SHORT NOTES ON ALASKA GEOLOGY 1995 Professional Report 117 Published by STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS MILTON A. WILTSE ACTING STATE GEOLOGIST 1995 SHORT NOTES ON ALASKA GEOLOGY 1995 Edited by Rodney A. Combellick and Fran Tannian Cover design by Ann-Lillian C. Schell Professional Report 117 Front cover: Exposure of till and outwash of the Elmendorf glacial advance at Goose Bay, west side of Knik Arm. (See paper by Reger and others, page 33.) Geologist Richard Reger examines Goose Bay peat of mid- Pleistocene age. Photograph by R.A. Combellick. Fairbanks, Alaska 1995 FOREWORD The Alaska Division of Geological & Geophysical Surveys (DGGS) here presents Short Notes on Alaska Geology 1995, the ninth issue in this series. There are ten papers, two each in Quaternary geology, structural geology, stratigraphy-sedimentology, and paleontology, and one each in economic geology and geochemistry. Almost all geo- graphic regions of the State are represented. Overall, they reflect the wide range of subjects and broad geographic distribution of current geologic research in Alaska. I want to take this opportunity to recognize the contributions of Tom Smith and Dick Reger, veteran DGGS geologists retiring this year, for their long service with DGGS (14 years and 19 years, respec- tively) and contributions to Alaskan geology. Tom began his Alaskan work in 1966 as a geophysicist; I knew him best during his six years STATE OF ALASKA (1975–81) with the University of Alaska Fairbanks (UAF). Since 1981 Tony Knowles, Governor Tom has served with DGGS–for the last four years as state geologist and director. Dick came to UAF in 1957 as an undergraduate student DEPARTMENT OF and has been in Alaska ever since, except for Ph.D. work and some NATURAL RESOURCES teaching in Arizona. He has been with DGGS continuously since 1975. John T. Shively, Commissioner Together Tom and Dick possess an important part of what is known about the geology of Alaska as carried about in the brains of living DIVISION OF GEOLOGICAL & geologists. Together they have more than 60 years of experience in GEOPHYSICAL SURVEYS Alaska and have published well over 150 articles, maps, and abstracts Milton A. Wiltse, Acting about Alaska geology. State Geologist They will, of course, also be missed as the fine and unique human individuals that they are. However, I want to reflect on the broader significance of the loss of so much knowledge and experience and implications for the status of geology in Alaska. For reasons I can’t go Division of Geological & Geophysical into here, experience is more important in geology than in any other Surveys publications may be inspected science, with the possible exception of biology. In most cases you can at the following loca tions. Address mail meet your needs in engineering or physics by hiring younger replace- orders to the Fairbanks office. ments. Often this is not the case in geology. Deep understanding of the proper scales of time and rates of processes requires years of field Alaska Division of Geological & experience with a variety of rocks and sediments in many localities. Geophysical Surveys In Alaska, those who have this experience represent a significant Attn: Publications 794 University Avenue, Suite 200 investment of time and money. They cannot be replaced except by a Fairbanks, Alaska 99709-3645 similar investment of time and money. My concern is not the occasional loss of geologists like Tom and Dick–this is inevitable–but failure to Department of Natural Resources develop and maintain a continuing supply of geologists with decades Public Information Center of Alaskan experience. Their ranks are getting thin, perhaps danger- 3601 C Street, Suite 200 ously so. Somewhere within the profession–DGGS, U.S. Geological Anchorage, Alaska 99510 Survey, University of Alaska, and industry–we must nurture a core of experience. The future of our state depends on it. This publication, released by the Division This brings me to my final point. These Short Notes are an im- of Geological & Geophysical Surveys, was portant vehicle for the accumulation of Alaskan geological experience produced and printed in Anchorage, Alaska emphasized above. In particular, I hope that more younger geologists by A.T. Publishing & Printing, Inc., at a cost will contribute to future volumes and thereby be encouraged to stay of $15 per copy. Publication is re quired by in Alaska and become qualified replacements for the likes of Tom Alaska Statute 41, "to determine the potential of Alaskan land for production of metals, Smith and Dick Reger. minerals, fuels, and geothermal resources; the location and supplies of groundwater and construction materials; the potential geologic hazards to buildings, roads, bridges, and other installations and structures; and shall conduct Don Triplehorn such other surveys and investigations as will Professor of Geology advance knowledge of the geology of Alaska." University of Alaska Fairbanks ii CONTENTS Page Radiocarbon age of probable Hayes tephra, Kenai Peninsula, Alaska Rodney A. Combellick and DeAnne S. Pinney ............................................................................................ 