Geologic Formations, continued
Undifferentiated Pleistocene deposits
Overlying the Ogallala formation in this area are deposits of clay, silt, sand, and gravel that are lithologically similar to the Ogallala formation, but are of Pleistocene age. Because of lack of data, it was not possible to subdivide these deposits into smaller units, so they are referred to as undifferentiated Pleistocene deposits. These deposits have been included as part of the Ogallala formation by previous investigators.
Character--The undifferentiated Pleistocene deposits consist of interbedded lenses of calcareous clay, silt, sand, gravel, and caliche. The proportions of the different sediments vary from place to place, and gradations from one lithologic type to another generally take place within short distances, both laterally and vertically. The sands and gravels of the undifferentiated Pleistocene deposits commonly are cross-bedded.
The finer materials of the Pleistocene deposits consist of clay and silt. The only known exposure of clay in this area occurs in a draw about 1.4 mile west of Ingalls in Gray County, where about 7 feet of mottled green and brown clay is exposed, the upper part of which contains nodules and thin layers of soft to very hard caliche. A section measured at this locality is given below. Clay was encountered in seven of the 26 test holes (1, 3, 4, 8, 15, 16, and 26) drilled in Finney and Gray counties. The clay ranges from pure clay to silty and sandy clay, and is tan, yellow-tan, gray, blue-gray, and black. The individual beds range in thickness from 2.5 to 46 feet. Many of the clay beds contain small invertebrate fossils.
Lenses of silt and sandy silt ranging in thickness from a few inches to about 65 feet were penetrated in test drilling. Although silt is likely to be encountered in any part of the Pleistocene deposits, it is thicker and more persistent at the top. Test hole 26 in southern Gray County penetrated nearly 80 feet of silt and sandy silt below the surface before encountering any coarser materials. The two test holes (hogs 28 and 29) in southwestern Ford County penetrated 90 feet of silt and sandy silt, which has been referred to the Kingsdown silt of Pleistocene and Recent age (Waite, 1942, pp. 162-166). The silt is tan, brown, yellow, green, reddish-tan, or gray. Many of the lenses are very calcareous and are white to light gray.
The sands in the Pleistocene deposits cannot be distinguished lithologically from the sands of the Ogallala formation. They are generally poorly sorted and range in texture from very fine- to coarse-grained and generally contain a few pebbles. The sands are composed principally of well-rounded to subangular grains of quartz, but also contain some feldspar and dark minerals. The dominant colors of the sands are tan, reddish-tan, and brown.
Fine to very coarse gravels make up the coarser sediments of the Pleistocene. Lenses of clean gravel are not numerous, but lenses of intermixed sand and gravel are common. The thickness of most of the gravel lenses encountered in test holes in this area ranges from a few feet to about 25 feet. Test hole 16 in southern Finney County, however, penetrated 85 feet of fine to coarse gravel between depths of 30 and 115 feet. Many thin lenses of silt and sand also occur in this interval. The gravels are composed chiefly of granite, feldspar, and quartz pebbles. Pebbles of sandstone, limestone, chalk, and shale, which are abundant in the basal gravels of the Ogallala, are only a minor constituent of the Pleistocene gravels. Water-worn pebbles of caliche and "mortar bed" that were derived from the Ogallala formation are commonly found in the Pleistocene gravels. Locally the sand and gravels are loosely to tightly cemented by calcium carbonate.
Caliche is found throughout the Pleistocene deposits as nodules, stringers, pipy concretions, or irregular beds intermixed or interbedded with the clay, silt, sand, and gravel. The color of the caliche is white to gray. In some places it is soft and powderlike, but in other places it is hard and concretionary. Although not common, a few beds of white to gray hard limestone occur in the Pleistocene deposits. Two beds of limestone are exposed in a draw and road cut about 1.2 miles west of Ingalls in Gray County. One bed of limestone near the top of the section is 0.5 foot thick and contains small grains of clear quartz (see measured section below). The other limestone bed, which is at the bottom of the section, is 2.5 feet thick. The weathered surface of the lower limestone is rough and cavernous.
