Red Eagle Formation

{{short description|Geologic formation in Kansas, Nebraska, and Oklahoma}}

{{Infobox rockunit

| name = Red Eagle Formation

| image =

| caption =

| type = Formation

| age = Carboniferous-Permian boundary

| prilithology = Limestone

| otherlithology = Shale

| namedfor = Red Eagle School, southwest of Foraker, Oklahoma

| namedby = K.C. Heald

| year_ts = 1916

| region = Midcontinent (Oklahoma, Kansas, Nebraska)

| country = United States

| coordinates = {{coord|36|52|21|N|96|33|56|W|region:US_type:city|display=inline,title}}

| unitof = Council Grove Group

| subunits = In Kansas and Nebraska:
*Howe Limestone
*Bennett Shale
*Glenrock Limestone

| underlies =

| overlies =

| thickness =

| extent =

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}}

The Red Eagle Formation (or Red Eagle Limestone) is a geologic formation ranging from Oklahoma, through Kansas, into southeast Nebraska of the United States.{{cite web | title = Geologic Unit: Red Eagle | series = Geolex — Significant Publications | work = National Geologic Database | publisher = United States Geological Survey | url = https://ngmdb.usgs.gov/Geolex/UnitRefs/RedEagleRefs_15684.html | access-date = 2021-02-12 }} Its members define the Carboniferous-Permian boundary in Kansas.{{cite journal |journal= Current Research in Earth Sciences |issue= 1 |date= January 2006

|author= Robert S. Sawin, Ronald R. West, Evan K. Franseen, W. Lynn Watney

|url= https://www.researchgate.net/publication/251528028

|title= Carboniferous-Permian Boundary in Kansas, Midcontinent, U.S.A

|volume= 252 |quote= ... the Carboniferous-Permian boundary in Kansas can now be confidently defined. Based [on fossil changes, the] boundary in Kansas can be placed at the base of the Bennett Shale Member of the Red Eagle Limestone.}}

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.{{cite web | title = Geologic Unit: Howe | series = Geolex — Significant Publications | work = National Geologic Database | publisher = United States Geological Survey | url = https://ngmdb.usgs.gov/Geolex/UnitRefs/HoweRefs_8567.html | access-date = 2021-02-12 }} The environment was an open, but very shallow sea with very little in the way of terrogenous sediments. As such, the topmost bed is particularly notable for algae beds and melon-sized stromatolites.

= Bennett Shale =

Named from exposures along the Little Nemaha River and its branches south of Bennet, Nebraska, the Bennett Shale member is a dark, carbonaceous shale, 2.5 to 15 feet thick.{{cite web | title = Geologic Unit: Bennett | series = Geolex — Significant Publications | work = National Geologic Database | publisher = United States Geological Survey | url = https://ngmdb.usgs.gov/Geolex/Units/Bennett_6834.html | access-date = 2021-02-12 }} 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, 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 Permian 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.{{cite web | title = Geologic Unit: Glenrock | series = Geolex — Significant Publications | work = National Geologic Database | publisher = United States Geological Survey | url = https://ngmdb.usgs.gov/Geolex/Units/Glenrock_8379.html | access-date = 2021-02-12 }} It is a hard limestone; fresh fractures sparkle in full sunlight from tiny calcite crystals.

The Glenrock is the oldest Carboniferous rock unit in Kansas.

Red Eagle Formation

Lithology

= Howe Limestone =

= Bennett Shale =

= Glenrock Limestone =

See also

References

Further reading