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Cretaceous Research 48 (2014) 139e152

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Cretaceous Research

journal homepage: www.elsevier .com/locate/CretRes

Origin and distribution of calcite concretions in Cretaceous Wall CreekMember, Wyoming: Reservoir-quality implication for shallow-marinedeltaic strata

Stephanie L. Nyman a, M. Royhan Gani b,*, Janok P. Bhattacharya c, Keumsuk Lee d

a The University of Waikato, Private Bag 3105, Hamilton, New Zealandb Earth and Environmental Sciences, University of New Orleans, 2000 Lakeshore Drive, New Orleans, LA 70148, USAc School of Geography & Earth Sciences, McMaster University, Hamilton, Ontario L8S4L8, CanadadKorea National Oil Corporation, Gyeonggi-do, South Korea

a r t i c l e i n f o

Article history:Received 8 December 2009Accepted in revised form 29 December 2013Available online

Keywords:Calcite concretionDiagenesisWyomingReservoir qualityShallow-marineTuronian

* Corresponding author.E-mail address: mgani@uno.edu (M.R. Gani).

0195-6671/$ e see front matter � 2014 Elsevier Ltd.http://dx.doi.org/10.1016/j.cretres.2013.12.009

a b s t r a c t

Calcite concretions reduce reservoir quality, but there are limited studies that examine 3D distributionand consequences for reservoir quality in outcrop analogs. We integrate petrography, diagenesis, andgeochemistry with 3D ground penetrating radar and borehole data to investigate the timing, 3D dis-tribution and origin of concretion growth within a mixed fluvial, tide influenced shallow-marine deltaicreservoir analog in Cretaceous outcrops in Wyoming.

Calcite concretions, varying in size and shape from 70 cm to 5.5 m in length and from 20 cm to 60 cmin height, fill up to 15% of the sandstone volume. Concretions range from almond shape, long, thin el-lipsoids, associated with tidal bar facies, to short, thick ellipsoids, within more fluvial-dominated dis-tributary-channel facies. 3D mapping shows concretions are moderate to highly connected forming anaggregate pattern with irregularly shaped branches.

Several concretions have clear nucleation sites that include carbonaceous muds, calcareous muds,marine shell material, and/or organic matter. Carbon-isotope values suggest carbon sources that includein-situ marine skeletal-fragments and organic carbon. Rather than reflecting an early or late origin, theseconcretions are much more complex and show a long-lived history of growth.

Cements are confined to the middle parts of the sandstone body, suggesting that initial preferentialflow paths become sites for later cementation and reduction of porosity. This will potentially reduceoverall reservoir volumes and may impede fluid flow in both horizontal and vertical directions. The 3Ddistribution of concretion must be taken into account in reservoir modeling and fluid flow simulations toavoid overestimation in recovery factors.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Calcite concretions change fluid flow dynamics and reducereservoir quality in many subsurface shallow-marine reservoirs(Kantorowicz et al., 1987; Saigal and Bjørlykke, 1987; Bjørkum andWalderhaug 1990; McBride et al., 1995; Morad and DeRos, 1994;Dutton et al., 2000; Dutton et al., 2002; White et al., 2003) butare not well understood. Although many studies document the 2Ddistribution of concretions, there are no studies, to the best of ourknowledge, that examine the 3D distribution in outcrop analogsand the consequences for reservoir production.

All rights reserved.

The purpose of this study is to document the 3D distribution ofcements in continuously-exposed cliff faces of a mixed-influenceddeltafront, augmented with shallow borehole and 3D groundpenetrating radar (GPR) data taken adjacent to the outcrop cliffface. This study forms part of a broader research program aimed at afull 3D reservoir characterization of a shallow-marine deltaicreservoir analog that includes sedimentology (Gani andBhattacharya, 2007), GPR imaging (Lee et al., 2007a,b) and fluidflow modeling (Tang, 2003).

This paper focuses on the petrography, diagenesis, andgeochemistry of calcite concretions in the Cretaceous Wall CreekMember in superb outcrops adjacent to the Powder River basin.Particularly, we aim to investigate the constraints on the timing andorigin of concretion growth and their relationship to porosity,permeability and fluid flow dynamics. This data are used to deter-mine the relationship and influences of the calcite concretions on3D

S.L. Nyman et al. / Cretaceous Research 48 (2014) 139e152140

GPR signals that have been collected in order to produce a 3Dmodelof reservoir heterogeneity in an ancient shallow-marine delta. Theseresults have major implications for reservoir characterization rela-tive to porosity and permeability predictions and fluid flow path-ways, particularly for Cretaceous reservoirs of onshore USA.

2. Geological setting

2.1. Basin framework

The Powder River Basin is a compressional foreland basin thatformed during the Sevier Orogeny (Merewether, 1996) and isasymmetric with a synclinal axis east of the BighornMountains andCasper Arch (Fig. 1). The basin formed due to localized tectonicmovements before Late Cretaceous (Markert and Al-Shaieb, 1984).The basin development became prominent during Late Cretaceousand Paleogene in the early stages of the Laramide Orogeny and therise of the Bighorn Mountains and Black Hills (Fig. 1). Folding andfaulting occurred during early Eocene westward tilting, caused byuplift of the Black Hills during the late Eocene, with continueddownwarping and regional tilting through the Miocene (Markertand Al-Shaieb, 1984).

2.2. Stratigraphy and burial history

The Frontier Formation consists of the Cenomanian Belle Four-che Member, the middle Turonian Emigrant Gap Member, and theupper Turonian Wall Creek Member (Fig. 2) (Tillman and Almon,1979). The Frontier forms a thick succession of non-marine stratawhich thins to marine sandstones interbedded with shale in thestudy area. Main source areas for the Frontier are believed to havebeen areas uplifted from movement along the Paris Thrust fault(Wiltschko and Door, 1983). Volcanic activity to the west of thedepositional basin was high, and is shown both by the abundantvolcanic rock fragments within the Wall Creek and older Frontiermembers (McBride et al., 2003), and numerous bentonite horizonsin the Frontier, many up to several meters thick (Bhattacharya andWillis, 2001). Abundant bentonites and bentonitic shales indicatethat this volcanic detritus was intermingled with other clastic

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detritus. Frontier successions were deposited into the westernborder of the north-south trending Cretaceous North AmericanInterior Seaway.

