Many shale beds are marked with faint trails and borings of worm-like creatures, and a few contain the remains of tiny trilobites. As the shoreline continued to move eastward, the foot-thick 87 m Death Canyon Limestone Member of the Gros Ventre Formation was laid down in clear water farther from shore.
It consists of two thick beds of dark blue-gray limestone that are separated by 15 to 20 feet 4. Following this the sea retreated to the west for a short time. The foot-thick 67 m Park Shale Member of the Gros Ventre Formation was deposited in the shallow muddy water resulting from this retreat. It is a gray-green shale that contains beds of platy limestone conglomerate along with fossils of trilobites and brachiopods. Periodically shoal areas were hit by violent storm waves that tore loose platy fragments of recently solidified limestone and swept them into nearby channels where they were buried and cemented into thin beds of jumbled fragments called 'edgewise' conglomerate.
By Late Cambrian, the shoreline had once again crept eastward, resulting in clearer water that was probably to feet 30 to 60 m deep. The foot-thick 30 m Gallatin Limestone was formed. It consists of blue-gray limestone that is mottled with irregular rusty or yellow patches. Now at its maximum extent, the sea covered all of Idaho , Montana , most of Wyoming and extended eastward across the Dakotas to connect with shallow seas that covered the eastern United States. Soon after, a slow uplift caused the sea to gradually retreat westward.
The site of the Teton Range emerged above sea level , where, as far as is known, it may have been exposed to erosion for nearly 70 million years. Dolomite is calcium-magnesium carbonate, but the original sediment probably was calcium carbonate mud that was altered by magnesium-rich sea water shortly after deposition. Corals and other marine animals were abundant in the clear warm seas at this time.
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Dolomite in the Devonian Darby Formation differs greatly from the Bighorn Dolomite; in the Darby is dark-brown to almost black, has an oily smell, and contains layers of black, pink, and yellow mudstone and thin sandstone. The sea bottom during deposition of these rocks was foul and frequently the water was turbid. Abundant fossil fragments indicate fishes were common for the first time.
Exposures of the Darby Formation are recognizable by their distinctive dull-yellow thin-layered slopes between the prominent gray massive cliffs of formations below and above. It is noted for the abundant remains of beautifully preserved marine organisms. The fossils and the relatively pure blue-gray limestone in which they are embedded indicate deposition in warm tranquil seas.
Cliffs of the Tensleep Sandstone can be seen along the Gros Ventre River at the east edge of the park. The Amsden, below the Tensleep, consists of red and green shale, sandstone, and thin limestone. The shale is especially weak and slippery when exposed to weathering and saturated with water. These are the strata that make up the glide plane of the Lower Gros Ventre Slide east of the park.
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The Phosphoria Formation and its equivalents of Permian age are unlike any other Paleozoic rocks because of their extraordinary content of uncommon elements. The formation consists of sandy dolomite, widespread black phosphate beds and black shale that is unusually rich not only in phosphorus, but also in vanadium, uranium, chromium, zinc, selenium, molybdenum, cobalt, and silver.
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The formation is mined extensively in nearby parts of Idaho and in Wyoming for phosphatic fertilizer, for the chemical element phosphorus, and for some of the metals that can be derived from the rocks as by-products. These elements and compounds are not everywhere concentrated enough to be of economic interest, but their dollar-value is, in a regional sense, comparable to that of some of the world's greatest mineral deposits. Mesozoic deposition changed from primarily marine to a mix of marine, transitional, and continental that varied over time as crustal conditions altered the region.
By the close of this era, 10, to 15, feet 3, to 4, m of sediment accumulated in 15 recognized formations. The most extensive non-marine formations were deposited in the Cretaceous period when the eastern part of the Cretaceous Seaway a warm shallow sea that periodically divided North America in that period covered the region.
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Their sediment came from rock eroded from a mountain chain east of the seaway interbeded with ash from volcanos west of the seaway in the Sierran Arc a long volcanic island chain like the modern Andes Mountains but in island form. This ash eventually became bentonite , a clay which expands in water and thus causes landslides in the park. Regional uplift in latest Cretaceous time caused the seaway to retreat and transformed the Grand Teton area into a low-lying coastal plain that was frequented by dinosaurs a fossilized Triceratops was found east of the park near Togwotee Pass.
Coalbeds were eventually created from the swamps and bogs left behind after the last stand of the seaway retreated. Coal outcrops can be found near abandoned mines in and outside of the eastern margin of the park. Outcrops of older Mesozoic-aged formations can be found north, east, and south of the park. The distribution of Mud cracks, fossilized reptiles and amphibians suggest deposition in a tidal flat environment with a sea several kilometers southwest of Jackson Hole.
