REGIONAL AQUIFERS IN KANSAS,

NEBRASKA, AND PARTS OF ARKANSAS,

COLORADO, MISSOURI, NEW MEXICO,

OKLAHOMA, SOUTH DAKOTA, TEXAS, AND

WYOMING GEOHYDROLOGIC FRAMEWORK

U.S. GEOLOGICAL SURVEV PROFESSIONAL t>APER 1414-B
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Regional Aquifers in Kansas, Nebraska, 

and Parts of Arkansas, Colorado, 

Missouri, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming 

Geohydrologic Framework

By DONALD G. JORGENSEN, JOHN O. HELGESEN, and JEFFREY L. IMES 

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1414-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1993
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government.

Library of Congress Cataloging in Publication Data

Jorgensen, Donald G.

Regional aquifers in Kansas, Nebraska, and parts of Arkansas, Colorado, Missouri, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming Geohydrologic framework / by Donald G. Jorgensen, John O. Helgesen, and Jeffrey L. Imes.

p. cm. (Regional aquifer-system analysis Central Midwest) (U.S. Geological Survey professional paper ; 1414-B)

Includes bibliographical references.

Supt. of Docs, no.: ! 19.16:1414-8

1. Aquifers Middle West. I. Helgesen, John O. II. Imes, Jeffrey L. III. Title. IV. Series. V. Series: U.S. Geological 

Survey professional paper ; 1414-B.

GB1199.3.M54J67 1993 93-32495 

551.49'0978 dc20 CIP

For sale by Book and Open-File Report Sales, U.S. Geological Survey 

Federal Center, Box 25286, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started in 

1978 following a congressional mandate to develop quantitative appraisals of 

the major ground-water systems of the United States. The RASA Program 

represents a systematic effort to study a number of the Nation's most 

important aquifer systems, which in aggregate underlie much of the country 

and which represent an important component of the Nation's total water 

supply. In general, the boundaries of these studies are identified by the 

hydrologic extent of each system and accordingly transcend the political 

subdivisions to which investigations have often arbitrarily been limited in the 

past. The broad objective for each study is to assemble geologic, hydrologic, 

and geochemical information, to analyze and develop an understanding of the 

system, and to develop predictive capabilities that will contribute to the 

effective management of the system. The use of computer simulation is an 

important element of the RASA studies, both to develop an understanding of 

the natural, undisturbed hydrologic system and the changes brought about in 

it by human activities, and to provide a means of predicting the regional 

effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in a series 

of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number, 

and where the volume of interpretive material warrants, separate topical 

chapters that consider the principal elements of the investigation may be 

published. The series of RASA interpretive reports begins with Professional 

Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Robert M. Hirsch 

Acting Director

CONTENTS

	Page

Abstract B1

Introduction 2

Purpose and scope 2

Approach 3

Procedure and techniques 3

Data compilation 4

Map preparation - 5

Determination of hydraulic properties 6

Porosity - 6

Hydraulic conductivity and intrinsic permeability - 8

Physical setting 10

Acknowledgments 10

Geologic and hydrologic history 11

Systems of the Precambrian 18

Cambrian System 21

Ordovician System 21

Silurian System 24

Devonian System - 24

Mississippian System 26

Pennsylvanian System - 28

Permian System 31

Triassic System - 34

Jurassic System 36

Geologic and hydrologic history Continued

Cretaceous System B36

Tertiary and Quarternary Systems 40

Geohydrology 42

Classification of subsurface hydrologic units 42

Geohydrologic units 42

Plains subregion 44

Western Interior Plains aquifer system 44

Western Interior Plains confining system 48

Great Plains aquifer system 50

Apishapa aquifer - 52

Apishapa confining unit 53

Maha aquifer 53

Overlying units in the Plains subregion 53

Ozark subregion 54

Ozark Plateaus aquifer system 55

St. Francois aquifer 58

St. Francois confining unit 61

Ozark aquifer 62

Ozark confining unit 65

Springfield Plateau aquifer 65

Summary 66

References cited 68

ILLUSTRATIONS

[Plates are in separate volume]

PLATE 1. Generalized correlation chart of geologic formations in Precambrian through Cretaceous rocks in Kansas, Nebraska, and

parts of Arkansas, Colorado, Missouri, Oklahoma, Texas, and Wyoming 

2. Geohydrologic sections from Colorado to Missouri and from Oklahoma to South Dakota 

3-12. Maps showing:

3. Altitude of the basement confining unit in Kansas, Nebraska, and parts of Arkansas, Colorado, Missouri, New 

Mexico, Oklahoma, South Dakota, Texas, and Wyoming

4. Altitude of lower units of the Western Interior Plains aquifer system in parts of Arkansas, Colorado, Kansas, 

Missouri, Nebraska, New Mexico, Oklahoma, South Dakota, and Texas

5. Altitude of confining unit that separates the upper unit from the lower units of the Western Interior Plains aquifer 

system in parts of Arkansas, Kansas, Missouri, Nebraska, Oklahoma, and Texas

6. Altitude of upper unit of the Western Interior Plains aquifer system in parts of Arkansas, Colorado, Kansas, 

Missouri, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

7. Thickness of the Western Interior Plains aquifer system in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, 

New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

8. Altitude of the Western Interior Plains confining system in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, 

New Mexico, Oklahoma, Texas, and Wyoming

9. Thickness of the Western Interior Plains confining system in parts of Arkansas, Colorado, Kansas, Missouri, 

Nebraska, New Mexico, Oklahoma, Texas, and Wyoming

10. Altitude of the Great Plains aquifer system in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South 

Dakota, Texas, and Wyoming

11. Thickness of the Apishapa aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, Texas, and 

Wyoming.

12. Thickness of the Apishapa confining unit in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, Texas, 

and Wyoming.

v
VI CONTENTS

PLATES 13-25. Maps showing:

13. Thickness of the Maha aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming.

14. Altitude of top of St. Francois aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Thickness of St. Francois aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Altitude of top of St. Francois confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Thickness of St. Francois confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Percentage of shale in St. Francois confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Altitude of top of Ozark aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Thickness of Ozark aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Altitude of top of Ozark confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Thickness of Ozark confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Percentage of shale in Ozark confining unit in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Altitude of top of Springfield Plateau aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma. 

Thickness of Springfield Plateau aquifer in parts of Arkansas, Kansas, Missouri, and Oklahoma.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

Page

FIGURE 1. Map showing location and extent of study area B3 

2. Map showing aquifer systems contiguous to Central Midwest regional aquifer-system analysis 4 

3 6. Graphs showing comparison of regional and reservoir porosity of:

3. Jurassic and Lower Cretaceous sandstone 6

4. Pennsylvanian and Permian rocks - 7

5. Mississippian limestone 7

6. Cambrian through Devonian rocks 7 

7 10. Graphs showing comparison of regional and reservoir permeability of:

7. Cambrian and Ordovician dolostone 9

8. Mississippian limestone - 9

9. Pennsylvanian and Permian rocks 9

10. Jurassic and Lower Cretaceous sandstone - 9 

11-16. Maps showing:

11. Physiographic subdivisions 11

12. Generalized land-surface altitude 12

13. Climatic characteristics of central United States, 1931-60 13

14. Estimated annual recharge to exposed Central Midwest RASA geohydrologic units", 1951-80 14

15. Major structural features 15

16. Regional geology of central United States - - 16 

17. Generalized geologic sections across study area 18 

18-30. Maps of study area showing:

18. Major faults------------------------------------------------------------------------- 19

19. Precambrian and Late Cambrian geographic and geologic conditions 20

20. Middle Ordovician geographic and geologic conditions - 23

21. Early Silurian geographic and geologic conditions- - .......... ........... ...... 25

22. Early Devonian geographic and geologic conditions 26

23. Early Mississippian geographic and geologic conditions - 27

24. Middle Pennsylvanian geographic and geologic conditions 29

25. Early Permian geographic and geologic conditions 33

26. Late Triassic geographic and geologic conditions 35

27. Late Jurassic geographic and geologic conditions 37

28. Early Cretaceous geographic and geologic conditions 38

29. Present conditions, including mountains of Laramide orogeny, extent of Ogallala Formation and glaciation, 

and estimated relative permeability distribution based on paleohydrology in Cambrian- and Ordovicianage rocks - - 40

30. Predevelopment equivalent-freshwater head in Cambrian and Ordovician rocks 43 

31. Cross section of major regional geohydrologic units in the Plains and Ozark subregions 44 

32-37. Maps of study area showing:

32. Dissolved-solids concentrations in water from Cambrian and Ordovician rocks 45

33. Extent of major aquifer systems 46

34. Estimated regional intrinsic permeability of lower units of the Western Interior Plains aquifer system 48

35. Estimated regional intrinsic permeability of upper unit of the Western Interior Plains aquifer system 49

36. Estimated regional intrinsic permeability of the Western Interior Plains confining system 51

37. Great Plains aquifer system in North America 52 

38. Cross section of Great Plains aquifer system showing Maha and Apishapa aquifers 53 

39-42. Maps showing:

39. Predevelopment potentiometric surface of the Maha aquifer, Great Plains aquifer system 54

40. Estimated regional intrinsic permeability of the Great Plains aquifer system 55

41. Dissolved-solids concentrations in Maha aquifer water 56

42. Geohydrologic units overlying regional aquifer systems in the Plains subregion 57
CONTENTS VII

FIGURES 43-46. Maps showing:

43. Thickness of the Great Plains confining system 58

44. Physiographic features of the Ozark subregion 59

45. Drainage features of the Ozark subregion 60

46. Predevelopment potentiometric surface of the Ozark aquifer - 64

TABLES

Page

TABLE 1. Major geochronologic and chronostratigraphic units B17

2. Generalized correlation of stratigraphic units to geohydrologic units in most of the Plains subregion 47

3. Generalized correlation of stratigraphic units to geohydrologic units in most of the Ozark subregion 61

CONVERSION FACTORS

Multiply inch-pound unit

inch (in.)

foot (ft)

foot squared (ft2)

mile (mi)

mile squared (mi2)

millidarcy (mD)

gallon (gal)

foot per mile (ft/mi)

foot per second (ft/s)

gallon per minute (gal/min)

By

25.40

0.3048

0.09290

1.609

2.590

9.87xlO-16

3.785

0.1894

0.3048

0.06309

To obtain metric unit

millimeter (mm)

meter (m)

meter squared (m2)

kilometer (km)

kilometer squared (km2)

meter squared (m2)

liter (L)

meter per kilometer (m/km)

meter per second (m/s)

liter per second (L/s)

Temperature in degree Fahrenheit (°F) can be converted to degree Celsius (°C) as follows:

°C = (°F - 32) / 1.8

SEA LEVEL

In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929) a geodetic datum derived from a general adjustment of the first-order level nets of 

both the United States and Canada, formerly called "Sea Level Datum of 1929."

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

REGIONAL AQUIFERS IN KANSAS, NEBRASKA, AND PARTS OF ARKANSAS,

COLORADO, MISSOURI, NEW MEXICO, OKLAHOMA, SOUTH DAKOTA,

TEXAS, AND WYOMING GEOHYDROLOGIC FRAMEWORK

By DONALD G. JORGENSEN, JOHN O. HELGESEN, and JEFFREY L. IMES

ABSTRACT

Regional aquifers are described within a 370,000-square-mile 

area extending from the foothills of the Rocky Mountains in 

Colorado to the Missouri and Mississippi Rivers in eastern Nebraska and Missouri, and from South Dakota to the Ouachita, 

Arbuckle, and Wichita Mountains of Arkansas and Oklahoma.

The present geohydrologic framework of aquifers and confining units in this area is controlled by topography, geologic structures, and hydraulic properties. All of these characteristics are 

the result of past geologic and hydrologic processes. From the 

end of the Precambrian to Late Cambrian time, the area was 

above sea level, and an uneven erosional surface had developed 

on the fractured crystalline rocks. From Late Cambrian through 

Middle Ordovician time, a transgressive but cyclic sea covered 

the area. The oldest deposits were mostly permeable sand followed by slightly permeable calcareous mud consisting of aragonite and algal remains.

During most of Silurian and Devonian time, nearly the entire 

area was above sea level, except for southern Oklahoma and 

northern Arkansas. Uplift diagenesis (diagenetic processes that 

occur during periods of uplift) greatly increased porosity and intrinsic permeability of the rocks. At the end of Devonian or the 

beginning of Early Mississippian time, a transgressing sea covered most of the area, and a very slightly permeable clay was 

deposited.

Calcareous mud was the dominant sediment deposited during 

much of Mississippian time. Tectonic activity increased as evidenced by uplifts, such as the Colorado-Wyoming uplift and the 

Nemaha uplift in Kansas. Subsiding basins, such as the Arkoma 

and Anadarko, received large quantities of sediment that covered the older rocks causing burial diagenesis of the calcareous 

muds, which in general, decreases primary porosity and permeability due to loading of sediments and selectively increases secondary porosity and permeability due to fracturing and 

dissolution.

Tectonic activity was at a maximum during Pennsylvanian 

time and decreased through the Permian. Uplifts, such as the 

Front Range, Apishapa, Criner, Amarillo, Wichita, Arbuckle, 

Ouachita, Ozark, Nemaha, and Cambridge-Central Kansas, 

were active. The Arkoma and Anadarko basins continued to subside and received as much as 20,000 feet of clay, calcareous 

mud, and sand. During the Permian, the eastern part of the 

area was tilted upward; the sea receded and regional groundwater flow commenced from east to west. In the Ozark uplift 

area, a small ground-water flow system began around the St. 

Francois Mountains.

During Triassic and Jurassic time, while the eastern part of 

the study area was above sea level, uplift diagenesis generally

increased secondary porosity and permeability. However, during 

Early Cretaceous time, a transgressive but cyclic sea deposited 

permeable sand and very slightly permeable clay over the western and central parts of the study area. During Late Cretaceous 

time, clay was deposited in thick layers, and burial diagenesis 

occurred throughout most of the area. At the end of the Cretaceous and into Tertiary time, major uplifts, such as the Rocky 

Mountains, were formed as part of the Laramide orogeny. Uplifts in the west accompanied the regional tilting of the study 

area downward to the east. Regional ground-water flow changed 

to west to east in the Lower Cretaceous sandstones and in prePennsylvanian rocks. The ground-water flow system near the St. 

Francois Mountains on the Ozark uplift continued to expand outward as Pennsylvanian and Permian rocks were removed by erosion.

Three major regional aquifer systems are identified in the 

area the Western Interior Plains aquifer system, the Great 

Plains aquifer system, and the Ozark Plateaus aquifer system. 

The Western Interior Plains aquifer system and the overlying 

Great Plains aquifer system are in the western part of the Interior Plains physiographic division. The Western Interior Plains 

aquifer system, the Western Interior Plains confining system, 

and the overlying Great Plains aquifer system, all overlie the 

basement. Overlying these geohydrologic systems are the Great 

Plains confining system and the High Plains aquifer. Water in 

both aquifer systems flows mostly west to east. The Ozark Plateaus aquifer system is in the Interior Highlands physiographic 

division, mostly in the Ozark Plateaus. In this area, water flows 

outward from the axis of the Ozark Plateaus. A transition zone 

in western Missouri, southeastern Kansas, and northeastern 

Oklahoma marks the location where the flow from the Western 

Interior Plains aquifer system and the Ozark Plateaus aquifer 

system meet and move vertically upward to the streams and the 

near-surface water table.

Rocks of the Western Interior Plains aquifer system consist 

mostly of dolostone, limestone, and shale of Cambrian through 

Mississippian age. At most locations, the aquifer units are permeable and water yielding except in deep basins where permeability is markedly decreased. The aquifer system is several 

thousand feet thick in the Anadarko basin. The aquifer system 

contains saline water with dissolved-solids concentrations ranging 

from about 10,000 to more than 200,000 milligrams per liter. Intrinsic permeability is small, ranging from 10~17 to 10~n feet squared.

The Western Interior Plains confining system restricts water 

flow between the Western Interior Plains aquifer system and the 

overlying Great Plains aquifer system at nearly all locations including the deep basins. The thick confining system consists 

mostly of layered shale, limestone, sandstone, and evaporite

Bl
B2 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

deposits of Late Mississippian through Jurassic age. The thickness of the confining system decreases from about 20,000 feet in 

the Anadarko basin to about zero along the periphery of the 

Ozark Plateaus, where it crops out.

The Great Plains aquifer system overlies the Western Interior 

Plains confining system and contains two regional aquifers and 

one confining unit. Both aquifers are composed predominantly of 

permeable Lower Cretaceous sandstone and are separated at 

most locations by a shale confining unit. Most recharge occurs in 

southeastern Colorado and northeastern New Mexico. Ground 

water flows east-northeast from these western recharge areas to 

discharge areas in central Kansas and eastern Nebraska.

Intrinsic permeability in the Great Plains aquifer system 

ranges from 10~13 feet squared in the Denver basin to more than 

10~10 feet squared near the eastern outcrops. The Maha aquifer 

(mostly Dakota Sandstone and equivalents) is the upper of the 

two major regional aquifer units and is more extensive than the 

underlying Apishapa aquifer (mostly Cheyenne Sandstone and 

equivalents). The Apishapa confining unit (mostly Kiowa Shale) 

separates the Apishapa and Maha aquifers. Dissolved-solids concentrations of water in the Great Plains aquifer system decrease 

from more than 20,000 milligrams per liter in western Nebraska 

to less than 1,000 milligrams per liter along outcrops in southeast Colorado, central Kansas, and eastern Nebraska.

The Ozark Plateaus aquifer system is within the Ozark Plateaus area. The aquifer system includes three regional aquifers 

and two confining units. They are in ascending order, the St. 

Francois aquifer, the St. Francois confining unit, the Ozark aquifer, the Ozark confining unit, and the Springfield Plateau aquifer. The St. Francois aquifer, which is the lowest geohydrologic 

unit of the Ozark Plateaus aquifer system, is composed of mostly 

Upper Cambrian sandstone, and lies on the basement. The aquifer is more than 1,000 feet thick near the Mississippi River Alluvial Plain, but typically is 200 to 500 feet thick. The St. Francois 

confining unit, which overlies and confines the St. Francois aquifer, is composed of Upper Cambrian shale, siltstone, dolostone, 

and limestone and is leaky because it transmits a considerable 

quantity of water.

The Ozark aquifer, the largest and most extensively used 

aquifer in the Ozark Plateaus area, is composed mostly of Upper 

Cambrian through Middle Ordovician fractured and permeable 

dolomitic rocks. The aquifer is typically about 1,000 feet thick 

and is the thickest unit in the Ozark Plateaus aquifer system. 

The Ozark confining unit restricts the movement of water between the Ozark aquifer and the overlying Springfield Plateau 

aquifer. The confining unit includes Upper Devonian through 

Lower Mississippian shale.

The Springfield Plateau aquifer is composed of fractured and 

permeable Mississippian limestone. Aquifer thickness is as much 

as 1,500 feet, but thicknesses of 100 to 400 feet are typical. The 

aquifer is overlain to the west by beds of very slightly permeable 

shale of Pennsylvanian age.

INTRODUCTION

The study area of the Central Midwest regional 

aquifer-system analysis (Central Midwest RASA) includes about 370,000 mi2 (fig. 1). It extends from the 

foothills of the Rocky Mountains in Colorado to the 

Missouri and Mississippi Rivers in eastern Nebraska 

and Missouri, and from South Dakota to the

Ouachita, Arbuckle, and Wichita Mountains of 

Arkansas and Oklahoma. The strata of interest are 

from Cambrian to Cretaceous age and are thousands 

to tens of thousands of feet thick in some areas. Several important regional aquifer systems that contains 

both freshwater and saline water (greater than 7,000 

milligrams per liter dissolved solids) are included in 

the study area. In much of the area, little was previously known about the regional flow and 

hydrochemistry within the aquifer systems or about 

relations among them.

Within the central United States, three other regional aquifer-system analyses (RASA) (fig. 2), which 

in places share geographic or hydrologic boundaries 

with Central Midwest RASA, were completed prior to 

this study. These RASA were the High Plains RASA 

(Weeks, 1978), the Northern Great Plains RASA 

(Dinwiddie, 1979), and the Northern Midwest RASA 

(Steinhilber and Young, 1979). The Gulf Coast RASA 

(fig. 2) is still being conducted in 1987 as this report 

is being written (Grubb, 1984).

PURPOSE AND SCOPE

The background, purpose, scope, objectives, and 

approach of the Central Midwest RASA are described 

in the project-planning report by Jorgensen and Signor (1981). The findings of the Central Midwest 

RASA are reported in five chapters: Chapter A is the 

summary chapter, which will collate the important 

findings reported in other chapters; chapter B (this 

report) describes the geohydrologic framework; chapter C describes the modeling analysis of the regional 

aquifer systems; chapter D describes the geohydrologic and model analyses of the Ozark Plateaus aquifer system; and chapter E describes the geohydrologic 

and model analyses of the Great Plains aquifer 

system.

The purpose of this chapter is to describe the regional aquifers and confining units in the Central 

Midwest and the hydrogeologic framework in which 

they exist. The aquifers and confining units described 

are within the stratigraphic section from Cambrian 

rocks through the Cretaceous Dakota Sandstone and 

its equivalents within the study area. The scope of 

the study does not specifically include the rocks that 

contain the High Plains aquifer. The information on 

the High Plains aquifer can be obtained from U.S. 

Geological Survey Professional Paper 1400-A through 

1400-E. Although at a few locations the High Plains 

aquifer is in direct connection with aquifer units of 

the Central Midwest RASA, it is a separate regional 

aquifer that overlies the units studied herein.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B3

APPROACH

A description of a ground-water hydrologic unit 

(geohydrologic unit) in this report includes the extent, thickness, altitude, and geologic framework of 

the rocks of the geohydrologic unit, as well as its hydraulic properties and hydrologic relations with other 

units. The correlation of geologic formations (strata) 

to geohydrologic units is termed its "geologic" framework. The delineation of geohydrologic units in reference to the framework of geologic formations is 

especially useful because formations are relatively 

well defined and generally are well known. Because 

of the large size of the study area, correlation of 

stratigraphic units across structural basins and State 

lines also was required. The usual concept of geologic 

framework in most investigations is expanded in this 

report to include discussion of geologic and hydrologic

history because these topics help to explain the hydraulic properties and water chemistry of the present 

hydrologic systems.

PROCEDURE AND TECHNIQUES

A geohydrologic unit, such as an aquifer, aquifer 

system, confining unit, or confining system, is defined 

largely on the basis of hydraulic conductivity and its 

resultant effect on ground-water flow. Water-bearing 

units (.aquifers) that contain relatively freshwater 

have a characteristic potentiometric surface that is 

continuous and relatively smooth. The surface is a 

useful tool in defining a geohydrologic unit. The potentiometric-surface map is based on altitude of the 

water level measured in wells finished in the aquifer 

unit. The configuration of the potentiometric surface

! Ouachita 

<{ Arbuckle, .,_. 'Mountains

35C

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

FIGURE 1. Location and extent of study area.
B4 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

is also helpful in identifying directions of ground-water flow and areas of recharge and discharge. In areas where fresh ground water is readily available and 

is developed, considerable hydrologic and hydraulic 

information are available. The information is used to 

delineate the geohydrologic systems. However, in 

most of the study area hydrologic information is not 

available, especially where aquifers contain water of 

variable density. In these areas the geohydrologic systems are delineated on the basis of hydrologic relations 

inferred from geologic and geochemical information.

DATA COMPILATION

Data that were needed for the definition of geohydrologic units and their evaluation were compiled and 

entered into data bases. These data included lithologic and geophysical logs, water-level measurements, 

chemical analyses, records of fluid (water, oil, and 

gas) withdrawal or injection, hydraulic properties,

and oil- and gas-reservoir properties. A data base of 

estimates of intrinsic permeability and dissolved-solids concentrations based on geophysical-log data was 

also created. The existing U.S. Geological Survey 

Ground Water Site Inventory (GWSI) computer-based 

data-storage and retrieval system was used to the degree possible.

Information from geophysical-log interpretations 

was essential in compiling maps of a geohydrologic 

unit. In most of the area, the lithologic and geophysical logs that were used were of test holes for petroleum. However, in the areas where the rocks contain 

freshwater, lithologic and geophysical logs were of 

water wells or test holes. Logs that were representative of an area, such as a county, were selected to be 

included in the project data base. Ideally, the chosen 

log was of a drill hole that penetrated the Cretaceous-to-Precambrian rock section. In areas for which 

numerous logs were available, such as near oil and 

gas reservoirs, only a few of the numerous logs avail0 200 400 KILOMETERS

EXPLANATION

CENTRAL MIDWEST REGIONAL AQUIFER-SYSTEM ANALYSIS

HIGH PLAINS REGIONAL AQUIFER-SYSTEM ANALYSIS 

(partly overlies Central Midwest RASA study area)

NORTHERN GREAT PLAINS REGIONAL AQUIFER-SYSTEM ANALYSIS 

NORTHERN MIDWEST REGIONAL AQUIFER-SYSTEM ANALYSIS 

GULF COAST REGIONAL AQUIFER-SYSTEM ANALYSIS

FIGURE 2. Aquifer-system analysis contiguous to Central Midwest regional aquifer-system analysis.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B5

able were selected. In other areas with few data, most 

available logs were selected.

Data of selected water-level measurements in wells 

were stored in the GWSI data base of the U.S. Geological Survey. Results of drill-stem tests were stored 

in a project file termed "Reservoir Parameter File." 

Hydrochemical data from many sources were entered 

in a "Hydrochemical File." Sources of data for this 

hydrochemical file included the U.S. Geological Survey WATSTORE Water-Quality file (Baker and 

Foulk, 1975), the National Uranium Resource Evaluation file (Arendt and others, 1979, p. 11), and the 

Petroleum Data Systems file (University of Oklahoma, 1980) as well as information from existing 

publications and other sources. Selected data from 

this hydrochemical file were used to create a project 

file termed "Hydrochemical Data Base" for waterchemistry maps.

Most of the chemical analyses of saline water were 

obtained from the petroleum industry. Large differences between the reported concentrations of dissolved solids from adjacent well sites typically 

characterized samples of saline water. The cause of 

these differences are difficult to determine. It is not 

known whether the differences are related to areal, 

vertical, and temporal variability, to errors resulting 

from the sampling procedure, or to methods of chemical analysis. For example, the exact source of many of 

the water samples is unknown. Some samples were 

obtained from drill-stem tests; others are "production" water. Some may be mixtures of in situ water 

and drilling fluids or of water from zones above or 

below the zone of interest. However, chemical analyses of water from adjacent wells located in the freshwater areas did not have large variability.

MAP PREPARATION

Maps showing the extent and altitude of the top of 

geohydrologic units were constructed using information from lithologic and geophysical logs and from topographic maps in outcrop areas. Typically maps of 

the altitude of geohydrologic units are more detailed 

in the Ozark area because they are based mostly on 

topographic control at outcrops, whereas in other areas, such as where the unit is deeply buried, less 

data are available. Thickness maps were made from 

measured data; however, if thickness information 

was not available, then the supplemental thickness 

was determined by calculating the difference between 

the altitudes of the top and bottom of the zone of interest. Fault locations were obtained from published 

geologic maps. Only major faults and those faults 

causing a major thickness discontinuity are shown on 

the thickness maps.

Many aquifers have a characteristic hydrochemistry that is the result of chemical processes occurring within the aquifers as well as the chemistry 

of water recharging the units. Maps showing preliminary interpretations of the dissolved-solids concentrations were prepared because more dissolved-solids 

data are available than any other type of chemical 

data. Selection of analyses used to prepare the dissolved-solids maps generally was governed by ionic 

balance and continuity with adjacent analyses. In the 

absence of analytical data, the concentration of dissolved solids was estimated from measurements of 

spontaneous potential from wireline-geophysical logs 

of boreholes or from cross plots of resistivity and porosity data also from wireline-geophysical logs. The 

procedure for estimating water resistivity and dissolved-solids concentration is described by Jorgensen 

(1989).

