ALONG-STRIKE AND DOWN-DIP VARIATIONS IN SHALLOW...

Journal of Sedimentary Research, 2011, v. 81, 159–184

Research Article

DOI: 10.2110/jsr.2011.15

ALONG-STRIKE AND DOWN-DIP VARIATIONS IN SHALLOW-MARINESEQUENCE STRATIGRAPHIC ARCHITECTURE: UPPER CRETACEOUS STAR POINT SANDSTONE,

WASATCH PLATEAU, CENTRAL UTAH, U.S.A.

GARY J. HAMPSON,1 M. ROYHAN GANI,2 KATHRYN E. SHARMAN,*1 NAWAZISH IRFAN,{1 AND BRYAN BRACKEN3

1Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, U.K.2Department of Earth and Environmental Sciences, University of New Orleans, 2000 Lakeshore Drive, New Orleans, Louisiana 70148, U.S.A.

3Chevron Energy Technology Company, 6001 Bollinger Canyon Road, San Ramon, California 94583-0719, U.S.A.

e-mail: [email protected]

ABSTRACT: The sequence stratigraphic architectures of shallow-marine deposits in the upper Cretaceous Star Point Sandstoneare analyzed over a large (c. 100 km), nearly continuous outcrop section aligned oblique to depositional strike. The unit consistsof five parasequences that predominantly comprise wave-dominated shoreface–shelf deposits. Two parasequences contain river-dominated delta-front deposits locally. Within each parasequence, wave-dominated shoreface–shelf deposits record 7–45 km ofESE- to ENE-directed progradation of a linear to moderately lobate shoreline that was supplied with sediment by longshoredrift and subjected to strong offshore sediment transport by storms. Wave-dominated shoreface sandstones in eachparasequence thin and wedge out over short distances (,, 500 m) at their updip pinchouts. Lower-shoreface sandstones in eachparasequence split down dip into multiple, vertically stacked, upward-coarsening bedsets separated by tongues of offshoremudstones in distal locations associated with rapid deepening of antecedent paleobathymetry. River-dominated delta-frontdeposits define progradation of strongly lobate shorelines in an overall direction oriented subparallel to the regional shorelinetrend and into locations sheltered from wave energy. These progradation directions are consistent with deflection of the deltasby wave-driven longshore currents.The arrangement of parasequences in the Star Point Sandstone defines an overall concave-landward shoreline trajectory,

with decreasing progradation and increasing aggradation through time. Along-strike variations in this trajectory pattern reflectincreased tectonic subsidence towards the north combined with highly localized, large-volume, fluvial sediment supply near thenorthwestern limit of the study area during deposition of an areally extensive (. 800 km2) river-dominated delta-front complex(Panther Tongue). This highly focused fluvial sediment flux probably occurred via a structurally controlled sediment entry pointbetween two active thrusts.

INTRODUCTION

Current, widely used sequence stratigraphic models of shallow-marinestrata emphasize variability down depositional dip at the expense ofchanges in facies character and stratigraphic architecture along deposi-tional strike (e.g., Martinsen and Helland-Hansen 1995). Thus, models ofalong-strike variability of sequence stratigraphic architecture remainlargely speculative and are based on relatively few well-documentedexamples, particularly at outcrop. Here we present and analyze a high-quality outcrop dataset from the Star Point Sandstone of central Utah,U.S.A., which represents a series of predominantly wave-dominatedshorelines and associated nearshore to shelfal strata. Exposures of thesestrata in the eastern Wasatch Plateau provide a large (c. 100 km), nearlycontinuous section aligned oblique to depositional strike. To date, thesestrata have been described by few previous workers, who have focused on

only specific parts of the outcrop belt (Flores et al. 1984; Dubiel et al.2000; Holman 2001). Coeval and contiguous strata are exposed in anoverall dip orientation in the well-documented Book Cliffs. The aims ofthis paper are threefold: (1) to present a parasequence-scale sequencestratigraphic framework for the Star Point Sandstone over the wholeeastern Wasatch Plateau outcrop belt; (2) to describe the facies characterand internal architecture of parasequences within this framework, withparticular emphasis on their up-dip and down-dip pinchouts; and (3) todocument and interpret along-strike variability in shallow-marine faciescharacter and stratigraphic architecture.

GEOLOGIC SETTING AND PREVIOUS WORK

The Star Point Sandstone was deposited along the western shoreline ofthe Cretaceous Western Interior Seaway, which extended from north tosouth across the North American continent (e.g., Kauffman and Caldwell1993; inset map in Fig. 1). The unit comprises shallow-marine sandstonesthat overlie and interfinger with the offshore deposits of the MancosShale, and it is overlain by the coal-bearing coastal-plain deposits of the

* Present address: Anadrill Schlumberger, Cabinda Gulf Oil Company Limited,

Malongo Terminal, Cabinda{ Present address: Pakistan Petroleum Limited, Exploration Department,

House No. 59/A, Ismail Zabeeh Road, Faisal Avenue, F-8/4, Islamabad, Pakistan

Copyright E 2011, SEPM (Society for Sedimentary Geology) 1527-1404/11/081-159/$03.00

Blackhawk Formation (Fig. 2; Spieker and Reeside 1925; Clark 1928;Spieker 1931). The Star Point Sandstone is late Santonian to earlyCampanian in age (Fouch et al. 1983) and forms the lower part of theMesaverde Group in the eastern Wasatch Plateau (Spieker and Reeside1925). In combination, the Star Point Sandstone, the BlackhawkFormation, and the Castlegate Sandstone form an eastward-thinningwedge of siliciclastic coastal-plain and shallow-marine strata that passesbasinward into the offshore Mancos Shale (Young 1955; Balsley 1980).The sediment in this wedge was eroded and transported from the Sevierorogenic belt to the west (e.g., Kauffman and Caldwell 1993; inset map inFig. 1), most likely from the Canyon Range Culmination c. 80 km west ofthe outcrop belt in the eastern Wasatch Plateau (DeCelles and Coogan2006). Tectonic subsidence near the western margin of the WesternInterior Seaway was produced by a combination of short-wavelength,thrust-sheet loading in the Sevier Orogen and long-wavelength subsidencerelated to subduction of the Farallon plate beneath North America (e.g.,Kauffman and Caldwell 1993; Liu and Nummedal 2004). Since the StarPoint Sandstone is located close to the coeval Sevier orogenic thrust-sheetload (, 100 km), it was probably deposited in the flexurally subsidingforedeep. During the Late Cretaceous, the Wasatch Plateau occupied apaleolatitude of approximately 42u N and had a warm, humid climate(Kauffman and Caldwell 1993).

Most published work on the Star Point Sandstone has focused on itscontext relative to the coal resources of the lower part of the BlackhawkFormation in the Wasatch Plateau coalfields (Spieker 1931; Doelling1972; Hayes and Sanchez 1979; Sanchez and Hayes 1979; Sanchez andBrown 1983, 1986, 1987; Sanchez et al. 1983a, 1983b; Flores et al. 1984;Brown et al. 1987; Sanchez 1990; Sanchez and Ellis 1990; Dubiel et al.2000; Gloyn et al. 2003; Quick et al. 2005). This work has establishedstratigraphic schemes for large areas of the southern and northernWasatch Plateau based on mapping of coal seams. The up-dip pinchoutsof several tongues of the Star Point Sandstone and their stratigraphicrelationships to adjacent coal seams have also been documented (Hayesand Sanchez 1979; Sanchez and Hayes 1979; Sanchez and Brown 1983,1987; Sanchez et al. 1983a, 1983b; Flores et al. 1984; Sanchez 1990;Dubiel et al. 2000). In the northwestern Book Cliffs, the Star PointSandstone comprises two sandstone tongues (Young 1955, modified afterClark 1928), in ascending stratigraphic order: the Panther Tongue, which

extends farther basinwards and comprises river-dominated deltaicdeposits with minor wave modification (Howard 1966; Newman andChan 1991; Posamentier and Morris 2000; Olariu et al. 2005; Olariu andBhattacharya 2006; Enge et al. 2010; Olariu et al. 2010), and the overlyingStorrs Tongue, which is thin-bedded and extends only a short distancebasinwards (Fig. 2A). These two tongues and overlying shallow-marinesandstones, which are assigned to the Spring Canyon Member of theBlackhawk Formation in the northwestern Book Cliffs, are all placed inthe Star Point Sandstone in the northern Wasatch Plateau (Clark 1928)(Fig. 2A). In the southern Wasatch Plateau, the Star Point Sandstone ismapped to comprise several sandstone tongues, which become progres-sively older and pinch out into the coastal-plain deposits of theBlackhawk Formation towards the south (Flores et al. 1984; Dubiel etal. 2000). These tongues record deposition in a variety of wave-dominateddeltaic sub-environments, including strandplains, spits, and barrierislands (Flores et al. 1984).

In a sequence stratigraphic context, the various sandstone tongues inthe Star Point Sandstone have been interpreted as parasequences (Dubielet al. 2000; Holman 2001; Mayo et al. 2003), although there are notablediscrepancies in the number and thicknesses of parasequences in differentinterpretations. The Panther Tongue is interpreted to record forcedregression of a river-dominated delta, due to its unusually large extentdown depositional dip and the absence of coeval coastal-lain deposits(Posamentier and Morris 2000). The unit contains prominent delta-frontclinoforms, which are top-truncated and overlain by a transgressiveerosion (ravinement) surface and overlying shallow-marine lag (Posa-mentier and Morris 2000; Hwang and Heller 2002; Howell et al. 2008).

DATASET AND METHODS

The Star Point Sandstone and the overlying Blackhawk Formation andCastlegate Sandstone crop out along the eastern edge of the WasatchPlateau in central Utah, where they form a continuous SSW–NNE-oriented cliff face that exposes up to 150 m of shallow-marine strata and350 m of overlying coastal-plain strata over a distance of c. 100 km(Figs. 1, 2B). This cliff face is oriented subparallel to the regionaldepositional strike of the wave-dominated deltaic shorelines thatconstitute the Star Point Sandstone (Flores et al. 1984; Dubiel et al.

FIG. 1.—Location of the Mesaverde Groupoutcrop belt, which includes the Star PointSandstone, Blackhawk Formation, and Castle-gate Sandstone, in the Wasatch Plateau andcontiguous Book Cliffs. The study area ishighlighted. The inset map (top right) shows thelocation of the outcrop-belt map on the westernmargin of the Late Cretaceous Western InteriorSeaway (after Kauffman and Caldwell 1993).

