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Regional SequenceStratigraphic Interpretations

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Marooned in Salina Canyon, Wasatch Plateau, Utah, circa 1910. Photograph courtesy of the family of C. T. Lupton.

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Stacking Patterns, Sediment VolumePartitioning, and Facies Differentiation in

Shallow-Marine and Coastal-Plain Strataof the Cretaceous Ferron Sandstone, Utah

Michael H. Gardner, Timothy A. Cross, and Mark Levorsen1

Analog for Fluvial-Deltaic Reservoir Modeling: Ferron Sandstone of UtahAAPG Studies in Geology 50

T. C. Chidsey, Jr., R. D. Adams, and T. H. Morris, editors

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ABSTRACTFluvial-deltaic strata of the Upper Cretaceous Ferron Sandstone, Western Interior Seaway, form a

clastic wedge consisting of eight short-term stratigraphic cycles. The cycles are arranged consecutive-ly in a seaward-stepping, vertically stacked, and landward-stepping stacking pattern. The stackingpattern is a product of fluctuations in accommodation-to-sediment supply (A/S) regimes described byintermediate-term, base-level cycles.

Each short-term stratigraphic cycle is a progradational/aggradational unit comprising a spectrumof coastal-plain, bay/lagoon/estuary, shoreface, and shelf facies tracts. Sediment volumes and sand-stone:mudstone ratios were measured separately in coastal-plain and shoreface facies tracts in four ofthe cycles. Total sediment and total sandstone volumes are partitioned differentially into the two faciestracts in a systematic manner that follows the stacking pattern. The total sediment volume and totalsandstone in the shoreface facies tract decreases regularly from seaward- to landward-stepping stack-ing patterns. The proportion of marine-to-nonmarine sandstone also decreases. This demonstratesincreasing sediment storage in continental environments during the transition from seaward- to land-ward-stepping stacking patterns.

Sediment volume partitioning is accompanied by systematic changes in numerous other strati-graphic and sedimentologic attributes which illustrate the two types of facies differentiation. The firsttype stratigraphic control on the types of geomorphic elements that occupy a geomorphic environ-ment is manifest by the transition from fluvial- to wave-dominated deltas in the progression fromseaward- to landward-stepping cycles. The second type a change in degree of preservation of orig-inal geomorphic elements is illustrated by conspicuous differences in the facies that compose theshoreface and coastal-plain facies tracts. Shorefaces of high-accommodation, landward-steppingcycles comprise homogeneous, cannibalized and amalgamated sandstones, whereas shorefaces oflow-accommodation, seaward-stepping cycles are lithologically heterogeneous containing diversefacies and well-preserved, original geomorphic elements. Distributary channelbelt sandstones of

1Department of Geology and Geological Engineering,Colorado School of Mines, Golden, Colorado

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INTRODUCTIONThis study illustrates the well-organized behavior of

the stratigraphic process-response system, and suggestsunderlying causes for this behavior. We observe system-atic variations in numerous stratigraphic and sedimen-tologic attributes of siliciclastic coastal-plain to shelfstrata that are coincident with stacking patterns of strati-graphic cycles. These organized, systematic variations of

stratigraphic and sedimentologic attributes are analyzedfrom the perspectives of conservation laws and strati-graphic base level. Stratigraphic base level describes the

balance between the energy required to change accom-modation space and the energy used by surficialprocesses to erode, transport, and deposit sediment.Base-level changes are manifest by changes in the ratioof accommodation-to-sediment supply (A/S). Changesin A/S conditions and mass conservation determine thevolumes and types of sediment which accumulate in dif-ferent environments.

Sediment is partitioned differentially into coastal-plain and shoreface facies tracts through time and

changing A/S conditions. Changes in the ratio of totalsediment volumes within these two facies tracts areaccompanied by changes in ratio of nonmarine-to-marine sandstone volumes. Sediment volume partition-ing reflects the balance among rates of sediment deliv-ery, rates of reworking and cannibalization of sediment,and rates of net sediment accumulation. Sediment vol-ume partitioning can be explained by variations in theA/S conditions that accompany stratigraphic base-levelcycles.

Sediment volume partitioning controls or influencessedimentologic and stratigraphic attributes of all scales

including the constituents, associations and successionsof facies, the degree of preservation of original geomor-phic elements, petrophysical attributes, stratigraphicarchitecture, and frequency of occurrence of hiatal sur-faces of different origins. Two types of facies differentia-tion are recognized and illustrated. One type is thechange in original geomorphic elements that occupy thesame environment under variable A/S conditions. Theother is the variable degree of preservation of originalgeomorphic elements and their proportions that enterthe stratigraphic record. This produces changes in facies

diversity and lithologic heterogeneity in strata that accu-mulated in the same environment.

Heterogeneous shoreface strata of seaward-steppingcycles are responses to lower A/S conditions comparedwith homogeneous sandy shoreface strata of higherA/S, landward-stepping cycles. Similarly, heteroge-neous distributary channelbelt deposits of landward-stepping cycles are responses to higher A/S conditionscompared with homogeneous channelbelt sandstones of

lower A/S, seaward-stepping cycles. In homogeneousstrata relatively more time is represented by stratigraph-ic surfaces of discontinuity than by rock, whereas in het-erogeneous strata relatively more time is represented byrock than by hiatal surfaces.

Stratigraphic and sedimentologic attributes of allscales and of many types show consistent, systematicpatterns of change when viewed from the perspectivesof conservation laws and stratigraphic base level. Thisorganization produces transitional facies constituents,associations, and successions within a continuum of thepreserved products of the same environment. The sedi-mentologic attributes of facies tracts commonly

described in facies models are mixtures of the prod-ucts of geomorphic elements that existed separately dur-ing base-level cycles. The next generation of facies mod-els should be constructed from a stratigraphic perspec-tive in which there is a continuum of transitional formsof facies associations and successions that are differentproducts of the same parent.

GEOMORPHIC AND STRATIGRAPHICBASE LEVEL CONCEPTS

We recognize three temporal and spatial scales ofallogenic cyclicity in the upper Ferron Sandstone (Figure1; Obradovich, 1991; Gardner, 1993; Gardner and Cross,1994; Gardner, 1995a, 1995b, 1995c). Cycles of each scalerecord a complete stratigraphic base-level cycle sensuWheeler (1959, 1964, 1966). Because our usage of strati-graphic base level follows Wheeler rather than the morecommon geomorphic usage, and because we incorpo-rate some sequence stratigraphy concepts into Wheelersoriginal definition, this section presents our understand-ing of stratigraphic base level.

M. H. Gardner, T. A. Cross, and M. Levorsen

landward-stepping cycles are composed of high diversity, well-preserved macroforms and bedforms,

whereas those of seaward-stepping cycles are composed of strongly cannibalized, amalgamated, low-

diversity macroforms and bedforms.

Sediment volume partitioning and facies differentiation are attributed to changing A/S conditions

that accompany short- and intermediate-term base-level cycles. The A/S conditions control or influ-

ence the position and volume of sediment accumulation, the types of geomorphic elements in an envi-

ronment, and the proportions and completeness of original geomorphic elements that enter the strati-

graphic record.

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by introduced the notion of considering not only degra-dation but sediment transport and accumulation in thedefinition of base level. (It is ironic that he incorrectly

attributed this stratigraphic sense of base level to Powell[1875]; he either misread or misunderstood Powell, orsimply chose to add this new dimension to Powellsdegradational concept of base level.) This notion of anequilibrium or balance between erosion and sedimenta-tion was supported through the years by others, but per-haps most influentially by Barrell (1917), Krumbein andSloss (1951), and Sloss (1962).

