Geologic Formations, continued
Cretaceous rocks including the Greenhorn limestone, Carlile shale, and Niobrara formation are exposed at the surface in Finney and Gray counties. The outcrops of these formations are shown on plate 1. Cretaceous rocks lying below the Greenhorn limestone are not exposed in this area and, therefore, are known only from subsurface data.
Various classifications have been applied to the series of Cretaceous sandstones and shales that lie below the Graneros shale in Kansas and adjacent areas. In February, 1942, several conferences were held in Lawrence by geologists of the State and Federal Surveys to discuss and adopt a uniform classification for these Cretaceous rocks. It was proposed to retain the use of the terms Cheyenne sandstone and Kiowa shale, and to restrict the term Dakota formation to include only those nonmarine beds classed as Upper Cretaceous that lie between the base of the Graneros shale and the top of the Kiowa shale. The term Dakota formation was formally adopted for use in all counties in the main area of outcrop in central Kansas. It was decided to retain use of the term Cockrum sandstone in Stanton and Morton counties (Latta, 1941; McLaughlin, 1942). For a more complete review of the history of the naming of these early Cretaceous units the reader is referred to a report by Waite (1942, pp. 135-137). Plummer and Romary (1942, p. 319) have redefined and subdivided the Dakota formation according to the present usage of the State Geological Survey of Kansas. Usage of the term Dakota formation is followed in the present report on Finney and Gray counties.
Cheyenne (?) sandstone
Character--The Cheyenne (?) sandstone does not crop out in Finney or Gray counties, and it has been penetrated only by deep oil and gas wells. Few data concerning the character and thickness of the Cheyenne (?) sandstone have been gained from the study of the logs of these wells owing to the lack of detail. The formations encountered below the Greenhorn limestone and above the Permian redbeds are similar in character and, therefore, are generally logged as one unit by oil-well drillers and described as a "group" by oil geologists.
The nearest outcrop of the Cheyenne sandstone is in south-central Kansas in Kiowa, Barber, and Comanche counties. Here the Cheyenne sandstone consists dominantly of light gray to yellow quartz sandstone, but contains minor amounts of sandy shale. Although light gray and yellow are the dominant colors, the sandstone in places is white or is stained tan, brown, red, and purple. The grains of the sandstone range in size from very fine sand to fine gravel. In some beds the texture of the sandstone is very fine, but other beds are conglomeratic--containing small pebbles of weathered chert, quartz, and clay. Locally a thin pebble zone occurs near the base of the formation. Common in this zone are pebbles of gray and pink quartzite, chert, and quartz that are as large as 3 inches in diameter. Pyrite crystals, needles of selenite, and concretions of limonite are locally common. The bedding of the sandstone is very irregular and discontinuous, cross bedding being extremely common throughout the formation. The formation as a whole is made up of lenses of limited lateral extent. Interbedded with the lenses of sandstone are pockets and lenses of sandy shale, and in places the sandstone grades laterally into sandy shale.
Distribution and thickness--The presence of the Cheyenne (?) sandstone beneath Finney and Gray counties is inferred by the great thickness of sediments lying below the Greenhorn limestone and above the Permian redbeds, and by the presence of this sandstone beneath adjoining areas. According to McLaughlin (1943, p. 118), the Cheyenne sandstone underlies all of Hamilton and Kearny counties, where it ranges in thickness from 33 to about 65 feet. A test hole drilled near the southwestern corner of Ford County penetrated at least 70 feet of sediments that have been tentatively assigned to the Cheyenne sandstone (Waite, 1942, p. 139). In southeastern Kiowa County, where the Cheyenne sandstone is exposed, the thickness ranges from about 30 to 50 feet. The variable thickness of the Cheyenne sandstone may be attributed to the uneven erosion surface upon which it was deposited.
Age and correlation--On the basis of scanty data, it is thought that a part of the sequence of sandstones and shales encountered above the Permian redbeds in this area is correlative with the Cheyenne sandstone of the type locality in southeastern Kiowa County. No data are available concerning the exact age of these beds in Finney and Gray counties, however. The Cheyenne sandstone at the type locality represents the oldest Cretaceous formation found in Kansas. Fossils collected from this sandstone in Texas County, Oklahoma, and other areas were identified and found to be Washita (Lower Cretaceous) in age (Schoff, 1939, p. 55).
Origin--Owing to the lack of outcrops and to the meager well-log data, it is impracticable to discuss the origin of the Cheyenne (?) sandstone in Finney and Gray counties. Schoff (1939, p. 55) found marine pelecypods in this sandstone in Texas County, Oklahoma, which he says is conclusive evidence of marine origin. He also states that
"The fine- to medium-grained sand of which the sandstone is composed suggests deposition in moderately shallow water off shore, rather than on or near the beach, where wave activity is ordinarily greatest."
