2011

U.S. Department of the Interior

U.S. Geological Survey

Bedrock Geologic Map of the Seward Peninsula, 

Alaska, and Accompanying Conodont Data

By Alison B. Till, Julie A. Dumoulin, Melanie B. Werdon, and Heather A. Bleick

Pamphlet to accompany

Scientific Investigations Map 3131

View of Salmon Lake and the eastern Kigluaik Mountains, central Seward Peninsula

i

Contents

Introduction ....................................................................................................................................................1

Sources of data ....................................................................................................................................1

Components of the map and accompanying materials .................................................................1

Geologic Summary ........................................................................................................................................1

Major geologic components ..............................................................................................................1

York terrane ..................................................................................................................................2

Grantley Harbor Fault Zone and contact between the York terrane and the Nome 

Complex ..........................................................................................................................3

Nome Complex ............................................................................................................................3

High-grade metamorphic and associated igneous rocks ....................................................5

Yukon-Koyukuk basin, Angayucham terrane, and the Kugruk Fault Zone ........................6

Igneous rocks ..............................................................................................................................6

Tertiary and active deformation ........................................................................................................7

Acknowledgments ........................................................................................................................................7

Description of Map Units .............................................................................................................................7

Surficial Deposits .................................................................................................................................7

Mesozoic and Cenozoic Igneous Rocks ..........................................................................................7

York Terrane ........................................................................................................................................12

York Mountains Succession ....................................................................................................12

Units with Uncertain Affinities ................................................................................................15

Grantley Harbor Fault Zone ..............................................................................................................17

Nome Complex ...................................................................................................................................18

Layered Sequence ....................................................................................................................18

Scattered Metacarbonate Rocks ...........................................................................................24

Metaturbidites ...........................................................................................................................26

High-Grade Metamorphic and Associated Igneous Rocks ........................................................27

Kugruk Fault Zone ..............................................................................................................................29

References Cited .........................................................................................................................................32

Appendix .......................................................................................................................................................54

Introduction .........................................................................................................................................54

Sources of data ..................................................................................................................................54

Geologic implications ........................................................................................................................55

Nome Complex and Kugruk Fault Zone .................................................................................55

York terrane and Grantley Harbor Fault Zone ......................................................................55

Figures

1. Map of northern Alaska showing major geographic areas, geological provinces, and the 

outline of the map area . .................................................................................................................2

2. Map of the Seward Peninsula, Alaska showing locations and names of Quaternary, Tertiary, 

and Cretaceous igneous rocks. Cenozoic volcanic rocks, pale yellow; Late Cretaceous 

tin-bearing granites, orange; compositionally diverse Early and Late Cretaceous rocks, 

red ..................................................................................................................................map sheet 2

Tables

1. Distribution of geologic units by quadrangle .....................................................................................40

2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations ..................................................................42

3. Selected U-Pb zircon analyses ............................................................................................................52

A–1. Conodont data from the Seward Penninsula ................................................................................58

A–2. Temperature ranges for Color Alteration Indices (CAIs) of conodonts ....................................75

Sheets

1. Preliminary bedrock geologic map of the Seward Peninsula, Alaska

2. Tectonic, metamorphic, geochronologic, and geographic data for the Seward Peninsula, 

Alaska

1

Introduction

This 1:500,000-scale geologic map depicts the bedrock 

geology of Seward Peninsula, western Alaska, on the North 

American side of the Bering Strait. The map encompasses all 

of the Teller, Nome, Solomon, and Bendeleben 1:250,000-scale 

quadrangles, and parts of the Shishmaref, Kotzebue, Candle, 

and Norton Bay 1:250,000-scale quadrangles (sh. 1; sh. 2).

Rolling, tundra-covered hills cover most of Seward Peninsula; trees and shrubs are present only in limited areas in the 

southern and eastern parts of the peninsula. Broad lowlands 

underlie large areas in central and northern Seward Peninsula. 

Part of the central area and large areas in northernmost and easternmost Seward Peninsula are an extensive, unvegetated lava 

field. Four glacially carved mountain ranges, the York, Kigluaik, 

Bendeleben, and Darby Mountains, reach heights of 1,000-

1,300 m (sh. 2); the highest point on the Peninsula, Mount 

Osborn, is in the Kigluaik Mountains. The York Mountains of 

western Seward Peninsula and hills adjacent to them on the east 

are underlain by bare, unvegetated carbonate rocks.

The map area covers 74,000 km2, an area slightly larger 

than West Virginia or Ireland.

Sources of Data

This geologic map is a compilation of published and 

unpublished geologic mapping and information derived from 

other published and unpublished sources. Published geologic 

maps at scales of 1:250,000, 1:63,360, and 1:50,000 were major 

sources and range in publication date from 1972 to 2005. More 

detailed studies, including theses, papers, and unpublished mapping, represent work done between 1980 and 2008.

The amount of geologic detail available varies significantly 

across the area of the map, because of variations both in degree 

of study and in quality of bedrock exposure. Bedrock exposure, 

outside of the mountain ranges, is generally poor in the northern 

peninsula, and better in southern parts of the peninsula. The 

most detailed geologic mapping on the peninsula has been concentrated in the York and Kigluaik Mountains, and the central 

Solomon quadrangle. The distribution of some metamorphic 

indicator minerals and conodont color alteration index (CAI) 

values presented on sheet 2 is limited by quality of exposure 

and amount of study in a given area.

Components of the Map and Accompanying

Materials

The geologic map and related supplemental information 

are presented in two oversized sheets, this text, three tables, and 

an appendix. The appendix includes an explanatory text and two 

tables.

The geologic map, Correlation of Map Units, List of Map 

Units, and sources of data are shown on sheet 1. The geographic 

names referenced in the text, metamorphic/tectonic subdivisions 

of the map area, and selected metamorphic and thermal history 

data are shown on sheet 2. Metamorphic and thermal history 

data are largely from the collections of the authors, but include 

all available information from government, industry, and academic sources.

Table 1 shows the distribution of the map units on the nine 

1:250,000-scale quadrangle maps of the map area, and augments geographic information provided in the Description of 

Map Units.

Geochronologic data in tables 2 and 3 were compiled from 

the literature; a few unpublished ages were included. Results 

that were shown by researchers to be analytically sound and 

geologically meaningful have been included in the tables, while 

less sound results (for example, 40Ar/39Ar age spectra lacking 

plateaus, K-Ar analyses with poor radiogenic yield) have been 

excluded. In a few cases, results that did not meet these criteria 

have been included; statements in the “comments” column of 

the table indicate when and why this was done. All ages mentioned in this report are listed in the tables.

The appendix includes discussion of sources and distribution of conodont data and geologic implications of the 

data. Table A–1 lists the conodont data by 1:250,000-scale 

quadrangle. Table A–2 summarizes the temperature ranges 

thought to correspond to color-alteration index (CAI) values 

of conodonts.

Geologic time-scale age boundaries used are those of 

Gradstein and Ogg (2005).

Geologic Summary

Major Geologic Components

Most of Seward Peninsula is underlain by rocks that were 

part of a Late Proterozoic to early Paleozoic continental margin; 

remnants of that margin are also present in the Brooks Range. 

Rocks of the Chukotsk Peninsula, 85 km west of the Seward 

Peninsula, across Bering Strait (sh.1, 2), probably were part 

of the same continental margin as well (Dumoulin and others, 

2002). The extensive high-pressure metamorphic rocks exposed 

in central Seward Peninsula (Nome Complex), the southern 

Brooks Range, and the Ruby geanticline are thought to record 

subduction of that continental margin during the Jurassic 

(Patton and Box, 1989; Christiansen and Snee, 1994; Roeske 

and others, 1995; Gottschalk and Snee, 1998) (fig. 1).

During the Early Cretaceous, contractional deformation 

ceased within the subduction zone, moved into the subjacent 

continental crust, and propagated to shallower levels. As a 

result, the continental margin was involved in a mountainbuilding episode, which involved thickening of the continental 

crust and movement of thrust sheets northward. We refer to this 

post-subduction contractional deformation of continental crust 

as the Brooks Range orogeny. Some exhumation of the Nome 

Complex blueschists by thrust faulting may have been part of 

this episode. Rocks in the York Mountains of Seward Peninsula 

likely experienced thrust faulting and shallow burial at this time, 

based on thermal indices (conodont color alteration indices; 

table A–2) from carbonate rocks and outcrop-scale structures in 

siliciclastic rocks.
2

Metamorphic fabrics in the Nome Complex have been 

related to subduction zone deformational processes (Thurston, 

1985; Patrick, 1988) and extensional collapse of the Brooks 

Range orogen after the mountain building and crustal thickening episode (Hannula and others, 1995; Amato and others, 

2002). 40Ar/39Ar and fission-track data indicate that significant 

cooling of the high-pressure metamorphic rocks now exposed 

on Seward Peninsula occurred in the period 120–70 Ma 

(Hannula and McWilliams, 1995; Dumitru and others, 1995); 

extensional deformation is thought to have occurred during that 

time span.

Amphibolite to granulite facies metamorphism overprinted 

the Nome Complex and other rocks during the mid-Cretaceous; 

at about the same time, a protracted period of magmatism began 

on Seward Peninsula and lasted until the end of the Cretaceous 

(fig. 2, on sh. 2). At least one suite of plutonic rocks formed 

in an island arc setting (Amato and Wright, 1997). During the 

Cenozoic, normal faulting created small mountain ranges and 

adjacent sedimentary basins, and mafic volcanic rocks accumulated in the central and northern parts of the peninsula.

In this text the term “metabasite” refers to metamorphosed 

mafic rocks of any nature, including originally intrusive and 

extrusive varieties.

Based on lithology, age, tectonic affinity, and metamorphic history, rocks of Seward Peninsula are divided into several 

tectonic subdivisions, illustrated on sheet 2.

York Terrane

Rocks of western Seward Peninsula are mostly lower 

Paleozoic and possibly older carbonate and siliciclastic rocks 

that retain primary sedimentary features except where they 

occur near granitic intrusions or where they are mica rich. We 

divide the York terrane into two parts: the “York Mountains succession”, a relatively well-studied stratigraphic sequence found 

mainly in the central York Mountains, and “Units of uncertain 

affinities”, a group of relatively poorly understood rocks (sh. 1). 

Thermal indicators, based on conodont color alteration 

index (CAI) values, show that the York terrane contains several 

provinces with different thermal histories, and therefore, different burial and tectonic histories (sh. 2, appendix 1). Some York 

terrane rocks are unmetamorphosed (most of the York Mountains succession), and some may have reached low greenschist 

facies conditions (Units with uncertain affinities). Siliciclastic 

rocks in units with higher thermal indices (units O<t, O<l) and 

a related unit (O<p) display open folds with a sub-horizontal 

165° 155° 145°

70°

65°

Ruby

Geanticline

Yukon-Koyukuk

Basin

Seward

Peninsula

Map area

Kugruk

fault zone

Cape

Lisburne

North Slope

Brooks Range

Areas underlain largely by rocks that 

underwent Jurassic blueschistfacies metamorphism

Angayucham terrane and associated 

oceanic rocks 

Figure 1. Map of northern Alaska showing major geographic area, geological provinces, and the outline of the map area.
3

axial plane cleavage; finer-grained rocks are slates or phyllites 

and are crenulated. These units probably experienced burial 

and deformation during the Brooks Range orogeny. Carbonate 

rocks with lower thermal indices, in the central York Mountains, were much more shallowly buried (sh. 2). Structures that 

separate different thermal provinces have yet to be delineated, 

but are important for defining the deformation history of the 

York terrane.

Carbonate strata of the York terrane correlate well with carbonate successions in three regions: the Brooks Range (northeast of the Seward Peninsula), the Farewell terrane of interior 

Alaska (southeast of Seward Peninsula), and the peri-Siberian 

terranes of northeastern Russia (Dumoulin and Harris, 1994; 

Dumoulin and others, 2002). Lithofacies and biofacies of York 

terrane carbonate rocks are especially similar to those of coeval 

strata in the western Brooks Range (Baird Mountains) and the 

Farewell terrane. Rocks in all three regions contain a distinctive biota characterized by both Siberian and Laurentian (North 

American) endemic forms, including many identical species. 

Detailed lithologic similarities between the three successions 

are also numerous (Dumoulin and others, 2002).

Grantley Harbor Fault Zone and Contact Between 

the York Terrane and the Nome Complex

Several lenses of low-grade metasedimentary rocks, probably fault bounded, sit on the structural contact between the 

York terrane and the Nome Group. This zone is distinguished 

on the map because the rocks are more penetratively deformed 

than similar lithologies in the York terrane, and less penetratively deformed than similar lithologies in the Nome Complex. 

Hannula and others (1995) considered these rocks part of a 

structurally coherent section that decreases in metamorphic 

grade from the Kigluaik Mountains northwest to the coast. 

However, there is a metamorphic discontinuity within the section. Metamorphic grade of the Nome Complex does decrease 

from the Kigluaik Mountains to the northwest; metabasites 

nearer the Kigluaik Mountains are blue amphibole-bearing, and 

those farther away contain lower grade pumpellyite-actinolite 

assemblages (Hannula and others, 1995) (see unit |np). However, a sliver of Nome Complex rocks that contain lawsonite 

and glaucophane pseudomorphs sits between the pumpellyiteactinolite grade rocks of unit |np and the subgreenschist facies 

unit of the Grantley Harbor Fault Zone (sh. 2). The sliver of 

schists that contain glaucophane and lawsonite pseudomorphs 

must have been structurally imbricated with the adjacent rocks.

Faults within the Grantley Harbor Fault Zone are part of 

the regionally important structural contact between the Nome 

Complex and the York terrane. The contact was interpreted as 

a thrust fault by Till and Dumoulin (1994), based on possible 

correlation with east-vergent structures on the Lisburne Peninsula, western Brooks Range (Patton and Tailleur, 1977; Moore 

and others, 2002). However, models for mid-Cretaceous crustal 

extension (Miller and Hudson, 1991) and evidence for extensional faulting within the York terrane (Toro and others, 2006) 

are consistent with an extensional detachment between the York 

terrane and the Nome Complex. The contact between the York 

terrane and the Nome Complex, which is very poorly exposed, 

may have been a thrust fault during the contractional mountainbuilding phase of the Brooks Range orogeny, and been reactivated multiple times as a thrust and(or) extensional surface.

Nome Complex

The low, rolling hills of central and eastern Seward Peninsula are underlain by lithologically varied rocks that have 

well-developed blueschist and greenschist metamorphic fabrics. 

These rocks underlie most of the peninsula, including the highly 

productive gold districts that have attracted geologists’ attentions since the 1899 Nome gold rush.

The metamorphic rocks consist of several thick mappable 

lithologic sequences, scattered carbonate rocks with an uncertain relation to those sequences, and small bodies of orthogneiss. Mesozoic ductile and penetrative deformation largely 

obliterated primary sedimentary and igneous textures. Sparse 

conodont and other fossil collections and zircon ages from 

orthogneisses provide limited age control, and were interpreted 

to indicate Neoproterozoic and Paleozoic protolith ages for the 

unit overall (Till and others, 1986).

In 1900, U.S. Geological Survey geologists created the 

first topographic and geologic maps of the newly discovered 

Nome gold fields. They first applied the name “Nome series” 

to the lithologically complex metamorphic rocks that underlie 

the placer deposits of southern Seward Peninsula (Brooks and 

others, 1901). Initially, the approach to differentiation of units 

was stratigraphic, and was based upon apparent superposition 

of lithologic units and a small number of megafossil collections. 

Within a few years, as additional megafossil ages conflicted 

with the perceived relations within the series, the name “Nome 

group” was proposed (Collier and others, 1908). In proposing 

the change, Collier and others (1908) noted that the unit was not 

a stratigraphic one, but rather was heterogeneous and metamorphic; no type section was proposed, and lithologic descriptions 

were very simple. In modern stratigraphic nomenclature the 

term “group” is for a set of related lithostratigraphic units; the 

term “complex” is for highly deformed rocks such as those 

exposed in central Seward Peninsula (North American Commission of Stratigraphic Nomenclature, 2005).

We include all rocks on Seward Peninsula that exhibit a 

common set of structural and (or) metamorphic features, likely 

formed in the same deformational event, in the Nome Complex. 

Although the bulk of the Nome Complex shows evidence of 

high-pressure metamorphism, rocks along the eastern, western, 

and northern boundaries of the complex crystallized at slightly 

different peak metamorphic conditions (sh. 2). In these cases, 

similarities in structural fabric elements and lithologic characteristics suggest that they were part of the same metamorphic 

event, and are therefore included in the complex. A number 

of the lithologies in central Seward Peninsula do not produce 

mineral assemblages diagnostic of metamorphic grade; in those 

cases, a structural style consistent with lithologies that do contain high-pressure minerals is used for inclusion in the complex. A few lithologies, such as fine-grained dolostones, do not 

manifest the structures common in most of the Nome Complex, 

and are exposed in isolated outcrops. Where available, color 
4

alteration index values (CAIs) of conodonts that are consistent 

with the conditions of high-pressure metamorphism were used 

to include these rocks.

We divide the Nome Complex into three parts (sh. 1). The 

designated “Layered sequence” consists of mappable lithologic 

units that occur in a consistent, layer-cake structural relation to 

one another over much of central Seward Peninsula. The designated “Scattered metacarbonate rocks” consists of volumetrically minor dolostones and marbles that are widely distributed. 

Units that are exposed only on the north and southeast coasts 

of the peninsula (DObm, D_bm, D_ks) are included in the 

designated “Metaturbidites”.

The character of the lithologies in the Nome Complex 

is consistent with formation on a continental shelf and slope. 

Some carbonate rocks (units _d, Od, Sd, Ddm of Scattered 

metacarbonate rocks) contain sedimentary features, megafauna, 

and (or) microfauna typical of shallow water conditions. Other 

rocks show features that indicate they formed in slope and 

basinal environments (Metaturbidites units DObm, D_bm). 

Metasedimentary rocks that formed from combined carbonate, 

siliciclastic, and graphitic components are common; metasedimentary rocks composed of intermixed mafic, carbonate, and 

siliciclastic components are also widespread. Chemical characteristics of the mafic rocks in the Nome Complex indicate that 

they formed during rifting of a continental margin (Werdon and 

others, 2005a; Ayuso and Till, 2007).

The age of the Nome Complex protolith is known from 

microfossils, megafossils, U-Pb zircon analyses, and detrital 

zircon analyses. Cambrian, Ordovician, Silurian, and Devonian 

fossils were collected from carbonate rocks (Till and others, 

1986). Small, Late Proterozoic orthogneiss bodies have been 

identified (Patrick and McClelland, 1995; Amato and Wright, 

1998; Till and others, 2006), as well as several Middle Devonian metagranitic bodies (Till and others, 2006; Gottlieb and 

Amato, 2008; Amato and others, 2009). Detrital zircon analyses reveal that very little of the protolith of the complex was 

deposited before 600 Ma, and some metamorphosed siliciclastic rocks are likely Devonian or younger (Amato and others, 

2003a; Amato, 2004; Till and others, 2006, 2007). Mafic rocks 

that formed during rifting of the continental margin have not 

been directly dated in the Nome Complex, but are thought to be 

Ordovician (see description of unit Ocs).

Penetrative ductile deformation and recrystallization of 

the sequence make geologic mapping and identification of the 

nature and precise age of the protolith extremely difficult. The 

presence of mafic boudins that contain blueschist-facies minerals in the Nome Complex was first noted by Sainsbury and 

others (1970); Thurston (1985) documented blueschist-facies 

minerals in a variety of lithologies, showing that high pressure/

low temperature metamorphism affected the entire Nome Complex. The Nome Complex, therefore, is a metamorphic complex 

initially formed during subduction of a continental margin. This 

indicates that lithologic units within the Nome Complex were 

removed from the surface of the subducting continental crust 

- but not necessarily in a way that retains their original stratigraphic relations. Based on available detrital zircon data, the 

structurally lowest parts of the Nome Complex are the youngest 

parts of its protolith (Till and others, 2006).

The metamorphic history of the Nome Complex is imperfectly known, especially its history after peak high-pressure/

low-temperature metamorphism. As is the case with many 

blueschist-facies metamorphic terranes, many lithologies in the 

Nome Complex do not contain mineral assemblages diagnostic 

of metamorphic grade. The same mineral assemblages may 

form, for example, at both high pressure (blueschist-facies) 

and low pressure (greenschist-facies) conditions. Further, 

greenschist- and blueschist-facies mineral assemblages can 

form at the same conditions in mafic rocks of slightly different compositions (Evans, 1990). Finally, in the Nome Complex 

greenschist-facies assemblages do overprint blueschist-facies 

minerals locally, but establishing the relation of greenschist 

assemblages to deformational events and the age of those events 

are challenging. Distinguishing the metamorphic history of the 

Nome Complex—especially the history after peak high-pressure 

metamorphism—has shown to be particularly difficult.

Based on thermobarometry and petrography, the metamorphic pressure-temperature path of the Nome Complex traversed 

the lawsonite-stable part of blueschist facies and reached peak 

pressure in the epidote-stable part of blueschist facies/eclogite 

facies (Forbes and others, 1984; Thurston, 1985). Conditions 

of peak pressure were estimated at 460 °C, 12 kb (Patrick and 

Evans, 1989). Temperature peaked during exhumation in albiteepidote-amphibolite-facies. This pressure-temperature path is 

identical to that documented in the Schist belt in the southern 

Brooks Range (Till and others, 1988; Gottschalk, 1998) and 

is similar to that in the Ruby geanticline (Roeske and others, 

1995) (fig. 1); the Nome Complex, Schist belt, and schists in the 

core of the Ruby geanticline probably formed during the same 

subduction episode.

Geochronologic studies to date have not clearly documented the timing of the high-pressure event on Seward Peninsula. Although Rb-Sr and K-Ar ages indicated a Jurassic age of 

metamorphism (Armstrong and others, 1986), 40Ar/39Ar plateau 

ages from white mica in the Nome Complex typically span the 

ages from 109 to 125 Ma (table 2); these ages are thought to 

represent minimum ages for blueschist-facies metamorphism 

(Hannula and McWilliams, 1995). The Rb-Sr ages are from 

essentially 2-point isochrons; therefore, their value is also 

limited. Sodic-calcic amphibole from a vein thought to have 

formed during decompression and heating of the Nome Complex yielded a 40Ar/39Ar plateau age of 138.6±1.0 Ma (Layer 

and Newberry, 2005; table 2); this age approximates the timing 

of peak temperature for the Nome Complex, and is a minimum 

age for peak pressure. White mica 40Ar/39Ar ages from metamorphically correlative rocks in the Ruby geanticline place a 

minimum age of 144 Ma on the blueschist-facies event (Roeske 

and others, 1995), and blueschist-facies rocks of the southern 

Brooks Range are thought to have reached peak pressure during 

the Middle Jurassic (Christiansen and Snee, 1994; Gottschalk 

and Snee, 1998). Based on the age of the vein-filling sodiccalcic amphibole and correlative nature of high-pressure/lowtemperature metamorphic events in the Brooks Range and Ruby 

geanticline, we believe that the Nome Complex reached peak 

pressure during the Jurassic.

The degree to which the dominant structural fabric in the 

Nome Complex is a product of exhumation processes, rather 
5

than subduction processes, is a matter of some controversy. 

Thurston (1985) and Patrick (1988) suggested that the parallelism of glaucophane and pseudomorphs after glaucophane 

with the dominant fabric indicates that the fabric was formed 

during high-pressure metamorphism. Miller and Hudson (1991) 

postulated that Seward Peninsula was part of a vast region that 

underwent crustal extension in the mid-Cretaceous in response 

to crustal thickening during the Brooks Range orogenic episode. Based on structural and metamorphic analysis, Hannula 

and others (1995) contended that the dominant fabric in the 

Nome Complex was related to the extensional episode, and the 

blueschist fabric was largely overprinted. Because many of the 

lithologies in the Nome Complex display the same metamorphic 

assemblages at blueschist or greenschist facies, this is a challenging problem to unravel.

Sheet 2 shows subdivisions of the Nome Complex that 

highlight small differences in metamorphic and(or) deformational history. In central Seward Peninsula, the greater part 

of the Nome Complex displays consistent metamorphic and 

deformational features. These rocks possess a penetrative fabric 

formed in a ductile setting and, in appropriate lithologies, 

contain minerals diagnostic of blueschist-facies conditions. 

Glaucophane and fine intergrowths of chlorite and albite that 

pseudomorph glaucophane are widespread in mafic, pelitic, and 

calcareous lithologies. One metabasite contains the eclogitefacies diagnostic minerals jadeitic pyroxene (omphacite) and 

garnet (Nome Complex-central; sh. 2). Exposures of the Nome 

Complex margins (west, north, and east) show slight variations 

in deformational and structural style. Descriptions of these 

variations are on sheet 2 and in the Description of Map Units.

High-grade Metamorphic and Associated

Igneous rocks

Amphibolite and granulite-facies metamorphic rocks are 

exposed in the Kigluaik, Bendeleben, and Darby Mountains 

and in a small area north of the Oonatut Granite Complex in the 

northwestern Bendeleben quadrangle (fig. 2, on sh. 2). These 

high-grade metamorphic rocks formed during the Cretaceous 

and have no identified direct counterparts in the Brooks Range, 

although potentially metamorphically correlative rocks are 

known in the Ruby geanticline (Roeske and others, 1995). 

On Seward Peninsula, some lithologic units in the high-grade 

metamorphic rocks are identical to lithologic units recognized 

in the Nome Complex (Till and others, 1986, Till and Dumoulin, 1994), and other lithologies are not known in the Nome 

Complex (for example, ultramafic and associated rocks that 

are exposed at the core of the Kigluaik Mountains). The oldest 

dated rock on Seward Peninsula (870 Ma), a foliated metarhyolite, is exposed in the southwestern Bendeleben Mountains 

(Gottlieb and Amato, 2007; Amato and others, 2009). No rocks 

of that age have been identified in the Nome Complex.

High-grade metamorphic assemblages record a polyfacial metamorphic history that has not been studied in detail. In 

some areas, high-grade metamorphic assemblages demonstrably 

overprint blueschist and greenschist-facies assemblages that 

formed during metamorphism of the Nome Complex (Thurston, 

1985; Till and others, 1986; Hannula and others, 1995). Kyanite 

is present in pelitic rocks in all three mountain ranges; kyanitebearing assemblages are typically overprinted by sillimanitebearing assemblages, and therefore represent an early part of the 

metamorphic history. Evidence for decompression is recorded 

in some of the high-grade metamorphic rocks. In rare lithologies 

high in aluminum and iron, earlier, higher pressure assemblages 

(orthoamphibole plus aluminosilicate) are overprinted by lower 

pressure assemblages (cordierite plus staurolite or garnet) (sh. 2).

The metamorphic history of rocks in the two east-west 

trending ranges (Kigluaik, Bendeleben) is broadly similar. 

Metamorphic grade in the Kigluaik Mountains increases 

towards the core of an antiform, or dome, defined by foliation 

and gneissic layering. Two-pyroxene gneisses, definitive of 

granulite facies, are present in the core of the antiform near 

Mount Osborn (Till, 1980; Lieberman, 1988; sh. 2). Peak 

metamorphic grade in the Kigluaik Mountains is thought to 

have occurred at about 91 Ma, immediately before or coincident with intrusion of the Kiglauik pluton (Amato and others, 

1994; Amato and Wright, 1998). Metamorphic isograds in the 

Kigluaik Mountains are closely spaced, a feature likely related 

to exhumation processes (Patrick and Lieberman, 1988; Miller 

and others, 1992; Calvert and others, 1999). In the central 

Bendeleben Mountains, foliation is also domed (Gottlieb and 

Amato, 2008). However, metamorphic zonation is less well 

known and apparently more complex than in the Kigluaik 

Mountains; the timing and conditions of peak metamorphism 

have yet to be directly documented. Also the relations of the 

two plutons in the Bendeleben Mountains to high-grade metamorphism is unknown; part of the Bendeleben pluton is older 

(104 Ma) and the Pargon is younger (86 Ma) than the Kigluaik 

pluton (Gottlieb and Amato, 2008). Rapid cooling (to <200 °C) 

of the Kigluaik gneisses and schists occurred between 87 and 

78 Ma (Calvert and others, 1999). U-Pb ages on zircon rims in 

cordierite schist and on zircon grains in igneous rocks in the 

Bendeleben Mountains seem to indicate that decompression 

occurred at about 88 to 85 Ma (Gottlieb and Amato, 2008); biotite and monazite cooling ages from the Bendeleben Mountains 

range from 87 to 81 Ma (Turner and Swanson, 1981; Gottlieb 

and Amato, 2007).

The high-grade metamorphic rocks of the Kigluaik and 

Bendeleben Mountains are structurally coherent and domed, 

whereas distribution of high-grade metamorphic rocks in the 

north-south oriented Darby Mountains is more complex. Metamorphic grade increases along the axis of the Darby range from 

north to south, culminating in the area around Mount Arathlatuluk (sh. 2). In the northern part of the range, Nome Complex 

rocks are present and have biotite-grade metamorphic overprints. The central part of the range contains staurolite- and kyanite-bearing assemblages; kyanite may be relict from an early 

metamorphic event. At Mount Arathlatuluk, small, biotite-granite stocks occur with granulite-facies (2 pyroxene) metamorphic 

assemblages (sh. 2); sillimanite is common. Zircon from a 

granite stock yielded a U-Pb age of 108 Ma, an age that broadly 

approximates the time of peak temperature (R. Friedman, written commun., 2009). The low-grade rocks in the northern Darby 

Mountains are juxtaposed with a slice of high-grade metamorphic rocks (on the west flank of the mountains) along a high-
6

angle reverse fault; the age of the fault is not known. At the time 

of intrusion of the Darby pluton, the metamorphic rocks were in 

shallow (<5 kb) crustal settings; the Darby pluton has andalusite 

in its contact zone (sh. 2). The Darby pluton yielded two U-Pb 

zircon crystallization ages of 100 Ma (Amato, written commun., 

2008; R. Friedman, written commun., 2009).

Although the three mountain ranges (Kigluaik, Bendeleben, and Darby Mountains) appear to describe a small orocline, 

the ranges do not have the same exhumation history. The apparent orocline is due to the intersection of structures of different 

ages. Biotite cooling ages from the Kigluaik and Bendeleben 

Mountains range from 87 to 81 Ma; biotite cooling ages are 

older in the Darby Mountains, ranging from 102 to 90 Ma. 

Apatite fission-track analysis indicates that the Kigluaik and 

(by inference) Bendeleben Mountains were cooled and uplifted 

during the Tertiary (Eocene-Oligocene; Dumitru and others, 

1995), whereas rocks in the northern Darby Mountains were at 

the surface during the early Eocene, as the Darby pluton (unit 

Kd) is basement to a small sedimentary basin of early Eocene 

age (Dickinson and others, 1987).

Yukon-Koyukuk Basin, Angayucham Terrane, and 

the Kugruk Fault Zone

The Yukon-Koyukuk basin sits along the eastern side of 

Seward Peninsula and contains Early Cretaceous subductionrelated volcanic rocks and related marine sedimentary rocks. 

The basin is flanked on three sides by terranes with continental affinity: Seward Peninsula on the west, Brooks Range on 

the north, and Ruby geanticline on the east (fig. 1). The basin 

is bordered by marine to non-marine conglomerates that are 

younger than the marine volcanic and sedimentary rocks within 

the basin and were derived from adjacent continental rocks 

(Patton and Box, 1989).

Along its eastern and northern boundaries, the YukonKoyukuk basin is separated from flanking continental rocks 

by a belt of mafic and ultramafic rocks and minor sedimentary 

rocks, the Angayucham terrane (Box and Patton, 1989). The 

Angayucham is thought to represent imbricated Devonian 

through Jurassic oceanic crust (Pallister and others, 1989). On 

the eastern and northern boundaries of the Yukon-Koyukuk 

basin, from the basin to its flanks, major units have the same 

structural stacking: marine volcanic and sedimentary rocks sit 

above younger, continentally derived conglomerates, which 

sit above oceanic rocks of the Angayucham terrane, which sit 

above schists with continental protoliths and high-pressure/lowtemperature metamorphic assemblages.

Eastern Seward Peninsula lacks this simple structural 

stacking. Instead, the marine volcanic and sedimentary rocks of 

the basin are directly juxtaposed with schists of the Nome Complex, with no intervening oceanic rocks (sh. 2). The oceanic 

rocks sit west of the Yukon-Koyukuk basin as isolated slivers 

within a fault zone flanked by the Nome Complex. The fault 

zone spans eastern Seward Peninsula from north to south, and 

was named the Kugruk Fault Zone by Sainsbury (1974). Nome 

Complex rocks are within the fault zone and flank the fault zone 

on both sides. Sedimentary rocks related to the Yukon-Koyukuk 

basin (the older part of unit TKs) are also caught as slivers 

within the fault zone.

The oceanic rocks of eastern Seward Peninsula are considered part of the Angayucham terrane and consist of metabasalt, 

Jurassic tonalite, and minor serpentinite. Mafic rocks throughout the belt are metamorphosed to blueschist or greenschist 

facies; fabrics in these rocks are weak to mylonitic. Mafic 

rocks in the northern part of the Kugruk Fault Zone also retain 

minerals from an earlier metamorphic event that predated the 

blueschist-greenschist facies event, while mafic rocks in the 

southern part of the fault zone contain a single blueschist or 

greenschist metamorphic assemblage and relict igneous phases. 

The age of blueschist-facies metamorphism is unknown, and it 

differs in style and conditions from the blueschist-facies event 

in the Nome Complex. Although the metamorphic grade of 

basaltic rocks in the Angayucham terrane elsewhere is generally prehnite-pumpellyite to low greenschist, blue amphiboles 

are known in correlative oceanic rocks on the flank of the 

Ruby geanticline (Dusel-Bacon and others, 1989; Roeske and 

McClelland, 1997).

