Lehigh University Lehigh Preserve Theses and Dissertations 1-1-1983 Geological investigation of the Railroad Ridge diamicton, White Cloud Peaks area, Idaho. Susan L. Gawarecki Follow this and additional works at: http://preserve.lehigh.edu/etd Part of the Geology Commons Recommended Citation Gawarecki, Susan L., "Geological investigation of the Railroad Ridge diamicton, White Cloud Peaks area, Idaho." (1983). Theses and Dissertations. Paper 2426. This Thesis is brought to you for free and open access by Lehigh Preserve. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Lehigh Preserve. For more information, please contact [email protected]. GEOLOGICAL INVESTIGATION OF THE RAILROAD RIDGE DIAMICTON, WHITE CLOUD PEAKS AREA, IDAHO by Susan L. Gawarecki A Thesis Presented to the Graduate Committee of Lehigh University in Candidacy for the Degree of Master of Science in Geological Sciences Lehigh University 1983 ProQuest Number: EP76702 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. uest ProQuest EP76702 Published by ProQuest LLC (2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 This thesis is accepted and approved in partial fulfillment of the requirements for the degree of Master of Science. Pecan*?* 7, '&£ Date BL Evejiserf. ;sor in Charge Charles B. Sclar, Chairman of Department n ACKNOWLEDGEMENTS I wish to thank the thesis committee, Dr. Edward B. Evenson, Dr. Bobb Carson, and Dr. Paul B. Myers, for being ready with advice when needed. Special thanks are due to my father, Stephen J. Gawarecki, for providing maps, publications, and advice; to the geologists at the Sawtooth National Recreation Area for the use of their air photos; to Dr. James M. Parks for his patient help with the statistical analyses; to David A. Chapin for his expert advice concerning the use of the computer text-processing program; and to Ric Pantonial and Russ Jeffcoat of the University of South Carolina Geology Department photo lab for prompt, professional service. I am especially grateful for Stephen K. Perry's invaluable labor as a field assistant, typist, and draftsman, and for his critical evaluation of this work. Financial support of the thesis fieldwork by Sun Oil Company, the laboratory research by Sigma Xi, and expenses incurred on the final draft by the Earth Sciences and Resources Institute, University of South Carolina, is gratefully acknowledged. m TABLE OF CONTENTS ACKNOWLEDGEMENTS iii ABSTRACT 1 1 INTRODUCTION 3 2 GEOLOGIC SETTING 5 2.1 GEOGRAPHY 5 2.2 BEDROCK GEOLOGY 8 2.3 QUATERNARY GEOLOGY 12 3 PREVIOUS WORK ON THE RAILROAD RIDGE DIAMICTON AND 18 SIMILAR DEPOSITS 4 FIELD INVESTIGATION 23 4.1 DIAMICTON CHARACTERISTICS AND EXTENT 23 4.2 SAMPLE SITES 32 4.3 DIAMICTON MORPHOLOGY 34 5 LABORATORY METHODS 37 5.1 SIZE ANALYSES 37 5.2 PROVENANCE OF MATRIX SAMPLES 39 6 RESULTS 40 6.1 SIZE ANALYSES 40 6.2 PROVENANCE 42 7 DISCUSSION 44 7.1 HYPOTHESES 44 7.2 SEDIMENTOLOGICAL PROPERTIES 46 7.3 PROVENANCE 54 7.4 GEOMORPHOLOGY 65 7.5 CHRONOLOGY OF GEOMORPHIC EVENTS 70 8 CONCLUSIONS 77 REFERENCES 83 APPENDICES 1 SIZE ANALYSIS DATA 87 2 PROVENANCE DATA, BOULDER LITHOLOGIES 89 3 PROVENANCE DATA, PEBBLE LITHOLOGIES 92 4 PROVENANCE DATA, HEAVY MINERAL SPECIES (WITH ALTERITES) 95 5 PROVENANCE DATA, HEAVY MINERAL SPECIES (WITHOUT ALTERITES) 98 VITA 101 IV LIST OF FIGURES Figure Page 1 Location map of study area. 6 2 Generalized bedrock geology of the White Cloud 9 Peaks area. 3 Glacial limits and moraine positions of the 14 northeastern White Cloud Peaks area. 4 Railroad Ridge, view east from Silver Rule cirque. 24 5 Sketch of brown zone in landslide escarpment. 29 6 Transects and measured slopes of the Railroad Ridge 35 diamicton and bedrock surfaces. 7 Size distribution of five matrix samples. 41 8 Cumulative size percentage plot of the Railroad 47 Ridge diamicton and other diamictons. 9 (a) Mean versus standard deviation for the Railroad 48 Ridge diamicton and other diamictons. (b) Skewness versus standard deviation for the Railroad Ridge diamicton and other diamictons. 10 Reconstruction of the White Cloud Peaks region prior 64 to the valley cutting episode. 11 Isopach map of reconstructed Railroad Ridge diamicton 66 thickness. 12 Cross section of the reconstructed Railroad Ridge 69 diamicton and profiles of alluvial fans. 13 Idealized sequence of geomorphic events. 71 (a) Development of the post-Challis erosion surface. (b) Deposition of the Railroad Ridge diamicton. (c) Erosion of the modern valleys. LIST OF TABLES Table Page 1 Pipette schedule for fine fraction based on 38 Stoke's Law at 25° C. 2 Formulas for size analysis statistical parameters. 38 3 Statistical parameters for five matrix samples. 