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ABSTRACT

Upheaval Dome (Canyonlands NationalPark, Utah) is an enigmatic structure previ-ously attributed to underlying salt doming,cryptovolcanic explosion, fluid escape, ormeteoritic impact. We propose that an over-hanging diapir of partly extrusive salt waspinched off from its stem and subsequentlyeroded. Many features support this inference,especially synsedimentary structures that in-dicate Jurassic growth of the dome over atleast 20 m.y. Conversely, evidence favoringother hypotheses seems sparse and equivocal.

In the rim syncline, strata were thinned bycircumferentially striking, low-angle exten-sional faults verging both inward (toward thecenter of the dome) and outward. Near thedome’s core, radial shortening produced con-strictional bulk strain, forming an inward-verging thrust duplex and tight to isoclinal,circumferentially trending folds. Farther in-ward, circumferential shortening predomi-nated: Radially trending growth folds and im-bricate thrusts pass inward into steep clasticdikes in the dome’s core.

We infer that abortive salt glaciers spreadfrom a passive salt stock during Late Triassicand Early Jurassic time. During MiddleJurassic time, the allochthonous salt spreadinto a pancake-shaped glacier inferred to be3 km in diameter. Diapiric pinch-off mayhave involved inward gravitational collapseof the country rocks, which intensely con-stricted the center of the dome. Sediments inthe axial shear zone beneath the glaciersteepened to near vertical. The central uplift

is inferred to be the toe of the convergentgravity spreading system.

INTRODUCTION

Upheaval Dome is located in CanyonlandsNational Park (Island in the Sky district), in thewestern part of the Colorado Plateau, southeast-ern Utah (Fig. 1). The dome is one of the mostenigmatic and controversial geologic structuresin North America. Hypotheses for its origin in-clude cryptovolcanic explosion, meteoritic im-pact, fluid escape, and subsurface salt diapirism.We document here a new explanation for the ori-

gin of Upheaval Dome—the pinched-off salt dia-pir hypothesis.

Upheaval Dome forms a mound that hasstrongly deformed uplifted beds in the center ofthe dome. Strata have been elevated 120–250 mabove their regional levels. Beds near the center ofthe dome are tightly folded and cut by faults hav-ing generally radial strikes. The central upliftpasses outward into a prominent rim syncline, theninto a rim monocline, outside of which strata showmerely gentle regional tilting (Fig. 2). The centerof the dome is a topographic depression eroded350 m below the surrounding escarpment, whichis breached by a canyon cut through its west wall

1547

Structure and evolution of Upheaval Dome: A pinched-off salt diapir

M. P. A. Jackson*D. D. Schultz-Ela

Bureau of Economic Geology, University of Texas, University Station Box X, Austin, Texas 78713

M. R. Hudec†

I. A. Watson Exxon Production Research Company, P.O. Box 2189, Houston, Texas 77252M. L. Porter

GSA Bulletin; December 1998; v. 110; no. 12; p. 1547–1573; 23 figures; 1 table.

*E-mail: [email protected].†Present address: Department of Geology, Baylor

University, Waco, Texas 76798.

Data Repository item 9891 contains additional material related to this article.

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Figure 1. Location map of northern Paradox basin (Utah and Colorado), showing UpheavalDome, known salt structures, and Tertiary intrusions (after Doelling, 1985).

JACKSON ET AL.

1548 Geological Society of America Bulletin, December 1998

(Fig. 3). The dramatic canyon relief and generallysuperb exposures make Upheaval Dome a leadingattraction for tourists and geologists.

Tectonic Setting

In Middle Pennsylvanian time, the Paradoxbasin formed as a northwest-trending forelandbasin to the basement-cored Uncompahgre uplift(Ohlen and McIntyre, 1965), which was thrustover the northeast edge of the basin along the Un-compahgre fault (Fig. 1; Frahme and Vaughn,1983; Ge et al., 1994b; Huffman and Taylor,1994). The deepest part of the trough adjoinedthe Uncompahgre uplift, and the basin thinnedtoward gentle crustal upwarps that bounded thebasin to the south and west. Folding and faulting

accommodated downward bending of the crustinto the axis of the Paradox trough.

Salt accumulated in the deepest part of theParadox basin shortly after the Uncompahgrethrust fault became active. Prograding sedi-ments shed from the Uncompahgre uplift ex-pelled the salt southwestward, forming a seriesof northwest-trending salt walls and anticlines(Baars, 1966; Ge et al., 1994a, 1997). Saltstructures decrease in amplitude and age of ini-tiation away from the Uncompahgre uplift.Truncations and lateral thickness changes indi-cate that diapirs grew mostly during Permiantime, but salt continued to flow until at least100 m.y. ago (Doelling, 1988). Near UpheavalDome, roughly 75 km southwest of the Un-compahgre fault, most salt structures are gentle

anticlines (Fig. 1), but small diapiric stocks arelocally exposed.

The Paradox basin has been affected by at leastthree more tectonic episodes since Late Creta-ceous time. (1) Crustal shortening related to theLaramide orogeny (Late Cretaceous–early Ter-tiary) reactivated the Uncompahgre fault andmay also have reactivated some of the smallerbasement faults within the basin. (2) Oligocenelaccoliths built the La Sal, Abajo, and HenryMountains. (3) The basin may have been slightlystretched in Cenozoic time (Ge and Jackson,1994; Hudec, 1995; Ge et al., 1996). Theseevents had negligible effects on the flat-lyingstrata around Upheaval Dome. Finally, the Col-orado Plateau was greatly uplifted after mid-Miocene time (e.g., Thompson and Zoback,

Figure 2. Structure contour map of Upheaval Dome and surroundings showing the base of the Wingate Sandstone. The circumferential tracesof the rim monocline and rim syncline are shown with dashed lines. L and H refer to structural lows and highs, respectively. The Buck Mesa wellis 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 themap of Huntoon et al. (1982) in the surrounding region. The structural high west of the dome could extend farther north, but the gentle dips therepreclude accurate contouring of the outcrop data.

1979), resulting in at least 1600 m of erosion overUpheaval Dome.

Stratigraphic Setting

The oldest known sedimentary rocks beneathUpheaval Dome are Cambrian-Mississippianclastic and carbonate rocks (Fig. 4). Passive-mar-gin sedimentation in the area ceased with the on-set of Ancestral Rockies deformation and led torestricted-marine conditions in Middle and LatePennsylvanian time. A carbonate shelf rimmedthe basin’s southern and western margins assaline facies accumulated in the axis of the basinnear the Uncompahgre uplift. As much as 2 kmof Paradox Formation evaporites collected here(Hite, 1960) and thin toward the basin margins.Borehole data suggest that roughly 720 m ofevaporites were deposited in the vicinity of Up-heaval Dome (Woodward-Clyde Consultants,1983). The evaporitic facies consist of 70%–90%halite in most places and minor amounts of lime-stone, dolomite, gypsum, anhydrite, black shale,and siltstone.

Restricted marine conditions ended in EarlyPermian time as the Uncompahgre highlands

shed a wedge of marginal marine and continentalclastic sediments (Cutler Group, Fig. 4) south-westward across the basin. In the area of Up-heaval Dome, the Cutler Group comprises threeformations; from bottom to top, these are theCedar Mesa Sandstone Member, the Organ RockMember, and the White Rim Sandstone. Only theupper two units may be exposed in the center ofUpheaval Dome (extreme deformation there hin-ders stratigraphic correlation). The Organ RockMember comprises fluvial dark-reddish-brownsiltstones and mudstones. The overlying WhiteRim Sandstone is a clean white sandstone de-posited in coastal eolian environments (Steele,1987). Sandwiched between finer-grained units,the resistant White Rim Sandstone weathers intoprominent ledges and benches. A major hiatus(TR-1 from 264 to 247 Ma) followed depositionof the White Rim Sandstone.

The Moenkopi Formation (Fig. 4) records a ma-rine transgression from the west that created a va-riety of fluvial to shallow-marine environmentsdominated by fine-grained sediments (O’Sullivanand MacLachlan, 1975; Molenaar, 1981). To mapthe center of Upheaval Dome, we divided theMoenkopi Formation into three informal units,

which are strata-parallel and continue at least 10km from the dome margins in basins to the southand west. The lower Moenkopi siltstone weathersbrownish-red to grayish-red. The lithologic varia-tion and weathering character define structureswell. The middle Moenkopi Formation comprisesreddish shale containing layers of fine-grained,yellow, flaggy, calcareous sandstone. This mem-ber separates the lower reddish Moenkopi memberfrom the upper Moenkopi siltstones that weatherto buff-gray or olive-gray featureless masses.

