Re-evaluation of the Albian–Cenomanian boundary in the U.S. Western Interior based on...

ynology 144 (2007) 77–97www.elsevier.com/locate/revpalbo

Review of Palaeobotany and Pal

Re-evaluation of the Albian–Cenomanian boundary in the U.S.Western Interior based on dinoflagellate cysts

Francisca E. Oboh-Ikuenobe a,⁎, Don G. Benson b, Robert W. Scott c,John M. Holbrook d, Mike J. Evetts e, Jochen Erbacher f

a Department of Geological Sciences and Engineering, University of Missouri-Rolla, Rolla, MO 65409-0410, USAb The irf group, Inc., 1522 Ehlinger Road, Fayetteville, TX 78940, USA

c Precision Stratigraphy Associates and Tulsa University, RR3 Box 103-3, Cleveland, OK 74020, USAd Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019-0049, USA

e 1227 Venice Street, Longmont, CO 80501, USAf Marine Geology and Deep Sea Mining, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover,

Federal Republic of Germany

Received 6 October 2004; received in revised form 16 August 2005; accepted 9 September 2005Available online 17 August 2006

Abstract

The position of the Albian–Cenomanian boundary in the U.S. Western Interior Basin has been the subject of debate becausethe ammonites and foraminifers that define the boundary are endemic. Traditionally, the boundary, as defined in Europe byplanktonic foraminifers and ammonites, is correlated with the last occurrence of the ammonite genus, Neogastroplites [Reeside,J.B., Cobban, W.A., 1960. Studies of the Mowry Shale (Cretaceous) and contemporary formations in the United States andCanada. U.S. Geological Survey Professional Paper 355, 126 pp]. More recently, the boundary was correlated with the firstoccurrence of Metengonoceras teigenensis [Cobban, W.A., 1951. Colorado shale of central and northwestern Montana andequivalent rocks of Black Hills. American Association of Petroleum Geologists Bulletin 35, 2170–2198]. These ammonites areassociated with bentonites, the ages of which have been extrapolated to the type region of France to date the base of theCenomanian from the Western Interior Basin. However, since cosmopolitan dinoflagellates are common to this region and theEuropean reference sections where the boundary is defined, they can be used to reevaluate the position of the Albian–Cenomanian boundary in the Western Interior Basin. In our study, 224 samples from 29 outcrop sections in Montana, Wyoming,Colorado, Oklahoma and New Mexico were analyzed for dinoflagellate cysts, as well as other palynomorphs, foraminifers,bivalves and ammonites; these fossils were used for graphic correlation. The recovery and preservation of the dinoflagellatecysts varied from poor to good, and diversity varied from low to moderate. Typical Late Albian to Early Cenomanian taxa,including Ovoidinium verrucosum, Ovoidinium scabrosum and Palaeohystrichophora infusorioides, dominate the assemblages;however, dinoflagellate ranges in the five sections in which the neogastroplitid zones are defined (Arrow Creek, Ayers Ranch,Belt Butte, Geyser, Teigen) suggest correlation with the uppermost Albian. Dinoflagellate ranges were confirmed in additionalMontana, Wyoming and northern Colorado sections by a few diagnostic taxa (Aptea polymorpha, Apteodinium grande, Ba-tioladinium jaegeri, Luxadinium propatulum, Chichaouadinium vestitum), and they were graphically correlated with published

⁎ Corresponding author. Tel.: +1 573 341 6946; fax: +1 573 341 6935.E-mail addresses: [email protected] (F.E. Oboh-Ikuenobe), [email protected] (D.G. Benson), [email protected] (R.W. Scott),

[email protected] (J.M. Holbrook), [email protected] (M.J. Evetts), [email protected] (J. Erbacher).

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78 F.E. Oboh-Ikuenobe et al. / Review of Palaeobotany and Palynology 144 (2007) 77–97

European ranges. The result is that the Albian–Cenomanian boundary correlates with the 97 million year old Clay SpurBentonite.© 2006 Elsevier B.V. All rights reserved.

Keywords: Late Albian; Early Cenomanian; dinoflagellate cysts; U.S. Western Interior; graphic correlation

1. Introduction

The Albian–Cenomanian boundary separates theLower and Upper Cretaceous series and has beendefined traditionally by ammonites in its type section inFrance. The base of the planktonic foraminifer Rotali-pora globotruncanoides 6 m below the first occurrence(FO) of Mantelliceras mantelli at the Mont Risousection in southern France now defines the base of theCenomanian (Gale et al., 1996). Correlation of thisboundary into the Western Interior Basin has been basedon the evolutionary stage of endemic ammonites.Interbedded, well-dated bentonites have been used tocalibrate the age of this boundary globally (Obradovichand Cobban, 1975). The geochronological position ofthis boundary has been frequently updated and waschanged from 97.0 Ma to 98.9 Ma in 1995 and to 99.6 Ma in 2004 (see Gradstein et al., 1995, 2004;Obradovich et al., 2002). Although foraminifers andsporomorphs have been used for biostratigraphiccontrol, benthic taxa of the former are also endemicand very few taxa of the latter have proved useful due totheir long ranges. Dinoflagellates provide the greatestpotential for direct correlation of the U.S. WesternInterior Basin into European stratotype referencesections as well as North African reference sections.

The primary objective of this study was to integratedinoflagellate and ammonite biostratigraphies by re-sampling five key sections in central Montana (ArrowCreek, Ayers Ranch, Belt Butte, Geyser, Teigen) usedfor setting up the ammonite zones in theWestern Interior(Reeside and Cobban, 1960; Eicher, 1960, 1965).Additional sections were sampled in Montana andWyoming (Fig. 1) to integrate the dinoflagellate specieswith ammonites, foraminifers and radiolarians. Thispaper shows that dinoflagellate cyst ranges constraincorrelation of the Albian–Cenomanian boundary inEurope with the section in the study area.

2. Stratigraphic setting

During the Late Albian and Early Cenomanian, thewarmer Tethys Sea was transgressed into the U.S.Western Interior several times, connecting it with thecooler Boreal Sea. Traditional sequence models (Wil-

liams and Stelck, 1975; Kauffman, 1984; Scott et al.,1998) show that the first north–south connectionbetween the Boreal and Tethyan provinces was madeduring the early Late Albian Kiowa-Skull Creek cycle(Fig. 2). Then both seaways were separated during theLate Albian to Early Cenomanian in SE Colorado,Oklahoma panhandle and NE New Mexico because ofregression. Full connection was reestablished during theMiddle Cenomanian when the Thatcher LimestoneMember of the Graneros Formation was depositedduring the Greenhorn Cycle. However, new evidence(Scott et al., 2001, 2004) suggests that two additionalthird-order transgressive/regressive episodes occurredbetween these two major flooding events and spannedthe Early–Late Cretaceous boundary in the WesternInterior Basin (Fig. 2).

In central Montana, Lower Cretaceous strata dis-conformably overlie Upper Jurassic strata. Aptian–Albian Kootenai Formation is the basal, wedge-shapedlithosome of nonmarine clastics that thins southeast-ward. It is disconformably overlain by the Fall RiverFormation, which is a transitional nonmarine to marine,cross-bedded sandstone up to 21 m thick (Maughan,1993; Porter and Wilde, 1999a,b). The top of the FallRiver Formation is a transgressive contact overlain bythe Thermopolis Formation, which is a marine intervalof mainly shale and thin beds of sandstone and bentonitethat in central Montana is comprised from base up of theSkull Creek Shale, the sandy member (equivalent withthe Muddy Sandstone) and the Shell Creek Shale (Fig.2; Porter et al., 1993, 1997). The basal Skull Creek isdark gray shale with thin sandstone beds and is up to53 m thick. It is disconformably overlain by the informalsandy member, which consists of thin sandstone bedsinterbedded with shale and is up to 95 m thick. Theupper marine Shell Creek Shale is dark gray, soft fissileshale about 31 m thick.