160 G.J. HAMPSON ET AL. J S R

2000). Several WNW–ESE-trending canyons cut through the cliff face,providing some 3D control on stratigraphic architecture. In addition, theWasatch Plateau exposures are contiguous with the WNW–ESE-orientedBook Cliffs, which expose the same strata in an overall dip orientation(Fig. 1). Thus, the existing stratigraphic framework of the shallow-marineBlackhawk Formation in the Book Cliffs (Balsley 1980; Howell and Flint2003; Hampson 2010) can be extended into the Star Point Sandstone andBlackhawk Formation of the Wasatch Plateau to provide a regionalcontext.

The continuity and degree of exposure of the Star Point Sandstoneoutcrops along the eastern edge of the Wasatch Plateau are excellent (e.g.,Fig. 2B), although most of the outcrops occur in vertical cliff faces or steepslopes that are inaccessible. Thus, many of the interpretations andcorrelations presented in this paper are based on low-angle aerialphotographs of the cliff faces acquired on overview flights. The photographsprovide a continuous view of strata along the main east-facing cliff face,except where canyons dissect this face and small gaps (, 5 km) occur.

Eight measured sections through the Star Point Sandstone werecollected from accessible WNW–ESE-trending canyons (Fig. 3). Themeasured sections record lithology, grain size and sorting, sedimentarystructures, paleocurrents, body-fossil and trace-fossil types, and biotur-bation intensity in the form of bioturbation index logs (e.g., Gani et al.2008). Conventional facies analysis has been carried out using thesemeasured sections. Facies identified in the measured sections havedistinctive weathering characteristics that allow them to be identified withreasonable confidence in the low-angle aerial photographs (Table 1).

In inaccessible parts of the outcrop belt, in between the measuredsections, simple logs over the entire Star Point Sandstone, BlackhawkFormation, and Castlegate Sandstone interval were constructed from thelow-angle aerial photographs at locations marked by prominenttopographic features, which are readily identified on topographicbasemaps (Fig. 3). The thickness of the Star Point–Blackhawk Forma-tion–Castlegate Sandstone interval in each photographic log (typicallyseveral hundred meters) was measured using topographic basemaps. The

relative thickness of the Star Point Sandstone and its constituentstratigraphic units, compared to the total Star Point–BlackhawkFormation–Castlegate Sandstone interval thickness, was then used toestimate the absolute thickness of each stratigraphic unit. Weatheringprofiles were used to interpret vertical facies successions in the Star PointSandstone in each photographic log (e.g., Table 1, Fig. 4). Thephotographic logs provide a proxy for ‘‘ground truth’’ measured sectionsin inaccessible parts of the outcrop belt.199 photographic logs were constructed, with spacings along the cliff face

and canyon walls of 0.2–26.9 km, corresponding to straight-line spacings of0.2–6.0 km (Fig. 3). The distribution of lithologic units was mapped inbetween the logs using the low-angle aerial photographs. This techniqueallows mapping of lithologic units along the main cliff face and canyonwallswith an estimated accuracy of c. 50 m horizontally and c. 10 m vertically.Although this accuracy is less than that achievable by LIDAR and similardigital data-capture techniques (e.g., Bellian et al. 2005; Pringle et al. 2006),it is nonetheless sufficient to construct a gross stratigraphic framework oversuch a large study area (c. 100 km 3 15 km; Figs. 1, 3) at reasonable timeand cost. Our gross stratigraphic framework is based on mapping ofstratigraphic units over 10 m thick, although thinner units (c. 1 m) can beconsistently distinguished in the photographs.Although the SSW–NNE-oriented cliff-face outcrops extend over a

large area and have a high degree of continuity, they present a large two-dimensional (2D) cross section with 3D control provided by WNW–ESE-trending canyon systems. Consequently, aspects of 3D stratigraphicarchitecture are poorly constrained if they occur at a scale smaller thanthe spacing of the cliff face and canyon walls. Some additional 3D controlis provided in a few locations by wells drilled behind the outcrop belt forcoal mining (e.g., Dubiel et al. 2000) and for hydrocarbon explorationand production.

FACIES ASSOCIATIONS, FACIES SUCCESSIONS, AND STRATIGRAPHIC UNITS

Eleven facies have been recognized in the Star Point Sandstone andstratigraphically adjacent Mancos Shale and lower Blackhawk Formation

FIG. 2.—A) Lithostratigraphic summary chart of the Star Point Sandstone and surrounding strata in the Wasatch Plateau and northwestern Book Cliffs (Fig. 1) (afterClark 1928; Young 1955; Dubiel et al. 2000). The Star Point Sandstone, Blackhawk Formation, and Castlegate Sandstone constitute the lower and middle parts of theMesaverde Group in the eastern Wasatch Plateau (Fig. 1). B) Photograph illustrating gross lithostratigraphy exposed in the SSW–NNE-oriented cliff face at the easternmargin of the Wasatch Plateau.

SHALLOW-MARINE STRATIGRAPHIC ARCHITECTURE, STAR POINT SANDSTONE 161J S R


(Table 1). These facies are grouped into five associations: (1) offshoreshelf, (2) wave-dominated shoreline–shelf, (3) river-dominated delta front,(4) marginal-marine back-barrier, and (5) coastal plain.

Offshore-Shelf Facies Association

Deposits of the offshore-shelf facies association (OS facies; Table 1)typify the Mancos Shale. These deposits comprise moderately to intenselybioturbated, siliciclastic mudstones containing a high-diversity trace-fossil assemblage that constitutes a Cruziana ichnofacies, implyingdeposition in an offshore setting below mean storm wave base(Pemberton et al. 1992). Thin sandstone beds are interpreted to recordepisodic influxes of sand in response to anomalously large storms, impliedby wave-rippled beds, and by wave-supported sediment gravity flows andriver-fed turbidites and hyperpycnites, implied by current-rippled beds.

Wave-Dominated Shoreline–Shelf and Marginal-Marine

Back-Barrier Facies Associations

Four facies are interpreted to represent wave-dominated shoreline–shelf deposits (dLSF, pLSF, USF, FS; Table 1). Successions of the wave-dominated shoreline–shelf facies association are similar to those that havebeen described comprehensively from the shallow-marine BlackhawkFormation in the Book Cliffs (e.g., Van Wagoner et al. 1990; Kamola andVan Wagoner 1995; Hampson and Storms 2003; Howell and Flint 2003),and are summarized briefly below. Facies are typically arranged inupward-coarsening successions up to several tens of meters thick thatgradationally overlie offshore-shelf deposits (OS facies) and exhibit aconsistent trend from distal lower-shoreface deposits (dLSF facies) attheir bases through proximal lower-shoreface deposits (pLSF facies) andupper-shoreface deposits (USF facies) to foreshore deposits (FS facies) attheir tops (Figs. 5A, 6). Boundaries between the various facies in thesesuccessions are generally gradational. The vertical facies successions aretypical of regressive, barred, sandy shoreface–shelf successions (Green-wood and Mittler 1985; Clifton 2006). Trace-fossil assemblages in thesesuccessions constitute a mixture of Cruziana and Skolithos ichnofacies inthe lower part (dLSF, pLSF facies) and Skolithos ichnofacies in the upperpart (USF facies), implying deposition in progressively shallower shelfalto nearshore environments (Pemberton et al. 1992). Mapping of lateralfacies trends define local shoreline paleogeographic and proximal-to-distal trends. Offshore-shelf deposits (OS facies) are poorly developed ormissing in paleolandward areas but become thicker and more fullydeveloped in a paleoseaward direction. In contrast, foreshore, upper-shoreface, and proximal lower-shoreface deposits (pLSF, USF, FS facies)thin and pinch out in a paleoseaward direction (cf. Van Wagoner et al.1990).

Stratigraphic units that contain the complete association of wave-dominated shoreline–shelf facies (dLSF, pLSF, USF, FS), upward-coarsening vertical facies successions, and proximal-to-distal facies trendsdescribed above record regression. In paleoseaward locations, suchregressive successions are abruptly overlain either by offshore-shelfdeposits (OS facies) or by thin (, 5 m), upward-fining successions ofdistal lower-shoreface deposits (dLSF facies) that grade into offshore-shelf deposits (OS facies) (e.g., 37–39 m in Fig. 5B). These vertical faciesrelationships record an increase in water depth, either directly across aflooding surface (in the former case) or via a transgressive, upward-deepening succession bounded below by a wave ravinement surface (sensu

Swift 1968) and above by a flooding surface (in the latter case) (e.g., 37–39 m in Fig. 5B). In paleolandward locations, regressive units are overlainby deposits of the marginal-marine back-barrier facies association (TIC,L facies; Table 1, Fig. 7). Vertical successions of these back-barrierdeposits typically comprise lagoonal siltstones (L facies) that overlie coalseams across a transgressive surface (sensu Embry 1993, equivalent to thesurface of maximum regression sensuHelland-Hansen and Gjelberg 1994)and are eroded locally by tidal-inlet(?) channels (TIC facies) across a tidalravinement surface (sensu Swift 1968) (e.g., 87–95 m in Fig. 5A). Thesesuccessions constitute the preserved remnants of barrier-island systemsthat developed and retreated during transgression. Thus, wave-dominatedshoreline–shelf deposits occur within regressive–transgressive tonguesthat are bounded by flooding surfaces and that correspond broadly toparasequences (sensu Van Wagoner et al. 1990).

Lower-shoreface deposits (dLSF, pLSF facies) in several parasequences‘‘split’’ in a paleoseaward location into smaller upward-coarseningsuccessions separated by offshore-shelf deposits (OS facies). Hummockycross-stratified sandstone beds within these smaller successions thickenand amalgamate upwards (Fig. 5B). The boundaries of the successions donot correlate in a paleolandward direction to flooding surfaces (i.e., theyare not marked by paleolandward displacement of the upper-shoreface,USF, and foreshore, FS, facies belts), but rather die out withinsuccessions of amalgamated hummocky cross-stratified sandstone beds(pLSF facies). Accordingly, these smaller stratigraphic units do notconstitute parasequences, although each superficially resembles the distalpart of a parasequence in vertical section. The units are insteadinterpreted as bedsets (sensu Van Wagoner et al. 1990). Robustidentification of parasequences requires tracing of facies architecturealong depositional dip, such that an abrupt landward facies shift of theupper-shoreface and foreshore facies belts (USF, FS facies), which marksretreat of the shoreline across a flooding surface, is demonstrated at thebase and top of each parasequence. Where such facies architecturescannot be demonstrated due to limited up-dip exposure, upward-coarsening trends in lower-shoreface and offshore-shelf deposits (OS,dLSF, pLSF facies) are ambiguous in origin, and may represent eitherparasequences or bedsets.