After another major hiatus (TR-3 from 240 to227 Ma) in Late Triassic time, the continentalChinle Formation (Fig. 4) spread across the top ofthe Uncompahgre uplift, eliminating the Paradoxbasin as a physiographic feature. We divided theChinle Formation into four map units, from bot-tom to top, (1) basal Moss Back Member sand-stone and conglomerate, which generally crop outas prominent gray ledges or dip slopes; (2) Petri-fied Forest and Church Rock Member shales (la-beled “Lower Chinle” in subsequent figures),which weather gray, blue-gray, or lavender, as dis-tinct from the yellowish-gray upper Moenkopishales; (3) another prominent sandstone aboutone-third up from the Chinle Formation base; thisfiner-matrix pebble conglomerate is probably theBlack Ledge sandstone of the Church Rock Mem-ber (Stewart et al., 1959); (4) shale and siltstoneweathering brick, brown, or orange-red are inter-preted to be the upper part of the Church RockMember (combined with the Black Ledge mem-ber as “Upper Chinle” in subsequent figures).

After a brief hiatus (J-0, from 210 to 206 Ma),sedimentation remained continental, with deposi-tion of the Jurassic Wingate Sandstone, a wet erg(the lower Wingate strata representing central ergfacies, and the upper Wingate strata representingdistal, less arid, back erg facies containing silty in-terbeds). The mainly fluvial Kayenta Formationand the dry erg Navajo Sandstone then accumu-lated. The Jurassic Navajo Sandstone is the high-est stratigraphic level exposed in Upheaval Dome.Using regional thicknesses of higher units derivedfrom the Book Cliffs area to the north (Molenaar,1981), we estimate that an additional 1600 to2200 m of section were deposited above thedome. That upper limit corresponds with thethickness of missing strata required to encase thecurrently unroofed La Sal laccoliths intruded inmiddle Cenozoic time some 55 km east of Up-heaval Dome. These Cretaceous and Tertiaryunits were eroded during Miocene–Holocene up-lift 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-

STRUCTURE AND EVOLUTION OF UPHEAVAL DOME

Geological Society of America Bulletin, December 1998 1549

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 TrailCanyon. The rim syncline passes through the Navajo Sandstone in the far wall of alcove D. Photograph by John S. Shelton.

cause of unloading produced by canyon erosionin a former meander in the Green River. Weknow 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 constric-tion rather than lateral extension in the domecenter (presented in the following), we rejectthe notion of a buried salt dome below Up-heaval Dome. Moreover, a preliminary reportby Louie et al. (1995) concluded from a seismicrefraction line across the dome that there is nolarge salt plug near the surface. Similarly, col-lapse due to salt dissolution, as envisaged byStokes (1948), is equally implausible becausestrata in the center of the dome rise more than100 m above their regional elevation (Fig. 2).

Bucher (1936) noted similarities between thestructures at Upheaval Dome and the SteinheimBasin, Germany, and proposed that UpheavalDome was cryptovolcanic. Structures in the cen-tral depression were interpreted to be a result of ex-plosive release of gases trapped near a shallow ig-neous intrusion. No igneous rocks have beenfound within 55 km of the dome center, althoughgeophysical anomalies (described in the follow-ing) around Upheaval Dome suggest that igneousrocks may underlie the Paradox salt. Kopf (1982)also interpreted deformation in the dome center toresult from sudden upward release of a fluid slurrytectonically overpressured by a deep fault system.

Boone and Albritton (1938) were the first tosuggest that Upheaval Dome might have beenproduced by meteoritic impact. They noted thatUpheaval Dome contained many features typicalof impact, including circular shape, central dome,peripheral folds, radial faults, and intense defor-mation. Shoemaker and Herkenhoff (1983, 1984)and Shoemaker et al. (1993) argued, for similarreasons, that there was an impact in Late Creta-ceous or Paleogene time (Fig. 5A). They inter-preted the thinning of Mesozoic strata observedby McKnight (1940) and Fiero (1958) to be dueto normal faulting rather than depositional onlap.They explained the lack of primary physical evi-dence for impact by suggesting that the crater andmuch of its floor had been deeply eroded. Krienset al. (1997) interpreted a lag deposit of erodedcobbles as impactite ejecta indicating that Up-heaval Dome formed possibly as late as a fewmillion years ago. Huntoon and Shoemaker(1995) proposed impact as the cause of Robertsrift, a breccia-filled fissure 10 km long locatedmore than 20 km away from the dome.

We present a new alternative to the impact hy-potheses. We propose that the structural and strati-graphic relations at Upheaval Dome—especiallythose indicating protracted growth of the struc-ture—can best be explained as the result of stempinch-off below an overhanging diapiric salt ex-

trusion (Fig. 5B; Schultz-Ela et al., 1994a, 1994b).The central part of the structure contains overbur-den strata pinched in around what we infer to bethe necked-off stem of a broadly overhanging,partly extrusive pancake of salt that was subse-quently removed by erosion. Pinched-off diapirsare common below the sea floor in the Gulf ofMexico and in other salt basins (e.g., Jackson et al., 1995), but their stems are difficult to imagewith seismic data because of the steep stratal dips,

large lateral variations in seismic velocity, andstructural complexity. To our knowledge, no stemsof entirely pinched-off diapirs are exposed at thesurface, except where greatly squeezed by oro-genic contraction. If our hypothesis is correct, thesuperb three-dimensional exposure and accessibil-ity of Upheaval Dome make it a prime candidateto examine the response of country rock to thenecking and pinching off of a diapir in an area rel-atively unaffected by orogeny.

JACKSON ET AL.


Figure 4. Stratigraphic section through formations at or below the surface of Upheaval Domeand younger eroded units. Data from the Buck Mesa #1 well log, Fiero (1958), Mattox (1968),and Woodward-Clyde Consultants (1983).


Present topography

Maximum possiblesediment thickness

Transient craterfloor

Lower boundary of in-situ brecciaInward-vergingthrust faults

Airfall breccia

Mixed brecciaCentral uplift Fault terraces

Overturned flapEjecta

Inward-vergingnormal faults

Figure 5. Schematic illustrations of hypotheses for meteoritic impact and salt dome pinch-off for the evolution of Upheaval Dome. (A) Impacthypothesis 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 di-apiric pinch-off inferred in the text.

Before pinch-off After pinch-off

Rimsyncline

Rimsyncline

Mapview

beneathsalt extrusion

Crosssection

Representativethrust wedge

Salt extrusion

Futurefaults

B


CIRCUMFERENTIAL FOLD SYSTEM

The geology of Upheaval Dome is shown inmaps (Figs. 6, 7, and 8) and two cross sections. Aconventional linear section trends roughly west-northwest across the entire dome and its sur-roundings (Fig. 15), and a circular section encir-cles the dome core to illustrate the roughly radialstructures there (Fig. 16).

The largest and most continuous structures inUpheaval Dome are three circular folds having ax-ial traces concentric about the core of the dome(Figs. 6 and 8). From the surrounding undeformedstrata toward the core of the dome, this circumfer-ential fold system comprises an outer rim mono-cline, a rim syncline, and an inner dome. In thestructural descriptions that follow, “inward-out-

ward” and “inside-outside” are relative to the cen-ter of Upheaval Dome. “Circumferential” is a syn-onym for the concentric or tangential direction.

The rim monocline defines the perimeter ofUpheaval Dome, separating the regional homo-cline from the rim syncline (Fig. 2). The rimmonocline trace is mostly outside the mesa con-taining the dome center (Fig. 6). The monoclinalbend is broad and gentle where it involves mas-sive Wingate Sandstone (northwest of the dome).Conversely, the monocline is a sharp kink whereit is defined by thinly interbedded Chinle clasticrocks (east of the dome).

Inward from the rim monocline, stratal dipsmeasured increase to a mean of 15°–20° and amaximum of 73° then decrease to zero as strataflatten in the floor of the rim syncline. Most of the

Navajo Sandstone—the youngest unit present—ispreserved within this syncline (Fig. 6). NavajoSandstone dip slopes define most of the rim syn-cline, but several erosional alcoves expose crosssections through the fold (Figs. 3 and 6).

Successively older units crop out toward thecore of Upheaval Dome (Fig. 6). Stratal dips be-come subvertical to overturned in the central up-lift; there, Moenkopi strata have been elevatedperhaps as much as 250 m above their regionaldatum outside the rim monocline, and surround-ing Wingate strata have been lifted 120 m. Theinward increase in dip is disrupted in two con-centric zones of steep dip, separated by zones ofgentle dip. A discontinuously preserved, innersteep zone 0.7–0.8 km from the dome center af-fects the upper Wingate Sandstone and lower

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Kayenta Formation (described in Inner Contrac-tional Systems section). A virtually continuousouter steep zone 1.2–1.6 km from the dome cen-ter affects the inner margin of the lower NavajoSandstone. There, dips steepen markedly from20°–30° to 40° and commonly higher (Fig. 8).Bounding surfaces of dune-scale Navajo Sand-stone cross beds become vertical to overturnedlocally (e.g., near the Syncline Loop Trail in thesouthwest). Southeast of the dome, at WhaleRock, the innermost Navajo strata dip steepens toa subvertical attitude within ~100 m of the innerNavajo contact (Fig. 9). Inward from the verti-cal Navajo strata, however, dips in the basalNavajo and underlying Kayenta strata flatten(around 40°).

