The area treated in this report lies in the heart of the Great Plains physiographic province. The Great Plains is a broad region extending several hundred miles eastward from the eastern margin of the Rocky Mountains and from Texas northward into Canada. The Great Plains are typified by relatively flat lying sedimentary rocks of Cretaceous age, or younger. Much of the surface area of the Plains region is mantled by nonmarine deposits of late Tertiary and Quaternary age. It is this mantle of nonresistant gently dipping to flat, beds and the relatively low precipitation that typify the region throughout its entire extent. The local relief is moderate, and ranges from the almost flat and undissected High Plains surface to the moderately fine-textured topography illustrated in this area and the cuestas and low scarps that characterize part of the belt of the Cretaceous outcrop farther east.
In the latitude of Norton and Phillips counties, the eastern margin of the Cretaceous outcrops extends to within a hundred miles of Missouri River, from where the Cretaceous formations extend westward under north-central and northwestern Kansas to reappear again in central Colorado where they are upturned sharply along the eastern flank of the Rocky Mountain Front Range.
Below the thick Cretaceous section, Paleozoic rocks rest on a basement complex of Pre-Cambrian crystalline rocks and exhibit a much more complex structural pattern, recording a history of repeated gentle folding and erosion. The intermittent deposition, folding, and erosion during Paleozoic time has produced conditions suitable for the accumulation of petroleum, as indicated by the numerous oil fields that extend from this area toward the south and east. The major structural feature in the Paleozoic rocks is a broad arch that extends from Phillips County toward the southeast and is generally referred to as the Central Kansas uplift (Moore and Jewett, 1942). The petroleum production of Norton County comes from wells drilled on the west, flank of this broad regional structure.
Although the pre-Cretaceous rocks of north-central Kansas are of great importance to the production of oil and gas, they are not known to contain potable waters; therefore, for the purposes of this report the discussion of stratigraphy will be confined to Cretaceous and younger sediments.
Summary of stratigraphy
[Note: The stratigraphic classification used in this report is that of the State Geological Survey of Kansas.]
The age of the outcropping rocks of Norton County and northwestern Phillips County is late Cretaceous (Gulfian), Pliocene, Pleistocene, and Recent. The subdivisions and stratigraphic classification of these strata are shown in Table 3 and in the cross sections on Plate 3. The areal distribution of their outcrops is shown on the geologic map (Pl. 1).
Table 3--Generalized section of the geologic formations of Norton County and northwestern Phillips County, Kansas.
|Quaternary||Recent||Alluvium||15-40||Sand, gravel, silt, and clay, well sorted along major valleys; poorly sorted in tributary valleys.||Yields abundant supplies of water to wells in major valleys; small supplies in tributary valleys.|
|Deposits underlying prominent terrace surfaces in the valleys of Sappa Creek, Prairie Dog Creek, and North Fork Solomon River.||35-85||Gravel, sand, and silt, generally coarse and well sorted in lower part, and fine-textured in upper part. Several buried soils in upper part.||Yields abundant supplies of water to wells.|
|Bignell silt member||0-20||Massive, well-sorted silt, light yellow gray to light tan. Blankets the uplands in some places.||Above the water table; yields no water to wells.|
|Peoria silt member||0-40||Massive, well-sorted silt, light yellow tan to ash gray. Brady soil at top. Underlies most uplands and gentle slopes.||Generally above water table; yields little or no water to wells.|
|Loveland silt, and Crete sand and gravel members||0-60||Massive silt, reddish tan to tan. Thick Loveland soil at top. Locally sand and gravel (Crete member) at base.||Basal sand and gravel, where present, yields moderate to large supplies of water to wells.|
|Meade(?) formation||Sappa and Grand Island members||20-30||Sand, gravel, and silt in lower part (Grand Island), grading into sandy silt and silt in upper part (Sappa). Crops out at only a few places in south-central Norton County, and northwestern Phillips County.||Where basal sand and gravel are below the water table, probably yields abundant supplies to wells at a few places only.|
|Tertiary||Pliocene||Ogallala formation||Kimball member||75 ?||Chert, sand, gravel, silt, in part cemented with calcium carbonate. Occurs at only a few places.||All known occurrences above the water table; yields no water to wells.|
|Ash Hollow member||90-150||Silt, gravel, sand, partly cemented with CaCO3, volcanic ash, and impure limestone; tan, reddish tan, and gray.||Yields moderate supplies of water to wells at many places.|
|Valentine member||0-100||Sand, gravel, silt (partly cemented by CaCO3, impure limestone, and opal-cemented lentils, gray, gray tan, and greenish gray.||Yields moderate to large supplies of water to wells at many places.|
|Cretaceous||Gulfian||Pierre shale||Sharon Springs shale member||100±||Black to coffee-colored fissile shale, a few beds of chalky shale, and bentonite in lower part.||Yields no water to wells.|
|Niobrara formation||Smoky Hill chalk member||600±||Chalky shale and chalk, blue gray, gray and yellow tan. A few bentonite beds.||Yields small supplies of mineralized water to wells at some places.|
The Niobrara formation of Cretaceous age underlies the entire area and crops out at many places along the valleys of North Fork Solomon River, Prairie Dog Creek, and Sappa Creek. It consists predominantly of chalks and chalky shales. Locally in northwestern Phillips County it is overlain by the Pierre shale, which consists of black fissile shale with thin beds of bentonite. The Ogallala formation of Pliocene age underlies most of the area with the exception of the major valleys. Owing to its widespread occurrence and generally porous texture, it is of great importance as a source of ground water. A blanket of eolian silt, classed as the Sanborn formation and divided into the Loveland, Peoria, and Bignell silt members, covers much of the upland areas, and deposits of gravel, sand, and silt underlie the prominent terrace surfaces along the major valleys. Alluvium is present, under the channels and flood plains of all the major streams and the lower reaches of all the important tributaries. Remnants of stream deposits classed as the Meade formation occur along the north part of the North Fork Solomon River Valley in south-central Norton County and along the south side of Prairie Dog Creek Valley in northwestern Phillips County. Somewhat younger stream deposits classed as the Crete sand and gravel member of the Sanborn formation occur at a level above the prominent terrace on the north side of Prairie Dog Creek Valley and at some places in the Valleys of North Fork Solomon River and Sappa Creek.
Throughout this area the Carlile shale of Cretaceous age underlies the Niobrara formation. Oil wells drilled in the area have encountered a sequence of pre-Carlile Cretaceous sediments above the Paleozoic rocks comparable to the sequence exposed in the outcrop belt farther east in Kansas.
Cretaceous System (Gulfian Series)
Formations of Pre-Niobrara age
At only a few places in the area covered by this report do wells obtain water from rocks occurring stratigraphically below the Niobrara formation. However, in southeastern Norton County, both north and south of Solomon River, a few wells have been drilled through the Niobrara formation and obtain meager supplies of mineralized water from the underlying formation. A few deep wells have also been drilled in the vicinity of Norton and at a few other localities throughout the area.
