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Geology of Kansas (1920)

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In its broad features the geology of Kansas is almost ideally simple. The state is a very typical part of the Great Plains region, which extends from the Dakotas to Texas and from the Rocky Mountains eastward to the Mississippi, and it has the uniformly gentle slope and simplicity of geologic structure which characterize the plains. The surface of Kansas has a general inclination from west to east, amounting to about ten feet per mile, the elevation of the western state boundary being about 3,500 to 4,000 feet, that of the eastern boundary from 750 to 1,000 feet (fig. 1). The rock formations of which this sloping plan is built lie almost flat, and are exposed in broad north-south bands across the state. In reality they sag slightly in central Kansas, the rock slope or dip being toward the west in the eastern counties and to the east in the western part of the state. The oldest beds appear at the surface in the east and dip-beneath the younger overlying formations which appear in succession as the state is crossed to the west (fig. 2).

Figure 1—Sketch diagram showing the east sloping plain east of the Rocky Mountains in Kansas and eastern Colorado.

Sketch diagram showing the east sloping plain east of the Rocky Mountains in Kansas and eastern Colorado.

Figure 2—Geologic section across Kansas showing the slight sag in the beds in central Kansas.

Geologic section across Kansas showing the slight sag in the beds in central Kansas.

Formation of the Rocks of Kansas

The rocks of Kansas, as classified on the basis of origin, belong to the sedimentary group. Rocks of igneous origin have been found in deep wells, but do not come to the surface within the borders of the state. [Note: A surface exposure of igneous rock has recently been discovered in west central Riley County, one mile east of Bala. It is a dark-colored basic rock and outcrops only in a very small area (Moore and Haynes, 1920).] The formation of the sedimentary rocks may be discussed briefly as an introduction to the summary of the stratigraphy of Kansas which follows.

Sedimentary rocks are those composed of the transported fragments or particles of older rocks that have undergone disintegration. The chief agencies of transportation are water—including rain, streams, lakes and the sea—wind, and glaciers; Deposition of the rock particles may take place along streams, at the bottom of lakes or the sea, where the wind drops its load, or beneath glaciers. Materials such as gravel, sand and clay are carried as solid particles, and after deposition may be consolidated to form conglomerate, sandstone or shale. Other materials are carried in solution and may be deposited chemically, as in the formation of salt or gypsum, or by the action of plants or animals, as in the formation of limestone or coal. Sedimentary rocks are usually made up of layers or beds, called strata, which can easily be separated.

By far the most important area of deposition in which sedimentary rocks are being formed is the bottom of the ocean. The bottom of the sea is covered with gravel, sand and mud, which are sorted and spread by the waves and currents. As these sediments gather they bury others already deposited. When compressed by the weight of overlying materials, and bound together by cement deposited between the grains, the originally unconsolidated sediments are hardened into firm rock.

The oil and gas deposits of the Midcontinent field are confined almost wholly to rocks Of the Pennsylvanian system, which outcrop in a broad belt across eastern Kansas and Oklahoma (plate I). In other districts oil and gas in commercial quantities occur in strata of geologic divisions as old as the Cambrian, but they have not yet been found generally in the older rocks of the Midcontinent field (Powers, 1917). It is known that in a number of localities, chiefly in Oklahoma, there are important oil and gas pools within the Mississippian; and at least from one locality in the Healdton field, possibly also in the Osage, commercially valuable oil has been found in Ordovician rocks. Oil and gas have been found also in the Permian and in the Cretaceous, although it is possible that locally, as in Kansas, the oil and gas in these strata have migrated upward from underlying Pennsylvanian formations. On account of the broader distribution of oil and gas which is thus indicated, and because exploration for these hydrocarbons is being carried much beyond the limits of the Pennsylvanian outcrops, it is desirable to consider briefly the general stratigraphy and the oil and gas prospects of the whole state so far as they are known.

Plate I—Map showing the geology of Kansas and the adjoining region. [Also available as a larger Adobe Acrobat version, 5.3 MB.]

Map showing the geology of Kansas and the adjoining region.

