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23-645: The Western Interior Seaway was an inland sea that existed from the Late Jurassic (161.2 ± 4.0 to 145.5 ± 4.0 million years ago [Ma]) to the end of the Paleogene (66 to 23.03 Ma). It existed in the middle of North America , extending from the Arctic Ocean to the Gulf of Mexico . It was roughly 3,000 miles (4,800 km) long and 1,000 miles (1,600 km) wide. The seaway was relatively shallow, with

46-419: A continent, not adjacent to it. The law of the sea does not apply to inland seas. In modern times, continents stand high, eustatic sea levels are low, and there are few inland seas. The Great Lakes , despite being completely fresh water , have been referred to as resembling or having characteristics like inland seas from a USGS management perspective. Lake Ontario is the only Great Lake connected to

69-602: A maximum depth estimated at 660 to 1,640 feet (200 to 500 m). A foreland basin existed just to the east of the Sevier orogenic belt , which was inundated by the Western Interior Seaway. A forearc on the western side of the basin made this deeper than the eastern side, encouraging the build-up of sediment and, in time, sedimentary rock. Erosion of the Western Cordillera also contributed to

92-440: Is "more or less" cut off from the ocean. It may be semi-enclosed, or connected to the ocean by a strait or "arm of the sea". An inland sea is distinguishable from a bay in that a bay is directly connected to the ocean. The term "epeiric sea" was coined by Joseph Barrell in 1917. He defined an epeiric sea as a shallow body of water whose bottom is within the wave base (e.g., where bottom sediments are no longer stirred by

115-501: Is a continental body of water which is very large in area and is either completely surrounded by dry land or connected to an ocean by a river , strait or " arm of the sea ". An inland sea will generally be brackish , with higher salinity than a freshwater lake but usually lower salinity than seawater . As with other seas, inland seas experience tides governed by the orbits of the Moon and Sun. What constitutes an "inland sea"

138-503: Is complex and somewhat necessarily vague. The United States Hydrographic Office defined it as "a body of water nearly or completely surrounded by land, especially if very large or composed of salt water". Geologic engineers Heinrich Ries and Thomas L. Watson say an inland sea is merely a very large lake. Rydén, Migula, and Andersson and Deborah Sandler of the Environmental Law Institute add that an inland sea

161-812: Is said by Eicher to overlie the Cloverly Formation , although Rice, Porter et al. , and Lash that in Montana and Wyoming the Kootenai Formation is geologically equivalent to the Cloverly Formation and thus conclude that the Thermopolis Shale overlies the Kootenai Formation. There is disagreement as to the stratigraphic definition of the basal member of the Thermopolis Shale, however. Eicher has argued that

184-857: Is unusually rich in marine vertebrate fossils, consisting primarily of skeletal material, teeth, and coprolites . A particularly rich marine vertebrate fossil zone exists in the lower beds of the Upper Thermopolis Member. Marine crocodile , plesiosaur (primarily Edgarosaurus muddi ), ray (primarily Pseudohypolophus and an unidentified species), sawfish (primarily Onchopristis ), and turtle (primarily Baenidae and Glyptops ) remains, as well as whole coprolites, are abundant. Hybodont shark (primarily Meristodonoides ), ganoid-scaled and teleost fish, and invertebrate fossil ammonoids (primarily Baculites ) are also found. Inland sea (geology) An inland sea (also known as an epeiric sea or an epicontinental sea )

207-699: The Atlantic Ocean below Niagara Falls . Modern examples might also include the recently (less than 10,000 years ago) reflooded Persian Gulf , and the South China Sea that presently covers the Sunda Shelf . At various times in the geologic past, inland seas covered central areas of continents during periods of high sea level that result in marine transgressions . Inland seas have been greater in extent and more common than at present. Fall River Sandstone The Fall River Sandstone

230-701: The Shell Creek Shale , separating them from the Mowry Shale. This effectively put the Thermopolis Shale below the Muddy Sandstone Formation. In 1998, Porter et al. identified the Shell Creek Shale as the upper member of the Thermopolis Shale, a position with which Lash agreed in 2011. Depending on the definition of the shale, and the location, the Thermopolis Shale varies widely in thickness. Chester N. Darton estimated

253-567: The Wind River Indian Reservation of Wyoming, using the inclusive definition, it was reported to be a more robust 320 to 450 feet (98 to 137 m) thick. It is only 10 feet (3.0 m) thick in the Shirley Basin of southwest central Wyoming. Generally speaking, the Thermopolis Shale consists of a dark gray to black shale, with thin layers of bentonite, sandy claystone , and siltstone interspersed throughout