The Wall Creek Member forms the top of a regional sandy toconglomeratic clastic wedge, which prograded eastward from theSevier mountain belt. Below the Wall Creek, a regional unconfor-mity marks the boundary with the Emigrant Gap member (Fig. 2).The Wall Creek is capped by a marine ravinement surface sepa-rating the uppermost sandstone body from the younger SageBreaks member of the Cody Shale (Willis et al., 1999). The WallCreek outcrops are located on the southeastern border of the Big-horn Mountains in Wyoming (Figs. 1, 3). The Wall Creek sandstoneis interpreted to consist of several delta lobes, indicated by sevendifferent sandstone bodies (Fig. 2; Gani and Bhattacharya, 2007;Sadeque et al., 2008). By factoring in both quality and accessi-bility of outcrop, the most southerly outcropping of sandstone body#6 at Raptor Ridge (Figs. 2, 3) was chosen for this study.

The stratigraphic thickness from surface to the bottom of theShannon sandstone of the Steele Member of the overlying CodyShale is 763 m (Hansley and Nuccio, 1992). The thickness of strata(Niobrara Member and Sage Breaks Member of the Cody Shale)from the bottom of the Shannon sandstone to the top of FrontierFormation and Wall Creek sandstone in eastern Natrona Countyand the western border of the Powder River Basin is approximately570 m (Merewether, 1996) (Fig. 2). Therefore the ultimate burialdepth of the Wall Creek sandstone was at least 1.35 km. This is aminimal approximation as any additional erosion and compactioncould not be quantified.

Using an average geothermal gradient of 29 �C/km, (Hansley andNuccio, 1992; Dutton et al., 2000) and a surface temperature of10 �Ce15 �C, (Spencer, 1987; McBride et al., 2003), the maximumburial temperature of the Wall Creek sandstone likely reachedapproximately 50 �Ce55 �C.

2.3. Outcrop sedimentology and cement mapping

At Raptor Ridge, Sandstone #6 is the uppermost parasequenceof the Wall Creek Member. Sandstone #6 shows a coarsening andthickening-upward facies succession and a lobate geometry with a

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Fig. 2. A) Cretaceous stratigraphy of the Powder River Basin, Wyoming. B) Outcrop section of the Wall Creek Member at Raptor Ridge site, where Sandstone #7 was not deposited.For location of the sections see Fig. 3. Present study deals with Sandstone #6, which contains channel and tidal bar facies. C) Lithologic and ichnologic symbols used in logs. (fromGani and Bhattacharya, 2007)

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shore-parallel elongation, suggesting a deltaic origin (Gani andBhattacharya, 2007). River- and tide-dominated facies (with asubordinate wave-dominated facies) are present only at RaptorRidge, where the sandbody is also the thickest, and shallow ter-minal (i.e. subaqueous) channel deposits suggest proximity to anupstream, main distributary channel. A strong flood tide-influenceis preserved within a prograding delta, indicated by abundantlandward-directed trough cross-strata and prolific double mud-drapes along foresets (tidal bundles). Terminal (i.e. subaqueous)distributary channels, filled with sediment gravity flow deposits,are encased within deltafront clinoforms.

Cliff photomosaics along depositional-dip show deltafront cli-noforms, dipping at about 4 degrees (Fig. 4A). Along depositional-strike, cliff shows bidirectional off-lapping clinoforms and meter-thick channelized bodies interpreted as subaqueous distributarychannels (Gani and Bhattacharya, 2007). These bedding geometriesare well imaged in GPR data just behind the cliffs (Fig. 4B). Thebedding diagrams have been interpreted to show terminaldistributary-channel elements intimately associated with seaward-dipping bar accretion elements, frontal splay elements, and tidally-reworked elements, with at least four orders of bounding surfaces(Gani and Bhattacharya, 2007).

Fig. 3. A) Location map showing the Wall Creek outcrop belt at the western margin of the Powder River Basin, Wyoming. The present study focuses at Raptor Ridge. B) Raptor Ridgesite, showing 3D GPR data and well locations behind the cliffs. Note the position of Figs. 2B, and 4.

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Fig. 4. A) Raptor Ridge photomosaic of cliff outcrop in dip direction, showing sea-ward (SE) progradation of deltaic clinoforms. B) GPR line in the dip direction, imaging similar clinoform-geometry. C) Diagram of cement and shaledistribution in outcrop.

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Fig. 5. Ternary diagram of cemented samples from 13 concretions from the RaptorRidge outcrop and core. Raptor Ridge sandstone have an average QFR composition ofQ48F23R29 and Q53F19R28 in outcrop and core, respectively.

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Shales and cement zones were identified in outcrop and core(Fig. 4C). Mapping of shales and cement zones is incorporated with3D GPR, laser scanning, and petrophysical studies for reservoirmodeling to determine the flow behavior of mixed-influenceddelta-fronts with complex facies architecture (Tang, 2003).

3. Methodology and technique

Outcrop concretions were sampled in both channel and tidal barfacies (Sandstone#6 of Fig. 2B). Representative samples were alsocollected to determine if there were differences as a result of sizeand shape variations between the concretions. Concretions inboreholes 8 and 9 were also sampled as these intersect the 3D GPRvolume (Fig. 3). A total of 172 sandstone samples were collected.Seventy-two samples were collected from cores 8 and 9 at a 20 cminterval through the host sandstone (34 samples) and at a 10 cminterval through the cemented “concretionary” zones (38 samples).Core samples are labeled bywell number and depth inmeters. Nineoutcrop concretions were also sampled. Horizontal transects werecollected from all concretions at a sampling interval of 20 cm. Inlarger concretions with thicknesses greater than 20 cm, verticaltransects were also collected. A total of 13 concretions weresampled, in which five are from core and eight from outcrop.

Thin section analysis was used to determine petrographic anddiagenetic features, and to quantify intergranular volume (IGV),cement, and porosity. Thin sections were set with a dual feldsparstain on half section and a blue epoxy for porosity. The plagioclase/feldspar stain is a rhodizonate solution containing potassium rho-dizonate, sodium cobaltinitrite, and barium chloride. The scanningelectron microscope (SEM) with energy dispersive spectrometer(EDS) capabilities and backscattered electron (BSE) detector wasused to distinguish between detrital and authigenic clays, and toidentify diagenetic features and composition of calcite cementedsamples. Carbon 13 and Oxygen 18 isotopic signatures werecollected from the calcite cements (134 samples) and analyzed toplace constraints on burial history and timing of precipitation. Thestable isotope geochemistry was analyzed on a VG 903 stableisotope ratio mass spectrometer by Stephen Taylor at the Universityof Calgary Stable Isotope Laboratory. Isotopic values are reportedrelative to the Pee Dee Belemnite (PDB) international standard withan accuracy of plus or minus 0.2&.

