Polk Creek Shale

The Polk Creek Shale is a Late Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892,[3] this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas.[2] Purdue assigned Polk Creek in Montgomery County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.

Polk Creek Shale Stratigraphic range: Ordovician
Type	Formation
Unit of	none
Sub-units	none
Underlies	Blaylock Sandstone
Overlies	Bigfork Chert
Thickness	50 to 225 feet[1]
Lithology
Primary	Shale
Location
Region	Arkansas, Oklahoma
Country	United States
Type section
Named for	Polk Creek, Montgomery County, Arkansas
Named by	Albert Homer Purdue[2]

Paleofauna

Graptolites

Amplexograptus[4] Climacograptus[4] C. mississippiensis[5] C. putillus[5] C. ulrichi[5] Dicellograptus D. complanatus[4][5] D. elegans[4] D. forehammeri flexuosus[4] Diplograptus[4] D. calcaratus[5] D. crassitestus[5]

Glossograptus[4] G. quadrimucronatus[5] Lasiograptus[4] Mesograptus[4] Nymphograptus N. velatus[4] Orthograptus O. quadrimucronatus[4] O. spinigerus[4]

See also

• List of fossiliferous stratigraphic units in Arkansas
• Paleontology in Arkansas

References

1. McFarland, John David (2004) [1998]. "Stratigraphic summary of Arkansas" (PDF). Arkansas Geological Commission Information Circular. 36: 19. Archived from the original (PDF) on 2016-12-21. Retrieved 2018-01-09.
2. Purdue, A.H. (1909). Slates of Arkansas. Geological Survey of Arkansas. pp. 30, 35.
3. Griswold, L.S. (1892). "Whetstones and the novaculites". Annual Report of the Geological Survey of Arkansas for 1890. 3.
4. Miser, Hugh D.; Purdue, A.H. (1929). "Geology of the De Queen and Caddo Gap quadrangles, Arkansas". U.S. Geological Survey Bulletin. 808: 40–42.
5. Decker, Charles E. (1935). "Graptolites of the Sylvan Shale of Oklahoma and Polk Creek Shale of Arkansas". Journal of Paleontology. 9 (8).