publisher=Indiana University Press|pages=310–328}}
*{{Cite journal |last1=Liu |first1=L. |last2=Gurnis |first2=M. |last3=Seton |first3=M. |last4=Saleeby |first4=J. |last5=Müller |first5=R.D. |last6=Jackson |first6=J.M. |year=2010 |title=The role of oceanic plateau subduction in the Laramide orogeny |journal=Nature Geoscience |volume=3 |pages=353–357 |doi=10.1038/ngeo829 |url=http://www.earthbyte.org/Resources/Pdf/Liu2010_NatureGeoscience.pdf |issue=5|bibcode = 2010NatGe...3..353L }}
*{{Cite journal |first1=Richard F.|last1=Livaccari|first2=Kevin|last2=Burke|first3=AMC|last3=Sengor|title=Was the Laramide orogeny related to subduction of an oceanic plateau? |journal=Nature |year=1981 |volume=289 |issue=5795 |pages=276–278 |doi=10.1038/289276a0|bibcode = 1981Natur.289..276L |s2cid=27153755}}
*{{cite journal|first=Jason|last=Saleeby|title=Segmentation of the Laramide Slab -- Evidence from the southern Sierra Nevada region|journal=Geological Society of America Bulletin|volume=115|pages=655–668|year=2003|doi=10.1130/0016-7606(2003)115<0655:sotlsf>2.0.co;2|bibcode=2003GSAB..115..655S|url=http://pages.uoregon.edu/ghump/Papers_files/Saleeeby_03.pdf}}
*{{Cite journal |first1=W.P.|last1=Schellart|first2=D.R.|last2=Stegman|first3=R.J.|last3=Farrington|first4=J.|last4=Freeman|first5=L.|last5=Moresi |title=Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab |journal=Science |date=16 July 2010 |volume=329 |issue=5989 |pages=316–319 |doi=10.1126/science.1190366 |pmid=20647465|bibcode = 2010Sci...329..316S |s2cid=12044269}}
* {{cite web|url=http://geology.utah.gov/utahgeo/geo/thrustfault5.htm|title=I thought that was the Laramide orogeny!|work=Utah's Sevier Thrust System|publisher=Utah Geological Survey|last=Willis|first=Grant C.|year=2000}}
{{refend}}

==External links==
{{commons}}
*[http://peterbird.name/publications/1998_Laramide/1998_Laramide.htm Maps, animation, detailed information (UCLA)]
*[https://archive.today/20050114060212/http://www.geology.wisc.edu/courses/g112/laram_yell.html  U. Wisconsin article]

[[Category:Orogenies of North America]]
[[Category:Cretaceous orogenies]]
[[Category:Paleogene orogenies]]
[[Category:Paleocene geology]]
[[Category:Eocene geology]]
[[Category:Cretaceous Canada]]
[[Category:Cretaceous Mexico]]
[[Category:Cretaceous United States]]
[[Category:Paleogene Canada]]
[[Category:Paleogene Mexico]]
[[Category:Paleogene United States]]
[[Category:Geology of the Rocky Mountains]]
[[Category:Black Hills]]