Mixed-Layer Glay in the Pierre Shale and Equivalent Rocks, Northern Great Plains Region GEOLOGICAL SURVEY PROFESSIONAL PAPER 1064-A Mixed-Layer Clay in the Pierre Shale and Equivalent Rocks, Northern Great Plains Region By LEONARD G. SCHULTZ GEOCHEMISTRY OF THE PIERRE SHALE AND EQUIVALENT ROCKS OF LATE CRETACEOUS AGE GEOLOGICAL SURVEY PROFESSIONAL PAPER 1064-A X-ray diffraction techniques for interpretation of mixed-layer illite-smectite clay, chemical composition of the clay, and developmental history of the clay UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1978 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Schultz, Leonard Gene, 1926- Mixed-layer clay in the Pierre Shale and equivalent rocks, northern Great Plains region. (Geochemistry of the Pierre Shale and equivalent rocks, northern Great Plains) (Geological Survey Professional Paper 1064-A) Bibliography: p. 27 1. Clay minerals Great Plains. 2. Geology, Stratigraphic Cretaceous. I. Title. II. Series. III. Series: United States Geological Survey Professional Paper 1064-A. QE389.625.S3 552'.5 77-26718 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03115-9 CONTENTS Page Page Abstract ........................................................................................ 1 Chemistry of mixed-layer clays Continued Introduction .................................................................................. 1 Structural formulas calculated from purified mixed-layer clay 12 General geology and mineralogy .................................................. 1 Formulas inferred for individual illite-, beidellite-, and Definition of mineral and mixed-layer terms ................................ 3 montmorillQnite-type layers ........................................ 15 Interpretation of X-ray diffraction traces of mixed-layer clay ...... 5 Structural OH" ............................................................... 16 Illite-smectite ......................................................................... 5 Illitic mixed-layer clay in bentonite .............................................. 18 Illite-beidellite-montmorillonite ............................................. 7 Depth diagenesis .......................................................................... 19 Peak positions of IS-ordered clay .......................................... 9 Main Pierre Shale study ........................................................ 20 Common proportions of illite:beidellite:montmorillonite ............. 10 Complementary studies .......................................................... 22 Chemistry of mixed-layer clays ..................................................... n Cuttings from deep wells ................................................ 22 Structural formulas calculated from whole-rock samples ...... H Montana disturbed belt .................................................. 23 Shale ............................................................................... 11 Summary and interpretation ......................................................... 24 Bentonite ...................................................... ..... ........ 12 Selected references ........................................................................ 27 ILLUSTRATIONS ————————————— Page FIGURE 1. Diagrammatic section of the Pierre Shale and some of the equivalent rocks ............................................................................... 2 2. Index map showing sample localities and pertinent physiographic features ................................................................................. 3 3. Schematic structure of an aluminum smectite or illite layer ......................................................................................................... 4 4. X-ray diffraction traces of four clay samples that illustrate the range of composition of mixed-layer illite-smectite in rocks of Pierre age and the new and old methods of expressing proportions of layers ................................................................................. 6 5. Graph showing relationship between the proportion of smectite and mixed-layer clay interpreted from peak heights and the percentage of illite-type layers interpreted from peak migration ..................................................................................... 7 6. Diagram used to interpret proportions of layers in mixed-layer clay ........................................................................................... 9 7. Graph showing relationship between the proportion of beidellite- and illite-type layers in mixed-layer clay determined from migra­ tion curves and the change in peak height after glycerol treatment of Li*-saturated and heated clay .................................. 10 8. Graph showing illite content of 11 IS-ordered mixed-clay samples determined from Sooa/Iw related to ^-spacing of the first basal reflection of the clay treated with ethylene glycol ........................................................................................................ H 9. Diagram showing proportions of layers in mixed-layer illitite-smectite in the Pierre Shale and equivalent rocks ....................... 12 10. Graphs showing cation abundance in structural formulas ............................................................................................................ 13 11. Diagrams showing tetrahedral Ali3, total layer charge, and interlayer Kv+ ions of structural formulas related to proportions of illite:beidellite:montmorillonite .......................................................................................................................................... 15 12. Differential thermal analysis curves typical of shale and bentonite of Pierre age ......................................................................... 17 13. Graph showing change in bulk density and porosity of shale as depth of burial increases .......................................................... 20 14. Map showing average porosity of samples from generalized localities of the pierre Shale and Equivalent strata ........................ 21 15. Maps showing average proportion of illite-type layers in mixed-layer illite-smectite from generalized localities of the Pierre Shale and equivalent strata ............................................................................................................................................................. 21 16. Graph showing common proportions of illite-type layers in mixed-layer clay originally deposited and that developed by depth diagenesis in the Pierre Shale and equivalent strata ............................................................................................................. 26 IV CONTENTS TABLES Page TABLE 1. Typical mineralogical composition of the Pierre Shale and equivalent rocks ............................................................................... 4 2. Average structural formulas of mixed-layer illite-smectite clay in the Pierre Shale and equivalent rocks .................................... 13 3. Chemical analyses and structural formulas for 15 purified samples of mixed-layer illite-smectite from the Pierre Shale and equiva­ lent rocks ............................................................................................................................................................................... 14 4. Average structural formulas of layers in mixed-layer illite-smectite from the Pierre Shale and equivalent rocks ........................ 16 5. Dehydroxylation peak temperature and size and amount of deviation from ideal structural water in 15 purified mixed-layer illite-smectites from the Pierre Shale and equivalent rocks ................................................................................................... 17 6. Mineralogy and dehydroxylation peak temperatures of samples of bentonite, adjacent shale, and an argillized sill of volcanic rock from the Dearborn River locality within the Montana disturbed belt and of three bentonite samples from equivalents of the Pierre Shale outside the belt that contain mixed-layer illite-smectite .................................................................................... 19 7. Mineralogy and dehydroxylation peak temperatures of shale and bentonite cuttings of Pierre age at depths of 10,000 feet or more in the Powder River basin and of samples from stratigraphically equivalent rocks from the nearest outcrops at the Salt Creek locality ..................................................................................................................................................................^ 22 8. Mineralogy and dehydroxylation peak temperatures of shale and bentonite samples from the Montana disturbed belt ............. 24 GEOCHEMISTRY OF THE PIERRE SHALE AND EQUIVALENT ROCKS OF LATE CRETACEOUS AGE MIXED-LAYER CLAY IN THE PIERRE SHALE AND EQUIVALENT ROCKS, NORTHERN GREAT PLAINS REGION By LEONARD G. SCHULTZ ABSTRACT INTRODUCTION Mixed-layer illite-smectite is the most abundant constituent in much of the Pierre Shale and equivalent rocks. X-ray diffraction data on both peak The Pierre Shale Project has been a long-term study by H. positions and intensities have been used to distinguish illite-, beidellite-, and A. Tourtelot, the late J. R. Gill, and L. G. Schultz of the montmorillonite-type