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Deposited in DRO: 26 January 2017 Version of attached le: Published Version Peer-review status of attached le: Peer-reviewed Citation for published item: Hall, R. and McNicoll, V. and Gr¤ocke, D. R. and Craig, J. and Jonhston, K. (2004) 'Integrated of the lower and middle in and , western .', Rivista italiana di paleontologia e stratigraa., 110 (1). pp. 61-68. Further information on publisher's website: https://doi.org/10.13130/2039-4942/6264

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Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk Rivista Italiana di Paleontologia e Stratigrafia volume I l0 no. I pp.61-68 April 2OO4

INTEGRATED STRATIGRAPHY OF THE LO\TER AND MIDDLE FERNIE FORMATION IN ALBERTA AND BRITISH COLUMBIA, \trESTERN CANADA

RUSSELL HALL', VICKI MCNICOLL" DARREN GRÒCKE" TAMES CRAIGI& KEVIN TOHNSTON

Receiaed Septenber 19, 2002: accepted Septenber 30,2003

Key toords: , ammonìtes, biochronology, coccoliths, U-Pb analyses, have recently been obtained from fossilif- U-Pb geochronolory, strontium isotopes, zircons, Fernie Fornration, erous volcano-sedimentary units in the North American Alberta, . Cordillera (Pílfy et al. 2000). There, volcanic products Abstact. The lower and nriddle parts of the Fernie Formirtion are interbedded with ammonite-bearing sediments that in central-western Alberta and sourh-eastern British Colurnbia, ranging provide good biochronological constraints. This integra- from to ?Brthonian (Earlv to MiddleJurassic) in age, and tion of biostratigraphic and geochronologic data has al- consisting mainly of fossiliferous drrk and black , con- lowed improved estimates for the numeric age of tain bentonitic clay horizons which have yielded radiometric rges using Jurassic stage boundaries. U-Pb analysis of zircon crystals. Here we report six nes' ases from the lowermost Red Deer Member (188.3 +1.5/-1 Ma); Highrvood Mem- Tectonism and magmatic events associated with ber (ca. 1/3 Ma;rnd 166.6 + 0.2 Ma); and Grey Beds (167.0 + 0.2 Ma, accretion of allochthonous terranes to the wesrern mar- + 165.6 0.3 Ma, and 165.4 + 0.3 Ma). Some of these bentonites.rre rs- gins of ancestral North America, beginning in about sociated with ammonites and coccoliths which provide biosrratigraph- MiddleJurassic time, are reflected in sediments ic constr;rints. Strontium, carbon and oxyten isotopes measured fronr Jurassic belemnite rostra have been compared in two secrions :rnd the resulting deposited farther east in the \lestern Canada Sedimen- curves are comp:rred with those from western Europe. tary Basin where volcanic ash layers are interbedded vrith ammonite-bearing dark shales of the Fernie For- Riassunto. Le parti inferiore e media della Formazione Fernie mation. In this paper s/e report six new U-Pb zircon nell'Alberta centro-occidentale e nella Columbia Britannica sudorien- ages from analysis of zircons in ash layers from cen- tale, la cui età va dal Pliensbachiano al ?Bathoniano (Gìurassico da infe- riore a medio), e che consistono principalmente in fossiliferi scuri tral-western Alberta (Bighorn Creek and irs easrern e calcari neri fossiliferi, contengono orrzzonri di argilla bentonitica che tributary) and south-eastern British Columbia (Ford- hanno fornito datazioni radiometriche con I'analisi U-Pb dei cristalli ing River) (Fig. t). di zircone. riportianio sei nuove datazioni dalla parte più bassa del Qui Detailed geochemical analyses on two sections, Mernbro Red Deer (188.3 +1.5/-1 Ma); dal Membro Highwood (ca. l73Ma,e'166.6 + 0.2 Ma) e dai Grey Beds (167.A + 0.2 Ma, 165.6 + 0.3 Bighorn Creek and its nearby easrern tributary have been Ma, e 165.4 + 0.3 Ma). Alcune di queste bentoniti sono associ,te con completed for strontium, oxygen and carbon isotopic ra- ammoniti e coccoliti, che forniscono le delimitazioni biostratigrafiche. tios. Variations in the strontium-isotope curve derived Gli isotopi dello stronzio, del carbonio e dell'ossigeno misurati da rostri from the analysis of belemnite rostra in these secrions di belemniti sono stati confrontati in due sezioni, e le curve risultanti vengono comparare con quelle dell'Europa nordoccidentale. allow for correlation with that previously generated in Europe (Jones et a|.1994a). lJnfortunately, biochronological constraints in Introduction these two sections depend on only intermittent occur- rences of ammonites, which occur as lateral impressions A significant number of new isotopic dates for cali- on bedding pianes; some levels have also yielded cocco- bration of the Jurassic time-scale, based on high precision lith floras.

