Green River Formation 557360 221603485 2008-06-25T06:55:53Z Thijs!bot 1392310 robot Adding: [[nl:Green River Formation]] The '''Green River Formation''' is an [[Eocene]] geologic formation that records the sedimentation in a series of intermountain lakes. The sedimentary layers were formed in a large area of interconnecting lakes, named for the present-day [[Green River (Utah)|Green River]], a tributary of the [[Colorado River]]. The area of the formation exists as three separate basins around the [[Uinta Mountains]] of northeastern [[Utah]]: an area in northwestern [[Colorado]] east of the Uintas, a larger area in the southwest corner of [[Wyoming]] just north of the Uintas known as ''Lake Gosiute'', and the largest area, which lies in northeastern Utah and western Colorado south of the Uintas, known as ''Lake Uinta''. [[Fossil Butte National Monument]] in [[Lincoln County, Wyoming]] is located in a part of the formation known as ''Fossil Lake'' because of the abundance of exceptionally well preserved fish fossils found in the area. ==Lithology and formation== The formation of the intermountain lake environment in the area during the Eocene was a result of the late [[Cretaceous]] [[Sevier orogeny]] to the west and the uplift of the [[Rocky Mountains]] during the [[Paleogene]] [[ Laramide orogeny]]. The Eocene sedimentary basins thus received sediments from all directions. The Uinta uplift shed sediments north, east and south into the basins. The [[Wind River Mountains]] of west central Wyoming provided sediments from the north into the Green River basin. The [[Front Range]], the [[Park Range (Colorado)|Park Range]] and the [[Sawatch Range]] of the Colorado Rockies provided sediments into the basins from the east. The [[Uncompahgre Plateau|Uncompahgre geanticline]] and the [[San Juan Mountains]] provided sediments from the south. To the west were the [[Wasatch Mountains]] of Utah and the ranges of eastern Idaho. The [[petrology|lithology]] of these landlocked lake sediments is varied and includes [[sandstone]]s, [[mudstone]]s, [[siltstone]]s, [[oil shale]]s, [[coal]] beds, saline [[evaporite]] beds, and a variety of lacustrine [[limestone]]s and [[dolostone]]s. [[Volcanic ash]] layers within the various sediments from the active [[Absaroka Mountains|Absaroka Volcanic field]] to the north in the vicinity of [[Yellowstone]] and the [[San Juan volcanic field]] to the southeast provide [[radiometric dating|dateable]] [[key bed|horizons]] within the sediments. The [[trona]] (hydrated sodium bicarbonate carbonate) beds of [[Sweetwater County, Wyoming]] are noted for a variety of rare evaporite minerals. The beds are the type locality for seven rare minerals: [[bradleyite]], [[ewaldite]], [[loughlinite]], [[mckelveyite-(Y)]], [[norsethite]], [[paralabuntsovite-Mg]], and [[shortite]] as well as an occurrence of [[moissanite]] (SiC). ==Cyclicity== The beds display a pronounced [[Milankovic cycle]]icity, with the precession, obliquity, and eccentricity orbital components all clearly detectable. This enables the beds to be internally dated with a high degree of accuracy, and [[astrochronological]] dates agree very well with [[radiometric]] dates.<ref name=Meyers2008>{{cite journal | author = Meyers, S.R. | year = 2008 | title = Resolving Milankovitchian controversies: The Triassic Latemar Limestone and the Eocene Green River Formation | journal = Geology | volume = 36 | issue = 4 | pages = 319–322 | url = http://www.unc.edu/~smeyers/pubs/Meyers_2008.pdf | accessdate = 2008-04-24 | doi = 10.1130/G24423A.1 }}</ref> ==Fossil zones== [[Image:Amphiplaga.jpg|thumb|200px|left|Amphiplaga brachyptera Fossil Fish from the Green River Formation]]Within the Green River Formation of southwest Wyoming in the area known as ''Fossil Lake,'' two distinct zones of very fine-grained lime muds are particularly noted for preserving a variety of complete and detailed [[fossil]]s. These layers are an Eocene [[Lagerstätten|Lagerst&auml;tte]], a rare place where conditions were right for a rich accumulation of undisturbed fossils. The most productive zone&mdash;called the ''18 inch layer''&mdash; consists of a series of laminated or [[varve]]d lime muds containing abundant fish and other fossils. These are easily split along the layers to reveal the fossils. This thin zone represents some 4000 years of deposition. The second fossil zone, the ''split fish layer'', is an unlaminated layer about six feet thick that also contains abundant detailed fossils, but is harder to work because it is not composed of fissile laminae. The limestone matrix is so fine-grained that fossils include rare soft parts of complete insects and fallen leaves in spectacular detail. More than twenty-two orders of insects are represented in the Green River collection at the [[Smithsonian Institution]] in Washington, D.C. alone. The Green River fossils date about 48 mya, but cover several million years, including the transition between the moist early Eocene climate and the slightly drier mid-Eocene. The climate was moist