Older Rocks of the Midcontinent Region


The rocks in the general region of the Midcontinent field range in geologic age from almost the oldest known to the youngest. The oldest rocks are granites and other crystalline rocks of probable Archeozoic age which are exposed in the southeastern part of Missouri, in the Arbuckle and Wichita mountains of Oklahoma, in the Rocky Mountains of Colorado, and, at points farther distant, north of Kansas. Since the exact age of these isolated patches of very ancient rocks is difficult or impossible to determine, it is most convenient to speak of them simply as Pre-Cambrian, for in all cases they are known to be older than the first sedimentary rocks of the Paleozoic. It is known that the Pre-Cambrian rocks extend everywhere beneath the later sedimentary formations, since they have been encountered in deep wells at many points outside the area of their outcrop. Geologic study indicates that any well drilled to a sufficient depth should strike the Pre-Cambrian; that is, that these crystalline rocks represent a "fundamental basement" or floor on which all the succeeding stratified rocks of the continent are laid down. According to abundant observation in all parts of the world, the Pre-Cambrian marks the lower limit of possible oil and gas deposits.

The Pre-Cambrian nowhere appears at the surface in Kansas, but drilling in the central part of the state has shown that it approaches the surface much more closely than was supposed. Sufficient tests have been made to indicate clearly the presence of a buried ridge or mountain range of granite which appears to trend in a direction slightly east of north from east Sumner County to the northern limits of the state. [Note: A detailed discussion of this granite is contained in another part of this report.] No evidence of metamorphism of the sedimentary rocks immediately overlying the granite has been found, and, it is probable that the ridge represents a part of the Pre-Cambrian floor.

Cambrian and Ordovician

The sedimentary formations which rest upon the Pre-Cambrian floor conform essentially to its surface. They are nearly horizontal over wide areas where the underlying crystalline rocks have not been deformed, but are upturned where the granite has been pushed more or less sharply upward by deep-seated mountain-making forces. Thus where the granites appear at the surface in Missouri, Oklahoma, Colorado or South Dakota, the oldest sedimentary rocks are upturned around them, the younger formations appearing, in the order of their age, farther away. (Plate II.) The exposure of these lower Paleozoic formations, even at a distance from Kansas, makes possible a more accurate conception of their character within the state than would be obtained from the record of deep borings alone.

Plate II—Geologic cross section in an east-west direction across the Kansas region. [Also available as a larger Adobe Acrobat version, 812 kB.]

Geologic cross section in an east-west direction across the Kansas region.

As studied in the Ozark region of Missouri, the rocks beneath the Mississippian and overlying the Pre-Cambrian include representatives of each of the geologic time divisions of the Paleozoic. The Cambrian and Ordovician systems of this region, consisting of dolomites, limestones, shales and sandstones, aggregate 2,000 to 2,500 feet in thickness. The succeeding Silurian and Devonian, however, are very thin and irregular in distribution and are practically confined to the northern, eastern and southern flanks of the Ozark uplift. The Silurian has been recognized in northeastern Oklahoma [The Silurian is represented by the St. Clair limestone about 100 feet in thickness (Taff, 1905).] and northern Arkansas (Williams, 1900), but beds of this period and of the Devonian are wanting throughout most of the region of the Great Plains. [Note: Northern Arkansas and Oklahoma (Chattanooga shaw and Sylamore sandstone), referred to the Devonian by various writers, are probably referable to the basal Mississippian (Shepard, 1892).]

West of Kansas, in the upturned strata of the Front Range of the Rocky Mountains (plate II), the strata of the Great Plains are well exposed and may be studied in some detail. Here the Cambrian is observed in certain localities, but it has a thickness of not more than fifty or sixty feet and for long distances it is absent altogether. The Ordovician, similarly, while recognized here and there, hasa maximum thickness of only 250 feet, and disappears north of Denver.

Cambrian and Ordovician strata are present in the Wichita and Arbuckle mountains and surrounding the Black Hills of South Dakota. Since these old formations come to the surface at various points on almost all sides of Kansas, it may be supposed that they underlie most of the state, but it should be noted that their thickness decreases very greatly from east to west, as shown by observations in Missouri and Colorado. Deep borings in southeastern Kansas indicate the thickness of sedimentary rocks beneath the Mississippian in parts of the state to be more than 2,200 feet (Iola), although granite has been reported only 1,000 feet below the Mississippian at Paola and Neodesha (?) (Haworth and Bennett, 1908). If the granite of central Kansas already mentioned is Pre-Cambrian, the older Paleozoic rocks are absent in this region, for the beds which immediately overlie the granite are apparently Pennsylvanian in age.

