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  Scott County Geohydrology

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Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Geologic Formations

Water Levels

Well Records

Logs of Test Holes

References

Plates

 

Geology

Summary of Stratigraphy

The rocks exposed in Scott County range in age from Upper Cretaceous to Recent. The areal distribution of the formations is shown on Plate 1. The oldest rocks cropping out in the county belong to the Smoky Hill chalk member of the Niobrara formation. This member is best exposed in the northern and northeastern part of the county where streams tributary to Smoky Hill River have cut through the plains surface into the underlying Smoky Hill chalk (Pl. 4B). Other exposures of the Smoky Hill are found also in the sides of several small tributary streams entering Dry Lake from the north and west near the southeastern corner of the county (Pl. 7A). The Pierre shale, which overlies the Niobrara formation in other areas, is absent in Scott County. The Ogallala formation of Tertiary age, which rests unconformably on the Smoky Hill chalk member of the Niobrara formation, is exposed in the sides of many of the stream valleys, but over large areas it is covered by younger deposits of sand and gravel overlain by loess. The undissected plains surface is mantled by deposits of loess ranging in age from Pleistocene to Recent. Dune sand covers an area of approximately 18 square miles near the southeastern corner of the county. A narrow belt of alluvium occupies the valley of Beaver Creek throughout its course in Scott County. The soils, alluvium, drifting dune sand, and terrace deposits are the most recent deposits in the area.

Plate 7A--Thin-bedded Smoky Hill chalk member of the Niobrara formation exposed in SW SE sec. 6, T. 20 S., R. 31 W.

black and white photo of outcrop, not much relief, rock hammer for scale, exposure 3-4 feet across

The character and ground-water supply of the geologic formations in Scott County are described briefly in the generalized section given in Table 1 and in more detail in the section on geologic formations and their water-bearing properties.

Geologic History

Parts of the following discussion are taken from a report by Darton (1906, pp. 45-46).

The exposed rocks in Scott County are underlain by older sedimentary rocks of pre-Cambrian age. The stratigraphic sequence of the rocks underlying the surface is fairly well known from the togs and well cuttings of each of the oil tests in the Shallow Water oil pool in south-central Scott County.

 

Table 1--Generalized section of the geologic formations in Scott County, Kansas.

System Series Formation Member Thickness
(feet)
Physical character Water supply
Quaternary Pleistocene and Recent Alluvium 0-20 ± Gravel, sand, silt and clay comprising stream deposits in Beaver (Ladder) Creek valley. Yields small supplies of relatively hard water to wells in Beaver (Ladder) Creek valley.
unconformable on older formations
Dune sand 0-50 ± Fine to medium sand. Mantles small areas in the southeastern part of the county. Except where reopened by recent blowouts, the dunes are stabilized by vegetation. Probably does not supply water directly to wells but is important as a favorable catchment area for ground-water recharge to adjacent and underlying formations.
unconformable on older formations
Loess 0-30 Light buff-colored silt containing fine sand and some clay. Loess deposits occur mostly above the water table and are relatively impermeable.
unconformable on older formations
Pleistocene Undifferentiated deposits, including channel deposits along Beaver (Ladder) Creek 0-200 ± Predominantly unconsolidated sands and gravels containing silt and clay. Basal channel deposits are cemented in at least one small exposure along Beaver Creek. Where saturated yield large supplies of moderately hard water to most of the wells in the shallow-water basin. Channel deposits are relatively permeable but generally occur above the water table.
unconformity
Tertiary Pliocene Ogallala formation 0-160 Gravel, sand, silt, caliche, and some silty clay. Contains hard and soft layers of sandstone and conglomerate, much of which is crossbedded and cemented with lime. Lower part locally contains mottled bentonitic clay ranging in color from reddish brown to Yields moderate to large supplies of moderately hard water to domestic and stock wells in many parts of the county. Constitutes the principal source of supply for many of the irrigation wells in Scott Basin.
unconformity
Cretaceous Gulfian* Niobrara formation Smoky Hill chalk 0-130 ± Alternative beds of soft chalk and chalky shale. Yields limited supplies of hard to very hard water to wells in the southeastern quarter of the country.
Fort Hays limestone Massive chalk beds separated by thin, soft, chalky shale. Not known to yield water to wells in Scott County.
Carlile shale Codell sandstone 180-230 Sandstone and sandy shale. Not known to yield water to wells in Scott County. The Codell sandstone member is reported to yield meager quantities of water to wells in Finney County. The Blue Hill shale and Fairport chalky shale members of the Carlile shale are relatively impermeable
Blue Hill shale Bluish-gray clay shale containing septarian concretions in upper part.
Fairport chalky shale Yellow chalky shale with thin limestone beds.
Greenhorn limestone Pfeifer shale, Jetmore chalk, Hartland shale, Lincoln limestone 0-55 Alternating beds of chalky shale and thin chalky limestones. Not known to yield water to wells in Scott County.
Graneros shale 25-100 Dark bluish-gray clay shale containing thin-bedded limestone and sand lenses. Relatively impermeable; not known to yield water to wells in Scott County.
Dakota formation 260-550 ± Sandstones, shales, and clays. Not known to yield water to wells in Scott County. The sandstones of the Dakota formation yield moderate supplies of soft water to wells in southeastern Gray County and in Ford County. The Kiowa shale is relatively impermeable.
Comanchean* Kiowa shale Black marine shale and a few thin limestone beds.
Cheyenne sandstone Fine to coarse-grained sandstone and sandy shale.
unconformity
Permian Leonardian and Guadalupian* Undifferentiated redbeds 1,150 ±    
* Classification of the State Geological Survey of Kansas

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  Kansas Geological Survey, Scott County Geohydrology
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Web version March 2003. Original publication date July 1947.
URL=http://www.kgs.ku.edu/General/Geology/Scott/04_geol.html