The Mowry Shale conformably overlies the Thermo-polis Formation and is bounded by the Arrow CreekBentonite bed at the base and the Clay Spur Bentonitebed at the top (Fig. 3). The Mowry Shale is mainly hardbrittle shale and siltstone up to about 60 m thick in thisarea. In central Montana, the Mowry Shale grades upinto the Big Elk Sandstone, which is a lithosome similarto sandstones in the Belle Fourche Member of the

Fig. 1. Location of sections studied. Reeside and Cobban (1960) provide detailed location and lithologic descriptions of sections in central Montana,and Eicher (1960, 1965) provided data on Wyoming sections (Appendix A).

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Frontier Formation in Wyoming. The Big Elk Sandstoneis best developed on the western side of the Mowrybasin in an area bounded by Great Falls and Lewiston onthe north and Bozeman and Billings on the south(Maughan, 1993). It is well developed in the WinnecookRanch section, where it is at least 15 m thick. Fivecentral Montana sections can be correlated relative tothe Arrow Creek Bentonite and sample positions in eachsection are integrated into a common scale (Fig. 3). TheWinnecook Ranch section can be correlated with thePike Creek section by both the Arrow Creek and ClaySpur bentonites.

The Belle Fourche Shale in Montana is comprised ofan informal lower shale member and the upper MosbySandstone Member (Porter and Wilde, 1999a,b). Thelower Belle Fourche Shale is dark gray, fissile, soft,noncalcareous shale with common ironstone concre-tions and is up to 90 m thick in central Montana. The

Mosby Sandstone consists of sandstone ledges 1–2 mthick separated by shale and it is up to 9 m thick. InWyoming, the Belle Fourche Shale is the lower memberof the Frontier Formation and encompasses severalsandstone allomembers (Bhattacharya and Willis,2001). The sandstone allomembers of the Belle FourcheShale were deposited either as prograding lowstanddeltas (Bhattacharya and Willis, 2001) or as incisedestuarine valley fill (Tillman and Merewether, 1994).Above these sandstone units is a marine floodinghorizon that contains Middle Cenomanian ammonitesof the Thatcher Limestone Member of the GranerosShale in southeastern Colorado (Cobban and Scott,1972; Kauffman et al., 1977). We identified a reduced“Thatcher” fauna with the ammonite, Borissiakocerasreesidei Morrow, and the inoceramids, Inoceramusarvanus Stephenson and Inoceramus eulesanus Ste-phenson, near Frewens Castle and Ampitheater sections,

Fig. 2. Stratigraphic framework of the middle Cretaceous units in the Western Interior showing correlations of lithostratigraphic units with neogastroplitid ammonite zones and bentonites with the agemodel of Hardenbol et al. (1998). Ages in the left column were calibrated by graphic correlation of the Mowrycs.1 database with the global MIDK3 database of Scott et al. (2000). References showinghow the position of the Albian–Cenomanian boundary has fluctuated greatly relative to lithostratigraphy and ammonite zones in the Western Interior are as follow: (1) Reeside and Cobban (1960), (2)Obradovich and Cobban (1975), (3) Cobban and Kennedy (1989), (4) Obradovich (1993) and (5) Kauffman et al. (1993). Hiatuses indicated in the depositional cycles can be seen in Scott et al. (2004Fig. 15).

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Fig. 3. Stratigraphic correlation of the Thermopolis Formation and Mowry Shale in sections measured by Reeside and Cobban (1960, numbers are their section numbers) with the Pike Creek section(PC) in central Montana (Porter et al., 1997) and the Timber Coulee section we measured on the Winnecook Ranch (WR). The base of the Arrow Creek Bentonite (AC) is the datum of six sections; thebase (FO) of Neogastroplites muelleri correlates the Timber Coulee section with the Mowry Shale, which correlates the Big Elk Sandstone with the Clay Spur Bentonite (CS) in the Pike Creek section.The composited scale of samples, which are indicated by horizontal dashes right of weathering profile in sections BB, GY, AC, ARC and TRS that comprise Mowry.3, is in meters; sample positions aremeasured from the top of the Arrow Creek Bentonite to integrate the ammonite occurrences with other species. Ammonite occurrences reported by Reeside and Cobban (1960) and species names areindicated by the spiral symbol; the fossil recovery of this study is indicated by the number of taxa of foraminifera (forams), radiolaria, dinoflagellates (Dinos) and spore–pollen (S-P). Bentoniteradiometric ages are from Obradovich (1993).

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Wyoming (Appendix A). Here the “Thatcher” fauna ismore than 61 m above the Clay Spur Bentonite (Tillmanand Merewether, 1994). About 10 km (6 mi) north of theFrewens Castle outcrop a bentonite in the Belle FourcheShale and 27 m below the “Thatcher” fauna is radio-metrically dated at 95.86±0.45 Ma (Obradovich, 1993,date 26). The Thatcher in Colorado is 0.9 m above abentonite bed that is dated at 95.78±0.61 Ma (Obrado-vich, 1993).

At the Arrow Creek section, we collected a floatspecimen of the Upper Cenomanian zonal ammonite,Metoicoceras mosbyensis Cobban, about 8 m below alenticular bioclastic sandstone channel-fill having thesame matrix as the ammonite. We infer that theammonite weathered from the base of this lenticularbed at 69.4 m in our measured section. This UpperCenomanian zone (Cobban, 1951, 1953, 1984, 1990,1993; Kennedy, 1988; Cobban and Kennedy, 1991) isfound in the Hartland Shale Member of the GreenhornFormation (Kauffman et al., 1993).

3. Material and methods

Two hundred and twenty-four samples from 29sections in Wyoming, central Montana, central andsoutheastern Colorado, northeastern New Mexico andthe Oklahoma panhandle were collected for an inte-grated sequence stratigraphic and biostratigraphic study.The samples were analysed for foraminifers, radiolar-ians, palynomorphs (spores, pollen, dinoflagellates,acritarchs), kerogen (dispersed organic matter) andcarbon isotopes. Megafossils were collected in theThermopolis Formation, Mowry Shale and the MosbySandstone of the Belle Fourche Shale. Sampling wasconcentrated on the siltstones and shales to improve thechances of recovering dinoflagellates and other marinemicrofossils. Facies information from outcrop sectionswas supplemented with photopans of adjacent rockexposures to catalog detailed facies architecture andinterrelationship of discontinuity surfaces in order to putkey sections into lateral context. Samples were pro-cessed using standard techniques for each fossil group(Traverse, 1988; Lipps, 1994), and standard microscopytechniques were used to identify the microfossils.

Fig. 4. Stratigraphic correlation of middle Cretaceous strata in sections measuMontana to southern Wyoming. Our digital file numbers for each sectiondepositional cycles of the sandy member of the Thermopolis Formation.interpolated by graphic correlation. Numbered sequence stratigraphic contaccontact. Our samples having fossil FOs are indicated by: Ag=ApteodiniuCv=Chichaouadinium vestitum, Es=Epelidosphaeridia spinosa, Hd=Hapmanitobensis, Na=Nyssapollenites albertensis, Ov=Ovoidinium verrucoalatum, Tm=Trochamina mellariolum in sections comprising the Mowrycs.