40 LIST OF PLATES Plate all plates in pocket 1 Map of the Railroad Ridge Diamicton 2 Boulder Lithologies, Long Form Data 3 Boulder Lithologies, Short Form Data 4 Pebble Lithologies, Long Form Data 5 Pebble Lithologies, Short Form Data 6 Heavy Mineral Data VI ABSTRACT The Railroad Ridge diamicton, capping four interfluves on the east flank of the White Cloud Peaks, Idaho, is one of many ridgetop deposits found throughout the American Cordillera. It is characterized by large granitic boulders in an unsorted matrix, a smooth, gently sloping surface morphology, and an estimated thickness of up to 520 feet (158 m). Previous investigators have tentatively regarded the Railroad Ridge diamicton as a glacial till. Several different hypotheses regarding depositional mechanisms are considered here; these include landslides, rockfalls, torrential streams, and saturated debris flows, such as mudflows and solifluction. Of these, the most reasonable alternative hypothesis is deposition by the action of mudflows, forming a fan morphology. Size analyses of five unweathered matrix samples and the resulting statistical determinations of mean, standard deviation, and skewness were compared to the same parameters from other diamictons. The results, confirmed by discriminant function analysis, favor the hypothesis of deposition by fan-building mudflows over glacial action, although no modern analog is known. Sedimentologically, mudflows can have characteristics similar to those of tills: large boulders may be present, the matrix is unsorted, and stratification is generally lacking. Geomorphological evidence supporting the fan-building mudflow hypothesis includes: 1. the deposit's smooth, slightly concave surface profile; 2. crude layering of boulders and a possible buried paleosol parallel to the deposit's surface; 3. its position relative to the source area; and 4. the extreme thickness of the deposit. Provenance data indicates that the Railroad Ridge diamicton occurring on the three southern ridges ("the Spur," Red Ridge, and "Trimline Ridge") has higher intrusive concentrations than that occurring on Railroad Ridge. The inverse spatial relationship is found for metasediment concentrations. Nowhere are extrusive lithologies common; most areas lack them completely. In some cases, provenance can also separate the Railroad Ridge diamicton from the valley tills deposited by the latest major glaciation. The source area for the granitic component of the Railroad Ridge diamicton is the White Cloud stock. Prior to valley cutting, drainage from the quartz monzonite highlands must have moved in part across Railroad Ridge. A tentative reconstruction of the source area indicates the central portion had drainage divides further to the east. Headward erosion has since moved the divides westward and pirated drainage of the stock away from Railroad Ridge. The age of the Railroad Ridge diamicton is probably Pliocene, as deduced from bounding geomorphic surfaces. The development of the post-Challis erosion surface on which the deposit rests took place over the course of the Miocene. The rejuvenation of the Salmon River system, causing the incision of the modern drainage in the study area, began no later than early Pleistocene. Deposition of the diamicton itself may have been a climatically induced event. 1 INTRODUCTION Many areas of the American Cordillera exhibit unusual ridgetop diamictons adjacent to high peaks (Atwood, 1915; Alden, 1924; Blackwelder, 1931a; Richmond, 1957; Scott, 1973; Madole, 1982). While many such deposits are recognized as predating the last major valley-cutting episode, little research on their age or origin has been carried out. The Railroad Ridge diamicton, as it is here informally designated, is an example of such a ridgetop deposit. It is located in the White Cloud Peaks area, Custer County, Idaho, and is described in detail by Ross (1929; 1937; unpubl.). There exist many questions regarding the origin, extent, and age of this deposit. In order to place the Railroad Ridge diamicton in a climatic and tectonic framework, investigation based on sedimentological and morphological considerations has been carried out. This extends beyond the early research of Ross and later work by Tshanz and others (1974), who based their theories solely on observational evidence. The Railroad Ridge diamicton has elicited controversy due to features inconsistent with such common alpine Quaternary deposits as valley glacial deposits, felsenmeer, rock glaciers, landslides, talus, and stream terrace deposits. These features are: 1. its postion capping four interfluves on the east side of the White Cloud Peaks at elevations up to 10,800 feet (3292 m); 2. the preponderance of \/ery large granitic boulders in an unsorted matrix; 3. the extreme deposit thickness, greater than 500 feet (152 m), attained on the divide between Big Boulder and Jim Creeks; 4. the smooth, gently-sloping surface profile on Railroad Ridge and adjacent ridges; and 5.