Maps of the configuration of the potentiometric 

surface in parts of aquifers containing freshwater 

were prepared to evaluate the continuity of an aquifer and to determine areas of recharge and discharge. 

A surface defined by equivalent-freshwater head is 

used in evaluating the lateral hydraulic continuity of 

permeable rocks. In parts of aquifers containing fresh 

ground water, maps showing the potentiometric surface were constructed to evaluate the flow system 

and areas of recharge and discharge. In parts of the 

aquifers containing variable-density fluid, a surface 

defined by equivalent-freshwater head is used. This 

surface of equivalent-freshwater head should be used 

with caution. Under certain conditions, flow direction 

may not be down the equivalent-freshwater head gradient. For rocks containing variable-density fluids, no 

potential field exists if density is not solely a function 

of pressure (Jorgensen and others, 1982; Hubbert, 1940). 

Nevertheless, the surface of equivalent-freshwater head 

is still useful if caution is exercised.

Altitudes of equivalent-freshwater head were determined from shut-in pressures of drill-stem tests in 

wells containing salinewater or by measurement of 

the water level in wells containing freshwater. The 

following equation, in consistent units, was used to 

calculate equivalent-freshwater head (he):

h=z

dg (1)

where

z is the altitude at the centerline of the rock section,

p is the pressure at the centerline of the rock section,

d is the density of freshwater, and

g is the acceleration due to gravity.
B6 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Pressure values from the drill-stem tests were adjusted to the centerline of the rock section tested. The 

adjustment to the pressure (pa) was calculated using 

the following equation in consistent units:

= df g(z -z) (2)

where

df is the density of the in situ (formation) water

and 

z is the altitude of the pressure gage used for

the drill-stem test.

Density of formation water increases with increasing concentration of dissolved solids and decreases 

with increasing temperature. In shallow wells containing freshwater, the correction for density is 

trivial, and the equivalent-freshwater head is considered 

equal to the altitude of the water level within the well.

Accuracy of the calculated equivalent-freshwater 

head values derived from results of drill-stem tests is 

difficult to evaluate because it is dependent on the 

accuracy of the recording gage, the conditions of the 

test, and the hydraulic character of the rock. Comparison of data from adjoining drill-stem tests in the 

same test hole or adjacent test holes indicates considerable differences. The differences may be due either 

to unknown inaccuracies, as reported in the drillstem test results, or to areal, vertical, or temporal variations, such as the effects of petroleum development.

DETERMINATION OF HYDRAULIC PROPERTIES

POROSITY

Porosity of a water-saturated rock is the ratio of 

its interstices to its total volume (Lohman, 1972, p. 

10). Porosity is an important element in determining 

both the storage coefficient and the hydraulic-conductivity properties of the materials in a geohydrologic 

unit. The relation among porosity, hydraulic conductivity, and other properties are described by 

Jorgensen (1980, p. 12-14). Additionally, the relation 

between effective porosity and permeability (or hydraulic conductivity) is extremely useful, especially in 

areas where porosity data are available but hydraulic-conductivity data are not. Porosity values were 

available throughout most of the study areas. Values 

were obtained from analysis of results from drill-stem 

tests, from laboratory analyses of rock cores of test 

holes, or from analyses of production data from oil or 

gas reservoirs. Measurement of porosity (or permeability) of fractured rock in the laboratory is nearly 

impossible because of the difficulty of obtaining a 

large enough rock sample to provide representative 

values of those properties and of arranging the fractured pieces in the same manner as they were in 

situ. Porosity (and permeability) of "repacked" 

samples of unconsolidated material may be erroneous. Reported porosity values for many oil and gas 

reservoirs are of unknown accuracy and were determined by generally unreported techniques. In situ porosity values can be determined from measurements 

made by wireline-geophysical equipment, specifically 

density (gamma-gamma), neutron, and sonic logs 

(MacCary, 1978, p. 9). Borehole-compensated dual-porosity logs (density and neutron), in combination with lithologic information, can also be used to calculate porosity.

Porosity values for this investigation were determined from borehole-compensated dual-porosity logs. 

These data were used to prepare maps of porosity. 

Log-determined porosity values were considered to be 

more representative of a regional geohydrologic unit 

than values reported from analyses of well data or 

from laboratory measurements of cores because these 

reported values represent local rock characteristics or 

portions of tested sections, not the entire thickness of the 

geohydrologic unit.

A comparison of reported porosity values for specific oil and gas reservoirs with the regionalized (logdetermined) porosity values read from the porosity 

maps was made for different lithologies and for different stratigraphic units. Reported reservoir values 

compared well with the regional values for rock sections that consisted of Jurassic and Lower Cretaceous 

sandstone (fig. 3). The correlation probably reflects a

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POROSITY OBTAINED FROM REGIONAL MAPS, IN PERCENT

FIGURE 3. Comparison of regional and reservoir porosity of 

Jurassic and Lower Cretaceous sandstone.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B7

dominance of primary porosity over secondary porosity, because primary porosity is more isotropic than 

the highly anisotropic fracture porosity.

Reported reservoir porosity values for Pennsylvanian and Permian rocks, Mississippian limestone, 

and Cambrian through Devonian rocks did not correlate well with regionalized porosity values (figs. 4, 5, 

and 6). The poor correlations are attributed partly to 

the effects of the heterogeneous secondary porosity, 

which is due mostly to fracturing and dissolution of 

rock material. Oil and gas reservoirs in a heterogeneous rock section typically have porosity values 

greater than average (Brown, 1985). This is especially true in fractured rocks with substantial secondary porosity. Secondary porosity in fractured 

reservoirs commonly is developed in a thin vertical 

section that usually is of limited lateral extent. Dissolution of rock material generally is local and occurs 

along permeable paths. Therefore, reported porosity 

values for oil and gas reservoirs tend to be site specific and may not be representative of the entire 

hydrostratigraphic section either vertically or areally. 

This is to be expected because most oil and gas reservoirs are anomalous subsurface zones. Another comparison, not shown, indicates a general trend of 

decreasing porosity with depth. This trend is most 

pronounced in sandstone rocks of the study area, 

which generally have predominantly primary 

porosity. The trend is less pronounced in carbonate 

rocks, which generally have predominantly secondary

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POROSITY OBTAINED FROM REGIONAL MAPS, IN PERCENT

FIGURE 4. Comparison of regional and reservoir porosity of 

Pennsylvanian and Permian rocks.

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POROSITY OBTAINED FROM REGIONAL MAPS, IN PERCENT

FIGURE 5. Comparison of regional and reservoir porosity of 

Mississippian limestone.

0 10 20 30 

POROSITY OBTAINED FROM REGIONAL MAPS, IN PERCENT

FIGURE 6. Comparison of regional and reservoir porosity of 

Cambrian through Devonian rocks.
B8 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

porosity. Porosity values of any type or source were not 

available for the deepest rocks in the study area. Estimates of porosity based on the relation of decreasing 

porosity with depth were made to supplement the 

geophysical-log or regionalized porosity values.

HYDRAULIC CONDUCTIVITY AND INTRINSIC PERMEABILITY

Hydraulic conductivity is the primary criterion in 

distinguishing between aquifers and confining units. 

Hydraulic-conductivity data for aquifers containing 

freshwater is obtained from aquifer tests using one 

well or more that completely penetrates a single 

aquifer. Unfortunately, few aquifer tests have been 

conducted in the study area. Hydraulic-conductivity 

data also can be estimated from specific capacity of a 

pumping well. Specific capacity is the ratio of discharge of water per foot of drawdown and is a function of hydraulic conductivity and well efficiency. The 

available specific-capacity data were from wells that 

generally were open to one aquifer or more and did 

not penetrate the complete thickness of the lower 

aquifer. Thus, the available specific-capacity data 

may not provide accurate estimates for an individual 

aquifer. Hydraulic-conductivity values determined 

from aquifer tests or specific-capacity data were 

stored in the GWSI file.

In rocks containing saline water, virtually no 

hydraulic-conductivity data are available. In these areas, permeability data were obtained from analysis of 

the results of drill-stem tests, laboratory analyses of 

cores, or oil-production tests. Intrinsic permeability 

(k) is the measure of the relative ease with which a 

rock or medium can transmit a fluid under a potential gradient, and it is a property of the rock alone. 

Hydraulic conductivity (K) is a measure of the ease of 

flow of water at a specified viscosity through a rock 

or medium. The equation, in consistent units, that relates the hydraulic conductivity and intrinsic permeability is:

kdg

(3)

where

K is hydraulic conductivity,

k is intrinsic permeability,

d is density of the fluid,

g is acceleration due to gravity, and

i> d is the dynamic viscosity of the fluid.

Because nearly all drill-stem tests are conducted in 

localized traps or reservoirs of permeable material, 

intrinsic-permeability values obtained by analysis of 

such tests may be representative of only the permeable sections of the reservoir or trap and may not be

representative of the average regional permeability. 

Similarly, intrinsic-permeability values from cores of 

fractured rock also are difficult to evaluate as to their 

representativeness of effective regional permeability. 

For example, nonfracture intrinsic-permeability values from a 20-ft core of fractured and vuggy 

dolostone removed from a borehole within the study 

area ranged from less than 0.1 mD to more than 

3,000 mD. The intrinsic permeability of the fractures 

in the rock core was not determined because it was 

not possible to represent the fractured rocks in the 

laboratory. Both laboratory tests and drill-stem tests 

generally are conducted on relatively thin rock sections of 20 ft or less, and the tests would not be representative of the thick regional-geohydrologic units.

To overcome these problems of estimating the average regional values, a method was developed to use 

data from wireline-geophysical borehole logs.

The intrinsic-permeability relation used is

k =

Nn

s. (4)

where

e is a rock constant that is determined for each

rock type, 

N is porosity,

m is the cementation factor, and 

S8 is the specific surface area.

The equation is obtairied by combining the Archie 

equations developed for resistivity logs with the 

Kozeny equation of flow through rocks. The equation 

is based on the assumption that intrinsic permeability is a function of a medium or rock factor, the first 

set of terms, and a porosity factor (P), the second set 

of terms.

A plot of the porosity factor versus intrinsic permeability for 10 carefully selected data sets defined the following empirical equation for intrinsic permeability:

k = (1.828 x (5)

Each data set included a porosity value, which was 

determined from a dual-porosity log, a cementation 

factor, which was determined from a cross plot of 

bulk resistivity versus porosity (MacCary, 1978, p. 

18), and a permeability value from an in situ test. 

The equation has a coefficient of determination (r2) of 

0.90. The equation was useful in estimating intrinsic 

permeability of rocks in which electrical conduction 

along grain surfaces was not significant irrespective 

of whether the rock was dominantly a porous medium or a fractured medium.

Intrinsic-permeability values from aquifer and 

specific-capacity tests, along with the calculated
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B9

estimates of permeability values using geophysicallog data and the above equation, were plotted on

maps and contoured to show regionalized permeability.

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ESTIMATED REGIONAL PERMEABILITY, IN FEET SQUARED

FIGURE 7. Comparison of regional and reservoir permeability of

Cambrian and Ordovician dolostone.

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ESTIMATED REGIONAL PERMEABILITY, IN FEET SQUARED

FIGURE 8. Comparison of regional and reservoir permeability of

Regional intrinsic-permeability values from maps

were compared to site-specific intrinsic-permeability

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in figures 7, 8, 9, and 10. The figures do not show a

correlation between regionalized permeability and

site permeability. Differences of two orders of

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ESTIMATED REGIONAL PERMEABILITY, IN FEET SQUARED

FIGURE 9. Comparison of regional and reservoir permeability of

Pennsylvanian and Permian rocks.

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ESTIMATED REGIONAL PERMEABILITY, IN FEET SQUARED

FIGURE 10. Comparison of regional and reservoir permeability of
BIO REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

magnitude are not unusual. It should be remembered 

that site permeability values for oil and gas reservoirs were measured on thin intervals (20 ft or so), 

whereas the regional permeability values calculated 

from geophysical-log data were for thick intervals 

(generally 100 to 1,000 ft). It is concluded that permeability values determined from maps constructed 

on the basis of geophysical-log data represent estimates of regional permeability, whereas permeability 

values reported for oil and gas reservoirs represent 

localized site values.

Regional intrinsic-permeability values from the 

maps were the initial estimates of permeability used 

in a digital model of regional ground-water flow. The 

modeling procedure itself can be used to further refine estimates of intrinsic permeability.

PHYSICAL SETTING

Much of the study area is laterally bounded by the 

Rocky Mountains on the west and the Missouri and 

Mississippi Rivers to the east. The area is part of two 

major physiographic divisions, the Interior Plains and 

the Interior Highlands (Fenneman, 1946). The Interior Plains includes the Great Plains province and 

the Central Lowland. The Interior Highlands includes the Ozark Plateaus and the Ouachita province 

(fig. 11). The Ouachita province includes the Arkansas Valley, which is between the Boston Mountains of 

the Ozark Plateaus and the Ouachita Mountains 

south of the study area.

Land-surface altitude ranges from less than 500 ft 

along the Fall Line between the Mississippi Alluvial 

Plain and the Ozark Plateaus to about 6,000 ft in the 

extreme western part of the study area adjacent to 

the Rocky Mountains (fig. 12). The topography of the 

Ozark Plateaus and most of the Arkansas Valley is 

hilly to rugged, whereas most of the Interior Plains 

area is relatively flat. Much of the Ozark Plateaus 

area is covered by hardwood forest, whereas the 

Plains area is mainly a mixture of grassland and row 

crops.

Climatic characteristics for the central United 

States are shown in figure 13. Average-annual precipitation for 1931-60, which included two major 

droughts (1933-37 and 1952-57), ranged from 12 in. 

in eastern Colorado to more than 40 in. in the Ozark 

Plateaus (Eagleman, 1976, fig. 3). Potential evapotranspiration greatly exceeded precipitation except in 

southern Missouri and northwestern Arkansas for 

this same period (fig. 13). Annual surface-water runoff ranged from 1 in. or less in western Kansas and 

eastern Colorado to more than 25 in. in the Ozark

Plateaus during 1931-60 (Busby, 1966). Annual surface-water runoff during 1951-80 exceeded 27 in. in 

part of the Ozarks (Hedman and others, 1987). Another regional study (Dugan and Peckenpaugh, 1985), 

which evaluated the quantity of water passing the 

root zone and reaching the water table during 1951- 

80, indicated that more than 15 in. per year of water 

was available for recharge in part of the Ozarks 

whereas less than 1 in. was available in western 

Kansas and eastern Colorado (fig. 14).

The eastern part of the study area has abundant 

water resources, especially surface water. Most of the 

western part of the study area is deficient in surface 

water but has substantial ground-water resources, especially the High Plains aquifer, which overlies the 

aquifers described in this report and has been studied previously (Gutentag and others, 1984).

ACKNOWLEDGMENTS

The plan for this investigation was developed with 

the assistance of the Arkansas Geological Commission, the Colorado Geological Survey, the Kansas 

Geological Survey, the Missouri Division of Geology 

and Land Survey, the Nebraska Conservation and 

Survey Division, the South Dakota Geological Survey, 

and the Oklahoma Geological Survey.

The study was greatly aided by a Liaison Committee between State agencies and the U.S. Geological 

Survey. The Liaison Committee not only disseminated information concerning the study to State 

agencies but also helped identify sources of data, defined areas of concern, and made valuable suggestions that aided the study. Committee members 

included: Orville Wise, Arkansas Geological Commission; Robert Longenbaugh, Office of Colorado State 

Engineer; William Hambleton, Kansas Geological 

Survey; Donald Miller, Missouri Division of Geology 

and Land Survey; Verlon Vrana, Nebraska Natural 

Resources Commission; and Robert Arndt, Oklahoma 

Geological Survey.

The study also was served by a stratigraphy advisory group that included: Orville Wise, Arkansas 

Geological Commission; Richard Pearl, Colorado Geological Survey; P. Alien Macfarlane, Kansas Geological Survey; Thomas Thompson, Missouri Division of 

Geology and Land Survey; Marvin Carlson, Nebraska 

Conservation and Survey Division; and Charles 

Mankin, Oklahoma Geological Survey. This group, 

along with Claire Davidson of the Geologic Names 

Committee of the U.S. Geological Survey, contributed 

significantly to the resolution of problems related to 

stratigraphic correlation and nomenclature.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK Bll

GEOLOGIC AND HYDROLOGIC HISTORY

Although structural deformation is not substantial 

throughout most of the study area, stratigraphic nomenclature differs markedly among States and the 

major structural areas (pi. 1 and fig. 15). Hundreds of 

names have been assigned to rock units within the 

thick stratigraphic interval studied. The stratigraphic 

names listed on plate 1 are believed to be representative of those most commonly used. The chart does not 

note every hiatus (a break in continuity of the rock 

record) but does show the major ones. Presence of a 

particular stratigraphic unit in a particular area, as

indicated by the chart, does not imply the occurrence 

of that unit everywhere in that area. Furthermore, 

many other names and subdivisions have been applied by different investigators in different locations, 

depending on observed or interpreted differences in 

the strata. The geohydrologic units defined in this report (aquifers, aquifer systems, confining units, and 

confining systems) consist of all or part of one or 

more geologic formations.

The study area lies within the stable interior of 

the North American continent. Since Precambrian 

time, most of the study area has undergone relatively 

gentle deformation involving upwarp and downwarp

105° 100' 95°

!

Boundary of studvi

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^COLORADO

QZARF PLATEAUS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

mm mm PHYSIOGRAPHIC-DIVISION BOUNDARY Dashed where approximate 

 PHYSIOGRAPHIC-PROVINCE BOUNDARY Dashed where approximate

 PHYSIOGRAPHIC-SECTION BOUNDARY

FIGURE 11. Physiographic subdivisions (modified from Fenneman, 1946).
B12 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

of the Earth's crust over large areas. Structurally, 

the study area has been dominated by broad basins 

and arches (fig. 15). Accordingly, most folding of sedimentary rocks has been subtle, and few major fault 

zones of regional significance occur. However, along 

the southern and western margins of the study area, 

strong crustal deformation by mountain-building 

forces resulted in intense folding and faulting. The 

lateral change from simple to complex geologic structure was the major factor in defining the southern 

and western boundaries of the study area. The structural change is relatively abrupt in most places but 

transitional in others.

The present areal distribution of major time-stratigraphic units in the Central Midwest study area is

shown in figure 16. Table 1 relates time-stratigraphic 

terminology to geologic time. The geologic cross sections in figure 17 illustrate the general regional continuity of the units; the greatest structural 

deformation is along the southern and western margins of the study area. Faulting (fig. 18) was substantial in these areas and caused large offset of rock 

units. Most faults in the interior of the study area 

have much less offset than the faults along the southern and western margins.

The present hydraulic characteristics, flow systems, and chemistry of the water within the geohydrologic units primarily are the result of past geologic 

and climatic events. However, present climate and 

human activities are now affecting water chemistry

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

- 4000 TOPOGRAPHIC CONTOUR Shows altitude of land surface, in feet. Contour 

interval varies. Datum is sea level

FIGURE 12. Generalized land-surface altitude.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B13

J FMAM J J A S 0 ND 

MONTH

 10 

 24 

200 MILES

200 KILOMETERS

EXPLANATION

CLIMATIC CHARACTERISTICS GRAPHS 

Moisture deficit

Moisture surplus

Potential evapotranspiration

Precipitation

Actual evapotranspiration

LINE OF EQUAL ANNUAL RUNOFF-Interval, in inches, varies 

LINE OF EQUAL ANNUAL PRECIPITATION-Interval 12 inches 

LINE OF EQUAL ANNUAL POTENTIAL EVAPOTRANSPIRATION-Interval 10 inches

FIGURE 13. Climatic characteristics of central United States, 1931-60 (precipitation and evapotranspiration from Eagleman, 1976; runoff from Busby, 1966).
B14 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

and the flow system. A summary of the 

paleohydrology follows and is presented in the context of geologic history with special emphasis on the 

changes and diagenetic processes that caused the 

present hydraulic characteristics, water chemistry, 

and flow systems.

The hydraulic characteristics of nearly all rocks 

are the result of diagenetic conditions of deposition

and structural deformation. In large parts of the 

study area, no hydrologic or hydraulic data exist. 

However, inferred interpretations on the probable hydraulic character of the rock probably can be made by 

relating the rock to its paleohydrologic history. Geology, especially historical geology, is closely related to 

paleohydrology. Thus, a presentation of the 

paleohydrology is subject to the same uncertainties

105' 95° 90"

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

RANGE OF MEAN ANNUAL RECHARGE Values in inches

| [ Less than 0.1 | | 0.5 - 1.0 |^| 5-10

| | 0.1 - 0.25 [ | 1-2 |m 10-15

| | 0.25 - 0.50 [ j 2-5 HI More than 15

RECHARGE AREA WHERE CENTRAL MIDWEST REGIONAL 

AQUIFER-SYSTEM ANALYSIS GEOHYDROLOGIC UNITS 

ARE NOT EXPOSED

FIGURE 14. Estimated annual recharge to exposed Central Midwest RASA geohydrologic units, 1951-80 (from Dugan and

Peckenpaugh, 1985).
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B15

as the geologic history; that is, there is not always 

visible evidence because the evidence has been removed or obliterated. Nevertheless, inferred interpretation of what likely occurred may be made.

Many diagenetic deposition and deformation processes in reference to paleohydrology can be grouped 

into those associated with uplift or those associated 

with burial. The diagenetic processes associated with 

uplift or sea recession, such as nearshore lithification 

both above and below sea level, extensional fracturing resulting from erosional unloading, near-surface 

dissolution, and dolomitization in the mixing zone 

near coastlines, in general tend to increase porosity 

and permeability. Near-surface dissolution and 

weathering usually result in a marked increase in

porosity and permeability. These diagenetic processes 

are termed "uplift" diagenesis herein.

Similarly, those diagenetic processes associated 

with subsidence of basins or rapid burial are termed 

"burial" diagenesis herein. These processes include 

compaction, pressure dissolution, thermal diagenesis 

of organic material, and thermal diagenesis of clay. 

Compaction decreases both porosity and permeability 

and releases pore water. Pressure dissolution dissolves rock material at points of great stress, such as 

grain contacts, and recrystallizes material in areas of 

decreased stress, such as pore space. Thermal diagenesis of organic material produces water, carbon dioxide (CO2), and hydrocarbons. Thermal diagenesis of 

clay generally alters smectite to illite and releases

105

1 MINNESOTA SOUTH DAKOTA

M \ __.- i-i-._. V-t - "- ,

NEBRASKA

Central Nebraska

Wet Mountains 

upMft

Sangre _

deCristo\Raton

 . .__. uplift \basm

Hugoton 

embayment

f\ \Arkoma basin

AmarMlo uplift ^. WMq

TEXAS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

EXTENT OF STRUCTURAL FEATURE

FIGURE 15. Major structural features (modified from Carlson, 1963; Merriam, 1963; Oetking and others, 1966, 1967; Bennison and Chenoweth, no date; Renfro, no date).
B16 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

90°

200 KILOMETERS

EXPLANATION

A'

QUATERNARY DEPOSITS

TERTIARY DEPOSITS

MESOZOIC ROCKS Cretaceous, Jurassic, and Triassic age

UPPER PALEOZOIC ROCKS Permian, Pennsylvanian, and Mississippian age

MIDDLE PALEOZOIC ROCKS Devonian and Silurian age

LOWER PALEOZOIC ROCKS Ordovician and Cambrian age

PRECAMBRIAN ROCKS

TRACE OF SECTION Shown in figure 17 

CONTACT

FIGURE 16. Regional geology of central United States (modified from Klnney, 1966).
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B17

TABLE 1. Major geochronologic and chronostratigraphic units

Subdivisions in use by the U.S. Geological Survey (map symbols)

Eon or 

Eonothem

Phanerozoic

Proterozoic 

(E)

Archean 

(A)

Era or 

Erathem

Cenozoic

(Gz)

Mesozoic 

(Mz)

Paleozoic 

(ft)

.ate Proterozoic 

IZ)

Middle 

Proterozoic 

(Y)

Early 

Proterozoic 

(X)

Late Archean

(W>

Middle Archean 

(V)

Early Archean 

IU)

Period, System, 

Subperiod. Subsystem

Quaternary 

(Q)

Neogene 

Subperiod or 

Subsystem (N)

Tertiary 

(T) Paleogene 

Subperiod or 

Subsystem (ft)

Cretaceous 

(K)

Jurassic 

(J)

Triassic 

CR)

Permian 

(P)

Pennsylvanian

r, . -, "P* Carboniferous

(C) Mississippian 

(M)

Devonian 

(D)

Silurian 

(S)

Ordovician 

(0)

Cambrian 

( )

Epoch or Series

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late

Early

Late

Middle

Early

Late

Middle

Early

Late

Early

Late

Middle

Early

Late

Early

Late

Middle

Early

Late

Middle

Early

Late

Middle

Early

Late

Middle

Early

Upper

Lower

Upper

Middle

Lower

Upper

Middle

Lower

Upper

Lower

Upper

Middle

Lower

Upper

Lower

Upper

Middle

Lower

Upper

Middle

Lower

Upper

Middle

Lower

Upper

Middle

Lower

None defined

Late (Y3 )

Middle (Y2 )

Early (Y1 )

Late (X3)

Middle (X2 )

Early (X1 )

None defined

None defined

None defined

pre-Archean (pA)3

Age estimates 

of boundaries 

(Ma) 1

-0.010

I

CC /1 C_1 Q\

5

1 A Q C -3\

55 (54 56)

CC /CO CC\

-96 (95-97)

-138 (135-141)

-205 (200-215)

O A f\

zyu (zyu oUoj

-~330

tJ\J\J \*V&*J tj l\JI

-~570 2

yuu

-1400

Z. IUU

''Ranges reflect uncertainties of isotopic and biostratigraphic age assignments Age boundaries not closely bracketed by 

existing data shown by ~.

2Rocks older than 570 Ma also called Precambrian (p ), a time term without specific rank, 

informal time term without specific rank.
B18 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

water. Burial diagenesis generally reduces primary 

porosity and permeability but can selectively increase 

porosity and permeability through dissolution by 

CO2-rich water.

FEET A O 2 

Zone of J <

10,000 i

5,000 

SEA 

LEVEL 

5.000 

10,000

complex O 

geology

/ \ ^^ Quaternary and Tertiary deposits

C/3 CC

< D

« O

U3 

C/5

FEET 

5,000

B

10,000 

1 5,000 

20,000 

25,000 

30.000 

35,000-

i 2

*

o

Zone of

complex Quaternary and

geology Tertiarydeposits Mesozoic rocks

B'

VERTICAL SCALE GREATLY EXAGGERATED 

0 100 200 300 MILES

0 100 200 300 400 KILOMETERS

EXPLANATION

FAULT Arrows show direction of movement

FIGURE 17. Generalized geologic sections across study area; trace 

of sections shown in figure 16.

SYSTEMS OF THE PRECAMBRIAN

Little is known about the important hydrologic 

events during the Precambrian. Most of what is 

known is inferred from the Precambrian-rock record. 

Precambrian rocks, which underlie the stratigraphic 

section of interest to this study (pis. 1, 2), consist 

mainly of crystalline igneous and metamorphic rocks 

of various types that together form a basement complex. Deep burial of these rocks at most locations has 

precluded detailed knowledge of their nature.

Information concerning faults and fractures in the 

Precambrian rocks is of special importance because 

the faults mark weak zones that were sometimes reactivated during later geologic time. The orientation 

of fractures, faults, and anticlines also is an indication of the direction and magnitude of the tectonic 

stresses that acted on the rocks. Fractures are the 

major pathways for ground-water flow in well-indurated rocks.

