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Anhydrite Deposits of the 

United States and Characteristics of 

Anhydrite Important for 

Storage of Radioactive Wastes 

Edited by WALTER E. DEAN and KENNETH S. JOHNSON 

With Introduction and Discussion 

By WALTER E. DEAN, KENNETH S. JOHNSON, and 

SERGE GONZALES 

and sections on 

Distribution and Geologic Characteristics of 

Anhydrite Deposits in the United States 

By KENNETH S. JOHNSON, SERGE GONZALES, and 

WALTER E. DEAN 

Physical Properties of Anhydrite 

By SHARON F. DIEHL and WILLIAM Z. SAVAGE 

Hydrogeology of Anhydrite 

By WILLIAM THORDARSON 

Chemical Properties of Anhydrite 

By ROBERT W. POTIER II and MICHAEL A. CLYNNE 

An inventory of the geologic, physical, hydrologic, and 

chemical characteristics of anhydrite deposits in the 

United States and evaluation of anhydrite as a possible 

medium for the storage of radioactive wastes 

U.S. GEOLOGICAL SURVEY BULLETIN 1794 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U. S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Any use of trade names in this report is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey 

Library of Congress Cataloging-in-Publication Data 

Anhydrite deposits of the United States and characteristics of anhydrite 

important for storage of radioactive wastes. 

(U.S. Geological Survey bulletin ; 1794) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1794 

1. Anhydrite-United States. 2. Radioactive waste disposal in the 

ground-United States. I. Dean, Walter, E. II. Johnson, Kenneth Sutherland, 

1934- .Ill. Series. 

QE75.B9 no. 1794 557.3 s 87-600220 

[QE391.A573] [553.6'3] 
CONTENTS 

ABSTRACT 1 

SECTION 1. INTRODUCTION AND DISCUSSION by Walter E. Dean, 

Kenneth S. Johnson, and Serge Gonzales 3 

Background 3 

Regional geologic characteristics important for waste storage 4 

Structure and geologic framework 4 

Dip or inclination of strata 4 

Faults and joints 4 

Nature and extent of adjacent strata 5 

Anhydrite deposits 5 

Depth of storage zone 5 

Thickness and extent 5 

Homogeneity 5 

Dissolution 6 

Hydrology 6 

Surface water 6 

Ground water 7 

Mineral resources 7 

Origin of evaporite deposits 7 

SECTION 2. DISTRIBUTION AND GEOLOGIC CHARACTERISTICS OF 

ANHYDRITE DEPOSITS IN THE UNITED STATES, by 

Kenneth S. Johnson, Serge Gonzales, and Walter E. Dean 9 

Summary 9 

Michigan basin 16 

Structure and geologic framework 16 

Salina Group 17 

Lucas Formation of Detroit River Group 19 

Michigan Formation 23 

Appalachian basin-Salina Group 24 

Adirondack uplift-Precambrian 26 

Saltviiie area (Virginia)-Maccrady Formation 27 

Illinois basin-St. Louis Limestone 28 

Forest City basin-Devonian, Mississippian, and Jurassic 28 

South Florida basin-Cretaceous and Tertiary 29 

Gulf Coast basin 31 

Structure and geologic framework 31 

Salt -dome cap rock 33 

Werner Formation 39 

Buckner Formation 40 

Ferry Lake Anhydrite 42 

Central Texas region-Edwards Limestone and McKnight Formation 44 

Permian basin 44 

Structure and geologic framework 44 

Contents Ill 
Permian basin-Continued 

Wellington Formation and Wichita Group 47 

Lower evaporites of Clear Fork Group 49 

Cimarron anhydrite and upper evaporites of Clear Fork Group 49 

Yeso Formation and Briggs Formation 49 

San Andres Limestone and Blaine Formation 50 

Artesia Group 51 

Cloud Chief Formation 51 

Castile Formation 52 

Salado Formation 58 

Rustler Formation and Alibates Dolomite Lentil 58 

Northern Denver basin-Pennsylvanian through Triassic 60 

Wyoming basins-Pennsylvanian through Jurassic 62 

Williston basin-Ordovician through Jurassic 65 

Sweetgrass Arch-Three Forks Formation and other Devonian units 66 

Eagle basin-Eagle Valley Evaporite 69 

Paradox basin-Paradox Member of Hermosa Formation 70 

San Juan basin-Todilto Formation 72 

Supai salt basin-Supai Formation 76 

Basin and Range Province of Arizona and southern Nevada 78 

Structure and geologic framework 78 

Picacho basin-Miocene evaporites 79 

Chandler basin-Miocene evaporites 82 

Phoenix basin-Luke Salt Member 84 

Red Rock basin-Miocene evaporites 85 

Tucson basin-Miocene evaporites 85 

Virgin Valley basin-Muddy Creek Formation 85 

Other basins in Arizona 86 

Southern Nevada and nearby areas-Permian through Tertiary 86 

Central Utah-Jurassic and Tertiary 88 

Eastern Great Basin-Permian 88 

Northwestern Nevada-Triassic or Jurassic 89 

Western Idaho and eastern Oregon-Triassic 89 

Southern California-Tertiary 89 

SECTION 3. PHYSICAL PROPERTIES OF ANHYDRITE, 

by Sharon F. Diehl and William Z. Savage 91 

Introduction 91 

Thermal properties 92 

Mechanical properties 92 

Elastic properties 93 

Discussion 93 

SECTION 4. HYDROGEOLOGY OF ANHYDRITE, 

by William Thordarson 95 

Porosity, hydraulic conductivity, and transmissivity of anhydrite 95 

Hydraulic characteristics of bedded anhydrite 95 

Intercrystalline porosity and hydraulic conductivity 95 

IV Contents 
Porosity, hydraulic conductivity, and transmissivity of anhydrite-Continued 

Hydraulic characteristics of bedded anydrite-Continued 

Fracture porosity and hydraulic conductivity 95 

Hydraulic characteristics of anhydrite in cap rock of salt domes 102 

Intercrystalline porosity in cap rock of salt domes 102 

Fracture porosity in cap rock of salt domes 102 

General hydrogeology of anhydrite 103 

Dissolution of anhydrite and interbedded salt 104 

Hydration of anhydrite to gypsum 104 

Data from springs 105 

Summary and conclusions 105 

SECTION 5. CHEJ\.UCAL PROPERTIES OF ANHYDRITE, 

by Robert W. Potter II and Michael A. Clynne 107 

Introduction 107 

Thermochemistry of anhydrite and related phases 107 

Crystallography of anhydrite and related phases 109 

Phase-equilibria and solubility relationships 110 

Kinetics of reactions involving anhydrite 112 

Sorption of radionuclides by anhydrite ll3 

Radiation effects on the chemistry of anhydrite ll3 

Summary 114 

REFERENCES CITED 117 

FIGURES 

2.1-2.4. Maps showing: 

2.1. Anhydrite deposits in the conterminous United States 9 

2.2. Major sedimentary basins in the conterminous United States 10 

2.3. Areas in the conterminous United States where thick beds of 

anhydrite are present at moderate depths 11 

2.4. Distribution and depth below land surface of Silurian and 

Devonian evaporite deposits in the Michigan and 

Appalachian basins 16 

2.5. Section showing stratigraphic succession in Michigan 17 

2.6. Generalized north-south cross section through the Michigan 

basin 18 

2.7. Diagram showing distribution of anhydrite and other facies near pinnacle 

reefs in northern and southeastern parts of Michigan basin 19 

2.8. Section showing stratigraphic sequence of part of Detroit River Group in 

the Michigan basin as determined from gamma-ray and neutron 

logs 20 

2.9. Photographs of nodular, pillar, and massive anhydrite from the Richfield 

Member of the Lucas Formation in the Michigan basin 21 

2.10. Photographs of reticulate, contorted, lamellar, and nodular anhydrite 

from the Lucas Formation and the Dundee Limestone, Michigan 

basin 22 

Contents V 
FIGURES-Continued 

2.11 Section showing stratigraphic sequence and gypsum deposits in the 

Mississippian Michigan Formation of the Michigan basin as determined 

from spontaneous potential and resistivity logs 23 

2.12. Generalized columnar sections of Salina Group in northeast Ohio and 

south-central New York 25 

2.13. Map showing thickness, in feet, and depth to the G-unit anhydrite at top of 

Salina Group in the Appalachian basin 26 

2.14. Generalized north-south cross section in northeastern Ohio 27 

2.15. Generalized stratigraphic section showing evaporite units in the lower part 

of the St. Louis Limestone in southwest Indiana 28 

2.16. Structural cross section showing thickening of Lower Cretaceous and lower 

Tertiary carbonate-anhydrite sequences into the South Florida basin 29 

2.17. Generalized geologic column of Lower Cretaceous strata in the South 

Florida basin 30 

2.18. Generalized stratigraphic sections showing lithology representative of 

Paleocene strata from southeastern Alabama to the South Florida 

basin 31 

2.19. Structure map on top of Lower Cretaceous strata in Gulf Coast basin 32 

2.20. Correlation chart of Jurassic and Lower Cretaceous strata in the Gulf Coast 

basin 33 

2.21. Diagram showing generation of Gulf Coast salt domes through geologic 

time 34 

2.22. Map showing five salt -dome basins and other principal regional structural 

features in Gulf Coast region 35 

2.23. Idealized section of salt dome 36 

2.24. Map showing salt domes of the Gulf Coast basin for which cap-rock data 

are available 37 

2.25. Columnar sections showing lithologic variability of cap rock among 10 

domes and on a single dome 38 

2.26. Cross section showing Werner Formation and overlying strata in 

southeastern Arkansas and northeastern Louisiana. 39 

2.27. Map showing thickness, in feet, and depth below land surface to top of 

anhydrites in Buckner Formation in southern Arkansas. 40 

2.28. North-south stratigraphic cross section showing Buckner and Smackover 

Formations in southern Arkansas 41 

2.29. Map showing thickness, in feet, and depth below land surface to top of 

Ferry Lake Anhydrite in Gulf Coast area 42 

2.30. North-south stratigraphic cross section showing the Ferry Lake Anhydrite 

and other units of the Lower Cretaceous Trinity Group in Caddo Parish, 

northwestern Louisiana, and Miller County, southwestern Arkansas 43 

2.31. Map of the Permian basin of Southwestern United States showing principal 

tectonic provinces and boundary of area underlain by anhydrite 45 

2.32. Paleogeographic maps of southwestern Texas and southeastern 

New Mexico during early and middle Ochoan time 46 

2.33. Diagram showing stratigraphic relationships of major anhydrite-bearing 

units in the Permian basin 47 

VI Contents 
FIGURES-Continued 

2.34. Representative well logs of major Permian units containing anhydrite in the 

Permian basin 48 

2.35. Columnar section of Permian upper Yeso Formation and lower San Andres 

Limestone in the San Andres Mountains of southern New Mexico 49 

2.36. Map of Permian basin area showing principal facies of the San Andres and 

Blaine Formations 50 

2.37. Map of the Delaware basin and surrounding region of southwestern Texas 

and southeastern New Mexico 53 

2.38. Diagrammatic east-west cross section of Castile and Salado Formations 

from Culberson County, Tex., to Winkler County, Tex. 54 

2.39. Map showing thickness distribution of anhydrite I member, Castile 

Formation 55 

2.40. Map showing thickness distribution of anhydrite II member, Castile 

Formation 56 

2.41. Diagrammatic illustration of a complete salinity cycle in the Castile 

Formation and lower part of the Salado Formation 57 

2.42. Photograph of blanket dissolution breccia correlative with halite I in the 

Castile Formation 57 

2.43. Contour map showing depth to top of laminated anhydrite in the Castile 

Formation 59 

2.44. Stratigraphic cross section in the northeastern part of the northern Denver 

basin 61 

2.45. Columnar section of Permian, Jurassic, and Lower Cretaceous strata in 

Colorado part of northern Denver basin 62 

2.46. Map showing major basins and uplifts in Wyoming and adjacent areas 63 

2.47. Stratigraphic cross section showing Gypsum Spring Formation and adjacent 

strata in western part of Wind River basin, Wyoming 64 

2.48. Map of Williston basin area in northwestern United States showing 

structural features 65 

2.49. Generalized columnar section of the Williston basin 67 

2.50. Stratigraphic cross section of Sweetgrass arch area 68 

2.51. Map showing distribution and thickness of Eagle Valley Evaporite in the 

Eagle basin, northwest Colorado 69 

2.52. Lithology and mechanical logs showing Eagle Valley Evaporite in two wells 

drilled in Eagle County, Colo. 70 

2.53. Index map of Paradox basin 71 

2.54. Columnar section showing typical evaporite cycle of the Paradox Member of 

the Hermosa Formation 72 

2.55. Structure-contour map on top of salt in Paradox Member of Hermosa 

Formation along Salt Valley anticline, Grand County, Utah 73 

2.56. Cross section through Salt Valley anticline in Grand County, Utah, showing 

thickened Paradox salt and arching of overlying strata 74 

2.57. Map showing distribution and depth to top of Todilto Formation in the San 

Juan basin area of northwestern New Mexico and southwestern 

Colorado 75 

2.58. Index map of Supai salt basin and surrounding area 76 

2.59. Generalized geologic cross section through Supai salt basin 77 

Contents VII 
FIGURES-Continued 

2.60. Composite lithologic column of upper member of the Supai Formation in 

Supai salt basin 78 

2.61. Map showing thickness, in feet, of upper member of the Supai 

Formation 79 

2.62. Detailed lithologic columns of two cores 8 km apart showing correlation 

of evaporite units in part of upper member of the Supai Formation 80 

2.63. Map showing basins of the Basin and Range Province in Arizona and 

southern Nevada that contain major nonmarine evaporite deposits 80 

2.64. Schematic cross section through Picacho basin of south-central 

Arizona 81 

2.65. Lithologic column showing selected parts of evaporite sequence 

penetrated by Exxon State (74)-1 well in the Picacho basin 82 

2.66. Graph showing percent thickness of anhydrite beds per 30-m interval of 

depth in the Exxon State (74)-1 well in the Picacho basin 83 

2.67. Graph showing number of anhydrite beds per 30-m interval of depth in 

the Exxon State (74)-1 well in the Picacho basin 83 

2.68. Graph showing total number of beds per 30-m interval of depth in the 

Exxon State (7 4 )-1 well in the Picacho basin 84 

2.69. Map showing location of gypsum deposits in southern California 90 

3.1-5.7. Graphs showing: 

3.1. Typical stress-strain curves for anhydrite 93 

3.2. Strength of anhydrite at 10-percent strain and different strain 

rates 93 

5.1. Solubility relationships of calcium sulfate minerals in 

pure water 109 

5.2. Solubility of anhydrite in pure water 109 

5.3. Solubility of gypsum and anhydrite in seawater concentrates 110 

5.4. Solubility of anhydrite in sodium chloride solutions at 200° Celsius 

as a function of the molality of sodium chloride 111 

5.5. Solubility of anhydrite in equilibrium with solid sodium chloride 

and a representative bittern brine as a function of 

temperature 111 

5.6. Effect of pressure on the solubility of anhydrite in pure water as a 

function of temperature 112 

5.7. Solubility of anhydrite at 1,000 bars as a function of temperature 

and sodium chloride concentration 112 

5.8. 55°-isotherm of the five-component NaCl-KCl-MgCh-NazS04-HzO 

system at sodium chloride saturation 113 

5.9. 83°-isotherm of the five-component NaCl-KCl-MgCh-NazS04-HzO 

system at sodium chloride saturation 114 

TABLES 

2.1. Summary of geologic data on anhydrite deposits in the conterminous United 

States 12 

2.2. Depth and thickness of various rock types in cap rock of selected salt domes 

in Gulf Coast basin 38 

VIII Contents 
TABLES-Continued 

3.1. Thermal properties of anhydrite 91 

3.2. Ultimate strength of anhydrite 92 

3.3. Mechanical properties of single crystals of anhydrite 94 

3.4. Mechanical properties of whole-rock anhydrite 94 

3.5. Sonic velocities of anhydrite 94 

4.1. Hydrologic data from tunnels, mines, weiis, and springs 96 

4.2. Intercrystaiiine porosity of bedded anhydrite 101 

5.1. Phases in the system CaS04-H2 0 108 

5.2. Thermochemical properties of calcium sulfate phases 108 

5.3. Kinetic reactions for which data are needed 114 

Contents IX 

Anhydrite Deposits of the United States and 

Characteristics of Anhydrite Important for Storage of 

Radioactive Wastes 

Edited by WALTER E. DEAN and KENNETH S. JOHNSON 

ABSTRACT 

All major anhydrite deposits within the conterminous United States are contained within 25 structural 

basins or geographic areas. These deposits are evaluated 

in terms of stratigraphic relationships of anhydrite to the 

entire deposit, thickness of the entire deposit, and 

relative abundance of anhydrite. Anhydrite beds thicker 

than 30 meters and present at moderate depths (greater 

than 300 meters and less than 1,500 meters) are 

particularly emphasized; a total of 20 anhydrite deposits 

contain beds that meet these criteria, at least on the basis 

of available literature. These deposits are characterized 

in terms of geologic age of the deposit, stratigraphy of the 

deposit, structure of the deposit, thicknesses and 

distributions of individual anhydrite beds, depths to 

individual anhydrite beds, other associated lithologies, 

relative purity of the anhydrite, and internal fabric of the 

anhydrite. 

Test data on the following mechanical and thermal 

properties were compiled from the literature: density, 

porosity, thermal conductivity, sonic velocity, Young's 

modulus, Poisson's ratio, and shear moduli. Based on 

this compilation, anhydrite appears to have several 

advantages over halite for proposed nuclear-waste 

isolation. It has a higher melting point and ductile 

deformation occurs at higher temperatures than for 

halite. Its ultimate strength at low confining pressures is 

two to three times that of halite and anhydrite is less 

ductile under these conditions. However, this brittle 

behavior of anhydrite at low confining pressures may 

enhance fracturing in the vicinity of the repository. 

An inventory was prepared from existing literature 

on the general hydrology, porosity, hydraulic conductivity, and transmissivity of anhydrite based on data 

obtained from outcrops, tunnels, mines, wells, and 

springs. The main hydrologic characteristic of anhydrite 

that makes it more favorable than halite as a medium for 

nuclear waste isolation is that it is about two orders of 

magnitude less soluble than halite. However, it is still a 

moderately soluble medium and is subject to many of the 

hydrologic problems that may potentially cause dissolution of salt. 

Data on the thermodynamics, crystallography, 

phase equilibria, solubility, kinetics of reactions, sorption 

characteristics for radionuclides, and radiation effects of 

anhydrite and related phases of calcium sulfate are 

evaluated from the available literature. The initial 

chemical properties of anhydrite that suggested its use as 

a potential medium for nuclear-waste isolation are its low 

solubility (relative to halite) and retrograde nature of the 

solubility-that is, solubility decreases with increasing 

temperature. This combination of solubility characteristics mean that fluids migrate more slowly in anhydrite than in halite and migrate away from a heat source 

rather than toward a heat source as they do in halite. The 

suitability of anhydrite as a waste-disposal medium is 

further enhanced by the facts that it appears to have a 

higher sorptive capacity for radionuclides than halite, it 

has a thermal conductivity about as high as that of halite, 

and it occurs in geologic environments that have been 

relatively stable for tens of millions to hundreds of 

millions of years. 

Abstract 

SECTION 1. Introduction and Discussion 

1 2 

By WALTER E. DEAN, KENNETH S. JOHNSON , and SERGE GONZALES 

BACKGROUND 

The quantity of high-level radioactive wastes has 

increased in the United States and throughout the world 

during the past three decades because of the generation 

of wastes in both the manufacture of nuclear weapons 

and the operation of nuclear electric powerplants. The 

proper management of these wastes requires that they be 

stored or disposed of in such a way that their radionuclides will not escape into the biosphere in amounts that 

would constitute a biological hazard (International 

Atomic Energy Agency, 1977). These wastes must 

therefore be isolated from the biosphere for long periods 

of geologic time. 

Many different geologic settings for either the 

storage or the disposal of high-level radioactive wastes 

have been proposed. They include the ocean seabed in 

either submarine-trench or abyssal-plain areas; the 

Antarctic ice sheet; isolated alluvial valleys in the 

Western United States; artificially formed "nuclear 

chimneys" in molten silicate rock; and mined caverns in 

many different rock types, such as salt (bedded salt and 

salt domes), clay and shale, granite, basalt, anhydrite, dry 

limestone (including chalk), and serpentinite. Most of the 

research in this country during the past 30 years has been 

devoted to subsurface storage in rock salt (halite), but, 

recently, an interest has been shown in further evaluating 

the other major rock types as potential storage media 

(Bredehoeft and others, 1978). Thus, the U.S. Geological 

Survey began a study of anhydrite, one of the rock types 

that has been considered as a potential depository for 

these wastes. 

This investigation presents an inventory of major 

anhydrite deposits in the United States and describes 

their geologic, structural, hydrologic, physical, and 

geochemical characteristics that are important for 

evaluating anhydrite as a potential medium for disposal 

of high-level radioactive wastes. Although the literature 

on all major deposits of anhydrite has been examined and 

1

0klahoma Geological Sutvey, Norman, Oklahoma. 2

Earth Resource Associates, Inc., Athens, Georgia. 

summarized, the emphasis of this report is on 20 deposits 

that contain individual beds of anhydrite more than 30 m 

(meters) thick and between 300 and 1,500 m beneath the 

Earth's surface. 

This preliminary survey of existing data constitutes 

the first step in assessing the suitability of anhydrite as a 

medium for storage of radioactive wastes. However, even 

at this early stage, a number of characteristics of anhydrite appear to be favorable for storing of high-level 

radioactive wastes: 

1. Many anhydrite beds have remained undisturbed and without significant dissolution or hydration 

for tens of millions to hundreds of millions of years, an 

indication of their long-term integrity. 

2. Anhydrite has a rather high thermal conductivity, and hence should dissipate large quantities of heat 

(which would be generated by high-level wastes) more 

rapidly than do most rocks. 

3. Although more brittle than rock salt, anhydrite 

nevertheless has a natural plasticity under conditions of 

moderate to high temperature and pressure, and thus 

should be capable of "self-sealing" fractures that may 

develop in it. 

4. The solubility of anhydrite in water is lower than 

that of halite and most other evaporite minerals, and the 

solubility is retrograde (it decreases with increasing 

temperature); thus, fluids trapped as inclusions migrate 

slower in anhydrite than in halite, and should migrate 

mvay from a heat source in the temperature range at 

which a waste repository would be expected to operate. 

5. Based on the limited data now available, the 

sorptive capacity of anhydrite for radionuclides appears 

to be significantly greater than that of halite, and even 

greater than that of some volcanic tuffs; this capacity 

would further reduce the possibility for escape of radionuclides from a waste repository. 

6. Indirect evidence suggests that the effects of 

radiation on the chemistry of anhydrite would be minor. 

7. Anhydrite deposits that are sufficiently deep and 

thick to be considered as potential repositories are 

widespread in this country and generally occur in areas 

that have low levels of seismicity and tectonic activity; 

Introduction and Discussion 3 
thus, the potential for earthquake damage to repository 

surface structures and subsurface mine workings is 

greatly reduced. 

8. Domestic anhydrite resources are so large that 

using one or several deposits as repositories would not 

adversely affect availability of anhydrite resources; 

repository sites far from existing mines could be selected, 

so proximity to mining activity would not be a problem. 

9. Anhydrite can be mined at relatively low cost; 

technology for the underground excavation of gypsum 

and anhydrite is well developed, and underground rooms 

that have been opened in these rocks have remained 

stable for long periods of time where adequate pillar size 

was used in the mine design and where water could not 

enter the mine opening. 

REGIONAL GEOLOGIC 

CHARACTERISTICS IMPORTANT FOR 

WASTE STORAGE 

The goal of radioactive-waste management is to 

isolate the waste from the biosphere until the radionuclides, through radioactive decay, no longer pose a 

hazard to man and his ecosystem. The length of time that 

different radioactive-waste materials must be isolated 

depends upon the type of waste and its level of 

radioactivity. The isolation period for certain low- and 

intermediate-level wastes ranges from less than 100 years 

to several thousand years; the isolation period for highlevel wastes may range from several thousand to several 

hundred thousand years. Circulating ground water is the 

natural mechanism by which radioactive material would 

most likely escape from a subsurface repository into the 

biosphere; thus, special attention must be given to the 

geologic and hydrologic characteristics of a region being 

considered for storage of radioactive waste (International Atomic Energy Agency, 1977). 

Many anhydrite deposits have existed beneath the 

Earth's surface for millions of years without significant 

change, and substantial parts of these deposits apparently 

have remained free of circulating ground water. By 

studying individual anhydrite deposits, together with the 

hydrology, geologic structure, and general geologic 

framework of the particular anhydrite-bearing basin, we 

can determine the geologic processes that have affected 

the region in the past and can forecast, in general terms, 

the future impact of such processes on a repository site in 

that basin. 

Because of the complexity of geologic processes, 

each repository site must be considered to be unique. 

General characteristics of the geologic environment that 

govern the suitability of a particular rock unit for waste 

storage were discussed in a report by the International 

Atomic Energy Agency (1977). Johnson and Gonzales 

4 Anhydrite Deposits of the United States 

(1978) later summarized the regional geologic characteristics relevant for storage of waste in salt deposits; 

much of their discussion is repeated here because it also 

generally applies to storage of waste in anhydrite 

deposits. The importance of these characteristics is 

discussed in the following paragraphs, and the specific 

characteristics for each of the anhydrite-bearing basins in 

the United States are discussed in subsequent sections of 

this report. 

Structure and Geologic Framework 

The regional geology and geologic history of an 

evaporite basin must be known to understand the 

processes that have acted on a potential repository site in 

the past and those that may affect containment of waste 

in the future. Regions that have been tectonically stable 

over the past tens to hundreds of millions of years are 

likely to remain stable, at least during the next several 

hundred thousand years. Areas of anticipated rapid uplift 

or strong structural deformation are less desirable for 

waste storage, because either uplift and concomitant 

denudation of the host rock or structural disruption and 

distortion might release radionuclides into the biosphere. 

Some of the more important structural elements that 

should be studied for each deposit include the following. 

Dip or Inclination of Strata 

The generally preferred dip of strata in bedded 

anhydrite deposits is less than a few degrees, as this dip 

would enable nearly horizontal underground workings to 

be designed in the same rock layers over large areas. 

Steep dips, or tight folds that have frequent reversals in 

dip, also indicate that the rocks were subjected to 

deformation or tectonic stresses that may have produced 

complex geologic structures and the stresses may still be 

active. 

Faults and Joints 

Faults and joints generally are not desirable in 

rocks that might be used for containment of waste. The 

self-healing plastic behavior of salt and shale, which 

commonly are interbedded with anhydrite, would 

probably close the fractures in these rock types. 

Fractures in anhydrite and interbedded carbonates might 

not be sealed as readily, however, because of the more 

brittle nature of the rocks, and therefore might be 

pathways for circulating ground water. Faults and joints 

also might cause physical discontinuities in the host rock 

that could adversely affect mining operations. A region 
that contains only a few faults or joints might be suitable 

for waste storage if these structural features are located 

and then either avoided or considered in the planning of 

the excavations for a repository. 

Nature and Extent of Adjacent Strata 

Thick beds of shale, salt, or other plastic-behaving 

rocks that have low permeability not only would help to 

protect the anhydrite from circulating ground water but 

also would tend to deform without fracturing if the 

repository area were subsequently disturbed. The least 

desirable adjacent strata would be those that contain 

large quantities of circulating ground water that might 

enter the repository and eventually exit contaminated 

with radionuclides. 

Anhydrite Deposits 

The geometry, thickness, depth, and stability of the 

host rock for a radioactive-waste repository are critical 

considerations to long-term containment of radionuclides. Bedded anhydrite deposits have persisted tens of 

millions to hundreds of millions of years at the same 

location and, with the exception of the hydrationdehydration history of each gypsum-anhydrite deposit, 

generally have remained in the form as originally 

deposited. The very existence of these anhydrite deposits, 

which are at least moderately soluble in water, indicates 

that they have not been disturbed appreciably by 

circulating ground water. In some areas, anhydrite has 

flowed plastically in the geologic past, chiefly in response 

to flowage of associated salt deposits, to form diapiric 

cap-rock structures that consist of enormous, massive 

sulfate bodies. The anhydrite cap rock formed on some of 

the salt domes and salt anticlines, however, appears to 

have been stable for appreciable periods of geologic time 

since the end of diapiric movement. 

Depth of Storage Zone 

A repository should be deep enough below the land 

surface to ensure that contained waste will not be 

exposed to the biosphere through erosion or denudation 

during the period that the waste is hazardous. To negate 

the slow removal of the land surface through erosion, 

which generally proceeds at an average rate of 2.5-7.5 m 

per 100,000 years in the continental United States (Ritter, 1967), and to avoid the circulation of shallow ground 

water that might dissolve soluble rock or that might 

breach the repository, the waste should be stored at least 

300 m beneath the surface. The rate of plastic flow of 

anhydrite that results from lithostatic pressure increases 

with depth; therefore, it probably is prudent to restrict 

mining operations in anhydrite to depths less than 1,500 

m. Thus, the most feasible depth range for a repository in 

anhydrite extends from 300-1,500 m beneath the land 

surface. In this report, anhydrite deposits within that 

depth range are referred to as being at "moderate" 

depths, those at lesser depths as being "shallow," and 

those at greater depths as being "deep." 

Thickness and Extent 

In general, a repository host rock must be 

sufficiently large to permit fractures that emanate from 

the immediate surroundings of the repository to dissipate 

and terminate without jeopardizing the containment 

characteristics of the host rock. The host rock also must 

be thick enough to provide for adequate heat dissipation. 

A single bed of anhydrite at least 30 m thick is believed to 

be adequate to provide the necessary containment for 

mine workings. Strata reported to be at least 25 m thick 

also have been seriously considered in this report 

because they might locally thicken to as much as 30 m or 

more. 

Homogeneity 

In general, a high degree of homogeneity or 

consistency is desirable in rock units that are considered 

for storage of radioactive wastes. Laminated and nodular 

anhydrites (the most common types of anhydrite in 

natural deposits) contain impurities (chiefly carbonate 

and clay minerals); but if the impurities are uniformly 

distributed, the rock may behave as a homogeneous unit 

and its overall characteristics will tend to be more 

uniform. Layers or irregular masses of other materials 

within anhydrite can adversely affect mining operations if 

they are encountered during repository construction. 

Heat dissipation also may be adversely affected if large 

quantities of certain impurities lie near the disposal zone. 

One of the major problems in compiling this 

inventory was determining the relative purity of anhydrite 

beds on the basis of published reports. For example, the 

Picacho basin in Arizona is described as containing 

" * * * slightly more than 1,800 m of massive anhydrite 

containing only minor interbeds of shale, tuff, halite, and 

limestone nodules" (Eberly and Stanley, 1978 p. 931). 

However, the lithologic and mechanical logs of the one 

deep test in that basin show that the degree of interbedding is considerable and that few anhydrite beds 

approach or exceed 30 m in thickness. Beds of anhydrite 

usually are described in the literature only in general 

terms, such as "relatively pure" or "massive." In terms of 

composition, these beds may indeed contain 90 percent 

or more calcium sulfate, which is "relatively pure" by 

most geologic standards. When examined in detail, 

Introduction and Discussion 5 
however, all beds of anhydrite contain several different 

levels of impurities. Chemical impurities may occur 

within the anhydrite crystals, but this is not a common 

problem because most naturally occurring compounds of 

calcium sulfate (usually anhydrite or gypsum) that are 

found in major evaporite deposits are still regarded as 

chemically pure. For example, anhydrite (or gypsum) 

crystals commonly contain lower levels of impurities than 

does reagent -grade calcium sulfate. 

Most lithologic units of anhydrite, including those 

described as "relatively pure" or "massive," contain 

impurities in the form of other lithologies such as shale, 

limestone, dolomite, and (or) halite. These lithologies 

may be present as interbeds (on a scale of centimeters to 

meters), interlaminations (on a scale of millimeters), 

matrix (nodular and mosaic anhydrite), or mixed crystals. 

The relationships of impurities to the anhydrite 

produce structures and textures that have been given 

various terms in the literature. In an attempt to sort out 

the complications of textural terms, Maiklem and others 

(1969) proposed a classification of anhydrite based on 

textures and structures. In discussing the geologic 

characteristics of specific anhydrite deposits and of individual beds within deposits, we refer to this classification 

where information is available. Principally, we want to 

determine if the anhydrite within a bed is (1) bedded 

(and on what scale), (2) mosaic, (3) nodular (which 

implies anhydrite separated by matrix, and therefore a 

high matrix-to-anhydrite ratio and large amounts of 

impurities), or (4) massive and has no apparent 

structures (rare). 

The most common forms of anhydrite are nodular 

and mosaic, which have been referred to by different 

authors as "nodular anhydrite," "chicken-wire anhydrite," or "mosaic anhydrite." These anhydrite units may 

vary considerably in amounts of impurities and in 

physical appearance. Where possible, we have included 

illustrations of anhydrite, but photographs of anhydrite 

have not been published for most deposits. 

Dissolution 

Because anhydrite is a moderately soluble rock, 

circulating ground water is one of the major threats to 

containment of radioactive waste in anhydrite beds. 

Anhydrite is about two orders of magnitude less soluble 

than is rock salt, but anhydrite dissolution and (or) 

hydration to gypsum still are important considerations in 

evaluating anhydrite as a potential repository host rock. 

Four requirements must be met for the dissolution of 

anhydrite: (1) a supply of water unsaturated with respect 

to calcium sulfate, (2) a deposit of anhydrite through 

which or against which the water flows, (3) an outlet to 

permit water that is rich in calcium sulfate to leave the 

anhydrite, and ( 4) energy (such as a hydrostatic head) to 

6 Anhydrite Deposits of the United States 

cause the water to flow through the system. An anhydrite 

bed at rather shallow depth may be in contact with 

circulating ground water along its upper surface and, to a 

lesser extent, along its base; thus, disposal zones should 

be sufficiently deep and distant from those areas where 

dissolution may occur. The natural protection of anhydrite from circulating ground water for long spans of 

geologic time is attested by the fact that anhydrite and 

associated salt beds of Cretaceous age and older 

generally have remained intact and undissolved beneath 

overlying sediments in thousands of square kilometers of 

such major basins as the Michigan, Appalachian, Gulf 

Coast, Permian, Williston, and Paradox. Evaporites in 

these basins, and those of other basins as well, have 

survived for more than 100 million years, a time span well 

beyond that of the hazardous period during which radionuclides must be isolated from the biosphere. 

Hydrology 

Special attention must be given to the hydrology of 

a prospective waste-storage area because of the extreme 

importance of understanding the circulation of water 

around or near a repository. A comprehensiv~ geohydrologic study of the entire region or basin .should include 

the following: establish spatial relationships, interconnections, and the direction, velocity, and volume of 

flow in all aquifers above and below the repository unit; 

identify recharge and discharge sites; and determine if 

anhydrite has been or is being dissolved, or is being 

hydrated to gypsum, as well as the potential for such 

processes to occur in the future. 

Surface Water 

The mere presence of surface streams, lakes, and 

ponds above an otherwise suitable repository site should 

not necessarily rule out its use, but a determination must 

be made that this water would not interfere with the 

short-term operation of a disposal facility or compromise 

the long-term containment of any emplaced wastes. Rock 

units beneath flood plains or other areas prone to 

flooding would be especially difficult to develop as a 

repository, because extreme conditions could lead to the 

flow of water into underground excavations through open 

shafts or boreholes unless special design features were 

implemented. Surface streams may undergo marked 

changes in their flow regimes over long periods of time, 

and thus such future behavior as the rate of incision and 

shifting of the streambed must be predicted to guard 

against breaching of the repository by erosional 

processes. 
Ground Water 

The repository must be free of circulating ground 

water, which represents the main threat to containment 

of radioactive waste. Thus, the nature and characteristics 

of water-bearing strata near a potential host rock are 

critical elements in establishing the suitability of a 

proposed repository. Investigations also are needed to 

fully ascertain the nature and characteristics of the 

ground water itself. In many areas, ground water is an 

important resource for municipalities, industry, and 

agriculture, and care must obviously be taken to protect 

these water resources. 

Mineral Resources 

Nonanhydrite mineral resources, such as 

petroleum, salt, potash, gypsum, and sulfur, may be 

present near an anhydrite deposit being considered as a 

waste repository. These minerals can be present in 

formations that overlie or underlie the anhydrite unit, or 

they can be interbedded with the anhydrite in some 

deposits; therefore, the consequences of future activities 

aimed at seeking and extracting mineral resources should 

be considered. In areas of past mineral exploration or 

extraction, all preexisting boreholes, mine shafts, solution 

cavities, and other manmade excavations that penetrate 

the anhydrite zone in the vicinity of a proposed repository 

represent potential migration paths for ground water, 

and must be plugged and sealed effectively. The area 

should have little or no potential for future mineral 

exploration at depths that would affect the integrity of the 

deposit. 

Anhydrite production in the United States now is 

rather small; most of the stone is used as a retarder in 

portland cement. Gypsum, on the other hand, is a major 

mineral commodity in the construction industry, and it is 

used chiefly in making wallboard, plasters, and special 

cements. Both anhydrite and gypsum are potential 

sources of sulfur, if the cost of extracting sulfur from 

these rocks becomes competitive with current methods of 

sulfur production. However, owing to the great 

abundance and widespread distribution of domestic 

anhydrite resources, no adverse impact on the future 

supply of this commodity is expected, even if radioactive 

wastes were stored in anhydrite at several sites. 

ORIGIN OF EVAPORITE DEPOSITS 

Evaporites are deposits of sediments or sedimentary rocks that are composed predominantly of 

minerals precipitated from brines that have been 

concentrated by evaporation. The classic theory for the 

origin of thick evaporite deposits is that they form on the 

floor of a standing body of water that has a restricted 

connection with the open sea. The restricted body of 

water may be on the scale of a deep ocean basin such as 

the Mediterranean Sea or, more commonly, an embayment, lagoon, or estuary. The restricted- or barred-basin 

theory was first proposed by Ochsenius (1877) and was 

later modified and applied to explain the origin of thick 

evaporite sequences by a number of investigators, most 

notably Adams (1944), King (1947), Scruton (1953), 

Dellwig (1955), Briggs (1958), Wardlaw and Schwerdtner (1966), Hite (1968), Dellwig and Evans (1969), 

Peterson and Hite (1969), Schmalz (1969), Raup (1970), 

Anderson and others (1972), and Dean and Anderson 

(1978). Examples of modern restricted environments 

that embody many of the features of the classic barred 

evaporite basin include the Gulf of Kara-Bogaz on the 

Caspian Sea (Dzens-Litovskiy and Vasil'yev, 1962), the 

Bocana de Virrila on the Peruvian coast (Morris and 

Dickey, 1957), and the northern part of Great Salt Lake, 

Utah, when it was largely cut off from the main part of 

the lake by a railroad causeway in 1959 (Madison, 1970; 

Whelan, 1972). 

The classic theory for the origin of evaporite 

deposits was modified in the mid-1960's when thick 

evaporite deposits that formed in arid supratidal flats, or 

"sabkhas," were discovered along the Trucial Coast of 

Arabia, adjacent to normal marine waters of the Persian 

Gulf, and when data on this origin were synthesized into 

the so-called sabkha model of evaporite accumulation 

and diagenesis (Kinsman, 1966; Shearman, 1966; Butler, 

1969). 

When the sabkha model was formulated, 

researchers began to recognize a number of features in 

ancient evaporites, particularly in those dominated by 

gypsum and anhydrite, that had modern analogs in 

sabkha evaporites. Of particular importance to this study 

is the fact that anhydrite, which is locally abundant in the 

sabkha sediments of the Trucial Coast, characteristically 

occurs as nodular masses closely resembling nodular or 

mosaic structures-probably the most common form of 

ancient anhydrite. Many evaporite researchers assume 

that the presence of nodular anhydrite in an ancient 

evaporite deposit is indicative of a sabkha-like origin, 

although such a universal interpretation has been 

questioned (Dean and others, 1975). Because the sabkha 

model provided a modern analog, which the deep-water 

interpretation lacked, widespread and mostly uncritical 

acceptance of the sabkha model tended to overemphasize 

the evidence that supported the subaerial origin of evaporites, especially the presence of nodular anhydrite. By 

the mid-1970's, however, researchers recognized that 

there are deep-water evaporites that were deposited 

below wave base; shallow-water evaporites that were 

deposited above wave base, but that contain no evidence 

Introduction and Discussion 7 
of complete desiccation; and subaerial sabkha evaporites 

that formed in marginal marine environments that were 

dry most of the time. These environments commonly 

have similar features, such as laminated and nodular 

anhydrite (Dean and others, 1975). 

A subaqueous environment appears more 

plausible for the accumulation of many ancient, thick 

evaporite deposits that consist of nearly monomineralic 

beds. Evaporation of water in a shallow-water or deepwater basin, which is separated from the open ocean by a 

sill or shelf, would produce brines of increasing 

concentration. Where the salinity of such a brine reaches 

about five times that of normal seawater, calcium sulfate 

would begin to precipitate. Anhydrite (CaS04) theoretically should be the most stable calcium-sulfate mineral to 

form under most salinity and temperature conditions that 

are expected in an evaporite basin. However, as discussed 

later in the section "Chemical Characteristics of Anhydrite," gypsum (CaS04·2H20) is the mineral that 

generally forms in modern evaporite deposits and in 

laboratory experiments. The contradiction between 

theoretical and observed data on gypsum and anhydrite 

formation remains unresolved. If studies of calciumsulfate mineralogy were restricted to laboratory synthesis 

and to modern deposits, the contradiction would seem to 

be resolved. However, the reason that anhydrite is the 

dominant calcium-sulfate mineral in ancient evaporite 

deposits must be explained. 

When the salinity of evaporating brine reaches 

about 10 times that of normal seawater, most of the 

calcium sulfate has been deposited and halite (NaCl) 

starts to precipitate along with gypsum (or anhydrite). 

When the salinity of the brine is about 20 times that of 

normal seawater, polyhalite (K2Ca2Mg(S04 )4 ·2H20) or, 

at higher temperatures, glauberite (Na2Ca(S04)2) are 

the sulfate minerals being formed. Polyhalite precipitates 

together with halite until the brine is saturated with 

respect to magnesium-bearing sulfates that are free from 

calcium and potassium. 

Theoretically, progressive isothermal evaporation 

of seawater generally should result in the precipitation 

of carbonates (calcite, dolomite, or both), calcium 

sulfate (gypsum or anhydrite), halite, potassium- and 

magnesium-bearing sulfates and chlorides, and finally 

potassium-free magnesium salts. In general, portions of 

this succession can be observed in many natural marine 

evaporite deposits. Most discrepancies between observed 

and theoretical evaporite deposits can be explained by 

one or a combination of the following three conditions: 

(1) complete evaporative concentration of seawater 

rarely occurs, and evaporation seldom progresses past 

the precipitation of halite; (2) equilibrium precipitation 

of evaporite minerals is the exception rather than the· 

rule; and (3) diagenesis may severely alter primary 

mineral facies. 

8 Anhydrite Deposits of the United States 

Condition 1 leads to the commonly observed early 

sulfate excess, which refers to the fact that in an evaporite 

deposit that is formed by complete evaporation of normal 

seawater, the ratio ofNaCl to CaS04 theoretically should 

be about 22:1 by volume. However, in most marine 

evaporite deposits, the NaCl to CaS04 ratio is about 3:1, 

is commonly less than 1:1, and may be as low as 1:100 

(that is, anhydrite largely predominates over halite). The 

common explanation for this deficiency of halite (or 

excess of anhydrite) is that evaporation in the basin was 

incomplete and the brines that contained most of the 

sodium, magnesium, and potassium were continually 

refluxed out of the basin. Postdepositional dissolution of 

halite also may produce an increase in anhydrite relative 

to halite. 

Condition 2, which also may account for discrepancies between theoretical and observed evaporite 

successions, is one of disequilibrium. Metastable minerals are common chemical precipitates under conditions 

of low temperature and pressure; two of the bestdocumented examples are aragonite and gypsum. As 

mentioned earlier, gypsum is almost invariably the 

calcium-sulfate mineral observed to form where seawater is evaporated under natural or laboratory conditions, even when anhydrite theoretically should form. 

The main cause of disequilibrium in the formation of 

evaporite minerals probably is related to precipitation 

kinetics; that is, precipitation is too rapid for equilibrium 

to be attained. The kinetics of equilibrium reactions 

requires that precipitation must occur under conditions 

of slow precipitation to prevent supersaturation; such 

conditions, however, are not common in the formation of 

evaporite minerals. 

Because the minerals in evaporite sequences are so 

soluble, one would expect postdepositional modifications 

to be widespread. Diagenetic alteration may be caused by 

percolation of solutions of differing composition through 

the evaporite strata, or it may be in response to ternperature. The abundant polyhalite in many evaporite 

deposits is a good example. Polyhalite is the most 

common, late-formed (halite- or posthalite-associated) 

sulfate mineral in natural evaporite deposits; this should 

be expected by theory, but the quantities actually found 

greatly exceed the theoretical amount. The abundance of 

polyhalite commonly is explained as the result of diagenetic alteration of anhydrite by potassium- and 

magnesium-rich solutions, an interpretation that is 

supported by polyhalite formation in modern evaporite 

deposits (Holser, 1966). Diagenesis has had a profound 

effect on most, if not all, evaporite sequences. Although 

problems of disequilibrium reactions still exist, diagenesis perhaps can account for most of the details that 

explain the discrepancies between theoretical and 

observed evaporite sequences. 
SECTION 2. Distribution a·nd Geologic 

Characteristics of Anhydrite Deposits in the 

United States 

By KENNETH S. JOHNSON,, SERGE GONZALES2

, and WALTER E. DEAN 

Summary 

Anhydrite deposits are widely distributed in the 

United States and are known to exist in 32 of the 48 

conterminous states (fig. 2.1). Some of the deposits are 

extensive, such as anhydrite beds of the Silurian Salina 

Group in the Michigan and Applachian basins, Jurassic 

1

0klahoma Geological Sutvcy, Norman, Oklahoma. 2

Earth Resource Associates, Inc., Athens, Georgia 

EXPLANATION 

E1J) Principal anhydrite basin or province 

discussed in this report 

' Other areas underlain by anhydrite beds 

c.-..:-.::)lndefinite border embracing scattered deposits 

and Cretaceous anhydrites of the Gulf Coast basin, and 

Permian anhydrites of the Permian basin. Deposits that 

contain some of the thickest anhydrite beds in the world 

include the Castile Formation in the Delaware basin part 

of the Permian basin and the unnamed Tertiary evaporites in the Picacho basin of southern Arizona. Most of the 

anhydrite deposits in the United States occur within or on 

the margins of major sedimentary basins (fig. 2.2) that 

received thick accumulations of sediment during periodic 

marine inundations of parts of the continent in the 

geologic past. 

Figure 2.1. Anhydrite deposits in the conterminous United States (modified from Smith and others, 1973). 

Distribution and Geologic Characteristics of Anhydrite Deposits 9 
EXPlANATION 

Major sedimentary basin 

Region of salt domes 

500 MILES 

Figure 2.2 Major sedimentary basins and other principal tectonic features in the conterminous United States. 

