University of Nevada, Reno Mid- to Late-Paleozoic Deformation on Buck Mountain, Nevada A thesis submitted in partial fulfillment of the Requirements for the degree of Master of Science in Geology by Ross J. Whitmore Dr. Patricia H. Cashman/Thesis Advisor May, 2011 ©By Ross J. Whitmore 2011 All Rights Reserved THE GRADUATE SCHOOL We recommend that the thesis prepared under our supervision by ROSS J. WHITMORE entitled Mid- To Late-Paleozoic Deformation On Buck Mountain, Nevada be accepted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Patricia H. Cashman, Ph.D. , Advisor James H. Trexler Jr., Ph.D. , Committee Member Robert S. Sheridan, Ph.D. , Graduate School Representative Marsha H. Read, Ph. D., Associate Dean, Graduate School May, 2011 i Abstract New detailed structural mapping of the strata capping Buck Mountain in White Pine Co., Nevada, has documented two distinct episodes of folding. The structures and angular unconformities at Buck Mountain are consistent with late-Paleozoic deformation and regional unconformities documented previously elsewhere in northern and central Nevada. Folds in the Morrowan-Atokan Ely Limestone are erosionally truncated and depositionally overlain by the mid-Desmoinesian Hogan Formation. The lacuna developed at this stratigraphic level is temporally consistent with a regional unconformity (“C5” of Snyder et al., 2000). This unconformity is an upper boundary on regional west- vergent folding. In addition, two disconformities are found on Buck Peak. Both disconformities correlate with known regional unconformities, one Desmoinesian- Missourian (“C6”) and the other Missourian to Sakmarian (mid-Wolfcampian) (“P1”). F1 folds are pre-Desmoinesian in age and are the oldest structures discussed. These folds range from close west-vergent to open, upright, and symmetric folds. The range of fold geometries is driven by localization of strain during shortening. F1 folds are erosionally truncated and refolded around a younger northwest fold axis. When F1 folds are restored, their original plunge is ~10° to the northeast. The map-scale syncline fold at Buck Mountain is a syncline developed in the Ely Limestone, Hogan Formation, and both Lower and Upper Strathearn formations and is therefore part of a second fold set (F2). It is a gentle to open, symmetric, upright, cylindrical fold plunging ~15° to the northwest (323°) with a wavelength of about 1 km ii and unknown amplitude. The age of this fold is poorly constrained at Buck Mountain (post-Sakmarian to Oligocene), but it appears to correlate with Mesozoic folds in adjacent ranges. No evidence was found for low-angle faulting on Buck Mountain. Previous work identified a single attenuation fault at the base of the mountain (Nutt, 2000). In addition, reconnaissance work described intense folding at the top of the range, suggesting the presence of a different low-angle fault there. However, this study found that the folds are not localized around structurally defined surfaces. Rather, they occur at all structural levels. Thick massive carbonate layers form gentle long wavelength folds and local minor faults with 2-3 meters of offset. Thinner-bedded carbonate layers form open folds with shorter wavelengths. The contrast in fold style and apparent intensity is interpreted as a competency response to shortening between thick- and thin-bedded carbonate layers. The presence of mid-Pennsylvanian folds at Buck Mountain is important because it: 1) correlates with other sub-C5 folds and faults in eastern Nevada and extends the known geographic extent of these structures, 2) helps constrain the orientation of the regional Pennsylvanian deformation, and 3) documents a regional eastward decrease in intensity of mid-Pennsylvanian folds and faults. iii Acknowledgments This project would not have been possible without the support of the National Science Foundation (grant EAR0510915 to Cashman and Trexler), two grants from the Nevada Petroleum Society, and the UNR Viola Vestal Coulter Graduate Scholarship. I would genuinely like to thank Pat Cashman and Jim Trexler for pushing me to be better. Thank you to Dan Sturmer for just being Dan. Thanks to Annika Taylor for being better to me than I am to myself. Thanks to Rachel Wearne and Liz Phillips for their helpful hands in the field. I am especially grateful to my Old Man and Ma, who have always pushed me to do better in all aspects of my life. I am truly thankful to the following people: Josh “Squirrel Bait” Michaels, Alex “Star money” Sarmiento, Sarah “Short-n’-feisty” O’Connor, Stephanie “Possibly the nicest person on the planet” Watts, Tristan “T-DOG” Ashcroft, Amie “BAHHH” Lamb, Betsy “I have Stigmata issues” Littlefield, and Crystal “the awesome” Robbins. I would like to thank the following