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The Callovian-Oxfordian Boundary In

The Callovian-Oxfordian Boundary In

Rivist;r Italiana di Paleontologia e Straticrafi;r vc)tunle I lu no.1 pp. 20 I -208 April 2004

THE CALLOVIAN- BOUNDARY IN BRITAIN: A REVIE\T OF KEY SECTIONS AND THEIR CORRELATION \TITH THE PROPOSED GLOBAL STRATOTYPE SECTION AND POINT FOR THE OXFORDIAN IN HAUTE PROVENCE.

KEVIN N. PAGE

Recei"Led September 19,2002; accepted July 10, 2003

Kq,u,ords, ammonites, Callovian, , GSSR , Ox- te di piano in questa cd altre località-chiave del Regno Unito, sintetiz- fordian, Scotland, stratotvpe, zonatlon. zandole e correlandolc con il c'rndideto GSSP in Altii Provenz-a. Que- str correlazione può fornire uno schenrr nel quale si possono inteqrare Abstract. The historical type area of thc' Oxfordian and inforrraz-ionì aggiuntive derivate daì siti inglesi, per esenrpio da studi its lowest subchronozone (Scarburgense Subchronozone of the Mariae sui nricrofossilì o sulla geochimica, per liutare la correlaz-ione globale Chronozone) lre in Great Britain, in southern central (Oxford) rnd delh b'rse dell'Oxfordi;rno. north eastern England (Scarborough), respectively. In neither district, however, are sequences sufficient complete to srrtisfl' ICS requirements for a GSSP Subsequent u,ork in Haute Provence, south erst lìrxnce, however, has revealed considerably expanded sequences in Terre Noire The Callovian-Oxfordian boundary in England facies which satisfv most ICS criteria and a GSSP for the Oxfordian Stage has norv been formally proposed in this region. One British sec- The term Oxfordian was proposed by d'Orbigny \X/er,mouth tion, horvever, on the corst near (Ham Cliff/ Red- (1842-1849) as the lowest of his four divisions (étages) cliff Point), is relativelv expanded and has the potential to comple- of what would now be termed "Upper By im- nrent the Frcnch candidate GSSP bv yielding additional infornration Jurassic". on microfossil assemblages (e.g. ostrocods, forlminifere, coccoliths plication the region around Oxford in southern central and holothurians). The sequence of ammonitc' faunas across the st:rge England would be the type area of the stage. Inevitably boundary :Ìt this .rnd other kev UK localities is reviewed, synrhesised therefore, as understanding has developed on the diae- and correlated uith the candidate GSSP in Haute Provence. This cor- nostic faunas of the Oxfordian, especially the ammo- relation can provide a framertork rvithin which rdditional information nites, there has been a strong focus on British and espe- derived fronr UK sites, for instance from microfossil or geochenTic;rl studies, can be integrated to assist global correletion of the base of the cially English sites, most particularly by workers such as Oxfordian St:rse. Buckman (1909-1930), Arkell (1933, 1935-1948, 1.939, 1941, 1947), Callomon (1964, 1968, 1990) and Wright Riassunto. IJarea tipo storica dell'Oxfordiano e della sutr sub- (1968, 1983). cronozona pìir bassr (Subcronoz-ona a Scarburgense della Cronozon;r In addition, the index fossil the accepted low- a Mariae) sì trovano in Gran Bretagna, rispettivanrente nell'lnghilterra of centro-meridionale (Oxford) ed orientale (Scarborough). in nessun dei est subchronozone of the lowest zone of the stage, Car- due distretti, tuttlvir, le sequenze sono sufficientemenre conrplete d;r dioceras scarburgense (Young 8r Bird), came from the soddisfare le richieste ICS per un GSSP Uno studio successivo in Alt,r North Yorkshire coast (north east England) at or near Provenzr, Francia sudorienrale, ha però rivelato sequenze considerevol- Scarborough (Callomon 1964, 1990) (Fig.t). Callomon rìente esp:Ìnse nella facies delle Terre Noire che soddisfano la nrageior parte dei critcri ICS, ed or;r è st;rto formalnrente proposto in questl (1990) consequently attempted to stabilise the use of the resìone un GSSP per I'Oxfordiano. lJn;r sezione briurnnic.r, rurt:rvi:r. subchronozone by proposing that a section in the latter sulla costa del Dorset vicino rVevrrouth (Ham Cliff / Redcliff Point), region, at Osgodbv Nab (section described by Vright è relativamente esprnsa ed ha il potenziale di conrpletare il candidato 1968, 1983), should be established as a stratotype for francese al CSSP fotnendo infornrazioni aggiuntive sulle lssoci.r.zioni a nricrofossili (es. ostracodi, forrnriniferi, coccoliti ed oloturie). Viene the subchronozone and therefore define the base of the passata in rrssegnr l;r sequenzl di f,rune rd rmnroniti attraverso il linri- Oxfordian Stage. The sections in the Scarborough dis-

