Americus Limestone

Americus Limestone
Stratigraphic range: Gzhelian PreꞒ Ꞓ O S D C P T J K Pg N ↓ [1]
The Americus Limestone beds form the first bench of the Flint Hills when approaching from the east. Placed near that bench, this sign is carved from the gray-toned Americus Limestone.[2][3]
Type	Formation member
Unit of	Foraker Formation of the lower Council Grove Group
Underlies	Hughes Creek Shale of the Foraker Formation
Overlies	Hamlin Shale member of the Janesville Shale
Lithology
Primary	Limestone, shale
Other	stromatolite limestone, lime-sand mudstone/grainstone, flint[4]
Location
Region	Kansas
Country	United States
Type section
Named for	Americus, Kansas
Named by	M. Z. Kirk, University Geological Survey of Kansas[5]
Year defined	1896

The Americus Limestone is a member of the Foraker Limestone Formation in eastern Kansas, where it is quarried as a distinctive ornamental stone. In outcrop, it is typically recognized as two relatively thin but persistent beds of hard limestone separated by shale that forms the lowest prominent bench of the many benches of the Flint Hills. The recognizable facie of the member in excavated or eroded exposures is two thin limestone beds separated a bed of shale and adjacent shales above and below having a particular gray or bluish color darker than higher limestones. A third, lower, highly variable algal limestone is often present and included as the base of the member. The unit is not particularly massive, the limestone pair totaling 3 to 4 feet (0.91 to 1.22 meters) in places, more in other locations but less to the North, and up to nearly to 9 feet (2.7 meters) at the type location of Americus, Kansas. The addition of the lower algal limestone as a base for the unit increases the thickness to over 18 feet (5.5 meters). Initially thought to be the lowest of the Permian rock of Kansas and as such classified as the lowest unit of the Council Grove Group, the unit is now dated within the uppermost Late Carboniferous.^[1]