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JOURNAL OF SEDIMENTARY RESEARCH, VOL. 75, NO. 2, MARCH, 2005, P. 280–299Copyright q 2005, SEPM (Society for Sedimentary Geology) 1527-1404/05/075-280/$03.00 DOI 10.2110/jsr.2005.021

DEPOSITIONAL AND STRATIGRAPHIC ARCHITECTURE OF THE SANTONIAN EMERY SANDSTONE OFTHE MANCOS SHALE: IMPLICATIONS FOR LATE CRETACEOUS EVOLUTION OF THE WESTERN

INTERIOR FORELAND BASIN OF CENTRAL UTAH, U.S.A.

CHRIS M. EDWARDS,* JOHN A. HOWELL,** AND STEPHEN S. FLINTStratigraphy Group, Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, U.K.

e-mail: [email protected]

ABSTRACT: The Santonian Emery Sandstone Member of the MancosShale is a continental to shallow marine succession that prograded intothe Cretaceous Western Interior Seaway of western North America.Sediment sourced from the uplifted Sevier Orogen to the west fed ashoreline in the adjacent subsiding north–south trending foredeep.These sandstones are now superbly exposed along a 120-km-long,strike-parallel, continuous outcrop in the cliffs of the Wasatch Plateauof central Utah. Shoreface parasequences are composed of coarsening-upward successions of hummocky cross-stratified and intensely biotur-bated sandstones, indicating deposition at a storm-dominated shore-line. Two distinct depositional complexes record eastward and north-eastward shoreline progradation at the northern and southernmost ex-tremities of the Plateau respectively. In the subsurface, Emery stratacomprise a thick succession of coal-bearing, coastal-plain deposits. TheEmery Sandstone records a period of long-term paralic progradationto aggradation, containing at least 17 parasequences arranged intothree, 600 kyr, regressive–transgressive cycles that are recognizable inboth complexes. Each cycle comprises only highstand and transgressivesystems tracts, and erosional sequence boundaries are absent. Absenceof erosional sequence boundaries is attributed to high rates of subsi-dence in the foreland basin at this time. Santonian glacio-eustatic sea-level fluctuations are proposed to account for the high-frequency cy-clicity, whilst longer-term aggradation may be a function of organiccontrols on shoreface stacking patterns by immobile raised coal mireslying landward of the shorefaces.

When placed in a temporal and spatial context, the Emery Sandstoneprovides a missing link in the understanding of long-term controls onLate Cretaceous depositional systems in the central Utah segment ofthe foreland basin, and allows inferences to be made regarding fore-land basin dynamics. In particular, thrust tectonics is postulated tohave played a major role in governing the architecture of Late Cre-taceous strata in central Utah. Marked along-strike thickening of theEmery Sandstone in particular is attributed to long-lived elevated ratesof subsidence in northern Utah and southern Wyoming during the LateCretaceous that is adjacent to concentrated zones of thrust nappes. Anorth-dipping depositional slope is inferred from this subsidence dis-tribution, aligned approximately parallel to the structural grain of thehinterland load. Northeastward progradational directions of successiveTuronian, Santonian, and early Campanian regressive wedges in thispart of the Western Interior Basin are attributed to the presence ofthis tectonically induced regional slope gradient. Sediment sourced tothese Late Cretaceous shorefaces is likely to have been sourced throughstructural recesses within the thrust front, resulting in a spatial align-ment of several successive regressive wedges and implicates an impor-tant, long-lived kinematic control on sediment supply. Of Late Creta-ceous regressive wedges, only the Emery Sandstone does not tempo-rally coincide with reported periods of active thrusting, suggesting thatthe regression was a consequence of factors other than uplift-related,elevated rates of sediment supply.

* Present address: ExxonMobil Exploration and Production Company, 233 Ben-mar, Houston, Texas 77060, U.S.A.

** Present address: Department of Earth Sciences/Centre for Integrated PetroleumResearch, University of Bergen, Allegtaten 41, N-5007 Bergen, Norway

INTRODUCTION

The Wasatch Plateau of central Utah exposes regressive shallow marineclastic wedges deposited in the Cretaceous, Western Interior Basin (Young1955; Kauffman 1977). Stacking of thrust sheets in the north–south trend-ing Sevier Highlands to the west generated an adjacent, asymmetricallysubsiding retro-arc foreland basin that received sediment from the upliftedorogen (Armstrong 1968; Royse et al. 1975; Wiltschko and Dorr 1983;DeCelles et al. 1995). During Phanerozoic sea-level highstand, a seawayextended from boreal Canada in the north to the Gulf of Mexico in thesouth (Fig. 1; McGookey et al. 1972; Kauffman 1977). Episodic fluctua-tions in sea-level and sediment supply caused shoreface successions toperiodically prograde basinward and recede landward creating a series ofclastic wedges encased by marine mudstones (Young 1955; McGookey etal. 1972; Kauffman 1977; Van Wagoner et al. 1990). These sedimentsrecord the interplay among eustasy, tectonics, and sediment supply duringdeposition, and are superbly exposed in a complex of canyons and cliffsstretching from the Wasatch Plateau in central Utah to the eastern BookCliffs in western Colorado (Fig. 1).

The exceptional quality of the Wasatch Plateau outcrop has given riseto a plethora of stratigraphic studies and serves as a natural laboratory inwhich to apply sequence stratigraphic principles to clastic sedimentary suc-cessions (e.g., Gardner 1995a; Kamola and Van Wagoner 1995; Van Wag-oner 1995; Dubiel 1999; Posamentier and Morris 2000). One such regres-sive wedge, the Santonian Emery Sandstone Member of the Mancos Shale,has however, remained largely unstudied in contrast to underlying andoverlying units, leaving a major void in the understanding of long-term(i.e., greater than 10 My) behavioral patterns of depositional systems inthis part of the foreland basin. The comprehensive documentation of re-gressive wedges in this sector of the foreland basin provides a uniqueinsight into the long-term controls on the evolution of depositional systems,and resulting stratigraphic architecture. Therefore, whilst the Emery Sand-stone has remained largely ignored, it does constitute a crucial link betweenolder and younger regressive wedges, in an otherwise well-understood sed-imentary basin.

Emery strata are exposed as a series of prominent cliffs in the middleto lower portions of the eastern escarpment of the Wasatch Plateau (Fig.2). The outcrop forms a 120-km-long continuous exposure along the west-ern flank of the San Rafael Anticline, extending northwards from InterstateHighway 70 in the south, to just north of the town of Price, before theoutcrop turns eastwards and forms the western edge of the Book Cliffs.Spieker and Reeside (1925) named the Emery Sandstone for a series ofprominent, beige and buff sandstones encased by gray siltstones of the BlueGate Shale at the foot of the Wasatch Plateau near the town of Emery,Utah (Fig. 2). When traced northward along the Plateau, these sandstonescorrespond to a sand-rich succession near the town of Price, that subse-quently became known as the Garley Canyon Sandstone Beds (Fouch etal. 1983). Regional correlations reveal that the Emery can be mapped west-wards into continental and coal-bearing strata from drill holes on the Wa-satch Plateau (Ryer 1984; Franczyk et al. 1992). It should be noted thatthe Emery Sandstone of the Wasatch Plateau should not be confused withthe misnamed Emery Sandstone of the Henry Mountains area of southernUtah (Hunt et al. 1953), which has subsequently been renamed the MuleyCanyon Member by Eaton (1990). This shallow marine to continental suc-

281SANTONIAN DEPOSITION IN THE WESTERN INTERIOR BASIN, CENTRAL UTAH

FIG. 1. —Geographic location of the Emery Sandstone outcrop belt, central Utah. A) Paleogeographic setting of the western United States during the Cretaceous. Thrust-sheet loading of the Sevier Orogen and Phanerozoic sea-level highstand created the Western Interior marine foreland basin, which stretched from Arctic Canada to theGulf Coast (modified from Kauffman 1984; Eaton and Nations 1991). B) Central Utah was a site of thrust-sheet stacking in the mountain belt to the west and sedimentswere deposited into the seaway in central and eastern Utah, where they are now exposed. C) Outcrop distribution and subsurface wells located along the Wasatch Plateauof Utah. Stratigraphic sections have been constructed along the Plateau (A–A9 and B–B9) and correspond to Figures 11 and 12. Sediment thickness for the Emery Sandstonederived from this study is given in meters and contoured in 50 meter increments.

cession was demonstrated to be younger than the Emery Sandstone of theWasatch Plateau (Peterson and Ryder 1975; Peterson et al. 1980).