School of Earth, Ocean & L.nvironn-rental Sciences, Universitv of Plvmouth, Drake Circus, Plvnrouth PL4 8AA, UK. E-mail: KevìnP(r bello-page.fsnet.co.uk 202 K. N. hge

entirelv in nrudrock facics (Wcitnlouth Mer.r.rber, Ox- ford Cl;r1' Fornration - fornrcrly Upper Oxford Clav) rnd irlthough thc irnrmonite frrun,r is frequentlv crushcd, at severxl levels nuclei ,rre pvritiscd :rnd verv occrrsion- ally body ch,rnrbe rs nr'ry be prrtly phosphatiscd. No irs- U sessnrent of r.nicrofossil assenrblrrges is currently avlil- 0 ,rble, irlthough prelinrinarl, u,ork ir-rdicates thrrt thcrc is

0 a good for:rnriniferan rrnd holothurian flunir (M. Hrrrt, pers. conr. 2002) arnd the lithologics present (c,rlclreous 6[11,) suggest thilt good ,rssenrbl,rgcs of ostr,rcods ,rnd coccoliths rnisht irlso be recover,rble. Indeed, the scc- tion hls thc potential to conrple nlent the currcnt cirndi- d:rte GSSP for the base of thc Oxfordian St:rgc, in Hiiute Provence, soLrth ca.rst France (FortwcnrÌler & Mrrrchand 1991, 1997), 's'here infornr:rtion of nricrofossil succes- sions is linritcd. Elservhcrc ir.r Britirin other known Cirllovi,rn-Ox- f o rdi an bo r.r n d,rry I o cal i t i e s irrc t yp i c irl I i' s trat i gr:,rph i c iil I y incompletc (c.g. Voodhilur, BLlckinghanrshire rnd Wîr- bovs, C,rnrbr"idr:cshire), or f,rurr,rllv too irnpoverishcd (e.g. Staffin B;rr', Isle of Skve, Scotlrrrd) to forr.n prinr:rrv rcfer- ence sectiorls. Thev neverthelcss vicld irdditional infornr,r- rStewartbY' Woodhama tion on thc boundary and its ch,rr,rcteristic faunls and are 'Stanton Ha'rcourt revierved bclorv. Follorving Clllonror.r (1993) lrrd Crrllo- mon & Cope (1995) the basc of the Oxforclian is drarvn rrt tlre birse ol ;tu'oodhatilezse Biohorizon, as utilised here, ,rnd not thc b:rse oi rhe paucìcostLlturt Biohorizon, rvhich is nou, consiclercd to be terrlin;rl C:lllovian (Fortrvcngler & Mrrcl.rrnd 1994, 1997:' Thicrn, et ,rl. 1997). liig. I - Map of (-ìrerrt Britrin shou irrg thc nr,rin Crrllovirrn-Oxkrrtl- l. Staffin Bav, Isle of Skye, Scotlond iln bouncl,rrv localities nrentionccl in the tc'xt. Thc C.rlkrvirn-C)xforclirrn bountllrv is l'cll e rpose cl on thc Dun- :tns shorc in St.rllin Bav Ic. N(ì-{737001, as rccorclcd bv Arrrlerson & Dunh,rrl (1966), Svke s (1915), Morton N Huclson (199-i), \i'right in \\'right t Cor (2001), Pegc (in Cor N Sunrblc'r 2002, pp. 105-+0S). Reccnt rc-errrnrin.rtiorr indicates th.rt thc