Locally the Pleistocene deposits contain beds of volcanic ash. Several large deposits of ash in the Meade formation (Pleistocene) in Meade County are being mined commercially. To my knowledge, the only deposit of volcanic ash in the Finney-Gray area is that exposed on the side of a small draw in the NW sec. 35, T. 29 S., R. 27 W., in southern Gray County. The ash is white to light gray and is loosely consolidated. The total thickness of the ash is not known, for all but about a foot of the deposit is covered.
The following measured sections indicate the lithology of the Pleistocene deposits at the surface.
|Section of undifferentiated Pleistoccne deposits in a draw and in a toad cut along highway US 50S, about 1.2 miles west of Ingalls, Gray County||Thickness
|9. Silt and clay; sandy; green-gray; containing splotches of lime||2.0|
|8. Limestone, sandy, medium hard, white||0.5|
|7. Silt, sandy, red, impregnated with irregular stringers and nodules of white lime||15.0|
|6. Sand, fine, to coarse gravel; lime-cemented; compact; gray||4.0|
|5. Sand, gravel, and pebbles; cross-bedded; tan to brown some pebbles are 2 or 3 inches in length||15.0|
|4. Sand, coarse, to very coarse gravel; loose; tan||4.0|
|3. Gravel, coarse, containing some pebbles 3 inches in length||1.0|
|2. Sand, coarse, to very coarse gravel; loose; tan||2.0|
|1. Limestone, porous, hard, gray. Weathered surface is rough and cavernous||2.5|
|Total thickness exposed||46.0|
|Section of undifferentiated Pleistocene deposits in a draw and a road cut along US highway 50S, about 1.4 miles west of Ingalls, Gray County||Thickness
|8. Sand, fine to coarse, red-tan and gray, impregnated with white lime in irregular stringers and splotches||10.0|
|7. Clay, silt, sand, and fine gravel; poorly sorted||5.0|
|6. Sand and gravel; lime-cemented. Forms bench||6.0|
|5. Sand, medium, to very coarse gravel; cross-bedded; having irregular, loose to compact lime-cemented zones||15.0|
|4. Clay, mottled, green and brown, containing nodules and thin layers of soft to very hard caliche||2.0|
|3. Clay, mottled, green and brown||5.0|
|2. Caliche, hard, white||0.5|
|1. Sand, fine and medium, gray to green-gray||3.0|
|Total thickness exposed||46.5|
Distribution and thickness--Pleistocene deposits are present nearly everywhere in Finney and Gray counties except in the Pawnee River drainage area, where Pawnee River and its tributaries have removed them and exposed Pliocene and Cretaceous rocks. In the Arkansas valley they are covered by alluvium, and south of the valley they are covered by dune sand. The Pleistocene deposits probably are very thin north of Arkansas River in the extreme eastern part of Gray County, and they probably are missing entirely beneath the Arkansas valley in eastern Gray County.
The thickness of the Pleistocene deposits ranges from a feather-edge to 300 feet or more. The maximum thickness in this area was encountered in test hole 16 in southern Finney County, where 313.5 feet of sediments tentatively have been assigned to the Pleistocene. In the Finney basin the Pleistocene deposits attain a maximum thickness of about 105 feet in the deepest part of the trough (test hole 3) and thin eastward and westward. In Gray County the thickness of the Pleistocene ranges from a featheredge to about 200 feet.
Origin--Most of the materials in the undifferentiated Pleistocene deposits represent channel and flood plain sediments that were laid down in much the same manner as the materials of the Ogallala formation. These sediments were derived from areas of Ogallala and Cretaceous deposits to the west and from the Rocky Mountains.
