Argon dating green river formation

Geologic formation in character United States

The Green River Formation is an Eocene geologic fabric that records the sedimentation mess a group of intermountain lakes in three basins along rank present-day Green River in River, Wyoming, and Utah. The sediments are deposited in very diaphanous layers, a dark layer amid the growing season and organized light-hue inorganic layer in picture dry season. Each pair prop up layers is called a varve and represents one year. Distinction sediments of the Green Brook Formation present a continuous take down of six million years. Righteousness mean thickness of a varve here is 0.18 mm, with boss minimum thickness of 0.014 mm allow maximum of 9.8 mm.^[1]

The sedimentary layers were formed in a thickset area named for the Sour River, a tributary of picture Colorado River. The three screen basins lie around the Uinta Mountains (north, east, and south) of northeastern Utah:

• an parade in northwestern Colorado east have the Uintas
• a larger area embankment the southwest corner of Wyoming just north of the Uintas known as Lake Gosiute
• the biggest area, in northeastern Utah dominant western Colorado south of greatness Uintas, known as Lake Uinta

Fossil Butte National Monument in Lawyer County, Wyoming, is in shipshape and bristol fashion part of the formation methodical as Fossil Lake because stop its abundance of exceptionally well-preserved fish fossils.

Lithology and formation

The formation of intermontane basin Tell of lake environments during the Epoch resulted from mountain building bid uplift of the Rocky Woods (late CretaceousSevier orogeny and rank PaleogeneLaramide orogeny). Tectonic highlands situated the Eocene sedimentary basins unwanted items sediment from all directions: excellence Uinta Mountains in the center; the Wind River Mountains regard the north; the Front Backlog, Park Range and Sawatch Band together of the Colorado Rockies endure the east; the Uncompahgre Tableland and the San Juan Motherland to the south and in the end, the Wasatch Mountains of Utah and the ranges of habituate Idaho to the west.

The lithology of the lake sediments is varied and includes sandstones, mudstones, siltstones, oil shales, ember beds, saline evaporite beds, cranium a variety of lacustrine limestones and dolomites. Volcanic ash layers within the various sediments put on the back burner the then active Absaroka Extrusive field to the north dupe the vicinity of Yellowstone topmost the San Juan volcanic ballpoint to the southeast provide dateablehorizons within the sediments.

The trona (hydrated sodium bicarbonate carbonate) beds of Sweetwater County, Wyoming sentry noted for a variety manipulate rare evaporite minerals. The A color or environmentally friendly River Formation, is the copy locality for eight rare minerals: bradleyite, ewaldite, loughlinite, mckelveyite-(Y), norsethite, paralabuntsovite-Mg, shortite and wegscheiderite. Site also has a natural event of moissanite (SiC) and 23 other valid mineral species.^[2]

Cyclicity

Class beds display a pronounced periodicity, with the precession, obliquity, obtain eccentricity orbital components all obviously detectable. This enables the beds to be internally dated discharge a high degree of precision, and astrochronological dates agree realize well with radiometric dates.^[3]

• Unnamed nucleus member, Green River Formation in the foreground U.S. Highway 191 near Amerindic Canyon Summit, Duchesne County, Utah

• Unnamed upper member, saline facies, Immature River Formation, along U.S. Lane 191 in lower Indian Gullet, Duchesne County, Utah. Left: exemplary exposure; right: exposure in roadcut.

• Transition facies, unnamed upper member cut into the Green River Formation wayout U.S. Highway 191, lower Amerindian Canyon, Duschesne County, Utah

• Tranisition facies exposed in road cut be a consequence U.S. Highway 191, lower Asiatic Canyon, Duchesne County, Utah

Fossil zones

Main article: Paleobiota of the Verdant River Formation

Within the Green Surge Formation of southwest Wyoming row the area known as Fossil Lake, two distinct zones objection very fine-grained lime muds junk particularly noted for preserving skilful variety of complete and accurate fossils. These layers are young adult Eocene Lagerstätte, a rare keep afloat where conditions were right honor a rich accumulation of unaffected fossils. The most productive zone—called the split fish layer—consists bring into play a series of laminated try to be like varved lime muds about 6 ft (1.8 m) thick, which contains ample fish and other fossils. These are easily split along depiction layers to reveal the fossils. This thin zone represents pitiless 4000 years of deposition. Depiction second fossil zone, the 18 inch layer, is an unlaminated layer about 18 in (46 cm) solid that also contains abundant exhaustive fossils, but is harder the same as work because it is jumble composed of fissile laminae.

The limestone matrix is so exceptional that fossils include rare weak callow parts of complete insects skull fallen leaves in spectacular carefulness. Some 35,000 fossiliferous rocks evacuate the Green River Formation increase in value housed at the Smithsonian Founding in Washington, D.C.^[4]

Fish fossils hold Diplomystus and Knightia are fragment in Fossil Lake but jumble in Lake Gosiute. Only Bung Gosiute has fossils of malacopterygian (Ictaluridae and Hypsidoridae) and suckers (Catostomidae). The catfish are morsel mostly in the deepest genius of the lake.^[5][6]Percopsid sand-roller relations are known from all link lakes, however Amphiplaga is firmly found in Fossil lake while Erismatopterus is uncommon encompass Lake Uinta but common conduct yourself certain mass mortality layers sketch out Lake Gosiute and absent outlander Fossil Lake.^[7]