Two sequences of sedimentary rocks, one likely midCretaceous, the other Late Cretaceous and Tertiary in age, are 

present within the fault zone. One sequence is dominated by 

coarse conglomerate rich in locally derived clasts, including 

Paleozoic marbles and dolostones (most from the Nome Complex) and mylonitic metabasites from the Angayucham terrane 

(Till and others, 1986). Mid-Cretaceous sedimentary rocks of 

the adjacent parts of the Yukon-Koyukuk basin are also carbonate-rich (Nilsen, 1989; Patton and others, 2005), and are likely 

part of the same depositional sequence. Generally finer grained 

sedimentary sequences that have thick coal seams yielded Late 

Cretaceous and Tertiary pollen (Till and others, 1986; Dickinson 

and others, 1987).

Movement on the Kugruk Fault Zone may have recurred 

over a long time interval. The 100-Ma Darby pluton retains 

its intrusive contacts and is elongate parallel to the fault zone, 

suggesting that a structural control to the pluton’s shape existed 

during the Cretaceous. Results from a coal drilling program in 

the northern part of the Kugruk Fault Zone show that Nome 

Complex schists sit structurally above Tertiary sedimentary 

rocks, where the schists must have been placed by reverse faulting (Retherford and others, 1986). Therefore, the Kugruk Fault 

Zone also was active during the Tertiary.

Igneous Rocks

Granitoid rocks intruded the Nome Complex during the 

Cretaceous (fig. 2, on sh. 2). Based on early reconnaissance 

work and K-Ar ages, three suites of plutons were recognized: 

an early alkalic group, 110 to 96 Ma; a calc-alkaline group, 95 

to 80 Ma; and a tin granite group, 80 to 69 Ma (Till and others, 

1986). These characterizations are in flux.

The alkalic rocks are part of a belt that extends east of 

Seward Peninsula into the Yukon-Koyukuk basin (Miller, 1989; 

Arth and others, 1989; Amato and Wright, 1998). The calcalkalic plutons core the Kigluaik Mountains and are common 

on eastern Seward Peninsula (Till and others, 1986; Amato and 

Wright, 1998). Magmatism continued with intrusion of plutons 
7

DESCRIPTION OF MAP UNITS

SURFICIAL DEPOSITS

Qs Surficial deposits, undivided (Quaternary)—Frost-rived rubble on slopes and broad low 

ridges; glacial moraine; glacially deposited sand, gravel, and boulders; fluvial gravel and 

sand; marine and fluvial terrace deposits; wetlands

MESOZOIC AND CENOZOIC IGNEOUS ROCKS

Qlj Lost Jim Basalt (Holocene)—A single basaltic lava flow and associated vent deposits, undisrupted by frost brecciation, located in central Bendeleben quadrangle (fig. 2, on sh. 2). The 

dark gray-black vesicular olivine basalt in eastern part of the unit exhibits pahoehoe flow 

features and lava tubes. Maximum age is constrained to be less than 0.8 Ma based on stratigraphic position above unit QTv (Turner and Swanson, 1981)

QTv Weathered volcanic rocks, undivided (Quaternary and Tertiary)—Basalt lava flows, vent 

deposits, maar volcanoes and associated pyroclastic rocks exposed in northern, central, eastern, and to a minor extent, southern Seward Peninsula (fig. 2, on sh. 2).

 Less weathered rocks are slightly to strongly fragmented by frost riving and locally 

overlain by windblown silt. These rocks include alkali olivine basalt and olivine tholeiite. 

Alkalic rocks contain phenocrysts of olivine with plagioclase, augite, and spinel in the 

groundmass. Tholeiitic rocks contain plagioclase, phenocrysts with augite, hypersthene, 

and alkalic dike swarms (Amato and others, 2003c; Gottlieb and 

Amato, 2008). During latest Cretaceous time, a suite of tinbearing granites intruded both the Nome Complex and adjacent 

rocks in western Seward Peninsula (Hudson and Arth, 1983).

Magmatic events on Seward Peninsula are coeval with 

similar events on Saint Lawrence Island, Alaska, approximately 

250 km southwest of Seward Peninsula, and in the OkhotskChukotsk volcanic belt on the Russian side of Bering Strait, and 

formed in the same general tectonic regime (Amato and Wright, 

1998; Miller and others, 2002; Amato and others, 2003b).

Better delineation of crystallization ages using U-Pb zircon 

geochronology and a deeper understanding of petrogenetic 

events using modern geochemical tools was initiated by Arth 

and others (1989) and Amato and others (1994). Continued 

study of the age and nature of petrogenetic events on Seward 

Peninsula is underway (for example, Amato and Wright, 1997; 

Gottlieb and Amato, 2008); the earlier delineation of plutonic 

suites is in the process of being revised.

In central, eastern, and northern Seward Peninsula, extensive plateau basalts, cinder cones, and very large maars formed 

during several episodes of volcanism as old as the Oligocene, 

and as young as the Holocene (Hopkins and others, 1971; 

Turner and Swanson, 1981).

Tertiary and Active Deformation

Geomorphologic, structural, and thermal data indicate 

active deformation on Seward Peninsula occurred in Tertiary to 

Recent times. Along the coastline south of the York Mountains, 

terraces were uplifted during the late Pleistocene (Sainsbury, 

1967). Active normal faults, which are marked by sag ponds, 

offset streams, scarps and other features, bound the Kigluaik 

and Bendeleben Mountains (Kaufman, 1985; Plafker and others, 

1994), and expose the high-grade metamorphic rocks. Apatite fission-track data show that significant slip on these faults 

started in the Eocene (Dumitru and others, 1995). A transition 

from Nome Complex detritus to detritus that also includes 

high-grade minerals was recognized in wells drilled in Tertiary 

(Paleogene) offshore basins (Forbes and others, 1984; Tolson, 

1987). Based on gravity data, basins sit below McCarthy Marsh, 

south of the Bendeleben Mountains, and the Imuruk basin, north 

of the Kigluaik Mountains (Barnes and Hudson, 1977; Barnes 

and Morin, 1988); these basins are likely the same age as those 

offshore.

Tertiary activity along the Kugruk Fault Zone included 

reverse faulting (Retherford and others, 1986) as well as early 

Eocene graben formation (Dickinson and others, 1987). Death 

Valley, in the northern Darby Mountains, is likely a Tertiary 

feature.

Acknowledgments

We are indebted to Anita G. Harris, who, with tremendous 

dedication and perseverance, processed hundreds of kilograms 

of rock and picked through vast numbers of metamorphic 

grains to find the conodonts contained in Nome Complex 

carbonate rocks. We are thankful for her willingness to take on 

such rocks, and for her good humor in helping us understand 

them. We are grateful to Travis Hudson for suggesting that we 

concentrate early mapping efforts (in the 1980’s) in the western 

Solomon quadrangle. His advice was right on the mark—it is 

the area in which the internal structure of the Nome Complex 

was most easily identified. We also thank Dr. Hudson, as well 

as Timothy R. Carr and Jaime Toro, for contributing previously 

unpublished conodont data from the Teller quadrangle. Sincere 

thanks to Jeff Amato for providing unpublished geochronology 

data.
8

olivine, and spinel in the groundmass (Swanson and others, 1981). These less weathered volcanic rocks underlie portions of the Lost Jim Basalt in central Bendeleben quadrangle, and 

include the Camille Basalt and Gosling Volcanics of Hopkins (1963), as well as small flows 

in valley centers on the south flank and south of the Bendeleben Mountains. Potassiumargon (K-Ar) determinations on basalt from Kugruk River canyon (Turner and Swanson, 

1981) and from the northwest flank of the Bendeleben Mountains (Kaufman and Hopkins, 

1985) indicate that the Gosling Volcanics were in part extruded between 0.9 and 0.8 Ma. The 

Camille Basalt is younger by an unknown amount of time. Equivalent to unit “Qv” of Till 

and others (1986). In southern Seward Peninsula, a small basaltic vent and associated flows 

yielded a 40Ar/39Ar whole rock age of approximately 0.8 Ma (Werdon and others, 2006).

 Other volcanic rocks are thoroughly fragmented by frost action. These are the most 

widely distributed and voluminous volcanic rocks on the peninsula; they underly most of 

the Imuruk Lake lava plateau but are mapped only where exposed through an otherwise 

1- to 6-m thick mantle of windblown silt. The rocks are mostly alkali olivine basalt with 

phenocrysts of olivine with plagioclase, augite, and spinel in the groundmass. Lesser olivine 

tholeiite contains plagioclase phenocrysts with augite, hypersthene, olivine, and spinel in the 

groundmass (Swanson and others, 1981). This part of the unit includes the Imuruk Volcanics 

of Hopkins (1963), which are between 2 and 5 Ma (Hopkins and others, 1971; Turner and 

Swanson, 1981). Flows of the Imuruk Volcanics were confined by modern valley systems 

that drained north from Imuruk Lake area and, as a result of subsequent stream incision, 

are exposed as bench remnants high on valley walls. South and east of Imuruk Lake, older 

volcanic rocks cap ridge tops. These older flows are between 26 and 29 Ma (Turner and 

Swanson, 1981). In southeastern Bendeleben quadrangle, basalt flows are interlayered with 

sedimentary rocks that have yielded early Eocene pollen (Dickinson and others, 1987). 

Equivalent to unit “QTv” of Till and others (1986).

 The older volcanic units contain xenoliths of dunite, harzburgite, chromite, granite, 

and schist (Hopkins, 1963). Dunite xenoliths are most common, and reached 7–8 cm across. 

Granite and schist xenoliths are smaller (less than 2 cm across) and occur only where the 

volcanics erupted through granitic or metamorphic bedrock. Similar xenoliths in correlative volcanic rocks in western Alaska and on Saint Lawrence Island have had more detailed 

study (for example, Wirth and others, 2002).

 The Late Quaternary Espenberg Maars, 30–50 km southwest of Cape Espenberg on 

northern Seward Peninsula, consist of four large craters ranging from 4 to 8 km in diameter 

surrounded by coeval tephra layers. These craters, known as Devil Mountain, Whitefish, 

North Killeak, and South Killeak Maars (fig. 2, on sh. 2), are each separate eruption craters 

excavating 100 to 300 m into Pleistocene sediments and lavas (Hopkins, 1988). The maars 

are surrounded by a thick blanket of pyroclastic surge and airfall tephra deposits. Cliffs 

around Devil Mountain Maar expose sequences of bedded surge deposits, airfall lapilli beds, 

scoria, massive pyroclastic flows and explosion breccia (Begét and others, 1996). This volcaniclastic sediment is evidence that the Espenberg Maars were formed by highly explosive 

hydromagmatic eruptions through permafrost, which ultimately created the unusually large 

maar craters. Devil Mountain Maar is 8 km long by 6 km wide, as much as 200 m deep, and 

covers over 30 km2. It is the largest known maar on earth; the three other maars on Seward 

Peninsula are also larger than any previously described maar.

Mafic volcanic rocks of this unit are one of several Cenozoic volcanic fields in western 

Alaska that extend from northern Seward Peninsula to Saint Lawrence Island and the Pribilof Islands on the Bering Sea shelf (Moll-Stalcup, 1994); the Pribilof Islands are about 840 

km south-southwest of Nome

TKv Felsic volcanic rocks (Tertiary and Cretaceous)—Rubble crop of volcanic rocks in northeastern part of the map area, in Bendeleben D–1 quadrangle (fig. 2, on sh. 2). Unit consists of 

two varieties of volcanic rock, both moderately to strongly limonite stained. One is a volcanic flow or tuff that contains up to 4% phenocrysts in an aphanitic, devitrified groundmass. 

Phenocrysts are predominately sanidine with rare quartz and plagioclase. No mafic minerals 

are present, but morphology of rare aggregates of sericite, opaques and limonite suggest the 

former presence of biotite. The second type of volcanic rock is fragmental and contains schist, 

devitrified volcanics, and angular quartz fragments in a felsic(?), sericite-bearing matrix. It 

may be a volcanic flow breccia or vent breccia rock. Age of unit is unknown. Felsic tuffs on 

Saint Lawrence Island have yielded a K-Ar age of 39.3 Ma (Patton and Csejtey, 1980)
9

Ktg Tin-bearing granitic stocks (Late Cretaceous)—Stocks of biotite granite exposed in outcrop, 

rubble, and float in northwestern Seward Peninsula. Includes stocks at Cape Mountain, 

Brooks Mountain, Black Mountain, Ear Mountain, and the Oonatut Granite Complex (fig. 

2, on sh. 2). The belt also includes bodies not exposed at the surface at Lost River Mines 

and Kougarok Mountain (fig. 2, on sh. 2). Stocks are dominantly biotite granite with lesser 

aplitic and pegmatitic phases (Hudson and Arth, 1983). Larger stocks, such as the Oonatut, 

are texturally zoned. Contacts with country rocks are sharply crosscutting, and contact aureoles are narrow. Epizonal stocks have high 87Sr/86Sr initial ratios and elevated Th, U, Hf, 

and Ta (Hudson and Arth, 1983). Potassium-argon (K-Ar) biotite ages range from 69.2±2 

to 80.2±3 Ma (Hudson and Arth, 1983). Tin lodes and placers are associated with the stocks 

(Reed and others, 1989). Tin and tungsten were commercially mined in Lost River area, 

western Teller quadrangle (Sainsbury, 1969b)

Kds Dikes and stocks (Cretaceous)—Dikes and rare stocks of a variety of compositions and ages 

mapped extensively in the York, Kigluaik, and Bendeleben Mountains, and near the Darby 

Mountains, but also present in the Nome Complex. Some, but not all, are shown on the map 

as small pink lines.

 The oldest dike known is an analcime-biotite-nepheline syenite that intruded the Nome 

Complex in central Solomon quadrangle and yielded a biotite 40Ar/39Ar age of 107 Ma 

(Werdon and others, 2005a). A group of alkalic dikes, nepheline syenite and pseudoleucite 

porphyries, are exposed as frost-riven rubble in Solomon C–2, C–3 and D–3 quadrangles 

and intruded portions of the Kachauik pluton and adjacent marble. The dikes are up to 10 m 

wide and have strike lengths up to 900 m. They strike mostly to the northeast and are vertical. Syenite of the Kachauik pluton is highly radioactive adjacent to the dikes, containing up 

to 0.15% U3O8, 1.05% ThO2 and 2% rare earth elements (Miller and Bunker, 1976). Dikes 

yielded a K-Ar biotite age of 96.3±3 Ma (Berry and others, 1976).

 Alkali feldspar granite to quartz monzodiorite pegmatite dikes and sills are common at 

the core of the Kigluaik Mountains, in the western Bendeleben Mountains, and in the Darby 

Mountains, but are not found in rocks of lower metamorphic grade. A foliated pegmatite 

dike that cut high-grade metamorphic rocks in the Bendeleben Mountains yielded a U-Pb 

zircon age of 99±2 Ma (Gottlieb and Amato, 2008).

 Dark-brown- to orange-weathering alkalic diabase dikes are widespread on Seward 

Peninsula, but best documented in high-grade metamorphic rocks that underlie mountain 

ranges. Alkalic diabase dikes cut high-grade rocks and Cretaceous plutons in the Kigluaik 

and Bendeleben Mountains; dikes are up to 5 m across and yield 40Ar/39Ar ages of approximately 83 Ma (Calvert and others, 1999; Amato and others, 2003c). Similar brown- to 

orange-weathering alkalic mafic dikes in the Nome Complex are exposed in scattered locations on southern Seward Peninsula; in Solomon quadrangle, mafic dikes yielded 40Ar/39Ar 

ages of 80 to 84 Ma (Werdon and others, 2005a; Newberry and others, 2005; Werdon and 

others, 2006).

 In the Bendeleben Mountains, light-tan- to orange-weathering, altered, porphyritic 

dikes, sills and small plugs of quartz latite are about the same age as the regionally widespread diabase dikes. In Bendeleben A–4 quadrangle, dikes are up to 12 m across and have 

aphanitic groundmass, feldspar and quartz phenocrysts, and altered mafic phenocrysts. 

Textures in dikes, sills and plugs indicate crystallization at shallower levels than the nearby 

granite bodies and pegmatite dikes. Gottlieb and Amato (2008) reported a U-Pb zircon age 

of 82±1 Ma for a hypabyssal porphyritic dike, likely from this group of dikes. Dikes may be, 

in part, equivalent to unit “Kql” (quartz latite porphyry) and unit “Khi” (hypabyssal intrusive 

rocks) mapped by Miller and others (1972), and the “rhyolites of the western Bendeleben 

Mountains” of Turner and Swanson (1981). Similar intermediate to felsic dikes are exposed 

in the southern Darby Mountains, but their age is unknown.

 In western Nome quadrangle, biotite- and hornblende-bearing granitic dikes and 

lesser tourmaline-bearing pegmatite dikes cut folded and coarsely recystallized marble 

(unit |mm). K-Ar ages of 80.5±0.8 Ma (biotite) and 84.2±0.9 Ma (hornblende) from the 

dikes are cooling ages (N. Shew, written commun., 1993); the hornblende age more closely 

approximates the intrusive age

Kp Pargon pluton (Cretaceous)—Fine-grained equigranular, fine- to medium-grained seriate granodiorite, monzodiorite, and locally monzogranite exposed in the western Bendeleben Mountains along the upper reaches of the Pargon River (fig. 2, on sh. 2). Granodiorite and quartz 
10

monzonite are the dominant lithologies. Upper contact of the pluton is preserved locally. 

Pargon pluton yielded a U-Pb zircon age of 86±1 Ma (Gottlieb and Amato, 2008)

Kdi Kigluaik diorite (Cretaceous)—Fine- to medium-grained potassic mafic rocks of the lower part 

of the Kigluaik pluton, including biotite hornblende diorite, quartz diorite, granodiorite, 

tonalite, and gabbro, exposed in the western Kigluaik Mountains (fig. 2, on sh. 2; Amato and 

others, 1994; Amato and Miller, 2004). Geochemical and isotopic data indicate these mafic 

rocks are genetically related to the Kigluaik granite (unit Kg), the upper, more voluminous 

part of the pluton (Amato and Wright, 1997). Mineral thermometry indicates intrusion at 

pressures of 3–5 kb; together, units Kdi and Kg are thought to have formed in a subduction 

zone setting (Amato and Wright, 1997). Crystallization age of 90±1 Ma (Amato and Wright, 

1998)

Kg Kigluaik granite (Cretaceous)—Fine- to medium-grained felsic rocks of the upper part of 

the Kigluaik pluton (fig. 2, on sh. 2), including leucocratic biotite granite and granodiorite (Amato and Miller, 2004). Unit is more extensively exposed than the mafic root, the 

Kigluaik diorite (unit Kdi), and contains minor amounts of alkali feldspar granite and quartz 

syenite (Amato and others, 1994; Amato and Wright, 1997). Contact with the underlying 

mafic root (Kdi) is a 10- to 20-m-thick “mixing/mingling” zone characterized by mafic 

enclaves in a granitic matrix; textures suggest that unit is the same age as unit Kdi (Amato 

and Wright, 1997). The upper contact of unit with the overlying metamorphic rocks is 

locally exposed (Amato and Wright, 1997). Geochemical characteristics of units Kg and Kdi

indicate formation in a subduction zone setting (Amato and Wright, 1997)

Ks Stocks, undifferentiated (Cretaceous)—Frost-riven outcrops, rubble fields, and float of felsic 

intrusive rocks at four localities align along a roughly north-south trend in Bendeleben C–3 

and D–3 quadrangles (fig. 2, on sh. 2). The northernmost, Crossfox Butte stock, is monzogranite to quartz monzonite with rare leucocratic syenite that contains several percent purple 

fluorite, muscovite, and minor scheelite. Country rock rubble around the stock consists of 

hornfelsed marble and calc-silicate rocks. A biotite K-Ar date of 91.5±2.8 Ma is considered 

suspect due to chloritization of the biotite (Till and others, 1986). The Asses Ears stock is 

monzogranite to syenogranite and strikingly porphyritic, with alkali feldspar phenocrysts 2 

to 4 cm long. The Virginia Butte stock is quartz monzonite to syenite that yielded a biotite 

K-Ar date of 94.8±1.9 Ma (Till and others, 1986). The southernmost, Nimrod Hill stock, 

is monzonite but contains rare biotite-rich diorite. Hornblende from Nimrod Hill yielded 

a K-Ar age of 96.3±2 Ma (N. Shew, written commun., 1990). Aeromagnetic data suggest 

the stock extends west under Imuruk Lake and also suggest a possible connection with the 

Virginia Butte and Asses Ears stocks to the north (J. Cady, written commun., 1986)

Kku Kugruk pluton (Cretaceous)—Frost-riven rubble in northeast corner of Bendeleben C–2 quadrangle (fig. 2, on sh. 2). Quartz monzonite to quartz monzodiorite. Green porphyritic rocks 

of approximately dioritic composition at the eastern margin of the pluton may be a border 

phase. Aeromagnetic data suggest that the pluton is larger than mapped (J. Cady, written 

commun., 1986). Biotite produced a K-Ar date of 94.8±2.8 Ma (Till and others, 1986)

Kwc Windy Creek pluton (Cretaceous)—Talus and frost-riven rubble at north end of the Darby 

Mountains in Bendeleben A–1 and A–2 quadrangles. Rock type is quartz monzonite that is 

locally cut by biotite granodiorite dikes (fig. 2, on sh. 2). Blocks or roof pendants of metamorphic rocks are locally common, especially in western portion of the pluton. A large block 

of marble, schist and calc-silicate hornfels is contained within eastern portion of the pluton. 

Miller and others (1972) found boulders of nepheline syenite in streams that drain east side 

of the pluton. Portions of pluton are altered and veined. Alteration consists of limonite staining, weak to strong sericitization of plagioclase, and variable chloritization and sericitization 

of hornblende. Two types of veins are present: (1) rare pieces of quartz vein material up to 

15 cm across containing several percent fluorite, 1 to 2 percent molybdenite, and galena 

and sphalerite; and (2) thin, mostly <3 mm but up to 1 cm, veinlets containing quartz and 

pyrite±fluorite, molybdenite, scheelite and minor galena and sphalerite. Although these 

veinlets crosscut each other, they do not constitute a stockwork system. Yielded a hornblende K-Ar age of 93.8±2.1 Ma (N. Shew, written commun., 1987), and a U-Pb zircon age 

of 96.5±0.2 (R.Friedman, written commun., 2009)

Kd Darby pluton (Cretaceous)—Elongate monzogranite, locally granodiorite pluton 80 km long 

and 3 to 8 km wide that extends along crest of the Darby Mountains in southeast part of the 

peninsula (fig. 2, on sh. 2). Outcrops are common in northern part of the pluton; frost-riven 
11

rubble predominates elsewhere. Pluton is characterized by phenocrysts of alkali feldspar up 

to 5 cm long. Some gradual zonation of mineralogy: hornblende content decreases slightly to 

north; plagioclase content decreases slightly to north with a corresponding increase in alkali 

feldspar and quartz contents. Rounded or ellipsoidal inclusions of a mafic igneous rock are 

common. K-Ar ages range from 96.4±3 Ma to 90.5±1.5 (Miller and Bunker, 1976). Yielded 

a U-Pb zircon age of 100.1±0.1 (R.Friedman, written commun., 2009)

Kkd Diorite (Cretaceous)—Hybrid diorite of the Kachauik pluton; exposed in Solomon B–2 quadrangle (fig. 2, on sh. 2). Unit is coarse grained and characterized by abundant biotite and 

may be a border phase of the monzonite-syenite (unit Kkms) of the Kachauik pluton (Miller 

and others, 1972)

Kkg Granodiorite (Cretaceous)—Granodiorite-quartz monzonite phase of the Kachauik pluton, 

exposed in frost-riven rubble, talus and outcrop in Solomon C–2 and D–2 quadrangles (fig. 

2, on sh. 2). Unit is cut by aplite, quartz latite porphyry, lamprophyre and alkaline dikes 

(Miller and others, 1972)

Kkms Monzonite-syenite (Cretaceous)—Monzonite-syenite phase of the Kachauik pluton; exposed 

as frost-riven rubble, talus and outcrop in Solomon B–2, C–2 and D–2 quadrangles (fig. 2, 

on sh. 2). This phase is the most voluminous phase of the pluton, and is cut by aplite, quartz 

latite porphyry, lamprophyre, and alkaline dikes. K-Ar hornblende cooling age of 99.9±3 Ma 

(Miller and others, 1972; Miller and Bunker, 1976)

Kkgm Gneissic monzonite (Cretaceous)—Gneissic monzonite of the Kachauik pluton; exposed in 

Solomon C–2 quadrangle (fig. 2, on sh. 2). Unit has a gneissic to trachytoid texture, and may 

be a border phase of the monzonite-syenite (unit Kkms) of the Kachauik pluton (Miller and 

others, 1972)

Kbk Bendeleben and Kuzitrin plutons (Cretaceous)—Monzogranite and granodiorite; outcrop, 

talus, rubble, and some cirque headwall exposures in eastern Bendeleben Mountains in 

Bendeleben A–2, A–3, B–2 and B–3 quadrangles, and small rubble fields north of the 

range in Bendeleben C–3 quadrangle (fig. 2, on sh. 2). Known as two separate plutons, 

aeromagnetic data show that they are connected at depth, and they have similar chemistry, 

mineralogy, and cooling histories; they are lobes of the same large body. Contacts of both 

Bendeleben and Kuzitrin lobes with surrounding metamorphic rocks are not sharp, but 

rather are broad, several-kilometer-thick zones of mixed metamorphic and granitic rocks. 

Percentage of granitic rocks in contact zone decreases with distance from the two lobes. 

The Bendeleben lobe is monzogranite to quartz monzodiorite; contacts between these two 

phases do not appear to be gradational. Inclusions of plagioclase-biotite-pyroxene-quartz 

schist are locally common, and spectacular exposures of large inclusions or blocks of schist 

are present on northeast side of ridge in sec. 7, T. 3 S., R. 19 W. (Bendeleben A–2 quadrangle). Varying degrees of assimilation of this schist may account for the mineralogical 

and lithological variations. The Kuzitrin lobe is predominantly monzogranite and less well 

exposed. A U-Pb zircon crystallization age of 104±1 Ma was obtained from a foliated part 

of western Bendeleben pluton (Gottlieb and Amato, 2008). Biotite from Bendeleben lobe 

yielded a K-Ar age of 81.1±2 (Miller and Bunker, 1976; location 61 on sh. 2); a biotite 

sample from Kuzitrin lobe (location 62 on sh. 2) yielded a K-Ar age of 83.0±1.4 Ma. The 

biotite ages record pluton cooling

Kdc Dry Canyon stock (Early Cretaceous)—Frost-riven rubble of nepheline syenite on west side of 

Darby Mountains in Solomon D–2 quadrangle (fig. 2, on sh. 2). Unit has a trachytoid fabric 

and yielded a K-Ar hornblende age of 108±3 Ma (Miller, 1972)

Kgr Granite and granodiorite (Early Cretaceous)—Equigranular biotite-hornblende quartz monzonite exposed along eastern boundary of map area in Candle quadrangle, at Granite Mountain 

and in the “J” shaped Quartz Creek pluton (fig. 2, on sh. 2). Quartz monzonite at the core of 

the zoned Granite Mountain body grades into adjacent rocks of unit Ksy; the two rock types 

are thought to be comagmatic. Monzonite of adjacent unit Ksy yielded a hornblende K-Ar 

age of 108.6±3 Ma (Miller, 1972). Both bodies of quartz monzonite are part of the “western Yukon-Koyukuk plutonic suite” of Miller (1989), a potassic and ultrapotassic belt that 

extends from Seward Peninsula eastward into the Yukon-Koyukuk basin. Equivalent to unit 

“Kgr” of Patton and others (2005)

Ksy Syenite, monzonite, and nepheline syenite (Early Cretaceous)—Syenite, monzonite, and subordinate quartz monzonite, monzodiorite, quartz syenite, nepheline syenite and related mafic 

alkaline rocks of Patton and others (2005); exposed along eastern boundary of map area, in 
12

Candle quadrangle (fig. 2, on sh. 2). Part of the “western Yukon-Koyukuk plutonic suite” of 

Miller (1989), a potassic and ultrapotassic belt that extends from Seward Peninsula eastward 

into Yukon-Koyukuk basin. Hornblende K-Ar age of 108.6±3 Ma was obtained from the 

monzonite phase of Granite Mountain pluton (Miller, 1972). Equivalent to units “Ksy” and 

“Knsy” of Patton and others (2005)

Kv Andesite and basalt flows and volcaniclastic rocks (Early Cretaceous)—Andesite and basalt 

flows interbedded with volcaniclastic rocks and volcanic greywacke; exposed along eastern 

boundary of the map in Candle quadrangle (fig. 2, on sh. 2). Calcareous tuffs in upper part of 

the unit contain abundant shelly material, including abundant early Early Cretaceous (Berriasian and Valanginian) marine mollusks; unit yielded K-Ar ages ranging from 137 to 120 

Ma (Patton and others, 2005). Equivalent to unit “Kv” of Patton and others (2005)

Kgu Granitic rocks, undifferentiated (Cretaceous)—Granitic dikes, sills and small plugs at widely 

scattered localities (fig. 2, on sh. 2). Most commonly these bodies occur within exposures 

of high-grade metamorphic rocks (unit |<h), but unit is also present in the Nome Complex 

and on islands off the south and west coasts of the peninsula. Unit includes small bodies 

of anatectic biotite granite in southern Darby Mountains at Mount Arathlatuluk (107.8±0.2 

U-Pb zircon age), thought to be melts of the surrounding high-grade metamorphic rocks. 

Several bodies in western and easternmost Bendeleben Mountains intruded high-grade metamorphic rocks; small granitic bodies intruded the Nome Complex north of Death Valley, 

just south of the east end of the Bendeleben Mountains, and in the northeast Bendeleben 

quadrangle, near the boundary between the Bendeleben and Candle quadrangles. Fairway 

Rock, a small island directly west of the peninsula near Little Diomede Island, is a porphyritic hypersthene-bearing granite, with orthoclase crystals up to 10 cm long that are locally 

aligned in a fabric (Shumway and Moore, 1964). Biotite from Fairway Rock yielded a K-Ar 

biotite age of 110.7±3 Ma, similar to ages to alkalic intrusives on Seward Peninsula (tables 2 

and 3). Little Diomede Island, King Island, and Sledge Island are biotite-hornblende quartz 

monzonites or granites of unknown age (Sainsbury, 1972; Sainsbury and others, 1972). 

Extremely variable accessory mineralogy. Undated bodies are assumed also to be Cretaceous 

in age

YORK TERRANE

YORK MOUNTAINS SUCCESSION

DSl Limestone (Devonian and (or) Silurian)—Light-gray-weathering, medium-dark-gray limestone exposed in a small, fault-bounded area in central Teller quadrangle. Lithofacies 

include cherty lime mudstone, peloidal wackestone, and lesser coralline packstone. Lower 

beds produced relatively long-ranging conodonts but upper beds yielded conodonts of 

middle Silurian (middle Wenlock) age and Silurian (probably middle to late Silurian) 

corals; the fauna indicates a warm, relatively shallow water, normal-marine depositional 

setting (table A–1; W. Oliver, unpub. fossil report, 1974; Till and Dumoulin, 1994). DSl

has also yielded corals thought to be of probable Middle or Late Devonian age (Oliver and 

others, 1975); the age of this collection was later revised to late Silurian (late Ludlow)-

early Late Devonian (Frasnian), probably late Silurian to Early Devonian, by A. Pedder 

(Dumoulin and Harris, 1994; Till and Dumoulin, 1994). This revised age is younger than 

that of any other definitively dated lower Paleozoic rocks in the York terrane. Lithology 

and age of unit broadly correlate with all or parts of units SOdl and SOul of the York terrane and units Sd, DOx (overlay), and Ddm of the Nome Complex. Equivalent to unit “Dl” 

of Sainsbury (1972)

SOdl Dark limestone (Silurian and Upper Ordovician)—Medium- to thick-bedded, light-brown to 

dark-gray limestone, dolomitic limestone, and dolostone, locally cherty, commonly very 

fossiliferous, exposed in a fault-bounded area in northeastern York Mountains (Teller quadrangle; “section on Don River” of Sainsbury and others, 1971).

 Ordovician rocks, at least 120 m thick, consist of wackestones and packstones, with 

peloids and skeletal grains in a micritic matrix. Fossils are Late Ordovician and include 

conodonts (table A–1; Dumoulin and Harris, 1994), corals (Oliver and others, 1975; R.J. 

Elias in Blodgett and others, 2002, p. 283), trilobites (Ormiston, 1978; Ormiston and 

Ross, 1979), and brachiopods, cephalopods, gastropods, ostracodes, pelecypods, and 

stromatoporoids (Sainsbury, 1969a; Sainsbury and others, 1971; Rohr, 1979, 1988; Potter, 
13

1984; Rohr and Potter, 1987; Rohr and others, 2003). Rugose corals (Bighornia) indicate a 

possibly Richmondian age (Dumoulin and Harris, 1994).

 The Silurian section, at least 220 m thick, consists mainly of mudstone and bioclastic 

wackestone and packstone and contains more dolostone than the Ordovician part of the 

unit. Shallowing-upward cycles, 5 to 8 m thick, occur throughout. Megafossils form local 

buildups and include corals (Oliver and others, 1975), stromatoporoids, bryozoans, and brachiopods of middle and late Silurian age (Sainsbury and others, 1971). Biostratigraphically 

diagnostic conodonts are of early and earliest late Silurian ages (table A–1; Dumoulin and 

Harris, 1994; Till and Dumoulin, 1994).

Features such as fenestral fabric, micritized bioclasts, algal lamination, conodont biofacies, and the abundance and diversity of corals and stromatoporoids all indicate that SOdl

was deposited in warm, shallow to very shallow water in a locally restricted platform setting. 

Ordovician conodonts and megafossils include both Siberian and Laurentian (North American) endemic forms (Dumoulin and Harris, 1994; Blodgett and others, 2002; Dumoulin and 

others, 2002). Silurian fossils are mainly cosmopolitan.