Anhydrite deposits in the United States cover a 

considerable span of geologic time and range in age from 

Precambrian to Tertiary. Geologic conditions favoring 

deposition of moderately thick to thick layers of anhydrite were repeated many times in various sedimentary 

basins. The oldest deposits are in the northern part of the 

country where Precambrian anhydrite occurs in the 

Adirondack Mountains and where Silurian anhydrite was 

deposited in the Michigan and Appalachian basins. The 

youngest deposits are in the Southwest where Tertiary 

anhydrite occurs in southern California and in the Basin 

and Range Province of Arizona and southern Nevada. 

The most numerous and widespread anhydrite deposits 

are those of Permian age, followed (in approximate 

10 Anhydrite Deposits of the United States 

order) by those of Jurassic, Mississippian, Triassic, Devonian, and Cretaceous age. 

Twenty stratigraphic units contain anhydrite beds 

that are as much as 30m thick and at moderate depths 

(fig. 2.3). The thickest beds are in the Castile Formation, 

which is as much as 600 m thick and contains anhydrite 

beds 30-105 m thick, and in an unnamed sequence in the 

Picacho basin, where anhydrite beds as much as 37 m 

thick occur in an 1,800-m-thick sequence that consists 

mainly of anhydrite. All units reported to contain anhydrite beds at least 30 m thick and at moderate depth are 

as follows: The A-2 anhydrite of the Salina Group in the 

Michigan Basin; G unit of the Salina Group in the 

Appalachian basin; cap rock on various salt domes, as 
EXPLANATION 

Area underlain by anhydrite beds 

- Anhydrite bed at least 25-30 m thick and 

in the range of 300-1500 m below land 

surface; name of anhydrite unit is shown 

Figure 2.3 Areas in the conterminous United States where thick beds of anhydrite are present at moderate depths. 

well as the Werner, Buckner, and Ferry Lake Formations 

in the Gulf Coast basin; Castile Formation, San 

Andres Limestone, and Artesia Group in the Permian 

basin; Wolfcampian strata and the Stone Corral 

Formation in the northern Denver basin; Gypsum Spring 

Formation in some of the Wyoming basins; Madison 

Group in two parts of the Williston basin; Three Forks 

Formation in the Sweetgrass Arch area; Eagle Valley 

Evaporite in the Eagle basin; Todilto Formation in the 

San Juan basin; unnamed anhydrite units in the Chandler 

and Picacho basins of Arizona; and the Pequop and 

Loray Formations of the eastern Great basin. In table 2.1 

we have summarized data on the age, thickness, depth, 

and structural setting for these 20 units and all other 

anhydrite units discussed in this report. 

The earliest major reports on gypsum and anhydrite distribution in the United States are those by 

Adams and others (1904) and Stone and others (1920). 

More recently, a comprehensive annotated bibliography 

of gypsum and anhydrite was prepared by Withington 

and Jaster (1960) and a nationwide mineral-resource 

map and bibliography were compiled by Withington 

(1962). A list of the anhydrite-bearing rock units of the 

United States was prepared by Smith and others (1973). 

In preparing this report we have also relied heavily upon 

the detailed studies of specific deposits published by the 

U.S. Geological Survey, the American Association of 

Petroleum Geologists, and various State geological 

surveys and geological societies. 

Distribution and Geologic Characteristics of Anhydrite Deposits 11 
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Table 2.1. Summary of geologic data on anyhydrite deposits in the conterminous United States 

Geologic age Thickness of 

Geologic province Stratigraphic unit (E, Early; M, anhydrite beds 

Middle; L, Late) (meters) 

Michigan basin----- Salina Group------------ L. Silurian------ Co01110nly 2-10, 

locally 1G-30. 

Lucas Formation of M. Devonian------ 2-15 

Detroit River Group. 

Michigan Forlll8tion------- L. Mississippian- l-10 

Appalachian basin--- Salina Group----------- L. Silurian---- 1-37 

Adirondack uplift--- Grenville Co111plex------ Prec811.brian------- As much as 60. 

Saltville area-----

Illinois basin-----

Forest City basin---

South Florida basinGulf Coast basin---

Central Texas------

Maccrady Formation------

St. Louis Li mea tone-------

Wapsipinicon and 

Cedar Valley Liaestones. 

Warsaw and St. Louis 

Limestones. 

Fort Dodge Formation------

Fort Pierce Formation----

Punta Gorda, Sunniland, 

Rattlesnake Hallllllock, and 

Gordon Pass Formations. 

Cedar Keys Limestone-----

Salt-dome cap rock------

Werner Forlll8tion---------

Buckner Formation------

Ferry Lake Anhydrite------

Edwards Limestone and 

McKnight Formation. 

Mississippian-----

L. Mississippian--

Devonian---------

Hiaaissi ppian-----

Jurassic---------

Cretaceous(?) or--

Jurassic( 1) 

E. Cretaceous 

E. Tertiary 

(Paleocene). 

Cretaceous to 

Holocene (source 

beds are Jurassic) 

H. Jurassic-------

L. Jurassic-------

E. Cretaceous----

E. Cretaceous----

Lenses to 30. 

1-15 

Co111110nly 2-5, 

locally as much 

as 30. 

CoTIIBOnly 2-5, 

locally as much 

aa 15. 

3-9 

----?------

Commonly 3-10, 

locally 30-50. 

lG-25 

25-240 

15-30 

Up to 30-60. 

3-30 

10-15 

Depth to 

anhydrite Structure 

(aeters) 

150-1,800 Simple, with 

gentle dips. 

200-1,300 SilllJlle-----

3Q-350 

300-2,100 

As much as 

800 

As llklch as 

500 

10G-1,000 

As much as 

300 

As much as 

300 

5-20 

3,000 

1, 5oo-3, ooo 

400-1,200 

100-1,000 

1,000-3,000 

1,000-3,000 

300-3,000 

300-2,500 

------do-------

Simple, with 

gentle dips. 

Complex and 

deformed. 

Complex and 

defor11ed. 

Simple-------

Simple-------

-----do-----

-----do-----

Simple------

------do-----

------do-----

Diapiric mass on 

top of salt domes, 

1-6 km diameter. 

Simple with 

gentle dips. 

-----do-----

-----do-------

Simple--------

Comments 

A-2 anhydrite is 15-30 m thick in small areas around 

pinnacle reefs. 

The formation contains interbeds of carbonates, salt, and 

anhydrite. 

Mined for gypsum around perimeter of basin. 

Anhydrite beds in A, C, and F units colllllOnly 1-10 m thick; 

G-unit anhydrite is 30-37 11 thick. and 1,50Q-2, 100 m deep. 

Oldest anhydrite reported in United States; metamorphosed 

and aixed with other rocks in highly complex region. 

Anhydrite occurs in irregular lenses and masses due to 

deformation and flowage. 

Anhydrite is impure and irregularly interbedded with 

limestone and dolomite. 

Where 30 • thick, unit is aostly anhydrite with interbeds 

of limestone. 

Anhydrite irregularly interbedded with limestone. 

Unit is gypsuza and is mined extensively. 

Unit is at great depth in basin. 

Anhydrite beds probably no more than several meters thick 

at depths less than 1,500 11; beds 30 11 thick or thicker 

are at depths of 2,000-3,000 •· 

Anhydrite beds reportedly as IIUCh as 25 m thick. 

Lithology of cap rock. co11l110nly is highly variable; upper 

part of cap rock conuaonly fractured, porous, and water 

bearing; costal domes still rising. 

Unit is 1,000-2,000 • deep in southern Arkansas. 

Anyhydrite beds reportedly 30-60111 thick and 1,000-1,500 m 

deep in southern Arkansas. 

Thick anhydrite beds are 300-1,500 11 deep in southern 

Arkansas and northern Louisiana. 

Edwards contains gypsum on outcrop; equivalent McKnight 

contains anhydrite in Maverick basin. 
c 

i 

a: 

c 

.. 

cs· 

::J 

It 

::J 

Q. 

C) 

CD 

0 

0 

co 

(;" 

0 

::r 

Qt 

a; 

; 

.. 

c;;· 

c!:. 

(') 

(It 

a 

> ::J 

::r 

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; 

c 

CD , 

0 

(It 

;: 

..... 

w 

Permian basin------ Panther Seep Formation----

Easly Creek Shale--------

Johnson Shale-----------

Wellington Formation and 

Wichita Group. 

Lower evaporites of Clear 

Fork Group. 

Cimarron anhydrite and 

upper evapori tea of 

Clear Fork Group. 

Yeso Formation-----------

Briggs Formation---------

San Andres Limestone and 

Blaine Formation. 

Artesia Group---------

Cloud Chief For~~~ation----

Castile Foi'IIIation--------

Salado Formation--------

Rustler Formation and 

Alibatea Doloaite Lentil. 

Northern Denver basin Minnelusa Formation------

Stone Corral Formation---

Lykins Forllatioo---------

Wyoming basins------ Minnelusa Formation-----

Goose Egg and Phosphoria 

(Park City) Formations. 

Spearfish Fonu.tion------

Gypslllll Spring Formation--

Preuss Formation--------

L. PennsylvanianE. Permian-------

-------do-----

-------do-------

-----do-----

------do----

-----do------

-----do----

------do----

E. and L. PerlllianL. Permian---

------do-----

----do-----

----do---

Pennsylvanian 

(Desmoinesian, 

Missourian, 

Vigilian) 

K. Permian------

(Wolfcampian) 

E. Permian-----

(Leonardian) 

L. Permian and 

E. Triassic. 

Pennsylvanian 

and E. Permian. 

Permian and 

E. Triassic. 

L. Permian and 

Triassic. 

Jurassic------

-------do-------

7-24 

3 

3 

1-10 

1-10 

2-10 

Commonly 2-15, 

as IIUch as 41. 

Le118es up to 40. 

CollllllOnly 1-10, 

locally 30-60. 

Co-only 1-10, 

locally 20-30. 

1-30 

23-105 

1-10 

1-15 

2-10 

Co_,nly 2-15, 

locally 17-23. 

Com10nly 5-10, 

locally 30 • 

2-12 

2-10 

2-15 

2-10 

15-38 

---?-------

Shallow---

Shallo---

Shallo---

100-1,500 

500-1,500 

100-1,500 

30o-1,500 

Shallo---

15-1,645 

300-1,200 

10-200 

30-1,000 

300-750 

100-600 

90Q-1,500 

90o-2,400 

60o-1,500 

600-2,400 

15-4,500 

15-4,500 

15-2,000 

100-5,000 

1,500-3,000 

Complex-------

Simple---------

------do-----

-----do-----

-----do-------

------do------

-----do------

Co~~plex-------

Simple-------

---do------

---do------

---do----

---do-----

---do----

Simple-------

----do-------

----do------

------do------

Simple-------

Simple to complex 

Simple-------

Simple to complex 

Complex------

Gypsum outcrops in San Andres Mountains, N. Hex. 

Thin gypstD mined at Blue Rapids, northeastern kansas. 

Thin gypsum 50 m deep in Nellaha County, Nebr. 

Wellington contains anhydrite and salt interbeds in 

Kansas and Oklahoma, and is equivalent to Wichita Group 

anhydrite and carbonates in Texas. 

Anhydrites mainly in Palo Duro basin and on Amarillo 

uplift; interbedded with salt and shale. 

Anhydrite, shale, aalt, and dolomite called Cimarron 

anhydrite in subsurface north of Alllarillo uplift; part 

of upper Clear Fork farther south in Palo Duro basin. 

Anhydrite, sandstone, and liP1estone in outcrops and 

subsurface of central and south-central Hew Mexico; 

gypsum 41 m thick crops out in San Andres Mountains. 

Gypsum lenses and irregular masses in structurally 

comples Malone Mountains of west Texas. 

Wideapread evaporite called Blaine north of Amarillo 

uplift and San Andres to the south; anhydrite beds 

30-60 11 thick and 120-1,645 m deep in east-central 

New Mexico. 

Anhydrite interbeds in northern shelf areas and in Midland 

and Palo Duro basins; thick. anhydrite reported on shelf 

in southeastern New Mexico at depth of 30D-900 m. 

One thick gypsu• crops out and grades into anhydrite at 

shallow depth in Anadarko basin; where more than 100 11 

deep, anhydrite is only 3-10 m thick. 

Contains thickest beds of anhydrite in United States; 

confined to Delaware basin where it is interbedded with 

thick salt beds. 

Extends across west Texaa, southeast New Mexico, and 

southern part of Palo Duro baain; interbedded with 

halite in most areas; major potash resources in Carlsbad 

district of southeastern New Mexico. 

Rustler in Delaware and Midland basi!UI and nearby shelf 

areas; upper part equivalent to Alibates Lentil of 

Texas Panhandle. 

Thin anhydrites interbedded with carbonates and soclastics. 

Thicker anhydrites (17-23 m) are at depth of about 1,000-

1,500 m in Nebraska. 

Haxirau• thickness at depth of 1,295 m in northeast Colorado. 

Thin anhydrites occur in a number of named units of 

formation. 

Thin anhydrites in Powder River basin and to south and 

east of Black Hills. 

Anhydrites of Goose Egg in eastern Wy0111ing grade into 

Phosphoria in western Wyoming; structure is complex 

around basin margins and on uplifts • 

Spearfish, present in vicinity of Black Hills uplift, 1 s 

equivalent to part of Goose Egg Formation. 

Thick anhydrite is undisturbed and at depths of 30Q-1,500 m 

locally in Wind River and Bighorn basins. 

Thin anhydrites at great depth in the overthrust belt in 

the Idaho-Utah-Wyoming border area. 
.... 

~ 

~ ::r 

~ .. 

i 

c 

CD 

"0 

0 

en 

~ 

2. 

~ CD 

c: 

::J 

i 

Q. 

f1 

S' 

• 

Table 2.1. Summary of geologic data on anhydrite deposits in the conterminous United States-Continued 

Williston basin-- Red River, Stonewall, 

and Interlake Formations. 

Winnipegosis, Prairie, 

Dawson Bay, Souris River, 

Duperow, Birdbear, and 

Three Forks Formations. 

Madison Group (Charles 

and Mission Canyon 

Formations). 

Big Snowy Group (Kibbey, 

Otter, and Heath 

Formations). 

Minnelusa, Opeche, 

Minnekahta, Spearfish, 

and Piper Formations. 

Ordovician and 

Silurian. 

Devonian-------

Mississippian-----

------do----

Pennsylvanian, 

Permian, 

Triassic, and 

Jurassic. 

1-6 

Co111110nly 2-10, 

locally 15. 

Commonly 2-10, 

locally 25-30. 

2-10 

2-10 

2,400-4,000 

1,500-4,000 

1,000-3,000 

3()()-1,500 

1,200-2,000 

Sweetgrass arch--- Souris River and L. Devonian---- 3-10 6D0-1,500 

Duperow Formations. 

Logan Gulch Member of -----do----- 12-30 600-1,500 

Three Forks Formation. 

Eagle basin----- Eagle Valley Evaporite-- H. Pennsylvanian- Co111110nly 5-30, 1D-2,000 

locally as nu~h 

•• 50. 

Paradox basin--- Paradox Kember of Hermosa H. Pennsylvanian-- 3-10 2D0-2,000 

Formation. 

San Juan basin----- Todilto Formstion------ H. Jurassic---- Co11110nly 25-30, 100-2,700 

locally as Dlllch 

as 40. 

Supai salt basin--- Supai Formation--------- E. Perlllian----- 1-6 18G-750 

Picacho basin---- Unna111ed evaporites-------- L. Tertiary Coaaonly 2-10 in 700-2,500 

(Miocene). upper part, 

co111110nly lD-37 

in lower part. 

Chandler basin----- ---------do--------- ------do------- Commonly 2-10, 700-1,200 

BOlle 2Q-106. 

Phoenix basin---- Luke Salt Member, Hickey -----do---- 2-10 300-1,500 

FoT1118tion. 

Red Rock basin--- Unnamed evaporites----- -----do------ ? 900 

Tucson basin------ ---------do----------- ------do--- 3 m and some 2,164 

crystals. 

Virgin Valley basin- Muddy Creek Formation----- -------do------ 1-5(?) 20Q-800 

Simple-------

-------do------

Simple to complex 

-----do-----

Simple-------

Simple-------

-----do--------

Complex and 

diapiric. 

Simple to complex 

Simple, with 

gentle dips. 

Si "'P le----------

Si~~~ple--------

--------do------

Simple; possible 

diapirism. 

Simple--------

-------do------

Complex and 

diapiric. 

Thin anhydrites at great depth. 

Only in the Prairie Forlll8tion iB anhydrite as much as 15 11 

thick, and it is at depth of 2,700 m. 

Charles Formation contains 25 m of anhydrite at depth of 

1,100 11 on northeast side of basin and 30 m of anhydrite at 

depth of 1,000-1,500 111 in central Montana trough. 

Thin anhydrite beds in Williston basin and central Montana 

trough. 

Thin anhydrite beds at moderate to great depth. 

Thin anhydrite interbedded with dolomite and some limestone. 

Anhydrite beds 12-30 11 thick over gentle arch and near 

complex Rocky Mountain front to west. 

Thick beds of anhydrite and salt have flowed plastically 

and form complex diapiric structures • 

The beds of anhydrite and thick beds of salt are flatlying at depths of 500-2,000 m, but have flowed plastically 

to for111 complex diapiric structures in north part of the 

basin. 

Single anhydrite bed in east half of basin; 300-1,500 11 deep 

in southeast part of basin; about 300 m deep on Chama 

platform in northeast part of basin. 

Thin anhydrite beds interbedded with red beds and halite. 

Thickest known anhydrite sequence in world, 1,800 11 thick; 

cons its of anhydrite (65 percent of total), clastics, and 

thin salt beds in nonD!Srine block-faulted basin; many 

anhydrite beds are 10-37 m thick. 

Anhydrite sequence is 500 m thick and contains anhydrite 

beds reported to be 20-106 m thick; nonmarine sediments 

in block-faulted basin. 

Thick nonmarine salt mass in block-faulted basin overlain by 

several thin anhydrite beds. 

Anhydrite sequence is 150 m thick, but thickness of 

anhydrite beds not known. 

One thin anhydrite bed and gypsum crystals on edge of blockfaulted basin; middle of basin may contain more anhydrite. 

Thick interbeds of bali te, glaube rite, and shale are locally 

folded and faulted. 
c 

~ c;: 

a: 

0 

:I 

• :I 

Q. 

C) 

CD 

0 

0 

CQ 

n 

0 

:I' • .. • 

c;;-

~ 

c:t 

C') 

tn 

2. 

)o 

:I 

:I' 

~ .. 

i 

c 

CD , 

0 

tn 

= tn 

.... 

Ul 

Southern Nevada and 

nearby areas. 

Central Utah------

Toroweap Fonaation---- Permian------- Co.-only 2-15, Shallow 

reported 30-60. 

Kaibab Formation-------- ------do---- Co-only 2-15, --do---

Moenkopi Formation------

Chinle Formation-----

Carmel For•stion-------

Curtis Formation-------

Horse Spring Formation--

Carmel, Arapien, and 

Sum~~~erville Formations. 

Flagstaff Limestone----

Triusic----

Triassic------

Jurassic-------

------do----

Tertiary-----

Jurassic------

E. Tertiary 

(Paleocene and 

(Eocene). 

lenses to 30. 

2-15 

2-15 

3-15 

2-10, lenses 

to 30, 

2-15 

2-10, lenses 

30-90. 

As lllUch as 13. 

--do---

----do---

--do---

--do---

--do--

15-3,600 

Shallow--

Eastern Great Basin- Pequop and Lorey Fonaations Permian------ eo-only 2-10, 

locally 3Q-60. 

15-2,000 

Simple to complex Contains thin sands and carbonates where anhydrite beds are 

30-60 m; few data on subsurface; gentle dips in southwestern 

Utah-northwestern Arizona and block faulted in Nevada, 

----do---- Few data on subsurface; gentle dips in southwestern Utahnorthwestern Arizona and block faulted in Nevada, co.-plex 

------do-----

-------do-----

Simple--------

Simple to complex 

Complex------

Simple to complex 

Sbtple-----

Complex------

in California. 

Few data on subsurface; gentle dips in southwestern Utahnorthwestern Arizona and block faulted in Nevada. 

Do. 

Present in southwestern Utah, but few subsurface data. 

Present in southwestern Utah; gypsum lens 30 m thick in 

crests of folds; few data on subsurface. 

Present in block-faulted area of southern Nevada. 

Gentle dip of thin anhydrite bet.ls in east; thick lenses in 

diapiric anticlines in west. 

Thin gypsum of lacustrine origin; crops out and at shallow 

depth. 

Most data are on outcropping gypsum; gypsum beds 30-60 m 

thick contain thin nonaulfate strata; four anhydrite beds, 

26-46 m thick, reported at depths of 457-1,403 m in Nevada; 

region is block faulted. 

Northwestern Nevada- Unnamed------:-------- Triassic or 

Jurassic • 

Lenses as much as 

30-60. 

More than 20 Complex----- Strata are faulted, folded, and associated with metamorphic 

rocks; thick lenses due to flowage. 

Western Idaho and Unna~~~ed--------------- Triassic-----

eastern Oregon. 

Southern California- Various units-------- L, Tertiary 

(Miocene and 

Pliocene), 

Lenses to 10. 

Coi!IIIOnly 1-10, 

lenses sa IIUCh 

as 30. 

Shallow--

Shallo---

Complex-----

Co.apler-----

Occurs as gypsum in irregular lenses as much as 10 11 thick; 

gypsum folded, faulted, associated with schist. 

Occurs as gypsum on scattered uplifted fault blocks; 

deposita are folded, faulted, and steeply dipping; thick 

lenses along crests of folds. 
I 1:::" •• • 

I er : I ·S!ll 

I .C: : ~ :" 

I ~~ ,-J! 

I ; 

I ; ' : ' ; ' : \i 

~' . : ' . ' ' 

... ·· 

.. .. .. .. ····· 

\, -

·. -- --1-----=.-·-· ---.. •. I e• 

/ . ····· ·r······ ············ 

Area underlain by anhydrites in Lucas Formation 

of Detroit River Group. Depth to top of 

anhydrite ranges from about 500ft ( 1 50 m) 

around perimeter to aboyt 4000 ft ( 1 200 m) 

in center 

1

. 

INDIANA OHIO 

: Area underlain by anhydrites 

of Salina Group 

100 MILES 

I 

160 KILOMETERS 

rJ' 

, -...,~I ',J WEST VIRGINIA 

CANADA 

NEW YORK 

0 

PENNSYLVANIA 

EXPlANATION 

Depth below land surface to top of 

Salina Group evaporites: 

I.---......,, Less than 1000 ft (305 m) 

t\S:Sj 1000 to 3000 ft (305-915 m) 

~ 3000 to 5000 ft (915-1524 m) 

~ More than 5000 ft (1524 m) 

Figure 2.4. Distribution and depth below land surface of Silurian and Devonian evaporite deposits in the Michigan and 

Appalachian basins. 

MICHIGAN BASIN 

Structure and Geologic Framework 

The Michigan basin is a major sedimentary and 

structural basin that encompasses all of Michigan's 

southern peninsula, as well as parts of Indiana, Ohio, and 

Ontario (fig. 2.4). It is bounded on the north and 

northeast by the Canadian shield, on the east and 

southeast by the Algonquin arch in Ontario and the 

Findlay arch in northern Ohio, on the southwest by the 

Kankakee arch in northern Indiana and northeastern 

Illinois, and on the west and northwest by the Wisconsin 

arch and Wisconsin dome. 

Because the basin lies in the tectonically stable 

interior of North America it is characterized by 

essentially flat -lying sedimentary rocks that are folded or 

16 Anhydrite Deposits of the United States 

faulted at only a few places. Strata dip gently (0.25° to 

0.5°) into the center of the basin from the adjacent arches 

and shield area at a rate of 5-10 m per km (kilometer). 

The deepest part of the basin underlies Clare and 

Gladwin Counties, in the central part of the southern 

peninsula of Michigan, where about 5,000 m of 

sedimentary rocks are believed to overlie the Precambrian (Ells, 1967). These sedimentary rocks include 

strata of Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Jurassic age. They are 

chiefly carbonates, shales, evaporites (salt and anhydrite), and sandstones (fig. 2.5). They are overlain at 

most places by Pleistocene glacial drift that averages 

between 60 and 90 m in thickness, but that is more than 

275 m thick locally. 

The basin may have first formed as an embayment 

as early as Cambrian time (Fisher, 1969). Throughout 

the remainder of the Paleozoic Era, the basin continued 

to subside more than the did adjacent regions, and thus it 
GEOLOGIC TIME-STRATIGRAPHIC ROCK-STRATIGRAPHIC TIME 

0 ~ 

~ OI 1.1.1 

-u 1- AGE GROUP FORMATION ~0 V) 

I.Lia... >- w Q.LLJ V) 

u 

0 u u v; v; N V) LLJV) 

0 <( 1-<( KIMMERIDGIAN 

~ ::s~ V) 

~ :::::> w ...... 

~ 

z z 

<( LLJ<( - 1- CONEMAUGH Grand River Fm. Z<( z <(-' <( 

> _, _ _, > 

>- >- V) >-Vl z ~z POTTSVILLE Saginaw Fm. z <CZ 1.1.1 LLJ 1.1.1 

Q. Q. 

z z Bayport Ls. 

<( ~<( -<( MERAMECIAN GRAND RAPIDS a: ~-' Q. Michigan Fm. 

inr- v; 

~>- ~ OSAGEAN Marshall Ss. V)-' V) V)Ck:: V) -<( ~ KINDERHOOKIAN Coldwater Sh ~LLJ 

MISSISSIPPIAN-DEVONIAN UnasSigned 

Ellsworth Sh 

LLJ (WeslernMtchigan) 

1- r------r------ ------- ::5 CHAUT AUQUAN Antrim Sh 

I-- SENECAN Squaw Bay Ls. 

Thunder Bay Ls. 

Potter Farm Fm 

Norway Point Fm. 

Four Mde Dam Fm. 

TRAVERSE Alpena Ls 

z z ERIAN Newlon Creek Ls. 

~ LLJ<( Genshaw Fm 

z c:Sz Ferron Point Fm OQ 0 Rockport Quarry Ls. > ~ > 1.1.1 1.1.1 Bell Sh 0 0 Rogers City Ls. 

Dundee Ls 

Anderdon Fm 

Lucas Fm DETROIT RIVER ULSTERIAN <( Amherstburg Fm u 

~ Sylvania Ss 

~ Bois Blanc Fm. a:> I-- u :::; 

0<:: ~ Garden Island Fm. 

~ s;;: 

'-' 

u BASS ISLANDS ~ Raisin River Dol. 

0 Put-in-Bay Dol 

N LLJ St Ignace Dol 

0 1-

::s CAYUGAN 

w SALINA Pte aux Chenes Sh -J 

<t 

a. - z z <( <( 

02 02 Engadine Dol 

:::::> :::::> _, UJ _, 

v; -' - 0 V) NIAGARAN 0 

~ Cordell Dol MANISTIQUE Schoolcraft Dol 

Hendncks Dol 

BURNT BLUFF Byron Dol 

L-- L1me Island Dol 

Figure 2.5. Stratigraphic succession in Michigan 

showing position of evaporite units as bars on right 

(modified from Michigan Geological Survey, 1964). 

received a great thickness of sediments in its central part. 

The major period of subsidence took place in Late 

Silurian time, which accounts in part for the deposition of 

the thick Salina salts in the Michigan basin. 

Of principal interest for this report are the 

sedimentary rocks and the geologic history of the Silurian, Devonian, and Mississippian Periods, because these 

strata contain the evaporite deposits in the Michigan 

basin (fig. 2.6). The formal lithostratigraphic nomenclature assigned to the strata in the Michigan basin in this 

report is that used by the Michigan Geological Survey. 

The Salina Group of Silurian age, one of the greatest 

accumulations of salt anywhere in the world, contains a 

number of anhydrite interbeds; one has a maximum 

thickness of 30 m. Anhydrite beds as much as 15 m thick 

are interbedded with salt and carbonates in the Devonian 

Detroit River Group, and anhydrite units as much as 

10 m thick are present in the Mississippian Michigan 

Formation. 

Salina Group 

The Upper Silurian Salina Group is a thick 

sequence of evaporites, carbonates, and clastics 

underlying the Michigan basin and the northern part of 

the Appalachian basin to the east (fig. 2.5). This marineevaporite section, which consists mainly of rock salt, is 

about 800 m thick in the central part of the Michigan 

basin, and contains anhydrite beds that commonly are 

2-10m thick. Toward the margins of the basin, several of 

the anhydrite beds are thicker than 10 m, and one of 

them is as much as 30m thick. Among the large number 

of studies done on the Salina Group are the 

comprehensive reports of Landes (1945), Ailing and 

Briggs (1961), Ells (1967), Briggs and Briggs (1974), 

Meso leila and others (1974 ), and Nurmi and Friedman 

(1977). Studies along the margins of the basin include 

those by Gill (1977), Huh and others (1977), and Budros 

and Briggs (1977). The potential use of salts in the Salina 

Group for radioactive waste disposal has been discussed 

by Briggs (1968), Landes (1972), and Johnson and 

Gonzales (1976, 1978). 

Carbonates (limestone and dolomite) that formed 

during Early Silurian time represent deposition in 

shallow and warm marine waters. This carbonate 

deposition reached optimum conditions later during the 

Middle Silurian, when the Niagaran reef platform 

developed along the borders of the Michigan basin 

(Briggs and Briggs, 1974). The reef bank ranges in width 

from 8-30 km and separates a back-reef lagoonal zone 

outside the basin from a shelf area and the central-basin 

area enclosed by the reef. The shelf area, which is about 

Distribution and Geologic Characteristics of Anhydrite Deposits 17 
A 

25 

I 

40 

50 MILES 

I 

80 KILOMETERS 

EXPlANATION 

Evaporite unit 

-

consisting in part 

of salt and (or) anhydrite 

B 

SEA 

LEVEL 

2000 ft 

(610 m) 

4000 

(1220 m) 

6000 

(1830 m) 

8000 

(2440 m) 

10,000 

(3050 m) 

Figure 2.6. Generalized north-south cross section through the Michigan basin showing principal evaporite units (modified 

from Johnson and Gonzales, 1978). 

20-30 km wide in the north and 30-60 km wide in the 

south, was a favorable site for the growth of numerous 

pinnacle reefs, many of which are prolific oil and gas 

reservoirs. 

The Salina evaporites were deposited after major 

growth of the Niagaran reefs ceased in the Michigan 

basin (Mantek, 1973; Briggs and Briggs, 1974). Marine 

regression led to restricted circulation of the waters in 

the Michigan basin, compared with those of the open 

ocean, and, as a result, the waters in the basin were 

evaporated until halite and anhydrite were deposited. 

Intermittent replenishment of marine water to the basin 

permitted deposition of thick evaporite sequences that 

extended throughout most of the southern peninsula of 

Michigan. During periods of marine transgression the 

basin was flooded, and carbonates and other normal 

marine sediments were deposited. Salina deposition 

therefore is characterized by a series of marine 

transgressions and regressions, and evaporites were 

formed during the regressions. 

Total thickness of the Salina Group ranges from 

several hundred meters around the perimeter of the 

basin to about 800 m near the depocenter. The depth 

to the top of the upper, or F evaporite ranges from 150 to 

300 m along the margins to more than 1,800 m in the 

center. Thickness of the evaporites decreases away 

18 Anhydrite Deposits of the United States 

from the middle of the basin chiefly due to depositional 

thinning, but also due in part to local dissolution of salt 

near the shallow edge of the basin. 

The Salina Group consists of a number of informal 

stratigraphic units; most units are composed predominantly of salt, carbonates, or shales, and several 

units contain anhydrite interbeds. Individual units have a 

similar lithologic character over a wide geographic area, 

and the distinctive mechanical log curves for each unit 

permit reliable correlations over large distances (Ells, 

1967). Landes (1945) established the basic subdivision of 

the group by recognizing units A through G, from oldest 

to youngest, and this nomenclature has continued to be 

used throughout the Michigan basin. 

The A-1 and A-2 evaporites, in the bottom part of 

the Salina, are typically massive salt units that are 60-120 

m thick in most of the basin (Mesolella and others, 1974). 

Both units commonly contain anhydrite beds 2-10 m 

thick at the base and (or) top of the salt within the basin, 

but the salt thins abruptly toward the basin margin and 

grades into moderately thick anhydrite near the Niagaran 

reef and some of the associated platform and back-reef 

areas. Anhydrite beds are more than 15 m thick locally 

along this narrow transition zone, and the A-2 anhydrite 

is a widespread bed about 10 m thick in the back-reef 
A-2 

carbonate 

A-2 

evaporite 

A-2 

anhydrite 

NORTHERN MICHIGAN 

OI 0 Datum: Top A-2 carbon

0

ate 

300 FEET 

t-1 ----'---.----'--_.1..,, 

50 15 0 100 METERS 

FEET METERS 

Halite 

"Rabbit Ears" L.:~~~:O:~~~ 

Anhydrite 

Ruff 

Formation 1----------

A-1 

anhydrite 

A-Q 

carbonate 

Organic 

reef 

Bioherm 

OIO 

50 15 

FEET METERS 

Organic 

reef 

Bioherm 

SOUTHEAST MICHIGAN 

Datum: Sea Level 

1000 FEET 

I 

300 METERS 

A-2 

evaporite 

Ruff 

Formation 

Figure 2.7. Distribution of anhydrite and other facies in vicinity of pinnacle reefs in northern and southeastern parts of 

Michigan basin (modified from Budros and Briggs, 1977). 

area on the north side of the basin. The anhydrite beds 

consist mainly of laminated limestone and anhydrite and 

nodular mosaic anhydrite (Gill, 1977; Nurmi and Friedman, 1977). 

Anhydrite beds also thicken abruptly in the vicinity 

of the small pinnacle reefs that typically are 100-1,000 m 

in diameter and that rise several hundred meters above 

the foreslope of the main reef bank (fig. 2.7). The A-1 

anhydrite is locally as much as 9-12 m thick in a narrow 

band around the pinnacle reefs, but it pinches out at the 

edge of reefs. The A-2 anhydrite is locally 15-30 m thick 

where it thickens sharply on the flanks and over the top of 

some of the pinnacle reefs. Although these are the 

thickest beds of anhydrite in the Salina Group in the 

Michigan basin, the area of each occurrence is only a 

little larger than the pinnacle reef itself. In general, the 

pinnacle reefs in the southern part of the Michigan basin 

are larger than those in the northern part (and therefore 

the area of each thick anhydrite deposit is larger), and 

they occur at shallower depths (less than 1,200 m). 

The younger B and F units are also thick evaporites 

that consist mainly of salt, but they usually contain 

interbeds of shale, dolomite, and anhydrite. Individual 

anhydrite beds in these units generally range from 2 to 

10m in thickness. The thick B salt unit is thinner toward 

the margin of the basin and grades into an anhydrite unit 

less than 15 m in thickness. The entire anhydritic B unit 

is more than 30 m thick in a small part of the northern 

Michigan basin (Mesolella and others, 1974), but this 

unit actually consists of anhydrite interbedded with salt 

and other rock types. In the upper peninsula of Michigan, 

gypsum beds 2-6 m thick are present near the northern 

limit of the Salina Group, just below the surface near St. 

Ignace and on St. Martin Island (Smith and Stone, 1920). 

Lucas Formation of Detroit River Group 

The Lucas Formation, in the Middle Devonian 

Detroit River Group, is a thick sequence of carbonates 

and evaporites that underlies most of the Michigan basin 

(fig. 2.8). Rock salt is the principal evaporite in the Lucas 

Formation in the north-central part of the basin, but 

anhydrite occurs in beds 2-15 m thick in this area and 

elsewhere beyond the salt area. Several beds of anhydrite 

2-10m thick are also present in the Dundee Limestone 

above the Detroit River Group. Comprehensive regional 

studies of the Lucas Formation and other formations in 

the Detroit River Group were made by Landes (1951), 

Briggs (1959), Ehman (1964), and Gardner (1974); and 

additional localized studies were done by Sloss (1953), 

Fugate (1968), Sutton (1968), Wirth (1968), Rooney and 

French (1968), and Matthews (1977). Gypsum resources 

and anhydrite in the Detroit River Group were reported 

by French and Rooney (1969) and Briggs (1970). 

Distribution and Geologic Characteristics of Anhydrite Deposits 19 
GAMMA-RAY NEUTRON LOG MARKER 

K--

j--

__ , __ 

H--

z 

0 

1-

<( 

:2 

a: 

0 

<( 

UNIT 

UPPER SALTS 

TOP OF 

DETROIT 

RIVER GROUP 

(BIG SALT) 

LOWER SALTS 

AND 

SOUR ZONES 

G-B 

MASSIVE 

ANHYDRITE 

AND 

RICHFIELD 

MEMBER 

OF LUCAS 

FORMATION 

AMHERSTBURG 

FORMATION 

A-BASE 

EXPLANATION 

.. Salt 

~ Anhydrite 

~ Dolomite 

~ Limestone 

FEET METERS 

0 0 

50 15 

100 30 

200 60 

Figure 2.8. Stratigraphic sequence of part of the Detroit River Group in the Michigan 

basin (modified from Briggs, 1970). 

Most of northern Indiana and Ohio and the 

southern peninsula of Michigan are underlain by evaporites in the Lucas Formation. The total thickness of the 

formation ranges from about 100 m around the 

perimeter of the Michigan basin to about 400 m in the 

north-central part of the basin in parts of Roscommon, 

Missaukee, and Clare Counties, Mich. (Gardner, 1974). 

Decrease in thickness toward the margins of the basin is 

due mainly to depositional thinning of salt beds. The 

depth to the top of the Lucas evaporites ranges from 

about 200-500 m around the perimeter of the basin to as 

much as 1,300 m in the center of the basin. 

Rock salt is the dominant lithology in the Lucas 

Formation in the north-central part of the basin, and 

dolomite is dominant elsewhere. Anhydrite typically 

makes up less than 50 percent of the total thickness of 

the Lucas Formation in all parts of the Michigan basin, 

20 Anhydrite Deposits of the United States 

although some parts of the individual members may 

contain 50-75 percent anhydrite (Briggs, 1970; Gardner, 

1974). 

The lower division of the Lucas Formation is the 

Richfield Member (Landes, 1951), which is 30-60 m 

thick in the center of the basin and consists of interbedded dolomite and anhydrite. The thickness of anhydrite beds decreases rapidly outward from the center of 

the basin toward its margins on the west and north. 

Typical structures of anhydrite in the Richfield Member 

are shown in figures 2.9 and 2.10. Anhydrite begins at the 

Figure 2.9 (facing page). Examples of nodular, pillar and 

massive anhydrite from the Richfield Member of the Lucas 

Formation (Middle Devonian) in the Michigan basin (from 

Gardner, 1974). 
.. 

• 

Distribution and Geologic Characteristics of Anhydrite Deposits 21 
22 Anhydrite Deposits of the United States 
Figure 2.10. (facing page). Examples of reticulate, 

contorted, lamellar, and nodular anhydrite from the Lucas 

Formation (A-C; E-J) and Dundee Limestone (D), Michigan 

basin (from Gardner, 1974). 

base of the Richfield Member as anhydrite laths in 

dolomite; it grades upward into discontinuous beds of 

nodular anhydrite (fig. 2.9, A and E), and finally into 

more continuous beds of nodular anhydrite. The upper 

bed of anhydrite in the Richfield Member (the so-called 

"big anhydrite" or cycle 1 of Matthews, 1977) is an 

excellent, widespread stratigraphic marker bed. The 

Richfield Member is an important oil-producing unit in 

the Michigan basin; in 30 fields, it accounts for about 10 

percent of Michigan's total production of hydrocarbons. 

The Richfield Member of the Lucas Formation is 

overlain by the Iutzi Member (Gardner, 1974), which is 

45-60 m thick in the center of the basin. Individual beds 

of anhydrite within the Iutzi are typically 2-10 m thick, 

and in places are as much as 15m thick. These beds make 

excellent stratigraphic markers that are correlative across 

the basin. The thickest anhydritic unit in the lutzi 

Member is the "massive anhydrite," which is 20-30 m 

thick over most of the basin where it is most massive. 

However, individual beds of anhydrite in this unit are no 

more than 15 m thick. All the anhydrite in the "massive 

anhydrite" unit is nodular. 

Above the Detroit River Group is the Dundee 

Limestone, which contains several anhydrite beds 2-10 m 

thick in the west half of the Michigan basin (Gardner, 

1974). Total thickness of the Dundee Limestone in this 

area is 30--75 m, and the anhydrite is interbedded with 

dolomite and some limestone. 

Michigan Formation 

The Michigan Formation, of Late Mississippian 

age, consists of clastic sediments and evaporites in the 

central part of the Michigan basin (fig. 2.11 ). Included in 

the formation are gypsum deposits that are being mined 

at and near the outcrop in two districts and anhydrite that 

is in the deeper subsurface. Gypsum and anhydrite beds 

range in thickness from 1-10m. Early studies of gypsum 

and anhydrite were done by Smith and Stone (1920) and 

Newcombe (1928), and later reports were published by 

Poindexter and others (1951) and Briggs (1970). 

The Michigan Formation is about 60 m thick at the 

perimeter of the basin and as much as 120--150 m thick in 

the center. Gypsum beds crop out locally on the east and 

west sides of the Michigan basin, but the top of the 

formation is as much as 350m below ground level in the 

center of the basin (Briggs, 1970). 

The lithologies of the Michigan Formation consist 

of interbedded sandstone, shale, gypsum, and anhydrite. 

About 15 separate gypsum or anhydrite beds have been 

reported (Briggs, 1970), but each bed is only 1-10 m 

thick. The principal emphasis of most studies has been on 

the gypsum in the formation. The amount and distribution of anhydrite in the various calcium sulfate beds 

is not reported, although the beds are probably anhydrite 

in the deeper subsurface. 

Mining of gypsum in Michigan is centered in the 

Grand Rapids-Grandville district in Kent County in the 

west and the Alabaster district in Iasco County in the east 

(Smith and Stone 1920; Newcombe, 1928). In Kent 

County, several beds 2-6m thick are being quarried and 

mined at depths as much as 30 m. In Iasco County, 

gypsum beds 5-7 m thick are being quarried from 

beneath thin deposits of glacial drift. 

UNIT 

Pencil gypsum 

Triple gypsum 

Brown lime 

Stray-stray 

National City gypsum 

Stray 

Sugar dolomite 

EXPlANATION 

~ Gypsum or anhydrite 

Figure 2.11. Stratigraphic sequence and 

gypsum deposits in the Mississippian Michigan Formation of the Michigan basin (modified from Briggs, 1970). Thickness not 

reported, but entire sequence probably no 

more than 150 m thick. 

Distribution and Geologic Characteristics of Anhydrite Deposits 23 
APPALACHIAN BASIN-SALINA GROUP 

The Late Silurian in the Appalachian basin of the 

Northeastern United States consists of a thick sequence 

of evaporites, carbonates, and shales that contain several 

anhydrite units. One of the anhydrite beds near the top of 

the Salina thickens into the deep basin, and reaches 

thicknesses of between 30 and 37 m at a depth of 

1,500-2,100 m below the surface. Regional studies of the 

Salina Group evaporites in the Appalachian basin have 

been done by Alling and Briggs (1961), Ulteig (1964), 

Fergusson and Prather (1968), Rickard (1969), Clifford 

(1973), Heyman (1977), Smosna and others (1977), 

Smosna and Patchen (1978), and Mesolella (1978). The 

formal nomenclature of these workers is used in this 

report. Johnson and Gonzales (1978) also studied the 

salts in the Salina Group as potential host rocks for 

disposal of radioactive waste. 

The Appalachian system, the dominant tectonic 

feature in the Eastern United States, consists of several 

structural belts that can be traced from northern Alabama through the New England States. Great 

thicknesses of Precambrian through Permian sedimentary rocks are present in the western part (Appalachian basin), and a large volume of metamorphic and 

igneous rocks occupy the eastern part (Blue Ridge and 

Piedmont provinces). 

The undeformed part of the Appalachian basin 

being considered in this report is an elongated 

sedimentary and structural basin that extends northeastward from Tennessee across parts of Kentucky, Virginia, 

West Virginia, Ohio, Maryland, Pennsylvania, and New 

York (fig. 2.2). This regional feature is bordered on the 

west and north by the Cincinnati, Findlay, and Algonquin 

arches and the Adirondack uplift, and on the east by the 

tightly folded and faulted Valley and Ridge province. The 

basin contains a southeastward-thickening prism of sandstones, limestones, dolomites, shales, and evaporites that 

total 2,000-7,000 m in thickness; they are characterized 

by low dips (less than 1 °) and some gentle folds. 

Comprehensive discussions of the Appalachian basin 

were given by Woodward (1958), Roth (1968), and 

Colton (1970). 

Sedimentation in the basin occurred throughout 

the Paleozoic Era and culminated at the end of this time 

with the final major orogeny (the Appalachian 

revolution) that determined the present geologic pattern. 

Salt and anhydrite deposits in the basin, which are 

principally Late Silurian in age, connect with the Salina 

salts of the Michigan basin to the northwest through the 

Chatham sag (a low place between the Findlay and 

Algonquin arches). 

The Upper Silurian Bass Islands Dolomite directly 

overlies the Salina Group evaporites in Ohio (Clifford, 

1973), whereas farther east, in Pennsylvania and New 

24 Anhydrite Deposits of the United States 

York, the overlying units are the Rondout Formation, 

Cobleskill, or Helderberg Limestone (Rickard, 1969; 

Heyman, 1977). Younger Devonian, Mississippian, 

Pennsylvanian, and Permian deposits are chiefly clastics; 

they comprise the outcropping rock units in all areas 

underlain by the evaporites. Many of the post-Silurian 

sandstones contain oil and gas, and major bituminouscoal resources are being mined from rocks of Pennsylvanian age in parts of Kentucky, Ohio, Pennsylvania, and 

West Virginia. 

Evaporites of the Salina Group underlie parts of 

New York, Ohio, Pennsylvania, and West Virginia (fig. 

2.4). The thickness of the Salina is typically between 150 

and 500 min the shallow subsurface, but increases to the 

southeast into the basin and reaches a maximum of more 

than 750 m in the deep subsurface of north-central and 

southwest Pennsylvania (Rickard, 1969). The depth to 

the top of moderately thick evaporites also increases 

from about 300 to 600 m in the north and northwest to 

more than 1,500 m in the deep basin to the southeast 

(fig. 2.4). 

The lithologies of the Salina Group can be 

correlated over large areas of the Appalachian basin. 

Landes (1945) originally established the major 

subdivisions of the Salina Group in the Michigan basin. 

The same subdivisions were later recognized in Ohio 

(Ulteig, 1964), and interbasin correlations are now well 

established through the work of Fergusson and Prather 

(1968), Rickard (1969), Jacoby (1969), Clifford (1973), 

Heyman (1977), and Mesolella (1978). Recognition and 

correlation of individual units over such a large area is 

greatly enhanced by the distinctive mechanical-log curves 

recorded for each unit in oil and gas tests. 

