EARLY EASTWARD TRANSLATION OF
SHORTENING IN THE SEVIER THRUST
BELT, NORTHEAST UTAH AND
SOUTHWEST WYOMING, U.S.A.
S. Lynn Peyton1,3, Kurt N. Constenius2, and Peter G. DeCelles1
ABSTRACT
Cross section restorations across the Sevier fold-thrust belt in northeast Utah and southwest Wyoming show
bed length discrepancies within the hanging wall of the Absaroka thrust, suggesting that shortening above the
Jurassic Preuss salt detachment was 8 to 14 km greater than shortening below the detachment. Interpretation of
newly reprocessed, two-dimensional seismic reflection lines over the hanging wall of the Crawford thrust shows
that the thrust is not offset across the salt detachment, indicating that: (1) the additional shortening within the
Absaroka hanging wall was transferred east before main movement on the Crawford thrust; and (2) the magnitude
of Paleocene and early Eocene shortening on the Medicine Butte thrust was essentially equal to subsequent extension on the middle Eocene to late Oligocene Almy-Acocks normal-fault system. Although early displacement on
the Crawford thrust could be responsible for the extra shortening above the Preuss salt detachment, surface and
subsurface geology suggest shortening from the western thrust system (Willard and Lost Creek thrusts) was transferred ~70 to 90 km east along the Preuss salt detachment between ~102 and 90 Ma, to the future location of the
Absaroka hanging wall. From south of the Little Muddy Creek area in southwest Wyoming, to its southernmost outcrop in northeast Utah, the old Absaroka thrust is interpreted to be a frontal imbricate of this pre-Crawford-thrust
shortening.
INTRODUCTION
The Sevier fold-thrust belt in the western U.S.A. is
one of the world’s best-documented thin-skinned retroarc fold-thrust belts (e.g., DeCelles, 2004, and references
therein), and the Utah-Wyoming-Idaho salient is one of
the most studied parts of this thrust belt. Synorogenic
sedimentary rocks, along with subsurface well and seismic data from petroleum exploration, closely constrain
the timing and evolution of the thrust belt in this region.
Thrusting in the Utah-Wyoming-Idaho salient progressed
overall from west to east, with episodic out-of-sequence
displacement on existing thrusts (Royse and others, 1975;
Lamerson, 1982; Coogan, 1992; DeCelles, 1994). Coogan
(1992) recognized two thrust systems with different basal
decollements: an older (~140 to 90 Ma) western system
consisting of the Willard, Meade, and Laketown thrusts
in northeast Utah and southeast Idaho; and a younger
(~90 to 50 Ma) eastern system consisting of the Crawford,
Medicine Butte, Absaroka, and Hogsback thrusts in northeast Utah and southwest Wyoming (figure 1). Both thrust
systems climb up-section to the east, with frontal detachments in the salt-rich lower part of the Jurassic Preuss Redbeds (figure 2). Total shortening from cross section restoration in this part of the Sevier thrust belt may be >150
Department of Geosciences, University of Arizona, Tucson, AZ 85721
Email: slpeyton@coalcreekresources.com
2
Snowslip Corp., Tucson, AZ 85704
3
Present address: Coal Creek Resources, Inc., Lakewood, CO 80228
1
km (Dixon, 1982; Lamerson, 1982; Coogan, 1992; Yonkee,
2005), or ~50% (Royse and others, 1975). A significant
component of deformation (up to ~25%) was also locally
accommodated by internal strain (Mitra, 1994). Yonkee
and Weil (2010) calculated that layer-parallel shortening
may vary from 5 to 30% in this area, which typically is not
included in estimates of shortening from cross sections.
Balanced cross section restoration of the Absaroka
thrust sheet of the eastern thrust system shows greater
shortening in Jurassic and Cretaceous beds above the
Jurassic Preuss salt detachment than in the underlying Mesozoic and Paleozoic sedimentary units (figure 3)
(Lamerson, 1982; West and Lewis, 1982; Coogan and Constenius, 2003). Coogan and Constenius (2003) attributed
this extra bed length to slip on the Preuss salt detachment
during Willard, Crawford, and Medicine Butte thrusting. In
this paper we investigate the amount and timing of this
“extra” shortening by integrating reprocessed reflection
seismic data interpretations with shortening estimates
from cross sections. We show that a significant amount
of this shortening can be attributed to the western thrust
system, either on the Willard or Lost Creek thrusts (figure
1), although earliest movement on the Crawford thrust of
the eastern thrust system cannot completely be ruled out.
This shortening cannot be due to late- or post-Crawford
Peyton, S.L., Constenius, K.N., and DeCelles, P.G., 2011, Early eastward
translation of shortening in the Sevier thrust belt, northeast
Utah and southwest Wyoming, U.S.A., in Sprinkel, D.A., Yonkee,
W.A., and Chidsey, T.C., Jr., editors, Sevier thrust belt: northern
and central Utah and adjacent areas: Utah Geological
Association Publication 40, p. 57-72.
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
Idaho
Thrust fault
Wyoming
Little Muddy
Creek
Wyoming
Precambrian crystalline basement outcrop
84A
H3
Plate 1
82
Old Absaroka thrust
Well
Almy normal fault
1
Colorado
st
Utah
Oil field
thru
Map area
Cra
wfo
rd
Plunging anticline
Willard thrust
Normal fault
Painter
Reservoir
J1
Plate 1 & Fig. 3C
6
hr
us
t
84
kt
82
1
9
Glasscock
Hollow
Acocks
normal
fault
Anschutz
Ranch
Anschutz
Ranch
East
st C
ci
di
th
ka
ro
sa
Butte
ne
Coalville
Ea
G E
R A N
fault
any
on
Fig. 3B
Fig. 3A
Ab
thru
ru
st
st
th
Lost Creek
Reservoir
Yellow
Creek
AH
J1
ee
Lo
st
t
normal
Salt
Lake
City
East
Painter
Reservoir
Evanston
Cr
us
thr
h
Wasatc
41o
H
A T C
W A S
en
d
Og
Ogden
1
7
2
st
J1
ru
82
e
M
Uinta fault zone
Rockport
Reservoir
112o
Young Absar
oka thrust
Utah
Seismic line
Hogsback thrust
58
0
10
N
20 km
111o
Figure 1. Location map of northeast Utah and southwest Wyoming showing major faults (black), seismic line locations (red),
locations of plate 1 and cross sections in figure 2 (purple), and oil fields (green). For clarity, only wells and oil fields discussed in
the text are shown on the map. 1: Amoco Deseret well; 2: Amoco Champlin No. 432C well.
slip. We conclude that shortening of the western thrust
system propagated as far east as the location of the hanging wall of the future Absaroka thrust, a distance of ~70 to
90 km, and that this distance was probably controlled by
the eastern limit of deposition of the Jurassic Preuss salt.
GEOLOGIC BACKGROUND
The western thrust system of the Sevier fold-thrust
belt in northeast Utah has a basal decollement within Neoproterozoic miogeoclinal metasedimentary rocks, whereas the eastern system has a basal decollement in Cambrian
shelf sedimentary rocks that ramps down to the west into
Precambrian crystalline basement (Schirmer, 1988; Coogan, 1992; Yonkee, 1992). The major thrust of the western
system, the Willard thrust (figure 1), was emplaced from
~140 to 90 Ma (Yonkee and others, 1997) and was not
active after ~90 Ma (DeCelles, 1994). Yonkee (2005) esti-
mated that Neoproterozoic to Mesozoic miogeoclinal sedimentary rocks in the hanging wall of the Willard thrust
were displaced at least ~60 km to the east. Other thrusts
include the Ogden and Lost Creek thrusts (figure 1), and
to the north of the study area the Paris, Meade, and Laketown thrusts. The eastern thrust system in northern Utah
consists of three major thrusts, the Crawford, Absaroka,
and Hogsback thrusts (figure 1), which were active from
~90 to 50 Ma (DeCelles, 1994). These thrusts carried Precambrian crystalline basement with overlying Paleozoic
and Mesozoic shelf rocks eastward along a decollement
in Cambrian shale (figure 2). Maximum displacements of
~30 km, ~40 km, and ~20 km have been documented for
the Crawford, Absaroka, and Hogsback thrusts, respectively (Dixon, 1982; Lamerson, 1982; Coogan, 1992). The
Medicine Butte thrust crops out between the Crawford
and Absaroka thrusts (M’Gonigle and Dover, 1992; Dover
and McGonigle, 1993) (figure 1), and soles into the Preuss
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
Rich Member
Sliderock Member
Gypsum Spring Member
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
Age
Lithology
Eocene
Ankareh Fm
Perm.