The Emery Sandstone is distinct from other depositional units within thissegment of the Western Interior because its deposition coincides with aperiod of unusually high accommodation. Roberts and Kirschbaum (1995)produced several sediment-thickness maps for Turonian to Campanian stag-es of the Late Cretaceous. They noted that for a 5 Myr period during theConiacian–Santonian, sediment accumulation in the Cretaceous foredeepwas double that of equivalent duration intervals in the Turonian and Cam-panian. Thus in contrast to the numerous other regressive wedges in thecentral Utah salient, the Emery Sandstone provides an opportunity to ex-amine a period of shoreline regression and its resulting stratigraphic ar-chitecture within a high-accommodation setting.

This manuscript documents the depositional and stratigraphic architec-ture of the Emery Sandstone along the eastern Wasatch Plateau, and inte-grates these findings with published data to provide an improved synthesisof middle-Late Cretaceous paleogeography. Attempts have been made totie shallow marine successions in outcrop with nonmarine equivalents inthe subsurface where the Emery provides a potential coalbed methane play

(Tabet and Quick 2003). The Emery Sandstone can then be placed in strati-graphic context with other underlying and overlying, well-documented re-gressive successions within this portion of the basin, providing some uniqueinsights into the long-term dynamic structural controls on foreland basindeposition. In particular, this paper examines the role of spatial variationsin supracrustal loading, timing of thrust sheet stacking and its effect onsediment supply and depositional style, and the geometry of thrusted ter-ranes in the routing and distribution of sediment. The role of nonmarineenvironments in the development of regional Santonian shoreface stackingpatterns is also discussed in light of documented time-equivalent strati-graphic units with important implications for future commercial exploita-tion of coalbed methane reserves.

STRATIGRAPHY

The Emery Sandstone lies stratigraphically above the Turonian FerronSandstone Member of the Mancos Shale and beneath the lower CampanianStar Point Sandstone and Blackhawk Formation of the Mesaverde Group(Fig. 2). These successions have been studied in considerable detail, and

282 C.M. EDWARDS ET AL.

FIG. 2.—Stratigraphy of the Wasatch Plateau. A) The Emery Sandstone Member is encased in shelfal siltstones of the Blue Gate Shale. Shallow marine regressivewedges (gray fill) include the Turonian Ferron Sandstone Member and the overlying Campanian Star Point Sandstone. B) In the foreground the terraces and slopes comprisethe Emery Sandstone Member. The badland slopes in the background characterize the Blue Gate Shale, which grades upwards into shallow marine and nonmarine unitsof the Star Point Sandstone and Blackhawk Formations, respectively. Photograph is taken from 1.5 km north of Interstate Highway 70 looking north in the direction ofthe town of Emery.

their relationships to relative sea-level changes are well documented (e.g.,Ryer 1984; Gardner 1995a; Kamola and Van Wagoner 1995; O’Byrne andFlint 1995; Taylor and Lovell 1995; Van Wagoner 1995; Posamentier andMorris 2000). The upper and lower parts of the marine Blue Gate ShaleMember of the Mancos Shale stratigraphically separate the Emery Sand-stone from these regressive units. Ryer (1984) described the Emery Sand-stone as a 250-m-thick, eastward-thinning, regressive wedge encased bymarine shales and consisting of delta-front sandstones deposited during aperiod of shoreline regression. Others have described these sandstones asa series of transgressive–regressive cycles, consisting dominantly of eitheroffshore to tidal-flat facies (Matheny and Picard 1985) or an aggradationalstack of storm-dominated shoreface sandstones deposited when the ratio ofsediment supply to accommodation creation was close to unity (Chan1990).

A number of studies have speculated upon the significance of the EmerySandstone in context with other surrounding stratal units, but in the absenceof a detailed analysis of the Emery succession itself (Fouch et al. 1983;Chan et al. 1991; Cole and Young 1991; Franczyk et al. 1992; Schwans1995; Shanley and McCabe 1995). Scoured surfaces in marine siltstonesand sandstones of the Prairie Canyon Member lying basinward of the Em-ery outcrops were perceived to be the products of prodeltaic plume dis-charge and have been speculatively correlated with the Emery shorefacesuccession (Fig. 3; Kellogg 1977; Fouch et al. 1983; Swift et al. 1987;Chan et al. 1991; Cole and Young 1991; Franczyk et al. 1992). However,recent mapping of these mud-rich sandstones demonstrates that they areyounger than the Emery Sandstone, and therefore are unlikely to have agenetic depositional relationship (Cole et al. 1997; Hampson et al. 1999).In a regional stratigraphic synthesis, Shanley and McCabe (1995) implied

that the Emery Sandstone contains an erosional sequence boundary thatcorresponds to a relative sea-level fall at the top of shoreface and conti-nental sediments of the John Henry Member in the Kaiparowits Plateau ofsouthern Utah. In contrast, Chan (1990) concluded that the Emery Sand-stone represents a balance between the rate of relative sea-level change andsediment supply, and the aggradational stack of shoreface parasequencesrecorded the deposition of shelf-margin systems tract strata (Chan 1990).Schwans (1995) related the deposition of the Emery Sandstone to a coevalangular unconformity in up-dip areas in the western Wasatch Plateau. Theangular unconformity was ascribed to progressive tilting, associated withproposed tectonism in the Sevier hinterland. The correlations of Santonianstrata made by Schwans (1995) were achieved by subsurface well-log cor-relations, yet the Emery Sandstone exposed on the eastern flank of theWasatch Plateau remained unstudied.

The age of the Emery Sandstone is constrained by recovered lower mid-dle to upper late Santonian macrofossils associated with the Clioscaphitesvermiformis ammonite biozone in the Garley Canyon Sandstone Beds andDesmoscaphites bassleri found at the top of the Emery Sandstone (Cobban1976; Fouch et al. 1983). The Santonian–Campanian boundary probablylies within overlying siltstones because Baculites aquilaensis was found 91m from the top of the Blue Gate Shale and has affinities with earliestCampanian Scaphites hippocrepis (Cobban 1976). According to the time-scale and biostratigraphic framework of Obradovich (1993) and Kauffmanet al. (1993), the duration of Emery Sandstone deposition may have beenas long as 1.8 Myr. (85.7–83.9 Ma). The Emery Sandstone is probably timeequivalent to progradational to aggradational shoreface and coal-bearingcoastal-plain deposits of the John Henry Member of the Straight CliffsFormation of southern Utah (Peterson and Ryder 1975; Peterson et al.


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FIG. 3.—Previous stratigraphic interpretations of the Emery Sandstone after A)Fouch et al. (1983); B) Chan et al. (1991); C) Cole et al. (1997); D) Shanley andMcCabe (1995). (A and B) A common conception is that the Emery contains asignificant stratigraphic surface that may be related to deposition of the Prairie Can-yon Member. C) This relationship was later resolved by Cole et al. (1997), whodetermined the Prairie Canyon Member to be younger than the Emery Sandstone.D) Shanley and McCabe (1995) suggested that an erosional surface lay within theEmery Sandstone that corresponds to a period of erosion in southern Utah.

1980; Franczyk et al. 1992), the Yale Point Sandstone of the Wepo For-mation of northeastern Arizona (Franczyk 1988), the Dalton SandstoneMember of northern New Mexico (Molenaar 1983), and an unnamed Mem-ber of the Mesaverde Formation in the northern Uinta Mountains of north-ern Utah (Molenaar and Wilson 1992). Thus, the Santonian stage in thesouthwestern United States was represented by widespread aggradation ofshallow marine and coal-bearing units (Roberts and Kirschbaum 1995).