The Carlile shale, which is about 300 feet thick, underlies the Niobrara formation. The Carlile has been divided into three members, the lowest of which is composed of calcareous shale with thin chalky beds in the lower part and is called the Fairport chalky shale member. The Blue Hill shale member overlies the Fairport and consists of about 200 feet of dark-colored, platy, noncalcareous shale containing zones of flat discoidal concretions in the lower part and zones of septarian concretions in the upper part. The Codell sandstone member occurs as a lentil above the Blue Hill shale member and immediately below the base of the Niobrara formation. The Codell sandstone member ranges in thickness from a few inches to as much as 20 feet where it is exposed on the outcrops, and consists predominantly of fine to very fine sand and silt. At some places where this part of the section is exposed, the Codell does not consist of a well-developed sandstone bed but of thin lentils of sand in the upper 15 to 20 feet of the Blue Hill shale member. These sand streaks in many places do not exceed 2 or 3 inches in thickness and are thought to be relatively nonpersistent. At a few localities a lentil of sand several feet in thickness and lithologically resembling the Codell occurs as much as 20 to 40 feet below the top of the Blue Hill shale member.
As none of the test holes drilled in this area penetrated the Carlile shale and as samples were not generally collected from the oil tests drilled in this area until a greater depth was attained, little detailed information on the exact nature of the Codell sandstone member in this area is available. Several of the deeper water wells in southeastern Norton County may obtain all or part of their water from the Codell sandstone member of the Carlile shale.
The Greenhorn limestone lies below the Carlile shale. It consists of alternating beds of chalky limestone and chalky shale and probably does not exceed 100 feet in thickness in this area. Next below the Greenhorn limestone is the Graneros shale which is a dark-gray to black, fissile, noncalcareous shale with lentils of sand. The Graneros shale overlies the Dakota formation, which is made up of clay, shale, siltstone, and sandstone. Although in areas farther east, and southeast the Dakota formation is an important source of ground water, no water wells drilled to the Dakota were found in the area of this report. Wells drilled into the Dakota toward the east in Smith and Phillips counties have encountered highly mineralized water in the formation and it is probable that waters of similar quality occur in the formation in this area. Below the Dakota formation are the Kiowa shale and Cheyenne sandstone of the early Cretaceous Comanchean Series.
The Niobrara formation was named in 1862 by Meek and Hayden from exposures along Missouri River near the mouth of Niobrara River in Nebraska. The first detailed description of this stratigraphic unit in Norton County is included in "The Geology of Norton County" by Hay (1885, pp. 18-20). Hay describes outcrops of Niobrara chalk along the three major valleys of the county. In 1897 Logan (pp. 219-221) described the occurrence of the Niobrara formation in western Kansas. He used a twofold subdivision of the Niobrara consisting of the Fort Hays limestone member as the lower division and the Pteranaodon beds or Smoky Hill chalk, a name proposed earlier by Cragin, as the upper division. In his description of the Niobrara, Logan mentions chert, which seems to be interstratified with the chalk and is well exposed in the vicinity of Norton and Prairie Dog Creek Valley. In the same year Williston (1897, pp. 237-246) described the stratigraphy of the Niobrara formation of western Kansas and its contained fossils. In 1925 the stratigraphy of the Niobrara formation in Russell County, Kansas, southeast of this area, was described in detail by Rubey and Bass (pp. 25-32), and in the following year Bass (1926, pp. 19-26) described the Niobrara formation in Ellis County immediately west of Russell County. A rough zonation of the Smoky Hill chalk member was proposed by Russell in 1929, and Elias in 1931 (pp. 29-43) described the Niobrara formation in Wallace County, Kansas.
The exposures of Niobrara in Norton County and northwestern Phillips County represent approximately the upper half of the Smoky Hill chalk member. However, the lower part of the Smoky Hill chalk member and the Fort Hays limestone member underlie the entire area covered by this report. Where it is exposed at the surface to the east and south, the Fort Hays consists of massive beds of chalky limestone as much as 4 feet in thickness, separated by thin beds of chalky shale and shaly chalk. The Fort Hays grades upward into chalky shales and shaly chalks composing the Smoky Hill chalk member. Where encountered in fresh exposures or penetrated by the drill, the Smoky Hill chalk member is typically bluish gray in color and contains a large percentage of calcium carbonate. On weathered exposures it is yellow, orange, light gray, or nearly white in color and has a shaly or claylike appearance. In many of the test holes penetrating the Niobrara formation in this area, a similar weathered zone was encountered immediately below the unconformity without regard to stratigraphic position. Although the Smoky Hill chalk member is predominantly shaly in appearance, at some localities thick massive beds of chalk have been observed (Pl. 9C), and thin beds of bentonite, occur at many stratigraphic positions. The upper part of the member is particularly characterized by numerous thin bentonite beds, which also occur in the overlying Pierre shale, as shown by the measured stratigraphic section in northwestern Phillips County.
For many years silicified zones in the Smoky Hill chalk member were thought to represent definite stratigraphic horizons. These zones have been observed at several localities in north-central Kansas at various stratigraphic positions but always near the eroded upper surface of the member. In a few places, the silicified chalk is cemented to overlying silicified deposits of the Ogallala formation. It is our conclusion that the silicified zones in the chalk were formed by secondary silicification of the uppermost exposed chalk beds probably at the same time as the silicification of zones in the overlying Ogallala formation (Landes and Keroher, 1942, p. 306; Frye and Swineford, 1946, pp. 58-59).
The maximum thickness of the Niobrara formation in Phillips County has been reported by Landes and Keroher (1942, p. 286) as 650 feet. They considered the thickness of the Fort Hays limestone member is about 50 feet and the remaining 600 feet of the formation they assign to the Smoky Hill chalk member.
Although the Niobrara formation yields meager supplies of mineralized water to wells at some places, the relatively impervious character of the formation prevents the movement of large quantities of water and renders it unsatisfactory as a general source of ground water. At some places, particularly where the chalk has been partially silicified, jointing in the upper part has permitted the entrance of water in sufficient quantities to supply small wells. Old stone well (no. 2-23-33aa) near Norton is an example of a well producing water from silicified chalk of the Niobrara formation. Also, faults occur in the Niobrara in some areas (Pls. 4C and 5A) and some water may move along the porous fracture zone's produced by the fault planes. Deep wells drilled into the chalk, particularly in southeastern Norton County, obtain water from depths of 250 to 400 feet. In most cases, although the water level in these wells stands up in the chalk, the source of the water is from the underlying Codell sandstone. Chemical analyses of water from several wells penetrating the Niobrara and Codell are shown in Table 5 and Figure 9.
The Pierre shale was named by Meek and Hayden in 1862 from exposures at old Fort Pierre in South Dakota. The Pierre shale of Kansas has been studied and described in detail by Elias (1931, pp. 43-131). He described several members in the Pierre shale and discussed their correlation with late Cretaceous units throughout North America. In the area covered by this report, only the lowermost of the members described by Elias, the Sharon Springs shale member, is exposed. The occurrence of Pierre shale in northwestern Phillips County was described by Landes and Keroher 1942, pp. 284-286).