The occurrence of multiple, vertically stacked bedsets in the distal partsof each parasequence has important implications for correlation in lower-shoreface and shelf strata, because a single complete upward-shallowingshoreface succession (dLSF, pLSF, USF, and FS facies) in proximallocations may correlate to multiple upward-coarsening successions ofstorm-event beds (dLSF and pLSF facies) in distal locations. The formersuccessions constitute parasequences, and their boundaries recordsignificant increases in water depth (c. . 10 m) and paleolandwarddislocations of the shoreline (. 1 km) (Hampson et al. 2008). The lattersuccessions constitute bedsets, and their boundaries represent minor (c.1 m) rises in relative sea level, reductions in sand supply, and/or decreasesin the intensity of storm waves (Storms and Hampson 2005; Sømme et al.2008; Hampson et al. 2008). In the Star Point Sandstone, previousworkers have interpreted upward-coarsening successions in distallocations as parasequences rather than bedsets (Dubiel et al. 2000;Holman 2001), with the result that the surfaces that bound these units donot correlate to landward displacements of the shoreline (i.e., floodingsurfaces sensu Van Wagoner et al. 1990) in proximal locations. Insubsurface datasets where data are sparse and different sandstone faciesare not easy to distinguish (e.g., in wireline logs), correlations of this typemay poorly characterize reservoir architecture (Hampson et al. 2008).

r

FIG. 3.—Geologic map of the eastern Wasatch Plateau (Fig. 1), showing the distribution of outcrop and well data used in this study (after Witkind et al. 1987; Weiss etal. 1990; Witkind and Weiss 1991; Dubiel et al. 2000; Doelling 2004). Measured sections and photographic logs shown in Figures 5–8 are located.


TABLE 1.—Summary sedimentology of facies associations in the Star Point Sandstone, lower Blackhawk Formation, and Mancos Shale. Intensity ofbioturbation is described using the bioturbation index (BI) scheme of Taylor and Goldring (1993). Weathering character is used to interpret facies

successions in photographic logs (e.g., Fig. 4).

Facies association FaciesLithology and

sedimentary structures Ichnology Process interpretation Weathering characteristics

Offshore shelf Offshore shelf (OS) Mudstone and siltstonewith rare beds of veryfine- to upper-fine-grained sandstone.Parallel lamination,wave and current-ripplecross-lamination.

Moderate to intensebioturbation (BI 5 3–5);Cruziana ichnofacies(Planolites, Paleophycus,Schaubcylindrichnus,Chondrites, Terebellina(sensu lato),Helminthopsis).

Predominantly siltstone andmudstone deposition fromsuspended-sedimentplumes, waning oscillatoryflows during major stormevents, and river-derivedhyperpycnal flows.

Soft, slope-forming, blue-gray shale.

Wave-dominatedshoreline-shelf

Distal lower shoreface(dLSF)

Non-amalgamated bedsof upper-fine-grainedsandstone withmudstone and siltstoneinterbeds. Hummockycross-stratification,minor wavy lamination,and wave-ripplecross-lamination.

Absent to intensebioturbation (BI 5 0–6);mixed Skolithos/Cruzianaichnofacies (Ophiomorpha,Cylindrichnus, Planolites,Paleophycus, Arenicolites,Skolithos,Schaubcylindrichnus,Thalassinoides,Asterosoma, Zoophycos,Chondrites, Terebellina(sensu lato),Helminthopsis).

Sandstone deposition fromwaning oscillatory flowsduring major stormevents. Interveningfairweather mudstones arepoorly to well preserved.

Soft, blue-gray shaleinterbedded with resistant,horizontal ledges ofyellow-gray sandstone.

Proximal lower shoreface(pLSF)

Amalgamated beds ofupper-fine-grainedsandstone. Swaly andhummocky cross-stratification, minor wavylamination, and wave-ripple cross-lamination.

Absent to intensebioturbation (BI 5 0–5);mixed Skolithos/Cruzianaichnofacies (Ophiomorpha,Skolithos, Cylindrichnus,Paleophycus,Thalassinoides,Asterosoma, Planolites).

Sandstone deposition fromwaning oscillatory flowsduring major stormevents. Interveningfairweather mudstonesare not preserved.

Massive, cliff-forming,yellow-gray sandstone.

Upper shoreface (USF) Upper-fine- to lower-medium-grainedsandstone. Trough andtabular cross-beds, minorplanar lamination, andswaly cross-stratification.

Absent to moderatebioturbation (BI 5 0–4);Skolithos ichnofacies(Ophiomorpha,Thalassinoides, Skolithos,Cylindrichnus,Paleophycus).

Migration of nearshore barsand rip channels due tolongshore and offshore-directed currentsgenerated by fairweather-wave approach.

Rugose, cliff-forming, off-white sandstone. Cross-beds visible locally.

Foreshore (FS) Upper fine-grainedsandstone. Planar-parallel lamination.

Absent to sparsebioturbation (BI 5 0–1);Skolithos ichnofacies(Ophiomorpha,Thalassinoides).

Swash lamination due tobreaking waves.

Rugose, cliff-forming, off-white sandstone. Parallelbedding visible locally.

River-dominateddelta front

Distal delta front (dDF) Non-amalgamated bedsof fine- to medium-grained sandstone withmudstone and siltstoneinterbeds. Graded,structureless-to-laminated sandstonebeds; rare hummockycross-stratification,and wave-ripple cross-lamination. Occurs nearclinoform toes.

Absent to intensebioturbation (BI 5 0–5);mixed Skolithos/Cruzianaichnofacies (Ophiomorpha,Skolithos, Thalassinoides,Arenicolites, Paleophycus,Planolites, Terebellina(sensu lato)).

Sediment-gravity-flowdeposits near toe ofsteeply dipping delta front;rare reworking by waningoscillatory flows duringmajor storm events.Intervening mudstones arepoorly to well preserved.

Soft, blue-gray shaleinterbedded with resistant,inclined ledges of yellow-gray sandstone.

Proximal delta front(pDF)

Amalgamated beds offine- to medium-grainedsandstone. Abundanttrough and tabular cross-beds, structureless, andgraded, structureless-to-laminated beds; rarehummocky cross-stratification, and wave-ripple cross-lamination.Contains steeply dipping(up to 15u) clinoforms.

Absent to moderatebioturbation (BI 5 0–4);Skolithos ichnofacies(Ophiomorpha, Skolithos,Paleophycus, Planolites).

Migration of dunes andsediment gravity flowsdown steeply dipping deltafront; rare reworking bywaning oscillatory flowsduring major stormevents. Interveningmudstones are notpreserved.

Cliff-forming, yellow-graysandstone containinginclined partings (beddingsurfaces).


River-Dominated Delta-Front Facies Association

Two facies are interpreted to represent river-dominated delta-frontdeposits (dDF, pDF; Table 1). Successions of the river-dominated delta-front facies association have been described from the Panther Tongue(Howard 1966; Newman and Chan 1991; Posamentier and Morris 2000;Hwang and Heller 2002; MacEachern et al. 2005; Olariu et al. 2005;Howell et al. 2008; Enge et al. 2010; Olariu et al. 2010) and also fromsome parts of the shallow-marine Blackhawk Formation in the BookCliffs (e.g., Kamola and Van Wagoner 1995; Hampson and Storms 2003;Hampson and Howell 2005; Charvin et al. 2010). Facies are arranged inupward-coarsening successions up to 20 meters thick that gradationally

overlie offshore-shelf deposits (OS facies) and exhibit a consistent trendfrom distal delta-front deposits (dDF facies) grading upwards intoproximal delta-front deposits (pDF facies) (Figs. 5C, 8). The successionsrecord thicker and more abundant sediment-gravity-flow sandstone bedstowards the top of the delta front. Trace-fossil assemblages constitute amixture of impoverished Cruziana and Skolithos ichnofacies (Pembertonet al. 1992), consistent with ecological stresses due to mixing of fresh andmarine waters, episodic sedimentation, and a high proportion ofsuspended sediment in the water column (MacEachern and Bann 2008).River-dominated delta-front successions contain prominent clinoformswith a concave-up shape and steep dips (up to 15u) (Fig. 8C). Channelizedscours that truncate and interfinger with the upper parts of the clinoforms

Facies association FaciesLithology and

sedimentary structures Ichnology Process interpretation Weathering characteristics

Marginal-marineback-barrier

Tidal-inlet? channels(TIC)

Heterolithic channel fillscomprising fine- tocoarse-grained sandstonewith carbonaceousmudstone and siltstoneinterbeds. Trough andtabular cross-beds,planar lamination, andcurrent-ripple cross-lamination. Lateral-accretion surfaces withsiltstone drapes.Discontinuous shell-hashand oyster-shell lags.

Absent to moderatebioturbation (BI 5 0–4);low-diversity trace fossilassemblage (Ophiomorpha,Thalassinoides, Paleophycus,Planolites).

Intermittent migration ofsandy dunes and ripples,alternating with depositionof mud and silt fromsuspension, withinmeandering channels.Large variations in flowvelocity across entire heightof point bars. Influxes ofbrackish-to-marine water.

Laterally discontinuousbodies of gray-brownshale with resistant,inclined ledges of yellow-gray or off-whitesandstone.

Lagoonal (L) Carbonaceous mudstoneand siltstone with rarebeds of very fine- toupper-fine-grainedsandstone. Parallellamination and wave-ripple cross-lamination.Monospecific fauna ofoysters.

Absent to moderatebioturbation (BI 5 0–4);low-diversity trace fossilassemblage (Thalassinoides,Planolites).

Deposition from suspension,with episodic wavereworking. Brackish salinity.

Soft, gray-brown shalelocally containing resistantledges of yellow-graysandstone.

Coastal plain Fluvial sandbodies (F) Channelized sandbodiescomprising very fine- tocoarse-grained sandstone.Trough and tabularcross-beds, planar-parallel lamination,and soft-sedimentfolding (water escape).Architectural elementsin sandbodies includelateral accretion,downstream accretion,simple ‘‘cut and fill’’,and fine-grained channelplugs. Some sandbodiesare arranged inmultistory andmultilateral complexes.

Bioturbation absent(BI 5 0); some channelshave root-penetrated tops.

Migration of sandy dunesand barforms within andadjacent to channels.Barforms accretedownstream and laterally,but are not present in allsandbodies. Channelabandonment results inreduced flow velocity anddeposition of mud and siltfrom suspension. Sandbodystacking reflects variety ofcontrols.