DATASET AND METHODOLOGY

Over 1800 m of outcrop has been logged along the length of the WasatchPlateau. A total of 13 measured sections give an average spacing along thePlateau length of 9 km. The thickness of the Emery ranges from 223 m inQuitchupah Creek (Section 2; refer to Fig. 1 for location) in the southernpart of the Plateau to 170 m in Haley Canyon (Section 10) in the northnear Price. In the subsurface the succession thickens to 570 m in the Cock-rell #1 well, 30 km to the west of Price, Utah, compared to 300 m inPhillips US ‘‘D’’ #1 well 23 km west of Section 1 at Interstate Highway70. The best exposed strata are located in the southernmost Wasatch Pla-teau, south of the town of Emery, and to the west of Price. Access tooutcrops is possible via well-maintained canyon tracks. Stratigraphic cor-relations have been achieved through a combination of physical tracing-out of stratal surfaces and visual correlations from photographic montages.In the subsurface of the Wasatch Plateau, a cored well (Cockrell Oil Cor-poration well 1207-2507 #1, Section 25, Township 12S, Range 7E, CarbonCounty, Utah) recovered a wide variety of nonmarine facies that enablewell-log response to be calibrated for the remainder of the uncored wells.

OUTCROP FACIES ASSOCIATIONS

In outcrop, two facies associations are present that collectively formrepeated coarsening-upward cycles. Facies association A is the dominantlithofacies type and consists of coarsening-upward successions of siltstones,with interbedded, fine-grained, bioturbated, and hummocky cross-stratifiedsandstones. Facies association B is volumetrically minor, but consists ofintensely bioturbated, medium-grained sandstone. Tidal-flat facies reportedby Matheny and Picard (1985), and delta-front facies of Ryer (1984) havenot been identified. Levels of bioturbation have been quantified using thestandardized scheme of Taylor and Goldring (1993), whereby a scale of 0to 6 reflects increasing intensity of burrowing.

Facies Association A: Coarsening-Upward Siltstones, and Fine-Grained, Bioturbated and Hummocky Cross-Stratified Sandstones

Description.—The bases of the prominent benches in the Emery Sand-stone are chiefly composed of monotonous, thinly laminated, light- to dark-gray, silty mudstone and more commonly, muddy siltstone (Fig. 4A). Thispoorly exposed but well represented facies is bioturbated by Paleophycus,Planolites, and Teichichnus burrows with bioturbation indices in the rangeof 3 to 4. The siltstones are crudely bedded on the centimeter to decimeterscale, and defined by very subtle grain-size variations. Rare sedimentarystructures include wavy laminae and irregular, fine, low-angle laminae.Thin, centimeter-thick, bentonitic ash layers form isolated orangey-white


FIG. 4.—Characteristics of facies association A. A) Gray concretionary siltstones form the base of upward-coarsening successions that are intercalated with hummockycross-stratified sandstones (HCS). 1.2 m Jacob’s staff for scale. B) Fine-grained, HCS, and bioturbated sandstones amalgamate to form thick sandstone bodies. A singleHCS bed is encased in bioturbated sandstones (arrow). C) Intensely bioturbated, fine-grained sandstones with complete reworking by Thalassinoides networks. Ten-centimeter graticules on Jacob’s staff for scale. D) HCS sandstones with meter-scale wavelengths. 1.5 m Jacob’s staff for scale. E) HCS beds commonly display wave-ripple caps. F) Fine-grained, wave-rippled sandstone and siltstone intercalations.


FIG. 5.—Example measured section of a single parasequence from Section 3 (Link Canyon) summarizing the key facies, facies associations, and interpreted key surfaces.For key see Figure 6.


FIG. 6.—Outcrop expression of the lower Emery Sandstone shoreface parasequences. A) In Haley Canyon (Section 11), proximal exposures consist of an upward-coarsening succession characterized by wave-rippled, laminated sandstones and interbedded bioturbated and HCS beds. Amalgamation of HCS beds increases upward, andthe parasequences are capped by marine siltstones (white arrows). B) When traced down depositional dip into Garley Canyon (Section 12), amalgamated beds becomeincreasingly rare with an attendant decrease in the abundance of wave-rippled beds. In addition, the sections become less sand prone. C) In the most distal locations tothe north of Price (Section 13), parasequences grade into blue-gray siltstones of the Mancos Shale.

bands within the dominantly siltstone succession. These poorly developedlayers commonly weather to produce thin, clay-rich bands. Small botryoidalconcretions, cored by carbonate fragments, lie embedded in the shaleswhere they weather against recessive siltstones (Fig. 4A). In the centralWasatch Plateau, the Emery section is dominated by these siltstones withonly a few thin sandstone ribs projecting from the weathered slopes.

The bulk of the Emery Sandstone is composed of partially amalgamated,tan-colored, bioturbated or hummocky cross-stratified (HCS), well-sorted,fine- to very fine-grained sandstones arranged in upward-coarsening and-thickening bedsets (Fig. 4B). Eastwards, these sandstones grade into graysiltstones described above. Bioturbated sandstones are characterized bypoorly defined bedding surfaces and internal sedimentary structures thathave commonly been destroyed as a result of intense sediment reworkingby burrowing organisms (Fig. 4C). Bioturbation indices range from 4 to 6,and in examples where burrowing intensity is fractionally lower, relict low-angle and hummocky cross stratification is occasionally preserved. Thedominant burrows are Thalassinoides and Asterosoma, but high-diversityassemblages are also present with accessory occurrences of Paleophycus,Rosselia, Planolites, Skolithos, and less common Arenicolites and Teichich-nus. The intense biogenic reworking results in a friable, poorly cemented,

and weathered deposit. Consequently bed thicknesses can be difficult toestimate, because beds appear to amalgamate, producing homogenizedsandstone packages up to 5 m in thickness.

In contrast, HCS sandstones occur as individual, tan-colored beds thatform sharp-based, lenticular to sheet-like bodies extending from tens tohundreds of meters and varying in thickness from less than 10 cm to upto 2 m (Fig. 4D). In the most sand-rich sections at the northernmost andsouthernmost limits of the Wasatch Plateau, pristine HCS beds commonlygrade upward into thin, symmetrical-ripple-laminated caps (Fig. 4E) pro-viding rare paleocurrent information. These ripples show oscillatory cur-rents were east–west (82.5º) in the northern part of the study area andnortheast–southwest (46.5º) in the southern part. Deformed HCS and con-volute laminae with good examples of water-escape structures are common.Inoceramid debris and pinnadae (?pinna sp.) bivalve shell fragments formwidely distributed, and thin bioclastic lags. Bioturbation intensity is no-ticeably lower in these HCS beds than in the bioturbated beds, with abioturbation index ranging from 1 to 3, and sedimentary structures aregenerally well preserved. Trace faunas occur as isolated Ophiomorpha, Sko-lithos, and Paleophycus.

Bioturbated and HCS Sandstone beds are commonly intercalated with


FIG. 7.—Examples of facies association C from the Cockrell #1 cored well. A) Cross-bedded sandstones of fluvial origin. B) Soft-sediment deformation in fluvial channelsandstones. C) Crevasse-channel carbonaceous sandstones. D) Coal flasers in a fine-grained sandstone matrix, interpreted as the deposits of a crevasse-splay lobe. E)Organic-rich shales and interbedded fine-grained sandstones of overbank deposits.

decimeter-thick, parallel-laminated and symmetrical ripple-laminated silt-stone with very fine-grained sandstone (Fig. 4F). The sandstones of theseheterolithic units display well-preserved symmetrical ripples with wave-lengths of a few centimeters and draped by thin, comminuted coal streaksand/or pyritized woody fragments (Fig. 4F). The finer, organic fraction ispenetrated by large sand-filled Thalassinoides burrows.