 Unit SOdl is at least partly correlative with unit SOul; it is also partly correlative 

with, but much more fossiliferous than, Silurian metacarbonate rocks in units Sd and DOx

(overlay) of this map. Faunas and lithofacies of SOdl correlate well with those from ageequivalent strata in the Baird Group (Tailleur and others, 1967; Dumoulin and Harris, 1994) 

and related units in western and central Brooks Range (units “DOb” and “DOc” of Till and 

others, 2008b) and of the Telsitna Formation and related rocks in the Farewell terrane of 

interior Alaska (Dumoulin and Harris, 1994; Dumoulin and others, 2002). SOdl is equivalent to units “SOdl” and “Sl” of Sainsbury (1969a, 1972)

SOul Limestone and dolostone, undifferentiated (Silurian and Ordovician)—Carbonate rocks 

equivalent to unit Ols and (or) unit SOdl, but less well studied than those units; exposed 

in three small fault-bounded areas in central part of the Teller quadrangle. The western and 

central exposures are limestone with corals of Late Ordovician (Sainsbury, 1969a,b; Sainsbury and others, 1971) or late Middle to early Late Ordovician (Oliver and others, 1975) 

age. The eastern exposure is near the eastern boundary of the York terrane and consists 

of very fine-grained, locally cherty, gray dolostone that contains long-ranging conodonts, 

domal to laminar stromatoporoids, and diverse tabulate and rugose corals of Silurian, probably late Llandovery-Wenlock age (table A–1). Conodonts from this locality have a CAI 

value of 5, one of the highest known from the York terrane (table A–1). Equivalent to unit 

“Oum” of Sainsbury (1969a,b, 1972)

Ols Limestone and shale (Ordovician)—Thin- to medium-bedded, pale-orange- to pale-yellowbrown-weathering, medium-gray to black limestone, dolomitic limestone, and dolostone 

with local shale and chert nodules. Unit Ols forms subdued slopes within, north of, and 

east of the York Mountains; the unit is generally fault bounded, but locally depositionally 

overlies unit Ol. The lower 7 to 30 m of Ols is fissile black shale and lesser interbedded 

black limestone and dolomitic limestone that contains calcified and pyritized radiolarians 

and sponge spicules (T. Carr and T. Hudson, written commun, 1982; Dumoulin and Harris, 

1994). Lower strata grade upward into flaggy, thin-bedded black limestone with shaly partings and soft-sediment deformation features, and then into thin-bedded, sparsely bioclastic 

limestone and dolostone that is graded, crossbedded, and bioturbated. Ols is at least 300 

m thick (Dumoulin and Harris, 1994), and it appears to contain the Early-Middle Ordovician boundary near its base (Dutro in Ross and others, 1982). The unit produced pandemic, 

cool-water conodonts of earliest Middle Ordovician (latest Arenig and earliest Llanvirn) age 

(table A–1; Dumoulin and Harris, 1994), as well as cephalopods, graptolites, gastropods, 

and trilobites (Ross, 1967; Sainsbury, 1969b; Dutro in Ross and others, 1982). The youngest 

beds in Ols occur in a small klippe, 0.5 km in diameter, west of the Mint River in the northwestern York Mountains (unit “Odl” of Sainsbury, 1969b) and consist of medium-bedded, 

mottled to laminated, gray to brown lime mudstone and dolostone that contain conodonts, 

corals, and cephalopods of late Llanvirn age (Flower, 1968; Sainsbury, 1969b; Dumoulin 

and Harris, 1994). Bedforms, sedimentary structures, and faunas indicate that Ols was 

deposited in a shallowing-upward, basin to peri-platform environment; the youngest strata 

accumulated in a mid- to outer-platform setting (Dumoulin and Harris, 1994). Lithofacies 

and biofacies of Ols correlate well with those of deeper water Middle Ordovician strata in 

the western and central Brooks Range (unit “O<c” of Till and others, 2008b; Dumoulin and 
14

Harris, 1994). Equivalent to units “Os” and “Oshd” of Sainsbury (1969a), “Olsh” and “Odl” 

of Sainsbury (1969b), and “Oshl” and “Oshd” of Sainsbury (1972)

Ol Limestone (Ordovician)—Mainly massive to thick-bedded, light-brownish-gray to mediumgray, fine-grained limestone with local chert nodules and lesser interbeds of argillaceous 

limestone and shale, widely exposed in and adjacent to the York Mountains in western and 

central Teller quadrangle. Unit Ol is at least 450 m thick (Dumoulin and Harris, 1994); it 

resembles unit Oal in containing 8- to 15-m-thick shallowing-upward cycles (Vandervoort, 

1985) and locally abundant trace fossils, but differs in containing more megafossils and 

lacking quartzose grainstone and ripple marks. Common rock types include lime mudstone, 

bioclastic wackestone, and fine grained to very fine grained peloid and intraclast grainstone. 

The upper 70 m of the unit is a distinctive blue-gray-weathering, white to pinkish-gray lime 

mudstone with rare trilobite fragments. Most exposures of Ol are bounded by faults, but at 

a few localities it appears to grade upward into unit Olsh. Sainsbury (1969b) suggested that 

Ol conformably overlies unit Oal, but megafossil and conodont data suggest that the lower 

part of Ol may be coeval with much of unit Oal. Unit Ol is chiefly of Early Ordovician 

(early and middle Arenig) age. The tightest ages are based on conodonts and include collections restricted to the Mac. dianae, Ac. deltatus-On. costatus, lower Oe. communis, and Re. 

andinus-T. laevis Zones (table A–1); the two youngest of these collections are from near the 

top of Ol and are definitively younger than any faunas recovered from unit Oal. Megafossils 

in Ol include brachiopods, cephalopods, echinoderm debris, gastropods, and trilobites (Ross, 

1965; Flower, 1968; Sainsbury, 1969b). Graptolitic shale of early Arenig age (T. fruticosus

Zone; C. Carter, 1994, unpub. fossil report) forms local lenses in Ol.

 Lithofacies and biofacies indicate that Ol accumulated in a range of subtidal to supratidal environments within a deepening-upward regime (Dumoulin and Harris, 1994); overall, 

Ol appears to have formed in somewhat deeper water than unit Oal. Conodont assemblages 

in Ol include both Siberian and Laurentian (North American) endemic forms (Dumoulin 

and Harris, 1994; Dumoulin and others, 2002); trilobites have Siberian affinities (Ormiston 

and Ross, 1979). Unit Ol correlates well with older parts of unit Od in the Nome Complex 

and the Baird Group (Tailleur and others, 1967; Dumoulin and Harris, 1994) in the western 

Brooks Range (unit “DOb” of Till and others, 2008b), and with the Novi Mountain Formation, lower Telsitna Formation, and related rocks in the Farewell terrane of interior Alaska 

(Dumoulin and Harris, 1994; Dumoulin and others, 2002). Equivalent to units “Ol” and 

“Olu” of Sainsbury (1969a,b, 1972)

Oal Argillaceous limestone and limestone (Ordovician)—Thin-bedded, argillaceous, silty and 

(or) dolomitic limestone, lesser massive micritic limestone, and local chert; rocks are light 

gray to medium gray and weather light gray to orange to tan. The unit is widely exposed 

in and adjacent to the York Mountains in western and central Teller quadrangle, and is at 

least 350 m thick (Dumoulin and Harris, 1994). Like unit Ol, it contains 8- to 15-m-thick 

shallowing-upward cycles (Vandervoort, 1985) and locally abundant trace fossils, but Oal is 

less fossiliferous than unit Ol and includes quartzose grainstone and ripple marks not seen 

in unit Ol. Common rock types in Oal are dolomitic, locally argillaceous lime mudstone and 

grainstone made up mainly of peloids and intraclasts with lesser bioclasts and ooids. Mudsupported strata are bioturbated, with bedding-plane feeding trails and subvertical burrows. 

Grain-supported rocks are planar to crossbedded with locally well developed oscillation and 

current ripples. Some grainstones contain 10 to 40 percent fine-sand- to silt-size non-carbonate grains, mainly quartz and lesser feldspar, with trace amounts of pyroxene, zircon, and 

leucoxene (Sainsbury, 1969b).

 Most exposures of Oal are fault bounded, and its original depositional relations with 

other units in the York Mountains are uncertain. Sainsbury (1969b) reported that Oal conformably underlies unit Ol, but megafossil and conodont data suggest that the upper part of 

Oal is coeval with much of unit Ol. Unit Oal is chiefly of Early Ordovician (Tremadoc-early 

Arenig) age; the tightest ages are based on conodonts (table A–1). The oldest conodonts 

represent the Ro. manitouensis Zone, and are older than any definitively dated faunas known 

from unit Ol. Younger collections in Oal, however, include those of Mac. dianae Zone age 

and overlap ages determined for unit Ol. Sparse megafossils in Oal include brachiopods, 

gastropods, and trilobite fragments (Sainsbury, 1969b); echinoderm debris, calcareous 

sponge spicules, and possible calcispheres were noted in thin sections. Various types of 

stromatolites occur locally and form biostromes as much as 5 m thick (Sainsbury, 1969b; 
15

Vandervoort, 1985).

 Lithologic and fossil data indicate that Oal was deposited in a range of subtidal to 

supratidal settings within a deepening-upward regime (Dumoulin and Harris, 1994); overall, 

Oal appears to have formed in somewhat shallower and more agitated water than unit Ol. 

Conodonts in Oal are scarcer and less diverse than in unit Ol, likely because Oal accumulated more rapidly and (or) suffered more terrigenous input. Conodont assemblages in 

Oal are mainly cosmopolitan but include a few Laurentian (North American) and Siberian 

endemic forms (Dumoulin and Harris, 1994; Dumoulin and others, 2002; J.E. Repetski, 

written commun., 2008).

 Some rocks presently included in unit O<l are similar in lithofacies, biofacies, and age 

to Oal (Vandervoort, 1985; Till and Dumoulin, 1994). Unit Oal also correlates well with 

parts of unit Od in the Nome Complex, the Baird Group (Tailleur and others, 1967; Dumoulin and Harris, 1994) in the western Brooks Range (unit “DOb” of Till and others, 2008b), 

and the Novi Mountain Formation, lower Telsitna Formation, and related rocks in the Farewell terrane of interior Alaska (Dumoulin and Harris, 1994; Dumoulin and others, 2002). 

Equivalent to unit “Oal” of Sainsbury (1969a,b, 1972)

UNITS WITH UNCERTAIN AFFINITIES

|l Limestone (Paleozoic)—Intensely deformed limestone that has yielded no fossils but is presumed to be of Paleozoic age (Sainsbury, 1972), exposed in several small outcrops in central 

Teller quadrangle, northeast of the York Mountains. Equivalent to western part of unit “|l” 

of Sainsbury (1972)

Ml Limestone, dolomitic limestone, and marble (Mississippian)—Intensely deformed and recrystallized medium-dark-gray carbonate rocks, locally cherty and intercalated with subordinate 

fine-grained siliciclastic strata, exposed on westernmost tip of Seward Peninsula (Teller 

quadrangle; Sainsbury, 1972). Unit has been intruded and locally highly altered by the Cape 

Mountain granite (unit Ktg) and associated tin-bearing fluids (Steidtmann and Cathcart, 

1922). A poorly preserved coral fauna of probable Late Mississippian age was obtained from 

these rocks; it resembles that found in parts of the Lisburne Group (Schrader, 1902; Bowsher 

and Dutro, 1957) of northern Alaska (Steidtmann and Cathcart, 1922; W. Sando, unpub. 

fossil report, 1984). Some authors have correlated rocks of this unit with the Lisburne Group 

that is exposed north of Seward Peninsula at Cape Lisburne; Grantz and others (1991), for 

example, included both successions in their Tigara subterrane of the Arctic Alaska terrane. 

Sainsbury (1972) interpreted these rocks as having been thrust above the slate of the York 

region (unit O<t of this map). Equivalent to unit “Ml” of Sainsbury (1972)

|gb Metagabbro (Paleozoic)—Dark-green-to black-weathering massive bodies of metagabbro 

exposed in rubble crop and small blocky cliffs associated with units O<t, O<p, and O<l

(Sainsbury, 1969b). Throughout the unit, igneous textures are retained in thin section. 

In central Teller quadrangle, east of the York Mountains, relict clinopyroxene grains are 

partially recrystallized to actinolite, but other igneous minerals are completely recrystallized to a metamorphic assemblage of epidote, albite, chlorite, and small amounts of calcite, 

titanite, opaque, and stilpnomelane. In western Teller quadrangle, igneous minerals are more 

completely retained but show undulatory extinction and are cut by brittle cracks; metamorphic actinolite and chlorite occur on cracks and grain boundaries on or near clinopyroxene; 

small amounts of brown hornblende are considered late magmatic. Plagioclase is partially 

recrystallized to a very fine mat of brownish material, including sericite. Veins and veinlets 

of sericite and calcite are present in some samples. A U-Pb zircon crystallization age from 

one of these less recrystallized bodies, northwest of the York Mountains, is 539±11 Ma 

(table 3; Amato and others, 2009). A detrital zircon sample collected from unit O<t near the 

U-Pb zircon sample contains a probability distribution peak near this age (J. Toro, written 

commun., 2006, 2007), and may represent reworking of gabbroic or related volcanic material. Another sample of unit O<t, collected from one of its southernmost exposures along the 

shoreline, contained a single Ordovician conodont. Metagabbro bodies are mapped near that 

locality, which raises the possibility that there might be two ages of gabbro in unit O<t: the 

dated gabbros (earliest Cambrian), and a younger set (Ordovician or younger)

O<l Limestone and dolomitic limestone (Ordovician to Proterozoic)—Light-gray- to grayishorange-weathering, medium-light-gray to medium-dark-gray limestone and dolomitic limestone that occurs widely in western, central, and northern parts of the Teller quadrangle. The 
16

unit forms low outcrops and extensive areas of rubble and is locally intruded by gabbro (unit 

|gb of this map; Sainsbury, 1972). Most exposures of O<l are fault bounded, but in western 

Teller quadrangle, it may depositionally overlie unit O<t (Sainsbury, 1969b, 1972). Beds 

are even to irregular and mostly 2 to 30 cm thick. Much of the unit is parallel laminated, but 

crossbedding occurs locally and some intervals are bioturbated. Other sedimentary features 

include fenestral fabric and intraclast conglomerate with clasts as much as 5 cm long. Lime 

mudstone, in part dolomitic and (or) argillaceous, is the main lithology in O<l; quartz silt 

to very fine sand makes up as much as 20 percent of some samples. Minor to trace amounts 

of chert, zircon, pyroxene, and antigorite(?) also occur in silty lime mudstone, suggesting 

that mafic rocks contributed detritus to this unit (Sainsbury, 1969b). Grainstone, composed 

mainly of intraclasts, peloids and rare bioclasts, is a notable subordinate lithology.

 Unit O<l contains rocks of more than one age. Sainsbury (1972) considered much of this 

unit to be Precambrian, but subsequent paleontological studies indicated that at least some 

strata are Ordovician. Unit O<l has produced dated fossil assemblages (mostly conodonts) at 

more than 10 localities (table A–1; T. Carr and T. Hudson, written commun., 1982; Vandervoort, 1985; Till and Dumoulin, 1994; Toro and others, 2006). A few collections consist only 

of poorly preserved conodonts, chitinozoans, or acrotretid brachiopods that merely indicate 

broad, mainly Paleozoic age ranges, but several conodont assemblages are tightly dated as 

early-middle Early Ordovician (table A–1) and correlate well with faunas from units Oal

and Ol. The gabbro that intruded O<l, however, is earliest Cambrian (unit |gb; Amato and 

others, 2009), which constrains the age of at least part of the unit to Early Cambrian or older.

 Metamorphic grade and degree of deformation vary within O<l. Some samples appear 

unmetamorphosed and undeformed in thin section, whereas other samples contain layers 

rich in metamorphic white mica, are recrystallized, and have a phyllitic or schistose fabric. 

CAI values of conodont collections from this unit are mostly 4–4.5, but are 5 and 6 at several localities (table A–1); these values indicate that host rocks reached temperatures of 190 

to >360 °C (table A–2). Relations between variations in CAI values, metamorphic textures, 

and structural level have not been documented.

 Lithofacies and biofacies of Ordovician strata in O<l match particularly well with those 

of unit Oal. Unit O<l also correlates with parts of unit Ol, the Baird Group (Tailleur and 

others, 1967; Dumoulin and Harris, 1994) in the western Brooks Range (unit “DOb” of Till 

and others, 2008b), and the Novi Mountain Formation, lower Telsitna Formation, and related 

rocks in the Farewell terrane (Dumoulin and Harris, 1994; Dumoulin and others, 2002). 

Equivalent to units “pOt” and “pOl” of Sainsbury (1969a), “pOal”, “pOa”, “pOl”, and 

“pOlu” of Sainsbury (1969b), and “Op_l”, “p_t”, “p_ld”, and part of unit “p_l” of Sainsbury (1972)

O<t Sandstone, siltstone, and limestone (Ordovician to Proterozoic)—Gray- to orange-weathering, 

gray to brown, locally calcareous sandstone to siltstone, interbedded with gray to black 

mudstone and local limestone, exposed in western Teller quadrangle. Beds are typically ≤5 

cm thick (20 cm maximum). Outcrop features, which include climbing ripples, crossbeds, 

parallel and convolute laminae, and graded beds, suggest a turbidite origin. Sandstone is 

very fine to coarse grained; some beds contain black shale fragments 1 to 2 mm long. Sand 

and silt clasts are angular to subrounded and consist of quartz, feldspar, sedimentary and 

metamorphic lithic grains, mica, chlorite, and minor tourmaline and zircon. Limestone is 

fine grained, ferroan, and contains as much as 10 percent silt to medium-sand-size grains 

of quartz and feldspar. In thin section, samples of O<t appear recrystallized but only mildly 

deformed. Sainsbury (1969b, 1972) suggested that O<t depositionally underlies unit O<l; its 

contact with unit Ml is a fault.

 Unit O<t likely includes rocks of more than one age. The unit was intruded by gabbro 

(unit |gb of this map; Sainsbury, 1972) that at one locality in the northeastern part of the 

outcrop belt of O<t has been dated as earliest Cambrian (Amato and others, 2009). However, 

southern exposures of O<t produced a single conodont of middle Early-Late Ordovician 

age at one site (table A–1; Till and Dumoulin, 1994) and conodont fragments of indeterminate Cambrian-Triassic age at two other sites (table A–1; T. Carr and T. Hudson, written commun., 1982). A detrital zircon sample of sandstone from eastern exposures has a 

major peak in cumulative probability distribution at 550 Ma and several other notable peaks 

between 640 and 720 Ma (J. Toro, written commun., 2006, 2007). The 550 Ma peak may 

include zircons derived from the gabbros (unit |gb) or their volcanic equivalents. Unit O<t, 
17

therefore, is in part Proterozoic (pre-intrusion of gabbros), and in part Ordovician or younger 

(based on fossil data).

 Unit O<t could correlate, at least in part, with Middle Ordovician-Lower Silurian 

graptolitic argillite and turbidites (Iviagik Group of Martin, 1970) exposed south of Cape 

Lisburne (Grantz and others, 1983; Moore and others, 1994, 2002; Harris and others, 1995). 

Metasandstone in the Iviagik Group has a range of compositions (Dumoulin, 2001; Moore 

and others, 2002) that are broadly similar to those observed in O<t but the metasandstone 

differs in containing more chert, including grains of radiolarian chert not seen in O<t. 

Equivalent to parts of “pOs” of Sainsbury (1969b) and “p_s” of Sainsbury (1972)

O<p Phyllite (Ordovician to Proterozoic)—Fine-grained, mainly pelitic and (or) calcareous phyllite exposed in west-central Teller quadrangle. Unit crops out on creeks, weathers gray to 

grayish-brown, and is layered and locally finely laminated. The phyllitic foliation surface is 

crenulated. Gray-weathering material is sericite-rich; brown-weathering rocks are calcareous. In thin section, grain size, composition, and oriented lenses of sericite and opaques 

define foliation. Thin sericitic layers alternate with layers that contain interlocking crystals 

of calcite that are matrix to disseminated rounded to subrounded plagioclase and quartz 

grains. Locally, carbonate grains are stained with iron oxide. No fossils have been found, but 

O<p was intruded by gabbro (unit |gb of this map) that crystallized in the earliest Cambrian (Amato and others, 2009). Unit |<t may be a more deformed and metamorphosed 

correlative of O<t. Equivalent to parts of units “pOs” of Sainsbury (1969a, b) and “p_s” of 

Sainsbury (1972)

GRANTLEY HARBOR FAULT ZONE

|p Phyllite and argillite (Paleozoic)—Phyllite, argillite, and lesser metasiltstone and fine-grained 

metacarbonate rocks exposed south and north of Grantley Harbor in central Teller quadrangle. Outcrops consist of brownish-orange- to black-weathering, silvery-gray to black, locally 

carbonaceous phyllite to argillite, with interlayers and lenses of tan to green metasiltstone 

to semischist and dark gray to black, locally tannish-orange metacarbonate. Lithologies are 

interlayered on a scale of centimeters, with metacarbonate layers as thick as 1.5 m. These 

rocks have yielded sparse conodont fragments of indeterminate Ordovician-Triassic age 

(table A–1; T. Carr and T. Hudson, written commun., 1982, 1984) and contain rare relict bioclasts, including probable recrystallized radiolarians and siliceous sponge spicules, observed 

in thin section. Unit |p in part resembles carbonaceous radiolarian-bearing rocks found in 

eastern exposures of unit DOx. Equivalent to part of unit “|b” of Hannula and others (1995) 

and parts of unit “p_s” and “p_nc” of Sainsbury (1972) 

|<l Metalimestone (Paleozoic and Proterozoic?)—Thinly layered to laminated, orange-and grayweathering, color-banded, white to dark-gray metalimestone exposed in a small area south 

of Grantley Harbor in south-central Teller quadrangle. Layers range from a few millimeters 

to 6 cm thick and reflect differences in composition and grain size. Darker layers are finer 

grained, more impure, and contain abundant organic material and white mica, whereas 

lighter layers are coarser grained and consist mostly of calcite and lesser silt-size quartz 

grains. The unit has a well-developed cleavage which is axial planar to tight to isoclinal 

folds, formed at low- or sub-greenschist facies conditions, and a second, lower temperature 

dissolution cleavage with associated tight folds (Hannula and others, 1995). Calcite-filled 

tension gashes are common (Hannula and others, 1995). No fossils have been positively 

identified, although a few forms noted in thin section could be relict bioclasts. Locally, this 

unit includes interlayers of red-weathering, green phyllite and appears to grade into unit 

|<t. Thinly interbedded lime mudstone and argillaceous limestone is the most likely protolith for |<l, which may be a more deformed and (or) metamorphosed correlative of unit Oal

and (or) unit O<l. Equivalent to unit “|sl” of Hannula and others (1995) and a small part of 

unit “p_l” of Sainsbury (1972)

|<t Metasiltstone and phyllite (Paleozoic and Proterozoic?)—Metasiltstone, metasandstone, and 

phyllite that form a small exposure south of Grantley Harbor in central Teller quadrangle. 

The unit consists of intercalated grayish-green metasiltstone to medium-grained metasandstone, in layers 1 cm to 1 m thick, grayish-green to silver phyllite and silty phyllite, and dark 

gray to black phyllitic shale. Percentage of these lithologies varies throughout the outcrop 

belt but metasiltstone and (or) metasandstone generally predominate. Some coarser grained 

layers appear to be graded, contain parallel laminae, and (or) show local cut-and-fill struc-
18

tures; shaly rip-up clasts as much as 4 cm long occur at several localities. Metasandstone 

and metasiltstone layers have a semischistose texture and consist mainly of quartz, calcite, 

and quartz-white mica aggregates (metamorphic lithic clasts?) in a matrix of white mica and 

chlorite; lesser clast types include feldspar, dolomite, and allanite(?). No fossils constrain the 

age of the unit, but lithofacies suggest they may be a more deformed equivalent of unit O<t. 

Equivalent to part of unit “|b” of Hannula and others (1995) and a small part of unit “p_s” 

of Sainsbury (1972)

NOME COMPLEX

LAYERED SEQUENCE

|np Metagabbro and metasediments (Paleozoic?)—Massive hills, tors and rubble piles of metagabbro and poorly exposed metasedimentary rocks on west side of the Kigluaik Mountains. 

Metagabbro bodies form flat-topped hills generally less than a kilometer across; one body 

exposed along sea cliffs is 9 km long. Metasedimentary rocks are poorly exposed and 

include metagraywacke and tuffaceous metasediments. Original igneous and sedimentary 

features are preserved. In thin section, metagabbro is coarse grained and partially to completely recrystallized to actinolite, epidote, chlorite, titanite, albite and quartz (Hannula and 

others, 1995; Till, unpub. data). The metagabbros are geochemically similar to metabasites 

from units Ocs and DOx (Ayuso and Till, 2007). The geometries of outcrop-scale structures 

are similar to those in the more completely recrystallized and deformed part of the Nome 

Complex. Hannula reported three pumpellyite and actinolite bearing samples from northern parts of the unit and one crossite-bearing sample from the central part, which indicates 

that metamorphic grade increases from northwest to southeast within the unit. The contact 

between units |np and Ocs to the southwest corresponds to the garnet isograd of Hannula 

and others (1995). Unit |np may be equivalent to unit Ocs. Equivalent to unit “|mvu” of 

Hannula and others (1995)

Ds Pelitic schist (Devonian?)—Tors of resistant, well-foliated quartz-rich schist. Pelitic rocks are 

the dominant lithology; calcareous schist is a minor component. Outcrop appearance of the 

pelitic schist is diagnostic of the unit, and shows 1- to 2-cm-thick bands of granular interlocking quartz grains interlayered with micaceous schist. In thin section, major minerals 

include quartz, muscovite, chlorite, chloritoid, and locally graphite, glaucophane and garnet. 

Quartz-segregation layers parallel foliation and trace intrafolial isoclinal and chevron-style 

folds axial planar to the foliation. Minor lithologic variation may occur at outcrop scale, 

typically with relatively thin calc-schist layers in quartz-rich schist.

Four detrital zircon samples were collected; only one yielded sufficient zircons for 

analysis. The youngest zircon population contains Early to Middle Devonian grains (Till and 

others, 2006). At least part of the protolith of the unit is Devonian or younger.

 Unit thickness is unknown. Typical examples of the unit crop out in northeast Solomon 

D–5 quadrangle. First described by Smith (1910). Equivalent to unit “p_st” of Sainsbury 

(1974) and unit “_p_s” of Till and others (1986), and unit “Ds” of Werdon and others 

(2005a,b) and Newberry and others (2005)

Dcs Pelitic, calcareous, and graphitic schist (Devonian)—Pelitic, calcareous, and graphitic lithologies interlayered on a scale of centimeters to meters, exposed in central Nome and Solomon 

quadrangles. Interlayering is gradational and intimate. The unit is composed predominantly 

of pale brown and gray weakly foliated to well-foliated schists dominated by plagioclase, 

calcite, quartz, white mica, and graphite. In the central Solomon quadrangle, where calcareous lithologies are subordinate to pelitic lithologies, the unit forms smooth rounded hills, 

or more commonly, is present in valleys and areas of subdued topography. Rarely forms 

outcrops; usually forms loose rubble on hills or in stream cuts; in low areas unit is covered by tundra. Ridge-top outcrops and ridge-flanking tors are more common in the Nome 

quadrangle, but not abundant. The unit may be present but unrecognized in exposures of the 

Nome Complex north of Kigluaik and Bendeleben Mountains.

 Pelitic rocks are light to dark gray weathering and contain pale-colored chloritoid, glaucophane or pseudomorphs of chlorite and albite after glaucophane, and in rare cases, garnet; 

at some localities, micaceous laminae alternate with quartz-rich laminae. Accessory minerals 

include epidote, clinozoisite, apatite, tourmaline, sphene, graphite, ilmenite, pyrite, rutile, and 

zircon. Calcareous schist is light to dark brownish-gray and commonly contains plagioclase, 
19

chloritoid, calcite, some dolomite, and rare garnet. Plagioclase commonly occurs as syn- and 

post-penetrative deformation metamorphic porphyroblasts. Accessory minerals include apatite, tourmaline, graphite, pyrite, rutile, and zircon. Gray-weathering, plagioclase-rich lithologies are interlayered with orange- or brown-weathering impure marble or calcareous schist in 

some localities, mica- and graphite-rich schists in other localities. Layers rich in chlorite and 

albite, with and without white mica and calcite, are generally less than 0.5 m thick.

 The unit includes relatively thin, but widely distributed, layers of light to dark gray 

or pale orange weathering millimeter-scale color laminated marble. Marbles are slightly 

impure, most commonly with small concentrations or disseminations of quartz, white mica, 

and graphite; marbles also can include iron carbonate, iron oxide, and rare sulfide minerals. 

Less common, but also broadly distributed, are layers typically less than 20 cm thick of pale 

tan- to white-weathering metaquartzite with fine laminations defined by minor iron carbonate, iron oxide, and white mica.

 Dark-gray- to black-weathering, graphitic metasiliceous rock, locally micaceous, contains millimeter-scale laminae enriched in graphite, white mica, and iron oxide, and occurs 

in layers meters to tens of meters thick; exposures are generally thinner than the graphitic 

metasiliceous layers in unit DOx.

 In the Nome quadrangle, a dark-gray to black-weathering rock with white millimeterto centimeter-thick lenses, layers, and irregular blobs of polycrystalline quartz forms layers 

a meter to several meters thick. Matrix to the quartz concentrations is typically rich in white 

mica, graphite, chlorite, and albite in varying abundances. Many exposures are resistant. 

Some of the polycrystalline quartz lenses and blobs trace intrafolial isoclinal folds; blobs on 

fold hinges are more equant. These features and other deformational characteristics of the 

Nome Complex are consistent with a protolith for Dcs that had quartz-rich alternating with 

mica-rich layers, although its present appearance is suggestive of a conglomerate. Unit Dcs

is equivalent to the “lumpy schist” or unit “pCPzspm” of Bundtzen and others (1994).

 A distinctive group of lithologies along the western margin of the unit in the Nome 

quadrangle coincides with a long, linear resistivity low and magnetic high (Burns and others, 

2005a,b). Pale-green- and pale-gray-weathering, locally brown-weathering schists locally 

display millimeter- to centimeter-thick layers of sugary white quartz. Rocks typically are 

interlayered concentrations of quartz with lesser iron carbonate and epidote versus white 

mica, medium-dark colored chloritoid, and locally epidote, iron carbonate, and chlorite. 

Chloritoid grains may occur in polycrystalline lenses within white mica laminae. Epidote 

grains contain brown (allanite) cores. Brown-weathering layers are calcareous. This group 

of lithologies locally contains Zn-Pb mineralization. A lens of carbonate clast conglomerate, 

10 to 15 m thick and ≥15 to 20 m long, sits between this group of distinctive lithologies and 

the thick pure marbles of unit DOx. The conglomerate is poorly sorted, matrix supported, 

interlayered with schist; its matrix is calcareous schist that contains abundant quartz and 

white mica. Clasts are rounded to angular, elongate to disc-shaped, and as much as 75 cm in 

maximum diameter. Most are light gray to beige dolostone and medium gray marble.

 Many detrital zircon samples contain small populations of Middle and Late Devonian 

zircons and large populations of early-middle Silurian zircons as well as older populations 

(Till and others, 2006; Till and others, 2008a). Therefore, much or all of the unit is Devonian 

or younger. Thickness of unit is greater than 1.2 km.

 A distinctive marble forms a small lens within or adjacent to Dcs in the Nome 

quadrangle. The marble is white to light gray, generally impure (5 to 15 percent quartz, 1 

to 5 percent white mica), and typically contains sand- to pebble-size clasts of dark gray 

to black, organic-rich marble. Most clast-bearing intervals appear to be clast supported 

and some may be graded. Clasts are rounded to angular in shape, commonly laminated, 

and generally ≤2 cm in diameter; a few clasts may be as much as 12 cm long. The clastbearing marble produced conodonts with CAI values of 5 at two localities (table A–1). One 

collection yielded a single element of Silurian(?) through Triassic age. The other collection, 

also a single conodont, is an Sb element of late Permian through Triassic (likely Triassic) 

age. Three possible scenarios that explain the presence of a Triassic marble in the otherwise 

Devonian and older Nome Complex include: (1) contamination of the conodont sample; (2) 

pre-metamorphic fault juxtaposition of Triassic and older rocks; and (3) a pre-metamorphic 

unconformable relation between Triassic and older rocks. The CAI value of this conodont is 

consistent with that of other Nome Complex rocks, and no rocks that could have produced 
20

such contamination (that is, rocks of known Permian or Triassic age and high thermal level) 

were being processed in the laboratory at the time the Seward Peninsula sample was run (A. 

Harris, written commun., 2005). Thus, the clast-bearing (Triassic?) marble was juxtaposed 

with Dcs before or during Jurassic metamorphism or may be a rare remnant of rocks that 

sat unconformably atop protoliths of the Nome Complex before those protoliths were 

metamorphosed. Because of the uncertainties in the origin of this marble and its uniqueness, 

we choose not extend the protolith age of the Nome Complex to Triassic

DOx Mixed marble, graphitic metasiliceous rock, and schist (Devonian to Ordovician)—Interlayered pure and impure marble, graphitic metasiliceous rock, pelitic schist, calc-schist, and 

mafic schist. Gray- and orange-weathering marble and dark gray-black-weathering graphitic 

metasiliceous rock are the most common lithologies in the unit, which is dominated locally 

by one or the other. Gray-weathering pure marble forms rounded ridgelines that extend 

along strike for several kilometers, and rounded hills of slabby, black graphitic metasiliceous 

rock can be recognized from great distances. The unit is defined by its position structurally 

below the Casadepaga schist (unit Ocs). Good exposures are rare; minor lithologies generally do not crop out. Lithologies thicken and thin along strike on a scale of kilometers, a 

feature which may be depositional as well as structural.

