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Geology of Part of the Greenhorn Range Oregon

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Geology of Part of the Greenhorn Range Oregon GEOLOGY OF PART OF THE GREENHORN RANGE AND VICINITY, MADISON COUNTY, MONTANA by John Neal Bubb A THESIS submitted to OREGON STATE COLLEGE in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE June 1961 7 APPROVED: Redacted for Privacy Assistant Professor of Geology In Charge of Major Redacted for Privacy Chairman of Department of Geology 7-7 Redacted for Privacy Chai n of (pahool Or- uate Committee Redacted for Privacy Deaf of Graduate School Date thesis is presented 4,1,4 ) 94 o Typed by Ruth Chadwick ACKNOWLEDGMENT I am indebted to Dr. D. A. Bostwick who suggested the thesis problem and provided encouragement and super. vision during all phases of the work. I am grateful to all members of the faculty of the department of Geology for their assistance and stimulation, particularly to Dr. I. S. Allison for careful editing of the thesis, to Dr. J. C. Cummings for suggestions concern. ing the sedimentary petrology, and to Mr. J. R. Snook for assistance with the metamorphic petrography. The many conversations and cheerful companionship of Douglas Manske during the field season were invaluable. Thanks are due to Hal. Christie, who donated several days helping measure etratigraphic sections in the thesis area. I wish to express appreciation to Dr. W. Lowell of the Indiana University, who pointed out and discussed several lower Paleozoic formations near the Indiana Uhl versity summer field camp. TABLE OF CONTENTS INTRODUCTION 1 STRATIGRAPHY . 5 Cherry Creek Group . , it 5 Thickness . 11 Lithology..... *4 11 Marbles . a # 1 . 13 Gneisses . 0* Schists . 15 Amphibolites . 17 Pegmatites . * . 19 Metamorphic Rank and Origin . *4* 20 Evolution of Local Cambrian Stratigraphic Nomenclature . 22 Flathead Formation . ..... a 24 Distribution and Physiographi Expression 25 11 Thickness . * . 25 Lithology # . 26 Lower Flathead Formation . 26 Upper Flathead Formation . 29 e and Correlation . 31 Origin and Depositional Environ 31 Meagher Limestone a . # 0 34 Distribution and Physlographic Expression 34 . ... Thickness 6 3 Lithology.... .. Age and Correlation . 36 Origin and Depositional Environment . 39 Park Shale... a 39 Distribution and Physiographic Expression a . 40 Thickness . Ito Lithology . 4 41 Age and Correlation . 41 Origin and Depositional Environment . 42 TABLE OF COA S (Continued Page im Limestone . 0 0 * Distribution and Phy siographic Expression . 4 0 Thickness, . Lithology . 0 0 as Age and. Correlation . Origin and Depositional Environment . Cambrian Hiatus in the Gravell Range . 50 Undifferentiated Devonian. , . 6 53 Distribution and Physiographic Expression . 9 54 Thickness . 54 Lithology..... 55 Fauna and Correlation . 56 Origin and Depositional Environment . , 57 Madison Group . , . 57 Lodgepole Formation . 58 Distribution and Physiographic Expression ... 0 0 59 Thickness . ... 59 Lithology . ... .. 61 Fauna and Correlation . 63 Origin and Depositional Environment . 64 Mission Canyon Limestone . 65 Distribution and Physiographic Expression . a 66 Thickness .. .... .. 68 Lithology 6 0 0 0 6 Age and Correlation . 70 Origin and Depositional Environmen 7o Amsden Formation... 71 Distribution and Physiographic Expression . 72 Lithology e . 73 Age and Correlation . 6 76 Origin and Depositional Enviro n 76 TABLE OF CO (Continued) Quadrant Formation . 77 Distribution and Physiographic Expression 4 0 0 * * 0 0 0 * 78 Thickness . , . 78 Lithology . ** . ** . Age and Correlation . P Origin and Depositional invironment . 83 Phosphoria Formation . 85 Distribution and Physiographic Expression . 4* 86 Lithology..... 86 Basal Sandstone Unit 86 Covered Zone..... 4 4 0 0 92 Chert Unit . 93 Fossiliferous Dolomite Unit . 95 Age and Correlation . 96 Origin and Depositional Environment . 97 Ellis? Group . 6 100 Distribution and Physiographic Expression . 101 Thickness . ..... 102 Lithology . ... .6 .... 102 Age and Correlation . 105 Origin and Depositional invironment . 106 Kootenai Formation . 0 4 108 Distribution and Physiographic Expression ..... 109 Thickness . .. 110 Lithology . .. 110 Lower Sandstones and Conglomerates . 110 Shales ., . 113 Gastropod and Other Limestones.. .. 113 Upper Sandstone . 115 and Correlation . 116 Origin and Depositional Environment 117 Colorado Group 119 Distribution and Physiographic Expression 119 Thickness . , 11 120 TABLE OF CO (Continued) Page Lithology 120 Shales and Muds nes . 120 Sandstones . 121 Age and Correlation . ... 122 Origin and Depositional Environment . 123 Tertiary Conglomerates and Tuffaceous Sediments 124 Age and Correlation . a a 126 Origin and Depositio Environmen 127 Quaternary Alluvium . 0 128 Glacial Deposits . 128 Valley Fill . 