SHORT NOTES ON ALASKA GEOLOGY 1997 Edited by James G. Clough and Frank Larson Cover design by Ann-Lillian C. Schell Professional Report 118 Recent research on Alaska geology Front cover: View of central Kigluaik Mountains on the Seward Peninsula. Peaks are composed of Thomp- son Creek Orthogneiss of Late Proterozoic to Early Precambrian age and metamorphosed at upper am- phibolite facies conditions about 91 million years Fairbanks, Alaska ago. Photograph by J.M. Amato. 1998 i Foreword This volume of Short Notes on Alaska Geology 1997 is the tenth volume in the series begun by the Alaska Division of Geological & Geophysical Surveys (DGGS) in 1976. The Short Notes series was started as a vehicle in which to sum- marize significant observations on Alaska geology that oth- erwise might not find their way into accessible literature. From the outset an effort has been made to attract the contri- butions of geologists from the public, private, and academic sectors of Alaska’s geologic community. DGGS has a mandate to advance the knowledge of the ge- STATE OF ALASKA ology of Alaska. Clearly, that task is too large to undertake Tony Knowles, Governor alone. By working together, much more can be accom- plished. I would like to reemphasize the inclusive nature of DEPARTMENT OF this publication. I strongly encourage readers of this issue NATURAL RESOURCES to become participants in our next volume. In a very real John T. Shively, Commissioner sense, the Short Notes series is a publication of Alaska’s DIVISION OF GEOLOGICAL & entire geologic community. GEOPHYSICAL SURVEYS Milton A. Wiltse Authors, as well as readers, benefit from contributions. The State Geologist and Director publication process is an effective mechanism for clarify- ing thoughts and eliciting focused comments and pertinent insight from professional peers. Many of you have interest- ing geologic stories to tell, and all of us would learn from Division of Geological & Geophysical Surveys reading about your observations and insights. I know that publications may be inspected at the following our colleagues in the private sector are working in areas locations. Address mail orders to the Fairbanks that are not on the near-term agendas of any government office. agencies. Our colleagues in academia are pursuing specific Alaska Division of Geological & problems that are outside the charter of either the private Geophysical Surveys sector or government geologists. Attn: Geologic Communications Section 794 University Avenue, Suite 200 I believe that all those who have contributed to the present Fairbanks, Alaska 99709-3645 http://wwwdggs.dnr.state.ak.us issue as authors, reviewers, editors, and publication staff [email protected] can take a great deal of pride in the fact that they have in- deed advanced the state of knowledge of the geology of Department of Natural Resources Alaska. Those of us who are recipients of their work are in Public Information Center 3601 C Street, Suite 200 their debt. Anchorage, Alaska 99510 Sincerely, This publication, released by the Division of Geological & Geophysical Surveys, was produced and printed in Fairbanks, Alaska by the University of Alaska Printing Services, at a cost of $9.00 per copy. Publication is Milton A. Wiltse required by Alaska Statute 41, “to determine the poten- State Geologist and Director tial of Alaskan land for production of metals, minerals, fuels, and geothermal resources; the location and sup- plies of groundwater and construction materials; the potential geologic hazards 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 Geochronologic investigations of magmatism and metamorphism within the Kigluaik Mountains gneiss dome, Seward Peninsula, Alaska Jeffrey M. Amato and James E. Wright ......................................................................................................................... 1 Composite standard correlation of the Mississippian-Pennsylvanian (Carboniferous) Lisburne Group from Prudhoe Bay to the eastern Arctic National Wildlife Refuge, North Slope, Alaska John F. Baesemann, Paul L. Brenckle, and Paul D. Gruzlovic ................................................................................. 23 Enigmatic source of oil from Chukchi Sea, northwestern Alaska Arthur C. Banet and Thomas C. Mowatt .................................................................................................................... 37 Emsian (late Early Devonian) fossils indicate a Siberian origin for the Farewell Terrane Robert B. Blodgett........................................................................................................................................................ 