Download Sedimentary record of the tectonic growth of a collisional continental

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The Geological Society of America
Special Paper 431
2007
Sedimentary record of the tectonic growth of a collisional continental
margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains
sequence, eastern Alaska Range, Alaska
Jeffrey D. Manuszak*
Kenneth D. Ridgway†
Department of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive,
West Lafayette, Indiana 47907-2051, USA
Jeffrey M. Trop
Department of Geology, Moore Avenue, Buckness University, Lewisburg, Pennsylvania 17837, USA
George E. Gehrels
Department of Geosciences, Gould-Simpson Building, University of Arizona, 1040 E. Fourth Street, Tucson, Arizona 85721, USA
ABSTRACT
Upper Jurassic-Lower Cretaceous sedimentary strata of the Nutzotin basin, the
Nutzotin Mountains sequence, crop out in the Nutzotin and Mentasta Mountains of
the eastern Alaska Range. These strata represent one of the best-exposed and leastmetamorphosed examples of a basin that is interpreted to have formed during collision of an allochthonous volcanic arc (i.e., the Wrangellia terrane) with a continental
margin. New stratigraphic, geologic mapping, and provenance data indicate that the
Nutzotin basin formed as a retroarc foreland basin along the northern margin (present coordinates) of the Wrangellia terrane. Coeval with basin development along the
northern margin, sedimentary basins and plutons located along the southern margin
of the Wrangellia terrane were being incorporated into a regional fold-and-thrust belt.
This fold-and-thrust belt, located south of the Nutzotin basin, exposed multiple structural levels of the Wrangellia terrane that were eroded and provided sediment that
was transported northward and deposited in the Nutzotin basin.
New sedimentologic and stratigraphic data from the 3 km thick (minimum
thickness) Nutzotin Mountains sequence define a three-part stratigraphy. The lower
part consists of Upper Jurassic (Oxfordian to Tithonian) conglomerate with outsized
limestone clasts (>10 m in diameter) and interbedded sandstone and shale that grade
basinward into mainly black shale with minor micritic limestone and isolated lenses
of conglomerate. The middle part of the stratigraphy consists of Upper Jurassic
(Tithonian) to Lower Cretaceous (Valanginian) normal-graded sandstone and shale
interbedded with massive tabular sandstone and lenticular conglomerate. The upper
part of the stratigraphy consists of Upper Jurassic (Tithonian) to Lower Cretaceous
*Present address: Malcolm Pirnie, 3101 Wilson Blvd, Suite 550, Arlington, Virginia, 22201, USA; [email protected]
†Corresponding author: [email protected]
Manuszak, J.D., Ridgway, K.D., Trop, J.M., and Gehrels, G.E., 2007, Sedimentary record of the tectonic growth of a collisional continental margin: Upper
Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska, in Ridgway, K.D., Trop, J.M., Glen, J.M.G., and O’Neill, J.M., eds., Tectonic
Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska: Geological Society of America Special Paper 431, p. 345–377, doi:
10.1130/2007.2431(14). For permission to copy, contact [email protected]. ©2007 The Geological Society of America. All rights reserved.
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Manuszak et al.
(Valanginian) mudstone with distinctive fossil-rich horizons and minor interbedded
sandstone. The overall stratigraphy of the Nutzotin Mountains sequence represents
a general upward-shallowing and upward-coarsening package that represents a general transition from distal mud-rich submarine-fan strata to more proximal sand-rich
submarine-fan strata that are in turn overlain by marine shelf strata. Feldspathic sandstone compositions (Q6F67L27), eastward and northeastward directed paleocurrent
indicators, diagnostic clasts in conglomerate, and detrital zircon U-Pb ages of 151–
147 Ma (n 8) and 159–156 Ma (n 2) indicate that sediment in the Nutzotin basin
was derived primarily from the Wrangellia terrane and the Chitina and Chisana arcs
that intrude the Wrangellia terrane.
The stages of deformation documented in the Nutzotin Mountains sequence provide insight into the growth of collisional continental margins by the tectonic incorporation of basinal strata. Our data show that strata of the Nutzotin basin have been
deformed into an accretionary wedge by north-dipping thrust faults and related overturned folds above a north-dipping décollement. Displacement on this décollement was
the product of northward underthrusting of basinal strata beneath the former continental margin and resulted in southward tectonic transport of distal basinal strata
of the Nutzotin Mountains sequence strata over both more proximal basinal strata
and the Wrangellia terrane. Previously published K-Ar ages from plutons that crosscut both the décollement and folded Nutzotin Mountains sequence strata indicate that
contractional deformation ended between 117 and 105 Ma. Regionally, the Nutzotin
Mountains sequence represents part of a series of Mesozoic sedimentary basins located
along the inboard margin of the Wrangellia composite terrane that have similar depositional styles and were all subsequently incorporated into accretionary wedges that dip
toward the former continental margin. These deformed strata define a continentalscale suture zone that extends along the northwestern Cordillera for over 2000 km.
Keywords: Nutzotin Mountains sequence, Wrangellia terrane, Nutzotin basin, Alaska
Range, Chisana arc.
INTRODUCTION
Collisional basins form along plate boundaries during arcarc, arc-continent, and continent-continent collisions (Dewey,
1977; Miall, 1995). Several active collisional basins are forming
near Taiwan, for example, due to the collision of the Luzon volcanic arc with the southeastern continental margin of China
(Lundberg and Dorsey, 1988; Teng, 1990; Chen et al., 2001). In a
similar tectonic setting, a series of sedimentary basins are forming near Papua New Guinea as a result of the collision of the Bismarck volcanic arc with the northeastern continental margin of
Australia (Silver et al., 1991; Cullen, 1996; Galewsky and Silver,
1997). Ancient examples of collisional basins are often difficult
to identify and study because their strata may be deformed, metamorphosed, and/or eroded during the final stages of collision. If
preserved, however, the stratigraphy and deformation of collisional basins provide a record of processes associated with the
growth of continents through suturing of island arcs, oceanic
plateaus, and microcontinents onto continental margins.
Upper Jurassic-Lower Cretaceous sedimentary strata of the
Nutzotin basin, the Nutzotin Mountains sequence, are part of a
series of Upper Jurassic-Lower Cretaceous basinal strata located
on or near the suture zone between arc-related rocks of the
allochthonous Wrangellia composite terrane and the Mesozoic
continental margin of western North America (Fig. 1; e.g., Pavlis,
1982; McClelland et al., 1992a; Manuszak, 2000; Ridgway et al.,
2002; Hampton et al., this volume; Kalbas et al., this volume).
The majority of the strata representing these Mesozoic basins
have undergone a high degree of structural and metamorphic
deformation (Berg et al., 1972). Metamorphism has destroyed
most of the fossils in these strata, so lack of age control is a major
obstacle in studying the development of these basins. Strata of the
Nutzotin basin, fortunately, have undergone limited metamorphism, and preservation of marine fossils provides adequate age
control (e.g., Richter, 1971, 1976; Richter and Jones, 1973; Richter
and Schmoll, 1973; Manuszak and Ridgway, 2000).
Our investigation of the Nutzotin Mountains sequence is
based on 26 measured stratigraphic sections (7500 m total thickness), clast counts from conglomerate (n 1784), paleocurrent
measurements (n 221), U-Pb age determinations of detrital zircons (n 10), petrographic and microprobe analyses of sandstone thin sections (n 17), and geologic mapping. With these
data, we reconstruct the evolution of depositional environments
and stages of basin development, identify the provenance of detritus for the basin, define the structural geometry of the basin within
the suture zone, and relate the development and deformation of
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Sedimentary record of the tectonic growth of a collisional continental margin
the Nutzotin basin with collision of the Wrangellia composite terrane against the continental margin of western North America.
GEOLOGIC SETTING AND PREVIOUS STUDIES
Tectonostratigraphic Terranes
South-central Alaska consists of three composite terranes that
are separated by major fault systems (e.g., Coney et al., 1980;
Plafker and Berg, 1994). From north to south, these terranes are
the Yukon composite terrane, the Wrangellia composite terrane,
and the Southern Margin composite terrane (Fig. 1; Foster et al.,
1994; Nokleberg et al., 1994a; Plafker et al., 1994; Plafker and
Berg, 1994). The Yukon composite terrane consists of structurally
dismembered Paleozoic metamorphic rocks that are para-autochthonous to North America and formed the late Paleozoic-early
Mesozoic continental margin of southern Alaska and the Yukon
Territory (Tempelman-Kluit, 1976; Hansen, 1990; Mortensen,
1992; Nokleberg et al., 1994a; Hansen and Dusel-Bacon, 1998).
The southern boundary of the Yukon composite terrane is marked
by a broad zone of deformation that consists of highly deformed
sedimentary, igneous, and metamorphic rocks and is commonly
referred to as the Alaska Range suture zone (Csejtey et al., 1982;
Ridgway et al., 1997; Cole et al., 1999; Ridgway et al., 2002). The
trace of the Denali fault follows the trend of the Alaska Range suture zone (Fig. 1; Ridgway et al., 2002). The Wrangellia composite terrane is juxtaposed against the southern margin of the Yukon
composite terrane within the Alaska Range suture zone. The
Wrangellia composite terrane is an amalgamation of three separate terranes (Wrangellia, Alexander, and Peninsular terranes;
Fig. 1B) that were probably sutured together during late Paleozoic
time (Jones et al., 1977; Jones and Silberling, 1979; Gehrels and
Saleeby, 1987; Gardner et al., 1988; Plafker et al., 1989) and are
presently exposed from western Alaska to southern British Columbia (Fig. 1). The terranes are interpreted to represent remnant
volcanic arc assemblages and overlying flood basalts and platform
carbonates that are allochthonous to North America (Packer and
Stone, 1974; Hillhouse and Grommé, 1984; Hillhouse and Coe,
1994). The Wrangellia composite terrane was located near the
equator during Late Triassic time, was translated northward relative to North America, and accreted to the western margin of North
America sometime between Late Triassic and early Tertiary time
(McClelland et al., 1992a; Plafker and Berg, 1994; Hillhouse and
Coe, 1994; Cowan et al., 1997; Butler et al., 2001; Trop et al.,
2002, 2005). The Southern Margin composite terrane is juxtaposed against the Wrangellia composite terrane along the Border
Ranges fault (Fig. 1). This terrane consists of an Upper TriassicPaleogene subduction-complex that was produced by northeastward to northwestward subduction (e.g., Plafker et al., 1994).
Mesozoic Sedimentary Basins
Mesozoic strata representing two sedimentary basins, the
Nutzotin and Wrangell Mountains basins, were deposited on the
347
Wrangellia composite terrane and are well preserved in southcentral Alaska (Fig. 1B; Trop et al., 2002). The Nutzotin basin,
the focus of this study, consists of at least 6 km of Upper JurassicLower Cretaceous sedimentary and volcanic strata that are preserved along the inboard margin (cratonward side) of the
Wrangellia terrane in a 35-km-wide and 250-km-long outcrop
belt (Figs. 2, 3). The oldest strata of the basin, the Nutzotin
Mountains sequence, disconformably overlie Triassic sedimentary and volcanic strata of the Wrangellia terrane along the
southern margin of the basin and are in fault contact with this terrane at other locations (Figs. 3, 4; Richter, 1976; Manuszak,
2000). The disconformable contact is best exposed at Misty
Mountain (Fig. 2B). The Nutzotin Mountains sequence consists
of an 3-km-thick package (minimum thickness) of Upper
Jurassic-Lower Cretaceous (Oxfordian–Valanginian) marine sedimentary strata (Fig. 3; Berg et al., 1972; Richter and Jones,
1973). These marine sedimentary strata are conformably overlain by the Chisana Formation, a 3-km-thick succession of
Lower Cretaceous (Hauterivian-Aptian) lava flows, tuff, mudstone, and volcaniclastic breccia (Fig. 3; Richter, 1976; Sandy
and Blodgett, 1996). The Chisana Formation has a gradational
contact with the Valanginian Buchia-bearing strata of the Nutzotin Mountains sequence (Manuszak, 2000). Stratigraphically
higher in the Chisana Formation, Berg et al. (1972) reported the
presence of the ammonite Shasticrioceras, which is indicative of an
Early Cretaceous (Barremian) age. In addition, 40Ar-39Ar ages from
samples collected 888 and 1036 m above the base of the Chisana
Formation give ages of 116.7 1.4 Ma and 113.4 1.5 Ma (Short
et al., 2005). The volcanic and related plutonic rocks of the
Chisana Formation have been interpreted as the product of
northward- to northeastward-directed subduction of an oceanic
slab beneath the Wrangellia composite terrane (Barker, 1988;
Plafker et al., 1989; Plafker and Berg, 1994). A relatively thin
(<90 m) package of possibly Upper Cretaceous nonmarine, unnamed strata overlies the Chisana Formation along an angular
unconformity (Fig. 3; Richter, 1976).
The Wrangell Mountains basin, located 80 km south of the
Nutzotin basin, formed on the outboard (southern) margin of the
Wrangellia composite terrane (WB in Fig. 1). Strata of this basin
consist of a 7-km-thick sequence of Upper Triassic-Upper Cretaceous sedimentary strata that are exposed in a 55-km-wide and
120-km-long outcrop belt in the Wrangell Mountains (Grantz
et al., 1966; MacKevett, 1969, 1978; Jones and MacKevett, 1969;
Trop et al., 1999; Trop, 2000; Trop et al., 2002). The Chitina foldand-thrust belt is well exposed along the southern margin of the
Wrangell Mountains basin and was active during Late JurassicEarly Cretaceous sedimentation in the basin (Fig. 1B; Gardner
et al., 1986; Trop et al., 2002; Trop and Ridgway, this volume). The
northwest-trending fold-and-thrust belt consists of southwestdipping thrust faults that juxtapose different stratigraphic levels of
the Wrangellia composite terrane and strata of the Wrangell
Mountains basin (MacKevett, 1978; Gardner et al., 1986; Trop
et al., 2002). Crustal shortening related to the Chitina fold-andthrust belt also produced regional northeast-verging folds with
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Manuszak et al.
Nor
a
nad
Ca ka
s
Ala
A
li
na
De KBt
KBa
Yuk
on
fault
th A
com
posi
te te
DB
NB
WCT
WB
mer
Tint
in
ican
a fa
rran
crat
ult
e
on
Fig. 1A
F
MB BR
SMCT
Figure 1B
GB
Denali fault
Pa
Pl cifi
at c
e
Gulf of Alaska
QB
KB
LK
Explanation of Map Units and Symbols
LK
EK
LJ
Kluane magmatic arc
Chisana magmatic arc
Chitina magmatic arc
major fault systems
NB
LK
undifferentiated sedimentary rocks
WB - Wrangell Mtns. basin, NB - Nutzotin
basin, MB - Matanuska Valley basin,
KBa - Kahiltna basin -Alaska Range,
KBt - Kahiltna basin -Talkeetna Mtns.,
DB - Dezadeash basin, GB - Gravina basin,
QB- Queen Charlotte basin
W
Fig. 2
P
Bo
rde
r
LK
LK
Mesozoic plutonic assemblages
B
WB
EK
B
Southern Margin composite
terrane (subduction complex)
Mesozoic sedimentary
basins
MB
LJ
CT
Yukon composite terrane (Early
Mesozoic continental margin)
Wrangellia composite terrane
(W, Wrangellia; A, Alexander
terrane; P, Peninsular terrane)
a
nad
Ca .S.
U
Ra
A
nge
0
km
100
s f
au
lt
LJ
60
140
Figure 1. (A) Map showing the composite terranes, Mesozoic sedimentary basins, and major faults of the northwestern North American Cordillera
(adapted from Nokleberg et al., 1994b). Inset in the upper right shows the location of Figure 1A. The Yukon composite terrane represents the late
Paleozoic-early Mesozoic continental margin of southern Alaska and the Yukon Territory. The boundary between the Yukon composite terrane and
the allochthonous Wrangellia composite terrane is marked by the Denali fault, and a broad zone of deformation consisting of highly deformed sedimentary, igneous, and metamorphic rocks that is referred to as the Alaska Range suture zone in the text. The Nutzotin basin is located in the Alaska
Range suture zone near the Alaska/Canada border. (B) Map showing composite terranes, Mesozoic sedimentary basins, and the axes of JurassicCretaceous magmatic arcs in east-central Alaska and western Yukon Territory. Note the location of the Chitina thrust belt (labeled CTB) discussed
in the text. Also note that the Nutzotin basin is located on the inboard (northern) margin of the Wrangellia composite terrane, whereas the Wrangell
Mountains basin is located on the outboard (southern) margin. See key for explanation of abbreviations. BRF = Border Ranges fault.
wavelengths up to 15 km that have been mapped between exposures of the Nutzotin basin and exposures of the Wrangell Mountains basin (e.g., Richter, 1976; MacKevett, 1978; Trop et al.,
2002). In this article, when we refer to the Chitina fold-and-thrust
belt, we are including both the well-exposed thrust faults in the
Wrangell Mountains and the regional folds that extend northward
to the Nutzotin basin.
Volcano-Plutonic Arcs
The composite terranes of east-central Alaska are intruded and
overlain by linear belts of Upper Jurassic-Upper Cretaceous igneous
rocks that have been interpreted as representing magmatic arcs (LJ,
EK, and LK in Figure 1B; Plafker et al., 1989; Nokleberg et al.,
1994a). Upper Jurassic-lowermost Cretaceous calc-alkaline plutonic rocks of the Chitina arc intrude the southern margin of the
Wrangellia composite terrane in south-central Alaska (LJ in Figure 1B; Plafker et al., 1989; Roeske et al., 2003), Yukon Territory
(Dodds and Campbell, 1988), and southeastern Alaska (Karl et al.,
1988). During late Early to early Late Cretaceous time, the Chisana
arc (EK in Fig. 1B) formed inboard (northward) of the remnant
Chitina arc. Plutonic and andesitic volcanic rocks of the Chisana arc
are discontinuously exposed from south-central to southeastern
Alaska (Berg et al., 1972; Plafker et al., 1989; Stowell et al., 2000;
Snyder and Hart, 2002, this volume). During latest Cretaceous time,
magmatism migrated farther inboard (northward), forming the Kluane arc (LK in Figure 1B; Plafker et al., 1989). Upper CretaceousLower Tertiary plutonic and volcanic rocks of the Kluane arc are
exposed from south-central Alaska to British Columbia (Monger et
al., 1982; Brew and Ford, 1984; Plafker and Berg, 1994; Trop et al.,
1999)andintrudeboththeWrangelliaandYukoncompositeterranes.
Major Faults
The Denali and Totschunda faults are the two major strikeslip faults present in the study area (Fig. 2). The Denali fault is a
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63oN
A
YCT
Ku
Ku
Kg
YCT
Jp
Qs
Qs
1
Ku
n=30
Kg
Ku
YCT
o
7
141 W
n=59
9
Fig.12
Riv
er
FA3,4
n=108
De
B
ts
To
er
Copper Riv
10
B
ch
QTv
un
Nabesna
11 1213
lt
Qs
YCT
lt
n=24
TKs
fau
Kc
QTv
fau
FA3,4
da
FA1,2
na
li
Kl
na
FA1,2
8
isa
6
Qs
YCT
YCT
Ch
Jp 54
144oW
C
3
2
Ri
ve
r
1
WCT
Na
be
sn
a
Jp
14
Kl
QTv
FA3,4
15 16
17
20
18 19
n=212
WCT
Kl
0
km
A
B
C
Denali
fault
Totschunda
fault
2400m
BC1FA5
Kl
Chisana
50
QTv
Lost Creek
decollement
B
22
Qs
62oN
Misty
Mountain
FA3,4 21
Kc
Orange
Hill
Kc
0
km
5
A
S.L.
?
?
?
-2400m
?
?
?
Explanation
Qs - Quaternary surficial deposits
Bedding dip indicator
QTv - Quaternary/Tertiary volcanic rocks
Fault (dashed where inferred)
TKs - Tertiary-Cretaceous sandstone and conglomerate
Decollement
Kc - Cretaceous Chisana Formation
Fold axis
FA1,2 - Nutzotin Mtns. Sequence - Facies Association 1, 2
River
FA3,4 - Nutzotin Mtns. Sequence - Facies Association 3, 4
Village
FA5 - Nutzotin Mtns. Sequence - Facies Association 5
Ku - Upper Cretaceous plutonic rocks (89-94 Ma K-Ar ages)
Kl - Lower Cretaceous plutonic rocks (105-117 Ma K-Ar ages)
Jp - Jurassic plutonic (163 ± 4 Ma K-Ar age) and meta. rocks
Paleocurrent data (Kozinski, 1985)
n=212
(arrows represent dominant flow direction
from several outcrops)
Ultramafic complex (ophiolite)
Paleocurrent data (this study)
WCT - Wrangellia composite terrane
(rose petals indicate dominant flow direction)
YCT - Yukon composite terrane
Figure 2. (A) Generalized geologic map of the Nutzotin basin. Map location indicated in Figure 1B. Black circles with white numbers mark the location of our 22 measured sections that are discussed in the text. Rose diagrams show paleocurrent data discussed in the text. Geology modified from
Richter et al. (1975) and Richter (1976). (B) Cross section showing structural relationships between the Nutzotin Mountains sequence, Wrangellia terrane, and the Yukon composite terrane. The cross section has no vertical exaggeration. Line of cross section shown on Figure 2(A). Notice the small
outlier of the Nutzotin Mountains sequence that is in depositional contact with the Wrangellia terrane in the center of the cross section at Misty Mountain. Also note that the Lost Creek décollement (black dashed line) is interpreted to have tectonically transported more distal strata of the Nutzotin
Mountains sequence southward over the Wrangellia terrane. Point B on the cross section is roughly along the axis of a large anticline in the Wrangellia terrane; these regional folds are discussed in the text. See text for additional discussion.