Many large faults in the study area are oriented to 

the northeast (fig. 18) and were formed during Precambrian time. This alignment parallels the alignment of the Colorado lineament (Warner, 1980), the 

Transcontinental arch (fig. 19), and the boundary between metamorphic and igneous Precambrian rocks 

in the region (Warner, 1980, p. 14; Sims, 1985). The 

dominant alignment of lineaments of the Precambrian basement in the northern midcontinent, as 

mapped by Sims (1985) and Hayes (1962), is N. 50° 

W. and approximately orthogonal.

Dake (1930, p. 194) stated that rhyolite, lava, and 

ash, along with granite, granite porphyry, and basic 

dikes formed a large land mass in the Ozark area 

during the Precambrian. He further stated that the 

land mass, which was almost 2,000 ft in altitude, was 

deeply eroded and faulted by Cambrian time. Precambrian faulting also is reported by Bridge (1930, p. 

135). El-Etr (1967, p. 1) reported the greatest density 

of lineaments is associated with the St. Francois 

Mountains. The core of the St. Francois Mountains is 

reported to be an epizonal granite batholith emplaced 

1,500 million years ago and is part of a broad belt of 

silicic igneous rocks of similar age that extends in the 

subsurface at least from Michigan through Oklahoma 

(Sides, 1978, p. 2).

Steeples (1982) and Yarger (1982) believe, on the 

basis of magnetic, seismic, and drilling investigations, 

that block faulting and possible dike intrusions, 

which normally are associated with continental rifting, exist along the central North American geophysical anomaly. The anomaly is about 50 mi west of and 

trends parallel to the Nemaha uplift, which extends 

from Nebraska through Kansas and into Oklahoma 

(fig. 15).
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B19

In northeastern Oklahoma, Dennison (1981, p. 26) 

outlines a series of parallel synclines and anticlines 

about 40 mi apart, trending N. 70° E. Also, the 

Labette fault in southeastern Kansas (not shown 

and the ancestral Nemaha uplift are identified as 

Precambrian structures. A Precambrian basin may 

have existed in Oklahoma. Recent seismic investigations indicate that more than 20,000 ft of Precambrian sedimentary rocks may underlie the Wichita 

Mountains (Brewer, 1982, fig. 26). A Precambrian rift 

is believed to have existed below the present 

Ouachita Mountains (Krueger and Keller, 1986, p. 

686). In addition, the Precambrian rift along the

northern end of the Mississippi embayment (fig. 15) 

is believed to be late Precambrian in age 

(Houseknecht and Matthews, 1985; Schwalb, 1982). 

In the area of the Precambrian basin in southern 

Oklahoma (fig. 19), the oldest sedimentary sequence 

was modified by injection of igneous intrusive rocks 

or was buried beneath volcanic rocks (Chenoweth, 

1968). Rascoe and Adler (1983, p. 982) state:

The origin of the Amarillo-Wichita uplift and the adjacent Anadarko and Ardmore basins were strongly 

influenced by the structural, stratigraphic, and thermal evolution of the southern Oklahoma aulacogen. 

This graben was emplaced on the Precambrian

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 * * * THRUST FAULT Sawteeth on overthrust side 

1 ' ' ' ' ' ' ' NORMAL FAULT Hachures on downthrown side

 CONCEALED FAULT Relative movement not shown

FIGURE 18. Major faults (modified from King, 1968; Sims, 1985; Krueger and Keller, 1986).
B20 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

craton as described by Ham, Denison, and Merritt 

(1964). It measures approximately 100 mi (160 km) 

wide * * * across southern Oklahoma * * *. More 

than 20,000 ft (6,100 m) of graywacke, layered chert, 

spillitic basalt, and rhyolite were deposited in the 

graben during Early and Middle Cambrian time, following which the trough margin in southwestern 

Oklahoma was injected by gabbro and granite to establish a stable block that was the precursor of the 

Amarillo-Wichita uplift.

It is not known if the southern Oklahoma 

aulacogen was a so-called failed arm of the continental rift below the present Ouachita Mountains.

The top of the basement surface represents a major unconformity, resulting from a long period of 

erosion or nondeposition (pi. 3). The permeable broken or weathered rock zone on the basement surface, sometimes termed "granite wash," is included 

in the rocks studied because of its sediment-like 

character. The faulting and fracturing of the competent rocks of the basement complex created anisotropic permeability and established permeable 

paths for ground-water flow.

J ! MINNESOTA

Boundary of stud

Shallow sea 

j(low Prefiambrian tslerids)

St. Francois_

) Littordl zone <'mountains-/^ ^ 

J (shallowicyclic sea: { ^ "XA NN J

Shallow isea 

(sandy i bottom

sand arid clcareous mud)

(erosional surface)

TtHsa 

 mountains

X

Turtle mountains

^v

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA 

SUBSIDENCE

-I- -I- -I- PRECAMBRIAN RIFT Queried where uncertain 

FIGURE 19. Precambrian and Late Cambrian geographic and geologic conditions.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B21

CAMBRIAN SYSTEM

Brown (1978), from an investigation in the northern Great Plains, reported that a wrench-fault tectonic system was active in Cambrian time and 

throughout Paleozoic time. Brown further reported 

that the tilting of blocks affected sedimentary deposition and that the faults themselves may be hydraulic 

barriers. The predominant direction of shear and 

faulting is northeast, with complementary fractures 

trending northwest.

The Precambrian surface, except possibly for one 

small subsiding basin, was exposed and was being 

eroded during Early and Middle Cambrian time. The 

unloading resulted from erosion-created extensional 

jointing. The joints (vertical fractures) were paths for 

water flow.

A cyclic but generally transgressive sea covered 

most, if not all, of the study area during Late Cambrian time. Paleogeographic maps (Scotese and others, 1979, fig. 3) indicate that nearly all the study 

area was near the equator and was covered by a 

shallow sea, except the low-lying Transcontinental 

arch, a lowland in parts of Colorado, New Mexico, 

and Texas and various islands (fig. 19).

Sand was the dominant sediment deposited in the 

shallow sea within the study area (Dott and Batten, 

1976, p. 199). Formations, such as the Reagan Sandstone and equivalent Sawatch Quartzite in central 

Colorado, and the Lamotte Sandstone and the 

equivalent Mount Simon Sandstone east of the study 

area, are predominantly sandstone originating from 

deposition of permeable sand nearshore during the 

Late Cambrian. Detritus from the Ozark uplift is believed to be the source of material for the Lamotte 

Sandstone (Bridge, 1930, p. 136). The Lamotte is a 

basal sand deposited on a surface of moderate relief 

(Merriam, 1963). Small areas, former islands of prePaleozoic basement rock, are found in northwestern 

Arkansas, central Kansas, southeastern Missouri, 

and north-central and northeastern Oklahoma. Each 

successive transgression further eroded and covered 

these areas (Chenoweth, 1968, p. 1675; Walters, 

1946, p. 660).

In the area of the Ozark uplift, cyclic deposits of 

clay, silt, fine sand, and carbonate mud occurred. The 

calcareous sediments now are represented by the 

Bonneterre Dolomite and by the Derby and Doe Run 

Dolomites of the Elvins Group.

Marine sand and calcareous mud were deposited in 

a sea with a salinity and chemical composition similar to that of the present ocean (Habicht, 1979, p. 2). 

During Late Cambrian time, the sand and calcareous 

mud had ample opportunity to lithify to sandstone 

and limestone. Lithification of littoral sediments

occurred when they were nearshore or when they 

were periodically above water level. The entire study 

area, except for a basin in southern Oklahoma (the 

present Anadarko basin), was above sea level at various times during the Late Cambrian. Saline water, 

which had been deposited with the sediments, probably was flushed from the thin mantle of Cambrian 

rocks and the subjacent rocks at all locations above 

sea level. Extensional jointing of the consolidated 

rocks, which resulted from erosional unloading, 

would have created secondary permeability. The increased permeability accelerated the flushing of saline-depositional water from the rocks. At some 

locations, sediments containing saline water were in 

contact with fresh ground water from the land 

masses, and dolomitization would have resulted. 

Ham (1950) reports that Cambrian dolomitic rocks in 

southern Oklahoma are diagenetic in origin.

The present thickness of Cambrian rocks is the result of initial sedimentation and subsequent erosion. 

The maximum thickness of Cambrian rocks is 350 ft 

in Kansas (Merriam, 1963, p. 175), more than 750 ft 

in southeastern Missouri, and more than 1,500 ft in 

southern Oklahoma (Ham, 1950) in the arcuate basin 

that extended from southern Oklahoma to the 

bootheel of Missouri.

ORDOVICIAN SYSTEM

Lower Ordovician rocks, which are predominantly 

dolostone at nearly all locations in the study area, lie 

unconformably on the Upper Cambrian rocks. However, Ross and Tweto (1980) state that in central 

Colorado, the Manitou Dolomite (equivalent to the 

Arbuckle Group) was deposited in a vast supratidal 

and subtidal carbonate mudflat. In northeastern 

Kansas, southeastern Nebraska, and northern Missouri, calcareous sediments also were deposited. Bunker (1981, p. 18) implies that some minor tectonic 

activity occurred along the Nemaha uplift prior to 

Middle Ordovician time. All or nearly all of the area 

of the Ozark uplift, including the St. Francois Mountains, was submerged. Sediments in the uplift area 

were predominantly calcareous mud, with the exception of some permeable sand, such as those that form 

the Gunter Sandstone Member of the Gasconade Dolomite. The bottom deposits in the sea in the area of 

the Ozark uplift were largely algal lime. Algal reefs 

are typical throughout the Gasconade Dolomite. Also, 

calcareous mud in lagoons with restricted circulation 

was dolomitized (Burgess, 1964, p. 47).

The sea advanced and retreated several times during Ordovician time. During periods of retreat, uplift 

diagenesis occurred. Exposed calcareous mud was
B22 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

lithified. Dolomitization and additional weathering 

occurred during the numerous changes in sea level. 

Major periods of retreat are marked by several 

unconformities in the area of the Ozark uplift and in 

the Forest City basin. For example, the Gasconade 

Dolomite and Roubidoux Formation are separated by 

a major unconformity. Permeability developed rapidly 

on exposed limestone and dolostone during the long 

periods of erosion.

In the Ozarks, most Lower Ordovician limestone 

has been replaced by dolomite, such as the Gasconade Dolomite (Borahay, 1973, p. 56). Erosion of some 

of the earliest Ordovician sediments and rocks had 

occurred on the ancestral Nemaha uplift and the 

Cambridge arch by the end of Early Ordovician time 

(Smith and Burchett, 1967).

In southern Oklahoma, an extensive basin rapidly 

formed as evidenced by the approximately 6,000 ft of 

Lower Ordovician sedimentary rocks that are present 

in southern Oklahoma (Adler, 1970, p. 1002). In 

southern Arkansas and eastern Missouri, another 

deep basin also was forming. The limestone layers in 

the basin were losing primary porosity as the result 

of compaction and pressure dissolution, and gaining 

secondary porosity as a result of thermal diagenesis 

of organic material. The subsiding basin with its normal faulting is reported to have been initiated by a 

crustal extension (Brewer, 1982, p. 38).

At the end of the Early Ordovician and the beginning of the Middle Ordovician, the retreat of the sea 

and the Ozark uplift exposed rocks and sediments 

throughout the entire study area except for a subsiding basin in Arkansas and Oklahoma. The duration 

of the erosion, which followed the retreat, varied 

within the study area. Ross and Tweto (1980, p. 51) 

suggest that the hiatus in Colorado may represent 10 

to 35 million years.

Erosion of Paleozoic sediments occurred along the 

flanks of the Transcontinental arch and the Ozark 

uplift, In Kansas, only a veneer of pre-hiatus Paleozoic sedimentary rocks remains along the eastern 

border. However, pre-hiatus rocks remain in Oklahoma and in the present Forest City basin in 

Nebraska.

During the period in which the Ozark uplift was 

formed, extensive uplift diagenesis, including jointing 

and near-surface weathering, occurred. For example, 

exposed Lower Ordovician rocks along the Arbuckle 

uplift in southern Oklahoma have joint sets that are 

parallel and perpendicular to the major Arbuckle 

fold. The joints, which are believed to be a product of 

tectonic activity that created the basin, have provided 

permeable flow paths and have aided aqueous diagenesis since their creation. "The 'Arbuckle limestones' are not as well jointed as the overlying 

Woodford, Chimneyhill, and Viola Formations, which 

are more competent ***" (Decker and Merritt, 1928, 

p. 12). (The Chimneyhill Limestone is part of the 

Hunton Group.) Joints in the Ordovician and Cambrian rocks along the Ozark uplift align about N. 25° 

W. and N. 70° E.

Ground-water flow systems developed in the uplifted areas and flushed the water from Early Ordovician and older rocks. In general, ground water is rich 

in CO2 in recharge areas. The slightly acid water 

typically dissolves the rock matrix, especially calcareous material; porosity and permeability are thus increased. Cementing occurs in discharge areas where 

the water is under reducing conditions; porosity and 

permeability may be decreased in inland discharge 

areas. Regional dolomitization of limestone occurred 

near the coastline in the zone of mixing between the 

inland fresh ground-water flow system and the saline 

depositional water in the rocks below sea level. In 

general, the processes of dolomitization and jointing 

increased secondary porosity and permeability. The 

widespread unconformity, usually a karst at the top 

of the older dolostone and limestone, formed an excellent aquifer and a path for easy ground-water movement. Sediment deposition during subsequent periods 

of transgression during the Middle Ordovician (fig. 

20) covered and preserved the unconformity surfaces. 

Very permeable onlapping sands were preserved. 

These sands are the parent material for the sandstones of the Harding Sandstone west of the study 

area in Colorado and New Mexico (not listed on plate 

1) and the St. Peter Sandstone in the remainder of 

the area. After the period of general transgression, a 

period of relatively stable sea levels ensued during 

which calcareous sediments, represented by the Viola 

Limestone, were deposited on approximately the 

same area as the sand.

In northern Arkansas, the Everton Formation, a 

Middle Ordovician sandstone and limestone, is 

unconformably overlain by the St. Peter Sandstone 

(Croneis, 1930, p. 24). This unconformity indicates 

that the widespread regional hiatus may have occurred within the Middle Ordovician Epoch and not 

at the end of the Early Ordovician Epoch. Possibly, 

the sand of the Everton is detritus from the elliptical 

Ozark uplift. Thickness maps by Caplan (1957) indicate that the Everton Formation in north-central Arkansas thickens to the south, as does the St. Peter 

Sandstone, but at a much greater rate. The thickness 

of the St. Peter and the Everton is about 600 ft at the 

southern boundary of the study area in Arkansas. 

Both formations consist of clean quartzose sand, 

which formed a permeable aquifer immediately after
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B23

deposition. The generally transgressive seas of 

Middle Ordovician time were interrupted by recessions; for example, four unconformities are recognizable in northern Arkansas. The unconformities mark 

the tops of permeable zones created by uplift diagenesis.

Deposition of calcareous mud, clay, and sand was 

continuous during the entire Middle Ordovician in 

the subsiding Oklahoma-Arkansas basin. Burial diagenesis, especially compaction, decreased the porosity of both the clay and sand. Calcareous sediments 

were lithified to limestone by pressure dissolution 

and recrystallization. Assuming a normal geothermal 

gradient, organic material in pre-Middle Ordovician

sediments would have been altered by thermal diagenesis at a slow-to-moderate rate that would have 

resulted in increased secondary porosity and permeability locally. Because the pre-Middle Ordovician 

rocks generally were buried at depths of a few hundred to a few thousand feet, ground-water circulation 

in these rocks was either not extensive or did not exist. Dolomitization of the limestone probably did not 

occur in the basin.

Middle and Upper Ordovician sediments in northwestern Arkansas were marine, shallow-water, biogenie calcite and aragonite mud. These sediments 

were the parent material of the Kimmswick

105° 100

! MINNESOTA

WYOMING 

Lowland 'Boundary of stud

Very shallow sea 

with islands

hatTow sea with . I 

sandy bottom 

KANSAS'^ *

Rapidly subsiding -

Oklahoma-Arkansas

ARKANSAS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 4 UPLIFT

WATER AREA T

SUBSIDENCE

FIGURE 20. Middle Ordovician geographic and geologic conditions.
B24 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Limestone, the Fernvale Limestone, the lower part 

of the Cason Shale, and other formations (Craig, 

1975, p. 61).

The existing rock record of the Late Ordovician is 

confined largely to the present Forest City basin and 

the ancient Oklahoma-Arkansas basin (figs. 15, 20). 

Clay of the Maquoketa, Sylvan, and Cason Shales 

was deposited, as well as calcareous mud. In general, sedimentary deposits were thin even in the 

Oklahoma-Arkansas basin. Dott and Batten (1976, 

p. 229) imply that the study area was astride the 

equator. However, Habicht (1979) shows the area at 

about 25° south of the equator. The Appalachian 

orogeny, east of the study area, may have been the 

source of the elastics present in the eastern part of 

the study area. The submergence of most of the 

study area, which was accompanied by a general encroachment of saline water into the existing fresh 

ground water within the rocks along the transient 

coast, resulted in widespread dolomitization. Thermal diagenesis of organic material, which selectively 

created secondary porosity, continued at a moderate 

rate in southern Oklahoma and at a slow rate in 

Kansas and central Arkansas.

The end of the Ordovician Period was marked by 

regional uplifting, continued development of the 

Oklahoma-Arkansas basin, and intermittent but 

generally transgressive seas. Secondary permeability 

had developed in Cambrian and Ordovician rocks in 

nearly all areas except the basins where burial diagenesis had, in general, decreased primary porosity 

and permeability.

SILURIAN SYSTEM

Little is known about the paleohydrology and geologic history of the study area during Early Silurian 

time. The location of land masses is interpreted 

largely from the limited occurrence of Lower Silurian 

rocks. Early Silurian seas apparently were quite restricted in the study area (fig. 21). The Silurian was 

characterized by uplift that exposed extensive land 

areas. Accordingly, a considerable volume of pre-Silurian rocks was removed by erosion from the study 

area. Jointing, which further increased permeability, 

resulted from erosional unloading. Those rock units 

above sea level were flushed of saltwater by ground 

water of meteoric origin. Extensive mixing of freshwater and saline water occurred in aquifers near the 

coasts, resulting in dolomitization.

Calcareous mud was deposited unconformably on 

Ordovician rocks in the Forest City basin during the 

Early Silurian. In the Oklahoma - Arkansas basin,

the upper part of the Cason Shale and the Brassfield 

Limestone are believed to be Silurian (Wise and 

Caplan, 1979, p. 1). The base of the Silurian in Kansas is characterized by extensively dolomitized oolitic 

limestone (Lee and Merriam, 1954). Thermal diagenesis of organic material, which locally resulted in increased secondary porosity and permeability, 

continued at a slow-to-moderate rate in southern 

Oklahoma and at a very slow rate in the remainder 

of the area during Early Silurian time.

The extent of the Middle Silurian sea is difficult 

to determine because most of the rock record, similar 

to the Lower Silurian, has been eroded. Scotese and 

others (1979, fig. 15) indicate that during the Middle 

Silurian the entire study area was submerged by a 

shallow sea with no large land masses. Permeable 

reef structures are characteristic of Silurian time, 

implying that the paleoequator may not have been 

too distant. Frezon and Glick (1959, p. 184) reported: 

"During Silurian time, the seas advanced over the 

eroded Ordovician rocks and may have covered the 

entire Ozark region." The submergence and marine 

sedimentation would have initiated region-wide 

burial diagenesis.

In the present Anadarko basin, Silurian rocks are 

mostly limestone and dolostone. The dolostone is reported by Amsden (1975, p. 1) to have been formed 

as a penecontemporaneous replacement that took 

place at the depositional interface. In the present 

Forest City and Salina basins, the rock record consists of limestone, which comprises the lower part of 

the Hunton Group. In the Oklahoma-Arkansas basin, the rock record is represented by dolomitic limestone and dolostone, which also are hydrocarbon 

reservoirs (Wise and Caplan, 1979, p. 13).

The study area including the present Anardarko 

basin was completely exposed during part of Late Silurian time. Uplift diagenesis, especially widespread 

surficial and subaerial dissolution along joints, resulted in increased porosity and permeability. The 

thin Lower and Middle Silurian rocks probably were 

flushed repeatedly by fresh meteoric water. Erosion 

exposed Precambrian quartzite and other competent 

basement rocks in central Kansas.

DEVONIAN SYSTEM

The paleogeography for the Early Devonian is 

shown in figure 22. Devonian rocks, which lie 

unconformably on older rocks, are preserved only in 

the deeper parts of the sedimentary basins. During 

the long Silurian Devonian hiatus throughout the 

continental lowland area, saline pore water was
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B25

displaced from rocks at shallow depth or flushed by 

fresh ground water of meteoric origin. Large-scale 

uplift and faulting at the end of the Early Devonian 

in the Ozarks resulted in extensive erosion and beveling of beds (Frezon and Glick, 1959, p. 184; Bush 

and others, 1980, fig. 4). No Middle Devonian rocks 

are present in the southern Oklahoma-Arkansas basin. It is possible, if the region was tilted downward 

to the north, that southern Oklahoma was above sea 

level, thus allowing uplift diagensis of Silurian and 

older rocks.

Initially, during the Late Devonian, the entire 

study area was above sea level, and extensive

erosion occurred. However, during Late Devonian 

time, submergence occurred throughout most of the 

area as the sea again returned and probably covered 

the eastern part of the study area from southeastern 

South Dakota to the Oklahoma and Texas panhandles and most of the Ozark uplift. Colorado, 

western Kansas, and western Nebraska probably 

were not submerged. Most Devonian sediments were 

calcareous mud with locally intercalated permeable 

sand lenses. Algal mounds and coral reefs developed 

in the Forest City basin and along the flanks of the 

Ozark uplift. The coral and other reefs are very permeable. The transgressive sea replaced fresh ground

105'

: MINNESOTA

Littoral zone (shallow SB^; 

mud and,shell

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

FIGURE 21. Early Silurian geographic and geologic conditions.
B26 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

water with seawater in the rocks not eroded during the 

Silurian-Devonian hiatus and probably induced subaerial dissolution of carbonate rocks near coastlines.

At the end of the Devonian Period, or possibly during very Early Mississippian time, transgressing seas 

are believed to have completely submerged the study 

area, exclusive of the Transcontinental arch. Sand 

and silt were deposited nearshore and clay farther 

offshore. For example, more than 500 ft of porous but 

slightly permeable clay were deposited in the rapidly 

subsiding basin in southern Oklahoma. Secondary porosity developed as a product of thermal diagenesis at 

a slow-to-moderate rate in the deeply buried sediments in the basin. Other clay, presently represented 

by the Chattanooga and Woodford Shales, probably 

was deposited offshore in a sea with restricted circulation. However, sand, such as the Sylamore Sandstone Member of the Chattanooga Shale, was 

deposited nearshore and preserved by the advancing sea.

MISSISSIPPIAN SYSTEM

During the earliest part of the Mississippian 

(Kinderhookian, pi. 1), dark clay continued to be deposited in the eastern part of the study area

105'

^\ ARKANSAS 4)

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

FIGURE 22. Early Devonian geographic and geologic conditions.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B27

(Carlson, 1963, p. 10). The clay, which is now represented by the Chattanooga Shale, is reported to have 

been deposited in a restricted circulation sea under 

euxinic conditions (Huffman, 1959; Craig and Varnes, 

1979). The very slightly permeable clay restricted the 

movement of water and other fluids to and from the 

underlying dolostone and sandstone layers. The 

euxinic conditions were modified abruptly by a transgressive sea with normal circulation.

The dominant positive element during Early Mississippian time was the Colorado-Wyoming uplift, 

whereas the dominant negative element was the subsiding Anadarko basin (fig. 23), in which more than

2,000 ft of pre-Chesterian sediment was deposited. 

Initial tectonic movement resulted in the emergence 

of the Nemaha uplift (Steeples, 1982), the ridge that 

separates the Salina basin from the Forest City basin. The extent of the Early Mississippian sea at approximately the time of maximum transgression is 

shown in figure 23 (modified from Craig and Varnes, 

1979). Initial sediments deposited in the transgressive sea are represented by detrital sand deposits in 

Oklahoma, Arkansas, and western Kansas. During 

the remainder of Early Mississippian time, calcareous 

sediments were deposited in the shallow equatorial 

sea.

100°

i MINNESOTA

Shallow- marine 

sediments

NEBRASKA

;'' \

hallow rriarin$ 

sediments \

^~x^n ^

, ^^/%k^

35'

Base modified from U.S. Geological Survey 

1:7,500.000, National Atlas. 1970

EXPLANATION

LAND AREA \ UPLIFT

WATER AREA SUBSIDENCE

FIGURE 23. Early Mississippian geographic and geologic conditions (modified from Craig and Varnes, 1979).
B28 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

The rock record of the Early Mississippian, exclusive of the initial elastics, is represented mostly by a 

cherty limestone. Exceptions are some siliceous 

dolostone in eastern Colorado and a shale in northwestern Arkansas on the north slope of the subsiding 

Arkoma foreland basin (Houseknecht and Matthews, 

1985, p. 337). The present carbonate rocks are mostly 

of biogenic origin and reflect alternating strong and 

weak energy zones in a widespread, clear-water, normal-marine depositional environment (Craig and 

Varnes, 1979, p. 395). In Kansas, Early Mississippian 

rocks are limestone, dolostone, and chert. Porosity 

and permeability of these rocks range from slight to 

moderate, being best developed in vuggy, weathered, 

tripolitic (diatomic) chert, or in crystalline dolostone 

(Brandt, 1967, p. 4). In the Anadarko basin of Oklahoma and Texas, more than 700 ft of Early Mississippian sediments were deposited.

Late Mississippian time (Meramecian and 

Chesterian) was characterized by cyclic but predominantly recessive seas. Uplift diagenesis acted on the 

extensive positive elements, which included the lowlying Transcontinental arch. Tectonic activity created 

uplifts transverse to the Transcontinental arch in Nebraska and Kansas. The dominant negative feature 

was the Arkoma foreland basin (Ouachita trough) 

where more than 5,000 ft of subsidence occurred. The 

Anadarko basin may be an ancillary foreland basin 

related to the subduction of the North American plate 

along a plane of weakness associated with the Precambrian rift that was located beneath the present 

Ouachita Mountains. Less subsidence occurred in the 

Anadarko basin; however, in an area from southwest 

Kansas to south-central Oklahoma more than 2,000 

ft of sediments were deposited. Deposition rates in 

the rapidly subsiding basins were much greater than 

typical. Compaction resulting from the rapid burial 

would have expelled water to vertically adjacent layers.

Biogenic carbonate was the dominant sediment 

throughout most of the area. However, silica that was 

derived from the weathered lowland and from altered 

clay formed chert. In the Anadarko basin, rapid subsidence resulted in Cambrian through Devonian 

rocks being buried to depths of more than 10,000 ft 

and, assuming normal geothermal gradient, heated to 

temperatures of more than 167°F. The burial temperature (and pressure) resulted in compaction and 

the release of water. Water, carbon dioxide, and hydrocarbons were generated by the moderate thermal 

diagenesis of organic material. Burial diagenesis increased secondary porosity by selective dissolution of calcareous material in the deeply buried carbonate rock.

A regional uplift, especially along the Transcontinental arch, and a retreat of the sea occurred at the

end of Mississippian time. A considerable amount of 

the Mississippian rock was removed on the shelf of 

the Transcontinental arch. Only the deeper parts of 

the Anadarko and Arkoma basins remained submerged. Many of the Mississippian deposits were 

eroded by the end of Mississippian time, especially 

over the Nemaha uplift in southeast Nebraska and 

northeast Kansas, on the Cambridge-Central Kansas 

uplift, and in south-central Oklahoma. Uplift diagenesis greatly increased the permeability of the exposed 

rocks, which were mostly Ordovician dolostone, by 

fracturing and dissolution.

