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The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in the dry season. Each pair of layers is called a varve and represents one year. The sediments of the Green River Formation present a continuous record of six million years. The mean thickness of a varve here is 0.18 mm, with a minimum thickness of 0.014 mm and maximum of 9.8 mm.〔Bradley, W. H. The varves and climate of the Green River epoch: U.S. Geol. Survey Prof. Paper 158, pp 87–110, 1929.〕 The sedimentary layers were formed in a large area named for the Green River, a tributary of the Colorado River. The three separate basins lie 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'' * the largest area, in northeastern Utah and western Colorado south of the Uintas, known as ''Lake Uinta'' Fossil Butte National Monument in Lincoln County, Wyoming is in a part of the formation known as ''Fossil Lake'' because of its abundance of exceptionally well preserved fish fossils. ==Lithology and formation== The formation of intermontane basin / lake environments during the Eocene resulted from mountain building and uplift of the Rocky Mountains (late Cretaceous Sevier orogeny and the Paleogene Laramide orogeny). Tectonic highlands supplied the Eocene sedimentary basins with sediment from all directions: the Uinta Mountains in the center; the Wind River Mountains to the north; the Front Range, Park Range and Sawatch Range of the Colorado Rockies to the east; the Uncompahgre Plateau and the San Juan Mountains to the south and finally, the Wasatch Mountains of Utah and the ranges of eastern Idaho to the west. The lithology of the lake sediments is varied and includes sandstones, mudstones, siltstones, oil shales, coal beds, saline evaporite beds, and a variety of lacustrine limestones and dolostones. Volcanic ash layers within the various sediments from the then active Absaroka Volcanic field to the north in the vicinity of Yellowstone and the San Juan volcanic field to the southeast provide dateable 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 Green River Formation, is the type locality for eight rare minerals: bradleyite, ewaldite, loughlinite, mckelveyite-(Y), norsethite, paralabuntsovite-Mg, shortite and wegscheiderite. It also has a natural occurrence of moissanite (SiC) and 23 other valid mineral species.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Green River Formation」の詳細全文を読む スポンサード リンク
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