In summary, it appears that a series of dolomite, shale and sandstone formations belonging to the Cambrian and Ordovician systems, possibly with thin local deposits of Silurian or Devonian age, underlie most of Kansas. These beds are more than 2,000 feet thick in the eastern part of the state, but probably become very much thinner or locally absent to the west.

Mississippian System

Upon the eroded surface of the rocks of the older Paleozoic in the Great Plains country is found the Mississippian system, or, as it is called by drillers, the "Mississippi lime." The Mississippian is a clearly defined, readily traceable stratigraphic unit, consisting chiefly of crystalline limestones containing a rather unusual amount of hard, flinty chert. In Oklahoma and northern Arkansas it includes important beds of shale and some sandstone, but where encountered by the drill in Kansas and throughout most of Missouri it is essentially a limestone series. An exception apparently is found locally in central Kansas, according to recent information from well records, which indicates a disappearance locally of the limestone and a partial replacement by clastic materials. The thickness of the system in the south central part of the Mississippi basin is more than 2,000 feet, but in Kansas it is not more than 300 or 350 feet.

As shown on the accompanying sketch map (plate I), the Mississippian appears at the surface in a band of varying width almost surrounding the area of older Paleozoic rocks in the Ozark highland. This band of outcrop extends across Missouri in an east-west direction just north of Missouri river, and swings to the south from Sedalia into the Joplin and Springfield region, where a considerable area in southwest Missouri, northeastern Oklahoma and northwestern Arkansas is covered by Mississippian rocks. The only portion of Kansas in which the Mississippian beds occur at the surface is a very limited area in the southeastern portion of Cherokee County in the extreme southeastern corner of the state. The boundary between the Mississippian and the succeeding Pennsylvanian crosses the state line from Missouri about fifteen miles north of the southern border of the state and passes into Oklahoma about nine miles from the east Kansas state line.

The rocks of the Mississippian area in Kansas have been referred to the Burlington and, Keokuk formations, but according to recent investigation by the writer there seems little doubt but that this area belongs in the Warsaw division. This is in accordance with the determination by Weller of a part of the Mississippian of the adjoining southwestern Missouri district (Stuart Weller, personal communication). The subdivisions of the Mississippian have not been recognized in other portions of the state, although it seems probable that the limestone encountered in deep wells belongs chiefly to the Osage group. It is possible that the oil-bearing sandstones and shales of Chester age in Oklahoma extend northward a short distance into Chautauqua County, Kansas, since wells near Sedan have reported oil within the "Mississippi lime." Deep wells at various points in Kansas northwest of the Mississippian outcrops above mentioned have encountered the limestone beds of the system. They show that the beds are gradually inclined in a west or northwest direction at a rate varying from eight to fifteen or twenty feet per mile.

The Mississippian has been recognized at points as far west as Douglas (3,110 feet depth), but to what distance farther west the limestones of this age extend cannot be stated on evidence at hand. It is apparently absent along most of the line in which the wells have encountered the granite ridge in the east central portion of the state. The Mississippian appears at the surface locally where the rocks of the Paleozoic are upturned along the flanks of the Front Range in Colorado.

The upper surface of the Mississippian limestone is very uneven, having been greatly eroded during pre-Pennsylvanian and early Pennsylvanian time. As indicated by well drillings and observations in southeastern Kansas, the top of the Mississippian has a variation in elevation of as much as 75 to 90 feet in distances of less than one-half mile. This evidence of erosion has been observed throughout the Mississippi basin, and has been described by many geologists. It should be noted, however, that although there is considerable irregularity in the surface of the Mississippian limestone within a limited district, observations over a wider area show a general conformity between the bedding of the Mississippian and that of the overlying Pennsylvanian. This indicates that notwithstanding the widespread and possibly long-continued erosion after the Mississippian, there was no important disturbance of the older beds before Pennsylvanian deposition.

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Kansas Geological Survey, Geology
Placed on web Sept. 15, 2017; originally published 1920.
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