Interpretation.—Blue-gray siltstones are pervasive throughout the stra-tigraphy of the Wasatch Plateau, forming badland topography on weatheredslopes. Fine grain size, coupled with few sedimentary structures and fullymarine ichnofacies, is indicative of an offshore-shelf setting that receivedonly suspended sediment. Bentonite clays are the products of volcanic ashfallout from the volcanic arc to the west. Unfortunately, they are not easilytraced through the succession, limiting their use for chronostratigraphiccorrelation.

The interbedded sandstones are interpreted to have been deposited in anoffshore-transition zone to lower shoreface setting. During storms, large-scale oscillatory shoaling waves redistributed sediment from the foreshoreand upper shoreface into lower shoreface areas as sheet-like, HCS sand-stones (Dott and Bourgeois 1982; Harms et al. 1982; Southard et al. 1990).The rapid deposition of sand resulted in water escape and soft-sedimentdeformation, manifest as contorted and recumbent laminae (Dott and Bour-geois 1982). As storms waned, oscillatory motions diminished, resulting inlower-flow-regime reworking of the upper surfaces of the HCS beds, gen-erating thin caps of symmetrical ripple cross-lamination (Cheel and Leckie1993). With continued waning energy, suspension fallout of organic debrisdraped the ripple crests. These symmetrical ripple crests provide crudeindications of paleoshoreline orientation, the long axis aligning parallel orsubparallel to the general trend of the coastline (Leckie and Walker 1982;Shanley et al. 1992; Hettinger et al. 1994). On this basis, shoreline orien-tations in the southern part of the study area were NW–SE whilst those inthe north were N–S. Fair-weather periods are reflected as continued periodsof hemipelagic deposition and biological reworking of sediment.

The abundant and diverse shallow marine ichnofaunas suggest primeconditions for burrowing organisms. Variations in bioturbation intensity of

storm-dominated, lower-shoreface bedforms has been discussed by Dottand Bourgeouis (1982), who considered an inverse relationship betweenstorm magnitude and/or duration between successive storm events and thedegree of biological mixing of the substrate. Diversity of biofacies is re-garded as an indicator of oxygenation in the water column and can berelated to styles and depth of burrow tiering (e.g., Bottjer et al. 1986;Savrda et al. 1991). Oxygen supply is likely to be enhanced during stormsurges and turbulence of the water column, thus allowing deep bioturbationto prevail (Bromley 1996). Thus, the intensely burrowed beds and the pre-dominance of Thalassinoides in the Emery may simply reflect a well-ox-ygenated lower shoreface related to storm-induced turbulent mixing. How-ever, Howell et al. (1996) questioned the plausibility of very thick (i.e.,greater than 20 cm) intensely bioturbated, lower-shoreface sandstone bedsfrom the central North Sea Fulmar Formation as being representative ofinter-storm periods. They proposed that the homogenized sandstone bodieswere the amalgamated products of low-magnitude, high-frequency stormevents, depositing numerous, decimeter-thick beds with sufficient interven-ing time for complete biogenic reworking. This model may also accountfor thick bioturbated beds in the Emery Sandstone.

The gradual upward transition from shelf siltstones through individualsandstones into amalgamated sandstone bodies, combined with upwardcoarsening of bedsets and a predominance of storm-generated structures, isinterpreted as the seaward progradation of a storm-dominated shorefaceparasequence (Fig. 5; Scott 1992; Walker and Plint 1992). In the northernpart of the study area, the most continuous dip-parallel exposures affordthe tracing of these parasequences to their down-dip terminations into theMancos Shale (Fig. 6). Proximal shoreface facies are not exposed in out-crop. Repetitive parasequences form the many buff-colored ledges in theslopes of the eastern Wasatch Plateau. The base of blue-gray siltstones thatsharply overlie the progradational shoreface units define flooding surfacesand are interpreted as parasequence boundaries (Posamentier et al. 1988;Posamentier and Vail 1988; Van Wagoner et al. 1988). These key surfacescan be traced along the Wasatch Plateau for great distances, forming thebasis for the correlation of time-equivalent strata.


FIG. 8.—Cored logs from the Cockrell #1 wellcharacterized by cross-bedded, fluvial channelsands, to carbonaceous, crevasse-channel andcrevasse-splay sandstones to coals and fine-grained, overbank facies. Facies indicatedeposition in a coastal-plain setting. Letterscorrespond to core photographs in Figure 7.


FIG. 9.—The Nayarit Coast of Mexico is considered a close modern analogue ofthe Emery Sandstone depositional setting. Small rivers that form deltaic promon-tories dissect laterally persistent strandplains fed by efficient longshore transport ofsediment. Major wave-dominated delta-front environments are a negligible compo-nent of the shoreline. After Curray et al. (1969).

Facies Association B: Intensely Bioturbated, Medium-GrainedSandstone

Description.—At the crest of one of the Emery parasequences are ir-regularly distributed, flat-based or low-relief, erosionally based, fine- tomedium-grained, poorly-sorted sandstone beds. These beds are distinctlycoarser than their subjacent lower shoreface facies, and form a thin, irreg-ular, laggy deposit that is highly variable in thickness and compositionbetween the three localities at which it is present. At Link Canyon (Section3) it consists of an inversely graded, fine to medium-grained, arenaceous,1.2-m-thick sandstone unit, containing large inoceramid shells up to 10 cmin length and abundant Arenicolites, Thalassinoides, Ophiomorpha, andSkolithos ichnogenera. This unit is overlain by a weakly trough cross-bed-ded 30-cm bed. Foresets dip at angle of repose towards the south (1858)and are locally disturbed by Thalassinoides, Ophiomorpha, Skolithos, andPlanolites. Abundant, disarticulated shelly detritus is also a distinctive fea-ture of this unit. At Interstate Highway 70 (Section 1) this facies associationis also located at the same stratigraphic level but is no thicker than 60 cm.Here it also contains abundant, fragmented bioclasts and is intensely bio-turbated by Rosselia and Asterosoma. Bioturbation indices are high at both

of these localities and seldom drop below 5. At Muddy Creek (Section 4),the same stratigraphic horizon is recognized by a sharp-based, 20-cm-thickbed that displays an abrupt increase in component grain size and a diversearray of clast types. Most notably there is an increase in chert grainsamongst medium-grained, subrounded to rounded, opaque and pink quartzgrains that constitute the bulk composition. This exotic array of clasts sep-arates this facies association from the more common arenites of previouslydescribed facies. Ichnofauna at this locality are low diversity and dominatedby large pellet-lined Ophiomorpha nodosa. At all localities, the top surfaceof these facies is a sharp contact with offshore siltstones of facies associ-ation A.

Interpretation.—Irregularly distributed, coarse-grained, bioturbatedbeds capping shoreface parasequences are typical of reworked transgressivelags that develop as a result of wave ravinement during landward migrationof the shoreline (e.g., Bhattacharya and Walker 1992). However, unlikemany previously described transgressive lags (e.g., Suter and Berryhill1985; Demarest and Kraft 1987) the coarse beds at the top of the Emeryparasequences are relatively thin and their basal surfaces are only mildlyerosional. In addition, their association with lower-shoreface deposits sug-gests that these sandstones are not the products of in situ (fair-weather)wave ravinement. Indeed, the coexistence of Rosselia and Asterosoma atSection 1 suggests a period of continued deposition at the top of the lowershoreface (e.g., Pemberton et al. 2001). Nonetheless, their position at thecrests of coarsening-upward parasequences suggests an intrinsic relation-ship to rising relative sea level. Rather than being the products of in situreworking, these sandstones are interpreted to have been transported off-shore during transgressive ravinement of proximal shoreface sectors, per-haps during storms. The minor basal erosion is considered a consequenceof gentle scour associated with basinward sediment transport and the mi-gration of three-dimensional dune forms across the sea floor, the unevendistribution of this facies probably reflecting an irregular nature to suchoffshore transport. The southward, shoreline-parallel paleoflow recorded bythe trough cross-stratification may be a product of geostrophic flows gen-erated by pressure gradients at the shoreface during intense storms (Duke1990), although this interpretation remains speculative in the absence ofmore substantial paleocurrent data. The ubiquitous sharp contacts at thetops of these beds with siltstones of facies association A defines a landwardshift in facies and a return to offshore deposition, and are interpreted asparasequence flooding surfaces.