 In western Solomon quadrangle and Nome quadrangle, there is a consistent general 

stacking pattern of lithologies within DOx. The structurally upper part of the unit is composed of mixed schist and marble, including pelitic schist, gray marble, orange-weathering 

impure marble, black schistose marble, and black metasiliceous rock; these lithologies are 

interlayered on a scale of meters and decameters. The uppermost lithology is commonly an 

orange-weathering marble that varies from pure to impure on a scale of meters. Impurities 

include chlorite, quartz, tremolite, and albite; impure layers also include intraclasts, most 

3 cm or less in diameter. One of the pure marble layers yielded Ordovician conodonts (see 

below). Other impure marbles in the upper part of DOx also contain intraclasts. Total thickness of the mixed schist and marble sequence varies from 250 m to over 2 km. The structurally lower parts of the unit are dominated by gray marble or black metasiliceous rock. Where 

the gray marble is dominant, it reaches thicknesses of 1–2 km and contains minor thin (less 

than 50 m) layers of metaquartzite, pelitic schist, and chlorite-albite schist. Where the black 

metasiliceous rock is dominant, it reaches thicknesses of around 500 m and is underlain by 

10–30 m of gray marble interlayered with thin bands of pelitic schist.

 Metabasites are found in both the mixed schist and marble sequence and within the 

thick, unit-dominating gray marble and black metasiliceous rock. These mafic rocks are 

boudins or layers of glaucophane-, epidote-, and garnet-bearing metabasite, or chlorite-, 

albite-, actinolite-bearing metabasite similar to those found in the Casadepaga schist. Within 

DOx, they occur in greatest volume south of Salmon Lake near the boundary between the 

Nome and Solomon quadrangles.

 The gray-weathering pure marble is pale gray to white on the fresh surface, and composed of coarse crystalline calcite. The graphitic metasiliceous rock is generally homogeneous, dark-gray or black, and compositionally limited to quartz, graphite, and very small 

amounts of white mica, albite, and chlorite. Graphite may be present in sufficient quantities 

to rub off on the hands. Locally a centimeter-thick banding of dark gray-black quartz-graphite schist and gray-black quartz-graphite-calcite schist are found.

 In Nome quadrangle, DOx contains several small rubble patches of carbonate conglomerate, as well as rubble and outcrops of light gray dolostone, locally mottled with 

orange, pink, or light brown, that retain relict sedimentary features. Conglomerate is matrix 

supported and contains rounded to angular clasts, as much as 8 cm long, of pale-orange to 

medium-gray dolostone; at one locality, the unit contains subordinate clasts of marble and 

quartz-white mica schist. The matrix is beige to orange pink or light brown dolomite with 

lesser quartz and white mica. Relict textures, seen in conglomerate clasts and in mottled 

dolostone rubble, include coated grains, crinoid ossicles, and possible brachiopod fragments.

 In northwestern Solomon quadrangle, DOx contains an interval of dolostone-clast 

conglomerate as much as 100 to 200 m thick and 480 m in lateral extent. The conglomerate ranges from matrix-supported (1 to 10 percent clasts) to clast-supported (>80 percent 

clasts) and contains interlayers and (or) lenses of clast-free schist and dolostone. Clasts are 

rounded to irregular; most have a flattened, ovoidal shape but some are rod-like. Sorting is 
21

poor; clasts range from a few millimeters to 70 cm in maximum dimension. Some clasts are 

finely laminated. Most clasts consist of light-gray- to rusty-weathering, very light gray, finegrained ferric dolostone with minor amounts of quartz, white mica, and calcite. About 1 to 5 

percent of clasts are medium light gray marble. The conglomerate matrix is quartz schist that 

also contains white mica, dolomite, chlorite, epidote, and chloritoid. A less extensive (several meters thick by 10 m long) but otherwise similar lens of dolostone-clast conglomerate 

occurs in unit Ocs in the Nome quadrangle. The dolostone clasts at both localities resemble, 

and may have been derived from, dolostone equivalent to that in unit _d.

 The age range of DOx is not strictly known. Conodonts of Ordovician age were 

obtained from a pure layer in the impure marble at the structural top of DOx (in the Solomon quadrangle). Marble in the Nome quadrangle produced conodonts of early Paleozoic 

age (table A–1, T. Carr and T. Hudson, written commun., 1982, 1984). Recrystallized radiolarians collected in northern Darby Mountains in banded calcite-bearing graphitic metasiliceous rock are of probable pre-Devonian age (B.K. Holdsworth, written commun., 1985).

 In the Teller quadrangle, part of the unit (shown with the diagonal line overlay) is distinct in age and lithology. Dolostone, dolomitic marble, and marble form an elongate belt, 

extending for almost 40 km, in the westernmost part of DOx in eastern Teller quadrangle; 

only the southern half of the belt has been examined. The unit forms rubble-covered hills; 

outcrops are rare. Dolostone is medium gray to dark gray and weathers light to medium 

gray, very pale orange, or dark yellow brown. Sedimentary structures include millimeter- to 

centimeter-scale parallel lamination and lesser color mottling that likely reflects bioturbation. Intraclasts (maximum 1 cm in diameter) and millimeter-scale burrows occur locally. 

In thin section, dolostone is mostly finely crystalline and non-ferroan; some samples 

contain minor amounts of fine-grained quartz and white mica, or rare clasts (bioclasts?). 

Marble is white to grayish black and has few relict sedimentary features other than locally 

well-developed parallel lamination. Conodonts of late Silurian-Devonian age have been 

recovered from two localities; a third locality produced a fauna of Silurian (late Llandovery-Ludlow) age (table A–1). Sedimentary structures and conodont biofacies suggest a 

warm, shallow-water depositional setting. Faunal and lithofacies data indicate that these 

rocks may correlate, at least in part, with unit Sd in the Nome Complex. Correlation with 

units Ddm and SOdl and SOul (York terrane) is also possible, although these units contain 

more abundant megafossils than DOx with diagonal line overlay. Shallow-water Silurian 

rocks also occur widely in the Brooks Range. Units that contain such strata and could correlate, at least in part, with DOx (overlay) include units “DOb” (Baird Group), “DOc”, and 

“DSc” of Till and others (2008b); Silurian lithofacies in unit “DSc” are an especially good 

match. Unit DOx (with overlay pattern) is equivalent to parts of units “|m” and “p_n” of 

Sainsbury (1972).

 Three detrital zircon samples have been collected from DOx in southern Seward Peninsula. One yielded largely Neoproterozoic zircons, another yielded zircon populations as 

young as Silurian, and the third yielded a robust population of Middle and Early Devonian 

zircons (Amato, written commun., 2008). Apparently, at least part of DOx must be Devonian 

or younger.

 On the eastern edge of the map area, on the boundary of Norton Bay and Candle 

quadrangles, exposures of metasedimentary rocks include calcareous, pelitic, and quartz-rich 

lithologies. These rocks have not been studied in detail; some may ultimately prove to have 

histories separate from the Nome Complex. These rocks are equivalent to units “|<us” and 

“}|q” of Patton and others (2005).

 Unit DOx is between 0.8 to 1.5 km thick, and best exposed in eastern Solomon D–5 

quadrangle and in east-central Solomon D–6 quadrangle. The unit includes parts of units 

“p_s” and “slate of the York region” of Sainsbury (1974)

Dg Granitic orthogneiss (Devonian)—Fine-grained, very light gray to orange-weathering, wellfoliated, white to light tan schist of granitic to tonalitic composition that forms the rounded, 

frost-riven slopes of Kiwalik Mountain and one small body in northern Darby Mountains. 

Commonly forms weathered boulders 0.5–1 m across. Crops out rarely; where foliation 

can be measured, it is parallel to the foliation in the surrounding schist. Contact crosses 

lithologic layering in surrounding schist. Layers and boudins of the orthogneiss which have 

chilled margins are commonly found in country rock close to the contact. Quartz, albite, 

K-feldspar, and white mica are the most common constituents. Accessory minerals include 
22

biotite, epidote, fluorite, magnetite and calcite. The unit yielded a U-Pb zircon age of 391±3 

Ma (J. Aleinikoff, written commun., 2005; Till and others, 2006). A small body associated 

with unit DOx in the northern Darby Mountains yielded an age of 390±4 Ma (Toro, written 

commun., 2006); a foliated body with a similar age was found in the high-grade metamorphic rocks of Bendeleben Mountains (Gottlieb and Amato, 2008). Middle Devonian granitic 

orthogneiss (also approximately 390 Ma) is known in eastern Brooks Range in a metamorphic belt with a similar history to the Nome Complex (Aleinikoff and others, 1993; Moore 

and others, 1997). Granitic orthogneiss with similar, but less well-defined age, is present 

in central Brooks Range and southern Ruby geanticline (Toro and others, 2002; Patton and 

others, 1987; Roeske and others, 1995)

Df Felsic schist (Devonian)—Light-orange to light-green-weathering, fine- to coarse-grained 

quartz-feldspar white mica schist. Crops out on the southwest flank of Kiwalik Mountain 

as platey rubble-crop of millimeter-scale laminated, very fine grained schist. Rarely, accessory black tourmaline lies in plane of foliation. Stream gravels along strike to the northwest 

of the rubble crop include a rock which has the appearance of a flattened matrix-supported 

conglomerate or fragmental volcanic, composed of clasts and matrix of the major minerals 

listed above. Clasts show greatly varying grain size and internal textures. U-Pb zircon age 

from laminated schist on the flank of Kiwalik Mountain is 391±5 Ma (J. Aleinikoff, written commun., 2005; Till and others, 2006); the fact that the schist contains a single zircon 

population supports an igneous protolith for the unit. The contact between Df and other parts 

of the Nome Complex may be a fault. Two metafelsites of essentially identical age were 

identified in eastern Brooks Range, where metafelsites occur in sections of rocks less metamorphosed than the Nome Complex (Aleinikoff and others, 1993; Moore and others, 1997)

Ocs Casadepaga Schist (Ordovician)—Light-green, silvery green and greenish-brown mafic, feldspathic, and calcareous schist. Typically occurs as frost-riven slabs and flakes that underlie 

rounded hills and dark-greenish-black tors and rubble piles several meters across. Tors of 

metabasite, abundant plagioclase porphyroblasts in dark-green, chlorite-rich schist, and the 

quartz-poor nature of the rocks are characteristic of this unit. The most common lithologies are dominated by components of mafic, feldspathic, and calcareous composition that 

are intermixed and interlayered on a scale of tens of centimeters; the layering may occur in 

repetitive couplets.

 Medium- to pale-grayish-green-weathering pelitic schists are common. Plagioclase, 

chlorite, white mica, and quartz in subequal amounts dominate; epidote, carbonate, and 

glaucophane (or pseudomorphs of chlorite and plagioclase after glaucophane) are typical. 

Titanite (sphene), rutile, and sulfides are present in minor amounts. Based on major element chemistry, the protoliths were shales and graywackes (Werdon and others, 2005a). 

Carbonate-rich schists or layers are typically buff or pale brown weathering and tend to 

be more recessive in outcrop than other lithologies. Carbonate layers are rare and thin and 

include both pure and impure varieties; they weather pale brown, black, or gray. Dark-greenweathering schists are rich in chlorite, epidote, actinolite, and plagioclase, and represent 

metamorphosed mafic material. Dark-green-weathering chlorite-rich schists spotted with 

white equant plagioclase grains typically contain few to no calcium-bearing phases. These 

are probably mafic rocks that were altered or weathered previous to metamorphism.

Boudins, lenses and layers of fine- to coarse-grained, massive metabasite comprise the 

greenish-black tors. In thin section these rocks are found to be composed of glaucophane, 

actinolite, chlorite, epidote, garnet, albite, white mica, titanite, and locally quartz, Fecarbonate, pyroxene, and barroisite. Coarser grained varieties have textures suggestive of a 

coarse-grained gabbroic protolith. Mafic schist layers in the surrounding rocks have mineral 

assemblages similar to the metabasite pods. The metabasites comprise two compositional 

groups (Werdon and others, 2005a,c). One group has weakly developed arc-like signatures 

(for example, slight Nb depletion in spidergrams) reflecting crustal contamination; the 

second group exhibits features associated with enriched mantle (E-MORB) and alkaline 

intercontinental rifts (no Nb depletion, small positive Ti anomalies in spidergrams) (Ayuso 

and Till, 2007). Metabasites from unit DOx fall into the same two compositional groups. 

The chemical characteristics are thought to indicate a tectonic setting related to the early 

stages of continental, rift-related magmatism (Ayuso and Till, 2007).

 In western Solomon quadrangle, the contact between Ocs and the overlying impure 

marble unit (Oim) is exposed. Near the contact, on all sides of a synform cored by Oim, a 
23

thin (few meters – tens of meters) layer of black weathering, platey, fine grained and finely 

laminated quartz-graphite schist is present. The amount of graphite in the rock is variable, 

though it is always black-weathering; thin laminae of lenses (mm- to cm-scale) that are more 

quartz-rich are common. Graphite is present as fine disseminated material in the quartz-rich 

matrix, as well as in lozenges several millimeters across. White mica is disseminated and 

minor. Semi-quantitative spectrographic analyses of a few samples from this layer show 

elevated values of Mo, V, Ag, and Zn (B. Gamble, written commun., 1985). Thin layers of 

mafic schist separate the graphitic layer from the overlying impure marble.

 No direct evidence exists for the depositional age of Ocs. Seven detrital zircon samples 

collected from widely distributed parts of the unit contain very similar grain populations. 

Most grains fall into the range of 600–700 Ma; several samples contain small populations 

of Ordovician or Cambrian grains (Amato and others, 2003a; Till and others, 2006; 2008a). 

Depositional age of the unit must be younger than 600 Ma (latter part of the Neoproterozoic), and is likely Ordovician or younger. Werdon and others (2005a) considered the unit to 

be Cambrian in age, based on an Rb-Sr isochron. The samples included in the isochron are 

a mix of mafic and pelitic rocks, so their assumption that the samples shared the same initial 

strontium isotopic composition is likely not correct; the isochron represents a mixing line 

between mafic and sedimentary protoliths.

 Unit Ocs is assigned an Ordovician age based on detrital zircon geochronology and 

on the occurrence in both this and the impure marble unit (Oim) of both metabasite schist 

layers and unfoliated metabasite pods. The protoliths of both units apparently contained 

pyroclastic or redeposited mafic material as well as intrusive mafic rocks. Metabasite layers 

indicate that production of mafic material was at latest syn-depositional – not simply postdepositional. We postulate that units Oim and Ocs were formed in the same basin. Because 

the impure marble unit yielded Early through Middle Ordovician conodonts, we believe that 

basin was formed during the Ordovician.

 The unit is 0.6 to 1.6 km thick and is best exposed in southeastern Solomon D–5 quadrangle, north of the Nome-Council road; in central Solomon D–5 quadrangle; and in eastcentral Solomon D–6 quadrangle. The Casadepaga schist was named and first described by 

Smith (1910). Partially equivalent to the “slate of the York region” of Sainsbury (1974), and 

unit “p_qms” of Miller and others (1972); equivalent to unit “Ocs” of Till and others (1986)

Oim Impure chlorite marble (Ordovician)—Buff- to orange-weathering, chlorite-, white mica-, and 

albite-bearing calcite marble that underlies rounded hills. Rare outcrops show well-foliated 

impure marble to calcareous schist. Impurities are most commonly chlorite and albite. 

Lenses (up to a meter across) and fine layers of chlorite and albite are diagnostic of the unit, 

and trace foliation and folds. Chlorite-albite lenses and layers are more abundant near the 

base of the unit; pods of fine-grained metabasite are also more common in the lower part of 

the unit. The pods can be recognized in the field as piles of massive, medium-gray rubble 

several meters across; one is 0.5 km across. Intraclasts occur in some exposures and are 

typically composed of black calcite and no more than 4 cm in diameter. Most commonly 

they are a minor component of the rock, but locally are concentrated in centimeters-thick 

layers. In rare instances the unit may include layers of pure marble or orange-weathering 

dark-gray dolostone. The unit is a minimum of 1.2 km thick. Conodonts of Early through 

Middle Ordovician age have been obtained from a dolostone lens in the upper part of the 

unit in Solomon D–6 quadrangle (84ATi281, table A–1). Excellent exposures of the unit 

can be found in central Solomon D–6 quadrangle. Equivalent to units “p_sm” of Miller and 

others (1972); “p_l” of Sainsbury (1974); and “Oim” and “|im” of Till and others (1986). 

In western Solomon quadrangle, the contact of Oim with underlying unit Ocs is marked by 

a lens of graphitic siliceous rock a few meters thick. Outcrops are black. Quartz and graphite 

vary in relative concentration, and yield a finely laminated appearance. Fine white mica and 

sulfide minerals are present in minor amounts. Semi-quantitative spectrographic analysis of 

these rocks shows they contain elevated amounts of Mo, Ag, Zn, and V

<n Metagranitic rocks (Late Proterozoic)—Pale-gray to pale-greenish-tan, locally green-weathering rubble crop and outcrop of small granitic, granodioritic, and tonalitic orthogneiss 

bodies. Weakly foliated to well-foliated, fine- to coarse-grained, with foliation defined by 

weak to strong alignment of micas. Coarsest grained varieties may contain lozenge-shaped 

feldspar grains and thin, millimeter-thick lenses of quartz that also parallel foliation. Plagioclase, quartz, ± microcline are dominant phases; chlorite, biotite, and white mica are minor 
24

phases, and are associated with epidote, garnet, and calcite at some localities. Accessory 

phases include opaque oxides, zircon, apatite, allanite, and titanite. Phengitic white mica 

compositions in microcline-bearing orthogneiss bodies are consistent with crystallization 

at blueschist-facies conditions (Evans and Patrick, 1987). In outcrop, foliation parallels 

surrounding schists of the Nome Complex; the metagranitic rocks were apparently folded 

in with metasedimentary rocks of the Nome Complex during the Mesozoic. Detrital zircons 

from metasedimentary rocks of unit Ocs collected immediately adjacent to a body of <n in 

east-central Nome quadrangle include a significant 600-Ma population, younger than the 

metagranitic rock (669±5 Ma, table 3; locality 3, sh. 2) (Till and others, 2006). Late Proterozoic intrusive age based on several U-Pb zircon analyses that range from approximately 

665 to 685 Ma (including errors) (table 3; Patrick and McClelland, 1995; Amato and Wright, 

1998; Till and others, 2006). Equivalent to parts of unit “pCPzg” of Bundtzen and others 

(1994) and unit “pCdog” and parts of unit “pCPzuog” of Amato and Miller (2004)

SCATTERED METACARBONATE ROCKS

|m Marble, undivided (Paleozoic)—Generally light-gray-weathering, white to medium-gray, 

medium to coarsely crystalline marble that forms rubble-covered hills and small outcrops 

that are widely but sparsely distributed through the map area. Marble is dominantly pure, but 

locally contains as much as 10 percent quartz, white mica, and (or) albite. At several localities in the western Bendeleben and Solomon quadrangles, |m contains conodonts, stromatoporoids and (or) colonial and rugose corals of Ordovician through Devonian or Silurian 

to Devonian age; combined age constraints from megafossils and microfossils at one locality 

suggest an age of Middle Devonian (table A–1; Till and others, 1986). Unit |m likely 

includes rocks of several different ages. It correlates at least in part with Ddm but lacks the 

lithologic features diagnostic of that unit; some parts of |m may be as old as Ordovician 

(table A–1). Occurrences that have yielded no fossils are assumed to be Paleozoic based 

on physical proximity to strata of known Paleozoic age. The relation of |m to rocks of the 

Nome Complex is uncertain; it is most commonly spatially associated with unit Ds. Equivalent to unit “|m” of Till and others (1986)

|d Dolostone, undivided (Paleozoic)—Generally light-colored, fine-grained, featureless dolostone 

that forms rubble-covered hills sparsely distributed through the map area. This unit likely 

includes rocks of several ages. Conodont faunas, obtained at seven localities, are mostly long 

ranging but one collection, in eastern Bendeleben quadrangle, may be Early Mississippian; 

another, in northwestern Solomon quadrangle, is middle Silurian-Early Devonian; and a 

third, in western Candle quadrangle, could be Ordovician (table A–1; Till and others, 1986). 

Occurrences that lack fossils are assumed to be Paleozoic based on physical proximity to 

strata of known Paleozoic age. Some rocks mapped as |d at Cape Deceit in the Kotzebue 

quadrangle may be part of unit DObm (T. Ryherd, written commun., 1985; Ryherd and Paris, 

1985). Unit |d may also include strata correlative with units _d, Od, Sd, and (or) Ddm that 

lack lithologic or faunal features diagnostic of these units. The relation of |d to rocks of the 

Nome Complex is uncertain. Equivalent to unit “|d” of Till and others (1986), and, in Candle 

and Norton Bay quadrangles, to part of “|cs” of Patton and others (2005)

|mm Marble of the Moon Mountains (Paleozoic)—Pale-gray- to white-weathering, coarsely crystalline calcite marble exposed only in western Nome quadrangle, in an area informally called 

the Moon Mountains (sh. 2) due to lack of vegetation. The marble has a layered appearance 

due to variations in grain size; layering is folded. Folds are cut by biotite-hornblende granitic 

dikes and lesser tourmaline-bearing pegmatites (see unit Kds for ages); gossan is spatially 

associated with the dikes. Overall large grain size of calcite in the marble is larger than typically found in unit |m

Ddm Dolostone, metalimestone, and marble (Devonian)—Medium- to dark-gray-weathering, 

dark-gray to black dolostone, metalimestone and marble, with minor associated chert, that 

typically weathers to fist-sized rubble but forms outcrops along river banks or sea cliffs. Unit 

Ddm is widely but sparsely distributed through the map area; it crops out in the northwestern and eastern Bendeleben quadrangle and the central and eastern Solomon quadrangle; it is 

best exposed in sea cliffs in the Solomon C–1 quadrangle. Outcrops are not foliated, but are 

strongly fractured, commonly brecciated, and may be veined with coarse-crystalline calcite 

or dolomite. Unit Ddm consists of fine-grained, mostly non-ferroan or slightly ferroan dolomite and subordinate fine- to coarse-crystalline calcite. Dolostone is the dominant lithology 
25

in eastern exposures; metalimestone and marble predominate in western and central exposures. Relict sedimentary structures include zebra dolomite, fenestral fabric, and millimeterscale (algal?) laminations. Thin section textures, where not obscured by recrystallization 

and dolomitization, are bioclastic and peloidal packstones and wackestones. Early to earliest 

Late Devonian conodonts have been found in 20 collections; tightest ages are earliest 

Emsian and latest Emsian-earliest Eifelian (table A–1). A megafauna of late Early, Middle, 

and early Late Devonian age consists of tabular and rugose corals, stromatoporoids, brachiopods, and rare bryozoans. Megafauna, microfauna, and sedimentary features all denote 

a warm, relatively shallow water depositional setting. Age and spatial relations suggest that 

Ddm may have been unconformably deposited on older parts of the Nome Complex, specifically units DOx and D_bm. Lithofacies and faunal data indicate that Ddm correlates well 

with the youngest strata in the Baird Group (Tailleur and others, 1967; Dumoulin and Harris, 

1994) and related rocks in western and central Brooks Range (units “DOb” and “DOc” of 

Till and others, 2008b) and may also correlate with the Beaucoup Formation (Dutro and 

others, 1979) and related rocks found throughout the Brooks Range (units “Dl” and “Dmu” 

of Till and others, 2008b). Equivalent to unit “Ddm” of Till and others (1986) and partly 

equivalent to unit “Ddl” of Miller and others (1972)

Sd Dolostone (Silurian)—Light-gray- to tan-weathering, light- to dark-gray, fine-grained, ferroan dolostone that forms two small rubble-covered hills, one in southeastern Bendeleben 

quadrangle and the other in southeastern Solomon quadrangle. At the northern locality, 

the main lithology occurs with lesser amounts of black dolostone and black marble. Color 

mottling, likely due to bioturbation, is notable at the southern occurrence. Other features of 

unit include possible fenestral fabric and relict bioclasts. Gray dolostone at both localities 

yielded conodont faunas of middle-late Silurian age (table A–1). Sedimentary structures 

and conodont biofacies indicate a shallow, warm-water depositional environment. Several 

other lithologically similar dolostones in southeastern Bendeleben and northeastern Solomon 

quadrangles contain Silurian-Early Devonian conodonts; these occurrences are presently 

mapped as unit |d but may, at least in part, belong to Sd. Shallow-water Silurian strata that 

correlate, at least in part, with Sd include units DOx (overlay) in the Nome Complex, SOdl

and SOul in the York terrane, and the Baird Group (Tailleur and others, 1967; Dumoulin and 

Harris, 1994) and related units in the western and central Brooks Range (units “DOb” and 

“DOc” of Till and others, 2008b). Equivalent to unit “Sd” (northern locality) and part of unit 

“|d” (southern locality) of Till and others (1986)

Od Dolostone (Ordovician)—Light-gray- to pink- to tan-weathering, gray to tan dolostone that 

forms small areas of rubble crop in tundra and local cliffs along river banks. Unit is best 

exposed along several rivers in northeastern Bendeleben quadrangle, but also crops out at 

isolated localities in northwestern and southeastern Bendeleben quadrangle and northwestern Solomon quadrangle. Depositional relations between Od and other units are nowhere 

preserved, but map patterns suggest possible associations with units Oim and Ddm. Unit Od

consists of fine-grained, mostly non-ferroan dolomite. Relict sedimentary features include: 

distinct color-mottling, reflecting an original partly bioturbated fabric; zebra dolomite, suggestive of evaporitic supratidal conditions; fenestral fabric, which generally occurs in tidal 

flat or shallow subtidal environments; and probable oncolites, which also indicate a shallowwater depositional environment. Conodont faunas represent at least three distinct ages: two 

discrete intervals in the Early Ordovician, and early to middle Middle Ordovician (table 

A–1). Most of the assemblages represent shallow to very shallow, warm-water biofacies, but 

one collection of middle to late Early Ordovician age from the Bendeleben D–2 quadrangle 

denotes a cooler and (or) deeper water setting (table A–1). A single collection of poorly 

preserved corals has also been obtained (Till and others, 1986). Most conodonts in Od are 

cosmopolitan forms, but Siberian and Laurentian (North American) endemics occur in a few 

collections (Dumoulin and others, 2002). The older (Early Ordovician) part of Od correlates 

with much of units Oal, Ol, and O<l in the York terrane; Middle Ordovician strata in Od are 

coeval with, but represent shallower water facies than, unit Ols in the York terrane. Od also 

correlates well in age and lithology with Early and Middle Ordovician rocks of the Baird 

Group (Tailleur and others, 1967; Dumoulin and Harris, 1994) in the western Brooks Range 

(unit “DOb” of Till and others, 2008b). Od strata that contain cooler and (or) deeper water 

biofacies resemble coeval deeper water rocks in unit “O<c” (Till and others, 2008b) in the 

Baird Mountains quadrangle. Equivalent to unit “Od” of Till and others (1986)
26

_d Dolostone (Cambrian)—Gray- to orange-weathering, light-gray or medium-gray to pinkishorange dolostone that forms hilltop rubble patches and subcrop on several small knobs in the 

northwestern Solomon quadrangle. The dolostone is non-ferroan to moderately ferroan and 

locally contains a few percent quartz and white mica. Structurally underlying the dolostone 

is a section of schist and marble several tens of meters thick. The upper third consists of 

quartz-white mica schist and chloritic marble; the lower two thirds is mostly marble containing about 10 percent quartz, white mica, and chlorite. The orange-weathering dolostone 

contains lapworthellids (table A–1), a phosphatic microfossil indicative of Early (to possible 

early Middle) Cambrian age and a shallow-water depositional environment. Unit _d correlates precisely with the oldest part of unit D_bm, which also contains lapworthellids, and 

may correlate with part of unit “O<c” (Till and others, 2008b) in the western Brooks Range. 

Equivalent to unit “_d” of Till and others (1986)

METATURBIDITES

D_bm Black marble (Devonian to Cambrian)—Dark-gray to black marble and subordinate fissile impure marble, calcareous schist, and mafic schist that crops out in eastern Solomon 

and western Norton Bay quadrangles. Unit is best exposed in sea cliffs along Norton Bay 

and forms rubble covered hills inland. Marble layers are 1 to 20 cm thick, with rhythmic 

alternations of purer, coarse-crystalline and more impure, fine-crystalline layers. Common 

green-weathering mafic dikes, sills, and plugs, 0.5 to 2 m across, intrude the carbonate 

strata; preserved contact metamorphic effects include bleached carbonate rocks and albite-, 

chlorite-, epidote- and tourmaline-bearing skarn assemblages. Mafic rocks consist of finegrained chlorite, actinolite, albite, and white mica; glaucophane inclusions are found in 

the albite. Commonly, mafic minerals form layers and are disseminated in the fine crystalline carbonate rock, suggesting that some mafic volcanism accompanied deposition of the 

carbonate strata. All of the mafic volcanic rocks were affected by regional metamorphism, 

as were the carbonate rocks. Marble protoliths were likely carbonate turbidites and periplatform ooze.

 Seven conodont faunas were obtained from six localities in D_bm (table A–1). Two 

faunas are middle to early late Silurian (Wenlock-Ludlow), one is middle Early Devonian 

(Siegenian), and one is late Silurian to Early Devonian. Two faunas from westernmost exposures of D_bm are considerably older: one middle Early through Late Ordovician and the 

other Early Cambrian. Thus, there is a gap of over 100 million years between the oldest and 

youngest faunas. At least three explanations can be invoked for this faunal distribution. If all 

conodont collections represent depositional ages, then the unit may represent two episodes 

of deposition of lithologically similar material—one Early Cambrian, one Late OrdovicianEarly Devonian, separated by a long interval of non-deposition. Or, deposition may have 

extended more or less continuously from Cambrian into Devonian time—present fossil collections from D_bm are few and future collections may eliminate the apparent hiatus. Alternately, some or all of the conodont collections could be reworked, and the depositional age 

of the entire unit could be late Silurian-Early Devonian or younger. In this case, the western 

faunas would represent material eroded from an older (Cambrian and Ordovician) carbonate 

platform source; the eastern faunas could represent erosion from a younger source or faunas 

contemporaneous with deposition.

 Unit D_bm may be a more deformed equivalent of unit DObm, and it is intercalated 

with, and possibly a facies equivalent of, unit D_ks. It is lithologically similar to, and 

may be partly coeval with, Silurian carbonate and siliciclastic turbidites in the west-central 

Brooks Range (unit “Spl” of Till and others, 2008b). The easternmost exposures of D_bm

include some outcrops of unit Ddm that are too small to be mapped separately. Equivalent 

to unit “D_bm” of Till and others (1986), and partly equivalent to unit “Dld” of Miller and 

others (1972) and units “|cs”, “|<us”, and “|<ss” of Patton and others (2005) 

D_ks Calcareous schist of Kwiniuk Mountain (Devonian to Cambrian)—Dark-brownish-gray, rustspotted, well-foliated, medium-grained schist composed predominantly of quartz, calcite, 

white mica, chlorite, plagioclase, and graphite. Locally shows millimeter-scale dark/light 

layering. Rusted spots (weathered iron carbonate?) up to 0.5 cm across are locally abundant. 

Fresh surfaces are gray. Interlayered on a meter to kilometer scale with units DObm and 

D_bm; age assigned to this unit based on that intimate relation. On Kotzebue Sound, unit is 

exposed in beach cliffs at Sullivan Bluffs (15 km west of Cape Deceit), where it shows relict 
27

crossbedding and graded bedding, and contains abundant pyrite. Equivalent to unit “D_ks” 

of Till and others (1986)

DObm Black metalimestone and marble (Devonian to Ordovician)—Dark-gray to black metalimestone and marble and subordinate dolostone exposed on sea cliffs on Kotzebue Sound. 

Rocks weather gray to yellowish-brown, commonly have fissile partings, and are well 

layered. Layers range from 2 to 50 cm thick, with rhythmic alternation of thicker, coarsecrystalline and thinner, fine-crystalline layers. Relict sedimentary structures include graded 

bedding, flame structures, loaded bed bottoms, channelized beds, and imbricated rip-up 

clasts. Three kilometers west of Cape Deceit, a 15- to 20-m-thick interval of dominantly 

matrix-supported carbonate breccia, with rounded and angular clasts as much as 5 m in 

diameter, occurs in the section, as well as thinner (≤1 m thick) intervals of carbonate-clast 

breccia. Local solution collapse features occur, and dedolomitization textures were seen in 

thin sections. Subordinate argillite, phyllite, and radiolarian chert are found about 2.4 km 

west of Cape Deceit; quartz-graphite schist and impure marble (containing as much as 20% 

graphite, quartz, albite, and white mica) are abundant in the western exposures.

 Unit DObm has yielded tightly dated fossil collections of Middle Ordovician through 

late Silurian age and some longer ranging collections that could be as young as Devonian 

(table A–1; Ryherd and Paris, 1987). The argillite-dominated interval west of Cape Deceit 

contains abundant Middle and Late Ordovician graptolite assemblages as well as Ordovician 

conodonts (Ryherd and Paris, 1987; Harris and others, 1995; Ryherd and others, 1995; 

Dumoulin and others, 2002). Higher in the unit, a continuous section of allodapic carbonate 

rocks, at least several hundred meters thick, produced a middle to late Silurian (Wenlock to 

Ludlow) conodont succession (table A–1; Dumoulin and others, 2002). Several conodont 

collections from eastern exposures of the unit could be as young as Devonian (table 

A–1). Well-layered metalimestone containing redeposited(?) rugose and colonial corals of 

Middle to Late Devonian age have been described from Willow Bay, 20 km east of Cape 

Deceit (Kotzebue A–1 quadrangle); these rocks may be part of DObm (T. Ryherd, written 

commun., 1985).

 Two small gabbroic plugs intrude DObm west of Cape Deceit. The plugs show relict 

ophitic textures and are partially recrystallized to a low-grade metamorphic assemblage of 

actinolite, epidote, and garnet. CAI values of conodont assemblages in this unit range from 

5.5–7 (table A–1) and may reflect the presence of hydrothermal fluids.