9:06 AM
WRANGELL LAVA
- 2000+ m andesitic
volcanic rocks
CHITITU FM.
- 1100 m marine
mudstone and
minor sandstone
Schultze MoonSchultze
shine
Fm.
Fm. Ck. Fm.
KENNICOTT FM.
- 150-800 m marine
mudstone, sandstone,
and conglomerate
Berg
Ck.
Fm.
KUSK. PASS FM.
Kotsina
Cong./
Upper
Root Gl.
Fm.
Holo./Pleist.
Pliocene
WRANGELL LAVA
- 2000+ m andesitic
volcanic rocks
BERG CREEK FM.
Oligocene
Unnamed
strata
Eocene
60
Paleocene
70
Maastrich.
80
KLUANE
MacCOLL RIDGE FM.
- 1100 m marine
sandstone, mudstone,
conglomerate, tuff
Kuskulana
Pass Fm.
Q
Miocene
Chititu
Fm.
Kennicott
Fm.
0
20 T
E
30 R
T
40 I
A
50 R
Y
MacColl
Ridge
Fm.
Moonshine
Creek,
Shultze,
Chititu
Fms.
Epoch/
System Arcs Nutzotin Mountains Stratigraphy
10
FREDERIKA
FM.- 450 m
sedimentary and
volcanic rocks
?
Frederika
Fm.
Age
(Ma)
Campan.
?
UNNAMED
NONMARINE
CLASTIC STRATA
?
Santonian
C Coniacian
R Turonian
E Cenoman.
100 T
A Albian
110 C
E
Aptian
120 O
U Barremian
S Hauteriv.
130
?
CHISANA FM.
- 3000 m lava flows,
tuff, breccia, and
minor mudstone
FA5
Valangin.
NIZINA MOUNTAIN FM.
- 250 m marine
mudstone, sandstone.
McCarthy
Fm.
LUBBE CREEK FM.
- 30-60 m marine
spiculite, mudstone,
and limestone
Nizina
Limestone
McCARTHY FM.
- 900 m marine mudstone,
limestone, and chert
CHITISTONE LIMESTONE
depositional hiatus
angular uncon.
disconformity
Tithonian
Kimm.
Oxfordian
Callovian
210 T
R
220 I
A
230 S
S
240 I
C
2
1
6
7
NUTZOTIN
MOUNTAINS
SEQUENCE
- 3000 m
marine
mudstone,
sandstone,
conglomerate
Bathonian
Bajocian
Aalenian
Toarcian
DZ
FA3,4
Nutzotin
Mountains
Sequence
FA1,2
Pleinsbach.
Sinemur.
Hettangian
NIZINA LIMESTONE
- 500 m marine limestone
and minor mudstone
Explanation
J
160 U
R
170 A
S
180 S
I
C
190
200
Chitistone
Limestone
NIKOLAI GREENSTONE
150
Berriasian
CHITINA?
Nizina
Mtn.
Fm.
Lubbe
Creek
Fm.
45
3
TALKEETNA
ROOT
GLACIER
FM.
-1100 m
marine mudstone,
sandstone,cong.
KOTSINA
CONG.
Chisana
Fm.
90
140
Lower
Root
Glacier
Fm.
~1000 m
Wrangell Mountains Stratigraphy
Page 350
CHISANA
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Period
GSA_SPE431_14_Ridgway.qxd
Norian
Carnian
Ladinian
McCarthy
Fm.
UNNAMED STRATA
(McCARTHY FM. equiv?)
marine mudstone,
limestone, and chert
Nizina
L.s.
NIZINA LIMESTONE
marine limestone
CHITISTONE LIMESTONE
NIKOLAI GREENSTONE
Chitistone
L.s.
Anisian
Olenekian
Nutzotin Mountains sequence lithology patterns
Fossiliferous shale,
siltstone, sandstone
Sandstone and siltstone
Graded sandstone, shale
Conglomerate
Shale, limestone, siltstone
Fossiliferous limestone
Nutzotin Mountains sequence
Buchia fossil ranges
1 - B. concentrica 5 - B. tolmatschowi
6 - B. sublaevis
2 - B. rugosa
3 - B. fischeriana 7 - B. crassicollis
4 - B. okensis
Figure 3. Stratigraphic chart showing the
stratigraphy of the Nutzotin and Wrangell
Mountains basins, stratigraphy of the
upper part of the Wrangellia terrane, and
the age ranges of associated volcanic
arcs. Also shown is the composite lithostratigraphic section of the Nutzotin and
Wrangell Mountains basins. Facies associations (FA1–FA5) discussed in the text
for the Nutzotin basin are labeled next to
the composite lithostratigraphic section.
Numbered vertical black bars in the Nutzotin Mountains sequence on the stratigraphy column correspond to age ranges
of Buchia species listed in key at bottom
of figure. Rectangle marked DZ on the
lithostratigraphic column marks the approximate stratigraphic position of sandstone sample from which detrital zircons
were collected and dated by U-Pb geochronology. Chart represents a synthesis of data presented in Richter (1976),
MacKevett (1978), Plafker et al. (1989),
Nokleberg et al. (1994a), and Trop et al.
(2002). Time scale is from Palmer and
Geissman (1999). Key at bottom of figure shows lithologic patterns and agediagnostic fossils of the Nutzotin Mountain
sequence.
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Chisana
Formation
Sedimentary record of the tectonic growth of a collisional continental margin
Northwest
351
Southeast
150 kilometers
18,19
20
21,22
Facies Ass. 5
15,16,17
FA3,4
2
FA3,4
3
n=30
n=31
7
FA3,4
FA3,4
n=19
Explanation
n=56
14
Upper Jurassic-Lower Cretaceous
9,10
1
Facies Associations 3,4
Conglomerate
8
Sandstone
n=57
Graded siltstone and shale
11
Shale and argillite
n=25
Fossiliferous mudstone
4,5,6
FA2
12,13
Volcanic rocks
FA1
FA2
n=218
Paleocurrent data
Decollement
?
?
Wrangellia composite terrane
Upper Jurassic
Gradational contact
unconformity
Penn.Triassic
Nutzotin Mountains Sequence
FA5
Gradational contact
Facies Associations 1,2
Nutzotin Mountains Sequence
Gradational contact
Lower Cret.
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Figure 4. Simplified northwest-southeast stratigraphic cross section through the Nutzotin basin showing lithostratigraphic relationships in the Nutzotin Mountains sequence. Numbers above each measured stratigraphic section correspond to location on the map shown in Figure 2. The Nutzotin
Mountains sequence has a depositional contact with Wrangellia along the south-central basin margin (measured sections 12, 13). Note that the Nutzotin Mountains sequence also has a fault contact with the Wrangellia terrane that is best documented in the northwestern part of the study area (measured sections 4, 5, 6). Also note that Facies Association 5 is only exposed in the southeastern part of the basin and that it has a gradational contact
with the overlying Chisana Formation. Notice the prevalence of east-directed paleoflow indicators in Facies Associations 3 and 4 (north is to the top
of the figure), whereas paleoflow indicators in Facies Association 1 are mainly to the northwest. Data for measured sections were collected as bedby-bed measurements using a Jacob staff. For detailed measured stratigraphic sections, see Manuszak (2000).
dextral fault system that spans more than 2200 km in a broad arc
from Alaska through British Columbia (Fig. 1A; Lanphere,
1978). Up to 400 km of Late Cretaceous-Tertiary displacement is
interpreted along the Denali fault based partly on correlation of
the Nutzotin basin as the offset equivalent of the Dezadeash basin
(Fig. 1A; Eisbacher, 1976; Jones et al., 1982; Nokleberg et al.,
1985; Plafker et al., 1989; Lowey, 1998). Much of this displacement is interpreted to have occurred during Eocene-Oligocene
time based on the ages of strike-slip basins exposed along the fault
system (Ridgway and DeCelles, 1993; Ridgway et al., 1995; Trop
et al., 2004). The Totschunda fault trends northwestward for 200
km from Canada to its junction with the Denali fault (Fig. 2A;
Richter and Matson, 1971). Displacement on the Totschunda fault
is dominantly dextral with maximum offsets of up to 4 km; faulting began at ca. 1 Ma (Plafker et al., 1977; Lisowski et al., 1987),
but possibly extends as far back as the Pleistocene time (Richter
and Matson, 1971). Recent earthquakes and neotectonic studies
indicate that the Denali and Totschunda faults are active structures
(Eberhart-Phillips et al., 2003; Matmon et al., 2006; Plafker et al.,
2006). GPS data indicate 8–9 mm/year dextral slip on the Denali
fault, with some slip likely on parallel strands north of the main
fault trace (Fletcher, 2002). Geodetic measurements across the
Totschunda fault show shear strain consistent with 5 mm/year
of dextral slip (Plafker et al., 1977).
SEDIMENTOLOIC AND STRATIGRAPHIC DATA
Our analysis of the sedimentologic and stratigraphic architecture of the Nutzotin Mountains sequence is based on 22 measured
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stratigraphic sections whose locations are shown on Figure 2. Five
facies associations within the Nutzotin Mountains sequence have
been identified based on grain size, geometry and thickness of
bedding, presence or lack of macrofauna and ichnofauna, and
types of sedimentary structures. General descriptions and depositional interpretations of the five facies associations are presented
in this section. Representative measured sections showing the
general stratigraphy of the Nutzotin Mountains sequence are
shown in Figure 4. For a more detailed discussion of the sedimentologic and stratigraphic data and more detailed measured stratigraphic sections, see Manuszak (2000).
Facies Descriptions
Facies Association 1
Description: Lenticular, matrix- and clast-supported conglomerate with interbedded shale. Facies Association 1 consists
of conglomerate that has an average bed thickness of 1–1.5 m,
lenticular geometries, and matrix- and clast-supported framework
(Fig. 5A). The conglomerate is poorly organized, has average
maximum clast sizes ranging from 6 to 29 cm, and contains outsized limestone clasts exceeding 10 m in diameter (Fig. 5B).
Upsection, the conglomerate is more commonly clast-supported,
has poorly developed normal grading, has average maximum clast
sizes of 6–8 cm, and contains interbedded shale and sandstone.
Shale lithofacies interbedded with the conglomerate include
minor thin limestone beds, disarticulated bivalve fossils, and carbonaceous plant debris. Sandstone lithofacies interbedded with
the conglomerate range in thickness from 2 to 100 cm and commonly display normal grading, tabular geometries, and isolated
pebble- to cobble-sized clasts. The lithofacies and bed thicknesses
common in Facies Association 1 are illustrated in our measured
stratigraphic section from Misty Mountain shown in Figure 6A.
Interpretation. We interpret Facies Association 1 to represent proximal, submarine-fan deposits. The matrix-supported
conglomerate and large outsized clasts are interpreted to be the
product of debris flows and rock-fall avalanches along proximal
portions of submarine canyons based on the coarse grain size, outsized clasts, poorly organized internal fabrics, and disarticulated
bivalve fossils (e.g., Lowe, 1982; Stow et al., 1996). Matrix
strength and momentum from the gravity flows permitted transportation of coarse-grained detritus and outsized clasts. Deposition occurred by rapid mass emplacement (“freezing”) when the
gravitational driving stress decreased below the matrix strength
(e.g., Johnson, 1965, 1970).
Lenticular, clast-supported conglomerate is interpreted to have
been deposited by gravelly debris flows transitional to densitymodified grain flows (e.g., Lowe, 1976a, 1982). The minor grading and lack of stratification suggests that fluid turbulence was
relatively unimportant as a clast-supporting mechanism. The
sandstone of Facies Association 1 is interpreted to be the deposits
of sandy turbidity currents based on the normal grading, grain
size, and tabular geometries (e.g., Bouma, 1962; Middleton,
1967; Lowe, 1976b). Suspension fallout is the interpreted depo-
sitional mechanism for the interbedded shale. The occurrence of
disarticulated bivalve fossils and plant debris within the shale is
suggestive of general proximity to marine shelfal environments.
Facies Association 2
Description: Nonfossiliferous, black shale with minor
amounts of red micritic limestone and lenticular conglomerate.
Massive black shale, that lacks macrofauna, is the most common
lithofacies in Facies Association 2 (Figs. 5C, 6B). Faint subhorizontal laminations and bioturbation are locally present throughout this facies association. Horizontal burrows less than a few
millimeters in diameter are most common and resemble Chondrites type 1–3 (e.g., D’Alessandro et al., 1986). Thin vertical
burrows are also observed but are uncommon. The Nereites trace
fossil Palaeodictyon occurs locally (Fig. 5D; e.g., D’Alessandro
et al., 1986). Red, silty limestone interbedded with the black shale
is up to 30 cm thick, lacks sedimentary structures, and becomes
less common upsection (Fig. 5C). Lenticular conglomerate
interbedded with the black shale occurs in beds that are 10 m in
width and a meter in thickness. These conglomerates are matrixsupported, poorly organized, and have clast sizes ranging from 3
to 50 cm. The lithologies and bed thicknesses that characterize
Facies Association 2 are shown in our measured stratigraphic section from Lost Creek (Fig. 6B).
Interpretation. We interpret Facies Association 2 to be
deposited mainly by deep-water hemipelagic sedimentation
and/or suspension fallout related to muddy turbidity currents on
distal parts of submarine-fan complexes (e.g., Stow et al., 1996).
This interpretation is based on the lack of sedimentary structures
indicative of tractive transport, and the bioturbation indicative
of the Nereites ichnofacies (e.g., Pemberton and MacEachern,
1992). Nereites ichnospecies, such as Paleodictyon, in mudstonesiltstone intervals are indicative of interdepositional colonization
and are common in deep-marine depositional environments (e.g.,
Seilacher, 1977; Walker, 1984; Buatois and Mangano, 2003). The
conglomerate lithofacies is interpreted to represent gravel-rich
channels that locally prograded into more distal parts of the
submarine-fan system (e.g., Shanmugam and Moiola, 1991).
Facies Association 3
Description: Normal-graded sandstone and shale. This
facies association consists of normal-graded sandstone and shale
beds that range in thickness from 1 to 50 cm (Fig. 5E). The lower
part of the graded beds is characterized by medium- to fine-grained
sandstone that commonly contains horizontal stratification, ripple
cross-stratification, rip-up clasts, and flute casts (Fig. 5F). The
upper part of the graded beds is characterized by shale that often
forms an abrupt contact with and less commonly is scoured into
by the overlying coarser sandstone beds (Fig. 5F). The shale often
contains horizontal and vertical burrows. The lithologies and bed
thicknesses common in Facies Association 3 are illustrated in our
measured stratigraphic section from Suslota Creek (Fig. 7A).
Interpretation. We interpret Facies Association 3 to represent
deposition in medial to distal environments within submarine-fan
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A
B
C
D
E
F
Fsr
Sm
Sr
Figure 5. Photographs of facies associations of the Nutzotin Mountains sequence. (A) Massive, unorganized conglomerate typical of Facies Association 1. Arrows point to boulder-size clasts. Bedded strata in lower part of photo are part of an individual outsized clast within the conglomerate. Person circled for scale. (B) Outsized limestone clast (white area in lower right) common in Facies Association 1. Black arrows point to edge of clast.
Person (circled) standing on clast for scale; bar scale next to person is 1.7 m. Dashed white lines (upper left) represent bedding in conglomerate and
shale that are laterally equivalent with outsized clast. (C) Interbedded black shale and silty limestone characteristic of Facies Association 2. Black
arrows point to prominent resistant limestone beds. Hammer circled for scale. (D) Trace fossil Paleodictyon in sandstone of Facies Association 2.
Black arrows point to honeycomb pattern characteristic of this trace fossil. Pencil (upper left) for scale. (E) Normal-graded sandstone and shale of
Facies Association 3. This is the most common lithofacies in the Nutzotin Mountains sequence. Lighter colored beds are sandstone and siltstone; the
darker beds are mudstone. Most sandstone beds in the photograph are <20 cm thick. Bedding in the photo dips to the left. Hammer circled for scale.
(F) Closeup photograph of normal-graded sandstone/shale characteristic of Facies Association 3. Black arrows point to erosional base of sandstone
that has scoured into underlying mudstone. Massive (Sm) and ripple-stratified (Sr) sandstone grade upward into ripple-laminated siltstone (Fsr) that
is overlain by massive shale. Coin (right center) for scale. (G) Amalgamated tabular sandstone of Facies Association 4. These sandstones are massive to weakly normal-graded. Bedding dips to the right and dashed white lines partly outline the base and top of an individual 35-cm-thick bed.
Black arrow points to hammer for scale. (H) Polymictic matrix-supported conglomerate characteristic of Facies Association 4 that is interbedded
with massive sandstone. Clast types: L limestone, D diorite, C chert, and Q quartz. Pen for scale. (I) Bioturbated shale with interbedded
thin tabular sandstone (black arrows) characteristic of Facies Association 5. Bedding is dipping to left. Person in lower center for scale. (J) Distinctive in situ fossil-rich horizon consisting of Buchia fossils that are common in Facies Association 5. Coin (white arrow) for scale. (K) Mudstone ripup clasts in matrix of Buchia shell hash and sandstone. Scale is 10 cm. (L) U-shaped horizontal trace fossil common on bedding surfaces of shale of
Facies Association 5. Coin (lower center) for scale.
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G
H
H
Q
C
D
L
I
J
K
L
Figure 5 continued
systems (e.g., Shanmugam and Moiola, 1991). The normalgraded sandstone/shale beds that characterize this facies association are best classified by the Bouma (1962) model for
turbidites and consist predominantly of Ta, Tb-d, and Te units. The
medium- to fine-grained sandstone at the base (Ta) grades upward to ripple-laminated sandstone (Tc) and less commonly into
laminated sandstone/ shale (Td) (Fig. 5F). These units are capped
by bioturbated shale (Te). The massive to graded Ta units were
most likely deposited rapidly by suspension fallout, whereas the
rippled to laminated Tb-d units were deposited more slowly under
tractive transport processes. The Te units are interpreted as being
deposited predominantly by suspension settling from midwater
or surface-water plumes, muddy turbidity currents, tails of sandy
turbidity currents, and/or hemipelagic processes.
Facies Association 4
Description: Tabular sandstone and clast-supported lenticular conglomerate. Facies Association 4 consists of tabular,
medium- to coarse-grained massive sandstone (Fig. 5G) interbedded with less common lenticular, pebble-cobble conglomerate
(Fig. 5H). The sandstone consists of amalgamated beds with an
average bed thickness of 0.5–1 m that are tabular on a scale of several kilometers. Interbedded conglomerate is moderately sorted
and has average maximum clast sizes ranging from 5 to 20 cm.
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Sedimentary record of the tectonic growth of a collisional continental margin
Explanation of Lithologic Patterns and Symbols
conglomerate
limestone
sandstone
dike/sill
shale
sandstone and shale
fossiliferous shale
covered interval
red silty limestone
limestone megaclast
carbonaceous shale
A
Facies
Association 1
(Misty Mountain 11 on Figure 2)
300
Figure 6. Representative measured stratigraphic sections for Facies Association 1
and Facies Association 2 that define the
lower part of the stratigraphy for the Nutzotin basin. Proximal lenticular conglomerate of Facies Association 1 is interpreted
to be laterally equivalent to the more distal black shale with isolated lenticular
conglomerate of Facies Association 2.
The inset for Facies Association 2 shows
the details of the lithologies characteristic
of this facies association. Facies Association 2 is dominated by shale with thin interbedded siltstone and silty limestone
beds. Lithology descriptions for the stratigraphic columns are shown at the top of
the figure. The stratigraphic sections do
not represent the complete thickness of
the facies associations. See text for additional discussion.
B
300
Facies
Association 2
(Lost Creek 6 on Figure 2)
Eroded
6
500
200
355
200
4
2
100
100
400
0
mud
0m
0m
300
s
m
p b
silt
s
m
p b
s
m
This facies association grades vertically and laterally into the
graded sandstone and shale beds of Facies Association 3. Our
measured stratigraphic section from Suslota Creek, shown on
Figure 7A, is representative of Facies Association 4 and illustrates
common lithologies, bed thicknesses, and the interbedded relationship with Facies Association 3.