SUBSURFACE FACIES

Four intervals from the Cockrell #1 core have been logged in detail,revealing a wide range of nonmarine facies lying between 1000 and 1600m depth below the surface of the Wasatch Plateau (Figs. 7, 8). The wellpenetrated 570 m of time-equivalent nonmarine strata to the shoreface unitsin outcrop west of Price. The succession constitutes coals, organic mud-stones, and siltstones with interbedded, variable-thickness sandstones.

Facies Association C: Interbedded Sandstones, Siltstones, Mudstones,and Coals

Description.—Sandstone facies are diverse, with variable grain sizes,sedimentary structures, and bedding surfaces. Individual sandstone beds arefine to medium-grained, flat-based to erosionally based, and are either well-sorted and cross-bedded, or carbonaceous and massively bedded. In theformer, units commonly fine upward from medium- to fine-grained sandand range from 3 to 7 m in thickness. Foresets of decimeter-scale cross-beds are dominantly planar, but a few examples have slight asymptoticbases indicating trough cross-bedding (Fig. 7A). Soft-sediment deformationstructures are commonly interspersed with pristine cross bedding. The car-bonaceous sandstones may also reach significant thickness, but they tendto be more variable than their cross-bedded counterparts. Soft-sediment


FIG. 10.—Cliff section of Emery benches south of Emery. Each bench represents a coarsening-upward, storm-dominated parasequence, capped by a marine floodingsurface. Photo taken looking south. Notice the thicker parasequences at the base of the photo and the flooding surface at the top of parasequence 6, which provides aregional datum for correlation. Parasequences overlying this flooding surface are aggradationally stacked.

→

FIG. 11.—Stratigraphic correlation of the Emery Sandstone Member along the length of the Wasatch Plateau. A flooding surface capping parasequence 6 provides thedatum for this correlation. Correlations are extended into the subsurface wells using gamma-ray logs are shown. Shoreface units occur in two areas (north and south) andare separated by a mudstone-rich intervening section. The succession is subdivided into systems tracts, and lithostratigraphic nomenclature of Fouch et al. (1983) appearson the right-hand side of the cross section. Three regressive–transgressive cycles are defined by highstand (HST) and transgressive systems tracts (TST). Note the northwardthickening along the length of the profile. Continuous and hashed lines give levels of high and low confidence in the correlation, respectively. Refer to Figure 1 for locationsof measured sections.

deformation and rip-up clasts are ubiquitous (Fig. 7B). A 6-m-thick, ero-sionally based, massive sandstone was recovered and contains concentratedleaf debris and an isolated, thin, cross-bedded interval. Other carbonaceoussandstones range from 0.2- to 1-m-thick, are flat-based rather than ero-sionally based, normally and inversely graded, massive to wavy bedded,and contain abundant organic debris and coal flasers (Fig. 7C, D).

Interbedded with sandstones are dark-gray organic mudstones and silt-stones (Fig. 7E). These sections are wavy-laminated, may contain very thin,fine-grained, sand laminae, and coal flasers, and reach a maximum thick-ness of 3 m. The core recovered a single incomplete coal bed at least 0.5m thick in addition to a number of other thinner coals. These coals rangein quality from low-grade fusains to clean vitrains. Early subsurface wellspenetrated several coalbeds 3–6 m thick (Edson et al. 1954), and, morerecently, coals as thick as 3.3 m have been reported from a well near CastleDale in the central Wasatch Plateau, occurring as six separate beds andreaching a cumulative thickness of over 10 m (Roberts and Kirschbaum1995). Present coal estimates suggest that a cumulative thickness of asmuch as 40 m in 17 beds may be present in the northern Wasatch Plateau(Tabet and Quick 2003).

Interpretation.—The erosionally-based, fining-upward, cross-beddedsandstones are considered to be the fills of fluvial channels (Allen 1964).Decreasing flow velocities towards the higher parts of the barform and asystematic decrease in grain size and bedform definition upward reflect the

lateral migration of the channel macroform across the flood plain (Allen1970a, 1970b; Bridge 1975, 1977). Bedload transport of sediment and themigration of straight- and sinuous-crested dune forms over the bar gaverise to cross-bed sets. Rapid rates of sedimentation during high flood stagesresulted in loading of the bar and soft-sediment deformation associated withwater escape.

Carbonaceous sandstones and organic fines represent adjacent overbankenvironments. Thick carbonaceous sandstones are attributed to crevassechannel deposits that received sand-grade sediment during flood-inducedbreaching of fluvial channel levees. Similarly, thinner sandstones were de-posited as distal equivalents to the crevasse channels on crevasse-splaylobes and in the most distal parts are interbedded with organic floodplainfines (Farrell 1987). The organic overbank fines most likely reflect highwater tables within the flood plain, occurring as peat swamps or lakes thatreceived wind-blown sediment and sediment from suspension during epi-sodic flooding.

Anoxic delta-top environments are indicated by coals, the thicker ex-amples of which are probably the products of raised mires whilst the thinnercounterparts may have been deposited in smaller lakes or low-lying mires(McCabe 1991). The widespread occurrence of thick coals provides a sen-sitive monitor of balanced rates of peat growth and accommodation gen-eration (McCabe and Parrish 1992; Bohacs and Suter 1997). Although thecontinuity of these coals is difficult to determine with any level of certainty


given the wide spacing of drill holes available, it is clear that coal-formingenvironments were prominent, long-lived features of the Santonian coastalplains in central Utah.

DEPOSITIONAL MODEL

Upward-coarsening successions comprising facies association A are par-ticularly prevalent in the northern and southern parts of the Wasatch Pla-teau. Central parts of the plateau are significantly muddier where sheetsandstones of facies association A are replaced by a monotonous successionof offshore siltstones. In a regional context, the Wasatch Plateau is alignedapproximately parallel to depositional strike, and thus the apparent pinchingand swelling of sandy facies along the outcrop belt is interpreted to berepresentative of a curvilinear trend to the shoreline, defining two deposi-tional promontories. In subsurface drill-hole data to the west, prograda-tional shoreface parasequences occur as upward-coarsening, serrated, gam-ma-ray log responses. In more proximal (westernmost) positions, thesewell-log motifs are replaced by sandy sections, consisting of blocky, fining,and coarsening-upward log motifs interspersed with muddier intervals thatcorrespond to coastal-plain deposits of facies association C (Fig 8).

A dominance of bidirectional current indicators in shoreface facies inoutcrop and a general absence of typical prodeltaic facies (e.g., climbing-rippled sandstone and mudstone interbeds, suppressed intensity and diver-sity of ichnofauna, etc.), suggests that these sandstones accumulated alonglong linear strandplains. Lateral transitions in mud-to-sand content thatmight be expected to occur across the mouths of wave-modified deltas (e.g.,Bhattacharya and Giosan 2003) are not apparent in the laterally continuouslower-shoreface facies of the Emery Sandstone that extend for many tensof kilometers along the plateau. Despite delta-front facies being absent,rivers draining the Sevier Orogen must have carried sediment to the Emeryshoreline, because such facies are represented in the subsurface (Fig. 8).We infer that in the southern part of the Wasatch Plateau a number of smallrivers, rather than a single large system, transported sediment northeast-wards to the northwest-trending shoreline. Similarly, in the northern partof the plateau, a number of smaller rivers are inferred to have carriedsediment eastwards to a coeval north-trending coastline. The lateral con-tinuity of the shoreface facies suggests that the coastline likely receivedsediment from symmetrical wave-dominated deltas attached to long strand-plains (Bhattacharya and Giosan 2003). Given these considerations, thepaleogeography of the Emery Sandstone may bear a close similarity to themodern Nayarit Coast of Mexico (Fig. 9; Curray et al. 1969; McCubbin1982; Walker and Plint 1992). Depositional promontories of this deltaic,wave-dominated strandplain appear to be related to a combination of delta-front fluvial deposition and efficient alongshore transport of sand to pro-duce long strandplains extending many tens of kilometers away from thedelta mouths (Bhattacharya and Giosan 2003). Thus the general lobate ex-pression of the Emery shoreline and the broad sandy promontories in south-ern and northern parts of the Wasatch Plateau most likely represent theclustering of small rivers that dissected the strandplain. Landward of theEmery shorefaces, the coastal plain is interpreted to have been dominatedby subaqueous organic-rich environments, most notably large, raised peatmires capable of producing thick coal seams.