In Phillips County the Pierre shale consists of black to dark gray-brown fissile, platy noncalcareous shale with numerous thin beds of bentonite and several zones of chalky shale. The shale typically contains thin veins and isolated crystals of gypsum and scattered nodules of limonite. Large septarian concretions, described by Elias as typical of the upper part of the Sharon Springs shale member, were not observed in the Pierre shale of this area. However, a few small concretionary limestones were observed at scattered localities. The maximum thickness of Pierre shale observed in outcrops was about 30 feet (Pl. 5B), and the maximum thickness encountered in test holes was 46 feet. Probably the total thickness of the Pierre shale in Phillips County is considerably less than 100 feet. Although no fossils were obtained from this formation in Phillips County, close similarity of lithology to that in Wallace and adjacent counties, described by Elias, and the stratigraphic thickness encountered above the top of the Niobrara formation suggest that all the Pierre shale of Phillips County should be classed as the lower part of the Sharon Springs member. The contact between the Niobrara formation and the Pierre shale is described by Elias (1931, pp. 29-31) as difficult to recognize in the field except by the use of acid, because the two units where they are in contact may be of similar color and lithologic appearance. However, he describes the contact as being sharp when checked for calcium carbonate content. In Phillips County, several beds of chalky shale occurring in the lower part of the Pierre attain a maximum thickness of more than 3 feet; as outcrops are generally meager, it is difficult in some places to distinguish with certainty Pierre shale from Niobrara formation. The occurrence of numerous thin bentonite beds in both the upper part of the Niobrara and the lower part of the Pierre shale is shown by the measured section in the SW sec. 6, T. 1 S., R. 19 W., Phillips County. For the purposes of this report the base of the Pierre shale is drawn at the top of the uniformly calcareous chalky shales which are here classed as the upper part of the Niobrara formation.
|Section measured along creek bank in the SW sec. 6, T. 1 S., R. 19 W., Phillips County|
|Pierre shale--Sharon Springs shale member|
|18. Shale, thin-bedded, dark gray; fine gypsum crystals and limonite along bedding planes||2.0|
|17. Shale, fissile, dark gray noncalcareous; ochre on bedding planes||1.3|
|16. Chalky paper shale, yellow brown||0.05|
|15. Shale, fissile, dark gray; noncalcareous; contains bands of ochre, gypsum crystals, and limonite||3.5|
|14. Bentonite, impure, with limonite and calcareous shale||0.1|
|13. Shale, fissile, dark gray; noncalcareous; bands of ochre, gypsum crystals, and limonite on bedding planes||5.0|
|12. Bentonite with gypsum and limonite||0.05|
|Smoky Hill chalk member|
|11. Chalky shale, thin-bedded, gray, weathers to yellow tan||1.5|
|10. Bentonite, yellow tan||0.3|
|9. Chalk, dark gray, massive||0.7|
|8. Bentonite, impure, yellow tan||0.05|
|7. Chalk, thin-bedded, dark gray, breaks with a conchoidal fracture on exposed surfaces, weathers to light orange||1.5|
|6. Bentonite, yellow tan||0.2|
|5. Chalk, massive, dark gray, weathers to light orange||0.9|
|3. Chalk, thin-bedded, dark gray||0.8|
|1. Chalk, thick-bedded, dark gray. From low water level in Prairie Dog Creek||2.0|
|Total measured||about 20.|
The occurrence of Pierre shale in northwestern Phillips County and adjacent Nebraska, lying east of widespread Pierre shale deposits of northwestern Kansas and isolated from that area by an extensive: region devoid of Pierre shale outcrops, has been explained by downwarping of the Long Island syncline on the west flank of the Stockton anticline (Landes and Keroher, 1942, p. 289. Faults have been observed at, many of the outcrops of Pierre shale (Pls. 4C and 5A) and it is possible that this faulting is associated with the structural movements that gave rise to the Long Island syncline.
No wells in this area are known to obtain water from Pierre shale.
Tertiary System (Pliocene Series)
The Ogallala formation was named by Darton in 1899 (pp. 734, 735, 741-742, pl. 84) from a locality in southwestern Nebraska. In 1920 Darton (p. 6) referred to the type locality as near Ogallala Station in western Nebraska. Elias, (1931) made a detailed study of the Ogallala formation in Wallace County and adjacent area of western Kansas and later (Elias, 1937) briefly described the Ogallala in Rawlins and Decatur counties immediately west of Norton County. In 1942 Elias described Tertiary fossil seeds and other plant remains of the central Great Plains. Lugn (1939) presented a classification of the Tertiary formations of Nebraska in which he considered the Ogallala as a group: containing the following formations in ascending order: Valentine, Ash Hollow, Sydney gravel, and Kimball.
Character and subdivisions--The Ogallala formation of Norton and Phillips Counties consists of a wide diversity of clastic sediments. It contains sand and gravel, silt, sandy silt, clay, bentonitic clay, and, locally, sandy limestone, silty limestone, volcanic ash, opaline-cemented sands and gravels, and chert (Pls. 6, 7, and 9A). The character of the Ogallala is shown by the logs of test holes and the measured sections, included in this report, and by the cross sections in Plate 3. The bluffs on the south side of Prairie Dog Creek Valley in the vicinity of Almena present exceptionally good exposures of the Ogallala formation, and a measured section-from that locality is given below.
|Section measured south of Almena, W2 sec. 16, T. 2 S., R. 21 W., Norton County, Kansas (Measured by M. K. Elias and John C. Frye)|
|24. Silt and fine sand, buff; contains nodules of calcium carbonate||4.0|
|Ogallala formation--Ash Hollow member (?)|
|23. Limestone, porous, hard, light cream; contains abundant gastropod molds||3.0|
|22. Covered. Two feet of mortar bed exposed about midway||35.0|
|21. Sand, silty, fine to medium, loosely cemented with calcium carbonate; contains Biorbia fossilia (Berry), Berryochloa amphoralis, and Celtis willtstoni (Cockerell)||6.4|
|20. Covered. Unconsolidated silt and sand, buff, poorly exposed at a few places||32.0|
|19. Sand, coarse to fine, and some silt; cemented with calcium carbonate||1.0|
|18. Sand, fine to medium, buff; contains a small amount of calcium carbonate cement||5.0|
|17. Volcanic ash, sandy at base (becomes impure to south) upper part locally cemented with calcium carbonate. At Calvert ash mine this bed contains Krynitzkia coroniformis Elias, Stipidium variegatum var. dartoni Elias, Celtis willistoni (Cockerell)||6.5|
|16. Silt and sand cemented with calcium carbonate, roughly bedded; contains Krynitzkia coroniformis Elias||6.5|
|15. Partly covered. Calcareous clay silt, greenish gray at top; buff silt and very fine sand with calcium carbonate concretions in middle; and greenish-gray calcareous clay silt at base||20.0|
|14. Silt, sand, and calcium carbonate||4.0|
|13. Sandy silt, buff, locally unevenly cemented with calcium carbonate||0.7|
|12. Silt, sand, and calcium carbonate, massive, light greenish buff||6.9|
|11. Sand, fine to medium, pale greenish tan||3.7|
|10. Silt, sand, and clay, calcareous, greenish brown||3.0|
|9., Silt, clay, and sand, greenish brown||1.8|
|8. Sand and some gravel||3.0|
|7. Sand, clay, and silt, greenish brown; contains abundant fragments of fossil vertebrates||2.5|
|6. Sand, medium, poorly sorted, uncemented, brown||3.0|
|4. Limestone, porous, hard, white; contains gastropod molds||1.0|
|3. Sand and silt, highly calcareous, irregularly bedded, gray to pink; upper part more calcareous and contains a few gastropod molds||3.2|
|2. Silt, with some clay and fine sand, massive, gray to gray green||5.5|
|1. Sand, fine, and silt, with some clay and coarse sand, highly calcareous, massive to irregularly bedded, gray. Covered in lower part to level of C. R. I. and P. R. R. tracks||5.3|
In spite of the wide diversity of rock types included within the Ogallala formation, the outcrops present a uniformity of aspect which makes the stratigraphic unit easy to identify for mapping purposes. Poorly sorted sandy silts and silty sands and gravels, commonly cemented loosely with calcium carbonate or containing nodules and stringers of calcium carbonate, predominate throughout the formation.
