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Geologic Map of Alaska Compiled by Frederic H. Wilson, Chad P. Hults, Charles G. Mull, and Susan M. Karl Pamphlet to accompany Scientific Investigations Map 3340 2015 U.S. Department of the Interior U.S. Geological Survey Front cover. Color shaded relief map of Alaska and surroundings. Sources: 100-meter-resolution natural image of Alaska, http://nationalmap.gov/small_scale/mld/nate100.html; rivers and lakes dataset, http://www.asgdc.state.ak.us/; bathymetry and topography of Russia and Canada, https://www.ngdc.noaa.gov/mgg/global/global.html. Back cover. Previous geologic maps of Alaska: 1906—Brooks, A.H., Abbe, Cleveland, Jr., and Goode, R.U., 1906, The geography and geology of Alaska; a summary of existing knowledge, with a section on climate, and a topographic map and description thereof: U.S. Geological Survey Professional Paper 45, 327 p., 1 sheet. 1939—Smith, P.S., 1939, Areal geology of Alaska: U.S. Geological Survey Professional Paper 192, 100 p., 18 plates. 1957—Dutro, J.T., Jr., and Payne, T.G., 1957, Geologic map of Alaska: U.S. Geological Survey, scale 1:2,500,000. 1980—Beikman, H.M., 1980, Geologic map of Alaska: U.S. Geological Survey Special Map, scale 1:2,500,000, 2 sheets. Geologic Map of Alaska Compiled by Frederic H. Wilson, Chad P. Hults, Charles G. Mull, and Susan M. Karl Pamphlet to accompany Scientific Investigations Map 3340 2015 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Director U.S. Geological Survey, Reston, Virginia: 2015 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov/ or call 1–888–ASK–USGS (1–888–275–8747). For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Wilson, F.H., Hults, C.P., Mull, C.G., and Karl, S.M., comps., 2015, Geologic map of Alaska: U.S. Geological Survey Scientific Investigations Map 3340, 197 p., 2 sheets, scale 1:584,000, http://dx.doi.org/10.3133/sim3340. ISSN 2329-1311 (print) ISSN 2329-132X (online) ISBN 978-1-4113-4000-8 Contents Introduction ....................................................................................................................................................1 Acknowledgments ........................................................................................................................................3 Description of Map Units .............................................................................................................................5 Unconsolidated Deposits ....................................................................................................................5 Sedimentary Rocks ..............................................................................................................................5 Cenozoic to Mesozoic .................................................................................................................5 Quaternary and Tertiary ....................................................................................................5 Tertiary to Mesozoic ...........................................................................................................6 Cenozoic to Paleozoic ...............................................................................................................16 Tertiary to Devonian .........................................................................................................16 Tertiary to Jurassic .................................................................................................16 Lower Cretaceous to Devonian ............................................................................25 Jurassic to Mississippian ...............................................................................................35 Triassic ..............................................................................................................................42 Paleozoic to Proterozoic ..........................................................................................................47 Permian to Devonian .......................................................................................................47 Carboniferous ..................................................................................................................49 Devonian to Neoproterozoic ..........................................................................................55 Silurian to Cambrian .......................................................................................................69 Ordovician to Proterozoic ...............................................................................................71 Cambrian to Proterozoic .................................................................................................73 Proterozoic ..................................................................................................................................74 Volcanic Rocks ..................................................................................................................................75 Cenozoic to Mesozoic ..............................................................................................................75 Quaternary to Tertiary .....................................................................................................75 Tertiary to Cretaceous .....................................................................................................76 Mesozoic ....................................................................................................................................82 Cretaceous to Jurassic ...................................................................................................82 