PARASEQUENCE SETS AND SYSTEMS TRACTS

Upward-coarsening parasequences stack to produce a vertical successionover 200 m thick in the most proximal outcrop sections. A total of 17parasequences have been identified, labeled 1 through 17 from oldest toyoungest. Much of the Emery Sandstone is marked by minor facies-tractoffsets across flooding surfaces, producing a thick stack of shoreface sand-stones in outcrop (Fig. 10). With only a restricted quantity of core andwell-log data available, outcrop-to-subsurface correlations remain tentative.However, where possible, flooding surfaces identified in outcrop have been

tied to coals in the nonmarine realm, because such lithologies in the sub-surface often reflect rising watertables associated with relative sea-level rise(Bohacs and Suter 1997).

Figure 11 is a correlation of the Emery shoreface parasequences alongthe length of the plateau. The thickness of the Emery Sandstone in thesubsurface is greater to the north where it thickens from over 350 m inPhillips US ‘‘D’’ # 1 well in the southwestern part of the Wasatch Plateauto over 500 m in the Cockrell # 1 core. The wholesale architecture of theEmery Sandstone is represented by initial progradation of the shoreline,followed by overall long-term aggradation. Such a thick succession of ag-graded shorefaces is consistent with the interpretation that the Emery Sand-stone represents a time of balance between sediment supply and accom-modation (Chan 1990). Significantly however, major basinward facies tractdislocations and erosional surfaces are absent within the Emery strata. Su-perposed upon the long-term aggradation are a series of higher-frequencyregressive–transgressive cycles that are characterized by a sequential evo-lution from highstand to transgressive systems tracts. These cycles occuras subtle changes in shoreface stacking pattern and are present in bothnorthern and southern parts of the Wasatch Plateau (Figs. 11, 12). Themeans of separating the two systems tracts is through the recognition offlooding surfaces that are of demonstrably greater magnitude than the par-asequence boundaries that separate individual highstand parasequences.Falling-stage and lowstand systems tracts are absent, and thus the meansof partitioning each cycle must be achieved through the recognition ofmajor flooding events. In this way, these cycles are distinct from conven-tional Exxon sequences (sensu Vail et al. 1977; Van Wagoner et al. 1988),because correlations cannot be made through the identification and tracingof subaerial exposure surfaces or surfaces of erosion. Three regressive–transgressive cycles are identified.

Cycle 1

Cycle 1 is perhaps the most stratigraphically significant of the threecycles, because it is the highstand systems tract of this cycle that constitutesthe oldest shoreface units of the Emery Sandstone in outcrop. In the sub-surface, a gentle cleaning upward of the gamma ray log, over at least 30m, identifies the outbuilding of the shoreline. This unusually thick para-sequence appears to be entirely conformable in the central and easternWasatch Plateau, reflecting normal progradation of the shoreline. Otheranomalously thick parasequences have been described from the CampanianBlackhawk Formation in the Book Cliffs that record the filling of accom-modation space following a major flooding event (Reynolds 1999; Hamp-son and Storms 2003). This initial parasequence is overlain by a thinnerbut equally sand-rich parasequence, defining a progradational parasequenceset (parasequences 1 and 2). In outcrop, this parasequence consists of afew thin sandstone ribs that project from the Mancos Shale in the northernpart of the study area but is more clearly defined by lower-shoreface sand-stones in the south. An abrupt flooding event at the top of this parasequenceforced the shoreline landward and offshore siltstone deposition resumedalong the eastern edge of the Wasatch Plateau.

Cycle 2

In outcrop, the lowermost part of this cycle is dominated by gray silt-stones in the northern part of the study area and by sandier, thin shorefaceparasequences in the south. The true architecture of the highstand systemstract of this cycle is represented in gamma-ray logs where successive up-ward cleaning and thickening motifs record the deposition of a prograda-tional parasequence set (parasequences 3 and 4). The youngest parase-quences in this cycle (parasequences 5 and 6) are well exposed in both thenorthern and southern parts of the plateau and continue the progradationalstacking pattern defined in the subsurface. These parasequences correspondto the Garley Canyon beds of Fouch et al. (1983). Their lateral continuity


FIG. 12.—Stratigraphic correlation parallel todepositional dip through Haley Canyonimmediately to the west of Price. The sectionhighlights the minimal offsets of facies tractsacross parasequence boundary flooding surfaces.The parasequences can be traced to their down-dip depositional pinchouts in the area north ofPrice. Note the similarity of stacking patternswith respect to that in the southern part of theWasatch Plateau in Figure 11.


FIG. 13.—The McCabe and Shanley (1992)model accounting for the organic control byimmobile raised mires on the long-termaggradation of shoreface strata. Similarstratigraphic relationships are envisaged in theaggradational stacking of the Emery Sandstone.

allows the tracing of the capping flooding surface along the entire lengthof the plateau, and has been used for the stratigraphic datum in Figure 11.This abrupt flooding event is all that constitutes the transgressive systemstract of cycle 2.

Cycle 3

The lower two thirds of cycle 3 comprises aggradational to prograda-tional stacking of shoreface parasequences. Early aggradation (parasequ-ences 8 to 12) is represented by a repetitious succession of sandstonebenches in the hillside, interpreted as early highstand systems tract depositsthat precede strong progradation associated with late highstand systemstract deposition (parasequences 13 and 14). At the top of parasequence 14lies an upward-thinning succession of parasequences (parasequences 15 to17) that record the successive landward migration of the shoreline as risingrelative sea level began to outpace sediment supply. This backsteppingpattern constitutes a thin transgressive systems tract capping the EmerySandstone Member prior to prolonged deposition of shelf siltstones of theBlue Gate Shale over the eastern Wasatch Plateau area. Accordingly, theflooding surface capping parasequence 17 represents the maximum floodingsurface of the Emery regressive wedge and corresponds to the top of thetransgressive systems tract and the base of a subsequent highstand systemstract as documented by Schwans (1995).

DISCUSSION

The Emery Sandstone provides an unusual record of long-term aggra-dational parasequence stacking, unbroken by erosional sequence boundar-ies. The sequence stratigraphic and paleogeographic significance of thesedeposits is analyzed through a discussion on: the role of organic accumu-lations in the aggradational stacking of shoreface strata; the origin of strati-graphic cycles; and the tectonic effects on long-term stratigraphic architec-ture, sediment thickness patterns, shoreface orientations, loci of sedimentinput points and depositional process dominance at the shoreline, in con-trast with younger and older fluvial-dominated regressive wedges.

Santonian Paleogeography of Central and Southern Utah: Implicationsfor Shoreface Stacking Patterns

The long-term balance between accommodation creation and sedimentsupply is worthy of further discussion, not least because thick successionsof aggradational paralic strata are relatively rare in published literature.McCabe and Shanley (1992) demonstrated that aggradational stacking pat-terns in the Santonian John Henry Member of southern Utah was intricatelycontrolled by the immobility of raised peat mires lying landward of storm-dominated shorefaces that prevented relative sea-level rises from inundatingthe coastal plain (Fig. 13). In a subsequent paper, Shanley and McCabe(1995) suggested that an erosional surface at the top of the John HenryMember could be correlated to a postulated sequence boundary within theEmery Sandstone. We find no evidence for this sequence boundary andinstead propose that the Emery Sandstone is time equivalent to the mainbody of the aggradational John Henry Member.