Laterally discontinuous,rugose, cliff-forming,yellow-gray or off-whitesandstone.

Aggradational floodplain(AF)

Root-penetratedcarbonaceous mudstonesand siltstones containingthin sheets and smallchannels of current-rippled and troughcross-bedded, very fine-to medium-grainedsandstone. Paleosolsand coals occur atspecific, mappablehorizons.

Absent to sparsebioturbation (BI 5 0–2);low-diversity trace fossilassemblage in a fewintervals only (Planolites,Teredolites, Paleophycus,Diplocraterion?).

Sandstone deposition fromwaning unidirectionalcurrents during major riverfloods. Interveningmudstones and siltstonesrecord deposition fromsuspension during smaller,more frequent floods.Paleosols and coals recordreduced clastic sedimentation.

Soft, gray-brown shalelocally containing withresistant ledges of yellow-gray sandstone. Coals arecommonly black, butrecent burning of exposedcoals produces redstaining.

TABLE 1.—Continued.


are interpreted as terminal distributary channels (Olariu et al. 2005;Olariu and Bhattacharya 2006). Mapping of lateral facies trends definelocal shoreline paleogeographic and proximal-to-distal trends. Offshore-shelf deposits (OS facies) are poorly developed or missing in paleoland-ward areas but become thicker and more fully developed in apaleoseaward direction. To compensate this trend, proximal delta-frontdeposits (pDF facies) thin and pinch out in a paleoseaward direction.

Stratigraphic units that contain the complete association of river-dominated delta-front facies (dDF, pDF), upward-coarsening verticalfacies successions, and proximal-to-distal facies trends described aboverecord regression. Such regressive successions are abruptly overlain byoffshore-shelf deposits (OS facies), laterally extensive hummocky cross-stratified sandstones, and interbedded siltstones (dLSF facies), orestuarine mudstones within flooded distributary channels (Hwang andHeller 2002). These vertical facies relationships record an increase inwater depth, either directly across a flooding surface (in the first case) or

via a transgressive, upward-deepening succession that is capped by aflooding surface (in the second and third cases). Transgressive successionsin the uppermost part of the Panther Tongue commonly contain lagdeposits above a basal transgressive erosion surface (e.g., waveravinement surface at 29 m in Fig. 5C) (Hwang and Heller 2002).River-dominated delta-front deposits therefore occur within regressive–transgressive tongues that are bounded by flooding surfaces, and thatcorrespond to parasequences (sensu Van Wagoner et al. 1990). On thisbasis, the Panther Tongue is considered as a single parasequence,although it contains multiple delta lobes arranged in an offlappingpattern that indicates forced regression (Hwang and Heller 2002). Inaddition, at least two wave-dominated shoreline–shelf parasequences inthe shallow-marine Blackhawk Formation of the Book Cliffs containriver-dominated delta-front deposits that define single or multiple lobesnear their down-dip pinchouts (Kamola and Van Wagoner 1995;Hampson and Storms 2003; Hampson and Howell 2005; Charvin et al.

FIG. 4.—A) Uninterpreted and B) interpreted cliff-face photograph illustrating interpretation of facies successions and stratigraphic units in a representativephotographic log. Three parasequences (Ksp 040, Ksp 030, and Ksp010) comprise wave-dominated shoreline–shelf deposits, whereas a fourth (Ksp 020) locally consistsof river-dominated delta-front deposits that contain relatively steeply dipping (up to 3u) clinoforms. One of the shoreline–shelf parasequences (Ksp 030) is subdividedlocally into two bedsets. The photograph is located in Figure 9.


FIG.5.—

Measuredsectionsillustratingfacies

successions,bioturbationintensity

(BI),g

rain

size,sedim

entary

structures,an

dsequence

stratigrap

hicinterpretationsin

theStarPointSan

dstone:A)complete

upward-

shallowing,

wav

e-dominated

shoreface–shelfsuccession(parasequence

Ksp

050)

overlainbycoal

seam

,lago

onal

siltstones,an

dtidal-inlet?

chan

nel

interpretedas

preserved

remnan

tsofatran

sgressivebarrier-islan

dsystem

(from

Coal

MineCreek

measuredsection,Figs.3,

9,10

),B)tw

oupward-coarseningsuccessionsofva

riab

lyam

alga

mated

storm

-eventbeds;regional

map

pingshowsthat

thesetw

osuccessionsoccurin

the

middle

andupper

parts

ofthesameparasequence

(Ksp

050),an

dthey

therefore

constitute

bedsets

(LinkCan

yonmeasuredsection,Figs.3,

9,10

),C)upward-shallowing,

river-dominated

delta-frontsuccession

(parasequence

Ksp

040;

Pan

ther

Tongu

e)that

istruncatedbyatran

sgressiveerosion(rav

inem

ent)

surfacelined

byacoarse-grained

lag(W

attisRoad

measuredsection,Figs.3,

9,10

).



2010). Thus, parasequences may contain the deposits of multiple river-dominated delta lobes, and also wave-dominated shoreline–shelf deposits(e.g., in an asymmetrical wave-dominated delta system; Charvin et al.2010). The deposits of individual delta lobes are more akin in scale tobedsets (cf. Enge et al. 2010) in wave-dominated shoreline–shelfparasequences, although their formative mechanisms may have beendifferent (Charvin et al. 2010).

Coastal-Plain Facies Association

Two facies are interpreted to represent coastal-plain deposits (F, AF;Table 1). Laterally discontinuous sandstones with a variety of internalarchitectures are interpreted to be fluvial sandbodies that resulted fromdeposition of bars adjacent to migrating channels (F facies). Fluvialsandbodies that erode directly into wave-dominated shoreline–shelfdeposits and river-dominated delta-front deposits may be deltaicdistributary channels, based on their context. Other fluvial sandbodiesare encased in root-penetrated mudstones and siltstones that containcoals and thin sheet sandstones, interpreted as floodplain deposits (AFfacies), and are less likely to be distributary in origin. Fine-grainedchannel plugs cannot be confidently identified throughout the outcropbelt, and are thus grouped with fine-grained floodplain deposits (AFfacies).

Sequence stratigraphic interpretation of the coastal-plain deposits is thesubject of ongoing work. Most of the fluvial sandbodies (F facies) in thelower part of the Blackhawk Formation have a single-story ormultilateral geometry, although a few have a multistory, multilateralgeometry and appear to be contained within deep erosional surfaces; thelatter are candidates for incised-valley fills (sensu Van Wagoner et al.1990).

STRATIGRAPHIC FRAMEWORK

The various facies and stratigraphic units described above wereinterpreted in each of the measured sections and photographic logs(e.g., Fig. 4), and then traced out along the cliff faces and canyon walls.Figure 9 presents the resulting stratigraphy along the cliff line and canyonfaces, over a distance of approximately 340 km (corresponding to astraight-line distance of approximately 100 km). Figure 10 shows thesame stratigraphy interpreted along a nearly straight line behind the cliffline between five of the measured sections, while Figure 11 presents mapviews of facies-belt extent at maximum regression within each para-sequence.

Five parasequences are interpreted (Ksp 050, Ksp 040, Ksp 030, Ksp020, and Ksp 010; Table 2), whose upper and lower boundaries constituteflooding surfaces marked by significant landward displacements of theshoreline and associated increases in water depth. The distal parts of twomore upward-coarsening units are exposed in the southern part of thestudy area, but they are not exposed in proximal locations; these unitswould constitute parasequences if their boundaries are associated withsignificant landward displacements of the shoreline in proximal locations(Ksp 070? and Ksp060?, as labeled in Figs. 9, 10), or bedsets withinparasequence Ksp 050 if not. Most of the parasequences split in apaleoseaward direction into multiple bedsets in their distal parts, but they

thin and pinch out abruptly in a paleolandward direction. Eachparasequence is described briefly below, in ascending stratigraphic order,and then generic aspects of their up-dip and down-dip pinchouts aredocumented.

Parasequence Ksp 050

Parasequence Ksp 050 crops out in the southern part of the study area(Figs. 9, 10, 11A), where it records progradation of a wave-dominatedshoreline. Within each parasequence, the up-dip and down-dip pinchoutsof foreshore and upper-shoreface deposits (USF and FS facies) were usedas respective proxies for the initial and final positions of the shorelineduring progradation (cf. Kamola and Huntoon 1995; Hampson andHowell 2005; Hampson 2010). The up-dip pinchout of these deposits inparasequence Ksp 050 is not exposed in the study area, whereas theirdown-dip pinchout intersects the cliff-face exposures in one location(Fig. 11A). Upper-shoreface and foreshore deposits therefore form a beltat least 15 km wide, implying that the shoreline prograded a similardistance during deposition of the parasequence (Fig. 11A, Table 2).Paleocurrents in upper-shoreface deposits are oriented towards the south-southeast (Fig. 11A), indicating transport of significant sediment volumesby longshore drift driven by oblique wave approach from the north ornortheast. The distance between the down-dip pinchouts of upper-shoreface and distal lower-shoreface sandstones (USF and dLSF facies)in each parasequence defines the width of a storm-reworked, nearshoresandstone belt during maximum regression of the shoreline (cf. Hampson2010). The width of this belt in parasequence Ksp 050 is approximately15 km (Fig. 11A, Table 2). Lower-shoreface deposits (pLSF and dLSFfacies) in the lower and paleoseaward part of the parasequence split intoseveral upward-coarsening bedsets (possibly including Ksp 070? and Ksp060?), which are arranged in a paleoseaward-stepping pattern in the up-dip part of the parasequence but are vertically stacked near its down-dippinchout (Figs. 9, 10, Table 2).Lower-shoreface sandstones (pLSF and dLSF facies) at a similar

stratigraphic level are mapped in the northwestern part of the study area,as part of the Trail Canyon Sandstone Member of the Mancos Shale(Hansen 1996). Correlation of these sandstones with parasequence Ksp050 implies that the subregional shoreline exhibited a broad curvaturefrom a NNW–SSE orientation in the south to a NNE–SSW orientation inthe north (Fig. 11A).Parasequence Ksp 050 is mapped to have a flat top defined by a single,

nearly horizontal surface (e.g., Sanchez et al. 1983a; Flores et al. 1984;Dubiel et al. 2000) and corresponds to parasequences 0, 21, 22, and 23of Dubiel et al. (2000), which were mapped using a combination ofoutcrop and subsurface well-log data. These latter units are correlated asa series of paleoseaward-stepping clinothems (sensu Rich 1951) whoseboundaries are not associated with major landward shifts of the shorelinein proximal locations, but with subtle wireline-log trends that correlate tointercalations of shale in distal locations (plate 1 in Dubiel et al. 2000); weinterpret these units as bedsets rather than parasequences.