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276-476: The "rusty beds" division is clearly distinguishable in many ways from the Cloverly Formation, and thus belongs to the Thermopolis Shale. Seeland and Brauch assigned the "rusty beds" to the Cloverly Formation in 1975, an assessment concurred with by Finn in 2010. Porter et al., however, classified the "rusty beds" as part of the Fall River Sandstone in 1997. What constitutes the upper boundary of

299-613: The Thermopolis Shale is disputed, making it difficult to identify what overlays the Thermopolis Shale. In 1922, Collier identified the beds below the Mowry Shale as the Nefsy shale member of the Graneros Shale . This left the Thermopolis Shale underlying the Graneros Shale. But Rubey assigned these rocks to the Mowry Shale in 1931, so that now the Thermopolis Shale underlay the Mowry Shale. Eicher redefined these beds in 1960 as

322-555: The Thermopolis Shale was also noted, a "muddy sand" layer about 15 to 55 feet (4.6 to 16.8 m) thick. No type locality was identified, but the formation was named for the town of Thermopolis in Hot Springs County, Wyoming —where, nearby, outcroppings of the shale were well exposed. Lupton's division of the Thermopolis Shale was adopted by the United States Geological Survey and used for

345-565: The Thermopolis Shale: Surface outcroppings of the Thermopolis Shale occur in central Canada , and the U.S. states of Montana and Wyoming . Marine-deposited rock thins toward the west, while nonmarine-deposited rock thins toward the east. The marine-deposited rock is primarily shale, with some limestone , sandstone , and siltstone . The nonmarine rock is primarily sandstone, with some coal , shale, "black" or carbonaceous shale , and siltstone. The Thermopolis Shale

368-462: The build-up of sedimentary rock on the western edge of the basin, while the more low-lying area to the east provided much less. Changes in the amount, type, rate, and other aspects of the sedimentation were caused by uplift , subsidence , sea level changes, and other factors. The water in the basin made at least two major advances and one major retreat during the Cretaceous, adding complexity to

391-584: The next 50 years. The stratigraphic history of the Thermopolis Shale was first outlined by geologist Don L. Eicher in 1962. The Thermopolis Shale belongs to both the Colorado Group and Dakota Formation . Both historically and currently, the stratigraphic units in these groups, and in the Thermopolis Shale, have been unclear, and the nomenclature used by geologists is not standardized. The identification of beds, members, and formations and their names have changed over time as well. The Thermopolis Shale

414-554: The rock and permitting the creation of riverine , marsh, and estuarine rock in addition to the principal shallow and deep marine rock. Dating of bentonite and palynological evidence indicate that the Lower Thermopolis Member was deposited between 100.3 and 98.5 Ma. A study of Inoceramidae bivalves confirmed a Late Albian age. Deposition of the upper three members of the Thermopolis Shale occurred over approximately 7 million years. The Thermopolis Shale

437-415: The shale. Depending on the stratigraphic definition of the formation, a gray, thinly-bedded sandstone member exists between the upper and lower members. For the purposes of this article, the definition of the Thermopolis Shale used by Porter et al. and Lash will be used, recognizing (as Condon does) that there is scientific disagreement about this issue. Using this definition, there are four members of

460-508: The size of the formation at 800 feet (240 m) (including the "rusty beds") in 1906. In 1914, Hintze described the formation as 720-to-770-foot (220 to 230 m) deep. Hewett and Lupton reported in 1917 that the shale (including the "rusty beds") to be 400 to 800 feet (120 to 240 m) thick in the Bighorn Basin , while Finn (not including the "rusty beds" reported a thickness in the same area of 125 to 230 feet (38 to 70 m). On

483-479: The wave above), as one with limited connection to an ocean, and as simply shallow. An inland sea is only an epeiric sea when a continental interior is flooded by marine transgression due to sea level rise or epeirogenic movement . An epicontinental sea is synonymous with an epeiric sea. The term "epicontinental sea" may also refer to the waters above a continental shelf. This is a legal, not geological, term. Epeiric, epicontinental, and inland seas occur on

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506-423: Was first identified in 1914 by geologist Ferdinand F. Hintze, Jr. He called it the "Lower Benton Shale", and included the Mowry Shale in the same formation. Hintze described three members: The basal "rusty beds", a lower shale, a 25-to-40-foot (7.6 to 12.2 m) thick "Muddy Sand" (muddy sandstone), and an upper shale member. (The fourth member of the "Lower Benton Shale" was the Mowry Shale.) The Thermopolis Shale

529-519: Was first named by geologist Charles T. Lupton in 1916. Lupton described the rocks as a formation lying conformably atop the Cloverly Formation, and conformably underlying the Mowry Shale. The Thermopolis Shale was the basal of four formations making up the Colorado Group. He described the Thermopolis Shale as Late Cretaceous in age, generally dark in color, from 710 feet (220 m) thick, and with sandstone lenses common. At least one member of

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