1 Geochemistry of saline lakes of the northeastern Yukon Flats, eastcentral Alaska Daniel B. Hawkins ...................................................................................................................................... 11 Geometry and deformation of a duplex and its roof layer: Observations from the Echooka anticlinorium, northeastern Brooks Range, Alaska Andrew J. Meigs and Teresa A. Imm ........................................................................................................... 19 Late-Wisconsin events in the Upper Cook Inlet region, southcentral Alaska Richard D. Reger, Rodney A. Combellick, and Julie Brigham-Grette ........................................................ 33 Stratigraphy and implications of a lakeside section, Glacial Lake, southwestern Kigluaik Mountains, Seward Peninsula, Alaska Richard D. Reger and David M. Hopkins ................................................................................................... 47 Lithofacies, petrology, and petrophysics of the Kemik Sandstone (Lower Cretaceous), eastern Arctic Slope, Alaska Rocky R. Reifenstuhl ................................................................................................................................... 53 A new species of the conodont amydrotaxis From the Early Devonian of southwestern Alaska Norman M. Savage and Robert B. Blodgett ................................................................................................ 69 Early Devonian and Late Triassic conodonts from Annette and Hotspur Islands, southeastern Alaska Norman M. Savage and George E. Gehrels ................................................................................................ 75 Mineralization and zoning of polymetallic veins in the Beaver Mountains volcano-plutonic complex, Iditarod Quadrangle, westcentral Alaska David Szumigala ......................................................................................................................................... 79 Possible thrust windows on the central Seward Peninsula, Alaska Lorne E Young ............................................................................................................................................. 97 Previous editions of Short Notes on Alaska Geology ................................................................................. 115 iii RADIOCARBON AGE OF PROBABLE HAYES TEPHRA, KENAI PENINSULA, ALASKA by Rodney A. Combellick1 and DeAnne S. Pinney1 INTRODUCTION of 0.96) but lacks bracketing ages. The mineralogy of a tephra he sampled near Kenai appears to correlate with Hayes volcano in southcentral Alaska (fig. 1) pro- the Hayes set but has a low similarity coefficient of 0.88 duced as many as eight closely spaced tephra deposits and lacks bracketing ages. about 3,650 ± 150 14C yr B.P. (3,730–4,150 cal yr B.P.) In this paper we describe the mineralogy, glass chem- (Riehle, 1985; Riehle and others, 1990). These layers are istry, and radiocarbon ages of tephra layers embedded in the most widespread of all tephras in the Cook Inlet region thick late-Holocene peat deposits along the Kasilof and and have been observed as far away as the lower Delta Kenai River estuaries. We conclude that a 3-cm-thick River area in central Alaska, more than 650 km northeast tephra at each location strongly correlates with the Hayes of the vent (Begét and others, 1991). set. Our data extend the apparent southeast limit of Hayes Hayes tephras have a bilobate distribution, one por- tephra deposits, show probable correlation with one of the tion directed south and the other northeast of the vent seven proximal tephras, and provide additional age control (Riehle and others, 1990, fig. 3). Riehle determined the for the eruption. likely dispersal axes of individual tephra deposits by comparing glass and ilmenite compositions of distal layers 1Alaska Division of Geological & Geophysical Surveys, 794 University with each of seven proximal layers, A–G, sampled about Avenue, Suite 200, Fairbanks, Alaska 99709-3645. 50 km northeast of the vent. On the Kenai Peninsula, less than 100 km southeast of the vent, the apparent absence of tephras that can be positively correlated with the Hayes set indicates that tephrafall to the southeast was less extensive than to the south and north- east. Riehle sampled a tephra