In eastern Colorado, uplift of the regional Sierra 

Grande arch caused the sea to retreat in all directions from the center of the State (Maher, 1953, p. 

913). Subaerial erosion and other uplift diagenesis at 

the end of Mississippian time developed an extensive 

karst with abundant sinkholes, caverns, and rubble 

breccia developed in the permeable limestone. A 

residual-clay regolith developed on top of the Mississippian rocks in Colorado (Devoto, 1980a, p. 57).

In the Ozark area of southern Missouri, erosion 

considerably decreased the loading, resulting in extensional jointing. McCracken (1971) reports a dominant joint set at N. 25° W. A regional flow system of 

fresh ground water of meteoric origin developed. Circulation probably extended downward to very slightly 

permeable strata, such as the Chattanooga Shale and 

equivalent, or to about a depth of 1,000 ft in the permeable carbonate rocks.

PENNSYLVANIAN SYSTEM

During the Early Pennsylvanian (Morrowan time), 

a cyclic but generally transgressive sea covered most 

of the permeable erosional surface that had developed 

by the end of the Mississippian. The east-central part 

of the study area either remained stable above sea 

level or was uplifted, whereas subsidence generally 

occurred in a wide arcuate belt along the western and 

southern parts of the study area. Strong compressive 

forces from the north and south developed. The principal directions of compression may be related to the 

collision of the African, the South American, and the 

North American plates. These stresses were relieved 

by thrust faulting, folding, and downwarping in the 

arcuate band. Block faulting occurred in Oklahoma 

along the preexisting Southern Oklahoma graben of 

Early Cambrian age (Edwards and Downey, 1967, p. 3).

Uplifts during Early Pennsylvanian time included 

the Amarillo-Wichita uplift (Frezon and Dixon, 1975, 

p. 182). Rapid uplift and erosion continued along the 

ancestral Front Range and the Apishapa-Sierra
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B29

Grande uplift (Devoto, 1980b, p. 17; see fig. 24). The 

uplift areas along the margins of the study area, in 

general, were easily eroded and provided coarse 

arkosic detrital material. More than 500 ft of socalled granite wash was deposited along the Amarillo 

uplift (Button, 1980, p. 16). The permeable granite 

wash was an aquifer and transmitted freshwater 

downdip to depths of thousands of feet. The lowlands 

interior to the study were, in general, sources of silt, 

clay, and carbonate mud. Gentle flexures developed

in Nebraska, Kansas, and Missouri during the Early 

Pennsylvanian. Faulting occurred and resulted in 

partial or complete dislocation of formations along 

the east flank of the Nemaha uplift. Anticlinal 

folding along the Cambridge arch-Central Kansas 

uplift and the Nemaha uplift continued. Synclinal 

folding resulted in subsidence in the Forest City 

basin, in the Salina basin, and in the Hugoton 

embayment (Prichard, 1975; Stewart, 1975; 

Wanless, 1975).

. VIOWA

Forest City1 >i 

basin \-^~-

Base modified from U.S. Geological Survey 

1:7,500.000. National Atlas, 1970

EXPLANATION

LAND AREA

WATER AREA

UPLIFT

SUBSIDENCE

AREA OF UPLIFT AND FAULTING

FIGURE 24. Middle Pennsylvanian (maximum Desmoinesian sea) geographic and geologic conditions (modified from

McKee and others, 1975, plate 15b).
B30 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Development of the Nemaha uplift and the Cambridge arch-Central Kansas uplift accelerated in response to the rapid tectonic movements during the 

Pennsylvanian (Carlson, 1970; Prichard, 1975; 

Stewart, 1975). Erosion on the Cambridge arch-Central Kansas uplift and the Nemaha uplift, which 

started during the Late Mississippian, removed a 

large quantity of rock in central Kansas and southeastern Nebraska and greatly enhanced permeability 

in the exposed Mississippian, Ordovician, and Cambrian rocks, as well as the exposed Precambrian 

basement rocks. Large-scale and permeable karst 

was developed on and near the erosional surface 

(Walters, 1946, p. 699). Detritus, especially chert 

from the Mississippian rocks, formed a very permeable aquifer on and along the ridges. Fresh ground 

water flushed the marine water from the exposed 

rocks in the positive areas above sea level.

The most rapid subsidence occurred in the 

downwarping Arkoma basin of central Arkansas and 

at a lesser rate in the Anadarko basin. Sedimentation was extremely rapid and kept pace with subsidence. Pre-Pennsylvanian rocks were buried to depths 

of nearly 20,000 ft. The deep burial was accompanied 

by an increase in temperatures to as much as 302°F 

in the Anadarko basin (Waples, 1982, p. 1152). Deep 

burial also occurred in the Arkoma basin. Thermal 

diagenesis of organic material in the deeply buried 

sediments was rapid, resulting in increased porosity 

and permeability in selected strata. During 

Morrowan time, deposition of very slightly permeable sediments occurred at a very rapid rate. If the 

water being squeezed from the compacted sediments 

was unable to dissipate and was trapped with the 

subsided sediments, the temperature of the confined 

water would have increased with burial, and hydrothermal pressuring would have resulted. The nearly 

impermeable overlying sediments would have confined the geopressure zone (pressure greater than 

hydrostatic). Within the zone, porosity increased 

greatly with the hydrothermal pressuring; consequentially the thermal conductivity of the zone was 

decreased and created an insulating blanket over the 

subjacent rocks. A large zone of geopressure in an 

area approximating the area of the Morrowan sediments may be of this origin.

In most of the subsiding basin, except the 

geopressure zone, compaction and other burial diagenesis resulted in nearly complete destruction of 

the already attenuated primary porosity. Joints in 

dolostone layers of the pre-Pennsylvanian rocks, except in the deeper parts of the Anadarko and 

Arkoma basins, probably remained open although 

narrower in width. However, primary porosity and

permeability in limestone layers at depths greater 

than 10,000 ft were mostly eliminated as the limestone was ductile. At these depths, the limestone 

layers restricted vertical movement of fluids, and 

thus became confining units. Thermal diagenesis of 

organic material and smectite at that depth resulted 

in a pressure increase as CO2, water, and hydrocarbons were generated and as clay water was liberated. The CO2-rich water probably escaped vertically 

into adjacent permeable dolostone and sandstone 

layers and locally increased secondary porosity and 

permeability as it selectively dissolved carbonate cement, limestone, and dolostone.

At some locations adjacent to faults in the subsiding basins, granulation, especially in sandstone, decreased primary porosity and permeability. However, 

the actual fault planes may have been permeable avenues that transmitted fluids from strata to strata.

Cyclic but transgressive seas were present during 

most of Middle and Late Pennsylvanian time 

(Merriam, 1963, p. 103; Fagerstrom and Burchett, 

1972, p. 385) and probably covered nearly all of the 

Ozark area (fig. 24). Thus, both marine and 

nonmarine sediments are present. Clay, silt, sand, 

plant material, and shell detritus with calcareous 

mud were deposited. Pennsylvanian sediments are 

important source beds for hydrocarbons in the study 

area (Volk, 1970, p. 673; Bucke, 1969, p. 3). Frezon 

and Dixon (1975, p. 188-189) report:

In Middle and Late Pennsylvanian time uplift and 

intense folding and faulting designated as the 

Ouachita orogeny occurred in eastern Oklahoma 

and Arkansas. During the orogenic period the depositional area that had been the Ouachita geosyncline developed into two new structural elements, 

the Ouachita uplift to the south and the Arkoma basin to the north.

Uplift in the Ouachita region apparently started as 

early as late Morrow *** time; uplift and, later compressive movements continued intermittently into 

Early Permian time. These movements caused folding and faulting in rocks as old as *** (Des Moines) 

and fracturing in rocks as young as Early Permian. 

These structures occur within a broad region that 

includes the east half of Oklahoma.

Overthrust faults * * * may not have developed until later Missouri or even Virgil time. Studies by 

Ham and Wilson (1967, p. 386-387) pointed out that 

some of the compressive forces responsible for the 

overthrust faulting produced strike-slip faulting in 

the Arbuckle Mountains during * * * (Virgil) time.

The compressive forces of later phases of the 

Ouachita orogeny created joint systems and belts of 

en echelon faults in rocks as young as Early Permian in the eastern half of Oklahoma. The joint
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B31

systems radiate outward from the Ouachita region * 

* * and are attributed to compression (Friedman, 

1964, p. 485-486). The en echelon faults *** are regarded by Friedman (1964, p. 486) as 'near surface 

features related to wrench faults at depth' ***.

In unfolded strata in eastern Oklahoma the joints 

that parallel folds of the Ouachita Mountains are 

regarded by Friedman (1964, p. 486) as 'relaxation 

fractures formed upon release of stored elastic 

strain energy.'

Subsidence along existing Ordovician faults was 

rapid in the Anadarko and Arkoma basins. In general, the rate of subsidence decreased rapidly northward out of the basins (Frezon and Dixon, 1975; 

Glick, 1975; Wilson, 1975). Deltas and alluvial fans 

of very permeable coarse-grained detritus, as thick 

as 750 ft, were deposited along the Amarillo uplift in 

Texas (Button, 1980, p. 24). Permeable coarse sand 

also was deposited near the Apishapa-Sierra Grande 

uplift and the Amarillo-Wichita uplift (fig. 24). Clastic sediment grading from sand to silt, to red and 

green continental clay, and finally to black marine 

clay was deposited away from the uplifts toward the 

basins. The coarse material forms the basal material 

of the Fountain Formation (Atokan or Middle Pennsylvanian not listed on plate 1) in central Colorado 

and a Lower-Middle-Upper Pennsylvanian arkose 

facies near uplifts in Oklahoma. These permeable 

sediments allowed limited water movement from 

near surface to the deeper aquifers in underlying 

older rocks (see pi. 2). However, the width of the 

coarse sediments was only a few tens of miles. Away 

from the uplifts, relatively impermeable clay and calcareous mud interbedded with sand were deposited 

in a cyclic pattern. The numerous clay layers formed 

a very effective seal, restricting vertical flow of water 

to and from the underlying Lower Pennsylvanian 

and pre-Pennsylvanian rocks and the permeable layers within the Pennsylvanian rocks.

Further burial in the deep basins resulted in continued rapid thermal diagenesis of pre-Pennsylvanian rocks. Porosity in fractured dolostone was 

selectively enhanced by dissolution. However, in general, the intense burial diagenesis decreased the porosity and permeability of older sediments and rocks. 

Porosity and permeability decreased in pre-Pennsylvanian limestone beds as they became more ductile 

with the increase in depth of burial. Limestone layers that had previously been relatively permeable 

were altered to less permeable confining-unit material at depths greater than about 10,000 ft. At shallower depths, porosity and permeability were 

reduced by pressure dissolution and recrystallization 

as well as compression. Clay layers, such as those 

deposited during Late Devonian and Early Mississippian time, were compacted to shale. Cambrian sandstone layers probably were cemented with pore-filling diagenetic clay.

Burial diagenesis in Arkansas ended with the 

complete development of the Ouachita uplift. The exact height of the uplift is unknown. Seismic data 

presented by Lillie and others (1983) indicate an uplift of about 13,000 ft. A height based on a projected 

anticline closure of 17,000 ft is possible (Glick, 1975, 

p. 172); however, erosion was rapid, and the height 

of the Ouachita Mountains at any time probably was 

much less than 17,000 ft.

By the end of the Pennsylvanian Period, most of 

the outer structural boundaries that control the 

present ground-water flow system were in place. The 

very slightly permeable clay formed an extensive 

confining system from Pennsylvanian time to 

present.

PERMIAN SYSTEM

The Early Permian was a time of decreased tectonic activity as compared with the Middle and Late 

Pennsylvanian. However, the effects of major Pennsylvanian tectonics were still being felt, and readjustment to stresses from the Ouachita orogeny was 

continuing. Sediments derived from Pennsylvanian 

uplifts were being deposited rapidly in the still-subsiding Anadarko basin.

The Early Permian environment is believed to 

have been arid and hot (Holdoway, 1978, p. 37-39), 

and the equator extended across the area (Habicht, 

1979; Scotese and others, 1979). The sea during the 

Early Permian, as during the Late Pennsylvanian, 

was cyclic with alternate recessions and transgressions. Parts or all of eastern South Dakota, eastern 

Nebraska, eastern Kansas, eastern Oklahoma, and 

probably northwestern Arkansas and western Missouri were low-lying coastal plains during most of 

the Early Permian. Thus, sediments and existing 

rocks were exposed many times during the Early 

Permian. Near the coasts, unconsolidated calcareous 

sediments were lithified after exposure.

The eastern boundary of the Early Permian sea, 

as shown in figure 25, is shown in eastern Kansas 

and eastern Oklahoma. This interpretation differs 

somewhat from that of McKee and Oriel (1967, figs. 

4, 5), who show the shoreline about 25 to 75 mi east 

of the present extent of Permian rocks. In central 

Oklahoma, this would have meant that about 5,000 

ft of Permian sediments shown by McKee and 

Oriel (1967, pi. 7) would have wedged out in about 

50 mi, which seems unlikely. Some of the decrease
B32 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

in thickness could be natural onlapping onto the existing uplifted Ozark area. However, if the Ozark uplift had been such a dominant positive element, the 

adjacent or onlapping sediments present today should 

reflect that condition. The rocks today are typically 

nearshore but do not include coarse-grained elastics 

and arkose. The modified interpretation (fig. 25) 

moves the extent of the sea eastward and is more 

consistent with conditions at the end of the Pennsylvanian. The eastern extent of the sea shown in figure 

25 may be typical for the Early Permian and represents one position of the sea in its general recessive 

trend westward. Similarly the extent of evaporites 

was considerably eastward of their present extent 

shown in figure 25.

During Early Permian (early Wolfcampian) time, 

the seaway to the east through the Ozark area was 

most likely closed by regional tilting upward to the 

east. The closing of the seaway restricted circulation 

and probably created conditions favorable for evaporite deposition in the bay in southern Missouri. Accordingly, dense sea brines displaced normal marine 

pore water in the subjacent strata near the flanks of 

the Ozark uplift. However, farther offshore to the 

west and south, greater than hydrostatic pore pressure in the underlying sediments undergoing compaction would have prevented the dense brines from 

sinking downward to great depths in the subsurface 

basin.

By the end of Wolfcampian time, as regional tilting 

continued, a positive element, which sloped away 

from the Ouachita uplift to the apex of the existing 

axis of the Ozark uplift, may have existed. If so, a 

topographically controlled regional ground-water system may have developed with flow northward to the 

Ozark uplift.

Erosional unloading in the eastern part of the 

study area caused additional jointing and increased 

permeability. Erosion decreased the depth and the 

temperature of the buried rocks, thus slowing the 

rate of thermal diagenesis of organic material over 

much of the eastern part of the study area. However, 

the rank of the Pennsylvanian coals along the eastern margin of the Ozark and Ouachita areas is indicative of a large degree of thermal diagenesis of 

organic material. The origin of the apparently 

anomalous heat that caused the diagenesis is unknown. The rank of coal decreases northward from 

anthracite near the Ouachita fold belt to bituminous 

in central Missouri (Hendricks, 1935; Damberger, 

1974). The mineral zones of the Ozark area are Mississippi Valley-type deposits; mostly lead and zinc 

that were deposited by hydrothermal solution(s) in 

permeable zones, such as fractures, joints, and reefs.

Fluid inclusions in the minerals indicate a saline 

source fluid and a depositional temperature of 194 

320 °F (Leach and others, 1985, p. 8). Because the 

temperature of mineralization approximately matches 

the geothermal gradient implied by the rank of the 

coals, it has been speculated that the source of heat 

for thermal diagenesis of coals may have been a mineralized solution that was the source of the lead and 

zinc. Paleomagnetic studies of carbonate rocks by 

Beales and others (1980) and McCabe and others 

(1983) indicate that this occurred during Late Pennsylvanian and Early Permian time.

Tectonic activity in Colorado continued from the 

Pennsylvanian into the Permian (MacLachlan, 1967, 

p. 86). Arkosic sediments, mostly permeable, continued to be deposited along the ancestral Front Range 

uplift and the Apishapa uplift (fig. 25). Sediments 

were deposited in epicontinental marine, marginal, 

and continental environments. Neritic sediments of 

the eastern part of the study area intertongued with 

and overlapped deltaic and alluvial deposits to the 

west (Mudge, 1967, p. 97).

Lower Permian sediments in northeastern New 

Mexico and the Texas and Oklahoma panhandles include permeable detritus from the Sierra Grande, 

Pedernal, and Amarillo uplifts (not shown in fig. 25). 

However, most of the detritus probably originated 

from the positive elements (highlands) to the northwest in Colorado (Dixon, 1967, p. 65).

In Oklahoma, the Anadarko basin continued to 

subside, and the Wichita Mountains continued to be 

uplifted (Chase and others, 1956, p. 36). Detritus 

from the Wichita uplift was the prominent source of 

depositional material. The detritus, derived from Paleozoic limestone, dolostone, and Precambrian granite, was permeable near the uplifts, but permeability 

decreased rapidly basinward. In south-central Oklahoma, about 5,000 ft of sediments of Early Permian 

age accumulated. Burial diagenesis was dominant; 

compaction forced water from the clay into adjacent 

permeable strata. Thermal diagenesis of clay and organic material yielded water, CO2, and hydrocarbons. 

The thickness of Early Permian sediments alone 

would have been great enough to sustain thermal diagenesis at rates from very slow to moderate of all 

pre-Permian rocks. Pre-Pennsylvanian rocks were 

buried beneath Permian sediments, and the thick 

section of Pennsylvanian rocks underwent compaction 

and rapid thermal diagenesis of clay and organic 

material. However, little unaltered organic material 

remained in pre-Pennsylvanian rocks and thus, 

very little additional CO2 was produced and selective enhancement of porosity and permeability was 

minimal.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B33

In Kansas and Nebraska, the shallow sea advanced and retreated in a cyclic manner. In general, 

after each sea recession, some of the exposed sediments were lithified, and exposed rocks and sediments were eroded in other places. During the Early 

Permian, silica gel was deposited along with calcareous sediments; the flint and chert beds of the Chase 

Group are of this origin. Later in the Early Permian,

layers of evaporites, such as halite, were precipitated 

in the euxinic sea; clay was also deposited in layers. 

The extensive very slightly permeable clay layers and 

the nearly impermeable salt and gypsum layers virtually sealed off vertical ground-water flow to prePermian rocks throughout most of the study area 

with the possible exception of flow along faults or 

fractures in areas of major uplift. Permeable coarse

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EVAPORITES

EXPLANATION

LAND AREA 

WATER AREA

i i ' i i PRESENT EXTENT OF LEONARDIAN ROCKS - Hachurcs 

point toward Leonardian rocks

AXIS OF UPLIFT

FIGURE 25. Early Permian (Wolfcampian-Leonardian) geographic and geologic conditions (modified from McKee and

Oriel, 1967).
B34 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

clastic material was deposited adjacent to the Wichita 

and Front Range uplifts; however, basinward the less 

permeable fine-grained sediments were deposited.

Late Permian time was characterized by a cyclic 

but mostly recessive sea as the eastern part of the 

study area continued to be tilted upward. By the end 

of Permian time, marine deposition only occurred in a 

small part of the study area. Extensive uplift, possibly as much as 2,000 ft, occurred along the southern 

part of the Ozark uplift probably during late 

Guadalupian time. This uplift may have caused 

brines of Early Permian age that had infiltrated into 

the rocks on the flanks of the Ozark uplift to move 

westward in the subsurface. Other tectonic activity 

decreased substantially and no other area of rapid 

uplift is known. However, large-scale but gentle flexing did occur. Erosion of the positive elements, which 

produced large quantities of detritus during Early 

Permian time, had beveled most positive features, 

such as the Ouachita Mountains, to such a degree 

that, in general, the topography of the area was almost flat. Evaporitic and other marine sediments of a 

restricted-circulation environment continued to be deposited in the center of the study area. Along the 

southern and southwestern boundaries of the study 

area, both continental and shallow marine sediments 

were deposited. In the eastern part of the study area, 

Lower Permian sediments and older rocks were exposed 

to erosion, and large alluvial plains developed.

By the end of Permian time, more than 20,000 ft of 

Permian and Pennsylvanian sediments had been deposited in the centers of the Anadarko and Arkoma 

basins. Burial diagenesis was active, especially in the 

deeper parts of the basins. In the Anadarko basin hydrothermal pressuring of the Morrowan geopressure 

zone increased with burial. Thermal diagenesis of organic material occurred at a rapid rate in Permian 

and Pennsylvanian rocks; however, thermal diagenesis of organic material in the pre-Pennsylvanian 

rocks probably was nearly complete by the end of the 

Permian. The Upper Permian clay layers formed extensive confining units. The evaporite deposits, especially halite and gypsum, were nearly impermeable. 

The sand layers were transmissive and were aquifers. Collectively, the confining units of clay and 

evaporite deposits severely restricted water flow to 

the underlying permeable Cambrian through Mississippian rocks and formed a confining system. In areas where depth to the evaporite deposits was 

shallow, 1,000 ft or less, such as in the Ozark uplift 

area, subsurface dissolution of evaporite deposits by 

ground water of meteoric origin probably occurred. At 

the end of the Permian, there was little topographic 

relief, and the regional westward flow of ground

water was probably sluggish. Erosion and removal of 

the very slightly permeable Pennsylvanian and possibly Permian rocks along the axis of the Ozark uplift 

would have expanded the ground-water flow system, 

which had started to form during the Early Permian, 

in the Ozark subregion.

TRIASSIC SYSTEM

In general, the Triassic Period was characterized 

by the relaxation of compressive forces that had existed during the Paleozoic. Crustal thinning, which 

resulted in rifting outside the study area, and 

subsidence of the Mississippi embayment started 

during the Triassic.

Deposition during Early Triassic time occurred 

only in northern Colorado and western Nebraska. 

Red clay, calcareous mud, and dolomite were deposited. The sediments are similar to those of Permian 

age, except they do not contain extensive halite and 

anhydrite beds. Conditions were somewhat similar to 

those of the Late Permian; however, the sea was less 

restrictive during Triassic time as compared to the 

Permian. Accordingly, sediments were more typical of 

normal marine-water circulation, and evaporite deposits were only deposited in some limited areas.

The land areas within the study area had little relief and, thus, were not major sources of sediment. 

Ground-water movement in the regional flow systems 

was sluggish. Because neither the magnitude of uplift 

nor the magnitude of subsidence was large, thermal 

diagenesis of organic material and its chain of diagenetic reactions probably continued at about the same 

rate as they had during the Permian.

At the end of Early Triassic time, the sea retreated, the entire study area emerged, and erosion 

ensued. Continental deposits of Middle Triassic age 

are not identifiable within the area. Dissolution of 

the soluble near-surface Permian and Triassic 

evaporite deposits to depths of several hundred feet 

resulted in increased secondary permeability. A limited proportion of the resulting dense brine probably 

infiltrated very slowly into or through the underlying 

confining units. There apparently was no substantial 

uplift in the Ozark area. Erosion along the axis of the 

Ozark uplift exposed older rocks in bands around the 

St. Francois Mountains. Karst with greatly enhanced 

porosity and permeability was developed in the exposed dolostone and limestone. The surficial Pennsylvanian shales marked, in general, the outward limit 

of the freshwater flow because the shale formed an 

extensive confining system restricting circulation of 

the meteoric ground water.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B35

Tectonic activity began again during Late Triassic time when uplift of the highlands of central 

Colorado took place. The highlands eroded rapidly 

and were the principal source of sediment that was 

deposited in the Dockum basin (fig. 26). Some sediment was transmitted into the basin from the lowlands to the east. The increased erosion was in 

part the result of a general climatic change from

the arid Permian to the more humid Triassic overbank mud.

(McGowen and others, 1979, p. 3). However, during 

Triassic time, the climate varied from humid to 

arid. A large lake formed in the Dockum basin, 

whose water level fluctuated with climatic change. 

Accordingly, the deposits in the lake are fluvial, 

deltaic, prodeltaic, and lacustrine in origin, and in 

general, consist mostly of permeable fine-grained 

sand and gravel and less permeable red mud and

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA

WATER AREA

PRESENT AREA OF LATE TRIASSIC ROCKS

? - SUBSIDENCE Queried where uncertain 

FIGURE 26. Late Triassic (maximum sea) geographic and geologic conditions (modified from McKee and others, 1959).
B36 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

JURASSIC SYSTEM

During the Early Jurassic, the entire study area 

was a low plain slightly above sea level. The climate 

was subtropical and ranged from humid to arid. The 

equator was believed to have extended through central Mexico near present-day Mexico City. The area 

south and southeast of the Ouachita uplift continued 

to subside slowly, forming the Mississippi 

embayment.

The sea advanced slightly into the study area during Middle Jurassic time, and continental deposits, 

mostly permeable arkosic sand, were deposited. The 

sand was the parent material for the Entrada Sandstone and similar sandstones. The sand of the 

Entrada is of eolian origin and grades northward into 

a muddy fluvial sand and finally into the marine 

sand of the Sundance Formation in eastern Wyoming, western Nebraska, and western South Dakota 

(Berman and others, 1980, p. 116-117).

The Late Jurassic sea submerged the western part 

of the study area. Variegated clay, silt, sand, and calcareous algal mud of the Morrison Formation were 

deposited in lakes on the flood plains and deltas 

along the coastal lowlands (Berman and others, 1980, 

p. 118). The geographic conditions of the Late Jurassic, including the probable maximum extent of the 

Late Jurassic sea and the approximate extent of the 

present-day Morrison Formation and equivalents, are 

shown in figure 27. The salinity of the sea varied 

from slightly brackish to normal marine.

The regional tilting (uplift of the eastern part of 

the study area) continued. The decrease of load by 

erosion of Permian and Pennsylvanian rocks resulted 

in extensional microfractures that enhanced permeability of the near-surface shale and other rocks. 

Ground water of meteoric origin probably moved 

downward through the fractures and dissolved 

evaporite beds at depths of as much as 1,000 ft. 

Thus, the subsurface extent of the salt beds slowly 

retreated in advance of the retreating extent of the 

outcropping Permian and Pennsylvanian rocks. The 

dissolution of the salt beds in the Permian rocks resulted in collapse of the overlying layers of shale, 

limestone, and sandstone, and further enhanced vertical permeability of the collapsed material. Ground 

water at the dissolution front would have been a 

dense brine, as it was probably saturated with sodium chloride. Some of the brine may have migrated 

downward through the underlying confining shale 

units into the underlying aquifer of Cambrian 

through Mississipian carbonate rocks along the eastern edge of the Ozark uplift. In general, the land surface sloped gently downward from east to west.

Ground-water movement was sluggish except for the 

Ozark flow system; deep regional flow systems did 

not develop.

At the end of Jurassic time, the sea receded until 

the entire study area was above sea level, and the 

Morrison deposits were extensively eroded. During 

the long period that the eastern part of the study 

area was above sea level, the regional ground-water 

flow system of the Ozark Plateaus became well established. Surficial weathering and other processes of 

uplift diagenesis were active. Karst developed on the 

exposed carbonate aquifer material. The outcrop area 

of the aquifers over the Ozark uplift expanded with 

the continued erosion and removal of the Pennsylvanian shale layers.

CRETACEOUS SYSTEM

At the beginning of the Early Cretaceous, the entire study area was above sea level and was undergoing uplift diagenesis. This condition was ended by a 

rapid transgression of the Cretaceous sea from the 

north and from the south. Moderately permeable 

fine-grained sand and intercalated clay were deposited on alluvial plains and in nearshore estuaries by 

a generally advancing sea (Franks, 1975, p. 469). 