 Unit DObm represents periplatform ooze, turbidites, and debris flow deposits derived 

from a carbonate platform that accumulated in slope and basinal environments (Dumoulin 

and Till, 1985; Ryherd and Paris, 1985, 1987; Harris and others, 1995; Dumoulin and others, 

2002). It correlates, at least in part, with unit D_bm and is intercalated with, and possibly a 

facies equivalent of, unit D_ks. DObm is lithologically similar to, and at least partly coeval 

with, Silurian carbonate and siliciclastic turbidites in the west-central Brooks Range (unit 

“Spl” of Till and others, 2008b). It also correlates in part with Middle Ordovician-lower 

Silurian graptolitic argillite and quartz-rich turbidites of the Iviagik Group of Martin (1970) 

that are exposed south of Cape Lisburne (Grantz and others, 1983; Moore and others, 1994, 

2002; Harris and others, 1995). Equivalent to unit “DObm” of Till and others (1986), and 

partly equivalent to units “Ml?”, “p_l”, and “|m” of Hudson (1977) and the Deceit Formation of Ryherd and Paris (1987)

HIGH-GRADE METAMORPHIC AND ASSOCIATED IGNEOUS ROCKS

|<h High-grade metasedimentary and metaigneous rocks (Paleozoic and Proterozoic)—Brown, 

light-brown, reddish-brown, black, and gray-weathering schist and gneiss exposed in the 

Kigluaik, Bendeleben, and Darby Mountains. Highest grade metamorphic assemblages are 

upper amphibolite to granulite grade; assemblages in all three ranges record multiple metamorphic events. Metamorphic foliations range from gneissic to schistose; locally, foliation 

is lacking and crystallization of metamorphic minerals appears to be static (Till and others, 

1986; Lieberman, 1988; Calvert and others, 1999). Lithologically variable on a scale of centimeters and meters, the unit includes pelitic, semi-pelitic, quartzose, calcareous, aluminous, 

mafic, ultramafic, and graphitic schist and gneiss. Dominant lithologies vary within each 

mountain range. Till and others (1986) recognized sequences of rocks lithologically similar to 

those mapped within the Nome Complex in western Bendeleben and northern Darby Moun-
28

tains. Thurston (1985), Patrick and Lieberman (1988), Hannula and others (1995) and Calvert 

and others (1999) showed that the high-grade metamorphic event in the Kigluaik Mountains 

overprinted blueschist-facies assemblages in the Nome Complex. At least part of |<h, perhaps a significant part, was originally blueschist-facies rocks of the Nome Complex.

Metamorphic foliations and lithologic layering in the Kigluaik Mountains define a 

dome, with highest-grade rocks in its core. The earliest-formed metamorphic assemblages 

known in the range are found at the base of the section, below Mount Osborn. There, garnets 

in pelitic rocks locally contain kyanite inclusions (Lieberman, 1988); garnet lherzolite 

occurs as large, meter-scale xenoliths in pegmatite and is present in abundance in glacial 

moraine (Till, 1980, 1981; Lieberman and Till, 1987). Garnet lherzolite is stable at eclogite 

facies (Evans, 1977; Spear, 1993). The dominant metamorphic fabric in the Kigluaiks postdates this high-pressure event and contains peak granulite-facies assemblages. Garnets in 

lherzolite are partially overprinted by spinel-bearing assemblages stable at granulite facies. 

Two-pyroxene semipelitic and mafic gneiss, diagnostic of the facies, are also found in the 

core of the range (Till and Dumoulin, 1994). Most of the rocks in the range crystallized at 

temperatures above the second sillimanite isograd (above the temperature stability of muscovite; sh. 2; Amato and Miller, 2004). Metamorphic grade decreases towards the flanks of 

the dome, where biotite-grade metamorphic assemblages overprint low-grade metamorphic 

assemblages of the Nome Complex (Thurston, 1985; Hannula and others, 1995; Amato and 

Miller, 2004). Metamorphic isograds along the flanks of the dome are closely spaced (Till, 

1980; Patrick and Lieberman, 1988; Miller and others, 1992; Amato and Miller, 2004).

Metamorphic foliations in the Bendeleben Mountains define a dome that spans the area 

between the large, ovoid pluton in the eastern part of the range and the smaller, irregularly 

shaped pluton in the west part of the range; the dome coincides with sillimanite-bearing peak 

thermal assemblages (Gottlieb and Amato, 2008). West of the dome, southwest of Mount 

Bendeleben, kyanite-bearing assemblages predate sillimanite-bearing assemblages in pelitic 

rocks (sh. 2; Till and Dumoulin, 1994; Till, unpub. data). Kyanite-bearing assemblages are 

apparently the oldest in the range.

 Metamorphic rocks in the Darby Mountains lack any domal structure; instead, mapscale folds of lithologic sequences with near-vertical axial planes are present where rocks 

exhibit higher-grade assemblages (Till and others, 1986). In the northern Darby Mountains, 

units of the low-grade Nome Complex are shallowly-dipping and partially overprinted by 

biotite-grade metamorphic assemblages (Till and others, 1986). Southward along the crest 

of the range, kyanite- and staurolite-bearing assemblages occur. Kyanite is texturally older 

and may be relict of an earlier metamorphic event. Farther south, the appearance of sillimanite and locally sillimanite plus K-feldspar in pelitic schists indicates an increase in 

metamorphic grade. Metamorphic grade culminates near Mount Arathlatuluk. There, rare 

two pyroxene schists are diagnostic of granulite facies, and small granitic bodies appear to 

be anatectic melts (sh. 2). The anatectic granites were formed around 108 Ma (R. Friedman, 

written commun., 2009). A fault-bounded block of high-grade rocks on the western flank of 

the Darby range contains similar high-grade metamorphic assemblages (formed above the 

second-sillimanite isograd) (sh. 2).

 In all three mountain ranges, decompression post-dated the thermal peak, and is recorded 

in aluminum- and iron-rich metasedimentary rocks. In these volumetrically minor but significant rocks, assemblages containing sillimanite or kyanite (± hercynite spinel) and orthoamphibole were overprinted by assemblages containing cordierite and staurolite or garnet 

(sh. 2). Corona or symplectite textures are common in these rocks. The aluminosilicate plus 

orthoamphibole assemblage is stable at moderate to high pressures, above about 5 kb, and 

the cordierite-bearing assemblage is stable at low pressures, below about 5 kb (Spear, 1993). 

While decompression assemblages apparently formed at about 82 Ma in the Bendeleben 

range (Gottlieb and Amato, 2008), similar assemblages in the Darby range are probably older: 

the 100-Ma Darby pluton cross-cuts the metamorphic gradient in the Darby range; andalusite 

formed in its contact aureole (sh. 2). Andalusite forms at pressures lower than 4 kb.

 These high-grade metamorphic rocks are equivalent to generalized units “|p_h”, 

“|p_g”, “|p_g” and units representing upgraded Nome Complex “Oimh”, “Ocsh”, 

“O_xh” and “_p_sh” of Till and others (1986)

|<m Marble (Paleozoic to Proterozoic?)—Light-gray-weathering, coarse-grained pure and impure 

marble interlayered with unit |<h. Commonly massive, though locally meter-thick layers 
29

are separated by thin (centimeter-scale) layers of fine-grained impurities. Thin sections show 

equilibrium metamorphic textures involving calcite, dolomite, phlogopite, tremolite, quartz, 

scapolite, diopside, and graphite. Equivalent to unit “|p_m” of Till and others (1986)

|<g Gneiss and orthogneiss (Paleozoic? and Proterozoic?)—Light-brownish-gray, light-orange to 

gray biotite-plagioclase-quartz gneiss and granitic orthogneiss and minor metasedimentary 

rocks exposed in rubble crop north of the Oonatut Granite Complex, northwest Bendeleben 

quadrangle (Hudson, 1979). Fabric in the gneiss is defined by discontinuous layers and 

lenses of plagioclase and quartz and discontinuous concentrations of biotite. Orthogneiss 

is fine grained, homogeneous in texture, with foliation defined by aligned and segregated 

muscovite and minor biotite. Calcite marble layers, less than 10 cm thick, are folded in 

with the orthogneiss at one locality. Minor hornblende-plagioclase-titanite amphibolite and 

pelitic metasedimentary rocks are found in southern part of the unit, and close to the Oonatut 

Granite Complex the metasedimentary rocks contain porphyroblasts of andalusite (Till, 

unpub. data). Contacts with the Nome Complex are thought to be structural (Hudson, 1979). 

Equivalent to units “p_gn” and “p_gog” of Hudson (1979)

<o Orthogneiss (Proterozoic)—Pale-gray-, tan- and orangish-tan-weathering outcrops and rubble 

fields of foliated and unfoliated metagranitic rocks that form a large, tabular, concordant 

body within high-grade rocks of the Kigluaik Mountains. Called the “Thompson Creek 

orthogneiss” after exposures in Nome D–1 quadrangle (Till, 1980; Amato and Miller, 2004), 

the rock is syenogranite to monzogranite in composition (Streckeisen, 1976). Potassiumfeldspar, plagioclase, and biotite are locally aligned in foliation; quartz and biotite lenses or 

layers up to a centimeter thick also parallel foliation. Allanite is locally 1 to 2 percent of the 

rock and is zoned with brown cores and orange rims; accessory zircon is also present. Quartz 

amphibolite layers that are parallel to metamorphic foliation in the orthogneiss are 1–2 m 

thick. Amato and Miller (2004) show the Thompson Creek orthogneiss on both the north 

and south flank of the antiform in the core of the Kigluaik Mountains (their unit “pCtog”). 

Orthogneiss yielded U-Pb zircon ages of 555±15 Ma (Amato and Wright, 1998) and 565±6 

Ma (Amato, 2004)

<v Metavolcanic rocks (Proterozoic)—Foliated lens- to sill-shaped bodies in western Bendeleben 

Mountains exposed in outcrop and rubble fields. Unit is up to 50 m thick. Very fine grain 

size and variation in abundance and relative proportion of biotite and hornblende suggest a 

volcanic protolith (Amato and others, 2009). Foliation is defined by the parallel alignment of 

biotite and feldspar. Grain size varies from layer to layer locally. Contacts and internal foliation are conformable to the foliation of the enclosing metamorphic rocks where exposed. 

These are the oldest dated rocks on Seward Peninsula, having yielded a U-Pb zircon age of 

870 Ma (Gottlieb and Amato, 2007, 2008; Amato and others, 2009)

KUGRUK FAULT ZONE

TKs Carbonate-rich conglomerate and sandstone; mudstone, siltstone and coal (Tertiary and 

Cretaceous)—Two separate sedimentary sequences, of broadly different age: tan to lightgray siltstone, sandstone, and pebbly sandstone, and light-gray-weathering conglomerate 

composed mostly of marble, metalimestone, and dolostone clasts, probably of mid-Cretaceous age; and a separate sequence of gray and brown siltstone, mudstone, sandstone, coal, 

and minor conglomerate of Late Cretaceous and Tertiary age. Both sequences are exposed 

in narrow slices along the Kugruk Fault Zone. Mid-Cretaceous carbonate-rich sandstone and 

siltstone are found in southeastern and east-central parts of the Bendeleben quadrangle; conglomerate is found in these areas as well but also forms scattered outcrops in southeastern 

Solomon and southwestern Norton Bay quadrangles, where it is the dominant lithology. The 

younger sequence is poorly exposed in northeastern and southeastern Bendeleben quadrangle; it has been explored for coal and uranium (Retherford and others, 1986; Dickinson and 

others, 1987).

 The older sequence, carbonate-rich sedimentary rocks, is better exposed. Carbonaterich sandstone and siltstone typically occur as rubble-covered hills but are best exposed 

in river-cliff outcrops in Bendeleben C–2 quadrangle. Rocks are friable to well indurated, 

calcite cemented, and form beds 5 to 60 cm thick; sedimentary structures include graded 

bedding, channels, small scale ripples, and crossbeds. Some fine-grained layers are rich 

in carbonaceous plant debris and coal seams are locally well developed. Most samples 

consist of poorly to moderately well sorted, angular to rounded grains. Clasts appear to 
30

have been derived primarily from adjacent metamorphic rocks; clast lithologies include 

marble, dolostone, plagioclase, monocrystalline and polycrystalline quartz, volcanic rocks 

(with felsitic and lathwork textures), blueschist-facies metabasite, radiolarian chert, phyllite, 

quartz-mica schist, and amphibolite. Carbonate clasts predominate at most localities.

 Conglomerate, associated with minor sandstone and pebbly sandstone, forms rounded 

knobs up to 25 m high and more extensive areas of rubble crop. Bedding is rarely evident, 

but sandy interbeds and crude grading are locally present. Rocks are very poorly sorted and 

have a matrix of calcite cement and carbonate sand. Cobbles are sub-rounded to rounded; 

maximum clast diameter at outcrops studied ranges from 52 to 72 cm. Pebble counts indicate that carbonate clast content varies from a low of 81 percent in Bendeleben C–2 quadrangle to a high of 98 percent in Bendeleben A–1 quadrangle. Marble and metalimestone 

versus dolostone ratios range from 1:2 in Bendeleben A–1 quadrangle to 3:1 in Bendeleben 

C–2 quadrangle. Non-carbonate clasts include chert, monocrystalline and polycrystalline 

quartz, quartz-mica schist, chlorite schist, and various greenstone lithologies that were likely 

derived from the adjacent unit }|m.

Two small outcrops of mafic clast conglomerate underlie carbonate conglomerate in 

Bendeleben C–2 quadrangle. Sorting in these rocks is poor; clasts are rounded to angular 

and as much as 30 cm in diameter. Clasts are mainly metavolcanic rocks, some of which 

contain blue amphibole; subordinate clast lithologies include radiolarian chert, marble, 

quartz, and quartz-mica schist.

 The calcareous sediments are locally intruded by sills (too small to show on this map) of 

probable Tertiary or Cretaceous age; the sediments are unmetamorphosed but deformed and 

vertical beds occur locally. No fossils constrain the depositional age of the conglomerates, 

but ages of some clasts have been determined. Carbonate clasts from six localities yielded 

21 conodont collections, 19 of which have CAI values of 5–6 (table A–1). Relatively wellconstrained clast ages are mainly Silurian and Devonian; the tightest ages are Middle to Late 

Ordovician, early to middle Silurian, middle to late Silurian (Wenlock-Ludlow), late Early 

Devonian (late Emsian), and Middle Devonian. Conodont biofacies of several of the Silurian 

clasts indicate a high-energy, shallow-water depositional setting (Till and others, 1986). The 

lithofacies, thermal level, age, and biofacies of the carbonate clasts correlate well with those 

of units Od, Sd, and Ddm; thus, carbonate cobbles in TKs most likely were derived largely 

from these units. Carbonate clasts of Silurian age and shallow-water biofacies appear to be 

volumetrically over-represented relative to the present areal distribution of such rocks. The 

carbonate-rich clastic rocks of TKs may have been deposited in a series of small alluvial fans.

 The mid-Cretaceous carbonate-rich sedimentary sequences exposed east of Seward 

Peninsula in the Yukon-Koyukuk basin (Nilsen, 1989; Patton and others, 2005) are thought 

to be correlative with the carbonate-rich sedimentary rocks of unit TKs.

 The younger sequence in TKs is exposed in creek bottoms in Bendeleben D–1 quadrangle and in a small area south of Death Valley, in Bendeleben A–1 quadrangle. In the northern 

locality, lignite, up to 30 m thick, is interbedded with siltstone, mudstone, and sandstone 

along a strike length of almost three-quarters of a mile, based on drilling results; bedding 

is steeply dipping (Retherford and others, 1986). Pollen assemblages of Late Cretaceous 

and Tertiary (Eocene to early Miocene?) ages have been found in finer grained parts of the 

sequence (Till and others, 1986; Haga, in Retherford and others, 1986). Drilling results show 

that schists of the Nome Complex sit structurally above parts of the sequence (Retherford 

and others, 1986).

 In southeastern Bendeleben quadrangle, the younger sequence is also exposed in a 

small area south of Death Valley. Early Eocene and younger sedimentary and basaltic rocks 

accumulated in a small graben and are interleaved with basaltic rocks (Dickinson and others, 

1987). Sandstone, mudstone, conglomerate and coal beds up to 55 m thick were documented 

in drill core. Sandstones in the core host an epigenetic and supergene uranium deposit (Dickinson and others, 1987). A similar sequence of sedimentary and volcanic rocks probably 

underlies Death Valley.

 Unit is equivalent to units “Kc” of Miller and others (1972), “Klcg” of Sainsbury 

(1974), “TKs” and “TKc” of Till and others (1986), and “Kcc” of Patton and others (2005); 

also partly equivalent to units “Kss”, “Kls”, and “TKs” of Sainsbury (1974)

Jt Spruce Creek tonalite (Jurassic)—Tan-weathering, recessive, quartz-poor, plagioclase-rich 

intrusive rock. Rubble along middle to upper portions of Spruce Creek, in the headwaters 
31

of the Kugruk River in Bendeleben B–2 and B–3 quadrangles, is 50 to 70 percent plagioclase, 5 percent hornblende, and 25 to 45 percent quartz. Alkali feldspar is absent. A more 

hornblende-rich (30 percent), quartz-free dioritic variety is locally present. Hornblende is 

preserved only in northernmost exposures of the stock, along west banks of the creek. Elsewhere, no primary mafic minerals are present; hornblende is altered to mixtures of chlorite, 

opaque minerals, and epidote. An odd textural variety of the stock was found in one locality. 

Approximately 70 percent of this rock consists of concentrically radiating, spherulite-like 

intergrowths of plagioclase and quartz, often surrounding cores or nucleus grains of quartz 

or plagioclase, 0.7 to 1.7 mm in diameter. Several small exposures of an intrusive similar to 

the tonalite, thought to be fault slivers, are found along an unnamed stream that flows into 

the Kugruk River in the northwest corner of Bendeleben C–1 quadrangle. Tonalite yielded 

a U-Pb zircon age of 163±3 Ma (J. Aleinikoff, written commun., 1987; Till and Dumoulin, 

1994). Equivalent to unit “}|t” of Till and others (1986)

}|m Metamorphosed mafic rocks and serpentinite (Mesozoic and Paleozoic?)— Tectonic assemblage of metagabbro, metabasalt, amphibolite, serpentinite, and minor chert, exposed in 

rubble fields and poor outcrops along the trend of the Kugruk Fault Zone. Mafic rocks 

include minor unmetamorphosed (but altered) rocks, rocks with relict igneous textures and a 

single metamorphic overprint, and rocks that have experienced more than one metamorphic 

event. Pumpellyite- and prehnite-bearing veins that cross foliation are common in many 

lithologies.

In outcrop, singly metamorphosed mafic rocks are light to medium green, medium 

and grayish green, massive to finely color laminated. The degree of deformation varies 

within the unit. In thin section, metamorphic minerals statically overprint igneous textures, 

are weakly to well-aligned in a foliation, or the rock texture is mylonitic, with undulose 

extinction, grain size reduction, and microboudinage. Metagabbros and metabasalts typically retain porphyroclasts of igneous clinopyroxene that have rims of actinolite or blue 

amphibole. Mineral assemblages reflect a variety of metamorphic facies: actinolite-epidotechlorite-plagioclase, blue amphibole-lawsonite(?)-chlorite, blue amphibole-epidote-chlorite, 

and blue amphibole-pumpellyite-chlorite. These greenschist-, lawsonite-blueschist-, epidote 

blueschist-, and transitional blueschist-pumpellyite-actinolite-facies rocks occur over the 

length of the fault zone and are intermixed. The presence of multiple facies may reflect 

compositional variation in the mafic rocks rather than significant differences in metamorphic 

history. The boundaries among these facies come close to intersecting at temperatures of 

about 275–350 °C and pressures of 6–8 kb and variations in bulk rock composition shift the 

boundaries in pressure-temperature space (Evans, 1990). These rocks may have formed at 

generally similar conditions.

 There are two groups of multiply metamorphosed rocks. Amphibolites composed of 

coarse actinolite overprinted by finer grained greenschist-facies assemblages are minor but 

widespread. In the northern part of the fault zone (Bendeleben D–1 and Kotzebue A–1 quadrangles) mafic rocks display evidence of an albite-epidote amphibolite facies event overprinted by a lower grade event. Blue-green amphibole, epidote, and albite, with and without 

garnet, occur in equilibrium metamorphic textures. These albite-epidote-amphibolite-facies 

assemblages are slightly to significantly overprinted by epidote-blueschist or greenschist 

assemblages, largely on mineral rims or cracks. The later metamorphic event is likely the 

same event that affected mafic rocks in the unit farther south.

 Rubble crop of light-green-weathering, dark-greenish-black serpentinite is found in 

two large lenses in eastern Solomon quadrangle and in smaller bodies, up to 30 m across, in 

beach cliffs on Kotzebue Sound. The southern lens is the largest and is closely associated 

with outcrops of mylonitic metabasite.

 Rare subcrop of dark rusty-brown-weathering volcaniclastic rocks occurs in Bendeleben B–2 quadrangle; rocks are fine- to medium-grained and composed of unsorted subrounded to angular clasts of aphanitic to porphyritic basalt. Basalt textures are variable; 

grain size, mineralogy, and vesicularity vary from clast to clast. Associated with these rocks 

are lesser light-gray- to orange-weathering, very fine grained porphyritic felsic rocks. Quartz 

and plagioclase phenocrysts sit in a slightly recrystallized, fine-grained matrix; disseminated 

iron oxides impart the orange color.

 Unit }|m is equivalent of unit “Pmv” of Miller and others (1972), unit “Jv” of Sainsbury (1974), and combined units “}|m”, “}|b”, and “}|s” of Till and others (1986)
32

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38

the southern Brooks Range, Alaska, and accompanying 

conodont data: U.S. Geological Survey Open-File Report 

2008–1149, 88 p., 2 sheets, sheet 1, scale 1:500,000; sheet 

2, scale 1:600,000.

Till, A.B., Schmidt, J.M., and Nelson, S.W., 1988, Thrust 

involvement of metamorphic rocks, southwestern Brooks 

Range, Alaska: Geology, v. 16, p. 930–933.

Till, A.B., Slack, J.F., Ayuso, R.A., Shanks, W.C., III, Dumoulin, J.A., Amato, J.M., Aleinikoff, J.N., and Bleick, H.A., 

2007, Setting and origin of base-metal sulfide deposits in 

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Alaska Miners Association 2007 Convention and Trade 

Show, p. 10, accessed April 6, 2009, at http://www.alaskaminers.org/abstracts2007.pdf

Tolson, R.B., 1987, Structure and stratigraphy of the Hope 

Basin, southern Chukchi Sea, Alaska, in Scholl, D.W., 

Grantz, A., and Vedder, J.G., eds., Geology and resource 

potential of the continental margin of western North 

America and adjacent ocean basins, Beaufort Sea to Baja 

California: Houston, Tex., Circum-Pacific Council for 

Energy and Mineral Resources, p. 59–72.

Toro, J., Burnette, L., Amato, J., Repetski, J.E., and Gehrels, G., 

2006, The Mint River fault—an extensional detachment 

in the York Mountains, Seward Peninsula, Alaska [abs.]: 

Geological Society of America Abstracts with Programs, v. 

38, no. 5, p. 84–85.

Toro, J., Gans, P.B., McClelland, W.C., and Dumitru, T.A., 

2002, Deformation and exhumation of the Mount Igikpak 

region, central Brooks Range, Alaska, in Miller, E.L., 

Grantz, A., and Klemperer, S.L., eds., Tectonic evolution 

of the Bering Shelf-Chukchi Sea-Arctic Margin and adjacent landmasses: Geological Society of America Special 

Paper 360, p. 111–132.

Turner, D.L., Grybeck, D., and Wilson, F.H., [1975?], Radiometric dates from Alaska—A 1975 compilation: Alaska 

Division of Geological and Geophysical Surveys Special 

Report 10, 64 p. 

Turner, D.L., and Swanson, S.E., 1981, Continental rifting—A 

new tectonic model for the central Seward Peninsula, in

Wescott, E., and Turner, D.L., eds., Geothermal reconnaissance survey of the central Seward Peninsula, Alaska: University of Alaska, Geophysical Institute, Report prepared 

for the Division of Geothermal Energy of the U.S. Department of Energy, Report 284, p. 7–36.

Vandervoort, D.J., 1985, Stratigraphy, paleoenvironment, and 

diagenesis of the Lower Ordovician York Mountain carbonates, Seward Peninsula, Alaska: Baton Rouge, Louisiana, Louisiana State University, Masters thesis, 141 p.

Watts, K.F., Harris, A.G., Carlson, R.C., Eckstein, M.K., Gruzlovic, P.D., Imm, T.A., Krumhardt, A.P., Lasota, D.K., 

Morgan, S.K., Enos, Paul, Goldstein, R., Dumoulin, J.A., 

and Mamet, B., 1994, Analysis of reservoir heterogeneities 

due to shallowing-upward cycles in carbonate rocks of the 

Upper Mississippian and Pennsylvanian Wahoo Limestone 

of northeastern Alaska: Department of Energy Report, 

Contract DE-AC22-89BC14471, 433 p.

Webby, B.D., Cooper, R.A., Bergström, S.M., and Paris, Florentin, 2004, Stratigraphic framework and time slices, in

Webby, B.D., Paris, Florentin, Droser, M.L., and Percival, 

I.G., eds., The great Ordovician biodiversification event: 

New York, Columbia University Press, p. 41–47.

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Freeman, L.K., and Layer, P.W., 2006, Geologic mapping 

and mineral investigations in the Casadepaga River-Bluff 

area and implications for the southern Seward Peninsula, 

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Convention and Trade Show, p. 3–5, accessed September 

20, 2009, at http://www.alaskaminers.org/abstracts2006.

pdf

Werdon, M.B., Stevens, D.S.P., Newberry, R.J., Szumigala, 

D.J., Athey, J.E., and Hicks, S.A., 2005a, Explanatory 

booklet to accompany geologic, bedrock, and surficial 

maps of the Big Hurrah and Council areas, Seward Peninsula, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigation 2005-1, 24 p.

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D.J., Athey, J.E., and Hicks, S.A., 2005b, Geologic map 

of the Big Hurrah area, northern half of the Solomon C-5 

quadrangle, Seward Peninsula, Alaska: Alaska Division of 

Geological and Geophysical Surveys Report of Investigation 2005-1A, 1 sheet, scale 1:50,000.

Werdon, M.B., Szumigala, D.J., Newberry, R.J., Athey, J.E., 

and Hicks, S.A., 2005c, Major-oxide, minor-oxide, traceelement, geochemical, and non-carbonate carbon data from 

rocks collected in the Solomon, Bendeleben, and Nome 

quadrangles, Seward Peninsula, Alaska in 2003 and 2004: 

Alaska Division of Geological and Geophysical Surveys 

Raw Data File 2005-2, 46 p.

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table showing isotopic age data in Alaska, in Plafker, G. 

and Berg, H.C., eds., The geology of Alaska: Boulder, 

Colo., Geological Society of America, The Geology of 

North America, v. G-1, Plate 8; 1 sheet, scale 1:2,500,000.

Wirth, K.R., Grandy, J., Kelley, K., and Sadofsky, S., 2002, 

Evolution of crust and mantle beneath the Bering Sea 

region: Evidence from xenoliths and late Cenozoic basalts, 

in Miller, E.L., Grantz, A., and Klemperer, S.L., eds., 

Tectonic evolution of the Bering Shelf-Chukchi Sea-Arctic 

margin and adjacent landmasses: Geological Society of 

America Special Paper 306, p. 167–193.
39
40

Table 1. Distribution of geologic units in 1:250,000-scale quadrangle maps in the map area 

[1diagonal overlay pattern]

Geologic unit Nome Solomon Bendeleben Teller Kotzebue Shishmaref Selawik Candle Norton Bay

SURFICIAL DEPOSITS

Qs X X X X X X X X X

MESOZOIC AND CENOZOIC IGNEOUS ROCKS

Qlj ---- ---- X ---- ---- ---- ---- ---- ----

QTv ---- X X X X ---- X X ----

TKv ---- ---- X ---- ---- ---- ---- ---- ----

Ktg ---- ---- X X ---- ---- ---- ---- ----

Kds X X X X ---- ---- ---- ---- ----

Kp ---- ---- X ---- ---- ---- ---- ---- ----

Kdi X ---- ---- ---- ---- ---- ---- ---- ----

Kg X ---- X X ---- ---- ---- ---- ----

Ks ---- ---- X ---- ---- ---- ---- ---- ----

Kku ---- ---- X ---- ---- ---- ---- ---- ----

Kwc ---- ---- X ---- ---- ---- ---- ---- ----

Kd ---- X X ---- ---- ---- ---- ---- ----

Kkd ---- X ---- ---- ---- ---- ---- ---- ----

Kkg ---- X ---- ---- ---- ---- ---- ---- ----

Kkms ---- X ---- ---- ---- ---- ---- ---- ----

Kkgm ---- X ---- ---- ---- ---- ---- ---- ----

Kbk ---- ---- X ---- ---- ---- ---- ---- ----

Kdc ---- X ---- ---- ---- ---- ---- ---- ----

Kgr ---- ---- ---- ---- ---- ---- ---- X ----

Ksy ---- ---- ---- ---- ---- ---- X X ----

Kv ---- ---- ---- ---- ---- ---- X X X

Kgu X X X X ---- ---- ---- ---- ----

YORK TERRANE

York Mountains succession

DSl ---- ---- ---- X ---- ---- ---- ---- ----

SOdl ---- ---- ---- X ---- ---- ---- ---- ----

SOul ---- ---- ---- X ---- ---- ---- ---- ----

Ols ---- ---- ---- X ---- ---- ---- ---- ----

Ol ---- ---- ---- X ---- ---- ---- ---- ----

Oal ---- ---- ---- X ---- ---- ---- ---- ----

Units with uncertain affinities

|l ---- ---- ---- X ---- ---- ---- ---- ----

Ml ---- ---- ---- X ---- ---- ---- ---- ----

|gb ---- ---- ---- X ---- ---- ---- ---- ----

O<l ---- ---- ---- X ---- ---- ---- ---- ----

O<t ---- ---- ---- X ---- ---- ---- ---- ----

O<p ---- ---- ---- X ---- ---- ---- ---- ----

GRANTLEY HARBOR FAULT ZONE

|p ---- ---- ---- X ---- ---- ---- ---- ----

|<l ---- ---- ---- X ---- ---- ---- ---- ----
41

Table 1. Distribution of geologic units in 1:250,000-scale quadrangle maps in the map area.—Continued

[1diagonal overlay pattern]

Geologic unit Nome Solomon Bendeleben Teller Kotzebue Shishmaref Selawik Candle Norton Bay

|<t ---- ---- ---- X ---- ---- ---- ---- ----

NOME COMPLEX

Layered sequence

|np ---- ---- ---- X ---- ---- ---- ---- ----

Ds ---- X X X ---- ---- ---- ---- ----

Dcs X X ---- ---- ---- ---- ---- ---- ----

DOx X X X X X ---- X X X

DOx1 ---- ---- ---- X ---- ---- ---- ---- ----

Dg ---- ---- X ---- ---- ---- ---- ---- ----

Df ---- ---- X ---- ---- ---- ---- ---- ----

Ocs X X X X X ---- X X ----

Oim X X X X X ---- ---- ---- ----

<n X X X ---- ---- ---- ---- ---- ----

Scattered metacarbonate rocks

|m ---- X X X X ---- ---- X X

|d ---- ---- X ---- X ---- ---- X X

|mm X ---- ---- ---- ---- ---- ---- ---- ----

Ddm ---- X X ---- ---- ---- ---- ---- ----

Sd ---- ---- X ---- ---- ---- ---- ---- ----

Od ---- X X ---- ---- ---- ---- ---- ----

_d ---- X ---- ---- ---- ---- ---- ---- ----

Metaturbidites

D_bm ---- X ---- ---- ---- ---- ---- ---- X

D_ks ---- X ---- ---- X ---- ---- ---- ----

DObm ---- ---- ---- ---- X ---- ---- ---- ----

HIGH-GRADE METAMORPHIC AND ASSOCIATED IGNEOUS ROCKS

|<h X X X X ---- ---- ---- ---- ----

|<m ---- ---- X ---- ---- ---- ---- ---- ----

|<g ---- ---- X ---- X ---- ---- ---- ----

<o X X X X ---- ---- ---- ---- ----

<v ---- ---- X ---- ---- ---- ---- ---- ----

KUGRUK FAULT ZONE

TKs ---- X X ---- ---- ---- ---- X X

Jt ---- ---- X ---- ---- ---- ---- ---- ----

}|m ---- X X ---- X ---- ---- X ----
42

Table 2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations. (table spans facing page)

[– not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Dalrymple (1979); localities are plotted on sheet 2; scale of map precludes labeling of all locality names]

Map

no. Field number

Geologic

unit

1:63,360-scale

quadrangle Locality

Lat (N) Long (W)

Method 

Deg Min Deg Min 

1 – Kgu [water] – Fairway Rock 65 37.4 168 44.5 K-Ar 

2 DT79P15 Kg [|<h] Teller A-1 Kigluaik Mountains 65 2.5 165 0.4 K-Ar 

3 91T-MR-50A Ocs Teller A-2 Southwest side of Tuksuk Channel 65 9.688 165 58.354 40Ar/39Ar 

4 91T-MR-51 Ocs Teller A-2 Northeast side of Tuksuk Channel 65 10.06 165 54.463 40Ar/39Ar 

5 91T-MR-38 Ocs Teller A-3 Northern edge of ridge between Gold Run and 

McAdam Creek

65 1.627 166 9.987 40Ar/39Ar 

6 91T-HD-2b Ocs Teller A-3 Confluence of Skookum Creek and Gold Run 65 2.038 166 11.742 40Ar/39Ar 

7 91T-LL-5 Ocs Teller A-3 Headwaters of Alder Creek near Sullivan Camp 65 4.219 166 6.942 40Ar/39Ar 