' Geoloey & Geophysics, University of Calsary, , Alberta T2N lN4, Canada. E-mail: hellr(r ucalgary.ca 'Geological Survey of Canada, 601 Booth St., Ottawa, Ontario KlA OE8, Canada 'School of Geographl, & Geologl', McMaster University, Hanrilton, Ontario LSS 4K1, Canada 'PO. Box 668, Bragg Creek, Alberta TOL OKO, Canada 62 R. Hdll, \'. ,llcNitoll, D. Griickc,.l . Craig Et K..f olnstott

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Geological Setting Rcrching maxinrunr thicknesses of only about 300 r'ìì. tìre Fcrnie Fornr.rtiorr is,r recessivc unit occurrinq as In the Foothills and Front R:rnse s of the C;rnrdi,rn isolirtcd outcrops irlonq vallev floors, and was intensely Rockv Mountains thc Fernie Fornrirrion represcnrs al- defornred bv Cretlceous o\.er-thrusring :rcconlpanying nlost the entireJur;lssic; its internrrl subdivision into in- Cordiller:rn tectonism. While nrost units rvithin the Fernie f o rn.r,r I nl e m b e rs r t h c i r I i t h o s t r:r t i u rir p l.r v ir n d b i o s t r;'rt i rÌ rrr- Fornri'rtion have been rerìsonably rvell-dated usinrÌ anlmo- phy, rvere sumrnariscd bv Hall (1981). Lou,cr and Mrdclle nite f:runirs, there are n.ranv faunal gaps (Hall 1984). Dat- Jurassic palrts of tl.re Iìernic Fornrirtion consist predonri- ins of upper Middle Jurirssic units (Hiuhrvood Men.rber, nantlv of grev and black sh:rles, l,'ith nrir-ror siltstones, Grev Bcds) is n'rade rrore difficult bv the strong faunal , conglonrcrates and linrcstones, the sourcc of provir.rcialitv der.eloped iurongsr :rnrnronires from Late detrital sediments bciÍrs on the cnton to the er.rst. Tl.rcsc B,rjocirn to t:rrly times (Callomon 1984). strata represent the voungest pilrts of the pirssivc rn,rrgin sequence, q,hich irccurlulirted on thc western ntirrgin of cratonic North Arrericrr thror,rgl.rout the Paleoz-oic rrncl Earlv Mesozoic. Thc uppernrost p,rrt of the Fernic l"or- Lithostratigraphy and descriptions of sections nlxtion (Pass:rge Be ds; Oxfordi,rn) rccords :1 conrplctc rc- Ilighorn Creek versrrl in basin polirritl., refle cting :rccretionarv rccronics Thc lorvermost Jurrssic scdinrents ;rt this loc.rlin'consist ol;t occurrins f,rrther rvest, r'hich resr-rltcd in dcvclopnrcnt thin (lÌ ur), plrosph:rtic-pcirirle lig iilling cleprcssions on rrn erosi()nirl surf.rcc clcvclopred ovcr l-orvcr Middle (Sulphur Moun- of ir subsidins forclrrnd brrsin u,ith influx of co;lrse clrìs- to Tri:rssic roclis t.rìn Iìrrnrrtion)l frlgnrcrrtccl;rrnnronites inclic.rtc.r [-.rte Sinenruli.rn .rgc tics, and volcanic rrnd igncous dctritus, from ,r \\'estcrlv for this pebblc bcd (Stcll.rre Subzonc, Obrtrsunr Zone). Above an S source - the rising iìncestrtl Rockv Mountrrins (Poulton nr thick coverccl inten,rl, thc Upper Plicnsb;rchi;rrr Rc'cl Deer Mcmber et rl. 199,1). cortsists oi 9 nr of hard. platl Lrl,rck, limestorrc rrnd shrìlc. The overli- Stratigraphy of tbe Fernie Formations 63