Age and correlation--The Pleistocene deposits of southwestern Kansas formerly were included with the Pliocene deposits and referred to the Ogallala formation. In 1940, Smith (1940, pp. 99-129) pointed out that there were thick deposits of Pleistocene age in southwestern Kansas, particularly in Meade and Clark counties. At that time Smith named several units, discarded or redefined some of the earlier names, and left part of the Pleistocene section unnamed. In 1941, Frye and Hibbard (1941) completed a study of the Pliocene and Pleistocene stratigraphy of the Meade basin, which is about 15 miles south of the Finney-Gray area. As a result of this study, they (Frye and Hibbard, 1941, pp. 410-420) described the Meade formation of Pleistocene age and the Kingsdown silt of Pleistocene and Recent age. The materials herein described as undifferentiated Pleistocene are believed to represent extensions of both the Meade formation and the Kingsdown silt, and may also include some material of Recent age in the upper part of the Kingsdown silt.
The presence of water-worn caliche and "mortar-bed" pebbles and volcanic ash indicate Pleistocene age for these deposits in Finney and Gray counties. The abraded pebbles of caliche and "mortar bed" are common in Pleistocene gravels, but have not been noted in basal gravels of the Ogallala formation (Frye and Hibbard, 1941, p. 405). The occurrence of volcanic ash in southern Gray County is further evidence suggesting a Pleistocene age for deposits in that area, for this ash probably is of the same age as the ash in the Meade formation in Meade County which contains undoubted Pleistocene fossils.
In addition to the lithologic evidence, there is fossil evidence that indicates Pleistocene age for these deposits. The following mollusks were collected by Thad G. McLaughlin from a bed of silty clay in the SE NE sec. 3, T. 27 S., R. 31 W., in the northeastern corner of Haskell County, and were identified by A.B. Leonard of the University of Kansas:
|Mollusks collected from a bed of silty clay in the SE NE sec. 3, T. 27 S., R. 31 W., Haskell County, Kansas|
|Aquatic forms||Terrestrial forms|
Menetus exacuous (Say)
Gyraulus cristatus (Linnaeus)
Gyraulus cf. hirsutus (Gould)
Gyraulus parvus (Say)
Lymnea parva (Lea)
Lymnea palustris (Muller)
Lymnea humilis (Say)
Lymnea caperata (Say)
Succinea grosvenori (Lea)
Vertigo cf. morsei (Sterki)
Pupilla muscorum (Linnaeus)
Vallonia cf. costata (Muller)
Discus anthonyi cronkhitei (Pilsbry)
|Mollusks and other fossils were recovered from several of the test holes drilled in Finney and Gray counties as listed below. Identifications were made by A.B. Leonard.|
|Test hole No.||Depth below land surface (feet)||Fossils|
|1||1.5-12.5||Fragments of snails|
|3||41-57||Fragments of snails|
|4||8-19||Fragments of snails|
|5||1-9||Vallonia cf. costata, Helisoma sp.|
|17-20||Vallonia costata, Gastrocopta sp.|
|16||10-18||Vallonia costata, fragmentary rodent bones|
|18-30||Vallonia costata, Discus sp.|
Many of the mollusks given in the preceding lists are identical with forms found in the Meade formation of Meade County where they are associated with Pleistocene vertebrates. According to Leonard (personal communication), the ostracodes recovered from test hole 16 are similar to forms taken from the Rexroad member of the Ogallala formation in Meade County, but the vertical range is not known.
The only known vertebrate fossils found in the undifferentiated Pleistocene deposits of this area are the fragmentary rodent bones recovered from test hole 16 and a fragmentary horse tooth collected from a railroad cut 1.7 miles west of Ingalls. This material was submitted to C.W. Hibbard of the University of Kansas for identification, but because of the fragmentary condition of the material he could make no further identification.
Water supply--The water supply of the undifferentiated Pleistocene deposits and the Ogallala formation are discussed together on pages 168-171.
Character--Terrace deposits are widely distributed along Arkansas valley and to a lesser extent along Pawnee valley. The terrace deposits along Arkansas valley are well exposed in several commercial gravel pits near Garden City, Cimarron, and Pierceville (pl. 1). These deposits consist of unconsolidated cross-bedded fine sand to very coarse gravel (pl. 12). The fine sand to medium gravel is composed chiefly of subrounded to well-rounded grains of quartz containing some grains of feldspar and dark minerals. Pebbles of quartz, feldspar, granites and other igneous rocks, sandstones, and concretionary material make up the coarser gravels. Many of the pebbles in the coarse gravels are 2 inches in their greatest diameter, and some are as large as 4 inches. The fine and coarse material generally occurs overlapping lenses. Locally these deposits are stained rusty brown or black. Clay balls ranging in diameter from about 1 inch to 8 inches occur locally in the lenses of coarse gravel.