Parasequence Ksp 040 crops out over most of the study area (Figs. 9,10, 11B) but has distinctly different facies character and stratigraphic

r

FIG. 6.—Photographs illustrating the wave-dominated shoreline–shelf facies association (Table 1): A) sandstone beds and siltstone interbeds exhibiting varying degreesof amalgamation at transition between distal and proximal lower-shoreface (dLSF, pLSF) facies, B) Ophiomorpha at bed top (pLSF facies), C) hummocky crossstratification (HCS) in sandstone bed (pLSF facies), D) well-sorted, trough cross-bedded, lower-medium-grained sandstone in upper-shoreface (USF) facies, E) wave-rippled surface and siltstone drape (USF facies), and F) Cylindrichnus ‘‘nests’’ preserved at bed tops (USF facies). Photographs A and D are taken from parasequence Ksp040 at Link Canyon measured section (Figs. 3, 9, 10), whereas photographs B, C, E, and F are taken from parasequence Ksp 050 at Coal Mine Creek measured section(Figs. 3, 5A, 9, 10).



architecture in the northern and southern parts of the study area. In thesouthern part of the study area, the parasequence records regression of aNNW–SSE-trending wave-dominated shoreline (Fig. 11B). The width ofthe upper-shoreface and foreshore facies belt implies that the shorelineprograded a distance of approximately 16 km during deposition of theparasequence (Fig. 11B, Table 2). Paleocurrents in upper-shorefacedeposits are again oriented towards the south and south-southeast(Fig. 11B), implying sediment transport by wave-driven longshore drift.The storm-reworked, nearshore sandstone belt in these deposits isapproximately 20 km wide (Fig. 11B, Table 2). Lower-shoreface deposits(pLSF and dLSF facies) in the paleoseaward part of the parasequencesplit into three upward-coarsening bedsets that are vertically stacked(Figs. 9, 10, Table 2).

In the northern part of the study area, parasequence Ksp 040constitutes the Panther Tongue, which records forced regression of astrongly lobate, river-dominated deltaic shoreline that had an overallNE–SW orientation (Posamentier and Morris 2000; Hwang and Heller2002; Howell et al. 2008; Enge et al. 2010; Olariu et al. 2010) (Fig. 11B).The up-dip and down-dip pinchouts of proximal delta-front deposits(pDF facies) are used as respective proxies for the initial and finalpositions of the deltaic shoreline during progradation. The up-dippinchout of these deposits is not exposed in the study area, and theirdown-dip pinchouts and local progradation directions, as recorded by theorientation of delta-front clinoforms, are highly variable along theoutcrop belt; a minimum of 7–14 km of progradation is interpretedlocally in directions ranging from southeastward to west-northwestward(Fig. 11B, Table 2), but these progradation distances may be significantunderestimates. The distance between the down-dip pinchouts ofproximal and distal delta-front deposits (dDF and pDF facies) is takento define the local width of a narrow (2–5 km), storm-reworked,nearshore sandstone belt during maximum regression of the deltaicshoreline (Fig. 11B, Table 2). The Panther Tongue contains multiple,laterally stacked delta lobes, which may correspond to bedsets (Enge et al.2010). However, their detailed geometry and plan-view stackingarrangement is beyond the scope of this study.

Mapping of the wave-dominated shoreline and river-dominated deltaicshoreline deposits within the same parasequence indicates that thesubregional shoreline exhibited a broad curvature from a NNW–SSEorientation in the south to a NE–SW orientation in the north (Fig. 11B).The river-dominated deltaic shoreline deposits lack overlying coastal-plain deposits and successive lobes exhibit an offlapping pattern,indicating a forced-regressive architecture developed during relative sea-level fall (Posamentier and Morris 2000). The wave-dominated shorelinedeposits lack clear evidence for deposition under such conditions, forexample the local development of foreshortened, ‘‘sharp-based’’ shorefacefacies successions (sensu Plint 1988) and correlative incised valleys,although the large shoreline progradation distance (c. 16 km) is consistentwith forced regression (Posamentier et al. 1992; Plint and Nummedal2000; Posamentier and Morris 2000). Either these wave-dominatedshoreline deposits contain only a subtle expression of forced regressionthat requires more detailed reconstruction of intra-parasequence strati-graphic architecture to be elucidated (e.g., Hampson 2000), or they record

deposition under conditions of rising relative sea level prior to the relativesea-level fall that forced progradation of the Panther Tongue deltacomplex.

In the southern part of the study area, parasequence Ksp 040corresponds to parasequences 1, 2, and 3 of Dubiel et al. (2000), whichwe interpret as bedsets for the same reasons as given in the discussion ofparasequence Ksp 050. The up-dip pinchout of parasequence Ksp 040into the Blackhawk Formation corresponds to Star Point Sandstonetongue 2 of Sanchez et al. (1983a) in the southern part of the study area.Tongue 1 of Sanchez et al. (1983a) is a landward-tapering sandbody thatis truncated at its paleoseaward limit by the upper-shoreface deposits ofparasequence Ksp 040; we infer that tongue 1 was deposited in a back-barrier setting (e.g., flood-tidal delta, washover fan).

In the northern part of the study area, the Panther Tongue isinterpreted as a single parasequence (cf. regressive–transgressive tongue)that records deposition during falling and lowered relative sea level, andduring subsequent transgression (Posamentier and Morris 2000; Hwangand Heller 2002). Transgressive deposits include estuarine, lower-shore-face, and lag deposits (Hwang and Heller 2002). We include thesetransgressive deposits within parasequence Ksp 040 because they liebeneath an extensive flooding surface, although they have been previouslyallocated at some locations to a different, additional parasequence(Holman 2001).


Parasequence Ksp 030 records progradation of a curved, NNW–SSE toNE–SW-trending wave-dominated shoreline across the study area(Figs. 9, 10, 11C). The width of the upper-shoreface and foreshore faciesbelt implies that the shoreline prograded a distance of 7–9 km in thesouthern part of the study area, although the progradation distance ispoorly constrained in the north (Fig. 11C, Table 2). Paleocurrents inupper-shoreface deposits are oriented towards both the south-southeastand north-northwest (Fig. 11C), which can be attributed to longshoredrift on either side of a poorly preserved (deltaic?) headland, to seasonalreversal of longshore currents, or to shoreline-parallel transport by tides.The storm-reworked, nearshore sandstone belt in parasequence Ksp 030is approximately 12 km wide (Fig. 11C, Table 2). Lower-shorefacedeposits (pLSF and dLSF facies) in the paleoseaward part of theparasequence split into two or more upward-coarsening bedsets that arevertically stacked (Fig. 9, Table 2).

Parasequence Ksp 030 is mapped in the southern part of the study areato have a flat top defined by a single, nearly horizontal surface (e.g.,Sanchez et al. 1983b; Flores et al. 1984; Dubiel et al. 2000) and correspondsto parasequence 4 of Dubiel et al. (2000). The up-dip pinchout ofparasequence Ksp 030 into the Blackhawk Formation corresponds to StarPoint Sandstone tongue 4 of Sanchez et al. (1983b) (equivalent to unnamedsandstone tongue of Hayes and Sanchez 1979; Sanchez and Hayes 1979) inthe southern part of the study area. Tongue 3 of Sanchez et al. (1983b) is achannelized sandbody that cuts into, and is amalgamated with, underlyingshoreface deposits in parasequence Ksp 040.

In the northern part of the study area, parasequence Ksp 030constitutes the Storrs Tongue, and only its distal components are

r

FIG. 7.—Photographs illustrating the marginal-marine back-barrier facies association (Table 1): A) sandstone at base of lagoonal (L) facies succession with Teredolites‘‘woodground’’ surface developed above coal seam, B) upward-coarsening succession of lagoonal siltstones and sandstones (L facies) overlying a coal seam, StraightCanyon measured section, C) heterolithic channel fill containing siltstone-draped lateral accretion surfaces and interpreted as a tidal-inlet channel (TIC facies), and locallyeroding into underlying lagoonal mudstones, coal, and foreshore sandstones, Coal Mine Creek measured section, D) oyster shell and E) horizontal Ophiomorpha chamberfrom lower part of channel fill (Fig. 7C). All photographs are taken from the lower part of the Blackhawk Formation: photograph A from c. 3 m above the top of the StarPoint Sandstone at Wattis Road measured section (Figs. 3, 9, 10), photograph B from c. 13–18 m above the top of the Star Point Sandstone at Straight Canyon measuredsection (Figs. 3, 9, 10), photographs C, D, and E from c. 0–8 m above the top of the Star Point Sandstone at Coal Mine Creek measured section (Figs. 3, 5A, 9, 10).


exposed. Here Holman (2001) identified four tongues of lower-shorefacedeposits (pLSF and dLSF facies) in this interval, which she interpreted asparasequences; we interpret these tongues as bedsets for the same reasonsas given in the discussion of parasequence Ksp 050.


Parasequence Ksp 020 records progradation of a NW–SE-trendingwave-dominated shoreline of complex geometry across the southern and

FIG. 8.—Photographs illustrating the river-dominated delta-front facies association (Table 1): A) structureless to parallel-laminated sandstone bed, interpreted as thedeposit of a waning sediment gravity flow, and variably bioturbated siltstones and silty sandstones in distal delta-front (dDF) facies, B) HCS in amalgamated sandstonebeds of the proximal delta-front (pDF) facies, and C) view oriented along local depositional dip through upward-coarsening succession (pDF facies) containingclinoforms. Photographs A and B are taken from parasequence Ksp 040 (Panther Tongue) at Wattis Road measured section (Figs. 3, 5C, 9, 10). Photograph C is takenfrom the same parasequence along the east wall of Huntington Canyon, opposite the entrance of Crandall Canyon (Fig. 3).


FIG.9.—

Pan

elshowingstratigrap

hyan

dfacies

architecture

intheStarPointSan

dstonemap

ped

alongthemainclifflinean

dcanyo

nfacesalongtheeasternedge

oftheWasatch

Plateau

(Figs.1,

3).Five

parasequencesareinterpretedwithconfidence

(Ksp

050,

Ksp

040,

Ksp

030,

Ksp

020,

Ksp

010),an

dthedistalparts

oftw

omore

potential

parasequences(K

Sp07

0?,Ksp06

0?)areexposedin

thesouthernpartofthe

pan

el.Most

oftheparasequencessplitinto

multiple

bedsets

intheirdistalparts.Someparasequencesap

pearto

exhibitseveralupdip

and/ordown-dip

pinchouts

within

thepan

el,dueto

theirregu

larre-entran

tgeometry

oftheclifflinewithrespectto

regional

depositional

strikean

ddip

orientations.Thetopoftheuppermostparasequence

indifferentpartsofthepan

elisusedas

alocaldatum.Measuredsectionsin

Figure

5an

dinterpretedcliff-face

photograp

hsin

Figures4an

d12

arelocated.