Wheeler (1964, 1966) made significant additions andmodifications to stratigraphic base-level concepts. Heargued that base level was a single, continuous, nonhor-izontal, undulatory, imaginary surface that rises and

falls with respect to the Earths surface. Where base levelis above the Earths surface, sediment will accumulate ifit is available. Where base level is below the Earths sur-face, sediment is eroded and transferred downhill to thenext site where base level is above the Earths surface.His stratigraphic base level is not a control, but a de-scriptor for measuring the energy budget between forcesand processes that change sediment storage capacity(accommodation space) and those that erode, transfer,and deposit sediment across the surface of the Earth. Ineffect, but not explicitly, Wheeler defined stratigraphic

base level as a potentiometric energy surface that de-scribes the energy required to move the Earths surfaceup or down to a position where gradients, sediment sup-

ply, and accommodation are in equilibrium. If theseforces are in balance neither deposition nor erosionoccurs, and the Earths surface is at equilibrium andcoincident with base level (Figure 2). Base leveldescribes the increase in topographic relief that resultsfrom deposition and its reduction by erosion. Base levelaccounts for deposition and erosion that occur at thesame time in different parts of a basin. This is a neces-sary condition of a physical system where energy andmass are conserved. Stratigraphic base level may beexpressed as the A/S ratio a ratio of the energy re-quired to change the accommodation at the Earths sur-

face and the energy required to erode, transport, anddeposit sediment. The A/S ratio is expressed as thedimensionless term Nm/Nm. Or, if sediment volume isconsidered instead of energy, the A/S ratio is expressedas the dimensionless term m3/m3. Wheeler (1959, p.701702) states:

In contrast with the popular concept, baselevel is neithera horizontal plane nor can it be defined solely in termsof sea level or relationships on the sea floor... Moreover,baselevel should not be conceived solely in its relation-

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Figure 2. Illustration of Wheelers conception of stratigraphic base level as an imaginary potentiometric energy surface that undulates withrespect to the Earths surface. It relates the energy required to change accommodation to the energy required to erode, transport, and deposit sed-iment. Where stratigraphic base level is above the Earths surface, sediment will accumulate, if available, building topography and bringing theEarths surface closer to base level. Where stratigraphic base level is below the Earths surface, erosion or bypass occurs and the removal of mate-rial reduces the topography bringing the Earths surface closer to base level. Where stratigraphic base level is coincident with the Earths surface,there is a state of equilibrium.


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ships to either erosion or aggradation alone, for its signif-icance is best appreciated in stratigraphy, sedimentation,or geomorphology if it is conceived as a surface at whichneither erosion nor sedimentation (can take) place.

Stratigraphic base level describes the erosionaldecay and construction of topography through deposi-tion that drives the partitioning or selective storage ofsediment volumes across a topographic profile. This isthe normal condition of sedimentation in a depositionalsystem linked by a common dispersal mechanism. Dur-ing a base-level cycle, the A/S ratio decreases unidirec-tionally to a limit (base-level fall minimum) that equatesto a sequence boundary in geographic positions wherethere is no accommodation. It then increases unidirec-

tionally to another limit (base-level rise maximum) thatsome place may be equivalent to the maximum floodingsurface of sequence stratigraphic terminology.

Sedimentologic and stratigraphic attributes of allscales and numerous types respond consistently andcoherently to these changes in A/S conditions, includingsmall-scale attributes such as texture and petrophysicalproperties, meso-scale attributes such as sedimentarystructures, facies diversity, and macroform types (sensu,Crowley, 1983) and mixtures, and large-scale attributes ofstratigraphic architecture (Gardner, 1993; Ramon and

Cross, 1997; Cross, 2000). The limits, or turnaroundpoints, of these unidirectional trends in A/S are correlat-ed throughout the spatial extent of each stratigraphiccycle. Stratigraphic cycles of each scale are the time-

bounded rock units that comprise all strata and hiatusproduced during a base-level cycle (Figure 3). The initia-tion points for stratigraphic cycles of all scales are pickedconsistently at the same turnaround position. In thisstudy, the initiation point was picked at the base-levelrise-to-fall turnaround because it is the most practical; itis the position most easily recognized, frequently docu-mented, consistently picked, and physically traceable.

Stratigraphic base-level concepts emphasize the cor-relation of all rocks and surfaces developed during a

base-level cycle divided into base-level rise and fall time

domains (Grabau, 1924; Busch, 1959; Wheeler, 1966;Gardner, 1993; Cross and Lessenger, 1998; Muto andSteel, 2000; Figure 3). This provides a more completeaccounting for how time is represented in a stratigraph-ic cycle as either rock or surface of stratigraphic discon-tinuity. By contrast, a parasequence, defined as an asym-metric upward-shoaling succession bounded by amarine flooding surface (Van Wagoner et al., 1990), onlyaccounts for the time of deposition during base-level fallin shallow-marine strata and does not recognize conti-nental and marginal-marine tidal strata that accumulat-

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Figure 3. Illustration of changes in cycle symmetry caused by volumetric partitioning and correlation of base-level cycles across shelf, shoreface,and coastal-plain facies tracts. Note how surfaces correlate to rocks at various positions of the depositional profile during a base-level cycle.

Stacking Patterns, Sediment Volume Partitioning, and Facies Differentiation

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ed during base-level rise; also see discussion by Arnott(1995). This more limited usage precludes considerationof sediment volume partitioning and excludes the possi-

bility of a significant proportion of time represented byshallow-marine strata formed during base-level rise.

In theory, the relative proportions of sediment vol-umes in coastal-plain and shoreface facies tracts varywith position of the short-term stratigraphic cycle in thestacking pattern, as first drawn and explained in a subsi-dence context by Barrell (1912, Figure 4, p. 399). This isone of several important responses to changes in A/Sconditions recorded by base-level cycles. As stratigraph-ic base level rises and intersects the Earths surface pro-gressively higher on the topographic profile, the A/Sratio increases and the sediment storage capacity inuphill positions increases. Since more sediment is storeduphill in continental environments, less sediment isavailable (conservation of mass) for downhill transportand accumulation in shoreface and shelf environments.Conversely, a decrease in the A/S ratio theoretically par-

titions more sediment volume into shoreface and shelfenvironments and less is stored uphill in continentalenvironments. The degree of sediment volume partition-ing in short-term stratigraphic cycles, as measured by theproportion of sediment volume stored in different faciestracts, produces systematic changes in cycle stacking pat-terns. These changes have been simulated and matchedwith field data using forward and inverse stratigraphicmodels (Cross and Lessenger, 1998, 1999, 2001).

STRATIGRAPHIC SETTINGAND STACKING PATTERNS

The Upper Cretaceous (Turonian-Coniacian) FerronSandstone is a regressive-transgressive clastic wedge thataccumulated at the site of a large delta in the foreland

basin, east-central Utah (Speiker, 1949; Armstrong, 1968;Cotter, 1975; Ryer, 1981; Gardner, 1993; Gardner andCross, 1994; Gardner, 1995a, 1995b, 1995c). During thatperiod, sea level was near a maximum highstand, and

both accommodation and sediment supply were high(Kauffman, 1977; Hancock and Kauffman, 1979;Schlanger et al., 1986; Haq et al., 1988; McDonough andCross, 1991; Sahagian and Jones, 1993; Figure 1). Conse-quently, time in the Ferron is represented much more by

rock than by stratigraphic surfaces of erosion and nonde-position. Regional unconformities are absent and distrib-utary channel deposits do not extend beyond the deltathey sourced, indicating an absence of incised valleys.

The upper Ferron Sandstone consists of eightprogradational/aggradational stratigraphic units short-term stratigraphic cycles arranged consecutive-ly in seaward-stepping, vertically stacked, and land-ward-stepping geometric patterns (Ryer, 1981; Gardner,1995c; Figure 4). Seven of these cycles are recognized inoutcrop, and the eighth and youngest cycle is recognized

from subsurface data. Each progradational/aggrada-tional unit contains a spectrum of coastal-plain, estu-ary/bay/lagoon, shoreface, and shelf facies tracts.Exceptionally continuous, three-dimensional exposuresplus a subsurface data base of geophysical well logs andcoal core logs enabled physical correlation of short-termcycles across all facies tracts. These stratigraphic cyclesare equivalent to a depositional episode (Frazier, 1974), agenetic increment of strata or genetic sequence (Busch,1959, 1971), a fourth-order regressive-transgressive cycle(Ryer, 1983), and are comparable to parasequence sets ofa fourth-order, high-frequency sequence (Van Wagoneret al., 1990). Subdelta lobes that compose the shorefacefacies tract correspond to parasequences of other Ferronworkers (e.g., Barton, 1994; Ryer and Anderson, 1995).They are considered autogenic because they are restrict-ed to the shoreface facies tract.