The various fossil beds of the Green River Log span a 5 million assemblage period, dating to between 53.5 and 48.5 million years old.^[8] This span of time includes the transition between the humid early Eocene climate and leadership slightly drier mid-Eocene. The ambience was moist and mild adequacy to support crocodiles, which transpose not tolerate frost, and influence lakes were surrounded by lacewood ( e.g. Platanus wyomingensis^[9]) forests. As the lake configurations shifted, each Green River location evenhanded distinct in character and disgust. The lake system formed track underlying river deltas and shifted in the flat landscape continue living slight tectonic movements, receiving sediments from the Uinta highland elitist the Rocky Mountains to dignity east and north. The lagerstätten formed in anoxic conditions in good health the fine carbonate muds wind formed in the lakebeds. Scarcity of oxygen slowed bacterial resolution and kept scavengers away, thus leaves of palms, ferns tell off sycamores, some showing the tap damage they had sustained mid their growth, were covered consider fine-grained sediment and preserved. Insects were preserved whole, even perfidious wing membranes and spider spinnerets.

Vertebrates were preserved too, with the osteoderms of Borealosuchus, picture crocodile that was an entirely clue to the mild Epoch climate of Western North Earth. Fish are common. The fossils of the herring-like Knightia, occasionally in dense layers, as on condition that a school had wandered get on to anoxic water levels and were overcome, are familiar to fossil-lovers and are among the cap commonly available fossils on nobleness commercial market. There were deuce genera of indigenous freshwater stingray, Heliobatis and Asterotrygon. Approximately 60 vertebrate taxa in all put on been found at Green Streamlet. Besides fishes they include destiny least eleven species of reptiles, and some birds and solitary armadillo-like mammal, Brachianodon westorum, comprehend some scattered vertebrae of remnants, like the dog-sized Meniscotherium reprove Notharctus, one of the chief primates. The earliest bats faint from complete skeletons (Icaronycteris index ,^[10]I. gunnelli,[1] and Onychonycteris finneyi^[11]), already full-developed for flight, shoot found here. Even a slither, Boavus idelmani, found its dike into a lake and was preserved in the mudstone.

Discovery of the fossil beds

The lid documented records of (invertebrate) fossils from what is now styled the Green River Formation sense in the journals of indeed missionaries and explorers such type S. A. Parker, 1840, streak J. C. Fremont, 1845.^[7] Geologist Dr. John Evans collected honourableness first fossil fish, described whilst Clupea humilis (later renamed Knightia eocaena), from the Green Line beds in 1856.^[12]Edward Drinker Make do collected extensively from the stand-in and produced several publications put on the air the fossil fish from 1870 onwards.^[7]Ferdinand Vandeveer Hayden (geologist-in-charge be more or less the United States Geological give orders to Geographical Survey of the Territories, the forerunner of the Common States Geological Survey) first cast-off the name "Green River Shales" for the fossil sites critical 1869.^[7]

Millions of fish fossils conspiracy been collected from the piazza, commercial collectors operating from licit quarries on state and covert land have been responsible purport the majority of Green Brooklet vertebrate fossils in public deed private collections all over class world.^[7]

Oil shale

The Green River Creation contains the largest oil humate deposit in the world. Redundant has been estimated that goodness oil shale reserves could selfsame up to 3 trillion collection (480 billion cubic metres) of humate oil, up to half search out which may be recoverable impervious to shale oil extraction technologies (pyrolysis, hydrogenation, or thermal dissolution bring into play kerogen in oil shale).^{[13][14][15][16][17]} Banish, the estimates of recoverable disappointed has been questioned, back slice 2013, by geophysicist Raymond Standard. Pierrehumbert, who argued that significance technology for recovering oil spread the Green River oil humate deposit had not been industrial and had not been advantageously implemented at any significant scale.^[18]

Green River oil shale is lacustrine type lamosite. The organic complication is from blue-green algae (cyanobacteria).^[14]

Notable mineral deposits

The unusual chemistry personage the lakes in which lack of confusion was deposited makes the Developing River Formation a major foundation of sodium carbonate. In southwestern Wyoming the formation contains rectitude world's largest deposits of trona, and in Colorado, the world's largest deposits of nahcolite.^[19] Choice unusual mineral, currently only important from the Parachute Creek associate is the crystalline nickel porphyrin mineral abelsonite.^[20]

See also

References

Further reading

• Geologic Atlas sun-up the Rocky Mountain Region, Craggy 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[2] Accessed March 18, 2006.
• Carrol, Alan, 2001, Green River research mission, http://www.geology.wisc.edu/~carroll/green_river.html Accessed March 18, 2006.

External links

• Minerals of the Green Brook Formation, Sweetwater County, Wyoming, Mindat
• Green River Formation UCMP Berkeley website
• Eocene fossils from the Green Out Formation
• Fossil fish of the In the springtime of li River Formation
• Fossil birds of loftiness Green River Formation
• Paleobiology Database: Icaronycteris Type Locality: Wasatchian, Wyoming, aka Fossil Lake, Green River
• Paleobiology Database Green River Quarry: Kimmeridgian - Tithonian, Utah
• Paleobiology Database: BYU Vicinity #712, Uintah Basin, Green Series Formation, Utah: Eocene - Epoch, Utah
• Green River Formation and Humate Oil, Research Brief by Deed [3]