University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1980 Glacial geology of the southern Flathead Valley Montana Keith L. Stoffel 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 Stoffel, Keith L., "Glacial geology of the southern Flathead Valley Montana" (1980). Graduate Student Theses, Dissertations, & Professional Papers. 7426. https://scholarworks.umt.edu/etd/7426 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]. COPYRIGHT ACT OF 1976 Th is is an unpublished manuscript in which copyright sub ­ s is t s . Any further r e p r in t in g of it s contents must be approved BY THE AUTHOR. Ma n s f ie l d L ibrary llNIVERSkTYr/).5 MONTANA Da t e : . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GLACIAL GEOLOGY OF THE SOUTHERN FLATHEAD VALLEY. MONTANA by Keith L. Stoffel B.S., University of Illinois, 1974 Presented in partial fu lfillm e n t of the requirements for the degree of Master of Science UNIVERSITY OF MONTANA 1980 Approved by: irman, Board of Examiners Dean, Graduate School Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: EP38227 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 OwMrtction PüWwhing UMI EP38227 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 uesf 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. ABSTRACT Stoffel, Keith L., M.S., Spring, 1980 Geology Glacial Geology of the Southern Flathead^Valley, Montana i<r » ) Director: Robert R. Curry ^ The Flathead lobe of the Cordllleran Ice sheet depositedÏ glacial d r ift In the southern Flathead Valley of Montana. Previous workers used geomorphic evidence to Identify three Pleistocene glacial d rift units In the valley: Mission till, St. Ignatius till, and Jocko diamlctons. The goal of this study was to use sedimentary petrologic studies and field mapping to define the stratigraphy of the glacial . drift units and to correlate the stratigraphie units with established glacial chronologies. Thirty-nine samples of southern Flathead Valley glacial sediments were analyzed for their grain size properties by means of hydrometer and sieve analyses. Clay mineralogy of the d r ift units was determined by x-ray diffraction methods. Representative samples of each strati­ graphie unit were examined to define the lithologie composition of their sand fractions. Results show that grain size properties, clay minéralogie composition, and sand fraction llthologles are all similar for each stratigraphie unit studied. Field evidence, radiocarbon dating, and relative age dating In­ dicate that Mission t i l l Is the youngest of the three stratigraphie units studied. A >20,380 year B.P. radiocarbon date from the front of the Mission moraine suggests that "late" Mission t i l l Is middle to late Wisconslnan (early Pinedale) in age. "Earlier" Mission till was apparently deposited by more extensive ice of the same glaciation. Soil development and surface geomorphology Indicate that St. Ignatius till Is significantly older than Mission till. Complex field relationships complicate the age estimation of the St. Ignatius t i l l , but evidence for deposition during early Wisconslnan time Is given. Field and laboratory data produced Indicate that the Jocko diamlctons are glacial tills , which represent the oldest (pre- Wlsconslnan) glaciation In the region. Age, extent, and source area of the Ice depositing the Jocko diamlctons have not been de­ termined, therefore correlation with other glacial chronologies remains speculative. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I extend my warmest appreciation to Dr. Robert Curry, who as my advisor provided guidance and encouragement throughout a ll phases of the study. I would also lik e to thank my committee members Dr. Graham Thompson and Dr. John Donahue for th eir helpful discussions and review of the manuscript. Richard Galster and the Seattle D is tric t of the U.S. Army Corps of Engineers provided funding for the radiocarbon dates. And of course, thanks to Dorothy, for infinite support and inspiration. n 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page ABSTRACT...............................................................................................................i i ACKNOWLEDGMENTS........................................................................................... i i i LIST OF FIGURES...........................................................................................v il CHAPTER I. BACKGROUND AND OBJECTIVES .................................................... 1 Introduction .............................................................................. 1 General Geographic and Geologic Setting ................. 5 Physiography ......................................................................... 5 Geology .................................................................................. 7 Previous W o r k ............................................................................ 10 Methods of Investigation .................................................... 11 I I . GLACIAL CHRONOLOGIES............................................................ 13 Glacial Chronology of the Cordllleran Ice Sheet. 13 General discussion ............................................................. 13 Orting glaciation ............................................................. 14 Alderton interglaciation ................................................ 16 Stuck g la c ia tio n....................................................................16 Puyallup interglaciation ................................................ 18 Salmon Springs glaciation ........................................... 20 Olympia interglaciation ................................................ 21 Fraser glaciation ............................................................. 22 Discussion of Cordllleran chronology problems . 24 i V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER Page Rocky Mountain Glacial Chronology .............................. 26 Introduction ..................................................................... 26 General discussion ........................................................ 26 Pre-Bull Lake glaciations ........................................... 28 Pre-Bull Lake/Bull Lake interglaciation .... 30 Bull Lake glaciations.........................................................31 Bull Lake nonglacial i n t e r v a l s ....................................34 Pinedale glaciations .................................................... 35 Altithermal interval .................................................... 37 Neoglaciation ..................................................................... 38 Early Neoglacial s ta d e .................................. 38 Audubon stade ..................................................................... 39 Gannett Peak s t a d e ............................................................. 39 Correlations ..................................................................... 40 I I I . FIELD OBSERVATIONS ................................................................. 41 Mission T ill .............................................................................. 41 St. Ignatius T ill......................................................................45 Jocko D ia m ic to n s......................................................................47 IV. LABORATORY OBSERVATIONS ........................................................ 51 Laboratory Methods ............................................................. 51 Grain size analyses ......................................................... 51 Grain size distribution cu rves ....................................51 V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER Page Discussion of grain size curves.... ............................. 56 Mission t i n...................................................................... 56 St. Ignatius t i l l ......................................................... 58 Jocko d ia m ic to n s..........................................................59