Moss (1932, p. 12) recognized and described terrace deposits along the Pawnee valley in western Hodgeman County. Similar deposits were noted along the south side of the Pawnee valley in Finney County. These deposits are shown to good advantage in a gravel pit in the SE sec. 25, T. 22 S., R. 27 W., where about 18 feet of cross-bedded sand and gravel is exposed. The sand and gravel are composed predominantly of grains and pebbles of quartz and granite. Granite pebbles are most abundant and generally are a bright red. Pebbles of quartzite, chert, schist, and dark-colored igneous rocks occur in smaller amounts. Most of the pebbles are well-rounded and range in diameter from less than one-half inch to 3 inches. Angular blocks of "mortar bed" occur in the lenses of coarser material.
Distribution and thickness--Terrace gravels border the present flood plain of Arkansas River in Finney and Gray counties. Because the exposed width of the terrace gravels is narrow, they have been mapped with the alluvium (pl. 1). The principal terrace lies 15 to 25 feet above flood-plain level and is most prominent along the south side of the valley. Good exposures of the gravel occur in several pits at the edge of the terrace. On the south side of the valley the presence of the gravel between good exposures is suggested at some places by the topographic expression of the terrace. In other places, however, even the terrace is obscured by erosion or masked by dune sand. The width of the terrace along the south side of the valley is not known because the southern boundary is covered by dune sand. It is believed, however, that the terrace extends nearly to the southern edge of the dune sand in this area. South of Garden City, terrace gravels are exposed in a pit about 1.5 miles south of the edge of the terrace and were encountered in a test hole drilled about 3.5 miles south of the edge (see log 14). South of Cimarron, terrace gravels were penetrated by a test hole drilled about 2 miles south of the edge of the terrace.
The thickness of the terrace gravels along the Arkansas valley is known only from the two test holes that penetrated these deposits. At test hole 14 south of Garden City the terrace gravels are 37 feet thick, and at test hole 23 south of Cimarron they are 68 feet thick (see logs 14 and 23).
The terrace gravels along the Pawnee valley are not widespread and occur only on the south side of the valley near the Finney-Hodgeman County line. They lie about 140 feet above the present flood plain of Pawnee River. The position of the gravel indicates that it is a remnant of a former terrace of Pawnee River.
Origin--The terrace gravels along the Arkansas valley were deposited by Arkansas River and those along the Pawnee valley by Pawnee River sometime during the Pleistocene period when the two rivers were flowing at a higher level than they are at present. Most of the material constituting the deposits along the Arkansas valley was derived from the Rocky Mountains. The gravels along the Pawnee valley probably were derived from areas of Tertiary and other rocks to the west.
Age and correlation--Vertebrate fossils of Pleistocene age have been taken from the terrace gravels along the Arkansas valley. These include remains of elephant, horse, bison, squirrel, prairie dog, and fragmentary bird and fish bones. Several teeth and a large tusk taken from the Smith Brothers gravel pit at the edge of the terrace south of Garden City were identified by C.W. Hibbard and E.S. Riggs as being Paraellephas cf. columbi (Falconer). A tooth identified as Equus sp. was also taken from this pit. Smith (1940. p. 125) collected fragmentary Bison and Equus material from the terrace deposits and states:
"it is probable also that the Bison willistoni (believed by O.P. Hay to be Bison alleni), Elephas primigenius, and Equus excelsus, reported by Martin from the vicinity of Garden City, were found in the terrace fill."
Mrs. H.T.U. Smith found a jaw bone in a gravel pit 1 mile east and three-quarters of a mile north of Garden City. It was originally identified by Hibbard as the lower jaw of Citellus elegans (Kennicott), but he later found it to be Citellus richardsonii (Sabine).