The general motif of volumetric partitioning isshown along one example topographic profile from theFerron Sandstone (Figure 3). The stacking pattern of

progradational/aggradational stratigraphic units ob-served and mapped in this study and by Ryer (1981) isthe product of changing A/S conditions of the interme-diate-term, base-level cycle (12 m.y. duration). Theshort-term (0.3 m.y.), seaward-stepping units (SC1-3;Figure 4) accumulated during lowest A/S. The vertical-ly stacked unit (SC4; Figure 4) accumulated during earlyintermediate-term, base-level rise. The landward-step-ping units (SC5-8; Figure 4) accumulated during lateintermediate-term base-level rise and highest A/S. Thearchitecture of these short-term cycles is described

below.

Seaward-Stepping SC2The seaward-stepping shoreface facies tracts of SC1

and SC2 record offlap in excess of 70 km (43 mi). The SC2shoreface extends over 60 km (37 mi) parallel to deposi-tional dip and forms the thickest and widest shorefacefacies tract capped by the most laterally continuous coalhorizon (a coal bed) in the upper Ferron Sandstone (Fig-ure 4). Discrete subdelta lobes are the dominant strati-graphic bodies and comprise upward-coarsening sand-stone successions with gently inclined, dip-orientedclinothems 1030 m (3398 ft) thick and 13 km (0.62

mi) long. Amalgamated distributary mouthbar sand-stones contain numerous inclined bedding surfaces thatextend hundreds of meters along depositional dip andstrike. Amalgamated sandstones are replaced laterally,on a kilometer-scale, by mudstone-dominated interdis-tributary bay strata.

Coastal-plain strata that overlie shoreface strata arethin but contain thick, isolated and disconnected chan-nelform sandstone bodies. They consist of amalgamated,erosive-based compound macroforms arranged in singleand amalgamated, multistory complexes with biconvex

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to flat-based, convex-upward geometries. Bedform andmacroform diversity is low with the latter dominated byhighly amalgamated, cut-and-fill and low-sinuositytypes. The principal bounding surfaces are thin, sand-stone-rich, basal channel lags tens of meters wide, andnumerous, shorter length reactivation surfaces. Thinmudstone-rich, lower delta-plain strata separate chan-nelforms, and consist of laterally discontinuous coalseams and crevasse-channel and crevasse-splay sand-stones. Multiple isolated distributary channel complexesproduce a low distributary-channelbelt to delta-plain

facies ratio in seaward-stepping stratigraphic cycles.

Seaward-Stepping SC3The SC3 shoreface facies tract is in the most basin-

ward position, and is the turning point between sea-ward- and landward-stepping stratigraphic cycles. Theshoreface facies tract has a dip-elongate geometry cen-tered over SC2 with landward and seaward limits posi-tioned, respectively, 20 km (12 mi) and 15 km (9 mi) sea-ward from those of SC2. Discrete subdelta lobes are

sandier than older upper Ferron shoreface strata.Because sedimentary structures are highly amalgamat-ed, resolution of internal sedimentary bodies withinshoreface sandstones is greatly reduced. Mudstone-richinterdistributary bay strata are volumetrically subordi-nate to encasing SC2 and SC4 strata.

At Dry Wash (Figure 4), near the seaward limit of thecoastal-plain facies tract, the shoreface facies tract isoverlain by a thick heterolithic succession of tidallyinfluenced strata that have approximately equal propor-tions by volume of base-level fall and rise strata. Tidal

strata containing recurved spits, washover fans, barriershorelines, bay strata, and other features indicative oftidal influence overlie a conspicuous transgressive sur-face of erosion that incises into progradational delta-front strata. These record in-phase, short- and interme-diate-term, base-level rise (tidal and transgressive stratain this area were first described by Stalkup and Ebanks,1986).

Large-scale deformation in the SC3 shoreface faciestract encompasses a tens of km2 area near the seawardlimit of underlying SC2 shoreface strata near the town of

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Figure 4. Cross section showing stacking pattern of short-term stratigraphic cycles in the upper Ferron Sandstone, and map of landward andseaward depositional limits of the shoreface facies tracts in the eight cycles.


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Ferron, Utah (Figure 4). The most impressive features ofthis deformation are several isolated, 25-m (82-ft) thick,100-m (328-ft) long, rotated sandstone lenses interpretedas slumped and rotated distributary bar-finger sand-stones. These foundered bar-finger sandstones demon-strate that distributary channels did not extend beyondtheir delta during in-phase, short- and intermediate-term, base-level fall (the lowest A/S ratio) when uncon-formity development is most likely.

Channelform sandstone bodies resemble those inolder seaward-stepping cycles and consist of erosive-

based, cut-and-fill and low-sinuosity macroforms. The Ccoal bed (Figure 4) is laterally continuous from the top ofthe shoreface facies tract and across the coastal-plainfacies tract. The C coal bed contains a regionally exten-sive volcanic ash bed (tonstein) that permits correlation

between marine-shelf and coastal-plain facies tracts.Landward of the landward depositional limit ofshoreface sandstones are the thickest and most extensive

bay-fill strata in the upper Ferron Sandstone near the

town of Emery, Utah (Figure 4). Heterolithic, mudstone-dominated, marginal-marine strata separate coevalcoastal-plain and shoreface sandstones. This severalkilometer-wide bay is inferred to have formed duringintermediate-term, base-level rise, and filled prior toprogradation of the shoreface facies tract of verticallystacked SC4.

Vertically Stacked toLandward-Stepping SC4

Relative to SC3, the shoreface facies tract of SC4 isnarrower and offset landward; its landward and sea-

ward limits are 5 and 30 km (3 and 19 mi), respectively,landward of those of the SC2 shoreface facies tract.Shoreface strata contain the thickest, coarsest and mostfluvial-dominated facies of all landward-stepping,shoreface facies tracts. The shoreface facies tract geome-try resembles landward-stepping SC5-SC7, but faciesand geomorphic constituents resemble those in sea-ward-stepping SC1-SC2. Near the landward deposition-al limit of the shoreface facies tract, SC4 contains twovertically stacked subdelta lobe successions that thickenabruptly seaward to the northeast along the Molen Reefescarpment. Other than these subdelta lobes, a distinct

stratigraphic break within the vertically stacked shore-face facies tract of SC4 was not identified, but two strati-graphic cycles may be represented. Vertically stackedfacies successions are present in equivalent marine-shelffacies but occur only locally in the coastal-plain faciestract.

The shoreface facies tract of SC4 contains amalga-mated sandstones separated by volumetrically subordi-nate interdistributary bay strata. Subdelta lobes up to 30m (98 ft) thick are the thickest of all cycles other thanSC2. South of Dry Wash, near the seaward depositional

limit of the shoreface facies tract, thick, mudstone-richlower delta-front deposits are overlain by lenticular, 3-m-thick (10-ft) sandwaves inferred to represent small-scale mouthbar sandstones that prograded basinward.Comparison of these facies with SC2 shoreface facies ata similar distance from its seaward limit demonstratesincreased partitioning of sediment landward in SC4.This may explain why coastal-plain strata that overliethe shoreface facies tract are the most organic-poor andcoarsest grained in the upper Ferron Sandstone.

Landward-Stepping SC5The SC5 shoreface facies tract contracted bidirec-

tionally; its landward depositional limit is almost coinci-dent with that of SC3 and its seaward limit is 7 km (4 mi)landward from that of SC4. Near the landward limit ofthe shoreface facies tract at Muddy Creek Canyon, dis-tributary channelbelt strata extensively incise wave-dominated shoreface strata (Figure 4). Steeply inclined,

seaward-dipping clinoforms segregate shoreface sand-stones into 2030 m (6698 ft) thick and less than 1-km-wide (0.6-mi) subdelta lobes measured parallel to depo-sitional dip. The paucity of distributary mouthbars andinterdistributary bays strata reflects dominance of waveand storm processes along a nonembayed coastline, asignificant contrast to shorefaces of seaward-steppingcycles. Coeval distributary channelbelt sandstones con-tain a diverse assemblage of moderately interconnected,low-sinuosity, high-sinuosity, and abandonment-fillmacroforms, typically 310 m (1032 ft) thick and hun-dreds of meters wide.