4. Petrography

Themean sand grains are upper fine grained, moderately sorted,and sub-angular to sub-rounded. The Raptor Ridge sandstones arefeldspathic litharenites to lithic arkoses with an average QFRcomposition of Q51F21R28 (Fig. 5). There is approximately equalabundance of K-feldspars and plagioclase within concretions.Calcic-plagioclase is, however, preferentially replaced by calcitecement as opposed to the alkali feldspars. Rock fragments includeprimarily volcanics, chert and sedimentary fragments, and subor-dinately mud clasts. Accessory minerals include biotite, with lesseramounts of chalcedony and carbonate grains. Rare phosphatic bonefragments and shell material are also present.

Themajor diagenetic cements are calcite and authigenic chlorite.Minor diagenetic cements include iron-oxide, kaolinite, and quartzovergrowths. Each of these diagenetic features is discussed below.Note that additional data supporting petrographic observations areprovided as Supplementary Material linked to this article.

4.1. Calcite

Calcite cement occurs as discrete concretions rather thandispersed in the surrounding host sandstone. The concretions form

elongate, tabular cemented zones within an un-cemented hostsandstone (Fig. 4A, C). Calcite composition is low-magnesium,ferrous calcite and is poikilotopic, pore filling, and at times grainreplacing. Iron content ranges from <1 to 12 weight percent,typically with higher iron concentrations located adjacent to ironbearing grains. Chlorite and kaolinite co-exist with calcite cementonly near the concretion margins, and form pore filling and porelining phases (Fig. 6A). Chlorite and kaolinite are seen in SEM im-ages, lining calcite cement.

4.2. Chlorite

Chlorite occurs as grain rims, and is absent along grain contacts.Chlorite is also present in minor amounts as grain replacements,especially of volcanic rock fragments and biotite. Pristine chloriterosettes “float” atop the earlier grain coating chlorite (Fig. 6B).

Initial precipitation of chlorite began probably after significantcompaction, indicated by grain coating chlorite, but with theabsence of chlorite between grain contacts (Fig. 6A). The replacingchlorite and pristine rosettes imply growth during and after theonset of framework grain dissolution (Fig. 6A). The grain coatingand pore filling chlorite likely indicates that fluid flow through thesystem was high (Stonecipher et al. 1984).

Conditions necessary for chlorite growth are basic, anoxic porewaters with available iron and magnesium (Foscolos, 1985; Jahrenand Aagaard, 1989; Boggs, 1992; Grigsby, 2001). Sources for ironand magnesium include altered biotite grains and volcanic rockfragments (Odin, 1988; Odin and Masse, 1988; Boggs, 1992;Ehrenberg, 1993; Bjørlykke, 1998), both of which are abundant inthese rocks. Free iron and magnesium may also occur in deposi-tional waters (Boggs, 1992), or in an iron/magnesium rich clayprecursor, such as odinite or glaucony, which commonly form indeltaic environments, and which are diagenetically altered tochlorite during shallow burial (Odin, 1988; Odin and Masse, 1988;Ehrenberg, 1993; Duan et al., 1996; Bjørlykke, 1998; Cookenbooand Bustin, 1999).

The dominance of altered volcanic rock fragments and biotitesuggest that this was the primary source of iron. Chlorite likelyformed from low temperature hydrolysis of volcanic detritus (Yehand Savin 1977; Lawrence et al., 1979). While the deltaic

Fig. 6. Photomicrographs of concretions (AeC, SEM images; DeG, thin-section microscopic images, where D and G are under plane-polar, and E and F are under cross-polar). A)Detrital grains with pore spaces filled with calcite cement (cc). Authigenic kaolinite (k) and chlorite (c) partially fill pore spaces not completely cemented by calcite and coat bothdetrital grains and cement margins. B) Authigenic grain coating chlorite (c), chlorite rosettes (cr), and authigenic kaolinite (k). C) Authigenic grain-coating chlorite (c), quartzovergrowth (q) as a later diagenetic phase, followed by authigenic kaolinite (k). D) Iron-oxide cements rimming altered volcanic grain (Rv) (cP e ca-plagioclase, M emuscovite, cc ecalcite cement). E) Pressure solution between quartz grains (arrowed). F) Organic matters (black areas). G) Porosity of host (i.e. un-cemented) rocks (p) (cP e ca-plagioclase, Q e

quartz).

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depositional setting of the Wall Creek sediments may have beenfavorable for the development of an iron-rich clay precursor, suchas odinite or glaucony, (e.g. Odin, 1988) the sandstones do notdemonstrate petrographic evidence of a clay precursor.

4.3. Kaolinite

Kaolinite is a minor cementing phase that occurs as euhedralbooklets that cover earlier diagenetic minerals (Fig. 6C). Kaolinite istypicallynotoverlappedbyotherdiageneticmaterials, suggesting thatit is a late stage cement that post-dates both chlorite and quartzovergrowths (Fig. 6C). Kaolinite preferentially precipitates inacidporewaters at burial depths typically<2 km (otherwise dickite will form).

Considering the following constraints and conditions, kaoliniteprobably precipitated during and after uplift and exposure of theWall Creek with consequent meteoric-water interaction. Uplift/exposure and the influx of meteoric-water resulted in the neces-sary conditions for kaolinite formation (Stonecipher et al., 1984).Many workers have reported meteoric recharge in the SecondFrontier (Fig. 2) as responsible for calcite precipitation (Duttonet al., 2000; McBride et al., 2003) and possible scenarios ofmeteoric infiltration in sediments of the Cretaceous WesternInterior Seaway (Tourtelot and Rye, 1969; Manheim and Sayles,1974; Carpenter et al., 1988; Ludvigson et al., 1989; Ludvigsonet al., 1994; McCay et al., 1995; Coniglio et al., 2000; Dettmanand Lohmann, 2000).

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4.4. Minor diagenetic phases

Quartz overgrowths were observed as euhedral crystals in mi-nor amounts only outside calcite concretions within the hostsandstone. SEM shows grain rimming chlorite engulfed by quartzovergrowths with kaolinite booklets “floating” atop the chloriteand quartz overgrowths (Fig. 6C).

Quartz precipitation began late in burial history but slightlyoverlapped chlorite precipitation, as indicated by the growth-geometry in SEM (Fig. 6C). Quartz overgrowths (QOG) are mini-mal, and precipitation was inhibited by either abundant graincoating of earlier-formed chlorite (Stonecipher et al., 1984;Ehrenberg, 1993; Bjørlykke, 1998) or temperatures for QOG pre-cipitation (Haszeldine and Osborne, 1993). Sources for silica prob-ablywere frompressure dissolution, as seen in thin section (Fig. 6E).