Interpretation. The massive sandstone of Facies Association
4 is interpreted as the deposits of high-density turbidity currents
and liquefied flows in broad channels within distinct lobes of the
medial regions of submarine-fan systems (e.g., Clark and Pickering, 1996). This interpretation is based on their tabular geometries, amalgamated beds, lack of sedimentary structures, and their
interbedded relationship to the graded beds of Facies Association
3 (e.g., Lowe, 1976b; Middleton and Hampton, 1976; Stow et al.,
1996). The lack of well-developed grading suggests that sediment
p b
was deposited rapidly from turbulent suspensions with little time
for lateral segregation of the grains within the current prior to
deposition (e.g., Hein, 1982). Similar sandstone-rich facies are
described from ancient submarine-fan deposits interpreted to have
formed by sandy, high-density turbidity currents (e.g., Hiscott and
Middleton, 1979; Lowe, 1982; Trop et al., 1999). The conglomerate interbedded with the massive sandstone is interpreted to represent deposits of high-density turbidity flows and/or pebbly
debris flows (e.g., Lowe, 1982; Stow et al., 1996).
Facies Association 5
Description: Fossil-rich mudstone. This facies association
consists predominantly of fossiliferous, bioturbated mudstone
with minor amounts of sandstone, conglomerate, fossiliferous
limestone, and lava flows (Fig. 5I). Distinct fossil-rich bivalve
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Explanation of Lithologic Patterns and Symbols
conglomerate
limestone
sandstone
sill
shale/siltstone
covered interval
silty coquina
volcanic breccia
carbonaceous shale
lava flows
Upward-fining
beds
B.
Facies
Association 5
(Bonanza Creek 19 on Figure 2)
100's m of volcanic breccia and flows
A.
Chisana
Formation
300
300
Facies
Associations 3, 4
(Suslota Creek 2 on Figure 2)
Nutzotin
Mountains
Sequence
Figure 7. Representative measured stratigraphic sections for Facies Associations 3 to 5. The inset diagram for Facies
Associations 3 and 4 shows closeup
of normal-graded beds (black triangles)
characteristic of this facies association.
Volcanic strata at 290 m on Bonanza Creek
section marks the contact with the overlying Chisana Formation. Stratigraphic
sections do not represent the complete
thickness of the facies associations.
Eroded
200
500
200
100
400
100
2.5
0m
0m
300
s
m
p b
0
s
m
p b
horizons (Fig. 5J), isolated articulated bivalve fossils, rip-up
clasts (Fig. 5K), abundant horizontal feeding traces (probably
Cruziana or Zoophycos; Fig. 5L), and vertical burrows, dewatering structures, and carbonaceous plant debris characterize this
facies association. The fossil-rich horizons occur as both coquina
(concentrations of disarticulated reworked shell fragments;
Fig. 5J) and articulated, in situ horizons of the bivalve Buchia.
The articulated bivalve horizons contain densely clustered Buchia
shells that are uniform in length (4 cm down the long axis of the
shell), and form 10–20 cm thick tabular beds. The coquina beds
are up to 1 m thick, are sometimes interbedded with the articulated Buchia horizons, are locally lenticular over a distance of
5 m, commonly contain mudstone rip-up clasts that are up to 30
cm in length (Fig. 5K), and have horizontally stratified tops that
grade upward into bioturbated, fossiliferous shale.
s
m
p b
Sandstone, interbedded with the fossiliferous shale, generally occurs in tabular beds but locally is lenticular. Bed thickness
ranges from 1 to 30 cm. Minor channelized pebbly conglomerate
beds are also interbedded with the fossiliferous shale. Intercalated
basaltic to andesitic lava flows occur throughout this facies association and increase upsection toward the gradational contact with
the Chisana Formation (Fig. 7B). The common lithologies, bed
thicknesses, and the gradational contact with the Chisana Formation that characterize Facies Association 5 are shown on our measured stratigraphic section from Bonanza Creek (Fig. 7B).
Interpretation. We interpret Facies Association 5 to have been
deposited on a marine shelf based on the abundance of nontransported, open marine bivalve macrofauna (e.g., Zakharov, 1987;
Kidwell, 1991), and the predominance of bioturbated shale containing plant debris (e.g., Leithold, 1989). The in situ deposits of Buchia
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Sedimentary record of the tectonic growth of a collisional continental margin
and the coquina beds are interpreted to represent fair-weather and
storm deposits, respectively, on a marine shelf. Similar deposits of
Buchia have been described from other Jurassic-Cretaceous strata
of Alaska and have been interpreted as forming in less than 150 m
water depth (Miller and Detterman, 1985; Clautice et al., 2000; Trop
et al., 2005). The presence of Cruziana or Zoophycos ichnofacies is
also consistent with a shelf interpretation (e.g., Bottjer et al., 1987;
Vossler and Pemberton, 1988; MacEachern et al., 2005). The intercalated volcanic flows that increase upsection in Facies Association 5 probably mark the beginning of volcanism associated with
the overlying 3000 m of volcanic strata represented by the Chisana
Formation. The Chisana Formation has been interpreted as representing a volcanic arc complex (Plafker and Berg, 1994). In this context, Facies Association 5 may represent the muddy marine shelf
that flanked the embryonic Chisana arc.
Paleodrainage
Conglomerate imbrication, ripple stratification, and flute
casts allow us to reconstruct sediment transport directions in the
Nutzotin basin (Figs. 2A, 4). The paleocurrent data presented in
Figure 2A were all collected from coarse-grained strata (Facies
Associations 1, 3, and 4) and have been restored to horizontal
based on bedding orientation. Conglomerate imbrication (n 24)
in Facies Association 1 along the southern part of the outcrop belt
indicates predominantly northwestward sediment dispersal
(Fig. 2A). These data indicate that in proximal depositional environments sediment transport was away from the Wrangellia terrane. Conglomerate imbrication (n 66), ripple stratification (n 121), and flute casts (n 10) from Facies Associations 3 and 4 in
the northwestern part of the outcrop belt record predominantly
eastward sediment dispersal with a smaller component of southeastward paleoflow (Figs. 2A, 4). The eastward paleoflow in Facies Associations 3 and 4 suggests transverse flow away from the
Wrangellia terrane. The more southeasterly directed paleoflow
may represent axial drainage within the basin. Paleocurrent data
from ripple stratification (n 212) from the southeastern part
of the outcrop belt, reported from Kozinski (1985) within our Facies Associations 3 and 4, display northward sediment transport
(Fig. 2A). These paleoflow data also support transverse flow away
from the margin of the Wrangellia terrane. No paleocurrent indicators were observed from Facies Association 5; however, the
lithology of clasts in conglomerate (discussed below) within this
facies association suggests that detritus was also being derived
from the Wrangellia composite terrane located to the south of the
Nutzotin basin. Due to a lack of reliable paleomagnetic data from
strata of the Nutzotin Mountains sequence or from any overlying
strata, the possible role of block rotation about a vertical axis on
the distribution of our paleocurrent data cannot be evaluated. Raw
paleocurrent data are available in Manuszak (2000).
Summary: Stratigraphy and Depositional Systems
Our measured stratigraphic sections and geologic mapping
data, combined with previous paleontologic and geologic map-
357
ping studies (Richter, 1971, 1976; Richter and Schmoll, 1973;
Richter and Jones, 1973), define a three-part stratigraphy for the
Nutzotin Mountains sequence as shown on Figure 4. The lowest
part of the stratigraphy consists of proximal lenticular conglomerate of Facies Association 1 that is laterally equivalent to more
distal black shale and isolated lenses of conglomerate of Facies
Association 2. Facies Associations 1 and 2 are Upper Jurassic
(Tithonian-Oxfordian) based on marine megafossils (Richter,
1971; Richter and Schmoll, 1973). Facies Association 1 is at least
500 m thick and is exposed only along the southern part of the outcrop belt (Figs. 2A, 4). Geologic mapping shows that Facies
Association 1 has a depositional contact with the underlying
Wrangellia terrane (Richter, 1971; Manuszak, 2000). This depositional contact is well exposed at Misty Mountain (Fig. 2B).
Facies Association 2 is at least 300 m thick and also is only
exposed along the southern part of the outcrop belt (Figs. 2, 4). At
all localities where Facies Association 2 was mapped, it rests with
a fault contact on top of Triassic strata of the Wrangellia terrane
(Fig. 4; Manuszak, 2000). A lateral facies transition between
Facies Associations 1 and 2 is inferred based on similarities in fossil ages, lithofacies, clast composition of conglomerate, and relative stratigraphic position with overlying facies associations.
Stratigraphic correlation between Facies Associations 1 and 2
cannot be verified by physical correlation because of the lack of
continuous exposure and the presence of several faults between
outcrops of the two facies associations.
The middle part of the stratigraphy consists mainly of normalgraded sandstone and shale of Facies Association 3 (Fig. 4).
Interbedded with the graded sandstone and shale are tabular
coarse-grained sandstone and conglomerate of Facies Association
4 (Fig. 4). Facies Associations 3 and 4 are Upper Jurassic (Tithonian) to Lower Cretaceous (Valanginian) based on marine megafossils (Richter, 1976). Facies Association 3 has a minimum thickness
of 1000 m and is best exposed in the central and northern parts of
the outcrop belt (Fig. 2A). This facies association gradationally
overlies the strata of Facies Associations 1 and 2, is laterally equivalent with Facies Association 5 in the upper part of the basin fill,
and locally grades directly upward into the overlying Chisana Formation based on field observations. Facies Association 4 is found
throughout the outcrop belt (Figs. 2A, 4), but the thickest exposures (up to 300 m) are found in the central and southeastern part
of the outcrop belt.
The upper part of the stratigraphy consists of fossiliferous, bioturbated shale of Facies Association 5. These strata are Upper Jurassic (Tithonian) to Lower Cretaceous (Valanginian) based on marine
megafossils (Richter, 1971; Richter and Jones, 1973). Facies Association 5 is best exposed in the southeastern part of the outcrop belt
where it has a minimum thickness of 300 m (Figs. 2A, 4). An attempt
to better define the upper age limit of Facies Association 5 by radiometrically dating lava flows at the base of the Chisana Formation
was unsuccessful because of significant alteration of feldspar (P.W.
Layer, 2000, personal commun.). The available age data, along with
the gradational contact between Facies Association 5 and the
Chisana Formation, indicate that the Tithonian-Valanginian Facies
Association 5 grades into the Chisana Formation, which has an
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Aptian upper age limit (see discussion in Geologic Setting and Previous Studies).
We interpret the Nutzotin Mountains sequence as being
deposited mainly by sand- and mud-rich submarine-fan systems
(Facies Associations 1–4) that bordered a muddy marine shelf
(Facies Association 5). The submarine-fan interpretation is based
on (1) the dominance of sediment gravity flow deposits, especially turbidites and debris-flow lithofacies similar to those
described from submarine-fan models (e.g., Mutti and Ricci Lucchi, 1972, 1975; Pickering et al., 1986; Mutti, 1992); (2) the lack
of wave-formed cross-stratification or evidence of extensive
reworking by wave or tidal currents in Facies Associations 1–4;
and (3) the presence of transported open-marine megafossils in
Facies Associations 1–4. Our data suggest that the submarine-fan
systems probably developed along a base-of-slope setting where
a confined inner fan channel (submarine canyon) broadened into
a less confined basinal setting. Evidence for base-of-slope deposition includes the relative abundance of fan lobe deposits, the
lack of syndepositional slump folds, abundant sediment gravity
flow deposits, and the presence of rock-fall avalanche deposits
(e.g., Galloway, 1998).
Proximal regions of the submarine-fan systems during Late
Jurassic (Tithonian-Oxfordian) time were dominated by broad
gravel-rich channels that were filled by debris flows (matrixsupported and clast-supported conglomerate) and rock-fall
avalanches (large outsized clasts) of Facies Association 1. These
strata grade basinward into the shale-rich deposits that contain
isolated lenticular conglomerate of Facies Association 2. During
Late Jurassic to Early Cretaceous (Tithonian-Valanginian) time,
the medial parts of the submarine-fan systems were dominated by
broad lobes that were on the scale of several kilometers wide
and are represented by the tabular massive sandstone and clastsupported conglomerate of Facies Association 4. The coarsergrained lobes are interbedded with overbank medial and distal
submarine-fan deposits that are represented by the thin-bedded,
normal-graded turbidites of Facies Association 3. We interpret
the medial overbank deposits as forming in response to overbank
flows adjacent to the submarine lobes of Facies Association 4
(e.g., Mutti, 1977; Pickering, 1985; Nelson and Maldonado,
1988). Facies Association 5 represents the shallowest marine
depositional environments in the Nutzotin Mountains sequence.
The bivalve-rich shale that characterizes this lithofacies is interpreted as representing a muddy marine shelf that probably
flanked the embryonic Chisana arc. The in situ Buchia faunas
documented in Facies Association 5 have been interpreted in
other strata as forming in less than 150 m water depth (Clautice
et al., 2000; Trop et al., 2005).
COMPOSITIONAL AND PROVENANCE DATA
Provenance data from the Nutzotin Mountains sequence
include clast composition of conglomerate (n 1784), petrographic analysis of sandstone thin sections (n 17), and detri-
tal zircon geochronology (n 10). Clast compositional data
from conglomerate were collected by identifying 100 individual clasts within a delineated rectangular area within individual
beds. Thin sections used for petrographic analysis were cut from
medium- to coarse-grained sandstone samples and stained for
both potassium and plagioclase feldspar. The stained thin sections were point counted with a polarizing microscope; 400
grains were counted from each thin section. We followed the
Gazzi-Dickinson convention (e.g., Gazzi, 1966; Dickinson,
1970) whereby sand-sized monomineralic components of lithic
fragments are tallied as individual mineral grains, and only
aphanitic grains are classified as lithic fragments (e.g., Ingersoll
et al., 1984). Detrital zircon grains were collected by pulverizing a medium-grained sandstone sample and separating out zircons from other minerals using standard magnetic, density, and
chemical separation techniques. Detrital zircon age determinations were performed using standard isotope dilution-thermal
ionization mass spectrometry as described by Gehrels et al.
(1991). All zircon populations were analyzed to delineate different age groups.
Conglomerate Data
Clast types in conglomerate of the Nutzotin Mountains sequence consist mainly of metabasalt/greenstone, limestone, chert,
quartz, granite/diorite, and fine-grained volcanic clasts. Conglomerate compositional data are plotted in Figure 8Aaccording to their
facies associations/stratigraphic position described in the previous
section. The data represent compiled clast counts from multiple
stratigraphic horizons within individual facies associations.
Metabasalt/greenstone clasts are dark gray green and exhibit
aphanitic to porphyritic textures in hand sample. Petrographic
analysis shows that these clasts have sericite and chlorite alteration and contain elongate phenocrysts of plagioclase and pyroxene. The percentage of metabasalt/greenstone clasts increases
upsection in the Nutzotin Mountains sequence (Fig. 8A). Limestone clasts range from light to dark gray, have micritic textures,
usually lack any observed macrofauna, and may contain calcite
veins. The relative abundance of limestone clasts decreases
upsection (Fig. 8A). Chert clasts are commonly black but some
are dark gray. Chert clasts comprise small percentages of the
overall clast types in each of the facies associations; however,
they do show a relative upsection decrease (Fig. 8A). Quartz
clasts are milky white and show a relative upsection decrease
(Fig. 8A). Plutonic clasts are dominantly felsic, ranging in composition from diorite to granite. Identifiable phenocrysts include
quartz, feldspar, amphibole, pyroxene, and biotite in a finegrained, white to light gray groundmass. Granite/diorite clasts
increase upsection but are not observed in Facies Association 5.
Volcanic clasts consist mostly of light gray, brown, and white
fine-grained tuffs that often contain small white, black, green, or
gray phenocrysts. The aphanitic volcanic clasts decrease upsection in relative abundance (Fig. 8A). Clasts in the “other” category occur in minor quantities (<5%) and include argillite,
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Sedimentary record of the tectonic growth of a collisional continental margin
A Conglomerate Clast Counts
100
97%
100 88%
80
Facies Association 5
n=102
80
B Sandstone Point Counts
% 60
% 60
40
40
20
0
G
20
0%
1%
0%
0%
2%
0%
L
C
Q
P
O
V
100
% 60
40
80
9%
0
L
C
3%
Q
13%
P
1%
3%
O
V
1%
Q
4%
Lv
5%
P
78%
Facies Associations 3, 4
n=2263
14%
20
2%
0
F
L
0%
C
3%
2%
Q
Lv
P
Figure 8. (A) Histograms showing the
clast composition of conglomerate from
the facies associations of the Nutzotin
Mountains sequence. Note the relative
upsection decrease in limestone, finegrained volcanic, and chert clasts, as well
as the upsection increase in metabasalt
clasts. Conglomerate data collected from
multiple stratigraphic horizons for each
facies association in our measured sections labeled 1, 2, 4, 5, 6, 11, 12, and 19 on
Figure 2. n total number of clast
counted. See text for additional discussion and for description of common clast
types. (B) Histograms showing sandstone
point-count compositional data from each
facies association. Note upsection relative
increase in feldspar and decrease in quartz
and volcanic lithic grains. See text for additional discussion.
100
100
Facies Associations 1, 2
n=769
53%
80
% 60
80
% 60
40
0
0%
C
40
27%
20
20
F
0%
L
% 60
44%
G
0
100
Facies Associations 3, 4
n=913
80
Facies Association 5
n=1968
359
58%
Facies Associations 1, 2
n=2924
40
15%
5%
G
L
C
8%
4%
5%
Q
P
O
10%
V
Explanation: G=metabasalt, L=limestone, C=chert, Q=quartz,
P=granite/diorite, O=other, V=extrusive igneous
26%
20
0
1%
2%
9%
L
C
Q
F
4%
Lv
P
Explanation: F=feldspar, L=limestone, C=chert,
Q=quartz, Lv=lithic volcanic, P=pyroxene/hnbl
sandstone, mafic-intrusive, and metasedimentary clasts (Fig. 8A).
Raw clast count data are available in Manuszak (2000).
Sandstone Data
Sandstones of the Nutzotin Mountains sequence can be classified as feldspathic wackes (e.g., Dott, 1964) or lithofeldspathic
subquartzose sandstones (e.g., Dickinson, 1970). The sandstones
point counted in this study are poorly to moderately sorted,
medium- to coarse-grained, and often exhibit some clay and/or
calcite alteration of framework grains. The framework modes of
17 sandstones from the Nutzotin Mountains sequence are shown
graphically in Figures 8B and 9. Recalculated and raw pointcount data, as well as photomicrographs of common framework
grains in sandstones, are available in Manuszak (2000).
The modal compositions for sandstones of the Nutzotin Mountains sequence are Q6F67L27, Qm4F67Lt29, Qm5P95K0, Lv71Lm15Ls14,
and Lvm72Lsm17Qp11 (Fig. 9). Note the low total quartz content (Q),
that plagioclase (P) represents 95% of the total monocrystalline
count, and that volcanic fragments (Lv) compose 71% of the unstable lithic grains. Plagioclase is most commonly observed as individual grains or as laths within volcanic lithic fragments. Common
unstable lithic grains include volcanic grains with trachytic, pilotaxitic, hyalopilitic, or felsitic textures; sedimentary grains of
siliceous mudstone, and brown to black mudstone; and metamorphic grains of quartz mica schist, mica schist, and foliated mud-
stone grains. Six of the seventeen thin sections analyzed in this
study contain substantial amounts of pyroxene and hornblende
grains (as high as 29% in one thin section). Microprobe analysis
indicates that some of these grains are calcium- and magnesiumrich clinopyroxenes.
The average sandstone composition for the Nutzotin Mountains sequence shown on Figure 9 overlaps the magmatic arc and
continental block-basement uplift provenance fields of Dickinson
et al. (1983). Note that sandstone from low in the stratigraphic
section (Facies Association 1) plots mostly in the magmatic arc
provenance field (Fig. 9), whereas sandstone from the middle of
the section (Facies Associations 3 and 4) overlaps both the magmatic arc and continental block-basement uplift provenance
fields. Sandstone from the upper part of the section (Facies Association 5) plots entirely in the continental block-basement uplift
provenance field (Fig. 9). Figure 8B shows the relative proportions of six common framework grain types based on facies association/stratigraphic position. Note the upsection relative increase
in feldspar and decrease in volcanic lithic and quartz grains.
Detrital Zircon Geochronology
U-Pb ages were determined on ten detrital zircons extracted
from a medium-grained sandstone of Facies Association 3 within
the South Noyes measured section (section 7 on Figures 2, 4). The
relative stratigraphic position of this sample within the Nutzotin
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Q
Explanation
Facies Association 5 (n=4)
Facies Associations 3, 4 (n=5)
Facies Association 1 (n=8)
Mean of all sandstones
Recycled
Orogen
Continental
Block-Basement
Uplift
Figure 9. Ternary diagrams showing modal
composition of sandstone from facies associations of the Nutzotin Mountains sequence. Dashed areas represent one
standard deviation from the mean modal
composition. Recycled orogen, magmatic
arc, continental block-basement uplift, and
mixed provenance fields from Dickinson
et al. (1983). Note that the average sandstone composition for Nutzotin Mountains
sequence overlaps the magmatic arc and
continental block-basement uplift fields.
