The Geomorphology and Geology of the Flint Hills Region of Kansas

Dina Wingfield

Created for ES 546, Field Geomorphology

Fall, 2007



photo by D. Wingfield

Table of Contents

Physiography Geology
Structural Features

References




Kansas Geomorphology and the Flint Hills Physiographic Region

Geologists have identified eleven distinct physiographic regions in Kansas (see map below, courtesy of Kansas Geological Survey). These regions were formed by complex interactions among physical features and processes such as deposition and erosion of sediments overtime, geographic location, slope and drainage of land surface, topography and surficial geology, and land use factors.Weather and climate variables throughout geologic history have also contributed to the formation of the present day regions.

Courtesy of Kansas Geological Survey

The Flint Hills Physiographic Region

Spanning over 82,000 square miles, Kansas lies in the heart of the North American Continent in a zone referred to as the Central Stable Region of the Canadian Shield (Merriam, 1963). The Flint Hills stretch almost border to border across the state, from Washington and Marshall counties in the north, to Cowley County in the south (Buchanan, 1984) before extending into Oklahoma. They are bordered on the west by the Smoky Hills, the Wellington-McPherson Lowlands, and a small southern stretch of the Arkansas River Lowlands. On the east, the Flint Hills neighbor the Osage Cuestas. They are bordered by the Glaciated Region further northeast.

A cross section of Kansas reveals that the surface topography of the state dips gently eastward. However, examination of the rocks underlyingthe Flint Hills shows an overall tendency to dip gently to the west and northwest (Zeller, 1968), and the landscape in the Flint Hills is at a higher elevation than surrounding areas, both eastward and westward.

Courtesy of Kansas Geological Survey


Flint Hills Geology

Though the Flint Hills have been roughly 4.5 billion years in the making, an examination of the surficial geology (surface rocks and features), reveals that their formation occurred primarily during the Permian Period some 290 to 250 million years ago (Buchanan, 1984). During the Permian, the area that is now known as the Flint Hills underwent periodic cycles of transgression and regression of seawaters (each cycle is termed a cyclothem). The transgression phases involved water encroaching onto the land, resulting in large expanses of flooded areas.The regression phases involved the water receding to lower levels, resulting in more shallow inland seas, and at times,dry, open lands (Merriam, 1963). Rocks that were laid down during this time exhibit what geologistscall "layer-cake stratigraphy" and are composed primarily of alternating layers of shales and limestones (Muilenberg, 1959), interbedded in places with sandstones (Buchanan, 1986). Generally speaking, it is believed that limestone depositions accumulated in areas of deep-sea waters (Buchanan, 1986). Shales accumulated in areas that were slightly above sea level or in near shore marine environments. Sandstones accumulated in areas of non-marine deposition, such as rivers, lakes or land (Muilenberg, 1959).

With respect to the Flint Hills region, the limestone layers that were deposited in the Permian Period contained an abundance of a mineral called chert, or flint (also regarded as a rock), from which the region drew its name. According to Merriam (1963), the overall composition of some limestone layers contains as much as one quarter to one third chert. Chemically, chert is a silicate, composed of silicon dioxide, and is one of the many varieties of quartz. The origin of chert is not fully understood, however, one hypothesis suggests that as the chemical composition of the Permian seas changed, sponges living in the open waters began producing spicules of silica that was extracted from the seawater (Muilenberg, 1963).

Well below the surface of the Permian hills lies the basement rock layers (Precambrian through Mississippian deposition).The east-west dipping of the basement rocks is responsible for much of the surface topography that is observed throughout the Flint Hills today. As previously mentioned, chert is extremely resistant to erosion. At the same time, the embedded layers of shale are easily eroded by both wind and water. This combination of erosion-resistant limestones and easily eroded shales, overlying a basement rock that is tilted toward the west, results in the distinct surface topography foundin the Flint Hills. This topography is characterized by steep, eastward facing slopes where the shale has eroded and the limestone layers remain, as well as much more gently sloping westward facing slopes (Buchanan, 1984). These slopes can easily be seen in the photograph below.


photo by D. Wingfield




Structural Features


As can be seen on the geologic cross section above, these basement rocks are tilted from the east to the west in the area, with the exception of a strong line of reverse tilt beneath the Flint Hills. This "reversal" occurs along the Nemaha Anticline, or Nemaha Uplift (see map below), an ancient granite "mountain range" that was uplifted following the Mississippian Period (Merriam, 1963). The eastern crest of the Nemaha Anticline is bordered by another tectonic feature, the Humboldt Fault Zone. This fault runs near parallel to the anticline (Steeples, 1981).

Historically, the Humboldt Fault was a tectonically active fault zone, and during periods of geothermal activity was responsible for the prominent uplift and deformation of Precambrian granitic rocks (Newell, et al, 1989; Stander, 1989). Subsequent layers were periodically deposited (and perhaps eroded as well) atop the uplift.Further deformation during the early Pennsylvanian Period gave rise to the NemahaAnticline. The Nemaha Anticline plunges assymetrically southward and is faulted in several areas along its route by both normal and reverse faults (Lee & Merriam, 1954; Merriam, 1963; Stander, 1989).




Courtesy of Kansas Geological Survey



References


Buchanan, R. (Ed.). (1984). Kansas Geology; An introduction to landscapes, rocks, minerals and fossils. Kansas Geological Survey Publication, University Press of Kansas.

Buchanan, R. (Ed.). (1986). Kansas Rocks and Minerals. (Rev. Ed). Kansas Geological Survey Publication, University Press of Kansas.

Kansas Geological Survey. World Wide Web
http://www.kgs.ku.edu/.

Lee, W. & Merriam, D.F., (1954). Cross sections in eastern Kansas. Kansas Geological Survey Publication, University Press of Kansas.

Merriam, D.F., (1963). The geologic history of Kansas. State Geological Survey Publication, University of Kansas Publications, Lawrence, KS.

Muilenberg, G., (1959). In the Flint Hills of Lyon, Chase, Morris and Wabaunsee Counties, Kansas. State Geological Survey Publication, University of Kansas Publications, Lawrence, KS.

Newell, K.D., Watney, W.L., Steeples, D.W., Knapp, R.W., & Cheng, S.W., (1989). Suitability of high-resolution seismic method to identifying petroleum reservoirs in Kansas-A geological perspective. In D. Steeples (Ed.), Geophysics in Kansas. Kansas Geological Survey Publication, University of Kansas Publications, Lawrence, KS.

Standler, T.W., (1989). Structural nature of the Humboldt fault zone in northeastern Nemaha County, Kansas. In D. Steeples (Ed.), Geophysics in Kansas. Kansas Geological Survey Publication, University of Kansas Publications, Lawrence, KS.

Trellian Web Page. World Wide Web http://www.trellian.com/webpage/

Zeller, D.E., (1968). The stratigraphic succession in Kansas. Kansas Geological Survey Publication, University of Kansas Publications, Lawrence, KS.




This page created to fulfill requirements of ES 546 Field Geomorphology
Comments or questions e-mail the author at dwingfield@usd329.com
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