Jurassic to Triassic ..........................................................................................................84 Triassic ...............................................................................................................................85 Paleozoic ....................................................................................................................................86 Permian..............................................................................................................................86 Carboniferous ...................................................................................................................87 Devonian............................................................................................................................87 Silurian ...............................................................................................................................88 Ordovician and Cambrian ...............................................................................................88 Proterozoic .................................................................................................................................88 Intrusive Rocks ...................................................................................................................................89 Cenozoic to Mesozoic ..............................................................................................................89 Quaternary or Tertiary .....................................................................................................89 Tertiary to Cretaceous .....................................................................................................89 Mesozoic and Paleozoic ..........................................................................................................96 Cretaceous to Paleozoic ................................................................................................96 Jurassic to Paleozoic ....................................................................................................100 Triassic to Paleozoic ......................................................................................................104 Paleozoic to Proterozoic ........................................................................................................106 Metamorphic Rocks .......................................................................................................................109 iii Cenozoic to Mesozoic ............................................................................................................109 Quaternary or Tertiary ...................................................................................................109 Tertiary to Mesozoic ......................................................................................................109 Mesozoic to Proterozoic .........................................................................................................110 Cretaceous to Paleozoic ................................................................................................110 Triassic to Proterozoic ...................................................................................................112 Paleozoic to Proterozoic .........................................................................................................119 Permian to Pennsylvanian .............................................................................................119 Carboniferous to Ordovician ........................................................................................121 Devonian to Proterozoic ...............................................................................................122 Silurian to Proterozoic ..................................................................................................127 Cambrian to Proterozoic ...............................................................................................128 Proterozoic ...............................................................................................................................130 Tectonic Assemblages and Mélange ..........................................................................................132 Cenozoic and Mesozoic .........................................................................................................132 Mesozoic to Paleozoic ...........................................................................................................132 Cretaceous to Paleozoic ...............................................................................................132 Jurassic to Permian .....................................................................................................138 Paleozoic to Proterozoic ........................................................................................................139 Bedrock .............................................................................................................................................142 References Cited and Additional Sources ...........................................................................................143 Figures 1. Map showing 1:250,000-scale quadrangles (153) that cover Alaska and map areas on sheets 1 and 2 ..............................................................................................sheet 1 2. Map showing geographic regions of Alaska, including two-letter abbreviations (in parentheses) included in the List of Map Units that are used to locate map