Qm
Lm
Magmatic
Arc
F
L
Qp
Ls
cy
rog
en
F
do
Magmatic
Arc
cle
Mixed
Lv
K
Re
Co
n
Ba tinen
sem tal
en Blo
t u ck/
plif
t
Qm
P
Lt Lvm
Mountain sequence is shown on Figure 3. We extracted individual zircons from the sandstone, sieved them according to size, and
divided them into populations based on color and degree of textural maturity. Ten grains were selected as representatives from
the zircon populations and analyzed. Analytical details and raw
data are shown on Table 1. The analysis of the ten grains shows
two age groups of 151–147 (n 8) and 159–156 Ma (n 2) (Fig.
10). These interpreted ages are based on the 206Pb/238U ratios
shown on Table 1.
Provenance Discussion
Our compositional data, combined with northward- and eastward-directed paleocurrent measurements (Fig. 2A), indicate that
most of the Nutzotin Mountains sequence was derived from
mainly Paleozoic-Triassic metavolcanic strata of the Wrangellia
terrane, Upper Jurassic-Lower Cretaceous igneous rocks representing the Chitina and Chisana arcs, and possibly sedimentary
strata of the Wrangell Mountains basin. The compositional data
indicate exhumation and progressive erosion of deeper stratigraphic/structural levels of the Wrangellia terrane during deposition of the Nutzotin Mountains sequence. Conglomerates in the
lower part of the section (Facies Associations 1 and 2), for example, are dominated by limestone and chert clasts (Fig. 8A) interpreted as being derived from the Upper Triassic-Lower Jurassic
Chitistone and Nizina Limestones and the McCarthy Formation
(Fig. 3). Conglomerates in the middle of the section (Facies Asso-
Lsm
ciations 3 and 4) contain a mixture of metabasalt/greenstone,
limestone, and chert clasts (Fig. 8A). The metabasalt/greenstone
clasts are petrographically similar to the metabasalt of the Lower to
Middle Triassic Nikolai Greenstone and Pennsylvanian-Permian
Skolai Group and reflect unroofing of deeper stratigraphic levels
of the Wrangellia terrane. Conglomerate in the upper part of the
basin fill (Facies Association 5) consists almost entirely of metabasalt/greenstone clasts that record exhumation of the basaltic
roots of the Wrangellia terrane during deposition of this part of the
Nutzotin Mountains sequence. Detritus from the Chitina arc is
represented by granite/diorite clasts, fine-grained volcanic clasts
(Fig. 8A), and detrital zircons with concordant U-Pb ages of ca.
159–147 Ma (Fig. 10). These ages are consistent with previously
published thermochronologic data from plutonic rocks of the
Chitina arc, which yield Late Jurassic U-Pb zircon crystallization
ages (153–150 Ma; Plafker et al., 1989; Roeske et al., 2003) and
Late Jurassic-Early Cretaceous K-Ar and Ar-Ar cooling ages
(146–138 Ma; MacKevett, 1978; Plafker et al., 1989; Roeske
et al., 1992, 2003). Another possible source for the dated detrital
zircons is Triassic-Jurassic diorites mapped by Richter (1976) that
yielded a K-Ar age of 163 4 Ma. These rocks are very limited
in their distribution and only one radiometric age is available, but
they crop out close to the Nutzotin Mountains sequence (labeled
Jp on Fig. 2).
Our sandstone compositional data also record the unroofing
of the Wrangellia terrane and associated arcs. Sandstones from
the lower part of the Nutzotin Mountains sequence (Facies Asso-
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361
TABLE 1. U-PB ISOTOPIC DATA AND APPARENT AGES
Apparent Ages (ma)
Grain
Type
WT.
(μg)
U
(ppm)
Pbc
(pg)
206Pb/204Pb
206Pb/208Pb
(raw)
(corr)
206Pb*/238U
207Pb*/235U
207Pb*/206Pb*
150.1
149.7
156.2
148.6
158.7
149.9
151.1
147.5
148.3
149.7
2.2
5.1
4.2
3.0
4.1
2.9
4.4
1.6
2.0
2.4
149.9
150.5
157.5
150.1
158.1
149.6
152.6
147.0
147.6
149.5
3.1
6.3
6.9
3.8
4.9
3.5
5.3
2.0
2.9
3.7
146
164
177
174
150
145
176
140
136
146
42
55
77
34
38
29
43
19
32
42
NOYES
ME
MR
MR
CR
MR
MR
CR
MR
MR
CE
22
11
13
9
13
16
14
21
19
16
347
163
163
347
176
199
150
316
264
246
20
8
15
6
5
5
7
7
10
14
595
343
248
758
695
941
452
1475
264
442
7.2
6.9
4.6
10.8
12.8
8.7
7.9
9.1
8.2
5.8
* radiogenic Pb
Zircon type: M Medium pink, C Colorless, R Rounded/Spherical, E Euhedral.
206Pb/204Pb (raw) measured ratio, uncorrected for blank, spike, or fractionation.
206Pb/208Pb (corr.) ratio corrected for blank, spike, and fractionation.
Pbc total common Pb in analysis.
All zircon grains were abraded in an air abrasion device to 2/3 of their original diameter.
U concentration has an uncertainty of up to 25% due to uncertainty in weight of grain.
Constants used: λ235 9.8485 10-10, λ238 1.55125 10-10, 238U/235U 137.88.
Data reduction from Ludwig (1991).
170
206Pb/ 238U
0.026
160
0.024
0.022
150
140
0.15
0.16
207Pb*
0.17
/
0.18
235U
Figure 10. U-Pb concordia plot for ten detrital zircons from Lower Cretaceous sandstone sample of Facies Association 3. Sample was collected
from measured section labeled 7 on Figure 2. Note the two age groups of
147–151 (n 8) and 156–159 Ma (n 2). Detrital zircon ages overlap
U-Pb zircon ages from Jurassic plutons in the Chitina arc (153–150 Ma;
Plafker et al., 1989; Roeske et al., 2003). See text for discussion. See
Table 1 and Manuszak (2000) for analytical details and raw data.
ciation 1) show a relative increase in volcanic lithic fragments
(Figs. 8B, 9) and relatively unaltered feldspars. We interpret these
sandstones as being derived from the volcanic edifice of the
Chitina arc. These sandstones plot mainly in the magmatic arc
provenance fields (Fig. 9). Sandstones from higher in the section
(Facies Associations 3 and 4) overlap both the magmatic arc and
continental block-basement provenance fields suggesting a
feldspar-rich source terrane. The most likely source terrane for
these sandstones is the 3000-m-thick Nikolai Greenstone and the
plutonic roots of the Chitina arc. Sandstones from the upper part
of the Nutzotin Mountains sequence (Facies Association 5) have
the highest percentage of feldspar and lowest percentage of volcanic lithic fragments. Feldspar in these sandstones is highly
altered by chlorite and epidote suggesting derivation mainly from
the mafic basement of the Wrangellia terrane (the Nikolai Greenstone and Skolai Group). Some of the feldspar in the upper part
of the Nutzotin Mountains sequence may have also been derived
from the deeper plutonic levels of the Chitina and Chisana arcs.
GEOLOGIC MAPPING AND CROSS SECTIONS
Figure 2B is a simplified regional cross section from the
southern margin of the Yukon composite terrane, through the Nutzotin basin, and into the Wrangellia terrane based on geologic
mapping during this study and by Richter (1976). This cross section illustrates the geometry of the suture zone between the
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allochthonous Wrangellia terrane and the former Mesozoic continental margin of North America (i.e., the Yukon composite terrane). Note that the suture zone contains a range of structural
styles including reverse, normal, and strike-slip faults. Also note
that the cross section shows regional folds that have wavelengths
on the order of 15 km. Figure 11 is an enlargement of the regional
cross section presented in Figure 2B that focuses on the structural
configuration of strata of the Nutzotin basin and the major structures that deformed the Nutzotin Mountains sequence. This cross
section shows a north-dipping regional décollement that transported the majority of the Nutzotin Mountains sequence southward over the Wrangellia terrane (labeled Lost Creek décollement
in Fig. 11). It also shows north-dipping thrust faults and related
folds within the Nutzotin Mountains sequence (e.g., area near
Buck Creek pluton in Fig. 11); major strike-slip faults that include
the Denali and Totschunda fault systems; and normal faults (e.g.,
area near southern end of cross section in Fig. 11). In the following sections, we discuss each of these structural styles and their
possible timing based on geologic mapping data.
Contractional Structures
We have identified a décollement horizon that displaced distal
basinal strata of the Nutzotin Mountains sequence southwestward
(present coordinates) over both more proximal basinal strata of the
Nutzotin Mountains sequence as well as the Wrangellia terrane.
Figure 12 is a reconnaissance field map of the Lost Creek area,
where the décollement is particularly well exposed. We informally
refer to the décollement as the Lost Creek décollement because of
the excellent exposures in this area. Attitudes collected from the
Buck
Creek
fault
Buck
Creek
pluton
C
2400m North
Denali
fault
Lost Creek décollement surface show that it has an average orientation of N70W/31NE. The footwall of the décollement includes
the McCarthy Formation, which consists of 100 m of dark gray,
micritic limestone interbedded with black chert, siliceous argillite,
and carbonaceous shale (Fig. 12). The hanging wall consists of Facies Association 1 of the Nutzotin Mountains sequence. Overturned
drag folds in the hanging wall of the décollement have axial surfaces that dip to the northeast (Figs. 12, 13A) indicating southwestward displacement of the hanging wall (e.g., Ramberg, 1963). This
tectonic transport direction is corroborated by monoclinal kink
bands in the footwall that show preferential development of central
limbs that dip steeply to the northeast; this orientation is indicative
of shear produced from the hanging wall moving to the southwest
(Figs. 12, 13B; e.g., Pfaff and Johnson, 1989). For a more detailed
discussion of the analysis of folds in the Nutzotin Mountain sequence see Manuszak (2000). Tertiary-Cretaceous dikes (Richter
and Schmoll, 1973) and a radiometrically dated, undeformed pluton (Suslota Pass Pluton of Richter et al., 1975) crosscut the Lost
Creek décollement indicating that the age of displacement along the
décollement in this area must be older than ca. 117–105 Ma. The
décollement is interpreted to have been truncated by the Totschunda
and Denali strike-slip faults (Fig. 11).
In the hanging wall above the décollement, north-dipping
thrust faults and overturned folds are common in the Nutzotin
Mountains sequence (Fig. 11). Many of these structures were
originally identified by the mapping of Richter and Jones (1973).
Thrust faults with displacements on the order of a few kilometers
are common throughout the area (e.g., Buck Creek fault in Fig. 11).
Figure 13C, for example, shows a thrust fault in the southwestern
part of the basin that juxtaposes Facies Association 3 in the hang-
B
Totschunda
fault
FA3,4
Lost
Lost
Creek
Creek
decollement pluton
Trn
FA3,4
FA3,4
A
South
Qs
YT
SL
FA1,2
FA1,2
Trl
A
A
T
T
Pu
Trn
Trn
-2400m
Pu
Trl
?
Vertical exagerration = 3:1
0
5
10
15
20 km
Nutzotin Mountains sequence
FA1,2 Facies Association 1, 2
FA3,4 Facies Association 3, 4
Qs
Quaternary surfical deposits
QTv Quaternary-Tertiary Wrangell Lava
Lower Cretaceous plutons
YT
Lower Paleozoic Yukon composite terrane
Wrangellia composite terrane
Trl
Upper Triassic Nizina Limestone and McCarthy Fm.
Trn Upper Triassic Nikolai Greenstone
Pu
A T
Strike slip fault
High-angle reverse/normal fault
Decollement
Bedding
Bedding dip indicator
Penn.-Permian Station Creek Formation
Figure 11. North-south cross section showing structural relationships between the Nutzotin Mountains sequence, the Wrangellia terrane, and the
Yukon composite terrane. Line of cross section shown on Figure 2. Bedding attitudes from this study, Richter et al. (1975) and Richter (1976). Radiometric dates are not available from the Buck Creek, Lost Creek, and Devil’s Mountain plutons, but they are interpreted as equivalent to a suite of
nearby plutons with 118–105 Ma K-Ar ages. See text for discussion.
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0
1 km 30
143o07’
363
both abrupt changes in thickness and lithofacies across syndepositional normal faults (Trop, 2000; Trop et al., 2002).
KJs
38
Los
FZ
Strike-Slip Structures
38
t
Cre
ek
Trm
De
32
KJs
co
lle
Trnl
Lo
st
me
nt
1
2
13
Trn
Trm
KJs
FZ
26
62o36’
ek
Cre
Qal
65
Trn
20
Explanation
Qs Quaternary deposits
KJs Nutzotin Mtns. sequence
Trm McCarthy Fm.
Trnl Nizina Limestone
Trn Nikolai Greenstone
FZ Fault zone
38
25
Strike/dip
bedding
Oblique-slip fault
Overturned
fold
Depo. Contact
Thrust fault
Inferred contact
1
Photo Locations
The Denali and Totschunda faults are the two dominant
strike-slip faults in the study area (Fig. 2A), and are shown in the
northern and central parts of the cross section in Figure 11. Both
faults are interpreted as accommodating mainly Cenozoic displacement (Richter and Jones, 1973; Plafker and Berg, 1994;
Eberhart-Phillips et al., 2003). The Denali fault juxtaposes the
Nutzotin Mountains sequence against Devonian metamorphic
rocks of the Yukon composite terrane (Fig. 11). The Totschunda
fault has been interpreted to be a relatively young (ca. 1 Ma) dextral strike-slip fault that has accommodated primarily horizontal
offsets (Fig. 13E; Plafker et al., 1977; Lisowski et al., 1987).
Lithofacies mapping suggests that the Totschunda fault may have
formed along a preexisting thrust fault that had juxtaposed Upper
Jurassic strata of Facies Associations 1 and 2 against younger Cretaceous strata of Facies Associations 3 and 4 (Fig. 11).
DISCUSSION
Stream
Figure 12. Simplified geologic map adjacent to the Lost Creek décollement in the northwestern part of the Nutzotin basin. Location of map
shown on Figure 2A. Photo location 1 is shown on Figure 13A; photo
location 2 is shown on Figure 13B. See text for discussion.
ing wall against Facies Association 5 and the Chisana Formation
in the footwall. Upright and overturned folds with wavelengths of
up to 2 km are common in the Nutzotin Mountains sequence
and are usually associated with nearby faults. Relatively undeformed Cretaceous plutons with K-Ar ages of ca. 117–105 Ma
(Richter et al., 1975) that crosscut both thrust faults and folds in
the upper plate provide a minimum age for the end of contractional deformation.
Extensional Structures
Normal faults are common in the study area and offset both
the Nutzotin Mountains sequence and the Chisana Formation
(Figs. 11, 13D; Richter and Jones, 1973). Note the normal faults
shown in the central and southern parts of the cross sections (e.g.,
near Misty Mountain on Figures 2B, 13D). The extensional deformation documented in the Nutzotin Mountains sequence needs
much more additional study, but we tentatively interpret this
deformation as correlative to better-documented Early to Late
Cretaceous (Albian-Campanian) normal faulting in the Wrangell
Mountains basin (Trop et al., 2002). In the Wrangell Mountains
basin, Upper Lower to Upper Cretaceous siliciclastic strata show
Development of the Nutzotin Basin
Figure 14 illustrates our interpretation of the stages of basin
development for the Nutzotin basin based on our new data as well
as data from previous investigations (e.g., Berg et al., 1972;
Richter and Jones, 1973; Richter, 1976; Kozinski, 1985). The earliest record of subsidence in the Nutzotin basin is represented by
Upper Jurassic (Oxfordian-Tithonian) submarine-fan strata of
Facies Associations 1 and 2. Proximal submarine-fan strata, consisting of conglomerate with outsized limestone clasts (Facies
Association 1), were deposited unconformably over the northern
margin (present coordinates) of the Wrangellia terrane (Fig. 14A).
This unconformity represents a ca. 50 m.y. depositional hiatus
between the underlying Upper Triassic-Lower Jurassic McCarthy
Formation and the overlying Upper Jurassic part of the Nutzotin
Mountains sequence (Fig. 3). The unconformity at the base of the
Nutzotin Mountains sequence marks a change from deep-marine,
fine-grained calcareous and siliceous strata (i.e., the McCarthy
Formation) that contain no detritus demonstrably linked to erosion of the Wrangellia terrane to coarse-grained, submarine-fan
strata of Facies Association 1 that clearly record exhumation and
erosion of the Wrangellia terrane. We interpret this unconformity
to partly represent a regional tectonic event that deformed and
exhumed the Wrangellia terrane based on the boulder conglomerate that overlies the unconformity (Facies Association 1). The
conglomerate of Facies Association 1 represents deposition by
debris flows and rock-fall avalanches in submarine canyons and
other proximal regions of submarine-fan systems (Fig. 14A).
Northward-directed paleocurrent data from Facies Association 1
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A
D
KJs
Trn
Trl
Trn
B
E
SE
NW
FA3,4
WCT
FA1,2
C
FA3, 4
FA3, 4
FA5
Kc
Kc
Figure 13. (A) Closeup photograph of overturned fold in hanging wall of the Lost Creek décollement. Fold is verging to the southwest. Hammer (circled) for scale. Photo is from Location 1 shown on Figure 12. (B) Kink fold in the footwall of the Lost Creek décollement. Person (circled) for scale.
View is to the southeast. Photo is from Location 2 shown on Figure 12. (C) Intrabasinal thrust fault that places Facies Associations 3 and 4 (labeled
FA3, 4) in the hanging wall over Facies Association 5 (FA5) and the Chisana Formation (Kc) in the footwall (low-lying hills in midground). White
barbed line shows fault trace; barbs on upthrown side of fault. Photo location is from area near measured section 18 on Figure 2A. View is to the
northeast. (D) Normal fault that juxtaposes Triassic Nikolai Greenstone (Trn) against younger Triassic Nizina Limestone (Trl) and the Nutzotin
Mountains sequence (KJs). Black line shows fault trace; black arrow shows relative displacement. Photo is from the Lost Creek area in the northwestern part of the basin along the southern basin margin. Person circled for scale. (E) Trace of the Totschunda strike-slip fault (white dashed line)
in the headwaters of the Nabesna River. View is to the south. WCT Wrangellia composite terrane. Note the juxtaposition of Facies Associations
1 and 2 (FA1, 2) with Facies Associations 3 and 4 (FA3, 4) along the fault system.
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Sedimentary record of the tectonic growth of a collisional continental margin
A Late Jurassic
365
B Latest Jurassic to Early Cretaceous
RA
Ps
FA3
?
RA
FA1
Tn
Ps
FA2
Tc
Tn
?
Tn
Tn
FA4
Tc
Tm
Tm
C Early to Late Early Cretaceous
D Late Early Cretaceous
RA
LP
RA
RA
Ps
FA3
Kc
Tn
Ps
Tn
Tn
FA5
FA4
Tn
Tc
Tm
LF
Tc
Tm
AP
E Latest Cretaceous to Tertiary
EXPLANATION
TKs
LP
DF
RA
Ps
Tn
Tn
Tc
Tm
A
AP
T
DF
Nutzotin Basin
TKs Unnamed Cret.? strata
Kc Chisana Formation
Nutzotin Mtns. Sequence
FA1 Facies Association 1
FA2 Facies Association 2
FA3 Facies Association 3
FA4 Facies Association 4
FA5 Facies Association 5
Yukon composite terrane
YT Precambrian-Paleozoic
metamorphic rocks
Wrangellia Terrane
Tm McCarthy Formation
Tc
Chitistone/Nizina Limestone
Tn Nikolai Greenstone
P
Ps Skolai Group
Volcano
Submarine fan
Decollement
Thrust fault
Normal fault
Dextral strike-slip fault
Figure 14. Simplified block diagrams showing stages of basin development for the Nutzotin basin. View is roughly to the northwest (present coordinates). See text for discussion. AP = Antler pluton; LP = Lost Creek pluton.
indicate that sediment dispersal was away from the northern margin of the Wrangellia terrane. The abundant limestone and chert
clasts in conglomerate and the volcanic lithic-rich sandstone of
Facies Association 1 (Figs. 8A, 9) indicate that the uppermost
units of the Wrangellia terrane (i.e., the Nizina and McCarthy
Limestones; Figure 3; Tc and Tm on Figure 14A) and the active
Chitina arc were the primary sources of sediment for this first
stage of basin development. Distal submarine-fan strata of Facies
Association 2, represented by mainly black shale with thin
micritic limestone and isolated conglomerate lenses, were
deposited predominantly by fine-grained turbidity flows and
hemipelagic processes in the distal regions of submarine-fan systems (Fig. 14A).