Minor iron-oxide cements rim altered volcanic fragments(Fig. 6D) and biotite, and in some cases may fill void spaces of thesedissolving detrital grains. This suggests iron-oxides are sourcedfrom the alteration of iron-rich detrital grains during shallowburial; however, additional iron would have been available fromthe deltaic depositional environment (Cookenboo et al., 1997;Cookenboo and Bustin, 1999).

Trace amounts of rhombic features with an Mg-calcite compo-sition are located in remnant pore spaces. These features are atranslucent brownish color in thin section, and EDS analysis reflectsiron, calcium, magnesium, suggesting alteration of a dolomiteprecursor to calcite. The rhombs are surrounded by calcite cement,however there are voids at the boundary between the cement andthe rhombs, and at rhomb centers. The rhombs are similar to thosedescribed in Yong and Boles (1996).

Fig. 7. A) 3D GPR model of the Raptor Ridge outcrop illustrating concretion distribution. Bfacies (B) and channel facies (B) (from Lee et al., 2007a).

Organic matter (Fig. 6F) is sporadically distributed through theRaptor Ridge site, however where present, primarily it is uniformlydistributed at a local scale. The organics do not typically coat grains,instead they are scattered throughout selective samples both neargrains and “floating” in pore spaces.

Trace amounts of pyrite are present in only a few concretionarysamples. Pyrite is also found in the Raptor Ridge mudstonesstratigraphically below these sandstones.

5. Calcite concretions

5.1. Concretion morphology

Concretions in the Raptor Ridge are not uniformly distributedwithin the sandstone and occur in both the lower channel de-posits and upper tidal bar deposits (Fig. 4A, C). The concretionsdo not follow bedding planes, and growth may terminate withina bed, or may cut across bedding surfaces. In the outcrops, con-cretions occupy 1.25% of the rocks in the depositional-dip di-rection and 10.9% in the depositional-strike direction (Fig. 4A).However, concretions present in cores, and illustrated by 3D GPRmodeling (Fig. 7) are volumetrically more abundant than what isrepresented in outcrop. In the tidal bar facies, concretionsrepresent 14.7% of the volume, versus about 10.5% in the channelfacies.

Concretions vary in size and shape from 70 cm to 5.5m in length(horizontal dimension on dip-direction cliff face), and from 20 cmto 60 cm in height (Figs. 4A, C and 8). Two concretions reach up to10 m in length; however these appear to be multiple coalescedconcretions. Due to erosional effects it is unknown as to what

, C) 3D GPR model of concretion-distribution prediction in the subsurface for tidal bar

Fig. 8. Concretion photographs: A) almond shape concretion in the tidal bar facies. Thin ellipsoidal concretion in the tidal bar facies shown in (B) dip and (C) strike direction. D)Rounded, slightly flattened concretion in the channel facies with an un-cemented calcareous mud nucleation site. E) Long ellipsoid shape concretion in the channel facies with anun-cemented carbonaceous mud nucleation site. F) Concretion in the channel facies with numerous scattered mud (calcareous) clasts and no central nucleation site. Dashed linesindicate concretion margins.

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“slice” of the concretion is exposed on the cliff face, whether it isnear the concretion center or closer to the width dimension mar-gins. The concretions range from almond shape (nearly sphericalbut with flattened edges), to long, thin ellipsoids, to short, thick

ellipsoids, to coalesced (Fig. 8). Generally those found in thechannel facies are more rounded to thick ellipsoids while the tidalbar facies contain the almond shaped and long, thin ellipsoids(Figs. 4A, C and 8).

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Fig.10. The isotopic values of calcite cement in concretions range from a d18O of �7.4to �16.1& (PDB, average ¼ �13.2), and d13C of: �1.3 to �11.3& (PDB, average ¼ �7.8).Carbon isotopic signatures reflect a mixed marine skeletal fragment, carbon from seawater, and organic matter carbon source.

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5.2. Nucleation sites

Several concretions have clear nucleation sites that consist ofeither calcareous or carbonaceous muds (Fig. 8D, E). Many con-cretions do not have an identifiable nucleation site. This may bebecause the exposed “slice” of concretion does not intersect itscenter. Numerous concretions without an identifiable centernucleation site commonly have calcareous mud clasts scatteredthroughout the concretion (Fig. 8F). Several concretions in thechannel deposits have broken shell material scattered throughout.Concretions with multiple locations of carbonate material andmuds may have provided multiple nucleation sites.

It has been reported in previous studies of the Frontier Forma-tion by Dutton et al. (2000, 2002) and McBride et al. (2003) thatthese concretions lacked any evidence of a nucleation site, and theunits did not contain any constituents that could source calciumcarbonate, concluding that the necessary ions for calcite precipi-tation were sourced outside the system.

5.3. Porosity destruction in concretions

Porosity within the host sandstone averages 10% (Fig. 6G).Concretionary samples are entirely cemented by calcite with minorchlorite, kaolinite, and minor porosity near concretion margins(Fig. 6A). Porosity loss after deposition is due to both compactionand cementation. Figure 9 plots intergranular mineral cement vs.intergranular volume (IGV), demonstrating the percent of originalporosity destroyed by compaction and cementation (diagram afterHouseknecht, 1987). The Raptor Ridge sandstones lost 50e90%original porosity due to cementation and 10e50% due to mechan-ical compaction.

5.4. Isotope geochemistry of concretions

The oxygen isotopic values range from a d18O of �7.4 to �16.1&(PDB, mean ¼ �13.2) (Fig. 10). Oxygen isotopic variations betweensamples reflect changes in pore water conditions due to mineralewater interaction, increasing temperatures, and/or fluid migrationevents. The more depleted d18O values represent precipitation fromfluids with a composition closer to that of fresh water (d18O ¼ �10

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to �12&, SMOW) (Law et al., 1990) or precipitation at elevatedtemperature. The d18O of Cretaceous marine water was close to �1(SMOW) (Shackleton and Kennett, 1975). The Raptor Ridge sedi-ments are much closer to a fluvial deltaic source, thereby thedepositional waters are expected to be more depleted.

Plots of IGV vs. d18O (Fig.11) showa loose trend ofmore enrichedd18O values with decreasing IGV, suggestive of an overall enrich-ment of pore water composition. However, these trends are lesssignificant when compared within concretions. Oxygen isotopicvalues fluctuate dramatically within a concretion as IGV decreases(i.e. deeper burial depths). Individual concretions show a variationof d18O depletion and enrichment trends suggesting possibly up tothree major changes in pore water composition.

