Water-bearing Formations, continued
Kingsdown SiltCharacter--The Kingsdown silt consists mainly of light buff to brownish silt, clay, and fine sand, but contains some light-colored sand and gravel at the bottom, and at the top it grades upward into loess. Some of the beds contain small calcareous nodules. Probably a part of the silt is reworked loess. Most of the beds are even-bedded--some of the beds being finely and evenly laminated.
In most places the contact between the lower water-laid silt, of the Kingsdown and the overlying loess is indistinguishable, making it difficult to differentiate between them. For this reason the Kingsdown silt, as redefined by Frye and Hibbard (1941, pp. 419, 420), locally includes loess at the top.
In Ford County the character of the Kingsdown silt is best revealed from the cuttings obtained from test drilling (see logs of test holes 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and 21). The base of the formation is not exposed in Ford County, but the upper part of the formation is exposed along Mulberry and Rattlesnake creeks and their tributaries. On the basis of samples from test holes, the Kingsdown silt may be described as being made up predominantly of soft light brown to reddish-brown to light gray limy silt, but it also contains a few nodules and streaks of lime and, locally at the base, a few beds of sand and gravel. The Kingsdown silt drills rather easily as there are no hard cemented beds to impede the progress of the drill.
Distribution and thickness--The areal extent of the Kingsdown silt in Ford County is shown in plate 1. The Kingsdown is widely exposed south of the Arkansas valley, the best exposures occurring along Mulberry Creek and especially along the headwaters of Rattlesnake Creek and its tributaries in the vicinity of Bucklin. Because the Kingsdown silt is relatively soft, it is commonly eroded to form a semi-badland type of topography, with numerous branching, closely spaced gullies (pl. 16A). Few exposures of the Kingsdown were found north of the Arkansas valley, and it is believed to occur only in isolated patches on the upland in this part of the county.
The reasons for the thinness of the Kingsdown north of the Arkansas valley are puzzling, but it is believed that this anomalous condition may be traceable to related tectonic causes. Smith (1940, p. 115) pointed out that drainage conditions at the time of deposition were undoubtedly different from those of the present and that, ultimately, deposition must have been due to a flattening or actual reversal of stream gradients as a result of crustal warping. He added that it was significant that the Kingsdown occurs in an area where:
(1) The general land surface is higher south of the Arkansas valley than on the north; (2) Arkansas River begins its swing northeastward into the very anomalous Great bend; (3) the Arkansas is perched as much as 180 feet higher than its tributary valleys, Buckner creek, Pawnee river and Walnut creek, on the north; and (4) the outer Arkansas valley and the sand-hill belt to the west are abnormally wide.
He further suggested that the inferred differential warping began possibly before the deposition of the Kingsdown, and continued during and after that event. As evidence of post-Kingsdown movement Smith referred to the broad arching of the depositional surface along an east-west axis as shown by an examination of the topographic maps.The localization of the Kingsdown silt, in southern Ford County doubtless is related to the abnormal breadth of the outer valley of Arkansas River in southeastern Kearny County, southern Finney County, and central Gray County as shown by the width of the sand-hill belt. Smith (1940, p. 138) suggested that this broad belt was formed probably by areal subsidence, continuous with but less regular in outline than that north of the river, and that this subsidence may have been a factor in leading to the deposition of the Rexroad or Kingsdown or both. It seems plausible that this subsidence and the deposition of the Kingsdown may be related to similar tectonic causes. Just prior to the deposition of the Kingsdown there was renewed downward movement of the structural trough in which the Rexroad and early Pleistocene sediments had been deposited. The effect of such downward movement was to trap the sediment of any through-flowing streams and to increase the quantity of material carried in from surrounding areas toward the middle of the trough.
According to Smith (1940. p. 112), the best exposures of the Kingsdown "formation" are found along Bluff Creek and its tributaries in Clark County, Kansas. A 5-foot bed of clean, even-bedded volcanic ash is also described as occurring near the base of the Kingsdown in the vicinity of an exposure in sec. 13, T. 30 S., B. 23 W.
Only the upper part of the formation is exposed in Ford County, but the entire formation was penetrated in 12 test holes (see logs 10-21) and in most of the wells south of the Arkansas valley. The thickness of the Kingsdown ranges from about 55 feet in test hole 12 to 123 feet in test hole 11, and appears to be the greatest beneath the divides north and south of Mulberry Creek. In the southwestern corner of the county the Kingsdown ranges in thickness from about 90 to 118 feet, (logs 19, 20 and 21) and was found to be 108 feet thick in test hole 15, four miles south and one mile west of Kingsdown. It was found to be 107.5 feet thick in the city well (467) at Bucklin (log 70) and 110 feet thick in an oil test southeast of Bucklin (log 71) in the NE 1/4 sec. 22, T. 29 S., R. 21 W.