The discontinuity of bedding, the cross-lamination, the assortment of the sands, the presence of land plants, and the absence of shells of marine animals in the sandstone in south-central Kansas suggested a continental stream origin to Twenhofel (1924, pp. 18-20). It is altogether possible that both writers are correct in their interpretations, and that the origin of the Cheyenne sandstone or its equivalent is not everywhere the same but that at some places it may be continental and at others marine.
Water supply--No wells have penetrated the Cheyenne (?) sandstone in this area in search of a water supply because of the great depth to which they would have to be drilled. Sufficient quantities of water for most purposes generally are obtained from higher formations.
A few wells in the Arkansas valley in Hamilton County obtain water from the Cheyenne sandstone--artesian water being encountered by wells that tap the sandstone at Coolidge. The wells are 285 to 325 feet deep but the water rises nearly to or above the land surface (McLaughlin, 1943, p. 119). There are also wells at Syracuse and Kendall that obtain water from the Cheyenne sandstone. The water from the Cheyenne sandstone in Hamilton County is moderately hard, but is satisfactory for most purposes. Water from the Cheyenne sandstone in southeastern Kiowa County, however, is usually too highly mineralized for ordinary uses.
Kiowa (?) shale
Character--There are no surface exposures of the Kiowa (?) shale in the area under discussion. All of the oil and gas tests drilled in Finney and Gray counties probably penetrated the Kiowa (?) shale, but owing to the lack of detail in the logs of these tests the Kiowa (?) shale cannot be differentiated from other Cretaceous formations. Test hole 18 (see log 18) in northern Gray County penetrated 267 feet of Cretaceous sediments below the base of the Greenhorn limestone, a part of which probably is equivalent to the Kiowa (?) shale. The lithology of the shales in this sequence differs somewhat from the Kiowa shale at the type locality in Kiowa County, Kansas. If the Kiowa shale or equivalent is not present in this test hole, the Dakota formation must be much thicker here than it is in adjacent areas. The Kiowa at the type locality in southeastern Kiowa County consists of shales with interbedded thin limestones. The shales in the lower part are black and are so thinly laminated that they are often referred to as paper shales. In the upper part the shales generally are gray to blue and are more limy than the shales in the lower part. Fossils are rare in the black shales, but they commonly are found in the upper lighter-colored shales. Thin beds of limestone consisting almost entirely of oyster shells are found throughout the formation. A few sandstone beds and lenses are found in the Kiowa shale, and gypsum, generally in the form of selenite, is common throughout.
Distribution and thickness--The Kiowa (?) shale probably underlies most or all of Finney and Gray counties. McLaughlin (1943, p. 120) believes that the Kiowa shale underlies all of Kearny County, which borders Finney County on the west, and Waite (1942, p. 140) states that the shale underlies the southern part of Ford County, but it is not definitely known whether or not it is present under the northern part of Ford County. A bluish-gray shale containing fragments of fossils encountered in the Phillips-Hausman well, in sec. 30, T. 22 S., R. 22 W., Hodgeman County, was referred by Moss (1932, pp. 33, 34) to the Kiowa shale. Test holes drilled in northern Haskell County penetrated dark shales which probably belong to the Kiowa shale (McLaughlin, oral communication).
No data concerning the thickness of the Kiowa (?) shale are available from the area being described, but data from nearby areas indicate that the thickness ranges considerably. The Kiowa shale was 44 feet thick in a test hole drilled in sec. 27, T. 29 S., R. 26 W., in southwestern Ford County (Waite, 1942, p. 140). According to McLaughlin (1943, p. 120), the thickness of the Kiowa in Hamilton County ranges from 49 feet near Coolidge to 131 feet in the southeastern part of the county. A thickness of 160 feet is reported for the Kiowa shale in a section at Avilla Hill in southern Comanche County (Twenhofel, 1924, p. 25).
Water supply--The Kiowa (?) shale, except for the sandy horizons, is relatively impermeable and supplies little or no water to wells. No wells are known to derive water from the Kiowa (?) shale in Finney and Gray counties.
Character--The Dakota formation is not exposed in Finney and Gray counties, but was encountered in six test holes drilled during the course of the present investigation (see logs 15, 16, 18, 24, 26, and 27). The logs of these test holes indicate that the Dakota formation consists of sandstone and shale or clay, and that the larger part of the formation is composed of light, gray, yellow-tan, yellow, and brown shale and sandy shale. Sandstone concretions and charcoal are found in the shale in some places (see log 26). Interbedded with the shale and clay are beds of fine- to medium-grained sandstone that range in color through light gray, tan, buff, red, reddish-brown, and brown. The beds of sandstone encountered by test drilling ranged in thickness from a few inches to about 15 feet. The sandstones probably occur as lenses of limited extent and not as massive beds of great geographic extent. Iron oxide seems to be the dominant cementing agent in the sandstones.