Fig.2 - Carbon, oxygen, and stron- Stable lsotopes 879/8651 lNgg 9971 rirrm isotone curves for the Highwood Member of the J, o o13c""rg%o1vpDB1 o18o""rg%o1veoe1 ^a Fernie Formation at Bighorn or Òr s] -1 012 3 -8-7-6-5-4-3-2-1 .ffi rffiTrTEtffit rffiT|frTffiT|.rlFTffiTffi Creek. Placemenr of Stage la{ anòZone boundaries (in col- ts-ra+ umns under "this study") based on variations in iso- tope curves, not ammonites

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ing Poker Chip Shale, 12 m thick, consists of more fissile and papery, calcareous siltstones with some poorly preserved lateral impressions of thinly laminated, black silty shales, and in its lower parts conlains a rich Late Pliensbachian ammonites (Hall et al. i998). ammonite fauna of early age (Falciferum to Bifrons Zones; The overlying Poker Chip Shale can here be seen in direct con- Hall 1987). tact with the Red Deer Member, and is almost continuously exposed The dark shales of the Poker Chip Shale grade upward fairly in low outcrops along both sides of the creek, providing a measured rapidly into grey, rusty- and yellow-weathering, sofrer shales of the stratigraphic thickness of at least l2 m. Its basal contact with the Red Highwood Member which here is 18 m thick. This unit contains thin Deer Member is marked by a change from hard and thicker-bedded bands of calcareous , often accompanied by rounded, black, black, calcareous siltstones to softer, more platy, black fine sihstones. phosphatic pebbles, numerous fragmented belemnite rostra, and abun- It is difficult to pick the upper contact with the overlying Highwood dant secondary gypsum and goethite. Near the top of the unit there are Member, as the color differences and weathering characters used to thin, orange-r.hite, soft bentonitic clay layers of volcanic origin. \fhile separate these members elsewhere are not so obvious here, The con- no ammonites have been found at this locality, on the west bank at the tact almost certainly lies somewhere just below a resistant pebble next cutbank upstream, a similar pebbly bed containing fragmented and cobble bed, with a black, sandy matrix, and containing abundant, and immediately overlying a yellow-white benroniric clay, current-oriented belemnite rostra (at 23.2 m on Fig. 3). has produced one partial external mold of a sonniniid ammonite, indi- The Highwood Member consists of just over 1O m of mainly cating an early Bajocian age. platy, dark grey shales with several thin, cemented horizons and five On Bighorn Creek the overlying Grey Beds are nor seen in soft, yel[ow-white-orange, bentonitic clay layers containing numerous contact with the Highwood Member, but are exposed along several fragmented belemnite rostra and rounded, black phosphatic pebbles. cutbanks farther upstream. In the section on the eastern tributary of Four metres of platy grey shales overlying the Highwood Member at Bighorn Creek and also at nearby lù/illson Creek, beds at this strati- the top of this section belong to the Grey Beds, and have yielded lat- graphic level have yielded very poorly preserved, partial ammonite im- eral impressions of Kepplerìtes cf. costidensus (Imlay), ?Cboffatia, and pressions most likely indicative of a latest Bajocian to Boreal Late Ba- TXenocephalites, suggesting a Boreal Late age. thonian age (Hall 1988, 1989).

East Tributary of Bighorn Creek Geochronological Methods An unnamed tributary flowing into Bighorn Creek from the northeast exposes an almost continuous section of the lower and mid- U-Pb analyses of zircon crystals from volcanic dle parts of the Fernie Formation. The basal contact with the resist- ashes were performed in the Geochronology Laborato- ant siltsrones of the underlying Sulphur Mountain Formation is exposed on the west bank, though the basal pebble lag is not seen ry at the Geological Survey of Canada, utilizing analytical here. The Red Deer Member consisrs of -8 m of hard, black, platy methods outlined in Parrish er al. (1987) with analysis on oa R. Hall, V ,IIcNicoll, D. Grócke, J. Craig L< K. lr,,bnston

