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Stratigraphy
Exposed Pre-Tertiary Rocks
The pre-Tertiary rocks outcropping in southwestern Kansas range in age from Upper Permian to Upper Cretaceous. They are widely exposed along Pawnee river, Buckner creek, and Sawlog creek at the northeast, and in the Red Hills and Ashland basin at the southeast. At the west, their outcrop areas are fewer and smaller, being limited to scattered areas along the larger stream valleys. Only casual observations on these rocks were made, and the following summary, included for completeness, is compiled from the literature.
Permian Rocks
Redbeds and associated rocks of Permian age are widely exposed in Clark County and in southeastern Meade County. These rocks have been collectively known as Cimarron, but .are now classified by the State Geological Survey according to series that are based on the Permian succession of western Texas. Subdivisions represented in the area here discussed are indicated in the following table, mainly from Norton (1939).
| Permian rocks of Clark and Meade counties, Kansas | |||
|---|---|---|---|
| Series | Formation | Member | Thickness in feet |
| Guadalupe | Taloga | 65 | |
| Day Creek dolomite | 2 | ||
| Whitehorse | Upper shale member | 38 | |
| Even-bedded member | 100 | ||
| Relay Creek dolomite | 22 | ||
| Marlow member | 110 | ||
The following descriptions are from Norton (1939).
The Whitehorse formation crops out in southern Clark County. Its lower member, the Marlow--
is a unit of poorly bedded, soft, ordinarily fine-grained, commonly cross-bedded sandstone, very difficult to subdivide into its individual layers. It weathers into deep canyons and massive bluffs. Locally some of its more resistant beds are composed of masses of "sandballs." . . . Many of the basal beds are prominently cross-bedded. In places they are more shaly or silty and some are veined. . . . The Relay Creek dolomite member is a variable member of sandstone 22 feet thick, with a dolomite bed, ranging from a few inches to a foot in thickness, at top and bottom. . . . In central and northern Clark County these beds are recognizable only as white streaks in the redbeds above a mass of featureless red sandstones, and below the next evenly bedded sandstone member. . . . Overlying the horizon of the Relay Creek dolomites and related beds is 100 feet of well bedded sandstones with thin intervening shaly siltstone partings, which also weather into canyons and promontories, but unlike the Marlow below, the individual beds of this member can be followed and correlated from place to place. . . . One of the more prominent and thicker sandstone beds has a deeper maroon color than the average and makes a good correlative marker. "Sand-balls" are present in these strata also, and the "sand-crystals" from which they developed were found in the lower beds of the member. Probably the best exposure of this member is in the Morrison oil field of Clark County. . . . The 38 feet of shale intervening between the even-bedded member and the Day Creek dolomite is a very distinctive unit of the Whitehorse. . . . Close to the base is a dolomitic horizon of two to three members, each about 1/2 foot thick, bedded in maroon clay shale. Calcite crystals of good size are present in an interlocking mass in the intervening shale. Above are some brick-red sandy clays, another calcareous sandy lentil near the middle of the member, a thin, hard red sandstone, more soft red sandstones, a last thin maroon shale, and above that 4-7 feet of gray-green sandy shale, more buff-colored immediately beneath the contact with the Day Creek dolomite.
The Day Creek dolomite is a single bed, typically about 2 feet thick, of fine-grained, dense dolomite, overlain and ordinarily underlain by gray shales. . . . In local areas, the dolomite has been partly altered to a siliceous rock which Cragin dignified by the name of "faresite".
This formation crops out in the area north and west of Ashland in Clark County. It makes an excellent horizon marker, and its outcrop has been mapped in detail by Putnam (in Suffel, 1930, pl. 17). This rock is being used as rip-rap on the dam at Clark County State Lake.
The Taloga ("Big Basin") formation crops out in Big Basin and in other parts of west-central Clark County.