The circumferential fold system of UpheavalDome perturbs a regional homocline dipping1.2° to the north-northwest. This homocline

forms the southern limb of the gentle Grays Pas-ture syncline (Huntoon, 1988). In the rim syn-cline is a crescentic low (Fig. 2), which is a typi-cal fold interference pattern where a rim synclineis superposed on a regional homocline (Ritz,1936). Two structural highs (stippled) are pre-sent: one is the inner circular dome describedabove; the other is a low, elongated periclinaldome adjoining the western flank of UpheavalDome, also noted by Fiero (1958).

SYNSEDIMENTARY STRUCTURES

A wide variety of synsedimentary features arepresent in Upheaval Dome but have not been ob-served elsewhere in the region. These featuresprovide evidence for deformation of UpheavalDome over at least 20 m.y., during deposition ofthe Chinle, Wingate, and Kayenta Formations

(Fig. 4). Deeper stratigraphic units (Moenkopiand Cutler Formations) are exposed only in thecore of the dome, where they are too deformed toreveal lateral stratigraphic variations. The uppercontact of the highest unit in the dome (NavajoSandstone) is not exposed and is generally toomassive and coated with desert varnish to exposelarge-scale internal geometries. Thus, althoughwe describe evidence of synsedimentary defor-mation for only three units, we do not exclude thepossibility of similar features in other formations.

Deformation During Deposition of the Chinle Formation

The upper Chinle Formation contains angulardiscordances of as much as 27° in alcoves B, C,and D on the east of the dome (Fig. 6), in the ex-treme south, and in Syncline Valley in the north-

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.

JACKSON ET AL.


west. If the truncating surfaces are restored tohorizontal, truncated strata dip consistently out-ward from the dome. This apparent radial sym-metry eliminates regional tilting as the cause. Be-cause of poor exposure, we cannot determine theorigin of all the observed truncations. If they areprimary, the truncated strata may have been fore-sets deposited by rivers draining outward from agentle dome. Alternatively, erosion may have cutacross gently domed strata. Either way, the trun-cations suggest doming late in the time of ChinleFormation deposition. These truncations are be-low the commonly discordant, faulted base of theWingate Sandstone.

Deformation During Deposition of the Wingate Sandstone

Wingate Internal Diastems. Panorama 9(Fig. 15, A and B), west of the Holeman Springsalcove, extends from outside the rim monoclineto the rim syncline. Here, the Wingate Sandstonethickens from ~50 m on the west edge of the pro-file to more than 75 m to the east. No faults offsetcontinuously traceable bedding in the top andbottom of the Wingate Sandstone. Instead, thethickness changes by a combination of onlapagainst the base of the Wingate strata and trunca-tion beneath a correlatable mid-Wingate surface.From a uniform thickness outside the rim mono-cline in the west, the Wingate Sandstone gradu-ally thins inward toward the center of the profileby excision of ~20 m of section beneath the mid-Wingate erosional truncation surface. From theother end of the section, the Wingate Sandstonealso thins westward because ~40 m of lowermostWingate strata onlap against the top of the ChinleFormation (the J-0 unconformity of Pipiringosand O’Sullivan, 1978).

Figure 11C is a schematic reconstruction ofthe inferred deformation. Stage 1 shows thelower Wingate strata thickening inward (right-ward) from point A, which we interpret as themargin of the shifting peripheral sink around thedome. Stage 2 shows a bulge forming in thelower Wingate strata over the flexed margin ofthe sink. The uplifted crest of the bulge betweenpoints C and D is then eroded. Truncations on theeastern (inward) limb of the eroded bulge are notvisible in this panorama, but are exposed farthereast in the Holeman Springs alcove. Stage 3shows deposition of the upper Wingate Sand-stone across the erosional surface.

Wingate Sandstone Growth Folds.WingateSandstone cliffs ring the depression eroded intothe center of Upheaval Dome. In these cliffs, thebasal Wingate Sandstone contact is deformedinto a train of prominent, mostly upright folds(Fig. 12), as noted by others (Shoemaker, 1954;Fiero, 1958; Mattox, 1968; Shoemaker and

Herkenhoff, 1983, 1984). They are best exposedon the northeast and southwest walls of the inte-rior depression (Figs. 6 and 8). Fiero (1958) as-serted that the fold axes parallel the dominantjoint system, and that slip on closely spacedjoint planes caused the folding, whereas otherworkers 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 limitedexposure in the third dimension and their distri-bution around most of the inner cliffs except forUpheaval Canyon, we conclude that these foldstrend radially and probably plunge outward.

The folds seem to have formed by circumfer-ential shortening of the basal Wingate Sandstone(see section on Inner Contractional Systems).Spacing between the antiforms generally rangesfrom 150 to 190 m. Given a typical WingateSandstone undeformed thickness of about 100 m,the wavelength to thickness ratio of these folds isfar smaller than values observed elsewhere in na-ture, theory, or experiment for a vast variety oflayer and matrix properties (reviewed by Priceand Cosgrove, 1990). Accordingly, it is improba-ble that the Wingate Sandstone buckled as a sin-gle layer of massive, lithified sandstone.

Further evidence corroborates the unusualfolding behavior of the Wingate Sandstone. Thetop contact of the Wingate Sandstone is alsofolded, but not in harmony with the bottom con-tact. The folds visible within the formation are also disharmonic with regard to the top andbottom contacts.

In the northeast wall of the interior depressionare the two best-exposed radial folds deformingthe base of the Wingate Sandstone. There, lowerWingate strata thin upward over the antiformsand thicken above the adjacent synforms, indica-tive of growth folds (Fig. 12).

These data suggest that folding began duringWingate Sandstone deposition, when the sands

were unlithified. Kriens et al. (1997, p. 23) con-cluded that local deformation of the WingateSandstone may have been due to “the presence offluids and/or a low degree of lithification,” re-sembling “soft-sediment landslides.”

Deformation During Deposition of the Kayenta Formation

Basal Kayenta Channels.Detachment faults(described in the section on Outer ExtensionalSystems) transect or follow much of the Wingate-Kayenta formation contact, which creates an ir-regular, wavy surface. However, this contact isalso wavy because Kayenta formation fluvialsand channels to 5–6 m deep were eroded into thetop of the Wingate back erg dunes and interdunes.Away from each channel, the sand packages thin,pinch out, and grade into shale drapes above ad-joining paleohighs. These large channels and pa-leohighs are well exposed in panoramas 9 (Fig.11) and 12 (Fig. 14). In panorama 9, the upperWingate contact is fairly smooth outside the rimmonocline of Upheaval Dome but deeply chan-neled inside the monocline, indicating that chan-neling was enhanced by increased fluvial gradi-ents related to deepening of the rim syncline at thestart of deposition of the Kayenta Formation.

Kayenta Formation Internal Diastems andInferred Shifting Rim Synclines. Repeatedand variable tilting is indicated by boundingsurfaces at the base of and within the KayentaFormation in spurs south of Upheaval Canyonnear the present axis of the rim syncline(panoramas 12–14; Figs. 13 and 14). These sur-faces divide the Kayenta Formation into lower,middle, and upper packages.

The lowest truncation surface, EB0, is the ero-sional base of the Kayenta Formation referred toin the preceding section. The truncation sense in-dicates that upper Wingate strata were tilted in-ward before they were obliquely planed off as

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 thewithdrawal syncline. This steepening is interpreted as due to the overriding front of a spread-ing salt glacier.

lower Kayenta strata began to accumulate(panorama 14 and Fig. 16, early Kayenta). Thenext-higher diastem, the intra-Kayenta EB1(panorama 13), also cuts downsection outward.The EB1 truncation surface is the base of an ero-sional channel complex and is marked by a chan-nel sandstone. This sense of truncation for boththe EB0 and EB1 surfaces suggests that subsi-dence was localized inboard (eastward) of theend of panorama 13 during deposition of thelower Kayenta Formation (Fig. 10, mid–earlyKayenta).

The upper truncation surface (EB2, panorama14 and Fig. 10, mid-Kayenta) cuts downsectioninward, opposite to the truncation sense of EB0and EB1. The EB2 surface is exposed in severalridges on both sides of Upheaval Canyon and ismarked by a pale, upward-fining sandy bar thattoplaps meter-scale foresets. The EB2 surface isthe preserved erosional base of an upper KayentaFormation channel-fill complex overlying a ge-netically unrelated middle Kayenta Formationchannel-fill complex. Both complexes are sand-prone, but comparison of cross-stratal styles, pa-leocurrents, and set thicknesses suggests that adiastem exists between the two fluvial packages.During the diastem, beds in the lower packagewere tilted outward by as much as 20°, thenplaned off. That indicates that strata outboard ofpanorama 14 were subsiding during depositionof the middle Kayenta Formation, very different

from the site of early Kayenta Formation subsid-ence (Fig. 10).