This correlation is corroborated by ammonite biostratigraphy. Peterson(1969) collected a single fragment of the middle Santonian ammonite,Clioscaphites vermiformis, within marine mudstones that project to shore-

face sandstones lying in the middle part of the John Henry Member (Cob-ban et al. 2000). The same fauna was also identified by Cobban (1976)from the middle and lower parts of the Emery Sandstone. The mutualoccurrence of this ammonite in both the Wasatch and Kaiparowits plateausin these strata suggests that the period of aggradational stacking was pene-contemporaneous in both areas and that the Emery Sandstone cannot becorrelated to an erosional sequence boundary in the Kaiparowits Plateau.Consequently, correlating the Emery Sandstone with the aggradational,coal-bearing interval of the John Henry Member might suggest that theorganic controls responsible for this architecture in the Kaiparowits Plateauextended northwards into the Wasatch Plateau and exerted the same influ-ence on the stacking of Emery parasequences. Hence shore-parallel, raisedmires lying up-dip of the Emery shorefaces may have contributed to thelong-term aggradational shoreface stacking pattern. Given the large quan-tities of coal already estimated in the subsurface of the Wasatch Plateau(e.g., Tabet and Quick 2003) this model can be applied as an additionalmeans to estimate positions, thicknesses, and geometries of coals associatedwith aggradationally stacked shorefaces.

Origin of Regressive–Transgressive Cycles

Multi-frequency stratigraphic cyclicity as a function of sediment supply,subsidence, and eustatic variables in Western Interior Cretaceous depositshave been frequently cited (e.g., Gardner 1995b; Kamola and Huntoon1995; Houston et al. 2000). Compelling evidence from subsurface seismicsurveys indicates that the Campanian regression of the Blackhawk For-mation of the Book Cliffs (lasting approximately 3.5 Myr, Fouch et al.1983) coincides with significant tectonic movement along the Charleston-Nebo thrust (Horton et al. 2004). Kamola and Huntoon (1995) and Houstonet al. (2000) ascribed tectonic controls on sediment supply as the primarycause of higher-frequency, 500–600 kyr regressive members in these strata,which they attributed to hinterland thrust motion. The effects of eustasy asa driving mechanism for these contrasting duration cycles were consideredinsignificant (Kamola and Huntoon 1995; Houston et al. 2000; Horton etal. 2004). The constrained age of the Emery Sandstone to 85.7–83.9 Maindicates an upper limit of individual parasequence duration approximatingto 100 kyr and a regressive–transgressive cyclicity representing some 600kyr, comparable to Blackhawk member-scale frequencies.

The model of Kamola and Huntoon (1995) and Houston et al. (2000)may have applicability to the Emery Sandstone wedge; however a numberof studies have concluded that a global glacio-eustatic signature can bedeciphered in the Late Cretaceous, and notably, that a high-frequency San-tonian component was responsible for a number of eustatic sea-level falls(Haq et al. 1988; Hancock 1993; Sahagian et al. 1996; Miller et al. 2003).Proposed age dates for the initiation of the Canyon Range, Pavant andNebo thrust sheets range from 90 to 97 Ma (Cross 1986; Heller et al. 1986;Talling et al. 1994). Active thrusting may have continued into the Santonianalong various salients (DeCelles 1994; Talling et al. 1994), but Villien andKligfield (1986) suggested that during the Coniacian to early Santonian theSevier Orogen in central Utah was in a period of relative inactivity. Hencein the case of the Emery Sandstone tectonic pulses cannot account fordepositional cyclicity alone. Moreover, the alongstrike uniformity of shore-face stacking patterns favors a regional, and arguably eustatic mechanism.

Many of the member-scale cycles documented from the Blackhawk For-


FIG. 14.—Paleogeographic reconstructions for the Late Cretaceous of central Utah, summarizing long-term shoreline trends. A) The Turonian upper Ferron Sandstoneprograded northeast along southern Castle Valley and coincides with the decay of an older deltaic succession (lower Ferron Sandstone) farther to the north (modified fromGardner 1995a). B) Similarly in the southern Wasatch Plateau, Santonian shorefaces belonging to the Emery Sandstone are interpreted to have prograded in a northeastwarddirection from an area to the southwest. The northern shorefaces of the Emery Sandstone are considered to have been oriented closer to N–S. C) Brief southward progradationof the Panther Tongue in the earliest Campanian punctuated the northeastward prograding trend. D) The trend returned during the deposition of the Storrs Member of theStar Point Formation. The long-term continuity of shoreline progradation direction implies a long-term control, perceived in this case to be alongstrike differential subsidence.Positions of the thrust trace are transcribed from Willis (2000), and no palinspastic reconstruction is applied. PX and PV correspond to Paxton and Pavant thrusts,respectively. Black fills indicate the presence of major coal-forming environments in the coastal plain.

mation are bounded by erosional sequence boundaries that developed dur-ing exposure and fluvial incision of the shelf during relative sea-level fall(Kamola and Huntoon 1992; Ainsworth and Pattison 1994; Kamola andVan Wagoner 1995; O’Byrne and Flint 1995; Taylor and Lovell 1995; VanWagoner 1995). In contrast, depositional cycles in the Emery Sandstonecontain no such surfaces or basinward shifts in facies. We propose that thiscontrast between the two regressive wedges reflects the higher-accommo-dation basin setting during the Santonian, driven largely by elevated ratesof subsidence in this segment of the basin. Thus although the Santonianperiod was characterized by high rates of subsidence, hinterland tectonismwas on a short-lived decline. This paradox implies a time lag between theonset of Canyon Range–Pavant–Nebo thrusting and the flexure of the lith-osphere that is consistent with several-million-year time scales of visco-elastic lithospheric response (Quinlan and Beaumont 1984).

Controls on Sediment Thickness, Shoreface Orientations, SedimentTransport Pathways and Shoreface Depositional Styles

Comparing well logs of similar facies composition from the northern andsouthern parts of the Wasatch Plateau, a north-dipping paleoslope of 0.18has been crudely calculated, on the basis of differences in compacted lith-

ological thickness. This northward-dipping basin bathymetry lying parallelto the axis of the crustal load is consistent with a southward-diminishingand long-lived high-subsidence setting for northern Utah, as suggested byRoberts and Kirschbaum (1995). This thinning is also consistent with a700-m-thick, unnamed, stacked shoreface succession along the northernflank of the Uinta Basin of northern Utah (Molenaar and Wilson 1992),and to the time-equivalent, 200-m-thick John Henry Member of the StraightCliffs Formation in southern Utah (Shanley and McCabe 1991; Hettinger1993). The inferred elevated rates of flexural subsidence correspond to, orare slightly later than, a period of thrust-sheet propagation focused in north-east Utah and southwest Wyoming that resulted in over 30 km of horizontalshortening between 89 and 84 Ma (DeCelles 1994).

High rates of subsidence inferred in northern Utah may account for thenorthwesterly skew of Emery shorefaces in the southern part of the WasatchPlateau. Similar paleoslopes are envisaged in the progradation of older andyounger strata and may suggest a long-term control on sedimentation pat-terns (Fig. 14A–D). The Ferron Sandstone (Fig. 14A) is a middle to lateTuronian, northeastward-prograding shallow marine and continental suc-cession that crops out in southern Castle Valley (Hale 1972; Ryer 1981;Gardner 1995a). Its northeastward sediment distribution pattern was attri-buted to structural uplift in the area of the present-day San Rafael Anticline


FIG. 15.—Possible sediment pathways in central Utah during the Turonian to earliest Campanian interval. Structural recesses or reentrants in the trace of the thrust frontcoincide with inferred sediment source areas providing a primary control on the delivery of sediment to Late Cretaceous shorelines. Structural map modified from Willis(2000).