The greatest number of vertebrate fossils taken from the terrace deposits in this area were discovered and collected by Allen Graffham in two gravel pits in sec. 9, T. 24 S., R. 32 W., northeast of Garden City, and were identified by C.W. Hibbard. A small milk tooth of Paraelephas cf. columbi (Falconer); three skulls, four lower jaws, and limb bones of Citellus richardsonii (Sabine); and three upper and two lower molars of Equus were found near the top of the sand and gravel in a pit in the NW NE of this section. A skull of Cynomys ludovicianus (Ord) was found in the same pit at the base of the silt that overlies the sand and gravel. Seven lower jaws and part of a skull of Cynomys ludovicianus (Ord) and two skulls and two lower jaws of Citellus richardsonii (Sabine) were taken from the base of the silt in a gravel pit in the NW SE of the same section. A lower molar of Equus and fragmentary bird and fish bones also were taken from the sand and gravel in this pit.
These fossils indicate a late Pleistocene age for the terrace gravels along the Arkansas valley. No fossils have been found in the terrace gravels along Pawnee valley, but their topographic position and lithology suggest that they also are of Pleistocene age.
Water supply--The terrace gravels along the south side of the Arkansas valley in many places are above the water table and, therefore, are not water bearing. Near the river, however, the lower part of the terrace gravels is saturated and supplies water to a few wells (figs. 8 AA' and 9 DD'). Seven stock and domestic wells (226, 352, 451, 471, 472, 473, and 480) that probably obtain water from these deposits were visited in Finney and Gray counties. The depths of the wells range from about 40 feet to 71 feet, and the depth to water level ranges from about 31 to about 70 feet below the surface.
Four samples of water were collected from wells (226, 352, 472, and 480) obtaining water from the terrace gravels (Pleistocene) that underlie the sand hills south of Arkansas valley; these were found to be remarkably uniform in mineral content. The total dissolved solids in the four samples analyzed ranged from 232 to 272 parts per million and the total hardness ranged from 188 to 235 parts. The waters were all moderately hard calcium bicarbonate waters, containing from 59 to 74 parts per million of calcium, 171 to 226 parts of bicarbonate, and only from 13 to 26 parts of sulfate. The fluoride content in all four samples was 0.4 part per million or less. The iron content of the samples showed a greater range in concentration than any other constituent, ranging from a low of 0.2 part per million to 4.2 parts.
No wells obtain water from the terrace gravels along the Pawnee valley in Finney and Gray counties, for they are everywhere above the water table.
Dune sand of Quaternary age is widely distributed along the south side of Arkansas valley in Finney and Gray counties, and occurs in smaller areas north of the valley in Finney County (pl. 1). It is composed predominantly of fine- to medium-grained quartz sand and contains smaller amounts of silt, clay, and coarse sand. The sand has been accumulated by the wind to form small hills, some of which are 60 or 70 feet high, and low mounds. Most of the sand hills are covered by vegetation, but locally there are areas of bare sand that are being subjected to the action of the wind. The origin of the sand is uncertain, but the nearby Pliocene and Pleistocene deposits and terrace deposits probably were important sources for the sand. Smith (1940, pp. 127, 128; 153-168) has given an excellent description of the dune sand in southwestern Kansas, including a discussion of its origin; the reader is referred to this paper for further details.
No wells obtain water from the dune sand in Finney and Gray counties, for it is everywhere above the water table. Because the sand is loose and highly permeable, the sand dunes probably serve as important catchment areas for ground-water recharge from local rainfall (p. 68).
Alluvium of late Quaternary age occurs in Arkansas valley, Pawnee valley and its larger tributaries, and Crooked Creek valley (pl. 1). The alluvium in Crooked Creek valley and the tributary valleys of Pawnee River is thin and occurs only as very narrow bands along the present channels; therefore, it is not shown on the geologic maps.