Evanston - Main Body
Miss.
Evanston - Hams Fork
Adaville Fm
Dev.
Lodgepole Limestone
Gallatin Limestone
Gros Ventre Fm
Frontier Fm
Figure 2. Stratigraphic column of rocks carried on thrusts east
of the Willard thrust. Modified from Royse and others (1975),
Lamerson (1982), Coogan (1992), and DeCelles (1994).
Aspen Shale
salt detachment. Displacement on the Medicine Butte
thrust was ~3 to 4 km, an order of magnitude less than on
the Crawford, Absaroka, and Hogsback thrusts (Constenius, 1996).
The major detachment horizons for the eastern thrust
system in the study area include the Cambrian Gros Ventre
Formation, Triassic Woodside and Dinwoody Formations,
Jurassic Twin Creek Limestone, Jurassic Preuss Redbeds,
and Cretaceous Frontier Formation (Royse and others,
1975; Lamerson, 1982). This paper focuses on the Jurassic
Preuss Redbeds, which are composed of siltstone, shale,
and sandstone beds, with salt (generally halite) in the
lower part of the unit (Coogan and Yonkee, 1985). Halite
in the Preuss Redbeds has been penetrated by many petroleum wells in the region, and is easily identified by its
characteristic signature on well logs. Preuss salt thickness
varies across the study area due to varying depositional
thickness, thrust repetition, and salt flowage (Lamerson,
1982). Greatest variation in salt thickness occurs in the
proximity of the Medicine Butte thrust, where Lamerson
(1982) documents thicknesses between ~0 and 1400 m.
Proximal Cretaceous and Tertiary synorogenic sedimentary rocks are widely exposed and well studied in
northeast Utah and southwest Wyoming, and have been
used to constrain the timing of individual thrusts (Armstrong and Oriel, 1965; Royse and others, 1975; Lamerson,
1982; DeCelles, 1994). The poorly dated (Neocomian?)
Kelvin
Bear River Fm
Gannett Group
Ephraim Conglomerate
Stump Fm
Preuss Redbeds
Preuss salt
++++++++++
Giraffe Creek Member
Twin Creek
Limestone
Mission Canyon Limestone
Bighorn Dolomite
Henefer Conglomerate
Cretaceous
Amsden Fm
Darby Fm
Hilliard Shale
Lower
Wells Fm
Sil.
Echo Canyon Conglomerate
Dinwoody Fm
Phosphoria Fm
Camb.
Upper
Weber Conglomerate
Jurassic
Thaynes Fm
Woodside Fm
Penn.
Tertiary
Green River Fm
Wasatch Fm
Leeds Creek Member
Watton Canyon Member
Boundary Ridge Member
Rich Member
Sliderock Member
Gypsum Spring Member
Nugget Sandstone
Ankareh Fm
XXXXXXXXXX
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
ssic
59
Norwood Tuff
Fowkes Fm
Paleocene
Detachment
Triassic
Olig.
Formation
Nugget Sandstone
XXXXXXXXXX
Thaynes Fm
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
60
ANSCHUTZ
ANSCHUTZ
RANCH
RANCH EAST
FIELD
FIELD
Acocks Medicine
Normal Butte
Fault
Thrust
A
WEST
EAST
KT
K
alt
s
uss
Pre
Jsp
J
TR
m
ach
det
ent
st
hru
ka T
o
sar
Ab
UPz
0
5 km
Medicine
Butte
Thrust
Acocks
Normal
Fault
K
Jsp
J
TR
UPz
12.9 km extra bed length
(without restoring extension)
B
Absaroka Thrust
ANSCHUTZ
RANCH
FIELD
WEST
ANSCHUTZ
RANCH EAST
FIELD
EAST
KT
K
Jsp
J
ss
Preu
salt
t
men
ch
deta
TR
UPz
0
st
ka Thru
Absaro
1
2
3
4
5 km
Jsp
J
TR
7.4 km extra bed length
(without restoring extension)
UPz
C
Medicine
Butte
Thrust PAINTER
Acocks
RESERVOIR
Normal
FIELD
Fault
Almy
Normal
Fault
WEST
PIN #3
EAST
KT
lt
Preuss sa
ent
detachm
Jsp
salt
K
st
Thru
Absaroka
0
Preuss salt detachment
8.4 km extra bed length
(without restoring extension)
J
TR
UPz
LPz
ru
Th
Ho
5 km
t
us
Almy
Normal
Fault
K
st
ck
a
gsb
J
TR
UPz
LPz
PIN #2
PIN #3
5
Acocks
Normal
Fault
Jsp
ine
dic
Me
r
Th
tte
Bu
PIN #2
ka
Absaro
roka
a
Abs
Thrust
st
Thru
PIN #3
Figure 3. Cross sections and restored sections through the hanging wall of the Absaroka thrust from: (A) Coogan and Constenius (2003) showing 12.9 km of extra bed length above the Preuss salt detachment; (B) West and Lewis (1982) showing 7.4 km
of extra bed length; and (C) this study (east end of plate 1; modified from Lamerson ,1982) showing 8.4 km of extra bed length.
LPz—Lower Paleozoic rocks; UPz—Upper Paleozoic rocks; TR—Triassic rocks; J—Jurassic rocks; Jsp—Jurassic Preuss and Stump
Formations; K—Cretaceous rocks; KT—Cretaceous-Tertiary or Tertiary rocks. Pink layer indicates salt.
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
61
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
Ephraim Conglomerate was deposited during movement
on the western thrust system, and is laterally equivalent to
the lower part of the Lower Cretaceous Gannett Group (figure 2) (Royse and others, 1975). The Aptian Bechler Conglomerate (also part of the Gannett Group) is tied to slip
on the Meade thrust by provenance and growth structure
relationships (DeCelles and others, 1993). Overlying strata of the Cretaceous Bear River Formation, Aspen Shale,
and Frontier Formation may record continued uplift and
erosion of the western system. The Cretaceous Henefer
Formation, Echo Canyon, and Weber Canyon Conglomerates were deposited ~89 to 84 Ma during movement on
the Crawford thrust (DeCelles, 1994). The Hams Fork Conglomerate of the Evanston Formation was deposited ~75
to 68 Ma, corresponding to Absaroka thrusting (Lamerson, 1982). The main body of the Evanston Formation is
late Paleocene (~62 to 58 Ma), corresponding to Hogsback
thrusting (DeCelles, 1994). The youngest synorogenic
sedimentary rocks are found in the Tertiary Wasatch and
Green River Formations, which were deposited ~57 to 51
Ma (Constenius, 1996, and references therein).
The Medicine Butte thrust has been interpreted as a
frontal imbricate of the Crawford thrust (Lamerson, 1982;
Coogan, 1992), based on the fact that it roots into salt of the
Jurassic Preuss Redbeds, eventually joining the Crawford
thrust (figure 3). Lamerson (1982) concluded that thrust
movement on the Medicine Butte thrust was episodic, with
movement during Paleocene time, and youngest displacement after early Eocene time, based on synorogenic sedimentary rocks. Lamerson (1982) also proposed that the
last phase of compressional movement on the Crawford
thrust was taken up by displacement in the weak Preuss
salt detachment, terminating in a series of frontal splays to
the east, and that movement on the Absaroka thrust then
folded the Medicine Butte thrust and resulted in further
imbrication. Similarly, Royse (1993) identified an extensive decollement in the Preuss salt that linked westward
to the Crawford thrust and was deformed by the Absaroka
thrust. Constenius (1996) noted that the Medicine Butte
thrust truncated and displaced units as young as late Paleocene (~63 to 59 Ma), and concluded that timing was coeval with movement on the Hogsback thrust. After regional
tectonic shortening ceased, the Preuss salt detachment accommodated extension from early middle Eocene to late
Oligocene time, ~49 to 27 Ma (Constenius, 1996). Approximately 3 km of extensional slip on the Almy-Acocks listric
normal-fault system (figure 1) reactivated the Medicine
Butte thrust and Preuss salt detachment.