By studying the outcrops of the Dakota formation in Hamilton County, McLaughlin (1943, p. 121) found that 40 to 45 percent of the formation consists of varicolored clay. Gray to buff, fine-grained, irregularly bedded sandstone constitutes the rest of the formation in Hamilton County. The ratio of sandstone to clay in the Dakota formation differs from place to place. Only about one-fourth of the formation is sandstone in Ness and Hodgeman counties (Moss, 1932, p. 32). This same ratio exists throughout most of the outcrop area of the Dakota formation in the central and northern part of the state.
The topmost beds of the Dakota formation grade into the overlying Graneros shale so that there is no sharp contact between the two. In southern Finney County and parts of southern Gray County, pre-Ogallala erosion has removed all Cretaceous sediments above the Dakota formation so that silts, sands, and gravels of the Ogallala formation (Pliocene) unconformably overlie the Dakota formation (figs. 8 and 9). The Dakota formation is underlain conformably by the Kiowa (?) shale.
Distribution and thickness--The Dakota formation underlies all of Finney and Gray counties, but is not exposed at the surface. In addition to the six test holes listed above, the Dakota formation has been encountered by all oil and gas tests drilled in the two counties and by wells 500 and 526 (see logs 52 and 56) in southern Gray County. Possibly other wells in southern Gray County not visited during the investigation also penetrate beds of the Dakota formation. The nearest outcrop of the formation is near Hartland in Kearny County; other outcrops are in southern Hamilton County and western Stanton County on the west and in southern Hodgeman County and northern and east-central Ford County on the east. The formation is also exposed at the surface in a small area in south-central Kansas and throughout a large area in the central and northern part of the state (Moore and Landes, 1937).
No dependable data are available concerning the thickness of the Dakota formation in the area being described. The test holes and wells that encountered the formation penetrate only the upper part, and the logs of the oil and gas tests are not sufficiently detailed to permit differentiation of the Cretaceous formations. The thickness of the Dakota formation in Hamilton County ranges from 130 feet in the southern part of the county to 314 feet at Kendall in the eastern part of the county (McLaughlin, 1943, p. 121). The Dakota formation penetrated by a test hole in sec. 27, T. 29 S., R. 26 W., in southwestern Ford County, was only 56 feet thick, but in the northeastern part of Ford County a water well penetrated about 235 feet of the Dakota (Waite, 1942, p. 144). It can be seen from these examples that, because of the lenticular nature of the Dakota formation, its thickness ranges within wide limits.
Age and correlation--The age and correlation of the Dakota formation are briefly discussed under the introduction to the section on the Cretaceous system on page 141.
Water supply--At most places in Finney and Gray counties, adequate supplies of water are obtained from formations above the Dakota formation, but in a few places in the southeastern part of Gray County the sediments above the Dakota contain very little or no water and it is necessary to penetrate the Dakota in order to obtain an adequate supply. In these places the water table is below the sands and gravels of Pliocene and Pleistocene age that supply water to most of the wells in other areas in Finney and Gray counties (fig. 9). Two (wells 500 and 526) of the 543 wells visited in Finney and Gray counties obtain water from the Dakota formation. Both of these wells are in the southeastern part of Gray County.
Well 500, in the NW sec. 24, T. 28 S., R. 27 W., is a domestic well 421 feet deep. According to George Slocum, driller, water-bearing sandstone (Dakota formation) was encountered in this well at a depth of 408 to 421 feet (see log 52). The water rose about 200 feet above the point at which it was first encountered. On December 4, 1940, the depth to water level in the well was measured and found to be 204.1 feet below land surface.
Well 526, in the NE 1/4 sec. 4, T. 29 S., R. 28 W., penetrated two sandstones separated by 59 feet of blue-black shale. According to the driller, the upper sandstone, which was encountered between depths of 280 and 292 feet, was very hard and yielded but little water. The lower sandstone, encountered between depths of 351 and 365 feet, was reported to be softer and coarser grained than the upper sandstone and to yield an adequate supply of water to the well. When the water-bearing sandstone was penetrated, the water rose more than 200 feet in the well. The depth to water level in the well is reported to be 130 feet below land surface.
Although water in the Dakota formation generally rises under artesian pressure, the water rises to a level approximately equal to that of the normal water table; hence there are no flowing wells in this area. The Dakota formation supplies water to flowing artesian wells in nearby areas, however. Flowing wells in Sawlog valley in southern Hodgeman County obtain water from the Dakota formation (Moss, 1932, pp. 45, 46). The wells start near the top of the formation and obtain artesian water at a depth of about 200 feet. Waite (1942, p. 145) reports that a flowing well (520, Ford County) in the NW 1/4 sec. 35, T. 29 S., R. 26 W., in southwestern Ford County, obtains a part of its water from the Dakota formation. A flowing well at Coolidge in western Hamilton County is in the Dakota formation (McLaughlin, 1943, p. 126).