Onlapping the EB2 truncation surface in theupper Kayenta Formation on panorama 12,four flat-topped fluvial channel complexeswere stacked imbricately as they migrated out-ward (Fig. 10, end Kayenta). That geometry in-dicates creation of accommodation space bygradual subsidence of a truncation surfacetilted inward as part of the rim syncline. Late inthe time of Kayenta Formation deposition,therefore, the rim syncline had already mi-grated inward to its present position (Fig. 10D),widening or renewed outward shift of the rimsyncline during deposition of the four channelcomplexes followed.

The simplest explanation for these shiftinglocations is that the rim syncline migrated asUpheaval Dome evolved over a lengthy period(Fig. 10). These shifting depocenters are typicalof salt tectonics, where lateral salt flow andsedimentary accommodation space are inti-mately linked.

Kayenta Growth Faults. Incomplete evi-dence suggests that many of the normal faultsoffsetting Wingate and Kayenta strata (de-scribed in the next section) may be the age ofthe Kayenta Formation. Several faults die outupward into the Kayenta Formation, and faultsoffsetting the Navajo Sandstone base are rare(we saw only one, at the west end of Syncline

Butte). This scarcity is partly because manyKayenta faults are cut by the present-day ero-sional surface before reaching the NavajoSandstone. However, in the few places thatNavajo Sandstone erosional remnants still restacross faulted strata (e.g., north side of alcoveB), the well-bedded Navajo basal strata are un-faulted. Another explanation for the upward ter-mination of faults within the Kayenta Forma-tion is that the faults could dissipate upwardamong many small slip surfaces within theKayenta strata. However, in widespread areaswhere the Kayenta Formation is well exposed,we see no evidence for such upward splaying offaults. Instead, the Kayenta faults die out up-ward with an abruptness typical of growthfaults. For example, stratigraphic separations infaults at the base of the Kayenta Formation areas follows: 30 m of separation dying out 20 mabove (panorama 14); 25 m of separation dyingout 20 m above (panorama 12). This upwarddecrease of throw is accommodated by 25–30 m of stratigraphic thickening of the lowerKayenta Formation in the hanging wall of thefault. We have not correlated meter-scale indi-vidual packages across faults to confirm thick-ening by growth faulting, but the impression ofsyndepositional faulting on several panoramasis striking.

OUTER EXTENSIONAL SYSTEMS

McKnight (1940) and Fiero (1958) both de-scribed major thickness variations in the WingateSandstone and Kayenta Formation within the rimsyncline of Upheaval Dome. Some variations areproduced by the stratigraphic variations de-scribed here. However, as noted by Shoemakerand Herkenhoff (1984), most thinning is due toslip on ramp-flat extensional faults surroundingthe dome. All these circumferential faults are ex-posed only inside the trace of the rim monocline,and so are inferred to be related to the formationof Upheaval Dome. Figures 14, 17, and 19 illus-trate the structural style of these faults (pano-ramas 4 and 5 in Fig. 17).

Three-dimensional exposures reveal the fol-lowing characteristics. The faults are either sim-ple listric faults or a series of ramps and flats.Even the ramps are low-angle faults, cutting bed-ding at a mean apparent angle of ~13° and rang-ing from 9° to 25° (standard deviation). Very lo-cally, however, ramp dips are near vertical overshort segments. The flats form detachmentsmostly at the base of the Kayenta Formation orWingate Sandstone. Extensional ramps betweenthese two levels are responsible for thinning theWingate Sandstone (panoramas 2, 4, 5, 6, 11, and14 in Figs. 14 and 17). Less commonly, rampsthin the Kayenta Formation as well (panorama 3,



Figure 10. Schematic restoration of the intra-Kayenta Formation geometries exposed in spurssouth of Upheaval Canyon. The changing patterns of subsidence and tilting suggest syndeposi-tional deformation, which we ascribe to the shifting peripheral sinks during diapiric growth.


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Figure 11. (A) Panorama 9 traced from photographs of Holeman Spring alcove and adjoining exposures farther west on the south side of Up-heaval Dome. Panorama location and view direction are shown in Figure 6. (C) Schematic reconstruction of synsedimentary deformation of theWingate Sandstone in panorama 9, exaggerated vertically by 2×.

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Fig. 17). In addition, local flats are commonwithin the Kayenta Formation and rare in the mid-dle Wingate Sandstone. Measurements from pho-tographs of oblique sections through exposedfaults offsetting the base of the Kayenta Forma-tion provide rough separations for the largest faultin each panorama. For the outward-verging faults,the mean stratigraphic separation is 35 ± 15 m,and the mean apparent slip is 120 ± 55 m (stand-ard deviation). For the inward-verging faults, the

mean stratigraphic separation is 25 ± 11 m, andthe mean apparent slip is 98 ± 24 m.

What was the effect of these faults on tectonictransport? Shoemaker and Herkenhoff’s (1984)schematic section portrays inward-dipping listricfaults linking with outward-dipping thrust sys-tems in the core of the dome (Fig. 5A). That link-age would transport rock inward to the core of the dome.

Our mapping confirms the existence of the in-

ward-dipping extensional fault systems but re-veals that they are only half of the extensionalpicture. As summarized in Figure 8, an equalnumber of extensional faults dip outward. As agroup, their abundance, lengths, and stratigraphicseparations are similar to the inward-dippingfaults. The outward-dipping faults cannot belinked with the inner thrust faults in the manneradvocated by Shoemaker and Herkenhoff (1983,1984). Most normal faults in the northern half of

JACKSON ET AL.


Figure 11. (B) Photograph of a similar viewto that in A; on the far right is the eastern por-tal of the alcove.

Figure 12. Northward view of radial growthfolds in the lower Wingate Sandstone in thenortheast cliffs of the inner depression. Thelowermost Wingate strata are isopachous andare interpreted to be prekinematic. Abovehere, strata thin over the antiform and thickenin the synform, indicating growth of the foldearly during deposition of the Wingate Sand-stone. The growth-wedge taper is extreme(~15°) on the right limb of the antiform butmuch less on the left limb; we interpret this asan initially asymmetric fold verging to theright. After a period of stability, indicated byoverlying isopachous units, the fold was tight-ened further into a symmetric fold late inWingate Sandstone deposition.

Figure 13. Photograph southwest acrossUpheaval Canyon showing truncation surfacesof variable dip within the Kayenta Formation.The view superimposes one spur (panorama14) on another (panorama 12) immediately tothe southwest. Compare with Figures 14 and17. Navajo Sandstone on Syncline Butte formsthe foremost skyline, behind which are flat-ly-ing strata outside the rim monocline and, justvisible, the snow-capped peaks of the HenryMountains laccoliths.

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Figure 14. Panoramas (Pan) traced from photographs of outward-verging extensional fault systems encircling Upheaval Dome. Panorama lo-cations and view directions are shown in Figure 6. The view directions of panoramas 2 and 13 have been reversed (“mirrored”) from the actualview 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 Sand-stone. C1 through C5 are channels. Scales are approximate because of perspective.



the dome transported rock outward, whereasmost normal faults in the southern half trans-ported rock inward. This is true whether the faultsare exposed inside or outside the trace of the pre-sent rim syncline.

INNER CONTRACTIONAL SYSTEMS

Contractional structures dominate the centerof Upheaval Dome (Fig. 7). Shoemaker andHerkenhoff (1984) inferred “convergent dis-placement” of rocks. We agree and recognizeboth radial and circumferential shortening, whichwas volumetrically balanced by vertical exten-sion. This bulk constriction is expressed by a dif-ferent structural style in each formation, de-scribed in the following in order of increasingproximity to the dome’s center.

Kayenta Fold-and-Thrust Belt

As noted by Shoemaker and Herkenhoff(1984), stratigraphic repetition due to thrusting ac-counts for the anomalously thick outcrop belt ofthe Kayenta Formation (Figs. 6, 15, and 19). TheKayenta Formation appears to be folded andfaulted everywhere in its outcrop belt between theinner Navajo Sandstone and Wingate Sandstonecliffs. As in the outer extensional systems, litho-logic variations in the fluvially deposited KayentaFormation caused faults to form ramps and flats.The typically lenticular depositional units resem-ble the anastomosing fault-bounded bodies, mak-ing faults difficult to recognize. However, the de-tails of these structures are spectacularly exposedwhere Upheaval Canyon cuts a radial section (Fig.19). From photogeology we infer that this exposed

section typifies deformation elsewhere in the con-tracted Kayenta Formation.