The cosmopolitan dinoflagellates in Europeanreference sections were integrated with the endemicammonites by graphic correlation. This is a quantita-tive technique that determines coeval relationshipsbetween two sections by an X/Y plot of the first andlast occurrence bioevents (FOs and LOs) (Shaw, 1964;Carney and Pierce, 1995). The elements of a graph arethe scaled X/Y axes, tops and bases of the fossils, andthe line of correlation (LOC). The stratigraphermanually positions the LOC so that FOs plot to theleft and LOs to the right, and in order to account fordepositional hiatuses indicated by the lithostratigraphicrecord. However, the position of the LOC is definedby the equation for a regression line. By conventionthe X axis plots the ranges in the database with olderevents on the left and the comparative section on theY axis with older samples on the bottom (Carney andPierce, 1995). In order to integrate the dinoflagellatecyst ranges with the Western Interior ammonite zonesof Late Albian to Lower Cenomanian age, we sampledthe same five key sections in central Montana (ArrowCreek, Ayers Ranch, Belt Butte, Geyser, Teigen) inwhich Reeside and Cobban (1960) defined the Neo-gastroplites zones. The samples were also processedand analyzed for foraminfera and radiolaria. TheThermopolis Formation, Mowry Shale and BelleFourche Shale in the five central Montana sectionswere correlated by the Arrow Creek Bentonite (Fig. 3)and the sample positions were integrated into a singlecomposite section, Mowry.3 (Appendix B), by theirspacing relative to the Arrow Creek Bentonite Bed.This section, in turn, was correlated with the PikeCreek, Winnecook Ranch, Muddy Creek, FrewensCastle, Arminto and Alcova sections by the Clay SpurBentonite (Figs. 1 and 4). The Pike Creek section wasused as the scale of this database, Mowrycs.1(Appendix C). Short sections from which only spotsamples were collected could not be graphed: NorthTeigen Ranch, South Teigen Ranch, LimestoneSchool, the Amphitheater and the Hams Fork sections(Fig. 4). Finally, the Western Interior data werecorrelated with bioevents in European and NorthAfrican reference sections (Appendix D), wherebiozones define the stage and substage boundaries

red by Eicher (1960, 1965), Porter et al. (1997) and by us from centralare Mowry.1, 2, 3, 12, 13 and 14. Porter et al. (1997) defined theBentonite radiometric dates are from Obradovich (1993); other agests from Scott et al. (2004): SB=sequence boundary, TS=transgressivem grande, Bj=Batioladinium jaegeri, Ca=Circulodinium asperum,socysta dictyota, La=Litosphaeridium arundum, Mm=Miliamminasum, Pi=Palaeohystrichophora infusorioides, Xa=Xiphophoridium1 database.


(Fiet and Masure, 2001; Monteil in Hardenbol et al.,1998; Williams et al., 2004; Brinkhuis et al., 2004).

4. Results and discussion

4.1. Sequence stratigraphy

The base of the Fall River Formation and the base ofthe unnamed sandy member of the ThermopolisFormation are sequence boundaries, and a third sequenceboundary occurs within the Belle Fourche Shale (Fig. 4)(Porter et al., 1993, 1997). The basal Fall RiverFormation sequence boundary is in the same strati-graphic position as the sequence boundary at the base ofthe Plainview Sandstone in Colorado, SB2 (Holbrookand Wright Dunbar, 1992; Scott et al., 2001), and theymay be synchronous. The sequence boundary betweenthe Skull Creek Shale and unnamed sandy member isprobably equivalent to the disconformity at the base ofthe Muddy Sandstone in Colorado, SB3 (Holbrook andWright Dunbar, 1992; Scott et al., 2001), and SB3.1 atthe base of the Lower Mesa Rica Sandstone member insoutheastern Colorado, Oklahoma panhandle and north-eastern New Mexico (Scott et al., 2004).

The unnamed sandy member of the ThermopolisFormation in the Pike Creek section represents aregional lowstand depositional phase recognizable in anorth-to-south transect of Montana (Porter et al.,1997). This lowstand event has been correlated withthe lowstand in Wyoming and Colorado representedby the Muddy Sandstone and in Alberta and BritishColumbia by the Viking Sandstone. Central Montanawas near the center of the depositional basin, whichremained marine during this lowstand event, whilesubaerial exposure and incised valleys formed in theneighboring marginal areas (Dolson et al., 1991;Porter et al., 1997). The sandy member consists offive smaller scale (10 to 22 m thick) depositionalcycles that are defined by thick intervals of shale withironstone concretions capped by thin sandstone beds(Fig. 4). The sandstone beds are bioturbated and ripplelaminated. The shales contain moderately diverseassemblages of Late Albian nearshore marine dino-flagellates (Porter et al., 1997). The age of thislowstand event represented by SB3 in Montana andnorthern Wyoming is Late Albian. The basal SkullCreek Shale is about 104.4 to 100.9 Ma and theoverlying Shell Creek Shale is about 99.25 to98.19 Ma (Obradovich et al., 1996). The ArrowCreek Bentonite overlies the Shell Creek Shale and isdated at 98.52±0.41 Ma (Obradovich, 1993 from theArrow Creek section, AC, Fig. 3). The sandy member

correlates with the Newcastle Sandstone in the BlackHills of South Dakota, which is about 98.94 Ma, andwith the Muddy Sandstone in northern Wyoming,which is dated about 100.6 to 100.3 Ma (Obradovichet al., 1996). The ages of strata bounding SB3 inColorado, New Mexico and Kansas are consistentwith the radiometric dates and are dated about 100 Maand 98 Ma, respectively, by graphic correlation with aglobal chronostratigraphic database (Scott et al., 1994,1998, 2000, 2001, 2004).

4.2. Dinoflagellate cysts

Late Albian extinction bioevents and Early Ceno-manian first appearance bioevents common to WesternEurope, North Africa and in the Western Interior Basinare the most diagnostic criteria of the Albian–Cenoma-nian boundary. Only species of dinoflagellates cysts arecurrently known to meet these requirements sincebenthic foraminifers, inoceramids and neogastroplitidammonites are endemic, and radiolaria are long ranging.Traditionally endemic neogastroplitid ammonites definethe biostratigraphic framework of Upper Albian–LowerCenomanian strata in the U.S. (Reeside and Cobban,1960; Kauffman et al., 1993). However, Albian–Cenomanian dinoflagellate zonal species of Europe arealso found in North America (Hardenbol et al., 1998;Fiet and Masure, 2001; Williams et al., 2004; Brinkhuiset al., 2004). Distinct spore and pollen assemblages haveregional stratigraphic utility in the Western Interior, andtheir ages are determined by the inferred ammonitecorrelations (Nichols, 1994). Albian–Cenomanian radi-olarians occur in the Mowry Shale, but do not define theboundary precisely.

The diversity of dinoflagellate cysts varies from lowto moderate, and they are poorly to well preserved (Fig.5). Fifty-five taxa were identified in the five centralMontana sections, and 117 taxa were found in the otherMontana and Wyoming sections that comprise Mow-rycs.1. Although many species are long ranging, somespecies became extinct close to the Albian–Cenomanianboundary as defined by ammonites in Europe, and a fewspecies first appeared during the Late Albian (Fig. 6).No FOs are recognized at the base of the Cenomanian inEurope. Several biostratigraphically significant specieshave been used to correlate the composite sections (Fig.6). The Western Interior ranges are generally similar tothose in Western Europe and North Africa, althoughsome bioevents are somewhat older in North Americaand some are slightly younger because of differences insample spacing, preservation, environments and perhapsmigration delays. Likewise, the FOs and LOs of some

Fig. 5. Selected biostratigraphically useful dinoflagellate cyst (A–G) and cyanobacteria (H) taxa used for correlation. (A) Chichaouadinium vestitum(Brideaux 1971) Bujak and Davies 1983; (B) Pseudoceratium interiorense Bint 1986; (C) Luxadinium propatulum Brideaux and McIntyre 1975; (D)Ovoidinium scabrosum (Cookson and Hughes 1964) Davey 1970; (E) Ovoidinium verrucosum (Cookson and Hughes 1964) Davey 1970; (F)Palaeohystrichophora infusorioides Deflandre 1935; (G) Florentinia resex Davey and Verdier 1976; (H) Tetranguladinium conspicuum YuJingxian et al. 1983. Fensome and Williams (2004) consider T. conspicuum a zygospore of cyanobacteria.


species vary between Boreal and Tethyan Europe(Verdier, 1975; Monteil in Hardenbol et al., 1998;Brinkhuis et al., 2004).