Local amalgamation of multiple thin coal seams pro-

duces irregular pod-shaped coals up to 8 m (26 ft) thick.Coals commonly overlie, but are replaced locally by, lat-erally extensive distributary and crevasse-channel sand-stones. The ratio between distributary channelbelt andvertical-accretion flood-plain strata is high compared toolder seaward-stepping cycles. Distributary channel-

belts contain a diverse assemblage of moderately inter-connected, low-sinuosity, high-sinuosity, and abandon-ment-fill macroforms, typically 310 m (1032 ft) thickand hundreds of meters wide. Channel macroformsform moderately interconnected kilometer-wide chan-nelbelts interdigitated along their margins with

crevasse-splay and crevasse-channel strata. Macroformshave high bedform diversity, with basal channel lagshundreds of meters wide, and subordinate boundingsurfaces of equal length represented by lateral anddownstream accretion surfaces.

Shoreface strata of SC6 through SC8 record contin-ued contraction of the shoreface facies tract. Shorefacecontraction is associated with increased thickness of coe-val coastal-plain strata. Discontinuous coal seams pro-duce lower confidence shoreface to coastal-plain correla-tions, but the increased thickness of coastal-plain strata in

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the upper part of the upper Ferron Sandstone demon-strates increased landward partitioning of sediment vol-

umes. Coastal-plain strata overlain by marine shelf mud-stones of the Blue Gate Shale Member in the most proxi-mal outcrops at Last Chance Canyon record acceleratedtransgression at the top of the upper Ferron in responseto intermediate-term base-level rise (Figure 4).

SEDIMENT VOLUME PARTITIONINGTo test whether sediment volumes change systemat-

ically with the stacking pattern of short-term strati-graphic cycles, sediment volumes were measured infour progradational/aggradational units in the upperFerron Sandstone. These units were mapped over a 110

km2 (68 mi2) area using 97 data points from outcropmeasured sections, geophysical well logs, core-derivedlithology logs, and cliff-tape calibrated photomosaics(Figure 5). The three-dimensional distribution of thesesediment volume measurements were normalized toaccount for paleogeographic variations in position andwidths of facies tracts, and incomplete preservation ofthe depositional system from the study area westward tothe thrust front. The most consistent and objective nor-malization procedure was to measure sediment volumes

in continental and marine facies tracts between the land-ward and seaward depositional limits of the shoreface

(delta front) facies tract of each short-term stratigraphiccycle (Figure 4).

Between these paleogeographic limits, the total sed-iment volume, and the total sandstone and mudstonevolumes were measured within shallow-marine andcoastal-plain strata. This allows comparison of total sed-iment volumes and lithology ratios of shoreface andcoastal-plain strata in seaward-stepping, verticallystacked, and landward-stepping progradational/aggra-dational units.

The three-dimensional distribution of these data iscollapsed into a two-dimensional thickness-distance plotshowing lithology distributions in coastal-plain andshallow-marine strata between the landward and sea-ward depositional limits of the shoreface facies tract(Figures 5 and 6). Plot orientation is parallel to deposi-tional dip, as determined from mapped orientations offacies tract boundaries and paleoflow analysis. The plotorigin is set a constant distance from the landward depo-sitional limit of the shoreface facies tract. Plots showmarine and nonmarine sandstone volumes, total sand-stone and mudstone volumes, and total sediment vol-umes for each progradational/aggradational unit. In

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Figure 5. Thickness-distance plot from the Ferron Sandstone showing the areal distribution of various lithologies in facies tracts between thelandward and seaward pinch-out of the shallow-marine facies tract of stratigraphic cycles 25. The orientation of this plot is parallel to the

progradation direction of all delta lobes and to depositional dip. Three-dimensionally distributed data points are collapsed to this depositional dipline, and data points plotted are correlated by linear interpolation. The vertical axis is thickness (m) and the horizontal axis is distance (km), withthe origin of the plot set a constant distance from the landward pinch-out of the shoreface facies tract.


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this case total sediment volume only refers to the sedi-ment volume between the landward and seaward depo-sitional limits of the shoreface facies tract and not thetotal sediment volume of the entire depositional system.Although these sediment volumes may be related tochanging sediment supply, it is important to emphasizethat these volumes cant be determined by this method.

Sediment volumes are expressed as: (1) sandstonevolume ratios of shallow-marine and coastal-plain stra-ta; (2) stratigraphic cycle total sandstone/mudstone vol-

ume ratio; and (3) total sediment volume of each strati-graphic cycle. Sediment volume and lithology ratioswere calculated for each locality to allow comparisonwith averaged values on thickness-distance plots. Thetotal sediment and total sandstone volumes calculated inthis manner decrease from seaward- to landward-step-ping stratigraphic cycles (Figure 5). The nonmarine:marine sandstone volume ratios of seaward-steppingunits 2 and 3 are 1:12 and 1:32, respectively; in verticallystacked unit 4 it is 1:6, and in landward-stepping unit 5

Figure 6. Examples of landward and seaward depositional limits of the shoreface facies tract of upper Ferron short-term cycles. (A) Seaward depo-sitional limit of SC1 along the Molen Reef escarpment. View looking west toward the town of Emery, Utah, of the Tununk Shale and FerronSandstone Members along the Molen Reef in southern Castle Valley. Note the seaward depositional limit of shoreface sandstone in SC1 of theFerronensis sequence near center of photo. From valley floor to cuesta top is approximately 330 m (1080 ft). (B) Landward depositional limit ofSC6 shoreface at Muddy Creek Canyon. These limits constrain sediment volume calculations summarized in Figure 5.


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it is 1:7. Even though data were collected within a strike-oriented swath about 8 km (5 mi) broad, the sampling ofchannelbelt sandstones in the coastal-plain facies tract,which is the primary residence of sandstone, is subject to

biased position of channelbelts; channelbelts could be inone position in one cycle and in another position inanother cycle. Otherwise, measurements of sandstone inthe shoreface facies tract and total sediment volume in

both facies tracts are not biased. Seaward-steppingcycles record increased sediment volumes in shorefacestrata, reduced sediment volumes in coastal-plain strata,and a basinward shift in accommodation; shorefaceprogradation dominates over coastal-plain aggradation.Vertically stacked cycles have little or no offset of faciestracts across cycle boundaries, little shift in the deposi-tional tracts limits of successive stratigraphic cycles, andsubequal sediment volumes in the two facies tracts.Conversely, landward-stepping stratigraphic cyclesrecord increased coastal-plain sediment volumes,reduced shoreface sediment volumes, and a landward

shift in accommodation; coastal-plain aggradation dom-inates over shoreface progradation. These results do notpresume a constant sediment supply but rather reflectchanges in the A/S ratio that allows for variable sedi-ment flux and storage capacity across environments lim-ited by accommodation.

Decreases in total sediment and total sandstone vol-umes reflect decreased shoreface facies tract widths inlandward-stepping cycles. Compared with seaward-stepping cycles, progressively increased accommodationand storage capacity in the coastal plain of verticallystacked and landward-stepping cycles reduces the totalsediment volume delivered to shallow-marine environ-ments. The shift to increased sandstone storage in thecoastal-plain facies tract of vertically stacked and land-ward-stepping cycles also reflects increased A/S condi-tions in these cycles.

Because accommodation measures the potentialspace available for sediment accumulation, the directionof sediment transport does not affect a thickness-dis-tance plot relating sediment volume to accommodation.Sediment delivered from out of the plane (e.g., along-shore transport) of the thickness-distance plot may affectthe aspect ratio but not the distribution of sediment vol-umes in linked facies tracts.

FACIES DIFFERENTIATION IN THESHOREFACE FACIES TRACT

Accompanying sediment volume partitioning aredifferences in stratal architecture, facies associations andsuccessions, lithologic diversity, stratification types, con-nectivity and continuity of lithosomes, and petrophysi-cal attributes of strata which are preserved within iden-tical facies tracts but in different portions of base-level

cycles. The term facies differentiation (Cross et al.,1993; Cross and Homewood, 1998) refers to thesechanges in sedimentological and stratigraphic attributesduring base-level cycles as first noted by Van Siclen(1958). Facies differentiation reflects both the degree ofpreservation of original geomorphic elements, and thevariations in types of geomorphic elements that existedwithin a depositional environment at different times andin different A/S regimes. The relative balance amongrates of sediment addition, removal (cannibalization andwinnowing), and net accumulation controls the degreeof preservation. Rates of these processes are stronglyinfluenced by sediment volume partitioning whichaccompanies changing A/S conditions during base-levelcycles.

