Short Notes on Alaska Geology 1999 Short Notes on Professional Report 119 State of Alaska Department of Natural Resources Division of Geological & Geophysical Surveys Milton A. Wiltse State Geologist 1999 EDITORIAL POLICY Short Notes on Alaska Geology is a collection of brief scientific papers describing recent geological investigations of limited scope. This publication is widely distributed to a state, national, and international audience that represents industry, academia, government agencies, and the general public. Manuscripts are accepted for consideration with the understanding that they have not been previously published and are not being submitted for publication elsewhere, that all persons listed as authors have given their approval for submission of the paper, and that any person cited as a source of personal communication has approved such a citation. Authors are encouraged to suggest appropriate reviewers and provide reviewers’ telephone numbers. SUBMISSION OF MANUSCRIPTS Authors should submit three paper copies of their draft manuscripts to Short Notes Editor, Alaska Division of Geologi- cal & Geophysical Surveys, 794 University Avenue, Suite 200, Fairbanks, Alaska 99709-3645. Contributors should retain one copy of all materials submitted. DGGS is not responsible for materials lost in the mail. In general, articles are limited to about 10 manuscript pages (approximately 2,000 words of text), including references, figures, and tables. All draft manuscripts will be examined and approved by the DGGS editor and at least two reviewers. After technical reviews are completed, copies of review forms and reviewed manuscript pages will be returned to the author for revision (if required) and resubmittal. Conflicts between reviewers and authors must be resolved to the satisfaction of the DGGS editor before final acceptance of manuscripts. Final submittals must be provided as double-spaced paper copy and on high-density IBM-compatible diskette (Microsoft Word or WordPerfect). Questions should be directed to the DGGS editor 907-451-5053. Major changes by the author—whether scientific or editorial—are not permitted after the manuscript is in galley form. TEXT PREPARATION Manuscripts should be double spaced with 1-inch margins on all sides. The title page should include the title of the article and the name(s) and affiliation(s) of the author(s). Because of the brevity of Short Notes articles, tables of contents, lists of illustrations, and abstracts are not required. Words to be printed in italics should be typed in italics. Use upper and lower case type as appropriate; do not use all caps. Specific guidelines for units of measure, abbreviations, and references are provided in Suggestions to Authors of Reports of the United States Geological Survey (7th edition) or Government Printing Office Style Manual 1973. Poten- tial authors are also encouraged to consult the latest issue of Short Notes for information. PREPARATION OF ILLUSTRATIONS Figures should be provided on an IBM-compatible diskette (either high-density 3½” floppy disk or 100MB Zip disk). Computer-generated drawings should be of a resolution of at least 300 dpi and saved in a format compatible with CorelDraw 7.0 or later, or as a TIF or EPS file if produced from another drawing program. Scans of printed figures or drawings should be saved as TIF or EPS format at 300 dpi resolution at approximately the size they will be shown. If figures are hand drafted and scanning technology is not available to the author at a reasonable cost, please supply high- resolution camera-ready prints of your figures. Line figures are generally published in black and white. Color art may be accepted with the understanding that the author will pay additional printing costs for colored figures. Current page-cost information can be obtained from the DGGS editor. Maximum size for figures is 6½” x 8½”. SHORT NOTES ON ALASKA GEOLOGY 1999 Edited by DeAnne S. Pinney and Paula K. Davis Division of Geological & Geophysical Surveys Professional Report 119 Recent research on Alaska geology Fairbanks, Alaska 2000 Front cover photo: Marine sedimentary rocks of the Nutzotin Mountains sequence (black strata in the foreground) in fault contact with the Wrangellia composite terrane in the Nutzotin Mountains, eastern Alaska Range. White strata in the midground is the Nizina Limestone. Gray strata in the background at the ridge crest is the Nikolai Greenstone. For scale, a person with a blue shirt can be seen on the ridgeline. View is to the north. (Photo by Jeffrey D. Manuszak) Back cover photo (top): View eastward along the west fork of Atigun River of prominent anticlinal hinge in the upper Kanayut Conglomerate (Lower Mississippian to Upper Devonian) within the Toyuk thrust zone, a major thrust zone in the central Brooks Range. See Chmielowski and others (this volume), “Duplex structure and Paleocene displacement of the Toyuk thrust zone near the Dalton Highway, north-central Brooks Range.” (Photo by Reia M. Chmielowski) Back cover photo (bottom): Excavator and bulldozer trench