The Red Eagle Formation (or Red Eagle Limestone) is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

ranging from

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

, through

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

, into southeast

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

of the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. Its members define the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

boundary in Kansas.

Lithology

In the Oklahoma type location, the Red Eagle is a single limestone unit, not further defined into members. However, from the far southeast Nebraska type section into northern Kansas, the Red Eagle Formation consists of three members, each with distinctive lithologies. In Nebraska and northern Kansas in particular, the formation stands out on riverside bluffs and road cuts as two blocky, light-colored limestones sandwiching a dark layer of shale.

Howe Limestone

Named from exposures south of Howe, Nebraska, the Howe Limestone member is a grey limestone, 4-5 feet thick, that weathers to buff or slightly yellow. The limestone exhibits brachiopods, baculites, and larger bivalve mollusks. The environment was an open, but very shallow sea with very little in the way of terrigenous sediments. As such, the topmost bed is particularly notable for algae beds and melon-sized

stromatolite Stromatolites ( ) or stromatoliths () are layered Sedimentary rock, sedimentary formation of rocks, formations (microbialite) that are created mainly by Photosynthesis, photosynthetic microorganisms such as cyanobacteria, sulfate-reducing micr ...

Bennett Shale

Named from exposures along the Little Nemaha River and its branches south of

Bennet, Nebraska Bennet is a city in Lancaster County, Nebraska, United States. It is part of the Lincoln, Nebraska Metropolitan Statistical Area. The population was 1,082 at the 2020 census. History Bennet was founded on July 29, 1871 when the railroad was ...

, the Bennett Shale member is a dark, carbonaceous shale, 2.5 to 15 feet thick. This very dark shale shows contrasting light-colored, circular, thin-shelled Orbiculoidea, roughly 1cm (1/3") in diameter. However, south of

Interstate 70 in Kansas Interstate 70 (I-70) is a mainline route of the Interstate Highway System in the United States connecting Cove Fort, Utah, to Baltimore, Maryland. In the US state of Kansas, I-70 extends just over from the Colorado border near the town o ...

, the member becomes increasing limestone to the point that within Oklahoma, the bed is completely limestone and the Red Eagle unit undivided by any significant shale bed. The Bennett is the youngest

rock unit in Kansas.

Glenrock Limestone

Named from exposures high in valley sides just northwest of Glenrock, Nebraska, the Glenrock Limestone member is lighter grey. It is a hard limestone; fresh fractures sparkle in full sunlight from tiny calcite crystals. The Glenrock is the oldest

rock unit in Kansas.

Lithology

Howe Limestone

Bennett Shale

Glenrock Limestone

See also

References

Further reading