The basal 7 feet of the lower shaly member of the formation, immediately overlying the Day Creek dolomite, is gray-green in color at some localities. . . . The upper and more prominent part of the Big Basin sandstone consists of 40 feet of sandstones and sandy shales, both locally lithified to a varying extent. The massive sandstones are normally cross-bedded, red and hard, with a crystalline sheen along a freshly broken face as if bonded with gypsum or some form of calcium carbonate. Three principal beds make bold cliffs, the lower 5 feet thick, the top one 8 feet thick, and an intermediate bed 2 feet thick. . . . Between these principal sandstone beds, the shales become more or less sandy from place to place (Norton, 1939).
Triassic (?) Rocks
Triassic rocks are widespread in northeastern New Mexico, and extend into the Texas panhandle and Cimarron County, Oklahoma (Stovall, 1938, pp. 585-587). Their occurrence farther east in the Oklahoma panhandle and in southwestern Kansas is debatable. In Texas County, Oklahoma, a small area of red rocks along Beaver creek west of Guymon is mapped by Gould and Lonsdale (1926, pp. 25-26) as very questionable Triassic. More detailed descriptions of these rocks are given by Schoff (1939, pp. 49-54), and the suggestion is made that both Triassic and Jurassic beds may be present. In Morton County, Kansas, near the boundary between sec. 12, T. 34 S., R. 43 W., and sec. 7, T. 34 S., R. 42 W., just east of Point Rock, a few small exposures are represented on the state geologic map (Moore and Landes, 1937) as possibly of Triassic age. These exposures occur along a small gully just north of the river, and in a bedrock ledge on the river bank. The rock consists of red chippy shale, and the exposed thickness is about 20 feet. It is overlain by fine-grained cross-bedded yellowish to buff sandstone containing some red bands, and having a minimum thickness of slightly more than 40 feet. No fossils of any kind were found in either division. The upper sandstone differs in appearance from typical Dakota, and may possibly be of Jurassic or Early Cretaceous age.
Lower Cretaceous Rocks
In this area, rocks of Early Cretaceous age are virtually restricted to the upper slopes of the Red Hills in Clark County. They are grouped in two divisions, the Cheyenne sandstone and the Kiowa shale. The following descriptions are drawn from discussions by Twenhofel (1924) and Bullard (1928).
Cheyenne Sandstone
The Cheyenne sandstone is best exposed at the type locality near Belvidere, in southeastern Kiowa County, where it reaches a thickness of 55 feet. In Clark County, where present at all, it is very much thinner. It lies unconformably on the Permian redbeds, and consists of strongly cross-bedded gray to yellowish sandstone, locally streaked or mottled with red and other colors, and containing some interbedded gray to yellowish and black shale. Bedding is discontinuous, and grain size, cementation, and other lithologic features are variable from place to place. Locally the rock is gypsiferous. Fossils of land plants are common. The sandstone exposed between the Permian redbeds and the Tertiary sand and gravel on the east side of Big Basin in western Clark County may belong to this formation, as may also the sandstone overlying redbeds at the Point Rock section in Morton County.
Kiowa Shale
The Kiowa shale is well exposed at Clark County State Lake" along the valley of Bluff creek about 13 miles north of Ashland (pl. 6). The thickness here is about 100 feet. According to Bullard (1928, p. 56), the rock--
consists typically of thinly laminated black shale grading into a yellowish clay in the upper part. The black shale of the lower portion of the Kiowa is especially characteristic, consisting of very thinly laminated, paper-like shale . . . The upper portion contains more lime and has a distinctly yellow color. . . . There are numerous thin layers of soft yellowish sandstone, particularly in the upper part. The formation contains throughout thin limestone layers, almost a fossil coquina, consisting of fragments of oyster shells. Fossils are exceptionally abundant, occurring in the limy and sandy layers throughout the formation. The black shale rarely contains fossils.
Vertebrate as well as invertebrate fossils have been found in the formation. Selenite is common throughout.
Upper Cretaceous Rocks
Upper Cretaceous rocks are far more widely exposed in southwestern Kansas than are those of Early Cretaceous age. The exposures are broad and continuous in the northeastern part of the area, but scattered and discontinuous at the west. The following formations, in upward order, are present: Dakota sandstone, Graneros shale, Greenhorn limestone, Carlile shale, and Niobrara formation. These have been described and mapped in detail in Hodgeman County by Moss (1932), and in Hamilton County and adjoining areas by Darton (1920) and Bass (1926), from whose reports the following descriptions are mainly summarized.