129 IGNEOUS ROCKS . IP * 131 Basalt . , . ... * 131 Age and Correlation ** 133 STRUCTURAL GEOLOGY . ...... * 134 Precambrian Structures . * 134 Laramide Structures . 15 Folding . 136 Faulting . 6 137 Willow Creek Area . Greenhorn Range Area . 131 Devils Lane Area . 3.42 Gravelly Range Area . 143 Joints ... ... 143 Post-Laramide Structures . 144 Analysis of Laramide Structu Geology . 3.114 GEOMORPHOLOGY . * a 149 HISTORICAL GEOLOGY a * * 0 152 BIBLIOGRAPHY . 159 LIST OF ILLUSTRATIONS PLATE Page 1. Index map showing location of thesis area . 2 2. Correlation chart . 4 0 0 9 3. Geologic map . 166 TABLE 1. Summary of stratigraphie units . 6 FIGURE 1. Cherry Creek quartzo-feldspathic gneiss . 14 2. Cherry Creek biotite schist and quartzo- feldspathic layers . a . a 16 3. Blocky outcrop of lower Flathead sandstone. 28 4 Pebbly sandstone and sandstone of lower Flathead formation . 28 5. Modal analysis of typical Flathead for- mation samples . 33 6. Cliffs of Meagher limestone . 37 7. Stacklike outcrop of Lodgepole limestone 60 8. Bold outcrop of massive Mission Canyon limestone . ...... 67 9. Fractured dolomitic quartz sandstone overlain by massive quartz sandstone . 80 10. Modal analysis of Quadrant samples . 11. Fluted outcrop of cross-laminated dolo- mitic quartz sandstone of lower Phesphoria formation . * . a 12. Cross-laminated dolomitic quartz sandstone of Phoaphoria formation . LIST OF ILLUSTRATIONS (Continued) FIGURE Page 13. Dolomitic quartz sandstone of lower Phosphoric formation . 89 14. Ledge forming chert unit of Phoephoria formation . * 94 15. Modal Analysis of Phosphoria samples . 100 16. Disconformable contact between Ellis? group and Kootenai formation . * a a 104 17, Outcrop of well fractured, blocky sand- stone in lower part of Kootenai formation. 112 18. Small drag fold in Madison group lime- stones . 139 19. Cherry Creek gneiss thrust upon massive limestones of Madison group . 139 20. East face of Sheep Mountain . * * Mr 141 21. Rounded accordant summits of Gravelly Range erosional surface . 0 GEOLOGY OF PART OF THE GREENHORN RANGE AND VICINITY, MADISON COUNTY, MONTANA INTRODUCTION The area of this report is in Madison County, Montana, and lies between lat. 45° 06' 08" and lat. 45" 09' 38" and between long. 112" 00' and long. 111' 441 36" It com- prises approximately 52 square miles and includes parts the Greenhorn and Gravelly Ranges (See index map, Plate I). Access is provided by the Call read from the town of Varney to the east, by a dirt road from the Ruby River near Warm Springs, and by unimproved dirt reads from Vir ginia City via Alder Gulch or the Axototl Lakes. A logging road from Timber Creek, near the Ruby River, to Romy Lake was being constructed at the end of the field season. The area la included in the Northern Rocky Mountain physiographic province defined by Fenneman (15). Maximum relief in the area studied is approximately 4217 feet; maximum elevation is 9697 feet at Sheep Mountain. Small, mostly intermittent streams that flow east to the Madison River drain the eastern side of the area, and small streams that flow west and south into the Ruby River drain the western part. Climatological data are not available for the area studied. Winters are usually cold, characterized by cold 185 s 1112 IIII 1110 1109 9 ID 2p miles SCALE 46 iButte MONTANA 4s ',Three Forks MADISON \\-P\ COUNTY DIIIonM 45 I DAHO YELLOWSTONE NATIONAL %Lima WYOMING PARK ) 44 44 1115 1114 1113 1112 1111 111o PLATEI. INDEX MAP SHOWING LOCAT 10 N OF THESIS AREA IN) waves and blizzards. Freezing temperatures and snowfall occur as late as June and as early as September. Summer days are warm; discomfort of hot days is relieved by cold nights. The area is semi-arid; ;recipitation, for 1941, was about 14 inches per year (66, p. 965). However, melt- ing snowbanks which persist in the meuntainoua areas through summer months, and summer rainstorms encourage the growth of conifers and grasses at higher elevations. Field work was done in approximately ten weeks during the summer of 1959. U. S. Geological Survey topographic maps of the Varney and Cameron quadrangles were enlarged to 1:21,000 for plotting the initial geology. Thickness of stratigraphic units was measured with a 100-foot steel tape and Brunton compass. Laboratory study was conducted during the school year 1959-1960. Petrographic examina- tion of 95 thin sections was made; modal analysis of sedi- mentary rocks was determined using the Wentworth integrat- ing stage. Staining with Titan Yellow (Clayton Red), following the procedures outlined by Friedman (17, p. 92 was used to distinguish between dolomite and calcite. The earliest geologic work recorded is that of Peale (46), who included the thesisarea in a reconnaissance map of the Three Forks Quadrangle. He referred the present Greenhorn Range, Gravelly Range, and Tobacco Root Mountains to the Jefferson Range. Condit, Pinch and Pardee (9)
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