Strata in the shoreface facies tract of seaward- andlandward-stepping progradational/aggradational unitsare very different in lithologic heterogeneity; facies asso-ciations and successions; angles, geometry, and aspectratio of clinoforms; and relative dominance of current-

formed versus wave-formed geomorphic elements.Landward-stepping shoreface sandstones deposited inhigher A/S regimes are homogeneous, coarser, dominat-ed by wave-generated and wave-reworked facies associ-ations, and have narrower facies tract widths (Figure 7).Seaward-stepping shorefaces deposited in lower A/Sregimes are heterolithic, characterized by much higherfacies diversity of mixed wave and current origins, andcontain many fully preserved bedforms and other pale-ogeomorphic elements (Figure 8). Observations of suchdifferences in stratigraphic and sedimentologic attribut-es of a facies tract with respect to stacking patterns weremade previously, but not explained, by Curtis (1970) fordeltas in the Gulf Coast and by MacKenzie (1972) forshorefaces in the Western Interior Seaway.

Lower delta-front facies in landward- and seaward-stepping stratigraphic cycles record the same water-depth transition from storm to fair-weather wave base,

but their stratigraphic and sedimentologic attributes arequite different. Lower delta-front successions of land-ward-stepping cycles are thinner (< 14 m [< 313 ft]thick), and sharp based because they prograde across theflat, shallow-water platform formed by the underlyingprogradational/aggradational unit. They consist of low-diversity, erosive-based co-sets of amalgamated hum-

mocky cross-stratified sandstone capped by symmetricalripples, and/or combined-flow asymmetrical ripples(Figure 9). This facies association records dominance ofsediment reworking over sediment accumulation and

burrowing, with limited preservation of individual bed-forms and other paleogeomorphic elements on theseafloor.

By contrast, thicker (< 110 m [< 333 ft] thick),lower delta-front facies in seaward-stepping cycles con-sist of a mixture of shallow-water sediment gravity

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flows, wavy laminated to hummocky cross-stratifiedsandstone, amalgamated co-sets of symmetrical andasymmetrical ripple-laminated sandstone, and numer-ous mudstone drapes, partings, and beds (Figure 10).Sandstones and mudstones are approximately equal inproportion, contain more carbonaceous plant debris andsoft-sediment deformation, and generally exhibit less

burrowing. Bed geometry ranges from amalgamated totabular and are broadly lenticular. Preservation of origi-nal geomorphic elements is high. These record numer-ous waning-flow river-flood and waning-flow stormevents.

Upper delta-front facies in landward-steppingcycles consist of 120 m [366 ft] thick, upward-coarsen-ing successions of well-sorted, fine to medium, amalga-mated hummocky to swaley (or amalgamated troughcross-stratified) sandstones (Figure 8). The transition

from lower to upper delta-front facies is sharp, reflectinga change in sandstone to mudstone ratio from about 5:1to 10:1. Seaward-dipping clinoforms are more steeplyinclined but cryptic because of lithologic homogeneity.Trace-fossil diversity is high and includes, in order ofdecreasing abundance, Skolithos, Ophiomorpha, Thalassi-noides, Planolites, Diplocraterion,Arenicolites, Rosselia, andChondrites.

Upward-coarsening successions of heterolithicmudstones and sandstones of upper delta-front facies inseaward-stepping cycles record increased fluvial influ-

ence. Facies and geomorphic constituents are diverseand include stacked distributary mouthbar sandstones,growth-faults and rotated-slump blocks, and interdis-tributary bay strata, as well as storm-generated hum-mocks and swales of the upper shoreface. Long, contin-uous mudstone drapes and beds separate sandstonesdeposited by waning-flow river-flood and storm events.Large- and small-scale bedforms are amalgamated tofully preserved. Burrows in sandstone tend to be restrict-ed to the upper portions of beds. Seaward-dipping cli-noforms are conspicuous due to the thick mudstonedrapes and less steep than in shorefaces of landward-stepping units. However, steeper clinoforms areobserved recording the lateral infilling of interdistribu-tary bays.

Facies differentiation in the shoreface facies tract isexplained by sediment volume partitioning in response

to base-level cycles. In seaward-stepping stratigraphiccycles, less sediment is stored in the coastal plain. A pro-portionally greater volume of sediment is delivered byrivers to paralic, delta-front, shoreface, and shelf envi-ronments. Consequently, the shoreline is more irregularwith lobate and elongate deltaic promontories andembayments. Interdistributary bay deposits are com-mon and show enhanced tidal influence, and a complexinterbedding of coal and carbonaceous muds, bay muds,crevasse splay/crevasse channel complexes, andwashover sands. The delta front is fluvial dominated,

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Figure 7. Schematic diagram showing the variation in geomorphology of the shoreface depositional system of seaward- and landward-steppingcycles.


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Figure8.Comparisonoffaciesassociationsandsuccessionsintheshore

facefaciestractofriver-dominatedseawar

d-andwave-dominatedlandward-steppingshort-termcycles.


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Figure 9. Examples of facies and stratigraphic architecture from the shoreface facies-tract of landward-stepping, high-A/S, short-term cycles. (A)Outcrop photo of large scale, low-angle, seaward-dipping clinoforms in SC6 near the head of Muddy Creek Canyon. A prominent, laterally con-tinuous clinoform in the middle of the cliff partitions multidirectional trough cross-stratified sandstone from overlying thinly bedded sandstones.The upper sandstone beds dip seaward at a slightly higher angle than the clinoform that separates the two facies types. (B) Highly amalgamat-ed trough cross-stratified sandstone (lower 2/3) and horizontal planar laminated sandstone of the shoreface in SC6 near the head of Muddy CreekCanyon. (C) Hummocky cross-stratified sandstone from lower delta front of SC5, 1.6 km (1 mi) south of Dry Wash. In lower half of photo, lower-to upper-delta front facies contact is shown by vertical change from interbedded to amalgamated sandstone. (D) 30-cm (12-in) thick, hummockycross-stratified sandstone bed with burrowed top. Sandstone bed consists of storm-generated, waning-flow succession of sedimentary structures.(E) Swaley cross-stratified sandstone consisting of shallow swales, several-meters wide, with gently dipping, low-angle, subparallel, concordantlaminations decreasing in dip upward. Upper shoreface sandstone of SC6 from Picture Flats.


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progrades rapidly, and rate of sediment accumulation ishigh. A broad, low-angle deltaic platform is constructedthat increases the frictional drag of incoming waves,thus dissipating wave energy. Higher rates of sedimentaccumulation and dissipated wave energy provide pro-portionally less time for waves and currents to reworkand cannibalize sediment delivered to the shoreface anddelta front. The resultant strata comprise a well-pre-served, diverse, heterolithic, mudstone-rich assemblageof river-flood and storm events of multiple shallowmarine environments.

By contrast, landward-stepping stratigraphic cyclesare characterized by more total sediment storage andincreased proportion of mud to sand in the coastal plain.Consequently, a reduced sediment volume that is initial-ly sandier is delivered to the delta front. Progradationand sediment accumulation rates are reduced in thesandier delta front, and waves and currents have pro-portionally more time to cannibalize and winnowshoreface sediment. Resulting delta-front facies are

homogeneous, sand-rich, and record significant sedi-ment redistribution and reworking by waves whichreduces facies diversity.

The progressive changes from fluvial- to wave-dom-inated delta-front facies in seaward- to landward-step-ping short-term cycles reflect the sensitivity of delta-front profiles to the balance between ocean waves andcurrents and sediment discharge from distributary chan-nels. Changes in offshore platform slope and delta-frontprofiles reflect variations in sediment flux. Wright andColeman (1973) showed that high-flux, river-dominateddeltas have low-gradient slopes, whereas low-flux,wave-dominated deltas have steeper depositionalslopes. Changes in delta morphology are accompanied

by changes in smaller scale geomorphic elements pre-served in the delta. These changes produce differentfacies mosaics and facies proportions within similarwater-depth facies associations of different short-termstratigraphic cycles.

Tidal deposits formed during base-level rise arecommon above shoreface strata irrespective of cyclestacking pattern. However, seaward-stepping cyclesshow the most complex facies mosaic reflecting a highproportion of interdistributary bay-fill strata. Tidal de-posits record delta-front reworking and compose inter-

distributary bay fills. Significantly, tidal deposits are bestdeveloped in SC-3 recording the intermediate-term turn-around from base-level fall to rise and are enhanced inall landward-stepping cycles (Figure 11). Hence, tidaldeposits in shallow-marine successions provide impor-tant recognition criteria for base-level rise at all scales.