The FOs of Palaeohystichophora infusorioides, Ap-teodinium grande and Epelidosphaeridia spinosa are

Late Albian in Europe, and are near the base of thesandy member of the Thermopolis Formation at PikeCreek (Fig. 6). At Muddy Creek, Wyoming, P.infusorioides is at the top of the Thermopolis Formationand the other species are in the basal Shell Creek Shale

Fig. 6. Ranges of selected dinoflagellate cyst taxa in the Skull Creek, Muddy, Shell Creek, Mowry and Belle Fourche lithostratigraphic units (inmeters thickness) comprising the Mowrycs.1 database in Montana andWyoming. Selected events are noted at margin and identified among the rangesby “V”.


Formation. All three species overlap the FO of Neo-gastroplites cornutus in the Thermopolis Formation.Xiphophoridium alatum appears in the upper part of theThermopolis sandy member at Pike Creek, and inEurope this species first appears in the lower part of theLate Albian. The FO of Ovoidinium verrucosum, whichspans the Albian–Cenomanian boundary in Europe,occurs in the Mowry Shale above the Arrow CreekBentonite within the ranges of Neogastroplites muelleri,Neogastroplites americanus and Neogastroplitesmaclearni; its LO occurs in the lower part of the BelleFourche Shale. The FOs of Dinopterygium cladoidesand Hapsocysta dictyota respectively mark the base of

the latest Late Albian in Italy, and they both occur in theMowry Shale. The LOs of Litosphaeridium arundum,Aptea polymorpha, Apteodinium grande and Chi-chaouadinium vestitum are generally considered tomark the top of the Albian (Verdier, 1975; Williams etal., 2004; Brinkhuis et al., 2004), as does the LO ofBatioladinium jaegeri (Williams and Bujak, 1985). InMontana and Wyoming, the LOs of these species occurat the Clay Spur Bentonite or a few meters above (Fig.6). However, L. arundum locally ranges into the basalCenomanian in the Western Interior and U.S. Gulf coast(Williams et al., 1993; Scott et al., 2003). Another latestAlbian marker species is Ovoidinium scabrosum (Fiet


and Masure, 2001; Monteil in Hardenbol et al., 1998),which ranges from the Thermopolis Formation to lowerBelle Fourche Shale in Montana and Wyoming.

4.3. Graphic correlation

The dinoflagellate ranges in the 11 Montana andWyoming sections (Mowrycs.1) were compared with

Fig. 7. Graphic correlation plot of the Mowrycs.1 composited Montana and WFoucher and Monteil in Hardenbol et al. (1998). FOs plot as□ and LOs plot aboundary as defined by European ammonites, whose FOs are shown aboveammonite zones. The rectangle at base of Arrow Creek shows the thickness oMontana Neogastroplitid ammonites and how they project into the European zEarly Cenomanian.

the dinoflagellate ranges in Europe (Hardenbol et al.,1998) where the Cenomanian base is defined byammonites and foraminifers. We tested which dino-flagellate bioevents have the same relative positions inboth regions (Fig. 7), and then correlated the Albian–Cenomanian boundary in Europe into the WesternInterior. Graphic correlation of these two range chartscorrelate the radiometrically dated Clay Spur Bentonite

yoming sections compared with the European dinoflagellate ranges ofs +. LOC A projects the Clay Spur Bentonite at the Albian/Cenomanian. LOC B projects the Arrow Creek Bentonite into basal Cenomanianf the bentonite and the error bar of the radiometric age. Note position ofones by each LOC. By LOCA, all are Late Albian; by LOCB, most are


(97.17±0.69 Ma) near the base of the Mantellicerasmantelli Zone in Europe and the Arrow Creek Bentonite(98.52±0.41 Ma) with the Stoliczkaia dispar Zone.

Two correlation interpretations are indicated byLOCs A and B, both of which imply uniform andcontinuous deposition (Fig. 7). If the neogastroplitidzones are Albian, LOC A applies and the Clay SpurBentonite correlates with the base of the Mantellicerasmantelli Zone at the base of the Cenomanian. LOC A isconstrained by the FOs of Apteodinium grande and Xi-phophoridium alatum and the LOs of Hystricho-sphaeridium schindewolfii, Batioladinim jaegeri,Luxadinium propatulum, Litosphaeridium siphoni-phorum and Psaligonyaulax deflandrei. The LOs ofChichaouadinium vestitum, Ovoidinium verrucosumand Oligosphaeridium totum plot left of LOC A in thelower Belle Fourche Shale and below the MiddleCenomanian Thatcher Limestone Member, so theseranges would be extended into the Early Cenomanian.

If the younger three neogastroplitid zones areCenomanian, then LOC B will apply and the ArrowCreek Bentonite correlates with the base of theCenomanian dated at 98.9 Ma by Hardenbol et al.(1998). LOC B is constrained by the FOs of Chi-chaouadinium vestitum, Luxadinium propatulum,Palaeohystrichophora infusorioides, Ovoidiniumverrucosum and Epeilidosphaeridium spinosa, andthe LO of Litosphaeridinium arundum. However, LOCB would project the LOs of three dinoflagellates intothe Middle Cenomanian, which is higher than reported.If the age of the Albian–Cenomanian is 99.6 Ma(Gradstein et al., 2004), then the mega-annum scale onthe X axis simply must be shifted right to the base of theMantelliceras mantelli Zone and the ages of other zonesshifted proportionately.

A third interpretation is constrained by twoadditional datums: the age of the Thatcher LimestoneMember at 95.78 Ma (Obradovich, 1993) and the ageof the Skull Creek Shale from about 104 to 101 Ma(Obradovich et al., 1996; Scott et al., 1998). This thirdLOC has a lower/older segment that is steeper than thehigher/younger segment, which implies that the rate ofsediment accumulation was greater during depositionof the sandy member, Dakota Sandstone-equivalent,than during deposition of the lower Belle FourcheShale. This alternative LOC hypothesis places mostFOs at its base to the left and at its top key LOswould be extended only into the Early Cenomanian.Also it would be consistent with regional correlationof the Skull Creek with the early part of the UpperAlbian as well as with other radiometric ages. The LOof Batioladinim jaegeri at the top of the Mowry Shale

correlates the Clay Spur Bentonite with the top of theStoliczkaia dispar Zone in Europe.

Both interpretations LOC A and B (Fig. 7) indicatethat some bioevents have similar ranges in the WesternInterior and Europe. However, four LOs are somewhatyounger in the Western Interior than in Europe: Hy-strichosphaeridium schindewolfii, Oligosphaeridiumtotum, Ovoidinium verrucosum, Chichaouadinium ves-titum and Apteodinium grande, and the FO of Odon-tochtinia costata is older in the Western Interior Basinthan in Europe.

This graphic correlation interpretation projects thebasal Cenomanian ammonite zone, Mantellicerasmantelli, into the lower part of the Belle FourcheShale. Graphic correlation also correlates the youngerthree neogastropilitid ammonite zones in the WesternInterior with the uppermost Albian Stolickzkaia disparZone in Europe dated here at 98.52–97.12 Ma. Finally,Metengonoceras aspenanum and Metengonoceras tei-genensis in the Western Interior Mowrycs.1 section arebelow the Clay Spur Bentonite at 181.6–204.3 m and194.5–195.7 m, respectively; the latter species alsooccurs with lowermost Cenomanian ammonites inFrance (Amédro et al., 2002), suggesting that thegenus originated in North America and migrated toEurope.