In Upheaval Canyon, ramp-flat thrust faults inthe Kayenta Formation form a thrust duplex. Thefloor thrust of the duplex detached along thelower Kayenta Formation contact; the roof thrust(poorly exposed and conjectural) is near the topof the formation (Figs. 15 and 19). Fault spacingdecreases and folding associated with the faultingincreases inward. Some thrust faults show nor-mal separation over parts of their trajectories,particularly those that continue downward intothe Wingate Sandstone near the rim syncline(Fig. 19B, center), suggesting that the lower partsof the faults had multiple displacement histories.

The thrust duplex in the Kayenta Formationappears to accommodate much more shorteningthan in the underlying Wingate and overlying

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Figure 15. Linear cross section across Upheaval Dome and surroundings as inferred from surface exposures and projection from the BuckMesa well. Trace of section is shown in Figures 6 and 7 (ends of the section project beyond the maps). Geology inboard (east) of northwest WingateSandstone cliff (gray in section) was projected from the cliff and slope exposures just north of the section line. Contacts and faults are dashed be-yond the zone of direct projection from the surface. Dotted lines show bedding traces within units. Figure 26 shows the inferred geometry of deepunits, including the Paradox salt.

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JACKSON ET AL.


Navajo Sandstones. That anomaly is explicable ifthe duplex formed mainly by shear due to flex-ural slip between the adjoining massive sand-stones as they folded. Tanner (1992) describedsmaller versions of such duplexes, which formedon the limbs of larger chevron folds (Fig. 19B, in-set); his duplexes have smooth roofs, no hanging-wall anticlines above each link thrust, and rela-tively small fault offsets. The roof and floorthrusts may both continue beyond the flexural-slip duplex. This type of duplex evolves wherethrust propagation was resisted by facies or thick-ness changes, or by transfer zones between faultspropagating on different movement horizons(Cruikshank et al., 1991). Thus, the Kayentathrust duplex may be caused as much by upwardflexure of the layered succession as by inwardcontraction.

Wingate Structures

Both radially and circumferentially trendingfolds have been mapped in the Wingate Sand-stone cliffs facing the central depression. The ra-dially trending antiforms distort the basal WingateSandstone contact (Figs. 12 and 20) and indicatecircumferential shortening. Most intervening ra-dial synforms have been eroded back to the sameencircling cliff as the radial antiforms and arepartly hidden by talus (Figs. 8 and 20B). A few ra-dial synforms are less eroded and retain a com-plex three-dimensional curvature. For brevity, weinformally refer to these doubly curved synformalradial lobes as “dog tongues” (name suggested byRudy Kopf, 1992, personal commun.).

The dog tongues preserve the lowest and mostinward exposures of the Wingate Sandstone

(Figs. 8 and 15). The most complete dog tongue isin the northeast corner of the Wingate Sandstonecliffs. Synformal Wingate strata there dip inwardto levels far below the contact with the ChinleFormation on either side of the lobe. The radialaxis of the dog tongue forms a trough borderedby radial antiforms. Farther inward, the sameWingate strata reverse steeply upward along acircumferential fold axis, like the upward-curledtip of a tongue (Fig. 20C).

Wingate strata in the tip of the best-exposed dogtongue appear to onlap the basal Wingate Sand-stone contact (Fig. 20C). The basal Wingate Sand-stone contact in the dog tongues is also discordantto Chinle Formation bedding (Fig. 20C) and to abedding-parallel cleavage in folded Chinle Forma-tion siltstone and shale. The contact is typicallymarked by rubble. We interpret this doubly discor-

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dant contact as a salt weld (see reconstruction sec-tion following). Just below the folds, the ChinleFormation 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 up-right, nearly isoclinal folds that trend circumfer-entially (Fig. 20C) and are cut by steep reversefaults. Such folds are well exposed on the easternside of the central depression near the inner edge

of Wingate Sandstone exposures (Figs. 20B and21). These folds do not appear to affect the spo-radically exposed basal Wingate Sandstone con-tact. Dips in much of the lower Wingate Sand-stone and upper Chinle Formation are typically

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Figure 17. Panoramas (Pan) traced from photographs of inward-verging extensional fault systems encircling Upheaval Dome. Panorama lo-cations and view directions are shown in Figure 6. The view direction of panoramas marked “mirrored” have been reversed from the actual viewso that the inward direction is consistent throughout the figure. Scales are approximate because of perspective.

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much less than the subvertical orientations ob-served in the upper Wingate Sandstone. As withthe radial antiforms and synforms described here,it is difficult to envision a well-lithified WingateSandstone folding internally in this extreme,strongly discordant manner.

Compared with the intensely faulted KayentaFormation, few visible faults cut the underlyingWingate Sandstone. The Wingate faults strikeradially and dip steeply (Fig. 8). They tend to cutthrough the radial antiforms and along theboundaries of the dog tongues. The radial faultscan be traced outward into the Kayenta Forma-tion, where they commonly curve into oblique orcircumferential orientations.

Deformation along the inner Wingate Sand-stone cliffs thus indicates both radial and circum-ferential shortening induced by radially inwardmovement. Farther inward, the circumferentialshortening in the older exposed units dominatesthe strain, as described in the following.

Chinle Deformation in Central Depression

Most of the Chinle Formation in the inner de-pression crops out on inward-facing slopes belowthe Wingate Sandstone cliffs (Fig. 6). The slopesare largely covered with talus exposing only smallwindows of the Chinle Formation. The resistantMoss Back Member (basal Chinle) and BlackLedge (mid-Chinle) sandy conglomerates cropout as ledges typically segmented by thrusts andreverse faults. Because most of the Chinle Forma-tion shales are weathered or covered, their inter-nal structure is poorly known. However, structuralvariation increases toward the center of the inte-rior depression from the relatively uniform out-ward dips below the Wingate Sandstone cliffs(Fig. 7). The innermost outcrops of the ChinleFormation are folded and faulted similarly to theunderlying Moenkopi Formation.

Central Moenkopi Formation Constriction

The Moenkopi Formation occupies most of thedome’s core. Structures are expressed well inbare, rugged terrane by variations in color andlithology (Fig. 7). The Moenkopi Formation inthe central uplift was radially and circumferen-tially shortened. A linear cross section (Fig. 15)captures structures with circumferential strikes,whereas a subcircular section (Fig. 16) crossessubradial strikes. Attitudes vary greatly over shortdistances, and structures tend to be irregular anddiscontinuous. The Moenkopi Formation out-crops can be divided into two sectors having dif-ferent structural styles: converging radial thrustsin the southwest half, and more circumferentiallyoriented folds and thrusts in the northeast half.

The southwestern zone of steep radial thrusts

has the most regular structure of the interior de-pression. The hanging walls moved in a counter-clockwise direction and imbricated the clockwise-dipping Moenkopi strata (Figs. 7 and 16). We likenthat movement to the closing of the leaves of acamera diaphragm, where circumferential short-ening increases inward. No marker lines are avail-able to determine the strike component of slip onthese thrusts. The left-lateral separation may havebeen derived all or in part from dip slip. Two ofthese thrusts continue outward as steep faults cut-ting upward through the Wingate Sandstone. To-ward the center, the thrusts merge, die out, lose de-finition where parallel lower Moenkopi strata areon both sides, or continue as clastic dikes.

The regular radial thrusts in the southwestgrade into highly variable structures in the north-eastern half of the interior depression. Structuresshow more local variation, including small folds,short faults, and abrupt attitude changes that re-sult in complex, extremely detailed outcrop pat-terns rather than the radial stripes exposed to thesouthwest (Fig. 22). Thrusts vary in strike andvergence. Folds are common and rarely cylindri-cal, varying from conical to irregular, and gener-ally persist less than 100 m.

Although the structural pattern in the northeastdefies simple characterization, the overall strainremains constrictional, as shown by subhorizon-tal radial and circumferential shortening and sub-vertical extension indicated by the presence ofthe central uplift. Crowding from inward move-ment of the rocks caused the constriction. Thecomplexity and intensity of the central deforma-tion, which has obscured large-scale synsedi-mentary structures, preclude detailed reconstruc-tion of the inner deformation history.

Dome Center and Clastic Dikes

Clastic dikes are abundant in the center of Up-heaval Dome. The dikes are composed of clean

white sandstone, presumably derived from the un-derlying White Rim Sandstone of the CutlerGroup. Other authors have described the WhiteRim outcrops as coherently emplaced blocks(McKnight, 1940; Mattox, 1968). However, themain lenticular dikes anastomose, branch intoveins, and are discordant with country rock. Allthese features indicate that the dikes are intrusive,as inferred by Fiero (1958), Shoemaker andHerkenhoff (1984), and Kriens et al. (1997). Inplaces, the sandstone is laminated but is generallymassive. The dike thickness is generally less than15 m but as much as 30 m. Lengths are typicallyless than 70 m, but the long dike complex in thecenter extends more than 400 m. In addition,more-isolated clastic quartzose dikes of unknownsource are exposed as far out as the outer part ofthe thrust duplex in the southern wall of UpheavalCanyon. Some clastic dikes are sourced by theMoss Back Member conglomerate (D. Bice,1997, personal commun.).