Anhydrite is reported in each of the subdivisions of 

the Salina Group in various parts of the Appalachian 

basin (Rickard, 1969; Clifford, 1973; Smosna and others, 

1977; and Mesolella, 1978), but only the uppermost unit 

appears to contain an anhydrite bed more than 15 m 

thick. Most of the other anhydrite beds are 1-10m thick, 

and they occur chiefly in the A, C, and F units. The 

anhydrites typically are interbedded with much thicker 

beds of salt, dolomite, and shale, and thus individual 

anhydrites are scattered throughout the stratigraphic 

column. 

The one thick anhydrite occurs at the top of the 

Salina Group; in northeast Ohio it is referred to as part of 

the G unit (Clifford, 1973; Heyman, 1977), whereas in 

south-central New York and northwestern Pennsylvania 

it is referred to as the Bertie Formation (Rickard 

1969; Mesolella, 1978) (fig. 2.12). For simplicity, we will 

use the term G-unit anhydrite throughout the region in 

this report. 
NORTHEAST 

OHIO 

SOUTH-CENTRAL 

NEW YORK 

Bass 

Island 

Rondout Formation, 

Cobleskill or 

Helderberg Lss METERS FEET 

0 0 

G 

a.. 

0 

a: 

E 

z 

0 

....J 

c 

(/) 

B 

A 

Lockport 

Group 

a.. 

0 

a: 

z 

....J 

(/) 

Bertie 

Formation 

Camillus 

Formation 

Q) 

(I) 

::J 

(.) 

co 

>- (/) 

c 

0 

·~ 

co 

E 

0 

LL 

c 

0 

c 

F, 

E 

0 

c 

B 

~ A 

Lockport 

Group 

* 

* 

* 

* 

* 

* 

* 

* 

* 

30 100 

120 400 

150 500 

EXPLANATION 

-

Salt 

Shale 

Dolomite 

Anhydrite 

-

*Thickness may in part be 

due to deformation 

Figure 2.12. Generalized columnar sections of Salina Group in northeast Ohio and 

south-central New York (modified from Rickard, 1969; Clifford, 1973). 

Thickness of the anhydrite in the G unit is 5-15 m 

in the north and west, where the unit is less than 900 m 

below the land surface, but increases toward the 

southeast to 30-37 m in parts of western Pennsylvania, 

eastern Ohio, and northern West Virginia (figs. 2.13 and 

2.14). In this area, just north and west of Pittsburgh, the 

top of the G unit is at a depth of 1,500-2,100 m. Figure 

2.13, which shows thickness and depth of the G-unit 

anhydrite, is based upon scattered data points that were 

selected from mechanical-log cross sections presented by 

Clifford (1973), Heyman (1977), and Mesolella (1978). 

The G unit clearly contains anhydrite south and east of 

the area shown in figure 2.13 (Rickard, 1969; Smosna 

and others, 1977; Smosna and Patchen, 1978), but it also 

contains an increasing percentage of nonanhydrite rocks; 

additional work must be done to verify the thickness and 

amount of anhydrite in the deeper parts of the basin. 

Distribution and Geologic Characteristics of Anhydrite Deposits 25 
40° 

EXPLANATION 

--Thickness of anhydrite beds in 

unit G; interval is 10 feet (3 meters) 

- --- Depth to top of anhydrite in unit G; 

in 1000's of feet (305 meters) 

40 50 MILES 

25 80 KILOMETERS 

Figure 2.13. Map showing thickness, in feet, and depth toG-unit anhydrite at top of Salina Group in the Appalachian basin 

(based on data from Clifford, 1973; Heyman, 1977; and Mesolella, 1978). 

In subsurface, the G unit is variously described as 

anhydrite in Ohio and adjacent areas (Clifford, 1973) and 

as anhydritic dolomite in much of the rest of the basin 

(Rickard, 1969; Smosna and others, 1977; Mesolella, 

1978). The area where the unit appears to consist mainly 

of anhydrite extends across much of eastern Ohio, 

western Pennsylvania, and northern West Virginia (fig. 

2.13). Outside this area, the formation contains many 

dolomite interbeds or consists mainly of dolomite. 

Further lithologic studies are needed to clarify facies 

changes between anhydrite and dolomite. 

The G-unit anhydrite is underlain and overlain by . 

beds of shale, shaley dolomite, or dolomite that range 

from 15 to 60 min thickness (fig. 2.12). The underlying 

beds are in the lower G unit (Camillus Formation, 

according to Rickard, 1969), whereas the overlying unit is 

referred to in various areas as the Rondout Formation, 

Cobleskill or Helderberg Limestone, the Bass Islands 

Dolomite, or an unnamed upper unit of the Salina 

Group. 

26 Anhydrite Deposits of the United States 

ADIRONDACK UPLIFT -PRECAMBRIAN 

Subsurface and surface data from the BalmatEdwards district in St. Lawrence County, N.Y., show that 

Precambrian rocks contain gypsum and anhydrite as part 

of a metamorphic complex (Brown and Engel, 1956; 

Brown, 1973). The sulfate unit, which is associated with 

gypsiferous schist and diopsidic marble, comprises part 

of the Grenville Complex in this northwest part of the 

Adirondack uplift (fig. 2.1). The relation of the gypsum 

and anhydrite· to the associated units suggests a 

sedimentary origin for the calcium sulfate beds. The 

sulfate unit thins and thickens abruptly because of 

intense deformation of the region, and the maximum 

thickness .occurs in the apex of a tight fold where gypsum 

and anhydrite are mixed with adjacent marble in a unit at 

least 60 m thick. Anhydrite has been found at depths 

greater than 800 m in some of the magnetite and 

lead-zinc-pyrite mines of the district. 
A 

Lake 

..A_214 (well permit 

Y number) 

-(;F62 

)J)07 OHIO I w. VA. 

___,......,.. _____ i <!o 

Post-Salina sedimentary rocks 

G-un it anhydrite (Bertie Formation) 

B 

1000 h 

1305 m) 

SEA 

LEVEL 

1000 ft 

1305 m) 

2000 ft 

1610 m) 

3000 h 

1914 m) 

4000 h 

11219 m) 

Pre-Salina sedimentary rocks 

Figure 2.14. Generalized north-south cross section in northeastern Ohio showing position and depth of G-unit anhydrite 

and principal salt units of the Salina Group (based on data from Clifford, 1973). 

SALTVILLE AREA (VIRGINIA}-

MACCRADV FORMATION 

Anhydrite and salt are present in a tectonic breccia 

in the Maccrady Formation of Mississippian age in the 

tightly folded and faulted Valley and Ridge province 

around Saltville in Smyth and Washington Counties of 

the western part of Virginia (fig. 2.1). The evaporites 

have been little studied, although brine wells and gypsum 

mines have operated here since the early 1800's. Gypsum 

and anhydrite occur together in the mines as lenses and 

irregular masses as much as 30m thick and 200m long. 

Cooper (1966) is the principal source of data on the 

Saltville area. 

The structure of the evaporite beds is complicated. 

Salt and anhydrite are preserved in a major fold-the 

Greendale syncline-which has been overturned on the 

south limb and has been overridden by Cambrian rocks 

that form the sole of the Saltville thrust (Cooper, 1966). 

The Maccrady beds are highly contorted with dips of 2SO 

to 70°. 

In some of the deeper brine wells of the area, the 

Maccrady Formation is 450-510 m thick and contains 

considerable amounts of salt, gypsum, anhydrite, 

dolomite, and limestone interbedded with red and green 

plastic shale (Cooper, 1966). The number of beds, lenses, 

or pods of gypsum and anhydrite varies from place to 

place, but nearly every borehole shows several 

occurrences of sulfate rocks. Hydration of anhydrite to 

gypsum apparently occurs as deep as 300 m in some 

wells, but in other wells anhydrite is still present at 

shallow depths. In the mines, gypsum and anhydrite 

occur together in masses and pods that are irregular in 

shape because of deformation and some flowage. 

Cores taken from the overturned (upper) limb of 

the Greendale syncline in 1961 provide some information 

on the character of the evaporites at depth. Salt and 

anhydrite occur in zones of tectonic breccia that contain 

fragments of shale, anhydrite, limestone, and dolomite 

Distribution and Geologic Characteristics of Anhydrite Deposits 27 
suspended in a matrix of salt (Cooper, 1966). Apparently, the original primary sequence that consisted of salt 

and anhydrite interbedded with the other rock types was 

sheared and broken up during overthrusting. Therefore, 

a large body of thick and undeformed anhydrite is not 

likely to be present at moderate depth in the Saltville 

area. 

ILLINOIS BASIN-ST. LOUIS LIMESTONE 

The St. Louis Limestone of Late Mississippian age 

contains several gypsum and anhydrite beds 1-15 m thick 

in the Illinois basin area of southern Illinois, southwest 

Indiana, and northwest Kentucky (fig. 2.15). Studies of 

these evaporites were reported by Saxby and Lamar 

(1957) in Illinois; by McGregor (1954), Bundy (1956), 

French and Rooney (1969), and Jorgensen and Carr 

(1972) in Indiana; and by McGrain and Helton (1964) in 

Kentucky. The evaporite-bearing zone in the lower part 

of the St. Louis Limestone generally ranges from 15 to 

75 m in thickness, and is typically from 100 to 1,000 m in 

depth. 

Limestone is the dominant rock type, even where 

evaporites make up part of the formation; gypsum, 

anhydrite, and dolomite are present as interbeds 1-15m 

thick. Gypsum and anhydrite beds are 1-5 m thick in 

most parts of the region, and only in two small areas of 

Illinois are they 10-15 m thick (Saxby and Lamar, 1957). 

Both gypsum and anhydrite typically are nodular. The 

uppermost evaporite beds in Indiana are more likely to 

be gypsum than are the lower beds, and anhydrite 

increases in proportion to gypsum with increasing depths 

(Bundy, 1956). In Illinois, the evaporites are chiefly 

gypsum at depths less than 250-300 m, and are mainly 

anhydrite at depths greater than 350-450 m (Saxby and 

Lamar, 1957). In all areas, the evaporite units are rather 

impure; typically, they consist of 75-90 percent anhydrite 

and (or) gypsum, and the rest is limestone and some 

dolomite. 

Commercial deposits of gypsum are being mined 

underground by two companies in the Shoals district of 

Martin County, Ind. (French and Rooney, 1969; Jorgensen and Carr, 1972). An inclined shaft and a vert~cal 

shaft have been opened to exploit a 5-m-thick gypsum 

bed in the St. Louis Limestone 100-150 m below the 

surface. 

FOREST CITY BASIN-DEVONIAN, 

MISSISSIPPIAN, AND JURASSIC 

Thin to moderately thick beds of anhydrite occur 

in Paleozoic carbonate sequences on the northeast shelf 

of the Forest City basin in central and southern Iowa 

28 Anhydrite Deposits of the United States 

z 

0 

~ LITHOLOGIC DESCRIPTION 

~ 

a: 

0 

LL 

Q) 

c: 

0 

t::'iii 

co Q) 

c..E 

a;::J 

c..rn c..·-

:::> 5 

_I 

tA 

l Limestone, tan to gray, fine- to medium-grained, 

T l crystalline, rounded CaC03 grains 

~ Gypsum and (or) anhydrite, white to gray 

T/1 

Limestone, gray, crystalline, pyritic, dolomitic 

I / 

/ 

1 I Limestone, gray to tan, crystalline, pyritic, dolomitic, I /I 

l I/ rounded CaC03 grains 

/ 

~\\\\\\\\ Gypsum and (or) anhydrite, white to gray 

I I Limestone, brown to tan, crystalline / 

/ I I 

I I/ Limestone, tan, granular, porous, dolomitic 

Q) T l c: 

~~ Gypsum and (or) anhydrite, white to gray; brown 

B rn 

Q) T /I Limestone, tan, fine-arained, crystalline, dolomitic 

E 1 1 ::J /I/ Limestone, gray, dense, dolomitic rn 

·:; 

~~ Gypsum and (or) anhydrite, white to gray; tan to gray 0 

_I limestone 

tA Limestone, dark-tan, crystalline t:: 

-

co Gypsum and (or) anhydrite, white to gray; tan to gray c.. 

Q; limestone 

:1: T T Limestone, dark-gray, fine-grained, gypsiferous, dolo-

_I 

0 T I mitic 

l Limestone, tan, medium- to fine-grained, crystalline 

T T 

T 

I I 

1 Limestone, dark-gray, fine-grained, crystalline 

1 I 

I Gypsum and (or) anhydrite, white to gray; gray 

crystalline limestone. 

\' I/ Limestone, tan to gray, fmely crystalline, dolomitic, /1 

l l porous 

-I I Limestone, blue-gray, dense, lithographic, pyritic, 

1- argillaceous l I 

Q) 

c: 

0 VERTICAL SCALE 'iii 

Q) 60 FEET E 0 20 40 

::J 

I I I I I I I 

E I I I Q) 0 5 10 15 METERS 

Iii 

(/) 

Figure 2.15. Generalized stratigraphic section showing 

evaporite units in the lower part of the St. Louis Limestone in 

southwest Indiana (modified from McGregor, 1954). Entire 

section shown here is in Meramecian Series of Mississippian 

System. 
fig 2.1). Anhydrite-bearing rock units are the Wapsipinicon and Cedar Valley Limestones of Devonian age and 

the Warsaw and St. Louis Limestones of Mississippian 

age. Gypsum also occurs as a single 9-m-thick bed in the 

Jurassic Fort Dodge Formation in outcrops and shallow 

subsurface in a small area of central Iowa. The Devonian 

occurrences were reported by Dorheim and Campbell 

(1958), Collinson and others (1967), and Sendlein 

(1973); the Mississippian deposits were described by 

Dorheim and Campbell (1958) and Perry (1971); and the 

Jurassic gypsum was described by Stone and others 

(1920). 

Anhydrite and gypsum beds of the Devonian and 

Mississippian formations are typically 2-5 m thick over 

most of the basin, although they are at least 15m thick at 

two localities in south-central Iowa. Near Albia, in Monroe County, Iowa, the upper 18 m of the Warsaw 

Limestone is chiefly anhydrite and gypsum, and this 

formation includes a 15-m-thick bed at a depth of 90 m 

that is mostly anhydrite (Dorheim and Campbell, 1958). 

Also, near Ottumwa, in Wapello County, Iowa, the 

Wapsipinicon Limestone contains a 30-m-thick interval 

at a depth of about 300 m that is mostly anhydrite but 

that has some interbeds of limestone (Dorheim and 

Campbell, 1958). Gypsum in the Wapsipinicon is being 

mined underground m Des Moines County m 

southeastern Iowa. 

Gypsum in the Fort Dodge Formation underlies an 

area of about 150 km2 near Fort Dodge, in Webster 

County, Iowa. Total thickness of the gypsum ranges from 

3-9 m, and it is buried beneath only 5-20 m of glacial 

drift. Gypsum in this area has been mined extensively 

since the late 1800's. 

SOUTH FLORIDA BASINCRETACEOUS AND TERTIARY 

The South Florida basin contains thick sequences 

of anhydrite and carbonate in both the Lower Cretaceous 

and the lower Tertiary (Paleocene). Some individual 

anhydrite beds in the Cretaceous are as much as to 50 m 

thick and exist at depths ranging from about 2,000 m to 

more than 3,000 m below the surface; thinner anhydrite 

beds extend farther updip to depths of about 1,500 m. 

The Paleocene anhydrite beds are generally less than 25 

m thick and arc at depths of 400-1,200 m. Principal 

references on the Lower Cretaceous anhydrites are Applin and Applin (1965), Ogclsby (1967), Rainwater 

(197lb ), Winston (1971, 1976), and Fcitz (1976), 

whereas principal references on anhydrites in the 

Paleocene arc by Rainwater (1970a, 1971b). 

The South Florida basin and other parts of 

peninsular Florida were tectonically stable throughout 

the Mesozoic and Cenozoic Eras (Rainwater, 1971b ). 

2 

------\_ ____ _ 

N 

EXPLANATION 

; Anhydrite 

Dolomite 

Limestone 

Well logs used in cross section: 

130 mi 

(210 km) 

Marl and chalk 

Sandstone 

1. Sun Oil Co., No. 1 Camp; Marion County 

3 

2. Humble 0 & R Co., No. 1 Jameson; Hillsborough County 

3. Composite log, Suniland field; Collier County 

Figure 2.16. Structural cross section showing thickening of 

Lower Cretaceous and lower Tertiary carbonate-anhydrite 

sequences into the South Florida basin (modified from 

Rainwater, 1971a, b). 

Distribution and Geologic Characteristics of Anhydrite Deposits 29 
> 

Ctl 

COo.. 

"' :J ~e 

0..~ 

Ctl 

z z 

<x: 

w "' "' e c.. O..:J 

J: >O u ... Cl~ 

u Ci5 

z 

<x: Q; 

Q) 0.. 

a: :J 

c: 0 

~ Ctl ... 

Q)~ 

u 

0 

0 

u 0.. 

:J 

e 

~ 

"' Q) 

"'C 

Ctl 

t5 

FORMATIONS 

Corkscrew Swamp 

450 

Rookery Bay 

500 

Panther Camp 

350 

Dollar Bay 

475 

Gordon Pass 

475 

Marco Junction 

350 

Rattlesnake Hammock 

600 

Lake Trafford 1 50 

Sunniland 275 

Punta Gorda 

Anhydrite 

500 

Unnamed 

850 

Coahuilan 

EXPLANATION 

I Anhydrite 

Limestone 

Dolomite 

LITHOLOGY 

....L ......1,_ 

---L-

/ / 

·" ·""" ·"" 

I I 

I / 

l l 

I I 

/ / 

~ 

I I 

J ~ 

I 

~ 

L 

I ~ 

I 

·" "" 1 

~ I ~ ~/ 

'""" ·" I I 

I 

/ / / / 

/ L 

Figure 2.17. Generalized geologic column of Lower Cretaceous strata in the 

South Florida basin (modified from Winston, 1976). Numbers are average thicknesses of formations, in feet. 

Regional subsidence during this time permitted 

deposition of more than 3,000 m of Cretaceous and 

Tertiary shallow-marine carbonates and evaporites (fig. 

2.16). A thinner sequence of interbedded carbonates and 

clastics was deposited in coastal-plain environments in 

the more slowly subsiding northern part of Florida. 

Strata in the region now dip gently to the south toward 

the deep part of the basin; they are not faulted, folded, or 

otherwise disturbed. The South Florida basin subsided at 

a faster rate than did adjacent areas, and most of the 

anhydrite accumulated in this basin. In general, the 

30 Anhydrite Deposits of the United States 

anhydrite units grade laterally into carbonates toward the 

north, and then into clastics where they are at still 

shallower depths (fig. 2.16). 

Lower Cretaceous (Comanchean) carbonateevaporite strata in the basin range in thickness from 

about 1,000 m in the north, where they interfinger with 

clastics, to more than 2,000 m near the basin center (fig. 

2.16). The thick carbonate-evaporite sequence has been 

subdivided into four groups consisting of 11 formations 

(fig. 2.17). Individual formations generally range in 

thickness from 50 to 300 m, and each consists of interbedded limestone, dolomite, and nodular anhydrite. 

Rock salt also is present in the deepest part of the basin 

in layers that are typically less than 3 m thick and that 

aggregate only about 10 m thick. 

Anhydrite beds in the various Lower Cretaceous 

formations are mostly 3-10 m thick, and they are typically 

about 1,500-3,000 m below the land surface. The thicker 

individual anhydrite beds, which are 15-50 m thick, are in 

the Punta Gorda, Sunniland, Rattlesnake Hammock, and 

Gordon Pass Formations. Feitz (1976) correlated the 

Punta Gorda Anhydrite with the Ferry Lake Anhydrite, 

which is present throughout much of the central and 

western parts of the Gulf Coast basin. An additional, 

even deeper group of carbonates and anhydrite occurs in 

the Fort Pierce Formation in the Upper Jurassic(?) or 

Lower Cretaceous(?) of the South Florida basin (Applin 

and Applin, 1965). 

Details on the character, thickness, distribution, 

and depth of individual Lower Cretaceous anhydrite beds 

are presented by Applin and Applin (1965). The thicker 

beds appear to be restricted to the deeper parts of the 

basin where they are more than 2,000 m below the 

surface. The updip limit of the evaporite facies in the 

Lower Cretaceous is in the Citrus-Sumter-Lake-Volusia 

County area, where the evaporites are at a depth of about 

1,500 m; in this area the anhydrite beds are probably no 

more than several meters thick. 

Lower Tertiary (Paleocene) strata of the South 

Florida basin and nearby areas are interbedded dolomite, 

anhydrite, and limestone in the Cedar Keys Limestone. 

These strata were deposited on a slowly subsiding shelf 

that had a restricted connection to the open ocean. They 

grade laterally into clastic sediments in northernmost 

Florida (figs. 2.16 and 2.18). 

Total thickness of the Paleocene carbonateevaporite sequence ranges from about 100m in the north 

to about 700 m in the south. Anhydrite beds were shown 

by Rainwater (1971b) to range from 10 m to about 25 m 

in thickness (fig. 2.18), although detailed information on 

individual anhydrite beds is not readily available. The 

depth to the top of anhydrite-bearing strata is about 
225 mi 

(360 km) 

Naheola 

Formation 

Porters Creek 

Formation 

FEET METERS 

ALABAMA 1 

N 

Anhydrite 

Dolomite 

Limestone 

GEORGIA 

225 mi 

(360 km) 

EXPLANATION 

Marl D Shale and siltstone 

Generalized stratigraphic sections for: 

1. Southeastern Alabama 

2 . Northwestern-peninsular Florida 

3. South Florida Basin 

3 

Figure 2.18. Generalized stratigraphic sections showing 

lithology representative of Paleocene strata from southeastern Alabama to the South Florida basin (modified from 

Rainwater, 1971 b). 

400 m in the north part and increases to about 1,200 min 

the deep part of the South Florida basin (fig. 2.16). 

Because these anhydrite beds are reported to be as much 

as 25 m thick and are at moderate depth, further study of 

their thickness, character, and distribution may be 

warranted. 

GULF COAST BASIN 

Structure and Geologic Framework 

The Gulf Coast basin referred to in this report is 

the northern part of the Gulf of Mexico basin, and it 

extends westward from Alabama through Mississippi and 

Louisiana into southern Arkansas and Texas, and 

southward under the Gulf of Mexico. This significant 

regional feature appears to have originated in the early 

Mesozoic, but did not reach maximum development, as 

measured by pronounced subsidence and sediment 

infilling, until the Cenozoic. The stratigraphic section 

ranges in thickness from less than 1,000 m along the 

arcuate northern boundary of the basin to possibly as 

much as 18,000 m in southern Louisiana and in the 

near-offshore regions of the Gulf of Mexico. 

Since the mid-Mesozoic, the depositional axis of 

the basin has shifted progressively southward toward the 

present-day Gulf of Mexico. The greatest sedimentation 

took place during the Tertiary and was dominated by 

clastic deposits. Regional facies changes are important 

aspects of petroleum exploration in this major 

petroleum-producing province. The development of the 

Cenozoic sequence was controled by prograding depositional systems, fluctuating water depths, and localized 

sedimentation rates that were dictated by faults. The 

evaporites of Jurassic and Early Cretaceous age are of 

special importance to this report because they are thick 

and widespread, and are source beds for the numerous 

salt domes in the Gulf Coast basin. 

The regional strikes of the various outcrop and 

subcrop belts essentially parallel the coastline. Cretaceous outcrops in the north give way to successively 

younger Cenozoic (Eocene to Pliocene-Pleistocene) 

intervals in a gulfward direction. Although the regional 

dip is also gulfward (south), faults and other structures 

create localized areas of dip reversal. The subsurface 

geology is complicated by facies changes, regional and 

local faulting, and numerous salt-related structures. The 

regional character of the Gulf Coast basin is seen in the 

structure map drawn on top of the Lower Cretaceous 

Distribution and Geologic Characteristics of Anhydrite Deposits 31 
1 oo o 

OKlAHOMA 

\ 

\ 

I 

I 

I 

go o 85 ° 

TENNESSEE 

ARKANSAS 

Figure 2.19. Structure map on top of Lower Cretaceous strata in Gulf Coast basin (modified from Rainwater, 1971a). 

Elevations, in meters, are below sea level. 

(fig. 2.19). Strata dip toward the Gulf at fairly uniform 

rates of about 0.5°-1 o in most areas; however, the dip is 

2°-3° in much of Texas, and it is reversed over the Sabine 

uplift in the Shreveport area and over the Wiggins arch in 

southeastern Mississippi. 

Each of the Jurassic and Lower Cretaceous 

evaporites in the basin (fig. 2.20) is a widespread unit that 

has been used as a stratigraphic marker in petroleum 

exploration. The Werner, Buckner, and Ferry Lake 

Formations are typically 15-100 m thick and consist 

mainly of anhydrite. They all occur at depths of less than 

1,500 m beneath the surface in southern Arkansas, and 

one or more of them also occurs at similar depths in parts 

32 Anhydrite Deposits of the United States 

of adjacent east Texas, northern Louisiana, and westcentral Mississippi. These anhydrite-bearing formations 

are more than 1,500 m deep elsewhere in the Gulf Coast 

basin, and they increase to more than 3,000 m deep 

toward the Gulf of Mexico. 

Regional structural trends of the Gulf Coast basin 

are disrupted in many places by diapiric salt domes that 

have their source in the deep-seated Louann Salt (Upper 

and Middle Jurassic). The domes, many of which have a 

cap rock composed mainly of anhydrite, formed initially 

near the northern edge of the salt deposits (fig. 2.21 ), and 

they progressively developed farther southward through 

geologic time in response to increasingly greater burial 
ERA SYSTEM SERIES GROUP EAST TEXAS LOUISIANA- MISSISSIPPI ALABAMA ARKANSAS 

Maness Sh 

Buda Ls 

Dantzler Fm Washita 1 Undifferentiated 

Grayson Sh 

Undifferentiated 

Georgetown Ls 

c Kiam ichi Fm Kiamichi Fm l'tl 

Q) 

Fredericks burg Andrew Limestone ~ 2 (.) 

en c Goodland Ls Goodland Ls :J l'tl 

u 0 E Q) 0 (.) u Paluxy Sand Paluxy Sand Paluxy Sand Paluxy Sand l'tl 

Q) 

u Glen Rose Ls Mooringsport Fm Mooringsport Fm Mooringsport Fm 

0 

N Trinity Rodessa Fm Rodessa Fm Rodessa Fm Rodessa, James, and 

Pearsall Fm Pearsall Fm Pine Island Fms 0 Pine Island Fm 

~ Sligo Fm Sligo Fm Sligo Fm Sligo Fm CJ) :J 

~ 

l'tl 

0 Hosston Fm Hosston Fm Hosston Fm Hosston Fm u w 

Cotton Schuler Fm Schuler Fm Cotton Valley Cotton Valley 

~ Valley Bossier Fm Bossier Fm 

Fm Fm 

Upper u 

'Cii 

en 

l'tl 

~ -, 

Middle 

1 Not part of Washita Gp 

2Thought to corre late with Washita and Fredericksburg Groups 

Figure 2.20. Correlation chart of Jurassic and Lower Cretaceous strata in the Gulf Coast basin (modified from Newkirk, 

1971; Rainwater, 1971 a; Johnson and Gonzales, 1978}. Principal anhydrite-bearing formations are stippled. 

by successively younger sediments. The great influx of 

Tertiary clastics clearly made a significant impact on the 

generation of domes nearest the present Gulf of Mexico. 

The Gulf Coast basin actually consists of several 

smaller basins that are separated by various positive 

structural features such as the San Marcos arch, Sabine 

uplift, Wiggins arch, and Monroe uplift. The salt-dome 

basins include: (1) South Texas, (2) Northeast Texas, (3) 

North Louisiana, ( 4) Mississippi, and (5) TexasLouisiana coast (fig. 2.22). The latter contains salt domes 

both onshore and offshore. 

For more comprehensive treatment of the geology 

of the Gulf Coast basin, references by Murray (1961 ), 

Halbouty (1967), the Lafayette and New Orleans 

Geological Societies (1968), and Mason and others 

(1971) provide both detailed discussion and extensive 

bibliographic citations. The comprehensive bibliography 

compiled by Braunstein (1970) also contains many useful 

references. 

Salt-Dome Cap Rock 

The Gulf Coast basin is one of the most significant 

salt-dome provinces in the world. As shown in figure 

2.22, more than 260 domes are either known or inferred 

Distribution and Geologic Characteristics of Anhydrite Deposits 33 
NORTH SOUTH 

Periphery of Position of present Edge of present 

sa lt basin shore line continental shelf Stage 1-about ~nd of I ~ Louann Salt t<me 

~++~!!!~!!~!~!!!!!!!!!!!!:::::::::::::::::::::::: ::::::::::::::::::::1 

(:;:::-::: .... :.) Holocene and Pleistocene [~~\~~~\\~~~\;1 Mesozoic 

Ancestral Gulf of Mexico 

Stage 11-about end 

of Cretaceous 

Stage III-about end 

of mid-Tertiary 

+++++++++++++++++++++++++ 

Stage IV'-present time 

Gulf of Mexico 

~ Late Tertiary ~ Jurassic Louann Salt 

CJ Early Tertiary **** Forward-moving zone of deformation 

Figure 2.21. Generation of Gulf Coast salt domes through geologic time (modified from Hanna, 1959; Johnson and 

Gonzales, 1978). 

from the onshore part of this region alone. About half of 

the known domes have cap rock, and many of these 

cap-rock units are composed mainly of anhydrite. The 

thickness of anhydrite in cap rock generally ranges from 

25 to 240m, and the depth ranges from 100m to more 

than 1,000 m. The lithology of cap rock is variable from 

dome to dome, as well as on any single dome, and the 

upper parts of the cap rock commonly are fractured and 

brecciated. Much of the data that follow on the nature 

and origin of cap rock are based on the report by Walker 

(1974). Additional general studies focusing on cap rock 

include those of Goldman (1933, 1952), Taylor (1937, 

1938), and Murray (1966, 1968). 

Because of several unique characteristics and 

economically important associations of petroleum, native 

sulfur, and salt, salt domes of the Gulf Coast basin have 

34 Anhydrite Deposits of the United States 

been the targets of intensive geologic and geophysical 

investigations. Spooner (1926), Atwater and Forman 

(1959), Durham (1960), Hawkins and Jirik (1966), 

Halbouty (1967), and the Louisiana Department of 

Conservation (1975) discussed the Gulf Coast salt domes 

from a regional perspective. Additional references, many 

about specific domes, individual dome-related features, 

and petroleum fields associated with domes, can be 

found in the extensive bibliography compiled by Braunstein and O'Brien (1968). Reports by Pierce and Rich 

(1962), Gera (1972), Anderson and others (1973), Ledbetter and others (1975), Martinez and others (1975, 

1976), Netherland, Sewell and Associates, Inc. (1976a, 

1976b), and Johnson and Gonzales (1978) focus more 

specifically on the potential use of salt in the Gulf Coast 

salt domes for the geologic storage of radioactive wastes. 
100 200 MILES 

160 320 KILOMETERS 

EXPLANATION 

Salt-dome basin; numbers such as ( 1 43) indicate 

known/suspected domes onshore 

~ Domal-arch structures between basins 

Bordering fault system 

Figure 2.22. Map showing five salt-dome basins and other principal regional structural features in Gulf Coast region 

(modified from Johnson and Gonzales, 1978). 

The exact origin of salt domes in the Gulf Coast 

basin is not fully understood, but most prevailing views 

involve flowage and upward movement of plastically 

deformed salt in response to overburden pressure from 

the overlying sediments (Martinez, 1974). Once the 

upward movement is started, the top of the lighter salt 

mass can intrude into and through the overlying, more 

dense sediments (fig. 2.21 ). In fact, some of the salt 

domes, particularly those in the coastal basins, appear to 

be tectonically active and may still be rising (Gera, 1972). 

Although most salt domes are roughly circular in 

plan view and range in diameter from about 1 km to 

more than 6 km, the diversity is great in dome 

geometries, dome-to-cap-rock relationships, and dometo-flank-rock orientations. The height of salt domes 

above their base is variable; it depends in part on the 

thickness of the parent salt layer (the Louann Salt), the 

amount of this salt that is mobilized, and the thickness of 

overlying sediments that have been pierced. Heights of 

3,000-6,000 m are not uncommon. Many domes flare 

outward at depth and may be connected at the base with 

the parent salt layer. Other domes, which are more 

constricted at depth and may be pinched off at the base 

and disconnected from the parent layer, give the 

appearance of an inverted teardrop in cross section. 

The theory most widely accepted on the o'rigin of 

cap rock is that it represents a residue of anhydrite and 

Distribution and Geologic Characteristics of Anhydrite Deposits 35 
other insoluble minerals that accumulate at the upper 

surface as the salt dome rises through water-bearing 

sediments and is dissolved (Goldman, 1933; Taylor, 

1937, 1938; Murray, 1966, 1968) (fig. 2.23). The anhydrite crystals, which make up about 99 percent of the 

water-insoluble residue in a dome salt (Gera, 1972; 

Walker, 1974), are then recrystallized and compacted to 

form a massive cap rock; this may locally be hydrated to 

form gypsum. The calcite and sulfur commonly present 

in cap rock arc secondary; they result from the reduction 

of anhydrite by sulfate-reducing bacteria (Feely and 

Kulp, 1957; Jensen, 1968). Walker (1974) pointed out 

that because of a number of cap rock features this theory 

should be modified. He postulated that most of the 

anhydrite was precipitated when ascending waters, 

having dissolved calcium sulfate and salt on the flanks of 

the dome, found geochemical conditions that were 

favorable for precipitation at the top of the dome. 

Walker (1974) studied cap rock on 39 salt domes in 

the Gulf Coast basin (fig. 2.24 ), and summarized a great 

deal of data on cap-rock lithology from wells drilled on 24 

of these domes (table 2.2). These data do not represent 

all the domes in the basin with cap rock, because Hawkins and Jirik (1966) reported that 181 domes are known 

to have cap rock. However, the compilation by Walker 

(1974), which is representative of cap rock at depths less 

than 1,200 m, is an excellent guide to the general 

character, thickness, and depth of anhydrite on salt 

domes. 

Cap rock is an irregular complex of rocks and 

minerals formed on the top of about half the domes in 

the Gulf Coast basin. Both shallow and deep domes have 

cap rock, but it is more likely to be present, and thickest, 

over the shallower domes (Walker, 1974). The ideal or 

mature sequence of rocks that form cap rock would be, in 

decending order, calcite-gypsum-anhydrite-salt (Murray, 

1966, 1968). In his study of cap rock on 24 shallow domes 

(table 2.2), Walker (1974) found this complete sequence 

in only 22 percent of the 94 wells examined, and found a 

variety of lithologic sequences in the remaining wells (fig. 

2.25). Other common dccending sequences include 

calcite-gypsum-salt (33 percent), calcite-anhydrite-salt 

(16 percent), calcite-salt (16 percent), and gypsumanhydrite-salt ( 4 percent). 

Cap rock not only is variable in lithologic sequence 

from dome to dome, but also can be variable between 

boreholes on a single dome. The anhydrite part of the cap 

rock, which is generally the thickest, is followed in 

thickness by calcite, gypsum, and celestite (Walker, 

1974). Interbeds of salt and (or) clastic sediments also 

may be present. Salt domes with thicknesses of cap rock 

greater than 100m are common (Murray, 1961, 1966). 

36 Anhydrite Deposits of the United States 

Surface 

Figure 2.23. Idealized section of salt dome showing 

development of gypsum and (or) anhydrite cap rock at the 

top and along part of the sides (modified from Walker, 1974). 

Calcite (block pattern) is above the gypsum and (or) 

anhydrite. 

Anhydrite has an average thickness of about 67 m 

in cap rock on the domes listed in table 2.2, but the 

thickness generally ranges from about 25-240 m on 

different domes, and can vary considerably on the same 

dome (Walker, 1974). Anhydrite is most common in the 

lower part of the cap rock, but it is not restricted to that 

position. Salt in the Gulf Coast basin contains an average 

of about 3 percent anhydrite (Kupfer, 1963). Therefore, 

dissolution of about 8 km of this salt would be needed to 

form 240 m of cap-rock anhydrite. 

The depth to the top of cap rock ranges from zero 

(Gyp Hill dome at Falfurrias, Tex.) to many thousands of 

meters. Of the domes listed in table 2.2, the depth to the 

top of cap rock ranges from 30 to 1,095 m and averages 

about 350 m; the depth to the top of anhydrite ranges 

from about 100 to 1,140 m and averages about 430 m. 

Anhydrite in cap rock typically consists of an 

interlocking mosaic of crystals, 0.05-2.1 mm in size, that 

have a low porosity and a slight preferred orientation in 

the horizontal direction. Minerals commonly dispersed in 

the anhydrite include trace amounts of calcite, dolomite, 

quartz, pyrite, sulfur, barite, and celestite (Walker, 

1974). Generally, the contact between anhydrite cap rock 

and underlying salt is gradational; the salt grades upward 
96° 94° 92° goo 

.23 ( .20 \ • 25 

I c:' I 

J.6 .35 .28 

32° ~ .39 I .31 

\ f .22 MISSISSIPPI ' .29 

~ J .30 .26 

f ' 34 I f~ • \, 

I ) ---; -..----- I TEXAS J 

) .27 ( 

I LOUISIANA ' ' ) \ .9 l .32 

.7 

' 37 

.19 

.5 .15 I • .24 

30° .14 .16 ;·4 

I 

\ 

100 MILES 

160 KILOMETERS 

Location of salt dome 

Map 

No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

Dome 

Allen 

Avery Island 

Belle Isle 

Black Bayou 

Brenham 

Bruinsburg 

Choctaw 

Challenger ~not 

shown on map) 

Clay Creek 

Clemens 

Cote Blanch 

Damon Mound 

Danbury 

Hockley 

Hull 

Humble 

Jeanerette 

Jefferson Is. 

Jennings 

State County or 

Parish 

Tex. Brazoria 

La. Iberia 

La. St. Mary 

La. Cameron 

Tex. Austin 

Miss. Claiborne 

La. lberville 

Abyssal Gulf of 

plarn Mexico 

Tex. Washington 

Tex. Brazoria 

La. St. Mary 

Tex. Brazoria 

Tex. Brazoria 

Tex. Harris 

Tex. Liberty 

Tex. Harris 

La. St. Mary 

La. Iberia 

La. Acadia 

Map Dome 

No. 

20 Kings 

21 Lake Wash. 

22 McBride 

23 Minden 

24 Napoleonville 

25 Oakley 

26 Oakvale 

27 Pine Prairie 

28 Raleigh 

29 Richmond 

30 Ruth 

31 Sardis Church 

32 Section 28 

33 Stratton Ridge 

34 Tatum 

35 Utica 

36 Venice 

37 Vinton 

38 Weeks Is. 

39 Winnfield 

State 

Miss. 

La. 

Miss. 

La. 

La. 

Miss. 

Miss. 

La. 

Miss. 

Miss. 

Miss. 

Miss. 

La. 

Tex. 

Miss. 

Miss. 

La. 

La. 

La. 

La. 

County or 

Parish 

Warren 

Plaquemines 

Jefferson 

Webster 

Assumption 

Hinds 

Jeff. Davis 

Evangeline 

Smith 

Covington 

Lincoln 

Copiah 

St. Martin 

Brazoria 

Lamar 

Copiah 

Plaquemines 

Calcasieu 

Iberia 

Winn 

Figure 2.24. Salt domes of the Gulf Coast basin for which cap-rock data are available (compiled from Walker, 1974). 

into a zone of friable anhydrite sand, which in turn grades 

into compact anhydrite cap rock. 

The upper part of the cap rock on most domes is 

highly fractured and brecciated; brecciation generally 

decreases downward toward the salt (Walker, 1974). 

These features generally have been attributed to the 

pressure exerted on the cap rock during upward 

movement of the salt diapir. The calcite part of the cap 

rock commonly is highly cavernous, and may have a 

porosity of as much as 50 percent; most of the 

Distribution and Geologic Characteristics of Anhydrite Deposits 37 
Table 2.2. Depth and thickness, in feet, of various rock types in cap rock of selected salt domes in the Gulf Coast basin 

(modified from Walker, 1974) 

[Depth to top is feet below surface. Leaders(---) indicate none of the lithology recovered. *indicates value from published data. Thickness data 

for each lithology are averages from all wells drilled on each dome] 

Depth 

(in feet) 

to top 

Cap 

Dome rock Salt 

Allen, Tex.----------- 995 

Belle Isle, La.------- 859 

Black Bayou, La.---- 1054 

Brenham, Tex.------- 1523 

Damon Mound, Tex.--- 220 

Hockley, Tex.--------- 452 

Hull, Tex.------------ 418 

Humble, Tex.---------- 1181 

Kings, Miss.------ 3593 

McBride, Miss.-------- 2095 

Minden, La.---------

Napoleonville, LB.--

Oakvale, Miss.------

Pine Prairie, LB.-

Richmond, Miss.-----

Ruth, Miss.-------

Sardis Church, Miss. 

Section 28, LB.-----

Stratton Ridge, Tex. 

Tatum, Miss.------

1175 

580 

1648 

173 

1717 

2331 

1210 

1753 

1391 

1134 

Utica, Miss.-------- 2641 

Venice, La.--------- 1875 

Vinton, La.--------- 528 

Winnfield, La.------ 100 

METERS 

200 

FEET 

650 

METERS 

50 

750 

250 100 850 

950 

300 150 

1050 

350 1150 200 

1250 

400 

1350 

1450 450 

1550 

1394 

1199 

2000* 

2253 

562 

1124 

787 

1307 

3845 

2190 

1905* 

773 

2396 

530 

1950 

2700* 

2300* 

1785 

1633 

1520 

3135 

3000* 

968 

460 

FEET 

150 

250 

350 

450 

550 

650 

750 

6 

Carbonate 

51 

283 

76.3 

74.8 

131.9 

128.2 

72.5 

60.2 

155 

95.5 

144 

104.7 

94.6 

169.3 

34 

402.2 

667 

20 

133.7 

108.2 

494 

381.5 

104 

160 

METERS FEET 

700J2300 

2400 

750 

Thickness (in feet) 

Gypsum 

246.7 

120.3 

66 

278.9 

110.7 

222.5 

22 

113.5 

157.8 

20 

23* 

108.6 

35 

231.7 

60 

METERS 

8 

I 800 

850 

900 

950 

Anhydrite 

166.3 

10* 

800* 

363 

419 

86.8 

66.2 

75 

586 

27.5 

702 

18.8 

196.5 

37* 

400* 

131.7 

194.2 

744'* 

83 

140 

FEET 

2600 

2700 

2800 

2900 

3000 

3100 

3200 

9 

Ratio 

Total 

sulfate 

Sulfate: Anhydrite: 

carbonate gypsum 

No. of 

wells 

METERS 

1100 

1150 

1200 

1250 

413.0 

130.3 

866 

363 

278.9 

529.7 

312 

66.2 

97 

586 

141 

702 

176.6 

216.5 

37 

423 

240.3 

229.2 

744 

315 

200 

FEET 

3550 

3650 

3750 

3850 

3950 

4050 

10 

8.10 

.46 

11.43 

4.85 

2-11 

4.13 

4.30 

1.10 

.62 

4.07 

1.35 

7.42 

1.04 

6.37 

.09 

.63 

1.80 

2.12 

1.95 

3.03 

1.25 

0.67 

.08 

12.12 

3.79 

.39 

3.41 

.24 

.12 

9.83 

17.39 

1.21 

5.55 

.36 

2.33 

EXPIANA TION 

~ Calcite 

• Gypsum 

~~ Anhydrite 

• Celestite 

~ Shale or gumbo 

• Salt 

1 Tatum dome, F. S. Co. Well No. 9 

2 Hull dome, F. S. Co. Well No. 4 

3 Belle Isle dome, F. S. Co. Well No.2 

4 Hockley dome, F. S. Co. Well No.6 

5 Stratton Ridge dome, Tolar Well No. 1 

6 Pine Prairie dome, F. S. Co. Well No. 6 

15 

7 

7 

7 

28 

4 

7 

5 

1 

4 

2 

10 

7 

12 

3 

1 

6 

5 

4 

7 Napoleonville dome, F. S. Co. D & L Well No.1 

8 Minden dome, Hudson Well No. 2 

9 Utica dome, L Little Well No. 1 

1 0 Kings dome, Hall Well No. 1 

Figure 2.25. Columnar sections showing lithologic variability of cap rock among 10 salt domes (modified from Walker, 1974). 

38 Anhydrite Deposits of the United States 
SOUTHWEST NORTHEAST UNION PROD. CO. UNION PROD. CO. UNION PROD. CO. BENEDUM & TREES TENSAS DELTA NO. A-1 CROSSETT NO. C-1 CROSSETT NO. E-1 HOLMES NO.1 8-22N-4E 9-23N-6E 12-19S-7W 4-17S-5W MOREHOUSE PARISH, LA. MOREHOUSE PARISH, LA. ASHLEY COUNTY, ARK. ASHLEY COUNTY, ARK. 

MONROE GAS ROCK 1 FEET METERS 

0 0 

ANNONA CHALK 

( RESTRICTED) 2 

UNCONFORMITY 1000 300 

UNCONFORMITY 2000 600 

3000 900 

COTTON VALLEY GROUP 

UNDIFFERENTIATED 

4000 1200 

u 

Ui 

(/) 5000 1500 <{ 

a: 

:::l 

-, 

6000 1800 

LOUANN SALT 

Anhydrite member 

WERNER FORMATION 

Red' bed member 7000 2100 

UNCONFORMITY 

MOREHOUSE BODO 2400 

FORMATION 

(PENNSYLVANIAN?) 10 MILES 

16 KILOMETERS 

SEA lEVEl DATUM 

1 Navarro Formation 2

Tongue of Austin Chalk 

Figure 2.26. Cross section showing Werner Formation and overlying strata in southeastern Arkansas and northeastern 

Louisiana (modified from Hazzard and others, 1947). 

hydrocarbons and sulfur found in cap rock are contained 

in these cavities. The cap rock in many domes also 

contains large amounts of ground water in its pore 

spaces. 

In summary, cap rock on many of the salt domes in 

Texas, Louisiana, and Mississippi contains thick masses 

of anhydrite at moderate depths. However, the thickness 

and character of anhydrite and other rock types in the cap 

rock vary considerably, and the upper part of the 

sequence on most domes is highly fractured, brecciated, 

and water bearing. Furthermore, because some of the 

domes in the coastal areas of the Gulf of Mexico appear 

to be tectonically active, the cap rock on these domes is 

moving closer to the land surface. 

Werner Formation 

The Werner Formation is a widespread anhydrite 

unit of Middle Jurassic age that underlies the Louann 

Salt of Middle and Late Jurassic age in the western and 

central part of the Gulf Coast basin (fig. 2.20). The 

anhydrite member of the formation is typically 15-30 m 

thick, and its depth ranges from about 1,000 m on the 

north to more than 3,000 m toward the Gulf of Mexico. 

The unit has been penetrated by few boreholes, and thus 

few data are available on it. The main references on 

anhydrite in the Werner Formation are Imlay (1943), 

Hazzard and others (1947), and Newkirk (1971). 

The Werner Formation consists of a lower, red-bed 

clastic member that grades upward into a relatively pure 

anhydrite member, which appears to be conformable 

with the overlying Louann Salt. The Werner Formation 

represents the first stage in a long period of evaporite 

deposition in the Gulf Coast basin; its distribution is 

believed to be similar to that of the Louann Salt but to 

extend farther updip (Newkirk, 1971). The unit underlies 

parts of southern Arkansas, northeastern Texas, 

northern Louisiana, Mississippi, and southwestern Alabama. Total thickness of the Werner Formation is 

commonly 30-60 m. The northern limit of the Werner in 

Arkansas is erosional and results from truncation by the 

Upper Jurassic Norphlet Formation. 