5. Concluding remarks

Dinoflagellate cysts currently provide the onlyavailable bioevents common to the Upper Albian toLower Cenomanian sections in the U.S. WesternInterior Basin and European and North Africanreference sections, and have been used to re-evaluatethe Albian–Cenomanian boundary in the WesternInterior. They were recorded in several key Montanaand Wyoming sections with defined ammonite zones.The dinoflagellate taxa were integrated with ammo-nites, foraminifers and radiolarians for graphiccorrelation, and support the original correlation ofthe Clay Spur Bentonite at the Albian–Cenomanianboundary as defined in France (97.0 Ma). Thisplacement is supported by the LOs of Apteapolymorpha, Apteodinium grande, Chichaouadiniumvestitum, Luxadinium propatulum, Batioladiniumjaegeri and Ovoidinium scabrosum in the top ofthe Mowry Shale and basal Belle Fourche Shale. Thealternative correlation of the base Cenomanian at theArrow Creek Bentonite would require that the rangesof six cosmopolitan species be extended muchyounger into the Cenomanian in the Western Interiorthan in Europe.


Acknowledgements

We thank C. Hemleben for processing radio-laria, W.A. Cobban for identifying ammonitesused in our database, and Stacy Story for helping

review the figures and revised manuscript. Thisstudy was funded by National Science Foun-dation grants to F.E. Oboh-Ikuenobe (EAR-9909199), R.W. Scott (EAR-9909601) and J.M.Holbrook (EAR-9909197).

Appendix A

Locations of measured sections. Number after section name indicates its data in Mowrycs.1 or Mowry.3 databases.R&C=Mowry Section number in Reeside and Cobban (1960). MT=Montana, WY=Wyoming, Co.=county.

Map initial
Name Lat./long. UTM Description
AC
Arrow Creek, MT-3; R&C#14 N47.3123, W110.4287 12 543051E, 5239897N NE1/4 NE1/4, Sec. 22, T18N, R10E AL Alcova, WY-1 N42.5329°, W106.70.23° 13 360203E, 4710342N NE NE NE Sec. 31, T30N, R82W AR Arminto, WY-1 N43.2511°, W107.2253° 13 319356E, 4791105N N1/2 Sec. 24, T38N, R87W ARC Ayers Ranch. MT-3; R&C#18 N47.0659, W108.9372 N47.0659, W108.9372 SW1/4 NE1/4, Sec. 16, T15N, R22E BB Belt Butte, MT-3; R&C#12 N47.3810, W110.8813 12 508960E, 5247292N SE1/4, Sec. 30, T19N, R7E FC Frewens Castle-1, WY N43.5583, W106.6185 13 369273E, 4823872N SE SE Sec. 31, T42N, R81W GY Geyser, MT-3; R&C#13 N47.2864, W110.4901 12 538556E, 5236901N SE1/4, Sec. 30 and NW1/4
NW1/4, Sec. 29, T18N, R10E
HF Hams Fork, WY N41.7426, W110.5037 12 541268E, 4621103N N1/2, SE, Sec. 3 T21N R116W LS Limestone School,
MT; R&C#10
N45.4609, W109.9084 UTM 12 585344E, 5034514N N1/2 SW1/4 NW1/4 Sec. 29, T4S, R15E
MC
Muddy Creek, WY-1 N44.1780, W106.7887 13 356646E, 4893328N NE Sec. 36, T49N, R83W MP Ampitheater, Johnson Co.,
WY-1
N43.6071, W106.6433 13 365500E, 4829700N CNW Sec. 14, T42N, R82W
NTR
North Tiegen Ranch, MT N47.0024, W108.5569 12 685731E, 5208108N CNL Sec. 19, T15N, R25E PC Pike Creek, MT-1 N46.8577°, W108.5536° 12 686475E, 192256N C E1/2 Sec. 28, T13N, R25E TRS Teigen Ranch, MT-3; R&C#20 N47.0024, W108.5569 12 685731E, 5208108N C, Sec. 4, T14N, R25E TR Teigen Ranch South,
MT-1; R&C#19
N47.0188°, W108.5966° 12 0682651, 5210059 SW NE Sec. 31, T15N, R25E
WR
Winnecook Ranch-1,MT; R&C#11
N46.3661, W109.6847
12 601172E, 5135347N SE and SW and NW Sec. 14, T7N, R16E
Appendix B

FOs and LOs of taxa in composited Mowry.3 section,Montana. Sections measured and collected by Reesideand Cobban (1960) and re-described and collected bythe authors in 2000 (refer to Fig. 3): 12-Belt Butte (BB),13-Geyser (GY), 14-Arrow Creek (AC), 18-Ayers (AY),19-Teigen Ranch (TR) and 20-Teigen Ranch South(TRS). Sample positions in each section calibrated totop of Arrow Creek Bentonite at 70.1 m at GeyserMontana. Thermopolis Formation −3 to 61.1 m; ArrowCreek Bentonite Bed 61.1–71.0 m; base Mowry Fm.71.0 m; Clay Spur Bentonite in section 19-Teigen at114.1–114.5 m. Arrow Creek Bentonite near Geyserdated at 98.52±0.41 Ma (Obradovich, 1993).

Foraminifera data by M.J. Evetts 01/01/02
Base/top (m) Ammobaculites impexus? 10.2 24.0 Ammobaculoides sp. cf. A. phaulus 80.5 80.5 Haplophragmoides sp. cf. H. multiplum 80.5 80.5
Haplophragmoides linki
80.5 80.5 Haplophragmoides sp. cf. H. gilberti 10.2 93.1 Miliammina ischnia 2.0 80.5 Miliammina manitobensis 2.0 80.5 Saccammina alexanderi 2.0 24.0 Saccammina lathrami 2.0 2.0 Trochammina gatesensis 10.2 24.0 Trochammina wetteri? 80.5 80.5 Verneuilina canadensis 10.2 24.0 Verneuilinoides hectori 10.2 10.2 Verneuilinoides perplexus 2.0 80.5 Clathrocyclas irrasa 80.5 99.3
Radiolaria data by J. Erbacher 29/05/02
Dactyliosphaera maxima? 76.5 76.5 Dactyliosphaera acutispina? 76.5 76.5
Ammonite data from Reeside and Cobban (1960) and R.W. Scott
Inoceramus n. sp. 84.5 84.5 Metengenoceras aspenanum 83.1 106.7 Metengonoceras teigenensis 96.5 97.8 Metoicoceras mosbyensis 122 122
(continued on next page)


Appendix B (continued)