units........................................................................................................................sheet 1 Tables 1. Quadrangle codes for Alaska ...........................................................................................................2 2. Alphabetical list of map units ....................................................................................................181 iv Geologic Map of Alaska Compiled by Frederic H. Wilson, Chad P. Hults, Charles G. Mull, and Susan M. Karl Introduction may allow resolution of these conflicts. Nonetheless, we hope that geologists who have worked in Alaska will recognize that This map and its associated digital databases are the result in incorporating their work, our regional correlations have of compilation and reinterpretation of published and unpub- required generalizing and grouping of units. We believe that this lished 1:250,000-scale and limited 1:500,000- to 1:63,360-scale map and its problems present a very good argument to justify mapping. Covering the entire state of Alaska, it reflects more and support further detailed and regional-scale studies focused than a century of work in the State by a host of geologists and on geologic mapping in Alaska. We also hope that the digital almost two decades of compilation work. There are two ver- data of this map will serve new workers in Alaska for some time sions of this map: a complete, detailed map found in the digital into the future. database, and a simplified, “generalized” map for print. Units Compilation this map was complex because the original described here are included in the detailed digital map. At the source maps were made by different generations of geologists, end of each unit description, we indicate to which generalized mapping with very different ideas. Several of the older maps map unit it is assigned on the print map. were completed before the concepts of accreted (suspect) Compilation of this map began in September 1996, using terranes or even plate tectonics existed. On the other hand, published 1:250,000-scale maps of central Alaska (Wilson and some of the more recent maps were so governed by terrane others, 1998). Description and correlation of geologic units to analysis that conventional stratigraphic nomenclature was not produce the units for this statewide map was an iterative pro- used or is obscured. For the present compilation, we adopted cess, and interim products—a series of regional geologic map a traditional stratigraphic approach and have avoided use of compilations—were released as the process continued (see ref- the sometimes controversial and commonly inconsistently erences shown with an * in the references cited). As the process defined or applied term “terrane.” Our decision to adopt a continued and additional geologic data were acquired, previ- traditional approach is evident in a map that emphasizes age ously released data, correlations, and our interpretations were and lithology of map units, rather than differences among updated as needed. Digital files of the final compilation of the fault-bounded packages of rocks. For a map of this scope and 153 1:250,000-scale quadrangles for the state are available on scale, a traditional approach seems to have more to offer to the Web [http://dx.doi.org/10.3133/sim3340]. The map sources a wider variety of users. It is far easier to construct a terrane we used are cited in the text and quadrangle codes are listed in map from a traditional geologic map than vice versa. However, table 1, on p. 2; within the digital files every line and polygon is in some cases, usage of the terrane names assigned to rock attributed to its respective source. assemblages is unavoidable. In compiling this map, many of the Many compromises have been made in strongly held classic terranes of the literature violate the standard definition perspectives to allow construction of this compilation. The of tectonostratigraphic terranes (Berg and others, 1972; Coney regional compilations mentioned above and cited in the refer- and others, 1980; Jones and others, 1983) because, although ences may show different interpretations of the geology of their they commonly are assemblages having a distinct history and respective regions. Each regional map reflects the mapping style possibly distinct stratigraphy, they cannot always be demon- and interpretations of its authors. All of these regional compi- strated as being fault-bounded. Additionally, the distinction lations, as well as digital versions of primary sources, form an between a terrane and an overlap assemblage can be the subject integral part of the database from which this statewide map is of a long discussion. In northern Alaska, and particularly in the constructed. As we built the statewide compilation, we did our Brooks Range, the concept of allochthons has been an important best to resolve conflicting interpretations and map data from part of geologic discussion, such that much of northern Alaska the regional compilations and from the individual source maps has been assigned to one terrane and the focus has been on the in areas where regional compilations have not been produced. allochthons. The allochthons, of which there are at least seven, We made every effort to preserve the original geologic map are reasonably well defined in the western Brooks Range, less information, incorporating new data where available, but we so in the eastern Brooks Range, and obscured by metamorphism were careful to not overinterpret the geologic data. Yet even our in the central Brooks Range. We were unsuccessful in devising willingness to make interpretations and compromises does not a schema to show the various