The depth to the Werner is as shallow as 

1,000-2,000 m in parts of southern Arkansas (fig. 2.26) 

and adjacent areas of west-central Mississippi and the 

northeast corner of Texas. From this region the Werner 

dips down into the Gulf Coast basin. It is 2,000-3,000 m 

deep across northern Louisiana, and is at even greater 

depths farther south and at most other locations in the 

basin. 

The anhydrite member is 15-30 m thick in most 

parts of southern Arkansas, where cores show that the 

rock has a medium-grained, dense granular texture; it is 

Distribution and Geologic Characteristics of Anhydrite Deposits 39 
clear to milky white and tinged with pink (Hazzard and 

others, 1947). The rock lacks either a calcareous or clay 

matrix. Descriptions of samples from several wells 

indicate that anhydrite probably is interbedded with 

dolomite or limestone in the basal few meters of the 

member (Hazzard and others, 1947). 

Therefore, the W crner anhydrite may be as much 

as 30m thick and may occur at moderate depths near its 

updip limit in southern Arkansas and adjacent States. 

More data arc needed to verify this thickness and depth, 

and to establish whether the anhydrite is a single bed or 

is an interbedded sequence of anhydrite and other strata. 

Buckner Formation 

The Buckner Formation (Upper Jurassic) is a 

widespread evaporite and clastic unit in the western and 

central part of the Gulf Coast basin (fig. 2.20). The unit 

ranges from 30 to 200 m in thickness and consists chiefly 

of anhydrite and clastics. Individual anhydrite beds may 

be as much as 60 m thick, and they are less than 1,500 m 

beneath land surface in several counties of southern 

Arkansas. Principal references on anhydrite in the 

Buckner Formation are Imlay (1943), Swain (1949), 

Oxley and others (1967), Dickinson (1968a, 1968b), Akin 

and Graves (1969), and Newkirk (1971). 

The Buckner Formation is a lagoonal deposit of 

evaporites interbedded with clastics, carbonates, and 

minor salt. Equivalent in part to a part of the underlying 

Smackover Formation, the Buckner also is equivalent to 

the lower part of the overlying Haynesville Formation. 

The Buckner Formation is characterized by anhydrite and red beds over much of the northern Gulf Coast 

basin, but it grades southward into marine shales. Thus 

the anhydrite-red bed sequence predominates in a belt 

75-100 km wide along the northern margin of the basin. 

Nonanhydritic strata equivalent to the Buckner are 

recognized over much of the basin, and these also are 

generally referred to as Buckner. 

Strata of the Buckner Formation are deep beneath 

the land surface in most parts of the basin; they are as 

shallow as 1,000-1,500 m only in southern Arkansas. In 

northeastern Texas the Buckn'er Formation is as shallow 

as 1,500-1,800 m (Swain, 1949), whereas in Louisiana 

and Mississippi it is generally 2,000-3,000 m deep at its 

updip margin. From all these areas, the Buckner and 

equivalent strata dip toward the Gulf of Mexico where 

they occur at depths in excess of 5,000 m. 

34or----------r9T4_o-----r--~--------~----------~9~3o--------------~------------~9~2o __________ ___ 

I 

~ 

'-----r--~ ~--- ) r---~ 

.......--c?Oo_..-- Thickness of Buckner Formation; interval is 

100 feet (30.5 meters) 

LOUISIANA 

·· • • • • · · $ ......• ·· Depth to top of Buckner Formation in 1000's of feet (305 meters) 

25 

40 

) 

l!i,·-·:·:·:=·!·'!1 Principal area of Buckner anhydrites 

A-8 Line of cross section shown on 

figure 2.28 

50 MILES 

80 KILOMETERS 

Figure 2.27. Map showing thickness, in feet, and depth below land surface to top of anhydrites in Buckner Formation in 

southern Arkansas. Based on data from Akin and Graves (1969). 

40 Anhydrite Deposits of the United States 
SOUTH NORTH 

A DATUM-TOP OF BUCKNER FORMATION B 

(.9 

z 

:::::io a::_J 

UJw 

UJU:: 

~ 

_J <X: 

•<X: f--

~6o z a: IO...J ::)0 Q<( UUJ~ o_J _JUJ IUJ >-CI: a::uu... _J-

~<( o<x: <x:u... 0~ u 

EXPLANATION 

Nonmarine shale 

Anhydrite 

Anhydritic sandstone 

and shale 

a: <X: (/) UJ 

:::::io ~0 z !n<x: o_J _J UJ<x: UJUJ 

Zw w~ I...J Ow ocr: (.9- a..~ Za:: UJU... ~a: :::<C <(u... ~<( f- <(<X: I ~ (/) u u 

FEET METERS 

0 I o 

100 30 

Modified grapestone facies 

Grapestone facies 

10 MILES 

Oolite facies 

~ 

~ Calcarenite-carbonate 

mudstone facies 

Interbedded facies 16 KILOMETERS 

Shaly to dense limestone 

Figure 2.28. North-south stratigraphic cross section (A-8 in fig. 2.27) showing Buckner and Smackover Formations 

in southern Arkansas (modified from Akin and Graves, 1969). 

The thickness of the Buckner Formation increases 

southward toward the Gulf of Mexico in all areas. It 

ranges from a few meters thick around the perimeter of 

the basin to several hundred meters thick at depths of 

several thousand meters. In places, the Buckner 

Formation is combined with the overlying anhydritic 

Haynesville Formation into a sequence of anhydrite 

interbeds as much as 500 m thick (Oxley and others, 

1967). 

The only area of anhydrite-bearing Buckner strata 

at moderate depths is in parts of Hempstead, Nevada, 

Ouachita, and Calhoun Counties of southern Arkansas 

(fig. 2.27). In this area, the top of the Buckner ranges 

from about 1,000-1,500 m below the surface and consists 

chiefly of anhydrite. Total thickness of the Buckner is 

30-60 m in much of this area of southern Arkansas, and 

locally it may be slightly more than 60 m thick. 

The anhydrite facies in the Buckner Formation of 

Arkansas (fig. 2.27) was deposited north of a barrier that 

restricted normal flow of marine water from the open 

ocean to the south (Akin and Graves, 1969). This barrier 

was a chain of east-west-trending structures. Within the 

evaporite basin to the north, the Buckner consists of 

dolomite at the base, nodular anhydrite in the middle, 

and nonmarine red shale at the top (fig. 2.28). Detailed 

information is not readily available on the thickness of 

the anhydrite zone in the middle of the formation nor on 

the thickness of the individual anhydrite beds within this 

zone, but figure 2.28 indicates the overall thickness of the 

anhydrite zone. 

The Buckner is considerably thinner over the crests 

of structural highs developed on the underlying Smackover Formation and is generally much thicker in the 

structurally low areas (Akin and Graves, 1969). Most of 

these variations in thickness result from original deposition of abnormally thick or thin beds of anhydrite; thus, 

thick anhydrite beds in this area are most likely to occur 

in the structural lows as mapped on the Smackover. 

Distribution and Geologic Characteristics of Anhydrite Deposits 41 
ARKANSAS 

20 __../Thickness of Ferry Lake Anhydrite 

--- 0 (including interbeds of shale and 

carbonates); interval is 50 feet 

(15 meters) 

OKLAHOMA • Little Rock .......... 5·········· Depth to top of anhydrite, in 1000's of 

feet (305 meters) 

32° 

31° 

Fort • 

Worth 

Alexandria • 

50 100 150 MILES 

100 200 KILOMETERS 

MISSISSIPPI 

I 

I 

I 

I 

I 

ALABAMA 

TEXAS LOUISIANA 

30° 

Houstone 

Figure 2.29. Map showing thickness, in feet, and depth below land surface to top of Ferry Lake Anhydrite in Gulf Coast 

a~ea. Ferry Lake consists of anhydrite interbedded with shale and carbonate. Based on data from Forgotson (1958, 1963) and 

H1ckey (1972). Cross section A-8 shown in figure 2.30. 

Ferry Lake Anhydrite 

The Ferry Lake Anhydrite, the only widespread 

evaporite deposit in the Lower Cretaceous of the Gulf 

Coast, is easily recognized on mechanical logs and in well 

samples. The unit is in the middle part of the Trinity 

Group and extends in the subsurface from eastern Texas 

to southwestern Alabama (fig. 2.20). Thickness of the 

Ferry Lake ranges from 15 m to about 120 m; the 

formation consists of individual anhydrite beds, each 

10 m to perhaps as much as 30 m thick, that are 

interbedded with black shale and carbonate. The depth to 

the top of anhydrite ranges from less than 300 m in the 

northwestern part of the Gulf Coast basin to more than 

3,000 m farther south toward the Gulf. Principal summary references are Shreveport Geological Society 

(1947), Forgotson (1957, 1958, 1963), McNamee (1969), 

and Rainwater (1970b, 1971a). 

42 Anhydrite Deposits of the United States 

The Ferry Lake Anhydrite was deposited in a 

broad belt that extends across the central part of the Gulf 

Coast region (fig. 2.29). The unit was laid down on a 

shallow-marine shelf that had limited connection with the 

open ocean and that had a small influx of clastic 

sediment. The seaward (southern) limit of anhydrite may 

coincide with an extensive barrier reef that probably was 

growing at the edge of a carbonate shelf (Rainwater, 

1971a). Ferry Lake strata are characteristically lenticular, but some individual beds can be correlated over 

moderate distances (Rainwater, 1970b ). Unequal rates 

of subsidence caused abnormally thick accumulations of 

anhydrite in depressions, whereas carbonates were 

deposited on the higher parts of the region. 

The Ferry Lake is composed of white to gray 

nodular anhydrite that is interbedded with dark-gray to 

black shale and lesser amounts of dolomite and 

limestone. Individual anhydrite beds in many places 
A B 

2 3 4 5 6 

GULFIAN SERIES Paluxy Formation 

COMANCHEAN 

SERIES 

3000 ft 

(914 m) 

4000 ft 

5000 ft (1219 m) 

(1524 m) Rusk 

Formation 

4000 ft 4000 ft 

4000 ft (1219 m) (1219 m) 

(1219 m) 

TRINITY GROUP 4000 ft 

(1219 ml 

< Ferry Lake 

Anhydrite 

c 5000 ft 

fl1524ml 

Rodessa 

Formation 

[ Pearsall 

6000 ft Formation 

(1829 m) (equivalent) 

Sligo 5 Formation 

Hosston Formation 

Schuler Formation 

~ - (1829 m) 

5000 ft 

(1524 m) 

6000 ft 

(1829 m) 

LIST OF WELLS 

1. Delta Drilling Co. Dildy-Johns No. 1; Miller Co., Ark., sec. 4 

T. 16 S., R. 28 W. 

2. James G. Brown L. 0. Davis No. 1; Miller Co., Ark., sec. 7 

T. 19 S., R. 27 W. 

3. Union Producing Co. Caddo Levee Brd. No. 8-1; Caddo Ph., 

La., sec. 26, T. 23 N., R. 16 W. 

4. Ohio Oil Co. Williams No.1; Caddo Ph., La., sec.3, T. 22 N., 

R.l5 W. 

5. Gulf Refining Co. Levee Brd. N Lease No. 280; Caddo Ph., La., 

sec. 20, T. 20 N., R. 16 W. 

6. Texas Co. J. C. Williams, Jr. No. 1; Caddo Ph., La., sec. 2 

T. 15 N., R. 15 W. 

Figure 2.30. North-south stratigraphic cross section showing the Ferry Lake Anhydrite and other units of the Lower 

Cretaceous Trinity Group in Caddo Parish, northwestern Louisiana, and Miller County, southwestern Arkansas (modified from 

Forgotson,1958). Horizontal distances not to scale. Line of cross section A-8 shown in figure 2.29. 

grade laterally into carbonates. Halite is not associated 

with the Ferry Lake Anhydrite at any place in the basin. 

Anhydrite beds in the Ferry Lake typically are 

3-10m thick in most parts of the Gulf Coast basin, but in 

some areas they exceed 15 m and may reach as much as 

30 m in thickness. The thicker individual beds occur in 

northern Louisiana and in nearby areas of southwestern 

Arkansas and eastern Texas (fig. 2.30). 

Total thickness of the Ferry Lake Anhydrite 

typically is 15-60 m in most parts of the Gulf Coast basin 

(fig. 2.29) In some areas of northwestern Louisiana and 

eastern Texas, the unit is 75 m to more than 120m thick. 

These areas include the Sabine uplift (Shreveport area) 

along the Louisiana-Texas State line, sites of maximum 

thicknesses in Webster Parish, La., and in Henderson 

and Anderson Counties, Tex. The top of the Ferry Lake 

Anhydrite is shallowest in the northern part of the basin 

where it is 300-1,500 m below the surface in southwestern Arkansas and parts of adjacent States (fig. 2.29). 

It is typically 1,200-1,500 m below the surface over the 

Sabine uplift. From these areas the Ferry Lake dips 

southward toward the Gulf of Mexico; it is 3,000-4,000 m 

deep in much of the southern part of the Gulf Coast 

basin. 

The Ferry Lake Anhydrite thins northward across 

southwestern Arkansas to become a sequence of limestone and anhydrite about 5 m thick near its updip 

depositional limit. Farther north, the limestone and anhydrite grade into gray shale and sandstone. At and near 

the outcrop in this area the thin anhydrite beds have been 

Distribution and Geologic Characteristics of Anhydrite Deposits 43 
altered to gypsum that is now being quarried. The 

northern limit of the Ferry Lake is an erosional feature 

across southeast Arkansas and northeast Louisiana (fig. 

2.29). 

In summary, the Ferry Lake appears to contain one 

or several anhydrite beds as much as 30 m thick at depths 

of 300-1,500 m in the northern part of the Gulf Coast 

basin. Two large areas where this may occur are in 

southwestern Arkansas and parts of adjacent states and 

over the Sabine uplift. Strata in these areas are essentially 

horizontal, but locally they are faulted. 

CENTRAL TEXAS REGION-EDWARDS 

LIMESTONE AND MCKNIGHT 

FORMATION 

Lower Cretaceous strata of central and southcentral Texas contain evaporites in two separate but 

related basins (fig. 2.1 ). Outcrops of the Edwards 

Limestone have interbeds of gypsum that were deposited 

in the Kirschberg lagoon, an Early Cretaceous feature in 

the central part of the State, whereas outcrops of the 

equivalent McKnight Formation contain anhydrite interbeds that had been deposited farther south in the 

Maverick basin. Individual beds of gypsum and anhydrite 

are 10-15 m thick and range in depth from zero to about 

2,500 m. References to evaporites in both areas include 

those of Barnes (1943), Winter (1962), Fisher and Rodda 

(1969), Rose (1972), and Bay (1977). 

Outcrops of nodular gypsum in the Kirschberg 

Evaporite Member of the Fort Terrett Formation 

(Edwards Group of Rose, 1972) are limited to small 

areas in Gillespie and Menard Counties, Tex. The sulfate 

unit at one time must have been a continuous bed that 

extended throughout a number of counties that make up 

the Kirschberg lagoon (Fisher and Rodda, 1969), but 

most of the unit is now dissolved; in its place is a 

widespread zone of brecciated rock that formed by 

collapse of overlying limestone and dolomite. Anhydrite 

has not been identified in this unit anywhere in the area. 

Total thickness of the Kirschberg Evaporite Member 

ranges from 12 to 25 m, and the remnant gypsum bed is 

typically 2-11 m thick. About 8 m of gypsum is being 

quarried near Fredericksburg in Gillespie County. 

The Maverick basin, located partly in Maverick, 

Zavala, and Dimmit Counties, Tex., contains about 

30-120 m of anhydritic strata that make up the McKnight 

Formation. The formation was divided by Winter (1962) 

into lower and upper members of shaly limestone that 

44 Anhydrite Deposits of the United States 

are separated by a middle member of black shale; all 

three members contain anhydrite beds that are thin, 

perhaps as much as 10-15 m thick. The top of the 

McKnight Formation is as little as several hundred 

meters beneath the surface in the northwestern part of 

the basin and about 2,500 m beneath the surface in the 

southeastern part of the basin. 

PERMIAN BASIN 

Structure and Geologic Framework 

The Permian basin is not a single structural basin, 

but a large region of the Southwestern United States in 

which salt, anhydrite, and other evaporites of Permian 

age were deposited along with red beds and carbonates. 

The five principal structural basins in the region are 

named the Delaware, Midland, Palo Duro, Anadarko, 

and Dalhart basins (fig. 2.31 ). The Permian basin, which 

is in the southwestern part of the tectonically stable 

interior of North America, is characterized by nearly 

flat -lying Permian and younger sedimentary rocks that 

are faulted at only a few places. Strata dip gently into 

each of the structural basins from adjacent arches and 

uplifts at a rate of 2-10 m/km (0.1°-0.5°). 

After a long period of tectonic stability, during 

which a thick sequence of lower and middle Paleozoic 

carbonates were deposited, much tectonic activity 

occurred in the area of the Permian evaporite basin 

during Pennsylvanian time. A series of pronounced 

uplifts and arches were created, and adjacent areas 

subsided to receive thick accumulations of Pennsylvanian 

and Permian sediments. This period of tectonism was 

followed by stabilization of the region before the Permian evaporites were deposited. 

During Permian time, a broad and shallow inland 

sea covered much of the Southwestern United States; it 

extended northward from West Texas into northwestern 

Kansas. Because of slow but continual subsidence 

beneath all parts of this inland sea, a thick sequence of 

red beds and evaporites (dolomite, anhydrite, and salt) 

was deposited within and north of the Delaware and 

Midland basins. 

Normal-marine water entered the Delaware and 

Midland basins from the open ocean to the southwest 

during most of Permian time, and, after passing over the 

reefs, it entered the shallow inland sea where evaporation 
eDenver 

\ 

COLORADO 

i , Puebloe \ 

••••• OF "1JV, •••• BOUNDAR): ••••• •········ 'lty, ••••••••••••••••• ••• ()r, 

···:::~~ ..... ~ I 

KANSAS 

e Dodge City 

TEXAS 

50 100 

80 160 

"~I 

::1 e Lyons 

-.; . Y

: 't : .,:, . W;chita1 j 

:H-

<:( 11 : / ~ : 

~,/ 

;1 

. 

Fort Worth :alias e 

150 MILES 

240 KILOMETERS 

Figure 2.31. Map of the Permian basin of Southwestern United States showing principal tectonic provinces and boundary of 

the area underlain by beds of anhydrite. Five principal structural basins (stippled) contain thick Permian evaporites. 

Distribution and Geologic Characteristics of Anhydrite Deposits 45 
of the water took place. Fresh water flowed seaward from 

land areas on the east and west and mixed with the 

marine and saline waters. Clastic sediments were 

deposited in alluvial and nearshore environments, 

whereas the evaporites were deposited in the more 

central parts of the inland sea or in the deeper parts of 

the various structural basins. Near the end of Permian 

time, a thick sequence of anhydrite and salt (Castile 

Formation) was deposited in a deep, restricted Delaware 

basin. The Castile Formation filled the Delaware basin, 

and so the youngest Permian evaporite units (Salado and 

Rustler Formations) extend beyond this basin a considerable distance into the Midland basin and northern 

shelf areas (fig. 2.32). 

The history of the Permian basin has been one of 

tectonic stability since deposition of the evaporites. 

Minor amounts of subsidence have continued in the 

various structural basins, but the Permian and younger 

strata are virtually free of deformation and in most areas 

have dips of less than 0.5°. The region has not been 

affected by mountain-building processes, nor has it been 

covered by massive Pleistocene glaciers that spread over 

most of the northern United States. 

General discussions of the geologic framework of 

various parts of the Permian basin, which place special 

emphasis on the occurrence and nature of evaporite 

deposits, are contained in the reports by Lang (1935, 

1939), King (1934, 1942, 1948), Adams (1944, 1965), 

Galley (1958), Jordan and Vosburg (1963), McKee, 

Oriel, and others (1967a, 1967b), Hartman and Woodard 

(1971), Anderson and others (1972), Brokaw and others 

(1972), Johnson (1978a), Johnson and Gonzales (1978), 

and Dutton and others (1979). 

The older evaporite deposits of the Permian basin 

are most widespread, whereas progressively younger 

evaporite units generally are more restricted to the 

southern part of the basin (fig. 2.33). Almost all anhydritic units in the basin consist of several to many beds of 

anhydrite, each typically 2-10 m thick, that are interbedded with other rocks such as limestone, dolomite, 

shale, sandstone, and halite (fig. 2.34). Exceptionally 

thick anhydrite beds are in: the Yeso Formation, which 

contains a gypsum bed 41 m thick in south-central New 

Mexico; the San Andres Limestone, which has several 

anhydrite beds more than 30m thick in east-central New 

Mexico; the Artesia Group, which has several anhydrite 

beds reported to be nearly 30 m thick in southeastern 

New Mexico; the Cloud Chief Formation, which contains 

a single bed of anhydrite 30 m thick in the Anadarko 

basin; and the Castile Formation, which consists of 

several anhydrite beds that typically are each 30-125 m 

thick in the Delaware basin. 

46 Anhydrite Deposits of the United States 

EARLY OCHOAN 

TIME 

NEW MEXICO 

r------

~ 

A 

~ ' ' "" ' " 

MIDDLE OCHOAN 

TIME 

NEW MEXICO 

,--------

!1.. 

\. 

' '"" ' ' 

B 

EXPlANATION 

Limestone 

Sandstone 

Red beds 

Anhydrite 

TEXAS 

TEXAS 

Salt 

Lowlands 

Limestone reefs; 

triangle on forereef side 

Figure 2.32. Paleogeographic maps of southwestern 

Texas and southeastern New Mexico during early (A) and 

middle (8) Ochoan time (from King, 1948). 

In addition to the principal Permian anhydrites to 

be discussed in this section, two other thin gypsum beds 

occur in the northeast corner of the Permian basin: the 

Lower Permian Easly Creek Shale contains 3 m of 

gypsum that has been mined at shallow depth at Blue 
z 

~ 

~ 

a: 

UJ 

0.... 

a: 

UJ 

0.... 

0.... 

::::> 

c 

<1l 

0 

~ 

(.) 

0 

c 

<1l 

·c. 

E 

<1l 

~ 

~ 

Southeastern New Mexico 

Southwestern Texas 

1 Dolomite Lentil of Quartermaster Formation. 

Texas Panhandle 

Western Oklahoma 

Oklahoma Panhandle Kansas 

Figure 2.33. Diagram showing stratigraphic relationships of major anhydrite-bearing units in the Permian basin. Nonanhydrite units are omitted. Vertical dimensions are not related to thickness of anhydrite units. 

Rapids in Marshall County, Kans. (Kulstad and others, 

1956); and the Lower Permian Johnson Shale contains 3 

m of gypsum about 50 m below the surface in Nemaha 

County, Nebr. (Burchett, 1970). Also, a single occurrence of gypsum of Late Pennsylvanian age is reported in 

the Permian basin area from the Panther Seep 

Formation (Virgilian and Missourian), which contains 

two outcropping gypsum beds 7 and 24 m thick in the San 

Andres Mountains of south-central New Mexico (Kottlowski and others, 1956). These beds of calcium sulfate 

may be thick beds of anhydrite in the subsurface. 

Wellington Formation and Wichita Group 

The oldest major evaporite unit in the Permian 

basin is Leonardian in age, and is referred to as the 

Wellington Formation in the Anadarko basin and in 

Kansas, the Panhandle lime (an informal name) in the 

Texas Panhandle, and as the Wichita Group in the Palo 

Duro basin (fig. 2.33). Anhydrite is the dominant lithology in most parts of the region, although it is interbedded with salt, shale, and dolomite. Individual anhydrite beds are typically 1-5 m thick, and the maximum 

Distribution and Geologic Characteristics of Anhydrite Deposits 47 
Wellington 

Formation 

1 

Cimarron 

evaporites 

San Andres 

Limestone 

3 

Alibates, Salado, 

and Artesia 

Castile 

Formation 

5 

Rustler and 

Salado Fms 

6 

Cloud Chief 

Formation 

7 

2100 It 

1641 m) 

2200 ft 

1672 m) 

2300 It 

1703 m) 

2400 It 

1734 m) 

2500 ft 

1765 m) 

1500 It 

1458 m) 

1600 ft 

1489 m) 

1700 It 

1520 m) 

2 

2600 ft 

1794 m) 

2800 It 

1855 m) 

3000 It 

1916 m) 

3200 It 

1977 m) 

3400 ft 

11038 m) 

3600 ft 

11099 m) 

3800 It 

11160 m) 

1600 It 

1489 m) 

1800 It 

1550 m) 

2000 ft 

1611 m) 

2200 It 

1672 m) 

2400 It 

1733 m) 

4 

3000 It 

1916 m) 

3400 It 

11038 m) 

3800 It 

11160 m) 

4200 It 

11282 m) 

4600 It 

11404 m) 

5000 It 

11526 m) 

600 ft 

1183 m) 

1 ODD It 

1305 m) 

1400 It 

1428 m) 

1800 ft 

1550 m) 

2200 ft 

1672 m) 

2600 It 

1794 m) 

100 It 

130 m) 

200 It 

160m) 

EXPLANATION 

- Salt 

~Gypsum or ~ anhydrite 

rz:=::::;::2l Dolomite or tz::=z:J limestone 

1=====1 Shale 

WELL LOCATIONS 

[/(;j Sandstone 

Depth below land 

surface given in 

feet (3000) and 

meters (305). 

Vertical scale 

1. Harper Co., Okla., sec. 9, T. 26 N., R. 25 W. 

(Jordan and Vosburg, 1963) 

2. Beaver Co., Okla., sec. 18, T. 5 N., R. 25 ECM. 

(Jordan and Vosburg, 1963) 

3. Swisher Co., Texas, sec. 17, blk. C-4. L & SV 

(Johnson, 1976) 

4. Hale Co., Texas, sec. 8, blk. JD, EL & RR 

(Johnson 1976) 

is variable 

5. Eddy Co., New Mexico, sec. 9, T. 22 S., R. 32 E. 

(Jones, Cooley, and Bachman, 1973) 

6. Lea/Eddy Cos., New Mexico. Composite section for 

Los Medanos area (Jones, 1975) 

7. Custer Co., Okla. Composite section for WeatherfordClinton area (Ham and Curtis, 1958) 

Figure 2.34. Representative well logs of major Permian units containing anhydrite in the Permian basin (modified from 

Johnson and Gonzales, 1978). 

anhydrite-bed thickness is about 10 m (fig. 2.34). 

Principal studies of the anhydrite and other evaporites of 

the Wellington Formation and Wichita Group are those 

of Kulstad and others (1956), Jordan and Vosburg 

(1963), Jones (1965), Johnson (1976), Walters (1976, 

1978), and Johnson and Gonzales (1978). 

Anhydrite units of the Wellington Formation and 

Wichita Group underlie central and western Kansas, 

western Oklahoma, and the Texas Panhandle. They are 

interbedded with salt and shale on the north flank of the 

Anadarko basin in a unit referred to as the Hutchinson 

Salt Member of the Wellington in Kansas and northwestern Oklahoma, and with dolomite and shale 

elsewhere in the region. 

Total thickness of the Wellington and Wichita 

ranges from 200 to 400 m in most parts of the region, and 

the greatest thickness is near the axis of the Anadarko 

48 Anhydrite Deposits of the United States 

basin (Jordan and Vosburg, 1963). The depth to the top 

of the evaporite unit is as shallow as 100 m in central 

Kansas, but increases to about 1,000 m southward into 

the Anadarko basin and westward into western Kansas. 

The evaporites are about 600 m deep over the Amarillo 

uplift in the Texas Panhandle; they plunge to about 

1,000 m in depth in the Dalhart basin and to nearly 

1,500 m in the Palo Duro basin. 

Anhydrite beds range in thickness from 1 to 10 m, 

and the thicker beds generally are in the lower and 

middle part of the sequence. Interbeds of salt, shale, and 

(or) dolomite also are commonly 1-10m thick. Salt beds 

of the Hutchinson Salt Member were to have been the 

host rock for a federally proposed (but now abandoned) 

radioactive-waste-repository site known as Project Salt 

Vault, at Lyons in central Kansas (Bradshaw and 

McClain, 1971). 
Lower Evaporites of Clear Fork Group 

The lower evaporites of the Clear Fork Group of 

Leonardian age contain beds of anhydrite 1-10m thick in 

most parts of the Texas Panhandle (fig. 2.33). Interbedded anhydrite and other strata make up about 

30-150 m of the basal part of the lower Clear Fork in the 

Palo Duro basin, but they thin northward to about 10m 

on the south flank of the Anadarko basin. Beds of shale, 

dolomite, and salt 1-10m thick are interbedded with the 

anhydrite. Limited data on this anhydrite sequence are 

available in reports by Jordan and Vosburg (1963), 

Johnson (1976), Johnson and Gonzales (1978), and 

Dutton and others (1979). 

Depth to the top of the lower anhydrites of the 

Clear Fork is less than 500 m along the Amarillo uplift 

and the east side of the Palo Duro basin. From these 

areas, the depth increases to the south and the west 

toward the axis of the Palo Duro basin where the 

anhydrites are more than 1,500 m deep. 

Cimarron Anhydrite and Upper 

Evaporites of Clear Fork Group 

A widespread subsurface unit of Leonardian age, 

referred to informalJy as the Cimarron anhydrite and 

thought to be the stratigraphic equivalent of the Stone 

Corral Formation, extends across western Kansas and 

western Oklahoma and into the Texas Panhandle where 

it makes up the lower part of the upper evaporites of the 

Clear Fork Group (fig. 2.33). The unit consists of beds of 

anhydrite 2-10m thick that are interbedded with beds of 

shale, salt, and dolomite of similar thickness. Total 

thickness of the Cimarron anhydrite sequence ranges 

from about 5 to 20 m north of the Amarillo uplift 

(fig. 2.34), and increases southward across the Palo Duro 

basin where the sequence of anhydritic interbeds is 50 m 

to almost 200 m thick in the deep part of the basin. Data 

on the Cimarron anhydrite are contained in reports by 

Merriam (1957), Jordan and Vosburg (1963), Johnson 

(1976), and Johnson and Gonzales (1978). 

The depth of the anhydrite is as shallow as 100m in 

central Kansas where the unit is part of the Stone Corral 

Formation (Merriam, 1957); it increases southwestward 

to about 600 m in the Anadarko basin and to about 

1,500 m in the Palo Duro basin. 

Yeso Formation and Briggs Formation 

The Yeso Formation of Leonardian age consists of 

interbedded limestone, sandstone, and anhydrite in the 

shelf area of south-central and central New Mexico. The 

formation is stratigraphicalJy equivalent to evaporites in 

the Wellington Formation, Wichita Group, lower and 

upper parts of the Clear Fork Group, and the Cimarron 

anhydrite farther northeast in the Permian basin 

(fig. 2.33). The most complete description of the Yeso 

was presented by Kottlowski and others (1956), who 

described outcrops of Yeso gypsum as much as 41 m 

thick in the San Andres Mountains of southern Socorro 

and northern Dona Ana Counties, N. Mex. Other brief 

descriptions include those of Weber and Kottlowski 

(1959), McKee, Oriel, and others (1967a), KelJey 

(1972b ), and Foster and others (1972). The Briggs 

Formation, also of Leonardian age, contains about 190m 

of anhydrite and gypsum interbedded with carbonates in 

the Malone Mountains of Hudspeth County, Tex. 

(Albritton and Smith, 1965). 

Thickness of the Y eso Formation, which is less 

than 300 m in northeastern New Mexico, increases 

southward to 600-1,000 min parts of Lincoln, Otero, and 

Chaves Counties, N. Mex. The depth to the top of the 

Yeso also increases from about 300m on the north to as 

much as 1,500 m on the south. 

San Andres 1---1-,.-'---,-_,.J 

Limestone >---J..-..-.--'----.-~ 

Glorieta 

Sandstone ~~'""' 

Yeso 

Formation 

Joy ita 

Sandstone 

Member 

Canas 

Gypsum 

Member 

Torres 

Member 

EXPLANATION 

Dolomite or 

limestone 

Gypsum 

Sandstone 

=~=1 Shale 

FEET METERS 

0 0 

Figure 2.35. Columnar section of Permian upper 

Yeso Formation (containing thick Canas Gypsum 

Member at the top) and lower San Andres Limestone 

in the San Andres Mountains of southern New 

Mexico (modified from Kottlowski and others, 1956; 

Summers and Kottlowski, 1969). 

Distribution and Geologic Characteristics of Anhydrite Deposits 49 
In outcrops of the San Andres Mountains (fig. 

2.35), the Y eso is about 275-480 m thick and contains 

numerous gypsum beds 2-41 m thick (Kottlowski and 

others, 1956). The gypsum beds arc light gray, fine 

crystalline, and medium bedded. Most gypsum units are 

2-15 m thick, but the Canas Member at the top of the 

formation has a single bed of massive to banded gypsum 

41 m thick. Data are not available on thickness and 

character of Yeso strata in the nearby subsurface, but the 

sulfate beds are undoubtedly anhydrite in part, and one 

or several of the anhydrite beds may be more than 30 m 

thick. Therefore, additional studies of the Y eso are 

needed near the San Andres Mountains, as well as north 

and east of the Sacramento Mountains. 

The Briggs Formation crops out in the Malone 

Mountains to the south of the Diablo platform, and 

consists mainly of gypsum and anhydrite, but is interbedded with thin to thick beds and lenses of limestone 

and dolomite (Albritton and Smith, 1965). Gypsum on 

the outcrop occurs as thin lentils and lenses and as 

irregular bodies as much as 40 m thick. The gypsum is 

white to light gray and is remarkably free of detrital 

matter, except for tan or brown ferruginous streaks. The 

unit is being quarried at Gypsum Switch for use in plaster 

and cement manufacture. 

Areas of exposure of the Briggs Formation are 

small, and the structure of the Malone Mountains is fairly 

complex. Fairly thick deposits of undisturbed anhydrite 

may exist in the formation at moderate depths near the 

mountains. 

San Andres Limestone and 

Blaine Formation 

The most widespread evaporite in the Permian 

basin is referred to as the San Andres Limestone in New 

Mexico and the southern part of the Texas Panhandle, 

and as the Blaine Formation north of the Amarillo uplift 

in Texas, Oklahoma, Kansas, and Colorado (fig. 2.33). 

The San Andres consists mainly of limestone and 

dolomite in the south, but these lithologies grade 

northward into a dolomite-anhydrite-halite facies and 

thence into an anhydrite-red beds-halite facies of the 

Blaine (fig. 2.36). Anhydrite beds in most areas are 

1-10 m thick, but they may exceed 30m in thickness in 

parts of central and cast-central New Mexico. Reports 

describing San Andres gypsum or anhydrite are: 

Summers and Kottlowski (1969), Mourant and Shomaker (1970) Kelley (1971, 1972a), Foster and others 

(1972), Jones (1974), Johnson (1976), Johnson and 

Gonzales (1978), and Dutton and others (1979); studies 

50 Anhydrite Deposits of the United States 

200 MILES 

I 

320 KILOMETERS 

Figure 2.36. Map of Permian basin area showing principal 

facies of the San Andres and Blaine Formations and area 

(shaded) where individual anhydrite beds are reported to be 

as much as 30 m thick. The name San Andres Limestone 

generally is applied to the facies south and west of Amarillo; 

the name Blaine Formation generally is applied to the facies 

north and east of Amarillo. 

of the Blaine Formation were reported by Jordan and 

Vosburg (1963), Fay (1964), Schumaker (1966), Johnson 

(1967, 1976, 1978b), Irwin (1977), Johnson and Gonzales (1978), and Holdaway (1978). 

Anhydrite occurs at various stratigraphic positions 

in the San Andres and Blaine Formations in almost all 

parts of the Permian basin. Anhydrite is interbedded with 

limestone, dolomite, halite, and some clastics just north 

of the shelf that borders the Delaware and Midland 

basins, and a similar lithologic association extends 

northward across the Palo Duro basin to the vicinity of 

the Amarillo uplift, Bravo dome, and Sierra Grande 

uplift (fig. 2.31). Within this broad area of eastern New 

Mexico and northwestern Texas the San Andres is 
typically 300-500 m thick, and in most areas individual 

anhydrite beds are 1-10m thick. The formation thins to 

the north and east due to depositional thinning and 

dissolution of interbedded salt at shallow depths near the 

outcrop and over the uplifts. 

Individual beds of anhydrite may be as much as 

30 m thick in all or part of Lincoln, Chaves, D~ Baca, 

Guadalupe, Roosevelt, and Lea Counties, N. Mex., and 

in parts of Bailey, Lamb, Cochran, Hockley, Lubbock, 

Y~a~um,. Te~ry,_ and Lynn Counties, Tex. (fig. 2.36). 

W1thm this d1stnct, the San Andres is 400-500 m thick 

and the depth to the top of the formation ranges fro~ less than 300m in the west to 900-1,400 min the center 

and the east. 

Studies of San Andres evaporites in the eastcentral New Mexico district are not detailed, although 

those by Summers and Kottlowski (1969), Mourant and 

Shomaker (1970), and Kelley (1971) indicated abnormally thick anhydrite (or gypsum) beds. Mourant and 

Shomaker (1970) described anhydrite or gypsum beds 

nearly 20-60 m thick at depths of 120-440 m in De Baca 

County; the thickest unit, 60 m at a depth of 440 m, is 

based on the sample log of a well drilled in sec. 26, 

T. 1 S., R. 26 E. Kelley (1971) described evaporites in the 

upper part of the San Andres in outcrops, and mentioned 

the presence of about 250 m of gypsum and a few thin 

beds of dolomite in sec. 15, T. 5 S., R. 11 E., Lincoln 

County. Summers and Kottlowski (1969) showed the log 

of a well in sec. 24, T. 7 S., R. 29 E., Chaves County, that 

contains anhydrite beds 10-15 m thick at a depth of 

about 900 m. The density log of the Cities Service No. 1 

State "BP" well drilled in sec. 2, T. 10 S., R. 36 E., Lea 

County, indicates the presence of 58 m of anhydrite, and 

several thin non-anhydrite beds about 1 645 m below the 

sui-face. ' 

Other data are not available that would enable 

further characterization of anhydrites in this east -central 

New Mexico district. However, the limited data do 

indicate the potential for thick beds at moderate depths, 

and thus more study is needed in this area. 

In the northern part of the Permian basin, strata of 

the same age as the San Andres contain interbedded 

anhydrite, red beds, and salt called the Flowerpot Blaine 

and Dog Creek Formations, but only the Bl~ine ha~ significant anhydrite beds. The Blaine Formation 

typically ranges from 15-100 m in thickness and commonly contains two to nine separate beds of anhydrite 

that are 3-10 m thick. The Blaine is exposed along the 

east side of the Permian basin, where outcrops of highpurity gypsum are mined extensively, and the formation 

dips to depths of 300 m to more than 1,000 m in other 

parts of the basin. 

Artesia Group 

. The Artesia Group of late Guadalupian age 

overhes the San Andres Limestone in eastern New 

Mexico and much of nearby Texas (fig. 2.33), where it 

consists mainly of anhydrite and halite interbedded with 

sandstone, shale, and dolomite. Most anhydrite beds are 

1-10m thick, but some may be as much as 30m thick. 

Studies of the Artesia Group that contain significant 

information on the evaporite strata are those of Tait and 

others (1962), Hayes (1964), Havenor (1968), Kelley 

(1972a, 1972b), Jones (1974), Sarg (1977), Johnson and 

Gonzales (1978), and Dutton and others (1979). 

The Artesia Group as defined by Tait and others 

(1972) consists of five formations, which are (in 

ascending order) the Grayburg, Queen, Seven Rivers, 

Yates, and Tansill. Anhydrite occurs in all five formations in many parts of the region. 

Thickness of the Artesia Group is about 250-

300 m to the northeast in the Palo Duro basin, and 

300-600 m to the south in the Midland basin and the 

shelf areas surrounding the Midland and Delaware 

basins. The depth to the top of the Artesia Group is 

300-600 m in most parts of the Palo Duro basin and 

600-1,200 min most parts of the Midland basin. In far 

eastern New Mexico, the top of the Artesia is about 

600 m below the surface, but the depth decreases 

westward to the Pecos River where the Artesia crops out. 

Anhydrite, salt, and red-bed clastics are interbedded in all five formations of the Artesia Group over 

most of the region (fig. 2.34). Individual rock units are 

typically 1-10 m thick, although some beds locally are 

20-30 m thick. 

Tait and others (1962) presented several subsurface cross sections of the Artesia Group, which 

indicate that several of the anhydrite beds are nearly 

30 m thick in some parts of the shelf area north of the 

Delaware basin. This thickness is shown especially on 

their cross section through parts of Lea and Eddy 

Counties, N. Mex., where the top of the Artesia Group is 

generally 300-900 m below the surface. Studies of the 

Artesia Group have not been done in this area with 

sufficient detail to establish firmly the thickness of 

individual anhydrite beds, but some beds as much as 

30 m thick probably are present at moderate depths. 

Cloud Chief Formation 

The Cloud Chief Formation is 60-100 m thick; it 

consists mainly of red-brown shale interbedded with 

sandstone and it contains several beds of gypsum or 

anhydrite that are typically 1-2m thick. A single bed of 

gypsum 30 m thick at the base of the formation crops out 

Distribution and Geologic Characteristics of Anhydrite Deposits 51 
in the eastern part of the Anadarko basin, but this bed is 

largely anhydrite in the shallow subsurface nearby. This 

bed of gypsum or anhydrite was referred to originally as 

the Cloud Chief Gypsum, but more recently it has been 

called the Moccasin Creek Gypsum Member at the base 

of the Cloud Chief Formation (Fay, 1965, 1979). The 

lower part of the Cloud Chief, including the thick bed of 

gypsum or anhydrite, is believed to be Guadalupian in 

age, whereas the upper part of the formation is Ochoan 

(Johnson, 1978a). Other principal references to the 

Moccasin Creek Gypsum Member are Ham and Curtis 

(1958) and Johnson (1978b ). 

Thick gypsum in the Moccasin Creek Member 

crops out in eastern Washita and Custer Counties, Okla. 

The unit is white to pinkish-white alabaster in much of 

the area, consists of 90-98 percent gypsum, and is 

quarried at several sites. The full thickness of the 

Moccasin Creek Member in this area is about 30m, but 

cores drilled into gypsum outcrops have found only 

5-15 m of anhydrite in the lower part of the bed at depths 

as shallow as 10m (Ham and Curtis, 1958). 

The Moccasin Creek Gypsum Member dips gently 

to the west, and much of the unit also grades laterally into 

red-brown shale in that direction. This bed is mostly 

anhydrite in the Anadarko basin where it is only about 

3-10m thick and from 100m to a maximum of 200m 

below the surface. Thus, the bed is as much as 30 m thick 

only on the outcrop and at a depth less than 100 m; at 

greater depths the equivalent anhydrite bed is much 

thinner. 

Castile Formation 

The evaporites of the Castile, Salado, and Rustler 

Formations of Ochoan age in the Delaware basin 

constitute the most extensive and thickest evaporite 

sequence in North America. These deposits are the 

culmination of evaporite deposition that began during 

Leonardian time in Kansas, then migrated toward the 

southwest as extensive Permian seas began to withdraw 

from the area of the Southwestern United States (fig. 

2.33). The series is more than 1,500 m thick within the 

Delaware basin and more than 450 m thick where these 

deposits extend north and east beyond the confines of the 

basin (fig. 2.32). 

The Castile Formation, which consists predominantly of anhydrite, is confined to the Delaware 

basin. The contact between the Castile and the 

underlying Bell Canyon Formation of the Delaware 

Mountain Group (Guadalupian) is gradational, and 

laminated siltstone and claystone change upward to 

laminated anhydrite within about 1 m (Anderson and 

others, 1972; Cys, 1978). Interbeds of halite in the 

52 Anhydrite Deposits of the United States 

Castile Formation and in the overlying Salado Formation 

are confined to the eastern half of the basin (fig. 2.37). 

The western limits of individual salt beds have been 

shown to be the result of dissolution of salt rather than 

the original limits of salt deposition (Anderson and 

others, 1972, 1978). Consequently, most beds of halite in 

the eastern part of the basin are correlative with beds of 

brecciated anhydrite in the western part of the basin that 

resulted from collapse and lowering of overlying stratigraphic units (fig. 2.38). Anderson (1982) calculated that 

an average of about 50 percent of the salt deposited in 

the Castile and lower Salado Formations has been 

dissolved, although more than 70 percent of the salt in 

certain individual beds has been dissolved. 

Anderson and others (1972) subdivided the Castile 

Formation into four anhydrite members and three halite 

members (fig. 2.38). The thickness of the lowermost 

anhydrite unit (anhydrite I) is fairly constant between 50 

and 60 m in the western part of the basin and increases to 

more than 100 m in the eastern part of the basin 

(fig. 2.39). The thickness of the anhydrite II member, like 

the thickness of anhydrite I, increases from west to east 

(fig. 2.40)-from a fairly uniform 23-30 m thick in the 

west to more than 60 m in the east. The anhydrite III 

member is 85-90 m thick over most of the basin. It also 

thickens from west to east, but at a much lesser rate than 

does either anhydrite I or anhydrite II. The lowest halite 

bed of the overlying halite III member is absent over the 

western part of the basin, and an anhydrite bed within 

halite III lies directly on anhydrite of anhydrite III. The 

lack of good halite marker beds and the relatively 

uniform thickness of anhydrite III make construction of a 

meaningful isopach map of this anhydrite unit difficult, 

but the unit is generally 85-105 m thick. The thickness of 

the anhydrite IV member is even more difficult to map 

because the uppermost halite bed of underlying halite III 

and the lowermost halite bed of the overlying Salado 

Formation are not present over much of the basin. 

Although the thicknesses of individual beds of 

anhydrite within the Castile Formation increase from 

west to east across the Delaware basin, the thickest 

composite sections of anhydrite occur in the western part 

of the basin (west of the 0-salt line in fig. 2.37) as a result 

of dissolution of halite interbeds. Most of the Castile 

Formation consists of remarkably distinct interlaminations of organically stained calcite and anhydrite (fig. 

2.41) that are assumed to represent annual increments of 

sedimentation (varves). Calcite-anhydrite couplets 

average about 2 mm in thickness (Anderson and others, 

1972). The petrologic and geochemical characteristics of 

the calcite-anhydrite laminations of the Castile have been 
105° 

CHAVES I 

i-------------~~ 

I I 

l I 

I EDDY 

l 

--i 

I 

I 

I 

I DELAWARE 

l 

l_ 

CULBERSON 

Horn / 

/ ~// DIABLO 

// PLATFORM 

/ / 

/ / JEFF DAVIS 

NEW MEXICO 

50 KILOMETERS 

103° 

YOAKUM 

I 1--------

l CENTRAL 

BASIN 

PLATFORM 

ANDREWS 

I 

__ j--~-

1 

I ECTOR 

I 

---t--1 I CRANE 

I 

Figure 2.37. Map of the Delaware basin and surrounding region of southwestern Texas and 

southeastern New Mexico. The line A-A' corresponds to the cross section in figure 2.38. 