The Upper Jurassic-Lower Cretaceous normal-graded sandstone and shale of Facies Association 3 and the tabular sandstone
and clast-supported conglomerate of Facies Association 4 represent the main phase of sedimentation and subsidence in the Nutzotin basin. The greater than 1000 m of strata associated with
Facies Associations 3 and 4 are the product of well-developed
transverse and axial submarine-fan systems (Fig. 14B). The bulk
of the sediment deposited in the submarine-fan systems was derived from the Wrangellia terrane and the remnant Chitina arc (RA
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in Fig. 14B) based on our compositional and paleocurrent data.
The exhumation of deeper stratigraphic levels of the Wrangellia
terrane (i.e., the Nikolai Greenstone and Skolai Group) is recorded
by the upsection relative increase of metabasalt/greenstone clasts
in conglomerate of the Nutzotin Mountains sequence (Fig. 8A).
The relative upsection increase in igneous clasts also reflects exhumation of deeper levels of the Chitina arc; this arc was built on
the southern margin of the Wrangellia terrane (Fig. 14B). Similarly, detrital zircons from sandstone of Facies Association 3 yield
concordant U-Pb ages that are consistent with previously published isotopic ages from plutons of the Chitina arc (e.g., Plafker
et al., 1989; Roeske et al., 1992; Nokleberg et al., 1994a). Sandstone compositional data from Facies Associations 3 and 4 of the
Nutzotin Mountains sequence indicate derivation from magmatic
arc and uplifted basement sources (Fig. 9), which we interpret as
being the volcanic-rich strata of the Wrangellia terrane and the
Chitina arc, and the plutonic rocks of the Chitina arc, respectively.
Eastward and southeastward paleoflow indicators from Facies Associations 3 and 4 are consistent with our compositional data and
the interpretation of mainly Wrangellia terrane sources for sediment of the Nutzotin basin.
The next stage of basin development recorded in the Nutzotin Mountain sequence is defined by Lower Cretaceous fossiliferous shale of Facies Association 5. The presence of sedimentary
structures indicative of tractive transport and the abundance of
nontransported open marine bivalve macrofauna indicate that
Facies Association 5 represents deposition on a marine shelf
(Fig. 14C). Exposures of these strata are limited to the southern
margin of the Nutzotin basin. More proximal, shallow-water
strata of Facies Association 5 are interpreted to grade basinward
into the more distal, upper part of Facies Association 3. Both Facies
Associations 5 and 3 have gradational contacts with the base of the
overlying Chisana Formation. Clast compositional data from
Facies Association 5 are dominated by metabasalt/greenstone clasts
(Fig. 8A) suggestive of derivation from the basaltic roots of the
Wrangellia terrane (i.e., the Nikolai Greenstone and Skolai Group).
Overlying the sedimentary strata of Facies Association 5 with a gradational contact are 3000 m of volcanic strata of the Chisana Formation (Fig. 3). The Chisana Formation represents a late Early
Cretaceous volcanic arc that was constructed 50 km northeast
of the exhumed and erosionally dissected Late Jurassic Chitina
arc (Fig. 1B; Berg et al., 1972; Plafker and Berg, 1994; Short
et al., 2005).
Regional shortening of the Nutzotin Mountain sequence
occurred on a series of north-dipping thrust faults and southverging folds during Late early Cretaceous time (Fig. 11). These
thrust faults are interpreted to sole into a basal décollement (e.g.,
the Lost Creek décollement; labeled LF in Fig. 14D). Displacement on this décollement resulted in the juxtaposition of more distal strata of the Nutzotin Mountains sequence over both more
proximal strata as well as the Wrangellia terrane (Figs. 11, 14D).
This crustal shortening must have occurred before emplacement
of the 117–105 Ma undeformed granitic plutons that crosscut both
the décollement and folded strata of the Nutzotin Mountains
sequence (labeled LP and AP in Figure 14D; Richter, 1976;
Manuszak, 2000).
Subaerial erosion, nonmarine deposition, and possibly normal
faulting characterize the Nutzotin basin during latest Cretaceous
time (Fig. 14E). Localized nonmarine strata containing conglomerate, shale, and coal were deposited over the already folded Nutzotin Mountain sequence and Chisana Formation. These unnamed
sedimentary strata are poorly dated but are thought to be Upper
Cretaceous in age (Richter, 1976). Normal faults that cut the entire Nutzotin Mountains sequence (Fig. 2B; Richter, 1976, this
study) require a more detailed analysis but potentially may be
related to Late Cretaceous extension that has been documented in
the Wrangell Mountains basin (e.g., Trop et al., 2002).
In summary, our stratigraphic, compositional, and structural
data from strata of the Nutzotin basin provide a record of a sedimentary basin that was at least in part deposited on the northern
margin of the Wrangellia terrane and was filled with sediment
derived from this terrane. Following deposition, these strata were
deformed by north-dipping thrust faults and related folds above a
north-dipping décollement. The stratigraphy that we have defined
for the Nutzotin Mountain sequence represents a general upwardshallowing and upward-coarsening sedimentary package. The
lower and middle parts of the Nutzotin Mountain sequence
(Facies Associations 1–4 on Fig. 4) represent a general transition
from distal mud-rich submarine-fan deposition to more proximal
sandstone-rich submarine-fan deposition. These submarine-fan
strata are in turn overlain by marine shelf strata (Facies Association 5 on Fig. 4). We interpret the Nutzotin basin, based on its
stratigraphy and on its regional tectonic setting (discussed in the
following section), as a retroarc foreland basin (Figs. 14A, 14B).
In general, contractional basins, such as foreland basins, are characterized by upward-coarsening and upward-shallowing stratigraphies because in these settings as the source terrane is being
exhumed it is also being tectonically transported by reverse faults
toward the basin center (see Jordan, 1995, and Miall, 1995, for
review). We rule out the Nutzotin basin as an extensional backarc
basin that formed adjacent to the Wrangellia terrane because the
stratigraphy of these types of basins is often characterized by
upward-fining and upward-deepening sedimentary packages (see
Marsaglia, 1995, for review). The reason for this is that in extensional backarc basins, the exhumed source terrane is generally
being tectonically transported away from the basin center by normal faults. Another important distinction between the stratigraphy of the Nutzotin Mountain sequence and the stratigraphy of
most extensional backarc basins is the ubiquitous presence of
interbedded volcanic and volcaniclastic strata throughout the
basin fill of extensional basins (e.g., Carey and Sigurdsson, 1984;
Busby-Spera, 1988).
Regional Basin Configuration and Tectonic Setting
The Nutzotin Mountains sequence represents part of a series
of sedimentary basins located along the inboard margin of the
Wrangellia composite terrane (the Gravina, Dezadeash, and
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Sedimentary record of the tectonic growth of a collisional continental margin
Kahiltna basins on Fig. 1A) that define a major suture zone in the
northwestern Cordillera (Rubin et al., 1990; McClelland et al.,
1992a; Rubin and Saleeby, 1992). To provide a perspective of the
development of this suture boundary in south-central Alaska, our
data from the Nutzotin basin, located on the inboard (northern)
margin of the Wrangellia composite terrane, are integrated with
geologic data from the Wrangell Mountains basin, a Late Triassic
to Late Cretaceous depocenter that formed along the outboard
(southern) margin of the terrane (WB in Figure 1B; MacKevett,
1978; Winkler et al., 1981; Trop et al., 1999; Trop, 2000; Trop
et al., 2002; Trop and Ridgway, this volume). The strata of the
Nutzotin and Wrangell Mountains basins both clearly rest depositionally on the Wrangellia composite terrane. Geologic and
paleomagnetic data indicate that the Wrangellia composite terrane was located near the equator during late Paleozoic-Late Triassic time and was subsequently translated 30° northward
relative to North America sometime between Late Triassic to
early Tertiary time (Hillhouse and Grommé, 1984; Hillhouse and
Coe, 1994; Plafker and Berg, 1994; Cowan et al., 1997; Stamatakos et al., 2001). The time of collision and the location of the
collision with respect to North America during northward displacement of the Wrangellia composite terrane is unclear and
highly debated (e.g., Umhoefer, 1987; McClelland and Gehrels,
1990; van der Heyden, 1992; Plafker and Berg, 1994; Cowan
et al., 1997; Mahoney et al., 1999; Housen and Beck, 1999; Butler et al., 2001). Our paleogeographic model presented in this section assumes Mesozoic collision of the Wrangellia composite
terrane at a northern paleolatitude followed by Cenozoic strikeslip fault shuffling; our model builds on reconstructions by Nokleberg et al. (1998), Ridgway et al. (2002), and Trop and Ridgway
(this volume). In our reconstruction, collision of the Wrangellia
composite terrane is time-transgressive, starting in southeastern
Alaska and progressing northward to south-central Alaska (e.g.,
Pavlis, 1982; McClelland et al., 1992a; Ridgway et al., 2002; Trop
et al., 2005; Kalbas et al., this volume). Whereas initial collision
of the south-central Alaska segment of the composite terrane took
place sometime during Late Jurassic-Cretaceous time, geologic
data from southeastern Alaska and western Canada indicate close
proximity of the composite terrane with the outboard margin of
the Yukon-Tanana and Stikine terranes by Middle Jurassic time
(e.g., McClelland and Gehrels, 1990; McClelland et al., 1992a;
van der Heyden, 1992; Kapp and Gehrels, 1998; Saleeby, 2000;
Gehrels, 2001).
Middle Jurassic (Bajocian-Callovian)
Middle Jurassic strata were not deposited or are not preserved in the Nutzotin basin. Strata of this age, however, are well
preserved in the Wrangell Mountains basin. The Middle Jurassic
Nizina Mountain Formation (Fig. 3) exposed in the southern
Wrangell Mountains was deposited in a retroarc position, inboard
(north) of Upper Jurassic arc plutons (WB on Figure 15A; Chitina
arc of Plafker et al., 1989; Roeske et al., 1989, 2003; Trop et al.,
2002). Previous investigations have interpreted the dominance of
fine-grained arc-derived detritus, the localization of sediment
367
accumulation adjacent to the Jurassic arc platform, and the presence of primary volcanic strata as indicators that Middle Jurassic
sedimentation was a product of erosion of an oceanic arc prior to
collision with inboard terranes (Fig. 15A; Trop et al., 2002, 2005;
Trop and Ridgway, this volume). North-dipping oceanic subduction during this time interval is based on detailed geochemical and
stratigraphic investigations of Jurassic arc-related igneous rocks
(e.g., Burns, 1985; Plafker et al., 1989; DeBari and Coleman, 1989;
DeBari and Sleep, 1991; Keleman et al., 2003; Rioux et al., 2005;
Clift et al., 2005a, 2005b; Trop et al., 2005; Draut and Clift, 2006).
The key point of this time interval for our discussion of the Nutzotin basin is that Middle Jurassic sedimentary strata accumulated
in shallow-marine depocenters that fringed a south-facing oceanic
island-arc along the southern margin of the Wrangellia composite
terrane, whereas age-correlative strata were not deposited along
the northern margin of the terrane in the area that would become the
Nutzotin basin. See Trop and Ridgway (this volume) for a more
detailed discussion of this paleogeographic time slice for southcentral Alaska.
Late Jurassic (Oxfordian-Tithonian)
The marked change in grain size and composition of sediment that defines the first stage of basin development in the Nutzotin basin is also clear in the stratigraphy of the Wrangell
Mountains basin (WB in Fig. 1B). In this basin, older Jurassic
sedimentary strata (Nizina Mountain and Lower Root Glacier
Formations in Fig. 3) contain abundant recycled primary volcanic
detritus derived from the active Chitina arc, whereas Upper Jurassic sedimentary strata (Kotsina Conglomerate and Upper Root
Glacier Formation in Fig. 3) contain metavolcanic, metaplutonic,
metasedimentary, and sedimentary detritus derived from the
Wrangellia terrane and the plutonic roots of the Chitina arc (Trop
et al., 2002). The abrupt introduction of coarse-grained, mixed
detritus into both the Nutzotin and Wrangell Mountains basins is
interpreted as the erosional product of Late Jurassic shortening in
the Chitina fold-and-thrust belt (CTB on Figures 1B, 15B). This
fold-and-thrust belt, located along the southern margin of the
Wrangell Mountains basin (MacKevett, 1978; Gardner et al.,
1986), exposed multiple structural levels of the Wrangellia terrane that were eroded and transported northward into the Nutzotin
and Wrangell Mountains basins (Trop et al., 2002).
We interpret the Late Jurassic introduction of coarse-grained
detritus, the exhumation and erosion of the Wrangellia terrane
and Chitina arc, and the northward transport of sediment documented in both the Nutzotin and Wrangell Mountains basins as
the first sedimentary evidence of the early stages of collision of
the Wrangellia composite terrane with inboard terranes that
formed the Mesozoic continental margin of North America. Both
of these basins were located inboard of the Chitina fold-andthrust belt, which had formed adjacent to the active Chitina arc
(Fig. 15B). Plutons representing this arc were foliated by pervasive syntectonic deformation during Late Jurassic time (MacKevett, 1978). In interpreting the Nutzotin basin as forming in a
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A 176-159 Ma
Middle Jurassic
Bajocian-Callovian
Inbo
ar d T
erran
st Plu
es (
tonic
Yuk
on-T
Com
a na
plex
na
Coa
separation unk
nown
/Stik
ine?
)
FKB
sep
FKB
ara
tion
unk
now
n
Wrangellia
composite
terrane
FNB
N
MB
FNB
A
arc deposits
conjectural Lower Jurassic fore
WB
Fu
tu
Initial deposition of McHugh Complex?
re
p
?
M
osi
tion
of U
?
ppe
Oceanic Plate
B 159-144 Ma
Late Jurassic
Oxfordian-Tithonian
Onset of subsidence and sedimentation along
suture zone. Sediment transport away from
Wrangellia composite terrane on submarine fans
(KB; Kahiltna basin in the northern Talkeetna Mtns).
r Ju
?
ras
sic
a
Future Castle
Mountain fault
Inboa
rd Te
Onset of subsidence and sedimentation
in Nutzotin basin along suture zone.
Sediment transport away from Wrangellia
composite terrane on proximal (NB) and
distal (DB) submarine fan environments.
rrane
s
DC
BLF
DB
NB
N
Wrangellia
composite
terrane
UNB
MB
arc
conjectural Lower Jurassic fore
subduction erosion?
deposits
CT
B
WB
M
sub
duc
tio
Oceanic Plate
Continued subsidence and submarine
fan deposition in Kahiltna basin (KB)
along suture zone. Sediment transport
away from Wrangellia composite terrane
Inboa
rd Te
rrane
s
C 144-112 Ma
Early Cretaceous
Berriasian-Aptian
DC
BLF
N NB
DB
UNB
MB
?
A
CT
B
or
rassic f
Conjectural Ju
?
Continued subsidence and submarine
fan deposition in Nutzotin basin along
suture zone. Sediment transport away
from Wrangellia composite terrane
on proximal (NB) and distal (DB)
submarine fan environments.
KB
Future Castle
Mountain fault
n ero
si on
Underthrusting of inboard margin
of Wrangellia composite terrane
along regional suture zone.
?
Wrangellia
composite
terrane
Rapid uplift and exhumation of
Jurassic arc plutons along thrust
faults (CTB, BLF). Fan-delta
deposition in forearc (MB) and
retroarc (WB) depocenters.
?
A
Yukon-Tan
ana
terrane?
ns
Initial collision and underthrusting
of inboard margin of Wrangellia
composite terrane along regional
suture zone.
?
KB
rc
plu
to
earc ba
sin
dep
osi
ts
Oceanic Plate
WB
Localized arc magmatism
(Chisana arc) along inboard
margin of Wrangellia terrane.
M
Continued shortening along
outboard margin prompts uplift
of remnant retroarc (WB) and
forearc basins (MB). Minor
calcareous shallow marine
deposition locally.
Figure 15. Sketch maps showing the
inferred paleogeographic evolution of
Mesozoic sedimentary basins in southern Alaska. Paleolatitudes are not shown
due to uncertainty in the paleoposition of
the Wrangellia composite terrane with
respect to North America (see Cowan et
al., 1997, for review). Current distance
between towns of Anchorage (#A) and
McCarthy (#M) is 390 km. See text for
discussion on the evolution of the Nutzotin basin (NB) and the Wrangell
Mountains basin (WB). See Trop and
Ridgway (this volume) for a more detailed discussion of the geology of the
Matanuska basin (MB) that is shown in
this figure. Modified from Trop and
Ridgway (this volume).
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Sedimentary record of the tectonic growth of a collisional continental margin
369
Yukon-Tan
ana terran
e
Figure 15 continued
Westward sediment transport in the
Kahiltna basin (KB) on fluvial,
shallow marine, and submarine-fan
deposystems. Detritus derived from
Yukon-Tanana terrane and
Wrangellia composite terrane.
KB
D 112-83 Ma
Early Late Cretaceous
Albian-Santonian
Diachronous westward closure and
subaerial uplift of Kahiltna collisional/
remnant ocean basin deposits (UKB).
Southward thrusting and folding of proximal
(UNB) and distal (UDB) collisional basin
deposits and Chisana arc rocks along northdipping decollement (LD). Folded basinal
strata locally intruded by 110-90 Ma plutons.
UKB
Wrangellia
composite
terrane
TKF
LD
Future Castle
Mountain fault
UDB
N
?
UNB
?
Chugach
terrane
A
M
s subduct
taceou
ion
Jurassic-Cre
com
ple
x
de
po
s
its
(M
WB
cHug
h Co
Oceanic Plate
mpl
ex)
Renewed deposition in outboard
basins (WB, MB) influenced by
syndepositional normal faulting.
Southward transport of
sediment derived mainly
from remnant JurassicCretaceous arcs uplifted
along Mesozoic suture zone.
Explanation for Figure 15 A-D
Geographic references
A - Anchorage
M - McCarthy
N - Nabesna
Basinal Deposits
DB - Dezadeash
KB - Kahiltna
MB - Matanuska - S. Talkeetna Mtns.
NB - Nutzotin
WB - Wrangell Mountains
(Prefixed with U=Uplifted)
(Prefixed with F=Future position)
Faults, Shear Zones
BLF - Bruin Bay-Little Oshetna fault
CTB - Chitina thrust belt
LD - Lost Creek decollement
TKF - Talkeetna fault
Depositional Features
Magmatism
Locus of active volcanism
Alluvial
Mid-Cretaceous Chisana arc rocks
Fluvial
U. Jur. Talkeetna-Chitina arc rocks
Lacustrine
Middle Jur. Talkeetna arc rocks
Fan-Delta
Marine Shelf
Lower Jur. Talkeetna arc rocks
Deformational Features
Submarine Fans
Active subduction zone
Marine environments
Active crustal shortening
Active
depositional
basin
Topographic uplifts via shortening
Active crustal extension
Uplifted
basinal
strata
retroarc setting, we infer a dual plate subduction scenario for the
northern Cordillera (e.g., Monger et al., 1982; Rubin et al., 1990;
Stanley et al., 1990; McClelland and Mattinson, 2000; Trop and
Ridgway, this volume) with subduction polarity of both plates
dipping northward, one beneath the Wrangellia composite terrane
and the other beneath the continental margin (see Figure 4B in
Trop and Ridgway, this volume). Structurally emplaced slivers of
ophiolitic rocks presently located in the northwestern corner of
the study area (Fig. 2A), as well as other ophiolitic slivers found
along the suture zone between the Wrangellia and Yukon composite terranes in south-central Alaska may represent fragments
of the consumed oceanic plate (e.g., Richter, 1976; Nokleberg
et al., 1994b, 1998; Patton et al., 1994). The size of this inferred
oceanic plate is presently unknown; it may have been a substantial oceanic plate as suggested by Ridgway et al. (2002, see their
Fig. 11A) or a small back-arc basin floored by transitional or
oceanic crust as suggested by McClelland and Mattinson (2000,
see their Fig. 10A).
Latest Jurassic-Early Cretaceous
In the Wrangell Mountains basin, the latest Jurassic-Early
Cretaceous interval is defined by a regional angular unconformity
(Fig. 3; MacKevett, 1978). This unconformity is a product of the
incorporation of basinal strata into the Chitina fold-and-thrust belt
that resulted in folding and structural imbrication of sedimentary
strata of the Wrangell Mountains basin, igneous rocks of the
Chitina arc, and the Wrangellia terrane (Fig. 15C; Trop et al.,
2002). Regional shortening, exhumation, and erosion within the
Chitina fold-and-thrust belt provided a large volume of sediment
for the Nutzotin basin that is recorded in the more than 1000 m of
strata in Facies Associations 3 and 4 of the Nutzotin Mountains
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sequence. Basinal subsidence needed to preserve such a thick
package of strata may have been a flexural response to the load
supplied by the Chitina fold-and-thrust belt and Chitina arc.
Regional exhumation of the Wrangellia terrane in the Chitina
fold-and-thrust belt also allowed unroofing and erosion of the
deeper stratigraphic/structural levels of the terrane, which is well
documented in our compositional and detrital zircon age data.