Analyses of the waters from the two wells (500 and 526) that tap the Dakota formation in Gray County are shown graphically in figure 20. The waters from both wells are soft sodium bicarbonate waters having respectively 433 and 296 parts per million of total dissolved solids, 150 and 70 parts of sodium and potassium, 266 and 207 parts of bicarbonate, and 40 and 108 parts of hardness. The analyses indicate that the water in the Dakota formation in this area has undergone a natural softening process in which calcium bicarbonate water has exchanged its calcium and magnesium for sodium by a base-exchange process. A detailed discussion of the process of base-exchange is given on pages 136 and 137. Both waters analyzed contain fluoride in undesirable amounts; the water from well 500 had 4.2 parts per million of fluoride and the water from well 526 had 1.8 parts.
Character--Conformably overlying the Dakota formation is the Graneros shale, which consists of gray, noncalcareous shale and a few thin beds or lenses of sandstone and sandy shale. The Graneros shale is not exposed in Finney and Gray counties, and only one test hole (No. 18) penetrated the formation. The top of the Graneros shale was encountered at a depth of 350 feet in test hole 18 (log 18). Generally there is a sharp lithologic break between the noncalcareous Graneros shale and the overlying calcareous beds of the Greenhorn limestone. The contact between the Graneros shale and the underlying Dakota formation is not distinct in many places, but consists of a transition zone in which sandstones and shales of the Dakota formation grade upward into sandstones and sandy shales of the Graneros shale. It was not practicable, therefore, to determine the lower contact of the Graneros in test hole 18.
The nearest exposure of the Graneros shale is along Sawlog creek in northern Ford County and southern Hodgeman County. The shale in northern Ford County generally is dark bluish-gray to black, but contains numerous flakes of yellow sandstone and an abundance of selenite crystals (Waite, 1942, p. 146). Transparent crystals of selenite, some of which are 6 inches or more in length, generally are found strewn along the outcrops. Interbedded in the shale are many thin lenses of sandy shale, sandstone, sandy limestone, and ironstone concretions.
The Graneros shale in Hamilton County consists of gray-black, fissile, argillaceous shale with a 5- to 16-inch bed of bentonitic clay about 10 feet below the top (McLaughlin, 1943, p. 126). It also contains 5 to 6 feet of thin-bedded fossiliferous limestone 20 to 22 feet above the base of the formation.
Distribution and thickness--The Graneros shale probably underlies all but the southern part of Finney and Gray counties, as shown by the geologic profiles in figures 8 and 9. The Graneros shale is 21 to 36 feet thick in Ness and Hodgeman counties (Moss, 1932, p. 31), a few feet to about 43 feet thick in Ford County (Waite, 1942, p. 148), 61 feet thick in Hamilton County (McLaughlin, 1943, p. 128), and about 200 feet thick in Otero County, Colorado (Dane, Pierce, and Reeside, 1937, p. 210). The thickness of the shale in Finney and Gray counties is not known, but it probably is between 40 and 50 feet. According to Dane, Pierce, and Reeside (1937, p. 210) the Graneros probably thickens westward at the expense of the overlying Greenhorn limestone, for the Greenhorn seems to be much thinner in Colorado than in western Kansas.
Water supply--No wells are known to obtain water from the Graneros shale in Finney and Gray counties. The quantity of water contained in the shale and interbedded lenses of sandstone probably is small because of the relatively low permeability of the sediments.
Character--The Greenhorn limestone consists of thin chalky and crystalline limestones separated by thicker beds of chalky shale that contain thin beds of bentonite. In the upper part of the formation limestone concretions occur in the shales. The limestones and shales arc light to dark gray when they are brought up in a drill hole and the bentonites are light pearly-gray. Weathering changes the color of the limestones to tan, buff, or orange-tan and the shales to tan, light gray, or orange-tan. The bentonites weather to red-brown or orange. The Greenhorn limestone grades upward into chalky shale beds of the overlying Fairport chalky shale member of the Carlile shale, but is sharply separated from the underlying Graneros shale.
The Greenhorn limestone has been divided into four members in central-western Kansas which, from top to bottom, are the Pfeifer shale, Jetmore chalk, Hartland shale, and Lincoln limestone members. Only a small part of the Greenhorn is exposed in the Finney-Gray area. The following descriptions of the lithologic character of the members have been adapted in part from Moss (1932, pp. 26-31), who described in detail the members in Ness and Hodgeman counties.