8 91T-LR-18 |np Teller A-3 North side of Right Fork, Bluestone River, 2.5 

miles from the road

65 6.257 166 19.997 40Ar/39Ar 

9 PT80-51D QTv Teller B-3 Eva Mountain 65 21.679 166 8.468 K-Ar 

10 PT80-50B QTv Teller B-3 Hill 1220 65 22.056 166 9.288 K-Ar 

11 PT80-50A QTv Teller B-3 Hill 1220 65 22.056 166 9.28 K-Ar 

12 73Ahp 7 QTv Teller B-4 Divide between California River and Arctic 

Creek

65 25.152 166 32.215 K-Ar 

13 AK104 Ktg Teller B-4 Black Mountain 65 28.633 166 44.433 K-Ar 

14 AK110 Ktg [Oal] Teller B-5 Lost River Mines 65 28.55 167 9.4 K-Ar 

15 PC2 [Ds] Teller C-1 Kougarok region 65 42.6 165 11.4 K-Ar 

16 PC1 [Ds] Teller C-1 Kougarok region 65 42.6 165 11.4 Rb-Sr 

17 BB45 Ktg Teller C-5 Brooks Mountain, approximate location 65 31.928 167 7.534 K-Ar 

18 AK108 Ktg Teller C-7 Cape Mountain 65 35.8 168 2.5 Rb-Sr 

19 77AH8 Ktg Teller C-7 Cape Mountain 65 35.8 168 2.5 K-Ar 

20 AK114 Ktg Teller D-3 Ear Mountain 65 55.1 166 13.8 K-Ar 

21 AK112 Ktg Teller D-3 Ear Mountain 65 55.133 166 13.8 Rb-Sr 

22 80-91-2 DOx Nome C-1 6.8 miles north of Nome 64 34.7 165 18.9 K-Ar 

23 04Z641 Dcs Nome C-1 Rock Creek, approximate location 64 36.9 165 24.9 40Ar/39Ar 

24 04Z638A 

WM#2

Dcs Nome C-1 Rock Creek, approximate location 64 36.9 165 24.9 40Ar/39Ar 
43

ages determined prior to 1976 have been recalculated and noted in the Remarks column to reflect recommended 1976 IUGS constants using 

Mineral

Age

(Ma)

Error

(Ma) Rock type Reference Remarks

Biotite 110.7 3 Granite Shumway and others, 1964 Age recalculated with 1976 constants; authors' reported age 108 

± 3.0 Ma; sample is from an outcrop of Kgu that is too small to 

show at map scale; given the latitude and longitude the sample 

plots on the shoreline in the water

Biotite 83.4 2.5 Gneissic granite Turner and Swanson, 1981 Location from Wilson and others (1994)

White mica 124.3 0.3 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

White mica 114.8 0.7 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

White mica 118.1 0.3 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

White mica 116.2 0.3 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

White mica 120.5 0.2 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

White mica 119.9 0.3 Schist Hannula and McWilliams, 1995 Age given is authors' reported weighted mean plateau age

Whole-rock 2.6 0.2 Basalt Turner and Swanson, 1981 Authors' comments: sample is a volcanic neck from the basalt 

flows; authors' reported location of sample is north of Teller at 

"Eva Mountain." Latitude and longitude were not reported and 

were determined based on authors' description and fig. 8

Whole-rock 2.5 0.3 Basalt Turner and Swanson, 1981 Authors' comments: sample is a volcanic neck from the basalt 

flows; authors reported location of sample is north of Teller at 

"Hill 1220." Latitude and longitude were not reported and were 

determined based on authors' description and fig. 8

Whole-rock 2.7 0.2 Basalt Turner and Swanson, 1981 Authors' comments: sample is a volcanic neck from the basalt 

flows; authors reported location of sample is north of Teller at 

"Hill 1220." Latitude and longitude were not reported and were 

determined based on authors' description and fig. 8

Whole-rock 2.92 0.14 Basalt Hopkins and others,1974 Age recalculated with 1976 constants; authors' reported age 2.84 

± 0.14 Ma; authors' reported location of the sample is "the divide 

between California River and Arctic Creek." Latitude and longitude were not reported and were determined based on authors' 

description, fig. 3, and additional description on p. 447

Biotite 79.1 2.9 Granite Hudson and Arth, 1983 Location based on authors' table 1

Biotite 80.2 3 Granite Hudson and Arth, 1983 Sample is from an outcrop of Ktg that is too small to show at 

map scale; given the latitude and longitude the sample plots in 

Oal

Mica 70.2 - Granite Puchner, C.C., written commun., 

1986

Sample is from drill core that is in Ds at the surface

- 72 - Porphyritic biotite 

granite

Puchner, C.C., written commun., 

1986

Sample is from drill core that is in Ds at the surface

Biotite 77 3 Granite Sainsbury, 1969b Age recalculated with 1976 constants; Author's reported age 75.1 

± 3.0 Ma; sample number is given in Turner and others, 1975

Whole-rock 

(multiple)

72.5 2 Granite Hudson and Arth, 1983 Whole rock / isochron age; location based on authors' table 1

Biotite 78.8 2.9 Granite Hudson and Arth, 1983 Location based on authors' table 1

Biotite 76.7 2.8 Granite Hudson and Arth, 1983 Location based on authors' table 1

Whole-rock 

(multiple)

73.1 1.6 Granite Hudson and Arth, 1983 Whole rock / isochron age; location based on authors' table 1

Phengite 162 6 Pelitic schist Armstrong and others, 1986 Authors' reported comments: low-grade pelitic schist

White mica 102.3 0.7 Vein Layer and Newberry, 2004 Age given is the authors' reported plateau age; sample is from 

drill core

White mica 112.3 0.8 Vein Layer and Newberry, 2004 Age given is the authors' reported plateau age; sample is from 

drill core
44

Table 2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations.—Continued (table spans facing page)

[– not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Dalrymple (1979); localities are plotted on sheet 2; scale of map precludes labeling of all locality names]

Map

no. Field number

Geologic

unit

1:63,360-scale

quadrangle Locality

Lat (N) Long (W)

Method 

Deg Min Deg Min 

25 90AG025 Dike [|mm] Nome C-3 Approximately 9.5 miles due north of Sinuk (at 

the mouth of Sinuk River) and 5 miles east of 

Bering Sea

64 43.837 166 18.614 K-Ar 

26 80-41-4 Ocs Nome D-1 3.3 miles southwest of Salmon Lake 64 51 165 8.5 K-Ar 

27 90P8-13b |<h Nome D-1 Kigluaik Mountains 64 53.567 165 27.817 40Ar/39Ar 

28 90J11-5 |<h Nome D-1 Kigluaik Mountains 64 59.633 165 24.8 40Ar/39Ar 

29 92.4A-115 Dike [|<h] Nome D-2 Kigluaik Mountains 64 53.11 165 48.93 40Ar/39Ar 

30 92.3A-101 Dike [Kgu] Nome D-2 Kigluaik pluton and associated dikes 64 54.584 165 44.026 40Ar/39Ar 

31 92.2A-40 Dike [<o] Nome D-2 Kigluaik pluton and associated dikes 64 54.967 165 37.133 40Ar/39Ar 

32 92.2A-40 Dike [<o] Nome D-2 Kigluaik pluton and associated dikes 64 54.967 165 37.133 40Ar/39Ar 

33 92.2A-46 Dike [<o] Nome D-2 Kigluaik Mountains 64 55.09 165 36.2 40Ar/39Ar 

34 90P8-4A <o Nome D-2 Kigluaik Mountains 64 55.183 165 31.817 40Ar/39Ar 

35 90P12-4b <o Nome D-2 Kigluaik Mountains 64 55.3 165 32.571 40Ar/39Ar 

36 90K12-7a <o Nome D-2 Kigluaik Mountains 64 55.3 165 33.05 40Ar/39Ar 

37 90K12-7b Dike [<o] Nome D-2 Kigluaik Mountains 64 55.53 165 33.05 40Ar/39Ar 

38 90P12-5b <o Nome D-2 Kigluaik Mountains 64 55.717 165 32 40Ar/39Ar 

39 924A-120 Kdi Nome D-2 Kigluaik pluton and associated dikes 64 56.183 165 47.45 40Ar/39Ar 

40 924A-119 Kdi Nome D-2 Kigluaik pluton and associated dikes 64 57.2 165 46.1 40Ar/39Ar 

41 89S-LMC-47 |<h Nome D-3 Kigluaik Mountains 64 50.583 166 2.817 40Ar/39Ar 

42 89MC-78 Dike [|<h] Nome D-3 Kigluaik Mountains 64 53.09 166 0.59 40Ar/39Ar 

43 68AMm285 Kd Bendeleben 

A-1 

Darby pluton 65 0.865 162 13.503 K-Ar 

44 84AGe79 Kwc Bendeleben A-2 Windy Creek pluton 65 8.748 162 34.518 K-Ar 

45 90S-EK-9 |<h Bendeleben A-6 Kigluaik Mountains 65 0.094 164 47.047 40Ar/39Ar 
45

ages determined prior to 1976 have been recalculated and noted in the Remarks column to reflect recommended 1976 IUGS constants using 

Mineral

Age

(Ma)

Error

(Ma) Rock type Reference Remarks

Biotite 80.5 0.8 Granitic Shew, N., written commun., 1993 Analyst's reported location is on "one of the many northwest trending ridges (boundary of section 5 and 8, T9S, R38W Kateel River 

meridian); elevation about 450 feet;" analyst's reported latitude 

and longitude: 64° 43' 50" N and 166° 18' 30" W; sample is from a 

granitic dike in |mm that is too small to show at map scale

Phengite 141 5 Schist Armstrong and others, 1986 Authors' reported comments: low-grade pelitic schist

White mica 83.7 0.5 Metapelite or 

orthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors reported 

"white mica separates from metapelite and orthogneiss" 

Biotite 83.9 0.4 Orthogneiss or 

paraorthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors reported 

"biotites from orthogneisses and paraorthogneisses"

Whole rock 83.3 0.9 Diabase dikes Amato and others, 2003c Age given is the authors' reported weighted mean plateau age; 

sample is from a diabase dike in |<h that is too small to show at 

map scale

Biotite 82.5 0.3 Dike Calvert and others, 1999 Age given is authors' reported plateau age; location given is 

based on authors' fig. 4

Hornblende 82.8 0.4 Dike Calvert and others, 1999 Age given is authors' reported plateau age; location given is from 

authors' table 1; authors' reported sample number: 922A-40

Biotite 82.1 0.3 Dike Calvert and others, 1999 Age given is authors' reported plateau age; location given is from 

authors' table 1

Whole rock 81.3 0.6 Diabase dikes Amato and others, 2003c Age given is the authors' reported weighted mean plateau age; 

sample is from a diabase dike in <o that is too small to show at 

map scale

Biotite 83.9 0.4 Orthogneiss or 

paraorthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors reported "biotites from orthogneisses and paraorthogneisses;" Location given 

is from authors' table 1

Hornblende 86.4 0.7 Amphibolite Calvert and others, 1999 Age given is authors' reported plateau age; authors reported the 

sample is from a "penetratively deformed amphibolite;" authors' 

reported location of 60° 8' 4" and –165° 31' 49" is mislocated; 

location given is based on authors' fig. 4

Hornblende 86.1 0.4 Amphibolite Calvert and others, 1999 Age given is authors' reported plateau age; authors reported the 

sample is from a "penetratively deformed amphibolite;" location 

given is from authors' table 1

Biotite 83.6 0.8 Diabase dikes Amato and others, 2003c Age given is the authors' reported weighted mean plateau age; 

sample is from a diabase dike outcrop in <o that is too small to 

show at map scale

Hornblende 85.6 0.4 Granodioritic 

orthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors reported the 

sample is from a "melt-filled extension fracture along a syntectonic shear band in a granodioritic orthogneiss"

Hornblende 82 0.3 Mafic phase igneous rockCalvert and others, 1999 Age given is authors' reported plateau age; location given is from 

authors' table 1

Hornblende 82.2 0.3 Mafic phase igneous rockCalvert and others, 1999 Age given is authors' reported plateau age; location given is from 

authors' table 1

White mica 83.1 0.5 Metapelite or 

orthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors reported 

"white mica separates from metapelite and orthogneiss"; location 

given is from authors' table 1

Whole rock 79.2 0.3 Diabase dike Amato and others, 2003c Age given is a weighted mean plateau age; sample is from a 

diabase dike in |<h that is too small to show at map scale

Biotite 94.4 2.9 Quartz monzonite Miller and others, 1972; Miller and 

Bunker, 1976

Age recalculated with 1976 constants; authors' reported age 92.1 

± 2.8 Ma; reported latitude and longitude 65° 01' N and 162° 11' 

W

Hornblende 93.8 2.1 Monzogranite Shew, N., written commun., 1987 Analyst reported that the sample is "an intrusive between Windy 

Creek and an unnamed northern tributary of Mosquito Creek. 

Sample was collected from the flat portion of ridge, approximately 490 meters south of peak 2764"

Biotite 83.8 1.1 Orthogneiss or 

paraorthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors' reported "biotites from orthogneisses and paraorthogneisses;" location given is 

based on authors' fig. 4
46

Table 2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations.—Continued (table spans facing page)

[– not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Dalrymple (1979); localities are plotted on sheet 2; scale of map precludes labeling of all locality names]

Map

no. Field number

Geologic

unit

1:63,360-scale

quadrangle Locality

Lat (N) Long (W)

Method 

Deg Min Deg Min 

46 92NA-107 Dike [|<h] Bendeleben A-6 Kigluaik Mountains 65 0.43 164 49.95 40Ar/39Ar 

47 83MS119b <o Bendeleben A-6 Eastern Kigluaik Mountains 65 0.8 164 56.7 K-Ar 

48 83MS119b <o Bendeleben A-6 Eastern Kigluaik Mountains 65 0.8 164 56.7 K-Ar 

49 89S-MC-54 |<h Bendeleben A-6 Kigluaik Mountains 65 1.548 164 47.799 40Ar/39Ar 

50 90-Hens <n Bendeleben A-6 Hen and Chickens Mountain 65 8.067 164 51.067 40Ar/39Ar 

51 PS80-14A Dike [|<h] Bendeleben A-6 Westernmost Bendeleben Mountains, approximate location65 10.536 164 39.075 K-Ar 

52 PT80-28 Kgu Bendeleben A-6 Westernmost Bendeleben Mountains, approximate location65 10.649 164 38.617 K-Ar 

53 PT80-30 Kgu Bendeleben A-6 Westernmost Bendeleben Mountains, approximate location65 10.649 164 38.617 K-Ar 

DT79P1 - - Kigluaik Mountains and Hen and Chickens 

Mountain

- - - - K-Ar 

54 DT79P4 <n Bendeleben A-6 Hen and Chickens Mountain 65 8.3 164 54.6 K-Ar 

DT79P11A - - Kigluaik Mountains and Hen and Chickens 

Mountain

- - - - K-Ar 

DT79P13 - - Kigluaik Mountains and Hen and Chickens 

Mountain

- - - - K-Ar 

55 DT79P14 - Bendeleben A-6 Kigluaik Mountains 65 1 164 59.1 K-Ar 

56 68AMm280 Kbk Bendeleben B-2 Bendeleben pluton 65 16 162 55 K-Ar 

57 83AGe90 Kbk Bendeleben B-3 Kuzitrin pluton 65 23.3 163 6.2 K-Ar 

58 84AKn106 QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

59 84AKn106a QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

60 84AKn106a QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

61 84AKn106c QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

62 84AKn106c QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

63 87AHP26 QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 
47

ages determined prior to 1976 have been recalculated and noted in the Remarks column to reflect recommended 1976 IUGS constants using 

Mineral

Age

(Ma)

Error

(Ma) Rock type Reference Remarks

Whole rock 82.4 1.3 Diabase dike Amato and others, 2003c Age given is the authors' reported weighted mean plateau age; 

sample is from a diabase dike in |<h that is too small to show at 

map scale

Biotite 84.9 2.5 Mafic gneiss Sturnick, 1984 Location based on author's table 1

Hornblende 85.6 2.6 Mafic gneiss Sturnick, 1984 Location based on author's table 1

White mica 83 0.8 Metapelite or 

orthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors' reported 

"white mica separates from metapelite and orthogneiss;" Location given is based on authors' sample location in fig. 4

Biotite 84.7 0.2 Orthogneiss or 

paraorthogneiss

Calvert and others, 1999 Age given is authors' reported plateau age; authors' reported 

"biotites from orthogneisses and paraorthogneisses"

Whole-rock 74.9 3 Basalt dike Turner and Swanson, 1981 Authors' reported comments: basalt dike intruding Precambrian 

basement; location approximated based on authors' fig. 5

Whole-rock 74.5 2.8 Rhyolite Turner and Swanson, 1981 Authors' reported comments: small dike / plug of vesicular 

rhyolite intruding Precambrian basement; location given is based 

on authors' fig. 5

Whole-rock 69 2.6 Rhyolite Turner and Swanson, 1981 Authors' reported comments: small dike / plug of vesicular 

rhyolite intruding Precambrian basement; location given is based 

on authors' fig. 5

Biotite 83.9 2.5 Schist Turner and Swanson, 1981 Authors' reported location of the samples is "metamorphic 

and igneous intrusive rocks from the Kigluaik Mountains and 

Hen and Chickens Mountain." Latitude and longitude were not 

reported

Hornblende 84.9 2.6 Amphibolite Turner and Swanson, 1981 Location from Wilson and others (1994)

Biotite 81.4 2.4 Pelitic gneiss Turner and Swanson, 1981 Authors' reported location of the samples is "metamorphic 

and igneous intrusive rocks from the Kigluaik Mountains and 

Hen and Chickens Mountain." Latitude and longitude were not 

reported

Biotite 87 2.6 Gneissic granite Turner and Swanson, 1981 Authors' reported location of the samples is "metamorphic 

and igneous intrusive rocks from the Kigluaik Mountains and 

Hen and Chickens Mountain." Latitude and longitude were not 

reported

Biotite 83 2.5 Granodiorite Turner and Swanson, 1981 Location from Wilson and others (1994)

Biotite 81.8 2.5 Quartz monzonite Miller and others, 1972; Miller and 

Bunker, 1976

Age recalculated with 1976 constants; authors' reported age 79.8 

± 2.4 Ma

Biotite 83 1.4 Monzogranite Till and others, 1986 Location based on authors' table 2

Plagioclase 0.81 0.09 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river 

is diverted westward by the lava"; age was first reported in 

Kaufman and Hopkins (1985) with reported location 65° 31' and 

–164° 09'; that location appears to be incorrect based on location 

given in Kaufman and others (1991) fig. 2, on sh. 2 

Whole rock 0.024 0.11 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"

Whole rock 0.1 0.16 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"

Whole rock 0.717 0.11 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"

Whole rock 0.719 0.13 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"

Whole rock 0.797 0.06 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"
48

Table 2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations.—Continued (table spans facing page)

[– not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Dalrymple (1979); localities are plotted on sheet 2; scale of map precludes labeling of all locality names]

Map

no. Field number

Geologic

unit

1:63,360-scale

quadrangle Locality

Lat (N) Long (W)

Method 

Deg Min Deg Min 

64 84AKn106d QTv Bendeleben B-4 Minnie Creek 65 24.566 163 47.432 K-Ar 

65 68AMm324 Kku Bendeleben C-2 Kugruk pluton, approximate location 65 41.94 162 35.97 K-Ar 

66 PT80-34 QTv Bendeleben C-2 Imuruk basalts: Gosling series, approximate 

location

65 33.062 162 57.242 K-Ar 

67 PT80-36A QTv Bendeleben C-2 Imuruk basalts: Gosling series, approximate 

location

65 33.062 162 57.242 K-Ar 

68 PT80-37 QTv Bendeleben C-2 Imuruk basalts: Kugruk series, approximate 

location

65 33.885 162 55.776 K-Ar 

69 PT80-38 QTv Bendeleben C-2 Imuruk basalts: Kugruk series, approximate 

location

65 33.885 162 55.776 K-Ar 

70 PT80-40 QTv Bendeleben C-2 Imuruk basalts: Kugruk series, approximate 

location

65 33.885 162 55.776 K-Ar 

71 PT80-35A QTv Bendeleben C-2 Imuruk basalts: Imuruk series, approximate 

location

65 33.188 162 57.865 K-Ar 

72 PT80-33 QTv Bendeleben C-2 Imuruk basalts: Imuruk series, approximate 

location

65 33.188 162 57.865 K-Ar 

73 85AGe43 Ks (overlay) Bendeleben C-3 Nimrod Hill 65 37.614 163 5.736 K-Ar 

74 83AGe124a Ks (overlay) Bendeleben C-3 Virginia Butte stock 65 42.833 163 8.65 K-Ar 

75 83AGe117 Ks (overlay) Bendeleben C-3 Asses Ears stock 65 44.5 163 10.8 K-Ar 

76 80-19-4 Ocs Bendeleben C-6 Left Fork Kougarok River flows into Kougarok 

River

65 31 164 42.9 K-Ar 

77 83AGe126 Ks (overlay) Bendeleben D-3 Crossfox Butte stock 65 47.283 163 17.35 K-Ar 

78 AHP66 QTv [Qs] Bendeleben D-3 Lava Camp Mine in the upper Inmachuk River 

Valley

65 53.1 163 7.5 K-Ar 

79 69AH228 Ktg Bendeleben D-6 Oonatut Granite Complex 65 50 164 35 K-Ar 
49

ages determined prior to 1976 have been recalculated and noted in the Remarks column to reflect recommended 1976 IUGS constants using 

Mineral

Age

(Ma)

Error

(Ma) Rock type Reference Remarks

Whole rock 1.748 0.57 Basalt Kaufman and others, 1991 Location given based on authors' fig. 2, on sh. 2 and reported 

location on "the right bank of Minnie Creek, where the river is 

diverted westward by the lava"

Biotite 94.8 2.8 Quartz monzonite 

to quartz monzodiorite

Till and others, 1986 Location based on authors' table 2

Whole-rock 0.82 0.08 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Gosling 

series" after Hopkins' (1963) Gosling volcanics. Latitude and 

longitude were not reported. Based on Turner's and Swanson's 

description, location was approximated using Hopkins' (1963) 

fig. 9

Whole-rock 0.91 0.09 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Gosling 

series" after Hopkins' (1963) Gosling volcanics. Latitude and 

longitude were not reported. Based on Turner's and Swanson's 

description, location was approximated using Hopkins' (1963) 

fig. 9

Whole-rock 26.4 1.4 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Kugruk 

series" after Hopkins' (1963) Kugruk volcanics. Latitude and 

longitude were not reported and were determined based on the 

type locality in the canyon of the Kugruk River, 3 miles east of 

Imuruk Lake (Hopkins, 1963, fig. 9 and p. C48) 

Whole-rock 28.1 1.4 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Kugruk 

series" after Hopkins' (1963) Kugruk volcanics. Latitude and 

longitude were not reported and were determined based on the 

type locality in the canyon of the Kugruk River, 3 miles east of 

Imuruk Lake (Hopkins, 1963, fig. 9 and p. C48) 

Whole-rock 28.8 1.8 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Kugruk 

series" after Hopkins' (1963) Kugruk volcanics. Latitude and 

longitude were not reported and were determined based on the 

type locality in the canyon of the Kugruk River, 3 miles east of 

Imuruk Lake (Hopkins, 1963, fig. 9 and p. C48) 

Whole-rock 2.2 0.2 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Imuruk 

series" after Hopkins' (1963) Kugruk volcanics. Latitude and 

longitude were not reported and were determined based on the 

type locality in the canyon of the Kugruk River, 3 miles east of 

Imuruk Lake (Hopkins, 1963, fig. 9 and p. C48) 

Whole-rock 2.2 0.2 Basalt Turner and Swanson, 1981 Authors' reported location of sample is "Imuruk basalts: Imuruk 

series" after Hopkins' (1963) Kugruk volcanics. Latitude and 

longitude were not reported and were determined based on the 

type locality in the canyon of the Kugruk River, 3 miles east of 

Imuruk Lake (Hopkins, 1963, fig. 9 and p. C48) 

Hornblende 96.3 2 Monzonite Shew, N., written commun., 1990 Analyst's reported location of sample is "small ridge NW [northwest] of x2995 (summit of Mount Arathlatuluk); sample collected 

from flat section of ridge, approx. 1/3 mile from the summit"

Biotite 94.8 1.9 Syenite Till and others, 1986 Location based on authors' table 2

Biotite 96.2 1.6 Monzogranite Till and others, 1986 Location based on authors' table 2

Phengite 156 5 Pelitic schist Armstrong and others, 1986 Authors' reported comments: low-grade pelitic schist

Biotite 91.5 2.8 Monzogranite to 

quartz monzonite

Till and others, 1986 Authors' reported comments: some biotite was chloritized, and 

this age should be considered suspect

Whole-rock 5.83 0.2 Basalt Hopkins and others, 1971 Age recalculated with 1976 constants; authors' reported age 5.7 

± 0.2 Ma; authors' reported comments: sample collected from 

the roof of the Lava Camp Mine tholeiitic basalt; sample number 

provided by authors' as AHP66 in table 2 is a subsample of 

66AHP 22 (stated in authors' table 1).

Biotite 69.2 2 Granite Hudson, 1979 Age recalculated with 1976 constants; author's reported age 67.5 

± 2 Ma; latitude and longitude not reported; location of sample is 

approximate
50

Table 2. Selected K-Ar, 40Ar/39Ar and Rb-Sr age determinations.—Continued (table spans facing page)

[– not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Dalrymple (1979); localities are plotted on sheet 2; scale of map precludes labeling of all locality names]

Map

no. Field number

Geologic

unit

1:63,360-scale

quadrangle Locality

Lat (N) Long (W)

Method 

Deg Min Deg Min 

80 69AH283 Ktg Bendeleben D-6 Oonatut Granite Complex 65 51 164 42 K-Ar 

81 70AMm150 Kkms Solomon C-2 Kachauik pluton 64 34 162 45 K-Ar 

82 71AGk259 Dike [Kkg] Solomon C-2 Kachauik dike swarm 64 43.5 162 53.1 K-Ar 

83 BLC-15-89 [Ddm] Solomon C-4 Bluff 64 34.058 163 40.274 40Ar/39Ar 

84 BLC-15-107 [Ddm] Solomon C-4 Koyana Creek - Bluff area 64 34.058 163 40.274 40Ar/39Ar 

85 BLC-30-212.2 [DOx] Solomon C-4 Koyana Creek - Bluff area 64 34.46 163 42.775 40Ar/39Ar 

86 04RN500C 

WM#2

Dcs Solomon C-5 Headwaters of Big Hurrah Creek, 3.8 miles east 

of Uncle Sam Mountain

64 37.807 164 8.568 40Ar/39Ar 

87 04SH119A DOx Solomon C-5 Road cut 0.2 miles south of the East Fork bridge 64 41.435 164 16.839 40Ar/39Ar 

88 04RN319A DOx Solomon C-5 Road cut 0.2 miles south of the East Fork bridge 64 41.435 164 16.839 40Ar/39Ar 

89 04MBW384C Dike [DOx] Solomon C-5 Hill slope 0.8 mile north of where Goodenough 

Cr. flows into Solomon River East Fork

64 42.616 164 10.949 40Ar/39Ar 

90 04Z156 DOx Solomon C-5 Hill slope 0.7 mile northwest of where Butte 

Creek flows into Solomon River East Fork

64 43.232 164 20.571 40Ar/39Ar 

91 04RN351B Dcs Solomon C-5 Confluence of Rock Creek with Coal Creek 64 44.602 164 14.53 40Ar/39Ar 

92 70AMm158B Kd Solomon D-1 Darby pluton 64 45.2 162 25.2 K-Ar 

93 70AMm158B Kd Solomon D-1 Darby pluton 64 45.2 162 25.2 K-Ar 

94 70AMm415A Kd Solomon D-1 Darby pluton 64 57 162 20 K-Ar 

95 70AMm45 Kkg Solomon D-2 Kachauik pluton, summit of Mt. Kachauik 64 45.878 162 51.878 K-Ar 

96 85ATi43 Kgu Solomon D-2 1/3 mile northwest Mt. Arathlatuluk 64 49.467 162 33.833 K-Ar 

97 70AMm218 Kdc (overlay) Solomon D-2 Dry Canyon stock, Darby Mountains 64 53.58 162 42.556 K-Ar 

98 04RN318A DOx Solomon D-4 Hill slope 1.7 miles north of where Goldbottom 

Creek flows into Niukluk River

64 57.676 163 56.412 40Ar/39Ar 

99 04RN355C Dcs Solomon D-5 Coal Creek, 0.8 miles downstream from Rock 

Creek

64 45.113 164 15.866 40Ar/39Ar 

100 83MS 92 Ocs Solomon D-6 4.2 miles northeast of Salmon Lake 64 57.1 164 50.8 K-Ar 

101 83MS 132 Ocs Solomon D-6 4.8 miles northeast of Salmon Lake 64 57.8 164 50.6 K-Ar 

102 61ATg40 Ksy Candle C-6 Western Candle quadrangle 65 41 161 31 K-Ar 

103 - Ksy Candle B-4 Granite Mountain 65 25.7 161 13 K-Ar 
51

ages determined prior to 1976 have been recalculated and noted in the Remarks column to reflect recommended 1976 IUGS constants using 

Mineral

Age

(Ma)

Error

(Ma) Rock type Reference Remarks

Biotite 71.1 2 Granite Hudson, 1979 Age recalculated with 1976 constants; author's reported age 69.4 

± 2 Ma; latitude and longitude not reported; location of sample is 

approximate

Hornblende 99.3 3 Monzonite Miller and others, 1972 Age recalculated with 1976 constants; authors' reported age 97.5 

± 3 Ma

Biotite 96.2 3 Nepheline syenite 

dike

Miller and others, 1972 Age recalculated with 1976 constants; authors' reported age 93.9 

± 3.0 Ma; sample is from an outcrop of a nepheline syenite dike 

in Kkg that is too small to show at map scale

White mica 109.1 0.7 Quartz-muscovite 

schist

Ford and Snee, 1996 Age given is the authors' reported plateau age; sample is from 

drill core that is in Ddm at the surface

White mica 109.6 0.2 Quartz-muscovite 

schist

Ford and Snee, 1996 Age given is the authors' reported plateau age; sample is from 

drill core that is in Ddm at the surface

White mica 109.1 0.2 Auriferous veins Ford and Snee, 1996 Age given is the authors' reported plateau age; sample is from 

drill core that is in DOx at the surface

White mica 117.7 1 Quartz-plagioclaseankerite-white 

mica vein/breccia

Layer and Newberry, 2004 Age given is the authors' reported plateau age; location given in 

Werdon and others, 2005c

Biotite 107.2 0.6 Alkalic dike Layer and Newberry, 2004 Age given is the authors' reported plateau age; location given in 

Werdon and others, 2005c

White mica 107.5 0.7 Quartz-white mica 

vein

Layer and Newberry, 2004 Age given is the authors' reported plateau age; location given in 

Werdon and others, 2005c

Biotite 83.9 0.3 Mafic dike Layer and Newberry, 2004 Age given is the authors' reported plateau age; authors' reported 

comments: unrelated to mineralization; location given by M. 

Werdon, written commun., 2008

White mica 112.8 0.3 Vein Layer and Newberry, 2004 Age given is the authors' reported plateau age; location given by 

Werdon, M., written commun., 2008

White mica 107.7 0.6 Quartz-ankeritewhite mica-plagioclase veinLayer and Newberry, 2004 Age given is the authors' reported plateau age; location given in 

Werdon and others, 2005c

Biotite 90.5 1.5 Quartz monzonite Miller and others, 1972 Age recalculated with 1976 constants; authors' reported age 88.3 

± 1.5 Ma

Hornblende 94.6 2.7 Quartz monzonite Miller and others, 1972 Age recalculated with 1976 constants; authors' reported age 92.8 

± 2.6 Ma

Biotite 96.4 3 Quartz monzonite Miller and Bunker, 1976 Age recalculated with 1976 constants; authors' reported age 94.0 

± 3 Ma

Hornblende 88.2 3 Quartz monzonite Miller and Bunker, 1976 Age recalculated with 1976 constants; authors' reported age 86.1 

± 3 Ma

Biotite 102.6 1.4 Granite Till, A., unpub. data Collector's comments: biotite granite that contains sillimanite and 

garnet along with biotite

Hornblende 108 3 Foyaite Miller, 1972 Age recalculated with 1976 constants; author's reported age 105 

± 3 Ma; authors' reported latitude and longitude 64° 53' N and 

162° 42' W

Amphibole 138.6 1 Vein Layer and Newberry, 2005 Age given is the authors' reported plateau age; location given by 

Werdon, M., written commun., 2008

White mica 106.5 0.8 Quartz-plagioclasewhite mica veinLayer and Newberry, 2005 Age given is the authors' reported plateau age; location given in 

Werdon and others, 2005c

Muscovite 156.4 4.7 Albitic schist Sturnick, 1984 Location based on author's table 1

Muscovite 152.2 4.6 Albitic schist Sturnick, 1984 Location based on author's table 1

Hornblende 105 5 Quartz monzonite Patton, 1967 Age recalculated with 1976 constants; author's reported age 102 

± 5 Ma; author's reported latitude and longitude of 65° 41 and 

161° 31' is assumed to be an approximate location

Hornblende 108.6 3 Monzonite Miller, 1972 Age recalculated with 1976 constants; author's reported age 106 

± 3 Ma; authors' reported latitude and longitude 65° 27' N and 

161° 13' W is assumed to be approximate location
52

Table 3. Selected U-Pb zircon analyses. (table spans facing page)

[- not reported. See “Remarks” column for details on units within brackets; latitude and longitude given are in North American Datum 1927;

Microprobe and TIMS—Thermal Ionization Mass Spectrometry]

Map

no.