We interpret the Upper Jurassic-Lower Cretaceous Nutzotin
Mountains sequence as being deposited in a retroarc foreland
basin located inboard (cratonward) of the active Chitina arc and
Chitina fold-and-thrust belt. Collectively, we interpret the main
phase of coarse-grained sedimentation in the Nutzotin basin; the
extensive development of the Chitina fold-and-thrust belt; and the
regional shortening and exhumation of the Wrangell Mountains
basin, Chitina arc, and the Wrangellia terrane to represent a main
phase of oblique collision between the Wrangellia composite terrane and the inboard terranes that formed the outer continental
margin. Inboard terranes, such as the Yukon composite terrane,
are interpreted to have been linked to North America by Middle
Jurassic time (e.g., Monger et al., 1982; Mihalynuk et al., 1994;
Monger and Nokleberg, 1996). A weak point in our interpretation
is that direct unequivocal sedimentological and compositional
evidence linking strata of the Nutzotin basin with inboard terranes
has not been found; this may be partly due to the lack of a detailed
detrital zircon provenance study for the strata of this basin. In
along-strike Upper Jurassic-Lower Cretaceous basins, however,
there is direct evidence of sediment derivation from continental
margin sources. In the Kahiltna basin of the Alaska Range (KBa
in Fig. 1A), for example, detrital zircons and diagnostic clasts in
conglomerate indicate derivation from inboard Paleozoic terranes
(Eastham, 2002; Ridgway et al., 2002; Hampton et al., 2005, this
volume; Kalbas et al., this volume). Kalbas et al. (this volume),
for example, report a significant population of detrital zircons
with Middle and Early Proterozoic ages from the Kahiltna assemblage in the western Alaska Range. East of the Nutzotin basin,
Kapp and Gehrels (1998) have reported U-Pb age determinations
from detrital zircons of the Upper Jurassic-Upper Cretaceous
Gravina basin (GB in Fig. 1A) that best fit with derivation from
the inboard Yukon composite terrane. In addition, geochemical
and neodymium isotopic data from Upper Jurassic-Lower Cretaceous strata of the Dezadeash basin (DB in Fig. 1A) also suggest
that a possible small component of continental margin crust provided sediment to the basin (Mezger et al., 2001).
Regionally, along-strike Upper Jurassic-Lower Cretaceous
sedimentary strata have similar submarine-fan facies, depositional
packages, and provenance as described for the Nutzotin Mountains sequence. For example, in the Kahiltna basin of the Talkeetna Mountains, located west of the Nutzotin basin (KBt in
Fig. 1A), a similar unroofing of the Wrangellia composite terrane
is clear in clast composition of conglomerate (Eastham and Ridgway, 2002; Ridgway et al., 2002). Strata of the Dezadeash basin
located in the Yukon Territory (Fig. 1B) were also derived mainly
from the Wrangellia composite terrane and transported eastward
by submarine-fan systems (e.g., Eisbacher, 1976, 1985; Lowey,
2006). Strata of the Gravina basin (Fig. 1A) exposed in the vicinity of Juneau, Alaska, show a similar upward-coarsening package
as documented in the Nutzotin basin with conglomerate derived
from the Wrangellia composite terrane (e.g., Cohen and Lundberg, 1993, see their Fig. 3). Strata of the Gravina basin near
Ketchikan, Alaska do not show an overall upward-coarsening
depositional package but do contain metavolcanic and metaplutonic clasts derived from the Wrangellia composite terrane (e.g.,
Rubin and Saleeby, 1991). U-Pb zircon ages from plutonic clasts
in this part of the Gravina basin have age ranges from 158 to 154
Ma (Rubin and Saleeby, 1991), roughly similar to the 159–147
Ma age ranges from detrital zircons of the Nutzotin Mountains
basin (Fig. 10). In both cases, the zircons are interpreted to have
been derived from exposed plutons of the Late Jurassic volcanic
arc that was constructed on the Wrangellia composite terrane.
The clast composition of conglomerates, the detrital zircon
ages, and eastward/northward paleoflow away from the Wrangellia composite terrane in the Nutzotin, Gravina, Dezadeash, and
Kahiltna basins all indicate that deeper stratigraphic/structural levels of the Wrangellia composite terrane, as well as plutons of the
associated Late Jurassic arc were being regionally exhumed,
eroded, and transported into adjacent basins along the inboard
margin of the Wrangellia composite terrane by at least Early
Cretaceous time. These inboard Upper Jurassic-Lower Cretaceous basins extended for 2000 km along the suture zone
between the Wrangellia composite terrane and inboard terranes
of continental margin affinities (Fig. 1A). As pointed out by
Pavlis (1982), McClelland et al. (1992a), and Ridgway et al.
(2002), these Late Jurassic-Early Cretaceous sedimentary
basins probably represent a main phase of collision of the
Wrangellia composite terrane with the Cordilleran continental
margin. Our findings from the Nutzotin basin are consistent
with such an interpretation.
There are, however, some differences in the Late JurassicEarly Cretaceous sedimentary basins that formed along the
inboard margin of the Wrangellia composite terrane that may be
important for paleogeographic reconstructions of western North
America. In southeastern Alaska, for example, strata of the Gravina basin are interpreted as having been deposited in extensional
and/or transtensional backarc and intra-arc basins, possibly associated with a major dextral fault system, following Middle Jurassic collision (e.g., McClelland et al., 1992a, 1992b; among
others). In the case of the Nutzotin basin, most of our data, in combination with data from the Wrangell Mountains basin, best fit
with deposition in a retroarc foreland basin that formed due to
flexural subsidence associated with the Chitina fold-and-thrust
belt. Stratigraphic data from the Kahiltna basin, located west of
the Nutzotin basin (Fig. 1A), also appear to be consistent with a
contractional basin origin (Ridgway et al., 2002; Kalbas et al., this
volume). The possible change from a Late Jurassic-Early Cretaceous strike-slip-dominated margin in southeastern Alaska to a
convergent-dominated margin in southcentral and southwestern
Alaska may be a function of along-strike changes in the tectonic
character of the collisional zone, possibly related to diachronous
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Sedimentary record of the tectonic growth of a collisional continental margin
closure of the suture zone (e.g., Pavlis, 1982; Nokleberg et al.,
1998; Ridgway et al., 2002).
Early to Late-Early Cretaceous
Growth of the Chisana arc was coeval with renewed subsidence and siliciclastic sedimentation in the Wrangell Mountains
basin (Berg Creek and Kuskulana Formations in Figure 3; Trop
et al., 2002) but marked the end of widespread clastic deposition
in the Nutzotin basin (Fig. 15D). Along strike in southeastern
Alaska near Juneau, strata of the Gravina basin (Fig. 1A) show a
similar transition from sedimentary to volcanic strata as documented in the Nutzotin basin (e.g., Cohen and Lundberg, 1993).
Along-strike basins to the west, the Kahiltna basins (Fig. 1A), do
not have Lower Cretaceous volcanic strata overlying Upper
Jurassic-Lower Cretaceous sedimentary strata (Eastham, 2002;
Kalbas et al., this volume). The significance of these along-strike
differences is poorly understood but likely important for thorough
paleogeographic reconstructions of the northwestern Cordillera.
Late-Early Cretaceous
We interpret the structural imbrication and the translation of
strata of the Nutzotin basin over the Wrangellia terrane to mark
the later stages of oblique Mesozoic terrane accretion in southcentral Alaska. In our interpretation, strata of the Nutzotin
retroarc foreland basin were incorporated into an accretionary
wedge (Fig. 14D; e.g., Sengör and Okurogullari, 1991; Ingersoll
et al., 1995) with the overriding North American continental margin providing the backstop against which the Nutzotin Mountains
sequence was imbricated and subsequently thrust over the
Wrangellia terrane (Fig. 15D). The structural style of north-dipping
thrust faults and south-verging folds documented for the Nutzotin
basin is consistent with an inferred northward-dipping subduction
zone between the northern margin of the Wrangellia composite
terrane and North America. The Nutzotin Mountain sequence,
which had been deposited on the downgoing plate that was transporting the Wrangellia composite terrane toward the continental
margin, was now tectonically incorporated into the overriding
plate as an accretionary wedge.
Our interpretation for the Nutzotin Mountain sequence is
consistent with previous studies of deformation of other Upper
Jurassic-Lower Cretaceous basinal strata in the suture zone. Mapping of the Gravina basin (labeled GB in Figure 1A, for example)
shows it to have been imbricated and underthrust to relatively
deep crustal levels (25–30 km) beneath the Yukon composite
terrane during middle Cretaceous time (McClelland et al., 1992a,
1992b, 1992c; McClelland and Mattinson, 2000). Crosscutting
relationships and U-Pb age determinations from syn- and posttectonic plutons suggest that underthrusting of the Gravina basin
began between 113 and 97.5 Ma and ended by 90 Ma in southeastern Alaska (Haeussler, 1992; McClelland et al., 1992c). West
of the Nutzotin basin, magnetotelluric surveys and seismic lines
across the suture zone in the central Alaska Range have been
interpreted as suggesting that Upper Jurassic-Lower Cretaceous
strata of the Kahiltna basin (labeled KB in Fig. 1A) were under-
371
thrust beneath the Yukon composite terrane during middle Cretaceous time (Stanley et al., 1990; Beaudoin et al., 1992).
The thrust faults documented in the Nutzotin basin are probably part of a regionally extensive thrust system that has been
documented along the northwestern Cordillera. This thrust system places Jurassic-Cretaceous sedimentary strata on top of rocks
equivalent to the Wrangellia composite terrane (Rubin et al.,
1990; Rubin and Saleeby, 1992). If the deformation recorded in
the Nutzotin basin is laterally equivalent to this thrust system that
has been described from Washington to southeastern Alaska, this
thrust system extends for over 2000 km and represents a series of
sedimentary basins that have been incorporated into accretionary
wedges defining a continental-scale suture zone.
Latest Cretaceous-Tertiary
Strata of the Nutzotin and Wrangell Mountains basins were
both gently folded and topographically inverted during latest
Cretaceous-Tertiary time. This deformation is recorded by angular unconformities that separate Cretaceous and older strata from
overlying Miocene-Quaternary strata in both basins (Fig. 3;
Richter, 1976; MacKevett, 1978). The timing of basin inversion
broadly overlapped with 1650 890 km of northward translation
of both basins along orogen-parallel dextral fault systems (e.g.,
Stamatakos et al., 2001). During northward translation, strata of
the Nutzotin basin were dismembered by the Denali fault system
(Fig. 14E; Richter and Jones, 1973; Eisbacher, 1976; Nokleberg
et al., 1985). Much of this displacement is interpreted to have
occurred during Eocene-Oligocene time based on ages of strikeslip basins along the fault system (e.g., Ridgway et al., 1999; Trop
et al., 2004). Deformation of strata of the Nutzotin basin continues to the present as recorded by surface ruptures along the
Totschunda fault associated with the 2003 Denali earthquake
(e.g., Eberhart-Phillips et al., 2003) and offset late PleistoceneHolocene geomorphic features (Matmon et al., 2006).
CONCLUSIONS
1. Stratigraphic, compositional, and provenance data from
the Upper Jurassic-Lower Cretaceous Nutzotin Mountains sequence are interpreted as representing deposition
in a retroarc foreland basin that was located on the northern margin of the Wrangellia terrane. Coeval with basin
development along the northern margin, sedimentary
basins and plutons located along the southern margin of
the Wrangellia terrane were being incorporated into a
regional fold-and-thrust belt. Sediment eroded from this
fold-and-thrust belt was transported northward and
deposited in the Nutzotin basin.
2. Compositional data and U-Pb detrital zircon ages from
the Nutzotin Mountains sequence record exhumation and
progressive erosion of the Wrangellia terrane, the strata of
the Wrangell Mountains basin, and the Chitina arc. All
these source areas were exposed in the fold-and-thrust
belt located south of the Nutzotin basin. Comparison of
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Manuszak et al.
stratigraphic and provenance data from the Nutzotin basin
with along-strike Upper Jurassic-Lower Cretaceous basins,
such as the Gravina, Dezadeash, and Kahiltna basins, shows
that deeper stratigraphic/structural levels of the Wrangellia
composite terrane, as well as plutons of associated Late
Jurassic arcs, were being regionally exhumed and eroded
and were providing sediment for basins along the inboard
margin of the terrane by at least Early Cretaceous time.
3. Collectively, we interpret the regional unconformity at the
base of the Nutzotin Mountains sequence (ca. 50 m.y. hiatus), the abrupt introduction of coarse-grained detritus
above the unconformity, the overall upward-coarsening
and upward-shallowing stratigraphy of the Nutzotin
Mountains sequence, the compositional record of exhumation and erosion of deeper levels of the Wrangellia
terrane, and the development of the fold-and-thrust belt
south of the Nutzotin basin as products of Late JurassicEarly Cretaceous collision of the Wrangellia composite
terrane with inboard terranes representing the continental
margin of North America.
4. The stages of deformation documented in strata of the
Nutzotin basin also provide insight into the growth of collisional continental margins by the tectonic incorporation
of basinal strata. In the case of the Nutzotin basin, strata
were incorporated into an accretionary wedge related to
underthrusting beneath the continental margin. Regionally, the Nutzotin Mountains sequence represents part of
a series of sedimentary basins located along the inboard
margin of the Wrangellia composite terrane that generally
have similar depositional styles and were subsequently
incorporated into accretionary wedges. These deformed
strata define a continental-scale suture along the entire
northwestern Cordillera.
ACKNOWLEDGMENTS
This research was supported by Donors of the Petroleum Research Fund, administered by the American Chemical Society, and
the National Science Foundation. Partial support for Manuszak’s
M.S. research was provided by the GSA John T. Dillon grant, the
AAPG Fred A. Dix grant, the Linda Horn Memorial scholarship
from Purdue University, the Sigma Xi Alexander Bache Fund, and
the Society of Petroleum Engineers’ research scholarship. We
thank Wrangell–St. Elias National Park and Preserve staff, especially Danny Rosenkrans, for their help and support of our field
activities; Brian Lareau, Mike DePersia, and Shane Smith for assistance in the field; and Arvid Johnson, Scott King, Rick Hoy, and
Kaj Johnson for useful discussions. Reviews by Jonathan Glen,
Marc Hendrix, and Brad Ritts were extremely helpful for improving the manuscript. This paper is dedicated to the late Don Richter,
who provided encouragement and helpful discussions on the geology of the eastern Alaska Range and Wrangell Mountains;
Don’s geologic map of the Nabesna quadrangle provided the foundation for our study.
REFERENCES CITED
Barker, F., 1988, Cretaceous Chisana island arc of Wrangellia, eastern Alaska:
Geological Society of America Abstracts with Programs, v. 19, p. 580.
Beaudoin, B.C., Fuis, G.S., Mooney, W.D., Nokleberg, W.J., and Christensen,
N.I., 1992, Thin, low-velocity crust beneath the southern Yukon-Tanana terrane, east-central Alaska: Results from TACT refraction/wide-angle reflection data: Journal of Geophysical Research, v. 97, p. 1921–1942.
Berg, H.C., Jones, D.L., and Richter, D.H., 1972, Gravina-Nutzotin belt: Significance of an upper Mesozoic sedimentary and volcanic sequence in southern
and southeastern Alaska: U.S. Geological Survey Professional Paper 800-D,
p. D1–D24.
Bottjer, D.J., Droser, M.L., and Jablonski, D., 1987, Bathymetric trends in the history of trace fossils, in Bottjer, D.J., eds., New concepts in the use of biogenic sedimentary structures for paleoenvironmental interpretation: Volume
and Guidebook, Pacific Section, Society of Economic Paleontologists and
Mineralogists, p. 57–65.
Bouma, A.H., 1962, Sedimentology of Some Flysch Deposits: Amsterdam, Elsevier, 168 p.
Brew, D.A., and Ford, A.B., 1984, The northern Coast Plutonic Complex, southeastern Alaska and northwestern British Columbia: U.S. Geological Survey
Circular 868, p. 120–124.
Buatois, L.A., and Mangano, M.G., 2003, Early colonization of the deep sea: Ichnologic evidence of deep-marine benthic ecology from the Early Cambrian
of northwest Argentina: Palaios, v. 18, p. 572–581.
Burns, L.E., 1985, The Border Ranges ultramafic and mafic complexes, southcentral Alaska: Cumulate fractionates of island-arc volcanics: Canadian
Journal of Earth Sciences, v. 22, p. 1020–1038.
Busby-Spera, C.J., 1988, Evolution of a Middle Jurassic back-arc basin, Cedros
Island, Baja California: Evidence from a marine volcaniclastic apron: Geological Society of America Bulletin, v. 100, p. 218–233, doi: 10.1130/00167606(1988)100<0218:EOAMJB>2.3.CO;2.
Butler, R.F., Gehrels, G.E., and Kodama, K.P., 2001, A moderate translation alternative to the Baja British Columbia hypothesis: GSA Today, v. 11, no. 6,
p. 4–10, doi: 10.1130/1052-5173(2001)011<0004:AMTATT>2.0.CO;2.
Carey, S.N., and Sigurdsson, H., 1984, A model of volcanogenic sedimentation in
marginal basins: Geological Society [London] Special Publication 16, p. 37–58.
Chen, W.S., Ridgway, K.D., Horng, C.S., Chen, Y.G., Shea, K.S., and Yeh, M.G.,
2001, Stratigraphic architecture, magnetostratigraphy, and incised-valley
systems of the Pliocene-Pleistocene collisional marine foreland basin of Taiwan: Geological Society of America Bulletin, v. 113, p. 1249–1271, doi:
10.1130/0016-7606(2001)113<1249:SAMAIV>2.0.CO;2.
Clark, J.D., and Pickering, K.T., 1996, Architectural elements and growth patterns
of submarine channels: Application to hydrocarbon exploration: American
Association of Petroleum Geologists Bulletin, v. 80, p. 194–221.
Clautice, K.H., Newberry, R.J., Blodgett, R.B., Bundtzen, T.K., Gage, B.G., Harris, E.E., Liss, S.A., Miller, M.L., Reifenstuhl, R.R., Clough, J.G., and Pinney, D.S., 2000, Interpretive bedrock geologic map of the Chulitna Mining
district, south-central Alaska: Alaska Division of Geological and Geophysical Surveys, 1 sheet, scale 1:63,360.
Clift, P.D., Draut, A.E., Keleman, P.B., Bluszatajn, J., and Greene, A., 2005a,
Stratigraphic and geochemical evolution of an ocean arc upper crustal section: The Jurassic Talkeetna volcanic formation, south-central Alaska: Geological Society of America Bulletin, v. 117, p. 902–925, doi: 10.1130/
B25638.1.
Clift, P.D., Pavlis, T.L., DeBari, S.M., Draught, A.E., Rioux, M., and Keleman,
P.B., 2005b, Subduction erosion of the Jurassic Talkeetna-Bonanza arc and
the Mesozoic accretionary tectonics of western North America: Geology,
v. 33, p. 881–884, doi: 10.1130/G21822.1.
GSA_SPE431_14_Ridgway.qxd
7/28/07
9:06 AM
Page 373
Sedimentary record of the tectonic growth of a collisional continental margin
Cohen, H., and Lundberg, N., 1993, Detrital record of the Gravina arc, southeastern Alaska: Petrology and provenance of Seymour Canal Formation sandstones: Geological Society of America Bulletin, v. 105, p. 1400–1414, doi:
10.1130/0016-7606(1993)105<1400:DROTGA>2.3.CO;2.
Cole, R.B., Ridgway, K.D., Layer, P.W., and Drake, J., 1999, Kinematics of basin
development during the transition from terrane accretion to strike-slip tectonics, Late Cretaceous early Tertiary Cantwell Formation, south central
Alaska: Tectonics, v. 18, p. 1224–1244, doi: 10.1029/1999TC900033.
Coney, P.J., Jones, D.L., and Monger, J.W.H., 1980, Cordilleran suspect tectonics:
Nature, v. 288, p. 329–333, doi: 10.1038/288329a0.
Cowan, D.S., Brandon, M.T., and Garver, J.E., 1997, Geologic tests of hypotheses
for large coastwise displacements: A critique illustrated by the Baja British
Columbia controversy: American Journal of Science, v. 297, p. 117–173.
Csejtey, B., Jr., Cox, D.P., Evarts, R.C., Stricker, G.D., and Foster, H.L., 1982, The
Cenozoic Denali fault system and the Cretaceous accretionary development
of Southern Alaska: Journal of Geophysical Research, v. 87, p. 3741–3754.
Cullen, A.B., 1996, Ramu basin, Papua New Guinea: A record of Late Miocene
terrane collision: American Association of Petroleum Geologists Bulletin,
v. 80, p. 663–684.
D’Alessandro, A.D., Ekdale, A.A., and Sonnino, M., 1986, Sedimentologic significance of turbidite ichnofacies in the Saraceno Formation (Eocene),
southern Italy: Journal of Sedimentary Petrology, v. 56, p. 294–306.
DeBari, S.M., and Coleman, R.G., 1989, Examination of the deep levels of an
island arc: Evidence from the Tonsina ultramafic-mafic assemblage, Tonsina, Alaska: Journal of Geophysical Research, v. 94, p. 4373–4391.
