Geochemistry of Salt-Spring and Shallow Subsurface Brines ... Rolling Plains of Texas and Southwestern Oklahoma

RI0155. Geochemistry of Salt-Spring and Shallow Subsurface Brines in the Rolling Plains of Texas and Southwestern Oklahoma, by B. C. Richter and C. W. Kreitler. 47 p., 25 figs., 6 tables, 1 appendix, 1986. ISSN: 0082335X: Print.

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ABSTRACT
Numerous salt-emission areas exist within the Permian outcrop in the Rolling Plains of Texas and southwestern Oklahoma. Sodium chloride waters underlie the area at relatively shallow depths, discharge from salt springs and salt seeps, and greatly impair the quality of ground and surface waters. This study distinguishes between brine derived from dissolution of halite by fresh, locally recharged ground water in a shallow ground-water system and brine derived from deep-basin brine aquifers. Halite dissolution brines typically have molar Na/Cl ratios of about 1, and Br/C and I/Cl weight ratios of less than 4 x 10^-4 and less than 1 x 10^-5, respectively. Deep-basin brines, in contrast, exhibit ratios of less than 1, greater than 2.5 x 10^-3, and greater than 1 x 10^-3, respectively.

Three groups of brines in the Rolling Plains can be distinguished according to these ratios: (I) halite-dissolution brine, found in samples from most salt springs and test holes in the north and west; (2) brine from deep-basin aquifers, evident in the shallow subsurface (30 to 100 ft or 9 to 30 m) in the south; and (3) brine exhibiting characteristics of both halite-dissolution and deep-basin brines, suggesting mixing. Other chemical constituents (Ca, Mg, and K) support this grouping of the brine data as well as our interpretation of different brine origins.

The isotopic composition (δ¹⁸O and δD) of the salt springs indicates a local meteoric origin for the halite-dissolution brines. Some brine samples from the shallow subsurface in the southeast plot on a line that includes deep-basin brine values and meteoric-water values as end points, suggesting dilution of deep-basin brine by meteoric ground water. The presence of deep-basin brine near land surface in the study area was not recognized in previous studies.

Keywords: Brazos River, brines, geochemistry, isotopes, Midland Basin, nuclear waste, Palo Duro Basin, Red River, Rolling Plains, springs, Texas

CONTENTS

ABSTRACT

INTRODUCTION

Purpose and scope

Previous work

Methodology

HYDROGEOLOGIC FRAMEWORK

Physiography and climate

Geologic setting

Lithology and depositional environments of principal hydrogeologic units

Pennsylvanian to Lower Permian marine section

Middle and Upper Permian evaporite section

Post-Permian section

Permian salt deposits

Ground-water flow

Salt-discharge areas

Red River basin

Salt Fork of the Brazos River

WATER CHEMISTRY

Halite-dissolution brine versus deep-basin brine

Hydrochemical facies

Data differentiation

Isotopic composition

Geographic distribution of brine types

SUMMARY AND CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

APPENDIX: salt-discharge areas

Red River basin

Salt Fork of the Brazos River

Figures

1. Brine-discharge areas in the Rolling Plains of North-Central Texas and southwestern Oklahoma

2. Structural elements of the Texas Panhandle

3. East-west cross section illustrating depositional systems in the Palo Duro Basin

4. Geologic map of the study area

5. Limits of salt strata in the Palo Duro Basin

6. Hydrologic units and apparent ground-water flow lines, Palo Duro Basin

7. Ground-water-flow model and mechanism of salt dissolution within the study area

8. Location of salt springs and test holes

9. Geochemical facies of salt-spring and shallow subsurface brines in the Rolling Plains of Texas and southwestern Oklahoma

10. Ratios of mNa/mCI and gBr/gCl versus mCI in deep-basin brines from the Palo Duro and Midland Basins

11. Ratios of mNa/mCI versus Cl of salt-spring and shallow subsurface brines in the Rolling Plains of Texas and southwestern Oklahoma

12. Ratios of gBr/gCl versus Cl of salt-spring and shallow subsurface brines in the Rolling Plains of Texas and southwestern Oklahoma

13. Major cation distribution in groups A, B, and C, and in deep-basin brines from the Palo Duro and Midland Basins

14. Magnesium versus chloride concentrations

15. Ratios of I/Cl versus Cl concentrations

16. Calcium versus chloride concentrations

17. Potassium versus chloride concentrations

18. Variation in calcium concentrations with sulfate and chloride concentrations, Group A brines

19. Molar ratios of (mCa + mMg)/SO₄ versus mNa/mCl

20. Variation in mCa/mMg ratios in Group C brines and deep-basin brines from the Palo Duro and Midland Basins

21. Plot of δD and δ¹⁸O for shallow, fresh ground water from municipal wells in New Mexico and the Texas Panhandle, for salt springs and test-hole samples from North Croton Creek, and for deep-basin brines from the Palo Duro Basin

22. Plot of δ¹⁸O versus depth for waters at the North Croton Creek area

23. Plot of chloride concentration versus depth in test holes at the North Croton Creek area

24. Geographic distribution of samples according to brine type

25. Plot of gBr/gCl ratios versus depth for four salt-emission areas, Jonah/ Salt Creek, Middle Pease River, North Croton Creek, and Haystack/Dove/Croton Creek

Figure A-1. Geologic cross section, Estelline Springs and Jonah Creek

Tables

1. Relationship between generalized stratigraphic and hydrogeologic units

2. Compilation of estimates of salt loads discharged at major brine-discharge areas

3. Chemical analyses, Group A brines

4. Chemical analyses, Group B brines

5. Chemical analyses, Group C brines

6. Chemical analyses of deep-basin brines, Palo Duro and Midland Basins



Citation
Richter, B. C., and Kreitler, C. W., 1986, Geochemistry of Salt-Spring and Shallow Subsurface Brines in the Rolling Plains of Texas and Southwestern Oklahoma: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 155, 47 p.