Evaporite deposits of a few beds of white gypsum calcium sulfate were likely formed after shallow bodies of salt water were cut off from the sea. A small amount of iron oxide creates the red color and the formation erodes into colorful hills east and south of the park. As the Triassic gave way to the Jurassic, wind spread salmon-red colored sand across the red beds of the Chugwater Formation to form the Nugget Sandstone.
The Nugget in turn was buried by the deposits of thin red shale and thick gypsum of the Gypsum Springs Formation. Later, a warm, muddy, shallow sea with abundant marine mollusks called the Sundance Sea started to spread from Alaska south to Wyoming. After the sea withdrew, the Jurassic and Lower Cretaceous-aged Morrison and Cloverly Formations were laid down on low-lying tropically humid flood plains.
These formations erode into colorful badlands of red, pink, purple, and green claystones and mudstones, and yellow to buff sandstones. Large and small dinosaurs roamed the abundant vegetation and swamps. Brightly colored rocks continued to be deposited as the final period of the Mesozoic, the Cretaceous dawned.
The Western Interior Seaway retreated eastward from the Teton region around 85 million years ago, marked by deposition of the Bacon Ridge Sandstone. Extensive coal swamps formed along and followed the retreating seashore, leaving coal beds 5 to 10 feet 3. Examples of these coal beds are visible in abandoned mines found in the eastern margin of the park. A modern analog of this depositional environment is the hot and humid climate of the Florida Everglades. About 5 feet 1. Fine-grained volcanic ash from volcanoes west and northwest of the Teton area was periodically deposited in the quiet shallow water of the Western Interior Seaway throughout Cretaceous time.
Ash deposited in this manner was later altered to bentonite ; a type of clay used in the foundry industry and as a component of oil well drilling mud. Elk and deer in Jackson Hole use exposures of bentonite as a bitter salt lick. Bentonite swells when wet, which causes landslides that sometimes block access roads into Jackson Hole. Cretaceous-aged rocks in the Teton region form part of a huge east-thinning wedge of crust that is locally almost 2 miles 3. Most of these rocks are from debris eroded from slowly rising mountains in the west. Bentonite, crude oil and natural gas are commonly produced from the various Cretaceous formations.
By the end of the Cretaceous, slightly more than 80 million years ago, the region's landscape was flat and monotonous; a condition that persisted during most of the Late Cretaceous. The period of uplift that resulted in the formation of the ancestral Rocky Mountains is called the Laramide orogeny. Mountains already existed west and southwest of Wyoming, with progressively older mountains up to Jurassic age trending west into Nevada.
Latest Cretaceous time saw the formation of a low broad northwest-trending arch along the approximate area of the present Teton Range and Gros Ventre Mountains. Part of the evidence for the first Laramide mountain building west of the Teton region is the several hundred cubic miles of quartzite boulders derived from the Targhee uplift , which was located north and west of the northern end of the present-day Teton Range. Streams carried boulders, sand, and clay from the uplift eastward and southeastward across what would become Jackson Hole. Flakes of gold and some mercury are in the resulting Harebell Formation.
Two huge depositional troughs were formed in central and southern Wyoming from fine-grained debris carried farther east and southeast. The tectonic setting of western North America changed drastically as the Farallon Plate under the Pacific Ocean to the west was shallowly subducted below North American Plate. Called the Laramide orogeny , the compressive forces generated from this collision erased the Cretaceous Seaway, fused the Sierran Arc to the rest of North America and created the Rocky Mountains.
This mountain-building event started in the Mesozoic 80 million years ago and lasted well into the first half of the Cenozoic era 30 million years ago.
Windows into the Earth: The Geologic Story of Yellowstone and Grand Teton National Parks
Some 60 million years ago, these forces uplifted the low-lying coastal plain in the Teton region and created the north-south-trending thrust faults of the nearby Wyoming Overthrust Belt. By about 34 million years ago, these forces had uplifted a broad part of western Wyoming into a continuous high plateau. A separate area of uplift called the Targhee Uplift formed north of park borders around this time. Subsequent erosion of the Targhee Uplift was driven by steepened stream gradients. Siegel has written about science since , most recently as science editor of The Salt Lake Tribune.
He contributed to the Pulitzer Prize-winning coverage of the Mount St. Windows into the earth : the geologic story of Yellowstone and Grand Teton national parks.
Robert Baer Smith , Lee J. Millions of years ago, the North American continent was dragged over the world's largest continental hotspot, a huge column of hot and molten rock rising from the Earth's interior that traced a mile wide, mile-long path northeastward across Idaho. Generating cataclysmic volcanic eruptions and large earthquakes, the hotspot helped lift the Yellowstone Plateau to more than 7, feet and pushed the northern Rockies to new heights, creating the jewel of the U.
Meanwhile, forces stretching apart the western U. Smith and Siegel offer expert guidance through this awe-inspiring terrain, bringing to life the grandeur of these geologic phenomena as they reveal the forces that have shaped -- and continue to shape -- the greater Yellowstone-Teton region.