The Little Muddy Creek area in southwest Wyoming
has been the focus of much study due to the outcrop of
two thrusts in the Absaroka system (figure 1) (Royse
and others, 1975; Vietti, 1977). Royse and others (1975)
and Lamerson (1982) demonstrated that a major lateral
ramp is exposed in the hanging wall of the western fault
in the Absaroka system (the old Absaroka thrust (OAT))
in this area, as the thrust climbs southward from Devonian through Jurassic strata in its hanging wall. These
rocks, and the OAT, were together deformed during slip
on the more eastward “young Absaroka thrust” (YAT). A
thick syntectonic conglomerate (the Little Muddy Creek
Conglomerate) was produced by slip on the OAT, and was
subsequently strongly deformed during slip on the YAT
(Vietti, 1977; Lamerson, 1982; Pivnik, 1990). South of the
Little Muddy Creek area, the oldest rocks found in surface outcrops on the hanging wall of the OAT are Jurassic
Preuss Redbeds, with Cretaceous rocks in the footwall (i.e.,
the hanging wall of the YAT) (Lamerson, 1982). Royse and
others (1975) interpreted that the OAT in the Little Muddy
Creek area was active during the mid-Santonian, whereas
the YAT moved during latest Cretaceous time.
Shortening discrepancies have been recognized within
the hanging wall of the Absaroka thrust; the section above
the Preuss salt detachment has been shortened significantly more than the section below. Coogan and Constenius (2003) identified ~13 km of excess bed length above
the Preuss salt relative to Jurassic Twin Creek Limestone
and older strata in the hanging wall of the Absaroka thrust
at Anschutz Ranch field (figure 3A). Similarly, cross sections by West and Lewis (1982) and Lamerson (1982)
show excess bed lengths of 7.4 km and 8.4 km, respectively, above the Preuss salt detachment (figures 3B and 3C).
AMOUNT AND TIMING OF SHORTENING
Shortening Estimates
We constructed a balanced cross section that extends
from the Wasatch Range on the west, into Uinta County,
Wyoming, on the east (figure 1, plate 1). The western part
of the cross section, consisting of the footwall and hanging
wall of the Willard thrust, and the Wasatch culmination,
was based on surface mapping by Coogan and King (2001)
and Coogan (2004a, 2004b). Seismic-reflection data, welllog data, and surface geologic maps were the basis of our
interpretation of the central part of the cross section in
the proximity of the hanging wall of the Crawford thrust
(Coogan, 2004a, 2004b, 2004c). We reinterpreted data
presented in Lamerson’s (1982) plate 4 to construct the
eastern part of the cross section across the Painter Reservoir oil field in the hanging wall of the Absaroka thrust (figure 3C). Shortening estimates calculated from this cross
section are 28 km, 24 km, and 28 km for the Lost Creek,
Crawford, and Absaroka thrusts, respectively. We did not
restore the Willard thrust, which is estimated to have
~60 km of displacement (Yonkee, 2005), or the Hogsback
thrust, estimated to have ~15 to 20 km of displacement
(Dixon, 1982).
To investigate the timing of shortening above the
Preuss salt detachment, we first reconstructed bed lengths
above and below the detachment. Differences in bed length
between formations above and below the Preuss salt are
apparent from restored cross sections (figure 3). We used
cross sections published by other authors (Lamerson,
1982; West and Lewis, 1982; Constenius, 1996; Coogan
and Constenius, 2003), along with our own cross section
(plate 1) to estimate: (1) the amount of extension on the
Almy-Acocks listric normal-fault system; (2) the amount
of shortening across the Medicine Butte thrust; and (3)
the difference in bed length between the top of the Jurassic
Nugget Sandstone and the Jurassic Stump Formation, using a pin in the down-dip part of the hanging wall and a
pin in the footwall of the Absaroka thrust. For a true estimate of shortening, early middle Eocene to late Oligocene
extension (Constenius, 1996) should be restored before
measuring bed lengths. In practice, the total amount of ad-
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
62
ditional shortening above the Preuss salt was calculated
by adding the amount of extension to the bed length difference. Table 1 shows that in the hanging wall of the Absaroka thrust in northeast Utah and southwest Wyoming
there is a discrepancy of ~8 to 14 km between shortening above and below the Preuss salt detachment. Internal
strain, or layer-parallel shortening was not included in our
calculations or cross section, although it may be important
in estimates of total shortening (Mitra, 1994; Yonkee and
Weil, 2010). We assumed that layer-parallel shortening
was similar above and below the Preuss salt detachment.
Timing of Shortening
Relations along the cross sections in figure 3 and plate
1 between the surface traces of the Crawford and Absaroka thrusts constrain timing of movement on the Preuss
salt detachment. (1) Folding above and below the Preuss
salt detachment is decoupled as fold hinges are not aligned
Table 1. Estimates of extension, bed length, and shortening.
and fold amplitudes are different. (2) The Preuss salt detachment is folded by hanging wall anticlines on the Absaroka thrust. (3) The long thrust flat in the Preuss salt in the
hanging wall of the Absaroka thrust does not have a corresponding flat in the footwall. Instead, the Absaroka thrust
forms a continuous footwall ramp through the Preuss
salt (figure 3A, plate 1). (4) Thrusts in the eastern part of
the Absaroka hanging wall that sole into the Preuss salt,
along with the Preuss isoclinal fold above Anschutz Ranch
East field, are beveled by the basal Evanston unconformity, whereas to the west the same unconformity is folded
and cut by the Medicine Butte thrust (figures 3A and 3C).
These observations suggest that thrusts above the Preuss
salt detachment to the east of the Medicine Butte thrust
are older than the youngest phase of slip on the Medicine
Butte thrust, and predate Absaroka thrust deformation.
The Medicine Butte thrust is located directly above a
fault-bend fold in the hanging wall of the Absaroka thrust,
suggesting that the fault-bend fold already existed and in-
Difference
(km)
Bed
length
difference
across
PSD (km)
Difference in
shortening
above and
below PSD
(km)
Difference in
shortening
excluding
MBT (km)
Cross section
source
Field
Extension Shortening
on AANF
on MBT
(km)
(km)
This study
(Plate 1)
Painter
Reservoir &
East Painter
Reservoir
2.6
2.1
-0.5
8.4
11.0
8.9
3.7
1.7
-2
4
7.7
6.0
1.5
2.1
0.6
9
10.5
7.0
0.9
1.2
0.3
7.3
8.2
7.0
1.4
1.4
0
12.9
14.3
12.9
1.5
2.5
1
8
9.5
7.0
1.1
0.5
-0.6
7.2
8.3
7.8
Lamerson (1982)
Plate 4
Lamerson (1982)
Plate 10
Lamerson (1982)
Plate 11
Coogan and
Constenius
(2003)
Constenius
(1996)
West and Lewis
(1982)
Painter
Reservoir &
East Painter
Reservoir
Yellow
Creek &
Glasscock
Anschutz
Ranch &
Anschutz
Ranch East
Anschutz
Ranch &
Anschutz
Ranch East
Anschutz
Ranch &
Anschutz
Ranch East
Anschutz
Ranch &
Anschutz
Ranch East
AANF--Almy-Acocks normal-fault system; MBT--Medicine Butte thrust; PSD--Preuss salt detachment
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
63
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
fluenced the trajectory of the Medicine Butte thrust where
it ramps to the surface from the Preuss salt detachment
(Constenius, 1996). This also implies that shortening on
the Medicine Butte thrust occurred after displacement
on the Absaroka thrust. Progressively deformed synorogenic sedimentary rocks of the Maastrichtian-Paleocene
Evanston and late Paleocene-early Eocene Wasatch Formations provide evidence of the timing of movement on
the Medicine Butte thrust. Similarly, evidence of the collapse of the thrust belt and top-to-west motion on the salt
detachment is seen where synextensional growth strata
of the early middle Eocene Fowkes Formation and late
Eocene-Oligocene Norwood Tuff have been downdropped
and rotated along the Acocks listric normal fault and the
extensionally reactivated part of the Medicine Butte thrust
(Constenius, 1996). Shortening on the Medicine Butte
thrust is similar in magnitude to the amount of extension on the Almy-Acocks normal-fault system (table 1).
In summary, our observations suggest that movement on
the Medicine Butte thrust postdates displacement on the
Absaroka thrust, whereas movement on the thrusts above
the Preuss salt detachment to the east of the Medicine
Butte thrust occurred before the Absaroka thrust was active.