The Pfeifer shale member of the Greenhorn limestone consists of chalky shale and some thin limestone beds and limestone concretions. At the top of the member is a chalky limestone known as the "Fence post" limestone, which is resistant to erosion and generally forms a ledge. The Pfeifer weathers to a tan or cream color. In western Hodgeman County its thickness is 19 feet. The lower part of the member is exposed in a quarry in the NW sec. 17, T. 29 S., R. 27 W., in southeastern Gray County (pl. 9), where the following section was measured.
|Section of the Pfeifer shale and Jetmore (?) chalk members of the Greenhorn limestone in a quarry in the NW sec. 17, T. 29 S., R. 27 W., Gray county.||Thickness
|Pfeifer shale member|
|6. Shale, chalky, thinly laminated, yellow, buff, and brown||1.0|
|5. Limestone, hard, chalky, yellow-tan||0.3|
|4. Shale, chalky, thinly laminated, buff to brown||0.4|
|3. Limestone, chalky, yellow to white||0.3|
|2. Shale, chalky, thinly laminated, yellow to white, containing thin beds of red-orange bentonite||2.5|
|Jetmore (?) chalk member|
|1. Limestone, hard, chalky, fossiliferous, yellow-tan||1.7|
|Total thickness exposed||6.2|
The Jetmore chalk member of the Greenhorn limestone consists of a series of thin chalky limestone beds separated by chalky shales. The chalky limestones are 3 to 6 inches thick and weather to white or light tan. The shales are 1 to 2 feet thick and weather to tan or orange-tan. Capping the member is a hard, fossiliferous limestone called "shell rock," which contains an abundance of the pelecypod Inoceramus labiatus. Bed 1 in the measured section given above contains an abundance of this fossil and probably represents the capping bed. The Jetmore chalk member is the most resistant part of the Greenhorn limestone, and where exposed it forms a prominent ledge. At the type locality south of Jetmore in central Hodgeman County the member is 22 feet thick.
The two lower members of the Greenhorn limestone, the Lincoln limestone and Hartland shale members, are not easily differentiated in this area. The upper part of the Lincoln-Hartland members consists of calcareous shale and thin beds of chalky limestone, and the lower part consists of chalky shale and thin beds of crystalline limestone. A few beds of bentonite 1 to 5 inches thick occur in the lower part of the Greenhorn. The upper part of the Lincoln-Hartland members weathers to light tan or gray and the lower part to orange-tan or buff. The aggregate thickness of the two members is about 80 feet.
Bass (1926, pp. 66-69) recognized only three members of the Greenhorn limestone in Hamilton County--the Bridge Creek limestone, Hartland shale, and Lincoln limestone members. According to Bass (1926, p. 69), the uppermost 25 feet of the Bridge Creek member of Hamilton County is equivalent to the Pfeifer shale member of Ellis County, and the remainder of the Bridge Creek member probably represents the Jetmore chalk member of central-western Kansas.
The harder limestone beds of the Greenhorn have been quarried in some places and used for fence posts and building stone. The "Fencepost" limestone has been used extensively for fence posts, buildings, road culverts, and other works. The hard limestone bed at the top of the Jetmore (?) chalk member of the Greenhorn has been quarried in the NW 1/4 sec. 17, T. 29 S., R. 27 W., in southeastern Gray County, where it has been used mostly as a building stone by farmers living near by.
Distribution and thickness--The area of outcrop of the Greenhorn limestone in the Finney-Gray area covers less than a quarter of a square mile in southeastern Gray County (pl. 1). The section exposed here includes the lower part of the Pfeifer shale member and the upper 1.7 feet of the Jetmore (?) chalk member. The Greenhorn underlies most of the area north of Arkansas River in Finney and Gray counties and a large area south of the river in Gray County. It has been removed by pre-Pliocene erosion in the southern part of Finney County and in the extreme southern, east-central, and western parts of Gray County (figs. 8 and 9). In a large area in central Gray County, the Greenhorn limestone is unconformably overlain by Pliocene (Ogallala formation) deposits and only the lower part of the Greenhorn is present (fig. 9, DD').
The thickness of the Greenhorn limestone in the Finney-Gray area is about 130 feet.
Age and correlation--The section of Greenhorn limestone exposed, in the quarry in the NW 1/4 sec. 17, T. 29 S., R. 27 W., in southeastern Gray County, has been correlated with the Pfeifer shale and Jetmore (?) chalk members of the Greenhorn on the basis of lithology and fossil content. Because of its hardness and abundant content of the fossil Inoceramus labiatus, the lower bed (bed 1) in this section is correlated with the hard "shell rock" found in other areas at the top of the Jetmore chalk member. The chalky shale and interbedded thin limestone beds found above bed 1 in the section are lithologically similar to beds of the Pfeifer shale member in other areas.
Where the Greenhorn limestone is buried and is known only from drill cuttings, it is generally not possible to differentiate between the members. The lower beds of the Fairport chalky shale member of the Carlile shale are similar in character to the upper beds of the Greenhorn limestone making it difficult to determine the Carlile-Greenhorn contact by the study of drill cuttings. The base of the Greenhorn limestone is easily identified from drill cuttings by a change from calcareous shale and limestone of the basal part of the Greenhorn to noncalcareous softer and darker clay-shale of the Graneros shale.