Thin lenticular bodies of well-sorted sand and sand and gravel have been penetrated by several of the test holes as shown by the logs. However, well-sorted sand or sand and gravel is rare in Ogallala outcrops. The general occurrence of sandy silts and silty sand and gravel beds loosely cemented with calcium carbonate gave rise to the widespread application of the term "mortar bed" to the Ogallala formation in northwestern Kansas. Although color differentiation should not be relied upon for correlation purposes, the lower part of the Ogallala section in Norton and Phillips counties is predominantly gray to gray green in color, whereas the upper part generally is characterized by a pinkish color.
The stratigraphic subdivision of the Ogallala formation is rendered difficult by the occurrence throughout its entire thickness of similar lithologies. In Nebraska the Ogallala has been classed by Lugn (1939) as a group consisting of four formational units. Because these several units are conformable they are. recognized with difficulty in field mapping; the State Geological Survey of Kansas classes the Ogallala as a formation and recognizes as members within it three units classed in Nebraska as formations. It is our judgment that in Norton County and northwestern Phillips County nearly an entire section of Ogallala is present, representing the Valentine, Ash Hollow, and Kimball members. The cross sections (Pl. 3) clearly show that the unconformable surface on which the Ogallala deposits were laid down is not flat but has relief of more than 100 feet in this area. The tracing of seed zones and lithologic types suggests that deposits here classed as Valentine member accumulated in the low areas on the pre-Ogallala erosion surface and thus represent fills in the early Pliocene valleys. The Valentine member thus thins toward the Cretaceous highs and probably pinches out entirely under part of the divide area between Prairie Dog Creek and Solomon River in the eastern part of Norton County and south of Sappa Creek Valley in northwestern Norton County. The Ash Hollow member is thought to be represented by many of the outcrops encountered along the major valley areas and to have been deposited over the entire area. Alluviation of this part of the Great Plains during the time of Ash Hollow sedimentation had built the surface of the alluvial plain (Frye, 1945) above the level of the pre-Pliocene major stream divides. Although deposits comprising the Kimball member of the Ogallala are thought to have originally been continuous over this part of Kansas, they are now represented only by isolated erosion remnants projecting above the general upper surface of Ogallala deposits. The crest of Twin Mounds south of Lenora, capped by resistant cherty beds, may represent the approximate stratigraphic position of the Algal limestone and thus mark the top of the Kimball member and of the Ogallala formation.
The recognition of the Valentine, Ash Hollow, and Kimball members is based primarily on plant fossils and a few distinctive lithologic types. Elias (1942) has described the fossil flora of the Ogallala formation and recognized floral zones characterized by three distinctive fossil seeds. He considers the zone of Stipidium commune to be roughly coincident with the Valentine member, the zone of Krynitzkia coroniformis to occur in the lower Ash Hollow and possibly uppermost Valentine, and the zone of Biorbia fossilia to comprise all but the lowermost part of the Ash Hollow. As the seeds occur widely in Ogallala deposits, they are quite useful in aiding the recognition of the several members. Their stratigraphic position in Norton and Phillips counties is noted in several measured sections included in this report.
Of the special lithologic types included in the Ogallala formation of this area, lenticular deposits of volcanic ash have proved to be the most useful stratigraphically. Detailed petrographic studies (Swineford and Frye, 1946) of volcanic ash from six localities in Norton County have been made. At five of these places the petrographic characteristics indicate that the ash represents the same fall, whereas a higher index of refraction at the sixth locality (NW NE sec. 36, T. 2 S., R. 25 W.) suggests a different ash fall not contemporaneous in age with the other ash deposits. The widespread ash typically exposed in the Calvert, mine (Pl. 7) has been placed by Swineford and Frye (1946) in the lower part of the Ash Hollow member.
Another distinctive lithologic type in this area is the silica-cemented lentils of sand and gravel. This rock type has been described in detail by Frye and Swineford (1946) and, although it occurs at several slightly different stratigraphic positions, the lentils for the most part have been placed by them in the zone of Stipidium commune and the lower part of the zone of Krynitzkia coroniformis and thus probably should be assigned to the lowermost part of the Ash Hollow member or the uppermost part of the Valentine member. Beds of soft limestone typified by molds of fossil snails and the absence of coarse sand or gravel occur at several stratigraphic positions within the formation and are well exposed in the vicinity of Almena and New Almelo.
Bentonitic clay, in places silty or sandy, is another distinctive lithologic type found in the Ogallala formation. Landes and Keroher (1942) have described the occurrence of this clay in Phillips County and Kinney (1942) has made a study of its properties and use. It is typically gray green to olive tan in color and occurs in lenticular bodies in the lower part of the formation. This clay has been assigned to the Cretaceous by some geologists, but its occurrence in some localities interstratified with and overlying typical calcium carbonate-cemented sand and gravel place it definitely within the Ogallala. The occurrence of this clay at the base of the Ogallala overlying Pierre shale at some places and upper Niobrara at other places suggests that it may be related to the erosional surface below the Ogallala formation.
Distribution and thickness--The ogallala formation underlies all of Norton and northwestern Phillips Counties, except where it has been removed by erosion along the valleys of the major streams and the lower parts of some of their tributaries, and in an area adjacent to North Fork Solomon Valley in southeastern Norton County where the relatively high position of the Niobrara formation has permitted the removal by erosion of the Ogallala formation from the upland areas. Westward from Norton County the Ogallala formation extends in an unbroken sheet to the Colorado state line. The thickness of the formation is shown in the cross sections (Pl. 3) and the logs of test holes in this report. It was penetrated by 28 test holes where its thickness ranged from 5 to more: than 250 feet; the average thickness penetrated by test holes is about 115 feet. The original thickness of the Ogallala formation at the close of the time of its deposition in this area probably ranged from a little more than 100 feet to about 300 feet.