Distribution and Geologic Characteristics of Anhydrite Deposits 53 
METERS FEET 

EXPLANATION 

D Anhydrite 

• Halite 

... • Blanket solution breccia 

--- Contact between Salado 

and Castile Formations 

100 =r- 300 6 

5:~MilES 

0 5 10 KILOMETERS 

EAST 

A' 

··.:~·:.: ... ·~~~.~~~·~;.;,;:::::::::~::.:~=~;:::::·.·::::~ .. =~~========~ . ~ .... ........ ---- --- ... 

. ;~;J'~'~~;~;,.-;;~;~;~;~:::~~:;;'"';~;!;,:!i:~;f~:,i.i/ijiXjf.~~i~.~;·~f~~~~:~~:§J:~~~~::~:;·~~~·m~· ~~·.,;Jiiiiiiiiiiiii··········~~~~~ 

Figure 2.38. Diagrammatic east-west cross section of Castile and Salado Formations from Culberson County, Tex. (A), to 

Winkler County, Tex. (A') (from Anderson and others, 1972). Location of cross section shown on figure 2.37. 

described by Udden (1924), Adams (1944), Anderson 

and Kirkland (1966), Kirkland and Anderson (1970), 

Anderson and others (1972), and Dean and Anderson 

(1974, 1978). 

Within individual anhydrite beds of the Castile 

Formation and the lower part of the overlying Salado 

Formation, cyclic variations in structures and textures of 

the anhydrite have been interpreted by Dean and Anderson (1978) as representing cyclic changes in salinity 

within the basin. An average petrologic cycle is about 4 m 

thick and represents a time span of about 2,700 years. A 

complete cycle begins with thin laminae couplets of 

anhydrite and calcite in which calcite may be the 

dominant component (fig. 2.41 ). The anhydrite within 

individual couplets increases in thickness upward within 

the cycle, and forms the calcite-banded anhydrite typical 

of most of the Castile Formation and the lower part of 

the Salado Formation (bedded massive anhydrite of 

Maiklem and others, 1969) (fig. 2.41). Near the end of a 

cycle, nodular anhydrite has formed by recrystallization 

within thicker anhydrite laminae. When fully formed, the 

nodular anhydrite has the appearance of bedded, 

54 Anhydrite Deposits of the United States 

nodular, mosaic anhydrite ofMaiklem and others (1969). 

A complete cycle ends with a bed of halite, mostly 

containing laminae of anhydrite, immediately overlying 

nodular anhydrite. In the western part of the basin, 

however, the dissolving of halite beds has left dissolution 

breccias that consist of elongate fragments of laminated 

anhydrite suspended in a matrix of anhydrite (fig. 2.42; 

Anderson and others, 1972, 1978). Anderson and others 

(1978) have shown that 0.3 m of dissolution breccia in the 

western part of the basin is equivalent to between 6 and 

9 m of halite in the eastern part of the basin. Therefore, 

the thick composite anhydrite sections in the western part 

of the basin consist of cyclic alternations of laminated and 

nodular anhydrite with some nodular zones overlain by 

dissolution-brecciated anhydrite. Laminated anhydrite 

occupies most of the 4-m-thickness of an average cycle. 

Most of the inferred salinity cycles are incomplete, 

because not every bed of nodular anhydrite is overlain by 

halite (or dissolution breccia). However, nodular anhydrite is best developed in complete cycles, and so the 

original laminated anhydrite that is immediately below a 

bed of halite (or dissolution breccia) is almost completely 

recrystallized into nodular anhydrite. 
EDDY 

EXPLANATION 

o Well control 

20 MILES 

30 KILOMETERS 

CONTOUR INTERVAL, 15 METERS 

53-METER CONTOUR ADDED 

GAINES 

LEA 

I i ANDREWS 

WINKLER 

WARD 

Figure 2.39. Thickness distribution of anhydrite I member, Castile Formation. Contour lines are dashed where inferred 

(modified from Anderson and others, 1972). 

Distribution and Geologic Characteristics of Anhydrite Deposits 55 
31° 

EDDY 

20 MILES 

30 KILOMETERS 

CONTOUR INTERVAL, 7.5 METERS 

27-METER CONTOUR ADDED 

0 

0 

oo 

0 

0 

0 

0 

LEA 

0 

103° 

GAINES 

I i ANDREWS 

i 

I 

I 

I 

l 

WINKLER 

WARD 

Figure 2.40. Thickness distribution of anhydrite II member, Castile Formation (modified from Anderson and others, 

1972). 

56 Anhydrite Deposits of the United States 
0 

0 

0 

N 

I lcm 

'$ _ ' rwt- ¢ L'ii: 

.:, =~:n; : ==:=:z.;;ij I 

B!!!!!lcm · 1nh 

Figure 2.41. Diagrammatic illustration (left) of a complete 

salinity cycle in the Castile Formation and lower part of the 

Salado Formation (modified from Dean and Anderson, 

1978). Right column consists of core photographs illustrating 

four different parts of a salinity cycle. 

Figure 2.42. Core photographs 

of blanket dissolution breccia correlative with halite I in the Castile 

Formation. 

At the base of a cycle, anhydrite may be less 

abundant than is calcite, although this is rare. In the 

typical calcite-banded anhydrite in the middle of a 

cycle-the material that makes up most of the Castilethe rock consists of 85-90 percent anhydrite and 10-15 

percent calcite (Dean and Anderson, 1978). The anhydrite beds of the entire Castile Formation average about 

85 percent anhydrite and 15 percent calcite (Dean and 

Anderson, 1974). 

Depth to the top of the the calcite-banded anhydrite of the Castile Formation ranges from less than 150m 

Distribution and Geologic Characteristics of Anhydrite Deposits 57 
in the western part of the basin to more than 1,200 m in 

the eastern part (fig. 2.43). 

Salado Formation 

The Salado Formation of Ochoan age is one of the 

principal evaporite units in the Permian basin, and one of 

the largest deposits of halite in North America (Brokaw 

and others, 1972). The Salado consists mainly of halite in 

the area of the Delaware and Midland basins and on the 

shelf areas north of the basins, but it also contains 

anhydrite beds 1-10m thick. In addition, the potassiumbearing minerals that are interbedded with halite in the 

central part of the formation are the principal sources of 

potash in the United States. The contact between the 

Castile and Salado Formations was considered by Adams 

(1944) to be an angular unconformity. Jones and his 

coworkers (Brokaw and others, 1972; Jones and others, 

1973) considered the contact to be conformable, but 

recent evidence presented by Anderson and others 

(1978) and Anderson (1982) suggests that the unconformity between the two formations suggested by Adams 

(1944) does exist. Whereas the Castile Formation is 

characterized by relatively pure lithologies (anhydrite or 

halite) and a dominance of anhydrite, the Salado 

Formation is characterized by less pure lithologies, by 

many thin interbeds of differing lithologies, and 

dominance of halite (85-90 percent of the formation; 

Brokaw and others, 1972) (fig. 2.34). 

Much recent study has focused on the possible use 

of the Salado salts as a host rock for radioactive waste at 

the Waste Isolation Pilot Plant (WIPP) site in southeast 

New Mexico, about 30 km east of Carlsbad. Among the 

recent reports on the Salado Formation are those of 

Adams (1969), Brokaw and others (1972), Jones and 

others (1973), Jones (1975), Cheeseman and Lorenz 

(1977), Powers and others (1978), and Anderson (1982). 

The thickness of the Salado Formation ranges from 

between 150 and 300 m over most of the western half of 

the Delaware basin to more than 700 m along the eastern 

margin of the basin (Anderson and others, 1972). Depth 

to the top of the Salado Formation is typically 300-750 m 

in most parts of the Delaware and Midland basins and on 

the shelf areas farther north. Within the Palo Duro basin, 

the depth ranges from 300-600 m. 

Anhydrite beds are common in the Salado 

Formation, particularly in the lower part, but none 

exceeds a thickness of about 10m. Most of the anhydrite 

occurs as thin (mostly less than 1 m) interbeds within 

halite. Although the anhydrite beds arc thin, they are 

laterally persistent and provide excellent marker beds for 

stratigraphic control (Lang, 1935, 1939; Adams, 1944; 

Jones, 1960; Jones and others, 1973). The thickest of the 

anhydrite marker beds in the Salado-the Cowden Anhy58 Anhydrite Deposits of the United States 

drite Member-occurs about 90 m above the CastileSalado contact and is about 6 m thick. Snider (1966) 

calculated that the cumulative thickness of anhydrite 

beds in the Salado Formation along the eastern margin of 

the Delaware basin increases from north to south-from 

about 60 min Lea County, N.Mex., to more than 200m 

in Reeves County, Tex.; this percentage increase is from 

about 11 to 30 percent of the entire formation. 

The calcite-banded anhydrite typical of the Castile 

Formation persists into the lower anhydrite units of the 

Salado Formation in the central part of the Delaware 

basin (Anderson, 1982). In the northern part of the basin, 

however, the anhydrite units of the Salado and even the 

upper part of the Castile have lost this typical banded 

character. Some anhydrite marker beds in the Salado 

Formation are interlaminated with thin, dark films, 

apparently of organic matter, but the couplets are on a 

scale of 1-2 em, rather than the 1-2 mm in the typical 

"banded anhydrite" of the Castile (Anderson, 1982). The 

anhydrite marker beds of the Salado almost everywhere 

contain inclusions of salt and stringers of magnesite or 

dolomite (Adams, 1944). 

Rustler Formation and 

Alibates Dolomite Lentil 

The Rustler Formation, youngest of the anhydritebearing units in the Permian basin, is limited to the 

Delaware and Midland basins and nearby shelf areas. 

The formation is Ochoan in age, and its upper part is 

believed to be equivalent to the anhydrite-bearing Alibates Dolomite Lentil of the Quartermaster Formation 

farther north in the Texas Panhandle (Fay, 1965; 

Johnson, 1978a). In subsurface the formation is mostly 

anhydrite and sail, but it also contains interbeds of 

dolomite, polyhalite, sandstone, and shale (Lang 1935, 

1939; Adams, 1944; Brokaw and others, 1972; Jones and 

others, 1973; Powers and others, 1978; fig. 2.34). Anhydrite beds in the Rustler and Alibates range from 1-15m 

in thickness. Jones (1960) described the Rustler in the 

subsurface in the northern part of the Delaware basin as 

containing 43 percent halite and other chloride minerals; 

30 percent anhydrite, polyhalite, gypsum, and other 

sulfate minerals; 17 percent clastic rocks; and 10 percent 

limestone, dolomite, and magnesite. Adams (1944) 

considered the Rustler to be composed of two main 

parts: an upper zone about 30-50 m thick that consists 

mainly of anhydrite interbedded with fine-grained 

clastics and dolomite; and a lower zone that consists of 

interbedded anhydrite, dolomite, sandstone and shale. 

The Rustler is best known from outcrops, but 

construction of a complete stratigraphic section is 
103° 

EDDY 

WARD 0 0 0 

31° 

20 MILES 

30 KILOMETERS 

CONTOUR INTERVAL, 150 METERS 

Figure 2.43. Depth to top of laminated anhydrite in the Castile Formation (modified from Dean, 1967). 

Distribution and Geologic Characteristics of Anhydrite Deposits 59 
difficult because the original lithologies have been highly 

altered by deformation, hydration, and dissolution. Most 

of the rocks exposed in outcrop are porous to even 

cavernous, friable, strongly jointed, and brecciated. The 

most persistent stratigraphic markers are two beds of 

dolomite-one in the lower part of the formation called 

the Culebra Dolomite Member and one in the upper part 

of the formation called the Magenta Dolomite Member 

(Adams, 1944). 

The thickness of the Rustler Formation ranges 

from about 75 to 180 m over most of the northern and 

eastern parts of the Delaware basin, and it generally 

increases toward the southern part of the basin. The 

Rustler is unconformably overlain by the reddish-brown 

clastic rocks of the Upper Permian Dewey Lake Red 

Beds. The depth to the top of the Rustler ranges from 

150 to 600 m in most parts of the Delaware and Midland 

basins and nearby shelf areas. 

The Alibates Dolomite Lentil of the Quartermaster Formation in most parts of the Texas Panhandle 

consists of two beds of anhydrite or dolomite, each 

2-10 m thick, separated by 2-6 m of red-brown shale. 

The Alibates crops out in bluffs overlooking several of 

the deeply incised streams and rivers of the region, and it 

is generally 100-200 m beneath the surface in divides 

between the major rivers. 

NORTHERN DENVER BASINPENNSYLVANIAN THROUGH TRIASSIC 

A fairly thick sequence of evaporites is present in 

the northern Denver basin in parts of western Nebraska, 

northeastern Colorado, and southeastern Wyoming (fig. 

2.1 ). Parts of the area also have been referred to as the 

Lusk embayment (Bates, 1955) and as the Alliance basin 

(MacLachlan and Bieber, 1963; Maughan, 1966; Rascoe 

and Baars, 1972). These reports, and those by Maher 

(1960), Momper (1963), Hoyt (1963), Larson and others 

(1963), Lane (1973), and Irwin (1977), are the principal 

sources of information on evaporite deposits in this area. 

Total thickness of the anhydrite-bearing strata ranges 

from 150 to 300 m, and the anhydrite is interbedded with 

carbonates, clastics, and several salt units. The evaporites 

occur in Wyoming and Nebraska in the Minnelusa 

Formation and its equivalents (Pennsylvanian and Lower 

Permian) and in the Lykins (or Goose Egg) Formation 

and its equivalents (Permian and Lower Triassic). 

Individual anhydrite beds are commonly 2-10 m thick, 

and some beds in the Lower Permian are reported to be 

as much as 23-30 m thick. Depth to the top nf the 

anhydritic units ranges from 600 to 2,400 m. 

60 Anhydrite Deposits of the United States 

Pennsylvanian and Permian strata in most parts of 

the northern Denver basin are composed of carbonates, 

red beds, and evaporites that were deposited in shallow 

marine or shelf environments. The region subsequently 

received a thick accumulation of Cretaceous sediments; 

the depocenter was to the west and southwest, adjacent 

to the Rocky Mountain front of Colorado and southeastern Wyoming. The basin is asymmetrical, and strata 

dip gently to the southwest across western Nebraska less 

than r. The strata generally are undeformed in the 

principal evaporite province of the basin (Nebraska 

Panhandle and adjacent areas). 

Strata in the Pennsylvanian and Lower Permian 

(Wolfcampian and Leonardian) in Wyoming and 

Nebraska are referred to as the Minnelusa Formation by 

many workers. Anhydrite beds occur with carbonates and 

clastics in the Desmoinesian, Missourian, and Virgilian in 

the far northern part of the basin (Hoyt, 1963). These 

beds are typically only 2-10 m thick and are at depths of 

from 900 to perhaps 1,500 m. 

Principal anhydrite beds are in the Wolfcampian 

and Leonardian Series. Wolfcampian strata are 

120-160 m thick in a large part of western Nebraska, and 

anhydrite makes up more than 50 percent of the strata in 

much of this area (MacLachlan and Bieber, 1963). 

Anhydrite beds are typically 2-15 m thick in the area and 

range from about 900 m deep in the northeast to about 

2,400 m deep in the southwest. The thickest Wolfcampian anhydrites reported are two beds 17 and 23 m thick 

at depths of 1,160 m in Sheridan County, Nebr. 

(fig. 2.44). 

Leonardian strata are mainly shales and siltstones, 

but anhydrite in the Stone Corral Formation at the top of 

the sequence is commonly 5-10 m thick and at a depth of 

600-1,500 m. The maximum thickness reported is 30m 

of anhydrite at a depth of 1,295 m in Phillips County, 

northeastern Colorado (fig. 2.45). 

Permian and Lower Triassic strata of the northern 

Denver basin, commonly 90-180 m thick, are variously 

placed in the Lykins Formation (Rascoe and Baars, 

1972) or in the Goose Egg Formation (Lane, 1973). 

These strata are further subdivided into a number of 

other units, and those that contain anhydrite beds include 

the Satanka Shale and Blaine Formation, and the 

Opeche, Minnekahta (or Sybille Member of some 

authors), Forelle, Ervay (all Permian), and Little 

Medicine (Triassic) Members of the Goose Egg 

Formation. The thickness of individual anhydrite beds 

throughout the Lykins Formation is typically 2-10m, and 

the maximum thickness is probably about 12m. Depths 

to these beds range from about 600-900 m in the 

northeast to as much as 2,400 m in the southwest. 
Sec. 2, 

T. 30 N., R. 51 W. 

EXPLANATION 

Sandstone 

Shale and siltstone 

Anhydrite 

Dolomite or limestone 

2 

Sec. 1, 

T. 28 N., R. 48 W. 

Salt 

3000 It - 1914 ml Depth below surface 

3 

Sec. 20, 

T. 26 N., R. 44 W. 

FEET METERS 

0 0 

Sundance Formation 

Goose Egg Formation 

(part) 

Leonardian 

Wolfcampian 

,-

1 

I 

I 

4 

Sec. 28, 

T. 21 N., R. 41 W. 

INDEX MAP 

SOUTH DAKOTA 

COLORADO 

4000 It 

11219 ml 

~igure 2.44. Stratigraphic cross section in the northeastern part of the northern Denver basin showing thick anhydrite beds 

1n the Wolfcampian part of the Minnelusa Formation (modified from Larson and others, 1963). Horizontal distances not to scale. 

Deformed gypsum beds 3-15 m thick crop out in the 

lower Lykins Formation (upper Satanka) along the 

northern Colorado Front Range (Story and Howell, 

1963). 

Thus, there arc two anhydrite units in the northern 

Denver basin that are moderately thick. The upper part 

of the Wolfcampian contains several anhydrite beds as 

much as 17-23 m thick at a depth of 1,160 m, and the 

Stone Corral Formation is at least 30m thick in one area 

at a depth. of 1,295 m. Additional study is needed to 

determine more accurately the character, distribution, 

thickness, and depth of the thicker anhydrites in· the 

southwest part of the Nebraska panhandle and in 

adjacent areas. 

Distribution and Geologic Characteristics of Anhydrite Deposits 61 
P. Doheny 

Mittelstadt No. 1 

Sec. 23, T. 10 N., R. 53 W. 

Logan County 

FEET 

0 

100 

200 

300 

400 

Stuarco et a/ 

Sprague Bros. No. 1 

Sec. 1 8, T. 1 0 N., R. 4 7 W. 

Sedgwick County 

METERS 

0 

[8] 

30 [ZJ -

60 

~ 90 

120 • 

Texota 

Hansen No. 1 

Sec. 30, T. 8 N., R. 43 W. 

Phillips County 

Morrison Formation 

Cedar Hills Sandstone 

EXPLANATION 

Sandstone § Dolomite 

Shale ~ Limestone 

Anhydrite ~ Dolomitic shale 

Salt ~~~~I Calcareous shale 

z 

<( 

a: 

~ 

<( 

u 

u.. 

...J 

~ 

z 

:::;!; 

~ 

c: 

w 

Q.. 

Figure 2.45. Columnar section of Permian, Jurassic, and Lower Cretaceous strata in Colorado part of northern Denver basin 

showing thick anhydrite reported in the Stone Corral Formation (modified from Irwin, 1977). 

WYOMING BASINS-PENNSYLVANIAN 

THROUGH JURASSIC 

Pennsylvanian through Jurassic strata in most of 

the Wyoming basins contain thin to moderately thick 

interbeds of anhydrite. Anhydrite-bearing units include 

the Minnelusa (Pennsylvanian and Lower Permian), 

Goose Egg (Permian and Lower Triassic), Phosphoria 

(Permian), Spearfish (Permian and Triassic), Gypsum 

Spring (Jurassic), and Preuss (Jurassic) Formations. 

Individual anhydrite beds are typically 2-10 m thick, 

62 Anhydrite Deposits of the United States 

although the Gypsum Spring Formation reportedly 

contains beds of anhydrite or gypsum that are as much as 

30m thick. 

The present-day basins and uplifts of Wyoming 

(fig. 2.46) were not present during, and did not have a 

significant impact upon, evaporite sedimentation in the 

region. Anhydrite was deposited as interbeds with clastics 

and some carbonates during the late Paleozoic and early 

Mesozoic in shelf, shallow-marine, and low-relief cOntinental environments that extended across large areas. 

Major sedimentary basins at that time were to the west 

and southeast of Wyoming. 
45° 

44° 

43° 

42" 

41° 

OBasins 

200 MILES 

I 

320 KILOMETERS 

EXPlANATION 

--Uplifts TT Thrust fault-Sawteeth on 

overthrust side of fault 

Figure 2.46. Map showing major basins and uplifts in 

Wyoming and adjacent areas. 

Development of the Wyoming basins as structural 

features occurred mainly during tectonic movements in 

Late Cretaceous and early Tertiary time. Paleozoic and 

Mesozoic rocks were uplifted, broadly folded, and block 

faulted to form the principal mountain ranges of Wyoming and adjacent areas (fig. 2.46). These same strata 

were later buried beneath a thick sequence of Tertiary 

continental sediments. As much as 5,000-9,000 m of 

sedimentary rocks overlie the Precambrian basement in 

various basins in Wyoming, and the anhydrite-bearing 

strata are commonly 300-4,500 m below the land surface 

in these basins. 

The Minnelusa Formation contains thin beds of 

anhydrite in the Powder River basin of eastern Wyoming 

and also in the area to the south and east of the Black 

Hills in South Dakota. The Minnelusa consists mainly of 

carbonates and sandstone in this region, but anhydrite 

beds 2-10m thick also are present mainly in the upper 

member, which is of Permian age. The top of the 

Minnelusa is less than 1,000 m deep in most of the South 

Dakota area and is as much as 2,000-4,500 m deep in the 

Powder River basin. Anhydrite crops out at some 

localities (Brady, 1958) and probably makes up most of 

the sulfate at depths greater than 15 m. Principal 

references on the geology and evaporites of the Minnelusa Formation are Brady (1958), Foster (1958), Smith 

(1967), Kinnison (1971), and Rascoe and Baars (1972). 

The Goose Egg and Phosphoria Formations are 

typically 100-250 m thick in various Wyoming basins. 

Evaporites are more prominent in the Goose Egg than in 

the Phosphoria, and they occur chiefly in the Powder 

River and Wind River basins (fig. 2.46), and to a lesser 

extent in the Hanna, Shirley, Laramie, and Big Horn 

basins (Lane, 1973). Work on the evaporites of the 

Goose Egg and Phosphoria Formations has been done by 

Privrasky and others (1958), Campbell (1962), McKee, 

Oriel, and others (1967a, 1967b), Rascoe and Baars 

(1972), and Lane (1973). 

The Goose Egg Formation consists mainly of red 

beds interbedded with anhydrite, limestone, dolomite, 

and (in the Powder River basin) salt. These strata were 

deposited around the northwestern margin of the large 

evaporite basins in the midcontinent (the Permian basin 

and the northern Denver basin). The Phosphoria 

Formation, on the other hand, was deposited on the 

shallow eastern shelf of a north-south trough that 

extended through Idaho and Utah. The Phosphoria 

Formation consists mainly of dolomites interbedded with 

limestone, phosphorite, clastics, and a few beds of anhydrite that are tongues extending westward from the 

Goose Egg Formation. 

Individual anhydrite beds in the Goose Egg 

Formation are typically 2-10 m thick, and locally some 

are as much as 15 m thick (Lane, 1973). Named 

members that are characterized by anhydrite beds in the 

subsurface are the Minnekahta (its equivalent, the 

Sybille), Forelle, and Ervay Members. Even in these 

members, however, the anhydrites are thin and are 

interbedded with shale. Sulfate beds in the Goose Egg 

crop out as gypsum on the flanks of the basins in eastern 

and central Wyoming. They undoubtedly are represented 

by anhydrite at depths greater than 15-30 m and dip to 

depths of 2,000-4,500 m in various basins. 

The Spearfish Formation, which crops out around 

the perimeter of the Black Hills, is a sequence of red beds 

and evaporites and is in part equivalent to the Goose Egg 

Formation of the Powder River basin. Gypsum and (or) 

anhydrite beds of the Spearfish are 2-10m thick in the 

area around the Black Hills and extend from outcrops to 

depths of 2,000 m. Information on the Spearfish evaporites in this region was presented by Maughan (1966), 

Bailey and Roscoe (1972), and MacLachlan (1972). 

The Gypsum Spring Formation consists mainly of 

clastics and carbonates, but a persistent bed of anhydrite 

(6rypsum at and near the outcrop) is interbedded with 

those rocks in the northwestern quarter of Wyoming 

Distribution and Geologic Characteristics of Anhydrite Deposits 63 
1 

Sec. 15, 

T. 5 N., R. 2 W. 

FEET METERS 

0 0 

100 30 

200 60 

300 90 

12 mi 

(19 km) 

2 3 

Sec. 5, 1 0 mi Sec. 4, 

T. 3 N., R. 1 W. (16 km) T. 2 N., R. 1 W. 

D 

CLOVERLY FORMATION 

MORRISON 

FORMATION 

SUNDANCE 

FORMATION 

GYPSUM 

SPRING 

FORMATION 

NUGGET 

SANDSTONE 

EXPlANATION 

Sandstone 0 0 0 0 0 0 Conglomerate 0 0 0 

Shale and ~ Anhydrite 

siltstone 

~ Limestone 

16 mi 

(25 km) 

4 

Sec. 24, 

T. 1 S., R. 1 E. 

2 g

1

WWind ~iver 300 bas1n 

4 

WYOMING 

INDEX MAP 

Figure 2.47. Stratigraphic cross section showing Gypsum Spring Formation and adjacent strata in western part of Wind River 

basin of Wyoming (modified from Burk and others, 1956). Horizontal distances not to scale. Index map shows location of wells. 

(fig. 2.47). The principal areas underlain by anhydrite in 

this formation include parts of the Wind River, Bighorn, 

and Green River basins, and the flanks of some of the 

adjacent uplifts (fig. 2.46). Thickness of the entire 

formation is typically about 60-90 m in these basins, but, 

toward the southeast, the unit thins and is truncated by 

the overlying Sundance Formation. The anhydrite bed is 

reported to be 15-38 m thick in various areas (Love and 

others, 1945; Burk and others, 1956); it consists mostly of 

anhydrite, but in some areas contains thin layers of red 

beds or other nonsulfate strata. Data on the Gypsum 

Spring evaporites have been presented by Love and 

64 Anhydrite Deposits of the United States 

others (1945), Love (1948), Burk and others (1956), 

Peterson (1957a, 1972), and Bullock and Wilson (1969). 

However, few data are readily available on the variation 

in thickness of the anhydrite and on the presence or 

absence of these interbedded strata. 

Depth to the top of anhydrite in the Gypsum Spring 

Formation ranges from less than 100 m along the flanks 

of the basins to as much as 4,500-5,000 m in the deep 

basins. The anhydrite unit is 300-1,500 m below the 

surface only on the upper (shallow) flank areas of the 

Wind River and Bighorn basins and adjacent uplifts. 

Anhydrite beds dip gently (as much as about 5°) on the 
110° 108° 106° 104° 102° 100° 98° 

CANADA 

48° 

' 1m 

I \~--~L~in~e~o~fc~ro~s~s-se~c.tio_n ____ _.~ 

: . ~ 

I Williston\~ 

N \~ z B A S I N 

rT' 

47" 

e Bismark 

45° 

MONTANA 

_ _5\.r·--------W-Y_O_M_I_NG------,-~?.--1 

~----~--~~----~----------~----------~------~r 

TERTIARY 

PRECAMBRIAN 

B 

10,0001! 

(3000 ml 

\~ 

~ e Rapid City 

I,~ 

I .\------------ -------

e Pierre 

NEBRASKA 

50 100 MILES 

80 150 KILOMETER 

EXPlANATION 

• • Thrust fault-Sawteeth on overthrust side of fault 

Figure 2.48. Map of Williston basin area in northwestern United States showing principal structural features adjacent to the 

basin and location of the central Montana trough (cross section modified from Reed, 1963). 

southwestern side of the Wind River basin and locally 

around the south and east flanks of the Bighorn basin; 

elsewhere in the region, the basin margins are 

structurally more complex and faults, tight folds, and 

steep dips are present. Additional study is needed to 

determine the character, thickness, and depth of the 

Gypsum Spring anhydrite in the generally undisturbed 

areas of the Wind River and Bighorn basins where the 

unit is known to be at moderate depths. 

To the southwest, in the Idaho-Utah-Wyoming 

stateline area, the Gypsum Spring Formation and the 

younger Jurassic Preuss Sandstone contain thin anhydrite interbeds at depths ranging between 1,500 and 

3,000 m (Burk and others, 1956; Peterson, 1957a; 

Maher, 1976). The structure of the anhydrite beds here is 

complicated because of intense folding and faulting 

within the overthrust belt just west of the Green River 

basin. 

WILLISTON BASIN-ORDOVICIAN 

THROUGH JURASSIC 

A number of Paleozoic and Mesozoic formations 

contain anhydrite in the Williston basin, a large 

sedimentary and structural basin that underlies most of 

North Dakota, eastern Montana, northwestern South 

Dakota, and part of southern Canada (fig. 2.48). Strata 

dip gently at an angle less than 1° toward the depocenter 

of the basin where a sequence of about 5,000 m of 

Distribution and Geologic Characteristics of Anhydrite Deposits 65 
sedimentary rock of Cambrian through Tertiary age is 

preserved (Carlson and Anderson, 1965). Major 

structural features in the basin are the Nesson anticline, 

a north-trending structure in northwestern North 

Dakota, and the Cedar Creek anticline, a structure that 

extends northwestward into Montana from the common 

corner of North Dakota, South Dakota, and Montana. 

An elongate locus of deposition, referred to as the central 

Montana trough, extends westward from the Williston 

basin. This area contains a thick sequence of evaporitebearing Mississippian strata that is best discussed here 

with sediments of the Williston basin. An earlier study of 

the Williston basin by Sandberg (1962) discussed the 

potential for subsurface disposal of radioactive wastes. 

Anhydrite-bearing formations were deposited in 

the Williston basin during each geologic period from the 

Ordovician through the Jurassic (fig. 2.49). In most of the 

formations the anhydrite beds are 2-10m thick and are 

1,200 m to more than 2,000 m deep. The maximum 

reported thicknesses are 15 m in the Devonian Prairie 

Formation and 25-30 m in the Mississippian Madison 

Group. 

A series of thin anhydrite beds are present in the 

Ordovician Red River and Stonewall Formations, and in 

the Silurian Interlake Formation (Fuller, 1961; Smith, 

1967; Ballard, 1969). Total thickness of these anhydritebearing strata ranges from about 60-120 m in the interior 

of the basin, and the individual anhydrite beds range 

from 1 to 6 m in thickness. Depths to tops of anhydrite 

beds are 2,400-4,000 m below the surface. 

Devonian strata contain thin anhydrite beds at 

several stratigraphic levels, including (in ascending 

order) the Winnipegosis, Prairie, Dawson Bay, Souris 

River, Duperow, Birdbear, and Three Forks Formations 

(Andrichuk, 1951; Sandberg and Hammond, 1958; Sandberg, 1961; Smith, 1967; Sandberg and Mapel, 1967). In 

most formations the anhydrite beds are typically 2-10 m 

thick and are from 1,500-4,000 m deep. Anhydrite beds 

in the Prairie Formation reach a maximum thickness of 

about 15 m at o1 depth of about 2,700 min Divide County, 

N.Dak. (Smith, 1967). The Prairie Formation reaches a 

maximum total thickness of nearly 150 m at the depocenter of the basin where it consists almost entirely of 

bedded halite and several interbeds of anhydrite and 

potash salts. 

Anhydrite also is present at a number of st~atigraphic levels in the Mississippian Madison Group (fig. 

2.49). It occurs chiefly in the Charles Formation, but also 

is present in the upper part of the underlying Mission 

Canyon Limestone (Smith and others, 1958; Andrichuk, 

1958; Maher, 1960; Smith, 1967; Cook, 1976). The 

principal area of anhydrite deposition was in the main 

part of the Williston basin, but anhydrite also was 

deposited in a second evaporite province that extended 

westward along the axis and shelf areas of the central 

66 Anhydrite Deposits of the United States 

Montana trough (Andrichuk, 1958; Craig, 1972). In the 

main part of the Williston basin, the anhydrite beds are 

typically 2-10 m thick and range from about 3,000 m 

deep in the basin center to about 1,200 m deep around 

the perimeter. Marafi (1972), however, referred to an 

anhydrite bed about 25m thick at a depth of 1,100 min 

Bottineau County, N. Dak., on the northeastern side of 

the basin. In the central Montana trough, in and around 

the Big Snowy uplift and Blood Creek syncline, the lower 

part of the Charles Formation is reported to contain 

anhydrite beds as much as 30 m thick at depths of about 

1,000-1,500 m (Maher, 1960). Blankennagel and others 

(1979) reported about 35 m of anhydrite and some 

interbedded dolomite in undifferentiated Madison strata 

at a depth of about 1,400 m in a well in south-central 

Montana. 

The Big Snowy Group also contains thin beds of 

gypsum and anhydrite deposited in the Williston basin 

and the central Montana trough (Mundt, 1956; Rawson, 

1969; Craig, 1972). Formations containing anhydrite 

include, in ascending order, the Kibbey, Otter, and 

Heath; thicknesses of individual anhydrite beds range 

from 2 to 10 m. Some of the sulfate beds crop out as 

gypsum on the flanks of uplifts in Fergus, Judith Basin, 

Cascade, and Meagher Counties (Perry, 1949), but all 

exist as anhydrite where they dip into nearby basins and 

synclines to depths of 300-1,500 m. 

The Pennsylvanian, Permian, Triassic, and Jurassic 

Systems contain thin anhydrite beds in the Williston basin 

(fig. 2.49). Individual anhydrite units are 2-10m thick, 

and typically occur at depths ranging from 1,200 to 2,000 

m. Formations containing anhydrite include, in ascending 

order, the Minnelusa, Opeche, Minnekahta, Spearfish, 

and Piper; these units were discussed by Francis (1957), 

Peterson (1957b), Maughan (1966), Dow (1967), Smith 

(1967), Mallory (1972), Rascoe and Baars (1972), and 

MacLachlan (1972). 

SWEETGRASS ARCH-THREE FORKS 

FORMATION AND OTHER 

DEVONIAN UNITS 

Upper Devonian strata in the Sweetgrass arch area 

of northwest Montana (fig. 2.48) comprise a thick 

sequence of carbonates and evaporites. Anhydrite beds 

in the sequence typically are 3-10m thick, but the Logan 

Gulch Member of the Three Forks Formation at the top 

of the sequence contains anhydrite beds as much as 30m 

thick at depths of 600-1,500 m. Other Devonian stratigraphic units that contain thinner anhydrite beds include 

the Souris River and Duperow Formations. Detailed 

studies of anhydrites in the Sweetgrass arch area have not 
Bakken Fm u 

Ui 

(/) Piper <( 

c:: Formation ::J 

"""') 

.S2 Dupe row 

a:~ Formation 

f-<( Spearfish 

Formation 

z Souris River <( 

~ Formation z c:: 

w ~ a.. z 

0 

> Dawson Bay Fm w 

0 

..Jz Minnelusa 

~~ Formation 

zz Prairie 

Z<( 

~> Formation 

Amsden Fm 

Winnipegosis 

Big Snowy Formation 

Group 

FEET METERS 

0 0 

Charles 

Formation z 

<( 

0. a: Interlake 

::J 

..J Formation 

:I Ui z 

<( 0 

a: 

a.. 

Ui 

(/) (.9 

Ui 

(/) 

~ 

500 150 

Mission c Canyon 

0 Limestone 

Ul Stonewall Fm 

z 

<( Stony Mountain "0 u Formation 

> t1l 0 

0 

~ c:: Red River 0 Formation 

Lodgepole 

Limestone 

EXPIANA TION 

- Salt lr>~'(d Clastics and 

carbonates 

Bakken Fm ~Anhydrite D Carbonates 

Figure 2.49. Generalized columnar section of the Williston basin showing evaporite units 

in Ordovician through Jurassic strata (modified from Smith, 1967; Dow, 1967). 

Distribution and Geologic Characteristics of Anhydrite Deposits 67 
been published, but general data on Devonian strata of 

the region, and some information on the evaporites, have 

been released by Sloss and Laird (1947), Andrichuk 

(1951), Belyea (1958), Billings Geological Society 

(1962), Peterson (1966), Sandberg and Mapel (1967), 

Baars (1972), and Sandberg and Poole (1977). 

During Late Devonian time, the Sweetgrass arch 

was connected with the Williston basin to the north and 

east, and some of the rock units are western extensions of 

those previously described in the Williston basin. Total 

thickness of Upper Devonian strata in the Sweetgrass 

arch area ranges from about 150 m in the southeast to 

about 450 m in the northwest (Sandberg and Mapel, 

1967). Since Devonian time, thick sequences of Jurassic 

and Cretaceous strata have been deposited, along with 

thinner sequences of other systems; the region is now 

characterized as undeformed and has gentle dips and few 

minor structures. The western boundary of the arch is the 

structurally complex overthrust belt along the Northern 

Rocky Mountain front. Petroleum now is being produced 

from a number of Mississippian through Cretaceous 

reservoirs at many locations over the arch. 

The Souris River and Duperow Formations consist 

mostly of dolomite and lesser amounts of interbedded 

anhydrite and limestone (fig. 2.50). Individual anhydrite 

beds are typically 3-10 m thick and are distributed 

throughout both formations at depths ranging from 

600-1,500 m. 

Renwar Oil Co. 

2 

Montalban Oils Inc. 

3 

General Petroleum Corp. 

No. 1 McKechnie 

Sec. 1, T. 31 N., R. 1 W. 

FEET METERS 

"l 100 30 

200 60 

28 mi 

(45 km) 

THREE FORKS 

FORM TION 

BIRDBEAR FM 

DUPE ROW 

FORMATION 

SOURIS RIVER 

FORMATION 

No. 1 Johnson 

Sec. 7, T. 27 N., R. 2 W. 

EXPLANATION 

~ Anhydrite 

~ Dolomite or 

limestone 

~ Shale -

17 mi 

(27 km) 

No. 88-30-P Holt 

Sec. 30, T. 25 N., R. 1 W. 

Sweetgrass 

Arch 

INDEX MAP 

Figure 2.50. Stratigraphic cross section of Sweetgrass arch area showing Three Forks Formation and other 

anhydritic units of the Upper Devonian (modifed from Billings Geological Society, 1962). Horizontal distances 

not to scale. Index map shows location of wells. 

68 Anhydrite Deposits of the United States 
The principal anhydrite unit of the Sweetgrass arch 

area is the Logan Gulch Member of the Three Forks 

Formation (also referred to as the Potlatch Anhydrite). 

This unit ranges from about 30 to 120 m in thickness in 

the subsurface, and the thickness generally increases 

westward across the arch. Sandberg and Mapel (1967) 

referred the upper part of the Potlatch to the Logan 

Gulch Member of the Three Forks Formation and used 

the term Logan Gulch in central Montana, southwest 

Montana, and Wyoming. 

Where the Logan Gulch anhydrite is thickest, it 

consists of anhydrite interbedded with lesser amounts of 

dolomite (C.A. Sandberg, oral commun., 1979). 

Individual anhydrite beds in this area and elsewhere 

range from 12-30 m in thickness, although one of the 

anhydrite beds may exceed 30 m. Away from the western 

depocenter, there appears to be a single bed of anhydrite 

that ranges from 15 to 30m in thickness (fig. 2.50). It is 

overlain by 5-20 m of gray calcareous shale, referred to 

as the Trident Member of the Three Forks Formation 

(Sandberg and Mapel, 1967). The depth to the top of the 

Logan Gulch anhydrite in the Sweetgrass arch area 

ranges from about 600 m along the crest of the arch to as 

much as 1,500 m on the east and west flanks. 

In summary, anhydrite in the Sweetgrass arch area 

occurs only in a single rock unit, the Logan Creek 

Member, that has thick anhydrite beds at moderate 

depths. No detailed study has been made of this unit, 

however, and additional information is needed to assess 

more thoroughly the character, distribution, thickness, 

and depth of these anhydrite beds. 

EAGLE BASIN-EAGLE VALLEY 

EVAPORITE 

The Eagle Valley Evaporite is a thick sequence of 

Pennsylvanian strata on the western side of the Rocky 

Mountains in northwest Colorado (fig. 2.51 ). Eagle basin 

is the name generally used for this region, but the term 

Maroon basin has also appeared in the literature. Total 

thickness of the evaporite unit is as much as 3,000 m, and 

anhydrite and (or) gypsum beds are as much as about 

50 m thick. Salt also is present in the Eagle Valley 

Evaporite in the subsurface, and diapiric flow of the salt 

into anticlines is one of the causes for complex structures 

and deformation of the anhydrite (or gypsum) beds. 

Reports dealing with the evaporites in this area include 

those by Katich (1958), Mallory (1966, 1971, 1977), and 

Peterson and Rite (1969). 

The Eagle Valley Evaporite was deposited in a 

landlocked marine trough between the Uncompahgre 

EXPLANATION 

[? . I Eagle Valley Evaporite 

MILES 

20 

32 

KILOMETERS 

2--' Thickness of Eagle Valley Evaporite or equivalent 

,.-, strata in lOOO's of feet (305 meters) 

Figure 2.51. Distribution and thickness of Eagle Valley 

Evaporite in the Eagle basin of northwest Colorado (modified 

from Mallory, 1977). 

and Front Range uplifts (fig. 2.51 ), and is restricted to an 

area about 80 km wide by 160 km long. The evaporites 

interfinger with red and maroon clastic sediments of the 

Middle Pennsylvanian (late Atokan and Desmoinesian) 

Minturn Formation. 

The Eagle Valley Evaporite consists principally of 

gypsum and anhydrite interbedded with gray shale, siltstone, and sandstone. In the subsurface near the town of 

Eagle and southeast of Glenwood Springs (near Cattle 

Creek station), Colo., boreholes have penetrated a 

substantial thickness ·of rock salt interbedded in the unit 

(fig. 2.52); and potash salts also have been reported from 

the Eagle area. Outcrops of gypsum are widespread 

along and overlooking the valleys of Eagle and Colorado 

Rivers near their confluence; they are present also at 

scattered locations along Fryingpan River, Cattle Creek, 

Gypsum Creek, and on the south flank of the White 

River uplift (Mallory, 1971). 

Thickness of the evaporite unit ranges from about 

500 m around the perimeter of the basin to as much as 

3,000 m near Eagle and Cattle Creek Station. Beds of 

gypsum and anhydrite are commonly 5-30 m thick and 

probably reach a thickness of 50 m. Outcropping gypsum 

beds that are plastically deformed appear to be much 

more than 50 m thick. The depth to anhydrite probably 

ranges from a few meters in some outcrop areas to 

several thousand meters in the depocenters. Boreholes 

Distribution and Geologic Characteristics of Anhydrite Deposits 69 
4000 It 

(1219 m) 

L _ 11 mi __j 

r-(17.7 km)- -, 

1000 ft 

(305m) 

c 

~E QjLL 

IXl 

z 

z 

> 

__, 

>-

(/) 

EXPlANATION 

FEET 

0 

Gypsum or 

anhydrite 

Salt 

Limestone or 

dolomite 

Mudstone, 

shale, or 

sandstone 

METERS 

0 

500 152 

z 1000 305 

w 

a.. 

1500 457 

2000 610 

Figure 2.52. Lithology of the Eagle Valley Evaporite in two 

wells drilled in Eagle County, Colo. (modified from Irwin, 

1977). Welis are California No. 1 Benton, sec. 14, T. 3 S., R. 

85 W. (left), and Chaplin No. 1 Black, sec. 4, T. 5 S., R. 84 W. 

(right). 

70 Anhydrite Deposits of the United States 

drilled at Eagle, at Cattle Creek station, and at a site 

15 km northwest of Eagle all penetrated anhydrite beds 

5-30 m thick (fig. 2.52). 

Since its deposition, the Eagle Valley Evaporite has 

been subjected to the following stresses: (1) load 

metamorphism, (2) Laramide orogenic movement, (3) 

growth of diapiric anticlines, and ( 4) local contortion 

from flowage and hydration of anhydrite (Mallory, 1971 ). 

Outcropping strata of the evaporate unit are deformed in 

most areas, and Mallory (1971) believed that the evaporite mass may still be rising within the cores of several 

anticlines. 

Anhydrite units in the areas of thick evaporites 

probably have been deformed to such an extent that they 

are not likely to be suitable for long-term containment of 

radioactive waste. However, one or several of the anhyqrite beds that interfinger with the Minturn Formation or 

the overlying Maroon Formation away from the evaporite depocenters may be sufficiently thick and uncleformed to be potentially suitable for this purpose. 

PARADOX BASIN-PARADOX MEMBER 

OF HERMOSA FORMATION 

The Paradox basin of southeast Utah and 

southwest Colorado contains a thick sequence of salt 

deposits interbedded with shale, dolomite, anhydrite, and 

(locally) potash in the Paradox Member of the Hermosa 

Formation (Middle Pennsylvanian). Anhydrite beds 

range in depth from several hundred meters to several 

thousand meters, but the thickness of individual anhydrites typically ranges only from 3 to 10 m and probably 

does not exceed 15 m. Along the crests of a series of 

salt-cored anticlines in the basin (fig. 2.53) is a thick cap 

rock that consists mainly of gypsum and anhydrite mixed 

in a jumbled mass with shale and dolomite. 

Salt and other evaporites of the Paradox Member 

underlie an area of 30,000 km2 in the Paradox basin, but 

the greatest thickness of evaporites is in the troughlike 

depression adjacent to the Uncompahgre uplift on the 

north side of the basin. The original thickness of evaporites in the trough area is estimated to have been between 

1,500 and 1,800 m (Hite and Lohman, 1973). Flowage of 

salt in the numerous diapiric salt anticlines has, however, 

caused the present thickness to range from 0 to more 

than 3,000 min a horizontal distance of 5 km or less. The 

maximum thickness of evaporites in the salt anticlines is 

nearly 4,200 m. Recent references on the general geology 

of this evaporite sequence include the work of Hite 

· (1960, 1968, 1970), Elston and Shoemaker (1961), Hite 

and Lohman (1973), and Johnson and Gonzales (1978). 

The evaporites of the Paradox Member consist of a 

sequence of cyclic sediments that include black shale, 

dolomite, anhydrite, halite, and (in some cycles) potash 
38° 

50 MILES 

100 KILOMETERS 

EXPLANATION 

- Salt anticline or salt dome 

Figure 2.53. Index map of Paradox basin showing distribution of Paradox evaporites and location of salt anticlines in 

northeastern part of basin (modified from Hite and Lohman, 1973). 

(fig. 2.54). A total of 29 evaporite cycles has been 

recognized in the deeper parts of the basin, and these 

have been numbered 1 through 29 in descending order 

(Hite, 1960; Hite and Liming, 1972; Hite and Lohman, 

1973). Each evaporite cycle can be correlated for 

considerable distances across the basin, although 

correlation is difficult where beds have been folded, 

faulted, and deformed by flowage into the salt anticlines. 