Water supply--According to Mr. George Slocum, well driller, water is generally found in the chalky limestone (Greenhorn) that lies above the dark shales in the vicinity of the quarry in southeastern Gray County. The water probably occurs in fractures and solution openings in the limestone. The water-yielding capacity of the formation probably is comparatively low; however, small supplies might be obtained by wells penetrating this formation. None of the wells visited in the Finney-Gray area are known to obtain water from the Greenhorn limestone, but there may be a few wells in southeastern Gray County that obtain water from this formation.
Character--The Carlile shale, which conformably overlies the Greenhorn limestone, consists predominantly of dark blue to black, noncalcareous, fissile clay-shale, chalky shale, and thin beds of chalky limestone. It is composed of three members, which are, from oldest to youngest, the Fairport chalky shale member, the Blue Hill shale member, and the Codell sandstone member.
The Fairport shale member of the Carlile constitutes about the lower one-third of the formation. It is not exposed in the Finney-Gray area, but was encountered in test holes 8, 9, 10, 13, 18, 19, and 21. The drill cuttings indicate that this lowest member of the Carlile shale consists predominantly of dark gray to black and yellow-tan calcareous shale containing some gray limestone, flakes of calcite, and hard, fine-grained concretions. Exposures of the Fairport shale member in Ness and Hodgeman counties show thick beds of chalky shale alternating with thin beds of chalk or chalky limestone (Moss, 1932, p. 23). The shale and chalk beds are tan, orange-tan, buff or light gray. Many thin, flat concretions occur in the lower part of the Fairport shale member and a few beds of bentonite occur in the shale. On a fresh surface the bentonite is white but weathers to a rusty-brown. The member contains many poorly preserved fossils. According to Moss (1932, p. 26), the most common fossils are Inoceramus fragilis, Prionotropis woolgari, Ostrea congesta, Globigerina, Gumbelina, and Serpula plana.
The Blue Hill shale member of the Carlile constitutes most of the upper two-thirds of the Carlile shale in the Finney-Gray area. The upper part of the member is exposed in a wide strip along the Pawnee valley in northeastern Finney County (pl. 1), and was encountered by test holes 1, 2, 6, and 7. The member consists of dark gray, bluish-black, and black noncalcareous shale containing thin scams of gypsum, selenite (gypsum) crystals, and in the upper part a zone of large septarian concretions. The Blue Hill shale member forms relatively steep and in many places barren, slopes on the north side of Pawnee River, where it is overlain by the Fort Hays limestone member of the Niobrara formation. On the south side of the valley the Fort Hays limestone member of the Niobrara has been removed by erosion, and as a result the slopes formed by the Blue Hill shale member of the Carlile shale are gentle and in most places sparsely covered by vegetation. In places the slopes are strewn with large calcareous septarian concretions (pl. 10), which generally arc several feet in diameter--the largest one observed in this area being about 6 feet long and about 2 feet in diameter. They are composed of bluish-gray, dense limestone with septaria of calcite. Some have a cone-in-cone structure developed as a layer on the outside surface. Moss (1932, p. 23) states that Prionotropis woolgari, Inoceramus fragilis, and species of Scaphites are commonly found in the concretions.
At the top of the Carlile shale is a sandy zone, which is equivalent to the Codell sandstone member of other areas. The term Codell sandstone bed was originally used in Ellis County as the name of the sandy bed at the top of the Blue Hill shale member (Bass, 1926, p. 28). Dane, Pierce, and Reeside (1937, p. 215) pointed out, however, that it was not desirable to apply names to units of less than member rank and, therefore, considered the Codell sandstone in eastern Colorado as a member of the Carlile shale, equivalent in rank to the Blue Hill shale and Fairport chalky shale members. Moore (1940, pp. 39, 40) also considers the Codell sandstone as a member of the Carlile shale. The Codell sandstone member in the Finney-Gray area consists of dark gray to black, noncalcareous, sandy shale and shaly sandstone. No true sandstone was noted in this area. The Codell sandstone member of the Carlile was encountered by test holes 1, 3, and 4.
The following measured section indicates the character of the Blue Hill shale member of the Carlile shale and the Fort Hays limestone member of the Niobrara formation. No sandy shale or sandstone (Codell sandstone member) was noted at the top of the Carlile shale at this locality.
|Section of Fort Hays limestone member of the Niobrara formation and Blue Hill shale member of the Carlile shale in the N2 sec. 2, T. 22 S., R. 29 W., Finney County.||Thickness
|Fort Hays limestone member|
|2. Limestone, chalky, fossiliferous, white. Weathers into small blocks||48.5|
|Blue Hill shale member|
|1. Shale, fissile, blue-gray, containing large septarian concretions, thin seams of gypsum, and selenite crystals||92.0|
|Total thickness exposed||140.5|
Distribution and thickness--The Carlile shale is present either at the surface or below the surface nearly everywhere in Finney and Gray counties north of the 2,550-foot contour line shown in figure 7. All of the Carlile shale south of this line and part of the Carlile north of this line was eroded away during the period of erosion that preceded the deposition of Tertiary sediments (figs. 8 and 9). Only the upper part of the Carlile shale is exposed along the Pawnee valley in the "panhandle" or northeastern part of Finney County (pl. 1).