We infer that some of these steep dikes wereemplaced along faults. In some places, faults vis-ibly connect with the ends of the dikes. Else-where, the same rock type is on either side of thedike such that an aligned fault would be obscure(Fig. 7). Most dikes intrude the lower MoenkopiFormation, but extend upward into the middleand upper Moenkopi Formation in their northernoutcrops. Quartz cementation makes the dikesmuch more resistant than the surrounding rocks,and they form towering spires and irregular wallsin the center of Upheaval Dome.

The microstructure of the clastic dikes is de-scribed and discussed in Part 3 (Data Repositoryitem 9891)1 but can be summarized as follows.Our nine thin sections contained abundant mi-

JACKSON ET AL.


1GSA Data Repository item 9891, supplementaldata, is available on request from Documents Secretary,GSA, P.O. Box 9140, Boulder, CO 80301. E-mail:[email protected].

Figure 17. (Continued).

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crofractures, typically masked by recementationof authigenic quartz between and in optical con-tinuity with the shards. Some microfractures aretransgranular and radiating; they must haveformed by cataclasis after or during a late stage ofdike injection. Electron beam-induced cathodo-luminescence of our Upheaval Dome sample re-veals that the quartz undulatory extinction iscaused by slightly misoriented grain fragmentsseparated by microfractures sealed with cement.Cross-cutting quartz veinlets provide evidencefor at least two events of alternating fracturingand diagenesis. Multiple deformation is consist-ent with episodic faulting during diapiric pinch-off but not with the instantaneous deformation in-duced by an impact.

The intruded lower Moenkopi Formation inthe center dips steeply or is overturned. Stratalstrikes are grossly similar to those of nearbydikes, but discordances are common. Attitudesin the Moenkopi Formation can vary abruptlyand nonsystematically near the larger dikes.Mattox (1968) and Huntoon and Shoemaker(1995) identified some of the dark brownish-redshales in the dome’s core as the Organ RockMember shale, which underlies the White RimSandstone in exposures of the Cutler Group else-

where. That possibility cannot be excluded be-cause of the similar appearance of the OrganRock and lower Moenkopi shales. However, ifthe Organ Rock Member shale were present, wewould expect to see much of the overlyingWhite Rim Sandstone—an exceptionally promi-nent and resistant marker—in place rather thanas discordant dikes.

SUMMARY OF EVIDENCE FOR IMPACT VERSUS PINCH-OFF

Shoemaker and Herkenhoff (1984) proposedthat a meteorite impact near the end of Cretaceousor in Paleogene time excavated a transient crater1.3 to 1.4 km deep. That became instantly modi-fied by gravity to a final diameter of 8 to 9 km,forming Upheaval Dome. Evidence they cited tosupport that hypothesis included the circular dim-pled shape, inward-verging listric normal faultsnear the periphery, inward-verging thrust faultsnear the center, folds plunging radially outwardfrom the center, crushed quartz grains in clasticdikes, and geophysical anomalies. They thoughtthat erosion removed 1–2 km thickness of the up-per part of the crater. Kriens et al. (1997) revisedthese estimates by proposing impact within the

last few million years and a smaller modifiedcrater. Kriens et al. (1997, p. 20 and 26) used acrater diameter of 5 km to calculate the rise of thecentral uplift, and advocated a modified transientcrater diameter “close to . . . . the walls of the pres-ent topographic crater,” which is only 2 km wide.The current central depression of Upheaval Domewas thought to be entirely erosional in origin byShoemaker and Herkenhoff (1984).

Table 1 summarizes the evidence for or againstmeteoritic impact and diapiric pinch-off at Up-heaval Dome. A full discussion of each criterionto explain our evaluation of the evidence can befound in Part 3 (see footnote 1). Despite the factthat Upheaval Dome is far better exposed thanany terrestrial impact crater, we consider that theevidence for impact there is sparse and equivocal.Part 3 contests the evidence for shatter cones, pla-nar deformation structures in clastic dikes, andejecta breccia. Kriens et al. (1997, p. 28) con-cluded that the most diagnostic evidence for im-pact (planar deformation features and shattercones) were “not well developed.” The scarcityof features diagnostic of impact in UpheavalDome might be ascribed to too much or too littleerosion. However, the many apparently missingfeatures would cover the complete range of shockzonation and depths. Thus, it seems implausiblethat only a few contestable features have beenfound in a superbly exposed, high-relief structurecontaining abundant thick sandstones.

In contrast, a wide range of structures (Table 1)attests to the gradual growth of Upheaval Domeas a salt structure. The strongest argument for di-apirism is the stratigraphic evidence indicatingprotracted growth of Upheaval Dome over atleast 20 m.y., which is incompatible with hyper-velocity impact.

VOLUME IMBALANCE INDICATES SALT LOSS AND PRIMARY THICKNESS CHANGES

The pinch-off and impact hypotheses can betested in two ways by comparing selected rockvolumes in Upheaval Dome. This section sum-marizes the data presented, together with themethodology and assumptions, in Part 2 (seefootnote 1).

First, we examined the variation in elevation ofthe base Wingate Sandstone horizon relative to itsregional elevation. That variation includes the de-pressed rim syncline and the elevated centralmound (the center of which is eroded). The vol-ume of rock depressed below the base WingateSandstone regional datum is 0.74 km3, comparedwith only 0.29 km3 to 0.33 km3 above the regionaldatum. This volumetric mismatch of 220% to260% can only be plausibly explained by the lossof 0.45 km3 to 0.41 km3 salt from Upheaval

TABLE 1. EVIDENCE FOR PINCH-OFF AND IMPACT HYPOTHESES

Observation Pinch-off favored Impact favored

incompatible Compatible Compatible Incompatiblewith impact with pinch-off with impact with pinch-off

Positive evidenceCircularity X XCentral uplift X XClastic dikes X XCrushed quartz grains X XInner constrictional zone X XOuter extensional zone X XRadial flaps (dog tongues) X XPresence of underlying salt X XGravity and magnetic anomalies X XContiguous anticline X XNearby salt structures X XRim syncline X XRim monocline X XGrowth folds X XGrowth faults X XShifting rim synclines X XTruncations and channeling X XOnlap X XMultiple fracturing and cementation X XSteep zones X XOutward-verging extension X XVolume imbalance X XShatter cones X XPlanar microstructures in quartz X XEjecta breccia X XSalt below rim syncline X X

Negative evidence Lack of salt at the surface X X Lack of nearby piercement diapirs X X Lack of meteoritic material X XLack of melt X XLack of in-situ breccia X XLack of shock-metamorphic minerals X X Lack of outer fault terracing X XLack of overturned peripheral flap X X

Dome since the Chinle Formation was deposited.Impact would allow lateral flow of Paradox saltbut would entail no loss of salt volume becausethe salt was not exposed to dissolution. Con-versely, the pinch-off hypothesis requires a con-siderable loss of salt as the emergent diapir andglaciers dissolved. The gross volumetric imbal-ance therefore supports diapirism and is incom-patible with impact.

SALT-TECTONIC HYPOTHESIS:A RECONSTRUCTION

We now attempt to reconstruct the evolution ofUpheaval Dome by diapiric pinch-off. Figure 18shows a seismic example with some similaritiesto the diapiric structure that we envisage. Thepinched-off stem is marked by a vertical sec-ondary salt weld. An erosional section throughthe necked stem would expose strata steepeninginward to form a central uplift, above which thesubhorizontal tertiary salt weld represents a saltglacier largely evacuated of salt by the overbur-den load. The former salt glacier here is stronglyasymmetric because the Gulf of Mexico has anextensive slope. In contrast, we envisage a sym-metric salt diapir and glacier above UpheavalDome, now eroded off.

Initiation of Diapirism

Published subsurface data are lacking, exceptfor one well, so the deep structure and early evo-lution are highly speculative. The sparse and am-biguous evidence for what initiated the inferreddiapirism can be accommodated in two hypothe-ses for the structural evolution: (1) salt tectonicsalone, or (2) initiation by impact followed by salttectonics.

Our hypothesis is illustrated in Figure 23. Geo-physical anomalies indicate basement uplift ordense rocks below the Paradox salt (see footnote1). One possibility is that emplacement of an ig-neous intrusion into the salt initiated salt up-welling by arching the overburden and softeningthe salt by adding heat and water. Alternatively,an irregular configuration of basement faultscarps generated by Pennsylvanian to Permianextension might have obstructed southwestwardflow of salt, squeezed ahead of prograding sedi-ments. Any such obstruction would favor localupwelling of salt (Ge et al., 1997). Upwelling andlocal stretching of overburden draped above thetilted corner of a basement fault block might ini-tiate a diapir that evolved into a passive stock dur-ing continued sedimentation.