Distribution and Geologic Characteristics of Anhydrite Deposits 71 
Individual evaporite cycles are commonly 30-100 m 

thick, and salt is the dominant rock type in almost all 

areas. The aggregate thickness of just the black shaledolomite-anhydrite part (called the marker beds) of each 

cycle is typically 10-20 m, and the thickness of individual 

anhydrite beds ranges from 3-10 m (fig. 2.54). More 

complete discussion of the evaporites and evaporite 

cycles was given by Herman and Sharps (1956), Herman 

and Barkell (1957), Hite (1968, 1970, 1977), Peterson 

and Hite (1969), and Hite and Lohman (1973). 

The major structural features of the Paradox basin 

are the salt -cored anticlines in the troughlike depression 

on the northeastern side of the basin. The anticlines, 

which occupy an area about 80 km wide and 200 km long, 

consist of long, undulating welts of thickened salt (figs. 

2.55 and 2.56) over which the younger rocks are arched 

(Shoemaker and others, 1958; Cater, 1970; Hite and 

Lohman, 1973). Five major anticlinal systems are in the 

basin; separate names have been given to the more 

pronounced segments of each system where the anti110ft 133m) 

hal1te ommed 

Disconformity 

EXPLANATION 

Halite 

m Anhydrite 

§Dolomite 

t == = -=j Black shale 

FEET METERS 

0 

10 

20 

30 

Disconformity 

Figure 2.54. Typical evaporite cycle of the 

Paradox Member of the Hermosa Formation 

(modified from Hite and Lohman, 1973). 

72 Anhydrite Deposits of the United States 

clines are breached and where the surface expression is a 

prominent flat-floored valley that exposes gypsum and 

other rocks. The principal salt-anticline systems are: (1) 

Lisbon Valley-Dolores Valley, (2) Moab Valley-Spanish 

Valley-Pine Ridge, (3) Gypsum Valley, (4) Castle ValleyParadox Valley, and (5) Salt Valley-Cache Valley-Fisher 

Valley-Sinbad Valley (fig. 2.53). Several smaller anticlines or domes that lie just southwest of Moab, Utah, 

along the Colorado River include Cane Creek anticline, 

Shafer dome, Lockhart anticline, Rustler dome, Gibson 

dome, and Meander anticline. 

Dissolution of halite at the upper surface of the 

thickened salt core has caused local development of a cap 

rock of insoluble material as much as several hundred 

meters thick along the crest of the salt anticlines (Hite 

and Lohman, 1973) (fig. 2.56). Cap rock in this region 

differs somewhat from that on Gulf Coast salt domes. 

The Gulf Coast variety was formed entirely from thin 

laminae and small crystals of anhydrite disseminated in 

the halite, whereas the Paradox basin cap rock includes 

this type of anhydrite and even greater amounts of 

insoluble black shale, dolomite, and anhydrite from the 

marker beds. Because of dissolution of interbedded salt 

and collapse of the various marker beds, the cap rock is 

generally chaotic and consists of a jumbled mass. The cap 

rock is generally porous, and in some anticlines all or part 

of it is saturated with brine (Hite, 1977). Most anhydrite 

originally present in the cap rock has been converted to 

gypsum. 

In an earlier appraisal of the Paradox basin for 

emplacement of radioactive wastes in salt deposits, Hite 

and Lohman (1973) concluded that the Salt Valley 

anticline and the Shafer dome had some potential for this 

use. Further study by the U.S. Geological Survey has 

centered on an evaluation of the geology, hydrology, 

mineral resources, and geothermal gradient of the north 

end of the Salt Valley anticline (Gard, 1976; Hite, 1977). 

SAN JUAN BASIN-TODIL TO 

FORMATION 

A thick bed of anhydrite in the Todilto Formation 

(Middle Jurassic) is present in the subsurface in the 

eastern half of the San Juan basin of northwestern New 

Mexico and part of adjacent Colorado (fig. 2.57). This 

bed is typically 25-30 m thick, and may be as much as 

40 m thick, and its depth below the surface ranges from 

less than 100 m in the southeastern part of the basin to 

2,700 m in the northeastern part. The bed crops out as 

gypsum on the southern and eastern sides of the basin. 

Studies of the Todilto gypsum-anhydrite unit include 

those by Weber and Kottlowski (1959), Anderson and 
Cresent 

R 19 E 

0 

0 

R 20 E 

MOAB 15 MILES (25 KM) 

3 

I 

I 

5 

EXPlANATION 

-1000- Structure contour lines 

on top of Paradox Member. 

Interval is 1000 ft (305 m) 

A B Line of cross section shown 

in figure 2.56 

0 Drill hole 

e Drill hole penetrating 

top of salt 

6 MILES 

I 

I 

10 KILOMETERS 

T 21 S 

T 22 S 

T 23 S 

Figure 2.55. Structure-contour map on top of salt in Paradox Member of Hermosa Formation along Salt 

Valley anticline, Grand County, Utah (modified from Hite and Lohman, 1973). 

Kirkland (1960), Tanner (1970, 1972), and Stapor 

(1972); regional summaries of the Jurassic System and 

the San Juan basin can be found in Peterson and others 

(1965), Santos (1975), Green and Pierson (1977), and 

Woodward and Callender (1977). 

The San Juan basin, in the eastern part of the 

Colorado Plateau, consists mainly of gently dipping strata 

that are only moderately deformed, mainly along the 

perimeter. The basin is nearly circular in plan and is 

strongly asymmetrical in cross section. Principal uplifts 

Distribution and Geologic Characteristics of Anhydrite Deposits 73 
5000 h 

(1500 m) 

COURTHOUSE SYNCLINE SALT VALLEY ANTICLINE 

Cap rock 5 

SEA 

LEVEL 

2 

Kmdb 

++++++++++++++++++++++++++++++++++++++++++++++ ~hu++ 

++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 

5000 h 

(1500 m) 

+ + ! ! ! ! ! ! ! ! ! ! Paradox Member (salt and associated strata) ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 'r~+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 

+++++++++++++++++++++++++++++7++++++++++++++++++++++++++++++++++++++++++ _._ ................ ...,.... ...................... ...:A:..&.i:....+....:t..:t .±..t...+ 7 + + + + + + + + + + + + . + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + -. --------- """\;t.±..+J.±.±....+...:t.±. ?.±.~+.....:t..±±..i"....!.!...+_!...±.!..~...!.. !._+_!.!.._+_+...:!:. 7 !_+_:!..!. !._+..:!..!. 

10,000 h 

(3000 m) 

\ . 

Pre-Paradox rocks ·'-' Pre-Paradox rocks 

\ 

WELLS USED IN SECTION 

1. Equity, Donahue No. 1 

2. Texaco, McKinnon No.1 

3. Continental, Gov't.-Hall No. 1 

4. Western Allies 

5. Pure, Salt Valley No. 1 

6. Union, Devils Garden-USA No. 1 

4 MILES 1 

I I 

5 6 KILOMETERS 

EXPlANATION 

Kmdb Mancos, Dakota, and Burro Canyon Formations 

Jmse Morrison, Summerville, and Entrada Formations 

J"Rnw Navajo, Kayenta, and Wingate Formations 

"Rem Chinle and Moenkopi Formations 

Pc Cutler Formation 

IPhu Hermosa (upper member) Formation 

Figure 2.56. Cross section through Salt Valley anticline in Grand County, Utah, showing thickened Paradox salt and arching 

of overlying strata (modified from Hite and Lohman, 1973). Cap rock, containing chaotic masses of gypsum and other 

insoluble rock, forms along the crest of the anticline. Line of cross section A-8 is shown in figure 2.55. 

bounding the basin are the Nacimiento uplift on the east, 

the San Juan Mountains to the north, and the Zuni and 

Defiance uplifts on the south and west (fig. 2.57). 

Structural features within the basin and the adjacent 

uplifts were formed mainly during Late Cretaceous and 

early Tertiary (Laramide) time, and broad epeirogenic 

uplift of the region occurred still later in the Tertiary 

Period (Woodward and Callender, 1977). 

Sedimentary rocks that fill the San Juan basin are 

continental and marine in origin, and range in age from 

Paleozoic through Cenozoic. Total thickness of these 

strata is as much as 4,000 m. Jurassic rocks are typically 

300-450 m thick in the basin, and they are overlain by as 

much as 2,000-2,500 m of Cretaceous and Tertiary strata 

in the northeast. 

The Todilto Formation consists of a lower petroliferous limestone unit that is widespread throughout the 

San Juan basin and an upper anhydrite unit that is 

restricted to the eastern half of the basin (fig. 2.57). The 

limestone commonly ranges from 1 to 6 m in thickness, 

whereas the thickness of the anhydrite is 25-30 min most 

areas; Tanner (1972) reported that locally it is as much as 

40 m thick. In outcrops along the south and east side of 

the basin, the anhydrite has been hydrated to gypsum, 

which is being or has been quarried at Rosario, San 

Ysidro, Mesita, and other localities (Weber and 

Kottlowski, 1959). 

74 Anhydrite Deposits of the United States 

Outcrops of the Todilto consist partly of laminated 

gypsum, but mostly of nodular gypsum. Anderson and 

Kirkland (1960) observed a laminated sequence of 

gypsum and limestone of marine origin. Gypsum is the 

dominant rock in the sequence in outcrop, and the dark 

laminae consist of microcrystalline calcite and minor 

amounts of bituminous matter and clastics. The overall 

purity of the unit is high; analyses showing that it contains 

92-98 percent gypsum at various localities (Weber and 

Kottlowski, 1959). In some areas, nodular gypsum is a 

significant part of the sulfate unit. Stapor (1972) 

described gypsum outcrops that are in the form of 

mounds and that consist of white, nodular gypsum interbedded with gray, fetid, laminated limestone. The 

mounds, which are flat -topped and steep-sided masses of 

gypsum 10-30 m high, were also described by Anderson 

and Kirkland (1960) and Tanner (1972); the mounds 

appear to have resulted chiefly from ground-water 

dissolution of a blanket gypsum deposit. 

Todilto gypsum also is present outside the San 

Juan basin. Small outcrops are present southeast of the 

basin, in parts of southeast Sandoval County, N. Mex., 

and in nearby areas (fig. 2.57). These occurrences are 

isolated and faulted, however, and it is unlikely that 

anhydrite underlies even a moderate-sized area. The 

equivalent Pony Express Member of the Wanakah 
l 

1_/ 

/ 

I ) 

37 o UT~_J £~LORAD2_ _ _L __ ARJZONAJNEW MEXICO 

. l 

fu.. 

::::i 

a.. 

=> 

UJ 

u 

z 

<( 

u:::: 

UJ 

0 

i 

! 

I 

106° 

f 

< ( 

) 

I 

) 

( 

0 100 MILES r-------t----------1 

0 160 KILOMETERS 

EXPLANATION 

--3- Depth to top of Todilto Formation 

in 1000's of feet (305 meters) 

- Gypsum outcrops 

Figure 2.57. Map showing distribution and depth to top of Todilto Formation in the San Juan basin area of 

northwestern New Mexico and southwestern Colorado. Shaded area shows where thick anhydrite is 

30D-1,500 m beneath the surface. Western limit of anhydrite is generalized from maps of Withington (1962), 

Staper (1972), and Tanner (1972). 

Formation crops out on the flanks of the San Juan 

Mountains and in other areas of southwest Colorado 

where undisturbed, thick anhydrite beds at moderate 

depth are unlikely. 

Todilto anhydrite is restricted mainly to the eastern 

half of the San Juan basin. The anhydrite dips gently 

northward and ranges in depth from about 300 m in 

Valencia County on the south to about 1,500 m in 

northern McKinley and Sandoval Counties (fig. 2.57). 

Throughout this area the Todilto is generally uncleformed, except .in the Puerco fault -belt area at the 

southeastern edge of the basin. In the northeastern part 

of the basin the top of the Todilto is 1,500 m to as much 

as 2,700 m below the surface. Still farther northeast, the 

Distribution and Geologic Characteristics of Anhydrite Deposits 75 
Todilto rises sharply and is present over parts of the 

Chama platform at depths of about 300 m. The Todilto 

anhydrite may be as much as 30 m thick and a little more 

than 300 m deep at various localities on the Chama 

platform. 

SUPAI SALT BASIN-SUPAI FORMATION 

A thick sequence of marine evaporites is present in 

the upper part (Lower Permian part) of the Supai 

Formation at moderate depths in east-central Arizona 

(fig. 2.1). The area is generally referred to as the Supai 

salt basin, but is also called the Holbrook basin in some 

reports. Rock salt is the dominant lithology in the upper 

member of the Supai, although anhydrite interbeds also 

occur in layers that range from 1 to 6 m in thickness. The 

evaporites of the Supai basin were described in detail by 

Peirce and Gerrard (1966) and Dean and Tung (1974), 

whereas Mytton (1973) and Johnson and Gonzales 

(1978) discussed aspects of the salt deposits as they relate 

to the storage of radioactive wastes. 

The Supai salt basin underlies about 6,000 km2 in 

Navajo and Apache Counties, Ariz., and is on the 

southern edge of the Colorado Plateau (fig. 2.58). 

A B Approximate line of cross section 

x·----x shown in figure 2.59 

Helium fields: 1 , Pinta Dome; CD 2, Navajo Springs; 3, unnamed 

34°30' r1 

I 

, __ _ 

34 °00' I )( 

A 

Bounded by the Mogollon Rim on the south, by the Black 

Mesa basin on the northwest, and by the Defiance uplift 

on the northeast, the basin contains sedimentary rocks 

that dip to the north and northeast at an angle of 0.5°-1° 

and form a dip slope called the Mogollon slope (fig. 

2.59). 

The Supai Formation, the thickest rock unit in the 

area, consists of red sandstone, siltstone, and mudstone 

interbedded with halite, anhydrite, gypsum, and potash. 

The total thickness of the Supai Formation ranges from 

about 500 m near the Arizona-New Mexico State line to 

more than 800 m n~ar Holbrook, Ariz. (Mytton, 1973). 

The Supai salt basin, a depositional center during Early 

Permian time, represents the area of maximum 

thickening of Permian strata in Arizona. A thick 

sequence of interbedded evaporites and clastics was 

deposited in shallow-marine waters that entered the 

basin from the south and that were cut off intermittently 

from the main body of seawater. 

The Supai Formation has been subdivided in the 

subsurface in this area into a lower and an upper 

member, separated by the Fort Apache Member (Peirce 

and Gerrard, 1966). Although some evaporites occur in 

the lower member and in the Fort Apache Member, the 

thickest evaporites are in the upper member of the 

110°00' 

10 20 MILES 

10 20 30 KILOMETERS 

Figure 2.58. Index map of Supai salt basin and surrounding area showing structural features and mineral deposits of 

east-central Arizona (modified from Mytton, 1973; Johnson and Gonzales, 1978). 

76 Anhydrite Deposits of the United States 
c 

u;· 

=:;o 

tT 

c 

ct. 

0 

:::s 

I» 

:::s 

Q, 

C) 

CD 

0 

0 

co 

c:;· 

(") 

:T 

I» 

; 

i 

u;· 

A 

8000 ft 

12400 ml 

6000 ft 

11800 ml 

4000 ft 

11200 ml 

2000 ft 

1600 ml 

SEA 

LEVEL 

MOGOLLON RIM 1~••-------------------------­ M 0 G 0 L L 0 N s L 0 p E 

HOLBROOK 

ANTICLINE 

~ 

I ;:;;;::;::: I J-, 1'/,, 

; 1, - , , 

1

,, r _ 

1 1 

/ V I- 1 I - 1 \ ; \ _::- M' 'issi ppi'n Redw'll limestone;,\ \ /' I ' 'I - I ,I r r r" !._ ;r - I-; r r - ' -\ '/ / ' - '- I r - r \ r I - r , I - • • ' I , '- ' / I ' I I '::_ I ~ I - I - / \ \ .,_ 1 I \ I 

II r ~ ~evon i'n M"tin Focm,ion, '" I ' ' '- I I' I-_: r I ~ ; \ I - ; -;- 1-_: \ ~~ I '.-- ' I\ I ' - r - r ', - ' I - I ' .:_ \ I Jr I I__- I/-;I I / r _; ; ::. // ' ' \ '- I \ \;I 

C'm bci,n Tonto Gmup I ' ' ' I , ' Pce;,mbci'n ' ' I I 7 , ' ' - \ - r I- '::: i/ - / ' I' / \ ' I \ ' -

'- I - I ,... ' -

10 15 20 25 MILES 

10 20 30 40 KILOMETERS 

B 

5- Figure 2.59. Generalized geologic cross section through the Supai salt basin showing position of upper member of the Supai Formation (modified from Brown and Lauth, 

2_ 1958; Johnson and Gonzales, 1978). Line of cross section A-8 is shown in figure 2.58. 

> 

:::s 

:T 

'< 

~ 

i 

c 

CD 

"0 

0 

C/) 

;; 

C/) 

..., 

..., 
formation, which lies between the Fort Apache Member 

and the overlying Permian Coconino Sandstone (fig. 

2.60). Thickness of the upper Supai ranges from about 

300 m around the perimeter of the basin to about 400 m 

near the center (fig. 2.61). The depth below ground level 

to the top of the evaporites ranges from about 180 to 

750 m; the greatest depths are found in the northeast part 

of the basin. 

1000 ft 

1305 ml 

1200 ft 

1366 ml 

COCONINO 

SANDSTONE 

SUPAI FORMATION 

Upper member 1200 ft----

["-j366-~ 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I :--------· 

I 

I 

I 

I 

I 

I I I 

I I 

I I 1400 ft I I I I 1427 mj I I 

I c 1

1 

El .2, 

8 : U I .OJ I 

-§f 

.CI 

;51 

..._ I 

0 I .._. I 

co I 

: g. : I Q: I 

1 ...._I 

I I 

I I 

I I 

I I 

I I 

I I 

I I 

I I 

I : 

I 1 

1 I __ _! : 

! 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I --------..L 

1600 ft 

1488 ml 

Fort Apache Member 

EXPlANATION 

-

Salt 

Anhydrite 

~ 

Dolomite 

D 

Shale and 

Sandstone 

Sandstone 

Figure 2.60. Composite lithologic column of upper member 

of the Supai Formation in Supai salt basin. Lithology below 

250 m (and all depth information) based upon core description 

of Scott Brothers Stratigraphic Test No.2 well, sec. 24, T. 15 N., 

R. 22 E; lithology above 250 m based upon interpretation of 

mechanical logs of Webb Resources, Inc., Mexico, and Arizona Land Co. No. 6-1 well, sec. 6, T. 14 N., R. 22 E. Location 

of wells shown on figure 2.61. 

78 Anhydrite Deposits of the United States 

Halite is the chief evaporite mineral in the upper 

Supai, although anhydrite is interbedded with the halite 

(figs. 2.60 and 2.62) and potash salts are distributed 

widely at one stratigraphic position. The thickness of 

individual halite beds ranges from 2 to 10 m at most 

places, and the layers of anhydrite are typically 1-6 m 

thick based on examination of mechanical logs and core 

descriptions; the thicker anhydrite beds are mainly near 

the top and the bottom of the evaporite sequence. 

Individual evaporite beds are laterally persistent in the 

basin; this observation is well established by our regional 

studies and by the detailed correlation (Dean and Tung, 

1974) of strata in two cores of the Supai evaporites 

drilled 8 km apart (fig. 2.62). Red-brown shale and 

siltstone beds and several beds of dolomite are interbedded with the evaporites. 

BASIN AND RANGE PROVINCE OF 

ARIZONA AND SOUTHERN NEVADA 

Structure and Geologic Framework 

The southern part of the Basin and Range Province 

in Arizona and southern Nevada contains a number of 

alluvium-filled valleys underlain by more than 2,000 m of 

Cenozoic sediments. An episode of late Miocene block 

faulting, dated by Eberly and Stanley (1978) at 12-13 

m.y. ago, created a horst-and-graben region in which the 

down-dropped blocks received thick accumulations of 

continental clastic sediments interbedded with some 

volcanic rocks and, in some grabens, thick evaporite 

deposits (Peirce, 1976; Eberly and Stanley, 1978). 

Evaporite deposits are reported in 10 of the 

troughlike basins. Thick evaporites are present in the 

Picacho, Chandler, Phoenix, Red Lake, and Virgin 

Valley basins, whereas thinner evaporite units are 

reported in the Red Rock, Tucson, Verde Valley, Tonto, 

and Safford Valley basins (fig. 2.63). Although halite or 

rock salt is reported from each of the basins, anhydrite 

has been drilled only in the Picacho, Chandler, Phoenix, 

Red Rock, Tucson, and Virgin Valley basins. The 

greatest thickness of anhydrite was found in the Picacho 

basin, where individual anhydrite beds as much as 37m 

thick are present in an 1,800-m-thick sequence that 

consists mainly of anhydrite. 

Evaporites in the region were deposited during late 

Miocene (or later) time, chiefly in the central part of each 

closed basin, but thick sequences of Miocene and postMiocene gravel, sand, and clay that envelope the evaporites were deposited in fluvial and lacustrine environments. The type of evaporite in each basin depended 

upon the chemical constituents carried into the basin by 

the then-existing drainage system. Volcanic rocks are 

interbedded locally with the nonmarine clastic sediments. 
110° 

' I I .W;n,low 

35-r I 

NAVAJO COUNTY APACHE COUNTY 

• • 

109° 

0 

<( u 

z :>< 0 LLl 

Nf::E 

5:1:3 

<r: LLl 

I 

I 

• 

z 

34°--------------------------------------~----L----------------------------------------&~L-~ 

10 

I 

I 

10 

20 

I 

I 

20 

I 

30 

30 

I 

I 

40 

40 

I 

I 

50 MILES 

I 

50 KILOMETERS 

EXPLANATION 

-BOO- Thickness of upper member-Interval 

is 100 feet (30.5 meters) 

® Wells: 

A Webb Resources 

B Scott Brothers Strat. Test No. 1 

C Scott Brothers Strat. Test No. 2 

Figure 2.61. Thickness, in feet, of upper member of the Supai Formation, and location of three wells shown in figures 

2.60 and 2.62 (modified from Peirce and Gerrard, 1966; Johnson and Gonzales, 1978). 

A nonmarine origin has been suggested for evaporites in 

the basins. On the basis of a bromine content in halite 

that is well below the threshold value indicative of marine 

halite, Eaton and others (1972) and Eberly and Stanley 

(1978) concluded that the Miocene Luke Salt Member of 

the Hickey Formation in the Phoenix basin probably was 

deposited in a saline lake. 

Picacho Basin-Miocene Evaporites 

A thick sequence of unnamed evaporites of late 

Tertiary (Miocene) age is present in the block-faulted 

Picacho basin of south-central Arizona (fig. 2.63). These 

strata consitute one of the thickest (1,800 m thick), if not 

Distribution and Geologic Characteristics of Anhydrite Deposits 79 
1000 ft 

1305 m) 

1100 ft 

1335 m) 

CORE 1 BED CORE 2 

1100 ft 

1335 m) 

1200 ft 

1366 m) 

13(){) ft 

1396 m) 

1400 ft 

1426 m) 

EXPLANATION 

-Halite 

~Anhydrite 

~Dolomite 

t==~=J Shale 

t/\\{}j Sandstone 

FEET METERS 

0 0 

20 

10 

40 

60 20 

80 

100 30 

Figure 2.62. Detailed lithologic columns of two cores 8 km 

apart showing correlation of evaporite units in part of upper 

member of the Supai Formation (modified from Dean and 

Tung, 1974). Core 1 is from Scott Brothers Stratigraphic Test 

No. 1 well, sec. 5, T. 14 N., R. 22 E; Core 2 is from Scott 

Brothers Stratigraphic Test No. 2 well, sec. 24, T. 15 N., 

R. 22 E. Locations of wells are shown in figure 2.61. 

the thickest, sequences consisting mostly of anhydrite 

reported from any part of the world. Individual anhydrite 

beds in the top 600 m of the sequence are typically 

2-10 m thick, whereas those in the lower part are 

commonly 10--37 m thick at depths ranging from about 

1,300 to 2,500 m. The occurrence of this anhydrite was 

reported by Peirce (1973, 1974, and 1976); a subsequent 

study by Eberly and Stanley (1978) summarized the 

geologic history and evaporites both here and in several 

other basins in Arizona. 

The Picacho basin, a north-northeast-trending 

structure about 50 km long and 15 km wide, is about 

90 km southeast of Phoenix in Pinal County, about 

midway between Phoenix and Tucson. The basin formed 

during late Miocene block faulting as one of a series of 

80 Anhydrite Deposits of the United States 

1w 112° __ 11o: __ .., n----7----.-' ----T T ! 

VIRGIN ,, I ,\ ; II I VALLEY.~ I ) I I l ., I ,~r-" I ! I 

36o\\_ j \ A~ R I Z 0 I N LA -l 

0\\ ' co ' I I 

REDXJ ,r--., ~ ( I I - I 

\LAKE ~ ....__,.., ( .<"! O L<> ( ', \ 

( I '-~-'f)' 'T-</ _./ \ 

\ 

~ 1 ~~~-<~ o 0 i r---suPAIIsALT\ 1 

(j) 0\\'k;(/ I ""---- BA$1N__.../ I \ ,.- 1 VERDE~ 1 --t- 1 l>! ~ VALLEY ,I '--~ ! I 

340;:_ ~ r.:' r--~, L__~ --1 

Y -----..___~ 1 ·••·· TONTO I ~ 

) ~ 1 PHOENIX ~ __l~i:~J 

f l ~L~.~.cH ~o~~~r•.·.··.s·.··.~ ... ·A·.F~:~\ ~ I "V-t- PltACHO •.• •• \; ! ' . \\ I 

( (____ 0<" __ L_~ ~REDjROC~ __ _Lj --- 1 I -tt----r- 1 

..:..,~ ,o /1 O TUCSON'd1·.·· . •··• l J 

32° """-....__ v/ rcJ 1 1 

- ' 1ft ---1 l 

f---------1100 MILES ...... -J....... .... c_~ ~. - j_ J 

<___ _l---

160 KILOMETERS 

Figure 2.63. Basins of the Basin and Range Province in 

Arizona and southern Nevada that contain major nonmarine evaporite deposits. Halite is present in all 10 basins 

(shaded), whereas anhydrite is reported from only 6 basins 

(line pattern). 

basin-and-range structures consisting of grabens or halfgrabens separated by mountain-forming horsts (Peirce, 

1976; Eberly and Stanley, 1978). 

Although most of the grabens or valleys in the 

region are filled with several thousand meters of 

conglomerate, sandstone, siltstone, claystone, and 

volcanic rock, the Picacho basin was also the site of a 

major episode of evaporite deposition during late 

Miocene time (fig. 2.64). Thick beds of anhydrite and 

some layers of salt were deposited in the central part of 

the Picacho basin, whereas the fringes of the basin 

received fluvial and lacustrine clastics. The clastics 

periodically were spread across the evaporite pan and 

became interbedded with the anhydrite layers. Overlying 

the evaporites is a sequence of red-brown claystone, 

sandstone, and conglomerate, containing a few interbeds 

of anhydrite, gypsum, and salt (Eberly and Stanley, 

1978). 

Few data are available on the structure within the 

basin, but complex features are not reported and Peirce 

(1974) pointed out that the anhydrite is not noticeably 

disturbed. 
2000 ft 

(610 ml 

SEA 

LEVEL 

NORTH-NORTHWEST 

Seismic profile 

p C A C H 0 8 A S N 

Exxon 

State (74)-1 

<>-

SOUTH-SOUTHEAST 

Pliocene and upper Miocene clastics 

2000 ft 

(610 ml 

4000 ft 

(1220 ml 

6000 ft 

(1830 ml 

8000 ft 

(2440 ml 

t I'; ;t I \ I'; 1

1 I i 

10 KILOMETERS 

Figure 2.64. Schematic cross section through Picacho basin of south-central Arizona showing thick nonmarine sequence of 

interbedded anhydrite and clastics (modified from Eberly and Stanley, 1978). 

The evaporite sequence is best understood from 

data released from a deep test hole, the Exxon State 

(74)-1, which penetrated 1,800 m of anhydrite-bearing 

strata in sec. 2, T. 8 S., R. 8 E. (figs. 2.64 and 2.65). The 

main sequence of anhydrite was penetrated between 718 

and 2,518 m, although the strata from 558-587 m also 

have been described as anhydrite on a commercial 

sample log (American Stratigraphic Company, 

AMSTRA T log D-3978). 

Anhydrite in the Exxon well is described as white in 

the upper part of the sequence and white, gray, and some 

mottled light brown below 1,353 m. The anhydrite is 

interbedded with brown and greenish-gray claystone and 

siltstone layers, along with a few thin tuff beds that are 

green and bentonitic (AMSTRAT log D-3978; Eberly 

and Stanley, 1978). Rock salt occurs in two beds above 

the main anhydrite and in four beds, 2-10m thick, in the 

depth range of 1,438-1,514 m (fig. 2.65). At depths from 

2,320 to 2,518 m, the anhydrite is white and light brown 

and contains limestone nodules, oolites, indistinct fossil 

fragments, and white and cream chert. 

Anhydrite makes up about 65 percent of the total 

thickness of strata within the 1,800-m-thick anhydrite 

sequence in the Exxon well. The percentage of anhydrite 

in the sequence generally increases with increasing depth 

(fig. 2.66). Also, both the number of anhydrite beds and 

the total number of beds in each 30 m of depth decrease 

with increasing depth (figs. 2.67 and 2.68). Because the 

amount of anhydrite increases with depth, more 

favorable thicknesses of anhydrite are likely at greater 

depths, particularly between 1,400 and 1,600 m. 

Thickness of individual anhydrite beds in the Exxon 

well ranges from 2-37 m, and many of the beds are more 

than 10 m thick (fig. 2.65). Beds in the top 592 m of the 

sequence (from 718 to 1,310 m) are typically 2-10 m 

thick, and they are interbedded with claystone and siltstone beds 2-15 m thick. In the lower part of the 

sequence, particularly at depths ranging from 1,310 to 

2,289 m, the anhydrite beds are commonly 10-37 m thick 

and are interbedded with fine clastic units 1-7 m thick. 

The maximum thickness for a single anhydrite bed is 

37m at a depth range of 1,594-1,631 m. Several other 

intervals of anhydrite beds are nearly 50 m thick, but they 

contain one or more claystone layers about 1 m thick. 

Fine- to coarse-grained clastics of probable late 

Miocene, Pliocene, Pleistocene, and Holocene age 

overlie the evaporites in the Picacho basin. The top 

110 m in the Exxon well (Eberly and Stanley, 1978) 

Distribution and Geologic Characteristics of Anhydrite Deposits 81 
1800 ft 

1549 m) 

2000 It 

1610 m) 

2200 ft 

1671 m) 

2356 ft 

1718 m) 

2400 ft 

1732 m) 

2600 ft 

1792 m) 

4200 ft 

11280 m) 

4400 It 

11341 m) 

4600 ft 

11402 m) 

4800 ft 

11463 m) 

5000 It 

11524 m) 

5000 ft 

11524 m) 

EXPlANATION 

5200 ft 

11585 m) 

5400 ft 

11646 m) 

5600 ft 

11707 m) 

5800 ft 

11768 m) 

~ 

Anhydrite 

-

Salt 

CJ 

Clay and 

other 

clastics 

FEET METERS 

0 0 

10 

50 

20 

100 30 

200 60 

Figure 2.65. Lithologic column showing selected parts of evaporite sequence penetrated by Exxon State (74)-1 well in sec. 2, 

T. 8 S., R. 8 E., in Picacho basin, Arizona. Lithology interpreted 

from mechanical logs, from American Stratigraphic Co. 

AMSTRAT log D-3978, and from descriptions of Eberly and 

Stanley (1978). 

consists of coarse unconsolidated gravels, and the 

interval from 110 to 198 m is unconsolidated sand with 

clay beds and scattered gravel lenses. From 198 to 718 m 

(top of anhydrite sequence), the strata consist mainly of 

beds of red-brown claystone that are silty and sandy and 

that contain nodules and stringers of gypsum and anhydrite; the reported occurrence of anhydrite at 558-587 m 

should be examined further. 

Chandler Basin-Miocene Evaporites 

The Chandler basin, about 40 km east of Phoenix 

in Maricopa and Pinal Counties (fig. 2.63), contains a 

82 Anhydrite Deposits of the United States 

thick sequence of evaporites in which anhydrite is the 

dominant rock type. Anhydrite beds range from 700 to 

about 1,200 m beneath the surface, and individual beds 

are reported to be 2-106 m thick. In many ways this 

deposit is similar to that of the Picacho basin, located 

about 40 km to the south. The evaporites in the Chandler 

basin were discovered in 1973 during the drilling of two 

deep boreholes, and were described briefly by Eberly and 

Stanley (1978). 

The Chandler basin is a large alluvium-filled valley 

about 50 km long and 25 km wide. The basin has had the 

same basic geologic history as have others in the arealate Miocene block faulting, followed by filling of the 

basin with gravel, sand, clay, and volcanics; and evaporite 
1200 

(/) 

a: 

w 1400 1-

w 

~ 

~ 

:i 

b: 

w 1600 

0 

2200 

2400 

20 40 60 

PERCENT OF ANHYDRITE IN 

EACH 30-METER INTERVAL 

80 100 

Figure 2.66. Graph showing percent thickness of 

anhydrite beds per 30-m interval of depth in the Exxon 

State (74)-1 well, drilled in the Picacho basin of Arizona 

(based on American Stratigraphic Co., AMSTRAT log 

D-3978). 

deposition in the central part of the basin during much of 

late Miocene time. 

Data on evaporites in the Chandler basin are 

limited to those available from the two deep boreholes 

600 

800 

1000 

1200 

(/) 

a: 

w 1400 1-

w 

~ 

~ 

:i 

1-

a.. 

w 

0 

2 3 4 5 7 

NUMBER OF ANHYDRITE BEDS 

Figure 2.67. Graph showing number of anhydrite 

beds per 30-m interval of depth in the Exxon State 

(74)-1 well, drilled in the Picacho basin of Arizona 

(based on American Stratigraphic Co., AMSTRA T log 

D-3978). 

drilled in 1973. Geothermal Kinetics Systems Corporation drilled the Power Ranches No.1 in NEY..SE¥4 sec. 1, 

T. 2 S., R. 6 E., and the Power Ranches No. 2 in 

SEY..NE¥4 of the same section in eastern Maricopa 

Distribution and Geologic Characteristics of Anhydrite Deposits 83 
(/) 

CI: 

w 

tu 

~ 

~ 

:i 

b: 

w 

Cl 

2200 

2 4 6 16 18 20 

TOTAL NUMBER OF BEDS 

Figure 2.68. Graph showing total number of beds 

(anhydrite and other rock types) per 30-m interval of 

depth in the Exxon State (74)-1 well, drilled in the 

Picacho basin of Arizona (based on American Stratigraphic Co., AMSTRAT log D-3978). 

County, Ariz. The No. 1 and No.2 wells have nearly the 

same surface elevation, and they penetrated the top of 

the anhydrite section at depths of 701 and 700 m, 

respectively. Total thickness of the anhydrite sequence is 

84 Anhydrite Deposits of the United States 

460 min well No.1 and 505 min well No.2, as shown on 

commercial sample logs (AMSTRAT logs D-4113 and 

D-4335, respectively). 

Anhydrite, which is described as being white and 

gray, contains thin stringers and partings of brown claystone and siltstone in the two wells; anhydrite beds are 

intercalated with beds of claystone, siltstone, and shale. 

Rock salt is not reported from either well. 

Based on the AMSTRAT sample logs, anhydrite 

makes up about 38 percent of the evaporite sequence in 

well No.1 and about 60 percent in well No.2. Thickness 

of individual anhydrite beds in well No. 1 typically ranges 

from 2 to 6 m, but one bed 14 m thick occurs at a depth 

of 936 m and another bed 21 m thick occurs at a depth of 

1,092 m. Many of the anhydrite beds in well No. 2 are 

2-10m thick, but in the upper part of the sequence the 

sample log indicates the following thick anhydrite units 

that contain stringers of siltstone and claystone: one bed 

30m thick at a depth of 700 m, a second bed 106m thick 

at a depth of 774 m, and a third bed 20m thick at a depth 

of 907 m. 

The percentage of anhydrite and the maximum 

thickness of anhydrite beds reported in these two sample 

logs are not consistent with each other, yet from other 

data in the area the evaporite sequence should be 

expected to correlate fairly well over the short 400-m 

distance that separates the two wells. Therefore, all data 

from these two wells must be more fully evaluated to 

establish which log most accurately represents the evaporite section at the site or if the evaporites change 

markedly over such a short distance. 

Upper Miocene and younger clastic sediments 

overlie the anhydrite and fill the Chandler basin. Both 

wells penetrate gravel and sand from the surface down to 

about 335 m; from 335 m to the top of anhydrite, they 

penetrate tan to brown claystone that is calcareous and 

bentonitic. 

Phoenix Basin-Luke Salt Member 

The Phoenix basin (also referred to as the Luke 

basin in some reports) contains a thick sequence of upper 

Miocene rock salt (halite) and shale interbeds at shallow 

depth in central Arizona (fig. 2.63). The domelike mass 

of salt is overlain by a thin sequence of anhydrite layers 

2-10 m thick at a depth of about 300 m. Beyond the 

flanks of the salt mass, anhydrite beds of similar thickness 

occur nearly 1,500 m below the surface. The salt body is 

near Luke Air Force Base, about 25 km west of Phoenix 

in Maricopa County, Ariz., and is believed to underlie 

slightly more than 100 km2 and to extend from less than 

300 m below the surface to a total depth of probably 
more than 3,500 m. Data presented here on the evaporites in the Luke Salt Member of the Hickey Formation 

are summarized from work by Eaton and others (1972), 

Mytton (1973), Peirce (1974, 1976), and Eberly and 

Stanley (1978). Johnson and Gonzales (1978) discussed 

the potential for disposal of radioactive wastes in salt 

beds in the Luke evaporites. 

An exploratory test hole drilled just east of Luke 

Air Force Base penetrated about 1,085 m of halite 

without reaching the base of the salt. The top of the salt 

is about 265 m deep in this borehole. A generalized 

lithologic log of this test hole, based on an interpretation 

of gamma ray-neutron logs by R. J. Hite of the U.S. 

Geological Survey, was presented by Mytton (1973), as 

follows: (1) top 245 m not described, (2) 20 m of 

anhydrite, (3) 150 m of halite that contains scattered 

shale interbeds 0.6-2.4 m thick, ( 4) 180 m of argillaceous 

halite, (5) 150 m of halite alternating with argillaceous 

halite, and ( 6) 400 m of halite that contains scattered 

shale interbeds 0.3-2 m thick. Several other boreholes 

have been drilled into the top of the salt, but only a few 

meters of core have been taken. 

Contact relationships between the salt and 

surrounding clastics are not yet clear, and so whether the 

salt flowed and caused diapirism is not known. The 

collapse of casing in several water wells and the presence 

of several open fissures in alluvium above the salt suggest 

that the salt may be rising and doming the overlying 

sediments (Eaton and others, 1972). 

Mechanical logs of several test holes drilled 

through the anhydrite near the crest of the salt mass 

suggest that the anhydrite occurs in beds 2-10 m thick 

and that it is interbedded chiefly with fine-grained clastics. Total thickness of the anhydrite-bearing unit in the 

several tests drilled in sec. 2, T. 2 N., R. 1 W., is 20-35 m, 

and the depth to the top of the anhydrite ranges from 300 

to 350 m. Whether the anhydrite is a cap rock consisting 

of the insoluble residue from an upward-moving and 

partly dissolved salt diapir or whether it consists of 

sedimentary layers of anhydrite is not clear. We prefer 

the latter interpretation because (1) in some places 10 m 

of non-anhydrite rock occurs between the anhydrite and 

the top of the salt, (2) anhydrite apparently is interbedded with other rock types, (3) bedded anhydrite is 

known in at least one well drilled in the Phoenix basin 

away from the thick salt mass, and ( 4) bedded anhydrite 

is known to be associated with salt in other basins of the 

region. 

In another test hole drilled 3-4 km farther west 

(Norris Oil Company No. 4 Tribal McBride, sec. 4, 

T. 2 N., R. 1 W.), anhydrite beds 2-4m thick are present 

in a sequence of strata nearly 20 m thick at a depth of 

1,465 m. Although the well was drilled to a total depth of 

2,040 m, it did not penetrate the Luke Salt Member. 

Red Rock Basin-Miocene Evaporites 

Anhydrite is reported in the Red Rock basin in 

south-central Arizona in Pinal and Pima Counties (fig. 

2.63). The basin is just east of the Picacho basin. Few 

data are available on this unnamed anhydrite unit, 

although a regional cross section by Eberly and Stanley 

(1978) showed the presence of about 150m of anhydritebearing strata of Miocene age at a depth of 900 m 

beneath the surface. These evaporites apparently have 

been penetrated only in the Elroy Development No. 1 

State (sec. 6, T. 12 S., R. 11 E.) well drilled in 1949. 

Additional data are needed to assess the general 

thickness, depth, and character of this evaporite unit. 

Because of its similarity and proximity to the Picacho 

basin this could be an important anhydrite unit. 

Tucson Basin-Miocene Evaporites 

The Tucson basin in Pima County in southeastern 

Arizona (fig. 2.63) contains an unnamed sequence of 

upper Miocene evaporites. Data on this evaporite unit 

are sparse, but Eberly and Stanley (1978) described 

abundant gypsum crystals at a depth between 564 and 

686 m and an anhydrite bed at a depth from 2,164-

2,167 min the 3,837-m-deep Exxon State (32)-1 test hole 

drilled in sec. 5, T. 16 S., R. 15 E. Other test holes in the 

Tucson basin are rather shallow, generally 300-1,000 m 

deep, and are not reported to have penetrated thick 

evaporites. 

Because the Exxon borehole was drilled on the 

eastern edge of the basin in the fan deposits, it did not 

adequately test whether a thick sequence of anhydrite 

exists at or near the depocenter. Eberly and Stanley 

(1978) postulated that the central part of the basin could 

contain thick anhydrite beds, perhaps similar in thickness 

to those of the Picacho basin, but this theory can be 

ascertained only by additional studies. 

Virgin Valley Basin-Muddy Creek 

Formation 

A thick sequence of evaporites crops out and is at 

shallow depths in the Virgin Valley basin in Clark 

County, southeastern Nevada, and its southward 

extension into the Detrital Valley of Mohave County, 

northwestern Arizona (fig. 2.63). Several hundred 

Distribution and Geologic Characteristics of Anhydrite Deposits 85 
meters of halite and glauberite are the principal evaporite rocks in the unit, although thin gypsum beds crop out 

in much of the area and anhydrite beds are reported in 

the subsurface. Rock salt was exposed at the surface in 

parts of the Virgin Valley before the formation of Lake 

Mead inundated some of the area. Salt could exist at the 

surface because annual precipitation is only 12-25 em. 

The general geology of the area and brief statements 

about the gypsum outcrops were presented by Longwell 

(1928, 1936), Mannion (1963), and Longwell and others 

(1965); the general suitability of the salts for possible 

storage of radioactive waste was summarized by Netherland, Sewell and Associates (1977) and Johnson and 

Gonzales (1978). 

Evaporites in the Virgin Valley-Detrital Valley 

area occur in the Muddy Creek Formation of late 

Tertiary (Miocene) age. Longwell and others (1965) 

stated that gypsum is abundant in outcrops of the Muddy 

Creek Formation, and that some of the beds are thick 

and extensive. Several boreholes drilled by Stauffer 

Chemical Company penetrated the evaporite section in 

Nevada and found anhydrite as a minor part of the total 

red bed-evaporite sequence (Mannion, 1963). According 

to detailed descriptions of these cores (Netherland, 

Sewell and Associates, 1977), most anhydrite occurs in 

bands and laminations that are interbedded with glauberite and shale at depths ranging from 200 m to more 

than 800 m. From these descriptions, it appears that 

individual anhydrite beds in the area may not be much 

more than several meters thick. 

Salt and adjacent rocks in the area are locally 

folded and faulted, and upward diapiric movement of salt 

is indicated by the domal bulges in which salt is or was 

exposed (Mannion, 1963). Tectonic movement along 

faults in the Las Vegas shear zone, which passes about 

30 km southwest of the evaporite mass, occurred as 

recently as 10,000 years ago, and there is evidence that 

the fault on the west side of Virgin Valley has been active 

during the Holocene (Netherland, Sewell and Associates, 

1977). 

Several boreholes drilled in the Detrital Valley 

area of northwestern Arizona found salt at a depth of 

125-180 m (Pierce and Rich, 1962). Longwell (1928) 

mentioned the occurrence of gypsum in the Muddy 

Creek Formation, but anhydrite has not been reported. 

The salt here is at least 150-210 m thick, has few 

impurities, and is largely recrystallized. Based on drilling, 

the salt is known to extend over more than several square 

kilometers. Although the salt is probably part of the 

Muddy Creek Formation, its exact relationship to the 

Virgin Valley deposit has not been established. 

Other Basins in Arizona 

Four other basins in the Basin and Range Province 

of Arizona that contain evaporites are the Red Lake, 

86 Anhydrite Deposits of the United States 

Verde Valley, Tonto, and Safford Valley basins (fig. 

2.63). Little is known about the subsurface in these 

basins, and thus knowledge of their evaporites is limited. 

The Red Lake basin in northwestern Arizona 

contains a thick mass of upper Tertiary (Miocene) rock 

salt about 450 m below the surface. The basin is in the 

northwest-trending Hualapai Valley, about 45 km north 

of Kingman in Mohave County. About 1,200 m of salt 

was drilled in one borehole, but the base of the salt was 

not reached. Geophysical work, principally based on 

gravity data, indicates that the mass of salt might extend 

about 20 km along the length of Hualapai Valley, about 

8 km perpendicular to the sides of the valley, and might 

be as thick as 3,000 m (Peirce, 1972, 1974, 1976). 

Anhydrite has not, however, been reported in this evaporite deposit. A brief discussion of this salt as a potential 

waste-repository unit was presented by Johnson and 

Gonzales (1978). 

The Verde Valley basin in central Arizona contains 

a sequence of interbedded evaporites and fine-grained 

clastic rocks in the Verde Formation of Pliocene age 

(Twenter and Metzger, 1963; Eaton and others, 1972). 

Nonmarine evaporites in this area include thenardite, 

mirabilitc, halite, and glauberite. Total thickness of the 

sequence is not known, but some beds consisting 

primarily of evaporites are as much as 20-27 m thick. 

The total area known to contain evaporites is about 

200 km2

• 

Eaton and others (1972) have shown that the 

Tonto basin contains deposits of halite. However, they 

did not present data concerning the thickness, depth, or 

character of the halite or any other evaporites that may 

be present. 

Safford Valley basin, in the southeastern part of the 

State, contains rock salt and highly saline ground water 

(Eaton and others, 1972). A test well in the area found 

rock salt from a depth of 710-713 m, underlain by clay to 

a total depth of 716 m. 

SOUTHERN NEVADA AND NEARBY 

AREAS-PERMIAN THROUGH TERTIARY 

Southern Nevada, as well as nearby parts of 

southwestern Utah, northwestern Arizona, and southeastern California, comprises a region that has many 

outcrops of gypsum beds that range in age from Permian 

through Tertiary (fig. 2.1 ). Some of the gypsum beds are 

reported to be about 30 m thick, and one is reported to 

be 30-90 m thick. Anhydrite has been found several 

meters back from the outcrop at several places. Few data 

are available on the sulfate beds in the subsurface, and 

most of the region has been deformed since deposition of 

the evaporite units. Principal references on Nevada 

include Stone and others (1920), Vanderburg (1937), 
Olson (1964), and Longwell and others (1965); 

references on Utah and Arizona are Stone and others 

(1920), Baker and others (1936), Withington (1964), 

Bissell (1969), Irwin (1971), and Rawson and Turner 

(1974); data on California are in reports by Ver Planck 

(1952) and Withington (1966). 