Continued advance of the sea moved the shoreline 

southward and eastward, and the very slightly permeable clay, the parent material of the Kiowa Shale 

and equivalents, was deposited offshore. The precise 

location of the eastern extent of the Kiowa sea is not 

known. However, it is likely that the sea covered the 

entire study area, with the exception of part of the 

Siouxana arch and the Ozark uplift (fig. 28). The sea 

filled the rapidly subsiding Mississippi embayment. 

Clay deposition was ended by a general recession of 

the sea, which in part was the result of the regional 

uplift of the eastern part of the study area. The uplift 

of the Pascola arch (not shown in fig. 28), which is in 

the bootheel of Missouri and in western Tennessee 

within the Mississippi embayment, may have taken 

place during Early Cretaceous time (Schwalb, 1982, 

p. 31). It is not known if this uplift was associated 

with the igneous intrusions of plutons that occurred 

along the southeastern study-area boundary in northeast Arkansas and the bootheel of Missouri.

Subsequent to the retreat of the sea, an extensive 

period of erosion ensued, which to a considerable degree leveled the eastern part of the study area and 

removed most of the Cretaceous sediments. The erosion exposed the permeable Cambrian and Ordovician rocks in southeastern South Dakota and 

northeastern Nebraska. Ground-water flow away
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B37

from the Siouxana arch developed and resulted in 

flushing and mixing of freshwater with the ambient 

ground water adjacent to the uplift.

Erosion also exposed the very slightly permeable 

Pennsylvanian and Permian shale in an area from 

southeastern Nebraska to eastern Oklahoma. Again, 

unloading resulted in extensional microfracturing of 

shale layers and jointing of layers of more competent 

rocks. Because the Cretaceous sea is not believed to 

have covered the uplifted Ozark area, erosion there

was uninterrupted and removal of the Pennsylvanian and Permian shale layers resulted in continued 

expansion of the flow system in the Ozark uplift 

area.

A second trend of sea advance followed the erosional period. The generally transgressive sea advanced to the south and east during the later stages 

of the Early Cretaceous and into the Late Cretaceous. The maximum extent of this sea is not 

known, but it is believed to have extended beyond

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

PRESENT AREA OF MORRISON FORMATION 

AND EQUIVALENT ROCKS

--- SUBSIDENCE Dashed where uncertain

FIGURE 27. Late Jurassic geographic and geologic conditions (from McKee and others, 1956).
B38 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

the present limits of the Dakota Sandstone and may 

have exceeded the maximum extent of the sea during the Early Cretaceous, as shown in figure 28. 

Contemporaneously deposited sediments, such as 

those preserved in the Dakota Sandstone and 

equivalents, are likely to change from marine to continental in a traverse from west to east or from 

north to south. Most sediments were moderately permeable sand with some intercalated clay and organic 

material that were deposited on a low-lying coastal 

and deltaic plain. In general, sediments in Kansas, 

Nebraska, and South Dakota represent chemically

resistant detritus, such as quartz and other silicates, 

from reworked rocks to the northeast of the study 

area; sand deposited in eastern Colorado and Wyoming was detritus from the highlands west of the 

study area. The nearshore sand deposits were porous and moderately permeable. Individual sand 

beds were discontinuous on a regional scale, but 

were generally contiguous with each other at some 

locations. Thus, hydraulic continuity existed 

throughout extensive areas. However, because the 

topography was moderate, strong flow systems did 

not develop.

105 95°

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

t

SUBSIDENCE

FIGURE 28. Early Cretaceous (maximum sea) geographic and geologic conditions.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B39

During Late Cretaceous time, burial diagenesis 

was again important. Relatively impermeable marine 

clay (rich in montmorillonite) was deposited offshore 

contemporaneously with nearshore sand and silt. 

These deposits are represented by the marine 

Graneros Shale and Dakota Sandstone (see table 2 

for list of Upper Cretaceous formations). Biogenic carbonate sediment (Greenhorn Limestone) was deposited conformably in a shallow open marine sea on the 

clay (Graneros Shale) as the transgressing sea neared 

its maximum coverage. Thin layers of calcareous and 

noncalcareous clay, parent material of the Carlile 

Shale, were deposited on the calcareous sediment of 

the Greenhorn Limestone in an offshore marine environment as the sea receded (Merewether and 

Cobban, 1981, p. 53) into North Dakota, Wyoming, 

and Montana.

As the recession ended, the sea advanced far to the 

south and east, perhaps to the same extent as the 

sea in which the clay of the Graneros Shale was deposited. The first deposits in the advancing sea were 

nearshore calcareous mud and shell detritus, parent 

material of the Niobrara Chalk. These sediments 

were followed by offshore clay, parent material of the 

Pierre Shale (table 2). The very slightly permeable 

clay restricted water flow to and from the underlying 

permeable sandstone (the Dakota and Cheyenne 

Sandstones). Rapid subsidence began in the Denver 

basin in the western part of the study area, probably 

as a result of compressive forces.

Near the end of the Late Cretaceous, rapid uplifts 

of the Laramide orogeny started (fig. 29). The 

Laramide orogeny is related to the collision of the 

Farallon and North American plates, which resulted 

in east-northeast compression in the study area. 

Many of the uplifts were apparently along previous 

planes of weakness that were associated with uplifts 

during Pennsylvanian time. Tweto (1980) in reference 

to the Laramide orogeny in Colorado, stated, "* * * 

the Precambrian basement had been driven by major 

faults and shear zones since Precambrian time, and 

further fracturing had occurred in the late Paleozoic, 

if not also at other times. Laramide deformation 

was markedly influenced by these preexisting 

features."

Sedimentation rates increased substantially as 

5,000 to 10,000 ft of clay were deposited in the rapidly subsiding Denver basin. The weight of the sediments compacted clay to shale (Pierre Shale) and 

released large quantities of water. The pore pressure 

in the Dakota and Cheyenne Sandstones and the preCretaceous limestones probably increased to more 

than hydrostatic and probably caused increased solution of calcite. The temperature of the rocks also

increased with burial. Thermal diagenesis of organic 

material increased to a slow to moderate rate. A 

study of the organic chemistry of the petroleum in 

the northern Denver basin by Clayton and Swetland 

(1980, p. 1613) indicated that the Carlile Shale, 

Greenhorn Limestone, and Graneros Shale along the 

axis of the basin are the source beds of the oil found 

in the "D and J sands" on the east flank of the basin. 

Thus, lateral migration of hydrocarbon of about 100 

mi has occurred and may have been preceded or accompanied by CO2-rich water, which in turn created 

secondary porosity and permeability by dissolution of 

carbonate material.

Faulting associated with the Laramide orogeny 

formed barriers to recharge in the foothills of the 

Rocky Mountains at some locations (Banta, 1986). 

High-angle faults, upthrown on the foothills side, 

eliminated or displaced outcrops of most pre-Cretaceous rocks along the foothills. In other places, outcrops along the foothills were not displaced, but 

basinward faulting created a barrier to water flow 

from the outcrops to the same rocks in the basin. 

Thus, the same formation may or may not have been 

part of the same aquifer across the fault. At a few 

locations, such as near Boulder and Canon City, Colorado, however, hydraulic connection between the foothill outcrops and the basin was not disrupted.

The hydraulic characteristics of rock material near 

the Laramide uplifts also were modified. For example, it is possible that the permeability of the 

coarse elastics of the Pennsylvanian- and Permianage Fountain Formation in central Colorado was decreased by calcite cementation as the pore pressure 

was decreased with the uplifting.

The sea withdrew northward out of the study area 

before the end of Late Cretaceous time; accordingly, 

the final Cretaceous sediments are continental in origin and lacustrine and fluvial in nature. The withdrawal of the sea initially did not decrease the load 

in the Denver basin and surrounding area because 

detritus eroded from the uplifts was being deposited 

rapidly on the plain above the basin. This alluvial 

sedimentation represents a loading cycle during 

which fluids tend to be pushed outward from the center of the basin. Thus, the CO2-rich fluids in the Denver basin may have moved outward accordingly 

(Ottman, 1984, p. 81). The acidic solution could have 

selectively dissolved carbonate cements and some 

feldspar in part of the Denver basin. However, along 

the southern flank of the basin freshwater mixed 

with the basinal water being moved updip. The mixed 

water probably was not saturated with silica, thus allowing dissolution of carbonate cements by CO2-rich 

solutions without back-cementing of silica.
B40 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

TERTIARY AND QUATERNARY SYSTEMS

The second major pulse of the Laramide orogeny 

occurred during Tertiary time, as evidenced by mountain building in central Colorado and Wyoming and 

in western South Dakota (fig. 29A). Extensive erosion 

of uplifts and widespread deposition of thick alluvium 

on the plains followed. The most extensive deposits 

were water-bearing sand and gravel, which were the 

parent materials of the Ogallala Formation (table 2). 

The maximum extent and the maximum thickness of

the original deposits are not known. These deposits 

probably extended from the Front Range to eastern 

South Dakota, eastern Nebraska, central Kansas, 

and central Oklahoma.

With time, the mountain building slowed and erosion of the existing alluvial material exceeded deposition of new elastics from the uplifts. Estimates of the 

thickness of Cenozoic material removed are as much 

as 2,000 ft. The present water-bearing Ogallala 

Formation (fig. 29A) is an erosional remnant of a much 

more extensive deposit. (Presently, the thickness of

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

MOUNTAINS OF LARAMIDE OROGENY 

PRESENT EXTENT OF OGALLALA FORMATION 

- APPROXIMATE MAXIMUM EXTENT OF CONTINENTAL GLACIATION

FIGURE 29. Present conditions in study area. A, Mountains of Laramide orogeny, and extent of Ogallala Formation and 

glaciation. B, Estimated relative permeability distribution based on paleohydrology in Cambrian- and Ordovician-age 

rocks.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B41

the Ogallala ranges from near zero to 1,000 ft, and 

100 to 200 ft is typical.) The Ogallala is directly underlain by Cretaceous and older rocks, except in 

west-central Nebraska, where it overlies older undifferentiated Tertiary material (Weeks and Gutentag, 

1981).

The unloading by the erosion of the Cenozoic sediments over the Denver and Anadarko basins has resulted in expansion of the rock mass and a decrease 

of pore pressure, thus ending the outward movement 

of water in the Denver basin and initiating an

inward movement of water toward the center of the 

basin as the pore pressure in the formations became 

less than hydrostatic. The rate of generation of CO2 

from diagenesis of organic material would have decreased. With the spending of the CO2-rich solution, 

increase of the pH, and the decrease in pressure, carbonate cement may have been precipitated.

Several regional ground-water flow systems were 

established by the end of the Laramide orogeny. Permeable zones, in the Cretaceous-age Dakota and 

Cheyenne Sandstones as well as in the Cambrian

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

PERMEABILITY Number is relative permeability: 

1 is most permeable, 5 is least permeable

i i I I EXTENT OF CAMBRIAN AND ORDOVICIAN ROCKS

B

FIGURE 29. Continued.
B42 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

(fig. 29.B) through Mississippian rocks, transmitted 

water very slowly in a general west-to-east direction, 

initiating the present flow systems in the Maha and 

Apishapa aquifers of the Great Plains aquifer system 

in the Cretaceous sandstones and the Western Interior Plains aquifer system in the MississippianCambrian rocks.

At the end of Tertiary time, the sea retreated to 

the Williston basin in North Dakota and south of the 

Ouachita folded area in Arkansas and southeastern 

Oklahoma. Extensive forests grew in the subtropical 

climate. The equator may have been located along a 

line from southern Texas to southern Florida. Organic material was abundant, and drainage patterns 

similar to the present were established.

The Quaternary Period was marked by episodes of 

extensive glaciation that were interspersed with 

much warmer interglacial periods. Although continental glaciation directly affected only the northeastern part of the study area (fig. 29A), the climatic 

changes affected the entire study area. The advance 

and retreat of the glaciers were accompanied by a 

lowering and raising of sea level. A change in sea 

level directly affects the water table and also the 

base level of erosion. These changes altered pore 

pressure in the subsurface. The glaciers also altered 

the regional topography and the ground-water flow 

paths. The cyclic loading and unloading by the ice affected stress distribution and probably caused some 

additional fracturing of competent rock. The 

unglaciated area within the area of study underwent 

erosion and associated diagenetic changes.

GEOHYDROLOGY

CLASSIFICATION OF SUBSURFACE HYDROLOGIC 

UNITS

A regional aquifer system can have more than one 

aquifer or confining unit. An aquifer or aquifer system may consist of several formations, one formation, 

or part of a formation. The property that distinguishes a confining unit is its leakance, which is its 

effective hydraulic conductivity divided by its thickness. From a regional perspective, an aquifer may 

contain a series of discontinuous confining units; 

however, the size of the discontinuous confining units 

is much smaller than the size of the delineated aquifer. In contrast, a confining unit may also contain 

discontinuous permeable zones. Again, the size of the 

permeable zones is much smaller than the size of the 

confining unit. For these reasons, the authors prefer 

to use geohydrologic units rather than hydrostratigraphic units to designate the subsurface 

hydrologic units.

In the hydrologic analysis of large regions, which 

contain many geohydrologic units, it is useful to 

group units into geohydrologic systems, such as an 

aquifer system or a confining system. An aquifer system consists of two or more aquifers in the same hydraulic system, which are separated at most locations 

by one or more confining units. A confining system 

contains two or more confining units separated at 

most locations by one or more aquifers that are not in 

the same hydraulic system.

GEOHYDROLOGIC UNITS

Geohydrologic units within the study area were defined by hydrologic relations and hydraulic properties 

of the rocks. The relation of the geohydrologic unit to 

ground-water flow is essential in conceptualization of 

regional aquifer systems. The flow within most regional aquifers, in general, is controlled by the altitudes of major recharge areas, major discharge areas, 

and major structural features. Thus, topography provides the major control for most regional aquifer 

systems.

The initial step in the delineation of the geohydrologic units was to identify water-bearing strata that 

contained freshwater. The term "water-bearing" indicates that the strata transmits and yields water and 

implies permeability. However, in most of the study 

area, little information was available as to either the 

hydraulic properties of the rock units or the hydrologic relations among them. In areas lacking hydraulic and hydrologic information, the permeability was 

inferred from lithology. For example, rock sections 

that included thick beds of shale or evaporite deposits 

separated by smaller sandstone or limestone layers 

were assumed to be confining units because the shale 

and evaporite deposits generally have very slight 

permeability.

The geohydrologic units within the study area, except adjacent to major structural uplifts, such as the 

Rocky Mountains, the Amarillo, Wichita, Arbuckle, 

and Ouachita uplifts, and other areas of complex 

stratigraphic relations, coincide or correlate to a considerable degree with the regional stratigraphic 

units. The major exception is along the physiographic 

boundary between the Interior Plains and the Interior Highlands (fig. 11). At this boundary, two regional ground-water flow systems are laterally 

adjacent. In general, the ground-water flow system 

that originates in the Ozark Plateaus extends outward until it meets the ground-water flow system
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B43

that underlies most of the western part of the Interior Plains. The approximate location of the boundary 

between these two flow systems is marked by a low. 

in the equivalent-freshwater head surface (fig. 30), 

which is nearly coincidental with a topographic low 

in eastern Kansas and northeastern Oklahoma (fig. 

12). The topographic low is a discharge area to both 

flow systems (fig. 31). The boundary parallels the 

physiographic boundary of the Central Lowland 

province in the Interior Plains.

The extent of the flow systems in most areas also 

is apparent from the map of the dissolved-solids

concentration (fig. 32). The Interior Highlands, except 

south of the Boston Mountains, has water with less 

than 1,000 mg/L (milligrams per liter) dissolved solids. For convenience, the two subregions of this regional analysis are referred to herein as simply the 

Plains subregion and the Ozark subregion. The geohydrologic units in the two subregions are described 

separately.

The lowermost confining unit in both the Plains 

and Ozark subregions is the basement confining unit. 

The basement confining unit is composed mostly of 

crystalline rocks. The rocks may be fractured and

100° 95° 90°

35C

100

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

EXTENT OF CAMBRIAN AND ORDOVICIAN ROCKS

-600 LINE OF EQUIVALENT-FRESHWATER HEAD Shows approximate 

altitude ofequivalent-freshwater head. Interval, in feet, varies. 

Datum is sea level

FIGURE 30. Predevelopment equivalent-freshwater head in Cambrian and Ordovician rocks.
B44 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

yield water at some locations, such as in the Denver 

basin and in southeastern South Dakota, but on a regional basis the basement unit is assumed to form 

the base of the regional flow system. The top of the 

basement unit varies from more than 34,000 ft below 

sea level in central Oklahoma to more than 1,000 ft 

above sea level in the St. Francois Mountains of the 

Ozarks to about 500 ft above sea level in southeastern South Dakota to more than 7,000 ft below sea 

level in the Denver basin along the Rocky Mountains 

in east-central Colorado (pis. 2, 3).

PLAINS SUBREGION

The Plains subregion contains six major regional 

geohydrologic units of which the Western Interior 

Plains aquifer system, the Western Interior Plains 

confining system, and the Great Plains aquifer system, were studied in detail (fig. 33, table 2, pi. 2). 

The Great Plains confining system was not studied in 

detail, and the High Plains aquifer was studied as a 

separate regional aquifer system (fig. 2).

WESTERN INTERIOR PLAINS AQUIFER SYSTEM

The Western Interior Plains aquifer system consists of water-bearing dolostone, limestone, and shale 

that directly overlie the basement confining unit in 

the western part of the Interior Plains physiographic 

division (pi. 2). The major stratigraphic units

WEST

included in the system are listed in table 2. A geologic formation within the aquifer system may be an 

aquifer in one part of the area and a confining unit in 

other parts. The Western Interior Plains aquifer system includes the lower units, a confining unit, and an 

upper unit (table 2). Equivalent-freshwater heads 

and water-chemistry data (figs. 30, 32) indicate that 

the lower units and the upper unit are part of the 

same flow system.

The lower units of the Western Interior Plains 

aquifer system, at most locations, consist of aquifers 

of water-bearing dolostone, limestone, and sandstone 

of Cambrian and Ordovician age, which include confining units of very slightly permeable shale or 

limestone at depths greater than 10,000 ft. These 

lower units of the aquifer system are separated at 

many locations from the overlying upper unit by a 

relatively thin confining unit composed of very 

slightly permeable shale, such as the Chattanooga 

and Woodford Shales. The upper unit of the aquifer 

system is an aquifer composed of permeable limestone of upper Devonian and Mississippian rocks.

Flow in the aquifer system is regionally (but not 

necessarily locally) from north-central Nebraska 

southeastward and otherwise from west to east toward a broad physiographic low (fig. 31). Discharge 

in the broad low area generally is upward to streams 

or to the near-surface water table. Two conspicuous 

discharge areas exist. The first is in Saline County, 

Missouri, where several salinewater springs are

EAST

o

U

-Zone of complex geology. Geohydrologic 

relations have not been defined with 

certainty and thus are not shown

ansition zone between 

flow systems

NOT TO SCALE

EXPLANATION

 > DIRECTION OF GROUND-WATER FLOW

FIGURE 31. Major regional geohydrologic units in the Plains and Ozark subregions. Section 

extends from central Colorado to St. Francois Mountains in southeastern Missouri.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B45

present. The second is in Henry County, Missouri, 

where salinewater discharges upward in low areas 

near the Osage River.

In northwestern Nebraska, the lower units of the 

Western Interior Plains aquifer system are separated 

laterally from similar permeable carbonate rocks in 

South Dakota and Wyoming by the Siouxana arch 

and the Chadron arch. At many locations along the 

western and southern boundaries of the study area

and near uplifts, such as the Front Range, Amarillo, 

Wichita, and Ouachita, complex faulting has disrupted the strata. At these locations, the hydraulic 

relations among specific strata are complex and generally unknown, and the aquifers cannot be described 

easily in terms of regional geologic formations. However, the hydrologic continuity of the geohydrologic 

system is implied by the continuous nature of the 

generalized map of equivalent-freshwater head (fig. 30).

105° 100° 95° 90°

40'

35C

WYOMING I '.j / XJ9HK£(J^TA

iW s ] \

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970 EXPLANATION

DISSOLVED-SOLIDS CONCENTRATION Values in milligrams per liter

0-1,000 100,000-200,000

1,000-20,000 

20,000 - 100,000

More than 200,000

 SO LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION Dashed where 

approximate. Interval, in thousands of milligrams per liter, varies

| | | | i APPROXIMATE EXTENT OF CAMBRIAN AND ORDOVICIAN ROCKS 

FIGURE 32. Dissolved-solids concentrations in water from Cambrian and Ordovician rocks (preliminary).
B46 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

The altitude of the top of lower aquifer units of the 

aquifer system is shown on plate 4. The altitude of 

the shale confining unit that separates the upper 

unit from the lower units is shown on plate 5. The 

altitude of the top of the upper aquifer unit of the 

Western Interior Plains aquifer system is shown on 

plate 6. All units of the system generally slope downward from the Missouri River and the Ozark uplift 

toward the Denver, Anadarko, and Arkoma basins, 

except along the Rocky Mountains. The thickest

sections of the aquifer system are in the Anadarko 

and Arkoma basins (pi. 7). These areas are where 

maximum deposition occurred. Additionally, these 

rocks have been protected, for the most part, from 

erosion since their deposition. Thus, uplift diagenetic 

processes, which generally are associated with uplift 

and erosion and result in large increases in permeability, have not acted in these areas. Accordingly, 

stratigraphic units in these deep areas are considerably less permeable than the same stratigraphic

105° 100

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

APPROXIMATE EXTENT OF MAJOR AQUIFER SYSTEMS 

\''/*//\( Great Plains aquifer system

Western Interior Plains aquifer system 

c^wvJyl Ozark Plateaus aquifer system

 APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 33. Extent of major aquifer systems.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK 

TABLE 2. Generalized correlation of stratigraphic units to geohydrologic units in most of the Plains subregion

B47

Geohydrologic unit

High Plains aquifer

Great Plains 

confining 

system

Great 

Plains 

aquifer 

system

Maha 

aquifer

Apishapa 

confining unit

Apishapa 

aquifer

Western 

Interior 

Plains 

confining 

system

Western 

Interior 

Plains 

aquifer 

system

Upper unit

Confining 

unit

Lower units

Basement confining unit

Principal stratigraphic unit(s)

Ogallala Formation and unconsolidated deposits

Pierre Shale, Niobrara Formation, Carlile Shale, 

Greenhorn Limestone, Graneros Shale (includes Lower 

Cretaceous)

Dakota Sandstone, "D" sandstone, "J" sandstone, and 

equivalent of Newcastle Sandstone

Kiowa Shale and equivalent of Skull Creek Shale

Cheyenne Sandstone and equivalent of Fall River and 

Lakota Sandstones

Morrison Formation, Sundance Formation, Entrada 

Sandstone, Dockum Formation, Elk City Sandstone, 

Doxey Shale, Big Basin Sandstone, Cloud Chief 

Formation, Day Creek Dolomite, Whitehorse 

Sandstone, Nippewalla Group, Sumner Group, Chase 

Group, Council Grove Group, Admire Group, 

Wabaunsee Group, Shawnee Group, Douglas Group, 

Lansing Group, Kansas City Group, Pleasanton Group, 

Marmaton Group, Cherokee Group, Atokan rocks, 

Morrowan rocks, and Springer Group

Meramecian, Osagean, and Kinderhookian rocks

Chattanooga and Woodford Shales

Hunton Group, Sylvan Shale, equivalent of Galena 

Dolomite, Viola Limestone, Simpson Group, Arbuckle 

Group, and Reagan Group

Mostly igneous and metamorphic rocks

Time-stratigraphic unit

Quaternary and Tertiary

Upper Cretaceous

Lower Cretaceous

Jurassic 

through 

Upper 

Mississippian 

(Chesterian)

Upper 

Mississippian 

through 

Upper 

Cambrian

Cambrian and Precambrian

formations in other areas that had undergone uplift 

diagenesis. For example, the dolostone and limestone 

in and adjacent to the Ozark uplift and the 

Cambridge arch-Central Kansas uplift and the 

Nemaha uplift in southeastern Nebraska and northeastern Kansas are fractured, have solution cavities, 

and are very permeable because they have undergone 

uplift diagenesis and surficial weathering for several 

extensive periods.

Regionalized intrinsic-permeability values for the 

lower aquifer units of the Western Interior Plains 

aquifer system are shown in figure 34, and values for 

the upper aquifer unit are shown in figure 35. The permeability estimates were made from borehole geophysical logs according to methods described previously.

The estimates of the intrinsic permeability for the 

lower units (fig. 34) vary from about IxlO"11 ft2 in 

eastern Kansas and western Missouri to about IxlO"17 

ft2 in the Anadarko basin in Oklahoma and to about 

IxlO"18 ft2 in the Denver basin. The intrinsicpermeability values shown in figures 34 and 35 are 

the thickness-weighted mean horizontal-permeability

values of the entire section. These vahies should be 

considered preliminary because they are to be used 

as initial estimates for computer simulation of the 

geohydrologic system. (The computer simulation will 

be discussed in chapter C of USGS Professional 

Paper 1414.) Intrinsic-permeability values clearly are 

affected by depth, as is indicated by the permeability 

values in the Arkoma, Anadarko, and Denver basins. 

In general, values of intrinsic permeability less than 

IxlO"15 ft2 are considered typical of confining units, 

not of aquifer material. The very slight permeability 

of the Western Interior Plains aquifer system is evidenced by the large equivalent-freshwater head in 

part of the Anadarko basin (fig. 30). Pressure from 

the overlying geopressure zone in the Morrowan sediments is attenuated downward into the aquifer system. However, because permeability in the aquifer 

system is so slight, the pressure is not dissipated rapidly by lateral flow. Ground water moves very slowly 

in the Western Interior Plains aquifer system because 

in most of the area the intrinsic permeability is very 

small and the hydraulic gradient is very slight. Small
B48 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

recharge through the overlying Western Interior Plains 

confining system probably also is a factor.

The dissolved-solids concentrations of water in the 

lower units of the Western Interior Plains aquifer 

system range from less than 1,000 mg/L to more than 

200,000 mg/L (fig. 32), a dense brine. The large concentrations are in part due to slow flow rate and long 

residence time. The brines originated in the geologic 

past. The eastern edge of the dense brine in Oklahoma 

(fig. 32) approximately aligns with the zone of halite dissolution in the overlying confining system; however,

because of very slight permeability and the large thickness of the confining system, the brine in the Western 

Interior Plains aquifer system is not believed to be dominantly of halite origin (S.C. Christenson, U.S. Geological 

Survey, oral commun., 1986).

WESTERN INTERIOR PLAINS CONFINING SYSTEM

The Western Interior Plains confining system restricts flow to and from the Western Interior Plains 

aquifer system. The extent and altitude of the top of

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

-10 LINE OF EQUAL ESTIMATED REGIONAL PERMEABILITY Value is the 

thickness-weighted mean horizontal intrinsic permeability. Interval, in 

feet squared, varies

EXTENT OF LOWER UNITS OF WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM

APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 34. Estimated regional intrinsic permeability of lower units of the Western Interior Plains aquifer system.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B49

the confining system are shown on plate 8. The altitude ranges from more than 3,000 ft below sea level 

in the Denver basin to more than 6,000 ft above sea 

level in northeastern New Mexico. In general, the top 

of the confining system slopes upward to the east toward a broad physiographic low near the outcrop 

area adjacent to the western perimeter of the Ozark 

subregion (pi. 2). The thickness of the confining system (pi. 9) ranges from zero in northeastern 

Nebraska and in the Ozark subregion to more than 

20,000 ft in the Anadarko basin. The confining

system is composed of rocks of Late Mississippian 

through Jurassic age (table 2).