Age and correlation--The beds in the type area of the Ogallala formation near Ogallala, Nebraska, have been studied by Elias (1931) and the fossil vertebrates have been described and discussed (Hibbard, 1933; Hesse, 1935; Stirton, 1936). Although a large collection of vertebrate fossils has been made from quarries in the Ogallala formation south of Long Island in northwestern Phillips County and a few fragmentary fossil vertebrates have been collected from several places in Norton County, detailed correlations on the basis of fossil vertebrates have not been made in this area. However, abundant collections of fossil seeds, made by us and identified by M. K. Elias, aid in the correlation of these deposits with the Ogallala formation of Nebraska and western and southwestern Kansas. The stratigraphic placement of the fossil seeds is shown in the measured sections. A list of fossil plants collected from the Ogallala in Norton and Phillips Counties is given below.
|Fossil seeds from the Ogallala formation
in Norton and northwestern Phillips
Counties, Kansas (Identified by M. K. Elias)
Biorbia fossilia (Berry)
Biorbia minor (Elias)
Celtis willistoni (Cockerell)
Krynitzkia coroniformis Elias
Panicum elegans mut. nebraskense Elias
Prolithospernum corrugatus Elias
Stipidium coloradoensis Elias
Stipidium commune Elias
Stipidium cf. grande Elias
Stipidium intermedium Elias
The Ogallala formation of Norton and northwestern Phillips counties is considered to be entirely of Pliocene age, as it has been correlated with deposits elsewhere in the Central Great Plains that have yielded characteristic Pliocene vertebrate faunas.
Water supply--The sand and gravel of the Ogallala formation is the most widespread source of ground water in Norton County. Most of the wells in the uplands obtain all or part of their water from this formation. The finer materials of the formation and those cemented with calcium carbonate generally are porous and hold considerable water but are not permeable enough to yield water freely. The coarser materials--gravel in particular--commonly yield abundant supplies of water. Although laboratory determinations, of coefficients of permeability of samples, from the Ogallala formation from Norton County were not made, determinations made on similar materials from Thomas County showed a range from 107 to 609 for uncemented sand and gravels (Frye, 1945, p. 65). Although these permeabilities are probably considerably less than the permeability of materials underlying the prominent terraces of Solomon River and Prairie Dog and Sappa Creeks, they indicate that relatively large supplies of water can be obtained from wells where a considerable thickness of Ogallala sediments is saturated.
The position of the water table in the Ogallala is shown on Plate 2 by contour lines and figures indicating the altitude of the water table and its depth below land surface, and on the cross sections in Plate 3. Details concerning individual wells producing from the Ogallala are given in Table 8. The chemical character of the water from the Ogallala formation is given in Tables 5 and 6, and is shown on Figures 9 and 10.
Although relatively thin in most places, deposits of Quaternary age were found to be the near-surface materials in a very large part of the area shown by the geologic map (Pl. 1). The Quaternary deposits are classed as Meade formation, Sanborn formation, terrace deposits, alluvium, and slope deposits.
Meade (?) Formation (Pleistocene Series)
Deposits tentatively classed as Meade formation occur south of Prairie Dog Creek Valley in the vicinity of Long Island and north of Solomon River Valley in south-central Norton County. In the vicinity of Long Island these deposits consist of sand and gravel containing abundant abraded pebbles of several distinctive rock types of the Ogallala formation and overlain by sandy silt. They occupy a topographic position well above that of the sand and gravel classed as the Crete member of the Sanborn formation, which in turn occurs topographically higher than the prominent terrace level along Prairie Dog Creek Valley. Thus at this locality the deposits assigned to the Meade formation constitute a dissected remnant of a high terrace. The topographic position of the sediments judged to be Meade in Solomon Valley is similar to that of the deposits in the Long Island locality. The south-central Norton County deposits,, however, consist primarily of fine sand and silt which contains a meager snail fauna. An auger hole revealed the presence of relatively well-sorted sand below the sand and silt.
The Meade formation has been correlated from its type locality in Meade County, Kansas, widely over the western and central parts of the state (Frye, Swineford, and Leonard, 1948). However, the distinctive Pearlette volcanic ash was not found in this area, and a meager collection of fossil snails from the south-central Norton County locality failed to yield diagnostic species which would have permitted definite correlation. Where observed, the Meade (?) formation occurs above the water table and is of small importance as a water-bearing formation. It may, however, underlie several square miles of northwestern Phillips County where the surficial materials consist entirely of the younger Sanborn formation.
Because of their small areal extent, these outcrops of Meade formation are included with the Sanborn formation on the geologic map (Pl. 1).
Sanborn Formation (Pleistocene Series)
Character and subdivisions--In 1931 Elias (pp. 163-181) described unconsolidated Pleistocene deposits consisting mostly of silt in northwestern Cheyenne County, Kansas, and named these deposits the Sanborn formation from the town of Sanborn located in Nebraska just north of the type area. In 1944 Hibbard, Frye, and Leonard made a reconnaissance of the Sanborn formation and its contained vertebrate and molluscan faunas in north-central Kansas. This report uses the classification and correlations of the Sanborn formation as described by Frye and Fent (1947) in central Kansas. Four members are recognized within the Sanborn formation in this area--Crete sand and gravel member at the base, grading upward into the Loveland silt member which is capped by the Loveland soil, the Peoria silt member terminated upward by the Brady soil, and the Bignell silt member terminated upward by the modern surface soil.The formation as a whole consists of three predominant lithologic types which directly reflect three environments of deposition. Stream deposits of sand and gravel representing the major channel fills of earliest Sanborn time occur in a terrace position above the prominent terraces of the major valleys and well below the uplands. The Crete sand and gravel is almost continuous along the north side of Prairie Dog Creek Valley throughout Norton County and northwestern Phillips County. Similar deposits of a local type occupy a tributary position to the major valleys in some places. Deposits of Crete sand and gravel were also observed at scattered localities along North Fork Solomon River and Sappa Creek Valleys. The second lithologic type occurs widely as a surficial material over much of the area mapped, as shown in Plate 1. It consists of eolian silts transported by winds from the flood plains of the major valleys of these counties and adjacent areas during periods of active alluviation and deposited as a nearly continuous mantle over the upland areas. The third lithologic type is minor in areal extent and thickness and consists of colluvial materials on steep slopes derived in part from the underlying bedrock (Pliocene or Cretaceous) and in part from the upland mantle of eollan silts. Two measured sections of the Sanborn formation and underlying Ogallala formation are given below.