53 Growth-position petrified trees overlying thick Nanushuk Group coal, Lili Creek, Lookout Ridge Quadrangle, North Slope, Alaska Paul L. Decker, Gregory C. Wilson, Arthur B. Watts, and David Work..................................................................... 63 Paleotopographic control on deposition of the lower Kayak Shale, northern Franklin Mountains, Brooks Range, Alaska David L. LePain ........................................................................................................................................................... 71 Cooling history of the Okpilak batholith, northeastern Brooks Range, as determined from potassium-feldspar thermochronometry Julie S. Paegle, Paul W. Layer, and Andrew W. West ................................................................................................. 87 First occurrence of a hadrosaur (Dinosauria) from the Matanuska Formation (Turonian) in the Talkeetna Mountains of south-central Alaska Anne D. Pasch and Kevin C. May ............................................................................................................................... 99 Petrography of the Tingmerkpuk Sandstone (Neocomian), northwestern Brooks Range, Alaska: A preliminary study Rocky R. Reifenstuhl, Michael D. Wilson, and Charles G. Mull ............................................................................... 111 Lower to Middle Devonian (latest Emsian to earliest Eifelian) conodonts from the Alexander Terrane, southeastern Alaska Norman M. Savage and Constance M. Soja ............................................................................................................. 125 Preliminary petrography and provenance of six Lower Cretaceous sandstones, northwestern Brooks Range, Alaska Marwan A. Wartes and Rocky R. Reifenstuhl ........................................................................................................... 131 Previous Editions of Short Notes on Alaska Geology ............................................................................................. 141 iii GEOCHRONOLOGIC INVESTIGATIONS OF MAGMATISM AND METAMORPHISM WITHIN THE KIGLUAIK MOUNTAINS GNEISS DOME, SEWARD PENINSULA, ALASKA by Jeffrey M. Amato1 and James E. Wright2 ABSTRACT Geologic mapping and detailed U-Pb geochronologic investigations with monazite and zircon have shown that metamorphism and magmatism are spatially and temporally related in the Kigluaik gneiss dome, exposed in the Kigluaik Mountains, Seward Peninsula, Alaska. Protolith ages from this high-grade metamorphic culmination range from Late Proterozoic through Devonian based on existing fossil data and new U-Pb zircon dates of 678 ± 4 Ma and 555 ± 15 Ma from orthogneiss within the metasedimentary section. A pre-120 Ma blueschist-facies metamorphism that likely affected the entire crustal section was followed by a thermal overprint that increased in metamorphic grade with structural depth from subgreenschist facies to granulite facies. Limited magmatism occurred at ~110-105 Ma based on U-Pb zircon dates from minor orthogneiss bodies, and these highly strained rocks indicate that significant deformation was associated with the thermal overprint. The high-temperature overprint has a minimum age of 91 Ma, based on U-Pb analyses of monazite from orthogneiss and metapelite and from pegmatite derived from partial melting of metasedimentary rocks. Monazite dates of 94-98 Ma may reflect incomplete resetting at 91 Ma. Extensive detailed U-Pb dating of zircon from the mafic root of the Kigluaik pluton using conventional and step-wise HF dissolution techniques yielded a 90 ± 1 Ma intrusive age, suggesting that mantle-derived magmatism was the heat source for high-temperature metamorphism. Diabase dikes cut the pluton, and similar dikes in the country rock intruded at 83 ± 1 Ma, based on 40Ar/39Ar dating of biotite and hornblende. INTRODUCTION An integral part of the analysis of deformed high- determine the spatial relationships between the pluton grade gneiss terranes is understanding the temporal and metamorphic rocks, and on U-Pb dating of zircon relationships between magmatism and metamorphism. to determine the pluton emplacement ages. Because of In the upper and upper middle crust, peak metamorphic the high grade of metamorphism, we used U-Pb temperatures are often low enough that 40Ar/39Ar techniques on monazite, an igneous and metamorphic geochronologic techniques can accurately constrain the mineral with a high closure temperature, to attempt to timing of metamorphism and associated deformation constrain the peak metamorphic age. Tectonic models (Foster and others, 1992). However, in the middle and and a petrogenetic investigation of the Kigluaik pluton lower crust, metamorphic