The carbon isotopic values range from d13C of: �1.3 to �11.3&(PDB, average ¼ �7.8) (Fig. 10). Sources for carbon are probablyfrommarine skeletal-fragments, sea water, and organic carbon, themore depleted carbon values representing a larger influence oforganic carbon.

Figure 12 demonstrates the calciteewater equilibrium relation-ship. Calcite must have precipitated at temperatures below 55 �C(maximum burial temperature). The d18O of pore water will re-

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Fig. 11. Oxygen isotopic signatures plotted against IGV values suggest an overall trend,though weak, of d18O enrichment with burial. However, enrichment trends withinindividual concretions are not evident and suggest fluxuations in pore water compo-sition through time.

Fig. 12. Possible d18O compositions of formation water and temperatures that could have precipitated Raptor Ridge calcite cement. See text for discussion.

S.L. Nyman et al. / Cretaceous Research 48 (2014) 139e152 149

equilibrate (likely deplete) during burial diagenesis due toincreasing burial temperatures and the dissolution/precipitation ofminerals, with one estimate of up to 3& at 300m (Irwin et al.,1977).

Initial depositional waters are interpreted to have been depletedin d18O, probably near meteoric composition of �10 to 12& (Lawet al., 1990), based on previous studies (Ludvigson et al., 1996;Coniglio et al., 2000; White et al., 2001; McBride et al., 2003),proximity to a fluvial source, and d18O values of cements precipi-tated at near surface depths. Pore water depletion may also havebeen influenced by the low temperature hydrolysis of the abundantvolcanic ash which may enrich d18O compositions of authigenicclays thereby depleting pore water compositions (Yeh and Savin,1977; Lawrence et al., 1979).

Figure 12 is the equilibrium diagram plotting d18O watercomposition against temperature. The left axis correlates theappropriate burial depth to temperature with a gradient of 29 �C/km and a surface temperature of 10 to 15 �C. If assumptions aremade regarding intergranular volumes corresponding to a partic-ular depth such as a 40% IGV at deposition (Houseknecht,1987), andthe minimal recorded IGV of 10% as the deepest burial, andassuming an even reduction of IGV during burial, then a thirdvertical axis of %IGV is extrapolated against burial depth and tem-perature. However, IGV values at depth is a gross overestimationbecause it assumes the lowest IGV value occurred at maximumburial, and thereby the final stages of compaction were not com-plete until that time.

Entertaining the previous assumptions, concretion sampleswere then plotted on the equilibrium diagramwith their measured

d18Ocalcite and IGV values. The plot shows a trend of d18O enrich-ment with increasing temperatures. This trend is best explained bymarine water infiltration from a marine transgression after thedeposition of the Wall Creek with subsequent deposition of theoverlying Cody Shale (Fig. 2A). Although this plot is a crude firstapproximation, it provides a solid first order interpretation of IGVvs. d18O and the relative timing of cement precipitation within andbetween concretions. Figure 12 illustrates that calcite precipitationbegan early, within the first 100 m of burial, but continued tomaximum burial depths of 1.35 km, and suggests that calcite con-cretions within tidal bar facies began near 100 m and ceased near900 m burial at about 40 �C. In contrast, the concretions withinchannel facies started precipitating closer to 200 m and continuedtheir growth to approximately 1300 m. However, the majority ofcalcite precipitation took place below depths of 800 m.

6. Discussion

6.1. Depositional waters

Initial depositional waters are hypothesized to be fresh tobrackish which is consistent with deposition in a deltaic environ-ment. The deltaic fresh to brackish waters were probably alkalinewith a low sulfate concentration (Boggs, 1992). Low sulfate con-centrations would result in little sulfate reduction resulting in littleto no pyrite precipitation leaving free iron ions in formation waters(Boggs, 1992). The trace amounts of pyrite may also indicate thatthe sedimentation rates were high, which would move the

S.L. Nyman et al. / Cretaceous Research 48 (2014) 139e152150

sediment column quickly through the sulfate reduction zone,limiting the amount of sulfide available to react with iron (Boggs,1992). As a result, Fe2þ in the system increases and becomesavailable to enter the carbonate lattice during calcite precipitation.

6.2. Authigenic cement phases

Calcite is the only carbonate mineral present in the concretions,revealing the Ca2þ/Fe2þ ratio must be high to precipitate a low-magnesium ferrous calcite and not an iron carbonate such assiderite. Calcite more enriched in iron in samples with lower IGVvalues suggest dissolved iron in formationwaters increased later inburial.

Chlorite and kaolinite co-exist with calcite cement only near theconcretion margins, and form pore filling and pore lining phases(Fig. 6A). Chlorite and kaolinite are seen in SEM images, lining calcitecement, indicating precipitation after calcite. Further evidence sup-ports post chlorite growth 1) calcite surrounding detrital-grain-coating chlorite does not occur in thin sections or SEM (Fig. 6A); 2)if chlorite began before calcite it would be expected that within thelater stages of concretion growth, therewould be higher percentagesof chlorite (and thereby lower volumes of calcite) filling pore spaces.Neither occurrence is observed in the Raptor Ridge sandstones.

6.3. Concretion growth patterns

The overall general trend of d18O enrichment with depth (Fig. 12)seen in the Raptor Ridge sandstones is interpreted to be a result of theinfiltration of marine fluids subsequent to the marine transgressiondepositing the overlying Cody Shale. The variations in d18O depletionand enrichment trends can be explained by the timing of precipita-tion onset, combinedwith d18Odepletion fromwater rock interactionandenrichment fromthemarine transgression. Interpretationsof IGVvalues and d18O signatures within concretions suggest some con-cretions may have grown over a short period of time with a highprecipitation ratewhile other concretionswithin the same sandstonemay have precipitated over long periods of time at low precipitationrates. The majority of Raptor Ridge concretion growth is interpretedto have occurred during early burial, primarily during physicalcompaction. At the point in which chemical compaction becomesdominant and physical compaction is close to completion (IGV valuesnear 27%) (Graton and Fraser, 1935; Fuchtbauer, 1967; McBride et al.,1991) precipitation rates began to decline. By the time these sedi-ments reached burial depths of 800 m, precipitation declineddramatically. IGV values suggest Raptor Ridge concretions beganprecipitation early in burial and lost most of their primary porositydue to cementation before compaction was complete. The thinellipsoidal concretions in the tidal facies are interpreted to havegrown predominantly in the horizontal direction due to decreasedpermeability in the vertical direction as opposed to the thicker con-cretions in the more permeable channel facies (Figs. 4A, C, and 9).