allochthons without obscuring the allow us to resolve all mapping conflicts or to converge differ- internal geology, which is similar from allochthon to alloch- ent mapping styles in some areas. Therefore, there are several thon. A related digital database assigns individual map units to areas on the map where it was necessary to separate map units their respective allochthons where possible. Users interested by “quadrangle boundary faults.” More time and fieldwork in the history of the names of formal stratigraphic units are 1 Table 1. Quadrangle codes for Alaska. [Code is the standard two-letter abbreviation used to refer to 1:250,000-scale quadrangles in Alaska. Column called “Quadrangle name” is the full name of the quad- rangle, which is used in the text of this document] Code Quadrangle name Code Quadrangle name Code Quadrangle name Code Quadrangle name AC Arctic DL De Long Mountains MK Mount Katmai SO Solomon AD Adak DN Denali ML Mount Michelson SP Survey Pass AF Afognak DP Demarcation Point MA Marshall SF Shishmaref AK Atka EA Eagle MC McCarthy SG Sagavanirktok AL Atlin FB Fairbanks MD Medfra SH Shungnak AM Amukta FI Flaxman Island MF Mount Fairweather SI Sitka AN Anchorage FP False Pass MG McGrath SK Skagway AR Ambler River FY Fort Yukon MH Mount Hayes SL Saint Lawrence AT Attu GI Gareloi Island MI Middleton Island SM Sleetmute BA Barter Island GO Goodnews Bay MR Meade River SN Simeonof Island BB Bristol Bay GU Gulkana MS Mount Saint Elias SR Seward BC Bradfield Canal HC Holy Cross MU Misheguk Mountain ST Saint Matthew BD Big Delta HE Healy MZ Melozitna SU Seguam BG Bering Glacier HG Hagemeister Island NB Nabesna SV Seldovia BH Bethel HP Hooper Bay NG Nushagak Bay SW Sutwik Island BI Baird Inlet HR Harrison Bay NI Nunivak Island TA Taylor Mountains BL Black HU Hughes NK Naknek TB Table Mountain BM Baird Mountains HW Howard Pass NL Nulato TC Tanacross BN Bendeleben IB Icy Bay NM Nome TE Teller BP Beechey Point ID Iditarod NR Norton Bay TI Trinity Islands BR Black River IK Ikpikpuk River NT Noatak TK Talkeetna Mountains BS Blying Sound IL Iliamna OF Offshore TL Talkeetna BT Bettles JU Juneau OP Ophir TN Tanana BV Beaver KB Kuskokwim Bay PA Port Alexander TR Taku River BW Barrow KC Ketchikan PE Petersburg TS Teshekpuk CA Candle KD Kodiak PH Point Hope TY Tyonek CB Cold Bay KG Kaguyak PI Pribilof Islands UG Ugashik CG Chignik KH Kantishna River PL Point Lay UK Umnak CH Chandalar KK Kiska PM Port Moller UL Unalakleet CI Circle KL Killik River PR Prince Rupert UM Unimak CL Chandler Lake KN Kenai PS Philip Smith Mountains UN Unalaska CM Cape Mendenhall KR Karluk RB Ruby UR Utukok River CO Coleen KT Kateel River RI Rat Islands UT Umiat CR Craig KW Kwiguk RM Russian Mission VA Valdez CS Christian KZ Kotzebue SA Samalga Island WA Wainwright CV Cordova LC Lake Clark SB Stepovak Bay WI Wiseman CY Charley River LG Livengood SC Saint Michael YA Yakutat DE Dixon Entrance LH Lime Hills SD Sumdum DI Dillingham LR Lookout Ridge SE Selawik 2 encouraged to visit the USGS National Geologic Map Database, rock section of the Description of Map Units (DMU). In the unit Geolex, a lexicon of geologic names (http://ngmdb.usgs.gov/ descriptions, for sedimentary rock units, the apparent strati- Geolex/geolex_qs.html). graphic position (lower, upper) is given after the unit label and Some of our map units use terms that other geologists name. For igneous rock units, the age of the unit (early, late) fol- have previously applied to terranes. We instead use such terms lows the unit label and name. In the text of the descriptions, lower as “sequence,” “assemblage,” and “complex” for groups of and upper are used to denote stratigraphic position, whereas late rock units characterized by a common history or environment. and early indicate age. In general, metamorphic rock units are Sequences, as used here, are groups of sedimentary rock units listed in increasing order of their inferred or interpreted protolith that display a coherent and consistent stratigraphy and associa- age, which in many cases is subject to significant uncertainty. tion. Assemblages consist of a mixture of sedimentary, igneous, In the limited number of cases for which we cannot interpret a and (or) metamorphic rock units within a still-recognizable protolith age, the metamorphic rocks are listed by increasing age stratigraphic framework that may be tectonically disrupted of the last metamorphism, either known or inferred. internally. Complexes are generally restricted to largely igne- In most cases, the time scale and terminology used is that ous or metamorphic rock assemblages that have no apparent of the International Commission on Stratigraphy’s International stratigraphic framework. An exception to this is the McHugh Chronostratigraphic Chart of 2008 (ICS2008). In a few cases, Complex, a tectonic mélange in southern Alaska, whose name is typically in describing Paleozoic sedimentary rocks, the original in common use. sources reported age terms that are not part of the ICS2008 In general, where terminology for lithologic packages of chart; the specific definition of these terms can be defined using rock units has come into common usage and where we could the “Geowhen” website: http://www.stratigraphy.org/bak/geow- justify or support its continued usage, we have used that termi- hen/index.html. In general, the descriptions using these other- nology. An example of such a lithologic association is the rocks than-ICS2008 terms provide an approximate equivalent term of the Angayucham, Tozitna, and Innoko assemblages, origi- from ICS2008. nally defined as separate terranes. The ease with which common Many of the map sources are drawn with faults forming the