The Pennsylvanian formations are a major part of 

the confining system (pi. 2) and consist mostly of 

shale and minor limestone and sandstone. In the 

deeper part of the Anadarko and Arkoma basins, the 

ratio of limestone to sandstone decreases. In the shallower areas, the ratio of limestone to sandstone exceeds 1. Adjacent to the Amarillo-Wichita and 

Apishapa-Sierra Grande uplifts (fig. 24), thick sections of permeable arkosic gravel of Pennsylvanian

105° 100°

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

10- LINE OF EQUAL ESTIMATED REGIONAL PERMEABILITY Value is the 

thickness-weighted mean horizontal intrinsic permeability. Interval, in feet 

squared, varies

i i i i EXTENT OF UPPER UNIT OF WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM

 APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 35. Estimated regional intrinsic permeability of upper unit of the Western Interior Plains aquifer system.
B50 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

and Permian age are present and are termed "granite 

wash," as they are believed to have been eroded from 

granitic uplift material. However, these permeable 

deposits extend only a few tens of miles from the uplift and are not important regionally.

The Permian formations in the Western Interior 

Plains confining system consist mostly of shale and 

minor evaporites, sandstone, and limestone. Triassic 

and Jurassic formations are mostly shale, sandstone, 

and limestone.

In general, the sandstone and limestone beds contained in the Western Interior Plains confining system are permeable; however, they do not extend 

areally across the extent of the confining system. 

Therefore, they are not a distinct hydraulic system 

regionally. The estimated thickness-weighted mean 

horizontal intrinsic permeability of the confining system ranges from about IxlO"16 to about 5xlO~13 ft2 

(fig. 36). The aquifer units in the Western Interior 

Plains confining system are, in general, more permeable than the aquifer units in the underlying and 

deeper Western Interior Plains aquifer system, because permeability and porosity generally decrease 

with depth. However, the vertical leakance of the 

confining system at most locations is considerably 

less than the vertical leakance of the Western Interior Plains aquifer system, because the confining system is very thick and includes thick confining units 

of shale as well as extensive layers of nearly impermeable evaporites.

The pressure of the pore water in the permeable 

units in the confining system varies both vertically 

and horizontally, which is consistent because these 

permeable units are not in a reasonably distinct hydraulic system. Pore pressure as measured in drillstem tests near the centerline of the permeable units 

is less than hydrostatic pressure throughout large areas. Large pressures exist in a geopressure zone near 

the base of the confining system in the Anadarko basin in Oklahoma. At this location, equivalent-freshwater head exceeds 6,000 ft in Morrowan sand and 

shale. This pressure affects the underlying dolostone.

GREAT PLAINS AQUIFER SYSTEM

The Great Plains aquifer system consists of two regional aquifers separated by a confining unit. The 

aquifers are mostly composed of Lower Cretaceous 

water-bearing sandstone. The Great Plains aquifer 

system is one of the most extensive aquifers in North 

America (Helgesen and others, 1982), extending from 

near the Arctic Circle in Canada to New Mexico (fig. 

37). In the United States, the two major regional

aquifers in the Lower Cretaceous rock section of the 

Great Plains aquifer system are the Apishapa and 

the Maha (fig. 38). In general, water in each aquifer 

flows from west-southwest to east-northeast, as was 

recognized by Barton (1905). However, at that time, 

sufficient data were not available for clearly differentiating between these two aquifers at most locations. 

Therefore, these two aquifers were termed the "Dakota aquifer system" by some investigators. The aquifers have also been called the "Dakota aquifer." 

Others have termed the upper major regional aquifer 

the "Dakota aquifer" and still others termed the 

lower major regional aquifer the "Dakota aquifer." 

The name Dakota also has been used in lithologic 

terms as the Dakota Sandstone, the Dakota Formation, and the Dakota Group. The controversy as to 

correlation and terminology were termed aptly the 

"Dakota controversy." Nearly all the controversies relate to correlation of lithologic units, not to hydrology. 

Many investigators prefer to name aquifers using the 

stratigraphic nomenclature.

In this report, the aquifers that consist mostly of 

Lower Cretaceous sandstone and that are part of the 

regional-flow system are termed the Great Plains 

aquifer system. The term Great Plains was chosen 

because, generally, the aquifer system is present at 

most locations in the Great Plains of North America 

and because the term has not been used to name a 

geologic formation or group of formations. The extent 

and altitude of the top of the Great Plains aquifer 

system, which includes the Apishapa (lower) and the 

Maha (upper) aquifers and the intervening Apishapa 

confining unit, are shown on plate 10. The altitude of 

the Great Plains aquifer system decreases from more 

than 6,000 ft above sea level in northeastern New 

Mexico, a recharge area, to less than 1,000 ft above 

sea level in southeastern South Dakota, a discharge 

area, and to more than 4,000 ft below sea level in the 

Denver basin.

Nearly all hydrologic information relating to hydraulic head, permeability, and water chemistry for 

the Great Plains aquifer system within the study 

area is for the Maha aquifer (figs. 39-41). The potentiometric surface for the Apishapa aquifer is suspected to be similar to the potentiometric surface for 

the Maha (fig. 39). However, in some areas there may 

be considerable head differences. For example, in central South Dakota just north of the study area, a substantial head difference between the two aquifers 

exists. The major recharge to the aquifer system is in 

southeastern Colorado and northeastern New Mexico 

(fig. 39). Most ground water flows from the major 

recharge area east-northeast toward the outcrop area
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B51

in central Kansas and eastern Nebraska. Near the 

southern and eastern extent of the Great Plains 

aquifer system, the aquifers are close to the land surface, and locally, recharge occurs (fig. 38).

Intrinsic permeability for both aquifers is mostly 

primary, except possibly in the Denver basin, because the aquifer material is mostly a slightly cemented sandstone. Permeability and porosity 

decrease with depth. The estimated thicknessweighted mean horizontal intrinsic permeability is

shown in figure 40. Permeability is greatest along 

the eastern extent of the aquifer system and least in 

the Denver basin.

The dissolved-solids concentrations of water in the 

Maha aquifer (Leonard and others, 1983) are shown 

in figure 41. Limited water-quality information 

within the study area indicates that in many 

locations, the water in the Apishapa aquifer has a 

greater dissolved-solids concentration than the water 

in the Maha aquifer.

105'

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 10 LINE OF EQUAL ESTIMATED PERMEABILITY Value is the thickness -

weighted mean horizontal intrinsic permeability. Interval, in feet squared, 

varies

i i i i i i EXTENT OF WESTERN INTERIOR PLAINS CONFINING SYSTEM

APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 36. Estimated regional intrinsic permeability of the Western Interior Plains confining system.
B52 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

APISHAPA AQUIFER

The Apishapa is the lower of the two major regional aquifers in the Great Plains aquifer system 

and at most locations is composed of permeable, partially cemented, medium-grained to very fine grained 

sandstone of the Cheyenne Sandstone and equivalents, such as the Fall River and Lakota Sandstones 

north of the study area. The name Apishapa refers to 

the water-bearing sandstone layers that occur in the 

major recharge area in the vicinity of the Apishapa 

River and adjacent areas in southeastern Colorado, 

northeastern New Mexico, and southwestern Kansas. 

The name Apishapa was selected because the name 

is not used formally as a stratigraphic name for a

Lower Cretaceous sandstone in the study area and, 

thus, is unique as an aquifer name.

Except for local outcrop areas in southeastern 

Colorado, the altitude of the top of the Apishapa 

aquifer is somewhat less than that of the Great 

Plains aquifer system shown on plate 10. The maximum thickness of the Apishapa aquifer exceeds 400 

ft; however, the typical thickness is between 100 and 

200 ft (pi. 11).

Adequate data to define the regional potentiometric surface for the Apishapa aquifer are not available. 

However, the potentiometric surface of the Apishapa 

within the study area is believed not to differ greatly 

from the potentiometric surface of the Maha aquifer 

as shown in figure 39.

Contours modified from 

Hitchon (1969), Lobmeyer 

(1980), and others

500 1000 MILES

__I

500 1000 KILOMETERS

5000

EXPLANATION

POTENTIOMETRIC CONTOUR Shows altitude of potentiometric surface of the 

Great Plains aquifer system. Hachures indicate depression. Contour interval is 

500,1000, and2000feet Datum is sea level.

LIMIT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 37. Great Plains aquifer system in North America (modified from Helgesen and others,

1982).
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B53

APISHAPA CONFINING UNIT

The Apishapa confining unit separates and restricts water flow between the Apishapa aquifer and 

the overlying Maha aquifer at most locations. The 

confining unit is composed of slightly permeable 

shale layers, which at most locations consist of the 

Kiowa Shale and the equivalent Skull Creek Shale 

north of the study area. The altitude of the top of the 

unit is not shown because the unit is thin compared 

to the contour interval that would be required to 

show the available data. However, the altitude is, in 

general, about 200 ft less than the altitude of the top 

of the Great Plains aquifer system (pi. 10). The confining unit is thin, generally less than 100 ft (pi. 12), 

and is not as extensive as the Maha aquifer (fig. 38).

MAHA AQUIFER

The Maha aquifer, which is the upper regional 

aquifer unit of the Great Plains aquifer system (fig. 

38), is more extensive than the underlying Apishapa 

aquifer. The Maha aquifer at most locations consists 

of water-bearing, partially cemented, medium- to 

fine-grained sandstone of the Dakota Sandstone and 

equivalents, such as the Newcastle Sandstone north 

of the study area and the "D" and "J" sandstones of 

informal oil field usage. The aquifer was named from 

exposures of the sandstone along the bluffs of the 

Missouri River valley between Blair and Ponca, Nebraska. This is the area the Maha (Omaha) Indians 

inhabited as reported by Lewis and Clark in 1803. 

The name Maha was chosen because the name had 

not been used to identify a geologic formation or 

group of formations. The altitude of the top of the 

Maha aquifer and the altitude of the Great Plains 

aquifer system (pi. 10) are the same except in a few

WEST

small areas where the Maha is absent and the 

Apishapa aquifer is present. The aquifer thickens 

from less than 100 ft in eastern Colorado to about 

600 ft in northeast Nebraska and exceeds 900 ft in a 

small area in central Nebraska (pi. 13).

OVERLYING UNITS IN THE PLAINS SUBREGION

The Western Interior Plains aquifer system does 

not crop out anywhere in the Plains subregion. Scattered outcrops may exist in the foothills of the Rocky 

Mountains. The Western Interior Plains confining 

system is at the land surface in much of the eastern 

part of the Plains area but is directly overlain by the 

High Plains aquifer farther west or by glacial drift and 

loess in eastern Nebraska and northeastern Kansas.

The Great Plains aquifer system is directly overlain by the Great Plains confining system in most 

places and by the High Plains aquifer, glacial drift, or 

loess along its eastern margin (fig. 42). The Great 

Plains confining system is as much as 8,000 ft thick 

(fig. 43). The confining units within thiF system are 

composed of shale, which include the Upper Cretaceous Graneros, Carlile, and Pierre Shales, and 

slightly permeable Tertiary clay and silt. The confining system also includes two extensive but minor 

aquifers. These aquifers are in the Greenhorn Limestone and the Niobrara Chalk. The confining system, 

at most locations, effectively restricts flow to and 

from the Great Plains aquifer system and the 

surficial High Plains aquifer if present, or to and 

from the water table in the soil zone.

The High Plains aquifer (fig. 2) mainly consists of 

permeable Tertiary and Quaternary sediments 

(Weeks and Gutentag, 1981). Where present, its character permits hydraulic connection with adjacent units.

EAST

Great Plains confining system

(Upper Cretaceous rocks)

Western Interior Plains confining system

(Pennsylvanian through Jurassic rocks

EXPLANATION

DIRECTION OF

GROUND-WATER

FLOW

NOT TO SCALE

FIGURE 38. Maha and Apishapa aquifers, Great Plains aquifer system. Section extends across 

Nebraska from the intersection of North Platte River and Wyoming-Nebraska Stateline on the 

west to Missouri River at northernmost extent of Nebraska-Iowa Stateline on the east.
B54 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

The glacial drift, which is mostly a till, consists of heterogeneous clay, silt, sand, and gravel and has a variable 

hydraulic character. Loess, which consists of uniform siltsize material, overlies the Great Plains aquifer system 

and the Western Interior Plains confining system at different locations and has moderate vertical permeability. 

The glacial drift and loess probably are a leaky confining 

system for the underlying aquifer units.

OZARK SUBREGION

The Ozark subregion (figs. 44, 45) corresponds to 

the Ozark Plateaus physiographic province and the 

Ouachita physiographic province north of the Arkansas River. The subregion is bounded by the Missouri 

River, the Mississippi River, the Mississippi Alluvial 

Plain, the Arkansas River, and the broad and very gentle 

regional topographic low from northeastern Oklahoma to 

the Missouri River in central Missouri (fig. 45).

In general, ground water flows outward from a 

topographic high along an axis from the St. Francois 

Mountains in southeastern Missouri to the tri-State 

corner of Missouri, Arkansas, and Oklahoma. Flow is 

also outward from a topographic ridge of the Boston 

Mountains in northwestern Arkansas. The Ozark 

Plateaus aquifer system is underlain by the 

basement confining unit that is composed mostly of 

igneous and metamorphic crystalline rocks. The base105° 100° 95° 90°

40'

35e

Base modified from U.S. Geological Survey 

1:7,500,000. National Atlas, 1970

EXPLANATION

 3000 POTENTIOMETRIC CONTOUR Shows altitude at which water would have 

stood in tightly cased wells. Contour interval, in feet, varies. Datum is 

sea level

i i i i i i i i EXTENT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 39. Predevelopment potentiometric surface of the Maha aquifer, Great Plains aquifer system.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B55

ment rocks are fractured and locally water yielding, 

such as in the St. Francois Mountains (fig. 44), but 

on a regional basis they are assumed to form the 

base of the regional flow system.

The altitude of the top of the basement ranges 

from more than 1,700 ft above sea level in the St. 

Francois Mountains to 15,000 ft below sea level in 

the Arkoma basin in Arkansas along the southern 

boundary of the Ozark subregion (pi. 3).

OZARK PLATEAUS AQUIFER SYSTEM

Nearly all ground water used in the Ozark subregion, either well water or spring water, is from the

three regional aquifers that are within a distinct 

hydraulic system. These three aquifers and the two 

confining units that separate the aquifers are termed 

the Ozark Plateaus aquifer system because of their 

widespread occurrence in the Ozark Plateaus 

physiographic province. The aquifer system overlies 

the basement confining unit and has an extensive 

outcrop area. The aquifer system is overlain by the 

Western Interior Plains confining system in a band 

that extends along the western and southern boundaries of the subregion.

The geohydrologic units of the Ozark Plateaus 

aquifer system are composed of sedimentary rocks 

that range in age from Cambrian through Mississippian

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LINE OF EQUAL ESTIMATED PERMEABILITY Value is the thicknessweighted mean horizontal intrinsic permeability. Interval, in feet squared, 

varies

EXTENT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 40. Estimated regional intrinsic permeability of the Great Plains aquifer system.
B56 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

(table 3). Boundaries between the geohydrologic units 

do not always conform to geologic-time divisions or to 

formation boundaries, but the delineated rock groups 

have similar hydrologic properties. All of the geohydrologic units that comprise the Ozark Plateaus aquifer system crop out in the Ozark Plateaus.

The lateral boundaries of each of the three regional aquifers generally are the same as those of

the Ozark subregion. The extent of the groundwater flow along the western boundary of the 

Ozark Plateaus aquifer system also is controlled 

by the thickness and permeability of the Western 

Interior Plains confining system. In general, 

ground water flowing westward moves laterally 

down the hydraulic gradient and downdip in the 

aquifer below the land surface and confining

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970 EXPLANATION

DISSOLVED-SOLIDS CONCENTRATION Values in milligrams per liter 

I I 0 - 1,000 J More than 20,000

1,000 - 20,000 No Data

-20 LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION Dashed where 

approximate. Interval, in thousands of milligrams per liter, varies

EXTENT OF MAHA AQUIFER

AREA WHERE GREAT PLAINS AQUIFER IS ABSENT

FIGURE 41. Dissolved-solids concentrations in Maha aquifer water (modified from Leonard and others, 1983).
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B57

system to below the broad topographic low that 

extends from northeastern Oklahoma into central 

Missouri, and then leaks upward (fig. 31). The 

downdip flow extends to a depth of about 500 feet. 

The Western Interior Plains aquifer system is laterally adjacent to the western boundary of the 

Ozark Plateaus aquifer system. In general, both

aquifer systems discharge water vertically upward Alluvial Plain.

through the thin (and therefore leaky) confining 

system to the streams or water table in the area of 

the broad topographic low. The flow system extends to about the Fall Line of northeastern Arkansas and the bootheel of Missouri. In general, 

flow across the Fall Line is intercepted by streams, 

marshes, and drainage canals in the Mississippi

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

WESTERN INTERIOR PLAINS CONFINING SYSTEM 

GREAT PLAINS CONFINING SYSTEM 

HIGH PLAINS AQUIFER 

GLACIAL DRIFT AND LOESS

- APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 42. Geohydrologic units overlying regional aquifer systems in the Plains subregion.
B58 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

ST. FRANCOIS AQUIFER

The St. Francois aquifer, the lowermost geohydrologic unit of the Ozark Plateaus aquifer system, consists of water-bearing sandstone, dolostone, and other 

rock and rests on the basement confining unit. The 

aquifer crops out around the St. Francois Mountains 

for which it is named and is overlain by the St. 

Francois confining unit.

The St. Francois aquifer is used extensively as a 

source of water for domestic and public supply in the 

outcrop area. Well yields generally are 100 to 500 

gal/min. The aquifer is not extensively used except 

near the outcrop area because in other areas the

overlying Ozark aquifer yields more water at a shallower depth.

The St. Francois aquifer, at most locations, extends to the boundaries of the Ozark subregion. The 

altitude of the top and extent of the aquifer are 

shown on plate 14. The altitude of the aquifer ranges 

from more than 1,000 ft above sea level at the outcrop near the St. Francois Mountains to more than 

7,000 ft below sea level in the Arkoma basin. Beyond 

the relatively small outcrop area (590 mi2) in and 

near the St. Francois Mountains, the aquifer dips 

into the subsurface and is buried beneath the other 

units of the Ozark Plateaus aquifer system. The aquifer is missing in the subsurface at several isolated

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 2000 LINE OF EQUAL THICKNESS OF GREAT PLAINS CONFINING SYSTEM 

Interval, in feet, varies

i i i i i EXTENT OF GREAT PLAINS CONFINING SYSTEM

FIGURE 43. Thickness of the Great Plains confining system.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B59

areas surrounding the St. Francois Mountains. The 

aquifer dips as steeply as 150 ft/mi to the east toward 

the Illinois basin and south toward the Mississippi 

Alluvial Plain, where it is buried to a depth of more 

than 3,200 ft. To the west, the dip is more gentle and 

broken by a series of small basins.

The aquifer includes the Lamotte Sandstone and 

Bonneterre Dolomite and their equivalents of Upper 

Cambrian age (pi. 1, table 3). The Lamotte generally 

is a sandstone with some silt, and locally grades to 

arkose and conglomerate. It is the most permeable of 

the geologic formations within the aquifer. The overlying Bonneterre Dolomite is predominantly a coarsegrained dolostone, which contains numerous small 

cavities, resting on a sandy dolostone. Kurtz and others 

(1975) report that the Lamotte Sandstone and 

Bonneterre Dolomite are not present in extreme southwestern Missouri. In the western one-third of the Ozark 

subregion, the aquifer is composed of the Reagan Sandstone (a nearshore fades of the Lamotte Sandstone), and 

the Bonneterre Dolomite. The St. Francois aquifer is 

thickest (more than 1,000 ft) in the eastern part of 

the subregion near the Mississippi Alluvial Plain but 

generally is between 200 and 500 ft thick (pi. 15).

OZARK 

^ 

PLATEAUS

PROVINCE

Boston Mountains

***** 

Arkansas Valley

OUAGHITA

Ouachita PROVINCE 

Mountains!

OKLAHOMA

35° - ____

EXPLANATION

LIMIT OF OZARK SUBREGION

BOUNDARY OF PHYSIOGRAPHIC PROVINCES

BOUNDARY OF PHYSIOGRAPHIC SUBDIVISIONS

FIGURE 44. Physiographic features of the Ozark subregion.
B60 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Generally, both the Lamotte and Bonneterre are 

permeable and yield water to wells; however, water 

yields from the Lamotte Sandstone generally are 

greater than those from the Bonneterre. Estimates of 

hydraulic conductivity, based on specific-capacity 

data, range from IxlO"4 to IxlO"6 ft/s in and near the 

outcrop area and tend to decrease away from the outcrop area. Little is known about the hydraulic properties of the Reagan Sandstone because few water wells 

are drilled deep enough to penetrate the formation; 

however, it is believed to be hydrologically similar to 

the Lamotte.

The hydraulic head of the St. Francois aquifer is 

mostly topographically controlled. The aquifer is recharged from infiltration of precipitation through the

soil zone at the outcrops. The aquifer also is 

recharged by flow from the fractured Precambrian 

rocks of the basement near the outcrop area. Beyond 

the outcrop area, ground-water movement is restricted by the overlying confining unit. The aquifer 

discharges upward through the confining unit to 

overlying aquifers downdip from the outcrop area. 

However, exact areas of this discharge are not known 

because the hydraulic head in the aquifer is known 

only at the outcrop area.

Few data are available on the chemistry of water 

in the aquifer; however, the data available indicate 

that the water is not dissimilar to that of the overlying Ozark aquifer, probably because the confining 

unit separating the aquifers is thin and leaky.

95° 90°

OKLAHOMA

60 MILES

I T 

30 60 KILOMETERS

EXPLANATION

 LIMIT OF THE OZARK SUBREGION

FIGURE 45. Drainage features of the Ozark subregion.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK 

TABLE 3. Generalized correlation of stratigraphic units to geohydrologic units in most of the Ozark subregion

B61

Geohydrologic unit

Western Interior Plains 

confining system

Ozark 

Plateaus 

aquifer 

system

Springfield 

Plateau 

aquifer

Ozark 

confining unit

Ozark 

aquifer

St. Francois 

confining 

unit

St. Francois 

aquifer

Basement confining unit

Principal stratigraphic unit(s)

Marmaton Group, Cherokee Group, Atokan rocks, 

Bloyd Shale, Hale Formation, Morrowan rocks, 

Pitkin Limestone, Fayetteville Shale, and Batesville 

Sandstone

Moorfield Formation, St. Louis Limestone, Salem 

Limestone, Warsaw Limestone, Boone Formation, 

St. Joe Limestone Member of Boone Formation, 

Keokuk Limestone, Burlington Limestone, and Fern 

Glen Limestone

*Choteau Group and Chattanooga Shale

Clifty Limestone, Penters Chert, Lafferty Limestone, 

St. Clair Limestone, Brassfield Limestone, Cason 

Shale, Fernvale Limestone, Kimswick Limestone, 

Plattin Limestone, Joachim Dolomite, St. Peter 

Sandstone, Everton Formation, Smithville 

Formation, Powell Dolomite, Cotter Dolomite, 

Jefferson City Dolomite, Roubidoux Formation, 

Gasconade Dolomite, Gunter Sandstone Member of 

Gasconade Dolomite, Eminence Dolomite, and 

Potosi Formation

Elvins Group, Derby and Doe Run Dolomites, Davis 

Formation

Bonneterre Dolomite and Lamotte Sandstone

Mostly igneous and metamorphic rock

Time-stratigraphic unit

Middle Pennsylvanian 

through Upper 

Mississippian 

(Chesterian)

Mississippian

Lower Mississippian 

and Upper Devonian

Middle 

Devonian 

through 

Uppermost 

Cambrian

Upper Cambrian

Upper Cambrian

Precambrian

'Designated Choteau Limestone by the U.S. Geological Survey.

Chemical analyses of water samples collected from 

the St. Francois aquifer in the outcrop area indicate 

dissolved-solids concentrations of 220 to 450 mg/L.

ST. FRANCOIS CONFINING UNIT

The St. Francois confining unit, the lower of the 

two confining units in the Ozark Plateaus aquifer 

system, restricts flow between the St. Francois aquifer and the overlying Ozark aquifer at most locations. 

The leaky confining unit is composed of very slightly 

permeable shale, and slightly permeable siltstone, 

dolostone, and limestone. The rocks are part of three 

formations in the Upper Cambrian Elvins Group 

the Davis Formation, the Derby Dolomite, and the 

Doe Run Dolomite (table 3).

The extent and altitude of the top of the confining 

unit are shown on plate 16. Well-log data are insufficient to define the top of the unit in much of its

extent; however, where there are insufficient data, 

contours are drawn so that the altitude of the top of 

the St. Francois confining unit is consistently lower 

than the top of the overlying Ozark aquifer for which 

there are more data. The unit crops out in about a 

400 mi2 area around the St. Francois Mountains and 

dips steeply away from the St. Francois Mountains at 

a rate of as much as 150 ft/mi, except to the west 

where the dip is more gentle. Most of the small isolated areas within the Ozark subregion where the St. 

Francois confining unit is not present in the subsurface are coincident with or near areas where the underlying St. Francois aquifer also is not present.

The thickness of the St. Francois confining unit, as 

determined from well-log data, ranges from nearly 

zero to 730 ft. The maximum thickness of the unit is 

in northwestern Arkansas (pi. 17). The confining unit 

generally is thicker to the northeast of the St. 

Francois Mountains and to the southeast where it
B62 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

dips below the Mississippi Alluvial Plain. The unit is 

thinner in western Missouri (ranging from 0 to 300 

ft), and the stratigraphic rock units pinch out a few 

miles west of the Ozark subregion in eastern Kansas 

and northeastern Oklahoma. The confining unit thins 

abruptly at the St. Francois Mountains where the 

confining rocks have been removed by erosion.

The shale content of a confining unit commonly is 

used as an indicator of the effectiveness of the confining unit. Although this generally is a good indicator 

because shale is generally less permeable than most 

rock types, other factors, such as presence of fractures, can negate the water-impeding ability of the 

shale. Shale in the St. Francois confining unit exists 

as distinct beds and usually is distributed throughout 

the limestone and dolostone mass as thin layers or 

beds. Thus, the confining ability of the unit also is 

dependent on the degree of cementation of the carbonate rock and the abundance of both fractures and 

solution openings.

The amount of shale within the St. Francois confining unit ranges from 0 to more than 40 percent 

and generally is less than 30 percent (pi. 18). The 

Davis Formation contains the largest percentage of 

shale of the three geologic formations. The data used 

to determine the percentage of shale were derived 

primarily from the hundreds of insoluble-residue 

analyses on file at the Missouri Division of Geology 

and Land Survey. Because the clay is reported to be 

from thin clay beds, insoluble-residue results should 

represent the percentage of shale. However, most 

data used to determine the percentage of shale in 

southeastern Kansas and northeastern Oklahoma 

were obtained from borehole geophysical logs.

The Davis Formation is not part of the St. 

Francois confining unit at isolated locations in westcentral and south-central Missouri. The Davis Formation thins to the southwest and becomes more clastic 

in a facies change to the Reagan Sandstone (Thacker, 

1974). The Derby and Doe Run Dolomites are more 

uniform in thickness and are part of the confining 

unit at nearly all locations.

Generally, substantial secondary porosity and perr 

meability have not developed in the limestone and 

dolostone of the Davis Formation or in the Derby and 

Doe Run Dolomites. The fine-grained nature of the 

dolostones is the probable reason for the slight permeability of the confining unit even in regions devoid 

of shale. However, the confining unit is more likely to 

be leaky in these areas as compared to areas with a 

large percentage of shale. There is evidence from well 

cores that the upper part of the Derby and Doe Run 

Dolomites is permeable along a northwest-trending 

reef zone passing through south-central Missouri.