The shoreface facies tracts of Ferron progradation-al/aggradational units contain good examples of the twotypes of facies differentiation. The first type strati-graphic control on the types of geomorphic elements thatoccupy a geomorphic environment is manifest by the

conspicuous change from fluvial- to wave-dominateddeltas in the transition from seaward- to landward-step-ping stratigraphic cycles. The only control on the changein delta morphology we can detect is the change in A/Sconditions that accompany the stacking pattern of small-scale stratigraphic cycles. Different delta types do notappear to have resulted from changes in climate,drainage-basin size, discharge, fetch, shelf width, waterdepth, tectonic regime, or other control. Instead, the fluxof sediment to the delta front varied as a function of dif-ferential sediment storage in the coastal-plain facies tractduring changing A/S regimes. As the sediment flux andcomposition changed, so did the relative balance

between fluvial input and marine reworking and cannibalization, and different delta morphologies resulted.The other type of facies differentiation a change indegree of preservation of original geomorphic elements is exemplified by conspicuous sedimentologic differ-ences in the facies that compose the shoreface facies tractsof seaward- and landward-stepping stratigraphic cycles.

Increased facies diversity and degree of preservation istypical of seaward-stepping cycles, whereas amalgama-tion, cannibalization and low facies diversity is typical ofshoreface deposits of landward-stepping cycles. Again,this change in the facies and architecture of shorefacedeposits is attributed to changing A/S conditions thatcontrol the proportions and completeness of original geo-morphic elements that are preserved.

FACIES DIFFERENTIATION IN THECOASTAL-PLAIN FACIES TRACT

Coastal-plain strata contain the same facies in allshort-term stratigraphic cycles, regardless of position inthe stacking pattern. However, the proportions of facies,geometry and size of architectural elements, and degreeof preservation of geomorphic elements change regular-ly with the stacking pattern. Stratigraphic cycles in thecoastal-plain facies tract contain alternating organic-poor, sand-rich facies (distributary-channel andcrevasse-splay/crevasse-channel sandstones) recording

base-level fall, and organic-rich, sandstone-poor facies(paludal and floodplain mudstones, carbonaceousshales and coal) recording base-level rise. These base-level changes produce cyclic coal-sandstone successions.

Although these facies coexist as laterally equivalentdeposits in both halves of a base-level cycle, the propor-tion is modulated by position within a cycle.

The coastal-plain facies tract of landward-steppingcycles contains greater sandstone and total sediment vol-umes but lower sandstone to mudstone ratios than thecoastal-plain facies tract of seaward-stepping cycles. Thistendency is progressive through the stacking pattern.

Coastal-plain strata of seaward-stepping cycles thinupward, and have progressively increasing sandstone-to-shale ratios, decreasing facies diversity, deeper chan-

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nel incisions, laterally extensive erosion surfaces, andthin aggradational paleosols and coal seams. Thin, later-ally extensive coals commonly cap seaward-steppingshort-term cycles. Coastal-plain strata of verticallystacked cycles contain laterally expanded multistory andmultilateral distributary-channelbelt sandstones whichinterfinger with heterolithic crevasse splay and crevassechannel deposits. Vertically stacked cycles also containhigher proportions of mudstone and carbonaceous mud-stone, poorly developed coals, the coarsest sedimentfraction, and approximately equal channelbelt-to-flood-plain volume ratios. Coastal-plain strata of landward-stepping units contain a high channelbelt-to-floodplain

ratio, channelbelt sandstones interfinger with a highproportion of crevasse-channel/crevasse-splay com-plexes, and amalgamated coal beds up to 10 m (32 ft)thick. Thick pods of locally developed coal seams com-monly flank channelbelt sandstones of landward-step-ping short-term cycles.

Distributary channels of approximately the samescale, morphology and bank-full dimension fed theshorefaces in all cycles. Yet many sedimentologic attrib-utes of distributary channelbelt sandstones are conspic-uously different in cycles at different positions in thestacking pattern (Figures 12 and 13). In distributary

channelbelt sandstones, the composition and thicknessof lag deposits, the types and geometries of channelsandstone bodies, the degree of preservation and pro-portion of original bedforms and macroforms, and thediversity of facies record changes in A/S regime andconcomitant sediment volume partitioning (Figure 14).

Distributary channelbelt sandstones in all cycleshave a grossly similar cross-sectional geometry and asimilar internal progression of facies changes. They havea characteristic funnel or longhorn steer cross-sec-tional shape (Figure 13). At the base, steep-sided chan-

nelbelt margins are narrow (the nose of the steer); thechannelbelt margins expand 4 to 10 times in widthtoward the top and have low-gradient margins (thehorns of the steer). The progression of facies attributesis from highly interconnected, amalgamated, cannibal-ized, laterally restricted, vertically stacked sandstone

bodies at the base, to expanded, more open frameworkand more fully preserved, laterally stacked sandstone

bodies toward the top. Even though channelbelt sand-stones in all cycles share this basic motif, several sedi-mentologic changes record the changes in A/S and thesediment volume partitioning that accompany the short-and intermediate-term base-level cycles.

Distributary channelbelt sandstones of high A/S,landward-stepping cycles are typically 1525 m (4982ft) thick and 11.5 km (0.60.9 mi) wide. They contain adiverse assemblage of moderately interconnected, cut-and-fill, low-sinuosity, high-sinuosity and abandon-ment-fill macroforms 520 m (1666 ft) thick (Figure 15).Macroforms often are separated by mud drapes or lags.Mud-matrix-supported, mud-boulder-intraclast lagdeposits on channel and macroform scour bases are upto 1 m (3 ft) thick and laterally continuous (hundreds ofmeters). Internal accretion and reactivation surfaces ofequal length record lateral and downstream barform

migration. Bedforms, cut-and-fill macroforms, andaccretionary macroforms are well preserved (low amal-gamation and little cannibalization). Facies diversitywithin macroforms is high, including thick and thin setsof trough cross-stratification, planar-tabular stratifica-tion, horizontal lamination, convolute lamination, andother structures indicative of fluidization, meter-scalefully preserved straight-crested dunes climbing the

backs of larger barforms, and thick sets of ripple andclimbing ripple lamination (Figure 16).

By contrast, channelbelt sandstones of low A/S, sea-

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Figure 10. Examples of facies and stratigraphic architecture from the shoreface facies tract of seaward-stepping, low-A/S, short-term cycles. (A)Delta-front and distributary mouthbar deposits of SC2 from the I-70 roadcut. Bar-front and bar-crest facies of distributary mouthbar depositsare well exposed in this roadcut oriented oblique to progradation. The 1.5-m-thick (4.9-ft) bar-front deposits are characterized by thinly bedded,laminated to combined-flow, ripple-laminated sandstone with disseminated organic fines and form the thin recessive zone separating the twomassive sandstones. Bar-front deposits overlie delta-front sandstones up to 10 m (32 ft) thick, and underlie bar-crest facies up to 15 m (4.9 ft)thick. Bar-crest facies are characterized by amalgamated, unidirectional trough and planar-tabular cross-stratified sandstone. Bar-crest facies atthis locality contain low-angle inclined clinoforms. The thinner tabular sandstone capping the cliff is another distributary mouthbar sandstone.Stacked mouthbar deposits record autogenic subdelta lobe switching. (B) Upward-coarsening delta-front sandstone that is overlain by heterolithic

interdistributary-bay deposits of SC2 from Dry Wash. (C) Close-up of shallow-water sediment gravity flow in 48-cm-thick (19-in.) sandstonebed from SC2 at Miller Canyon. Graded, structureless sandstone (Bouma A) at base is overlain by horizontally laminated sandstone (Bouma B),with small scale hummocky and swaley cross-stratification at top. (D) Fully preserved hummock with waning flow cap (parallel lamination, sym-metrical aggradational wave ripples, asymmetrical aggradational wave ripples) from SC3 at Dutch Flat. (E). Very well-preserved hummockswith waning flow caps, interbedded burrowed mudstones, and beds with various symmetrical and asymmetrical wave ripples from SC3 at DutchFlat. (F) Soft-sediment deformation in the lower delta front of SC2 at the I-70 roadcut. Compaction of the underlying mud-rich, SC1 delta frontmay have contributed to the extensive soft-sediment deformation and sand-rich delta front of SC2 at this locality. (G) Listric normal growth

faults in shoreface of SC1 in Muddy Creek Canyon. (H) Soft-sediment synclinal, trough-like depression with bounding anticlinal ridges formedby slump block from SC3 shoreface loading the shelf mudstones of SC2 from Dutch Flat.