terminology can be used is, in part, dependent on our knowl- boundary between bedrock and surficial or unconsolidated map edge or perceived understanding of the rock units. This pack- units. Logically, this indicates that the fault is likely Quaternary aging occurs at either extreme of our spectrum of knowledge. in age, offsetting the surficial units as well as the bedrock unit; Thus, packaging very old metamorphic rocks is relatively easy however, in the majority of cases, we do not believe this was the because age and protolith history is unknown. In other cases, author’s intention. Nevertheless, in the majority of these cases, such as the Nixon Fork terrane, now part of the White Mountain we have presented the map data as shown on the source map. sequence of Decker and others (1994), we have reasonably good Locally, along major fault systems, some authors have mapped constraints on the nature of the rock units and can confidently broad shear zones, particularly in the Tanana (Reifenstuhl and package them. others, 1997) and the Eagle quadrangles (Day and others, 2014). This compilation is unique in that it is associated and While the fault systems are typically shown outside of these integrated with a rich database of information provided in respective map areas, the shear zones are not mapped, although digital spatial datasets and attribute databases on the Web they presumably are there. We have chosen not to show these [http://dx.doi.org/10.3133/sim3340]. Included are descriptions shears zones on the printed map; however, they are preserved in of original source maps and a table that links map units from the digital data files. individual maps to a regional code, called NSACLASS. In the Throughout the text, many locations are described as being spatial datasets and the related attribute databases, the source within named 1:250,000-scale quadrangles. Figure 1 shows of every line and polygon is referenced. For every polygon the location of these quadrangles around the state to help guide source listed, the original map unit description is preserved in users to areas of interest. While complete quadrangle names the NSAunits table. Additional attributes concerning lithology, are used in the text and on fig. 1, sheet 1; table 1 provides the age, and geologic setting for map units are available as well. standard two-letter abbreviation used within the databases. The Databases of radiometric ages also are provided. A readme file alphabetically organized list of map units on the printed map describing these databases and their structure is available on indicates in which loosely defined region or regions each map the publication’s Web site. The approximately 450 map units unit appears; fig. 2 , sheet 1, shows the general area of each presented here are derived by combining the more than 1,300 region. The regions are defined such that the central region detailed NSACLASS assignments used to construct the state- includes both the west-central and east-central subregions. This wide database. An NSAkey table provides a short description is similarly true for northern and southern regions and their for each NSACLASS. respective subregions. The Seward Peninsula, Alaska Peninsula, In the following descriptions, units are generally organized and Aleutian Islands regions are not subdivided. by sedimentary, igneous, or metamorphic rock units, and within each category, listed in chronological order from youngest to Acknowledgments oldest. However, in several cases, rock units or assemblages of mixed rock types are grouped with the dominant rock unit part of the assemblage; for example, the sedimentary and volcanic rock A compilation on this scale could only be done with units of the Orca Group are placed together in the sedimentary the assistance of many geologists, far more knowledgeable 3 about the geology of various regions of Alaska than we are. digital support from Nora Shew and Keith Labay that were criti- USGS emeritus scientists and volunteers were important cal in making this compilation possible. The Alaska Department contributors to this effort, providing many insights, much of Natural Resources Division of Oil and Gas provided strong data, and very much appreciated advice. They included Robert encouragement and financial support to assist with the prepa- Detterman (deceased), William Patton, Jr. (deceased), Donald ration of two of the regional maps. Technical (peer) review of Richter (deceased), Bill Brosgé (deceased), Robert Chapman the manuscript by Thomas Bundtzen, Cynthia Dusel-Bacon, (deceased), Donald Grybeck (deceased), Florence Weber, Hank M.L. (Weecha) Crawford, George Gehrels, Maurice Colpron, Schmoll, Lynn Yehle, David Brew, Thomas Hamilton, and and David Houseknecht; geologic names review by Robert Warren Coonrad. Active USGS staff who contributed to this B. Blodgett; and editorial reviews by Jan Zigler and Claire effort, providing data and participating in discussions, included Landowski are greatly appreciated and helped to improve the Dwight Bradley, Jeanine Schmidt, Alison Till, Julie Dumoulin, text and map. Finally, the ongoing support of management, Rick Saltus, Marti Miller, Cynthia Dusel-Bacon, and Peter including Kate Johnson, Bruce Gamble, Marti Miller, and Larry Haeussler. We are extremely grateful for the GIS and general Meinert, made it all possible. 4

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Map showing 1:250,000-scale quadrangles (153) that cover Alaska and map . classic terranes of the literature violate the standard definition Chandalar LG. Livengood. SC. Saint Michael. YA. Yakutat. DE. Dixon Entrance. LH.
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