Red Eagle Formation

Red Eagle Formation
Red Eagle Formation
Stratigraphic range: Carboniferous-Permian boundary
Type	Formation
Unit of	Council Grove Group
Sub-units	In Kansas and Nebraska:; Howe Limestone; Bennett Shale; *Glenrock Limestone
Lithology
Primary	Limestone
Other	Shale
Location
Coordinates	36°52′21″N 96°33′56″W / 36.87250°N 96.56556°W
Region	Midcontinent (Oklahoma, Kansas, Nebraska)
Country	United States
Type section
Named for	Red Eagle School, southwest of Foraker, Oklahoma
Named by	K.C. Heald
Year defined	1916

The Red Eagle Formation (or Red Eagle Limestone) is a geologic formation ranging from Oklahoma, through Kansas, into southeast Nebraska of the United States.^[2] Its members define the Carboniferous-Permian boundary in Kansas.^[1]

Lithology[edit]

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.^[2]

Howe Limestone[edit]

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.^[3] 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[edit]

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.^[4] 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[edit]

Named from exposures high in valley sides just northwest of Glenrock, Nebraska, the Glenrock Limestone member is lighter grey.^[5] 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.

References[edit]

^ ^a ^b Robert S. Sawin, Ronald R. West, Evan K. Franseen, W. Lynn Watney (January 2006). "Carboniferous-Permian Boundary in Kansas, Midcontinent, U.S.A". Current Research in Earth Sciences. 252 (1). ... 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b ^c "Geologic Unit: Red Eagle". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2021-02-12.
^ "Geologic Unit: Howe". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2021-02-12.
^ "Geologic Unit: Bennett". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2021-02-12.
^ "Geologic Unit: Glenrock". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2021-02-12.