Field

number Regional belt or assemblage

Geologic

unit Quadrangle Locality

Lat (N) Long (W)

Deg Min Deg Min 

1 SP90-6 High-grade metamorphic and associated igneous rocks

|<h Teller A-1 Kigluaik foliated syenite 65 0.251 165 18.991 

2 03JT23 York terrane |gb [O<t] Teller C-5 York Mountains 65 34.323 167 26.327 

3 05ATi10A Nome Complex <n Nome C-1 Basin Creek 64 40.399 165 14.073 

4 87SB65-5 Nome Complex <n Nome D-1 Salmon Lake 64 54.41 165 6.4 

5 89SB69-1 High-grade metamorphic and associated igneous rocks

<o Nome D-1 Thompson Creek 64 56.816 165 15.433 

6 - High-grade metamorphic and associated igneous rocks

<o Nome D-1 Thompson Creek 64 56.816 165 15.433 

7 APK92-19 Nome Complex <n Nome D-1 Dorothy Creek 64 48.512 165 16.639 

8 92.4A-119 Mesozoic and Cenozoic igneous rocks Kdi Nome D-2 Kigluaik granodiorite 64 57.233 165 46.433 

9 92.4A-120 Mesozoic and Cenozoic igneous rocks Kdi Nome D-2 Kigluaik granodiorite 64 56.15 165 48.083 

10 05D2-R28a Nome Complex Dg [DOx] Bendeleben A-1 Small body near north end of 

Darby pluton

65 1.719 162 21.059 

11 84Age79 Nome Complex Kwc Bendeleben A-2 Windy Creek pluton 65 8.712 162 34.8 

12 04MBW-935a High-grade metamorphic and associated igneous rocks

<v Bendeleben A-4 Bendeleben Mountains 65 7.933 163 56.986 

13 04MBW-935a High-grade metamorphic and associated igneous rocks

<v Bendeleben A-4 Southern Bendeleben 65 7.933 163 56.986 

14 - Mesozoic and Cenozoic igneous rocks Kp Bendeleben A-4 Pargon pluton 65 11.373 163 41.243 

15 03SP-15 Nome Complex <n Bendeleben A-6 Small body north of Kigluaik 

Mountains

65 7.92 164 49.799 

16 05ATi8A Nome Complex Df Bendeleben B-1 Near Kiwalik Mountain 65 28.183 162 17.617 

17 - Mesozoic and Cenozoic igneous rocks Kbk [|<h] Bendeleben B-2 Bendeleben pluton 65 14.92 163 8.46 

18 81ATi159 Nome Complex Dg Bendeleben C-1 Kiwalik Mountain 65 30.05 162 11.55 

19 84AGe164 Kugruk fault zone Jt Bendeleben C-4 Spruce Creek 65 31.342 162 36.139 

- High-grade metamorphic and associated igneous rocks

|<h - Bendeleben Mountains - - - - 

20 APK92-1 Nome Complex <n Solomon B-6 Cape Nome 64 26.325 164 59.886 

21 RA-AK-05-

11

Nome Complex <n Solomon B-6 Cape Nome 64 26.325 164 59.886 

22 85ATi118 High-grade metamorphic and associated igneous rocks

Kd Solomon D-1 Darby pluton 64 48.222 162 27.6 

23 85ATi43 High-grade metamorphic and associated igneous rocks

Kgu Solomon D-2 Mount Arathlatuluk 64 49.476 162 33.6 
53

localities are plotted on sheet 2; scale of map precludes labeling of all locality names; in the Remarks column, SHRIMP—Sensitive High-Resolution Ion 

Mineral

dated

Interpreted

age

(Ma)

Interpreted

age error

(Ma) 2-sigma Rock type Reference Remarks

Zircon 110 5 Metasyenite Amato and Wright, 1998 Analysis by W. McClelland; Location approximated 

from fig. 2, on sh. 2 in Amato and Wright, 1998

Zircon 541 6 Gabbro Amato and others, 2006 Location provided by collector; Sample is from a 

|gb outcrop that is too small to show at map scale

Zircon 669 5 Orthogneiss Till and others, 2006 Latitude and longitude based on 05ATi10(A-D)

Zircon 678 4 Felsic orthogneiss Amato and Wright, 1998 Age analysis by TIMS

Zircon 555 15 Orthogneiss Amato and Wright, 1998 Age analysis by TIMS

Zircon 565 6 Orthogneiss Amato, 2004 Author reports 565 ± 6 Ma is the average of three 

206Pb/238U ages; Age analysis by SHRIMP

Zircon 681 3 Orthogneiss Patrick and McClelland, 1995 Location approximated from a map in Patrick and 

McClelland, 1995

Zircon 89 1 Hornblende biotite 

granodiorite

Amato and Wright, 1998 Age analysis by TIMS; Location provided by 

authors

Zircon 91 1 Hornblende biotite 

granodiorite

Amato and Wright, 1998 Age analysis by TIMS; Location provided by 

authors

Zircon 390 3 Orthogneiss Jeff Amato, written comm. 2008 Age analysis by SHRIMP; Location provided by 

collector; Sample is from a small body of Dg that is 

too small to show at map scale

Zircon 96.5 0.2 Quartz monzonite Richard Friedman, written comm., 2009 Age analysis by TIMS

Zircon 870 6 Metarhyolite Gottlieb and Amato, 2007 Authors' written comm. 2008: rock type is metarhyolite; Age analysis by SHRIMP

Monazite 86 1 Metarhyolite Gottlieb and Amato, 2007 Authors' reported comments: cooling age and rock 

type is metarhyolite; Age analysis by SHRIMP

Zircon 86 1 Granite Gottlieb and Amato, 2008 Approximate location; Age analysis by SHRIMP

Zircon 687 9 Orthogneiss Jeff Amato, written comm. 2008 Age analysis by SHRIMP

Zircon 392 5 Metafelsite Till and others, 2006 Latitude and longitude based on 05ATi8(A-D)

Zircon 104 1 Foliated biotite 

granite

Gottlieb and Amato, 2008 Age analysis by SHRIMP; sample is from margin of 

Bendeleben pluton as mapped by collector

Zircon 391 3 Granitic orthogneissTill and others, 2006 Location is the same as 05ATi7

Zircon 163 3 Tonalite John Aleinikoff, written comm., 1986 –

Zircon 390 - Foliated biotite 

granite

Gottlieb and Amato, 2008 Sample location not given; Age analysis by 

SHRIMP

Zircon 676 15 Orthogneiss Patrick and McClelland, 1995 Location approximated from figure 2 in Patrick and 

McClelland, 1995

Zircon 669 5 Orthogneiss John Aleinikoff, written comm., 2005 –

Zircon 100.1 0.1 Monzogranite Richard Friedman, written comm., 2009 Age analysis by TIMS

Zircon 107.8 0.2 Granite Richard Friedman, written comm., 2009 Age analysis by TIMS
54

Appendix

Conodont Data from the Seward

Peninsula

By Julie A. Dumoulin, Anita G. Harris, and

John E. Repetski

Introduction

Numerous conodont collections were made, mainly during 

the 1980’s, to support geologic mapping on the Seward Peninsula. In this section we present table A–1, which lists virtually 

all conodont collections from this area that were examined by 

paleontologists of the U.S. Geological Survey as well as a few 

additional collections from unpublished industry reports. The 

table provides the location, age, geologic unit, and thermal level 

of these collections, as well as the sample collector and identifier (ID) and some explanatory remarks.

Sources of Data

Table A–1 contains 194 entries encompassing 234 collections. Most entries consist of a single collection, but some 

include two or more collections from the same location (typically, a measured section) that have identical ages and thermal 

levels. Fewer than half of the entries in this table have been 

previously published. Citations for published collections, 

mostly from the Bendeleben and Solomon quadrangles, are 

given in the remarks column. Cited references generally present 

faunal lists for the collections they include and may also contain 

more detailed age and (or) biofacies information than is given 

here. Transcriptions of original fossil reports (including faunal 

lists) for about half of the collections in table A–1 can be found 

online in the Alaska Paleontological Database at http://www.

alaskafossil.org. The remarks column in table A–1 contains 

a note for all samples that were found in this database as of 

09/10/07; the database is not yet complete, however, and more 

collections from the Seward Peninsula may be added later.

Conodont data are organized by quadrangle, listed from 

northwest (Teller) to southeast (Norton Bay). Sample locations 

are based on latitudes and longitudes supplied by the collector. 

Most samples were collected prior to common usage of GPS 

units by field geologists; thus, accuracies of these locations 

cannot be quantified. Most locations were verified using original field maps and (or) notes of the geologists who collected 

them. In some cases, latitudes and longitudes from the original 

database and (or) published references were corrected to reflect 

locations documented on the field maps.

The collectors’ original field numbers are given for all 

samples. Some collections, mainly those that are relatively 

age-diagnostic, also have a U.S. Geological Survey collection 

number; this is the number under which fossil collections are 

generally filed in the U.S. Geological Survey repository. An 

Examination and Report (E&R) shipment number is provided 

for most samples; for the samples listed in this appendix, this 

is the identifying number of the unpublished U.S. Geological 

Survey report in which the collection was first described. The 

E&R number includes the year in which the report was written; for example, E&R No. A-85-23B was written in 1985. It is 

important to note that the composition and age of most collections listed herein have not been reevaluated since they were 

originally analyzed; all samples that have been reexamined 

more recently are identified in the remarks column. Many E&R 

reports can be found in the Alaska Geology technical archives 

unit in the Alaska Science Center, Anchorage, Alaska.

U.S. Geological Survey geologists collected most of the 

samples listed in this table, but students or employees of academia or industry submitted half of the samples from the Teller 

quadrangle. Anita G. Harris (formerly Epstein) and John E. 

Repetski identified the majority of the collections, but Timothy 

R. Carr, then with Atlantic Richfield Company, identified several 

collections submitted by geologists from the Anaconda Minerals 

Company. We thank Dr. Carr and Travis Hudson for allowing us 

to include these previously unpublished data in our table.

The data table contains two fields for geologic unit represented by the collection, headed “Geologic unit (this map)” 

and “Geologic unit (source map).” Unit designation in the 

current map is given for all samples. Where this name appears 

in brackets, it indicates an outcrop of the unit in question is too 

small to show at the scale of the current map. The source map 

unit is taken from the cited reference for previously published 

faunas, or was provided by the collector for unpublished collections.

Color changes in conodonts reflect the thermal history of 

the rocks that contain them (Epstein and others, 1977). Harris, 

Repetski, and their co-workers determined the conodont color 

alteration index (CAI) for almost all the collections in the 

database. Temperature ranges for CAIs were established from 

plots of experimental data by Epstein and others (1977) and 

Rejebian and others (1987); a CAI of 1 indicates a temperature 

range of less than 50–80 °C, whereas a CAI of 6 indicates 

temperatures in excess of 360 °C (table A–2). CAI can be 

equated to burial depths for a given geothermal gradient; for 

example, in the Appalachian basin, overburdens of ~3,600–5,500 

m produced a CAI of 3 (Harris and others, 1978). Although there 

is a general correspondence between CAI and metamorphic 

history, CAI can be affected by multiple factors, some of which 

are not related to metamorphism. Some implications of CAIs 

of conodonts from the Seward Peninsula are discussed briefly 

below.

All samples listed herein were processed in order to obtain 

conodonts. In a few cases, the samples produced no conodonts 

but did yield other phosphatized or phosphatic fossils (such as 

lapworthellids) that provide age information. Such samples are 

noted in the remarks column.

Most collections in the database are stored at the U.S. Geological Survey in Reston, Virginia. However, faunas collected 

by geologists of Amoco Oil Corporation (a single sample in the 

Seward Peninsula database) are not part of the USGS collection but were examined by Anita Harris at the Amoco offices 

in Oklahoma during the 1980’s. Harris determined the age and 

CAI of the collections; Amoco provided sample locations.
55

Geologic Implications

Conodont data constrain the geologic, biogeographic, and 

thermal histories of the Seward Peninsula. A full discussion of 

these topics is beyond the scope of this text, but we highlight 

here some implications of the conodont collections, particularly 

those previously unpublished and (or) used to define the ages 

and affinities of the geologic units in the accompanying map.

Nome Complex and Kugruk Fault Zone

Most of the conodont data from the Nome Complex 

and Kugruk Fault Zone included here have been previously 

published and interpreted (Dumoulin and Till, 1985; Till and 

others, 1986; Till and Dumoulin, 1994; Harris and others, 1995; 

Dumoulin and others, 2002); highlights of these findings are 

summarized here. Conodonts constrain the age, biofacies, and 

thermal level of parts of the Nome Complex and of carbonate clasts in the conglomerate of unit TKs in the Kugruk Fault 

Zone.

Dolostones of the Nome Complex produced many more 

identifiable conodonts than did calcitic marbles and metalimestones (Till and others, 1986). This situation, which is the 

opposite of that found in unmetamorphosed carbonate rocks, 

introduced an unavoidable bias into our conodont collections. 

Conodont faunas from relatively pure carbonate strata that 

formed in shallow to very shallow water settings and were 

likely dolomitized during early diagenesis are over-represented 

in our database relative to their areal distribution within the 

Nome Complex. Nevertheless, conodonts have been obtained 

from a variety of lithofacies in the Nome Complex that formed 

in both shallow- and deep-water settings.

Shallow-water carbonate rocks of Cambrian through Devonian age, included in the Nome Complex by Till and others 

(1986), form small, discontinuous outcrops that are widely distributed across the central and eastern Seward Peninsula (units 

_d, Od, Sd, and Ddm). Conodonts from these units (table A–1) 

provide biofacies data that strengthen depositional interpretations based on sparse sedimentary features, as well as precise 

age determinations that allow detailed correlations with lower 

Paleozoic strata of the York terrane and the Central belt of the 

Brooks Range (Till and others, 2008b). Conodont faunas from 

units Od and Sd correlate especially well with faunas from 

York terrane units Oal, Ol, O<l, SOdl, and DSl. 

Deeper-water carbonate rocks of early Paleozoic age, also 

included in the Nome Complex (Till and others, 1986), crop out 

in the northeastern and southeastern parts of the Seward Peninsula (units DObm and D_bm, respectively). Conodonts constrain the ages of these two units (table A–1), and indicate that 

Silurian carbonate turbidites are a significant component of both.

Conodonts provide some age constraints for parts of 

the Nome Complex dominated by non-carbonate lithologies, 

although carbonate layers in these rocks are mainly impure calcitic marbles that yielded few fossils (see table 3 in Appendix B 

of Till and others, 1986). Unit Oim produced a single conodont 

assemblage of Early-Middle Ordovician age, and unit DOx produced several collections of early Paleozoic age (table A–1). An 

enigmatic single conodont of probable Triassic age from marble 

in the Nome quadrangle (table A–1; Till and others, 2006) 

may indicate the presence of a fault-bounded upper Paleozoic 

sequence within unit Dcs.

Conodont data also illuminate the thermal history of the 

Seward Peninsula. Conodont CAIs from the Nome Complex 

are mainly 5–6 (dominantly 5–5.5) and indicate that the rocks 

containing these conodonts reached temperatures of 300–360 °C 

or greater (tables A–1, A–2; sh. 2; Rejebian and others, 1987). 

Temperature estimates for CAIs are derived from an Arrhenius 

plot of experimental data (table A–2; Epstein and others, 1977; 

Rejebian and others, 1987); each CAI value denotes a range of 

temperatures. For a given CAI value (for example, 5), the lower 

temperature (300 °C) represents a longer heating duration (500 

million years) and the higher temperature (480 °C) corresponds 

to a shorter heating time (1 million years). Peak temperatures 

experienced by conodont-bearing rocks of the Nome Complex 

were likely closer to the high end of the CAI thermal range, 

because these temperatures were produced by blueschist and 

(or) greenschist metamorphic events that were, geologically 

speaking, relatively short-lived. This interpretation is supported 

by calcite-dolomite thermometry of Nome Complex samples, 

which indicates temperatures of 425–480 °C (Patrick and 

others, 1985).

Twenty percent of Nome Complex conodont assemblages 

include specimens with CAIs as high as 6.5, 7, and 8. These 

higher values generally occur in collections that contain a range 

of CAIs, and are commonest in units Od and, most notably, 

DObm, where values greater than or equal to 7 occur in almost 

two thirds of the collections. Saline and (or) corrosive fluids 

involved in episodes of dolomitization or mineralization can 

produce anomalously high CAIs (Till and others, 1986; Rejebian and others, 1987). Textural studies of conodonts with high 

CAIs and the rocks that contain them suggest that most of the 

highest CAIs in the Nome Complex reflect hydrothermal alteration related to dolomitization and (or) faulting.

Numerous conodonts obtained from conglomerate clasts in 

unit TKs in the Kugruk Fault Zone suggest that these cobbles 

were derived largely from carbonate rocks of the Nome Complex. Age, biofacies, and thermal level of the carbonate clasts 

correlate particularly well with those of units Sd and Ddm. The 

abundance of carbonate clasts in unit TKs conglomerate that 

contain conodonts of Silurian age and shallow-water biofacies 

implies that such rocks once were more widely distributed on 

the Seward Peninsula.

York Terrane and Grantley Harbor Fault Zone

Most conodont data from the York terrane and Grantley 

Harbor Fault Zone included here have not been previously 

published, although preliminary summaries of some of these 

data are found in Dumoulin and Harris (1994), Till and Dumoulin (1994), Harris and others (1995), and Dumoulin and others 

(2002). Ordovician and Silurian strata of the York terrane previously were relatively well dated by megafossils (for example, 

Sainsbury 1969a, 1969b, 1972 and references therein), but 

conodonts provide tighter ages for much of this stratigraphy, 

particularly Early Ordovician rocks that contain few megafossils (units Oal, Ol). Conodonts also indicate that several units 
56

considered Precambrian by Sainsbury (1972) are at least partly 

of Ordovician age (such as rocks included in units O<l and O<t

of this map). Questions that might profitably be addressed in the 

future using detailed conodont sampling include the age range 

and geographic distribution of Ordovician strata within composite units such as O<l and O<t, and the amount of age overlap 

between units Oal and Ol.

Most rock units in the Grantley Harbor Fault Zone that 

were sampled for conodonts were barren. However, unit Pzp

produced a few fragmentary conodonts that indicate an Ordovician-Triassic age (table A–1; T. Carr and T. Hudson, written 

commun., 1982, 1984).

Conodonts contribute greatly to our understanding of 

the paleobiogeography of the York terrane. Conodont assemblages from several units, most notably Ol and SOdl, include 

both Siberian and Laurentian (North American) endemic 

forms, a pattern that is also seen in megafaunas from these 

rocks (Dumoulin and Harris, 1994; Blodgett and others, 2002; 

Dumoulin and others, 2002). Similar mixed biogeographic 

affinities characterize conodonts in unit Od of the Nome Complex, the Baird Group and related rocks in the Central belt of 

the Brooks Range, and lower Paleozoic strata of the Farewell 

terrane in interior Alaska. These faunal correlations, along with 

detailed lithofacies matches between coeval strata in these successions, suggest that lower Paleozoic rocks on Seward Peninsula, in the Brooks Range, and in the Farewell terrane may once 

have been part of a single continental fragment situated between 

Siberia and Laurentia (Dumoulin and others, 2002).

Conodont CAIs from the York terrane generally are lower 

than those from the Nome Complex and define three thermal 

provinces (table A–1; sh. 2). The first province consists of outcrops of units Oal, Ol, and Ols between lat 65°23.9’ and 65°33’ 

N. and long 167°14’ and 167°23’ W. (Teller B–5 and C–5 quadrangles) that have CAIs mainly of 2–2.5. These values indicate 

temperatures of 60–150 °C (table A–2) and demonstrate that 

these York terrane rocks are still within the oil window; a CAI 

of 3, denoting temperatures of 120–190 °C, approximates 

the thermal limit of oil preservation (Bird and others, 1999). 

The second province contains rocks with slightly higher CAIs 

(3–3.5); these rocks are located in the Don River area (Teller 

B–4 quadrangle), and consist mainly of unit SOdl. CAIs 

elsewhere in the York terrane are mostly 4–4.5 and delineate a 

third province; these values are found in units Oal, Ol, and Ols

where they occur outside of the first province, as well as unit 

DSl and much of unit O<l.

Higher CAIs of 5–6, equivalent to those found in the Nome 

Complex, occur in a few conodont assemblages from the York 

terrane (table A–1). Some higher values likely reflect contact 

metamorphic effects associated with intrusion of Cretaceous 

dikes and plutons (for example, a few outcrops of units Oal

and Ol in the Teller B–5 and C–5 quadrangles; Toro and others, 

written commun., 2006). Other high CAIs occur near the western edge of the York terrane (unit SOul in the Teller C–2 quadrangle). Lastly, CAIs greater than or equal to 5 characterize all 

three conodont assemblages obtained from unit O<t and several 

assemblages from unit O<l. Recrystallization and schistose to 

semi-schistose fabrics characterize most of unit O<t and parts of 

unit O<l; these rocks may be part of a more deformed and (or) 

mildly metamorphosed structural plate that underlies parts of 

the York terrane (Toro and others, 2006).

As outlined above, CAIs from the York terrane are not 

simply correlated with unit age—that is, older rocks do not have 

consistently higher CAIs than younger rocks. Thus, these CAIs 

were most likely not produced by simple burial metamorphism. 

Instead, York terrane thermal data may reflect tectonic burial by 

thrust sheets, as has been proposed to explain CAI patterns in 

the western Brooks Range (Harris and others, 1987). Additional 

conodont sampling, in concert with detailed structural studies, 

could help define the composition and extent of discrete thrust 

sheets within the York terrane.
57
58

Table A–1. Conodont data from the Seward Peninsula. (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

AS-001 Teller A-3 65 14.37 166 18.54 Ordovician-Triassic |p p_s 

AS-031 Teller B-2 65 19.96 165 47.57 early Paleozoic DOx p_nl 

07AD11A Teller B-3 65 21.49 166 24.72 middle Early Ordovician ("Low Diversity Interval") O<l p_l 

AS-004 through -007 Teller B-3 65 22.45 166 27.54 Early-early Middle Ordovician O<l p_l 

85AKn12 Teller B-4 65 24 166 35.8 latest Early Ordovician-earliest Middle Ordovician 

(Reutterodus andinus Zone to Tripodus laevis Zone)

Ol Ol 

6-30-85D, C Teller B-4 65 25.9 166 34.2 middle Early Ordovician (Macerodus dianae Zone

to Acodus deltatus-Oneotodus costatus Zone)

Ol Ol 

7-21-84C-F Teller B-4 65 29.68 166 55.34 Late Ordovician SOdl SOdl 

7-21-84G Teller B-4 65 29.68 166 55.34 Late Ordovician SOdl SOdl 

7-21-84H Teller B-4 65 29.68 166 55.34 latest Ordovician (Gamachian)-early Silurian (age 

constrained by overlying samples)

SOdl SOdl 

7-21-84I-K Teller B-4 65 29.68 166 55.34 Very probably early Silurian SOdl SOdl or Sl 

7-22-84A Teller B-4 65 29.68 166 55.34 early Silurian (earliest Llandovery-Llandovery C5) SOdl SOdl or Sl 

7-22-84B, C, E, F Teller B-4 65 29.91 166 55.75 early late Silurian (Ludlow) SOdl Sl 

7-22-84G Teller B-4 65 29.91 166 55.75 early late Silurian (Ludlow, probably early Ludlow) SOdl Sl 

7-22-84H-J Teller B-4 65 29.91 166 55.75 early late Silurian (Ludlow)-Middle Devonian SOdl Sl 

68ADu27 Teller B-4 65 29.8 166 56 middle-early late Silurian (latest Wenlock-early 

Ludlow)

SOdl Sl 

68ADu19, 25 Teller B-4 65 29.8 166 56 middle Silurian (late Wenlock); age constrained by 

co-occurring and (or) overlying megafossils

SOdl Sl 

68ADu18 Teller B-4 65 29.8 166 56 Late Ordovician; age constrained by underlying 

samples

SOdl SOdl 

7-21-84A Teller B-4 65 29.85 166 55.88 early Silurian SOdl Sl 

7-21-84B Teller B-4 65 29.85 166 55.88 probably early Silurian SOdl Sl 

03JT25 Teller B-5 65 23.9 167 16.75 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Oal Oal 

7-23-84A-H, K Teller B-5 65 24.5 167 17.6 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Oal Oal 

7-3-85I Teller B-5 65 24.3 167 0.8 Early Ordovician (Rossodus manitouensis Zone to 

Macerodus dianae Zone)

Ol Ol 

03JT26 Teller B-5 65 24.74 167 16.7 Early (but not earliest) Ordovician; Rossodus manitouensis Zone or younger

Oal Oal 
59

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

5 5 – – Anaconda Carr Sample collected by Anaconda Minerals Co. from graphitic shale; location 

approximate. Conodonts identified by T. Carr, Atlantic Richfield Co., 1982, 1984.

7 7 – – Anaconda Carr Sample collected by Anaconda Minerals Co.; location approximate. Conodonts 

identified by T. Carr, Atlantic Richfield Co., 1982, 1984.

4-4.5 4.5 12111-CO – Dumoulin Harris, Repetski Sample re-examined by J.E. Repetski, 8/10.

5 5 – – Anaconda Carr Samples (4) collected by Anaconda Minerals Co.; location approximate. 

Conodonts identified by T. Carr, Atlantic Richfield Co., 1982, 1984.

3.5 4 10018-CO A-85-23A Kaufman Harris Entry in Alaska Paleontological Database.

4 4 10215-CO, 

10216-CO

A-85-23F Harris Harris, Repetski Samples re-examined by J.E. Repetski, 2/08. Entries in Alaska Paleontological 

Database.

3.5 3.5 10241-CO 

through 

10244-CO

A-85-23H Harris Harris Age revised by A.G. Harris in 1995. Entries in Alaska Paleontological Database. 

All 4 samples are from measured section 84ADn118 near the Don River. Section 

started at lat/long given here, and ended at lat/long given for samples 7-22-84B 

through J. Precise locations were not determined for each sample.

3 3 10245-CO A-85-23H Harris Harris Age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. 

Sample from measured section 84ADn118 near the Don River.

3 3 – A-85-23H Harris Harris Entry in Alaska Paleontological Database. Sample from measured section 

84ADn118 near the Don River.

3 3 11242-SD 

through 

11244-SD

A-85-23H Harris Harris Entries in Alaska Paleontological Database. All 3 samples from measured section 

84ADn118 near the Don River.

3 3 11245-SD A-85-23H Harris Harris Entry in Alaska Paleontological Database. Sample from measured section 

84ADn118 near the Don River.

3 3 11246-SD 

through 

11249-SD

A-85-23H Harris Harris Entries in Alaska Paleontological Database. All 4 samples from measured section 

84ADn118 near the Don River.

3 3 11250-SD A-85-23H Harris Harris Entry in Alaska Paleontological Database. Sample from measured section 

84ADn118 near the Don River.

3 3 11251-SD 

through 

11253-SD

A-85-23H Harris Harris Entries in Alaska Paleontological Database. All 3 samples from measured section 

84ADn118 near the Don River.

3 3 8345-SD A-84-14 Dutro Harris Entry in Alaska Paleontological Database. From measured section near the Don 

River.

3 3 8337-SD, 

8343-SD

A-84-14 Dutro Harris Entries in Alaska Paleontological Database. From measured section near the Don 

River.

3 3 D2036-CO A-84-14 Dutro Harris Entry in Alaska Paleontological Database. From measured section near the Don 

River.

3 3 11254-SD A-85-23H Harris Harris Entry in Alaska Paleontological Database.

3 3 11255-SD A-85-23H Harris Harris Entry in Alaska Paleontological Database.

2.5 2.5 11971-CO – Toro Repetski Sample from massive micritic limestone.

4 4 10231-CO 

through 

10239-CO

A-85-23G Harris Repetski Samples re-examined by J.E. Repetski, 2/08. Entries in Alaska Paleontological 

Database. All 9 samples are from a measured section along Koteebue Creek.

4 4 10230-SD A-85-23F Harris Harris, Repetski Sample re-examined by J.E. Repetski, 2/08. Entry in Alaska Paleontological 

Database.

2.5 3 11972-CO – Toro Repetski Sample from brown-gray, massive, medium-bedded micritic liimestone.
60

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

7-3-85D-G, C-A Teller B-5 65 25.1 167 1.5 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

03JT27 Teller B-5 65 25.24 167 16.42 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Oal Oal 

03JT28 Teller B-5 65 25.37 167 17.24 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Ol Ol 

02JT14 Teller B-5 65 26.84 167 18.97 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Ol Ol 

02JT13 Teller B-5 65 26.92 167 19.41 middle Early Ordovician (Macerodus dianae Zone) Ol Ol 

02JT16 Teller B-5 65 27.03 167 18.15 probably Ordovician Oal Oal 

02JT12 Teller B-5 65 27.09 167 19.77 Early Ordovician (most likely Macerodus dianae

Zone or younger Ibexian)

Ol Ol 

02JT11 Teller B-5 65 27.24 167 20.03 middle Early Ordovician (Acodus deltatus-Oneotodus costatus Zone)

Ol Ol 

02JT17 Teller B-5 65 27.39 167 18.31 early Early Ordovician (Rossodus manitouensis

Zone)

Oal Oal 

03JT06 Teller B-5 65 29.29 167 16.01 Early Ordovician; most likely M. dianae or A. 

deltatus-O. costatus Zone.

Oal Oal 

7-1-85J, H Teller B-5 65 29.6 167 4.5 earliest Middle Ordovician (latest Arenig-early 

Llanvirn)

Ols Oshl, Olsh 

(69b)

03JT10 Teller B-5 65 30 167 17.21 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Ol Ol 

85ATi116B Teller B-6 65 28.2 167 36.8 middle Early-Late Ordovician O<t p_s 

85ADn24A Teller C-1 65 32.3 165 20.6 late Silurian-Early Devonian DOx (overlay 

pattern)

DOx 

85ADn25A Teller C-1 65 33.1 165 23.64 Silurian (late Llandovery-Ludlow) DOx (overlay 

pattern)

DOx 

85ADn20B Teller C-1 65 39.9 165 29.7 late Silurian-Devonian DOx (overlay 

pattern)

DOx 

7-8-85A Teller C-2 65 33 165 57.7 Silurian (probably late Llandovery-Wenlock); age 

constrained by co-occurring corals

SOul Oum 

82AH105 Teller C-2 65 36.62 165 53.86 middle Early Ordovician O<l p_l 

7-20-84A Teller C-2 65 38.4 165 55.3 middle Early Ordovician (Rossodus manitouensis

Zone to "Low Diversity Interval")

O<l p_l 

AS-14 Teller C-3 65 31.95 166 3.72 Cambrian-Triassic O<l Op_l 

7-20-84C Teller C-3 65 33.2 166 8.3 Early Ordovician (early to middle Arenig) O<l Op_l 

7-8-85C Teller C-3 65 33.8 166 19.5 early-middle Early Ordovician (Rossodus manitouensis Zone to Macerodus dianae Zone)

O<l Op_l 

7-20-84B Teller C-3 65 33.9 166 8.2 Early-Middle Ordovician O<l Op_l 

7-20-84E, F Teller C-3 65 34.2 166 9.5 Silurian (Llandovery-middle Wenlock); age constrained by adjacent collections

DSl Dl 
61

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

4 4 10223-CO 

through 

10229-CO

A-85-23F Harris Harris, Repetski Samples re-examined by J.E. Repetski, 2/08. Entries in Alaska Paleontological 

Database. All 7 samples are from a measured section between the Don and Lost 

Rivers.

2.5 2.5 11973-CO – Toro Repetski Sample from thin-bedded, platy, argillaceous limestone with trace fossils.

2.5 2.5 11974-CO – Toro Repetski Sample from thick-bedded gray limestone with discontinuous partings.

2 2.5 11959-CO – Toro Repetski Sample from thin-bedded gray limestone.

2 2 11958-CO – Toro Repetski Sample from thin-bedded gray limestone.

~6.5 ~6.5 11960-CO – Toro Repetski Sample from thin-bedded, tan-weathering limestone.

2 2 11957-CO – Toro Repetski Sample from thick-bedded gray-brown limestone.

2 2 11956-CO – Toro Repetski Sample from thin-bedded gray limestone.

5 5.5 11961-CO – Toro Repetski Sample from thin-bedded, orange-weathering limestone.

2 2.5 11964-CO – Toro Repetski Sample from brownish-red micritic limestone.

4 4 10221-CO, 

10222-CO

A-85-23F Harris Harris, Repetski Age revised by A.G. Harris in 1995. Entries in Alaska Paleontological Database. 

Trilobites on strike with higher sample are of Llanvirn age (Ross, 1965; Sainsbury, 1969b).

2 2.5 11966-CO – Toro Repetski Sample from medium- to thick-bedded gray micritic limestone.

5.5 5.5 10212-CO A-85-23D Dumoulin, 

Till

Harris –

5.5 5.5 11306-SD A-85-23J Dumoulin Harris Entry in Alaska Paleontological Database.

6 7 11399-SD A-85-23K Dumoulin Harris Age revised by A.G. Harris in 1994.

5 5.5 11231-SD A-85-23E Dumoulin Harris –

5 5 10979-SD A-85-23E Harris Harris –

4 4 – – Anaconda Carr Sample collected by Anaconda Minerals Co.; location approximate. Conodonts 

identified by T. Carr, Atlantic Richfield Co., 1982.

4.5 4.5 9917-CO A-85-10 Harris Repetski Sample re-examined by J.E. Repetski, 2/08. Entry in Alaska Paleontological 

Database.

6 6 – – Anaconda Carr Sample collected by Anaconda Minerals Co.; location approximate. Conodonts 

identified by T. Carr, Atlantic Richfield Co., 1982.

4 4 10587-CO A-87-9 Harris Harris –

4 4.5 10214-CO A-85-23E Harris Harris –

4 4 10586-CO A-87-9 Harris Harris –

4 4 11534-SD, 

11535-SD

A-87-8A Harris Harris –
62

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

7-20-84G, H Teller C-3 65 34.4 166 9.2 Silurian (Llandovery-middle Wenlock); age constrained by adjacent collections

DSl Dl 

7-20-84I Teller C-3 65 34.4 166 9.2 middle Silurian (middle Wenlock) DSl Dl 

07AD9Z Teller C-3 65 34.62 166 20.33 middle Early Ordovician ("Low Diversity Interval") O<l Ol 

07AD10A Teller C-3 65 34.69 166 20.4 middle Early Ordovician ("Low Diversity Interval") O<l Ol 

7-22-84K Teller C-4 65 30.1 166 55.2 Middle Ordovician-Silurian Ol? Ol? 

7-22-84L Teller C-4 65 31.3 166 54.2 Middle-Late Ordovician Ol? Ol? 