The following history (Fig. 23) combines themost internally consistent interpretation of avail-able data with mechanically reasonable processes.The restoration cannot be area balanced because

the circular dome did not undergo plane strain: in-ward-moving rocks increased the cross-sectionalarea, whereas outward-moving rocks decreasedthe area. Thus, the restoration had to be schematicand was carried out as follows. (1) To emphasizethe strains, we ignored compaction. (2) Individualfaults were omitted, but progressive thickeningand thinning by strain is schematically portrayed.(3) Strata were unfolded by vertical shear. (4) Thecross section was pinned at both ends, so that theoverall length remained constant. (5) The diapirdiameter approximates the value estimated for thetime of Chinle Formation deposition in Part 2 (seefootnote 1).

Stage 1: End of Pennsylvanian Time

By the end of Honaker Trail Formation depo-sition (stage 1), we envisage an emergent, passive

stock surrounded by a gentle rim syncline. Ingeneral, crests of passive stocks are periodicallyburied but continually break through their veneerof overburden to remain close to the depositionalsurface.

Stage 2: End of Chinle Formation Deposition

At this stage, we envision that the stock was stillemergent. The gradually thickening overburdenwould have increased the pressure on the saltsource layer, causing the salt to flow at increasingrates up the emergent stock. The climate was rela-tively wet, so much of the salt probably dissolvedas fast as it emerged. However, enough salt sur-vived that the stock began to extrude as a salt glac-ier, forming a flange that overhung surroundingstrata (for detailed discussions of this type of salttectonics, see Fletcher et al., 1995; Talbot, 1995;

JACKSON ET AL.


Figure 18. A pinched-off diapir shown by reflection seismic image in the Gulf of Mexico (fromHall and Thies, 1995, Fig. 4.3).


Figure 19. (A) Photograph and (B) broaderinterpreted panorama 15 (Pan—traced fromphotographs) of the Kayenta Formationthrust duplex and the abrupt transition intothe adjoining extensional system farther west(left). Both views are northward across Up-heaval Canyon; the dome center is to the right.Note the steepened deformation front of theduplex (extreme right). See Figures 14 or 15for stratigraphic explanation; one (or more) ofthe Kayenta Formation EB units is stippled.Scale varies greatly because of perspective,but the Wingate Sandstone (black) is about80–100 m thick. Inset shows a similar butsmaller duplex produced by folding in south-west England (after Tanner, 1992).

Figure 20. Views of dog tongues. Wingatestrata in the lobes are ~60 m below the adjoin-ing elevation of their basal contact. (A) Photo-graph looking radially outward at the north-east cliffs of the inner depression.

Figure 21. Northward view of several cir-cumferential, upright, tight to isoclinal folds inupper Wingate and lower Kayenta strata. Notethe abrupt transition between the Wingate-Kayenta steep zone in the twin spires (center)and open-folded Kayenta Formation on theright. At the extreme left are the northern cliffsof the inner depression.

A

A


Black Ledge

Roof thrust

Floor thrust

Pan 15

West EastDome center

~1 m

B

Figure 19. (Continued).

B

Domecenter

Upturnedtip of tongue

C Jk

Jw

Domecenter

?

Inferredsalt weld

Upturnedtip TRc

D

Jk

Jw

Upright isoclinal folds,Variably verging thrusts

Domecenter

Basalflap

Weld at base ofdog tongue

TRc

E

Jw

Flap = future dog tongue

Salt flange

Domecenter

TRc

Figure 20. (Continued). (B) to (E) idealized diagrams showing (B) radial fold traces on a Wingate horizon, where the central trace defines thedog tongue flanked by two higher antiforms (cf. Fig. 12); (C) radial cross section, and (D–E) schematic restoration of the dog tongue, showing itsinferred origin as a flap overlying a flange of glacial salt that was subsequently removed to form a salt weld.

B

B C

D E



Talbot and Alavi, 1996). Chinle Formation stratacurrently truncated against the basal WingateSandstone contact in the dog tongues may haveoriginally terminated against the overhanging saltface (Figs. 20E and 23).

If primary, the angular truncations sporadi-cally exposed in the upper Chinle Formationsuggest that local tilting took place (e.g., alcovesB, C, and D). The apparently radial tilts of thesetruncations suggest that they were related togrowth of a rim syncline around a dome. The de-gree of faulting during deposition of the ChinleFormation is unknown; some of the faults ex-posed today in the core of the dome may haveformed during the growth phase of the inferreddiapir and were reactivated during pinch-off.

Stages 3 and 4: End of Wingate Sandstone toEnd of Kayenta Formation Deposition

Onlap, truncation, and channeling in Wingateand Kayenta strata indicate shifting axes ofsubsidence and deposition. We deduce shifts inthe sites of active salt withdrawal, an erraticpattern typical of growing salt domes (e.g.,Seni and Jackson, 1983). Many of the inward-

dipping and outward-dipping Kayenta growthfaults may have initiated near the hinge lines of these localized depotroughs. The dogtongues are thought to represent upper Wingatestrata onlapping emergent salt, the presence ofwhich prevented lower Wingate strata from ac-cumulating locally (Figs. 20 and 23). Thisemergent salt would have been an early abortedphase of glacial extrusion before the main ex-trusion during Navajo Sandstone deposition.Growth folds in the lower Wingate Sandstonesuggest that the central part of the dome hadbegun to fold radially, indicating that theflanks of the dome were beginning to slide in-ward. This process accelerated during finalpinch-off later.

Stage 5: End of Navajo Sandstone Deposition

Salt Extrusion. We infer that glacial saltspread fastest during deposition of the NavajoSandstone. The inferred glacier reached a widthof at least 3 km. Collision between the outward-spreading glacier and inward-gliding strata isrecorded by the zone of abrupt steepening in theNavajo Sandstone (Figs. 8 and 23). The steep

zone suggests that the outer edge of the extrudingsalt extended well outside the present limits ofthe central depression during Navajo Sandstonedeposition (Figs. 6 and 23).

Diapir Pinch-Off. Two lines of evidence sug-gest—but do not prove—that the most plausibletime of pinch-off was during the extrusion of saltthat occurred during Navajo Sandstone deposi-tion. (1) Most of the constrictional deformation inthe Wingate Sandstone appears to have occurredbefore it was lithified, indicating that pinch-offcould not have occurred too late in the geologichistory. The radial growth folds indicate that wallrocks may have begun to move radially inwardduring early deposition of the Wingate Sand-stone. (2) Physical models (Jackson et al., 1997;B. C. Vendeville, 1996, personal commun.) indi-cate that where salt is forced rapidly up and out ofa feeder stock closing by lateral compression, saltextrudes vigorously during stem pinch-off.

The outward migration of steep zones (Fig. 8)suggests that the dome originally widened up-ward. Pinch-off of the feeder produced differentresults at different structural levels. For example,in the narrowest part of the diapir (MoenkopiFormation and Cutler Group), pinch-off continued

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.


Pc

cJwJk

Pc

c

RR

RR

RR

Pc

Jw

Pc

cJwJkJn

RR

Rimmonocline

BuckMesa

Weld

1000

2000

3000

4000

5000

6000

ElevationftElevation

m

0

Stage 6: Post-Navajo

Base salt � geometry unknownBase salt � geometry unknownBase salt � geometry unknown

Central upliftRimsyncline

Paradox saltParadox saltParadox salt

Stage 5: End NavajoGlacial spreading

Stage 4: End Kayenta

Stage 2: End Chinle

Stage 1: End Pennsylvanian

Steepening

Contraction

Weld

Inward-verging extensionRegionaltilt

Outward-verging extension

Rim syncline

Stage 3: End Wingate Future dog tongueSalt flange Eroded bulge

c

Base salt omittedBase salt omittedBase salt omitted

Dog tongueDog tongueDog tongue

Passive diapir

Salt flange

500

1000

1500

msl 0 ms

Figure 23. Schematic reconstruction of the salt-tectonic evolution of Upheaval Dome.

until rocks from opposite sides met at the center,completely closing the feeder during deposition ofthe Navajo Sandstone. That resulted in the highlyevolved constrictional features preserved in theMoenkopi Formation in the central depression.The White Rim Sandstone clastic dikes, whichcould have been emplaced along MoenkopiFormation faults during the earlier growth phaseof the dome, would have been rotated, distorted,and possibly reactivated during pinch-off.

The soft-sediment response of the WingateSandstone in the dog tongues also suggests thatthe weight of Wingate strata overburden expelledsalt from the early, abortive Chinle Formationsalt flanges at that time. Expulsion produced asalt weld, juxtaposing suprasalt Wingate strataagainst subsalt Chinle strata (Figs. 20 and 23).The unlithified dog tongues were then stronglyfolded during constrictional pinch-off.