(ID by W. Cobban, 2000; collected as float)
Neogastroplites americanus 84.5 84.5 Neogastroplites cornutus −3.0 71.2 Neogastroplites muelleri 83.1 99.1
Dinoflagellate cyst data by D.G. Benson 01-01-02
Aptea attadalica 16.9 16.9 Apteodinium grande 76.6 76.6 Apteodinium granulatum? 114 114 Batioladinium jaegeri 18.4 80.5 Caligodinium aceras 18.4 111.6 ID as Kalyptea Canninginopsis colliveri 53.6 111.6 Canningia microciliata 84.1 114 Canningia sp. cf. C. reticulata 2 2 Cassiculosphaeridia reticulata 2 18.4 Chichaouadinium boydii 18.4 80.5 Chichaouadinium vestitum 2 80.5 Cleistosphaeridium aciculare 18.4 99.2 Cribroperidinium edwardsii 16.9 111.6 Cribroperidinium exilicristatum 2 80.5 Cribroperidinium intricatum 2 2 Cribroperidinium muderongense 89.1 99.2 Cyclonephelium brevispinatum 84.1 93.1 Dingodinium cerviculum 2 18.4 Florentina abbreviata 89.1 89.1 Florentinia berran 99.6 99.6 Florentinia cooksoniae 16.9 111.6 Florentinia sp. cf. F. laciniata 16.9 18.4 Florentinia mantellii 111.6 111.6 Florentinia sp. cf. F. resex 85.8 89.5 Ginginodinium evittii 53.6 89.5 Hystrichodinium pulchrum 85.8 85.8 Hystrichosphaerina schindewolfii 53.6 89.5 Litosphaeridium arundum 18.4 85.8 Luxadinium propatulum 16.9 80.5 Odontochitina sp. cf. O. rhakodes 76.6 76.6 Odontochitina operculata 53.6 111.6 Oligosphaeridium albertense 16.9 111.6 Oligosphaeridium anthrophorum 53.6 111.6 Oligosphaeridium complex 53.6 111.6 Oligosphaeridium pulcherrimum 18.4 111.6 Ovoidinium scabrosum 73.1 111.6 Ovoidinium verrucosum 73.1 114 Palaeohystrichophora infusorioides 24 99.2 Palaeoperidinium cretaceum 18.4 89.5 Pervosphaeridium truncatum 18.4 18.4 Pseudoceratium eisenackii 16.9 111.6 Pseudoceratium expolitum 16.9 20.7 Pseudoceratium securigerum 16.9 16.9
Pterospermella australiensis
10.2 76.6 Pterospermella harti 24 111.6 Spinidinium echinoideum 24.0 89.5 Spiniferites cingulatus 89.1 111.6 Spiniferites sp. cf. S. membranaceus 16.9 16.9 Spiniferites twistringiensis 53.6 93.1 (ID as Spiniferites ramosus multibrevis) Stiphrosphaeridium anthophorum (ID Oligosph.) 18.4 111.6 Subtilisphaera perlucida 24 24 Surculosphaeridium phoenix 73.1 93.1 Trichodinium cf. brevispinosum 2 2 Wrevittia cassidata (ID as Gony.) 16.9 16.9 Xenodiscus sp. cf. X. plotei 99.6 99.6
Miospore data by D.G. Benson 01-01-02
Acanthotriletes varispinosus 16.9 111.6 Appendicisporites spinosus 18.4 18.4 Appendicisporites sp. cf. A. tricornitatus 99.2 99.2 Asteropollis asteroides 20.7 20.7 Baculatisporties comaumensis 16.9 111.6 Camarozonosporites insignis 80.5 99.2 Cerebropollenites mesozoicus 2 114 Cicatricosisporites brevilaesuratus 16.9 76.6 Cicatricosisporites hallei 16.9 80.5 Classopollis classoides 24 111.6 Classopollis simplex 2 99.6 Clavifera triplex 2 93.1 Costatoperforosp. foveolatus 16.9 108.8 Cyathidites australis 2 114 Cyathidites minor 2 114 Desmocysta sp. cf. D. plekta 18.4 80.5 Dictyophyllidites harrisii 18.4 111.6 Distaltriang. mutabilis 16.9 76.6 Distaltriangulisporites perplexus 76.6 80.5 Gleicheniidites circiniidites 2 114 Gleicheniidites senonicus 2 111.6 Inaperturopollenites hiatus 2 114 Laevigatosporites gracilis 18.4 108.8 Leiofusa jurassica 99.6 99.6 Lycopodiumsp. austroclavatidites 18.4 58.1 Lycopodiumsp. reticulumsporites 16.9 16.9 Ornamentifera echinata 18.4 76.6 Osmundacidites wellmanii 18.4 85.8 Pilosisporites trichopappilosus 16.9 16.9 Rubinella major 16.9 16.9 Schizosporis reticulates 80.5 80.5 Stereisporites antiquasporites 18.4 53.6 Tigrisporites reticulates 80.5 80.5 Todisporites minor 16.9 58.1 Vitreisporites pallidus 16.9 114.9
Appendix C

FOs and LOs of taxa in Mowrycs.1 composited database of nine sections in Montana and Wyoming (Figs. 3and 4, Appendix A). Scale in meters in Pike Creek section (Fig. 4), Grassrange Area, Montana (Porter et al., 1997).Top Kootenai Fm. at 6.7 m; top Fall River Fm. at 13.4 m; top Skull Creek Sh. at 66.4 m; top sandy member at160.8 m; top Shell Creek Sh.= top Thermopolis Sh. at 192.0 m; top Mowry Sh. at 212.3 m; top of section in BelleFourche Sh. at 222 m. Mega-annums calibrated from MIDK3 global database, which combines Western Interior


sections with those of MIDK3 (Scott et al., 2000). Ranges of some taxa in MIDK3 may not be the same as knownmaximum ranges because the included sections may not span the maximum time. Blank entries indicate species notin MIDK3 database.

Taxa
Pike CreekFO (m)
Pike CreekLO (m)

MIDK3 DatabaseFO (Ma)

(contin

MIDK3 DatabaseLO (Ma)

Acanthotriletes varispinosus
66.300 208.950 101.887 88.441 Ammobaculites euides 141.609 85.802 146.312 96.956 Ammobaculites impexus 111.775 339.043 97.018 93.861 Ammobaculites mosbyensis 341.006 368.914 93.876 92.467 Ammobaculites obliquus 146.044 146.312 100.398 96.495 Ammobaculoides phaulus 145.777 179.146 97.090 96.495 Ammobaculoides plummerae 332.486 340.500 97.090 93.823 Ammobaculoides whitneyi 146.312 146.312 100.380 100.011 Appendicisporites jansonii 165.047 175.656 99.202 99.089 Appendicisporites spinosus 119.633 119.633 99.184 99.184 Appendicisporites unicus 159.694 166.653 100.377 95.529 Aptea attadalica 118.196 213.613 100.398 97.190 Aptea polymorpha 66.300 227.330 124.494 96.393 Apteodinium grande 146.044 302.388 113.543 89.404 Apteodinium granulatum 207.926 211.250 124.490 91.761 Apteodinium maculatum 200.333 243.762 132.774 95.834 Apteodinium reticulatum 66.300 69.700 113.727 95.262 Asteropollis asteroides 121.838 125.408 97.976 97.975 Baculatisporties comaumensis 109.700 224.968 100.690 96.867 Batioladinium jaegeri 117.885 213.700 116.207 96.393 Batioladinium micropodum 66.300 66.300 121.531 101.887 Borissiakoceras reesidei 320.810 321.063 95.341 93.927 Bourkidinium psilatum 159.694 159.694 99.488 96.393 Caligodinium aceras 117.885 221.521 112.22 96.76 Callialasporites dampierii 145.025 145.320 97.867 97.865 Camarozonosporites insignis 179.146 209.206 101.748 97.43 Canningia microciliata 182.596 211.250 Canningia reticulata 103.917 240.407 123.026 96.62 Canninginopsis colliveri 66.300 261.921 133.695 90.250 Cassiculosphaeridia reticulata 103.917 249.266 132.202 89.404 Catastomosystis spinosa 221.300 221.300 98.959 96.985 Cavaspongia euganea 221.521 221.521 96.762 96.762 Cerebropollenites mesozoicus 103.917 213.400 100.715 97.001 Chichaouadinium boydii 119.633 214.821 99.184 97.108 Chichaouadinium vestitum 66.300 298.457 109.836 94.839 Chlamydophorella discreta 219.737 219.906 118.916 90.771 Chlamydophorella nyei 66.300 261.921 129.069 90.778 Cicatricosisporites brevilaesuratus 118.196 175.656 101.760 98.049 Cicatricosisporites hallei 66.300 261.921 101.887 96.279 Circulodinium asperum 204.300 213.613 100.817 97.488 Circulodinium distinctum 195.271 261.921 133.695 88.775 Classopollis classoides 117.885 243.782 101.760 96.568 Classopollis simplex 103.917 242.000 101.031 96.416 Clathrocyclas irrasa 125.408 221.521 98.757 96.762 Clavatipollenites hughesii 69.700 218.041 101.793 94.109 Clavifera triplex 103.917 221.521 100.715 96.762 Cleistosphaeridium aciculare 117.885 197.067 100.398 97.535 Coronifera albertii 221.300 221.300 124.487 96.985 Coronifera oceanica 179.232 211.618 119.445 89.404 Costatoperforosp. foveolatus 111.100 299.383 100.651 95.623 Cribroperidinium cooksoniae 197.633 197.802 133.695 95.564 Cribroperidinium edwardsii 66.300 208.950 133.695 89.414 Cribroperidinium exilicristatum 66.300 258.884 102.129 90.693 Cribroperidinium intricatum 103.917 103.917 112.59 90.778
ued on next page)