on Lewis Ridge, Donlin Creek property, southwestern Alaska. Trench is approximately 1,300 feet long and part of a 3.7-mile trenching program by Placer Dome Exploration Inc. during the 1997 and 1998 field seasons. Light-colored rocks are igneous dikes and sills, and darker rocks are Kuskokwim Group shale and graywacke. Note the core drill rig in the background to the right of center. (Photo by David J. Szumigala) i OREWORD The biennial Short Notes on Alaska Geology volume is a publication supported by Alaska’s entire geologic community. Alaska has a large and extended community of highly talented earth scientists, many of whom encounter geologic issues of great interest in the course of performing work associated with their primary obligations. In the press to meet organizational mandates, many of these stories could be lost in spite of the interest they hold for all of us. This realization led the Alaska Division of Geological & Geophysical Surveys to establish the Short Notes on Alaska STATE OF ALASKA Geology series so that there would be a vehicle to share Tony Knowles, Governor these insights. By intent and tradition the Short Notes on Alaska Geology series has been an inclusive publication. DEPARTMENT OF NATURAL RESOURCES Contributors to this biennial publication step forward from John T. Shively, Commissioner the ranks of private-sector firms, academia, and government agencies. DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS This volume of Short Notes on Alaska Geology 1999 is the Milton A. Wiltse culmination of two years of predominantly volunteer efforts State Geologist and Director by your colleagues to author 11 articles about stratigraphic, structural, geochronologic, mineral deposit, and paleontologic geologic phenomena observed within the state. These papers contain significant observations and new Division of Geological & Geophysical Surveys data with regional implications that advance the knowledge publications may be inspected at the following of Alaska’s geologic framework and will be cited frequently locations. Address mail orders to the Fairbanks in years to come. office. Editing the “Short Notes” volume, like authoring the papers Alaska Division of Geological & it contains, is an extra duty placed on top of ongoing work. Geophysical Surveys This year we owe our thanks to DeAnne Pinney, who Attn: Geologic Communications Section 794 University Avenue, Suite 200 graciously stepped up to that task. I believe that everyone Fairbanks, Alaska 99709-3645 who has participated in keeping the DGGS Short Notes on http://wwwdggs.dnr.state.ak.us Alaska Geology publication series viable over the years has [email protected] demonstrated a commitment to the finest traditions of Department of Natural Resources collegial science. Authors, editors, reviewers, and Public Information Center publication staff have labored diligently for our benefit. To 550 W 7th Ave., Suite 1250 all of them, I say thank you. Anchorage, Alaska 99501-3557 This publication, released by the Division of Geologi- cal & Geophysical Surveys, was produced and printed Milton A. Wiltse in Fairbanks, by Commerical Printing, at a cost of State Geologist and Director $9.00 per copy. Publication is required by Alaska Statute 41, “to determine the potential of Alaskan land for production of metals, minerals, fuels, and geother- mal resources; the location and supplies of groundwater and construction materials; the potential geologic haz- ards to buildings, roads, bridges, and other installations and structures; and shall conduct such other surveys and investigations as will advance knowledge of the geology of Alaska.” ii CONTENTS The Soda Creek Limestone, a new upper Lower Devonian formation in the Medfra Quadrangle, west-central Alaska R.B. Blodgett, D.M. Rohr, E.A. Measures, N.M. Savage, A.E.H. Pedder, and R.W. Chalmers 1 Duplex structure and Paleocene displacement of the Toyuk thrust zone near the Dalton Highway, north-central Brooks Range R.M. Chmielowski, W.K. Wallace , and P.B. O’Sullivan 11 Borehole breakouts and implications for regional in situ stress patterns of the northeastern North Slope, Alaska C.L. Hanks, M. Parker, and E.B. Jemison 33 Measured section and interpretation of the Tingmerkpuk sandstone (Neocomian), northwestern DeLong Mountains, western Arctic Slope, Alaska D.L. LePain, K.E. Adams, and C.G. Mull 45 Stratigraphic architecture of the Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, Nutzotin and Mentasta mountains, Alaska J.D. Manuszak and K.D. Ridgway 63 Stratigraphy, depositional systems, and age of the Tertiary White Mountain basin, Denali fault system, southwestern Alaska K.D. Ridgway, J.M. Trop, and A.R. Sweet 77 Late Devonian (early Frasnian) conodonts from Denali National Park, Alaska N.M. Savage, R.B. Blodgett, and P.F. Brease 85 Geology and gold mineralization at the Donlin Creek prospects, southwestern Alaska D.J. Szumigala, S.P. Dodd, and A. Arribas, Jr. 91 Preliminary 40Ar/39Ar ages from two units in the Usibelli Group, Healy, Alaska: New light on some old problems D.M. Triplehorn, J.