Irig. 3 - Carbon, oxyren, and stron- Bighorn Greek Stable lsotopes tìunr isotope curves for the East Tributary Hishrvood Member and Grey 87948697 lNgg 9g7l ,r13c"".6 %o 118o"".g v* (VPDB) (VPDB) Bcds, Fernie Fontation, at Height Stage, Zone Ammonites ll a\ Bishorn Creek east tributary. (m) rs'^\ rs' ro' This study y'165.4Ma c' s' oj -1 1 3 -8 -6 -4 -2 O Pl:rcenrent of Stage and Zone 37 6 boundaries (in columns under o "rhis stud1"') based on varia- o 36 3 tions in isotope curves, not -î o anrnronites found in this sec- .a tron. E o N' d) I o rai 34 o .q C o 6 m .s l o 32 o o N .5} R É o .9 6 o {F' (prc 6 .9 E l N te- o ,Gl/ 30 L |ar I .9 I c E î o 6 f L -:, .-o 29 E .g s ---:i fr o c 166.6Ma tùl ^Po .q i;l fat i-7 v o 28 o -l *-aa_^ 3 E G -.-l rTl'r = o -.i-1 offi r c IT o'-8" 27 .E a o rt #, 'ó' .q b :l--'1 rai èo o 'o'o fU. o.n' o m a il! I l o\. Q taP oP -9 a ,S /l'O

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a Triton TI thermal ionization mass spectrometer. Treat- The upper 2 m of the Red Deer Member has yielded menr of analytical errors follows Roddick (1987), with er- lateral impressions of Amaltheus cf. stokesi (J. Sowerby), rors on the ases reported at the 2o level. All of the zircon ? Amauroceras, ?Aveyronicerds and Protogrammoceras, in- crystals chosen for analysis were well faceted and opti- dicating correlation with the Margaritatus Zone (Upper cally clear, without fractures or apparent inherited cores. Pliensbachian). Strata 1.2 - 1.4 m above a bed with abun- Multigrain zircon fractions analyzed were very strongly dant pectinid bivalves have produced coccoliths consistent air abraded followinc the method of Krogh (1982). with a Late Pliensbachian age: CrEidolithws cavus, C. crassus, and Lotbaringius sigillatus. On the east tributary a bentonitic clay layer occurs in the Red Deer Member, 1 m above the lntegrated biochronology and geochronology basal contact of the Fernie with the Triassic. Analysis of 5 zircon fractions from this bentonite resulted in a spread of In this section dates derived from U-Pb anal,vses data intersecting concordia from 189-188 Ma, reflecting per- of zircons are compîred with the ases for Jurassic starle haps a snrall degree of inheritance or Pb loss. A preliminary boundaries on the tinre scale proposed by Pílfy et al. age interpretation of 188.3 +1.5/-1 Ma is assigned based on (2000). the weighted average of the ttnPb/tt*l-J ases of the analyses The thin phosphate-pebble veneer at the birse of and thc range of errors on those ages. Further data are re- the Fernie Formation on Bighorn Creek has yielded ser'- quired to refine this age interpretation. This provides an Ear- eral partial specimens ol Epophioceras cf. breoni (Reynès) ly Pliensbachian age for these strata which is consistent with and Asteroceras stellare (J. Sowerbv), indicatinr correla- a coccolith flora, including Biscutum nonum, Crepidolithus tion with the lowermost Upper Obtusum crassus, M itrolitbus elegans, Parhabdolith us liasicws, Similiscu- Zone (Hall1987\. tum praecarium, and Tubirhabdus patulus which occurs just Stratigraplry of tbe Fernie Formations 65

NW European Boreal à 8751p651 S Boreal Ammonite (NBs 987) Stratigraphic ò13Ccarb %o (VPDB) ò18ocarb %" UPDB) E scheme Gycles Jp i' ^6q i\o a. "x.r -3-2-10123 -10 -8 -6 -4 -2 0 ZOne SUOZOne S) S' S' S) O' o,scus I hollandi

England (belemnites) O Ri^F orn Creek (BC) O England (oyste6) C -;; Sr error - ; East Tributarv O Scotland I t2se to CM, PortugalA f ú R7 z € zf o E o I @ a g @ veovilensis ìf\^fr macrescens I convergens ffe

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Fig.4 - Composite carbon, oxygen, and strontium isotope curves for the Aalenian-Bajocian-Bathonian interval, showing data from western Europe and results from this study at Bighorn Creek and its eastern tributary. Ammonite subzones are assumed to be of equal dura- tion. Note the highly negative oxygen-isotope values (very warm paleotemperatures) from Bighorn Creek in the Lower Bajocian; all samples are defined as non-diagenetic based on Jones et al. (1994a).