Precipitationpatternsmay indicate paleo-fluidmigration throughthe system. From outcrop observations and a detailed 3D GPRmodelof the studied concretions (Lee et al., 2007a), it appears that manyconcretions initially grow upward from their nucleus. Precipitationthen appears to shift to the concretion flanks and bottom. Early up-ward growth reflects initial sediment dewatering in early burialwhere fluids commonly are expelled upwards. This was followed byfluid movement downward and laterally as a result of increasedconfiningpressures at thepointwhere compactionnears completion.

6.4. Reservoir quality

At Raptor Ridge in sandstone #6 reservoir quality is reducedprimarily due to calcite cementation. Calcite precipitation in these

sandstones was enhanced as a result of minimal deposition ofdetrital clays, leaving a porous and permeable sandstone open to ahigher volume of fluid flow.

The outcrop shows similar cross-sectional concretionmorphology as described in other studies (e.g. Bjørkum andWalderhaug, 1990; McBride et al., 1995; Klein et al., 1999; Duttonet al., 2000; McBride et al., 2003), and suggests a relatively lowoverall volume of concretionary cements. However, a 3D GPRmodel of the Raptor RidgeWall Creek sandstones (Lee et al., 2007a)illustrates that concretions are highly interconnected forming anaggregate patternwith irregularly shaped branches (Fig. 7), and areconcentrated within the tidal bar (14.7%) and channel deposits(10.54%). Cluster analysis of the GPR attributes (instantaneousamplitudes and wave numbers) calibrated with the cores and theoutcrop was used to construct 3D concretion models (Lee et al.,2007a).

The locally pervasive calcite cement in the Wall Creek hasimportant implications for reservoir quality and prediction,particularly for Cretaceous reservoirs of onshore USA. Carbonatecement most commonly occurs as non-uniformly distributed con-cretions that typically cements the most permeable facies first. Thiswill potentially reduce overall reservoir volumes and may impedefluid flow in both the horizontal and vertical directions. Initialtracer flow modeling results show that the cements cause signifi-cant fingering and inhibit development of a “piston” likedisplacement (Tang, 2003). The 3D distribution of concretionaryfeatures must be taken into account in reservoir modeling and fluidflow simulations. Without the inclusion of possible concretions inpermeability and fluid flow modeling, flow models may defineincorrect paths, permeability may be overestimated and overallrecovery factors may be incorrectly estimated (Dutton et al., 2002;White et al., 2003).

7. Conclusions

1. Sedimentological and petrographic analysis reveals that delta-front sandstones of the Cretaceous Wall Creek parasequence#6 show abundant concretionary calcite cements, with lesseramounts of chlorite, kaolinite, quartz overgrowth and iron-oxide cement.

2. IGV values suggest calcite precipitation began early during thefirst 100 m of burial, and continued up to near maximum burialdepths, with the most intense precipitation occurring between300 and 800 m.

3. Slightly depleted d13C values of calcite cement indicate thesource of carbon is from both alteration of organic matter, seawater, andmarine skeletal carbonate. Petrographic observationssuggest both a local source and external source for organicmatter. Late stage calcite likely received Ca from dissolution ofCa-plagioclases associated with the abundant volcanic frame-work grains and bentonites within the immediately adjacentmuddy strata.

4. The difference between d18Ocalcite compositions reflect precipi-tation throughout burial history from a combination of porewater depletion from diagenetic reactions, increased tempera-ture, and bentonite horizons, and the influx of enriched watersof marine composition resulting from the marine transgressionand subsequent deposition of the overlying Cody Shale.

5. Raptor Ridge concretions appear to nucleate from carbonaceousmud clasts and organic matter. Concretions lacking an identifi-able nucleus may be due to the “slice” of concretion exposed inoutcrop, or may in fact be lacking a nucleus.

6. The growth of the Raptor Ridge concretions do not follow thetraditional concentric center-to-margin pattern. Instead, IGVvalues in many Wall Creek concretions suggest precipitation

S.L. Nyman et al. / Cretaceous Research 48 (2014) 139e152 151

begins near a nucleation site and commonly grow upwards inthe direction of fluid flow; as the direction of fluid migrationchanges, so does the pattern of growth within the concretions,resulting in more complex growth patterns.

7. Reservoir quality is reduced in the Wall Creek due to calcitecementation. Concretion growth was enhanced from theabsence of detrital clays, resulting in higher initial permeabilityand fluid flow regimes. 3D imaging shows that concretions areconfined to the middle of the volume, rather than beingdispersed throughout, and consist of overlapping lenses thatreach a volume percent of up to 15%. 3D modeling of cement isan important aspect in reservoir characterization demonstratingthat outcrop and core samples alone may lead to an over-estimation of porosity and incorrect fluid flow pathways.

Acknowledgments

Funding for this research was provided by BP, Cheveron, and theDepartment of Energy DOE Grant # DE-FG0301ER15166. Thanks arealso due to Chuck Howell, Nahid Gani, and Randy Griffin for helpingin the field. We greatly thank Sven Egenhoff and an anonymousreviewer for their through reviews, which improved the quality ofthe manuscript.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.cretres.2013.12.009.

References

Bhattacharya, J.P., Willis, B.J., 2001. Lowstand deltas in the Frontier Formation,Powder River basin, Wyoming: implications for sequence stratigraphic models.American Association of Petroleum Geologists, Bulletin 85, 261e294.

Bjørkum, P.A., Walderhaug, O., 1990. Geometrical arrangement of calcite cementa-tion within shallow marine sandstones. Earth-Science Reviews 29, 145e161.

Bjørlykke, K., 1998. Clay mineral diagenesis in sedimentary basins e a key to theprediction of rock properties. Clay Minerals 33, 15e34.

Boggs, S., 1992. Petrology of sedimentary rocks. In: McConnin, R.A. (Ed.). MacmillianPublishing Company, New York, 707 p.

Carpenter, S.J., Erickson, J.M., Lohmann, K.C., Owen, M.R., 1988. Diagenesis offossiliferous concretions from the Upper Cretaceous Fox Hills Formation, NorthDakota. Journal of Sedimentary Petrology 58, 706e723.

Coniglio, M., Myrow, P., White, T., 2000. Stable carbon and oxygen isotope evidenceof Cretaceous sea-level fluctuations recorded in septarian concretions fromPueblo, Colorado, U.S.A. Journal of Sedimentary Research 70, 700e714.

Cookenboo, H.O., Bustin, R.M., Wilkes, K.R., 1997. Detrital chromian spinel used toreconstruct the tectonic setting of provenance: implications for orogeny in theCanadian Cordillera. Journal of Sedimentary Research 67, 116e123.

Cookenboo, H.O., Bustin, R.M., 1999. Pore water evolution in sandstones of theGroundhog Coalfield, northern Bowser Basin, British Columbia. SedimentaryGeology 123, 129e146.