Most of the evaporites in the region were deposited 

in a shelf or platform environment on the east side of the 

Cordilleran geosyncline. The region lies mainly within 

the central part of the Basin and Range Province, and is 

typified by elongate north-trending mountain ranges 

separated by wide topographic basins; the eastern part of 

the region is in the Colorado Plateau. The major 

episodes of deformation and igneous activity began in the 

Cretaceous Period and continued into Tertiary time. 

Thus, most of the evaporite-bearing strata have been 

involved in mild to complex folding, thrust faulting, 

plutonic and volcanic activity, and block faulting (Longwell and others, 1965). 

Gypsum in southern Nevada is exposed in the 

uplifted blocks that form the Virgin, Muddy, Frenchman, 

and Spring Mountains. It occurs in the following 

outcropping formations: the Permian Toroweap and 

Kaibab Formations, the Triassic Moenkopi and Chinle 

Formations, the Tertiary Horse Spring and Muddy Creek 

Formations. Anhydrite has been found in some of these 

units as little as 5-60 m back from the outcrop, and 

undoubtedly it is the dominant form of sulfate in the 

moderate to deep subsurface. 

The Spring Mountains contain the Arden or Blue 

Diamond area in which gypsum beds of the Toroweap 

and Kaibab Formations commonly are 2-5m thick, but 

may be as much as 23 m thick (Longwell and others, 

1965). Gypsum beds as much as 6 m thick have been 

commercially mined here for more than 50 years. At a 

depth of 30-60 m from the surface the gypsum grades 

into anhydrite. Steeply dipping beds of gypsum more than 

15 m thick also are reported in the Kaibab Formation 

(also called Kaibab Limestone) south of this area in 

the northeast corner of San Bernardino County, Calif. 

(VerPlanck, 1952). 

Frenchman Mountain and nearby areas contain 

gypsum in the Kaibab, Moenkopi, and Horse Spring 

Formations, and deposits in these units have been mined 

intermittently since 1938. Farther north, in the Muddy 

Mountains and vicinity, gypsum is present in the Toroweap, Kaibab, Chinle, and Horse Spring Formations. 

Gypsum beds in all these areas are commonly 2-15 m 

thick, although Jones and Stone (in Stone and others, 

1920) reported that they were informed of a "massive 

body of pure white gypsum 30-90 m thick" that dips 

40°-70° in the area south of Moapa. The Virgin 

Mountains contain abundant gypsum beds. Most of them 

are in Permian strata, but some minor gypsum beds 

occur in Triassic and lower Tertiary formations. 

Southwestern U tab and northwestern Arizona 

contain gypsum and anhydrite in the Permian Toroweap 

and Kaibab Formations, the Triassic Moenkopi Formation, and the Jurassic Carmel and Curtis Formations. 

Individual sulfate beds are typically 2-10 m thick, but 

units in the Toroweap and Curtis that are predominantly 

sulfate are reported to be 30-60 m thick. Much of this 

area is on the west side of the Colorado Plateau and is 

not as deformed as the rest of the region. 

The Toroweap contains anhydrite in the subsurface 

and gypsum in outcrop from Wayne County, Utah, 

southwestward to northern Mohave County, Ariz. 

Sulfate beds are mainly in the upper part of the 

formation, and individual beds typically are 2-10 m thick. 

Rawson and Turner (1974) showed that in northwestern 

Arizona the upper part of the formation is a gypsum 

member 30-60 m thick that has thin interbeds of 

sandstone and carbonate. 

The overlying Kaibab Formation consists mainly of 

limestone, but contains much gypsum, dolomite, and red 

beds in the upper part. The upper gypsiferous member is 

commonly 30-60 m thick, and individual gypsum beds 

are typically 2-10 m thick. Withington (1964) reported 

15 m of white gypsum just south of La Verkin in 

Washington County, Utah. 

The Moenkopi Formation of southwestern Utah 

and northwestern Arizona contains thin interbeds of 

gypsum that range from 1 to 3 m in thickness. 

The Carmel Formation consists mainly of sandstone and shale, but also has interbeds of gypsum 3-15 m 

thick in much of the area. The unit is a southwestern 

extension of the thick evaporites in the Arapien 

Formation of central Utah. 

Extensive deposits of gypsum in the Curtis 

Formation crop out in parts of Iron, Washington, and 

Kane Counties of southwestern Utah. Withington 

(1964), in summarizing the occurrences in this area, 

mentioned one bed that ranges from 2 m to as much as 

30 m in thickness in the crest of anticlines, and also 

reported a location that has about 28 m of gypsum mixed 

with clay. 

In southeastern California, a series of deformed 

gypsum beds of Permian age (probably Kaibab 

Formation) occurs with metamorphosed rocks in eastern 

Riverside County (VerPlanck, 1952; Withington, 1966). 

Lenses and irregular masses of gypsum range from 2 to 

30 m in thickness and can be traced for short distances 

along the outcrop. Gypsum beds are steeply dipping and 

are intimately associated with gypsiferous schist, 

quartzit~, and other metamorphosed rocks. 

Distribution and Geologic Characteristics of Anhydrite Deposits 87 
Thus, moderately thick layers of anhydrite 

probably are present in the subsurface in parts of 

southern Nevada and nearby areas, but existing data do 

not permit an adequate description of the character, 

distribution, thickness, and depth of the anhydrite units. 

The region has been the site of structural deformation 

and igneous activity since deposition of the evaporites, 

and we are not sure if any areas exist where thick 

anhydrite is at moderate depth and is undeformed. 

Several outcropping units contain gypsum beds 

reportedly 3~90 m thick, and some of these probably 

grade into thick anhydrite units in the subsurface. 

CENTRAL UTAH-JURASSIC AND 

TERTIARY 

The Carmel, Arapien, and Summerville Formations (Jurassic) of central Utah (fig. 2.1) contain gypsum 

beds that typically are 2-10 m thick and are deformed 

locally to lenses and irregular masses as much as 3~90 m 

thick. A gypsum bed as much as 13 m thick also occurs in 

the Tertiary (Paleocene and lower Eocene) Flagstaff 

Limestone. Although all these units probably contain 

anhydrite in the subsurface, too few data are available on 

their subsurface character to confirm this. In the western 

part of this area, a thick sequence of salt in the Arapien 

Formation has flowed plastically and has distorted interbedded gypsum units along the Sevier and Sanpete 

Valleys. Principal references to Jurassic evaporites in 

central Utah are Gilliland (1951), Hardy (1952), Withington (1964), Pratt and others (1966), Moulton (1975), 

and Freeman (1976). Stanley and Collinson (1979) 

presented information on gypsum in the Flagstaff 

Limestone. 

Strata in the eastern part of the region dip gently 

off the west flank of the San Rafael swell. They are, 

however, highly distorted, folded, and faulted in the 

western part of the region where thick beds of salt were 

deposited in a rift valley and subsequently were deformed 

into complex anticlinal structures. The western half of 

the region is part of the Basin and Range Province and 

also is part of the overthrust belt. 

Gypsum beds in the Carmel and Summerville 

Formations can be traced for long distances along the 

western flank of the San Rafael swell. The Carmel 

Formation consists of 10~200 m of green shale and 

sandstone interbedded with limestone and white gypsum. 

Gypsum beds commonly range from 2 to 10 m in 

thickness and are restricted to the upper part of the 

88 Anhydrite Deposits of the United States 

formation. The Summerville, which is about 300m above 

the Carmel, is composed mainly of sandstone and siltstone, but contains a bed of gypsum as much as 3m thick. 

These undeformed strata dip gently westward and are 

about 1,000 m below the surface along the Emery-Sevier 

County line; they are 2,000--3,000 m deep across the east 

half of Sevier County. 

The Arapien Formation consists of more than 

2,500 m of evaporites and shale that fill a rift zone, 25 km 

wide and at least 100 km long, that trends northnortheast through Sevier and Sanpete Counties. Recent 

subsurface studies have shown the correlation of the 

Arapien with typical Carmel strata farther east (Moulton, 1975; Freeman, 1976). 

Outcrops of the Arapien Formation in the Sevier 

Valley consist of red and gray shales interbedded with 

sandstone, limestone, salt, and lenses of gypsum (Pratt 

and others, 1966). Gypsum beds average about 8 m in 

thickness, but some of the lenses and irregular masses 

are locally 3~90 m thick. Such anomalous thickening is 

due to plastic flow of the rock in salt anticlines that have 

steeply dipping flanks of 20°-40°. The presence of anticlinal folding in Holocene gravels in the valley shows that 

upward flowage of the plastic salt beds still continues. 

Depth to anhydrite is probably about 15-30 m in the 

anticlines, and depth to the Arapien evaporites ranges 

from 1,800 to 3,600 min the seven wells drilled into the 

salt away from the crest of the anticlines. 

The Flagstaff Limestone (Paleocene and Eocene) 

consists of limestone, dolomite, mudstone, and gypsum 

deposited in a large lake that covered much of central 

Utah (Stanley and Collinson, 1979). The gypsiferous 

interval, which is as much as 30 m thick, consists of 

nodular gypsum in dolomite and bedded gypsum with 

alternating laminae of gypsum and black-brown carbonaceous mudstone. The bedded gypsum zone is as much as 

13 m thick and can be identified over an area of about 

500 km2 in the Wasatch Plateau. 

EASTERN GREAT BASIN-PERMIAN 

A large region in the eastern part of the Great 

Basin contains gypsum and anhydrite deposits in the 

Permian Pequop and Loray Formations (fig. 2.1 ). The 

region includes parts of White Pine and Elko Counties in 

northeastern Nevada and parts of Millard, Juab, and 

Tooele Counties in northwestern Utah. Outcropping 

gypsum beds range in thickness from several meters to 

perhaps 3~60 m. A deep petroleum test well in Nevada 
penetrated a thick section of Permian gypsum and anhydrite interbedded with limestone and siltstone (Lintz, 

1957). Data on outcropping strata were presented by 

Hodgkinson (1961) and Bissell (1964, 1970). 

Strata in this part of the Basin and Range Province 

are deformed as a result of Tertiary block faulting. 

Gypsum beds, which are exposed in the uplifted 

mountain blocks, are undoubtedly present as anhydrite at 

moderate depths in the mountain blocks or where deeply 

buried in the down-dropped valleys. 

Outcrops of the Pequop and Loray Formations 

contain interbeds of gypsum in a sequence that consists 

mostly of siltstone and limestone. Most of the gypsum 

beds apparently are 2-10m thick, although Bissell (1964) 

described a 28-m -thick unit of the Loray in White Pine 

County that consists of hard gypsum and anhydrite, 

earthy gypsum, and minor interbeds of clay. Hodgkinson 

(1961) illustrates a columnar section in the Gold Hill 

district of Tooele County, Utah, where about 60 m of the 

Summit Springs is mainly alabaster gypsum that contains 

thin interbeds of dolomite. Presumably these sulfate beds 

are anhydrite at depths as shallow as 15-30 m. A large 

area on the east side of the Great Basin is underlain by 

these Permian strata, and thick, undeformed anhydrite 

beds may be present at moderate depth in some part of 

this region. 

The deep borehole reported by Lintz (1957) is the 

Standard Oil Company of California and Continental Oil 

Company No. 1 Summit Springs Unit well, and is in sec. 

32, T. 20 N., R. 60 E., in the central part of White Pine 

County, Nev. Anhydrite was first found at a depth of 457 

m in this well and was present as interbeds for the next 

1,567 m. The thicker units that are predominantly anhydrite, as reported by Lintz (1957), include 34 m (at a 

depth of 457 m), 26m (at a depth of 518 m), 46 m (at a 

depth of 566 m), and 26 m (at a depth of 1,403 m). 

Anhydrite in these units is white, and is interbedded with 

gray or red siltstone and gray limestone. This series of 

anhydrite beds is assigned to the Summit Springs Evaporite Member of the Pequop Formation. 

NORTHWESTERN NEVADA-TRIASSIC 

OR JURASSIC 

Gypsum is reported at seven separate localities in 

Pershing, Lyon, and Mineral Counties in northwestern 

Nevada (fig. 2.1). Most of the deposits are rather small, 

although several of them (especially the Empire and 

Lovelock deposits in Pershing County) are commercially 

important and have been quarried to make gypsum 

products. The geologic ages of these deposits are not 

known, but their geologic setting and general character 

are similar and all deposits are believed to be Triassic or 

Jurassic in age. Limited data on these gypsum deposits 

were given by Stone and others (1920), Olson (1964), 

Archbold (1969), and Johnson (1977). 

Gypsum outcrops in this part of the Basin and 

Range Province cover small areas that are structurally 

complex. They are typically faulted and folded, and are 

closely associated with metasedimentary rocks. The 

gypsum typically occurs as lenses or irregular beds that 

are reported to be as much as 30--60 m thick. Boreholes 

drilled in the gypsum deposits have found anhydrite at 

depths of 20--100 m below the surface. 

Thick layers of undisturbed anhydrite may be 

present in the subsurface of northwestern Nevada, but 

too few boreholes penetrate the Triassic and Jurassic 

strata of the region to allow description of the character, 

distribution, thickness, and depth of the anhydrite layers. 

Because of the general structural complexity of the 

region, special attention must be paid to the structural 

setting of any thick anhydrite subsequently discovered in 

northwestern Nevada. 

WESTERN IDAHO AND EASTERN 

OREGON-TRIASSIC 

Gypsum beds of Triassic age crop out along and 

near the Snake River in Washington County, Idaho, and 

Baker County, Oreg. (fig. 2.1 ). The gypsum occurs in 

irregular lenses as much as 10 m thick and grades into 

anhydrite at shallow depth in one of the several surface 

mines of the area. The area is structurally complex, and 

the gypsum locally is faulted and contorted and is 

associated with chlorite schist. Moore (1937) and 

McDivitt (1952) reported on these deposits. 

SOUTHERN CALIFORNIA-TERTIARY 

The southern half of California has many scattered 

but small deposits of gypsum that are of late Tertiary 

(Miocene and Pliocene) age (fig. 2.69). Individual 

gypsum beds of nonmarine origin typically range from 1 

to 10m in thickness, but lenses of gypsum are as much as 

30 m thick along the crests of folds where the rock has 

been squeezed from the flanks. Most deposits are folded 

and faulted and have moderate to steep dips. Principal 

reports on California deposits are those by Ver Planck 

(1952, 1957), Withington (1966), and Runvik (1972). 

Distribution and Geologic Characteristics of Anhydrite Deposits 89 
100 200 MILES 

160 320 KILOMETERS 

EXPLANATION 

• Gypsum deposit of Tertiary age 

X Gypsum deposit of Permian age 

Figure 2.69. Map showing location of gypsum deposits in 

southern California (modified from Ver Planck, 1952; Withington, 1962). 

The thickest deposits are in the Fish Creek 

Mountains of Imperial County where gypsum beds are 

folded and squeezed to a thickness of as much as 30 m. 

The normal dip of strata in the area is about 25°-35° 

toward the axis of a shallow synclinal basin. In an 

open-pit mine, anhydrite lenses are present at a depth of 

15m; these lenses gradually increase downward until the 

entire mass becomes anhydrite. 

Other moderately thick deposits include 3-10 m of 

gypsum in the Quatal Canyon area of Ventura County 

and 3 m of gypsum in parts of Santa Barbara and 

Ventura Counties. 

90 Anhydrite Deposits of the United States 
SECTION 3. Physical Properties of Anhydrite 

By SHARON F. DIEHL and WILLIAM Z. SAVAGE 

INTRODUCTION 

The following is a compilation of test data from the 

literature on the mechanical and thermal properties of 

anhydrite. The properties included are density, porosity, 

thermal conductivity, Young's modulus, Poisson's ratio, 

Table 3.1. Thermal properties of anhydrite 

shear modulus, and sonic velocity. The data are 

presented in tables and include brief explanations where 

necessary. Discrepancies in the thermal properties for 

anhydrite (table 3.1) are due to lithologic factors-bedding, schistosity, or fracturing, as well as to experimental 

error. 

[Leaders (- - -) indicate no data; glcm8, grams per cubic centimeter; cal!( em)( s )CCC), calories per (centimeter)( second)( degree Celsius); cal/(g)COC), 

calories per (gram)( degree Celsius)] 

Thermal 

Sample 

locality Densi~y ~onductivtty 

(g/cm ) (10- cal/(cm)(s)(°C) 

L8tchberg 2.91 

tunnel, 

Switzerland. 

Switzerland------- 2.96 

Red Sea----------- 2.83 

Do-------- 2.91 

Asmani Limestone, 

Gach Saran, Iran. 

Bancroft, Ontario, 

Canada. 

2.95 

2.94 

2.95 

2.95 

2.94 

2.95 

2.95 

2.94 

2.96 

2-94 

England---------- 2.95 

2.92 

2.93 

2.92 

2.93 

2.85 

Gulf coast------- 2.93 

New Mexico------- 2.82 

Iran-------------

13.4 

13.0 

10.8 

12.3 

8.2 

8.5 

8.4 

7.3 

7.0 

7.0 

7.8 

7.9 

8.0 

7.7 

14.1 

12.7 

13.0 

13.3 

13.5 

13.5 

13.7 

12.9 

11.7 

Heat Average coefficient 

capacity of linear 

(cal/(g)(°C) thermal expansion 

0.215 

13.1x10-6 

at 20° to 200°C 

Remarks 

Average of 3 

samples 

Red Sea site 

225; average 

of 6 samples. 

Red Sea site 

227; average 

of 3 samples 

deeper core. 

Rock probably 

contains gypsum, 

which would 

account for lower 

values of heat 

conductivity. 

Light-gray anhydrite. 

---------do---------. 

Light-pink anhydrite. 

Dolomitic anhydrite, 

>so percent CaS04. 

---------do---------

---------do---------

Gulf coast, average 

of 3 samples. 

Carlsbad, N. Mex.; 

average of 3 samples. 

References 

Clark (1966). 

Rybach (1975). 

Wheildon, Evans, 

and Girden 

(1974) 0 

Do. 

Zierfuss (1969). 

Khan (1976). 

Evans (1979). 

Bullard and 

Niblett (1951). 

Herrin and 

Clark (1956). 

Coster 094 7). 

Physical Properties of Anhydrite 91 
Table 3.2 Ultimate strength of anhydrite 

[MPa, 108 Pascals; Pa, Pascals] 

Anhydrite Confining Temperature Ultimate 

sample pressure (degrees strength locality (MPa) Celsius) (X 108 Pa) Reference 

Blaine, Okla.--- 0 24 

50 24 

100 24 

200 24 

Do------- 100 24 

100 24 

100 150 

100 150 

100 300 

100 300 

200 24 

200 24 

200 150 

200 150 

200 300 

200 300 

Germany--------- 0.1 25 

20 25 

30 25 

40 25 

50 25 

75 25 

100 25 

100 150 

50 150 

Alberta, Canada- 0 24 

17 24 

35 24 

52 24 

69 24 

Hockley Dome, 314 24 

Houston, Tex. 310 24 

329 150 

317 300 

Texas----------- 101 24 

THERMAL PROPERTIES 

Thermal conductivity is a measure of heat 

conducted in a unit time across an element of surface 

(Clark, 1966). It is a function of temperature, pressure, 

and crystallography of the mineral concerned. Seipold 

and Gutzeit (1974) determined from uniaxial tests on 

anhydrite that pressure had little effect on thermal conductivity, either perpendicular to or parallel to layering. 

Zierfuss (1969) determined that samples of 

dolomite or limestone composed of more than 50 percent 

anhydrite were the best heat conductors. He mentioned 

92 Anhydrite Deposits of the United States 

1.28 Handin and Hager 

2.76 (1957). 

3.73 

4.95 

3.73 Handin and Hager 

3.45 (1958). 

3.31 

3.24 

3.73 

4.35 

4.95 

5.17 

5.56 

5.20 

6.62 

6.03 

0.80 Muller and 

2.00 Siemes (1974). 

2.40 

2.60 

2.80 

3.40 

3.80 

3.50 

2.70 

.41 Clark (1966). 

1.08 

1. 45 

1.88 

2.08 

2.52 Do. 

5.54 

1.00 

1.82 

3.24 Do. 

porosity as an important factor because heat conductivity 

decreases as porosity increases. Robertson (1979, fig.13) 

showed the decrease of thermal conductivity with 

temperature for the temperature range 0° to 110 octo be 

-2.95 x 10-3 cal/cm sec/100 °C. 

MECHANICAL PROPERTIES 

Ultimate strength is the maximum stress difference 

a material can sustain under given conditions of pressure, 

temperature and strain rate. Ultimate strength values for 
anhydrite from various localities in the world are listed in 

table 3.2. 

The ultimate strength of anhydrite increases with 

increasing confining pressure at room temperature. 

Anhydrite behaves brittlely at or below 50 MPa confining 

pressure and at small strains (1-3 percent). Typical 

stress-strain curves for anhydrite are shown in figure 3.1. 

At 100-300 MPa confining pressure, the elastic 

limit is reached at 1-3 percent strain. Beyond the elastic 

limit, curves are nearly horizontal (fig. 3.1); there is no 

change in strength with continuing flow. At higher 

confining pressures (300-400 MPa ), work hardening (an 

increase in strength with continuing flow) is evident. 

Thus, anhydrite can undergo a large permanent deformation at high confining pressure without fracturing (fig. 

3.1). 

Muller and Briegel (1978) investigated the effect of 

temperature and strain rate on the strength of anhydrite. 

Curves for the lower "geologic" strain rates were 

extrapolated. Figure 3.2 shows that decreasing strain rate 

causes a decrease in strength for given temperatures in 

excess of 100 °C. Ultimate strength generally decreases 

as temperature rises, whereas ductility increases. 

Muller and Briegel (1977) determined the effect of 

grain size on the strength of anhydrite. Fine-grained 

anhydrite is stronger at room temperature than coarsegrained anhydrite; the opposite is true at temperatures 

higher than 400 °C. 

Anhydrite deforms by translation gliding along the 

(001) and (012) planes and by twin gliding along the 

(101) plane (Ramez, 1976). 

Stephens (1964) observed a phase transition (a 

change in optical domains) in compressing anhydrite, 

beginning at 1,960±5 MPa and ending at 3,400 MPa, 

with a volume decrease of 4.1 percent. A transition also 

was noted in a sample of rock salt containing 15.7percent 

ui 

(/) 

w 

a: 

1--

(J)_ 

~~ ;:::() 

Z(J) 

w<( 

a: a.. Wco 

~~ o-

_J 

<( 

x 

<( 

STRAIN, IN PERCENT 

500 

400 

30 

Figure 3.1. Typical stress-strain curves for anhydrite for 

various confining pressures (modified from Miller and Siemes, 

1974). 

§'g 

<{ 

u 500 (/) 

~ 

Cll8 100 -ro (/) 50 a.. w 

a: ~ 1- (/) (/) ...J 

;J. 7 10 <{ 

u i= 5 (/) 

z 

w ~ co a: 

tf:6 1 ~ u.. 0.5 Ci 

0 

8 5o 0.1 ...J 

TEMPERATURE, IN DEGREES CELSIUS 

Figure 3.2. Strength of anhydrite at 1 0-percent strain and 

different strain rates. The confining pressure is 150 MPa 

(modified from Muller and Briegel, 1978). 

anhydrite, but at a higher pressure (2,450 MPa). Kahn 

(1975) also reported a phase transition in anhydrite that 

was induced by strain from a nuclear explosion within the 

Tatum salt dome. Results from these two experiments 

indicate that a high-pressure polymorph of anhydrite 

exists. 

ELASTIC PROPERTIES 

The elastic moduli values in table 3.3 show that 

anhydrite is anisotropic along its orthorhombic crystal 

directions. The whole-rock values in table 3.4 are more 

realistic, because single crystals of anhydrite are rare in 

nature. 

The sonic-velocity values in table 3.5 are field data, 

except for the single laboratory value reported by 

Schwerdtner and others (1965). The laboratory value, 

which is based on calculations from a single crystal of 

anhydrite, is low compared with the field data. 

DISCUSSION 

Compared with halite, anhydrite has several 

advantages for nuclear-waste isolation. It has a higher 

melting point than halite, and ductile deformation occurs 

at higher temperatures. Its thermal conductivity is 

comparable to halite and its ultimate strength at low 

confining pressures is two to three times that of halite. 

However, brittle behavior at low continuing pressures 

may cause enhanced fracturing in the vicinity of the 

repository. 

Physical Properties of Anhydrite · 93 
Table 3.3. Mechanical properties of single crystals of anhydrite (modified from Schwerdtner and others, 

1965) 

[Subscripts indicate unit-cell dimensions: 1,parallel to c-ruds; 2, parallel to b-axis; and s, parallel to a-rods. GPa, 109 Pascals;] 

Young's modulus 

(GPa) 

Shear modulus 

(GPa) Poisson's ratio 

91.0 175.1 104.3 9.2 26.5 32.5 0.069 0.116 0.136 0.274 0.134 0.160 

Table 3.4 Mechanical properties of whole-rock anhydrite 

[Leaders(---) indicate no data; g/cm8 , grams per cubic centimeter; GPa, 109 Pascals; MPa, 108 Pascals] 

Porosity Young's Modulus of 

Density (volume modulus rigidity Poisson's 

(g/cm3) percent) (GPa) (GPa) ratio 

2.93 0.44 12.0 

2.93 .54 26.0 

3.02 72.0 to 28.0 0.295 

74.0 

75.0 .250 

• 385 to 

.323 

Table 3.5 Sonic velocities of anhydrite 

[km/s, kilometers per second] 

Sonic 

velocity 

(km/s) Remarks 

Cohesion 

(MPa) 

43.0 

42.0 

4.10 

5.00 

3.51 

4. 64 

4. 95 

United States midcontinent and Gulf Coast 

Bashkir and Tatar, USSR-----------------

Average of 3 samples; Red Sea site 225---

Average of 3 samples; Red Sea site 227---

94 Anhydrite Deposits of the United States 

Remarks References 

Sample 95.0 Muller and 

percent CaS04• Briegel (1977). 

Sample 90.8 Do. 

percent CaS04. 

Clark (1966). 

Hofer and Menzel 

(1964). 

Link (1962) • 

References 

Clark (1966). 

Do. 

Schwerdtner and others (1965). 

Wheildon and others (1974). 

Do. 
SECTION 4. Hydrogeology of Anhydrite 

By WILLIAM THORDARSON 

Data are sparse on the hydrogeology of anhydrite. 

Therefore, only information on the general hydrogeologic properties of anhydrite as observed in outcrops, 

tunnels, mines, wells, and springs is presented. 

POROSITY, HYDRAULIC CONDUCTIVITY, 

AND TRANSMISSIVITY OF ANHYDRITE 

Anhydrite is apparently a confining bed if it has no 

fractures and permeable interbeds and if it has not been 

dissolved or hydrated to gypsum. Fractures depend both 

on how the anhydrite was formed and on how much it has 

been structurally deformed. For example, bedded anhydrite may have few fractures, whereas anhydrite in the 

cap rock of salt domes may have many fractures because 

of considerable structural deformation. Permeable interbeds or permeable impurities in anhydrite may consist of 

salt, sandstone, siltstone, or limestone. Dissolution of 

anhydrite or associated gypsum by ground water may 

form openings along bedding planes, widened fractures, 

karst holes, or even intercrystalline holes. 

The data presented here on porosity, hydraulic 

conductivity, and transmissivity of bedded anhydrite, 

anhydrite in the cap rock of salt domes, and gypsum are 

from tunnels, mines, wells, and springs (table 4.1). 

Hydraulic Characteristics of 

Bedded Anhydrite 

lntercrystalline porosity and hydraulic 

conductivity 

Data for the intercrystalline porosity of bedded 

anhydrite and bedded gypsum from a few scattered 

localities in the United States and elsewhere is presented 

in table 4.2. The geologic sources of the samples are not 

well described, and some may be from cap rock of salt 

domes. The purity of the samples is not described, except 

for the samples of dolomitic anhydrite from Switzerland 

that are 55-95 percent anhydrite. The mean intercrystalline porosity of 37 samples of bedded anhydrite is 1.1 

percent, and the range is from 0.0 to 4.7 percent. The 

mean intercrystalline porosity of 34 samples of bedded 

gypsum is 15.9 percent, and the range is from 0.1 to 24.8 

percent. 

The intracrystalline porosity within cleavage planes 

of anhydrite crystals contained in dolomite of the San 

Andres Limestone, N. Mex., is the same as or greater 

than the intercrystalline porosity between dolomite 

crystals (Waldschmidt and others, 1956). Nodular anhydrite in the Prairie Formation in the Williston basin of 

Canada may have a permeable granular matrix but the 

organic matrix may be more impermeable than the 

granular matrix (Shearman and Fuller, 1969). 

The intercrystalline hydraulic conductivity of 

bedded anhydrite is probably extremely low because 

anhydrite beds make impermeable seals in many oil 

fields. The low intercrystalline hydraulic conductivity of 

bedded anhydrite may be due primarily to the dense 

fabric of compacted, flat, lath-shaped anhydrite crystals 

(Shearman and Fuller, 1969). A dolomitic anhydrite in 

the Wellington Formation, Okla., had a hydraulic 

conductivity that was nearly zero (Blazenko, 1964). Ibrahim and Katz (1972) also reported a sample of anhydrite 

with a hydraulic conductivity equal to zero, as indicated 

by unsuccessful injection of mercury in a porosity test. 

Fracture porosity and hydraulic conductivity 

The following observations suggest that the 

fracture porosity of bedded anhydrite is probably 

extremely low. Bedded anhydrite forms an impermeable 

seal for oil in many oil fields (Edie, 1958; Sharma, 1966; 

Ells, 1967; Shearman and Fuller, 1969). A layer of 

anhydrite and dolomite in Michigan acts as a seal that 

prevents dissolution of underlying salt (Dellwig, 1955). 

Fractures are common in limestones in the oil fields of 

Saskatchewan, Canada, but they are absent or rare in 

associated anhydrite beds (Edie, 1958). Impermeable 

anhydrite makes up 45 percent of the Cedar Keys 

Limestone in Florida (Wilson and others, 1973). 

Hydraulic characteristics of either anhydrite or limestone 

in the Cedar Keys Limestone could not be determined 

during hydraulic injection tests in a single well. 

Therefore, the fracture porosity of bedded anhydrite 

generally is inferred to be low, even though quantitative 

laboratory measurements have not been made. 

Hydrogeology of Anhydrite 95 
~ Table 4.1. Hydrologic data from tunnels, mines, wells, and springs 

> :J 

:::T 

'< 

[yr, year; km, kilometer; m, meter; em, centimeter; L/min, liters per minute; m8

, cubic meters; m2

, square meters) 

~ 

; 

c 

C'D 

'8 

til 

:::+ 

til 

2. 

... 

:::T 

C'D 

c: 

2. 

[ 

til 

~ 

Location 

Water-diversion tunnel, 

La Lechere, France. 

Railway tunnel, 

Le Braus, France. 

Water-diversion tunnel, 

Tignes, France. 

Water-diversion tunnel, 

La Courbaisse, France. 

Do----------

Water-diversion 

tunnel, Saint-Jean 

Maurienne, France. 

Formation 

and age 

Unknown----------

-----do-----

-----do-----

-----do-----

Triassic----

Triassic----

Rock type 

Anhydrite--

Anhydrite--

Anhydrite; 

shale. 

Anhydrite--

Anhydrite; 

Anhydrite; 

gypsum; 

dolomitic 

limestone 

in diapir. 

Comments Reference 

Walls and ceiling have not expanded and Sahores {1962). 

no rockfalls have occurred in 10 yr. 

In one place, water seeps through 

sandy beds in anhydrite and hydrates 

it to gypsum. 

100 m from the entrance, abundant flow Do. 

of water streams down wall, but no 

expansion has occurred. Other places 

have permeable interbeds of sand or 

clay, and gypsification of anhydrite 

has formed slabs of raised crust on wall. 

In 40 yr, walls arched inward or caved 

in, floor raised or lowered 0.5 m, 

and pillars dislocated. 

Anhydrite appears perfectly dry and dense 

without visible fractures, but contains 

many veins of gypsum. Shale surrounding 

anhydrite is highly fractured and has 

abundant inflows of water. 

Anhydrite has marked schistosity and a 

network of open fractures. Gypsum 

growing in fractures pushes blocks 

off wall. 

Anhydrite is dense and completely dry 

for 750 m. Gypsum in pulverized 

chaotic zone 80 m long has inflows 

of water in roof. Rock bursts in 

anhydrite may or may not be due to 

expansion during gypsification. 

Triassic is completely dry; impervious 

cover of shales of Liassic protected 

Triassic from infiltration of water. 

Do. 

Do. 

Gignoux and 

Barbier 

(1955). 

Gignoux and 

Barbier 

(1955). 
:::1: 

~ 

0 

cc 

CD 

0 

0 

cc 

"< 

g, 

)> 

~ 

;r 

~ ; 

co 

...... 

Hauenstein tunnel, 

Germany. 

Kappelisberg tunnel 

Potash mines, 

Germany. 

Mine of Grozon, near 

Arbois, France. 

Mine, Victor, N.Y. 

Mines, Oakfield, 

N.Y. 

Mines, Akron, N.Y. 

Shaft, Buffalo, N.Y. 

Mine, Garbutt, N.Y. 

Do----------

Mine, Akron, N.Y. 

Mine, Fletcherville, 

Ohio. 

Mine, Holston Valley, 

Va. 

Mine, Fort Dodge 

Iowa. 

-----do-----

-----do-----

Permian-----

Not reported 

Camillus Shale, 

Salina Group, 

Silurian. 

-----do-----

-----do-----

-----do-----

Camillus Shale, 

Silurian. 

-----do-----

-----do-----

Not reported 

Anhydrite--

----do-----

Anhydrite in 

salt diapir. 

Anhydrite--

Gypsum--

---do---

---do---

---do---

Gypsum---

---do---

---do---

---do---

Maccrady Formation, ---do---

Mississippian. 

Not reported ---do---

Heaving of rock floor may or may not be 

due to inflows of water. 

------------------do------------------

Flows of brine as much as 30 L/min 

and some gas. Flows decreased 

over periods of days or years. 

8-m-wide mine with flat ceiling; 

never had rockfalls during period of 

more than 100 yr despite abundant 

condensation from air that coats 

anhydrite with film of water. Thin 

film of gypsum only. 

Minor water seepage except for 

large amount of water in upper 9 m 

of shaft. 

Much water in mines--------------------

Small flow of water in mines-----------

Water in gypsum layer at depth of 13-

14 m; 10,900-m3-per-day pump 

could not draw down water in 6-m2 

shaft. 

Some water in mines---------------------

Mine is dry-----------------------------

Considerable water inflow; 21,800 m3 

per day pumped from shaft when 

first opened; now pumping much less. 

Considerable water pumped from mine-----

Workings filled with water--------------

Water pumped from sumps into underground 

channel in gypsum. 

Bendel (1948). 

Do. 

Baar (1977). 

Sahores (1962). 

Newland (1929); 

Lintner (1937) 

Newland (1929). 

Do. 

Do. 

Newland and 

Leighton (1910: 

Do. 

Do. 

Adams and otherE 

(1904). 

Do. 

Do. 
~ Table 4.1. Data from tunnels, mines, wells, and springs-Continued 

)> 

:;, 

::r 

l 

i 

i , 

0 

0 

;: 

0 

-:;: 

CD 

c: 

:;, 

~ 

i 

0 

Location 

Mine, Centerville, 

Iowa. 

Shaft, northeast 

Michigan. 

Quarry, Northern 

peninsula, Michigan. 

Mine, Ontario, 

Canada. 

Mine, Caledonia, 

Ontario, Canada. 

Mine, Hockley salt 

dome, Houston, Tex. 

Well, ERDA No. 6, 

New Mexico. 

Well, ERDA No. 8, 

New Mexico. 

Well, ERDA No. 9, 

New Mexico. 

Belco oil well, 

New Mexico. 

Shell Bootleg well, 

New Mexico. 

Formation 

and age 

-----do-----

Rock type 

---do---

Michigan Formation, ---do---

Mississippian. 

Salina Group, 

Silurian. 

Camillus Shale, 

Silurian. 

-----do-----

Cap rock of salt 

dome. 

Castile Formation, 

Permian. 

-----do-----

-----do-----

-----do-----

-----do-----

---do---

---do---

---do---

Gypsum---

Anhydrite--

---do---

---do---

---do---

---do---

Comments 

Some water near surface. Artesian water 

in shaft flows 300 m3 per day from 

1.2-m-thick limestone overlying gypsum. 

Inflowing water flooded shaft-----------

Water in quarry is source of trouble----

Great inflows during sinking shaft to 35- m depth. 

Unsuccessful attempt to sink shaft due to 

trouble from ground water. 

Gypsum nearly watertight; only minor 

water seeps into mine; difficulty sinking 

shaft due to considerable water leakage 

from overlying unconsolidated sediments 

and cavernous limestone cap rock. 

Significant flow of brine containi.ng 

Na2so4 and H2s-rich gas at 

depth of 826 m; no observed decrease 

in flow during first 10 days, possibly 

a brine pocket. 

No flow of fluid in drill-stem test. 

-------------------do-------------------

Significant flow of brine and H2s gas 

decreased over 1- to 2-day flow period, 

indicating brine was in pocket. 

Flow of brine decreased over several days 

indicating brine was in pocket. 

Reference 

Stone and otherb 

(1920); Kay 

(1915). 

Grimsley (1904). 

Do. 

Cole (1925). 

Dyer (1925). 

Stenzel (1943). 

Lambert and 

Mercer (1977); 

Powers and 

others (1978). 

Do. 

Do. 

Lambert and 

Mercer (1977). 

J. W. Mercer 

(written 

commun. , 1980) 
::t 

~ 

c8 

~ 0 

co 

"< 

2. 

,. 

:::s 

::r 

l 

ii 

co 

co 

Oil well, sec. 23, 

T. 24 S., R. 29 E., 

New Mexico. 

Oil well, Sec. 3, 

T. 24 S. , R. 29 E., 

New Mexico 

Hole No. 3, sec. 26, 

T. 20 S., R. 26 E., 

New Mexico. 

Castile Springs, 

Culberson County, 

Tex. 

Stinking Spring, 

Culberson County, 

Tex. 

Major Johnson Springs, 

Pecos River, N. Mex. 

Dillon No. 91 oil 

well, Pine Island 

oil field, Caddo 

Parish, La. 

Well, Michigan---

Well, Holston Valley 

Va. 

Do---------

Black River Springs, 

Pecos Valley, 

N. Mex. 

Blue Springs, Pecos 

Valley, N. Mex. 

-----do-----

-----do-----

Castile Formation, 

Permian. 

-----do-----

-----do-----

Seven Rivers 

Formation, 

Permian. 

Ferry Lake Anhydrite, Cretaceous. 

---do---

---do---

Gypsum, 

anhydrite, 

sandy clay, 

cave breccia. 

Anhydrite 

and gypsum. 

-----do-----

Gypsum and 

dolomite. 

Anhydrite 

and 

limestone. 

Michigan Formation, Gypsum---

Mississippian. 

Maccrady Formation 

Mississippian. 

-------do--------

Unknown----------

-------do--------

Gypsum and 

salt. 

-----do----

Gypsum---

Gypsum and 

limestone. 

Slight show of gas and hole full of salt 

water at depth of 559-561 m. 

Exceptionally large yield of brine at 

depth of 526 m. 

Injection tests in 62-m deep well 

indicated very low to low trans 

missivity, hydraulic conductivity 

greatest in cave breccia. 

May be artesian water from Delaware 

Mountain Group aquifer that underlies 

Castile Formation. 

-------------------do-------------------

Average 24,000 m3-per-day discharge; 

artesian water from leakage in gypusm 

at Lake McMillan 4.8-6.4 km to north. 

Tritium tracer test showed travel 

time between lake and springs to be 

about 3 months. 

14 m3-per-day of oil from well 

completed in anhydrite. 

Strong pumps would be needed to mine 

gypsum. 

Dry to total depth of 83 m--------------

Brine at depth of 59 m------------------

Spring----------------------------------

Spring----------------------------------

Cooper (1962). 

Do. 

Meinzer and 

others (1927). 

Davis and 

Kirkland (1970) 

Do. 

Cox (1967); 

Meinzer and 

others (1927); 

Reeder and 

Thatcher (1963) 

Crider (1929); 

Spooner, (1935) 

Grimsley (1904). 

Eckel (1903). 

Do. 

Lee {1925). 

Lee {1925). 
0 Table 4.1. Data from tunnels, mines, wells, and springs-Continued 0 

> :I 

:t' 

'< 

~ 

;: 

i , 

0 

0 

;: 

2. 

g: 

CD 

c: 

:I 

;: 

Q. 

~ S" 

0 

Location 

Springs, Virginia----

Salt springs, western 

Kansas and Oklahoma. 

Big Gypsum Cave, 

Evansville, Kans. 

Springs, Axel Heiberg 

Island, Canada. 

Formation Rock type 

and age 

Maccrady Formation Gypsum------

Mississippian. 

Permian--- Red beds, 

salt, and 

anhydrite. 

Medicine Lodge Gypsum------

Gypsum Member, 

Blaine Formation, 

Permian. 

Permian--- Anhydrite---

Comments 

Springs containing high sulfate; may 

originate in gypsum. 

Salt springs from dissolved salt and 

anhydrite flow from red beds. 

Stream flows though gypsum cave. 

Saline springs in center of Base Camp 

Diapir. 

Reference 

Withington 

(1965). 

Frye and Schof 

(1942). 

Grimsley and 

Bailey (1899) 

Hoen (1964). 
Table 4.2 lntercrystalline porosity of bedded anhydrite. 

[Leaders ( ---) indicate insufficient data) 

Number 

of 

samples 

Porosity in 

percent 

Geologic source Mean Range Reference 

Anhydrite, United States------- 2 3.4 

Do--------------- 1 o.o 

Dolomitic anhydrite, Okla.---- Well log 

Dolomitic anhydrite, Switzerland 13 0.7 

Anhydrite, Iran---------------- 21 1.1 

Gypsum, United States--------- 2 2.6 

Anhydritic gypsum, Switzerland- 1 0.1 

Soft gypsum, France------------ 30 17 

Gypsum, U.s.s.R.--------------- 1 24.8 

Some data on hydraulic conductivity and transmissivity of fractures in bedded anhydrite are available in the 

literature (table 4.1) and are described next. 

Injection tests in a 62-m-deep well in New Mexico 

showed that gypsum, anhydrite, sandy clay, and breccia in 

the Castile Formation have a low transmissivity (Meinzer 

and others, 1927), as indicated by a low rate of injection 

of water (1.3 L/min (liters per minute)) in the bottom 

25 m of the hole. 

Some wells have tapped brine and gas in anhydrite 

of the Castile Formation at depths between 526 and 823 

m. These wells include several oil wells (Cooper, 1962; 

Lambert and Mercer, 1977; Powers and others, 1978) 

and one test well, ERDA No. 6. In two oil wells, the flow 

of brine decreased over a 1- to 2-day flow period, which 

suggests that the brine is contained in a pocket or 

fractures or in solution cavities nearby. The brine in the 

ERDA No. 6 well is between 570,000 and 1,000,000 

years old, but the connection to the underlying aquifer of 

the Delaware Mountain Group is unknown (Powers and 

others, 1978). The concentration of deuterium and 

oxygen-18 isotopes in brine in the ERDA No. 6 well 

indicate that the brine is not from a meteoric source or 

from evaporation of meteoric water or sea water; the 

composition of the brine probably is related to exchange 

between clay in the rock and water (Lambert, 1978). 

In drill-stem tests of two other test wells, ERDA 

No. 8 and ERDA No. 9, in anhydrite of the Castile 

Formation, the anhydrite did not yield water from 

fractures (Lambert and Mercer, 1977; Powers and 

others, 1978). 

Two wells were drilled in gypsum and salt in the 

Holston Valley in Virginia; one well was dry, but brine 

was found at 59 min one well (Eckel, 1903). 

Ground water has flowed from isolated reservoirs 

in fractured bedded anhydrite in mines in salt diapirs and 

salt deposits of the Zechstein Formation (Permian) in 

Germany (Baar, 1977). The initial outflow of brine was 

2.8-4.0 Raymer and Biggs (1963). 

Ibrahim and Katz (1972). 

1.0-3.0 Blazenko (1964). 

0.2-1.3 Mueller and Briegel (1977). 

0.1-4.7 Zierfuss (1969). 

1.3-4.0 Meinzer (1923). 

Mueller and Briegel (1977). 

Baron and others (1963). 

Shreiner and others (1967). 

either a maximum flow under high gas pressure, or the 

outflow gradually reached a maximum flow. The flow 

gradually decreased to a low flow rate during a period 

ranging from days to more than 10 years. The fractures 

apparently are poorly connected hydraulically as indicated by the decrease in flow rate with time. For example, 

a drill hole hit a fissured system in anhydrite at a depth of 

578 m. The initial outflow of brine was 4 L/min, but 

decreased to 0.5 L/min in 3 days. This isolated reservoir 

had a small volume of brine. An adit in a potash mine hit 

a fractured dipping anhydrite bed at a depth of 794 m. A 

flow of brine increased for 6 months to a maximum flow 

rate of 30 L/min, and then decreased gradually for 13 

years to a low rate of 1 L/min. In another mine, the inital 

flow rate from a fractured bed of anhydrite was 20 L/min, 

but decreased to 5 L/min after 2.5 years. Pressure 

grouting that was done in an attempt to stop the flow in 

this mine caused the flow rate to increase rather than to 

decrease. Anhydrite beds may be pulled apart by salt 

flowage during tectonic deformation causing possible 

increases in fracture porosity (Baar, 1977). 

Ground water in many gypsum mines in New York, 

Iowa, Virginia, and Canada flowed either from fractures 

or from solution cavities in the gypsum (table 4.1 ). 

Records of water inflow are not available for many 

gypsum mines, perhaps because water inflows were too 

minor to report. During sinking of some shafts in gypsum 

mines, large inflows of water from overlying sedimentary 

rocks either impeded the work or caused abandonment 

of the mine (table 4.1). 

Some data are available on the occurrence of 

ground water in anhydrite in tunnels that have been 

driven through anhydrite rocks in France and Switzerland. Anhydrite and gypsum in the waterdiversion tunnel at Saint-Jean-de-Maurienne, France 

were completely dry because they underlie an impervious 

cover of Lias shale (table 4.1; Gignoux and Barbier, 

1955). Anhydrite in the water-diversion tunnel of the 

Hydrogeology of Anhydrite 101 
factory near La Courbaisse, France, was dense and 

completely dry for a distance of 750 m, but gypsum was 

found in a pulverized chaotic zone that had inflows of 

water in the roof (table 4.1; Gignoux and Barbier, 1955). 

