The geology of the Grand Teton area consists of some of the oldest rocks and one of the youngest mountain ranges in North America. The Teton Range, partly located in Grand Teton National Park, started to grow some 9 million years ago. An older feature, Jackson Hole, is a basin that sits aside the range.
The 2.5 billion year old metamorphic rocks that make up the east face of the Tetons are marine in origin and include some volcanic deposits. These same rocks are today buried deep inside Jackson Hole. Paleozoic rocks were deposited in warm shallow seas while Mesozoic deposition transitioned back and forth from marine to non-marine sediments with the Cretaceous Seaway periodically covering the area late in that era.
Precambrian deposition, metamorphism, and intrusion Perhaps 3 billion years ago in Precambrian time, sand, limey ooze, silt and clay were deposited in a marine trough (accurate dating is not possible, due to subsequent partial recrystallization of the resulting rock). Between these layers were volcanic deposits, probably from an island arc. These sediments were later lithified into sandstones, limestones, and various shales. These rocks were below the surface when orogenies (mountain-building episodes) around 2.8 to 2.7 billion years ago intensely folded and metamorphosed them, creating alternating light and dark banded gneiss and schist.Geology of U.S. Parklands, page 592, "Precambrian Rocks", paragraphs 1-2Roadside Geology of the Yellowstone Country, page 5, paragraph 1 Today these rocks dominate the east side of the Teton Range with good examples easily viewable in Death Canyon and other canyons. The green to black serpentine created was used by Native Americans to make bowls.
Sometime around 2.5 billion years ago, blobs of magma intruded into the older rock, forming plutons of granitic rock.Geology of U.S. Parklands, page 592, "Precambrian Rocks", paragraph 2 Extensive exposures of this rock are found in the central part of the range. About 1.3 to 1.4 billion years ago in Late Precambrian, thick black diabase dikes intruded as well, forming the prominent vertical dikes seen today on the faces of Mount Moran and Middle Teton (the dike on Mount Moran is ).Geology of National Parks, page 566, section 3 Some of the large dikes can be seen from the Jenny Lake and String Lake areas.
More than 700 million years elapsed between intrusion of the black dikes and deposition of the first Paleozoic sedimentary rocks. The Precambrian rocks were uplifted during this gap in the geologic record known as an unconformity; exposed to erosion they were gradually worn to a nearly featureless plain, perhaps resembling the vast flat areas in which similar Precambrian rocks are now exposed in central and eastern Canada. At the close of Precambrian time, about 600 million years ago, the plain slowly subsided and the site of the future Teton Range disappeared beneath shallow seas that were to wash across it intermittently for the next 500 million years.
Paleozoic deposition Deposition resumed in the Cambrian period and continued through the Paleozoic era, creating nine major formations which together are thick (the only geologic period in the Paleozoic not represented is the Silurian). These formations were deposited in a shallow sea and later became a discontinuous mix of dolomites, limestones, sandstones, and shales. These formations are relatively undeformed for their age even though periodic upwarp exposed them to erosion, creating uncomformities. Fossilized brachiopods, bryozoans, corals, and trilobites are found in the carbonate rocks with the best examples found outside of the park in the Alaska Basin. The most complete examples of these formations are found to the west, north, and south of park borders.For the whole paragraph: Geology of National Parks, page 566, section 4
On the edge of a shallow seaway
Early in Cambrian time a shallow seaway, called the Cordilleran trough, extended from southern California northeastward across Nevada into Utah and Idaho. The vast gently rolling plain on Precambrian rocks to the east was drained by sluggish westward-flowing rivers that carried sand and mud into the sea. The site of the Teton Range was part of this plain. Slow subsidence of the land caused the sea to spread gradually eastward during Middle Cambrian time flooding the Precambrian plain. Sand accumulated along the beaches just as it does today. As the sea moved still farther east, mud was deposited on the now-submerged beach sand. In the Teton area, the oldest sand deposit is the thick Flathead Sandstone. The partly marine Flathead Sandstone is reddish-brown, very hard, brittle and exposures can be found on the north and west flanks of the Teton Range and Gros Ventre Range.
Mud was laid down on top of the Flathead Sandstone as the shoreline advanced eastward across the Teton area. The resulting soft greenish-gray shale with beds of purple and green sandstone near its base, became the thick Wolsey Shale Member of the Gros Ventre Formation. Some shale shows patterns of cracks that formed when the accumulating mud was briefly exposed to the air along tidal flats. Small phosphatic-shelled animals called brachiopods inhabited these tidal flats but as far as is known, nothing lived on land. Many shale beds are marked with faint trails and borings of worm-like creatures, and a few contain the remains of tiny trilobites.
Covered by a shallow sea
As the shoreline continued to move eastward, the 285-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 of shale. The Death Canyon contains abundant fossil of brachiopods and trilobites in some places. Following this the sea retreated to the west for a short time. The 220-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. Underwater expanses of algae flourished in places on the sea bottom and built extensive reefs. 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. These are widespread in the shale and in overlying and underlying limestone layers.
By Late Cambrian, the shoreline had once again crept eastward, resulting in clearer water that was probably deep. The 100-foot-thick (30 m) Gallatin Limestone was formed. It consists of blue-gray limestone that is mottled with irregular rusty or yellow patches. Interrupting the limestone are a few beds of 'edgewise' conglomerate that are indicative of sporadic storms. 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.
Uplift puts the area back on the sea's edge
The Ordovician Bighorn Dolomite forms ragged hard massive light-gray to white cliffs 100 to high. 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.
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.
The Mississippian Madison Limestone is thick and is exposed in spectacular vertical cliffs along canyons in the north, west, and south parts of the Tetons. 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. The Fossil Mountain Ice Cave—Wind Cave system on the west side of the Teton range was dissolved out of this rock by water.
The Pennsylvanian system is represented by the Amsden Formation and the Tensleep Sandstone. 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.
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. 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
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, 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. Their sediment came from rock eroded from a mountain chain east of the seaway interspersed 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.For the whole paragraph: Geology of National Parks, page 566-567, section 5
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.
Sundance Sea covers older deposits