Dettman, D.L., Lohmann, K.C., 2000. Oxygen isotope evidence for high-altitudesnow in the Laramide Rocky Mountains of North America during the LateCretaceous and Paleogene. Geology 28, 243e246.

Duan, W.M., Hedrick, D.B., Coleman, M.L., Pye, K., White, C.D., 1996. A preliminarystudy of the geochemical and microbiological characteristics of modern sedi-mentary concretions. American Association of Limnology and Oceanography 41,1404e1414.

Dutton, S.P., Willis, B.J., White, C.D., Bhattacharya, J.P., 2000. Outcrop characteriza-tion of reservoir quality and interwell-scale cement distribution in a tide-influenced delta, Frontier Formation, Wyoming, USA. Clay Minerals 35, 95e105.

Dutton, S.P., White, C.D., Willis, B.J., Novakovic, D., 2002. Calcite cement distributionand its effect on fluid flow in a deltaic sandstone, Frontier Formation, Wyoming.American Association of Petroleum Geologists, Bulletin 86, 2007e2021.

Ehrenberg, S.N., 1993. Preservation of anomalously high porosity in deeplyburied sandstones by grain coating chlorite: Examples from the NorwegianContinental Shelf. American Association of Petroleum Geologists, Bulletin 77,1260e1286.

Foscolos, A.E., 1985. Catagenesis of argillaceous rocks. In: McIlreath, I.A., Morrow, D.W.(Eds.), Diagenesis, Geoscience Canada Reprint Series, 4, pp. 177e188.

Fuchtbauer, H., 1967. Influence of different types of diagenesis on sandstoneporosity. In: Seventh World Petroleum congress Proceedings, 2Elsevier, NewYork, pp. 353e369.

Gani, M.R., Bhattacharya, J.P., 2007. Basic building blocks and process variability ofa mixed-influence ancient river delta. Journal of Sedimentary Research 77,284e302.

Graton, L.C., Fraser, H.J., 1935. Systematic packing of spheres with particular relationto porosity and permeability. Journal of Geology 43, 785e900.

Grigsby, J.D., 2001. Origin and growth mechanism of authigenic chlorite in sand-stones of the lower Vicksburg Formation, South Texas. Journal of SedimentaryResearch 71, 27e36.

Hansley, P.L., Nuccio, V.F., 1992. Upper Cretaceous Shannon Sandstone reservoirs,Powder River Basin, Wyoming: Evidence for organic acid diagenesis? AmericanAssociation of Petroleum Geologists, Bulletin 76, 781e791.

Haszeldine, R.S., Osborne, M., 1993. Fluid inclusion temperatures in diageneticquartz reset by burial: Implications for oil field cementation. In: Horbury, A.D.,Robinson, A.G. (Eds.), Diagenesis and Basin Development, 36American Associ-ation of Petroleum Geologists Studies in Geology, pp. 35e48.

Houseknecht, D.W., 1987. Assessing the relative importance of compaction pro-cesses and cementation to reduction of porosity in sandstones. American As-sociation of Petroleum Geologists, Bulletin 71, 633e642.

Irwin, H., Curtis, C., Coleman, M., 1977. Isotopic evidence for source of diageneticcarbonates formed during burial of organic-rich sediments. Nature 269,209e213.

Jahren, J.S., Aagaard, P., 1989. Compositional variations in diagenetic chlorites andillites, and relationships with formation-water chemistry. Clay Minerals 24,157e170.

Kantorowicz, J.D., Bryant, I.D., Dawans, J.M., 1987. Controls on the permeability anddistribution of carbonate cements in Jurassic sandstones: Bridgeport Sands,southern England, and Viking Group, Troll field, Norway. In: Marshall, J.D. (Ed.),Diagenesis of Sedimentary Sequences. Blackwell, Oxford, pp. 103e118.

Klein, J.S., Mozley, P., Campbell, A., Cole, R., 1999. Spatial distribution of carbon andoxygen isotopes in a laterally extensive carbonate-cemented layers: implica-tions for mode of growth and subsurface identification. Journal of SedimentaryResearch 69, 184e191.

Law, E.W., Burrows, S.M., Aronson, J.L., Savin, S.M., 1990. A Petrologic, geochrono-logic, and oxygen isotopic study of the diagenesis of the Muddy Sandstone, eastflank of the Powder River Basin. Clay Minerals Society, 27th Annual Meeting,Program and Abstracts, p. 110.

Lawrence, J.R., Dreever, J.I., Anderson, T.F., Brueckner, H.K., 1979. Importanceof alteration of volcanic material in the sediments of Deep Sea Drilling site323: chemistry 18O/16O and 87Sr/86Sr. Geochimica et Cosmochimica Acta 43,573e588.

Lee, K., Gani, M.R., McMechan, G., Bhattacharya, J.P., Nyman, S.L., Zeng, X., 2007a.Three-dimensional facies architecture and three-dimensional calcite concretiondistributions in a tide-influenced delta front, Wall Creek Member, FrontierFormation, Wyoming. American Association of Petroleum Geologists, Bulletin91, 191e214.

Lee, K., MacMechan, G.A., Gani, M.R., Bhattacharya, J.P., Zeng, X., Howell Jr., C.D.,2007b. 3-D architecture and sequence stratigraphic evolution of a forcedregressive top-truncated mixed-influenced delta front, Cretaceous Wall Creeksandstone, Wyoming, USA. Journal of Sedimentary Research 77, 303e323.

Ludvigson, G.A., Witzke, B.J., Hammond, R.H., 1989. Sedimentologic, petrographic,and isotopic study of fossiliferous carbonate concretions from shales of thegreenhorn marine cycle, eastern margin of the Cretaceous Western InteriorSeaway (WIS). Geological Society of America, Abstracts with Programs 21,A309.

Ludvigson, G.A., Witzke, B.J., González, L.A., Hammond, R.H., Plocher, O.W., 1994.Sedimentology and carbonate geochemistry of concretions from the greenhornmarine cycle (Cenomanian-Turonian), eastern margin of the Cretaceous West-ern Interior Seaway. In: Shurr, G.W., Ludvigson, G.A., Hammond, R.H. (Eds.),Perspectives of the Eastern Margi of the Cretaceous Western Interior Basin,Geological Society of America, Special Paper, 287, pp. 134e174.

Ludvigson, G.A., González, L.A., Witzke, B.J., Brenner, R.L., 1996. Oxygen isotopiccomposition of freshwater runoff to North American Cretaceous western inte-rior basin. Geological Society of America, Abstracts with Programs 28 p. A66.