Origin--The origin of the Kingsdown silt has been discussed under Geologic history, page 39. Probably a part of the material comprising these deposits is reworked eolian loess, and a part of the basal sand and gravel was undoubtedly derived from erosion of the Ogallala. Lacustrine deposition is suggested by the finely and evenly-bedded lamination. The cause of deposition probably is related to differential downwarping with a resultant flattening or actual reversal of stream gradients.
Age and correlation--Smith (1940, p. 111-112) suggested the name "Kingsdown formation" as a revival of Cragin's loosely-defined "Kingsdown marl" (1896), of supposed late Pliocene age, and redefined the term to include beds of Pleistocene age only. He also points out that it was included in the "Tertiary man" as mapped by Hay. Because it is composed largely of silt it was called the Kingsdown silt by Frye and Hibbard (1941, p. 419), who included the loess overlying the water-laid deposits as the upper part of the formation; this usage is followed in the present report. The loess may have been deposited during the Recent epoch.
The Kingsdown silt has yielded very few fossils, and so far as known, none have been collected from these deposits in Ford County. Hay (1917, p. 42) reported that Cragin found Elephas columbi along the upper part of Bluff Creek, in Clark County; and Williston (1897, p. 303) reported teeth of Equus occidentalis from Bluff Creek, but no details of the location are given. Smith (1940, p. 114) reported that Hibbard found one vertebra of Bison in the Stephenson ranch section in sec. 13, T. 30 S., R. 23 W in Clark County. Hibbard states (Frye and Hibbard, 1941, p. 420):
"The only fossils recovered from the formation, Taxidea taxus (Schreber), Cynomus ludovicianus Ord, and Bison bison Linneaus, are identical with forms living ... during the Recent epoch."Water supply--The Kingsdown silt is composed mainly of relatively impervious material that yields little or no water; moreover, most of the formation lies above the water table. The sand and gravel near the base of the formation might contain water in places where they lie below the water table. It is more likely, however, that the saturated deposits of the underlying Rexroad member of the Ogallala constitute the principal source of water to wells in the southern part of Ford County. As the formation consists mainly of silt overlain by loess, probably little or none of the rain falling upon its surface percolates downward to the water table.
Dune sandDune sand occurs mainly in a belt of varying width along the south side of the Arkansas River in Ford County, but is found also in an area of several square miles on the north side of the river, north of Ford, and in another area several square miles in extent in the southwestern part of the county (pl. 1). The thickness of the dune sand ranges from a few feet to a maximum of 70 feet. The dunes, except where reopened by recent blowouts, are old and well stabilized, and may date back well into the Pleistocene. The dunes on the south side of the river were derived at least in part from the terrace deposits. In places the soil zone is thin and attempts at cultivation have stripped the protective cover allowing the upper surface to be subjected to renewed wind action (pl. 16B). Smith (1940, pp. 165-168) pointed out that the present river floodplains along the Arkansas valley could not have been a source for the dune sand, contrary to the assumptions of previous writers (Darton, 1916, p. 42; 1920, p. 3), because no movement of sand from the channel toward the dune belt is to be observed. He contends further that few if any dunes of any consequence are to be found either on the floodplain or the lowest terrace, and that the dune belt is far too wide to have been supplied from the present valley unless there was extensive movement of migratory dunes.
He suggests that older and higher terraces, as yet unrecognized, or the sands of older formations, including the Kingsdown and the Ogallala, may have been the source or sources of dune-building sand.
The dunes on the north side of Arkansas River, north of Ford, may have been derived from the underlying Ogallala, although any contribution from this formation would necessarily be limited to source areas where the cemented beds at the top were eroded away, so as to uncover the softer beds of sand below.
The dunes in southwestern Ford County are the northern extension of a much larger expanse of sand dunes in northeastern Meade County. Smith (1940, p. 167) suggested that the sand was derived, either wholly or in part, from the strand flats of a lake that may once have occupied a part of the Meade basin and that the sand probably came from the west. In connection with a discussion of the existence of a temporary lake that may have occupied an area northeast of Meade and west of Fowler after the close of Pleistocene time, Frye (1940, p. 14) pointed out that the sand dunes north of Fowler have the aspect of beach dunes.