FIG. 10.—Simplified correlation panel show-ing stratigraphic framework of the Star PointSandstone and overlying Blackhawk Formationand Castlegate Sandstone in the eastern WasatchPlateau. The top of the uppermost Star PointSandstone parasequence in different parts of thepanel is used as a local datum. Coal-zonestratigraphy in the Blackhawk Formation istaken from Sanchez and Brown (1983, 1986,1987), Flores et al. (1984), Sanchez et al. (1983a,1983b), Brown et al. (1987), Sanchez and Ellis(1990), Dubiel et al. (2000), Gloyn et al. (2003),and Quick et al. (2005). Stratigraphy in the PriceCanyon area of the northern Book Cliffs is takenfrom Van Wagoner et al. (1990), Kamola andVan Wagoner (1995), and Hampson et al. (2005).Keys to facies and stratigraphic surfaces are thesame as for Figure 9.


central parts of the study area (Figs. 9, 10, 11D). In the southern part ofthe study area, the parasequence contains a nearly linear belt of upper-shoreface and foreshore deposits that record approximately 13 km ofshoreline progradation and contain a range of paleocurrent orientations(Fig. 11D, Table 2). However, in the central part of the study area, theparasequence contains a N–S-elongate lobe of river-dominated delta-front deposits containing clinoforms that indicate approximately 8 km ofdeltaic shoreline progradation towards the south (Figs. 4, 11D). Thesedelta-front deposits onlap onto and are traced towards the south intodistal lower-shoreface deposits (dLSF facies), whereas their northern limitis marked by a curved belt of lower-shoreface deposits (pLSF and dLSFfacies) that trend NW–SE (Fig. 11D). We interpret this paleogeographyto represent an asymmetrical wave-dominated delta (sensu Bhattacharyaand Giosan 2003), in which the updrift, northern delta flank isrepresented by wave-dominated strandplain and spit system and thedowndrift, southern delta flank comprised a sheltered embayment thatwas partly infilled by a river-dominated bayhead delta. This interpreta-tion implies that upper-shoreface and foreshore deposits should occur tothe north of, and be contiguous with, the proximal delta-front deposits(pDF facies); the apparent absence of these upper-shoreface andforeshore deposits is attributed to their inferred position to the west ofthe outcrop belt, although they may also have been truncated bytransgressive erosion at the top of the parasequence. Similar river-dominated delta-front deposits are documented in the down-dip parts ofwave-dominated shoreface–shelf parasequences in the shallow-marineBlackhawk Formation of the Book Cliffs (Kamola and Van Wagoner1995; Hampson and Storms 2003; Charvin et al. 2010), whereasymmetrical delta interpretations have been proposed (Hampson andHowell 2005; Charvin et al. 2010). This interpretation is also implicit inFlores et al.’s (1984) paleogeographic reconstructions of wave-dominateddeltas containing barrier-island and spit systems in the Star PointSandstone. The storm-reworked, nearshore sandstone belt in parase-quence Ksp 020 is approximately 10 km wide according to ourinterpretation of an asymmetrical wave-dominated deltaic shoreline(Fig. 11D, Table 2).

In the southern part of the study area, parasequence Ksp 020corresponds to parasequences 5 and 6 of Dubiel et al. (2000), which weinterpret as bedsets for the same reasons as given in the discussion ofparasequence Ksp 050. The up-dip pinchout of parasequence Ksp 020into the Blackhawk Formation is not identified in coal-resource maps,although only sparse data are available near the pinchout to constructsuch maps (Sanchez and Brown 1983).

In the central part of the study area, Holman (2001) identified twotongues of lower-shoreface deposits (pLSF and dLSF facies) inparasequence Ksp 020. We interpret these tongues as bedsets, althougheach has been previously interpreted as a parasequence based on theirupward-coarsening trends in grain size (Holman 2001). In the northernpart of the study area, parasequence Ksp 020 is represented by an intervalof Mancos Shale that separates the Star Point Sandstone below from theSpring Canyon Member of the Blackhawk Formation above (Fig. 10).


Parasequence Ksp 010 records progradation of a linear to weaklylobate, NW–SE-trending wave-dominated shoreline across the centraland northern parts of the study area (Figs. 9, 10, 11E). The width of theupper-shoreface and foreshore facies belt implies that the shorelineprograded a distance of approximately 45 km (Fig. 11E, Table 2).Paleocurrents in upper-shoreface deposits are oriented towards the south-southeast (Fig. 11E), implying sediment transport by wave-driven long-shore drift. The storm-reworked, nearshore sandstone belt in parase-quence Ksp 010 is at least 15 km wide but extends beyond the easternlimit of the study area (Fig. 11E, Table 2). Lower-shoreface deposits

(pLSF and dLSF facies) in the paleoseaward part of the parasequencesplit into three upward-coarsening bedsets that are vertically stacked(Figs. 9, 10, Table 2).In the central part of the study area, parasequence Ksp 010 corresponds

to parasequences 7 and 8 of Dubiel et al. (2000), which we interpret asbedsets for the same reasons as given in the discussion of parasequence Ksp050. Holman (2001) also interpreted a single parasequence here, which wasallocated to the Spring CanyonMember of the Blackhawk Formation. Theup-dip pinchout of parasequence Ksp 010 into the Blackhawk Formationcorresponds to Star Point Sandstone tongue 5 of Sanchez and Brown(1987). Tongue 6 of Brown et al. (1987) is a poorly exposed, laterallydiscontinuous sandbody that is locally amalgamated with underlyingshoreface deposits in parasequence Ksp 010.Parasequence Ksp 010 constitutes the lower part of the Spring Canyon

Member of the Blackhawk Formation in the northwestern Book Cliffs(labeled Price Canyon in Fig. 10). We tentatively interpret parasequenceKsp 010 to correspond to four tongues of lower-shoreface deposits (pLSFand dLSF facies) mapped by Van Wagoner et al. (1990; their fig. 12) inthe lower 35 m of the Spring Canyon Member. Van Wagoner et al. (1990)interpreted each of these tongues as a distinct parasequence (their fig. 12),but we instead interpret them as bedsets because their boundaries are notmarked by landward shifts of the shoreline in proximal locations to thewest of the area mapped by Van Wagoner et al. (1990).

Shallow-Marine Strata above Parasequence Ksp 010

Four parasequences have previously been documented directly aboveparasequence Ksp 010 in the upper part of the Spring Canyon Member ofthe Blackhawk Formation in the northwestern Book Cliffs (labeled PriceCanyon in Fig. 10) (Sowbelly, Hardscrabble, Heiner, and Helperparasequences of Kamola and Van Wagoner 1995, corresponding toparasequences SC4-7 of Hampson and Howell 2005). The oldest of theseparasequences is comparable in shoreline type, thickness (17 m),progradation distance (13–21 km), and width of storm-reworkednearshore sandstone belt (12 km) to those described above in the StarPoint Sandstone (Kamola and Huntoon 1995; Hampson and Howell2005; Hampson 2010). However, the three younger parasequences havesignificantly smaller progradation distances (1–4 km) despite beingsimilar in facies character and interpreted shoreline type (Kamola andHuntoon 1995; Hampson and Howell 2005; Hampson 2010).

Up-Dip Pinchouts of Parasequences

The up-dip pinchouts of four parasequences (Ksp 040, Ksp 030, Ksp020, and Ksp 010) are well exposed in the southern and central parts ofthe study area (Figs. 9, 10, 11). All four pinchouts occur over shortdistances (, 500 m; e.g., Fig. 12A–D) in a depositional-dip orientation,while each case is mapped between multiple (3–5) cliff faces to be linear orslightly sinuous in plan view over distances of 3–7 km (Fig. 11B–E).Similarly abrupt up-dip pinchouts of wave-dominated shoreface sand-stone tongues are documented in the Book Cliffs (e.g., Balsley 1980; VanWagoner et al. 1990; Anderson 1991; Kamola and Van Wagoner 1995).Two types of up-dip pinchout are observed. The first type consists of a

landward-tapering sandstone wedge of pLSF, USF, and FS facies with agently dipping (, 1u), concave-upward lower surface (Fig. 12A, B).Facies boundaries are parallel to the top of the wedge and onlap its lowersurface. This facies architecture suggests that the lower surface of thewedge had a paleoseaward-dipping geometry, and the surface is thusinterpreted as a wave ravinement surface (sensu Swift 1968) whosegeometry mimics the profile of the retreating shoreface that cut it.Shoreline–shelf sandstones in the wedge itself are interpreted to have beendeposited during subsequent shoreface regression. The second type of up-dip pinchout consists of a landward-tapering sandstone wedge of pLSF,USF, and FS facies with an upper boundary that descends in a



paleolandward direction and truncates facies boundaries that are parallelto the base of the wedge at successively deeper positions (Fig. 12C, D).These pinchouts are interpreted to record erosional truncation at themargins of sandstone- and mudstone-filled channels, which may haveformed as the result of regressive erosion by distributary channels, forced-regressive erosion at the base of incised valleys, and/or transgressiveerosion by tidal-inlet channels. Deep (up to 18 m) erosion by mudstone-filled channels occurs locally at the top of each parasequence in locationsother than their up-dip pinchouts (e.g., Fig. 12E, F), suggesting thatincision and subsequent abandonment of deep channels was not confinedto the stratigraphic level at the top of any particular parasequence. Both

types of pinchout geometry are locally modified by postdepositionalcompaction.

Down-Dip Pinchouts of Parasequences

Each parasequence is interpreted to contain multiple bedsets (sensuVan Wagoner et al. 1990) (Table 2, Figs. 9, 10), each containing upwardincreases in grain size and bed amalgamation. Bedsets are particularlyevident in the down-dip parts of wave-dominated shoreline–shelfparasequences, where they are stacked vertically and separated bytongues of offshore shale (Figs. 9, 10). These shale tongues occur where

r

FIG. 11.—Maps of facies-belt extent at maximum regression in each parasequence of the Star Point Sandstone, in ascending stratigraphic order: A) Ksp 050; B) Ksp040 (Panther Tongue Member, northern Book Cliffs); C) Ksp 030 (Storrs Tongue Member, northern Book Cliffs); D) Ksp 020, and E) Ksp 010. These last twoparasequences are assigned to the Spring Canyon Member of the Blackhawk Formation in the northern Book Cliffs. Up-dip pinchouts of parasequences shown inFigure 12A–D) are located.

