University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1968 Preliminary report on the geology geochemistry and sedimentology of Flathead Lake northwestern Montana Gary L. Decker The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Decker, Gary L., "Preliminary report on the geology geochemistry and sedimentology of Flathead Lake northwestern Montana" (1968). Graduate Student Theses, Dissertations, & Professional Papers. 7170. https://scholarworks.umt.edu/etd/7170 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. PRELIMINARY REPORT ON THE GEOLOGY, GEOCHEMISTRY, AND SEDIMENTOLOGY OF FLATHEAD LAKE, NORTHWESTERN MONTANA By Gary L. Decker B.A. University of Montana, 1966 Presented in partial fulfillment of the requirements for the degree of Sc I'e e. Master of Arts UNIVERSITY OF MONTANA 1968 Approved by: - . Chairman,/Board of Examiners ean, Graduate Sch/)ol August 6, 1968 Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: EP37971 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT UMI EP37971 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS CHAPTER PAGE ABSTRACT ............................................... 1 INTRODUCTION ............................................. 4 Location ............................................... 4 Geography of Flathead Lake ............................ 4 Climate ................................................. 5 Previous Work in A r e a .................................. 9 Reason for Study ...................................... 9 Present Study ........................................ 10 Acknowledgements ...................................... 11 GEOLOGY OF THE A R E A ...................................... 13 Structure.............................................. 13 Bedrock Descriptions ................................ > 16 Ravalli Group (undifferentiated) ................... 16 Piegan Group (undifferentiated) ..................... 20 GLACIAL HISTORY OF FLATHEAD VALLEY ..................... 22 SEDIMENTOLOGY OF FLATHEAD L A K E ......................... 25 Size Distribution...................................... 25 Mineral Content Exclusive of Clay-minerals .......... 26 Organic Content . ................................... 29 Sediment Source .......................... 29 Rate of Sedimentation.................................. 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER PAGE Clay M i n e r a l s ........................................ 32 Distribution of clay-minerals in l a k e ............. 33 Source of clay-minerals in Flathead Lake ........ 36 CHEMISTRY OF FLATHEAD L A K E ........................... 39 Possible Authigenic Miner a l s ....................... 39 C a l c i t e ............................................ 39 S i l i c a ............................................ 40 Kao linite .............. 42 H e m a t i t e ................... 43 CURRENTS IN FLATHEAD L A K E .............................. 50 SUMMARY .......................................... 51 SUGGESTION FOR FUTURE W O R K ........................... 53 Chemistry of Flathead Lake ..... ............... 53 Core Sampling ...................................... 53 BIBLIOGRAPHY ................................... 54 APPENDIX I: LABORATORY PROCEDURES ................... 59 APPENDIX II: CLAY A N A L Y S E S ............................ 73 APPENDIX III: SIZE AND CLAY P E R C E N T A G E S ............. 84 APPENDIX IV: CLAY SAMPLE LOCATIONS FROM FLATHEAD VALLEY .............. 86 APPENDIX V: PROCEDURE FOR GRAVITY DETERMINATIONS . 8? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES FIGURE PAGE 1 . INDEX MAP AND DRAINAGE SYSTET-IS, FLATHEAD LAKE AREA, NORTHWEST M O N T A N A ....................... 6 2. GEOGRAPHY OF FLATHEAD L A K E ....................... 7 3. CLIMATE OF THE FLATHEAD V A L L E Y ................... Ô 4. GRAVITY PROFILE ACROSS FLATHEAD VALLEY SOUTH OF FLATHEAD L A K E ....................... U - 5. GRAVITY PROFILE ACROSS THE BIG DRAW ...... 15 6. GRAVITY PROFILE "C" ACROSS THE BIG DRAW ...... 