03JT12 Teller C-5 65 30.59 167 18.87 Late Cambrian through early Paleozoic Ol Ol 

7-5-85A Teller C-5 65 30.6 167 20.1 Middle Ordovician Ols Oshl, Olsh 

(69b)

7-5-85B, C Teller C-5 65 30.6 167 20.1 middle Early-earliest Middle Ordovician Ols Oshl, Olsh 

(69b)

7-5-85D, E Teller C-5 65 30.6 167 20.1 earliest Middle Ordovician (latest Arenig) Ols Olsh 

93BK44 Teller C-5 65 30.67 167 19.79 late Early Ordovician (middle Arenig; lower Oe. 

communis Zone)

Ol Ol (at/near 

top of unit)

93BK46 Teller C-5 65 30.7 167 20.59 late Early to early Middle Ordovician (middle-late 

Arenig)

Ols Olsh (69b) 

7-5-85H Teller C-5 65 30.75 167 22 middle Early Ordovician ("Low Diversity Interval" 

to lower Macerodus dianae Zone)

Ol Ol 

7-5-85I Teller C-5 65 30.75 167 22 probably middle Early Ordovician (early middle 

Arenig)

Ol Ol 

7-5-85F Teller C-5 65 30.75 167 22 middle Early Ordovician (early middle Arenig) Ol Ol 

03JT11 Teller C-5 65 30.78 167 18.48 middle Early Ordovician (Macerodus dianae or A. 

deltatus-O. costatus Zone)

Ol Ol 

02JT33 Teller C-5 65 30.87 167 14.61 middle Early Ordovician (Macerodus dianae Zone) Ol Ol 

93BK47 Teller C-5 65 31.1 167 21.52 middle Early Ordovician (Macerodus dianae Zone) Oal Oal 

93BK8 Teller C-5 65 31.05 167 19.2 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

03JT07 Teller C-5 65 30.69 167 13.69 probably Middle-Late Ordovician [Ols] Olsh (69b) 

93BK39 Teller C-5 65 31.53 167 22.57 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK9 Teller C-5 65 31.7 167 19.09 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK10 Teller C-5 65 31.7 167 18.71 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK22 Teller C-5 65 31.7 167 19.13 middle Early Ordovician (Macerodus dianae Zone to 

lowest Acodus deltatus-Oneotodus costatus Zone)

Ol Ol 
63

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

4 4 11536-SD, 

11537-SD

A-87-8A Harris Harris –

4 4 11538-SD A-87-8A Harris Harris –

4 4.5 12109-CO – Dumoulin Harris, Repetski These rocks mapped as small, fault-bounded area of Ol by Sainsbury (1972). 

Age and lithofacies most like those of unit Oal, however. Sample re-examined 

by J.E. Repetski, 8/10.

4 4.5 12110-CO – Dumoulin Harris, Repetski These rocks mapped as small, fault-bounded area of Ol by Sainsbury (1972). 

Age and lithofacies most like those of unit Oal, however. Sample re-examined 

by J.E. Repetski, 8/10.

3 4 – A-87-9 Harris Harris These rocks mapped by Sainsbury (1969a) as Ol, but lithofacies and conodonts 

more like those of unit SOdl.

3 3.5 10588-CO A-87-9 Harris Harris These rocks mapped by Sainsbury (1969a) as Ol, but lithofacies and conodonts 

more like those of unit SOdl.

~5.0 ~5.0 11968-CO – Toro Repetski –

2 2 10203-CO A-85-23B Harris Harris From measured section near the Mint River. USGS no. was incorrect in original 

E&R.

2 2 10204-CO, 

10205-CO

A-85-23B Harris Harris From measured section near the Mint River. USGS no. was incorrect in original 

E&R.

2 2 10206-CO, 

10207-CO

A-85-23B Harris Harris From measured section near the Mint River. USGS no. was incorrect in original 

E&R.

2 2.5 11160-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by Repetski, 2/08.

2 2 11161-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by Repetski, 2/08.

2 2 10208-CO A-85-23B Harris Harris Sample re-examined by J.E. Repetski, 6/09. From measured section near the 

Mint River. USGS no. was incorrect in original E&R.

2 2 10209-CO A-85-23B Harris Harris From measured section near the Mint River. USGS no. was incorrect in original 

E&R.

2 2 10210-CO A-85-23B Harris Harris From measured section near the Mint River. USGS no. was incorrect in original 

E&R.

2 2 11967-CO – Toro Repetski Sample from medium- to thick-bedded gray micritic limestone.

2 2 11962-CO – Toro Repetski Sample from fossiliferous gray limestone.

2 2.5 11162-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11149-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

N.D. N.D. 11965-CO – Toro Repetski Sample from brown, smooth, dolomitic limestone. Fauna consists of numerous, 

mostly fragmental chitinozoans; age based on examination of these by A. Achab, 

2/08. Sample is from an outcrop of Ols too small to show on map.

2.5 2.5 11159-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2.5 11150-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11151-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2.5 11155-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.
64

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

93BK7 Teller C-5 65 31.78 167 18.96 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK6 Teller C-5 65 31.81 167 18.95 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK33 Teller C-5 65 31.88 167 19.75 middle Late Cambrian-Triassic O<l p_l, pOal 

(69b)

03JT22 Teller C-5 65 32.03 167 22.42 Early Ordovician (probably Macerodus dianae or A. 

deltatus-O. costatus Zone)

Ol Ol 

03JT21 Teller C-5 65 32.43 167 22.57 Early Ordovician (Macerodus dianae or A. deltatusO. costatus Zone)

Ol? p_l, pOal 

(69b)

93BK37A Teller C-5 65 32.43 167 22.93 Early, but not earliest, Ordovician ("Low Diversity 

Interval" to Reutterodus andinus Zone)

Ol Ol 

93BK37C Teller C-5 65 32.44 167 22.61 Early Ordovician; most likely "Low Diversity Interval" to Macerodus dianae Zone

Ol Ol 

93BK15 Teller C-5 65 32.59 167 18.14 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK17 Teller C-5 65 32.64 167 18.06 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK51 Teller C-5 65 32.65 167 18.57 Cambrian-Middle Devonian O<l p_l, pOul 

(69b)

93BK29 Teller C-5 65 32.74 167 19.42 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

93BK20 Teller C-5 65 32.77 167 18.03 early to middle Middle Ordovician (Histiodella holodentata Zone to Cahabagnathus sweeti Zone)

Ols Odl (69b) 

03JT03 Teller C-5 65 32.8 167 9.82 probably Middle-Late Ordovician O<l p_l, pOal 

(69b)

7-1-85B Teller C-5 65 32.81 167 18.13 Middle Ordovician Ols Olsh (69b) 

7-1-85A Teller C-5 65 32.81 167 18.1 Middle Ordovician (late Arenig-early Caradoc) Ols Odl (69b) 

7-1-85D, C Teller C-5 65 32.8 167 18.5 middle Early Ordovician ("Low Diversity Interval" 

to Acodus deltatus-Oneotodus costatus Zone)

Ol Ol 

93BK50 Teller C-5 65 32.87 167 18.8 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Ol Ol 

7-1-85F Teller C-5 65 33.3 167 17.8 Ordovician-Devonian Ol? p_l, pOul 

(69b)

5726-1 Teller C-5 65 35 167 15 early Middle Ordovician? [Ols] – 

AS-52 Teller C-6 65 31.18 167 31.25 Cambrian-Triassic O<t p_s 

AS-22-TC Teller C-6 65 31.96 167 43.53 Cambrian-Triassic O<t p_s 

05AD34G Nome C-1 64 35.17 165 23.35 late Permian-Triassic (likely Triassic) Dcs – 

06AD5A Nome C-1 64 35.24 165 23.12 Silurian(?)-Triassic Dcs – 

83ADn75 Kotzebue A-2 66 2.3 162 37.2 Silurian-Middle Devonian DObm DObm 

7-18-84A Kotzebue A-2 66 5.4 162 48.22 Ordovician-early late Silurian (early Ludlow) DObm DObm 
65

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

2 2 11148-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11147-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 4 – O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08; indeterminate conodont fragment. 

2 2.5 11970-CO – Toro Repetski Sample from medium- to thick-bedded, tan-weathering limestone with trace 

fossils.

2 2 11969-CO – Toro Repetski Sample from medium- to thin-bedded, orange-weathering limestone. Rocks 

mapped by Sainsbury (1972) as p_l, but thermal level more like that of unit Ol.

2.5 2.5 11157-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 3 11158-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11152-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11153-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

N.D. N.D. – O-94-21 Kennedy Harris, Repetski Fauna consists of acrotretid brachiopod fragment.

2.5 2.5 11156-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 2 11154-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

N.D. N.D. 11963-CO – Toro Repetski Sample from dark-gray metalimestone with thin argillite bands. Fauna consists 

of 2 chitinozoans and 1 possible gastropod fragment; age based on examination 

of chitinozoans by A. Achab, 2/08.

2 2.5 10219-CO A-85-23F Harris Harris, Repetski Entry in Alaska Paleontological Database.

1.5 2 10220-CO A-85-23F Harris Harris, Repetski Entry in Alaska Paleontological Database.

2.5 3 10217-CO, 

10218-CO

A-85-23F Harris Harris, Repetski Entries in Alaska Paleontological Database.

2 2.5 11163-CO O-94-21 Kennedy Harris, Repetski Sample re-examined by J.E. Repetski, 2/08.

2 3 – A-85-23F Harris Harris, Repetski Entry in Alaska Paleontological Database. Rocks mapped by Sainsbury (1972) as 

p_l, but thermal level more like that of unit Ol.

2 2 – – AMOCO Harris Sample likely slightly mislocated or taken from float in riverbed; probably from 

nearby Odl or Olsh of Sainsbury (1969b).

6 6 – – Anaconda Carr Sample collected by Anaconda Minerals Co.; location approximate. Conodonts 

identified by T. Carr, Atlantic Richfield Co., 1982.

6 6 – – Anaconda Carr Sample from gray carbonate layer, collected by Anaconda Minerals Co.; location 

approximate. Conodonts identified by T. Carr, Atlantic Richfield Co., 1982.

5 5 Mes. 35059 WRMTA-05-1 Dumoulin Harris Till and others (2006). See Dcs unit description for discussion of this collection.

5 5 – WRMTA-06-1 Dumoulin Harris –

5.5 6 10896-SD A-83-42C Dumoulin Harris Dumoulin and Till (1985); Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 – A-87-8 Harris Harris Sample from base of ~380-m-thick measured section west of Cape Deceit.
66

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

7-18-84C Kotzebue A-2 66 5.39 162 48.28 middle-early late Silurian (early Wenlock-early 

Ludlow)

DObm DObm 

7-18-84D, E Kotzebue A-2 66 5.37 162 48.34 middle-early late Silurian (early Wenlock-early 

Ludlow)

DObm DObm 

7-18-84F Kotzebue A-2 66 5.3 162 48.7 middle-early late Silurian (latest Wenlock-early 

Ludlow)

DObm DObm 

7-18-84G Kotzebue A-2 66 5.26 162 48.9 middle-early late Silurian (latest Wenlock-early 

Ludlow)

DObm DObm 

7-18-84H, I, J, and K Kotzebue A-2 66 5.24 162 49 middle-early late Silurian (latest Wenlock-early 

Ludlow)

DObm DObm 

7-18-84L Kotzebue A-2 66 5.24 162 49 early late Silurian (early Ludlow; Ozarkodina crassa

Zone)

DObm DObm 

7-18-84M Kotzebue A-2 66 5.2 162 49.2 early late Silurian (early Ludlow) DObm DObm 

7-18-84O, P Kotzebue A-2 66 5.17 162 49.4 early late Silurian (early Ludlow; upper Ozarkodina 

crassa through Ancoradella ploeckensis Zone)

DObm DObm 

7-18-84Q Kotzebue A-2 66 5.13 162 49.7 early late Silurian (latest early to early middle 

Ludlow; Ancoradella ploeckensis Zone)

DObm DObm 

83ADn44 Kotzebue A-2 66 5.37 162 48.37 middle middle Silurian (middle Wenlock) DObm DObm 

83ADn74 Kotzebue A-2 66 5.89 162 45.36 Ordovician-Devonian |d |d 

84ADn79C Kotzebue A-3 66 3.9 163 12.3 middle-early late Silurian (possibly early-middle 

Wenlock)

DObm DObm 

82ADu45 Bendeleben 

A-1

65 1 162 1 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

83ADn27 Bendeleben 

A-1

65 2.1 162 5.51 middle-late Silurian (Wenlock-middle Pridoli) Sd Sd 

84ADn54 Bendeleben 

A-1

65 3 162 10.25 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Od Od 

83ADn34O Bendeleben 

A-1

65 4 162 1 Middle Devonian TKs TKc 

83ADn34H Bendeleben 

A-1

65 4 162 1 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

83ADn34I Bendeleben 

A-1

65 4 162 1 late Early Devonian (late Emsian) TKs TKc 

83ADn34M Bendeleben 

A-1

65 4 162 1 late Early-Middle Devonian TKs TKc 

83ADn34L Bendeleben 

A-1

65 4 162 1 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

83ACl96 Bendeleben 

A-1

65 5 162 7.1 late Early Devonian (earliest Emsian) Ddm Ddm 

83ACl94 Bendeleben 

A-1

65 5 162 8 middle to late Early Ordovician ("Low Diversity 

Interval" to Reutterodus andinus Zone)

Od Od 

84ADn57B Bendeleben 

A-1

65 5.9 162 8.1 middle Early Ordovician-Devonian (probably 

Ordovician)

Od Od 
67

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

5.5 5.5 11533-SD A-87-8 Harris Harris Sample 171 m above base of Cape Deceit measured section.

5.5 6 11520-SD, 

11521-SD

A-87-8 Harris Harris Samples 196 and 217 m above base of Cape Deceit measured section.

5.5 7 11522-SD A-87-8 Harris Harris Sample 233 m above base of Cape Deceit measured section; collection consists 

of normal marine cosmopolites.

5.5 6 11523-SD A-87-8 Harris Harris Sample 265 m above base of Cape Deceit measured section.

5.5 7 11524-SD 

through 

11527-SD

A-87-8 Harris Harris Samples 271 m (H, I), 289 m (J), and 320 m (K) above base of Cape Deceit 

measured section.

5.5 7 11528-SD A-87-8 Harris Harris Sample 320.5 m above base of Cape Deceit measured section.

5.5 7 11529-SD A-87-8 Harris Harris Sample 332 m above base of Cape Deceit measured section.

5.5 7 11530-SD, 

11531-SD

A-87-8 Harris Harris Samples 348 and 358.5 m above base of Cape Deceit measured section.

5.5 7 11532-SD A-87-8 Harris Harris Sample 378 m above base of Cape Deceit measured section.

5.5 7.5 10907-SD A-83-42C Dumoulin Harris Dumoulin and Till (1985); Till and others (1986). Entry in Alaska Paleontological Database.

7 7 – A-83-42C Dumoulin Harris Dumoulin and Till (1985); Till and others (1986). Entry in Alaska Paleontological Database.

5.5 6 11062-SD A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 10725-SD A-83-9 Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. Sample is a clast from the conglomerate; species association indicates relatively high energy, shallow-water depositional setting.

5.5 6 10904-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Species association indicates shallow, warm-water depositional setting.

5.5 7 9897-CO A-84-37D Dumoulin Harris, Repetski Till and others (1986); age revised by A.G. Harris in 1995, and confirmed by J.E. 

Repetski in 2008. Entry in Alaska Paleontological Database. Species association 

is characteristic of normal marine conditions.

5.5 6 10903-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5.5 5.5 – A-83-42C Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. Sample is a clast in the conglomerate.

5 5 10891-SD A-83-42F Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5.5 5.5 10892-SD A-83-42C, F Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5 – A-83-42C Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. Sample is a clast in the conglomerate.

5.5 5.5 10893-SD A-83-42C,

A-84-50C

Carroll Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 6 9800-CO A-83-42C Carroll Harris, Repetski Till and others (1986); sample re-examined and age confirmed by J.E. Repetski, 

2/08. Entry in Alaska Paleontological Database. Species association indicates 

warm, shallow-water biofacies.

7 7 – A-84-37C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.
68

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

82ADu53 Bendeleben 

A-1

65 9.33 162 10.07 middle Early Devonian (middle Siegenian)-Middle 

Devonian 

Ddm Ddm 

82ADu57 Bendeleben 

A-1

65 9.04 162 7.98 Middle Ordovician-Middle Devonian Ddm Ddm 

83ADn61 Bendeleben 

B-1

65 15.5 162 17.7 Middle Devonian Ddm Ddm 

83ADn88 Bendeleben 

B-1

65 16.4 162 15.3 Ordovician-Devonian Ddm Ddm 

84ATi88B Bendeleben 

B-1

65 26.58 162 3.7 Middle Ordovician-Middle Devonian |d |d 

83ATi227 Bendeleben 

B-1

65 26.7 162 3.94 Early Mississippian |d |d 

82ADu78RR Bendeleben 

C-2

65 30.5 162 41.1 Silurian-Devonian TKs TKc 

82ADu78II Bendeleben 

C-2

65 30.5 162 41.1 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

82ADu78JJ Bendeleben 

C-2

65 30.5 162 41.1 early-middle Silurian TKs TKc 

82ADu78DD Bendeleben 

C-2

65 30.5 162 41.1 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

82ADu78MM Bendeleben 

C-2

65 30.5 162 41.1 Middle-Late Ordovician TKs TKc 

82ATi197B Bendeleben 

C-5

65 35 164 25.88 Ordovician-Permian (most probably Ordovician) [Od] Od 

84AKn151 Bendeleben 

C-5

65 39.92 164 20.33 Phanerozoic DOx O_x 

82ATi195B Bendeleben 

C-6

65 32.01 164 36.68 Middle Devonian-earliest Mississippian (Kinderhookian)

Ddm Ddm 

82ADu68 Bendeleben 

C-6

65 37 164 33 Middle Ordovician-Middle Devonian; when combined with megafossil data from this locality, age is 

restricted to Middle Devonian

|m |m 

82ADu69 Bendeleben 

D-2

65 46 162 46 middle Early Ordovician ("Low Diversity Interval" 

to Macerodus dianae Zone)

Od Od 

82ADu73 Bendeleben 

D-2

65 47.58 162 44.93 late Early Devonian (early Emsian) Ddm Ddm 

82ADu71 Bendeleben 

D-2

65 48.09 162 46.02 early to middle Middle Ordovician Od Od 

83ACl113B Bendeleben 

D-2

65 52.7 162 35 Early/Middle Devonian boundary (latest Emsianearliest Eifelian)

Ddm Ddm 

83ADn85 Bendeleben 

D-2

65 53.6 162 35.7 late Early Devonian (Emsian)-Middle Devonian Ddm Ddm 

83ACl114 Bendeleben 

D-2

65 53.83 162 39.17 middle to late Early Ordovician (Macerodus dianae

Zone to Oepikodus communis Zone)

Od Od 

82ADu76 Bendeleben 

D-2

65 54 162 35 late Early Devonian (early Emsian) Ddm Ddm 
69

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

5 5 10723-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

7 7 – A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 10908-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 – A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

8 8 – A-84-37C Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 29218-PC A-83-42F Till Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. A recollection at this locality (84ATi88B) yielded older 

conodonts; see Till and others (1986) for discussion.

4.5 4.5 10902-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5.5 10894-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 6 10901-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5 10909-SD A-83-42C Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. Sample is a clast in the conglomerate.

5.5 5.5 9799-CO A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5 – A-83-10 Till Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is from 

an outcrop of Od too small to show on map.

N.D. N.D. – A-85-15 Kaufman Harris Till and others (1986). Entry in Alaska Paleontological Database. Collection 

consists of phosphatic, non-conodont skeletal fragments.

5.5 5.5 – A-83-10 Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 – A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 7 9611-CO A-83-9 Dumoulin Harris, Repetski Till and others (1986); age revised by A.G. Harris in 1995; sample re-examined 

and age confirmed by J.E. Repetski in 2008. Entry in Alaska Paleontological 

Database. Species association is characteristic of very shallow, warm-water 

depositional setting.

5 6.5 10727-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

6 7 9612-CO A-83-9 Dumoulin Harris Till and others (1986); sample re-examined and age revised by J.E. Repetski in 

2008. Entry in Alaska Paleontological Database.

5 5 10900-SD A-83-42C Carroll Harris Till and others (1986). Entry in Alaska Paleontological Database. Shallow-water 

species association. 

5 5.5 10910-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 9679-CO A-83-42A Carroll Harris, Repetski Till and others (1986); sample re-examined and age confirmed by J.E. Repetski 

in 2008. Entry in Alaska Paleontological Database. Species association is characteristic of the North Atlantic Province early to middle Arenig cool-water faunas.

5 5.5 10729-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.
70

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

82ADu75 Bendeleben 

D-2

65 54.74 162 35.5 late Early Devonian (early Emsian)-Middle Devonian Ddm Ddm 

82ADu74 Bendeleben 

D-2

65 55.66 162 35.41 Middle Ordovician-Middle Devonian Ddm Ddm 

84ATi224 Bendeleben 

D-5

65 46 164 11 Middle Ordovician-Middle Devonian Od Od 

84ADn80A Bendeleben 

D-5

65 47 164 10 early to middle Middle Ordovician (Histiodella holodentata Zone to lower Amorphognathus tvaerensis

Zone; possibly H. holodentata Zone to Cahabagnathus sweeti Zone)

Od Od 

82ADu63 Bendeleben 

D-5

65 50.37 164 22.59 probable middle Early to Middle Devonian Ddm Ddm 

84ATi15Y Solomon C-1 64 33.5 162 27.33 Ordovician-Triassic D_bm D_bm 

84ATi15Z Solomon C-1 64 33.5 162 27.33 middle Early Ordovician (middle Arenig)-Late 

Ordovician 

D_bm D_bm 

84ADn5H Solomon C-1 64 34.6 162 24 middle-early late Silurian (Wenlock-Ludlow) D_bm D_bm 

84ATi8AA Solomon C-1 64 34.87 162 22.5 late Early-latest Middle Devonian (Emsian-Givetian) Ddm Ddm 

84ATi8AB Solomon C-1 64 34.92 162 22.5 late Early Devonian (Emsian) Ddm Ddm 

84ADn10A Solomon C-1 64 37 162 17 middle-early late Silurian (Wenlock-early Ludlow) [Sd] |d 

84ATi23 Solomon C-1 64 37.45 162 13.8 middle Early Devonian (Siegenian) D_bm D_bm 

84ADn2A Solomon C-1 64 38 162 14 Middle Devonian Ddm Ddm 

84ATi57 Solomon C-1 64 38.6 162 22.4 Early through possibly early Middle Cambrian D_bm D_bm 

84ADn3A Solomon C-1 64 39 162 13 Middle Devonian Ddm Ddm 

84ADn3B Solomon C-1 64 39 162 13 Middle Devonian Ddm Ddm 

84ADn16 Solomon C-1 64 39.9 162 23.5 Middle Devonian Ddm Ddm 

84ADn31 Solomon C-1 64 44.5 162 18.3 late Silurian-Early Devonian D_bm D_bm 

82ADu59 Solomon C-3 64 44.73 163 27.66 middle to late Early Devonian Ddm Ddm 

83ADn2 Solomon C-4 64 34.04 163 41.27 Phanerozoic Ddm Ddm 

84AGe133 Solomon C-5 64 44.72 164 25.7 Ordovician-Middle Devonian DOx O_x 

83ADn25 Solomon D-1 64 49.51 162 17.51 middle Silurian-most of Middle Devonian Ddm Ddm 

82ADu17 Solomon D-1 64 50.9 162 13.68 Silurian-Middle Devonian; when combined with 

megafossil data from this locality, age is restricted to 

Middle Devonian

Ddm Ddm 

84ATi112 Solomon D-1 64 52.9 162 9.9 Middle Devonian Ddm Ddm 

83SK28A Solomon D-1 64 53.18 162 11.13 latest Early-earliest Middle Devonian Ddm Ddm 
71

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

5 5 10728-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 – A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 – A-85-15 Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

8 8 9889-CO A-84-37A Dumoulin Harris Till and others (1986); sample re-examined and age revised by J.E. Repetski in 

2008. Entry in Alaska Paleontological Database. Species association is characteristic of a rather shallow and warm-water biofacies.

5.5 5.5 – A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

6 6 – A-85-23I Till Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample taken 

from black marble in 5–10 cm thick layers. 

5.5 5.5 10213-CO A-85-23D Dumoulin Harris Till and others (1986). Sample taken a few feet north of 15Y from black marble 

in 1–5 cm thick layers. 

5 6 11058-SD A-84-37A, C Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska 

Paleontological Database. 

5 5.5 10996-SD A-84-37 Till, 

Dumoulin

Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 10997-SD A-84-37 Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 11031-SD A-84-37B Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska 

Paleontological Database. Sample is from an outcrop of Sd too small to show on 

map.

5 5 11173-SD A-85-23C Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 10993-SD A-84-37 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 10060-CO A-85-23C Till Harris Till and others (1986). Entry in Alaska Paleontological Database. The phosphatic 

microfossil Lapworthella indicates a shallow-water depositional environment.

5 5.5 11030-SD A-84-37B Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 10994-SD A-84-37 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 10995-SD A-84-37 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 11059-SD A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 6 10726-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

N.D. N.D. – A-83-42F Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Collection 

consists of a pyritized and phosphatized spine steinkern.

6 6 – A-85-15 Gamble, 

Dumoulin

Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 10745-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Stromatoporoids and corals from this locality are of early Late Devonian (Frasnian) age; 

the conodonts may be redeposited, or may have been collected from an older 

stratigraphic horizon than the megafossil-bearing rocks.

5.5 5.5 10724-SD A-83-9 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 11057-SD A-84-37A Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5.5 10897-SD A-83-42C Karl Harris Till and others (1986). Entry in Alaska Paleontological Database.
72

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

83SK31A Solomon D-1 64 57.93 162 9.04 late Early Devonian (middle Siegenian-Emsian) Ddm Ddm 

84ADn52B Solomon D-1 64 59.5 162 3.7 late Early-Middle Devonian TKs TKc 

84ADn52C Solomon D-1 64 59.5 162 3.7 Middle Devonian TKs TKc 

83ADn5 Solomon D-3 64 45.24 163 28.66 latest Early-earliest Late Devonian; when combined with megafossil data from this locality, age is 

restricted to Middle Devonian-earliest Late Devonian

Ddm Ddm 

84ADn75Z Solomon D-5 64 48 164 12.5 Ordovician DOx O_x 

83ADn32 Solomon D-5 64 54.38 164 28 middle Silurian-Early Devonian [|d] |d 

84ADn108D Solomon D-5 64 54.93 164 29.58 Early through possibly early Middle Cambrian _d _d 

82ACl91 Solomon D-5 64 55.2 164 14.6 Ordovician-Devonian (probably Early-Middle 

Ordovician)

|m |m 

83ADn29B Solomon D-5 64 56 164 18 late Silurian-Devonian [|m] |m 

83ADn29A Solomon D-5 64 55.77 164 18.29 Early Ordovician (Rossodus manitouensis Zone to 

"Low Diversity Interval")

Od Od 

82ACl94 Solomon D-5 64 57.5 164 26.2 middle Early to earliest Middle Ordovician (most 

likely "Low Diversity Interval" to Histiodella sinuosa Zone)

Od Od 

84ATi281 Solomon D-6 64 49.58 164 55.33 Early (but not earliest) through Middle Ordovician Oim Oim 

85APa106 Candle A-5 65 1.8 161 23.2 Middle Ordovician-Middle Devonian (possibly 

Ordovician)

|d 

85APa120 Candle A-6 65 0.2 161 50.5 Includes faunal elements of two ages: Early Ordovician (Rossodus manitouensis Zone to Macerodus 

dianae Zone) and Early (Emsian)-Middle Devonian

|d 

84ADn42 Candle B-6 65 27 161 58.7 Ordovician-Triassic |d |d 

85ADn2B Norton Bay 

C-6

64 44.43 161 32.3 middle-early late Silurian (Wenlock-Ludlow) D_bm D_bm 

85ADn3A Norton Bay 

C-6

64 44.8 161 31.21 late Silurian-Middle Devonian [Ddm] Ddm 

85ATi1A Norton Bay 

D-5

64 48.8 161 20.9 late Early Devonian-Early Mississippian [Ddm] Ddm 

85APa101 Norton Bay 

D-6

64 53.4 161 31.9 Silurian-Triassic |d |d 

84ADn51K Norton Bay 

D-6

64 54.6 161 57.9 Ordovician-Permian TKs TKc 

84ADn51M Norton Bay 

D-6

64 54.6 161 57.9 late Silurian-Devonian TKs TKc 

84ADn51N Norton Bay 

D-6

64 54.6 161 57.9 Middle Ordovician-Middle Devonian TKs TKc 

84ADn51O Norton Bay 

D-6

64 54.6 161 57.9 Middle Ordovician-Middle Devonian TKs TKc 
73

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

5 5.5 10898-SD A-83-42C Karl Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 5.5 11060-SD A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5.5 6 11061-SD A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5.5 5.5 10895-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 6 10059-CO A-85-23C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5 5 10906-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is from 

an outcrop of |d too small to show on map.

N.D. N.D. 9937-CO A-85-15 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Collection 

consists of the phosphatic microfossil Lapworthella, which indicates a shallowwater depositional setting.

5 6 – A-83-9 Carroll Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 6.5 10905-SD A-83-42C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is from 

an outcrop of |m too small to show on map.

4 4 9801-CO A-83-42C Dumoulin Harris Till and others (1986); age revised by J.E. Repetski, 2/08. Entry in Alaska 

Paleontological Database. The CAI of this collection is lower than values from 

other collections in the Nome Complex. The collection may represent laboratory 

contamination, or a remnant of a structurally higher thrust sheet. Species association indicates a warm, shallow-water depositional setting.

5.5 5.5 9610-CO A-83-9 Carroll Harris Till and others (1986); sample re-examined and age confirmed by J.E. Repetski, 

2/08. Entry in Alaska Paleontological Database.

7 7 9938-CO A-85-15 Till Harris Till and others (1986). Entry in Alaska Paleontological Database.

~5.0 ~5.0 – A-86-16 Patton, 

Dumoulin

Denkler Entry in Alaska Paleontological Database.

6 6 – A-85-23D Patton, 

Dumoulin

Harris Collection may have sampled two rock types of different age, or older conodonts 

may have been reworked into a younger rock.

5 5 – A-84-37C Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database.

5.5 6 11229-SD A-85-23D Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995.

5 5 11230-SD A-85-23D Dumoulin Harris Sample is from an outcrop of Ddm too small to show on map.

~5.0 ~5.0 – A-86-16 Till Denkler Entry in Alaska Paleontological Database. Sample is from an outcrop of Ddm

too small to show on map.

5 5 – A-86-16 Patton, 

Dumoulin

Denkler Entry in Alaska Paleontological Database.

5.5 6 – A-85-15 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5.5 5.5 11134-SD A-85-15 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5.5 – A-84-37B Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5.5 – A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.
74

Table A–1. Conodont data from the Seward Peninsula.—Continued (table spans facing page)

[Ages listed have not been revised to reflect all changes in stratigraphic terminology that have occurred since the ages given here were 

Ordovician conodont zonation, Series, and Stage usage herein follows that given in Harris and others (1995). Geologic unit (source map) from cited 

to map units of Till and others (1986). For Teller quadrangle, source map units refer to map units of Sainsbury (1972) if unspecified; (69b) indicates a 

column. Alaska Paleontological Database found online at http://www.alaskafossil.org. E&R, Examination and Report by USGS paleontologist;

on sheet 2; see table A-2 for temperature ranges for CAI values]

Lat (N) Long (W) Geologic unit

Field no. Quadrangle Deg Min Deg Min Age (This map)

(Source

map) 

85APa104 Norton Bay 

D-6

64 57.97 161 37.12 Early Ordovician ("Low Diversity Interval" to 

Reutterodus andinus Zone)

[Od] Od 

83ADn92B Norton Bay 

D-6

64 58 161 57.5 middle-early late Silurian (Wenlock-Ludlow) TKs TKc 

83ADn92CC Norton Bay 

D-6

64 58 161 57.5 Middle Ordovician-Middle Devonian TKs TKc 

83ADn92AA Norton Bay 

D-6

64 58 161 57.5 Middle Ordovician-Middle Devonian TKs TKc 

83ADn92BB Norton Bay 

D-6

64 58 161 57.5 Silurian-Permian; probably middle Silurian-late 

Early Devonian (early Emsian)

TKs TKc 
75

determined. For example, the Middle/Upper Ordovician boundary has been revised downward considerably (see, for example, Webby and others, 2004).

reference (if published) or provided by collector. For Bendeleben, Candle, Kotzebue, Norton Bay, and Solomon quadrangles, source map units refer

map unit of Sainsbury (1969b). Unit in bracket (for example, [Ols]) indicates outcrop too small to show on map, or other issue explained in remarks

ID, conodont fauna identifier; N.D., not determined; USGS no., number under which collection is filed in USGS repository. Localities are plotted

Color

Alteration

Index (CAI)

Min Max USGS no.

E&R

shipment no.

Sample

collector

Sample

ID Remarks

~5.0 ~5.0 10312-CO A-86-16 Patton, 

Dumoulin

Denkler Entry in Alaska Paleontological Database. Sample is from an outcrop of Od too 

small to show on map.

5 5.5 10836-SD A-83-42B Dumoulin Harris Till and others (1986); age revised by A.G. Harris in 1995. Entry in Alaska Paleontological Database. Sample is a clast in the conglomerate; species association 

indicates relatively high energy, shallow-water depositional setting.

5 5.5 – A-84-37A Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

5 5.5 – A-85-15 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

6 7 – A-85-15 Dumoulin Harris Till and others (1986). Entry in Alaska Paleontological Database. Sample is a 

clast in the conglomerate.

Table A–2. Temperature ranges for Color Alteration Indices 

(CAIs) of conodonts.

[Taken from Epstein and others (1977), Rejebian and others (1987), 

and Watts and others (1994). Temperature ranges for conodonts 

from an Arrhenius plot of experimental data. For CAI values ≤5.5, 

ranges represent heating durations of 500 m.y. to 1 m.y. (lower 

temperature is 500 m.y.-value); for values ≥6, ranges cover durations of 500 m.y to 1,000 years]

Minimum CAI Temperature (°C)

1 <50–80

1.5 50–90

2 60–140

2.5 100–150

3 120–190

3.5 150–200

4 190–250

4.5 250–300

5 300–480

5.5 >360

6 360–550

6.5 440–610

7 490–720

8 >600