and mild enough to support [[crocodile]]s, which do not tolerate frost, and the lakes were surrounded by [[sycamore]] forests. As the lake configurations shifted, each Green River location is distinct in character and time. The lake system formed over underlying river deltas and shifted in the flat landscape with slight tectonic movements, receiving sediments from the Uinta highland and the [[Rocky Mountains]] to the east and north. The lagerstätten formed in anoxic conditions in the fine carbonate muds that formed in the lakebeds. Lack of oxygen slowed bacterial decomposition and kept scavengers away, so leaves of palms, ferns and sycamores, some showing the insect damage they had sustained during their growth, were covered with fine-grained sediment and preserved. Insects were preserved whole, even delicate wing membranes and spider spinnerets. Vertebrates were preserved too, including the scales of ''[[Borealosuchus]]'', the crocodile that was an early clue to the mild Eocene climate of Western North America. Fish are common. The fossils of the herring-like ''[[Knightia]]'', sometimes in dense layers, as if a school had wandered into anoxic water levels and were overcome, are familiar to fossil-lovers and are among the most commonly available fossils on the commercial market. There was even an indigenous freshwater [[stingray]], ''[[Heliobatis]]''. Approximately sixty vertebrate taxa in all have been found at Green River. Besides fishes they include at least eleven species of reptiles, and some birds and one [[armadillo]]-like mammal, ''[[Brachianodon westorum]]'', with some scattered vertebrae of others, like the dog-sized ''[[Meniscotherium]]'' and ''[[Notharctus]]'', one of the first primates. The earliest known [[bat]]s (''[[Icaronycteris|Icaronycteris index]]'' and ''[[Onychonycteris|Onychonycteris finneyi]]''), already full-developed for flight, are found here. Even a snake, ''[[Boavus idelmani]]'', found its way into a lake and was preserved in the mudstone. ===Discovery of the fossil beds=== A Dr. John Evans collected and had described the first fossil fish from the Green River beds in 1856. The specimen was identified as ''[[Knightia]] eocaena''. [[Edward Drinker Cope]] collected extensively from the area and produced a publication on the fossil fishes in 1871. Millions of fish fossils have been collected from the area. ==Oil shale== The Green River Formation contains the largest [[oil shale geology|oil shale]] deposits in the world. The 213 billion [[ton]]s of oil shale contain an estimated 2.38 x 10<sup>11</sup>m<sup>3</sup> (1.5 trillion US [[barrel (unit)|barrels]]) of [[shale oil]].<ref>[http://pubs.usgs.gov/sir/2005/5294/pdf/sir5294_508.pdf USGS Scientific Investigations Report 2005–5294, ''Geology and Resources of Some World Oil-Shale Deposits'']</ref> ==See also== * [[List of fossil sites]] ''(with link directory)'' ==References== * ''Geologic Atlas of the Rocky Mountain Region'', Rocky Mountain Association of Geologists, 1972, Denver Colorado * King, Philip B., 1977, ''The Evolution of North America'', Revised edition, Princeton University Press *Gaggiano, Tom, ''The Green River Formation'' http://www.fossilnews.com/2000/grnrv/grnrv.html Accessed March 18, 2006. *Carrol, Alan, 2001, ''Green River'' research project, http://www.geology.wisc.edu/~carroll/green_river.html Accessed March 18, 2006. *[http://www.mindat.org/loc-4235.html Minerals of the Green River Formation, Sweetwater County, Wyoming, Mindat] *[http://www.ucmp.berkeley.edu/tertiary/eoc/greenriver.html Green River Formation]UCMP Berkeley website *[http://www.coloradomtn.edu/campus_rfl/staff_rfl/kohls/eocene.shtml Eocene fossils from the Green River Formation] *[http://www.fossilmuseum.net/Fossil_Galleries/GreenRiverFish.htm Fossil fish of the Green River Formation] *[http://www4.ncsu.edu/~dtksepka/Green%20River%20Avifauna.html Fossil birds of the Green River Formation] *[http://paleodb.org/cgi-bin/bridge.pl?action=displayCollectionDetails&collection_no=37809 Paleobiology Database: Icaronycteris Type Locality: Wasatchian, Wyoming, aka Fossil Lake, Green River] *[http://paleodb.org/cgi-bin/bridge.pl?action=displayCollectionDetails&collection_no=49626 Paleobiology Database Green River Quarry: Kimmeridgian - Tithonian, Utah] *[http://paleodb.org/cgi-bin/bridge.pl?action=displayCollectionDetails&collection_no=60584 Paleobiology Database: BYU Locality #712, Uintah Basin, Green River Formation, Utah: Eocene - Eocene, Utah] * Green River Formation and Shale Oil, Research Brief by Rand [http://www.rand.org/pubs/research_briefs/RB9143/index1.html] {{Reflist}} [[Category:Paleontological sites]] [[Category:Geologic formations]] [[Category:Geology of Utah]] [[Category:Geology of Colorado]] [[Category:Natural history of Wyoming]] [[Category:Natural history of Utah]] [[Category:Natural history of Colorado]] [[Category:Geology of Wyoming]] [[Category:Geology of the Rocky Mountains]] [[Category:Eocene]] [[ca:Formació de Green River]] [[es:Formación Green River]] [[nl:Green River Formation]]