Appendix C (continued)

Taxa
Pike CreekFO (m)
Pike CreekLO (m)



Cribroperidinium muderongense
117.885 221.300 133.695 96.403 Cyathidites australis 103.917 262.765 101.760 96.265 Cyathidites minor 66.300 290.128 101.887 95.751 Cyclonephelium brevispinatum 182.596 191.221 133.695 95.548 Cyclonephelium compactum 202.864 261.921 113.543 93.672 Cyclonephelium distinctum 66.300 191.600 101.887 96.403 Cyclonephelium membraniphorum 249.266 390.777 98.287 89.404 Cyclonephelium paucispinum 117.885 213.318 114.896 95.743 Dactyliodiscus lenticulatus 202.695 202.864 97.222 97.219 Dactyliosphaera acutispina 175.313 211.250 97.998 97.998 Dactyliosphaera maxima 175.312 211.618 97.222 97.190 Desmocysta plekta 119.633 179.146 Diconodinium pusillum 118.300 118.300 111.978 100.453 Dictyophyllidites harrisii 119.633 208.339 Dingodinium cerviculum 66.300 211.618 121.531 96.441 Dinogymnium albertii 247.579 247.747 133.695 89.414 Dinopterygium cladoides 118.563 399.291 103.752 89.723 Dinopterygium reticulatum 179.800 221.300 98.757 96.985 Dinopterygium tuberculata 210.710 211.132 99.926 94.264 Distaltriang. mutabilis 118.196 180.943 99.215 97.993 Distaltriangulisporites perplexus 66.300 260.511 124.487 89.414 Downiesphaeridium multispinosum 66.300 258.884 106.479 94.633 Ellipsodinium imperfectum 158.142 210.710 112.744 97.094 Ellipsodinium rugulosum 210.710 211.132 98.317 88.785 Epelidosphaeridia spinosa 129.828 358.142 102.044 90.467 Eurydinium glomeratum 183.129 390.777 97.936 89.877 Florentina abbreviata 187.388 196.297 101.748 97.297 Florentinia berran 186.800 210.919 99.491 97.225 Florentinia cooksoniae 66.300 213.400 114.201 90.693 Florentinia deanei 73.500 399.291 113.917 88.441 Florentinia laciniata 118.196 206.714 99.215 89.404 Florentinia mantellii 208.950 399.291 116.062 89.723 Florentinia radiculata 261.921 262.090 122.719 90.651 Florentinia resex 118.563 399.291 122.617 89.723 Fromea amphora 66.300 258.884 212.254 89.404 Fromea fragilis 224.968 240.407 111.715 90.693 Fromea glabella 71.200 242.926 101.751 94.708 Ginginodinium evittii 66.300 276.465 102.129 95.898 Gleicheniidites circiniidites 103.917 262.765 101.748 96.160 Gleicheniidites senonicus 66.300 269.766 101.887 96.032 Glomospira glomerosa 169.597 169.597 99.005 98.509 Gubkinella graysonensis 219.906 222.268 129.154 95.339 Haplophragmoides gilberti 247.496 286.459 Haplophragmoides linki 132.045 179.146 104.636 96.956 Haplophragmoides multiplum 132.045 179.146 98.509 98.045 Haplophragmoides uniorbis 103.917 183.129 100.816 97.936 Hapsocysta dictyota 207.926 232.392 100.111 94.264 Hedbergella delrioensis 157.777 368.914 128.914 88.507 Hedbergella planispira 207.294 368.914 123.981 88.298 Heterohelix globulosa 156.851 157.777 97.594 88.298 Hystrichodinium pulchrum 174.386 184.225 121.531 97.505 Hystrichosphaerina schindewolfii 153.367 187.771 124.892 97.786 Inoceramus arvanus 320.810 330.501 95.398 94.809 Inoceramus athabaskensis 150.400 160.200 99.567 99.297 Inoceramus eulesanus 320.810 321.063 95.369 95.337 Involutina kansasensis 145.777 146.312 100.416 100.380 Isabelidinium globosum 219.737 219.900 96.951 90.693 Ischyosporites crateris 69.700 205.862 101.793 96.767


Januasporites spiniferus
66.300 118.563 102.543
(contin

100.583
Kalyptea aceras 179.800 213.400 101.760 97.155 Kiokansium corollum 262.765 262.934 100.11 94.205 Kiokansium polypes 261.921 262.090 119.444 90.251 Kiokansium unituberculatum 141.227 146.044 114.277 93.672 Kleithriasphaeridium eoinodes 117.590 117.890 132.774 95.564 Laevigatosporites gracilis 119.633 209.403 Leberidocysta chlamydata 207.757 207.926 111.242 89.404 Lecaniella foveata 136.409 172.274 101.031 94.031 Leiofusa jurassica 197.450 210.919 99.244 94.031 Litosphaeridium arundum 69.700 211.618 113.543 97.086 Litosphaeridium siphoniphorum 302.388 Luxadinium primulum 71.200 302.388 101.751 95.030 Luxadinium propatulum 66.300 235.918 102.129 96.344 Lycopodiumsp. austroclavatidites 111.100 240.576 100.651 96.619 Lycopodiumsp. reticulumsporites 118.196 118.196 99.215 99.215 Lycopodiumsporites marginatus 66.300 211.618 129.135 97.190 Marker bed “X” Bentonite 345.552 347.175 93.797 93.606 Marker bed Arrow Creek Bentonite 160.554 170.042 98.313 98.100 Marker bed Clay Spur Bentonite 211.300 212.313 97.201 96.974 Marker bed Thatcher Mbr. 320.810 322.799 95.400 93.410 Metengenoceras aspenanum 181.638 204.254 97.855 97.651 Metengonoceras teigenensis 194.479 195.725 97.572 97.508 Micrhystridium inconspicuum 71.000 71.200 101.747 91.383 Microdinium crinitum 150.800 150.800 99.556 90.778 Miliammina inflata 141.227 164.067 100.715 100.112 Miliammina ischnia 103.917 247.496 101.084 96.127 Miliammina manitobensis 103.917 217.936 102.828 96.749 Muderongia asymmetrica 66.300 276.465 118.193 94.732 Neogastroplites americanus 182.979 183.375 97.835 97.655 Neogastroplites cornutus 104.875 170.233 99.540 98.108 Neogastroplites maclearni 184.850 221.725 97.647 97.443 Neogastroplites muelleri 146.500 196.971 97.858 97.572 Nyssapollenites albertensis 66.300 118.300 101.887 96.408 Odontochitina costata 66.300 150.800 101.887 88.775 Odontochitina operculata 117.885 234.923 124.494 89.404 Odontochitina rhakodes 118.562 175.408 112.590 98.548 Odontochitina singhii 146.514 206.714 113.543 96.318 Oligosphaeridium albertense 117.885 291.053 133.695 89.414 Oligosphaeridium anthrophorum 117.885 213.400 98.433 97.001 Oligosphaeridium complex 69.700 261.921 133.695 89.404 Oligosphaeridium pulcherrimum 66.300 213.400 133.695 89.404 Oligosphaeridium totum 66.300 262.090 116.666 95.529 Ornamentifera echinata 119.633 175.656 99.184 98.049 Osmundacidites wellmanii 109.700 213.612 100.690 97.488 Ovoidinium scabrosum 155.055 247.578 115.246 96.045 Ovoidinium verrucosum 125.407 276.464 98.944 94.734 Palaeohystrichophora infusorioides 69.700 342.883 102.069 88.441 Palaeoperidinium cretaceum 66.300 258.884 124.490 94.642 Pareodinia ceratophora 66.300 214.675 112.999 96.393 Perinopollenites sp. cf. P. elatoides 66.300 69.700 101.887 100.274 Pervosphaeridium cenomaniense 167.456 208.674 112.380 97.317 Pervosphaeridium pseudhystrichodinium 235.092 261.921 113.926 89.404 Pervosphaeridium truncatum 119.633 262.08 90,132.774 95.553 Pilosisporites trichopappilosus 118.196 276.464 102.543 95.898 Prolixosphaeridium conulum 258.884 376.588 100.480 89.404 Protoellipsodinium touile 224.799 224.968 132.202 96.867 Psaligonyaulax deflandrei 376.588 387.939 Pseudobolivina variana 145.776 308.443 100.416 93.443 Pseudoceratium anaphrissum 123.221 204.300 133.695 97.286 Pseudoceratium eisenackii 71.200 258.884 124.494 95.295
ued on next page)