Because the Davis Formation is absent in part of the 

reef zone, it is possible that the underlying St. 

Francois aquifer and the overlying Ozark aquifer locally are hydraulically connected. Fracture zones are 

evident in the Derby and Doe Run strata and may 

increase leakance locally, especially in the vicinity of 

faults. However, in Arkansas, the faults mostly have 

been sealed.

OZARK AQUIFER

The Ozark aquifer is mostly composed of waterbearing dolostone and is the most permeable and the 

most extensively used aquifer in the Ozark subregion. The aquifer with the exception of the St. 

Francois Mountains area, is at land surface or nearly 

at land surface throughout most of the area that generally is termed the "Ozark area" or the "Ozarks." 

The aquifer is accordingly called the Ozark aquifer 

because of the association with the Ozarks. The rocks 

of the aquifer are fractured dolostone with some limestone, sandstone, chert, and shale. The dolostone contains solution cavities. Sandstone, where it exists as 

massive bodies, generally is clean, well sorted, and 

permeable; however, in northern Arkansas, it is well 

cemented, slightly fractured, and much less permeable. The aquifer at most locations, is underlain by 

the St. Francois confining unit and overlain by the 

Ozark confining unit. The aquifer crops out in a large 

area over the Ozark uplift and is a greatly dissected 

karst with numerous streams and springs.

Stratigraphically, the aquifer is present in Upper 

Cambrian through Middle Devonian rocks (table 3). 

The basal formation of the Ozark aquifer is the 

Potosi Formation. In eastern Missouri, the upper 

boundary of the aquifer is coincident with the base of 

the Maquoketa Shale, which usually is underlain by 

the Kimmswick Limestone. West and south of the extensive outcrop area of the aquifer, the base of the Chattanooga Shale is the upper boundary of the aquifer.

The altitude of the top of the Ozark aquifer is 

shown on plate 19. Where the aquifer dips into the 

subsurface, it is generally overlain by Upper Devonian rocks of the Ozark confining unit; however, in 

the north-central part of the Salem Plateau (fig. 44) 

the aquifer is in direct contact with as much as 200 ft of 

Pennsylvanian shale, which is a confining material.

Near the Fall Line along the Mississippi Alluvial 

Plain, the aquifer dips to the southeast at about 45 

ft/mi. In eastern Kansas and western Missouri, the 

aquifer dips to the west at about 14 ft/mi. A ridge of 

the Ozark aquifer extends southwestward and can be 

recognized by the surface expression of a chain of island-like outcrops extending from southwest Missouri
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B63

into northeast Oklahoma. This ridge approximates 

the axis of the Ozark uplift. In northern Arkansas, 

the regional dip is about 26 ft/mi southward and increases to about 175 ft/mi or more near the southern 

boundary of the subregion.

The Ozark aquifer is the thickest (typically about 

1,000 ft) geohydrologic unit in the Ozark subregion 

(pi. 20). In southeast Kansas, the aquifer thickness 

ranges from about 700 to 1,200 ft. The thickness is 

less uniform within short distances in northeastern 

Oklahoma where Precambrian topographic relief affected the thickness of sediments that today are rocks 

of the Ozark aquifer. The aquifer is only 270 ft thick 

near the Oklahoma-Kansas border where the basement confining unit directly subcrops beneath the 

aquifer.

The hydraulic conductivity of the Ozark aquifer 

has been estimated from specific-capacity data and 

has been inferred from the density of fractures and 

the degree of development of solution openings. In 

general, the more that rocks have been uplifted, the 

more they have been fractured, the more dissolution 

along the fractures has occurred, and correspondingly, the greater the hydraulic conductivity. The areas of greatest hydraulic conductivity are 

concentrated along a line trending westward from the 

St. Francois Mountains where the hydraulic conductivity may be as much as IxlO"3 ft/s. In areas where 

dissolution has occurred and springs are numerous, 

the hydraulic conductivity is extremely large and locally exceeds IxlO"1 ft/s. Hydraulic conductivity of 

near-surface aquifer material is more developed in 

the valleys as compared to the interfluves. Hydraulic 

conductivity decreases to the south to as little as IxlO"8 

ft/s near the southern boundary of the subregion.

The Potosi Formation is the most permeable Cambrian formation within the aquifer. This massive 

dolostone contains numerous druse cavities lined 

with finely crystalline quartz. It has a relatively uniform thickness (about 100 to 300 ft) throughout much 

of the area, and an extensive network of solution 

channels has developed along fractures. The overlying 

Eminence Dolomite is also a Cambrian formation with 

lithology similar to the Potosi, but secondary porosity has 

not been developed to the same degree.

The lower part of the Gasconade Dolomite and the 

Roubidoux Formation, which are Ordovician rocks, 

are important water-yielding zones, especially in the 

southern and southwestern parts of the Ozark subregion (Harvey, 1980; Lamonds, 1972). The Gasconade 

is primarily dolostone but contains a major waterbearing sandstone member (Gunter Sandstone Member) that extends throughout northwestern Arkansas 

and southern Missouri. The Roubidoux Formation is

a sandy, cherty dolostone with sandstone beds that 

generally are water bearing. The stratigraphic sequence from the Jefferson City Dolomite through the 

Smithville Formation mostly consists of dolostone 

with minor shale, chert, and sandstone. These formations generally are not as permeable as the lower 

rocks, the Gasconade Dolomite and the Roubidoux 

Formation. Of the Ordovician rocks younger than the 

Smithville Formation, the St. Peter Sandstone is the 

most important water-bearing formation. It is a 

clean, quartzose sandstone with little indication of 

bedding in the eastern part of the Ozark subregion, 

but it is slightly shaly in the western part. The remainder of the Ordovician formations are dolostone 

and limestone with minor shale and sandstone, with 

the exception of the Cason Shale in Arkansas and the 

equivalent Sylvan Shale in Oklahoma. These latter 

formations are distinct shale units with minor dolomitic sandstone. The shale layers are competent and 

fractured, and do not yield water to wells but allow 

regional leakage of water. None of the younger Ordovician rocks are important regional sources of water, but the Kimmswick Limestone, the Plattin 

Limestone, and the Joachim Dolomite yield small 

quantities of water to domestic wells.

Limestone and chert of Silurian and Devonian 

age are the uppermost rocks in the Ozark aquifer 

in the north-central and southern part of the subregion. The rocks are less permeable than the 

lower rocks in the aquifer and generally are not 

used as a water source. The rocks are fractured but 

have lesser hydraulic conductivity because solution-channel permeability has not been well developed. The Mississippi Alluvial Plain adjacent to the 

Fall Line is a major discharge area. In general, 

most water flowing across the Fall Line is intercepted by streams, drainage canals, and marshes 

adjacent to the Fall Line.

Water in most of the Ozark aquifer is unconfined, and 

its occurrence and flow are controlled by topographic relief. Throughout the outcrop area, ground water moves 

toward the major rivers and their tributaries (figs. 45, 

46), and hundreds of springs have developed. Typically, 

flow in these springs is local because most recharge to 

springs is in the upland intervalley areas and is discharged in nearby stream valleys. The Mississippi River 

valley is a major regional discharge area for regional flow 

from the Ozark aquifer. The Missouri River valley east of 

Saline County, Missouri (not shown), also is a major discharge area.

In southwest Missouri, southeast Kansas, and 

northeast Oklahoma, flow in the Ozark aquifer is 

outward to the periphery or boundary of the subregion. This western boundary is marked by the broad,
B64 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

gentle physiographic low that extends around the 

western edge of the Ozark Plateaus. The Western Interior Plains confining system is the surficial material in the physiographic low and overlaps the Ozark 

Plateaus aquifer system, of which the Ozark aquifer 

is a part. Water flows upward through the confining 

system. The leakance of the confining system controls

the quantity of upward leakage out of the Ozark Plateaus aquifer system to the physiographic low. In 

northern Arkansas, most flow is through the permeable zones of the Roubidoux Formation and the 

Gunter Sandstone Member of the Gasconade Dolomite. Along the Oklahoma-Arkansas State line, flow 

is toward the broad physiographic low in northeastEXPLANATION

AQUIFER ABSENT

 600- - POTENTIOMETRIC CONTOUR Shows altitude at which water level would 

have stood in tightly cased well. Dashed where approximate. Contour 

interval 200 feet. Datum is sea level

2000 LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION 

Interval 1000 milligrams per liter

MAJOR DIRECTION OF REGIONAL FLOW IN OZARK AQUIFER

MAJOR DIRECTION OF FLOW IN WESTERN INTERIOR PLAINS AQUIFER SYSTEM

FIGURE 46. Predevelopment potentiometric surface of the Ozark aquifer.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B65

ern Oklahoma. In general, north of the Boston Mountains in Arkansas, regional flow is northward toward 

the potentiometric low associated with the White 

River drainage. To the south of the Boston Mountains, flow is inferred to be toward the Arkansas 

River valley. In this area, the rocks of the Ozark Plateaus aquifer system are beneath a thick confining 

system and substantial secondary permeability has 

not developed.

OZARK CONFINING UNIT

The Ozark confining unit, the uppermost confining 

unit of the Ozark Plateaus aquifer system, restricts 

flow between the underlying Ozark aquifer and the 

overlying Springfield Plateau aquifer. The Ozark confining unit is named for its position relative to the 

underlying Ozark aquifer that it confines. The leaky 

confining unit is composed mostly of shale, shaley 

limestone, and limestone. The formations generally 

included are the Upper Devonian Chattanooga Shale 

and the Lower Mississippian Chouteau Group (designated Chouteau Limestone by the U.S. Geological 

Survey) (table 3). Not all of the geologic formations in 

the confining unit are present everywhere in the 

Ozark subregion. Commonly in the western and 

southern part of the subregion, only the Upper Devonian shale and the Lower Mississippian shale and 

limestone are included in the confining unit. In extreme eastern Missouri, Ordovician, Silurian, and Devonian formations are included as part of this 

confining unit.

The Ozark confining unit is missing from the 

subsurface in small localities in southeast Kansas, 

southwest Missouri, northeast Oklahoma, and northwest Arkansas (pi. 21). The formations of the 

confining unit also are absent in the subsurface 

throughout a large area in the northern part of the 

Salem Plateau and along the Mississippi Alluvial 

Plain where the rocks have been removed by erosion. 

The altitude of the confining unit ranges from more 

than 1,500 ft above sea level at outcrops to more 

than 5,000 ft below sea level in the Arkansas River 

valley in Arkansas.

The thickness of the Ozark confining unit ranges 

from near zero to more than 1,600 ft in the Ozark 

subregion (pi. 22). At most locations the unit is less 

than 100 ft thick and, therefore, is relatively thin in 

comparison to other geohydrologic units in the Ozark 

subregion. The confining unit is thinnest in a narrow 

west-trending belt from southwest Missouri to southeast Kansas, where wells penetrate less than 10 ft of 

the confining unit. To the south of this belt, the unit 

gradually thickens except at scattered locations in 

northeast Oklahoma and southwest Missouri where

the unit is locally absent. The sequence of rocks has 

been identified and named as a confining unit on the 

basis of regional hydrologic relations. However, local 

lithologic and thickness variations can increase the 

leakance to the degree that confinement is minimal. 

The shale content of the Ozark confining unit, which 

is an indicator of the degree of confinement, ranges 

from 0 to 100 percent (pi. 23).

Along the northeastern boundary of the Ozark subregion, the confining unit is lithologically more complex than elsewhere in the subregion. Limestone 

predominates in this area; shale also is present in 

significant quantities, and sandstone is present in 

minor quantities. The thickness of the major shale 

formations may total as much as 100 ft. Many of the 

limestone formations also have included shale. In the 

northern and northwestern parts of the subregion, 

the lithology varies from mostly shale to mostly limestone, depending on the presence or absence of the 

three formations of the Chouteau Group (table 3). 

Southward, the confining unit is represented solely 

by the Chattanooga Shale.

SPRINGFIELD PLATEAU AQUIFER

The Springfield Plateau aquifer is composed of water-bearing limestone and is exposed at many locations on the Springfield Plateau, from which its name 

is taken, in southwestern Missouri. The aquifer, except along the Fall Line, extends outward from the 

outcrop area to the periphery of the Ozark subregion 

and dips into the subsurface along the west and 

south boundaries of the subregion, where it is overlain by nearly impermeable shale layers of the Western Interior Plains confining unit. The aquifer is the 

uppermost unit of the Ozark Plateaus aquifer system 

and at most locations overlies the Ozark confining unit.

Water from the aquifer is used extensively for 

stock and domestic purposes in the outcrop area. The 

aquifer also is present in the subsurface south of the 

Boston Mountains in Arkansas. In this area, the water in the aquifer contains more than 1,000 mg/L dissolved solids, probably because near-surface permeability 

has not been developed, and thus, the slow-moving water 

probably dissolves minerals as it passes through the confining unit. The aquifer south of the Boston Mountains is 

unused because of greater dissolved-solids concentrations 

and small well yields.

The Springfield Plateau aquifer includes several 

Mississippian formations. In northwest Arkansas, the 

most permeable zone is in the Boone Formation and 

the St. Joe Limestone Member of the Boone. Elsewhere, the aquifer includes several minor limestone 

formations from the basal Pierson Formation, which 

is equivalent to part of the Boone Formation, to the
B66 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

uppermost Moorefield Formation. The Moorefield 

Formation is included as part of the Springfield Plateau aquifer in northeastern Oklahoma. The shale 

content of the Moorefield Formation increases in 

northern Arkansas, where the formation is considered part of the overlying confining unit. In the 

southwestern part of the Ozark subregion, the 

Springfield Plateau aquifer includes the rocks from 

the basal part of the Boone Formation through the 

Moorefield Formation. The Boone Formation is similar to the Burlington and Keokuk Limestones and is 

moderately permeable. Outcrops of the aquifer typically 

do not form karsts in Oklahoma, but springs have developed in the solution openings along fractures.

The Springfield Plateau aquifer crops out around 

the western and southern perimeter of the Salem 

Plateau and along the axis of the Ozark uplift. In 

western Missouri, the top of the aquifer dips west to 

northwest into the subsurface at about 11 ft/mi (pi. 

24). The dip increases to about 30 ft/mi in northeastern Oklahoma near the Kansas border. At the extreme southwest edge of the subregion and beneath 

the Boston Mountains in northern Arkansas, the 

southward dip of the aquifer is as much as 140 ft/mi. 

The aquifer is not present in the area adjacent to the 

Mississippi Alluvial Plain (fig. 44) nor in the subsurface at two small areas near the western edge of the 

Springfield Plateau and at the southern and southwestern edge of the subregion in Arkansas and Oklahoma. To the west and south, the Springfield Plateau 

aquifer is thicker than the relatively uniform thickness of 100 to 400 ft that is present throughout most 

of the subregion (pi. 25).

In southwestern Missouri and eastern Kansas, the 

more important geologic formations in the aquifer, 

due to their relatively greater thickness and permeability, are the Burlington and Keokuk Limestones. 

These two formations are both of medium to coarsely 

crystalline bedded limestone and contain abundant 

gray chert, mainly in the form of nodules. Dissolution 

of the very soluble limestone along fractures has created an extensive network of permeable channels, 

which in many cases have been enlarged to the point 

where the rock matrix has collapsed, producing caves 

and other large karst features with extremely large 

permeability. The underlying Fern Glen Limestone 

and Pierson Formation, which are equivalent to part 

of the Boone Formation (pi. 1), are moderately permeable but are not as thick as the Burlington and 

Keokuk Limestones and do not contain extensive networks of solution channels.

Hydraulic-conductivity values from aquifer tests of 

the Springfield Plateau aquifer are not available. Estimates of hydraulic conductivity based on specific

capacity generally are not available because nearly 

all wells of sufficient diameter to permit measurement of drawdown are open to both the Springfield 

Plateau aquifer and the underlying Ozark aquifer.

The Springfield Plateau aquifer is mostly recharged at its outcrop areas. In general, water moves 

locally from high intervalley recharge areas to low 

discharge areas along the streams that dissect the 

area. Regionally, lateral flow in the Springfield Plateau aquifer is believed to be similar to that in the 

underlying Ozark aquifer. In the western part of the 

area, the aquifer receives upward discharge from the 

Ozark aquifer. In the eastern part of the outcrop 

area, conditions are reversed, and water is discharged downward to the underlying Ozark aquifer.

The Springfield Plateau aquifer is overlain along 

the western and southern borders by rock that restricts or confines flow to and from the aquifer. The 

overlying confining material is the eastern edge of 

the Western Interior Plains confining system, which 

is composed of layers of very slightly permeable shale 

and of layers of moderately permeable limestone, 

sandstone, and coal. The limestone is slightly fractured and has a small permeability, except near land 

surface where dissolution has markedly increased 

permeability. The same geologic formations comprising the Springfield Plateau aquifer exist near St. 

Louis in the northeast corner of the subregion near 

the junction of the Missouri and Mississippi Rivers. 

These rocks are not in the Springfield Plateau aquifer flow system. They form two local and isolated flow 

systems. The rocks have hydraulic characteristics 

that are similar to the Springfield Plateau aquifer. 

The rocks at this location are about 900 ft thick and 

thicken abruptly to the east, attaining a thickness of 

more than 1,500 ft within a few miles.

SUMMARY

The 370,000-mi2 study area extends from the foothills of the Rocky Mountains in Colorado to the Missouri and Mississippi Rivers in eastern Nebraska and 

Missouri, and from South Dakota to the Ouachita, 

Arbuckle, and Wichita Mountains of Arkansas and 

Oklahoma. This report describes the major regional 

aquifers within the study area and their geologic 

framework within the Cambrian through the lower 

sandstones in the Cretaceous rock section.

From the end of the Precambrian to Late Cambrian time, the study area was above sea level, and 

an uneven erosional surface had developed. The crystalline rock was fractured by the resultant stresses 

from large compressive forces from the north and
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B67

south, and northwest- and northeast-trending lineaments were formed.

From Late Cambrian through Middle Ordovician 

time, a transgressive but cyclic sea covered the area. 

The first deposits were mostly permeable sand followed by slightly permeable calcareous mud consisting of aragonite and algal remains. During periods of 

uplift above sea level or sea-level recession, uplift diagenesis occurred, which in general greatly increased 

porosity and intrinsic permeability. Uplift diagenesis 

includes dissolution of minerals in rocks along fractures, dolomitization of limestone near shorelines 

where fresh ground water and salinewater mix, and 

extensional fracturing that results from removal of 

overburden by erosion.

During most of Silurian and Devonian time, nearly 

the entire area was above sea level, except for southern Oklahoma and northern Arkansas. Again, uplift 

diagenesis greatly increased porosity and intrinsic 

permeability of the rocks. At the end of the Devonian 

or at the beginning of Early Mississippian time, a 

transgressing sea covered most of the area, and clay 

was deposited.

Calcareous mud was the dominant sediment deposited during much of Mississippian time. Tectonic 

activity increased as evidenced by uplifts, such as the 

Colorado-Wyoming and the Nemaha uplifts. Subsiding basins, such as the Arkoma and Anadarko, received large quantities of sediment that covered the 

older rocks, thus causing burial diagenesis. Processes 

of burial diagenesis include compaction, thermal diagenesis of organic materials, thermal diagenesis of 

clay, and pressure dissolution at grain contacts with 

recrystallization in pores. In general, burial diagenesis 

decreased primary porosity and intrinsic permeability; 

however, CO2-rich water, a product of thermal diagenesis, selectively increased secondary porosity and permeability by local dissolution of carbonate minerals.

Tectonic activity reached its maximum during 

Pennsylvanian time and decreased during the Permian. Uplifts, such as the Front Range, Apishapa, 

Criner, Amarillo, Wichita, Arbuckle, Ouachita, 

Ozark, Nemaha, and Cambridge-Central Kansas, 

were active. The Arkoma and Anadarko basins continued to subside and received as much as 20,000 ft 

of sediments. The dominant sediment was clay, with 

lesser calcareous mud, sand, and evaporite minerals. 

During the Permian, the eastern part of the area was 

tilted upward; the sea receded; and regional groundwater flow commenced from east to west. In the 

Ozark uplift area, a ground-water flow system began 

around the St. Francois Mountains.

During Triassic and Jurassic time, the eastern 

part of the study area was above sea level, and uplift

diagenesis was active again. However, during the 

Early Cretaceous, a transgressive but cyclic sea deposited permeable sand and slightly permeable clay 

over the western and central parts of the study area. 

During Late Cretaceous, clay was deposited in thick 

layers and burial diagenesis occurred throughout 

most of the area. At the end of the Cretaceous and 

into the Tertiary, major uplifts, such as the Rocky 

Mountains, were formed as part of the Laramide 

orogeny. Uplifts in the west accompanied the regional 

tilting of the study area downward to the east. Regional ground-water flow from west to east started in 

the Lower Cretaceous sandstone and in pre-Pennsylvanian rocks. In the Ozark area, the ground-water 

flow system near the St. Francois Mountains continued to expand as Pennsylvanian and Permian rocks 

were removed by erosion.

The geohydrologic units generally correlate with 

the regional stratigraphic units, except adjacent to 

major structural features and in other areas of complex stratigraphic relations. The major exception is 

along and adjacent to the physiographic boundary between the Interior Plains and the Interior Highlands. 

At this location, the Western Interior Plains aquifer 

system and the Ozark Plateaus aquifer system are 

laterally adjacent. In general, water flow in the Western Interior Plains aquifer system is very slow from 

the west to the east. The mostly fresh ground-water 

flow system originating in the Ozark Plateaus extends outward until it meets the saline ground-water 

flow system that underlies most of the western part 

of the Interior Plains. The approximate boundary of 

the transition zone between these two flow systems is 

marked by a broad low in the potentiometric surface 

that is nearly coincidental with a broad topographic 

low. Water in both aquifer systems moves upward to 

the water table, springs, or streams in the topographically low area. The areas underlain by the two 

regional flow systems are referred to herein as the 

Plains subregion and the Ozark subregion.

The Plains subregion contains three major regional-geohydrologic systems. These systems, in ascending order, are the Western Interior Plains 

aquifer system, the Western Interior Plains confining 

system, and the Great Plains aquifer system, all 

overlying the basement confining unit. Overlying 

these geohydrologic units are the Great Plains confining system and the High Plains aquifer.

Rocks of the Western Interior Plains aquifer system consist mostly of dolostone, limestone, and shale 

of Cambrian through Mississippian age. The geohydrologic units in the aquifer system are hydraulically 

connected. At most locations, the aquifer units are 

permeable and water yielding except in deep basins
B68 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

where permeability is greatly decreased. The aquifer 

system is several thousand feet thick in the 

Anadarko and Arkoma basins. The aquifer system 

contains saline water and brine with dissolved-solids 

concentrations of about 10,000 to more than 200,000 mg/ 

L. Intrinsic permeability ranges from 10"11 to 10~17 ft2.

The Western Interior Plains confining system confines water flow to and from the Western Interior 

Plains aquifer system at nearly all locations including the deep basins. The thick confining system consists of layered shale, limestone, sandstone, and 

evaporite deposits of Late Mississippian through Jurassic age. The thickness of the confining system decreases from about 20,000 ft in the Anadarko basin to 

nearly zero along the periphery of the Ozark Plateaus 

where it crops out.

The Great Plains aquifer system overlies the Western Interior Plains confining system and contains two 

regional aquifers and one confining unit. Both aquifers are composed predominantly of water-bearing 

Lower Cretaceous sandstone and are separated at 

most locations by a shale confining unit. Most recharge occurs in southeastern Colorado and northeastern 

New Mexico. Ground water flows east-northeast from 

these western recharge areas to discharge areas in central Kansas and eastern Nebraska.

The Apishapa aquifer, the lower of two aquifers in 

the Great Plains aquifer system, is composed of permeable, slightly cemented, medium-grained to very 

fine grained sandstone of the Cheyenne Sandstone 

and its equivalents. Aquifer thickness ranges from 0 

to 400 ft, but 100 to 200 ft is typical. The Apishapa 

confining unit restricts water movement between the 

Apishapa aquifer and the overlying Maha aquifer. 

The confining unit, which is typically less than 100 ft 

thick, mostly is composed of slightly permeable 

Kiowa Shale and equivalents. Intrinsic permeability 

ranges from 10~13 ft2 in the Denver basin to more 

than 10-10 ft2.

The Maha aquifer is the upper aquifer of the Great 

Plains aquifer system and is more extensive than the 

underlying Apishapa aquifer. The Maha aquifer consists of permeable sandstone of the Dakota Sandstone 

and its equivalents. Dissolved-solids concentrations 

range from about 1,000 mg/L along outcrops in southeastern Colorado, central Kansas, and eastern Nebraska to more than 20,000 mg/L in western 

Nebraska.

The Great Plains confining system overlies and restricts flow to and from the Great Plains aquifer system and the overlying High Plains aquifer or to and 

from the near-surface water-table aquifer. The confining system mostly consists of very slightly permeable 

Cretaceous shale. The extensive confining system,

which is more than 8,000 ft thick in the Denver basin, generally thins eastward.

The Ozark subregion approximately corresponds to 

the Ozark Plateaus and adjacent areas of the Interior 

Plains and Ouachita physiographic provinces. The 

Ozark Plateaus aquifer system, which is underlain by 

the basement confining unit, is located within the 

Ozark subregion. In general, freshwater flows outward from the central area of the Ozark Plateaus to 

the periphery, where the water is discharged upward. 

The basement confining unit consists of igneous and 

metamorphic rocks that generally are fractured, saturated, and locally yield water to wells.

The St. Francois aquifer, which is the lowest aquifer of the Ozark Plateaus aquifer system, is composed 

of water-bearing Upper Cambrian rocks, mostly sandstone that directly overlies the basement. The aquifer 

is more than 1,000 ft thick near the Mississippi Alluvial Plain, but typically is 200 to 500 ft thick. The St. 

Francois confining unit, which overlies and confines 

the St. Francois aquifer, is composed of Upper Cambrian 

shale, siltstone, dolostone, and limestone, and it is leaky 

as it transmits a considerable amount of water.

The Ozark aquifer, the largest and most widely 

used aquifer in the Ozark subregion, is composed 

mostly of water-bearing Upper Cambrian through 

Middle Devonian fractured dolomitic rocks. The aquifer is typically about 1,000 ft thick and is the thickest 

unit of the Ozark Plateaus aquifer system. The Ozark 

confining unit restricts the movement of water between 

the Ozark aquifer and the overlying Springfield Plateau 

aquifer. The confining unit includes Upper Devonian and 

Lower Mississippian shale.

The Springfield Plateau aquifer is composed of 

fractured and water-bearing Mississippian limestone. 

Aquifer thickness is as much as 1,500 ft, but thicknesses of 100 to 400 ft are typical. The aquifer is 

overlain to the west by beds of very slightly permeable shale of Pennsylvanian age. The shale confines 

or restricts water movement between the Springfield 

Plateau aquifer and the water table. At most locations, such as along the eastern boundary of the 

Ozark subregion, the shale restricts upward flow 

from the Springfield Plateau aquifer. Pennsylvanian 

shale also overlies the aquifer south of the Boston 

Mountains. In this area permeability of the aquifer 

material is very slight, and the quantity of water 

flowing to the south is very small.

REFERENCES CITED

Adler, F.J., 1970, Future of petroleum provinces of the MidContinent Region 7: American Association of Petroleum
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B69

Geologists Memoir 15, v. 2, p. 985-1120.

Amsden, T.W., 1975, Hunton Group (Late Ordovician, Silurian, 

and Early Devonian) in the Anadarko basin of Oklahoma: 

Oklahoma Geological Survey Bulletin 121, 209 p.