teachers for their impact on my life: John Spengler, Kathryn Bott, Janelle Adams, Cindy Hoack, Bill Nesse, Ken Hopkins, Ed Ripley, and Bruce Douglas. I would also like to thank my students for being reasonably entertaining in class. I know that many of you caught something I threw out. I am sure to have forgotten someone, so I am sorry. There are really too many people to thank. I have so many people that have encouraged me and egged me on. I cannot wait to be a cheerleader for the wonderful people who have made this experience better. I could not have done it without a lot of loving support form a lot of loving individuals. iv The following bands/composers were instrumental (no pun intended) in helping me through the hard days of graduate school: A Perfect Circle, Bloodsimple, Bad Religion, Bach, Beethoven, Corporate Avenger, Coal Chamber, Cold, Crux Shadow, Dry Kill Logic, D.J. Irean, Dropkick Murphy, The Foo Fighters, Full Devil Jacket, Five Finger Death Punch, Godsmack, Garbage, Incubus, The Killers, Muse, Mudvayne, Motograter, Mushroomhead, Mozart, Monster Magnet, Marilyn Manson, Orgy, Queens of the Stone Age, Radiohead, The Red Hot Chili Peppers, Rob Zombie, Ray La Montaigne and the Pariah Dogs, Rammstein, Slipknot, System of a Down, Skinny Puppy, Snot, Tool, Vivaldi, White Zombie, and Yo Yo Ma. I am also grateful for the three months I spent living and working on Buck Mountain. The three months there have taught me more about myself than the previous 25 years of my life. This experience has been one of the most challenging and trying times of my life and I would not trade it for anything. v Table of Contents Abstract…………………………………………………………………….i Acknowledgments………………………………………………………….iii Table of Contents…………………………………………………………..v List of Figures………………………………………………………………vii Introduction………………………………………………………………...1 Background…………………………………………………………………5 Brief Structural History of Eastern Nevada………………………….5 Unconformity Scheme…………………………………….………...9 Mid- to late-Paleozoic Unconformities……………………………..10 Mid- to late-Paleozoic Deformation…………………………………14 Regional Setting………………………..……………………………15 Structural Descriptions of Buck Mountain...………………………..19 Methods……………………………………………………………………..21 Paleozoic Stratigraphy……………………………………………………..23 Mississippian Strata………………………………………………….24 Pennsylvanian Strata…………………………………………………25 Permian Strata………………………………………………………..28 Tertiary Volcanic Rocks...…………………………………………...32 Structure…………………………………………………………………….33 Pennsylvanian Folding (F1)...………………………………………..33 Interpretation of west-vergent folds………………………………….35 Post Early-Permian Folding (F2)…………………………………….37 Post Eocene High-Angle Normal Faults……………………………..39 vi Summary of Geologic History of the Buck Mountain area.…………42 Discussion……………………………………………………………………48 Regional Extent & Significance of Pennsylvanian & Permian Unconformities…………………………………………….…48 Age and Orientation of Structures……………………………………53 Implications for Late Paleozoic Tectonic Models……………………56 Conclusions………………………………………………………………….60 Importance of This Work…………………………………………….60 Future Work ……………………………………………………........60 References…..………………………………………………………………..62 Appendix…….……………………………………………………………….68 Figures……….……………………………………………………………….71 vii List of Figures Figure 1………………………………………………………………………..71 Location Map Figure 2………………………………………………………………………..72 Large-scale structure map Figure 3………………………………………………………………………..73 Unconformity Scheme Figure 4………………………………………………………………………..74 Map showing locations mentioned in text Figure 5………………………………………………………………………..75 Location Map showing: the Ruby Mountains, Diamond Mountains, Alligator Ridge mine, and Bald Mountain mine Figure 6………………………………………………………………………..76 Stratigraphic column of rocks found on Buck Mountain Figure 7………………………………………………………………………..77 Oblique aerial photo of Buck Mountain Figure 8………………………………………………………………………..78 Photo of Ely Limestone Figure 9………………………………………………………………………..79 Photo of Ely Limestone poking through Hogan Formation Figure 10..……………………………………………………………………..80 Photo of limestone rip-up clasts at the Base of the Hogan Formation Figure 11..……………………………………………………………………..81 Photo of Hogan Formation viii Figure 12..……………………………………………………………………..82 Photo of Lower Strathearn Formation Figure 13..……………………………………………………………………..83 Stereogram of both pre-mid-Desmoinesian and post-Sakmarian folds Figure 14..……………………………………………………………………..84 Photo and stereogram of a west-vergent pre-mid-Desmoinesian fold at “Dover Cliff” Figure 15..……………………………………………………………………..85 Photo and stereograms of pre-mid-Desmoinesian folds at “Syncline Ridge” and “Train Ridge” Figure 16..……………………………………………………………………..86 Stereogram showing restored pre-mid-Desmoinesian fold orientation Figure 17..……………………………………………………………………..87 Photo and stereogram of