Water supply--The dune sand lies above the water table nearly everywhere, and for this reason probably does not supply water directly to wells. The areas that are mantled with dune sand provide the opportunity for effective recharge to the underlying groundwater reservoir, because of the high porosity of the sand deposits as indicated by the relative absence of surface drainage in such areas. Probably a rather large percentage of the rain that falls on such areas moves downward to join the water table.
Terrace gravelAt many places along the south side of Arkansas River, deposits of fairly coarse gravel are found in a terrace about 15 to 25 feet above the level of the river, and averaging about 20 feet above. They were deposited by Arkansas River at some time during the Pleistocene when it was flowing at a higher level than at present. These Quaternary terrace deposits have been described by Smith (1938, 1940, p. 125, 126). The deposits range in thickness from a few feet to about 20 feet, and the material consists of beds of clean, unconsolidated, cross-bedded sand and lenticular beds of gravel. The terrace gravels are well exposed in several commercial pits on the south side of Arkansas River in the vicinity of Dodge City, the locations of which are shown on the geologic map (pl. 1). The terrace deposits were mapped with the alluvium in plate 1. According to Smith (1940, pp. 125, 126), the deposits are probably late Pleistocene in age on the basis of a few vertebrate fossils that have been recovered; and, because the terrace deposits are situated lower topographically than the Kingsdown, he suggests that they are younger than that formation.
The terrace deposits are not a source of water in Ford County because any water that they may have contained before the river became intrenched to its present level has since drained out.
AlluviumAlluvium of late Quaternary age is found principally in the Arkansas valley and in the valleys of some of the other streams in Ford County, (pl. 1). Some of the streams are still in the process of downcutting so that there is little or no alluvium along the greater part of their courses in Ford County. Streams with little or no alluvium include Mulberry, Crooked and Rattlesnake Creeks south of the Arkansas valley, and Coon and Cow creeks in the northeastern part of the county.
The character of the alluvium is typical of stream-laid deposits and ranges in texture from silt to sand and coarse gravel. The youngest deposits consist largely of sand and silt deposited over the flood plain in time of flood or under normal conditions in the channel of the stream. Beneath the finer surface deposits are layers of sand and gravel slightly older but of similar origin. Possibly a part of the valley fill in some places is of late Pleistocene age, and represents the basal part of a cut and fill terrace deposit. The sand and gravel deposits are best developed in the alluvium of the Arkansas valley. The smaller valleys are partly filled with alluvium consisting mainly of silt and fine sand.
The thickness of the alluvium in the Arkansas valley in Ford County, as revealed by test drilling, ranges from about 15 feet in the eastern part of the county (logs 48 and 49) to about 40 feet in the central and western part of the county (logs 6, 7, 8, and 9). The alluvium is 33 to 42 feet thick along the south side of Arkansas River just east of Ford (logs 63, 64, 65). It is possible that in some places the alluvium in the Arkansas valley attains a thickness of 50 feet or more.
The alluvium is underlain by the Ogallala formation in most parts of the Arkansas valley, but near and east of Ford the alluvium rests unconformably on the Dakota formation.
Scanty data indicate that the thickness of the alluvium along Sawlog valley and some of its tributaries ranges from a few feet up to an estimated maximum of 25 or 30 feet.
The alluvial sand and gravel deposits are very permeable and yield large quantities of water to wells tapping them. In the Arkansas valley the alluvium is the source of supply for many irrigation, domestic, and stock wells. The yields of wells tapping the alluvium in the Arkansas valley range from a few gallons a minute to about 1,000 gallons a minute. The yields of wells in the smaller stream valleys generally are adequate for domestic and livestock purposes.
The hardness of 13 samples of ground water obtained from the alluvium ranges from 187 to 1,577 parts per million (fig. 20). The waters from alluvium were of two distinct types--differentiated by content of sulfate. Those low in sulfate, about half of those analyzed had less than 15 parts per million--are very similar in chemical character and mineral content to Ogallala waters. The others usually contain more than 300 parts of sulfate but have about the same bicarbonate content as the waters with low sulfate. Twelve of the 13 samples from the alluvium contained less than 0.15 parts per million of iron, but one sample contained 26 parts. The fluoride content of the samples of water from the alluvium ranged from 0.1 to 1.9 parts per million, and five of the samples contained more than 1.0 part.
Kansas Geological Survey, Ford Geohydrology|
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Web version April 2002. Original publication date Dec. 1942.