TABLE 2.—Parameters defining gross facies architecture in the five mapped parasequences of the Star Point Sandstone.

Parasequence

Parasequence stacking pattern(shoreline trajectory relative to

underlying parasequence)Shoreline type

and morphologyDistance of shoreline

progradationWidth of storm-reworked,nearshore sandstone belt

Organization of lowershoreface and inner shelf

sandstones

Ksp 010 Strongly progradational (ascendingregressive trajectory of c. 0.02u,based on compacted thicknesses).

Linear to weakly lobatewave-dominated shorelinetrending NW–SE.

c. 45 km . 12 km 3 vertically stacked bedsetsin expanded sectionbeyond pinchout of pLSFsandstones in underlyingparasequence Ksp 020(Fig. 10). Interpreted tocontain 4 additionalpaleoseaward-stepping tovertically stacked bedsetsnear down-dip pinchout(figure 12 of Van Wagoneret al. 1990).

Ksp 020 Moderately progradational (ascendingregressive trajectory of 0.03–0.06u,based on compacted thicknesses) insouthern part of study area.

Weakly to moderatelylobate wave-dominatedshoreline trending NW–SE, with local lobate river-dominated deltaicshoreline.

c. 13 km c.10 km 2 paleoseaward-steppingbedsets near down-dippinchout; upper bedsetcomprises local river-dominated delta lobe(paleoseaward of crosssection in Fig. 10).

Ksp 030 Strongly retrogradational, but poorlyconstrained by dataset, in northernpart of study area.

Weakly to moderatelylobate wave-dominatedshoreline trending NNW–SSE (southern part ofstudy area) to NE–SW(northern part of studyarea).

7–9 km c. 12 km 2–4 vertically stackedbedsets in expandedsection beyond pinchoutof pLSF sandstones inunderlying parasequenceKsp 040 (paleoseaward ofcross section in Fig. 10).

Weakly progradational (ascendingregressive trajectory of c. 0.36u,based on compacted thicknesses) insouthern part of study area.

Ksp 040 Strongly progradational (forcedregressive trajectory of c. 20.02uwithin the parasequence), but poorlyconstrained by dataset, in northernpart of study area.

Strongly lobate river-dominated deltaicshoreline trending NE–SW in northern part ofstudy area.

. 7–14 km 2–5 km Multiple laterally stackeddelta lobes (bedsets?),which are not fullyresolved in dataset.

Moderately progradational (ascendingregressive trajectory of c. 0.04u,based on compacted thicknesses) insouthern part of study area.

Linear to weakly lobatewave-dominated shorelinetrending NNW–SSE insouthern part of studyarea.

c.16 km c. 20 km 3 vertically stacked bedsetsin expanded sectionbeyond pinchout of pLSFsandstones in underlyingparasequence Ksp 050(Fig. 10).

Ksp 050 Not constrained by dataset. Linear to weakly lobate(?)wave-dominated shorelinetrending NNW–SSE.

. 15 km c. 15 km 3 vertically stacked bedsetsnear down-dip pinchout;possibly 2 or more furtherbedsets in up-dip locations(including Ksp 060?, Ksp070?) (Fig. 10).


FIG.12

.—A,C,E)Uninterpretedan

dB,D,F)interpretedcliff-face

photograp

hsillustratingtheup-dip

pinchoutgeometries

ofparasequencesthat

comprise

wav

e-dominated

shoreline–shelfdeposits:A,B)

landward-tap

eringsandstonewedge

withaconcave-upwardlower

surface,

Ksp

030in

cliffface

south

ofMuddyCreek

(Figs.9,

11C);C,D)landward-tap

eringsandstonewedge

withan

erosional,concave-upward

upper

surface,

Ksp

010in

cliffface

northeast

ofFerronCreek

(Figs.9,

11E),an

dE,F)deeperosionbyfine-grained

chan

nel

fillinto

thetopofKsp

040in

cliffface

northeast

ofConvu

lsionCan

yon(Fig.9).


a parasequence expands in thickness paleoseaward of the pinchout ofupper-shoreface and proximal lower-shoreface deposits (USF and pLSFfacies) in the underlying parasequence (Figs. 9, 10), suggesting that theyreflect deposition in the deep water that characterized these locations.Similar architectures have been documented in more detail in para-sequences in the Blackhawk Formation exposed in the Book Cliffs(Pattison 1995; Hampson 2000; Hampson and Storms 2003; Sømme et al.2008). In the Star Point Sandstone parasequences, sandstone beds indistal lower-shoreface deposits (dLSF facies) occur up to c. 100 m belowforeshore deposits (FS facies), suggesting that they were deposited inwater of similar or greater depths (Figs. 9, 10). Thus, storms were capableof transporting and reworking sand in such water depths.

CONTROLS ON GROSS STRATIGRAPHIC ARCHITECTURE

Parasequence stacking patterns in the southern Wasatch Plateau areprogradational (Figs. 9, 10) (Dubiel et al. 2000), while those in thenorthern Wasatch Plateau are more variable and, from base to top,consist of strongly progradational (Panther Tongue), retrogradational(Storrs Tongue), and progradational (Spring Canyon Member) patterns(Figs. 9, 10) (Howell and Flint 2003). In the northwestern Book Cliffs, theinternal architecture of the Panther Tongue implies deposition duringfalling and lowered relative sea level (Posamentier and Morris 2000;Hwang and Heller 2002), and the base of the unit is interpreted torepresent a major sequence boundary (Krystinik and DeJarnett 1995;Howell and Flint 2003). The top of the Storrs Tongue is interpreted as amaximum flooding surface (Krystinik and DeJarnett 1995; Howell andFlint 2003). The two contrasting parasequence stacking patterns in thesouthern and northern Wasatch Plateau are in part coeval (Table 2,Figs. 9, 10, 11), indicating that some of the controls on gross stratigraphicarchitecture varied along regional depositional strike.

The differences in parasequence stacking pattern between the southernand northern Wasatch Plateau are quantified below using the shorelinetrajectory concept (Helland-Hansen and Martinsen 1996; Helland-Hansen and Hampson 2009). Shoreline trajectory is a descriptive toolthat considers the combined effect of sediment supply and relative sealevel in creating shallow-marine stratigraphic architecture. The likelycontrols on along-strike variations in stratigraphic architecture are theninterpreted in the descriptive context of the reconstructed shorelinetrajectories.

Parasequence Stacking and Associated Shoreline Trajectories

Figure 13 shows reconstructed shoreline trajectories for the southernand northern Wasatch Plateau. Each parasequence is represented by aregressive–transgressive ‘‘sawtooth.’’ Longer-term patterns in shorelinetrajectory, corresponding to parasequence stacking patterns, are recordedby trends in the position of successive ‘‘sawteeth’’ (e.g., Table 2).

The up-dip and down-dip pinchouts of foreshore and upper-shorefacedeposits (USF and FS facies) or proximal delta-front deposits (pDFfacies) have been used as respective proxies for the initial and finalpositions of the shoreline during regression, as in the facies-belt mapsshown in Figure 11 (cf. Kamola and Huntoon 1995; Hampson andHowell 2005; Hampson 2010). The down-dip pinchout of foreshoredeposits may underestimate the shoreline position at maximum regression(by up to c. 3 km), because transgressive erosion and reworking is likelyto have removed foreshore deposits from the down-dip part of eachtongue; upper-shoreface and proximal delta-front deposits are less likelyto have been removed by transgressive erosion, but they extend a smalldistance (, 1 km) paleoseaward of the shoreline position at maximumregression. Several of the interpreted positions of wave-dominatedshorelines were projected for large distances into the line of section used

FIG. 13.—Measured shoreline trajectory forthe study interval. Trajectories along the north-ern and southern Wasatch Plateau (inset map)are shown in gray and black, respectively.Trajectories in the northern Wasatch Plateau aremeasured subparallel to regional depositionaldip (WNW–ESE), whereas those in the southernWasatch Plateau are measured oblique to thisorientation. The measured trajectories are notcorrected for postdepositional compaction.


to calculate trajectories in the southern Wasatch Plateau (from c. 10 kmfor parasequence Ksp 040 to c. 80 km for parasequence Ksp 010; insetmap in Fig. 13), on the assumption that these shorelines are linear orweakly lobate (Fig. 11). River-dominated deltaic shorelines in thePanther Tongue are strongly lobate (Fig. 11B), and the associatedshoreline trajectory in the northern Wasatch Plateau was measured at alocation where the outcrop belt constrains the down-dip pinchout ofproximal delta-front deposits perpendicular to the subregional shorelineorientation (line of section shown in inset map in Fig. 13). Shorelinetrajectories in the Spring Canyon Member of the Blackhawk Formation(parasequences SC4-SC7 in Fig. 13) are taken from the northwesternBook Cliffs (Hampson 2010; line of section shown in inset map inFig. 13). Along-strike variations in trajectory are constrained by theoutcrop belt in parasequences Ksp 020 and Ksp 040, and are shown asbold horizontal bars in Figure 13.

The vertical component of shoreline trajectory in each parasequence iscalculated relative to the flooding-surface datum at the base of theparasequence (cf. Hampson 2010). The horizontal component oftransgressive shoreline trajectory associated with each parasequence-bounding flooding surface is determined from the paleolandwarddislocation of upper-shoreface or proximal delta-front deposits acrossthe surface. In order to estimate the vertical component of shorelinemigration during transgression, each flooding surface is assigned a typicalmodern shelf dip of 0.02u (cf. Hampson 2010). The use of floodingsurfaces at the base of successive tongues as multiple datum surfacesminimizes the effects of differential compaction on the calculatedshoreline trajectory, and also removes most of the effects of angularrotation arising from differential tectonic subsidence (Hampson et al.2009). Decompaction of the study interval, which has been buried up to c.2.5 km (Nuccio and Roberts 2003), would increase each verticalincrement of shoreline trajectory.

