Preliminary Investigation of the Geologic Setting and Chemical Composition of the Pierre Shale Great Plains Region GEOLOGICAL SURVEY PROFESSIONAL PAPER 390 Preliminary Investigation of the Geologic Setting and Chemical Composition of the Pierre Shale Great Plains Region By HARRY A. TOURTELOT GEOLOGICAL SURVEY PROFESSIONAL PAPER 390 A contribution to the geochemistry of sedimentary processes UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEW ART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows: Tourtelot, Harry Allison, 1918- Preliminary investigation of the geologic setting and chemical composition of the Pierre shale, Great Plains region. Washington, U.S. Govt Print. Off., 1961. iv, 74 p. illus., maps, diagrs., tables. 30 cm. (U.S. Geological Survey. Professional paper 390) Part of illustrative matter in pocket. Bibliography: p. 69-72. 1. Shale Great Plains. 2. Geology Great Plains. 3. Bocks- Analysis. I. Title. II. Title: Pierre shale, Great Plains region. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, B.C. CONTENTS Page Page Abstract.._ _-___-__-_--______-______-___--__-__--_- 1 Chemical composition Continued Introduction _______________________________________ 2 Major constituents Continued Relation of chemical composition and clay Plan of study, _____________________________________ 2 minerals._ ______-_--___-_-------_-------- 27 Acknowledgments__ ___-_-___---_-____---_--_______ 3 Changes in composition on weathering _.__ 27 Distribution of Pierre shale and equivalent rocks. ______ 3 Road cut, Fergus County, Mont _______ 28 Stratigraphic relations of the Pierre shale and equivalent Spillway of Oahe Dam, S. Dak ___ _ 30 rocks_ ____________________________________________ 4 Comparable core and surface samples. _ _ __ 32 Historical summary.____________________________ 4 Conclusions._ _____________--__-_--_---- 36 Correlation of units.____________________________ 5 Comparison with other shales________________ 37 Description of units.____________________________ 7 Regional variation in composition _________ 44 Facies belts._---__----------_-_-.-_-_-__------_ 9 Minor constituents ._.-___-___-__---_--------- 44 Geochemical history___----------_____-__-----_--_ 10 Mode of occurrence.______.__-___-__-------- 44 Spectrographic data _.___-____--_------_--_ 47 Samples -_--_-_-----__________________________-____ 12 Analytical methods---------------- -- 47 Terminology ___________________________________ 12 Statistical distribution_________________ 47 Field investigations.____________________________ 13 Comparison with other shales_____-_----- 50 Laboratory investigations..._.--___-_____________ 13 Stratigraphic and geographic variation.... 52 Physical composition._______________________________ 16 Chemical data_____-______---_------_----_ 54 Size analyses.__________________________________ 16 Fluorine, zinc, arsenic, selenium, uranium, Mineralogy _________________________________ 19 and equivalent uranium _______________ 54 Material coarser than 74 microns _____________ 19 Carbon..._-----__--___---------_------ 57 X-ray analyses _____________________________ 19 Interrelations._____-______---___----------- 58 Chemical composition_______________________________ 22 Interrelated physical and chemical characteristics.______ 61 Average composition of selected samples of Pierre Data on pH of samples.------------------.------ 61 shale.-------___-___-________________________ 22 Atterberg limits._______--__-_-___-------------- 62 Major constituents._____________________________ 22 Summary_ __________________--___-_-------------- 65 Mode of occurrence_________________________ 25 Literature cited_______________________---__------ 69 Statistical distribution_____________________ 25 Index __.____-__--_---_--------_------------------- 73 ILLUSTRATIONS [All plates in pocket] PLATE 1. Map showing distribution of Pierre shale and sample localities. 2. Generalized Stratigraphic sections of Pierre shale. 3. Distribution of elements by Stratigraphic zone. 4. Distribution of elements by geographic region. Page FIGURE 1. Distribution and thickness of Pierre shale___________________.______.__-_____---_-_------_------ _-- 3 2. Stratigraphic relations of Pierre shale._______________________-______----_-_-_-_-_-_-_-_--------------- 6 3. Particle-size classification of Pierre shale and comparison of size distribution_______________-__-----_------_ 17 4. Histograms and diagrammatic cumulative curves representing different kinds of particle-size distribution ______ 18 5. Cumulative curves showing particle-size classification for samples of Pierre shale _________________________ 19 6. Statistical distribution of major constituents in 17 samples..