Dakota Sandstone
The Dakota crops out along Bluff creek and other streams in northern Clark County, at a few places on the north side of the Arkansas in Ford County, and along Sawlog creek and Buckner creek in Hodgeman County. At the west, there are scattered outcrops on the south bank of the Arkansas just west of Hartland in Kearny County, along Bear creek and its northern tributary in Hamilton and Stanton counties, and along tributaries of North Fork of the Cimarron in northern Morton County and southern Stanton County. The maximum exposed thickness of the formation in this area is about 80 feet. The complete section is nowhere exposed, however, and its thickness may reach or even exceed 350 feet. No detailed studies of the formation have yet been made in this area.
Typical exposures of the Dakota show a fine-grained thin-bedded to massive sandstone, which commonly exhibits cross-bedding. The color ranges from gray through the characteristic buff to rusty brown. The cement is calcium carbonate in some places, iron oxide in others, and silica in a few others. The last forms a very hard, quartzitic rock. All the sandstone beds are more or less lenticular, and are interbedded with variegated clay or shale or both. The formation as a whole is distinctly ferruginous, and ironstone concretions are common in many places.
Graneros Shale
The Graneros shale crops out along Sawlog creek, Buckner creek, and Pawnee river in Hodgeman County, along the north side of Arkansas river in Hamilton County and in western Kearny County, and at several scattered localities south of the river in Hamilton County. Its thickness is variable, the maximum being 65 feet. The formation consists mainly of bluish-gray to gray-black fissile argillaceous shale. In places it contains beds and lenses of sandstone, sandy shale, and sandy limestone, and locally there are a few thin layers of fossil oysters. In Hamilton County a thin band of bentonitic clay is reported. Selenite crystals are present in many outcrops.
Greenhorn Limestone
The distribution of the Greenhorn limestone is similar to that of the Graneros shale. Its thickness ranges from 122 to 132 feet. The formation consists of a series of thin chalky and crystalline limestones separated by thicker beds of chalky shale, which contain thin bentonite beds (Moss, 1932, p. 26). From bottom to top, the follow ... ing members are distinguished: Lincoln limestone, Hartland shale, Jetmore chalk, and Pfeifer shale. In Hodgeman County the lower two of these are not satisfactorily differentiated, and in Hamilton County the upper two are not distinctly separable, being grouped together as the Bridge Creek limestone. Subdivisions, as their names imply, are distinguished on the basis of relative proportions of limestone and shale. The Fencepost limestone bed, widely quarried for the use indicated by its name, lies at the top of the formation.
Carlile Shale
The Carlile shale crops out along Pawnee river and Buckner creek in the northeastern part of the area, and along tributaries of the Arkansas in northern Hamilton County. Its maximum thickness is about 260 feet. The formation consists of bluish-black noncalcareous fissile shale above, grading downward into lighter-colored calcareous shale containing thin beds of chalky limestone. The lower part is designated as the Fairport chalky shale member, and the upper part as the Blue Hill shale member. The latter has a sandy zone at the top, and contains large calcareous concretions, in part septarian, in the upper part.
Niobrara Formation
This formation crops out along Pawnee river in northeastern Finney County, and along a few tributaries of the Arkansas in northern Hamilton County. Only the lower part of the formation is exposed in this area, and in Hamilton County this has a thickness of 73 feet. Two members are recognized: the Fort Hays limestone member below, and the Smoky Hill chalk member above. The Fort Hays member consists of massive beds of chalky limestone separated by thin beds of clayey to chalky shale. The limestone tends to be gray on fresh surfaces, but buff on weathered surfaces. This member has a thickness of 61 to 80 feet. The Smoky Hill chalk is composed of soft beds of chalk alternating with chalky shale, and containing numerous thin layers of bentonite.
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Kansas Geological Survey, Geology
Placed on web Feb. 8, 2017; originally published September 15, 1940.
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