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Figure11.

TidalfaciesandrecurvedspitfromSC3atDryWashrecordingtheturnaroundfromseaward-tolandward-steppingshort-termcycles.

(A)Photomosaicoflocallydeveloped

transgressive,tidal-channel-inletfaciesinSC3atDryWash.Thesedepositscr

opoutneartheheadofDryWashalonga600-m-long(2000-ft)canyoncutorientedtodepositionaldip.Expo-

surescompriseaseriesof14offlapping510-m-thick(1632ft),imbricated,

accretionarysandstonelensesthatareencasedinburrowedmudstonesandthatoftencontainonetoseveral

thicklybedded,unidirectionalsandwaves.(

B)Transversecross-sectionalview

lookingnorthwestoflaterallyaccreting,

imbricatedsandstonelensesfromSC3tidalinletatDryWash.At

thethickestportionofthedrum-stick-shapedsandstonelens,t

heweightofthesandstonelenshasdeformedunderlyingSC3delta-frontsandstonesintoabroadsynform.

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Figure 12. Diagram summarizing changes in distributary channelbelt architecture of landward- and seaward-stepping short-term cycles.

Figure 13. Examples showing variable distributary channelbelt architecture of landward- and seaward-stepping short-term cycles. (A) Outcropphoto of moderately interconnected sandstone lenses of distributary channelbelt from landward-stepping SC7 at Emery mine. (B) Distributarychannelbelt sandbodies of seaward and landward-stepping cycles. SC2 at I-70 roadcut. Bars on scale are 3 m.


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ward-stepping cycles are of comparable thickness butonly a few hundred meters wide. They contain a lowdiversity of highly amalgamated cut-and-fill and low-

sinuosity, erosive-based macroforms 510 m (1632 ft)thick (Figure 17). Bedforms and macroforms are strong-ly cannibalized and amalgamated, resulting in very lowfacies diversity (typically >95% by volume of thin sets ofamalgamated and top-truncated, trough cross-stratifiedsandstone). Channel and macroform scour bases areoccasionally and discontinuously overlain by sand-matrix-supported, mud-pebble-intraclast lags 220 cm(0.88 in.) thick.

These channels do not extend beyond their delta,nor do they incise below associated delta-front deposits(one notable exception is the SC5 distributary channel-

belt at Cedar Ridge), and the scale of incision conforms

to macroforms composing the channelbelt. These areattributes of freely migrating channels constructing achannelbelt unimpeded by valley confinement. The sizeof these larger channelforms may lead to the misinter-pretation of them as valley fills and highlights the limi-tation of size as a criterion for valley fill recognition. Inthis case, the increased size of Ferron distributaries ofseaward-stepping cycles reflects higher delta subsidencepromoted by the higher sediment volumes and morerapid progradation (Morgan, 1973). Higher delta subsi-

dence is also reflected by growth faults, large slumps,and pervasive soft-sediment deformation in the shore-face facies tract of seaward-stepping cycles.

The coastal-plain facies tracts of Ferron prograda-tional/aggradational units contain good examples offacies differentiation produced by differences in degreeof preservation of geomorphic elements under varyingA/S regimes. In high-accommodation, landward-step-ping stratigraphic cycles, coastal-plain facies are diverse,reflecting good preservation of multiple, diverse geo-morphic elements (Figure 18). Many of the original bed-forms and barforms of distributary channels are fully ornearly fully preserved. By contrast, the diversity ofcoastal-plain facies in low-accommodation, seaward-stepping stratigraphic cycles is very low, reflecting pres-ervation of only those geomorphic elements that are

most easily preserved. The original bedforms and bar-forms of distributary channels are intensely cannibalizedand amalgamated (Figure 12).

FACIES MODELS IN ASTRATIGRAPHIC CONTEXT

Facies models summarize the facies associationspresumed indicative and characteristic of particular sed-imentary environments. They are constructed through

114


Figure 14. Plot showing diversity difference of sedimentary structures from distributary channelbelt deposits of landward- and seaward-steppingshort-term cycles. The increased proportion of higher-energy and more amalgamated, cannibalized structures in distributary channelbelt depositsof seaward-stepping, short-term cycles reflects decreased preservation of the upper part of channel fills.

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Figure15.

Diagramsummarizingm

acroformscomposingdistributarychannelbeltoflandward-andseaward-stepping,

short-termcycles.

Seaward-steppingcyclesaredominatedbycut-

and-fillmacroforms,whereaslandward-steppingcyclescontainadiverseassem

blageofmacroformtypes.


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Figure 16. Examples of facies and stratigraphic architecture from the coastal-plain facies-tract of landward-stepping, short-term cycles. (A) Distributarychannel sandstone complex containing a diverse assemblage of macroformsseparated by meter-scale mudstone drapes and lags. From SC6 at Dog Valley.(B) Amalgamated trough cross-stratified sandstone from the base of the dis-tributary channel (nose of the longhorn steer) of Figure 16A. Backpack restson channel scour base. (C) Meter-scale climbing sandwave (analogous toclimbing ripples) from near the top of the distributary channel sandstone at Dog Valley. (D) Mudstone lag (at persons head) separating over-lying low-sinuosity macroform from top of the longhorn steers nose at Dog Valley. (E) Close-up of convolute bedding in soft-sediment-deformedsandstone of SC5 channel at Ivie Creek. High shear stress on partially liquefied bedforms results in dewatering and development of these soft-sediment deformation features. (F) Detail of thick (meter-scale) boulder/cobble mudstone ripup-clast lag at channel base. (G) Abandonment fillmacroform of SC4 along Coal Cliffs.

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Figure17.Examplesoffaciesandstratigraphicarchitecturefromthe

coastal-plainfacies-tractofseaward-stepping,sho

rt-termcycles.

(A)

Outcrop

photomosaicoftransverse,cross-sectional

viewof25-m-thick

(82-ft)and280-m-wide(919-ft),

distributarychannelbeltfromsea-

ward-steppingSC2atWillowSpringsWash.Thelowerportionofthe

channelbeltconsistsoffourcut-and-fillmacroformsthatareoverlainbylaterallyexpandedsandstonesthatconsistoffourto

fivelow-sinuositya

ndcrevasse-channelmacroforms.(B)Ama

lgamated,1

020-cm-thick(48-in.)setsoftroughcross-strat-

ifiedsandstonefrom

thedistributarychannelbeltatWillowSpringsWash.(C)Viewlookingwestofero

sionalbasalcontact

ofhighlyamalgama

teddistributarychannelbeltinseaward-ste

ppingSC2atWillowSpringsWash.Basalcontactsformhigh-

lyirregular,concav

e-upwardsurfacewithupto5m(16ft)oflocalreliefwhereincisedinlessresistant,

intraformational

interdistributary-baydepositsofSC1.(D)Lateralpinch-outsofcut-and-fillsandstonelensesagainstc

hannel-basebound-

ingsurfaceofseaward-steppingSC2channelbeltatWillowSpringsWash.


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Figure 18. Summary of sedimentologic and stratigraphic attributes of upper Ferron distributary channelbelts that change as a function of short-term cycle stacking pattern.

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synthesis, reduction and simplification of observationsfrom multiple specific examples to abstract the es-sence, or the essential facies elements of a particularenvironment, from the noise, or variations from what-ever is perceived as the norm (Walker, 1984, 1990). Theonly requirement for selection of examples is that theymust be a product of a particular geomorphic environ-ment. Facies models are constructed with the presump-tion that the preserved stratigraphic record of an envi-ronment is similar to, and a composite of, all geomorphicelements in that environment. Accordingly, the geomor-phic elements in an environment are preserved in thesame ratios as facies in strata. This presumption requiresthat the mosaic of geomorphic elements that form thepatchwork quilt on the Earths surface at an instant intime aggrade in place to form a stratigraphic faciesmosaic of identical complexity and areal distribution. Iffacies associations and successions representing a singledepositional environment are collected from differentstratigraphic cycles, or different halves of the same base-

level cycle, the resulting facies model of that deposition-al environment is derived from a mixture of unrelatedelements that may never have coexisted (Figure 18).