(Gardner 1995a). In light of regional subsidence distributions, a tectonicslope could have played a similar role in dictating the broad shorefacearchitecture. The earliest Campanian Panther Tongue of the Star PointSandstone (Fig. 14C) represents a short-lived departure from the long-term,northeastward sediment distribution pattern. However, sediment distribu-tion patterns during deposition of this unit were towards the southwest(Newman and Chan 1991), and parallel to the structural grain of the Sevierorogenic belt, suggesting that sediment transport orientations were con-trolled by the geometry and position of the foredeep, and therefore, regionalslope gradients. The Storrs Member of the Star Point Sandstone, which

overlies the Panther Tongue, is also of early Campanian age (Fig. 14D)and consists of shallow marine and continental deposits that stepped pro-gressively basinward from southwest to northeast along the length of theWasatch Plateau (Flores et al. 1984; Dubiel 1999). Northeast-steppingshorefaces of this interval merge with the southeastward prograding shore-faces belonging to the lowermost part of the Blackhawk Formation (Ka-mola and Van Wagoner 1995) in the subsurface of the western and south-western parts of the Wasatch Plateau (D. Tabet, written communication2003). Schwans (1995) concluded that local thickness changes in the EmerySandstone Member were controlled by the position of lineament offsets in


the thrust trace, giving localized areas of increased subsidence. From thisstudy, it is also likely that at a regional scale the thickness contrasts andsediment distribution patterns along strike are governed by foreland basinsubsidence heterogeneity and spatial non-uniformity of thrusting events inthe orogen.

A common trend amongst Late Cretaceous regressive wedges in centralUtah is the locations of the sediment input points. As discussed, the Emeryrivers draining the Sevier highlands are inferred to have been concentratedin the southernmost and northernmost extremities of the Wasatch Plateau.These sediment-transport pathways coincide spatially with the location ofsediment input points related to the deposition of the Turonian lower andupper Ferron Sandstone Members (Cotter 1975; Ryer and McPhillips 1983;Ryer 1984; Ryer and Lovekin 1986; Gardner 1995a). The longevity ofthese zones of sediment input is exhibited by the southward progradationof the Panther Tongue Member in the northern part of the Wasatch Plateau(Newman and Chan 1991) and the northeastward and southeastward pro-gradation of the earliest Campanian Storrs Member (Flores et al. 1984;Dubiel 1999). The long-term existence of these northern and southern sed-iment input points in central Utah shows a close correspondence with majorstructural offsets or recesses in the trace of the thrust front (Fig. 15). Thus,although the shoreline orientation appears to be controlled by the distri-bution of subsidence, the spatial position of the regressive wedges appearsto be controlled by the distribution of major thrusts.

Although the points of sediment entry into the basin during Emery de-position may correspond with that of overlying and underlying strata, somefundamental differences in depositional style exist between these regressiveevents. The upper Ferron and Panther Tongue members have a stronglyprogradational architecture and are characterized by river-dominated deltaiccoastlines, relatively unmodulated by wave or storm activity (Newman andChan 1991; Gardner 1995a). Parasequences are reported to comprise coars-ening-upward successions composed of delta-front and distributary-channelsandstones (Newman and Chan 1991; Gardner 1995a). In contrast, the com-paratively gentle Emery regression produced a succession of laterally con-tinuous parasequences ornamented by beds deposited by storm events andreworking of the shoreface with little evidence of deltaic influence.

The contrasting depositional style of the Emery Sandstone with respectto the upper Ferron and Panther Tongue members could be attributed tochanges in rates of sediment supply or the depositional response to a re-duced wave fetch. Quantifying wave fetch is tenuous without better controlon the eastward extent of the seaway for each of the respective regressions.However, it is considered unlikely that variations in wave fetch played amajor role, because in each regression described above, the basinward ex-tent of their shorelines is constrained to a 15 km zone between the easternedge of the Wasatch Plateau and the western margin of the San RafaelAnticline. Presumably any loss of wave fetch would be similar in eachregression. Dominance of riverine processes occurring at the onset of upperFerron and Panther Tongue regressions may instead reflect elevated ratesof sediment supply either as a consequence of relative sea-level fall, as inthe case of the Panther Tongue (Posamentier and Morris 2000), or fromhinterland tectonics, as in the case of the Ferron Sandstone (Gardner1995a). As discussed, the Santonian in central Utah is reported to havebeen a period of relative tectonic quiescence (Villien and Kligfield 1986), andmajor sequence bounding unconformities pertaining to relative sea-level fallsare not identified in the Emery Sandstone. We propose that the wave-dominatedshorelines of the Emery Sandstone are thus a reflection of low sedimentationrates relative to that of the Ferron and Panther Tongue regressions, perhapscontrolled by subsidence-suppressed eustatic sea-level falls.

CONCLUSIONS

1. The Emery Sandstone Member comprises 17 upward-coarsening,storm-dominated parasequences composed of HCS and heavily bioturbatedsandstones exposed in outcrops along the eastern edge of the Wasatch

Plateau. Shoreline progradation was confined to two spatially disjunct de-positional complexes at the northern and southern extremities of the Wa-satch Plateau. The southern, NW–SE oriented shoreline prograded towardsthe NE concomitantly with eastward regression of a N–S trending coastlinein the north. Shorelines are interpreted to have consisted of linear strand-plains dissected by numerous small rivers.

2. The broad-scale architecture of the Emery regression is progradationalto aggradational. Prolonged aggradation indicates a fine balance betweensediment supply and accommodation creation that may have been regulatedby the presence of raised peat mires lying landward of the shoreline. Wavedominance at the shoreline is proposed to reflect modest rates of sedimentsupply during a period of high accommodation.

3. Superposed on the overall aggradational trend are three higher-fre-quency regressive–transgressive cycles that lack sequence boundaries. Thecyclicity in this wedge is considered to reflect subsidence-suppressed eu-static sea-level falls during a period of tectonic quiescence in the westwardthrust belt. High rates of subsidence coupled with hinterland tectonic qui-escence may reflect a delay between crustal loading and viscoelastic re-sponse of the lithosphere.

4. An improved long-term (. 10 Myr) understanding of the EmerySandstone allows a number of inferences to be made regarding forelandbasin evolution. The architecture of successive regressive wedges in centralUtah was controlled by the geometries of the bounding thrust belt. Con-centrated thrust complexes in northern Utah are attributed to the inferredgeneration of a northward-dipping depositional slope. This slope is consid-ered the primary control on the progradation direction of successive shore-line regressions during the Late Cretaceous. Inferred sediment conduits thatfed the Emery Sandstone shorelines are reflected in equivalent depocenterpositions of older and younger clastic wedges. These geographic points ofsediment delivery appear to coincide with offsets or embayments in thetrace of the thrust belt. Consequently, the geometry of the thrust belt isconsidered to be a first-order control in the supply of sediment to LateCretaceous shorefaces.

ACKNOWLEDGMENTS

This paper forms part of a PhD thesis carried out by the first author for whichthe University of Liverpool and ENI London Technical Exchange are gratefullyacknowledged for their financial support. Jonathan Craig at ENI-LTE is particularlythanked for his foresight and engagement in the project. We thank Dave Tabet (UtahGeological Survey) for his helpful field advice and reviewing of the manuscript.The manuscript benefited greatly from detailed discourses with Trevor Elliott (Uni-versity of Liverpool) and Rob Gawthorpe (University of Manchester) and from re-views by Janok Bhattacharya, Marjorie Chan, and John Holbrook. In addition theUtah Geological Survey are thanked for providing facilities and core data. Bob Jones(BP) and the Natural History Museum, London, are thanked for their attempts todate mollusc fragments from field collections. The views expressed in this paper arethose of the authors and not necessarily representative of those at ENI-LTE.

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Received 3 December 2003; accepted 26 August 2004.

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