DeBari, S.M., and Sleep, N.H., 1991, High-Mg, low-Al bulk composition of the
Talkeetna island arc, Alaska: Implications for primary magmas and the
nature of arc crust: Geological Society of America Bulletin, v. 103, p. 37–47,
doi: 10.1130/0016-7606(1991)103<0037:HMLABC>2.3.CO;2.
Dewey, J.F., 1977, Suture zone complexities: A review: Tectonophysics, v. 40,
p. 53–67, doi: 10.1016/0040-1951(77)90029-4.
Dickinson, W.R., 1970, Interpreting detrital modes of graywacke and arkose:
Journal of Sedimentary Petrology, v. 40, p. 696–707.
Dickinson, W.R., Beard, L.S., Brackenridge, G.R., Erjavec, K.L., Ferguson, R.C.,
Inman, K.F., Knepp, R.A., Lindberg, F.A., and Ryberg, R.T., 1983, Provenance of North American sandstones in relation to tectonic setting: Geological Society of America Bulletin, v. 94, p. 222–235, doi: 10.1130/0016-7606
(1983)94<222:PONAPS>2.0.CO;2.
Dodds, C.J., and Campbell, R.B., 1988, Potassium-argon ages of mainly intrusive
rocks in the Saint Elias Mountains, Yukon and British Columbia: Geological Survey of Canada Paper 87-16, 43 p.
Dott, R.H., 1964, Wacke, graywacke and matrix: What approach to immature sandstone classification?: Journal of Sedimentary Petrology, v. 34, p. 625–632.
Draut, A.E., and Clift, P.D., 2006, Sedimentary processes in modern and ancient
oceanic arc settings: Evidence from the Jurassic Talkeetna Formation of
Alaska and the Marianas and Tonga arcs, western Pacific: Journal of Sedimentary Research, v. 76, p. 493–514, doi: 10.2110/jsr.2006.044.
Eastham, K.R., 2002, Sedimentological and provenance analysis of the Upper
Jurassic-Upper Cretaceous Kahiltna assemblage: Basin development and
tectonics of the Alaska Range suture zone [M.S. thesis]: West Lafayette,
Indiana, Purdue University, 292 p.
Eastham, K.R., and Ridgway, K.D., 2002, Stratigraphic and provenance data from
the Upper Jurassic-Upper Cretaceous Kahiltna assemblage of south-central
Alaska, in U.S. Geological Survey Studies in Alaska: U.S. Geological Survey Professional Paper 1662, p. 45–53.
Eberhart-Phillips, D., Haeussler, P.J., Freymueller, J.T., et al., 2003, The 2002
Denali fault earthquake, Alaska: A large magnitude, slip-partitioned event:
Science, v. 300, p. 1113–1118, doi: 10.1126/science.1082703.
Eisbacher, G.H., 1976, Sedimentology of the Dezadeash flysch and its implications for strike-slip faulting along the Denali fault, Yukon Territory and
Alaska: Canadian Journal of Earth Sciences, v. 13, p. 1495–1593.
Eisbacher, G.H., 1985, Pericollisional strike-slip faults and synorogenic basins,
Canadian Cordillera, in Biddle, K.T., and Christie-Blick, N., eds., Strike-Slip
373
Deformation, Basin Formation, and Sedimentation: Society of Economic
Paleontologists and Mineralogists Special Publication 37, p. 265–282.
Fletcher, H.J., 2002, Crustal deformation in Alaska measured using Global
Position System [Ph.D. thesis]: Fairbanks, Alaska, University of AlaskaFairbanks, 135 p.
Foster, H.L., Keith, T.E.C., and Menzie, W.D., 1994, Geology of the YukonTanana area of east-central Alaska, in Plafker, G., and Berg, H.D., eds. The
Geology of Alaska: Boulder, Colorado, Geological Society of America,
Geology of North America, v. G-1, p. 205–240.
Galewsky, J., and Silver, I., 1997, Tectonic controls on facies transitions in an
oblique collision: The western Solomon Sea, Papua New Guinea: Geological Society of America Bulletin, v. 109, p. 1266–1278, doi: 10.1130/00167606(1997)109<1266:TCOFTI>2.3.CO;2.
Galloway, W.E., 1998, Siliciclastic slope and base-of-slope depositional systems:
Component facies, stratigraphic architecture, and classification: American
Association of Petroleum Geologists Bulletin, v. 82, p. 569–595.
Gardner, M.C., MacKevett, E.M., and McClelland, W.C., 1986, The Chitina fault
system of southern Alaska: An Early Cretaceous collisional suture zone:
Geological Society of America Abstracts with Programs, v. 18, p. 108.
Gardner, M.C., Bergman, S.C., Cushing, G.W., MacKevett, E.M., Plafker, G.,
Campbell, R.B., Dodds, C.J., McClelland, W.C., and Mueller, P.A., 1988,
Pennsylvanian pluton stitching of Wrangellia and the Alexander terrane,
Wrangell Mountains, Alaska: Geology, v. 16, p. 967–971, doi: 10.1130/
0091-7613(1988)016<0967:PPSOWA>2.3.CO;2.
Gazzi, P., 1966, Le arenarie del flysch sopracretaceo dell’Appennino modense;
correlazioni con il flysch di Monghidoro: Minerallogica et Petrographica
Acta, v. 12, p. 69–97.
Gehrels, G.E., 2001, Geology of the Chatham Sound region, southeast Alaska and
coastal British Columbia: Canadian Journal of Earth Sciences, v. 38, p.
1579–1599, doi: 10.1139/cjes-38-11-1579.
Gehrels, G.E., and Saleeby, J.B., 1987, Geologic framework, tectonic evolution,
and displacement history of the Alexander terrane: Tectonics, v. 6,
p. 151–173.
Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, J.P., 1991, U-Pb
geochronology of detrital zircons from a continental margin assemblage in
the northern Coast Mountains, southeastern Alaska: Canadian Journal of
Earth Sciences, v. 28, p. 1285–1300.
Grantz,A., Jones, D.L., and Lanphere, M.A., 1966, Stratigraphy, paleontology, and
isotopic ages of upper Mesozoic rocks in the southwestern Wrangell Mountains, Alaska: U.S. Geological Survey Professional Paper 550-C, p. 39–47.
Haeussler, P.J., 1992, Structural evolution of an arc-basin: The Gravina belt in central southeastern Alaska: Tectonics, v. 11, p. 1245–1265.
Hampton, B.A., Ridgway, K.D., and Gehrels, G.E., 2005, Detrital zircon record
of the configuration and evolution of the Alaska Range suture zone, southcentral Alaska: Preliminary results: Abstracts with Programs: Geological
Society of America, v. 37, no. 7, p. 81.
Hampton, B.A., Ridgway, K.D., O’Neill, J.M., Gehrels, G.E., Schmidt, J., and
Blodgett, R.B., 2007, this volume, Pre-, syn-, and postcollisional stratigraphic framework and provenance of Upper Triassic–Upper Cretaceous
strata in the northwestern Talkeetna Mountains, Alaska, in Ridgway, K.D.,
Trop, J.M., Glen, J.M.G., and O’Neill, J.M., eds., Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska: Geological Society of America Special Paper 431, doi: 10.1130/2007.2431(16).
Hansen, V.L., 1990, Yukon-Tanana terrane: A partial acquittal: Geology, v. 18,
p. 365–369, doi: 10.1130/0091-7613(1990)018<0365:YTTAPA>2.3.CO;2.
Hansen, V.L., and Dusel-Bacon, C., 1998, Structural and kinematic evolution of
the Yukon-Tanana upland tectonites, east-central Alaska: A record of late
Paleozoic to Mesozoic crustal assembly: Geological Society of America
Bulletin, v. 110, p. 211–230, doi: 10.1130/0016-7606(1998)110<0211:
SAKEOT>2.3.CO;2.
Hein, F.J., 1982, Depositional mechanisms of deep-sea coarse clastic sediments,
Cap Enrage Formation, Quebec: Canadian Journal of Earth Sciences, v. 19,
p. 267–287.
GSA_SPE431_14_Ridgway.qxd
374
7/28/07
9:06 AM
Page 374
Manuszak et al.
Hillhouse, J.W., and Coe, R.S., 1994, Paleomagnetic data from Alaska, in Plafker,
G., and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, Geology of North America, v. G-1, p. 797–812.
Hillhouse, J.W., and Grommé, C.S., 1984, Northward displacement and accretion
of Wrangellia: New paleomagnetic evidence from Alaska: Journal of Geophysical Research, v. 89, p. 4461–4467.
Hiscott, R.N., and Middleton, G.V., 1979, Depositional mechanics of thickbedded sandstones at the base of a submarine slope, Tourelle Formation
(Lower Ordovician), Quebec, Canada, in Doyle, L.J., and Pilkey, O.H.,
eds., The Geology of Continental Slopes: Society of Economic Paleontologists and Mineralogists, Special Publication 27, p. 397–326.
Housen, B.A., and Beck, M.A., Jr., 1999, Testing terrane transport: An inclusive
approach to the Baja B.C. controversy: Geology, v. 27, p. 1143–1146, doi:
10.1130/0091-7613(1999)027<1143:TTTAIA>2.3.CO;2.
Ingersoll, R.V., Bullard, T.F., Ford, R.L., Grimm, J.P., Pickle, J.D., and Sares,
S.W., 1984, The effect of grain size on detrital modes: A test of the GazziDickinson point-counting method: Journal of Sedimentary Petrology, v. 54,
p. 103–116.
Ingersoll, R.V., Graham, S.A., and Dickinson, W.R., 1995, Remnant ocean basins,
in Busby, C.J., and Ingersoll, R.V., eds., Tectonics of Sedimentary Basins:
Cambridge, Massachusetts: Blackwell Science, p. 363–393.
Johnson, A.M., 1965, A model for debris flow [Ph.D. thesis]: University Park,
Pennsylvania, Pennsylvania State University, 248 p.
Johnson, A.M., 1970, Physical Processes in Geology: San Francisco, Freeman,
577 p.
Jones, D.L., and MacKevett, E.M., Jr., 1969, Summary of Cretaceous stratigraphy
in part of the McCarthy Quadrangle, Alaska: U.S. Geological Survey Bulletin 1274-K, 19 p.
Jones, D.L., and Silberling, N.J., 1979, Mesozoic stratigraphy: The key to tectonic
analysis of southern and central Alaska: U.S. Geological Survey Open-File
Report 79-1200, 37 p.
Jones, D.L., Silberling, N.J., and Hillhouse, J., 1977, Wrangellia: A displaced terrane in northwestern North America: Canadian Journal of Earth Sciences,
v. 14, p. 2565–2577.
Jones, D.L., Silberling, N.J., Gilbert, W., and Coney, P., 1982, Character, distribution and tectonic significance of accretionary terranes in the central Alaska
Range: Journal of Geophysical Research, v. 87, p. 3709–3717.
Jordan, T.E., 1995, Retroarc foreland and related basins, in Busby, C.J., and Ingersoll, R.V., eds., Tectonics of Sedimentary Basins: Cambridge, Massachusetts, Blackwell Science, p. 331–362.
Kalbas, J.L., Ridgway, K.D., and Gehrels, G.E., 2007, this volume, Stratigraphy,
depositional systems, and provenance of the Lower Cretaceous Kahiltna
assemblage, western Alaska Range: Basin development in response to
oblique collision, in Ridgway, K.D., Trop, J.M., Glen, J.M.G., and O’Neill,
J.M., eds., Tectonic Growth of a Collisional Continental Margin: Crustal
Evolution of Southern Alaska: Geological Society of America Special Paper
431, doi: 10.1130/2007.2431(13).
Kapp, P.A., and Gehrels, G.E., 1998, Detrital zircon constraints on the tectonic
evolution of the Upper Jurassic-Lower Cretaceous Gravina belt, southeastern Alaska: Canadian Journal of Earth Sciences, v. 35, p. 253–268, doi:
10.1139/cjes-35-3-253.
Karl, S.M., Johnson, B.R., and Lanphere, M.A., 1988, New K-Ar ages for plutons
on western Chicagof Island and on Yakobi Island, in Galloway, J.P., and
Hamilton, T.D., eds., Geologic Studies in Alaska by the U.S. Geological Survey during 1987: U.S. Geological Circular 1016, p. 164–168.
Keleman, P.B., Hanghoj, K., and Greene, A.R., 2003, One view of the geochemistry of subduction-related magmatic arcs with an emphasis on primitive
andesite and lower crust, in Rudnick, R.L., ed., The Crust: Treatise on Geochemistry, v. 3, Oxford, Elsevier-Pergamon, p. 593–659.
Kidwell, S.M., 1991, The stratigraphy of shell concentrations, in Allison, P.B., and
Briggs, D.E.G., eds., Taphonomy: Releasing the Data Locked in the Fossil
Record: New York, Plenum Press, p. 211–290.
Kozinski, J., 1985, Sedimentology and tectonic significance of the Nutzotin
Mountains sequence, Alaska [M.S. thesis]: Albany, New York, State University of New York at Albany, 132 p.
Lanphere, M.A., 1978, Displacement history of the Denali fault system, Alaska
and Canada: Canadian Journal of Earth Sciences, v. 15, p. 817–822.
Leithold, E.L., 1989, Depositional processes on an ancient and modern muddy
shelf, Northern California: Sedimentology, v. 36, p. 179–202, doi: 10.1111/
j.1365-3091.1989.tb00602.x.
Lisowski, M., Savage, J.C., and Burford, R.O., 1987, Strain accumulation across
the Fairweather and Totschunda faults, Alaska: Journal of Geophysical
Research, v. 92, p. 11,552–11,560.
Lowe, D.R., 1976a, Grain flow and grain flow deposits: Journal of Sedimentary
Petrology, v. 46, p. 188–199.
Lowe, D.R., 1976b, Subaqueous liquefied and fluidized sediment flows and their
deposits: Sedimentology, v. 23, p. 285–308, doi: 10.1111/j.1365-3091.1976.
tb00051.x.
Lowe, D.R., 1982, Sediment gravity flows: Part 2, Depositional models with special reference to the deposits of high-density turbidity currents: Journal of
Sedimentary Petrology, v. 52, p. 279–297.
Lowey, G.W., 1998, A new estimate of the amount of displacement on the Denali
fault system based on the occurrence of carbonate megaboulders in the
Dezadeash Formation (Jura-Cretaceous), Yukon, and the Nutzotin Mountains sequence (Jura-Cretaceous), Alaska: Bulletin of Canadian Petroleum
Geology, v. 46, p. 379–386.
Lowey, G.W., 2006, Reassembling the Nutzotin-Dezadeash Basin: New evidence
from the Dezadeash Formation, Yukon, and implications concerning the
accretionary history of the Wrangellia composite terrane: Geological Society of America Abstracts with Programs, v. 38, no. 5, p. 80.
Ludwig, K.R., 1991, A computer program for processing Pb-U-Th isotopic data:
U.S. Geological Survey Open-File Report 88-542, 34 p.
Lundberg, N., and Dorsey, R., 1988, Synorogenic sedimentation and subsidence
in a Plio-Pleistocene collisional basin, eastern Taiwan, in Kleinspehn, K.,
and Paola, P., New Perspectives in Basin Analysis: New York, SpringerVerlag, p. 265–280.
MacEachern, J.A., Bann, K.L., Bhattacharya, J.P., and Howell, C.D., Jr., 2005,
Ichnology of deltas: Organism responses to the dynamic interplay of rivers,
waves, storms, and tides, in Giosan, L., and Bhattacharya, J.P., eds., River
Deltas: Concepts, Models, and Examples: SEPM Special Publication 83,
p. 49–85.
MacKevett, E.M., Jr., 1969, Three newly named Jurassic formations in the
McCarthy C-5 quadrangle, Alaska: U.S. Geological Survey Bulletin 1274-A,
p. A37–A49.
MacKevett, E.M., 1978, Geologic map of the McCarthy Quadrangle, Alaska: U.S.
Geologic Survey, Map I-1032, scale 1:250,000.
Mahoney, J.B., Mustard, P.S., Haggart, J.W., Friedman, R.M., Fanning, C.M., and
McNicoll, V.J., 1999, Archean zircons in Cretaceous strata of the western
Canadian Cordillera: The “Baja B.C.” hypothesis fails a “crucial test”: Geology, v. 27, p. 195–198, doi: 10.1130/0091-7613(1999)027<0195:AZICSO>
2.3.CO;2.
Manuszak, J.D., 2000, Sedimentary and structural record of Late Jurassic-Early
Cretaceous collisional tectonics, Nutzotin and Mentasta Mountains, east-central Alaska [M.S. thesis]: West Lafayette, Indiana, Purdue University, 291 p.
Manuszak, J.D., and Ridgway, K.D., 2000, Stratigraphic architecture of the Upper
Jurassic-Lower Cretaceous Nutzotin Mountains sequence, Nutzotin and
Mentasta Mountains, Alaska, in Pinney, D.S., and Davis, P.K., eds., Short
Notes on Alaskan Geology 1999: Fairbanks, Alaska, Division of Geological
and Geophysical Surveys Professional Paper 119, p. 63–75.
Marsaglia, K.M., 1995, Interarc and backarc basins, in Busby, C.J., and Ingersoll,
R.V., eds., Tectonics of Sedimentary Basins: Cambridge, Massachusetts,
Blackwell Science, p. 299–329.
Matmon, A., Schwartz, D.P., Haeussler, P.J., Finkel, R., Lienkaemper, J.J., Stenner, H.D., and Dawson, T.E., 2006, Denali fault slip rates and Holocene–late
Pleistocene kinematics of central Alaska: Geology, v. 34, p. 645–648, doi:
10.1130/G22361.1.
McClelland, W.C., and Gehrels, G.E., 1990, The Duncan Canal shear zone: Arightlateral shear zone of Jurassic age along the inboard margin of the Alexander terrane: Geological Society of America Bulletin, v. 102, p. 1378–1392,
doi: 10.1130/0016-7606(1990)102<1378:GOTDCS>2.3.CO;2.
GSA_SPE431_14_Ridgway.qxd
7/28/07
9:06 AM
Page 375
Sedimentary record of the tectonic growth of a collisional continental margin
McClelland, W.C., and Mattinson, J.M., 2000, Cretaceous-Tertiary evolution of
the western Coast Mountains, central southeastern Alaska, in Stowell, H.H.,
and McClelland, W.C., eds., Tectonics of the Coast Mountains, Southeastern Alaska and British Columbia: Geological Society of America Special
Paper 343, p. 159–182.
McClelland, W.C., Gehrels, G.E., and Saleeby, J.B., 1992a, Upper Jurassic-Lower
Cretaceous basinal strata along the Cordilleran margin: Implications for the
accretionary history of the Alexander-Wrangellia-Peninsular terrane: Tectonics, v. 11, p. 832–835.
McClelland, W.C., Gehrels, G.E., Samson, S.D., and Patchett, P.J., 1992b, Protolith relations of the Gravina belt and Yukon-Tanana terrane in central
southeastern Alaska: The Journal of Geology, v. 100, p. 107–123.
McClelland, W.C., Gehrels, G.E., Samson, S.D., and Patchett, P.J., 1992c, Structural and geochronologic relations along the western flank of the Coast
Mountains batholith: Stikine River to Cape Fanshaw, central southeastern
Alaska: Journal of Structural Geology, v. 14, p. 475–489, doi: 10.1016/
0191-8141(92)90107–8.
Mezger, J.E., Creaser, R.A., Erdmer, P., and Johnston, S.T., 2001, A Cretaceous
back-arc basin in the Coast Belt of the northern Canadian Cordillera: Evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon: Canadian Journal of Earth
Sciences, v. 38, p. 91–103, doi: 10.1139/cjes-38–1–91.
Miall, A.D., 1995, Collision related foreland basins, in Busby, C.J., and Ingersoll,
R.V., Tectonics of Sedimentary Basins: Cambridge, Massachusetts, Blackwell Science, p. 393–424.
Middleton, G.V., 1967, Experiments on density and turbidity currents: Part 3,
Deposition of sediment: Canadian Journal of Earth Sciences, v. 4, p. 475–505.
Middleton, L.T., and Hampton, M.A., 1976, Subaqueous sediment transport and
deposition by sediment gravity flows, in Stanley, D.J., and Swift, D.J.P.,
eds., Marine Sediment Transport and Environmental Management: New
York, Wiley, p. 197–218.
Mihalynuk, M.G., Nelsen, J., and Diakow, L.J., 1994, Cache Creek terrane entrapment: Oroclinal paradox within the Canadian Cordillera: Tectonics, v. 13,
p. 575–595, doi: 10.1029/93TC03492.
Miller, J.W., and Detterman, R.L., 1985, The Buchia zones in Upper Jurassic
rocks on the Alaska Peninsula: U.S. Geological Survey Circular 945,
p. 51–53.
