Geologic Map of Alaska

204 Pages·2015·5.6 MB·English

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
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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