|Section measured along steep cut bank on W. side of creek in the SE sec. 13, T. 1 S., R. 24 W., Norton County, Kansas. (Measured by Stafford C. Happ and John C. Frye.)|
|15. Silt and very fine sand below surface with no soil development, indistinct bedding, light yellow tan (Bignell silt member?). Some fossil snails present||1.5|
|14. Soil (Brady), dark brown to brown black, blocky; indistinct contacts at top and bottom||1.5|
|13. Silt, with some very fine sand, massive, yellow tan (Peoria silt member). Snails collected from zone 3-5 feet above base included Pupilla muscorum (Linnaeus), Helicodiscus parallelus (Say), Succinea grosvenori Lea, Vallonia gracilicosta Reinhardt||14.0|
|12. Soil (Loveland), brown to reddish brown, compact sandy silt with a few pebbles, indistinct contacts at top and bottom. Lower 0.5 foot contains fossil vertebrates and the following fossil snails: Vertigo tridentata Wolf, Succinea grosvenori Lea, Vallonia gracilicosta Reinhardt, and Pupilla muscorum (Linaeus)||3.5|
|11. Silt, sandy with occasional small pebbles, compact, irregular vertical structure, pinkish buff (Loveland silt member)||1.5|
|10. Sand, silt, and some gravel, massive, buff||1.0|
|9. Silt, sandy, massive, brown||1.0|
|8. Sand, fine, silty, massive, with some pebbles, tan||1.0|
|6. Sand, stratified, tan; contains streaks of uncemented silt and pebbles (dominantly mortar-bed material)||1.5|
|5. Sand, gravel, and silt, lenticular, irregularly bedded, tan (pebbles of Ogallala type)||2.0|
|4. Gravel (mostly derived from the Ogallala formation); minor disconformity at base||0.8|
|3. Silt, with some sand and gravel, irregularly bedded, greenish gray. Distinct unconformity at base||3.2|
|2. Silt, sandy, calcareous, greenish||0.8|
|1. Sand with some silt, massive, green gray. Partly covered in lower part||4.5|
|3-23-11. Section measured in road cut in the NW sec. 11, T. 3 S., R. 23 W., Norton County, Kansas. (Measured by Claude W. Hibbard and John C. Frye [Hibbard, Frye, and Leonard, 1944]).|
|4. Silt, massive, gray to yellow tan (Peoria silt member). Citellus richardsonii (Sabine) 2.5 feet and 21 feet above base. Fossil snails 4 feet above base include Vallonia gracilicosta (Muller), Succinea grosvenori Lea, and Pupilla blandi Morse; 20 feet above base, Succinea grosvenori Lea, Pupilla muscorum (Linnaeus), Pupilla blandi Morse, and Discus cronkhitei (Newcomb)||25.0|
|3. Soil (Loveland). Sand, fine, and gilt, blocky to massive; contains nodules of caliche in lower part; Citellus richardsonii (Sabine)||3.5|
|2. Silt and fine sand, a few patches and streaks of caliche, light gray buff (Loveland silt member). Citellus richardsonii (Sabine) and Geomys sp. Bed 2 pinches out laterally on unconformable surface of the Ogallala formation||4.4|
|Ogallala formation--Ash Hollow member|
|1. Sand, silt, and gravel, cemented loosely throughout with calcium carbonate, gray. Fossil vertebrates 12.5 feet below top||31.0|
On the upland divides, where the Sanborn formation consists predominantly of eolian silts with minor amounts of colluvial materials in the basal part, three stratigraphic units have been recognized on the basis of two distinct unconformities. For the most part these unconformities are not marked by deep erosion or intricate dissection of the area, but rather by episodes of weathering that have given rise to well-developed soil profiles now buried below overlying silts. The most prominent of these soil profiles occurs at the top of the Loveland member on the divide areas, and is several times as thick as the modern soil profile at the surface. It is well exposed in road cuts in the vicinity of Norton and elsewhere throughout the area, and has been encountered in test holes and auger borings. The depth of leaching in all exposures where it was checked exceeds 30 inches and the upper part of the soil is colored dark brown by organic material and oxidation. An accumulation of clay occurs below the dark-brown zone and a prominent red color extends downward into the Loveland silt member for several feet at most laces. Concentration of caliche in the form of nodules and stringers has been observed at depths of 4 to 6 feet below the top of the soil. The Loveland silt member on the divides rarely exceeds a thickness of 20 feet.
The Peoria silt member overlies the Loveland and consists predominantly of light yellowish-tan massive uniform calcareous silt. At the base of the Peoria member there is a gradational transition zone which is judged to represent the initial slow accumulation of silt that later culminated in the deposition of the member. This slow initial deposition allowed weathering processes to leach part of the calcium carbonate from the silts as they were deposited. The Peoria silt member is terminated upward by the Brady soil, which is somewhat thicker than the modern top soil which it resembles in road cuts and auger holes.
The uppermost division of the Sanborn formation consists of discontinuous thin deposits of eolian silt resting on the surface of the Brady soil. This uppermost member has been named Bignell from a locality in Nebraska (Schultz and Stout, 1945) and is terminated upward by the modern top soil (Pl. 8). Its occurrence is sporadic and is largely confined to the divide areas.
Colluvial deposits on some slopes are not properly classed as part of the Sanborn formation. However, for the purposes of field mapping, such slope deposits are included with the Sanborn formation on the geologic map (Pl. 1), where they are of sufficient thickness to conceal the underlying rocks in gullies and along road cuts.
Where the Sanborn formation is thick, the topography is generally characterized by rounded slopes and a deep, fertile soil. Where road cuts have been made through these silt members, they display in some degree the characteristic of loess in that they stand in steep cuts for long periods of time. On the broad interdivide areas in western Norton County the Sanborn formation underlies flat upland surfaces.
Distribution and thickness--As shown on Plate 1, the Sanborn formation and minor amounts of associated slope deposits underlie the surface of a very large part of Norton County and northwestern Phillips County. The thickness of this unit is shown by logs of test holes and measured sections included in this report and in the plotted cross sections shown on Plate 3. The uppermost or Bignell silt member is generally 3 to 5 feet in thickness but a total thickness of 20 feet was penetrated in one test hole. The underlying Peoria silt member is as much as 40 feet thick, and is commonly 15 to 25 feet thick. The next older member, the Loveland silt member, in the upland areas ranges in thickness from a featheredge to as much as 15 feet, and the basal or Crete sand and gravel member is commonly more than 30 feet thick.
