Geology of Kansas

Mississippian limestones and cherts of the Ozark Plateau are exposed in extreme southeastern Kansas in Cherokee County.[5] This area was part of the Tri-state district of the nineteenth and twentieth centuries. Galena was a center of lead and zinc mining in the area.[6]

The Cherokee lowlands is a region of southeast Kansas immediately north and west of the Ozark plateau in Cherokee, Labette, Crawford and Bourbon Counties. The lowlands are developed on areas of gently rolling hils developed on the shale and sandstone of the Cherokee Group of Pennsylvanian age. The Cherokee Group is noted for rich deposits of coal in Kansas and across the midwestern United States.[7]

The Osage cuesta region underlies twenty counties in southeastern Kansas. The cuestas are a region of east to southeast facing escarpments (50 to 200 feet high) formed on resistant limestone units which dip gently to the west and northwest. Areas between escarpments are underlain by shales. The cuesta region contains coal, black shale and some oil shales. Lamproite sills occur within the cuesta units of Woodson and Wilson counties. These unusual igneous rocks were intruded in the Cretaceous Period.[8][9]

The Chautauqua Hills represent a narrow region in southeast Kansas of sandstone capped ridges and rolling hills. The Pennsylvanian age sandstones were deposited in a large river valley. The sandstones are the Tonganoxie Sandstone Member of the Stranger Formation and Ireland Sandstone Member of the Lawrence Formation. The hills occur in the western portions of Montgomery, Wilson and Woodson counties and the eastern edges of Chautauqua, Elk and Greenwood counties. The sandstones continue into northern Oklahoma.[10]

The Flint Hills developed on the north–south exposure of Permian cherty limestones. The region extends from Marshall County in the north, to Cowley County and on into northern Oklahoma where they are known as the Osage Hills. The Permian limestones contain abundant weathering resistant chert (or flint) and the residuum and soils of the hilltops and the streambeds of the region contain abundant cherty gravels. Surface exposures of the rare igneous kimberlites occur in Riley and Marshall counties. The kimberlite diatremes are of Cretaceous age. No diamonds have been found in the Kansas kimberlite occurrences. Garnet crystals from the kimberlites have been reported in local stream gravels.[11][12][13]

The Red Hills cover a section of southern Kansas in Clark, Comanche, and Barber counties along the Oklahoma border. The Red Hills are named for their color derived from the Permian red beds which outcrop and underlie the region. The red color is produced by abundant iron oxides in the weathering sediments. The region is underlain by red shales, siltstones, and sandstones along with interbedded dolomites and gypsum evaporite layers. Massive gypsum deposits are mined near Sun City in northwestern Barber County. The Gyp Hills near Medicine Lodge were named for the gypsum of the Blaine Formation. The soluble gypsum, anhydrite and dolomite produce many caves in the area.[14][15] The Big Basin of Clark County is a 2 km diameter, 35 m deep, dissolution collapse feature that formed by the dissolution of salt beds in the subsurface.

The Smoky Hills constitute a large area of north central Kansas. The area is underlain by Cretaceous sediments. Rocks outcropping in the area include the sandstones of the Dakota Formation, the Greenhorn Limestone, and the thick Niobrara Chalk. Stratigraphically the Dakota is overlain by the Greenhorn and that by the Niobrara. The Dakota outcrops in the eastern portion of the region as gently westward dipping resistant ridges. Although the sandstones are the most resistant and therefore most prominent the Dakota includes shales and clays. The formation contains abundant brown iron oxides and many concretions are found in the area. In the western portions of the area the bedrock is fossiliferous chalk of the Niobrara Formation which includes the Smoky Hill Chalk member noted for abundant fish and marine reptile fossils.[16][17]

The western third of Kansas is in the High Plains area. The highest point in Kansas, Mount Sunflower (4,039 feet (1,231 m)), is located in the High Plains physiographic region. The tectonic uplift of the Rocky Mountains during the Cenozoic resulted in erosion and deposition of vast quantities of non-marine sediments eastward across the High Plains. The Ogallala Formation consists of a large wedge of unconsolidated sands and silts that is a significant aquifer under the plains. The Ogallala contains a sandstone layer cemented with opal. In the southwest corner of the state in Morton County rocks of Jurassic age outcrop along the Cimarron River. Loess deposits cover much of the High Plains in north and northwest Kansas.[18][19]

The northeast corner of the state, north of the Kansas River and east of the Big Blue River, is covered by glacial debris deposited during the Pre-Illinoian glaciations which occurred 600,000 years ago in the Pleistocene. The Pennsylvanian and Permian bedrock is buried under thick deposits of glacial debris, largely loess. A variety of glacial erratics were left by the melting glaciers. Many of these are of Sioux Quartzite carried south from the Sioux Falls, South Dakota area.[20]

The Wellington-McPherson Lowlands of south central Kansas in Sumner, Sedgwick, Harvey and McPherson counties is underlain by fluvial sediments deposited in the ancestral Arkansas River valley during the Pleistocene Epoch one to two million years ago. The sediments consist largely of sands, silts, and gravels. These include the Equus Beds Aquifer sediments, named for the Pleistocene modern horse fossils they contain. Also under this area is the Permian Hutchinson salt bed which reaches a thickness of 400 feet (120 m). The area also contains inactive sand dunes.[21]

The Arkansas River Lowlands follows the course of the Arkansas River through southwest and south-central Kansas. The broad floodplain contains large quantities of sand and silt carried from the Rocky Mountains by the river. A significant area of sand dunes occur on the south side of the plain formed by the prevailing winds from the glaciers to the north during the Pleistocene.[21]

Humboldt Fault (red) and Midcontinent Rift (green) in Kansas and Nebraska

The Nemaha uplift is a deep fault zone which runs diagonally across east Kansas and extends from just south of Omaha, Nebraska to Oklahoma City. This fault zone directly overlies a granite "high" in the Precambrian basement and is structurally active as the Humboldt Fault. Some fifty miles to the west the southernmost extension of the Proterozoic Midcontinent Rift System extends into northeastern Kansas.[23]

The northern two-thirds of Kansas is underlain by a Proterozoic sequence known as the Central Plains Orogen. The igneous and metamorphic rocks of this orogenic zone are considered to be an extension of the 1.7 Ga fold belt exposed in Colorado and Wyoming.[24] The southern approximately one-third of the state is underlain by the Southern granite-rhyolite province dating to 1.35 to 1.48 Ga.[24][25]