Appendix C (continued)

Taxa
Pike CreekFO (m)
Pike CreekLO (m)



Pseudoceratium expolitum
117.885 302.388 113.543 95.614 Pseudoceratium securigerum 118.195 290.127 99.215 95.751 Pterodinium cingulatum 117.885 249.434 120.044 90.651 Pterodinium cornutum 195.270 261.921 119.445 96.279 Pterospermella australiensis 111.775 269.766 116.537 94.630 Pterospermella harti 125.000 221.521 100.809 96.749 Reophax pepperensis 336.460 368.914 96.285 92.467 Rhopalosyringium mosquense 221.520 221.520 98.757 96.762 Rubinella major 118.195 118.195 Rugubivesiculites rugosus 71.100 218.041 101.754 88.785 Saccammina alexanderi 103.916 389.358 102.323 89.088 Saccammina lathrami 103.916 103.916 101.717 93.443 Schizosporis reticulatus 179.145 179.145 97.920 97.335 Sepispinula huguoniotii 202.695 358.142 113.917 89.414 Spinidinium echinoideum 125.000 218.041 99.070 96.912 Spiniferites cingulatus 155.185 232.744 100.746 96.544 Spiniferites lenzi 261.921 262.090 123.811 94.675 Spiniferites membranaceus 117.885 198.400 98.763 89.568 Spiniferites ramosus ramosus 197.801 229.861 124.487 88.775 Spiniferites twistringiensis 153.366 191.221 117.966 89.841 Spirolocammina planula 160.764 176.207 99.387 98.117 Spirolocammina subcircularis 136.409 161.946 101.031 100.300 Stereisporites antiquasporites 119.633 153.366 Stichomitra navalensis 182.444 203.856 97.525 97.525 Stichomitra tosaensis 197.000 197.000 98.111 98.111 Stiphrosphaeridium anthophorum 119.633 210.920 132.774 94.049 Subtilisphaera cheit 118.562 399.290 112.590 89.130 Subtilisphaera deformans 146.044 261.921 112.389 96.279 Subtilisphaera perlucida 125.000 261.921 129.069 96.279 Surculosphaeridium phoenix 172.054 191.220 112.789 112.332 Tanyosphaeridium salpinx 73.500 73.500 101.688 94.401 Taurocusporites segmentatus 131.750 206.714 101.812 89.414 Tigrisporites reticulatus 69.700 197.043 102.325 96.823 Todisporites minor 118.196 247.578 100.945 96.507 Trichodinium brevispinosum 103.916 103.916 99.519 99.519 Trichodinium castanea 117.885 249.266 132.774 90.250 Trichodinium spinosum 66.300 69.700 101.887 96.318 Tricolpites micromunus 69.700 150.800 101.793 94.109 Trilobosporites marylandensis 66.300 66.300 101.887 97.084 Trithyrodinium suspectum 213.400 213.700 97.155 90.693 Trochammina depressa 135.606 161.946 101.209 95.403 Trochammina gatesensis 111.775 358.714 99.348 93.002 Trochammina mellariolum 217.936 316.457 96.749 94.452 Trochammina rutherfordi 210.106 220.872 102.160 94.718 Trochammina wetteri 132.045 368.914 101.584 92.467 Trochammina wickendeni 183.691 386.520 97.227 89.954 Trochamminoides apricarius 261.436 368.914 96.148 92.467 Verneuilina alameda 226.697 226.697 96.797 96.211 Verneuilina canadensis 111.775 175.550 102.932 96.720 Verneuilinoides hectori 111.775 334.671 104.636 93.888 Verneuilinoides kansasensis 137.747 161.946 100.943 100.757 Verneuilinoides perplexus 103.916 368.914 101.973 92.467 Veryhachium reductum 224.968 229.861 99.713 94.031 Veryhachium rhomboidium 207.925 234.923 100.809 90.651 Vitreisporites pallidus 109.700 234.000 100.715 96.712 Wallodinium anglicum 175.217 204.300 98.763 91.383 Wrevittia cassidata 118.196 118.196 113.825 91.721 Xenodiscus plotei 197.450 197.450 114.261 95.564 Xiphophoridium alatum 156.098 166.968 102.434 89.568


Appendix D

Comparison of FOs of selected dinoflagellates. Sources: Italy—Fiet and Masure (2001); Europe—Hardenbolet al. (1998); Montana and Wyoming (MT-WY)—this study (meter position above base of Pike Creek section);western Kansas (W KS)—Scott et al. (1998). European ages in Ma from Hardenbol et al. (1998). Ages inMIDK3 calibrated by graphic correlation of the Mowrycs.1 database with the MIDK3 database (Scott et al.,2000).

Substage
Marches-Ombrie, Italy Europe (Ma) MT-WY (m) W KS MIDK3 (Ma)
“Vraconian”
H. dictyota 207.9—top Mowry 100.11 U. Albian C. asperum 204.3—top Mowry 100.82
E. spinosa
L. Alb.—100.05 129.8—sandy mbr. Hartland 102.44 O. verrucosum L. Alb.—99.89 125.4—sandy mbr. Dakota 98.94 X. alatum L. Alb.—102.78 156.1—sandy mbr. 102.43 P. infusorioides L. Alb.—99.63 69.7—sandy mbr. Glencairn 102.07 A. grande L. Alb.—101.59 146.0—sandy mbr. Glencairn 113.54 D. cladoides M. Alb.—106.88 118.6—sandy mbr. Glencairn 103.75
M. Albian
D. multispinosum 66.3—Skull Creek 106.48 L. arundum E. Alb.—110.19 69.7—sandy mbr. 113.54 P. pseudhystrichodinium 235—Belle Fourche 113.93 O. scabrosum Apt.—115.90 155.1—sandy mbr. 115.25
Base L. Alb.
S. cheit 118.6—sandy mbr. Glencairn 112.59 O. rhakodes 118.6—sandy mbr. Glencairn 112.59
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