________._______-------____--_--_------------ 26 7. Diagrams showing changes in chemical composition resulting from weathering of Claggett shale, Fergus County, Mont.----________________________________________________________-____-_-_-______--_-_-_------- 29 8. Diagrams showing changes in chemical composition resulting from weathering of Verendrye member of Pierre shale, Stanley County, S. Dak________________________________________---_-__-_-____-_----__-------- 31 9. Stratigraphic relations of samples of equivalent materials from core and outcrop..----_-__.---__..____ -------- 33 10. Graphic comparison of average contents on as-reported basis of selected major elements with other pelitic rocks- - 38 in IV CONTENTS Page FIGURE 11. Graphic comparison of average contents on recalculated basis of selected major elements with other pelitic rocks_ . 40 12. Distribution in geologic time of potassium and sodium in Russian clays and some North American shales______ 43 13. Distribution of elements determined by semiquantitative spectrographic analysis ___________________________ 48 14. Histograms showing distribution of elements compared with crustal abundance and other data. ______________ 51 15. Distribution of selected elements by stratigraphic zone and geographic region______________________________ 54 16. Statistical distribution of fluorine and relations of fluorine to phosphorus ________________________________ 55 17. Statistical distribution of zinc, arsenic, and selenium. ___________________________________________________ 55 18. Relation between carbonate and organic carbon____ _____________________-_______._-___--__--_--___---- 58 19. Diagrams showing relations between selected elements__-____________________--__-__-___--------_ .____.. 59 20. Statistical distribution of pH and the relation of pH to soluble sulfur and sodium oxide ___________________ 62 21. Liquid limits and plastic limits plotted against plasticity indexes and other data. ___________________________ 63 22. Relation between liquid limit and content of montmorillonite, percentage of material finer than 3.6 microns, sodium oxide, and pH_____________________________________..__________---_____-_-___--___------_--- 64 TABLES Page TABLE 1. Location and description of samples from the Pierre shale and equivalent rocks, and some older shales of Creta­ ceous age, and an index to analytical work,________________________ _________________________________ 14 2. Distribution by stratigraphic zone and geographic region of samples included in this study_________________ 16 3. Size analyses of 38 samples of Pierre shale and equivalent rocks__________________________ ________________ 17 4. Mineralogy of material coarser than 74 microns in 22 basic samples of shale and marlstone of Pierre shale and equivalent rocks._________________________________________________________________________________ 20 5. X-ray analyses of 22 basic samples of Pierre shale and equivalent rocks.___________________________________ 20 6. Comparison of average composition of 17 samples of Pierre shale and equivalent rocks with average compositions of montmorillonite and illite_______________________________________________________________________ 22 7. Chemical analyses of 22 basic samples of shale and marlstone from Pierre shale and equivalent rocks__----_-_- 23 8. Duplicate chemical analyses of two samples of claystone and related data________________________________ 24 9. Chemical analyses of core and outcrop samples from the Gregory, Crow Creek, and DeGrey members of the Pierre shale______________________________________________________________________________________ 33 10. Calculated mineralogical and chemical composition of claystone and marlstone from equivalent stratigraphic positions of members of the Pierre shale____-_-----------_-------------------_-__-------- ._______---_ 34 11. Comparison of average composition of Pierre shale and equivalent rocks with other pelitic rocks _____________ 37 12. Comparison of average composition of Pierre shale and equivalent rocks with other pelitic rocks, excluding moisture, carbonate and phosphate minerals, and acid-soluble sulfur as sulfur trioxide_____________________ 41 13. Chemical composition of major constituents of Pierre shale and equivalent rocks by geographic region, excluding moisture, carbonate and phosphate minerals, and acid-soluble sulfur as sulfur trioxide_____________________ 44 14. Semiquantitative spectrographic analyses for minor elements in 67 samples from Pierre shale and equivalent rocks, and some older shales of Cretaceous age_____________________________________________________________ 45 15. Different modes of occurrence