0.2 m above the base of the formation. Strata from 3.2 - 8.1 ammonites.4 mabhews and Amauroceras ir rhe same interval. m above the base yield a coccolith flora consisting of Bri- On Bighorn Creek, the overlying Poker Chip Shale cutum grandis, B. noeltm, Crepidolitbws crassus, Crucirbab- near its base contains the ammonites Harpoceras cf. H. dus primulus, Lotharingius hauffi, L. sigillatus, Ortbogonoides falciferum (J. Sowerby) , Hildaites cÍ. H. serpentinifurmis hamihoniae, andTwbirhabdus patwlus, consistent with a Late Buckman, Dactylioceras cf. atbleticum (Símpson), and Pliensbachian age, confirmed by partial impressions of the Polyplectus cf. swbplanatzs (Oppel) [subsequently re-as- Stratigrapby of tbe Fernie Formations 67

belenrnites s,ere then thoroughly cleaned using deionised n'ater and tive excursion also has not been recorded at Cabo Mondego dried at roon.ì terì.rperature. The subsequent cher.nicrl treiìtn.ìent \\':ts (Portugal) and so may only be a local northern European first described byJones (1992) and ìs outlined inJones et al. (1994r). seaway phenomenon. The strontium-isotope curve is rela- Strontium-ìsotope meiìsurenlents rvere performed on a modilied VG Isomass 54E thermal ìoniz-ation nrass spectroÌleter. All '-Sr/'"Sr values tively stable in the Aalenian and drops dramatically to less were internallv norm,rlised ro '-Sr/s^Sr rltio of O.l19.{ and the result- radiogenic values at the Laeviuscula-Sauzei Zone boundary ant data rvere then adjusred usins e Nationrrl Bureau of Standlrds 982 and continues until the upper SubfurcarumZone in the Ba- INBS 987) value of 0.710250. jocian, after which the strontium curve becomes more vari- able. The variability in the strontìum-isotope curve here Isotopic Results and Discussion may be real, but due to a lack of other biostratigraphically Based on the strontium-isotope curve generated weil-constrained localities with which to correlate we are from Scotland, England and Portugal (Jones et ^1.1994a, less confident with this part of the curve. The only tie-point b; Gròcke 2001; et al. 2002) it is possible to cor- Jenkyns available from Bighorn Creek is the occurrence of one par- relate the Biehorn Creek sections, that have relatively poor tial lateral impression of a sonniniid ammonite from a peb- biostratigraphy, with a NW European Boreal ammonite ble bed, indicating anEarly Bajocian age. scheme. The variations in strontium-isotope ratios fron-r belemnites at Bishorn Creek show reasonable scatter com- pared to the European data when plotted on the same scale Conclusions €ig. a). However, stratigraphically the variation is minor and is almost sinusoidal in nature (Figs. 2, 3), which has In this study we have synthesized biostratigraphic been reported elser.vhere and may reflect rlobal orbital cy- and numerical ages with secular isotopic curves in three cles (Grócke 2001 ; Jenkyns et al. 2002) . How this is pos- stratigraphic sections through the Lower and Middle sible considering the long residence tin-re of strontium in Jurassic parts of the Fernie Formation in Alberta and the oceans is difficult to understand and more research is British Columbia. The Early Pliensbachian and Early required in producing high-resolution strontium-isotope Bajocian U-Pb ages obtained from zircons in volcanic stratigraphy in orbitally-calibrated successions. ash layers are in general agreement with ammonites and Due to the scatter in strontiunr-isotope ratios (which coccoliths from some of the enclosing strata. Another have all been diagenetically screened using the methodolory three U-Pb ages, obtained from zircons in bentonites ofJones eral.1994a) we have adopted a ts/o-pronsed meth- interbedded with siltstones that yielded ammonites sug- od of correlation by also assuming that the carbon-isotope gesting Late Bathonian ages, are older than expected, but variation is global in nlture in contrast to oxyeen, which this interpretation depends on which of several previ- reflects local environmental conditions. Usine both stron- \Ve ously published Jurassic time-scales is applied. have tium and carbon it is possible to correlate the Bighorn Creek compared strontium and carbon isotopic curves from the sections with a NW European Boreal ammonite scheme unfossiliferous Highwood Member (Bajocian and Batho- with a high degree of confidence (Fig. a) and it has subse- nian) with established curves from NW Europe in order quently allowed a N\W European Boreal ammonite scheme to test use of such geochemical variations for intercon- to be drawn against the Bighorn Creek sections (Figs. 2, tinental correlation. 3). The only major discrepancy with this method was the absence of a LaeviusculaZone positive carbon-isotope ex- AclenouÌedgmenrs. Ve wish to thankJ. Pílfy and G. \Westermann cursion (Fig.2), as recorded in Scotland; however, this posi- for rhe criticri revision of the nrrnuscriot.

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