16 7. CORRELATION CHART OF BELT SUPERGROUP ............ 19 6. MOVEMENT OF GLACIERS AND POSITION OF MORAINES IN FLATHEAD LAKE A R E A ............................ 24 9. DISTRIBUTION OF MONTMORILLONITE IN FLATHEAD LAKE . 35 10. Eh and pH DATA FOR FLATHEAD L A K E .................. , 41 11. SEDIMENTARY CHEMICAL END-MEMBER ASSOCIATIONS . 42 12. STABILITY RELATIONS OF SOME PHASES IN THE SYSTEM K20-Al2Ü3-Si02-H20 ....................... 43 13. SAMPLE LOCATIONS IN FLATHEAD L A K E ................ 72 14. X-RAY DIFFRACTION GRAPH SHOWING EFFECTS OF VARIOUS TREATMENTS .............................. 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES TABLE PAGE 1 . SEDIMENT PARAMETERS OF 12 SELECTED SAMPLES .... 26 2. SUSPENDED SEDIMENT CARRIED IN FLATHEAD RIVER . 32 3. CLAY-MINERAL PERCENTAGES IN BELT BEDROCK, FLATHEAD LAKE SEDIIŒNTS AND GLACIAL DRIFT . 33 4. CLAY-MINERAL PERCENTAGES OF SAMPLES TAKEN OUTSIDE OF FLATHEAD L A K E ....................... 38 5. CHEMICAL ANALYSES OF FLATHEAD LAKE AND FLATHEAD RIVER .......................................... 44 6. SETTLING Tims FOR PARTICLES OF VARIOUS SIZES . 63 7. PROGRAM FOR COMPUTATION OF VARIOUS SEDIMENT PARA­ METERS .......................................... 66 8. COMPARISON OF COMPUTER-DERIVED AND MANUALLY- DERIVED SEDIMENT PARAMETERS ................... 68 9. SEDIMENT THIN-SECTION DESCRIPTIONS .............. 70 10. CLAY-SIZE SETTLING TIME UNDER CENTRIFUGAL ACCELERATION..................... 76 11. PRECISION OF X-RAY QUANTITATIVE ANALYSIS IN PERCENTS ........................................ 83 12. SIZE AND CLAY PERCENTAGES IN FLATHEAD LAKE .... 84 13. CLAY SAMPLE LOCATIONS FROM FLATHEAD VALLEY .... 86 14. GRAVITY DATA .................... 90 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V TABLE PAGE PLATES 1. LAKESHORE GEOLOGY OF FLATHEAD LAKE In folder 2. SEDIMENT-SIZE DISTRIBUTION WITHIN FLATHEAD LAKE .........................................In folder Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Flathead Lake has a maximum depth of 360 feet, is 27 miles long, averages ? miles wide, and covers an area of about 200 square miles. Six major drainage systems encompassing an area of over 7500 square miles feed into the lake. The climate of the area is considered semi- arid with an average rainfall of about fifteen inches and an average annual temperature of about The present study consisted of sampling the lake sediments and analyzing these sediments for size distribu­ tion and mineral content. In addition, chemical data (including temperature and pH measurements) were collected from the lake water, and a portion of the lakeshore geology , was mapped. The lake is located at the southern end of the Rocky Mountain Trench and is bounded on the east and west sides by north-south striking normal faults which form a graben structure. Inclination of strata in the area is generally to the northeast with dips ranging between 20° and 45°. Bedrock consists of the Ravalli and Piegan Groups, belonging to the Precarabrian Belt Supergroup. The Ravalli Group consists of thin to medium bedded, gray to reddish argillites, and quartzites, whereas the Piegan Group is com­ posed of limestones, dolomites, and calcareous gray, green. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 and purple argillites. The area was extensively glaciated at least twice during Wisconsin time by ice moving south along the Rocky Mountain Trench, Terminal moraines of the last two advances are found in the Flathead Valley south of Flathead Lake. Sediment size distribution is directly related to the position of the Flathead River delta and the shorelines of the lake. Coarse material near shore grades into silts and clays. Sediments on the Flathead River delta at the north end of the lake are well sorted sands which grade rapidly southward to poorly sorted silts and silty-clays. Minerals found in the lake were : clays, quartz, calcite, plagioclase, orthoclase, and minor to trace amounts of magnetite, hypersthene, biotite, chlorite, hematite,