Arendt, J.W., Butz, T.R., Cagle, G.W., Kane, V.E., and Nicols, 

C.E., 1979, National Uranium Resources Evaluation 

Program Hydrochemical and stream sediment 

reconnaissance procedures of the uranium resource 

evaluation project: Kansas Geological Survey Report-K/UR100, 56 p.

Baker, C.H., Jr., and Foulk, D.G., 1975, National water data 

storage and retrieval system Instructions for preparation 

and submission of ground-water data: U.S. Geological 

Survey Open-File Report 75-589, v. 2, chap. A-H.

Banta, E.R., 1986, Hydrogeologic control of the Dakota aquifer 

near Pueblo, Colorado: U.S. Geological Survey WaterResources Investigations Report 85-4186, 23 p.

Beales, F.W., Jackson, K.C., Jowett, E.G., Pearce, G.W., and Wu, 

Y., 1980, Paleomagnetism applied to the study of timing 

stratigraphy with special reference to ore and petroleum 

problems, in Stragway, D.W., ed., The continental crust and 

its mineral deposits: Geologic Association of Canada Special 

Paper 20, p. 83-126.

Bennison, A.P., and Chenoweth, P.A., (no date), Geologic highway 

map of northern Great Plains region: American Association 

of Petroleum Geologists Map 12, scale 1:1,875,000, 1 sheet.

Berman, A.E., Poleschook, D., Jr., and Dimelow, T.E., 1980, 

Jurassic and Cretaceous Systems of Colorado, in Kent, H.C., 

and Porter, K.W., eds., Colorado geology: Rocky Mountain 

Association of Geologists, p. 111-134.

Borahay, Abd, 1973, Petrography, diagenesis and environment of 

deposition of the Gasconade Formation, Lower Ordovician, 

southern Missouri: University of Missouri at Rolla, Ph.D. 

dissertation, 194 p.

Brandt, E.O., 1967, Kansas, in Smith, Russel, ed., Stratigraphic 

cross section of Paleozoic rocks, Oklahoma, to Saskatchewan: 

American Association of Petroleum Geologists Cross Section 

Publication 5, p. 4-6.

Brewer, J.A., 1982, Study of southern Oklahoma aulacogen, using 

COCORP seismic-reflection profiles, in Gilbert, M.C., and 

Donovan, R.N., eds., Geology of eastern Wichita Mountains, 

southwestern Oklahoma: Oklahoma Geological Survey 

Guidebook 21, p. 31-39.

Bridge, Josiah, 1930, Geology of the Eminence and Carareva 

quadrangles: Missouri Bureau of Geology and Mines, v. 24, 

2d ser., p. 134-150.

Brown, Alton, 1985, Empirical relation between carbonate 

porosity and thermal maturity An approach to regional 

porosity prediction Discussion: American Association of 

Petroleum Geologists Bulletin, v. 69, no. 11, p. 2024-2028.

Brown, D.L., 1978, Wrench-style deformational patterns 

associated with a meridional stress axis recognized in 

Paleozoic rocks in parts of the Williston Basin: Symposium 

of the Montana Geological Society, Billings, 1978, 

Proceedings, p. 17-31.

Bucke, D.P., 1969, Effect of diagenesis upon clay mineral content 

of interlaminated Des Moinesian sandstones and shales in 

Oklahoma: Norman, University of Oklahoma, Ph.D. 

dissertation, 123 p.

Bunker, B.J., 1981, The tectonic history of the Transcontinental 

arch and Nemaha uplift and their relationship to the 

Cretaceous rocks of the central Mid-continent region, in 

Brenner, R.L., and others, eds., Cretaceous stratigraphy and 

sedimentation in northwest Iowa, northeast Nebraska, and

southeast South Dakota: Iowa Geological Survey Guidebook

Series 4, p. 1-24. 

Burgess, W.J., 1964, Stratigraphic dolomitization in Arbuckle

rocks in Oklahoma: Tulsa Geological Society Digest, v. 32, p.

45-47. 

Busby, M.W., 1966, Annual runoff in the conterminous United

States: U.S. Geological Survey Hydrologic-Investigations

Atlas HA-212, scale 1:7,500,000, 1 sheet. 

Bush, W.V., Haley, B.R., Stone, C.G., Holbrook, D.F., and

McFarland, J.D., III, 1980, A guidebook to the geology of the

Arkansas Paleozoic area: Arkansas Geological Commission,

36 p. 

Caplan, W.M., 1957, Subsurface geology of northwestern

Arkansas: Arkansas Geological and Conservation

Commission Information Circular 19, 14 p. 

Carlson, M.P., 1963, Lithostratigraphy and correlation of the

Mississippian System in Nebraska: Nebraska Geological

Survey Bulletin 21, 46 p.

 1970, Distribution and subdivision of Precambrian and 

Lower and Middle Paleozoic rocks in the subsurface of 

Nebraska: Nebraska Geological Survey Report of 

Investigation, 3, 23 p.

Chase, G.W., Frederickson, E.A., and Ham, W.E., 1956, Resume 

of the geology of the Wichita Mountains, Oklahoma, in 

Petroleum Geology of Southern Oklahoma: American 

Association of Petroleum Geologists, v. 1, p. 36-55.

Chenoweth, P.A., 1968, Early Paleozoic (Arbuckle) overlap, 

southern mid-continent, United States: American Association 

of Petroleum Geologists Bulletin, v. 52, no. 9, p. 1670-1688.

Clayton, J.L., and Swetland, P.J., 1980, Petroleum generation 

and migration in the Denver basin: American Association of 

Petroleum Geologists Bulletin, v. 64, no. 10, p. 1613-1633.

Craig, L.C., 1975, Stratigraphy and conodant faunas of the Cason 

Shale and the Kimmswick and Fernvale Limestones of 

Northern Arkansas, in Headrick, K.N., and Wise, O.A., eds., 

Contributions to the geology of the Arkansas Ozarks: 

Arkansas Geological Commission, p. 61-95.

Craig, L.C., and Varnes, K.L., 1979, Paleotectonic investigations 

of the Mississippian System in the United States History of 

the Mississippian System An interpretive summary, in 

Paleotectonic investigations of the Mississippian System in 

the United States, Part II: U.S. Geological Survey 

Professional Paper 1010, p. 371-405.

Croneis, Carey, 1930, Geology of the Arkansas Paleozoic area: 

Arkansas Geological Survey Bulletin 3, 457 p.

Dake, C.L., 1930, The geology of the Potosi and Edgehall 

quadrangles: Missouri Bureau of Geology and Mines, v. 23, 

2d series, p. 193-197.

Damberger, H.H., 1974, Coalification patterns of Pennsylvanian 

coal basins of the Eastern United States, in Carbonaceous 

materials as indicators of metamorphism: Geological Society 

of America Special Paper 153, p. 53-73.

Darton, N.H., 1905, Preliminary report on the geology and under 

ground water resources of the Central Great Plains: U.S. 

Geological Survey Professional Paper 32, 433 p.

Decker, C.E., and Merritt, C.A., 1928, Characteristics of Arbuckle 

limestone: Oklahoma Geological Survey Circular 15, 56 p.

Dennison, R.E., 1981, Basement rocks in northeastern Oklahoma: 

Oklahoma Geological Survey Circular 84, 83 p.

Devoto, R.H., 1980a, Mississippian stratigraphy and history of 

Colorado, in Kent, H.C., and Porter, K.W., eds., Colorado 

geology: Rocky Mountain Association of Geologists, p. 57-70.

 1980b, Pennsylvanian stratigraphy and history of 

Colorado, in Kent, H.C., and Porter, K.W., eds., Colorado
B70 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

geology: Rocky Mountain Association of Geologists, p. 71-101.

Dinwiddie G.A., 1979, Plan of study for the Northern Great 

Plains regional aquifer system analysis in parts of Montana, 

North Dakota, South Dakota, and Wyoming: U.S. Geological 

Survey Water-Resources Investigations Report 79-34, '20 p.

Dixon, G.H., 1967, Northeastern New Mexico and TexasOklahoma Panhandles, in Paleotectonic investigations of the 

Permian System in the United States: U.S. Geological 

Survey Professional Paper 515-D, p. 65-80.

Dott, R.H., Jr., and Batten, R.L., 1976, Evolution of the earth: 

New York, McGraw-Hill Book Company, 504 p.

Dugan, J.T., and Peckenpaugh, J.M., 1985, Effects of climate, 

vegetation, and soils on consumptive water use and groundwater recharge to the Central Midwest regional aquifer 

system, Mid-continent United States: U.S. Geological Survey 

Water-Resources Investigations Report 85-4236, 78 p.

Dutton, S.P., 1980, Depositional systems and hydrocarbon 

resource potential of the Pennsylvanian system, Palo Duro 

basin, Texas Panhandle: Texas Bureau of Economic Geology, 

Geologic Article 80-8, 49 p.

Eagleman, J.R., 1976, Visualization of climate: Lawrence, 

University of Kansas Press, 142 p.

Edwards, A.R., and Downey, M.W., 1967, Oklahoma, in Smith, 

Russel, ed., Stratigraphic cross-section of Paleozoic rocks: 

American Association of Petroleum Geologists Cross Section 

Publication 5, p. 1-3.

El-Etr, H.A., 1967, The technique of lineaments and linear analy 

sis and its application in the minerogenic province of 

southeast Missouri: Columbia, University of Missouri, Ph.D. 

dissertation, 249 p.

Fagerstrom, J.A., and Burchett, P.R., 1972, Upper Pennsylvanian 

shoreline deposits from Iowa and Nebraska Their 

recognition, variation, and significance: Geological Society of 

America Bulletin, v. 83, p. 367-388.

Fenneman, N.M., 1946, Physical divisions of the United States 

[map]: U.S. Geological Survey, scale 1:7,000,000, 1 sheet.

Franks, P.C., 1975, The transgressive-regressive sequence of the 

Cretaceous Cheyenne, Kiowa, and Dakota Formations of 

Kansas, in Gilbert, M.C., and Donovan, R.N., eds., Geology 

of eastern Wichita Mountains, southwestern Oklahoma: 

Geological Association of Canada Special Paper 13, p. 469-521.

Frezon, S.E., and Dixon, G.H., 1975, Texas panhandle and 

Oklahoma, in McKee, E.D., and Crosby, E.J., coordinators, 

Paleotectonic investigations of the Pennsylvanian System in 

the United States, Part I: Introduction and regional analyses 

of the Pennsylvanian System: U.S. Geological Survey 

Professional Paper 853, p. 177-195.

Frezon, S.E., and Click, E.E., 1959, Pre-Atoka rocks of northern 

Arkansas: U.S. Geological Survey Professional Paper 314-H, 

p. 171-189.

Friedman, M., 1964, Petrofabric techniques for determination of 

principal stress direction in rocks: International Conference 

on State of Stress in the Earth's Crust, Santa Monica, Calif., 

1963, Proceedings, p. 450-552.

Glick, E.E., 1975, Arkansas and northern Louisiana, in McKee, 

E.D., and Crosby, E.J., coordinators, Paleotectonic 

investigations of the Pennsylvania System in the United 

States, Part I: Introduction and regional analyses of the 

Pennsylvanian System: U.S. Geological Survey Professional 

Paper 853, p. 157-176.

Grubb, H.F., 1984, Planning report for the Gulf Coast Regional 

aquifer-system analysis in the Gulf of Mexico Coastal Plain, 

United States: U.S. Geological Survey Water-Resources 

Investigations Report 84-4219, 30 p.

Gutentag, E.D., Heimes, F.J., Krothe, N.C., Luckey, R.R., and

Weeks, J.B., 1984, Geohydrology of the High Plains aquifer 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Professional Paper 1400-B, 63 p.

Habicht, J.K.A., 1979, Paleoclimate, paleomagnetism, and 

continental drift: American Association of Petroleum 

Geologists Studies in Geology 9, 37 p.

Ham, W.E., 1950, Geology and petrology of the Arbuckle 

Limestone in the southern Arbuckle Mountains, Oklahoma: 

New Haven, Conn., Yale University, Ph.D. dissertation, 83 p.

Ham, W.E., Dennison, C.E., and Merritt, C.A., 1964, Basement 

rocks and structural evolution of southern Oklahoma: 

Oklahoma Geological Survey Bulletin 93, 302 p.

Ham, W.E., and Wilson, J.L., 1967, Paleozoic epiorogeny and 

orogeny in the central United States: American Journal of 

Science, v. 265, p. 332-407.

Harvey, E.J., 1980, Ground water in the Springfield-Salem 

Plateaus of southern Missouri and northern Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 80- 

101, 66 p.

Hayes, W.C., 1962, Precambrian surface showing major 

lineaments: Missouri Geological Survey map, scale 

1:500,000, 1 sheet.

Hedman, E.R., Skelton, John, Freiwald, D.A., 1987, Flow 

characteristics for selected springs and streams in the Ozark 

subregion, Arkansas, Kansas, Missouri, and Oklahoma: U.S. 

Geological Survey Hydrologic Investigations Atlas HA-688, 

scale 1:750,000, 4 sheets.

Helgesen, J.O., Jorgensen, D.G., Leonard, R.B., and Signer, D.C., 

1982, Regional study of the Dakota aquifer (Darton's Dakota 

revisited): Ground Water, v. 20, no. 4, p. 410-414.

Hendricks, T.A., 1935, Carbon ratios in part of ArkansasOklahoma coal field: American Association of Petroleum 

Geologists Bulletin, v. 19, no. 7, p. 937-947.

Hitchon, Brian, 1969, Fluid flow in western Canada sedimentary 

basin Part 2, Effect of geology: Water Resources Research, 

v. 5, no. 2, p. 460-469.

Holdoway, K.A., 1978, Deposition of evaporites and red beds of 

the Nippewalla Group, Permian, western Kansas: Kansas 

Geological Survey Bulletin 215, 43 p.

Houseknecht, D.W., and Matthews, S.M., 1985, Thermal maturity 

of carboniferous strata, Ouachita Mountains: American 

Association of Petroleum Geologists Bulletin, v. 69, no. 3, p. 

335-345.

Huffman, G.G., 1959, Pre-Desmoinesian isopachous and 

paleogeologic studies in central mid-continent region: 

American Association of Petroleum Geologists Bulletin, v. 

43, no. 11, p. 2544-2573.

Hubbert, M.K., 1940, Theory of ground-water motion: Journal of 

Geology, v. 48, no. 8, pt. 1, p. 785-944.

Jorgensen, D.G., 1980, Relationships between basic soilsengineering equations and basic ground-water flow 

equations: U.S. Geological Survey Water-Supply Paper 2064, 

40 p.

 1989, Using geophysical logs to estimate porosity, water 

resistivity, and intrinsic permeability: U.S. Geological 

Survey Water-Supply Paper 2321, 24 p.

Jorgensen, D.G., Gogel, Tony, and Signer, D.C., 1982, 

Determination of flow in aquifers containing variable density 

water: Ground Water Monitoring Review, v. 2, no. 2, p. 40 

45.

Jorgensen, D.G., and Signer, D.C., 1981, Plan of study for the 

Central Midwest regional aquifer-system analysis in parts of 

Arkansas, Colorado, Kansas, Missouri, Nebraska, New 

Mexico, Oklahoma, South Dakota, and Texas: U.S.
REGIONAL AQUIFERS GEOHYDROLOGIC FRAMEWORK B71

Geological Survey Water-Resources Investigations Report SI206, 28 p. 

King, P.B., compiler, 1968, Tectonic map of North America, in

National Atlas: U.S. Geological Survey, scale 1:7,500,000, 1

sheet. 

Kinney, D.M., 1966, Geologic map of the United States: U.S.

Geological Survey, scale 1:7,500,000, 1 sheet. 

Krueger, J.M., and Keller, G.R., 1986, Interpretation of crustal

structure from regional gravity anomalies, Ouachita

Mountains area and adjacent Gulf Coastal Plain: American

Association of Petroleum Geologists Bulletin, v. 70, no. 6, p.

667-689. 

Kurtz, V.E., Thacker, J.L., Anderson, K.E., and Gerdemann, P.E.,

1975, Traverse in Late Cambrian strata from the St.

Francois Mountains, Missouri, to Delaware County,

Oklahoma: Missouri Department of Natural Resources

Report of Investigations 55, 118 p. 

Lamonds, A.G., 1972, Water-resources reconnaissance of the

Ozark Plateaus province, northern Arkansas: U.S. Geological

Survey Hydrologic Investigations Atlas HA-383, scale

1:500,000, 2 sheets. 

Leach, D.L., Viets, J.G., Rowan, E.L., 1985, Fluid-inclusion,

petrography, and geochemical studies, in Pratt, W.P., ed.,

Midcontinent Strategic and Critical Minerals Project 

Objectives and status, October 1985: U.S. Geological Survey

Open-File Report 85-597, 16 p. 

Lee, Wallace, and Merriam, D.F., 1954, Preliminary study of the

structure of western Kansas: Kansas Geological Survey, Oil

and Gas Investigation 11, 23 p. 

Leonard, R.B., Signer, D.C., Jorgensen, D.G., and Helgesen, J.O.,

1983, Geohydrology and hydrochemistry of the Dakota

aquifer, central United States: Water Resources Bulletin, v.

19, no. 6, p. 903-911. 

Lobmeyer, D.H., 1980, Preliminary potentiometric-surface map

showing freshwater heads for the Lower Cretaceous rocks in

northern Great Plains of Montana, North Dakota, South

Dakota, and Wyoming: U.S. Geological Survey Open-File

Report 80-757, scale 1:1,000,000, 1 sheet. 

Lohman, S.W., 1972, Definition of selected ground-water terms 

Revisions and conceptual refinements: U.S. Geological

Survey Water-Supply Paper 1988, 21 p. 

MacCary, L.M., 1978, Interpretation of well logs in a carbonate

aquifer: U.S. Geological Survey Water-Resources

Investigations Report 78-88, 30 p. 

MacLachlan, M.E., 1967, Oklahoma, in Paleotectonic

investigations of the Permian System in the United States:

U.S. Geological Survey Professional Paper 515-E, p. 85-92. 

Maher, J.C., 1953, Permian and Pennsylvanian rocks of

southeastern Colorado: American Association of Petroleum

Geologists Bulletin, v. 37, no. 5, p. 913-939. 

Maxey, G.B., 1964, Hydrostratigraphic units: Journal of

Hydrology, v. 2, p. 124-129. 

McCabe, Chad, Van Der Voo, Rob, and Pecor, D.R., 1983,

Diagenetic magnetite carries ancient sedimentary remanence

in some Paleozoic sedimentary carbonates: Geology, v. 11, p.

221-223. 

McCracken, M.H., 1971, Structural feature map of Missouri:

Missouri Geological Survey and Water Resources, scale

1:500,000, 1 sheet. 

McGowen, J.H., Granata, G.E., and Seni, S.J., 1979, Depositional

framework of the lower Dockum (Triassic), Texas Panhandle:

Texas Bureau of Economic Geology Report of Investigation

97, 60 p. 

McKee, E.D., Crosby, E.J., and others, 1975, Paleotectonic

investigations of the Pennsylvanian System in the United

States Part III. Plates: U.S. Geological Survey Professional 

Paper 853, 17 pi.

McKee, E.D., and Oriel, S.S., 1967, Paleotectonic maps of the 

Permian System: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map 1 450, 164 p.

McKee, E.D., Oriel, S.S., Ketner, K.B., MacLachlan, M.E., 

Goldsmith, J.W., MacLachlan, J.C., and Mudge, M.R., 1959, 

Paleotectonic maps of the Triassic System: U.S. Geological 

Survey Miscellaneous Geologic Investigations Map 1-300, 33 

p., scale 1:500,000, 9 sheets.

McKee, E.D., Oriel, S.S., Swanson, V.E., MacLachlan, M.E., 

MacLachlan, J.C., Kitner, K.B., Goldsmith, J.W., Bell, R.Y., 

Jameson, D.J., and Imlay, R.W., 1956, Paleotectonic maps of 

the Jurassic System: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map 1-175, 6 p., scale 1:500,000, 9 

sheets.

Merriam, D.F., 1963, Geologic history of Kansas: Kansas 

Geological Survey Bulletin 162, 317 p.

Merewether, E.A., and Cobban, W.A., 1981, Mid-Cretaceous 

formation(s) in eastern South Dakota and adjoining areas 

Stratigraphic, paleotologic, and structural interpretations, in 

Brenner, R.L., and others, eds., Cretaceous stratigraphy and 

sedimentation in northwest Iowa, northeast Nebraska, and 

southeast South Dakota: Iowa Geological Survey Guidebook 

4, p. 43-56.

Mudge, M.R., 1967, Central Midcontinent region, in Paleotectonic 

investigations of the Permian System in the United States: 

U.S. Geological Survey Professional Paper 515-F, p. 97-123.

Oetking, Philip, Feray, D.E., and Renfro, H.B., 1966, Geological 

highway map of the Mid-continent region, Kansas, Missouri, 

Oklahoma, and Arkansas: American Association of 

Petroleum Geologists Map 1, scale 1:1,875,000, 1 sheet.

 1967, Geological highway map of the southern Rocky 

Mountain region, Utah, Colorado, Arizona, and New Mexico: 

American Association of Petroleum Geologists Map 2, scale 

1:1,875,000, 1 sheet.

Ottman, J.P., 1984, Evolution of formation fluids in the "J" 

sandstone, Denver basin, Colorado, in Jorgensen, D.G., and 

Signer, D.C., eds., Geohydrology of the Dakota aquifer 

Proceedings of the First C.V. Theis Conference on 

Geohydrology: Worthington, Ohio, National Water Well 

Association, p. 77-91.

Prichard, G.E., 1975, Nebraska and adjoining parts of South 

Dakota and Wyoming, in McKee, E.D., and Crosby, E.J., 

coordinators, Paleotectonic investigations of the 

Pennsylvanian System in the United States, Part I: 

Introduction and regional analyses of the Pennsylvanian 

System: U.S. Geological Survey Professional Paper 853, p. 

115-126.

Rascoe, Bailey, Jr., and Adler, F.J., 1983, Permo-Carboniferous 

hydrocarbon accumulations, Mid-Continent, U.S.A.: 

American Association of Petroleum Geologists Bulletin, v. 

67, no. 6, p. 979-1001.

Renfro, H.B., (no date), Geological highway map of Texas: 

American Association of Petroleum Geologists Map 7, scale 

1:1,875,000, 1 sheet.

Ross, R.J., Jr., and Tweto, Ogden, 1980, Lower Paleozoic 

sediments and tectonics, Colorado, in Kent, H.C., and Porter, 

K.W., eds., Colorado geology: Rocky Mountain Association of 

Geologists Symposium on Colorado geology, p. 47-56.

Schwalb, H.R., 1982, Geologic-tectonic history of the area 

surrounding the northern end of the Mississippi embayment: 

University of Missouri-Rolla Journal, p. 31 42.

Scotese, C.R., Bambach, R.K., Barton, C., Van Der Voo, R., and 

Ziegler, A.M., 1979: Paleozoic base maps: Journal of Geology,
B72 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

v. 87, no. 3, p. 217-277.

Sides, J.R., 1978, A study of the emplacement of a shallow 

granite batholith The St. Francois Mountains, Missouri: 

Lawrence, University of Kansas, Ph.D. dissertation, 124 p.

Sims, P.K., compiler, 1985, Precambrian basement map of 

Northern Midcontinent, U.S.A.: U.S. Geological Survey 

Open-File Report 85-0604, 16 p., scale 1:1,000,000, 1 sheet.

Smith, Russell, and Burchett, Raymond, 1967, Nebraska in 

Smith, Russell, ed., Stratigraphic cross section of Paleozoic 

rocks, Oklahoma to Saskatchewan: American Association of 

Petroleum Geologists Cross Section Publication 5, p. 7-9.

Steeples, D.W., 1982, Structure of the Salina-Forest City 

interbasin boundary from seismic studies: University of 

Missouri-Rolla Journal, no. 3, 39 p.

Steinhilber, W.L., and Young, H.L., 1979, Plan of study for the 

northern Midwest regional aquifer-system analysis: U.S. 

Geological Survey Water-Resources Investigations 79-44, 20 p.

Stewart, G.F., 1975, Kansas, in McKee, E.D., and Crosby, E.J., 

coordinators, Paleotectonic investigations of the 

Pennsylvania System in the United States, Part I: 

Introduction and regional analyses of the Pennsylvanian 

System: U.S. Geological Survey Professional Paper 853, p. 

127-156.

Thacker, J.L., 1974, A study of the subsurface stratigraphy of 

the Upper Cambrian in western Missouri: University of 

Missouri-Rolla, M.S. thesis, 130 p.

Tweto, Ogden, 1980, Summary of Laramide orogeny in Colorado, 

in Kent, H.C., and Porter, K.W., eds., Colorado geology: 

Rocky Mountain Association of Geologists Symposium on 

Colorado, p. 129-134.

University of Oklahoma, 1980, Petroleum data system of North 

America Users guide: Norman, University of Oklahoma 

Press, 300 p.

U.S. Geological Survey, 1984, Geologic time chart, in 

Stratigraphic notes, 1983: U.S. Geological Survey Bulletin 

1537-A, p. A1-A4.

Volk, R.W., 1970, Petroleum potential of eastern Colorado, 

western Nebraska, southeastern Wyoming, and 

northeastern New Mexico: American Association of 

Petroleum Geologists Memoir 15, p. 673-691.

Walters, R.F., 1946, Buried Pre-Cambrian hills in northeastern

Barton County, central Kansas: American Association of 

Petroleum Geologists Bulletin, v. 30, no. 5, p. 660-729.

Wanless, H.R., 1975, Missouri and Iowa, in McKee, E.D., and 

Crosby, E.J., coordinators, Paleotectonic investigations of 

the Pennsylvanian System in the United States, Part I: 

Introduction and regional analyses of the Pennsylvanian 

System: U.S. Geological Survey Professional Paper 853, p. 

97-114.

Waples, D.W., 1982, Time and temperature in petroleum 

formation Application of Lopatin's method to petroleum 

exploration Reply: American Association of Petroleum 

Geologists Bulletin, v. 66, p. 1152.

Warner, L.Q., 1980, Colorado lineament, in Kent, H.C., and 

Porter, K.W., eds., Colorado geology: Rocky Mountain 

Association of Geologists Symposium on Colorado, p. 11 21.

Weeks, J.B., 1978, Plan of study for the High Plains regional 

aquifer-system analysis in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming: U.S. Geological Survey Water-Resources 

Investigations Report 78-70, 28 p.

Weeks, J.B., and Gutentag, E.D., 1981, Bedrock geology, altitude 

of base, and 1980 saturated thickness of the High Plains 

aquifer in parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, and Wyoming: 

U.S. Geological Survey Hydrologic Investigations Atlas HA648, 1:2,500,000, 2 sheets.

Wilson, R.F., 1975, Eastern Colorado, in McKee, E.D., and 

Crosby, E.J., coordinators, Paleotectonic investigations of 

the Pennsylvanian System in the United States, Part I: 

Introduction and regional analyses of the Pennsylvanian 

System: U.S. Geological Survey Professional Paper 853, p. 

245-264.

Wise, O.A., and Caplan, W.M., 1979, Silurian and Devonian 

rocks of northern Arkansas: Arkansas Geological 

Commission Information Circular 25, 14 p.

Yarger, H.L., 1982, Regional interpretation of Kansas 

aeromagnetic data, in Steeples, D.W., and Starnes, S.A. 

eds., Assessment of geothermal resources of Kansas: Kansas 

Geological Survey Report to Geothermal Division of U.S. 

Department of Energy, Kansas Geological Survey Open-File 

Report 82-22, v. 1, section 3, 101 p.

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