Possible scenarios resulting in additional shortening
above the Preuss salt in the hanging wall of the Absaroka
thrust are: (A) late movement on the Crawford thrust
(~86 to 84 Ma, before Absaroka thrusting) where slip was
transferred to the Preuss salt instead of upward to the surface; (B) early movement on the Crawford thrust (~89 to
87 Ma); and (C) pre-Crawford movement on the western
thrust system (Willard or Lost Creek thrusts, older than
~90 Ma; DeCelles, 1994).
Simple fault-bend fold and fault-propagation fold
diagrams illustrate the geometry of the Crawford thrust
predicted by these different scenarios (figure 4). If the
additional shortening was the result of late movement
on the Crawford thrust, with slip being transferred to
the Preuss salt detachment instead of the surface, as suggested by Lamerson (1982), then the part of the Crawford
thrust that ramped to the surface above the detachment
would have been carried passively along the salt detachment. Thus, the Crawford thrust would have been offset
eastward toward the foreland along the salt detachment,
and the dip of the hanging wall strata would reflect the
ramp-flat-ramp geometry of the offset Crawford thrust below (figure 4A). If the additional slip was transferred to
the salt detachment during early movement on the Crawford, then a fault-bend fold anticline would have formed
where the thrust changed from a ramp to a flat in the
Preuss salt detachment. Depending upon the amount of
displacement, the east-dipping limb of this anticline could
be preserved either in the footwall or hanging wall of the
Crawford thrust when it ramped to the surface (figure 4B).
If the additional shortening was transferred east from the
Willard or Lost Creek thrusts, pre-dating the Crawford
thrust, then the Preuss salt detachment would be offset by
later Crawford thrusting (figure 4C). In figure 4C we have
shown the Crawford thrust forming as a fault-propagation
fold to illustrate that the end result of this scenario may
look similar to figure 4B, where dips in the hanging wall
of the Crawford thrust roll to the east near to the thrust.
An important distinction between the second and third
scenarios is whether there has been displacement along
the Preuss detachment in the hanging wall of the Crawford
thrust. If the slip was transferred east during early Crawford movement, then there should be no displacement in
the Preuss salt in the hanging wall of the Crawford thrust
(figure 4B). If slip was associated with Lost Creek or Willard thrusting it would result in displacement along the
Preuss detachment in the hanging wall of the Crawford
thrust (figure 4C).
SEISMIC DATA
Predictions for the geometry of the Crawford thrust
from the proposed scenarios were tested using seismic-reflection data. Five, two-dimensional (2D) seismic lines that
cross the hanging wall and the surface trace of the Crawford thrust were reprocessed (figure 1). These lines were
originally acquired by Exxon in 1982 and 1984. Modern
processing techniques including pre-stack time migration
resulted in dramatic improvement in data quality over the
original processing. Two exploration wells provided ties
between the 2D seismic data and subsurface geology. The
Amoco Deseret well (section 2, T. 6 N., R. 5 E.), drilled in
1980, reached a total measured depth of 5318 m (17,448
ft) within Cambrian rocks in the hanging wall of the Crawford thrust. The Amoco Champlin No. 432C well (section 1,
T. 6 N., R. 5 E.) reached a total measured depth of 4232 m
(13,883 ft) within the Cretaceous rocks in the footwall of
the Crawford thrust, after penetrating Cretaceous through
Ordovician rocks of the hanging wall. We integrated surface mapping (Coogan and King, 2001; Coogan, 2004a,
2004c, 2006) with the well and seismic data to produce
our interpretations. Figure 5 shows a pre-stack time migration of seismic line 82J19 both without (figure 5A) and
with (figure 5B) our interpretation.
A depth section of line 82J19 was calculated by applying an interval-velocity model to the pre-stack time migration (figure 5C). A few key faults and formation tops are
dashed to provide a reference frame for comparison to
figure 5B. Notice that beds in the footwall of the Crawford
thrust dip to the west in the depth section, in agreement
with wells and surface geology. The time section displays
significant velocity pull-up due to the higher velocities of
the older rocks in the hanging wall of the Crawford thrust.
Similarly, at the northwest end of the time section, the
Crawford fault and the rocks in its hanging wall seem to
flatten. This is due to high velocity rocks on the Willard
thrust hanging wall causing velocity pull-up. On the depth
section, the Crawford thrust dips uniformly west. Although
our depth section is not perfect (there appear to be velocity problems beneath the Crawford thrust to the west of
the Champlin well), it illustrates the dangers of interpreting only time sections in this structurally complex area.
Footwall cutoffs below the Crawford thrust are well
imaged on the reprocessed seismic data, allowing us to
confidently interpret the location of the Crawford thrust.
Strong reflections are visible from the base of Jurassic Twin
Creek Limestone and the Triassic Woodside-Dinwoody
Formations in the hanging wall of the Crawford thrust.
These reflections have a constant dip, and do not indicate
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
64
A Late movement on the Crawford thrust. Crawford thrust (CT) cuts to surface. Later shortening transfered from ramp to flat in Jurassic Preuss salt detachment (PSD) to form structures to east, offsetting CT.
West
East
CT
West
East
CT
K
PSD
Mz
UPz
LPz
PCx
B Early movement on the Crawford thrust. Initial CT shortening transfered from ramp to flat in Jurassic
salt (PSD) to form structures to east. Later CT cuts to surface.
West
East
West
East
CT
K
PSD
PSD
Mz
UPz
LPz
PCx
C Pre-Crawford movement on western thrust system. Shortening from Willard or Lost Creek thrust
(LCT) transfered to east along PSD to form structures to east. Later CT forms by fault propagation folding and cuts to surface.
West
East
West
CT
East
K
LCT
PSD
PSD
LCT
Mz
UPz
LPz
PCx
Figure 4. Schematic cross sections showing possible timing scenarios for transfer of displacement east on the Preuss salt detachment. CT—Crawford thrust; PSD—Preuss salt detachment; LCT—Lost Creek thrust; PCx—Precambrian crystalline rocks; LPz—
Lower Paleozoic rocks; UPz—Upper Paleozoic rocks; Mz—Mesozoic rocks; K—Cretaceous rocks. Red lines are active thrusts, black
dashed lines are future thrusts, and black solid lines are previously active thrusts.
any folding or dip changes that might be expected to result from post-Crawford shortening along the Preuss salt
detachment. All five seismic lines show that the Crawford
thrust has not been offset along the Preuss salt detachment. The Twin Creek Limestone is poorly imaged above
the Nugget Sandstone in the hanging wall of the Crawford
thrust due to its complex structure and near-vertical to
overturned dip (plate 1).
DISCUSSION
Timing
Interpretation of the seismic data allows us to evaluate timing scenarios discussed earlier and outlined in figure 4. Key observations from the seismic data include: (1)
the Crawford thrust, which is well delineated by footwall
cutoffs and hanging wall stratigraphy, forms a continuous
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
65
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
A
0
AMOCO
DESERET 1
NW
AMOCO
CHAMPLIN 432C
SE
Time (s)
1.0
2.0
3.0
Migration artifacts?
4.0
~2 km
82J19 pre-stack time migration
B
0
AMOCO
DESERET 1
NW
rd
lla
Wi rust
th
AMOCO
CHAMPLIN 432C
SE
Jtc
1.0
Time (s)
Kf
Jn
TRa
TRt
TRwd
UPz
2.0
rd
Crawfo
3.0
thrust
LPz
Ka
Kbr
Kg
Jsp
Medicine Butte
thrust
Jtc
Jn
TRa
TRt
TRwd
UPz
4.0
LPz
~2 km
C
PCx
82J19 pre-stack time migration
AMOCO
DESERET 1
NW
AMOCO
CHAMPLIN 432C
SE
0
Depth (km)
2
4
e Butte
Medicin
thrust
Jn
6
TRwd
ford
Craw
st
thru
Jn
8
10
12
~2 km
82J19 depth section
Figure 5. (A) Uninterpreted pre-stack time migrated seismic reflection profile 82J19. (B) Interpreted pre-stack time migrated
seismic reflection profile 82J19. Interpretation was based on synthetic seismograms from the Deseret and Champlin wells and surface geology (Coogan and King, 2001), and was used in the construction of the balanced cross section in plate 1. (C) Depth section
calculated from pre-stack time migrated section using an interval velocity model. Dashed lines represent interpretation from B for
comparison. Seismic data courtesy of ExxonMobil. PCx—Precambrian crystalline rocks; LPz—Lower Paleozoic rocks; UPz—Upper
Paleozoic rocks; TRwd—Triassic Woodside and Dinwoody Formations; TRt—Triassic Thaynes Formation; TRa—Triassic Ankareh
Formation; Jn—Jurassic Nugget Sandstone; Jtc—Jurassic Twin Creek Limestone; Jsp—Jurassic Preuss and Stump Formations;
Kg—Cretaceous Gannett Group; Kbr—Cretaceous Bear River Formation; Ka—Cretaceous Aspen Shale; Kf—Cretaceous Frontier
Formation.