The base of the Carlile shale is not exposed in the Finney-Gray area and none of the test holes penetrated the entire formation so the total thickness is not known with certainty. A core hole drilled by the Phillips Petroleum Company north of Ransom in Trego County encountered 261 feet of Carlile shale (Moss, 1932, p. 24). According to Bass (1926, pp. 26, 30), the Carlile shale is about 300 feet thick in Ellis County where the Fairport chalky shale member of the Carlile ranges in thickness from 85 to 115 feet and the Blue Hill shale and Codell sandstone members together are 175 to 215 feet thick. The sandy shale of the Codell sandstone member is as much as 34.5 feet thick in the northwestern corner of Finney County (see log 1), but seems to be absent entirely in other parts of Finney and Gray counties. In Ness and Hodgeman counties, the sandy beds at the top of the Carlile shale are as much as 41 feet thick, but the sand generally is confined to the upper 15 to 20 feet (Moss, 1932, p. 22).
Water supply--Because of their low permeability, most parts of the Carlile shale contain little or no water available to wells. No wells are known to obtain water from the formation in Gray County and only five (wells 1, 8, 46, 47, and 57) of the 400 wells visited in Finney County tap this formation. Wells 1 and 8 obtain meager supplies of water from a sandy shale in the Codell sandstone member, and wells 46, 47, and 57 tap the Blue Hill shale member. Of these five wells only well 1 is in use.
The Codell sandstone member of the Carlile yields adequate supplies of water to domestic and stock wells in other areas where it contains beds of permeable sandstone. In this area, however, the Codell sandstone member consists almost entirely of sandy shale having a relatively low permeability. The Blue Hill shale and Fairport chalky shale members of the Carlile consist almost entirely of shale, and in most places do not yield sufficient water to supply wells. Any movement of water through the Carlile shale would take place largely through bedding planes and fissures.
Of the five wells that tap the Carlile shale in Finney County, only one well (1) tapping the Codell sandstone member was sampled for analysis. The water from this well is a moderately hard calcium bicarbonate water containing 57 parts per million of calcium, 228 parts of bicarbonate, 259 parts of dissolved solids, 213 parts of hardness, and 1.4 parts of fluoride. This water is very similar in quality to that found in the Ogallala formation.
Character--The Niobrara formation consists of beds of chalky limestone, chalk, and chalky shale, and unconformably overlies the Carlile shale. The Niobrara is divided into two members--the Fort Hays limestone member below and the Smoky Hill chalk member above.
The Fort Hays limestone member is composed of thick massive beds of chalky limestone and chalk separated by thin beds of chalky shale (pl. 9B). The limestone and chalk beds range in thickness from less than a foot to about 6 feet. The shale partings in most places are less than 4 inches thick. Weathered exposures of the Fort Hays limestone member are white, tan, or cream. The limestone in the lower part of the member generally is harder and less chalky than that found higher up in the member. In the N2 sec. 2, T. 22 S., R. 29 W., in northeastern Finney County, the lower part of the member is exposed at the top of a high hill where it forms a protective cap on the less resistant Carlile shale. Here the lower part of the Fort Hays limestone member consists of white, relatively hard limestone that weathers into small tabular pieces. Because of its resistance to erosion, the Fort Hays limestone member, where exposed, generally forms an escarpment. Exposures of the member in most places are strewn with pebbles of chalk which obscure the outcrop. The contained fossils include Inoceramus deformis, Ostrea congesta, and abundant foraminifera (Moss 1932, p. 21).
The contact of the Fort Hays limestone member of the Niobrara with the underlying Carlile shale is marked by an abrupt change from the light-colored calcareous beds of the Fort Hays limestone member to the dark-colored noncalcareous beds of the Carlile shale. In places the contact is marked by a zone of sandy, noncalcareous shale (Codell sandstone member of Carlile shale).
Conformably overlying the Fort Hays limestone member is the Smoky Hill chalk member of the Niobrara formation. The Smoky Hill chalk member is not known to crop out in this area, but was encountered in test holes 1 and 2 (see logs 1 and 2). It consists of alternating beds of soft chalky shale and chalk. Where unweathered the beds are light to dark gray, but on weathered exposures they are white, tan, buff, or yellowish-pink (Moss, 1932, p. 15). Cuttings from test holes indicate that the beds all have the same general appearance and nearly the same hardness, but on weathered exposures even the thinnest beds stand out. According to Moss (1932, p. 15), the slight differences in the composition of different beds are brought out through differential erosion. Thin beds of bentonite and pyrite concretions are common in the member. The bentonite beds are light-colored when unweathered, but weather to a rusty-brown.