Age and correlation--The Sanborn formation includes the deposits referred to in 1885 by Hay (p. 21) as "chalky sandy marl of Pliocene age." Subsequently it was called "Tertiary marl" or "Plains marl" by many of the early workers in the central Great Plains region. When Elias (1931) applied the name Sanborn to these deposits farther west in Kansas, he considered them to be of Pleistocene age. In 1944 a reconnaissance of the Pleistocene deposits of north-central Kansas was made by Hibbard, Frye, and Leonard, and collections of both vertebrate and invertebrate fossils from these deposits were made at many localities. One of the sections studied at that time included the exposures of Loveland and Peoria members of the Sanborn which cap the Ogallala bluffs south of the City of Norton. A measured section from that locality is included in this report and the stratigraphic placement of fossils is shown. The Loveland soil has been traced into Nebraska where it is included within the Citellus zone of earlier Nebraska classification. Condra, Reed, and Gordon (1947) have traced the Peorian loess and Loveland loess from western Iowa across Nebraska to the Colorado line. These units have been traced southward from Nebraska as far as central Kansas (Frye and Fent, 1947) but are here classed as members of the Sanborn formation. In the Missouri Valley area these two stratigraphic units occur above and below deposits of glacial till, and the Peoria member of the Sanborn has been established as post-Iowan in age and the Loveland member as pre-Iowan. In fact, a well-developed soil was formed on the top of the Loveland before it was overridden by the Iowan ice, and for that reason it is quite probable that this member may be as old as the Illinoian glacial epoch. The Bignell member is separated from the Peoria by a well-developed profile of weathering, and it is thought to be latest Pleistocene in age.
Fossil snails were collected from the Sanborn formation during the course of field work for this report. They have been identified by A. Byron Leonard and are given in the measured sections. All species obtained from the Loveland and Peoria members are listed below.
|Fossil snails from the Loveland silt member
of the Sanborn formation in Norton County
(Identified by A. Byron Leonard)
|Pupilla muscorum (Linnaeus)
Succinea grosvenori Lea
Vallonia gracilicosta Reinhardt
Vertigo tridentata Wolf
|Fossil snails from the Peoria silt member
of the Sanborn formation in Norton and
Phillips counties (Identified by A. Byron Leonard)
|Columella alticola ingersol
Discus cronkhitei (Newcomb)
Euconulus fulvus (Mtiller)
Helicodiscus parallelus (Say)
Pupqilla blandi Morse
Succinea grosvenori Lea
Vallonia gracilicosta Reinhardt
Vallonia pulchella (Miiller)
Vertigo modesta Gould
Vertigo coloradensis Cockerell
Water supply--On the upland divide areas the Sanborn formation occurs entirely above the water table and therefore does not yield water to wells. The fine-textured composition and low permeability of these silts probably retard the downward percolation of water into the underlying formations. The Crete sand and gravel member, on the other hand, is an important source of ground-water supplies, particularly in a strip averaging about 2 miles in width along the north side of Prairie Dog Creek Valley, and at scattered localities along the margins of Sappa Creek Valley and North Solomon River Valley. Analyses of water from two wells in the Crete member are listed in Table 6 and shown on Figure 11.
Terrace deposits of major valleys (Pleistocene and Recent Series)
Character and extent--Broad smooth terrace surfaces (Pl. 4A) trenched by relatively narrow channels characterize the major valleys of this area. Their extent, is shown on the geologic map (Pl. 1) and their thickness and character are given by cross sections in Plate 3 and logs of test, holes at the end of this report.
Although the terrace surface along each major valley is in general continuous, there are minor breaks in level which indicate that the broad terraces were developed during several episodes, and thus each should probably be considered as a terrace complex rather than as a single terrace. The more recognizable breaks in the terrace surface--that is, where a generally flat terrace area drops to a slightly lower level--are shown by dashed lines on the geologic map. These variations in surface level, however, are not reflected by variations in the, character of the deposits below the terrace surface or in the level of the eroded bedrock valley floor.
For the most part, each terrace is underlain at depths ranging from 40 to 80 feet by deposits of sand and gravel immediately above the Cretaceous bedrock surface. The deposits of sand and gravel grade upward into sand, sandy silt, and well-stratified silts in the upper part of the terrace fill. At many places an alluvial soil band has been observed in the upper part, of the terrace deposits (Pl. 9B) and in the cuttings from several of the test holes.
After the major valleys had eroded bedrock below the level of the Crete sand and gravel the basal member of the Sanborn formation, they filled their valleys with alluvium to develop the terraces. The episode of cut and fill that produced terraces in the major valleys also affected the minor tributaries. In many of the more important tributary streams of Norton and northwestern Phillips counties remnants of terraces which represent an extension of the major terrace levels can be observed (Pl. 10B). However, owing to their small areal extent, discontinuous nature, and small importance as water-bearing material, the remnants of terraces in the tributary valleys have been included with the alluvium on the geologic map (Pl. 1).
Age and correlation--The terrace deposits along all the major valleys are of late Pleistocene and Recent age. This is attested by their relationship to the Crete and Loveland members of the Sanborn formation. The Crete sand and gravel deposits and the Loveland silt and its contained soil were dissected during the period of erosion that developed the present valley, and therefore the terrace deposits are younger than Crete and Loveland and are probably Wisconsinan in age. The relationship of the Peoria silt member of the Sanborn formation to the terrace deposits is not clear. It is possible that the prominent soil band in the upper part of the terrace silts corresponds in age to the Brady soil that marks the top of the Peoria silt member of the Sanborn formation and occurs below the Bignell silt member of the Sanborn formation. This relationship, however, is not clearly demonstrated by field observations. Other evidence for the extreme youth of the terraces is their relation to the stream courses. At many places along each of the three major streams narrow promontories and islands of terrace deposits project into meander loops of the streams (Pl. 1). As the meanders move downstream, they will cut off the promontories to form islands and eventually eradicate them. In a short span of geologic time, the streams will have meander belts of uniform width without projections of terraces into them.
Collections of fossil snails were made from the terrace deposits along North Fork Solomon Valley and Prairie Dog Creek Valley and a few fossil snails were collected from alluvium. They have been identified by A. B. Leonard and are listed below.
|Fossil snails collected from terrace deposits
of late Plestocene and Recent age
and Recent alluvium in Norlon County
(Identified by A. Byron Leonard)
|Discus shimeki (Pilsbry)
Euconulus fulvus (Müller)
Gastrocopta armifera Sterki
Gyraulus parvus (Say)
Hawaiia miniscula (Binney)
Helisoma trivolvis (Say)
Helicodiscus parallelus (Say)
Physa hawnii Lea
Pupoides marginatus Say
Pupilla blandi Morse
Pupilla muscorum (Linnaeus)
Succinea grosvenori Lea
Vallonia gracilicosta Reinhardt
Vertigo modesta Gould
Correlation of these terraces with other described terraces toward the east is possible only in the case of the North Fork Solomon River. Here a prominent terrace named Kirwin by A. R. Leonard (Report in preparation) has been traced by him across Osborne, Smith, and Phillips counties and found to be continuous with the prominent, terrace mapped across southern Norton County. For the purpose of this report the terrace of Prairie Dog Creek Valley is named the Almena terrace from the town of that name built on its surface. The Almena terrace has been traced across Norton and Phillips counties and into Nebraska, where it is thought to merge with one of the terraces of Republican River Valley. However, as an adequate correlation with a named and described terrace in Nebraska has not yet been made, it is thought preferable to use a local name for this terrace. The terrace of Sappa Creek Valley has not been traced beyond the limits of the area shown in the geologic map. (Pl. 1).