The overall, long-term shoreline trajectory of the Star Point Sandstoneis ascending regressive, with a mean trajectory across the stackedparasequences of 0.09u (Fig. 13). In more detail, the long-term shorelinetrajectory in the lower Star Point Sandstone (parasequences Ksp 050 toKsp 030) is ascending regressive in the southern Wasatch Plateau butregressive (parasequences Ksp 050 to Ksp 040) and then transgressive(parasequences Ksp 040 to Ksp 030) in the northern Wasatch Plateau(Table 2). In the middle to upper Star Point Sandstone and overlyingSpring Canyon Member (parasequences Ksp 030 to SC7), the trajectory isalso ascending regressive, but with an increasingly steep angle thatrecords decreasing progradation and increasing aggradation (Fig. 13;Table 2). The vertical component of shoreline trajectory for the intervalcomprising parasequences Ksp 040 to Ksp 010 is larger in the northernWasatch Plateau than in the southern Wasatch Plateau (Fig. 13),reflecting the greater thickness of this interval in the north (Fig. 10).This lateral variation in trajectory is explored further below.

The overall concave-landward shoreline trajectory of the middle toupper Star Point Sandstone and overlying Spring Canyon Member(parasequences Ksp 030 to SC7) records a gradual, long-term decrease insediment supply to the shoreline relative to the long-term rate of relativesea-level rise. Although this may reflect an increasing rate of relative sea-level rise or decreasing sediment flux due to allogenic controls (e.g.,Kamola and Huntoon 1995), it is most simply explained by autogenicretreat of the shoreline system under conditions of constant sedimentsupply and relative sea-level rise (autoretreat sensu Muto and Steel 1992;Muto et al. 2007). Lengthening and aggradation of the fluvial profileduring shoreline progradation under such steady forcing conditionswould have resulted in increased sediment storage on the coastal plain,which then limited the extent of further progradation and eventuallyresulted in retreat of the shoreline at the major flooding surface whichcaps the Spring Canyon Member. The various Star Point and SpringCanyon shorelines lay only a short distance (c. 20–100 km in the regional,

WNW–ESE direction of depositional dip) from the Canyon RangeCulmination, which is interpreted to have formed the eastern limit ofelevated topography in the Sevier orogenic belt during Santonian–Campanian times (DeCelles and Coogan 2006). Consequently, the coevalcoastal plains were narrow (c. 20–100 km in a WNW–ESE direction).Autoretreat of these short coastal-plain and shoreline systems would haverequired relatively low sediment flux and/or high tectonic subsidence, withthe latter being consistent with deposition in a flexurally subsiding foredeep.

Along-Strike Variations in Parasequence Stacking and Shoreline Trajectory

The differences in long-term shoreline trajectory in the lower Star PointSandstone (parasequences Ksp 050 to Ksp 030) between the southern andnorthern Wasatch Plateau (Fig. 13; Table 2) can be accounted for byspatial variations in tectonic subsidence and sediment supply alongregional depositional strike (SSW–NNE). The larger vertical componentof shoreline trajectory in the northern Wasatch Plateau indicates thattectonic subsidence was greater here than in the southern WasatchPlateau. This higher tectonic subsidence rate is consistent with retro-gradational stacking of the Storrs Tongue (parasequence Ksp 030) abovethe Panther Tongue (parasequence Ksp 040) in the northern WasatchPlateau, but it does not account for the strongly progradational stackingof the Panther Tongue above underlying parasequence Ksp 050. High,localized sediment supply must be invoked to explain the latterrelationship, which is consistent with the river-dominated deltaiccharacter of the Panther Tongue (Fig. 11B). The forced regressivecharacter of the Panther Tongue also accounts for its large prograda-tional extent (50 km, Posamentier and Morris 2000) and requires a short-term relative sea-level fall of c. 20 m. There is no evidence for acomparable relative sea-level fall in the wave-dominated shorelinedeposits of parasequence Ksp 040 in the southern Wasatch Plateau(e.g., an attenuated, ‘‘sharp-based’’ shoreface succession sensu Plint1988), although such evidence may well be below the resolution of ourstratigraphic analysis to date.

High, localized sediment supply to the Panther Tongue may reflect thepresence of a long-lived, structurally controlled sediment entry point nearthe northwestern limit of the study area (Edwards et al. 2005). Thissediment entry point may coincide with a structural recess between thePaxton thrust and Charleston–Nebo thrust system (Fig. 14), both ofwhich were active during the Campanian (Horton et al. 2004; DeCellesand Coogan 2006). During Panther Tongue deposition, sediment fluxthrough this entry point was elevated relative to periods represented byunderlying and overlying parasequences (Edwards et al. 2005). Highertectonic subsidence in the northern Wasatch Plateau likely reflects greaterflexural subsidence here, due to loading by stacked thrust sheets in thenearby Santaquin and Wasatch culminations (Fig. 14) (Johnson 2003;Horton et al. 2004). The relative sea-level fall recorded by the internalstratigraphic architecture of the Panther Tongue, and the relative sea-level rises recorded by parasequence-bounding flooding surfaces suggestthe operation of a low-amplitude (, 30 m), high-frequency (, 400 kyr)allocyclic control on relative sea level, most likely glacio-eustasy undergreenhouse conditions (cf. Miller et al. 2003).

Two further aspects of the Panther Tongue delta system (Fig. 11B) arenoteworthy. Firstly, the delta system prograded southward, subparallel toregional depositional strike. Similar river-dominated delta-front depositsin other parasequences in the Star Point Sandstone and the BlackhawkFormation have an orientation subparallel to the regional shoreline trend(Fig. 11D; Kamola and Van Wagoner 1995; Hampson and Storms 2003;Charvin et al. 2010), which is attributed to southward deflection of thedelta by wave-driven longshore currents (cf. Bhattacharya and Giosan2003). Secondly, the Panther Tongue delta system is much larger(. 800 km2 in area) than other river-dominated delta-front deposits inthe Star Point Sandstone and Blackhawk Formation (e.g., river-


dominated delta-front deposits in parasequence Ksp 020 are c. 30 km2 inarea; Fig. 11D). The Panther Tongue may therefore represent thedowndrift flank of an asymmetric wave-dominated delta, as proposedfor much smaller deposits of similar facies character in the BlackhawkFormation (Hampson and Howell 2005; Charvin et al. 2010), althoughneither wave-dominated spit deposits nor a wave ravinement surface havebeen documented from the eastern margin of the Panther Tongue deltasystem as implied by this interpretation. Alternatively, the PantherTongue delta system may have built out into a sheltered embaymentbounded on its eastern margin by seafloor topography above an activelygrowing structure (e.g., San Rafael Swell thrust; Fig. 14). Thisinterpretation is difficult to reconcile with the occurrence of wave-dominated shorelines, implying an open, non-sheltered setting, in

underlying and overlying parasequences. Further work is required tosatisfactorily address these aspects of the Panther Tongue delta system,including characterization of its lateral pinchouts, and of regionalthickness trends in the unit that contains it (parasequence Ksp 040).

CONCLUSIONS

The upper Santonian to lower Campanian Star Point Sandstone isexposed in a large (c. 100 km), nearly continuous section aligned obliqueto depositional strike along the eastern edge of the Wasatch Plateau incentral Utah. The unit is diachronous, and becomes younger from southto north. The upper part of the Star Point Sandstone in the northernWasatch Plateau is coeval and contiguous with the lower part of the

FIG. 14.—Map of north central Utah duringdeposition of the Star Point Sandstone, showingactive and inactive thrusts (after Neuhauser1988; Johnson 2003; Horton et al. 2004; DeCellesand Coogan 2006), interpreted highlands of theSevier fold-and-thrust belt (DeCelles and Coo-gan 2006), mapped shorelines for parasequencesKsp 040 and Ksp 030 (Panther Tongue andStorrs Tongue, respectively) (Fig. 11B, C), andinterpreted direction of wave-driven longshoredrift (Fig. 11). The location of the study areais shown.


Spring Canyon Member of the Blackhawk Formation in the depositional-dip-oriented Book Cliffs.

Outcrop mapping of the Star Point Sandstone using low-angle aerialphotographs and measured sections reveals that the unit comprises fiveparasequences (labeled Ksp 050, Ksp 040, Ksp 030, Ksp 020, and Ksp 010,from oldest to youngest). Each parasequence records 7 to 45 km of ESE- toENE-directed progradation of a predominantly linear to moderatelylobate, wave-dominated shoreline. Parasequence-bounding flooding sur-faces record 3 to . 19 km of shoreline retreat. Upper-shoreface depositscontain SSE-directed, shoreline-parallel paleocurrents that record sedimenttransport by wave-driven longshore currents. Lower-shoreface depositsextend paleoseaward of these upper-shoreface deposits to form broad (5–20 km) belts of hummocky cross-stratified sandstones that record strongoffshore sediment transport by storms. Wave-dominated shorelineparasequences pinch out up dip over short distances (, 500 m) aslandward-tapering sandstone wedges. Lower-shoreface deposits in eachparasequence split down dip into multiple, vertically stacked, upward-coarsening bedsets separated by tongues of offshore shale in distallocations associated with rapid deepening of antecedent paleobathymetry.

Strongly lobate river-dominated delta-front deposits occur locally withintwo parasequences. In the younger example (parasequence Ksp 020), suchdeposits define a minor (c. 30 km2 in area) protuberance into a spit-boundedembayment that is aligned subparallel to the regional shoreline trend; thesedeposits are interpreted to represent an asymmetric wave-dominated delta.In the older example (parasequence Ksp 040; Panther Tongue), river-dominated delta-front deposits are much more areally extensive(. 800 km2) although they also exhibit a progradation direction subparallelto the regional shoreline trend into a location sheltered from wave energy.

The arrangement of parasequences in the Star Point Sandstone definesan overall concave-landward shoreline trajectory, with decreasingprogradation and increasing aggradation through time. Along-strikevariations in this trajectory pattern reflect a combination of two controls.First, tectonic subsidence was greater towards the north. Second, a highlylocalized, large-volume, fluvial sediment supply was routed via astructurally controlled sediment entry point near the northwestern limitof the study area during deposition of the older, widespread river-dominated delta-front complex (parasequence Ksp 040; Panther Tongue).

ACKNOWLEDGMENTS

We thank Chevron for funding and support of this work. MRGacknowledges the Donors of the American Chemical Society PetroleumResearch Fund (ACS PRF #50310-DNI8) for support of this research. Wealso thank Stacy Atchley and Mike Blum for their constructive and insightfulreviews, and Janok Bhattacharya, Russell Dubiel, Sanjeev Gupta, JohnHowell, Howard Johnson, and Turid Knudsen for thought-provokingdiscussions of aspects of the work presented here. We are indebted to JohnSouthard for his careful copy editing.

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Received 7 December 2009; accepted 18 October 2010.


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