Both vertebrate and invertebrate fossils occur in the Smoky Hill chalk. Most of the large museums of the world have vertebrate fossils on exhibit that were taken from this member in central and western Kansas. They include birds, dinosaurs, crocodiles, mosasaurs, turtles, and fish. Inoceramus grandis and Ostrea congesta are most abundant among the larger invertebrates (Moss, 1932, p. 19). Foraminifera, chiefly Globigerina and Gumbelina, are abundant in the chalky beds, and, according to Moss (1932, p. 19), probably make up more than half of the calcareous material of the chalk.
It is generally difficult to determine the contact between the two members of the Niobrara formation on the basis of test-hole or well cuttings. On weathered exposures, however, differences of hardness and general lithology are more apparent. In comparing the two members, Bass (1926, p. 24) states that the Fort Hays limestone member seems slightly coarser in texture and is somewhat harder, that the individual beds are much thicker than those of the Smoky Hill chalk member, and that the percentage of shale is much smaller in the Fort Hays limestone member.
Distribution and thickness--Only the Fort Hays limestone member of the Niobrara formation is exposed in the Finney-Gray area. It. is exposed in a wide band above the Carlile shale north of Pawnee River in northeastern Finney County (pl. 1). Both members of the formation are present beneath younger sediments in the northern part of Finney County except in parts of the buried trough in the western part of the county (fig. 8). The Niobrara formation has been completely removed by erosion in Gray County except possibly in the extreme northwestern corner, where the lower part of the Fort Hays limestone member may be present under the Ogallala formation.
The thickness of the Niobrara formation in Logan County, Kansas, where it is overlain conformably by the Pierre shale, is approximately 800 feet (Moss, 1932, p. 15). Pre-Ogallala erosion, however, has truncated the Niobrara to the south and east so that the maximum remaining thickness of the formation in Finney County is only about 300 feet. Only the lower part of the Smoky Hill chalk member of the Niobrara formation is present in this area. The greatest thickness is in the north-central part of Finney County, where it is approximately 225 feet. The Fort Hays limestone member of the Niobrara is 55 feet thick at the northwestern corner of Finney County (see log 1). Moss (1932, p. 21) found the member to be 80 feet thick in Ness County, which adjoins Finney County on the northeast. No complete sections of the member are exposed in the outcrop area in Finney County, but it is thought that the thickness of the member in northeastern Finney County also is approximately 80 feet.
Water supply--The Niobrara is not an important water-bearing formation in Finney and Gray counties. The beds of soft chalky shale and chalk that make up the Smoky Hill chalk member are relatively impervious and do not supply water to any wells in this area. The beds of chalky limestone of the Fort Hays limestone member, however, are moderately hard and, therefore, are subject to fracturing. These fractures and resulting solution openings afford passageways for the movement of ground water within the member. The success of a well penetrating the Fort Hays member depends entirely on whether or not fractures or solution openings are encountered. (See p. 49.)
Four of the recorded wells in Finney County obtain water from the Fort Hays limestone member of the Niobrara, two of which (wells 38 and 40) are in the northwestern part of Finney County where the Pliocene and Pleistocene sands and gravels are above the water table and, therefore, are barren of water. Both are dug wells and are reported to yield adequate supplies of water for domestic and stock use. Well 40 reportedly yielded a sufficient quantity of water for the drilling of two nearby oil wells. Wells 2 and 7 obtain water from the Fort Hays limestone member in the area of outcrop. Well 2, a dug stock well, is reported to have a very small yield, and well 7, which is a 6-inch drilled well, was abandoned because the yield was too small even for stock use.
Many small springs (nos. 15, 16, 17, 18, 63, 66, and 103) are fed by fractures in the Fort Hays limestone member in its area of outcrop in northeastern Finney County. The springs are all in the bottom or on the sides of draws tributary to Pawnee River. The estimated discharges of the springs range from about one pint to 3 or 4 gallons a minute. Twin Spring (66), in the SE sec. 34, T. 22 S., R. 30 W., became famous in the early days as a stopping point for travelers. It was called Twin Spring because there were two openings through which water was discharged. In 1940, however, water was discharging from only one opening. The water issues from a fracture in the limestone at the rate of 2 or 3 gallons a minute.
One sample of water was collected from a well (38) tapping the Fort Hays limestone member. The water from this well is very similar to the sample of water from the Codell sandstone member of the Carlile shale and to many from the Ogallala formation. It had 290 parts per million of total solids, 238 parts of hardness, 54 parts of calcium, 266 parts of bicarbonate, and 1.0 part of fluoride. The content of iron and chloride was negligible.
Kansas Geological Survey, Geology
Web version April 2002. Original publication date Dec. 1944.
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