Closing of the diapir stem at Cutler Groupand Moenkopi Formation levels would haveended diapiric pinch-off. Higher stratigraphicunits originally adjoined wider parts of the over-hanging diapir, so they did not completely closeoff before inward gliding stopped (Fig. 23).Thus, higher stratigraphic units never developedstructures such as in the Moenkopi Formationbecause they never moved close enough to thecenter to produce the requisite amount of strain.Pinch-off ended late during, or after, depositionof the Navajo Sandstone. The base of theNavajo Sandstone is strongly folded by the rimsyncline, which is unlikely to have continueddeepening after pinch-off ended. The uppercontact of the Navajo Sandstone is no longerpreserved.

Examples of allochthonous salt sheets overly-ing pinched-off stems are common in the Gulf ofMexico (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 observedby us on proprietary seismic data from the NorthSea, northwest Germany, and west Africa. How-ever, the mechanism for diapiric pinch-off is un-known. Pinch-off is the core of our hypothesis forUpheaval Dome, yet we are unsure how it occurs(Fig. 5B).

We do not regard this gap in knowledge as ev-idence against the pinch-off hypothesis for thefollowing reasons. (1) The lack of detailed me-chanical knowledge reflects a gap in salt tecton-ics theory generally rather than an anomaly spe-cific to Upheaval Dome. (2) Three-dimensionalseismic data indicate that the process occurswhether or not we understand it. (3) The limitedphysical modeling of dome pinch-off in brittlecountry rock (Lemon, 1985) reproduces severalof the main features observed at Upheaval Dome:a rim syncline that deepened markedly whenpinch-off began, a central uplift with subvertical

strata below the pinched-off diapir, peripheralnormal faults, and numerous unconformities.However, because gravity gliding was not per-mitted in Lemon’s (1985) physical models, nocentral zone of contraction formed in them.

How do inward-moving strata overcome theoutward pressure exerted by the salt stem? Themost likely mechanism for pinch-off is gravitygliding of the country rocks down an inward-dipping top salt surface into the weaker rockcomposing the salt diapir (Fig. 5B). The processwould be enhanced by salt dissolution. The diapirpinches off as a result of being the partially but-tressing toe of a radially inward-dipping spread-ing system. Gravity spreading is driven by theloss of gravity potential, which results in an ex-cess volume of rock depressed below regional el-evation compared with the volume of rock raisedabove regional elevation. Part 2 (see footnote 1)examines the implication of volume imbalancesfor understanding the process of pinch-off, forexplaining primary thickening, and for estimat-ing the diameter of the vanished diapir.

Stage 6: Present Day

Pinch-off would have ended salt rise, which al-lowed Cretaceous strata to bury the allochthonoussalt sheet. During Tertiary time, Upheaval Domewas uplifted and eroded. Because soluble salt wasmore easily removed than the surrounding rocks,the present topographic surface may partly reflectthe original shape of the overhanging lower con-tact of the allochthonous salt. However, outsidethe mesa surrounding Upheaval Dome, erosionwas greater and all strata were deeply dissected.

CONCLUSIONS

1. We propose that pinch-off of a salt diapirbest explains the sedimentary and deformationalstructures at Upheaval Dome. Evidence summa-rized here suggests that inward constriction ofoverburden strata accompanied necking of thestem of a broadly overhanging salt extrusion,subsequently removed by erosion.

2. In the rim syncline, the Wingate Sandstoneand overlying Kayenta Formation are greatlythinned by circumferential extensional faults.These low-angle normal faults are either simplelistric faults or series of ramps and flats. Most ex-posed faults slipped during or after deposition ofthe Kayenta Formation. Normal fault vergenceshows a strong dichotomy: in the north, mostfaults transported rock outward from the dome,whereas in the south, most faults transported rockinward.

3. In the core of the dome, the bulk strain isconstrictional, and includes both radial and cir-cumferential shortening. Radial shortening dom-

inates the periphery of the dome core, but cir-cumferential shortening predominates farther in-ward. In the western sector of the dome’s core,the hanging walls of radial thrusts moved coun-terclockwise and imbricated the persistentlyclockwise-dipping Moenkopi Formation, like theclosing of a camera’s leaf diaphragm. Elsewherein the dome core, strain is highly variable, but isconstrictional overall.

4. In the core of the dome, many steeply dip-ping clastic dikes link with the radial fault sys-tems. The lenticular sandstone dikes form acontinuous network more than 400 m long, pre-sumably derived from the underlying WhiteRim Sandstone. Their intrusive origin is indi-cated by branching, anastomosing veins anddiscordance with country rock.

5. Arguments have been advanced for theformation of Upheaval Dome by either meteoriticimpact or salt tectonic processes. We think thatevidence favoring meteoritic impact is sparse, be-ing restricted to a lag deposit of cobbles, part oftwo weakly developed shatter cones, and undocu-mented planar structures in quartz. The paucity oftypical impact features in Upheaval Dome mightbe ascribed to too much or too little erosion. How-ever, these missing features cover the full range ofshock zonation and depths. It seems implausiblethat so few have been found in a structure that isbetter exposed in three dimensions than any ter-restrial impact structure.

6. We think that the weight of the evidencestrongly favors salt tectonics. Evidence favoringdiapiric pinch-off includes a lack of the followingfeatures associated with hypervelocity impact:meteoritic material, melt, in situ breccia, shock-metamorphic minerals, outer fault terracing, andoverturned peripheral flap. Conversely, the pres-ence of the following features at Upheaval Domeall favor diapirism: rim syncline, rim monocline,steep zones in inner limb of rim syncline, out-ward-verging extension, radial synformal flaps(dog tongues), underlying mother salt and nearbysalt structures, multiple episodes of microfractur-ing and sealing, and postemplacement microfrac-turing in the clastic dikes. Volume imbalance be-tween uplifted and depressed regions of the domeindicates massive salt loss of at least 0.4 km3 af-ter deposition of the Chinle Formation.

The most compelling evidence for diapirism inUpheaval Dome is the wide range of synsedi-mentary structures spatially restricted to this cir-cular structure. They include angular truncations,onlap surfaces, channeling, growth faults, growthfolds, shale diapirs, and shifting rim synclines.These signs of synsedimentary deformation lo-calized around the dome indicate gradual growthover at least 20 m.y. and exclude the possibilityof geologically instantaneous deformation re-quired by hypervelocity impact.



JACKSON ET AL.


7. Many details of the structural evolution arespeculative because subsurface data are sparse.We envisage that a passive stock less than 1 km indiameter and surrounded by a gentle rim synclineemerged in Pennsylvanian time. The salt re-mained at or near the surface throughout Permian,Triassic, and Early Jurassic time. Increasing sedi-mentary load on the Paradox source layer belowincreased the flow rate of salt up the diapir, even-tually resulting in extrusion of salt glaciers nearthe end of Chinle Formation deposition and dur-ing Navajo Sandstone deposition, when a saltglacier spread to an estimated diameter of 3 km.

8. Growth folds in the lower Wingate Sand-stone indicate that the walls of the diapir began tomove inward during Early Jurassic time. Wethink that this inward movement was producedby gravity spreading along an inward-dipping topsalt surface. Spreading culminated in completepinch-off of the diapir during deposition of theNavajo Sandstone. Pinch-off produced constric-tional strain and structural thickening in the cen-ter of the dome, with concurrent extensionaround the dome periphery.

ACKNOWLEDGMENTS

The National Park Service allowed us to mapthe dome and sample the clastic dikes. The lateGene Shoemaker provided stimulating discus-sions in the field and showed us two examples offaults (panoramas 4 and 5). Ray Fletcher assistedwith the field work and contributed useful dis-cussion. John Shelton kindly supplied his obliqueaerial photographs of Upheaval Dome. SteveLaubach led the investigation of quartz mi-crostructure and provided invaluable advice onmicrofracturing. Hongxing Ge helped in severalways, especially in digitizing the geologic andtopographic maps. Joseph Yeh calculated the vol-umetrics from data digitized by Syed Ali. Illustra-tions were drawn by us and by Nancy Cottington,Dick Dillon, Chris Conly, Randy Hitt, and JanaRobinson. Mark Anders, Dave Bice, Ian Davison,and Bryan Kriens diligently reviewed the manu-script, and Jay Melosh critically read sectionsdealing with impact. The project was funded byExxon Production Research and by the AppliedGeodynamics Laboratory consortium, compris-ing the following oil companies: Agip S.p.A.,Amoco Production Company,Anadarko Petro-leum Corporation,Arco Exploration and Produc-tion Technology/Vastar Resources Inc., BHPPetroleum (Americas) Inc., BP Exploration Inc.,Chevron Petroleum Technology Company,Conoco Inc., Société Nationale Elf AquitaineProduction, Exxon Production Research Com-pany, Louisiana Land and Exploration Company,Marathon Oil Company, Mobil Research andDevelopment Corporation, PanCanadian Petro-

leum, Petroleo Brasileiro S. A., Phillips Petro-leum Company, Saga Petroleum, Shell Oil, Sta-toil, Texaco Inc., and Total Minatome Corpora-tion. Permission to publish was granted by theDirector, Bureau of Economic Geology, and bythe management of Exxon Production Research.

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