Manheim, F.T., Sayles, F.L., 1974. Composition and origin of interstitial waters ofmarine sediments, based on deep sea drill cores. In: Goldberg, E.D. (Ed.), TheSea, Marine Chemistry, 5Wiley, New York, pp. 527e568.

Markert, J.C., Al-Shaieb, A., 1984. Diagenesis and Evolution of Secondary Porosity inUpper Minnelusa Sandstones, Powder River Basin, Wyoming. In:McDonald, D.A., Surdam, R.C. (Eds.), Clastic Diagenesis, American Association ofPetroleum Geologists Memoir, 37, pp. 367e389.

McBride, E.F., Diggs, T.N., Wilson, J.C., 1991. Compaction of Wilcox and Carrizosandstones (Paleocene-Eocene) to 4420m, Texas Gulf Coast. Journal of Sedi-mentary Petrology 61, 73e85.

McBride, E.F., Milliken, K.L., Cavazza, W., Cibin, U., Fontana, D., Picard, M.D.,Zuffa, G.G., 1995. Inhomogeneous distribution of calcite cement at the outcropscale in Tertiary sandstones, northern Apennines, Italy. American Association ofPetroleum American Association of Petroleum Geologists, Bulletin 79, 1044e1063.

McBride, E.F., Picard, M.D., Milliken, K.L., 2003. Calcite-cemented concretions in theCretaceous sandstone, Wyoming and Utah, U.S.A. Journal of SedimentaryResearch 73, 62e484.

McCay, J.L., Longstaffe, F.J., Plint, A.G., 1995. Early diagenesis and its relationshipto depositional environment and relative sea level fluctuations (Upper Creta-ceous Marshybank Formation, Alberta and British Columbia). Sedimentology42, 161e190.

S.L. Nyman et al. / Cretaceous Research 48 (2014) 139e152152

Merewether, E.A., 1996. Stratigraphy and tectonic implications of upper CretaceousRocks in the Powder River Basin, Northeastern Wyoming and SoutheasternMontana. United States Geological Survey, Bulletin 1917-T, T1eT92.

Morad, S., DeRos, L.F., 1994. Geochemistry and diagenesis of strata bound calcitecement layers within the Rannoch Formation of the Brent Group, MurchisonField, North Viking Graben (northern North Sea)dComment. SedimentaryGeology 93, 135e141.

Odin, G.S., 1988. The verdine facies identified in 1988. In: Odin, G.S. (Ed.), GreenMarine Clays. Developments in Sedimentology, 45Elsevier, Amsterdam,pp. 131e148.

Odin, G.S., Masse, J.P., 1988. The verdine facies from the Senegalese continentalshelf. In: Odin, G.S. (Ed.), Green Marine Clays, Developments in Sedimentology,45. Elsevier, Amsterdam, pp. 83e106.

Sadeque, J., Bhattacharya, J.P., MacEachern, J.A., Howell, C.D., 2008. Differentiatingamalgamated parasequences in deltaic settings using Ichnology: an examplefrom the Upper Turonian Wall Creek Member of the Frontier Formation,Wyoming. In: MacEachern, J.A., Bann, K.L., Gingras, M.K., Pemberton, S.G. (Eds.),Applied Ichnology 52. SEPM, Short Course Notes, pp. 343e362.

Saigal, G.C., Bjørlykke, K., 1987. Carbonate cements in clastic reservoir rocks fromoffshore Norway e relationships between isotopic composition, texturaldevelopment and burial depth. In: Marshall, J.D. (Ed.), Diagenesis of Sedimen-tary Sequences. Blackwell, Oxford, pp. 313e324.

Shackleton, N.J., Kennett, J.P., 1975. Late Cenozoic oxygen and carbon isotopicchange at DSDP site 284: implications for the glacial history of the NorthernHemisphere. In: Kennett, J.P., et al. (Eds.), Initial Reports of the Deep Sea DrillingProject, 29, pp. 801e807.

Spencer, C.W., 1987. Hydrocarbon generation as a mechanism for overpressuring inRocky Mountain region. American Association of Petroleum Geologists, Bulletin71, 368e388.

Stonecipher, S.A., Winn, R.D., Bishop, M.G., 1984. Diagenesis of the Frontier For-mation, Moxa Arch: A function of sandstone geometry, texture and

composition, and fluid flux. In: McDonald, D.A., Surdam, R.C. (Eds.), ClasticDiagenesis, American Association of Petroleum Geologists Memoir, 37, pp. 289e316.

Tang, H., 2003. Geostatistical integration of geophysical, well bore and outcrop datafor flow modeling of a deltaic reservoir analog [unpublished PhD thesis]. Lou-isiana State University, Louisiana, 131 p.

Tillman, R.W., Almon, W.R., 1979. Diagenesis of Frontier Formation offshore barsandstones, Spearhead Ranch Field, Wyoming. In: Scholle, P.A., Schluger, P.R.(Eds.), Aspects of Diagenesis, Society of Economic Paleontologists and Miner-alogists Special Publication, 26, pp. 337e378.

Tourtelot, H.A., Rye, R.O., 1969. Distribution of oxygen and carbon isotopes in fossilsof Late Cretaceous age, Western Interior region of North America. GeologicalSociety of America, Bulletin 80, 1903e1922.

White, T., González, L., Ludvigson, G., Poulson, C., 2001. Middle Cretaceous green-house hydrologic cycle of North America. Geology 29, 363e366.

White, C.D., Novakovic, D., Dutton, S.P., Willis, B.J., 2003. A geostatistical model forcalcite concretions in sandstone. Mathematical Geology 35, 549e575.

Willis, B.J., Bhattacharya, J.P., Gabel, S.L., White, C.D., 1999. Architecture of a tide-influenced river delta in the Frontier Formation of Central Wyoming, U.S.A.Sedimentology 46, 667e688.

Wiltschko, D.V., Door, J.A., 1983. Timing of deformation in overthrust belt andforeland of Idaho, Wyoming and Utah. American Association of PetroleumGeologists, Bulletin 67, 1304e1322.

Yeh, H., Savin, M.S., 1977. Mechanism of burial metamorphism of argillaceoussediments: O-Isotope evidence. Geological Society of America, Bulletin 88,1321e1330.

Yong, I.L., Boles, J.R., 1996. Depositional control on carbonate cement in the SanJoaquin Basin, California. In: Crossey, L.J., Loucks, R., Toten, M.W. (Eds.), Silici-clastic Diagenesis and Fluid Flow: Concepts and Applications, 55SEPM, SpecialPublication, pp. 13e22.