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
66
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
fault and is not offset along the Preuss salt detachment
(figure 5); and (2) the hanging wall stratigraphy of the
Crawford thrust dips uniformly west indicating the fault
has a simple footwall ramp geometry.
Although the Crawford thrust does not appear to be
offset along the Preuss salt detachment, synorogenic sedimentary rocks and structural relationships indicate that
the Medicine Butte thrust was active after Crawford and
Absaroka thrusting (Lamerson, 1982; Constenius, 1996).
Comparison of estimated shortening and later extension
on the Medicine Butte thrust (table 1) shows that net offset of the Crawford thrust along the Preuss salt detachment by post-Absaroka shortening and extension would
have been small (probably < 1 km) and may not be detectable with seismic data. Thus, the lack of offset of the
Crawford thrust along the salt detachment, along with the
simple footwall ramp geometry, imply that late movement
on the Crawford thrust (but pre-Absaroka) cannot explain
the additional ~6 to 13 km of bed length above the Preuss
salt in the hanging wall of the Absaroka thrust (table 1).
Early movement on the Crawford thrust, with displacement transferred east along the Preuss salt detachment rather than to the surface, could have produced geometries very similar to our observations, provided the
east-dipping limb of the hanging wall anticline ultimately
remained in the Crawford hanging wall (figure 4B). A
Triassic-cored anticline mapped in the Lost Creek area
directly above the Crawford thrust (Coogan, 1992, 2004a,
2004b), is consistent with this scenario. However, similar
geometries are also generated by eastward propagation of
shortening from the western thrust system, followed by
later Crawford thrusting with folding produced by faultpropagation folding rather than fault-bend folding (figure
4C).
Surface geology provides evidence that shortening
from the western thrust system was responsible for the
excess bed length in rocks above the Preuss salt detachment in the Absaroka thrust sheet. In the hanging wall of
the Crawford thrust, imbricates of the Lost Creek thrust
caused tight folding of the Twin Creek Limestone (plate
1). The Lost Creek thrust climbs up-section from west to
east, from a detachment in the Gypsum Spring Member of
the Twin Creek Limestone just east of the surface trace of
the Willard thrust, to the Preuss salt detachment just west
of the surface trace of the Crawford thrust near Lost Creek
reservoir (Coogan and Constenius, 2003). Recognition of
the Lost Creek thrust at the level of the Preuss salt detachment in the hanging wall near the trace of the Crawford
thrust, strongly suggests that the Lost Creek thrust is continuous with the Preuss salt detachment in the footwall
of the Crawford thrust, and was offset by Crawford slip,
similar to relations in figure 4C.
If shortening occurred in the area of the future Absaroka thrust during Willard or Lost Creek thrusting, then
synorogenic sediment derived from the western thrust
system (Gannett Group, and Bear River, Aspen, or Frontier
Formations, figure 2) should vary in thickness over the
structures, with possible underlying erosional truncation
of formations (i.e., Jurassic Stump Formation). The Lower Cretaceous Gannett Group, and Bear River and Aspen
Formations were folded by this shortening (plate 1), indicating that some slip and folding along the Preuss detach-
ment occurred after Aspen deposition (after ~102 Ma). We
studied well logs from Painter Reservoir and East Painter
Reservoir fields (figure 1) along with logs from several kilometers to the east and west. However, complex structure,
regional thinning, and deviated well paths, made it difficult to recognize presence of stratigraphic thinning in the
Gannett Group, Bear River Formation, or Aspen Shale, or
erosional truncation of the Stump Formation, that could
record slip prior to 102 Ma. Major shortening on the Crawford thrust occurred from ~89 to 84 Ma (DeCelles, 1994)
and, as discussed above, likely postdated shortening along
the detachment. Therefore, the preferred interpretation is
that shortening along the salt detachment occurred during deposition of the Cenomanian-Turonian Frontier Formation (~102 to 90 Ma). Unfortunately, the Frontier has
been eroded from the hanging wall of the Absaroka thrust
in this region.
Implications
Figure 6 shows a sequential restoration of plate 1,
with slip transferred eastward along the Preuss salt detachment (Lost Creek thrust) during deposition of the
Cenomanian-Turonian Frontier Formation (~102 to 90
Ma). Frontal structures of the detachment are located ~70
to 90 km east of the Willard thrust front, causing a widening of the thrust belt and the wedge-top depozone (DeCelles and Giles, 1996) by the same amount. The location
of these structures was likely controlled by the eastern
limit of deposition of the Preuss salt, which is found as far
east as the hanging wall of the Absaroka thrust, but is not
present in its footwall (J. Coogan, Western State College
[currently Petro Matad], personal communication, 2009).
Mechanical modeling of thrust belts has shown that
when the basal detachment is within a very weak horizon,
such as salt, the thrust belt has: (1) a larger width (up to
500 km) than when the detachment is within a stronger
horizon; (2) a very low-angle taper; and (3) frontal thrust
structures that verge in opposite directions (Davis and
Engelder, 1985). While we do not observe any evidence for
symmetrical vergence of thrusts above the Preuss salt detachment on the hanging wall of the Absaroka thrust, the
occurrence of salt can explain the large distance from the
Willard thrust to the frontal structures of the Preuss detachment, the corresponding low taper angle of the thrust
wedge (figure 6B), and the location of the frontal thrusts
at the eastern edge of the Preuss salt. The significant decrease in yield strength of the detachment achieved when
the Lost Creek thrust reached the Preuss salt resulted in
the wedge taper angle becoming supercritical. Thus, the
thrust belt widened by propagating ~70 to 90 km east,
with little or no thrusting between the frontal structures
and the previous wedge. This is a minimum estimate of
widening because our sequential restoration does not include layer-parallel shortening. The load of the wedge likely induced flow of the salt eastward along the detachment,
resulting in salt thickening in the frontal thrusts, now the
hanging walls of the Medicine Butte and Absaroka thrusts
(Lamerson, 1982). Subsequent slip on the Lost Creek and
Crawford thrusts served to build taper internally within
the thrust wedge (figures 6C and 6D).
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
WT
LCT/PSD
K
TR-J
70 km
WT
K
TR-J
T
LC
Jsp
pCx
Zs
LPz
T
TR-J
K
LC
CT
Jsp
LCT/PSD
LCT/PSD
Jsp
Figure 6. A. Sequential restoration of cross section from plate 1 from the Willard thrust on the west to the Absaroka thrust on the east. Location of plate 1 is shown on figure 1.
(A) Stratigraphic configuration at ~105 Ma after shortening along the Willard thrust. (B) During early Lost Creek thrusting, displacement was transferred east along the Preuss
salt detachment. The Frontier Formation thins across the eastern thrusts. (C) Later Lost Creek thrusting resulted in fault propagation folding and the Lost Creek thrust cutting
to surface.
10 km
UPz
T
W
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
C. Late Lost Creek - fault propagation folding and thrusts cut to surface (~102 to 90 Ma)
Deposition of Frontier Formation
Zs
LPz
UPz
B. Early Lost Creek - shortening propagates eastward along Preuss salt (~102 to 90 Ma)
Deposition of Frontier Formation
Zs
LPz
UPz
A. Post-Willard, pre-Lost Creek (~105 Ma)
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
67
pCx
pCx
T
LPz
Zs
LPz
Zs
LC
T
UPz
UPz
T
TR-J
TR-J
W
K
K
T
C
K
SD
LCT/P
SD
LCT/P
HT
HT
T
OAYAT
Evanston Fm., Main Body
BT
M
T
OAYAT
T T
OA YA
Hams Fork Cgl., Evanston Fm.
Jsp
Figure 6. B. (D) Geometry at ~84 Ma after the Crawford thrust cuts to surface. (E) Shortening on the Absaroka thrust folded the Preuss salt detachment. (F) Between ~70 and
55 Ma shortening was accommodated on the Medicine Butte thrust, Hogsback thrust, and Young Absaroka thrust. pCx—Precambrian crystalline rocks; Zs—Proterozoic sedimentary rocks (note that Neoproterozoic to Cambrian Geertsen Canyon Quartzite is included with Lower Paleozoic rocks on the hanging wall of the Willard thrust); LPz—Lower
Paleozoic rocks; UPz—Upper Paleozoic rocks; TR-J—Triassic and Jurassic rocks; Jsp—Jurassic Preuss and Stump Formations; K—Cretaceous rocks; WT—Willard thrust; LCT—
Lost Creek thrust; PSD—Preuss salt detachment; CT—Crawford thrust; OAT—Old Absaroka thrust; YAT—Young Absaroka thrust; MBT—Medicine Butte thrust; HT—Hogsback
thrust; Al—Almy normal fault; Ac—Acocks normal fault. Long-dashed line shows estimated erosion surface.
F. Post-Medicine Butte (~55 Ma)
E. Post-Absaroka (~70 Ma)
W
TR-J
LCT/PSD
T
W
CT
T
pCx
Zs
UPz
LC
T
CT
LC
LPz
Al
10 km
Henefer Fm., Echo Cyn. Cgl. and
Weber Cyn. Cgl.
T
D. Post-Crawford (~84 Ma)
Ac
MB
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Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
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Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
Comparison with Other Areas and Thrust Belts
Approximately 20 km south of Lost Creek Reservoir,
the Crawford thrust has been interpreted as a blind thrust
that did not ramp up through the Cretaceous section to the
surface (Coogan and Constenius, 2003). Instead, it formed
a triangle zone with the East Canyon backthrust (figure
1). Shortening from the Crawford thrust was transferred
westward along the backthrust in the Preuss salt detachment, and possibly also eastward onto the Medicine Butte
thrust (DeCelles, 1994; Coogan and Constenius, 2003).
This along-strike change in geometry of the Crawford
thrust, along with backthrusting at the Preuss level, is also
consistent with a low taper wedge, and suggests that the
backthrust in the Preuss detachment may have formed before movement on the Crawford thrust. Coogan and Constenius (2003) interpreted a duplex, which formed during
late movement on the Crawford thrust, with the Preuss
salt detachment forming the roof thrust. Without crosscutting relationships between the Crawford thrust and the
Preuss salt detachment, we cannot determine whether the
excess bed length in the Absaroka hanging wall in the vicinity of Anschutz Ranch field is due to Lost Creek, Willard, or Crawford thrusting; however, our results to the
north suggest that displacement from the western thrust
system was transferred east along the Preuss salt detachment, forming both the East Canyon backthrust and the
structures now in the hanging wall of the Absaroka thrust,
with later Crawford thrusting reactivating the East Canyon backthrust (figure 1).
North of our study area, along the southeastern IdahoWyoming border, Coogan and Yonkee (1985) documented
that the Meade thrust, which is part of the western thrust
system, has a thrust flat for 30 km along the Preuss salt
detachment, supporting our idea that displacement from
the western thrust system was transferred many tens of
kilometers along the salt detachment. South of the UintaCottonwood arch, the Charleston and Nebo thrusts have a
prominent thrust flat in evaporites of the Jurassic Arapien
Shale. Here, displacement was transferred ~35 km to the
east during the first phase of motion, between ~100 and
80 Ma (Constenius and others, 2003).
Davis and Engelder (1985) discussed examples of
fold-thrust belts with salt detachments around the world
which have a taper of <1°, including the Appalachian Plateau, the Franklin Mountains of northwest Canada, and
the Zagros Mountains of Iran. The Jura Mountains, where
Mesozoic sedimentary rocks have been folded above a
detachment in Triassic evaporites, are a 70-km-wide fold
belt. The Simply Folded belt of the Zagros Mountains is
wider than 200 km in places. The Potwar Plateau of northern Pakistan, part of the Himalayan fold-thrust belt, has a
width of 100 to 150 km and a taper of 0.8° ± 0.1° (Jaume
and Lillie, 1988). Thus, regions underlain by a salt detachment have wide thrust belts, low taper angles, and saltcored anticlines, similar to patterns along the Preuss detachment.
Old or Early Absaroka thrust
From Painter Reservoir field in the north to Anschutz
Ranch East field to the south, the western imbricate of the
Absaroka thrust, which we refer to as the old Absaroka
thrust (Lamerson, 1982; Early Absaroka fault of Royse
and others, 1975; OAT of figure 6) can be interpreted from
cross sections to be the frontal thrust of the Preuss salt detachment (plate 1, figure 3). In outcrops east of Evanston,
Wyoming, the Jurassic Preuss Redbeds are the oldest formation observed in the hanging wall of the OAT, forming a
hanging wall flat that can be traced for over 10 km (Dover
and McGonigle, 1993). Lamerson (1982) observed that between the outcrops east of Evanston and Rockport Reservoir (figure 1), wells that penetrated the Absaroka thrust
east of the hanging wall cutoff of the Jurassic Nugget Sandstone encountered Preuss Redbeds in the hanging wall
of the OAT. Thus, the Preuss Redbeds in the hanging wall
of the OAT are carried on a thrust flat throughout much
of the study area. This hanging wall thrust flat does not
have a corresponding flat in the footwall of the Absaroka
thrust, suggesting that it formed before the OAT and was
part of the Lost Creek thrust system. However, rocks in the
footwall of the OAT imply a different timing. Cretaceous
rocks in the footwall of the OAT (hanging wall of the YAT)
include the Frontier and Hilliard Formations (Lamerson,
1982). If, as we suggest, the OAT was a frontal imbricate of
the Lost Creek thrust and was active during Frontier deposition (~102 to 90 Ma), then it would be impossible for the
Hilliard Shale, which is younger than the Frontier, to be
present in the footwall. We therefore propose that there
were two episodes of shortening on the OAT. The first episode involved shortening on the Preuss salt detachment
during the time of Frontier deposition and Lost Creek
thrusting. This formed the hanging wall thrust flat with
Preuss Redbeds over Frontier Formation in the footwall.
Later movement during mid-Santonian time coincided
with Hilliard deposition (Lamerson, 1982), with the OAT
ramping up from the Cambrian, merging with the existing
thrust plane at the Preuss salt detachment for several kilometers, and incorporating Hilliard Shale into the footwall
(figures 6D and 6E). In the Little Muddy Creek area, overturned Paleozoic, Jurassic, and Lower Cretaceous rocks
crop out in the hanging wall of the OAT. Evidence of older
Lost Creek thrusting on the Preuss salt detachment is not
apparent in this area. North of Little Muddy Creek, early
shortening along the Preuss detachment has not been
documented in the hanging wall of the Absaroka thrust.
However, Coogan and Yonkee (1985) recognized different
styles of shortening above and below the Preuss salt detachment along parts of the Meade thrust (western thrust
system) and Crawford thrust (eastern thrust system) in
southeast Idaho and adjacent parts of Wyoming.
CONCLUSIONS
We have shown using seismic data and cross sections
that: (1) Paleocene to early Eocene shortening on the Medicine Butte thrust was essentially offset by middle Eocene
to Oligocene extension of a similar magnitude on the AlmyAcocks normal-fault system; and (2) excess shortening in
the hanging wall of the Absaroka thrust is likely the easternmost deformation of the Lost Creek or Willard thrust,
and is therefore related to the earliest phase of thrusting
in this part of the Sevier belt. Key facts supporting this
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
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Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
last conclusion are: (1) the Crawford thrust is not offset
along the Preuss salt detachment, indicating that shortening was transferred east before main movement of the
Crawford thrust, and (2) the presence of the Lost Creek
thrust at the Preuss salt level in the hanging wall of the
Crawford thrust, suggesting that the Lost Creek thrust is
offset across the Crawford thrust. Timing constraints from
synorogenic sedimentary rocks and folded Lower Cretaceous strata indicate that this shortening was probably
transferred east ~102 to 90 Ma, during deposition of the
Frontier Formation. This is in contrast to previous interpretations that the Jurassic Preuss salt detachment to the
east of the Crawford thrust is a footwall imbricate of the
Crawford (e.g., Lamerson, 1982). Sequential restorations
show that this displacement was likely transferred ~70 to
90 km east, to the location of the future hanging wall of
the Absaroka thrust. The eastern extent of this deformation was controlled by the depositional limit of Preuss salt.