Water supply--The terrace deposits constitute the most important source of ground-water supply for irrigation, municipal, and industrial wells in this area. The relatively coarse-textured sand and gravel that constitutes the lowermost part of the valley fill under much of the terrace surfaces is quite permeable. In most places it, lies below the water table and is saturated with water. Along many of the major valley courses ground water moves from the adjacent Ogallala formation and Crete sand and gravel member of the Sanborn formation laterally into the terrace deposits, thus contributing to the replenishment of water in this material. The major stream channels lie below the water table and are fed by ground-water seepage throughout their courses across Norton and Phillips counties. The relatively shallow depth to the deposits and shallow static level contribute to the availability of ground-water supplies from terrace deposits. The chemical character of water obtained from these materials is shown by the analyses in Tables 5 and 6 and Figures 9 and 10.
Alluvium (Recent Series)
In major valleys--Deposits of alluvium occur along the valleys and underlie the flood plains of all the major valleys of this area. The alluvium consists predominantly of sand and gravel with some silt and very small amounts of clay. In most cases the valley flat or flood plain that forms the upper surface of the Recent alluvium along Solomon River and Prairie Dog and Sappa Creeks is from 15 to 25 feet below the adjacent terrace surfaces. The flood plains in turn stand pronouncedly above the channel floors. There are indications that these flood plains are being built upward by deposits of sand and silt during each major flood; thus the alluvial deposits of this area are still in the process of accumulating.
The areal extent of alluvium in the major valleys is shown on the geologic map (Pl. 1). Detailed information concerning thickness of Recent alluvium is not generally available as only a few test holes were drilled on the flood-plain surface. The inferred thickness in many places is shown by the cross sections in Plate 3.
The body of ground water contained in the terrace deposits is continuous with the. water in the alluvium, and wells drilled into this material should obtain large quantities of water at shallow depths. Their small areal extent, however, renders them a minor source of water in this area.
In tributary valleys--The character of the alluvium occurring in the valley flats of tributary streams is quite diverse. This is largely because alluvial deposits are representative of the rocks underlying their drainage basins. The source of sediments varies from one tributary valley to another. As a result, where the watershed is underlain by rocks of the Ogallala formation, the alluvial deposits consist predominantly of fragments of Ogallala rocks. Likewise, where the watershed is underlain largely by rocks of Niobrara formation, the alluvium contains an abundance of water-worn pebbles and grains of Niobrara chalk. For this reason it is impossible to generalize concerning all the tributary valleys of the area. For the most part, however, in their lower courses they contain coarse alluvial material saturated in part and serve as a source of moderate supplies of ground water of variable quality to wells. Chemical analyses of water obtained from wells in the alluvium are given in Tables 5 and 6 shown on Figure 10.
The development of the present topography of Norton County and northwestern Phillips County has been entirely in response to events during Pleistocene and Recent times. During Pliocene time streams flowing east and southeast from the Rocky Mountain region deposited sediments which accumulated in the lower parts of former broad valleys and later, as these valleys were filled, the streams shifted laterally and developed an extensive almost featureless plain of alluvium (Frye, 1945). Early in Pleistocene time the then-existing streams, in response to climatic or structural control, started to cut valleys below the surface of this vast constructional plain. The nature of events in this area during earliest Pleistocene time is not known because deposits of Nebraskan and Aftonian age have not been found. Furthermore, only scattered remnants of deposits of Kansan and Yarmouthian age have been observed in the area. They are adequate, however, to indicate that by Kansan time the major valleys had become entrenched approximately halfway from the surface of the Ogallala alluvial plain to the present maximum depth of bedrock cutting, and that these Kansan-Yarmouthian valleys were later alluviated.
By Illinoian or Sangamonian time, the bedrock floors of the major valleys had been cut to within approximately 30 feet of the present bedrock floors, and the major valleys were again alluviated, as is demonstrated by the deposits of the Crete sand and gravel member of the Sanborn formation. The rapidly aggrading valley floors of this age probably served as a source of eolian silts that were spread over the uplands and on valley slopes and which now constitute the Loveland member of the Sanborn formation. Late Sangamonian time represented a period of essential equilibrium when the topography was more subdued than now and the area was not being actively eroded. Prevalent grasslands of that time aided the development of the deep Loveland soil.
The period of erosion during which the Loveland surface was dissected and valleys were cut below the level of the Crete sand and gravel member of the Sanborn formation must have been followed by rapid alluviation which brought a large quantity of fine sediments into the valleys of this region. This is suggested by the extensive deposits of eolian silt which form a nearly continuous blanket over the upland areas and valley slopes, and which are here classed as the Peoria member of the Sanborn formation. The fact that the Peoria deposits are for the most part eolian in origin is attested by their uniformly fine texture, lack of bedding, molluscan fauna, stratigraphic position above an extensive well-developed soil undisturbed by physical processes, and by the topographic position of these silts which form an almost unbroken blanket over the highest elements of the topography-uplands, parts of the valley slopes, and high terraces alike. No other known process of transportation and deposition can account for these facts.
The Bignell silt member of the Sanborn, which occurs at scattered localities above the Peoria member, attests to minor recurrence of comparable conditions during latest Pleistocene time. That the topography and drainage pattern acquired its present aspect by about mid-Pleistocene time is suggested by the general concordance of the Loveland soil topography with the present topography and the parallelism of the Crete sand and gravel member of the Sanborn with the major terrace deposits and present channel course. These same data, however, demonstrate that the local relief has increased markedly since mid-Pleistocene time, both by the dissection and lowering of the major valley levels and by an increase in height, of many of the upland areas by the deposition of several feet of eolian silt. The presence of undistorted fossil rodent burrows, terminating at the top of the Loveland soil, extending downward into the Loveland silt member, and containing fossil Citellus richardsonii, strongly suggests that these deposits have not moved down slope by creep except in local areas. Greater relief and steeper slopes existing at the present time, however, are more conducive to creep, and at many places where a thin silt mantle overlies sloping surfaces on the Ogallala formation small slump terraces, sometimes referred to as "catsteps," can be observed (Pl. 10A).
Several physiographic features worthy of note are suggested by the geologic map. At several locations along the major valleys, particularly west of Almena, streams have breached saddles in narrow spurs, leaving isolated remnants of earlier Pleistocene deposits projecting as hills above the prominent terrace surfaces. The sharp hairpin turn in the course of Prairie Dog Creek, which now reverses the direction of flow in the vicinity of Woodruff and passes to the west and northwest around a hill capped by the resistant silicified lentils of the Ogallala formation, is also of interest. The earlier Pleistocene course of Prairie Dog Creek is thought to have been, at least in part, through the saddle south of this resistant hill, and the deposits are now exposed in the cut along the Chicago, Burlington, and Quincy Railroad. This anomalous course of Prairie Dog Creek is thought to have given rise to the long parallel tributary Elk Creek and the development of gentle, almost imperceptible natural levees along the main stem of Prairie Dog Creek.
Kansas Geological Survey, Geology
Placed on web July 18, 2008; originally published Dec. 1949.
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