Anhydrite, in the water-diversion tunnel near Tignes, 

France, appeared dry and dense and without visible open 

fractures, but it contained many veins of gypsum that 

sealed out water, thus preventing abundant water in the 

surrounding fractured shales from flowing through the 

anhydrite (table 4.1; Sahores, 1962). Hydration of anhydrite to gypsum in the Hauenstein and the Kappelisberg 

tunnels may or may not have caused expansion of the 

tunnel floor (Bendel, 1948). Rock bursts of anhydrite in 

the water-diversion tunnel of the factory near La Courbaisse, France, have been attributed to the expansion of 

anhydrite after hydration to gypsum (table 4.1; Gignoux 

and Barbier, 1955). However, in some tunnels and mines 

in France, the anhydrite heaves due to deformation 

pressures, and little expansion due to hydration to 

gypsum occurs; an exception is the railway tunnel near Le 

Bra us, France, where raised slabs of gypsum occur on the 

walls. 

The preceding observations indicate that bedded 

anhydrite may yield either minor amounts of water or no 

flowing water from fractures; therefore, the hydraulic 

conductivity and transmissivity of bedded anhydrite 

through fractures are low to extremely low. Because 

measurements of actual flows of water are not available, 

no estimates of values of hydraulic conductivity or transmissivity can be made. 

The presence of gypsum or anhydrite in fractures 

indicates that water has flowed through or is flowing 

through anhydrite. In such places, ground water is likely 

to flow again or to continue to flow. For example, if 

fractures that are filled with gypsum are opened again by 

earth movements, then water probably will flow again 

from the fractures until they are resealed by gypsum. In 

the unsaturated zone of downward ground-water 

movement, hydration of anhydrite to gypsum probably 

takes place along fractures; the fractures are first 

widened by solution, and then anhydrite between the 

fractures is altered to gypsum (Lotze, 1957; Olive, 1957). 

Anhydrite either may be deformed plastically with 

no apparent fractures or may be fractured or faulted 

(Lotze, 1957; Laubscher, 1975). Basement faults in the 

Gulf Coastal Plain terminate in the ductile anhydrite in 

the Buckner Formation. The Buckner anhydrite may 

have flowed significantly during Early Cretaceous time, 

as indicated by the disappearance of a conjugate pair of 

small faults in anhydrite in the Cretaceous Glen Rose 

Formation in the Blackfoot Field, Anderson County, Tex. 

(Fowler, 1964). 

Gypsum veins may have originated within anhydrite and other rocks due either to mechanical force of 

102 Anhydrite Deposits of the United States 

crystallization or to high-pressured water that pushed 

apart the rock. Hypothetically, in high-pressured water, 

as the rocks are exhumed by erosion the lithostatic rock 

pressure lessens, but the fluid pressure is available to 

fracture the rocks by the hydraulic injection of water 

(Shearman and others, 1972). 

Hydraulic Characteristics of Anhydrite in 

Cap Rock of Salt Domes 

Anhydrite occurs in the cap rocks of salt domes 

where it is concentrated when solution of the upper part 

of the salt leaves grains of insoluble anhydrite that had 

been disseminated in the salt (Hoy and others, 1962; 

Bodenlos, 1970). Gypsum and limestone usually overlie 

the anhydrite; the gypsum is the result of the hydration of 

anhydrite by ground water, and the limestone overlying 

the gypsum is formed as a byproduct of bacterial sulfate 

reduction. The anhydrite in the cap rock is different from 

the laminated and nodular anhydrite in bedded-anhydrite 

deposits. The cap rock has a gneissic texture that is cut by 

many horizontal, vertical, and diagonal fractures. Most 

anhydrite along these fractures is hydrated to gypsum. In 

addition, the production of native sulfur throughout the 

cap rock has in places created porosity due to dissolution 

of anhydrite. 

lntercrystalline porosity in cap rock of salt domes 

The porosity of anhydrite in the cap rock is low 

compared with the porosity of the gypsum and limestone 

cap rocks that are above the anhydrite (Marx, 1936). The 

gypsum and limestone are porous and cavernous, and, in 

places, caverns or anhydrite sand are found at the contact 

of the anhydrite with the salt below (Judson and Stamey, 

1933; O'Donnell, 1935; Taylor, 1937). Reported 

measurements of intercrystalline porosity in cap rock are 

not available, but, where the anhydrite is dense and does 

not contain sulfur or gypsum, the intercrystalline porosity 

is probably low. Any gypsum that is present may or may 

not increase the porosity of the anhydrite. 

The intercrystalline porosity of some anhydrite in 

the cap rock is increased by widening of the cleavage in 

anhydrite crystals; the result is called emphasized 

cleavage (Goldman, 1952). Emphasized cleavage may 

form early in the deformation of anhydrite before stress 

becomes strong enough to produce fractures. 

Fracture porosity in cap rock of salt domes 

Reported measurements of fracture porosity or of 

fracture transmissivity in anhydrite of cap rock are not 
available. The numerous fractures in the anhydrite, 

however, suggest that the values of fracture porosity and 

fracture transmissivity probably are much greater than 

those in bedded anhydrite. Faults in anhydrite cap rock 

may be filled by porous anhydrite sand (O'Donnell, 

1935). 

Gypsum at a depth of 60 m below the surface in a 

mine in the cap rock of the Hockley salt dome is nearly 

watertight and contains only minor water seeps (Stenzel, 

1943). These seeps may come either from fractures or 

from solution openings in the gypsum. 

Stalactites in the roof and salt bubbles on the floor 

of the Carey salt mine, which is about 90 m below the 

anhydrite cap rock in the Winnfield salt dome, probably 

were created by drips from brine from inclusions in the 

salt or brine in fractures in the salt under the anhydrite 

cap rock (Hoy and others, 1962). 

GENERAL HYDROGEOLOGY OF 

ANHYDRITE 

Many general factors determine the hydrogeology 

of a particular anhydrite bed. These include the type of 

ground-water basin; the distribution, movement, and 

discharge of water in the basin; the position of the water 

table; the presence of water in the unsaturated zone and 

sinkholes above the water table; the presence of artesian 

aquifers or confining beds above, below, or lateral to the 

anhydrite bed; and chemical and microbiological reactions that take place in anhydrite. 

The type of ground-water basin controls the 

distribution, movement, and discharge of ground water in 

artesian aquifers, fractures, and solution openings near 

or in anhydrite. At least three different types of artesian 

ground-water basins that contain anhydrite are known: 

(1) basins in which the flow of artesian water is from one 

side of the basin to the other; (2) basins in which the flow 

of artesian water is from both sides of the basin toward 

the center of the basin; (3) basins in which the flow of 

artesian water is from the center of the basin toward the 

sides of the basin (Drescher, 1965). The first type of 

basin is represented by the Delaware and Paradox basins; 

the second is represented by intermontane basins of the 

Southwest; and the third is represented by the Michigan 

basin. Movement of ground water in most basins is 

complex. Water may move along bedding or vertically 

across bedding through fractures, interstices, or semipermeable membranes of shale beds. Water may be 

discharged through springs or through underflow to 

another basin. In some basins, the presence of chlorideor sulfate-rich waters in springs or wells indicate that salt, 

anhydrite, or gypsum is being dissolved. 

Fracturing of anhydrite or dissolution of anhydrite 

by thermal waters may be related to igneous activity or 

structural deformation during the hydrogeological 

history of a ground-water basin. The association of 

extrusive and intrusive igneous rocks with evaporite 

rocks and with the faulted basement that underlies 

evaporite rocks has been reported by many geologists 

(Hoen, 1964; Tazieff, 1970; Wilson, 1975). Diapirs are 

common in evaporite deposits, especially in structurally 

deformed rocks (Hoen, 1964; Henry and Zolnai, 1971). 

The positions of the water table or potentiometric 

surface determine the possibility for forming caverns or 

sinkholes. Descending water in the unsaturated zone or 

ascending artesian flow of water through anhydrite may 

cause solution. Solution and collapse features may also 

occur where fractures connect pressurized freshwater 

aquifers and evaporites, or where evaporites are in 

contact laterally with freshwater aquifers. Mechanisms 

for lateral and vertical dissolution of evaporites linked 

hydraulically with undersaturated aquifers and recognition of features created by these mechanisms have been 

described by Anderson (1978), Anderson and others 

(1978), and Anderson and Kirkland (1980). 

Artesian aquifers or confining beds may occur 

above, below, or lateral to anhydrite beds. Anhydrite 

beds commonly are overlain either by carbonate rocks 

that may be artesian aquifers or by salt beds that may be 

impermeable. Krumbein (1951) has described anhydrite 

deposits that are bounded above or below by either red 

beds or marine beds. Aquifers near evaporite deposits 

described by Johnson and Gonzales (1978), and artesian 

aquifers near salt domes that have anhydrite cap rocks 

were described by Anderson and others (1973). 

Several chemical and bacterial reactions can alter 

anhydrite to gypsum, calcite, and (or) sulfur. Native 

sulfur occurs in gypsum, anhydrite, limestone, and 

dolomite of the cap rock overlying salt domes in the Gulf 

coastal plain (Ellison, 1971). Bacteria that live on 

hydrocarbons reduce the sulfate from gypsum and anhydrite to hydrogen sulfide, which then is reoxidized to 

native sulfur, possibly by reaction with sulfate (Feely and 

Kulp, 1957), but more likely by reaction with elemental 

oxygen (Davis and Kirkland, 1970; Kirkland and Evans, 

1976). In this same reaction calcite is formed, as in the 

following reaction (Davis and Kirkland, 1970): 

CaSs + COz + HzO--- > 4S + CaC03 + HzS. Limestone 

buttes or castiles are large, vertical pipelike masses of 

calcite that have replaced gypsum and anhydrite in the 

Castile Formation in the Delaware basin of New Mexico 

and Texas. The castiles probably were formed by sulfatereducing bacteria that subsisted on hydrocarbons in 

artesian ground water that rose along fractures (Davis 

and Kirkland, 19_70). The calcite in the castiles has some 

porosity; therefore, large castiles form the reservoir rock 

for several shallow oil fields in the Castile Formation 

(West Texas Geological Society, 1960). 

Hydrogeology of Anhydrite 103 
DISSOLUTION OF ANHYDRITE AND 

INTERBEDDED SALT 

Dissolution either of anhydrite or of salt that is 

interbedded in anhydrite may form channels for groundwater movement. Beds of dissolution breccia have been 

identified as fossil pathways for ground-water movement 

(Landes, 1959; Anderson and others, 1972; Anderson 

and Kirkland, 1980). Breccias in the Castile Formation, 

described in the reports by Anderson and colleagues, are 

composed of fragments of anhydrite that were left along 

bedding planes after salt beds were dissolved from 

beneath the anhydrite beds. Where these openings 

collapsed, vertical breccias or vertical breccia pipes 

formed in the anhydrite. Hypothetically, vertical pathways were formed either from artesian ground-water 

from the underlying Delaware Mountain Group aquifer 

or from water in the unsaturated zone working down 

from the surface. Castile Spring and Stinking Spring on 

the outcrop of the Castile Formation may be derived 

from artesian water of the Delaware Mountain aquifer 

(Davis and Kirkland, 1970). 

The maximum depths at which solution of salt or 

anhydrite has been found typically range from 150 to 

550 m (Frye and Schoff, 1942; Newland, 1929; Landes 

and others, 1945; and Anderson and others, 1972). 

Earlier occurrence of thermal water within any of the 

basins that contain evaporites probably would have 

accelerated deep solution of the salt and anhydrite. In 

general, because of the common, close association of 

thermal water with volcanic rocks, thermal water may 

have existed wherever volcanic rocks formed in a basin. 

Observations of dissolution of anhydrite in outcrops, mines, tunnels, or springs are rare. However, many 

reports in the literature mention dissolution of both 

gypsum and anhydrite as a group. 

Laboratory experiments on the solution of gypsum 

and anhydrite in both distilled water and salt water at 

23 oc are described by James and Lupton (1978). These 

experiments show that the solution rate of gypsum in 

flowing distilled water is linear according to the 

differential rate equation -dc/dt =kc, but the solution 

rate of anhydrite is proportional to the square of the 

subsaturation concentration of calcium sulfate on the 

right side of a second-order differential rate equation 

-dc/dt = kc2

• The specific rate of dissolution of anhydrite-the constant, k, on the right side of the differential 

rate equation-increases linearly as water velocity 

increases from 0.02 m/s (meter per second) to 0.75 m/s. 

These experiments were used by James and Lupton 

(1978) to predict runaway solution of anhydrite at low 

temperature and high water velocity. However, at and 

above temperatures of 40 °C, k may become low because 

the solubility of anhydrite decreases as temperature 

mcreases. Nevertheless, the second-order kinetic 

1 04 Anhydrite Deposits of the United States 

equation for the dissolution of anhydrite should be 

considered seriously to avoid accelerating the dissolution 

of anhydrite. 

HYDRATION OF ANHYDRITE TO 

GYPSUM 

Hydration of anhydrite to gypsum may be caused 

by circulating ground water. Thus, the presence of 

gypsum is commonly an indicator of past or present 

ground-water movement through anhydrite. In some 

places, dissolution of anhydrite has formed karst, large 

underground channels, or sinkholes that may provide 

channels for more dissolution of anhydrite. 

Hydration of anhydrite to gypsum may occur where 

anhydrite contacts an aquifer or where anhydrite 

contains a fault, a fracture, or a permeable interbed that 

is a conduit for ground water (Holliday, 1970). On a 

microscopic scale, cleavages within the individual anhydrite crystals become important channels for hydration 

(Deer and others, 1962). An example of hydration of 

anhydrite to gypsum near an aquifer occurs in rocks of 

Late Jurassic Purbeckian Age in England where the 

deepest anhydrite bed adjacent to an aquifer is 

completely hydrated to gypsum, whereas shallower anhydrite beds have been only partly hydrated (Howitt, 1964). 

Examples of hydration of anhydrite to gypsum along 

cross fractures and bedding planes occur in the anhydrite 

of the Blaine Formation in Oklahoma (Muir, 1934) and 

in an anhydrite formation in Italy (Lori and Frosio, 

1962). Water seeping through sandy interbeds has 

hydrated the anhydrite to gypsum in part of the waterdiversion tunnel at La Lechere, France, (Sahores, 1962). 

If subject to continued dissolution, the gypsum itself may 

become a conduit for ground water, as illustrated by the 

brecciated, soft, porous, sugary gypsum along solution 

channels adjacent to anhydrite in the Medicine Lodge 

Gypsum Member of the Blaine Formation, Kans. (Kulstad and others, 1956). Hence, anhydrite that contains 

gypsum may have a greater hydraulic conductivity than 

does unaltered anhydrite. 

Hydration of anhydrite produces two types of 

gypsum; namely, porphyroblastic secondary gypsum and 

alabastrine secondary gypsum. The porphyroblastic 

secondary gypsum consists of scattered, rather large 

porphyroblasts of gypsum crystals that contain many 

corroded relicts of anhydrite (Holliday, 1970). Porphyroblasts are early diagenetic minerals in some anhydrite 

beds, but they are related to the circulation of more 

recent ground water in other anhydrite beds (Holliday, 

1970). Alabastrine secondary gypsum is very fine 

grained, nonporphyroblastic gypsum. Water amounts 

range from 0.01 to 0.69 percent in the chemical analyses 

of four of six anhydrite samples reported by Deer and 

others (1962). 
Large-scale alteration of anhydrite to large masses 

of gypsum that may contain karst caverns or sinkholes 

has been observed on outcrops of anhydrite (Hensler, 

1968). In an outcrop, an anhydrite bed may be hydrated 

at the top, side, bottom, or interior of the bed (Bailey and 

Fredericton, 1931). Karst in gypsum has been found in 

many outcrops of anhydrite, and in some areas the 

solution of salt occurs in the same evaporite section as 

gypsum (Gould, 1905; Landes and others, 1945). In New 

Mexico, the flow of the Pecos River goes into solution 

channels in the gypsiferous Seven Rivers Formation 

beneath McMillan reservoir and emerges 5 km to the 

south in Major Johnson Springs (Reeder and Thatcher, 

1963). 

The depth of hydration of anhydrite is commonly 

90-150 m below the surface. Gypsum has been found at 

a depth of more than 1,000 m in the San Andres 

Limestone of Permian age in Texas (Murray, 1964), but 

gypsum rarely is found below a depth of 610 m (West, 

1964) because, below this depth, the temperature 

generally is higher than 42 oc and anhydrite is the stable 

mineral above 42 oc (Murray, 1964). 

Hydration of anhydrite to gypsum may cause the 

rock to expand, as shown by increases in thickness of beds 

after alteration (Newland, 1929; Anderson and Kirkland, 

1966; Hite, 1977) or by large bulging shells or spalling in 

quarries, tunnels, and outcrops, sometimes with violent 

explosions (Allen, 1971; Gignoux and Barbier, 1955; 

Sahores, 1962; Brune, 1965; Beales and Oldershaw, 

1969). This expansion after hydration may result in an 

increase in hydraulic fracture conductivity. However, 

other investigators have not found evidence for 

expansion on hydration of anhydrite to gypsum (Kulstad 

and others, 1956; Sahores, 1962; and Holliday, 1970). 

The amount of expansion may be determined by the 

amount of flow through the rock carrying sulfate away, 

the degree of saturation of the water with respect to 

anhydrite, the amount of confinement of the anhydrite, 

and the salinity and composition of the water. 

DATA FROM SPRINGS 

Data on springs that flow from anhydrite or 

gypsum are presented in table 4.1. Some of the water in 

these springs is actively dissolving anhydrite or gypsum, 

as indicated by saturation values of calcium and sulfate. 

Some springs appear to have artesian water that passes 

through anhydrite or gypsum. 

SUMMARY AND CONCLUSIONS 

Data on the hydrogeology of anhydrite are sparse 

and scattered in the literature. Anhydrite is apparently a 

confining bed if it does not have fractures, permeable 

interbeds, dissolution, or hydration to gypsum. 

Bedded anhydrite apparently has a low mean value 

of intercrystalline porosity (about 1 percent). However, 

bedded gypsum has mean values of intercrystalline 

porosity that may be either low (about 1 percent), or 

much higher (about 20 percent), depending perhaps on 

how much gypsum had been dissolved and carried away. 

The intercrystalline hydraulic conductivity of anhydrite 

apparently is zero or near zero; the fracture porosity and 

fracture transmissivity of bedded anhydrite are inferred 

to range from zero to low. Fractures may be rare or 

absent in bedded anhydrite, and in many oil fields bedded 

anhydrite forms an impervious seal. In addition, 

fractured reservoirs in bedded anhydrite appear to be 

isolated reservoirs in which fractures are poorly 

connected. 

The anhydrite in the cap rock of salt domes 

probably has a low intercrystalline porosity. However, the 

fracture transmissivity in places is probably much greater 

than that in bedded anhydrite, because the cap rock has 

been highly fractured and because dissolution or 

hydration to gypsum has probably increased the fracture 

transmissivity in the cap rock. 

Many other factors affect the hydrogeology of 

anhydrite. Dissolution of either anhydrite or interbedded 

salt may form channels for ground-water movement. 

Hydration of anhydrite to gypsum may increase the 

intercrystalline or fracture openings by replacing anhydrite with gypsum, which may be more transmissive to 

ground water than is anhydrite. General factors that 

affect the hydrogeology of anhydrite include type of 

ground-water basin, movement and discharge of ground 

water in the basin, position of the water table, presence of 

water and sinkholes in the unsaturated zone, artesian 

aquifers or confining beds near anhydrite, and chemical 

and bacterial reactions that take place in anhydrite. 

Hydrogeology of Anhydrite 105 

SECTION 5. Chemical Properties of Anhydrite 

By ROBERT W. POTTER II and MICHAEL A. CL YNNE 

INTRODUCTION 

Several geochemical criteria must be met in 

considering anhydrite as a radioactive waste-repository 

medium (Committee on Radioactive Waste Management, 1978): 

1. Radioactive heat and radiation should not reach 

levels high enough to produce physical and chemical 

reactions in the repository rock that would compromise 

geological containment. 

2. Interaction of water, repository rock, and waste 

material should be controlled to minimize the rate of 

dissolution of the waste form. 

3. Water in the repository, if present, should not 

react chemically or physically with the repository rock to 

increase its permeability, which would compromise 

geological containment. 

4. The properties of the geochemical system of the 

radionuclides, the repository rock, and its associated 

water should restrict or prevent the mobility of the 

radionuclides and should delay or prevent their 

migration to the biosphere. 

The United States, as part of the International 

Nuclear-Fuel Cycle Evaluation (INFCE) Program, has 

agreed to certain thermal-loading criteria for salt repositories. These criteria (Arbital and others, 1979) may be 

summarized in three categories: 

Very-near-field: 

Maximum high-level waste (HLW) temperature shall 

be 500 °C. Maximum spent-fuel pin temperature shall 

be 200 °C. 

Less than 1 percent of the rock adjacent to the canister 

shall be allowed to exceed 200 °C. 

Near-field: 

Less than 25 percent of the rock at the canister horizon 

shall be allowed to exceed 200 °C. 

Far-field: 

Maximum surficial displacement due to thermal 

expansion and room closure shall be 1.5 m. 

The chemical properties of anhydrite that were the 

first indications that it could be used as a potential 

waste-repository medium are its low solubility relative to 

halite and the retrograde nature of its solubility; that is, 

the solubility decreases as temperature increases. 

Because of retrograde solubility, migration of fluid 

inclusions in anhydrite would be away from the heat 

source, rather than toward it as with halite. Anhydrite 

also appears to have a higher sorptive capacity for 

radionuclides than halite, occurs in favorable geologic 

environments, and has a thermal conductivity as high as 

that of halite. 

This section of the present report summarizes the 

data now available from the literature for the chemical 

properties of anhydrite and related phases of calcium 

sulfate, and indicates how the data relate to the suitability 

of anhydrite as a waste-repository medium. In particular, 

we examine the current knowledge of the phase equilibria, crystallography, thermochemistry, and kinetics of 

reaction for calcium sulfate; the sorptive capacity of 

anhydrite for radionuclides; and effects of radiation on 

anhydrite and related phases. 

The reported phases in the system CaS04-HzO, 

which are relevant to the use of anhydrite as a wasterepository medium, are listed in table 5.1. The references 

cited are those considered to be most relevant to 

evaluating anhydrite as a repository host rock and were 

selected from more than 500 references. 

THERMOCHEMISTRY OF ANHYDRITE 

AND RELATED PHASES 

The thermochemical properties of anhydrite have 

been thoroughly evaluated by Parker and others (1971) 

and by Robie and others (1978). As a result of these and 

other investigations, the data for the thermochemical 

properties of anhydrite are known over its entire stability 

range. The data are sufficiently accurate for the appraisal 

of anhydrite as a waste-repository medium. The thermochemical properties of gypsum also are summarized in 

Chemical Properties of Anhydrite 107 
Table 5.1 Phases in the system CaS04-H20. 

[Note: Dehydration reactions appear to progress from gypsum to bassanite to soluble anhydrite to anhydrite; hydration 

reactions progress from anhydrite to bassanite to gypsum] 

Composition Mineral or phase name Remarks 

Caso4 •2HzO-----

CaS04·o.sH2o---

Gypsum------------------ Stable phase. 

Bassanite (hemihydrite)- Metastable phase. 

"Soluble anhydrite"----- Metastable phases; n 

(water of hydration) 

varies from 0 to 1; 

serious questions as to 

whether the phase is 

distinct from bassanite. 

Caso4---------- Anhydrite--------------- Stable. 

the two reports cited and appear to be known sufficiently. 

Thermochemical data for phases of calcium sulfate are 

summarized in table 5.2. 

Thermochemical data for the two compounds of 

calcium sulfate intermediate in hydration between anhydrite and gypsum have been evaluated by Naumov and 

others (1971). They list thermochemical properties for 

25 °C, and additional heat -capacity equations for temperatures to approximately 100 °C. In the tabulation by 

Naumov and others (1971), both bassanite and "soluble 

anhydrite" are indicated as having one-half water of 

hydration. These authors gave the difference in free 

energy between bassanite and "soluble anhydrite" at 

25 oc as about 200 cal (calories), but many crystallographic studies indicate that no structural differences 

exist between bassanite and "soluble anhydrite" that 

contain as much as one water of hydration. The starting 

materials used by Naumov and others (1971) to determine the thermochemical properties were precipitates 

produced by specific chemical procedures (Farnsworth, 

1924; Kelley and others, 1941) rather than wellcharacterized equilibrium phases. Thus, the materials 

could have been kinetically controlled metastable 

precipitates. Naumov and others (1971) also suggested 

that some of the prepared materials were amorphous, 

which probably accounts for the scatter in their data on 

solubility and composition. Because of the contradictory 

crystallographic data, the uncertainties in the thermochemical data, the highly variable solubility data, and the 

lack of well-characterized starting materials, the 

existence of two distinct phases is uncertain. 

Data on thermochemical properties of the lower 

hydrates would be useful only in assessing the consequences of a flooded anhydrite repository after a thermal 

pulse if the reactions are equilibrium-controlled. Current 

evidence, however, suggests that the reactions are 

kinetically controlled. Hence, data on reaction kinetics 

would be more pertinent than would data on equilibrium 

thermochemistry. Further work on the thermochemistry 

Table 5.2 Thermochemical properties of calcium sulfate phases 

108 

[~G, ~H, Sr, and Cp are the standard free energy of formation, enthalpy, and entropy at constant temperature, and heat 

capacity at constant pressure, respectively. Water of hydration is the value of 11 in the general formula CaS04·nH20. KJ, 

kilojoules; J, joules] 

Water of t:.G t:.H sr Cp 

Phase hydration (KJ/mole) (KJ/mole) (J/mole) (J/mole) 

Anhydrite------------ o.o -1321.7 -1434.1 106.69 99.66 

"Soluble anhydrite"-- 0.5 -1460.3 -1574.5 134.31 124.22 

Bassanite------------ 0.5 -1461.3 -1576.6 130.54 119.41 

Gypsum--------------- 2.0 -1797.2 -2022.6 194.14 186.02 

Anhydrite Deposits of the United States 
~10 

:t 

~ 

<( 

ffi 8 0 

.....I 

:;2 

~ 6 c... ..,. 

0 

(f) 

J 4 (/) 

~ 

<( 

~ 2 

\ . 

\\/Bassamte 

40 

"\ 

' "\. 

"\. 

"\. 

" " -----" -"::: .... ,. ....... --:...-

80 

--- 120 160 

TEMPERATURE, IN DEGREES CELSIUS 

200 

Figure 5.1 Solubility relationships of calcium sulfate minerals 

in pure water. Dashed lines represent metastable equilibria. 

of phases of calcium sulfate should be deferred until 

adequate data on crystallography and appropriate kinetic 

paths of the lower hydrates are available. 

CRYSTALLOGRAPHY OF ANHYDRITE 

AND RELATED PHASES 

X-ray powder diffraction data for gypsum and 

anhydrite and the resulting crystallographic conclusions 

700 

650 \ 600 

550 

a: \ w 500 c... 

CllZ 

~Q 450 <(I- 0 CI::J \ (.!).....I 

-o 400 

j(/) 

~0 350 0 

~~ 300 \ ~~ 0 -c.? \ :::o 250 Ill ......I 

3:;2 

0 200 \ (/) 

150 ~ o, 

are moderately well known and understood. Recent 

crystal structure refinements for anhydrite (Morikawa 

and others, 1975) and gypsum (Cole and Lancucki, 1974) 

are available. Both of these references summarize data 

from older literature. Powder X-ray diffraction data for 

anhydrite have been evaluated by Swanson and others 

(1955) who compared their data for synthetic anhydrite 

with earlier data. Grattan-Bellew (1975) has made an 

exhaustive study of the X-ray powder diffraction characteristics of gypsum, including the effects of preferred 

orientation. 

Crystallographic data for the lower hydrates of 

calcium sulfate are less well understood. Studies by Jung 

(1925), Ransdell and Partridge (1929), Bunn (1941), and 

Cano and Chatelain (1958) stated that no crystallographic differences exist between bassanite and 

"soluble anhydrite" from no water of hydration to as 

much as one water of hydration. Conversely, detailed 

studies by Florke (1952) and Gay (1965, 1965b), and 

Florke (1952) have shown that a variety of structures 

exist between bassanite and anhydrite. Gay (1965a,b) 

observed intergrowths of fibrous crystals of gypsum and 

lower hydrates, which may explain the variable water 

analyses. Further work on the problem should be 

approached using more modern methods, such as highresolution electron microscopy. Such studies should 

determine the various domains and intergrowths that are 

present and should provide the necessary characterization of starting materials and products required for 

kinetic studies. 

100 8, 

0'8-q,--o- Cb 50 

--0 

0

50 100 150 200 250 300 350 400 

TEMPERATURE, IN DEGREES CELSIUS 

Figure 5.2 Solubility of anhydrite in pure water (data from Dickson and others, 1963; Booth 

and Bidwell, 1950; d, Ans and others, 1955; Ravich, 197 4). 

Chemical Properties of Anhydrite 109 
PHASE-EQUILIBRIA AND SOLUBILITY 

RELATIONSHIPS 

The properties of anhydrite that were the first 

indications that it could be used as a waste-repository 

medium are its solubility, which is relatively low 

compared with that of halite, and the retrograde nature 

of its solubility to temperatures as high as 200°-250 °C. 

The stability of anhydrite in the presence of bitterns is 

important in assessing the behavior of a repository 

should it flood after a thermal period. Phase equilibria 

among anhydrite, brines, and common impurities such as 

carbonates and clays are significant in assessing the 

performance of a repository. 

Anhydrite is the stable form of CaS04 at all 

temperatures expected in a waste repository. The anhydrite structure is stable to about 1,150 °C, at which point 

it undergoes a polymorphic transition (Gay, 1965b); it 

does not begin to decompose until 1,450 oc is exceeded. 

Relevant phase-equilibria data for anhydrite and various 

salts have been summarized by Rowe and others (1972). 

In the dry systems that have been studied to date 

involving salts commonly found in evaporite deposits, 

none of the liquidus surfaces is lowered sufficiently to 

cause melting at the temperatures estimated for repositories. However, data are sparse for multicomponent 

phase equilibria in dry systems involving anhydrite. 

The solubility of calcium sulfate in pure water is 

low (about 2.0 g!kg (grams per kilogram) H20 at 20 °C) 

and retrograde (decreasing to about 25 mglkg (milligrams per kilogram) H20 at 350 °C) (figs. 5.1 and 5.2). 

Experimental evidence indicates that the solubility of 

anhydrite becomes prograde at temperatures in excess of 

the critical point of pure water (Booth and Bidwell, 1950; 

Morey and Hesselgesser, 1951). However, whether the 

critical surface is continuous, as it is for halite, is still 

unresolved (Keevil, 1942; Ravich, 1974). Solubility 

relationships become more difficult to resolve at lower 

temperatures, due to a strong tendency for metastability 

exhibited by calcium sulfate. Figure 5.1 is a synthesis of 

the published data for solubilities of calcium -sulfate 

minerals in pure water as a function of temperature as 

high as 200 °C. Data on the solubility of the "soluble 

anhydrite" phase are unreliable and have been omitted 

from figure 5.1. Figure 5.2 shows anhydrite solubility in 

water as high as 360 °C. 

The best value for the transition of gypsum to 

anhydrite in equilibrium with pure H20 at 1-bar pressure 

seems to be 45°± 15 oc, although the published-literature 

values range from 33 oc to 107 °C. The transition 

temperature, which is lower as salinity increases, is 

20°±3 oc in solutions saturated with respect to halite 

(Hardie, 1965; 1967). 

The data for pure water show that anhydrite 

maintains its retrograde solubility over the expected 

11 0 Anhydrite Deposits of the United States 

z 

0 6 

i= 

::::> 

....J 

0 

en 5 u. 

0 

~ 4 <( 

a: 

<..? 

0 

....J 3 5:2 

a: 

w 

a.. 2 .,j' 

0 

en 

«< 

u 1 

en 

~ 

<( 

a: 

<.? 00 2 3 4 5 6 7 8 9 

DISSOLVED SOLIDS CONCENTRATION, IN MULTIPLES OF 

AVERAGE SEAWATER CONCENTRATION (35 PER MIL) 

Figure 5.3 Solubility of gypsum (dashed line) and anhydrite 

(solid line) in seawater concentrates at constant temperature 

as a function of the amount of concentration of the seawater 

(data from Posnjak, 1940; and Hara and others, 1934}. 

temperature range in an operating waste repository. 

However, both pressure and high concentrations of complexing ions will significantly increase anhydrite solubility 

and consequently could alter the retrograde nature of the 

solubility curve. Figure 5.3 illustrates the effect of 

increasing ionic strength (the sum of the effective 

concentrations of all dissolved ions) expressed as 

multiples of seawater concentration (ionic strength of 

0.75) at constant temperature for both gypsum and 

anhydrite. The solubility of CaS04 increases rapidly as 

ionic strength increases, reaches a maximum, and then 

steadily declines as the ionic strength increases. The 

decline with increasing ionic strength illustrated in figure 

5.3 is due to a strong, common-ion effect because 

seawater contains calcium and sulfate. Figure 5.4 

illustrates an example of the absence of a strong common 

ion effect. In this diagram, the solubility of anhydrite as a 

function of sodium chloride content is plotted for 200 °C. 

As in the common-ion effect, the solubility initially 

increases rapidly but then increases more slowly at high 

sodium chloride concentrations. This relationship 

implies that at high ionic strengths, hydrolysis reactions 

are occuring that limit the amount of calcium sulfate that 

can exist in solution. 

Solubility studies of anhydrite in a halite-saturated 

solution as a function of temperature indicate that the 

solubility remains rather low and that the retrograde 

nature of the solubility is maintained to temperatures as 

high as 235°±10 oc (fig. 5.5) (Clynne and Potter, 1979). 

Stewart and Potter (1979) pointed out that brines to be 

expected in an evaporite environment would be bitterns 

rather than simple, saturated sodium chloride brines. 

The solubility of anhydrite in bitterns is lower, and the 
'It 

0 

X 

200 

0150 

fJ) 

IC 

u 

u. 

0 

~ 100 ...J 

:3 

0 

~ 

50 

A 

c 

<> 

• 

EXPLANATION 

Blount and Dickson (1969) 

Zdanovskii (1949) 

Marshall and Slusher (1968) 

Clynne and Potter (1979) 

2 4 6 

MOLALITY OF NaCI 

8 10 12 

Figure 5.4 Solubility of anhydrite in sodium chloride solutions at 200° Celsius 

as a function of the molality of sodium chloride. 

change from retrograde to prograde solubilty occurs at 

higher temperatures (fig. 5.5) (Clynne and Potter, 1979) 

than in halite-saturated brines. This behavior can be 

attributed to higher ionic strength of bitterns and to 

strong common-ion effects due to the high calcium 

concentrations in bittern brines. 

Marshall and Slusher (1968) show that in a 

saturated solution in equilibrium with CaS04, Ca2 + and 

so~- become increasingly associated to the neutral 

species CaSO~ as temperature and ionic strength 

increase. Because CaS04, is less soluble than Ca2

+ plus 

so~-, CaS04 shows a decrease in solubility as 

temperature increases. At high temperatures, CaSO~ 

decomposes and other complex ions, such as CaCI+, 

HS04 and in more complex systems NaHSO~, become 

important (Bischoff and Seyfried, 1978). The interplay of 

these large ions and the looser structure of water at high 

temperatures cause the retrograde-to-prograde shift in 

anhydrite solubility to occur at different temperatures in 

different systems. 

10r----------------.------------------~----------------~~------~ 

8 

0 

0 

X 6 

~ ~ 

:3 

0 

~ 

..,.4 

0 

fJ) 

IC 

u 

2 

EXPLANATION 

• Saturated NaCI 

e NBT-6 

0 Marshall and others (1964) 

0 Zdanovskii (1949) 

J~ */ ""D:-8--a+-+---

'· ............_. ___ 100 oL-------------~~:!•=====·~~-::-1-~-------------~------_J 200 300 

TEMPERATURE, IN DEGREES CELSIUS 

400 

Figure 5.5 Solubility of anhydrite in equilibrium with solid sodium chloride and a 

representative bittern brine (NBT -6) as a function of temperature. NBT -6, natural bittern #60. 

Chemical Properties of Anhydrite 111 
TEMPERATURE, IN DEGREES CELSIUS 

~igure 5.6 Effect of pressure on the solubility of anhydrite 

1n pure water as a function of temperature (data from d 'Ans 

and others, 1955). Solubility curve for 1,000 bars is dashed 

where extrapolated. 

. .confining pressure increases the solubility of anhydnte m pure water. Because the increase is greatest at 

temperatures less than 150 oc (fig. 5.6), increasing 

pressure extends retrograde solubility to higher temperatures. However, as the concentration of sodium chloride 

in solution is increased under a confining pressure of 

1,000. ~ar~, th~ transition from retrograde to prograde 

solubility IS shifted towards lower temperatures (fig. 5.7) 

(Blount and Dickson, 1969; Dickson and others, 1963). 

For example, the solubility of anhydrite is continuously 

retrograde to as high as 300 oc along the vapor-saturated 

surface for a 6-molal sodium chloride solution. The 

transition from retrograde to prograde for a 6-molal 

sodium chloride solution at a total pressure of 500 bars 

occurs at about 275 oc, whereas at 1,000 bars the 

transition occurs at about 250 °C. The change from 

retrograde to prograde solubility as a function of 

increased pressure and ionic strength in sodium chloride 

solutions is at temperatures and pressures that pose no 

difficulties for the use of anhydrite as a repository 

medium, but the effect may not be the same for natural 

brines. We cannot evaluate this possibility because no 

data for natural brines are available. 

Another unresolved problem is the stability of 

anhydrite in bittern brines. Essentially, this involves 

phase equilibria in the system Na, K, Mg, Ca, Cl, and S04 

at low temperatures. The current knowledge on this 

system has been summarized by Braitsch (1971) (figs. 5.8 

and 5.9). These diagrams for 55 oc (fig. 5.8) and 83 oc 

(fig. 5.9) show that the most likely alteration product of 

anhydrite is polyhalite, which would result in a volume 

112 Anhydrite Deposits of the United States 

0.05 r--~-----r------,----,----,----.----

0 

N 

:r: 

~ 0.04 a: 

8 

...J 

::;;;: 0.03 a: 

w 

a.. 

(/) 

~ 0.02 0 

~ 

~ 

~ 0.01 

(/) 

u "' 

1000 bars 

~o~o~~~-~2~o~o~~2~5~0--~3oLo--3~5-0--4-0L0----450 

TEMPERATURE, IN DEGREES CELSIUS 

Figure 5.7 Solubility of anhydrite at 1 ,000 bars as a function 

of temperat~re and sodium chioride concentration (from 

Blount and Dtckson, 1969). Solubility curves are dashed where 

extrapolated. M, molar. Reprinted with permission of Pergamon Press, Ltd. 

expansion of about 7 percent. The rate at which this 

alteration proceeds is slow, comparable to that of the 

dehydration of gypsum. The equilibria at lower 

temperatures are not well established due to the extreme 

slug.gishness of the reactions involved (Autenrieth, 1958; 

Brattsch, 1971). The most important data needed for the 

assessment of the degree of interaction of bittern brines 

and anhydrite are kinetic rates and the paths of the 

reactions. Both natural occurrences (Braitsch, 1971) and 

experimental data (for example Perova, 1970a,b) clearly 

show that the primary phases to form from bittern brines 

would be poly halite, gypsum, and possibly one or more of 

the lower hydrates of calcium sulfate. Formation of these 

alteration products would remove water from the system, 

but significant volume expansion could cause the formation to fracture and enhance fluid mobility. 

Phase equilibria in the system N a, K, Mg, Ca, Cl, 

and so4, plus carbonates and silicates, at elevated 

temperatures and pressures generally are unexplored, 

although limited data are available for some simpler 

assemblages. Reaction rates at waste-repository temperatures should be fast enough that equilibrium data would 

be preferable to kinetic data for identifing stable 

assemblages. If these assemblages are different from 

those observed in natural systems, the reactions 

producing them are of interest. Most reactions should 

produce a less permeable rock, unless the volume 

changes are large enough to cause the formation to 

fracture. 

KINETICS OF REACTIONS INVOLVING 

ANHYDRITE 

Data on the kinetics of reactions pertinent to 

assessing anhydrite as a waste-repository medium are 
Mg 

Figure 5.8 55°-isotherm of the five-component system NaCI-KCI-MgCI2-Na2S04-H20 at sodium 

cloride saturation. Calcium-sulfate fields (dashed lines) approximated. Crystallization paths are heavy 

lines; transition lines, fine lines. 1, kainite; 2, langbeinite; and 3, leonite (modified from Braitsch, 1971). 

scant. At temperatures as high as 200 oc, the only 

available data are those on the solubility of gypsum and 

anhydrite in sodium chloride and seawater solution 

(Marshall and others, 1964; Marshall and Slusher, 1966, 

1968). At temperatures lower than 110 °C, several 

workers (Zen, 1965; Hardie, 1965) have recorded 

thermodynamic data as a function of time, which would 

permit extraction of kinetic data. In general, data for the 

kinetics of reactions in the pertinent systems are 

inadequate. Table 5.3 lists the reactions and temperature 

ranges for which data would be most useful. 

SORPTION OF RADIONUCLIDES BY 

ANHYDRITE 

Data for the sorption of radionuclides on anhydrite 

are meager, consisting of only two internal reports from 

the U.S. Department of Energy National Laboratories 

(Serne and others, 1977; Fried and others 1978). The 

tentative conclusion that can be drawn from these data is 

that anhydrite has a higher fixative capacity than does 

halite, and appears to have a greater fixative capacity 

than docs volcanic tuff for certain radionuclides. 

Experiments on the fixative capacity for Tc04 and 103 

showed that tuff removed less than 1 percent of the ions 

from solution, whereas anhydrite stripped 4 percent of 

the Tc04 and 59 percent of the I03 from solution. 

Although these results are promising, experimental data 

for a wider range of radionuclides is needed to allow 

quantitative estimates of the fixative capacity of anhydrite 

under realistic conditions. 

RADIATION EFFECTS ON THE 

CHEMISTRY OF ANHYDRITE 

No data on the effects of radiation on the chemistry 

of anhydrite could be found. The chemical and physical 

effects of radiation are expected to be minor, although 

radiation-induced distortion of the crystal lattices of 

minerals generally increases their solubility and 

Chemical Properties of Anhydrite 113 
Mg 

Vanthoffite 

D'ansite 

Thenardite 

\ 

\ 

\ 

-<)\ 

~ 

~\ 01~.\ 

~\ 

Sylvite 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

Figure 5.9 83°-isotherm of the five-component system NaCI-KCI-MgCI2-Na.2S04-H20 at sodium 

cloride saturation (modified from Braitsch, 1971). Calcium-sulfate fields (dashed lines) approximated. 

Crystallization paths are heavy lines; transition lines, fine lines. 

Table 5.3. Kinetic reactions for which data are needed 

[All reactions are in the presence of brines] 

Temperature 

Reaction range 

(°Celsius) 

Gypsum - anhydrite 0-50 

Anhydrite -

= polyhalite 25-300 

Gypsum = polyhalite 0-50 

Bassanite - anhydrite 25-200 

Anhydrite -

~ goergeyite 25-200 

Anhydrite - glauberite 25-200 - decreases their thermal stability. Indirect evidence, such 

as the absence of any change in color of anhydrite 

exposed to high-level waste during project Salt Vault 

(Bradshaw and McClain, 1971 ), may indicate that the 

effects are probably slight; however, experimental studies 

114 Anhydrite Deposits of the United States 

are needed to document the presence or absence of 

radiation effects. 

SUMMARY 

Data collected from the literature on the chemical 

properties of anhydrite support the concept of using 

anhydrite as a waste-repository medium or as an overpack to protect high-level waste canisters. Available 

thermodynamic, crystallographic, and phase-equilibria 

data are extensive, and only limited additional data are 

needed in these areas to assess the behavior of a waste 

repository in anhydrite. However, data on the reaction 

kinetics of anhydrite alteration, on the sorption of radionuclides by anhydrite, and on the effects of radiation on 

anhydrite chemistry are not sufficient for evaluating 

anhydrite as a potential repository media. 

The thermochemical properties of anhydrite 

(CaS04 ) and gypsum (CaS04·2H20) are well known; 

two mutually consistent and verified sets of data are 
available. The data for the lower hydrates of calcium 

sulfate (bassanite, CaS04 ·O.SH20; "soluble anhydrite," 

CaS04 ·nH20) are inadequate, but these are metastable 

phases that would not be expected to occur under 

equilibrium conditions; they could be involved in the 

alteration of anhydrite if a repository flooded after a 

thermal pulse. Thermochemical data for the calcium 

sulfate-water system are adequate. 

Crystallographic data on both anhydrite and 

gypsum are adequate; powder X-ray diffraction data are 

available and the anhydrite and gypsum crystal structures 

are known. However, crystallographic data for the lower 

hydrates of calcium sulfate are inadequate; available data 

are contradictory and need clarification. These data 

would be of use in kinetic studies of the hydration of 

anhydrite. Additional data would have to be obtained 

using a high-resolution electron microscope with diffraction capabilities, because available evidence suggests the 

presence of fine intergrowths and structural zones. 

Phase-equilibria and solubility data for anhydrite 

and other phases of calcium sulfate are voluminous. Data 

for high temperatures indicate that the solubility of 

anhydrite remains low and retains its retrograde character to 200 °C, a temperature that is not likely to be 

exceeded in the rocks around a waste repository 

according to present design estimates. The only possibility for reversing the retrograde solubility at less than 

200 oc would be if the change in solubility of anhydrite 

with pressure in concentrated brines is significantly 

greater than it is in sodium chloride-saturated solutions. 

The data necessary to evaluate this effect are unavailable; 

however, such data could be obtained readily using a 

gold-bag autoclave system. 

Data on phase equilibria in the system Na-KMg-Ca-Cl-S04 are necessary to assess the consequences 

of repository flooding after a thermal pulse. Available 

data for low-temperature equilibria are extensive and 

suggest that if anhydrite alters, the product would be 

gypsum or polyhalite, depending upon the composition of 

the brine. Alteration of anhydrite would increase the 

rock volume, which might reduce its permeability and 

restrict migration of fluids through the repository. If the 

initial porosity were low, however, the volume expansion 

could cause fracturing and thereby significantly increase 

migration of fluid. More data on the kinetics of alteration 

reactions are needed for a full assessment, because 

anhydrite alteration reactions proceed slowly at low 

temperatures. 

Anhydrite rocks typically contain small amounts of 

other minerals, and therefore the stability of anhydrite 

coexisting with carbonate, silicate, and bittern-mineral 

impurities at elevated temperature and pressure should 

be evaluated. Sparse data suggest that significant 

problems will not be encountered, but more experimental data on these equilibria should be obtained using 

a gold-bag autoclave system. 

The sorptive capacity of anhydrite appears to be 

significantly greater than that of halite, and for some 

radionuclides greater than that of tuff. However, data are 

too limited for adequate evaluation. 

No data are available on the effects of radiation on 

the chemistry of anhydrite. 

Chemical Properties of Anhydrite 115 

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Maps 

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 7 1/2- or 15 -minute quadrangle formats (scales mainly 1 :24,000 or 1 :62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photo geologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List.) 

"Publications of the Geological Survey, 1879- 1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982, 1983, 1984, 1985,1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only 

"Price and A vallablllty List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only. 

Selected copies of a monthly catalog "New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092. 

Note.--Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications.