Structure and evolution of Upheaval Dome: A pinched-off salt diapir
M. P. A. Jackson*
D. D. Schultz-Ela
M. R. Hudec†
I. A. Watson
M. L. Porter
}
} Bureau of Economic Geology, University of Texas, University Station Box X, Austin, Texas 78713
Exxon Production Research Company, P.O. Box 2189, Houston, Texas 77252
ABSTRACT
Upheaval Dome (Canyonlands National
Park, Utah) is an enigmatic structure previously attributed to underlying salt doming,
cryptovolcanic explosion, fluid escape, or
meteoritic impact. We propose that an overhanging diapir of partly extrusive salt was
pinched off from its stem and subsequently
eroded. Many features support this inference,
especially synsedimentary structures that indicate Jurassic growth of the dome over at
least 20 m.y. Conversely, evidence favoring
other hypotheses seems sparse and equivocal.
In the rim syncline, strata were thinned by
circumferentially striking, low-angle extensional faults verging both inward (toward the
center of the dome) and outward. Near the
dome’s core, radial shortening produced constrictional bulk strain, forming an inwardverging thrust duplex and tight to isoclinal,
circumferentially trending folds. Farther inward, circumferential shortening predominated: Radially trending growth folds and imbricate thrusts pass inward into steep clastic
dikes in the dome’s core.
We infer that abortive salt glaciers spread
from a passive salt stock during Late Triassic
and Early Jurassic time. During Middle
Jurassic time, the allochthonous salt spread
into a pancake-shaped glacier inferred to be
3 km in diameter. Diapiric pinch-off may
have involved inward gravitational collapse
of the country rocks, which intensely constricted the center of the dome. Sediments in
the axial shear zone beneath the glacier
steepened to near vertical. The central uplift
*E-mail: jacksonm@begv.beg.utexas.edu.
†Present address: Department of Geology, Baylor
University, Waco, Texas 76798.
Figure 1. Location map of northern Paradox basin (Utah and Colorado), showing Upheaval
Dome, known salt structures, and Tertiary intrusions (after Doelling, 1985).
is inferred to be the toe of the convergent
gravity spreading system.
INTRODUCTION
Upheaval Dome is located in Canyonlands
National Park (Island in the Sky district), in the
western part of the Colorado Plateau, southeastern Utah (Fig. 1). The dome is one of the most
enigmatic and controversial geologic structures
in North America. Hypotheses for its origin include cryptovolcanic explosion, meteoritic impact, fluid escape, and subsurface salt diapirism.
We document here a new explanation for the ori-
Data Repository item 9891 contains additional material related to this article.
GSA Bulletin; December 1998; v. 110; no. 12; p. 1547–1573; 23 figures; 1 table.
1547
gin of Upheaval Dome—the pinched-off salt diapir hypothesis.
Upheaval Dome forms a mound that has
strongly deformed uplifted beds in the center of
the dome. Strata have been elevated 120–250 m
above their regional levels. Beds near the center of
the dome are tightly folded and cut by faults having generally radial strikes. The central uplift
passes outward into a prominent rim syncline, then
into a rim monocline, outside of which strata show
merely gentle regional tilting (Fig. 2). The center
of the dome is a topographic depression eroded
350 m below the surrounding escarpment, which
is breached by a canyon cut through its west wall
JACKSON ET AL.
Figure 2. Structure contour map of Upheaval Dome and surroundings showing the base of the Wingate Sandstone. The circumferential traces
of the rim monocline and rim syncline are shown with dashed lines. L and H refer to structural lows and highs, respectively. The Buck Mesa well
is in the southeast quadrant of the dome. Elevations (in feet [1 ft = 0.3408 m]) were measured by us within the rim monocline and taken from the
map of Huntoon et al. (1982) in the surrounding region. The structural high west of the dome could extend farther north, but the gentle dips there
preclude accurate contouring of the outcrop data.
(Fig. 3). The dramatic canyon relief and generally
superb exposures make Upheaval Dome a leading
attraction for tourists and geologists.
Tectonic Setting
In Middle Pennsylvanian time, the Paradox
basin formed as a northwest-trending foreland
basin to the basement-cored Uncompahgre uplift
(Ohlen and McIntyre, 1965), which was thrust
over the northeast edge of the basin along the Uncompahgre fault (Fig. 1; Frahme and Vaughn,
1983; Ge et al., 1994b; Huffman and Taylor,
1994). The deepest part of the trough adjoined
the Uncompahgre uplift, and the basin thinned
toward gentle crustal upwarps that bounded the
basin to the south and west. Folding and faulting
1548
accommodated downward bending of the crust
into the axis of the Paradox trough.
Salt accumulated in the deepest part of the
Paradox basin shortly after the Uncompahgre
thrust fault became active. Prograding sediments shed from the Uncompahgre uplift expelled the salt southwestward, forming a series
of northwest-trending salt walls and anticlines
(Baars, 1966; Ge et al., 1994a, 1997). Salt
structures decrease in amplitude and age of initiation away from the Uncompahgre uplift.
Truncations and lateral thickness changes indicate that diapirs grew mostly during Permian
time, but salt continued to flow until at least
100 m.y. ago (Doelling, 1988). Near Upheaval
Dome, roughly 75 km southwest of the Uncompahgre fault, most salt structures are gentle
anticlines (Fig. 1), but small diapiric stocks are
locally exposed.
The Paradox basin has been affected by at least
three more tectonic episodes since Late Cretaceous time. (1) Crustal shortening related to the
Laramide orogeny (Late Cretaceous–early Tertiary) reactivated the Uncompahgre fault and
may also have reactivated some of the smaller
basement faults within the basin. (2) Oligocene
laccoliths built the La Sal, Abajo, and Henry
Mountains. (3) The basin may have been slightly
stretched in Cenozoic time (Ge and Jackson,
1994; Hudec, 1995; Ge et al., 1996). These
events had negligible effects on the flat-lying
strata around Upheaval Dome. Finally, the Colorado Plateau was greatly uplifted after midMiocene time (e.g., Thompson and Zoback,
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
Figure 3. Oblique air photo looking west. From foreground to background are Trail Canyon,
Upheaval Dome, Upheaval Canyon, and the Green River. In the extreme foreground, alcoves A
(containing Alcove Spring) through D appear counterclockwise from bottom left in Trail
Canyon. The rim syncline passes through the Navajo Sandstone in the far wall of alcove D.
Photograph by John S. Shelton.
1979), resulting in at least 1600 m of erosion over
Upheaval Dome.
Stratigraphic Setting
The oldest known sedimentary rocks beneath
Upheaval Dome are Cambrian-Mississippian
clastic and carbonate rocks (Fig. 4). Passive-margin sedimentation in the area ceased with the onset of Ancestral Rockies deformation and led to
restricted-marine conditions in Middle and Late
Pennsylvanian time. A carbonate shelf rimmed
the basin’s southern and western margins as
saline facies accumulated in the axis of the basin
near the Uncompahgre uplift. As much as 2 km
of Paradox Formation evaporites collected here
(Hite, 1960) and thin toward the basin margins.
Borehole data suggest that roughly 720 m of
evaporites were deposited in the vicinity of Upheaval Dome (Woodward-Clyde Consultants,
1983). The evaporitic facies consist of 70%–90%
halite in most places and minor amounts of limestone, dolomite, gypsum, anhydrite, black shale,
and siltstone.
Restricted marine conditions ended in Early
Permian time as the Uncompahgre highlands
shed a wedge of marginal marine and continental
clastic sediments (Cutler Group, Fig. 4) southwestward across the basin. In the area of Upheaval Dome, the Cutler Group comprises three
formations; from bottom to top, these are the
Cedar Mesa Sandstone Member, the Organ Rock
Member, and the White Rim Sandstone. Only the
upper two units may be exposed in the center of
Upheaval Dome (extreme deformation there hinders stratigraphic correlation). The Organ Rock
Member comprises fluvial dark-reddish-brown
siltstones and mudstones. The overlying White
Rim Sandstone is a clean white sandstone deposited in coastal eolian environments (Steele,
1987). Sandwiched between finer-grained units,
the resistant White Rim Sandstone weathers into
prominent ledges and benches. A major hiatus
(TR-1 from 264 to 247 Ma) followed deposition
of the White Rim Sandstone.
The Moenkopi Formation (Fig. 4) records a marine transgression from the west that created a variety of fluvial to shallow-marine environments
dominated by fine-grained sediments (O’Sullivan
and MacLachlan, 1975; Molenaar, 1981). To map
the center of Upheaval Dome, we divided the
Moenkopi Formation into three informal units,
which are strata-parallel and continue at least 10
km from the dome margins in basins to the south
and west. The lower Moenkopi siltstone weathers
brownish-red to grayish-red. The lithologic variation and weathering character define structures
well. The middle Moenkopi Formation comprises
reddish shale containing layers of fine-grained,
yellow, flaggy, calcareous sandstone. This member separates the lower reddish Moenkopi member
from the upper Moenkopi siltstones that weather
to buff-gray or olive-gray featureless masses.
After another major hiatus (TR-3 from 240 to
227 Ma) in Late Triassic time, the continental
Chinle Formation (Fig. 4) spread across the top of
the Uncompahgre uplift, eliminating the Paradox
basin as a physiographic feature. We divided the
Chinle Formation into four map units, from bottom to top, (1) basal Moss Back Member sandstone and conglomerate, which generally crop out
as prominent gray ledges or dip slopes; (2) Petrified Forest and Church Rock Member shales (labeled “Lower Chinle” in subsequent figures),
which weather gray, blue-gray, or lavender, as distinct from the yellowish-gray upper Moenkopi
shales; (3) another prominent sandstone about
one-third up from the Chinle Formation base; this
finer-matrix pebble conglomerate is probably the
Black Ledge sandstone of the Church Rock Member (Stewart et al., 1959); (4) shale and siltstone
weathering brick, brown, or orange-red are interpreted to be the upper part of the Church Rock
Member (combined with the Black Ledge member as “Upper Chinle” in subsequent figures).
After a brief hiatus (J-0, from 210 to 206 Ma),
sedimentation remained continental, with deposition of the Jurassic Wingate Sandstone, a wet erg
(the lower Wingate strata representing central erg
facies, and the upper Wingate strata representing
distal, less arid, back erg facies containing silty interbeds). The mainly fluvial Kayenta Formation
and the dry erg Navajo Sandstone then accumulated. The Jurassic Navajo Sandstone is the highest stratigraphic level exposed in Upheaval Dome.
Using regional thicknesses of higher units derived
from the Book Cliffs area to the north (Molenaar,
1981), we estimate that an additional 1600 to
2200 m of section were deposited above the
dome. That upper limit corresponds with the
thickness of missing strata required to encase the
currently unroofed La Sal laccoliths intruded in
middle Cenozoic time some 55 km east of Upheaval Dome. These Cretaceous and Tertiary
units were eroded during Miocene–Holocene uplift of the Colorado Plateau.
Hypotheses for Origin of Upheaval Dome
Upheaval Dome was first described by
Harrison (1927) as “Christmas Canyon Dome.”
He suggested that salt flowed into the dome be-
Geological Society of America Bulletin, December 1998
1549
JACKSON ET AL.
cause of unloading produced by canyon erosion
in a former meander in the Green River. We
know of no such evidence for such a meander.
McKnight (1940), Fiero (1958), and Mattox
(1968) also postulated an underlying salt dome.
Given the strong evidence for lateral constriction rather than lateral extension in the dome
center (presented in the following), we reject
the notion of a buried salt dome below Upheaval Dome. Moreover, a preliminary report
by Louie et al. (1995) concluded from a seismic
refraction line across the dome that there is no
large salt plug near the surface. Similarly, collapse due to salt dissolution, as envisaged by
Stokes (1948), is equally implausible because
strata in the center of the dome rise more than
100 m above their regional elevation (Fig. 2).
Bucher (1936) noted similarities between the
structures at Upheaval Dome and the Steinheim
Basin, Germany, and proposed that Upheaval
Dome was cryptovolcanic. Structures in the central depression were interpreted to be a result of explosive release of gases trapped near a shallow igneous intrusion. No igneous rocks have been
found within 55 km of the dome center, although
geophysical anomalies (described in the following) around Upheaval Dome suggest that igneous
rocks may underlie the Paradox salt. Kopf (1982)
also interpreted deformation in the dome center to
result from sudden upward release of a fluid slurry
tectonically overpressured by a deep fault system.
Boone and Albritton (1938) were the first to
suggest that Upheaval Dome might have been
produced by meteoritic impact. They noted that
Upheaval Dome contained many features typical
of impact, including circular shape, central dome,
peripheral folds, radial faults, and intense deformation. Shoemaker and Herkenhoff (1983, 1984)
and Shoemaker et al. (1993) argued, for similar
reasons, that there was an impact in Late Cretaceous or Paleogene time (Fig. 5A). They interpreted the thinning of Mesozoic strata observed
by McKnight (1940) and Fiero (1958) to be due
to normal faulting rather than depositional onlap.
They explained the lack of primary physical evidence for impact by suggesting that the crater and
much of its floor had been deeply eroded. Kriens
et al. (1997) interpreted a lag deposit of eroded
cobbles as impactite ejecta indicating that Upheaval Dome formed possibly as late as a few
million years ago. Huntoon and Shoemaker
(1995) proposed impact as the cause of Roberts
rift, a breccia-filled fissure 10 km long located
more than 20 km away from the dome.
We present a new alternative to the impact hypotheses. We propose that the structural and stratigraphic relations at Upheaval Dome—especially
those indicating protracted growth of the structure—can best be explained as the result of stem
pinch-off below an overhanging diapiric salt ex-
1550
Figure 4. Stratigraphic section through formations at or below the surface of Upheaval Dome
and younger eroded units. Data from the Buck Mesa #1 well log, Fiero (1958), Mattox (1968),
and Woodward-Clyde Consultants (1983).
trusion (Fig. 5B; Schultz-Ela et al., 1994a, 1994b).
The central part of the structure contains overburden strata pinched in around what we infer to be
the necked-off stem of a broadly overhanging,
partly extrusive pancake of salt that was subsequently removed by erosion. Pinched-off diapirs
are common below the sea floor in the Gulf of
Mexico and in other salt basins (e.g., Jackson
et al., 1995), but their stems are difficult to image
with seismic data because of the steep stratal dips,
large lateral variations in seismic velocity, and
structural complexity. To our knowledge, no stems
of entirely pinched-off diapirs are exposed at the
surface, except where greatly squeezed by orogenic contraction. If our hypothesis is correct, the
superb three-dimensional exposure and accessibility of Upheaval Dome make it a prime candidate
to examine the response of country rock to the
necking and pinching off of a diapir in an area relatively unaffected by orogeny.
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
A
Transient crater
floor
Central uplift
Mixed breccia
Overturned flap
Ejecta
Fault terraces
Airfall breccia
Maximum possible
sediment thickness
Inward-verging
normal faults
Present topography
Inward-verging
thrust faults
B
B
Lower boundary of in-situ breccia
Before pinch-off
After pinch-off
Representative
thrust wedge
Map
view
beneath
salt extrusion
Future
faults
Cross
section
Salt extrusion
Rim
syncline
Rim
syncline
Figure 5. Schematic illustrations of hypotheses for meteoritic impact and salt dome pinch-off for the evolution of Upheaval Dome. (A) Impact
hypothesis modified from Shoemaker and Herkenhoff (1984) by adding a specific present topographic profile, transient crater profile (dotted),
typical lower limit of pervasive fracturing (shaded), and other features typical of impact craters. (B) Maps and cross sections illustrating the diapiric pinch-off inferred in the text.
CIRCUMFERENTIAL FOLD SYSTEM
The geology of Upheaval Dome is shown in
maps (Figs. 6, 7, and 8) and two cross sections. A
conventional linear section trends roughly westnorthwest across the entire dome and its surroundings (Fig. 15), and a circular section encircles the dome core to illustrate the roughly radial
structures there (Fig. 16).
The largest and most continuous structures in
Upheaval Dome are three circular folds having axial traces concentric about the core of the dome
(Figs. 6 and 8). From the surrounding undeformed
strata toward the core of the dome, this circumferential fold system comprises an outer rim monocline, a rim syncline, and an inner dome. In the
structural descriptions that follow, “inward-out-
ward” and “inside-outside” are relative to the center of Upheaval Dome. “Circumferential” is a synonym for the concentric or tangential direction.
The rim monocline defines the perimeter of
Upheaval Dome, separating the regional homocline from the rim syncline (Fig. 2). The rim
monocline trace is mostly outside the mesa containing the dome center (Fig. 6). The monoclinal
bend is broad and gentle where it involves massive Wingate Sandstone (northwest of the dome).
Conversely, the monocline is a sharp kink where
it is defined by thinly interbedded Chinle clastic
rocks (east of the dome).
Inward from the rim monocline, stratal dips
measured increase to a mean of 15°–20° and a
maximum of 73° then decrease to zero as strata
flatten in the floor of the rim syncline. Most of the
Navajo Sandstone—the youngest unit present—is
preserved within this syncline (Fig. 6). Navajo
Sandstone dip slopes define most of the rim syncline, but several erosional alcoves expose cross
sections through the fold (Figs. 3 and 6).
Successively older units crop out toward the
core of Upheaval Dome (Fig. 6). Stratal dips become subvertical to overturned in the central uplift; there, Moenkopi strata have been elevated
perhaps as much as 250 m above their regional
datum outside the rim monocline, and surrounding Wingate strata have been lifted 120 m. The
inward increase in dip is disrupted in two concentric zones of steep dip, separated by zones of
gentle dip. A discontinuously preserved, inner
steep zone 0.7–0.8 km from the dome center affects the upper Wingate Sandstone and lower
Geological Society of America Bulletin, December 1998
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Geological Society of America Bulletin, December 1998
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Bedding attitude
Foot trail to overlooks
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Central map corners
Cross section trace
Panorama number
and limits of view
Holeman Spring alcove
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A B C D Alcoves in Trail Canyon
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Lower
Moenkopi Fm. (
1 km
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Upper
Moenkopi Fm. (
Chinle Fm. ( )
(Black Ledge cg. dashed)
Wingate Fm. (Jw)
Kayenta Fm. (Jk)
Navajo Fm. (Jn)
marked by L brackets. Locations and view directions of panoramas in Figures 11, 13, and
14 are marked with large numbers and pairs of arrows; intersection point marks the observer’s position.
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Figure 6. Geologic map of Upheaval Dome. The Chinle Formation is undifferentiated
except for the Black Ledge member, and the middle and upper Moenkopi intervals are
combined. Geologic details in the central depression appear in Figure 7; corners are
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Geological Society of America Bulletin, December 1998
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Figure 7. Geologic maps of the central depression, showing (A) stratigraphic units and
faults, and (B) stratigraphic contacts, bedding attitudes, faults, fold axes, drainage net-
work, and the linear and circular lines of sections in Figures 15 and 16.
A
Figure 7. (Continued).
B
1554
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
Figure 8. Summary map of Upheaval Dome outer structures. Circumferential fold traces are dotted. Transport directions (large black arrows)
of hanging walls of extensional faults are dominantly inward in the south and outward in the north.
Kayenta Formation (described in Inner Contractional Systems section). A virtually continuous
outer steep zone 1.2–1.6 km from the dome center affects the inner margin of the lower Navajo
Sandstone. There, dips steepen markedly from
20°–30° to 40° and commonly higher (Fig. 8).
Bounding surfaces of dune-scale Navajo Sandstone cross beds become vertical to overturned
locally (e.g., near the Syncline Loop Trail in the
southwest). Southeast of the dome, at Whale
Rock, the innermost Navajo strata dip steepens to
a subvertical attitude within ~100 m of the inner
Navajo contact (Fig. 9). Inward from the vertical Navajo strata, however, dips in the basal
Navajo and underlying Kayenta strata flatten
(around 40°).
The circumferential fold system of Upheaval
Dome perturbs a regional homocline dipping
1.2° to the north-northwest. This homocline
forms the southern limb of the gentle Grays Pasture syncline (Huntoon, 1988). In the rim syncline is a crescentic low (Fig. 2), which is a typical fold interference pattern where a rim syncline
is superposed on a regional homocline (Ritz,
1936). Two structural highs (stippled) are present: one is the inner circular dome described
above; the other is a low, elongated periclinal
dome adjoining the western flank of Upheaval
Dome, also noted by Fiero (1958).
(Fig. 4). Deeper stratigraphic units (Moenkopi
and Cutler Formations) are exposed only in the
core of the dome, where they are too deformed to
reveal lateral stratigraphic variations. The upper
contact of the highest unit in the dome (Navajo
Sandstone) is not exposed and is generally too
massive and coated with desert varnish to expose
large-scale internal geometries. Thus, although
we describe evidence of synsedimentary deformation for only three units, we do not exclude the
possibility of similar features in other formations.
SYNSEDIMENTARY STRUCTURES
A wide variety of synsedimentary features are
present in Upheaval Dome but have not been observed elsewhere in the region. These features
provide evidence for deformation of Upheaval
Dome over at least 20 m.y., during deposition of
the Chinle, Wingate, and Kayenta Formations
Deformation During Deposition
of the Chinle Formation
The upper Chinle Formation contains angular
discordances of as much as 27° in alcoves B, C,
and D on the east of the dome (Fig. 6), in the extreme south, and in Syncline Valley in the north-
Geological Society of America Bulletin, December 1998
1555
JACKSON ET AL.
west. If the truncating surfaces are restored to
horizontal, truncated strata dip consistently outward from the dome. This apparent radial symmetry eliminates regional tilting as the cause. Because of poor exposure, we cannot determine the
origin of all the observed truncations. If they are
primary, the truncated strata may have been foresets deposited by rivers draining outward from a
gentle dome. Alternatively, erosion may have cut
across gently domed strata. Either way, the truncations suggest doming late in the time of Chinle
Formation deposition. These truncations are below the commonly discordant, faulted base of the
Wingate Sandstone.
Deformation During Deposition
of the Wingate Sandstone
Wingate Internal Diastems. Panorama 9
(Fig. 15, A and B), west of the Holeman Springs
alcove, extends from outside the rim monocline
to the rim syncline. Here, the Wingate Sandstone
thickens from ~50 m on the west edge of the profile to more than 75 m to the east. No faults offset
continuously traceable bedding in the top and
bottom of the Wingate Sandstone. Instead, the
thickness changes by a combination of onlap
against the base of the Wingate strata and truncation beneath a correlatable mid-Wingate surface.
From a uniform thickness outside the rim monocline in the west, the Wingate Sandstone gradually thins inward toward the center of the profile
by excision of ~20 m of section beneath the midWingate erosional truncation surface. From the
other end of the section, the Wingate Sandstone
also thins westward because ~40 m of lowermost
Wingate strata onlap against the top of the Chinle
Formation (the J-0 unconformity of Pipiringos
and O’Sullivan, 1978).
Figure 11C is a schematic reconstruction of
the inferred deformation. Stage 1 shows the
lower Wingate strata thickening inward (rightward) from point A, which we interpret as the
margin of the shifting peripheral sink around the
dome. Stage 2 shows a bulge forming in the
lower Wingate strata over the flexed margin of
the sink. The uplifted crest of the bulge between
points C and D is then eroded. Truncations on the
eastern (inward) limb of the eroded bulge are not
visible in this panorama, but are exposed farther
east in the Holeman Springs alcove. Stage 3
shows deposition of the upper Wingate Sandstone across the erosional surface.
Wingate Sandstone Growth Folds. Wingate
Sandstone cliffs ring the depression eroded into
the center of Upheaval Dome. In these cliffs, the
basal Wingate Sandstone contact is deformed
into a train of prominent, mostly upright folds
(Fig. 12), as noted by others (Shoemaker, 1954;
Fiero, 1958; Mattox, 1968; Shoemaker and
1556
Figure 9. Cross section through Whale Rock (Fig. 6), in the southeast part of the dome,
showing the abrupt, anomalous steepening of Navajo Sandstone dips on the inner limb of the
withdrawal syncline. This steepening is interpreted as due to the overriding front of a spreading salt glacier.
Herkenhoff, 1983, 1984). They are best exposed
on the northeast and southwest walls of the interior depression (Figs. 6 and 8). Fiero (1958) asserted that the fold axes parallel the dominant
joint system, and that slip on closely spaced
joint planes caused the folding, whereas other
workers reported radial axes (Shoemaker, 1954;
Shoemaker and Herkenhoff, 1983, 1984) and
a lack of shattering in the folded sandstones
(Mattox, 1968, Plate 4, Fig. 2). From the limited
exposure in the third dimension and their distribution around most of the inner cliffs except for
Upheaval Canyon, we conclude that these folds
trend radially and probably plunge outward.
The folds seem to have formed by circumferential shortening of the basal Wingate Sandstone
(see section on Inner Contractional Systems).
Spacing between the antiforms generally ranges
from 150 to 190 m. Given a typical Wingate
Sandstone undeformed thickness of about 100 m,
the wavelength to thickness ratio of these folds is
far smaller than values observed elsewhere in nature, theory, or experiment for a vast variety of
layer and matrix properties (reviewed by Price
and Cosgrove, 1990). Accordingly, it is improbable that the Wingate Sandstone buckled as a single layer of massive, lithified sandstone.
Further evidence corroborates the unusual
folding behavior of the Wingate Sandstone. The
top contact of the Wingate Sandstone is also
folded, but not in harmony with the bottom contact. The folds visible within the formation
are also disharmonic with regard to the top and
bottom contacts.
In the northeast wall of the interior depression
are the two best-exposed radial folds deforming
the base of the Wingate Sandstone. There, lower
Wingate strata thin upward over the antiforms
and thicken above the adjacent synforms, indicative of growth folds (Fig. 12).
These data suggest that folding began during
Wingate Sandstone deposition, when the sands
were unlithified. Kriens et al. (1997, p. 23) concluded that local deformation of the Wingate
Sandstone may have been due to “the presence of
fluids and/or a low degree of lithification,” resembling “soft-sediment landslides.”
Deformation During Deposition
of the Kayenta Formation
Basal Kayenta Channels. Detachment faults
(described in the section on Outer Extensional
Systems) transect or follow much of the WingateKayenta formation contact, which creates an irregular, wavy surface. However, this contact is
also wavy because Kayenta formation fluvial
sand channels to 5–6 m deep were eroded into the
top of the Wingate back erg dunes and interdunes.
Away from each channel, the sand packages thin,
pinch out, and grade into shale drapes above adjoining paleohighs. These large channels and paleohighs are well exposed in panoramas 9 (Fig.
11) and 12 (Fig. 14). In panorama 9, the upper
Wingate contact is fairly smooth outside the rim
monocline of Upheaval Dome but deeply channeled inside the monocline, indicating that channeling was enhanced by increased fluvial gradients related to deepening of the rim syncline at the
start of deposition of the Kayenta Formation.
Kayenta Formation Internal Diastems and
Inferred Shifting Rim Synclines. Repeated
and variable tilting is indicated by bounding
surfaces at the base of and within the Kayenta
Formation in spurs south of Upheaval Canyon
near the present axis of the rim syncline
(panoramas 12–14; Figs. 13 and 14). These surfaces divide the Kayenta Formation into lower,
middle, and upper packages.
The lowest truncation surface, EB0, is the erosional base of the Kayenta Formation referred to
in the preceding section. The truncation sense indicates that upper Wingate strata were tilted inward before they were obliquely planed off as
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
Figure 10. Schematic restoration of the intra-Kayenta Formation geometries exposed in spurs
south of Upheaval Canyon. The changing patterns of subsidence and tilting suggest syndepositional deformation, which we ascribe to the shifting peripheral sinks during diapiric growth.
lower Kayenta strata began to accumulate
(panorama 14 and Fig. 16, early Kayenta). The
next-higher diastem, the intra-Kayenta EB1
(panorama 13), also cuts downsection outward.
The EB1 truncation surface is the base of an erosional channel complex and is marked by a channel sandstone. This sense of truncation for both
the EB0 and EB1 surfaces suggests that subsidence was localized inboard (eastward) of the
end of panorama 13 during deposition of the
lower Kayenta Formation (Fig. 10, mid–early
Kayenta).
The upper truncation surface (EB2, panorama
14 and Fig. 10, mid-Kayenta) cuts downsection
inward, opposite to the truncation sense of EB0
and EB1. The EB2 surface is exposed in several
ridges on both sides of Upheaval Canyon and is
marked by a pale, upward-fining sandy bar that
toplaps meter-scale foresets. The EB2 surface is
the preserved erosional base of an upper Kayenta
Formation channel-fill complex overlying a genetically unrelated middle Kayenta Formation
channel-fill complex. Both complexes are sandprone, but comparison of cross-stratal styles, paleocurrents, and set thicknesses suggests that a
diastem exists between the two fluvial packages.
During the diastem, beds in the lower package
were tilted outward by as much as 20°, then
planed off. That indicates that strata outboard of
panorama 14 were subsiding during deposition
of the middle Kayenta Formation, very different
from the site of early Kayenta Formation subsidence (Fig. 10).
Onlapping the EB2 truncation surface in the
upper Kayenta Formation on panorama 12,
four flat-topped fluvial channel complexes
were stacked imbricately as they migrated outward (Fig. 10, end Kayenta). That geometry indicates creation of accommodation space by
gradual subsidence of a truncation surface
tilted inward as part of the rim syncline. Late in
the time of Kayenta Formation deposition,
therefore, the rim syncline had already migrated inward to its present position (Fig. 10D),
widening or renewed outward shift of the rim
syncline during deposition of the four channel
complexes followed.
The simplest explanation for these shifting
locations is that the rim syncline migrated as
Upheaval Dome evolved over a lengthy period
(Fig. 10). These shifting depocenters are typical
of salt tectonics, where lateral salt flow and
sedimentary accommodation space are intimately linked.
Kayenta Growth Faults. Incomplete evidence suggests that many of the normal faults
offsetting Wingate and Kayenta strata (described in the next section) may be the age of
the Kayenta Formation. Several faults die out
upward into the Kayenta Formation, and faults
offsetting the Navajo Sandstone base are rare
(we saw only one, at the west end of Syncline
Butte). This scarcity is partly because many
Kayenta faults are cut by the present-day erosional surface before reaching the Navajo
Sandstone. However, in the few places that
Navajo Sandstone erosional remnants still rest
across faulted strata (e.g., north side of alcove
B), the well-bedded Navajo basal strata are unfaulted. Another explanation for the upward termination of faults within the Kayenta Formation is that the faults could dissipate upward
among many small slip surfaces within the
Kayenta strata. However, in widespread areas
where the Kayenta Formation is well exposed,
we see no evidence for such upward splaying of
faults. Instead, the Kayenta faults die out upward with an abruptness typical of growth
faults. For example, stratigraphic separations in
faults at the base of the Kayenta Formation are
as follows: 30 m of separation dying out 20 m
above (panorama 14); 25 m of separation dying
out 20 m above (panorama 12). This upward
decrease of throw is accommodated by 25–
30 m of stratigraphic thickening of the lower
Kayenta Formation in the hanging wall of the
fault. We have not correlated meter-scale individual packages across faults to confirm thickening by growth faulting, but the impression of
syndepositional faulting on several panoramas
is striking.
OUTER EXTENSIONAL SYSTEMS
McKnight (1940) and Fiero (1958) both described major thickness variations in the Wingate
Sandstone and Kayenta Formation within the rim
syncline of Upheaval Dome. Some variations are
produced by the stratigraphic variations described here. However, as noted by Shoemaker
and Herkenhoff (1984), most thinning is due to
slip on ramp-flat extensional faults surrounding
the dome. All these circumferential faults are exposed only inside the trace of the rim monocline,
and so are inferred to be related to the formation
of Upheaval Dome. Figures 14, 17, and 19 illustrate the structural style of these faults (panoramas 4 and 5 in Fig. 17).
Three-dimensional exposures reveal the following characteristics. The faults are either simple listric faults or a series of ramps and flats.
Even the ramps are low-angle faults, cutting bedding at a mean apparent angle of ~13° and ranging from 9° to 25° (standard deviation). Very locally, however, ramp dips are near vertical over
short segments. The flats form detachments
mostly at the base of the Kayenta Formation or
Wingate Sandstone. Extensional ramps between
these two levels are responsible for thinning the
Wingate Sandstone (panoramas 2, 4, 5, 6, 11, and
14 in Figs. 14 and 17). Less commonly, ramps
thin the Kayenta Formation as well (panorama 3,
Geological Society of America Bulletin, December 1998
1557
JACKSON ET AL.
West
Northeast
Cliff bend
Rim monocline
Holeman
Springs Alcove
C
E
cave
B
A
D
Navajo (Jn)
Kayenta (Jk)
A
A
Wingate (Jw)
Chinle (TRC)
C
Figure 11. (A) Panorama 9 traced from photographs of Holeman Spring alcove and adjoining exposures farther west on the south side of Upheaval Dome. Panorama location and view direction are shown in Figure 6. (C) Schematic reconstruction of synsedimentary deformation of the
Wingate Sandstone in panorama 9, exaggerated vertically by 2×.
Fig. 17). In addition, local flats are common
within the Kayenta Formation and rare in the middle Wingate Sandstone. Measurements from photographs of oblique sections through exposed
faults offsetting the base of the Kayenta Formation provide rough separations for the largest fault
in each panorama. For the outward-verging faults,
the mean stratigraphic separation is 35 ± 15 m,
and the mean apparent slip is 120 ± 55 m (standard deviation). For the inward-verging faults, the
1558
mean stratigraphic separation is 25 ± 11 m, and
the mean apparent slip is 98 ± 24 m.
What was the effect of these faults on tectonic
transport? Shoemaker and Herkenhoff’s (1984)
schematic section portrays inward-dipping listric
faults linking with outward-dipping thrust systems in the core of the dome (Fig. 5A). That linkage would transport rock inward to the core of
the dome.
Our mapping confirms the existence of the in-
ward-dipping extensional fault systems but reveals that they are only half of the extensional
picture. As summarized in Figure 8, an equal
number of extensional faults dip outward. As a
group, their abundance, lengths, and stratigraphic
separations are similar to the inward-dipping
faults. The outward-dipping faults cannot be
linked with the inner thrust faults in the manner
advocated by Shoemaker and Herkenhoff (1983,
1984). Most normal faults in the northern half of
Geological Society of America Bulletin, December 1998
B
Figure 11. (B) Photograph of a similar view
to that in A; on the far right is the eastern portal of the alcove.
Figure 12. Northward view of radial growth
folds in the lower Wingate Sandstone in the
northeast cliffs of the inner depression. The
lowermost Wingate strata are isopachous and
are interpreted to be prekinematic. Above
here, strata thin over the antiform and thicken
in the synform, indicating growth of the fold
early during deposition of the Wingate Sandstone. The growth-wedge taper is extreme
(~15°) on the right limb of the antiform but
much less on the left limb; we interpret this as
an initially asymmetric fold verging to the
right. After a period of stability, indicated by
overlying isopachous units, the fold was tightened further into a symmetric fold late in
Wingate Sandstone deposition.
Figure 13. Photograph southwest across
Upheaval Canyon showing truncation surfaces
of variable dip within the Kayenta Formation.
The view superimposes one spur (panorama
14) on another (panorama 12) immediately to
the southwest. Compare with Figures 14 and
17. Navajo Sandstone on Syncline Butte forms
the foremost skyline, behind which are flat-lying strata outside the rim monocline and, just
visible, the snow-capped peaks of the Henry
Mountains laccoliths.
Geological Society of America Bulletin, December 1998
1559
Fluvial incision surface
Navajo (Jn)
Outward verging extension
Cliff bend
(not fold)
Kayenta (Jk)
Eroded
in mid Jk
Wingate (Jw)
Pan 14
View to SW
Extension = early Jk
Outer thrust
imbricates
Upper Jk
0
Chinle (TRC)
100 m
0
400 ft
Erosional base, EB2
Pan 13
EB0
View to NE (mirrored)
Extension = early Jk
Dune scour surface
Jk
EB2
EB1
Back-erg
complex
Central-erg
complex
0
0
Syncline Butte
400 ft
C5
C4
C3
C2
100 m
Upper Kayenta channel-fill
complex
EB2
Lower and middle
Kayenta
channel-fill
complex
PH
Pan 12
C1
View to SSW
Extension = early Jk
0
100 m
0
400 ft
Jn
Pan 2
View to SE (mirrored)
Extension = syn or post Jk
Jk
0
0
100 m
400 ft
Figure 14. Panoramas (Pan) traced from photographs of outward-verging extensional fault systems encircling Upheaval Dome. Panorama locations and view directions are shown in Figure 6. The view directions of panoramas 2 and 13 have been reversed (“mirrored”) from the actual
view so that the outward direction from the dome center is consistent throughout the figure. EB—erosional base of fluvial channel complex;
PH—paleohigh draped by Kayenta shale that grades laterally into channel sandstones filling an erosional scour in the top of the Wingate Sandstone. C1 through C5 are channels. Scales are approximate because of perspective.
1560
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
TRC
Jn
Bend in section
Azimuth of
section = 301°
Boundary
of map
2000
Elevation (m)
A
500 m
0
2000 ft
Boundary
of map
Azimuth of
section = 106°
6000
Elevation (ft)
B
0
Bend in section
1000
3000
Figure 15. Linear cross section across Upheaval Dome and surroundings as inferred from surface exposures and projection from the Buck
Mesa well. Trace of section is shown in Figures 6 and 7 (ends of the section project beyond the maps). Geology inboard (east) of northwest Wingate
Sandstone cliff (gray in section) was projected from the cliff and slope exposures just north of the section line. Contacts and faults are dashed beyond the zone of direct projection from the surface. Dotted lines show bedding traces within units. Figure 26 shows the inferred geometry of deep
units, including the Paradox salt.
the dome transported rock outward, whereas
most normal faults in the southern half transported rock inward. This is true whether the faults
are exposed inside or outside the trace of the present rim syncline.
INNER CONTRACTIONAL SYSTEMS
Contractional structures dominate the center
of Upheaval Dome (Fig. 7). Shoemaker and
Herkenhoff (1984) inferred “convergent displacement” of rocks. We agree and recognize
both radial and circumferential shortening, which
was volumetrically balanced by vertical extension. This bulk constriction is expressed by a different structural style in each formation, described in the following in order of increasing
proximity to the dome’s center.
Kayenta Fold-and-Thrust Belt
As noted by Shoemaker and Herkenhoff
(1984), stratigraphic repetition due to thrusting accounts for the anomalously thick outcrop belt of
the Kayenta Formation (Figs. 6, 15, and 19). The
Kayenta Formation appears to be folded and
faulted everywhere in its outcrop belt between the
inner Navajo Sandstone and Wingate Sandstone
cliffs. As in the outer extensional systems, lithologic variations in the fluvially deposited Kayenta
Formation caused faults to form ramps and flats.
The typically lenticular depositional units resemble the anastomosing fault-bounded bodies, making faults difficult to recognize. However, the details of these structures are spectacularly exposed
where Upheaval Canyon cuts a radial section (Fig.
19). From photogeology we infer that this exposed
section typifies deformation elsewhere in the contracted Kayenta Formation.
In Upheaval Canyon, ramp-flat thrust faults in
the Kayenta Formation form a thrust duplex. The
floor thrust of the duplex detached along the
lower Kayenta Formation contact; the roof thrust
(poorly exposed and conjectural) is near the top
of the formation (Figs. 15 and 19). Fault spacing
decreases and folding associated with the faulting
increases inward. Some thrust faults show normal separation over parts of their trajectories,
particularly those that continue downward into
the Wingate Sandstone near the rim syncline
(Fig. 19B, center), suggesting that the lower parts
of the faults had multiple displacement histories.
The thrust duplex in the Kayenta Formation
appears to accommodate much more shortening
than in the underlying Wingate and overlying
Geological Society of America Bulletin, December 1998
1561
JACKSON ET AL.
A
South
East
West
Elevation (m)
1600
100 m
0
0
400 ft
No vertical exaggeration
1300
B
West
North
East
Elevation (ft)
5000
4500
Figure 16. Approximately circular cross section in the inner depression. The right and left ends of the section connect on the east side to form a
continuous ring. Trace of section is shown in Figure 7B. The section plane is viewed outward from the map center.
Navajo Sandstones. That anomaly is explicable if
the duplex formed mainly by shear due to flexural slip between the adjoining massive sandstones as they folded. Tanner (1992) described
smaller versions of such duplexes, which formed
on the limbs of larger chevron folds (Fig. 19B, inset); his duplexes have smooth roofs, no hangingwall anticlines above each link thrust, and relatively small fault offsets. The roof and floor
thrusts may both continue beyond the flexuralslip duplex. This type of duplex evolves where
thrust propagation was resisted by facies or thickness changes, or by transfer zones between faults
propagating on different movement horizons
(Cruikshank et al., 1991). Thus, the Kayenta
thrust duplex may be caused as much by upward
flexure of the layered succession as by inward
contraction.
1562
Wingate Structures
Both radially and circumferentially trending
folds have been mapped in the Wingate Sandstone cliffs facing the central depression. The radially trending antiforms distort the basal Wingate
Sandstone contact (Figs. 12 and 20) and indicate
circumferential shortening. Most intervening radial synforms have been eroded back to the same
encircling cliff as the radial antiforms and are
partly hidden by talus (Figs. 8 and 20B). A few radial synforms are less eroded and retain a complex three-dimensional curvature. For brevity, we
informally refer to these doubly curved synformal
radial lobes as “dog tongues” (name suggested by
Rudy Kopf, 1992, personal commun.).
The dog tongues preserve the lowest and most
inward exposures of the Wingate Sandstone
(Figs. 8 and 15). The most complete dog tongue is
in the northeast corner of the Wingate Sandstone
cliffs. Synformal Wingate strata there dip inward
to levels far below the contact with the Chinle
Formation on either side of the lobe. The radial
axis of the dog tongue forms a trough bordered
by radial antiforms. Farther inward, the same
Wingate strata reverse steeply upward along a
circumferential fold axis, like the upward-curled
tip of a tongue (Fig. 20C).
Wingate strata in the tip of the best-exposed dog
tongue appear to onlap the basal Wingate Sandstone contact (Fig. 20C). The basal Wingate Sandstone contact in the dog tongues is also discordant
to Chinle Formation bedding (Fig. 20C) and to a
bedding-parallel cleavage in folded Chinle Formation siltstone and shale. The contact is typically
marked by rubble. We interpret this doubly discor-
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
A
Inward verging extension
Pan 11
View to NE (mirrored)
0
Extension = late syn
or post Jk
100 m
400 ft
0
Extension = syn or post Jk
?
Pan 10
View to SSE
0
50 m
0
200 ft
Pan 6
Holeman
Alcove
View to NE
Extension = syn or post Jk
0
50 m
200 ft
0
Pan 5
View to WNW (mirrored)
Extension = syn Jk
Pan 4
Shale diapir
0
0
Kayenta (Jk)
Navajo (Jn)
Alcove Spring
View to NW
Extension = syn to post Jk
0
50 m
0
200 ft
50 m
200 ft
Chinle (TRC )
Wingate (Jw)
Figure 17. Panoramas (Pan) traced from photographs of inward-verging extensional fault systems encircling Upheaval Dome. Panorama locations and view directions are shown in Figure 6. The view direction of panoramas marked “mirrored” have been reversed from the actual view
so that the inward direction is consistent throughout the figure. Scales are approximate because of perspective.
dant contact as a salt weld (see reconstruction section following). Just below the folds, the Chinle
Formation appears to be relatively undeformed,
but exposures are poor in quality.
At the upper, outer end of the dog tongues, ex-
posed upper Wingate strata are deformed into upright, nearly isoclinal folds that trend circumferentially (Fig. 20C) and are cut by steep reverse
faults. Such folds are well exposed on the eastern
side of the central depression near the inner edge
of Wingate Sandstone exposures (Figs. 20B and
21). These folds do not appear to affect the sporadically exposed basal Wingate Sandstone contact. Dips in much of the lower Wingate Sandstone and upper Chinle Formation are typically
Geological Society of America Bulletin, December 1998
1563
JACKSON ET AL.
much less than the subvertical orientations observed in the upper Wingate Sandstone. As with
the radial antiforms and synforms described here,
it is difficult to envision a well-lithified Wingate
Sandstone folding internally in this extreme,
strongly discordant manner.
Compared with the intensely faulted Kayenta
Formation, few visible faults cut the underlying
Wingate Sandstone. The Wingate faults strike
radially and dip steeply (Fig. 8). They tend to cut
through the radial antiforms and along the
boundaries of the dog tongues. The radial faults
can be traced outward into the Kayenta Formation, where they commonly curve into oblique or
circumferential orientations.
Deformation along the inner Wingate Sandstone cliffs thus indicates both radial and circumferential shortening induced by radially inward
movement. Farther inward, the circumferential
shortening in the older exposed units dominates
the strain, as described in the following.
Chinle Deformation in Central Depression
Most of the Chinle Formation in the inner depression crops out on inward-facing slopes below
the Wingate Sandstone cliffs (Fig. 6). The slopes
are largely covered with talus exposing only small
windows of the Chinle Formation. The resistant
Moss Back Member (basal Chinle) and Black
Ledge (mid-Chinle) sandy conglomerates crop
out as ledges typically segmented by thrusts and
reverse faults. Because most of the Chinle Formation shales are weathered or covered, their internal structure is poorly known. However, structural
variation increases toward the center of the interior depression from the relatively uniform outward dips below the Wingate Sandstone cliffs
(Fig. 7). The innermost outcrops of the Chinle
Formation are folded and faulted similarly to the
underlying Moenkopi Formation.
Central Moenkopi Formation Constriction
The Moenkopi Formation occupies most of the
dome’s core. Structures are expressed well in
bare, rugged terrane by variations in color and
lithology (Fig. 7). The Moenkopi Formation in
the central uplift was radially and circumferentially shortened. A linear cross section (Fig. 15)
captures structures with circumferential strikes,
whereas a subcircular section (Fig. 16) crosses
subradial strikes. Attitudes vary greatly over short
distances, and structures tend to be irregular and
discontinuous. The Moenkopi Formation outcrops can be divided into two sectors having different structural styles: converging radial thrusts
in the southwest half, and more circumferentially
oriented folds and thrusts in the northeast half.
The southwestern zone of steep radial thrusts
1564
B
Pan 3
View to WNW
Extension = syn or end Jk
?
0
0
?
?
100 m
400 ft
Figure 17. (Continued).
has the most regular structure of the interior depression. The hanging walls moved in a counterclockwise direction and imbricated the clockwisedipping Moenkopi strata (Figs. 7 and 16). We liken
that movement to the closing of the leaves of a
camera diaphragm, where circumferential shortening increases inward. No marker lines are available to determine the strike component of slip on
these thrusts. The left-lateral separation may have
been derived all or in part from dip slip. Two of
these thrusts continue outward as steep faults cutting upward through the Wingate Sandstone. Toward the center, the thrusts merge, die out, lose definition where parallel lower Moenkopi strata are
on both sides, or continue as clastic dikes.
The regular radial thrusts in the southwest
grade into highly variable structures in the northeastern half of the interior depression. Structures
show more local variation, including small folds,
short faults, and abrupt attitude changes that result in complex, extremely detailed outcrop patterns rather than the radial stripes exposed to the
southwest (Fig. 22). Thrusts vary in strike and
vergence. Folds are common and rarely cylindrical, varying from conical to irregular, and generally persist less than 100 m.
Although the structural pattern in the northeast
defies simple characterization, the overall strain
remains constrictional, as shown by subhorizontal radial and circumferential shortening and subvertical extension indicated by the presence of
the central uplift. Crowding from inward movement of the rocks caused the constriction. The
complexity and intensity of the central deformation, which has obscured large-scale synsedimentary structures, preclude detailed reconstruction of the inner deformation history.
Dome Center and Clastic Dikes
Clastic dikes are abundant in the center of Upheaval Dome. The dikes are composed of clean
white sandstone, presumably derived from the underlying White Rim Sandstone of the Cutler
Group. Other authors have described the White
Rim outcrops as coherently emplaced blocks
(McKnight, 1940; Mattox, 1968). However, the
main lenticular dikes anastomose, branch into
veins, and are discordant with country rock. All
these features indicate that the dikes are intrusive,
as inferred by Fiero (1958), Shoemaker and
Herkenhoff (1984), and Kriens et al. (1997). In
places, the sandstone is laminated but is generally
massive. The dike thickness is generally less than
15 m but as much as 30 m. Lengths are typically
less than 70 m, but the long dike complex in the
center extends more than 400 m. In addition,
more-isolated clastic quartzose dikes of unknown
source are exposed as far out as the outer part of
the thrust duplex in the southern wall of Upheaval
Canyon. Some clastic dikes are sourced by the
Moss Back Member conglomerate (D. Bice,
1997, personal commun.).
We infer that some of these steep dikes were
emplaced along faults. In some places, faults visibly connect with the ends of the dikes. Elsewhere, the same rock type is on either side of the
dike such that an aligned fault would be obscure
(Fig. 7). Most dikes intrude the lower Moenkopi
Formation, but extend upward into the middle
and upper Moenkopi Formation in their northern
outcrops. Quartz cementation makes the dikes
much more resistant than the surrounding rocks,
and they form towering spires and irregular walls
in the center of Upheaval Dome.
The microstructure of the clastic dikes is described and discussed in Part 3 (Data Repository
item 9891)1 but can be summarized as follows.
Our nine thin sections contained abundant mi1GSA Data Repository item 9891, supplemental
data, is available on request from Documents Secretary,
GSA, P.O. Box 9140, Boulder, CO 80301. E-mail:
editing@geosociety.org.
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
TABLE 1. EVIDENCE FOR PINCH-OFF AND IMPACT HYPOTHESES
Observation
Positive evidence
Circularity
Central uplift
Clastic dikes
Crushed quartz grains
Inner constrictional zone
Outer extensional zone
Radial flaps (dog tongues)
Presence of underlying salt
Gravity and magnetic anomalies
Contiguous anticline
Nearby salt structures
Rim syncline
Rim monocline
Growth folds
Growth faults
Shifting rim synclines
Truncations and channeling
Onlap
Multiple fracturing and cementation
Steep zones
Outward-verging extension
Volume imbalance
Shatter cones
Planar microstructures in quartz
Ejecta breccia
Salt below rim syncline
Negative evidence
Lack of salt at the surface
Lack of nearby piercement diapirs
Lack of meteoritic material
Lack of melt
Lack of in-situ breccia
Lack of shock-metamorphic minerals
Lack of outer fault terracing
Lack of overturned peripheral flap
Pinch-off favored
Impact favored
incompatible
with impact
Compatible
with pinch-off
Compatible
with impact
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
crofractures, typically masked by recementation
of authigenic quartz between and in optical continuity with the shards. Some microfractures are
transgranular and radiating; they must have
formed by cataclasis after or during a late stage of
dike injection. Electron beam-induced cathodoluminescence of our Upheaval Dome sample reveals that the quartz undulatory extinction is
caused by slightly misoriented grain fragments
separated by microfractures sealed with cement.
Cross-cutting quartz veinlets provide evidence
for at least two events of alternating fracturing
and diagenesis. Multiple deformation is consistent with episodic faulting during diapiric pinchoff but not with the instantaneous deformation induced by an impact.
The intruded lower Moenkopi Formation in
the center dips steeply or is overturned. Stratal
strikes are grossly similar to those of nearby
dikes, but discordances are common. Attitudes
in the Moenkopi Formation can vary abruptly
and nonsystematically near the larger dikes.
Mattox (1968) and Huntoon and Shoemaker
(1995) identified some of the dark brownish-red
shales in the dome’s core as the Organ Rock
Member shale, which underlies the White Rim
Sandstone in exposures of the Cutler Group else-
Incompatible
with pinch-off
X
X
X
X
X
X
where. That possibility cannot be excluded because of the similar appearance of the Organ
Rock and lower Moenkopi shales. However, if
the Organ Rock Member shale were present, we
would expect to see much of the overlying
White Rim Sandstone—an exceptionally prominent and resistant marker—in place rather than
as discordant dikes.
SUMMARY OF EVIDENCE
FOR IMPACT VERSUS PINCH-OFF
Shoemaker and Herkenhoff (1984) proposed
that a meteorite impact near the end of Cretaceous
or in Paleogene time excavated a transient crater
1.3 to 1.4 km deep. That became instantly modified by gravity to a final diameter of 8 to 9 km,
forming Upheaval Dome. Evidence they cited to
support that hypothesis included the circular dimpled shape, inward-verging listric normal faults
near the periphery, inward-verging thrust faults
near the center, folds plunging radially outward
from the center, crushed quartz grains in clastic
dikes, and geophysical anomalies. They thought
that erosion removed 1–2 km thickness of the upper part of the crater. Kriens et al. (1997) revised
these estimates by proposing impact within the
last few million years and a smaller modified
crater. Kriens et al. (1997, p. 20 and 26) used a
crater diameter of 5 km to calculate the rise of the
central uplift, and advocated a modified transient
crater diameter “close to . . . . the walls of the present topographic crater,” which is only 2 km wide.
The current central depression of Upheaval Dome
was thought to be entirely erosional in origin by
Shoemaker and Herkenhoff (1984).
Table 1 summarizes the evidence for or against
meteoritic impact and diapiric pinch-off at Upheaval Dome. A full discussion of each criterion
to explain our evaluation of the evidence can be
found in Part 3 (see footnote 1). Despite the fact
that Upheaval Dome is far better exposed than
any terrestrial impact crater, we consider that the
evidence for impact there is sparse and equivocal.
Part 3 contests the evidence for shatter cones, planar deformation structures in clastic dikes, and
ejecta breccia. Kriens et al. (1997, p. 28) concluded that the most diagnostic evidence for impact (planar deformation features and shatter
cones) were “not well developed.” The scarcity
of features diagnostic of impact in Upheaval
Dome might be ascribed to too much or too little
erosion. However, the many apparently missing
features would cover the complete range of shock
zonation and depths. Thus, it seems implausible
that only a few contestable features have been
found in a superbly exposed, high-relief structure
containing abundant thick sandstones.
In contrast, a wide range of structures (Table 1)
attests to the gradual growth of Upheaval Dome
as a salt structure. The strongest argument for diapirism is the stratigraphic evidence indicating
protracted growth of Upheaval Dome over at
least 20 m.y., which is incompatible with hypervelocity impact.
VOLUME IMBALANCE
INDICATES SALT LOSS
AND PRIMARY THICKNESS CHANGES
The pinch-off and impact hypotheses can be
tested in two ways by comparing selected rock
volumes in Upheaval Dome. This section summarizes the data presented, together with the
methodology and assumptions, in Part 2 (see
footnote 1).
First, we examined the variation in elevation of
the base Wingate Sandstone horizon relative to its
regional elevation. That variation includes the depressed rim syncline and the elevated central
mound (the center of which is eroded). The volume of rock depressed below the base Wingate
Sandstone regional datum is 0.74 km3, compared
with only 0.29 km3 to 0.33 km3 above the regional
datum. This volumetric mismatch of 220% to
260% can only be plausibly explained by the loss
of 0.45 km3 to 0.41 km3 salt from Upheaval
Geological Society of America Bulletin, December 1998
1565
JACKSON ET AL.
Dome since the Chinle Formation was deposited.
Impact would allow lateral flow of Paradox salt
but would entail no loss of salt volume because
the salt was not exposed to dissolution. Conversely, the pinch-off hypothesis requires a considerable loss of salt as the emergent diapir and
glaciers dissolved. The gross volumetric imbalance therefore supports diapirism and is incompatible with impact.
SALT-TECTONIC HYPOTHESIS:
A RECONSTRUCTION
We now attempt to reconstruct the evolution of
Upheaval Dome by diapiric pinch-off. Figure 18
shows a seismic example with some similarities
to the diapiric structure that we envisage. The
pinched-off stem is marked by a vertical secondary salt weld. An erosional section through
the necked stem would expose strata steepening
inward to form a central uplift, above which the
subhorizontal tertiary salt weld represents a salt
glacier largely evacuated of salt by the overburden load. The former salt glacier here is strongly
asymmetric because the Gulf of Mexico has an
extensive slope. In contrast, we envisage a symmetric salt diapir and glacier above Upheaval
Dome, now eroded off.
Initiation of Diapirism
Published subsurface data are lacking, except
for one well, so the deep structure and early evolution are highly speculative. The sparse and ambiguous evidence for what initiated the inferred
diapirism can be accommodated in two hypotheses for the structural evolution: (1) salt tectonics
alone, or (2) initiation by impact followed by salt
tectonics.
Our hypothesis is illustrated in Figure 23. Geophysical anomalies indicate basement uplift or
dense rocks below the Paradox salt (see footnote
1). One possibility is that emplacement of an igneous intrusion into the salt initiated salt upwelling by arching the overburden and softening
the salt by adding heat and water. Alternatively,
an irregular configuration of basement fault
scarps generated by Pennsylvanian to Permian
extension might have obstructed southwestward
flow of salt, squeezed ahead of prograding sediments. Any such obstruction would favor local
upwelling of salt (Ge et al., 1997). Upwelling and
local stretching of overburden draped above the
tilted corner of a basement fault block might initiate a diapir that evolved into a passive stock during continued sedimentation.
The following history (Fig. 23) combines the
most internally consistent interpretation of available data with mechanically reasonable processes.
The restoration cannot be area balanced because
1566
Figure 18. A pinched-off diapir shown by reflection seismic image in the Gulf of Mexico (from
Hall and Thies, 1995, Fig. 4.3).
the circular dome did not undergo plane strain: inward-moving rocks increased the cross-sectional
area, whereas outward-moving rocks decreased
the area. Thus, the restoration had to be schematic
and was carried out as follows. (1) To emphasize
the strains, we ignored compaction. (2) Individual
faults were omitted, but progressive thickening
and thinning by strain is schematically portrayed.
(3) Strata were unfolded by vertical shear. (4) The
cross section was pinned at both ends, so that the
overall length remained constant. (5) The diapir
diameter approximates the value estimated for the
time of Chinle Formation deposition in Part 2 (see
footnote 1).
Stage 1: End of Pennsylvanian Time
By the end of Honaker Trail Formation deposition (stage 1), we envisage an emergent, passive
stock surrounded by a gentle rim syncline. In
general, crests of passive stocks are periodically
buried but continually break through their veneer
of overburden to remain close to the depositional
surface.
Stage 2: End of Chinle Formation Deposition
At this stage, we envision that the stock was still
emergent. The gradually thickening overburden
would have increased the pressure on the salt
source layer, causing the salt to flow at increasing
rates up the emergent stock. The climate was relatively wet, so much of the salt probably dissolved
as fast as it emerged. However, enough salt survived that the stock began to extrude as a salt glacier, forming a flange that overhung surrounding
strata (for detailed discussions of this type of salt
tectonics, see Fletcher et al., 1995; Talbot, 1995;
Geological Society of America Bulletin, December 1998
A
Figure 19. (A) Photograph and (B) broader
interpreted panorama 15 (Pan—traced from
photographs) of the Kayenta Formation
thrust duplex and the abrupt transition into
the adjoining extensional system farther west
(left). Both views are northward across Upheaval Canyon; the dome center is to the right.
Note the steepened deformation front of the
duplex (extreme right). See Figures 14 or 15
for stratigraphic explanation; one (or more) of
the Kayenta Formation EB units is stippled.
Scale varies greatly because of perspective,
but the Wingate Sandstone (black) is about
80–100 m thick. Inset shows a similar but
smaller duplex produced by folding in southwest England (after Tanner, 1992).
A
Figure 20. Views of dog tongues. Wingate
strata in the lobes are ~60 m below the adjoining elevation of their basal contact. (A) Photograph looking radially outward at the northeast cliffs of the inner depression.
Figure 21. Northward view of several circumferential, upright, tight to isoclinal folds in
upper Wingate and lower Kayenta strata. Note
the abrupt transition between the WingateKayenta steep zone in the twin spires (center)
and open-folded Kayenta Formation on the
right. At the extreme left are the northern cliffs
of the inner depression.
Geological Society of America Bulletin, December 1998
1567
East
West
Dome center
Pan 15
c
B la
kL
ge
ed
Roof thrust
Floor thrust
B
B
~1 m
Figure 19. (Continued).
C
C
B
B
Jk
Dome
center
Jw
?
Upturned
tip
TRc
Inferred
salt weld
Dome
center
Upturned
tip of tongue
D
E
E
Upright isoclinal folds,
Variably verging thrusts
Dome
center
Jk
Flap = future dog tongue
Dome
center
Jw
Salt flange
Jw
TRc
Basal
flap
Weld at base of
dog tongue
TRc
Figure 20. (Continued). (B) to (E) idealized diagrams showing (B) radial fold traces on a Wingate horizon, where the central trace defines the
dog tongue flanked by two higher antiforms (cf. Fig. 12); (C) radial cross section, and (D–E) schematic restoration of the dog tongue, showing its
inferred origin as a flap overlying a flange of glacial salt that was subsequently removed to form a salt weld.
1568
Geological Society of America Bulletin, December 1998
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
Figure 22. Annotated photograph looking north-northeast from the dome center at folds (defined by dotted bedding), imbricated thrust faults
(teeth on hanging wall), and clastic dikes. Turret Rock (located in Fig. 7A) is shown by arrows in the center. The larger trees are 2–3 m tall.
Talbot and Alavi, 1996). Chinle Formation strata
currently truncated against the basal Wingate
Sandstone contact in the dog tongues may have
originally terminated against the overhanging salt
face (Figs. 20E and 23).
If primary, the angular truncations sporadically exposed in the upper Chinle Formation
suggest that local tilting took place (e.g., alcoves
B, C, and D). The apparently radial tilts of these
truncations suggest that they were related to
growth of a rim syncline around a dome. The degree of faulting during deposition of the Chinle
Formation is unknown; some of the faults exposed today in the core of the dome may have
formed during the growth phase of the inferred
diapir and were reactivated during pinch-off.
dipping and outward-dipping Kayenta growth
faults may have initiated near the hinge lines
of these localized depotroughs. The dog
tongues are thought to represent upper Wingate
strata onlapping emergent salt, the presence of
which prevented lower Wingate strata from accumulating locally (Figs. 20 and 23). This
emergent salt would have been an early aborted
phase of glacial extrusion before the main extrusion during Navajo Sandstone deposition.
Growth folds in the lower Wingate Sandstone
suggest that the central part of the dome had
begun to fold radially, indicating that the
flanks of the dome were beginning to slide inward. This process accelerated during final
pinch-off later.
Stages 3 and 4: End of Wingate Sandstone to
End of Kayenta Formation Deposition
Stage 5: End of Navajo Sandstone Deposition
Onlap, truncation, and channeling in Wingate
and Kayenta strata indicate shifting axes of
subsidence and deposition. We deduce shifts in
the sites of active salt withdrawal, an erratic
pattern typical of growing salt domes (e.g.,
Seni and Jackson, 1983). Many of the inward-
Salt Extrusion. We infer that glacial salt
spread fastest during deposition of the Navajo
Sandstone. The inferred glacier reached a width
of at least 3 km. Collision between the outwardspreading glacier and inward-gliding strata is
recorded by the zone of abrupt steepening in the
Navajo Sandstone (Figs. 8 and 23). The steep
zone suggests that the outer edge of the extruding
salt extended well outside the present limits of
the central depression during Navajo Sandstone
deposition (Figs. 6 and 23).
Diapir Pinch-Off. Two lines of evidence suggest—but do not prove—that the most plausible
time of pinch-off was during the extrusion of salt
that occurred during Navajo Sandstone deposition. (1) Most of the constrictional deformation in
the Wingate Sandstone appears to have occurred
before it was lithified, indicating that pinch-off
could not have occurred too late in the geologic
history. The radial growth folds indicate that wall
rocks may have begun to move radially inward
during early deposition of the Wingate Sandstone. (2) Physical models (Jackson et al., 1997;
B. C. Vendeville, 1996, personal commun.) indicate that where salt is forced rapidly up and out of
a feeder stock closing by lateral compression, salt
extrudes vigorously during stem pinch-off.
The outward migration of steep zones (Fig. 8)
suggests that the dome originally widened upward. Pinch-off of the feeder produced different
results at different structural levels. For example,
in the narrowest part of the diapir (Moenkopi
Formation and Cutler Group), pinch-off continued
Geological Society of America Bulletin, December 1998
1569
Stage 6: Post-Navajo
Elevation
m
Rim
syncline
Buck
Mesa
Central uplift
1500
Rim
monocline
Elevation
ft
6000
5000
Weld
4000
1000
3000
2000
500
1000
Paradox salt
msl
0
0
Base salt – geometry unknown
Glacial spreading
Stage 5: End Navajo
Steepening
Jn
Jk
Jw
Rc
R
Pc
Base salt omitted
Stage 4: End Kayenta
Regional
tilt
Outwardverging extension
Contraction
Inward-verging extension
Dog tongue
R
Weld
Stage 3: End Wingate
Salt flange
Jk
Jw
Rc
Pc
Future dog tongue
Eroded bulge
Jw
Rc
R
Pc
Stage 2: End Chinle
Salt flange
Rc
R
Pc
Stage 1: End Pennsylvanian
Passive diapir
Figure 23. Schematic reconstruction of the salt-tectonic evolution of Upheaval Dome.
1570
Geological Society of America Bulletin, December 1998
Rim syncline
ms
STRUCTURE AND EVOLUTION OF UPHEAVAL DOME
until rocks from opposite sides met at the center,
completely closing the feeder during deposition of
the Navajo Sandstone. That resulted in the highly
evolved constrictional features preserved in the
Moenkopi Formation in the central depression.
The White Rim Sandstone clastic dikes, which
could have been emplaced along Moenkopi
Formation faults during the earlier growth phase
of the dome, would have been rotated, distorted,
and possibly reactivated during pinch-off.
The soft-sediment response of the Wingate
Sandstone in the dog tongues also suggests that
the weight of Wingate strata overburden expelled
salt from the early, abortive Chinle Formation
salt flanges at that time. Expulsion produced a
salt weld, juxtaposing suprasalt Wingate strata
against subsalt Chinle strata (Figs. 20 and 23).
The unlithified dog tongues were then strongly
folded during constrictional pinch-off.
Closing of the diapir stem at Cutler Group
and Moenkopi Formation levels would have
ended diapiric pinch-off. Higher stratigraphic
units originally adjoined wider parts of the overhanging diapir, so they did not completely close
off before inward gliding stopped (Fig. 23).
Thus, higher stratigraphic units never developed
structures such as in the Moenkopi Formation
because they never moved close enough to the
center to produce the requisite amount of strain.
Pinch-off ended late during, or after, deposition
of the Navajo Sandstone. The base of the
Navajo Sandstone is strongly folded by the rim
syncline, which is unlikely to have continued
deepening after pinch-off ended. The upper
contact of the Navajo Sandstone is no longer
preserved.
Examples of allochthonous salt sheets overlying pinched-off stems are common in the Gulf of
Mexico (Wyatt et al., 1993; Diegel et al., 1995;
Fletcher et al., 1995; Rowan, 1995) and Red Sea
(Heaton et al., 1995) and have also been observed
by us on proprietary seismic data from the North
Sea, northwest Germany, and west Africa. However, the mechanism for diapiric pinch-off is unknown. Pinch-off is the core of our hypothesis for
Upheaval Dome, yet we are unsure how it occurs
(Fig. 5B).
We do not regard this gap in knowledge as evidence against the pinch-off hypothesis for the
following reasons. (1) The lack of detailed mechanical knowledge reflects a gap in salt tectonics theory generally rather than an anomaly specific to Upheaval Dome. (2) Three-dimensional
seismic data indicate that the process occurs
whether or not we understand it. (3) The limited
physical modeling of dome pinch-off in brittle
country rock (Lemon, 1985) reproduces several
of the main features observed at Upheaval Dome:
a rim syncline that deepened markedly when
pinch-off began, a central uplift with subvertical
strata below the pinched-off diapir, peripheral
normal faults, and numerous unconformities.
However, because gravity gliding was not permitted in Lemon’s (1985) physical models, no
central zone of contraction formed in them.
How do inward-moving strata overcome the
outward pressure exerted by the salt stem? The
most likely mechanism for pinch-off is gravity
gliding of the country rocks down an inwarddipping top salt surface into the weaker rock
composing the salt diapir (Fig. 5B). The process
would be enhanced by salt dissolution. The diapir
pinches off as a result of being the partially buttressing toe of a radially inward-dipping spreading system. Gravity spreading is driven by the
loss of gravity potential, which results in an excess volume of rock depressed below regional elevation compared with the volume of rock raised
above regional elevation. Part 2 (see footnote 1)
examines the implication of volume imbalances
for understanding the process of pinch-off, for
explaining primary thickening, and for estimating the diameter of the vanished diapir.
Stage 6: Present Day
Pinch-off would have ended salt rise, which allowed Cretaceous strata to bury the allochthonous
salt sheet. During Tertiary time, Upheaval Dome
was uplifted and eroded. Because soluble salt was
more easily removed than the surrounding rocks,
the present topographic surface may partly reflect
the original shape of the overhanging lower contact of the allochthonous salt. However, outside
the mesa surrounding Upheaval Dome, erosion
was greater and all strata were deeply dissected.
CONCLUSIONS
1. We propose that pinch-off of a salt diapir
best explains the sedimentary and deformational
structures at Upheaval Dome. Evidence summarized here suggests that inward constriction of
overburden strata accompanied necking of the
stem of a broadly overhanging salt extrusion,
subsequently removed by erosion.
2. In the rim syncline, the Wingate Sandstone
and overlying Kayenta Formation are greatly
thinned by circumferential extensional faults.
These low-angle normal faults are either simple
listric faults or series of ramps and flats. Most exposed faults slipped during or after deposition of
the Kayenta Formation. Normal fault vergence
shows a strong dichotomy: in the north, most
faults transported rock outward from the dome,
whereas in the south, most faults transported rock
inward.
3. In the core of the dome, the bulk strain is
constrictional, and includes both radial and circumferential shortening. Radial shortening dom-
inates the periphery of the dome core, but circumferential shortening predominates farther inward. In the western sector of the dome’s core,
the hanging walls of radial thrusts moved counterclockwise and imbricated the persistently
clockwise-dipping Moenkopi Formation, like the
closing of a camera’s leaf diaphragm. Elsewhere
in the dome core, strain is highly variable, but is
constrictional overall.
4. In the core of the dome, many steeply dipping clastic dikes link with the radial fault systems. The lenticular sandstone dikes form a
continuous network more than 400 m long, presumably derived from the underlying White
Rim Sandstone. Their intrusive origin is indicated by branching, anastomosing veins and
discordance with country rock.
5. Arguments have been advanced for the
formation of Upheaval Dome by either meteoritic
impact or salt tectonic processes. We think that
evidence favoring meteoritic impact is sparse, being restricted to a lag deposit of cobbles, part of
two weakly developed shatter cones, and undocumented planar structures in quartz. The paucity of
typical impact features in Upheaval Dome might
be ascribed to too much or too little erosion. However, these missing features cover the full range of
shock zonation and depths. It seems implausible
that so few have been found in a structure that is
better exposed in three dimensions than any terrestrial impact structure.
6. We think that the weight of the evidence
strongly favors salt tectonics. Evidence favoring
diapiric pinch-off includes a lack of the following
features associated with hypervelocity impact:
meteoritic material, melt, in situ breccia, shockmetamorphic minerals, outer fault terracing, and
overturned peripheral flap. Conversely, the presence of the following features at Upheaval Dome
all favor diapirism: rim syncline, rim monocline,
steep zones in inner limb of rim syncline, outward-verging extension, radial synformal flaps
(dog tongues), underlying mother salt and nearby
salt structures, multiple episodes of microfracturing and sealing, and postemplacement microfracturing in the clastic dikes. Volume imbalance between uplifted and depressed regions of the dome
indicates massive salt loss of at least 0.4 km3 after deposition of the Chinle Formation.
The most compelling evidence for diapirism in
Upheaval Dome is the wide range of synsedimentary structures spatially restricted to this circular structure. They include angular truncations,
onlap surfaces, channeling, growth faults, growth
folds, shale diapirs, and shifting rim synclines.
These signs of synsedimentary deformation localized around the dome indicate gradual growth
over at least 20 m.y. and exclude the possibility
of geologically instantaneous deformation required by hypervelocity impact.
Geological Society of America Bulletin, December 1998
1571
JACKSON ET AL.
7. Many details of the structural evolution are
speculative because subsurface data are sparse.
We envisage that a passive stock less than 1 km in
diameter and surrounded by a gentle rim syncline
emerged in Pennsylvanian time. The salt remained at or near the surface throughout Permian,
Triassic, and Early Jurassic time. Increasing sedimentary load on the Paradox source layer below
increased the flow rate of salt up the diapir, eventually resulting in extrusion of salt glaciers near
the end of Chinle Formation deposition and during Navajo Sandstone deposition, when a salt
glacier spread to an estimated diameter of 3 km.
8. Growth folds in the lower Wingate Sandstone indicate that the walls of the diapir began to
move inward during Early Jurassic time. We
think that this inward movement was produced
by gravity spreading along an inward-dipping top
salt surface. Spreading culminated in complete
pinch-off of the diapir during deposition of the
Navajo Sandstone. Pinch-off produced constrictional strain and structural thickening in the center of the dome, with concurrent extension
around the dome periphery.
ACKNOWLEDGMENTS
The National Park Service allowed us to map
the dome and sample the clastic dikes. The late
Gene Shoemaker provided stimulating discussions in the field and showed us two examples of
faults (panoramas 4 and 5). Ray Fletcher assisted
with the field work and contributed useful discussion. John Shelton kindly supplied his oblique
aerial photographs of Upheaval Dome. Steve
Laubach led the investigation of quartz microstructure and provided invaluable advice on
microfracturing. Hongxing Ge helped in several
ways, especially in digitizing the geologic and
topographic maps. Joseph Yeh calculated the volumetrics from data digitized by Syed Ali. Illustrations were drawn by us and by Nancy Cottington,
Dick Dillon, Chris Conly, Randy Hitt, and Jana
Robinson. Mark Anders, Dave Bice, Ian Davison,
and Bryan Kriens diligently reviewed the manuscript, and Jay Melosh critically read sections
dealing with impact. The project was funded by
Exxon Production Research and by the Applied
Geodynamics Laboratory consortium, comprising the following oil companies: Agip S.p.A.,
Amoco Production Company, Anadarko Petroleum Corporation, Arco Exploration and Production Technology/Vastar Resources Inc., BHP
Petroleum (Americas) Inc., BP Exploration Inc.,
Chevron Petroleum Technology Company,
Conoco Inc., Société Nationale Elf Aquitaine
Production, Exxon Production Research Company, Louisiana Land and Exploration Company,
Marathon Oil Company, Mobil Research and
Development Corporation, PanCanadian Petro-
1572
leum, Petroleo Brasileiro S. A., Phillips Petroleum Company, Saga Petroleum, Shell Oil, Statoil, Texaco Inc., and Total Minatome Corporation. Permission to publish was granted by the
Director, Bureau of Economic Geology, and by
the management of Exxon Production Research.
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MANUSCRIPT RECEIVED BY THE SOCIETY MARCH 10, 1997
REVISED MANUSCRIPT RECEIVED JANUARY 23, 1998
MANUSCRIPT ACCEPTED MARCH 17, 1998
Printed in U.S.A.
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1573