Facies models are specific to each environment; theydo not mix or merge the facies of laterally linked envi-ronments. A facies model for laterally linked braidplain-lake-alluvial fan environments does not exist, but eachenvironment has its own models. Environments identi-fied as geomorphically distinct have separate faciesmodels attached to them. Multiple facies models existfor different river morphologies (e.g., braided, meander-ing, anastomosed) and for different delta morphologies(wave-, fluvial-, and tide-dominated).

Facies models are static. Facies attributes, associa-tions, and successions are collapsed from multiple exam-ples into a single geomorphic and sedimentologic char-acter set presumed to exist at an instant in time. Faciesmodels are constructed with the presumption that thestratigraphic products (preserved depositional rem-nants) of a particular depositional environment are sim-ilar from place to place and from time to time. Faciesmodels do not recognize that geomorphic elements atthe same positions on a depositional profile may differin different A/S regimes, even in the two halves of a sin-gle base-level cycle. Nor do they recognize that given

identical geomorphic elements in a particular environ-ment, changes in degree of preservation (volume andproportion) of those elements will create major differ-ences in the facies observed in the stratigraphic record.Although facies differentiation has not been a focus ofmost sedimentologic and stratigraphic studies, it has

been hinted at, noted, suggested, or described from avariety of environments in a handful of papers (e.g., Bar-rell, 1912; Van Siclen, 1958; Curtis, 1970; MacKenzie,1972; Bridge and Leeder, 1979; Brett and Baird, 1986; Gal-

loway, 1986; Cross, 1988; Carter et al., 1991; Borer andHarris, 1991; Boyd et al., 1992; Cross et al., 1993; Sonnen-feld and Cross, 1993; Cant, 1995; Mellere and Steel, 1995;Gardner et al., 1995, Kerans and Fitchen, 1995; Talling etal., 1995; Ramon and Cross, 1997; Cross, 2000).

None of these characteristics of facies modelsemploys four-dimensional stratigraphic appreciation forthe accumulation of sediment. Facies models ignore thefact that sediments accumulate during the migration oflaterally linked environments. The mosaic of geomor-phic environments does not aggrade in place producinga stratigraphic product that closely resembles the geo-morphic parent.

This study demonstrates that stratigraphic processesinfluence the types of geomorphic elements which com-pose an environment, as well as the proportion anddegree of preservation of elements which enter the strati-graphic record. Changing A/S conditions during base-level cycles control stacking patterns and sediment vol-ume partitioning. The latter contributes to the two types

of facies differentiation discussed previously. The nextgeneration of facies models should be constructed from astratigraphic perspective in which there is a continuumof transitional forms of facies associations and succes-sions that are different products of the same parent.

CONCLUSIONSAt the scale of the upper Ferron Sandstone clastic

wedge, sediment accumulated in different paleogeo-graphic positions through time form a series of strati-graphic cycles arranged in a seaward-stepping, vertical-ly stacked, and landward-stepping stacking pattern (Fig-ure 19). Geographic partitioning of sediment volumes atthis scale is related to the changes in A/S conditions dur-ing an intermediate-term, base-level cycle.

Within each stratigraphic cycle, sediment was parti-tioned into depositional environments in different vol-umes and ratios. Superposition of the two scales of base-level cycles causes systematic changes in sediment vol-ume partitioning through time. The total sediment vol-ume and total sandstone in the shoreface facies tractdecreases regularly from seaward- to landward-step-ping stacking patterns. The proportion of marine-to-nonmarine sandstone also decreases. This demonstrates

increasing sediment storage in uphill continental envi-ronments during the transition from seaward- to land-ward-stepping stacking patterns (Figure 20).

One product of the changing A/S regime and sedi-ment volume partitioning is a change in delta morphol-ogy. Deltas in seaward-stepping cycles are fluvial domi-nated, whereas those in landward-stepping cycles arewave-dominated. The change in delta morphology isrelated to the change in sediment storage capacity uphillin continental environments. This is an illustration of

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geomorphic facies differentiation, where stratigraphicprocesses control the types of geomorphic elements thatoccupy a particular depositional environment.

Sediment volume partitioning at the scale of short-term stratigraphic cycles also affects the rate of net sedi-ment accumulation in different environments, andreflects the balance between rates of sediment additionand rates of sediment reworking and cannibalization.Changes in A/S conditions during a short-term cyclecontrol or modulate the degree of cannibalization and

amalgamation of geomorphologic elements that com-pose an environment. Variations in facies diversity,facies associations and successions, lithologic hetero-geneity, and petrophysical properties within a faciestract are manifestations of changing A/S conditions.Shorefaces of high-accommodation, landward-steppingcycles comprise homogeneous, wave-dominated sand-stones, whereas shorefaces of low-accommodation, sea-ward-stepping cycles are lithologically heterogeneousand river-dominated containing diverse facies and well-preserved original geomorphic elements. Tidal deposits

are present within all stratigraphic cycles, are most com-mon immediately above the shoreface facies tract, butshow the most complex mosaic in seaward-steppingcycles reflecting the increased proportion of interdistru-tary bay-fill strata. Distributary channelbelt sandstonesof high A/S, landward-stepping cycles are composed ofhigh-diversity, well-preserved macroforms and bed-forms, whereas those of seaward-stepping cycles arecomposed of strongly cannibalized, amalgamated, low-diversity macroforms and bedforms. The latter chan-

nelforms show increased size and may be misinterpret-ed as valley fills recording unconformity developmentunder conditions of no accommodation. These examplesillustrate the other type of preservational facies differen-tiation, where stratigraphic processes control the pro-portions and ratios of original geomorphic elements thatare preserved. It is important to emphasize that faciesdifferentiation describes the tendency for specific faciesassociations, proportions and degree of preservationwithin a facies tract. It is not an absolute attribute of thefacies tract composing a specific stratigraphic cycle. For

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Figure 19. Wheeler (time-space) diagram showing distribution of three time-space domains within facies tracts that compose seaward-stepping,vertically stacked, and landward-stepping stratigraphic cycles of the Ferron sequence. This diagram relates changes in the stacking pattern,

stratal geometry, sediment volume distributions, and facies arrangements to variations in accommodation within base-level cycles.

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example, wave-generated sedimentary structures occurwithin river-dominated as well as wave-dominateddeltas and reflect the three-dimensional geomorphology

and variability in processes operating within a deposi-tional system.Sediment volume partitioning and facies differentia-

tion in different A/S regimes create radically differentfacies constituents, associations, and successions fromthe same geomorphic environment. The stratigraphicproducts are transitional forms along a continuum fromhigh to low A/S conditions for each facies tracts. Exist-ing facies models assume the products of geomorphicenvironments are similar regardless of time, place, andcondition of accumulation. Facies models are insensitiveto stratigraphic controls on facies associations and suc-cessions. Moreover, most are incorrectly constructed

from observations of facies elements that never coexist-ed. If facies models are to be useful for stratigraphic pre-diction, they must be calibrated to A/S conditions thatdrive volumetric partitioning and facies differentiation.A new generation of stratigraphically sensitive faciesmodels is required and they need to be placed into anA/S context.

Systematic changes in numerous stratigraphic andsedimentologic attributes emphasize the well-ordered

behavior of the stratigraphic process-response system,

and demonstrate systematic linkages among attributesof all scales and many types. These attributes are com-plementary records of multiple, interdependent process-

es which may be analyzed from the simple perspectivesof conservation laws and stratigraphic base level. Thesystematic organization of disparate and diverse datatypes is the basis for robust stratigraphic prediction.From knowledge of attributes at one scale, attributes ofother types and scales are predictable.

ACKNOWLEDGMENTSThis paper reports part of the Ph.D. research of the

first author. Financial support was provided by theIndustrial Associates of the Genetic StratigraphyResearch Program administered by T. A. Cross, the

American Chemical Society Petroleum Research Fund,the American Association of Petroleum Geologistsgrants-in-aid program, the SEPM Donald SmithResearch grant, the Sigma Xi grants-in-aid program, theU.S. Geological Survey Branch of Coal Resources, andthe Utah Geological Survey. We thank these organiza-tions, companies, and societies for their support. Helpfulreviews by Ron Steel and John Cater are gratefullyacknowledged.

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Figure 20. Illustration of variability of stacking patterns of the shoreface facies tract as a function of changes in the A/S ratio.


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