Another possible, but we think less likely, interpretation is
that this shortening is related to earliest movement on the
Crawford thrust.
The old Absaroka thrust south of the Little Muddy
Creek area experienced two episodes of shortening. The
first episode was during Lost Creek thrusting and Frontier
deposition, and resulted in the formation of the frontal
imbricate of the Lost Creek thrust, placing Jurassic Preuss
Redbeds over Frontier Formation beneath the Preuss salt
detachment. The second episode of thrusting occurred
during deposition of the Hilliard Shale and resulted in the
old Absaroka thrust ramping up from the Cambrian and
merging with the Preuss salt detachment and Lost Creek
thrust for several kilometers.
ACKNOWLEDGMENTS
Funding was provided by Williams Production RMT
Company, Chevron, and ExxonMobil. We thank Steve Natali
and Mary Sue Purcell for facilitating the Williams donation,
and Jerry Kendall for his efforts to provide the ExxonMobil
data. Rick Bogehold and Mark Vogel at Excel Geophysical
Corporation reprocessed the seismic data and allowed us
use of their facilities. IHS provided well data and Petra
software. Divestco donated WinPICS seismic interpretation software. TGS Nopec donated digital well logs. P2
Energy Solutions donated a land grid. Velocity Data Bank
provided check-shot surveys at a much-reduced rate. GeoLogic Systems LLC donated Lithotect structural analysis
software and Bob Ratliff assisted with its use. We thank
Jim Coogan for many useful discussions, ideas, and data
throughout the project. Rick Sorenson and Rich Bottjer at
Cirque Resources in Denver helped with well log interpretation. Interesting discussions with Facundo Fuentes and
Gary Gray improved our interpretation. We thank Adolph
Yonkee and Doug Sprinkel for their constructive reviews.
REFERENCES
Armstrong, F.C., and Oriel, S.S., 1965, Tectonic development of Idaho-Wyoming thrust belt: American Association of Petroleum Geologists Bulletin, v. 49,
no. 11, p. 1847-1866.
Constenius, K.N., 1996, Late Paleogene extensional collapse of the Cordilleran foreland fold and thrust
belt: Geological Society of America Bulletin, v.
108, no. 1, p. 20-39.
Constenius, K.N., Esser, R.P., and Layer, P.W., 2003, Extensional collapse of the Charleston-Nebo salient
and its relationship to space-time variations in
Cordilleran orogenic belt tectonism and continental stratigraphy, in Raynolds, R.G., and Flores, R.M.,
editors, Cenozoic systems of the Rocky Mountain
region: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, p. 303353.
Coogan, J.C., 1992, Thrust systems and displacement
transfer in the Wyoming-Idaho-Utah thrust belt:
Laramie, University of Wyoming, Ph.D. dissertation, 496 p.
Coogan, J.C., 2004a, Interim geologic map of the Francis
Canyon quadrangle, Lost Creek drainage, Morgan,
Rich, and Summit Counties, Utah: Utah Geological
Survey Open-File Report 425, scale 1:24 000.
Coogan, J.C., 2004b, Interim geologic map of the Lost
Creek Dam quadrangle, Lost Creek drainage, Morgan and Weber Counties, Utah: Utah Geological
Survey Open-File Report 426, scale 1:24 000.
Coogan, J.C., 2004c, Interim geologic map of the Peck
Canyon quadrangle, Lost Creek drainage, Morgan
and Rich Counties, Utah: Utah Geological Survey
Open-File Report 427, scale 1:24 000.
Coogan, J.C., 2006, Interim geologic map of the Horse
Ridge quadrangle, Morgan, Rich and Weber Counties, Utah: Utah Geological Survey Open-File Report 480, scale 1:24 000.
Coogan, J.C., and Constenius, K.N., 2003, Structural continuity of the Sevier thrust belt across the Uinta
arch: American Association of Petroleum Geologists field trip guidebook, p. 1-17.
Coogan, J.C., and King, J.K., 2001, Progress report: geologic map of the Ogden 30' x 60' quadrangle, Utah
and Wyoming - Year 3 of 3: Utah Geological Survey
Open-File Report 380, scale 1:100 000.
Coogan, J.C., and Yonkee, W.A., 1985, Salt detachments
in the Jurassic Preuss Redbeds within the Meade
and Crawford thrust systems, Idaho and Wyoming,
in Kerns, G.J., and Kerns, R.L., Jr., editors, Orogenic
patterns and stratigraphy of north-central Utah
and southeastern Idaho: Utah Geological Association Publication 14, p. 75-82.
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas
71
Peyton, S.L., Constenius, K.N., and DeCelles, P.G.
Davis, D.M., and Engelder, T., 1985, The role of salt in
fold-and-thrust belts: Tectonophysics, v. 119, p.
67-88.
DeCelles, P.G., 1994, Late Cretaceous-Paleocene synorogenic sedimentation and kinematic history of
the Sevier thrust belt, northeast Utah and southwest Wyoming: Geological Society of America Bulletin, v. 106, no. 1, p. 32-56.
DeCelles, P.G., 2004, Late Jurassic to Eocene evolution
of the Cordilleran thrust belt and foreland basin
system, western U.S.A.: American Journal of Science, v. 304, p. 105-168.
DeCelles, P.G., and Giles, K.A., 1996, Foreland basin systems: Basin Research, v. 8, p. 105-123.
DeCelles, P.G., Pile, H.T., and Coogan, J.C., 1993, Kinematic history of the Meade thrust based on provenance of the Bechler Conglomerate at Red Mountain, Idaho, Sevier thrust belt: Tectonics, v. 12, p.
1436-1450.
Dixon, J.S., 1982, Regional structural synthesis, Wyoming salient of western overthrust belt: American
Association of Petroleum Geologists Bulletin, v.
66, no. 10, p. 1560-1580.
Dover, J.H., and McGonigle, J.W., 1993, Geologic map
of the Evanston 30' x 60' quadrangle, Uinta and
Sweetwater Counties, Wyoming: U.S. Geological
Survey Miscellaneous Investigations Series Map
I-2168, scale 1:100 000.
Jaume, S.C., and Lillie, R.J., 1988, Mechanics of the Salt
Range-Potwar Plateau, Pakistan: a fold-and-thrust
belt underlain by evaporites: Tectonics, v. 7, no. 1,
p. 57-71.
Lamerson, P.R., 1982, The Fossil Basin area and its relationship to the Absaroka thrust fault system, in
Powers, R.B., editor, Geologic studies of the Cordilleran thrust belt: Rocky Mountain Association
of Geologists, v. 1, p. 279-340.
M’Gonigle, J.W., and Dover, J.H., 1992, Geologic map of
the Kemmerer 30' X 60' quadrangle, Lincoln, Uinta, and Sweetwater Counties, Wyoming: U.S. Geological Survey Miscellaneous Investigations Series
Map I-2079, scale 1:100 000.
Mitra, G., 1994, Strain variation in thrust sheets across
the Sevier fold-and-thrust-belt (Idaho-Utah-Wyoming): implications for sections restoration and
wedge taper evolution: Journal of Structural Geology, v. 16, no. 4, p. 585-602.
Pivnik, D.A., 1990, Thrust-generated fan-delta deposition; Little Muddy Creek Conglomerate, SW Wyo-
ming: Journal of Sedimentary Petrology, v. 60, no.
4, p. 489-503.
Royse, F., Jr., 1993, An overview of the geologic structure of the thrust belt in Wyoming, northern Utah,
and eastern Idaho, in Snoke, A.W., Steidtmann, J.R.,
and Roberts, S.M., editors, Geology of Wyoming:
Geological Survey of Wyoming Memoir 5, p. 272311.
Royse, F., Jr., Warner, M.A., and Reese, D.L., 1975, Thrust
belt structural geometry and related stratigraphic
problems Wyoming-Idaho-northern Utah, in Bolyard, D.W., editor, Symposium on deep drilling
frontiers of the central Rocky Mountains: Rocky
Mountain Association of Geologists Guidebook, p.
41-54.
Schirmer, T.W., 1988, Structural analysis using a thrustfault hanging-wall sequence diagrams; Ogden duplex, Wasatch Range, Utah: American Association
of Petroleum Geologists Bulletin, v. 72, no. 5, p.
573-585.