Monger, J.W.H., and Nokleberg, W.J., 1996, Evolution of the North America
Cordillera: Generation, fragmentation, displacement, and accretion of successive North America plate-margin arcs, in Coyner, A.R., and Fahey, P.L.,
eds., Geology and Ore Deposits of the North American Cordillera, Symposium Proceedings, Reno-Sparks, Nevada, April 1995: Reno, Nevada, Geological Society of Nevada, p. 1133–1152.
Monger, J.W.H., Price, R.A., and Tempelman-Kluit, J.D., 1982, Tectonic accretion and the origin of the two major metamorphic and plutonic welts in the
Canadian Cordillera: Geology, v. 10, p. 70–75, doi: 10.1130/0091-7613(1982)
10<70:TAATOO>2.0.CO;2.
Mortensen, J.K., 1992, Pre-Mid-Mesozoic tectonic evolution of the YukonTanana terrane, Yukon and Alaska: Tectonics, v. 11, p. 836–853.
Mutti, E., 1977, Distinctive thin-bedded turbidite facies and related depositional environments in the Eocene Hecho Group (south-central Pyrenees, Spain):
Sedimentology, v. 24, p. 107–131, doi: 10.1111/j.1365-3091.1977.tb00122.x.
Mutti, E., 1992, Turbidite sandstones: Agip Special Publication, Milan, 276 p.
Mutti, E., and Ricci Lucchi, F., 1972, Turbidites of the northern Apennines: Introduction to facies analysis (English translation by T.H. Nilsen, 1978): International Geology Review, v. 20, p. 2170–2195.
Mutti, E., and Ricci Lucchi, F., 1975, Turbidite facies and facies associations, in
Examples of Turbidite Facies and Facies Associations from Selected Formations of the Northern Apennines: Field Trip Guidebook A-11, 9th International Sedimentology Congress, Nice, France, p. 21–36.
Nelson, H., and Maldonado, A., 1988, Factors controlling depositional patterns of
Ebro turbidite systems, Mediterranean Sea: American Association of Petroleum Geologists Bulletin, v. 72, p. 698–716.
Nokleberg, W.J., Jones, D.L., and Silberling, N.J., 1985, Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range,
375
Alaska: Geological Society of America Bulletin, v. 96, p. 1251–1270, doi:
10.1130/0016-7606(1985)96<1251:OATEOT>2.0.CO;2.
Nokleberg, W.J., Plafker, G., and Wilson, F.H., 1994a, Geology of south-central
Alaska, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 311–365.
Nokleberg, W.J., Parfenov, L.M., Monger, J.W.H., Baranov, B.V., Byalobzhesky,
S.G., Bundtzen, T.K., Feeney, T.D., Fujita, K., Gordey, S.P., Grantz, A.,
Khanchuk, A.I., Natal’in, B.A., Natapov, L.M., Norton, I.O., Patton, W.W.,
Jr., Plafker, G., Scholl, D.W., Sokolov, S.D., Sosunov, G.M., Stone, D.B.,
Tabor, R.W., Tsukanov, N.V., Vallier, T.L., and Wakita, K., 1994b, CircumNorth Pacific tectono-stratigraphic terrane map: U.S. Geological Survey,
Open-File Report 94-714, 2 sheets, scale 1:5,000,000; p. 0–211.
Nokleberg, W.J., Parfenov, L.M., Monger, J.W.H., Norton, I.O., Khanchuk, A.I.,
Stone, D.B., Scholl, D.W., and Fujita, K., 1998, Phanerozoic tectonic evolution of the circum-North Pacific: U.S. Geological Survey Open-File
Report 98-574, 125 p.
Packer, D.R., and Stone, D.B., 1974, Paleomagnetism of Jurassic rocks from
southern Alaska and their tectonic implications: Canadian Journal of Earth
Sciences, v. 11, p. 976–997.
Palmer, A.R., and Geissman, J., 1999, 1999 Geologic Time Scale: Boulder, Colorado, Geological Society of America.
Patton, W.W., Box, S.E., and Grybeck, D.J., 1994, Ophiolites and other maficultramafic complexes in Alaska, in Plafker, G. and Berg, H.C., eds., The
Geology of Alaska: Boulder, Colorado, Geological Society of America, The
Geology of North America, v. G-1, p. 671–686.
Pavlis, T.L., 1982, Origin and age of the Border Ranges fault of southern Alaska
and its bearing on the Late Mesozoic tectonic evolution of Alaska: Tectonics, v. 1, p. 343–368.
Pemberton, S.G., and MacEachern, J.A., 1992, Trace fossil facies models: Environmental and allostratigraphic significance, in Walker, R.G., and James,
N.P., eds., Facies Models: Response to Sea Level Change: Geological Association of Canada Publications, p. 47–72.
Pfaff, V.J., and Johnson, A.M., 1989, Opposite senses of fold asymmetry: Engineering Geology, v. 27, p. 3–38, doi: 10.1016/0013-7952(89)90030-6.
Pickering, K.T., 1985, Kangfjord turbidite system, Norway, in Bouma, A.H., Normark, W.R., and Barnes, N.E., eds., Submarine Fans and Related Turbidite
Systems: New York, Springer-Verlag, p. 237–244.
Pickering, K.T., Stow, D.A.V., Watson, M., and Hiscott, R.N., 1986, Deep-water
facies, processes, and models: A review and classification scheme for modern and ancient sediments: Earth-Science Reviews, v. 23, p. 75–174, doi:
10.1016/0012-8252(86)90001-2.
Plafker, G., and Berg, H.C., 1994, Overview of the geology and tectonic evolution of Alaska, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska:
Boulder, Colorado, Geological Society of America, The Geology of North
America, v. G-1, p. 989–1021.
Plafker, G., Hudson, T., and Richter, D.H., 1977, Preliminary observations on late
Cenozoic displacements along the Totschunda and Denali fault systems:
U.S. Geological Survey Circular 751-B, p. B67–B69.
Plafker, G., Nokleberg, W.J., and Lull, J.S., 1989, Bedrock geology and tectonic
evolution of the Wrangellia, Peninsular, and Chugach terranes along the
Trans-Alaska Crustal Transect in the northern Chugach Mountains and
southern Copper River basin: Journal of Geophysical Research, v. 94,
p. 4255–4295.
Plafker, G., Casey Moore, J., and Winkler, G.R., 1994, Geology of the southern
Alaska margin, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska:
Boulder, Colorado, Geological Society of America, The Geology of North
America, v. G-1, p. 389–450.
Plafker, G., Carver, G., Cluff, L., and Metz, M., 2006, Historic and paleoseismic
evidence for non-characteristic earthquakes and the seismic cycle at the
Delta River crossing of the Denali fault, Alaska: AGU Chapman Conference
on the Active Tectonics and Seismic Potential of Alaska, Abstracts with Program, p. 49.
Ramberg, H., 1963, Evolution of drag folds: Geological Magazine, v. 100,
p. 97–105.
GSA_SPE431_14_Ridgway.qxd
376
7/28/07
9:06 AM
Page 376
Manuszak et al.
Richter, D.H., 1971, Reconnaissance geologic map of the Nabesna A-2 Quadrangle, Alaska: U.S. Geological Survey Map I-655, scale 1:63,360.
Richter, D.H., 1976, Geologic map of the Nabesna Quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series, Map I-932, 1 sheet,
scale 1:250,000.
Richter, D.H., and Matson, N.A., Jr., 1971, Quaternary faulting in the eastern
Alaska Range: Geological Society of America Bulletin, v. 82, p. 1529–1540,
doi: 10.1130/0016-7606(1971)82[1529:QFITEA]2.0.CO;2.
Richter, D.H., and Jones, D.L., 1973, Structure and stratigraphy of the eastern
Alaska Range, Alaska: American Association of Petroleum Geologists
Memoir, v. 19, p. 408–420.
Richter, D.H., and Schmoll, H., 1973, Geologic map of the Nabesna C-5 Quadrangle, Alaska: U.S. Geological Survey Map GQ-1062, scale 1:63,360.
Richter, D.H., Lanphere, M.A., and Matson, N.A., 1975, Granitic plutonism and
metamorphism, Eastern Alaska Range, Alaska: Geological Society of
America Bulletin, v. 86, p. 819–829, doi: 10.1130/0016-7606(1975)86
<819:GPAMEA>2.0.CO;2.
Ridgway, K.D., and DeCelles, P.G., 1993, Stream-dominated alluvial-fan and
lacustrine depositional systems in Cenozoic strike-slip basins, Denali fault
system, Yukon Territory, Canada: Sedimentology, v. 40, p. 645–666, doi:
10.1111/j.1365-3091.1993.tb01354.x.
Ridgway, K.D., Sweet, A.R., and Cameron, A.R., 1995, Climatically induced floristic changes across the Eocene-Oligocene transition in the northern high latitudes, Yukon Territory, Canada: Geological Society of America Bulletin,
v. 107, p. 676–696, doi: 10.1130/0016-7606(1995)107<0676:CIFCAT>
2.3.CO;2.
Ridgway, K.D., Trop, J.M., and Sweet, A.R., 1997, Thrust-top basin formation
along a suture zone, Cantwell basin, Alaska Range: Implications for development of the Denali fault system: Geological Society of America Bulletin,
v. 109, p. 505–523, doi: 10.1130/0016-7606(1997)109<0505:TTBFAA>
2.3.CO;2.
Ridgway, K.D., Trop, J.M., and Sweet, A.R., 1999, Stratigraphy, depositional systems, and age of the Tertiary White Mountain basin, Denali fault system,
southwestern Alaska, in Pinney, D.S., and Davis, P.K., eds., Short Notes on
Alaskan Geology, 1999: Fairbanks, Alaska, Division of Geological and
Geophysical Surveys Professional Paper 119, p. 77–84.
Ridgway, K.D., Trop, J.M., Nokleberg, W.J., Davidson, C.M., and Eastham, K.R.,
2002, Mesozoic and Cenozoic tectonics of the eastern and central Alaska
Range: Progressive basin development and deformation in a suture zone:
Geological Society of America Bulletin, v. 114, p. 1480–1504, doi:
10.1130/0016-7606(2002)114<1480:MACTOT>2.0.CO;2.
Rioux, M., Hacker, B., Mattinson, J., Kelemen, P., Blusztajn, J., Hanghoj, K., and
Amato, J., 2005, Tectonic and geochemical evolution of the accreted Talkeetna arc, south-central Alaska: Implications for a type section of intraoceanic arc crust: Eos (Transactions, American Geophysical Union), 86
(52), Fall Meeting Supplement, Abstract V44C-07.
Roeske, S.M., Mattinson, J.M., and Armstrong, R.L., 1989, Isotopic ages of glaucophane schists on the Kodiak Islands, southern Alaska, and their implications for the Mesozoic tectonic history of the Border Ranges fault system:
Geological Society of America Bulletin, v. 101, p. 1021–1037, doi: 10.1130/
0016-7606(1989)101<1021:IAOGSO>2.3.CO;2.
Roeske, S.M., Pavlis, T.L., Snee, L.W., and Sisson, V.B., 1992, 40Ar/39Ar isotopic
ages from the combined Wrangellia-Alexander terrane along the Border
Ranges fault system in the eastern Chugach Mountains and Glacier Bay,
Alaska, in Bradley, D.C., and Ford, A.B., eds., Geologic Studies in Alaska
by the U.S. Geological Survey, 1990: U.S. Geological Survey Bulletin 1999,
p. 180–195.
Roeske, S.M., Snee, L.W., and Pavlis, T.L., 2003, Dextral slip reactivation of an
arc-forearc boundary during Late Cretaceous-Early Eocene oblique convergence in the northern Cordillera, in Sisson, V.B., Roeske, S.M., and Pavlis,
T.L., eds., Geology of a Transpressional Orogen Developed during RidgeTrench Interaction along the North Pacific Margin: Geological Society of
America Special Paper 371, p. 141–170.
Rubin, C.M., and Saleeby, J.B., 1991, The Gravina sequence: Remnants of a midMesozoic oceanic arc in south-southeast Alaska: Journal of Geophysical
Research, v. 96, p. 14,551–14,568.
Rubin, C.M., and Saleeby, J.B., 1992, Thrust tectonics and Cretaceous intracontinental shortening in southeast Alaska, in McClay, K.R., ed., Thrust Tectonics: London; New York, Chapman and Hall, p. 407–417.
Rubin, C.M., Saleeby, J.B., Cowan, D.S., Brandon, M.T., and McGroder, M.F.,
1990, Regionally extensive mid-Cretaceous west-vergent thrust system in
the northwestern Cordillera: Implications for continent-margin tectonism:
Geology, v. 18, p. 276–280, doi: 10.1130/0091-7613(1990)018<0276:
REMCWV> 2.3.CO;2.
Saleeby, J.B., 2000, Geochronologic investigations along the Alexander-Taka terrane boundary, southern Revillagigedo Island to Cape Fox areas, southeast
Alaska, in Stowell, H.H., and McClelland, W.C., eds., Tectonics of the Coast
Mountains, Southeast Alaska and Coastal British Columbia: Geological
Society of America Special Paper 343, p. 107–143.
Sandy, M.R., and Blodgett, R.B., 1996, Peregrinella (Brachiopoda; Rhynchonellida) from the Early Cretaceous, Wrangellia terrane, Alaska, in Copper, P.,
and Jin, J., eds., Brachiopods, Proceedings of the Third International Brachiopod Congress: A.A. Balkema/Rotterdam/Brookfield, p. 239–242.
Seilacher, A., 1977, Pattern analysis of Paleodictyon and related trace fossils, in
Crimes, T.P., and Harper, J.C., eds., Trace Fossils 2: Geological Journal Special Issue 9, UK, Liverpool, Seel House Press, p. 289–334.
Sengör, A.M.C., and Okurogullari, A.H., 1991, The role of accretionary wedges
in the growth of continents: Asiatic examples from Argand to plate tectonics: Swiss Geological Society, v. 84, p. 535–597.
Shanmugam, G., and Moiola, R.J., 1991, Types of submarine fan lobes: Models
and implications: American Association of Petroleum Geologists Bulletin,
v. 75, p. 156–179.
Short, E., Snyder, D.C., Trop, J.M., Hart, W.K., and Layer, P.W., 2005, New findings on Early Cretaceous volcanism within the allochthonous Wrangellia
terrane, south-central Alaska: Stratigraphic, geochronologic, and geochemical data from the Chisana Formation, Nutzotin Mountains: Geological Society of America Abstracts with Programs, v. 37, no. 7, p. 81.
Silver, E.A., Abbott, L.D., Kirchoff-Stein, K.S., Reed, D.L., Bernstein-Taylor, B.,
and Hilyard, D., 1991, Collision propagation in Papua New Guinea and the
Solomon Sea: Tectonics, v. 10, p. 863–874.
Snyder, D., and Hart, W., 2002, Petrologic development of Wrangell volcanic field
basement granitoids from White Mountain, Nabesna, Alaska: Eos (Transactions, American Geophysical Union), v. 83, p. 47.
Snyder, D.C., and Hart, W.K., 2007, this volume, The White Mountain Granitoid
Suite: Isotopic constraints on source reservoirs for Cretaceous magmatism
within the Wrangellia Terrane, in Ridgway, K.D., Trop, J.M., Glen, J.M.G.,
and O’Neill, J.M., eds., Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska: Geological Society of America
Special Paper 431, doi: 10.1130/2007.2431(15).
Stamatakos, J.A., Trop, J.M., and Ridgway, K.D., 2001, Late Cretaceous paleogeography of Wrangellia: Paleomagnetism of the MacColl Ridge Formation, southern Alaska, revisited: Geology, v. 29, p. 947–950, doi: 10.1130/
0091-7613(2001)029<0947:LCPOWP>2.0.CO;2.
Stanley, W., Labson, V., Nokleberg, W., Csejtey, B., and Fisher, M., 1990, The
Denali fault system and Alaska Range of Alaska: Evidence for underplated
Mesozoic flysch from magnetotelluric surveys: Geological Society of
America Bulletin, v. 102, p. 160–173, doi: 10.1130/0016-7606(1990)102
<0160:TDFSAA>2.3.CO;2.
Stow, D.A., Reading, H.G., and Collinson, J.D., 1996, Deep seas, in Reading,
H.G. ed., Sedimentary Environments: Processes, Facies, and Stratigraphy:
Cambridge, Massachusetts, Blackwell Science, p. 395–453.
Stowell, H.H., Green, N.L., and Hooper, R.J., 2000, Geochemistry and tectonic
setting of basaltic volcanism, northern Coast Mountains, southeastern
Alaska, in Stowell, H.H., and McClelland, W.C., eds., Tectonics of the Coast
Mountains, Southeastern Alaska and British Columbia: Boulder, Colorado:
Geological Society of America Special Paper 343, p. 235–256.
Tempelman-Kluit, D.J., 1976, The Yukon crystalline terrane: Enigma in the Canadian Cordillera: Geological Society of America Bulletin, v. 87, p. 1343–1357,
doi: 10.1130/0016-7606(1976)87<1343:TYCTEI>2.0.CO;2.
Teng, L.S., 1990, Geotectonic evolution of late Cenozoic arc-continent collision
in Taiwan: Tectonophysics, v. 183, p. 57–76, doi: 10.1016/0040-1951
(90)90188-E.
GSA_SPE431_14_Ridgway.qxd
7/28/07
9:06 AM
Page 377
Sedimentary record of the tectonic growth of a collisional continental margin
Trop, J.M., 2000, Sedimentary basin development within the Wrangellia composite terrane, Mesozoic Wrangell Mountains basin, southern Alaska: A longterm record of terrane migration and arc construction [Ph.D. thesis]: West
Lafayette, Indiana, Purdue University, 310 p.
Trop, J.M., and Ridgway, K.D., 2007, this volume, Mesozoic and Cenozoic tectonic
growth of southern Alaska: A sedimentary basin perspective, in Ridgway,
K.D., Trop, J.M., Glen, J.M.G., and O’Neill, J.M., eds., Tectonic Growth of a
Collisional Continental Margin: Crustal Evolution of Southern Alaska: Geological Society of America Special Paper 431, doi: 10.1130/ 2007.2431(04).
Trop, J.M., Ridgway, K.D., Sweet, A.R., and Layer, P.W., 1999, Submarine fan
deposystems and tectonics of a Late Cretaceous forearc basin along an
accretionary convergent plate boundary, MacColl Ridge Formation,
Wrangell Mountains, Alaska: Canadian Journal of Earth Sciences, v. 36,
p. 433–458, doi: 10.1139/cjes-36-3-433.
Trop, J.M., Ridgway, K.D., Manuszak, J.D., and Layer, P., 2002, Mesozoic sedimentary-basin development on the allochthonous Wrangellia composite terrane: A long-term record of terrane migration and arc construction, Wrangell
Mountains basin, Alaska: Geological Society of America Bulletin, v. 114, p.
693–717, doi: 10.1130/0016-7606(2002)114<0693:MSBDOT>2.0.CO;2.
Trop, J.M., Ridgway, K.D., and Sweet, A.R., 2004, Stratigraphy, palynology, and
provenance of the Colorado Creek basin, Alaska, U.S.A.: Oligocene transpressional tectonics along the central Denali fault system: Canadian Journal
of Earth Sciences, v. 41, p. 457–480, doi: 10.1139/e04-003.
Trop, J.M., Szuch, D.A., Rioux, M., and Blodgett, R.B., 2005, Sedimentology and
provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains,
377
Alaska: Bearing on the accretionary tectonic history of the Wrangellia composite terrane: Geological Society of America Bulletin, v. 117, p. 570–588,
doi: 10.1130/B25575.1
Umhoefer, P., 1987, Northward translation of “Baja British Columbia” along the
Late Cretaceous to Paleocene margin of western North America: Tectonics,
v. 6, p. 377–394.
van der Heyden, P., 1992, A Middle Jurassic to Early Tertiary Andean-Sierra arc
model for the Coast Belt of British Columbia: Tectonics, v. 11, p. 82–97.
Vossler, J.M., and Pemberton, S.G., 1988, Ichnology of the Cardium Formation
(Pembina oilfield): Implications for depositional and sequence stratigraphic
interpretations, in James, D.P., and Leckie, D.A., eds., Sequences, Stratigraphy, Sedimentology: Surface and Subsurface: Canadian Society of Petroleum Geologists, Memoir 15, p. 237–254.
Walker, R.G., 1984, Turbidites and associated coarse clastic deposits, in Walker,
R.G., ed., Facies Models, 2nd ed.: Toronto, Ontario, Geological Association
of Canada, p. 171–188.
Winkler, G.R., Silbermann, M.L., Grantz, A., Miller, R.J., and MacKevett, E.M., Jr.,
1981, Geologic map and summary geochronology of the Valdez Quadrangle,
southern Alaska: U.S. Geological Survey Open-File Report 80-892-A,
1 sheet, scale 1:250,000.
Zakharov, V.A., 1987, The bivalve Buchia and the Jurassic-Cretaceous boundary
in the Boreal Province: Cretaceous Research, v. 8, p. 141–153, doi:
10.1016/0195-6671(87)90018-8.
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