The alluvium consists of stream-laid deposits that range in texture from clay and silt to sand and very coarse gravel. The upper 2 to 6 feet of the alluvium in Arkansas valley consists of silt and fine to coarse sand that has been deposited over the flood plain in time of flood or under normal conditions in the channel of the stream. Beneath the finer surficial deposits are layers of coarse granitic sand and gravel that are slightly older but of similar origin. The lithology of the coarser alluvial deposits is similar to the lithology of the terrace gravels described above. The alluvium grades into the terrace gravels, so the lower part of the valley fill in some places is probably of late Pleistocene age and represents the basal part of a cut and fill terrace deposit.
The thickness of the alluvium in the Arkansas valley in Finney and Gray counties as revealed by test drilling ranges from about 30 feet to 59 feet, and is thickest in central and eastern Gray County (logs 9, 10, 11, 12, 13, 21, and 22). The thickness of the alluvium, however, ranges considerably both along and across the valley.
The alluvium in Pawnee valley consists of 10 to 15 feet of silt and clay underlain by coarse sand and gravel. The coarser deposits are composed chiefly of limestone and chalk pebbles of Cretaceous age, but also contain some granitic sands and gravels. Silts and clays are intermixed with the coarser deposits. The thickness of the alluvium along Pawnee valley ranges from a few feet to an estimated maximum of about 30 feet. The alluvium in the valleys tributary to Pawnee valley is similar to the Pawnee valley alluvium but in most places is much thinner.
The alluvium in Crooked Creek valley in southern Gray County consists chiefly of sand and sandy silt, and probably is not more than a few feet thick. It is unimportant as a source of water.
The alluvial sands and gravels in Arkansas valley make up the most permeable deposits in Finney and Gray counties, and wells that tap them yield large quantities of water. The alluvium is the source of supply for many irrigation, domestic, and stock wells, and for a few industrial wells. The yields of the wells tapping the alluvium in the Arkansas valley range from a few gallons a minute to about 3,750 gallons a minute. The alluvium in the Pawnee valley and its tributaries has a low permeability because of the large amount of silt and clay it contains. It will supply sufficient water for domestic and stock purposes, however, and is important because it is the only shallow source of water in parts of the Pawnee River drainage basin.
Thirteen analyses indicate that several types of waters may be obtained from the alluvium in the Arkansas valley. Three of the 13 samples analyzed were moderately hard calcium bicarbonate waters (analyses 362, 449, and 457) whereas the other 10 were very hard waters with sulfate as the chief constituent. Three types are shown graphically in figure 19. Number 449 is a moderately hard calcium bicarbonate water, number 476 is a moderately mineralized calcium sulfate water, and number 268 is a highly mineralized water of mixed type.
The three calcium bicarbonate waters analyzed were similar in chemical character and in mineral content to waters from the Ogallala formation and the Pleistocene deposits. All three of these samples were collected from wells east of the heavily irrigated area around Garden City. Two of the wells (263 and 449) are on the south side of the river and one (well 457) is north of the river.
The other waters from the Arkansas valley alluvium are the hardest waters found in Finney and Gray counties. With but one exception (analysis 476), all of these waters contained in excess of 500 parts per million of sulfate and seven of the ten samples analyzed contained more than 900 parts. Only one of the samples had less than 1,000 parts per million of total dissolved solids, five samples had between 1,000 and 2,000 parts, and three samples had more than 2,000 parts. Five of the samples analyzed had from 462 to 1,000 parts per million of total hardness, and five samples had from 1,000 to 1,641 parts. All of the waters in the upper range of mineral concentration were collected from wells in the heavily irrigated area surrounding Garden City.
The fluoride content of the three samples of calcium bicarbonate water from the alluvium was less than 1.0 part per million, whereas each of the other waters analyzed contained more than 1.0 part and one sample (297) had 2.5 parts. Ten of the 13 samples from the alluvium contained less than 0.09 part per million of iron, one had 0.27 part (analysis 349), and two had more than 1.0 part (analyses 449 and 476).
Kansas Geological Survey, Geology
Web version April 2002. Original publication date Dec. 1944.
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