Vietti, J.S., 1977, Structural geology of the Ryckman
Creek anticline area, Lincoln and Uinta Counties,
Wyoming, in Heisey, E.L., Lawson, D.E., Norwood,
E.R., Wach, P.H., and Hale, L.A., editors, Rocky
Mountain thrust belt geology and resources: Wyoming Geological Association 29th Annual Field
Conference, p. 517-522.
West, J., and Lewis, H., 1982, Structure and palinspastic
reconstruction of the Absaroka thrust, Anschutz
Ranch area, Utah and Wyoming, in Powers, R.B.,
editor, Geologic studies of the Cordilleran thrust
belt: Rocky Mountain Association of Geologists
Guidebook, v. 2, p. 633-639.
Yonkee, W.A., 1992, Basement-cover relations, Sevier
orogenic belt, northern Utah: Geological Society
of America Bulletin, v. 104, no. 3, p. 280-302.
Yonkee, W.A., 2005, Strain patterns within part of the
Willard thrust sheet, Idaho–Utah–Wyoming thrust
belt: Journal of Structural Geology, v. 27, p. 13151343.
Yonkee, W.A., DeCelles, P.G., and Coogan, J.C., 1997, Kinematics and synorogenic sedimentation of the
eastern frontal part of the Sevier orogenic wedge,
northern Utah: Brigham Young University Geology
Studies, v. 42, pt. 1, p. 355-375.
Yonkee, W.A., and Weil, A.B., 2010, Reconstructing the
kinetic evolution of curved mountain belts: internal strain patterns in the Wyoming salient, Sevier
thrust belt, U.S.A.: Geological Society of America
Bulletin, v. 122, no. 1/2, p. 24-49; doi: 10.1130/
B26484.1.
2011 UGA Publication 40—Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., editors
4 km of uplift based on Coogan (1992)
t
ul
Fa
C
k Th
Cr
ee
Xfc - Farmington Canyon Complex
(crystalline Proterozoic rocks)
Ct - Tintic/Flathead
ch
at
as
W
st
Lo
st
ru
Wasatch Mountains
Ogd
rd
ust
rust
Th
en Thr
Ogd
e
Willa
st zon
en thru
Xfc
rust
k Th
st Cr
ee
Lo
al
t
ul
Fa
O
Cg
m
Nor
Ct
D
TR
wd
PIP
Mm
Imbricate of Willard thrust
later reactivated by normal
faulting.
rd
Willa
rust
Th
Canyon
Canyon
Zmc - Maple
Canyon
ZYp - Perry
Zkc - Kelley
Zcc - Caddy
Zi - Inkom
Canyon
Hole
Zm - Mutual
Zb - Browns
Proterozoic metasedimentary
rocks of Willard Thrust Sheet
Cg Gallatin - Gros Ventre
Ct - Tintic/Flathead
Mm - Madison
Dd -Darby
O Bighorn
PIP - Phosphoria, Wells & Amsden
TRwd - Woodside & Dinwoody
Tw - TKe - Wasatch & Evanston
Willard Thrust
Lost Creek Thrust
Crawford Thrust
Lost Creek Thrust
Willard Thrust
Lower Paleozoic rocks of Willard Thrust Sheet
Upper Paleozoic rocks of Willard Sheet
Neoproterozoic to Cambrian
Geertsen Canyon Quartzite is
included with Lower
Paleozoic rocks for this cross
section
Cg
Mm
Dd
O
PIP
t
rus
Mm
Dd
O
Cg
TRwd
PIP
TRt
TRa
Jtc
ust
ek Thr
t Cre
Los
st
rd Thru
Willa
AMOCO
DESERET #1
2-6N-5E
Ct - Tintic/Flathead
PIN #1
PIN #2
ek
TRt - Thaynes
TRwd - Woodside & Dinwoody
PIP - Phosphoria, Wells & Amsden
Mm - Madison
Dd - Darby
O Bighorn
Cg Gallatin - Gros Ventre
Jn - Nugget
TRa - Ankareh
Jtc - Twin Creek
wfo
Cra
ust
rd Thr
ust
rd Thr
wfo
Cra
Jsp - Stump & Preuss
t Cre
Los ust
Thr
AMOCO
CHAMPLIN 432C
1-6N-5E
Interpretation based on seismic line 82J19, well control and surface geology
Vertical to overturned TRt - Jtc
beds in front of Willard Thrust
were part of fault propagation fold
in front of nascent Willard thrust.
Presence of TR beds on hanging
wall of Lost Creek thrust (LCT)
implies a LCT ramp through the TR
and a flat at deeper formations.
TRt TRa Jn
Jn
D M
TRwd
Wi
d Th
llar
Overturned Devonian and
Mississippian beds are thicker
than those in hanging wall of
Crawford Thrust. Interpreted
to be remnant sliver of
hanging wall of Willard Thrust
sheet.
Preuss
B
salt
st
ru
Th
ent
detachm
rd
fo
aw
Cr
t
PIN #3
Kf
Crawford Thrust
8.4 km extra bed length
(without restoring extension)
Preuss salt detachment
River
r
JKg - Ganne
Kbr - Bear
Ka - Aspen
Kf - Frontie
PIN #3
Lost Creek Thrust
PIN #3
Absaroka
Thrust
PIP
Mm
Dd
O
Cg
TRwd
TRa
TRt
Jn
Jtc
Jsp
Almy
Normal Fault
Tw
TKe
CHEVRON
#1-35 Fed.
35-16N-121W
WYOMING
PIN #2
AMOCO
#1 AMFC
4-6N-8E
UTAH
Acocks
Normal Fault
Med
Tw
TKe
ici
ne
Bu
ru
Th
TKe
tte
Almy
Normal Fault
Tf - Fowkes
st
Tw
Tf
Acocks
Normal Fault
AMOCO
#1 Sulphur Sprg. Unit
4-15N-120W
t
st
st
ru
Craw
k Th
ee
Cr
Thrus
Lo
oka
Absar
salt
Ke
Te
#22-6A
SE NW 6
15N-119W
Jtc
Jsp
JKg
Kbr
Ka
Tw
ford
Ka
Th
rust
PIP
Mm
Dd
O
Cg
Jn
TRa
TRt
Jtc
Jsp
Kg
Kbr
TRwd
Mm
Dd
O
Cg
PIP
Ka
Kbr
JKg
Jsp
Jtc
Jn
TRa
TRt
TRwd
Kf
ka Thr
Absaro
ust
Thru
Hogsback
Kh - Hilliard
st
Ke
Te
Kav
Ct - Tintic/Flathead
Jtc - Twin Creek
Jsp - Stump & Preuss
TRwd - Woodside & Dinwoody
PIP - Phosphoria, Wells & Amsden
Mm - Madison
Dd - Darby
O Bighorn
Cg Gallatin - Gros Ventre
TRt - Thaynes
Jn - Nugget
TRa - Ankareh
aville
- Ad
Old Absaroka Young Absaroka
Thrust
Thrust
Kh - Kf
complex
sturcture
CHEVRON
#1-2A Fed.
2-15N-119W
Geometry of the Old Absaroka
thrust is bedding-parallel at the
base of the Jurassic Preuss, but
there is no evidence for a
corresponding thrust flat in the
footwall of the Absaroka thrust,
indicating shortening occurred
before Absaroka thrusting.
Modified from Lamerson (1982)
#22-5A
SE NW 5
15N-119W
#13-5A
NW SW 5
15N-119W
#33-6A
#13-6A
NW SE 6
NW SW 6
15N-119W 15N-119W
#42-1D
SE NE 1
15N-120W
#33-1D
NW SE 1
Medicine
15N-120W
Butte Thrust
CHEVRON
PAINTER RESERVOIR FIELD
PIN #1
PIN #2
Plate 1. (A) Balanced cross section and (B) restored sections across the Absaroka thrust, and C) the Crawford and Willard thrusts. See figure 1 for location. (click for larger view)
WEST
A
-11,000 m
-10,000 m
-9000 m
-8000 m
-7000 m
-6000 m
-5000 m
-4000 m
-3000 m
-2000 m
-1000 m
0m
1000 m
2000 m
3000 m
EAST
72
Early Eastward Translation of Shortening in the Sevier Thrust Belt, Northeast Utah and Southwest Wyoming, U.S.A.
2011 UGA Publication 40—Sevier Thrust Belt: Northern and Central Utah and Adjacent Areas