Hcnrici Subchrrrrtozonc is trict, howeve r, :rre very thin and hiuhly condensed in chir- prc'scnt in llcd SS5b (of I'lorton 3. Hutlson 1995) of thc Dunrns Cì;rv lVlenrbcr, St;rffin Sh.rlc Fornr:rtion.rnd rrt lclst.rs high:rs l.lZ to 1.3{ nr mosite-oolite sandstone and linrestone fircies, irnd ve rrr sig- ;rbovc thc b.tsc of Bctl 556 (r,ith Q. cl. l:otrici ). nificantly, faunal discontinuities,rre locally denronstrable. The lou cst re corcle d Qtcttstcdtotcr,Ls oi tlre l..rnrbcrti Their potenti,rl for rnagnetic, isotopic, geochrononlctric Subclrronozonc.ìre present.rt.rrouncl 1.7 nr ,rbovc the b.rsc of SS6, al- irnd micropalleontological studies, i1s reconlnlended bv thcrugh the brsrl l-.rnrbcrti Subchronozonc , praclantbarti frun.r (scc con- the Internation:rl Comnlission on Stratigraphr' (Rerrirnc clusions) is not vct rccognisecl. Ttprcil lanbarti Biohorizrrn i.rurrrs rrc present benvccn 1.7 to 2.05 nl irbove thc brsc oi SS6. inclucling tvpic:rl et al. 1996), is thcrefore much reduccd. Neverthcless, :'rs lanbcrti (1. dc C. Sowerbr') .rncl irctlucn r Eutspidot'uts ltirsutunt charr:rcteristic f,run,rs do occur ,rnd the :rrea h;rs beor the Q. lnr | (B.rvle) lMl.-l'hcbrse oÎthe Oxîorrli.rnlicsrrtrrrounrl -l.5.lnt.tLrovctlre source of manv typc specimens, thc district is still irrpor- b;rsc of SS(r, rrs inclicrrtcd bv Cìrz/rocc;;r.t cl. u'oodlunutst'Arkell riol txnt for discussions of the st;rge boundirrv. lll,rrchand, s'ith C.r'rllocoir,s cr gr..sc.r'úlr.gor.sc (\bung.rnd 13ird) ([nr] In contrast :rn expanded, rlbeit periodicallv poorlv rnd []!{ l) .rt .l.S I nr. The low clive rsitv t,l the sc Borc.rl f.runrs, clonri- exposed, section ne,rr Redcliff Point, e,rst of Wel,rrouth nrtctl bv crrtlioccr.rticls is ;rpprrent,.rlth,rugh tlre prcscnce of co:t'rrt.tor.r Euasltidotarts rt onc lcvel is not.rblc, .'rs .rt Lìron (sce bclou in Dorset (south wesr EnÍjl:lnd; Arkell 1947; Wrisht ).

1986; Callomon & Cope 1995; Page 1994; Page in Cox 2. Brore. Sutherland. Scotlancl & Sunrbler 2002,pp.31-34; Chirpnrrn 1999), has fcrv of (ìo..rst.rl crposur-r's in tlrc Bror.r cstu;rrr' INC9090] | rrncl irrlrrncl, these drawbacks, and avail;rble fossil evidence irrdicrrtes rrlong thc lJron lLirer Ic.g. NC S9S0.]lìì pxrviclc se'ctions in the l-rrr- that a nlore explnded and complete sequence is prcse nt, bcrti Chronozonc (Svkcs 1975). crucirllv inclucling relcrence \ccti()n\ for tlre tcrnrin.rl Callovi,rn. Hcnrici rnrl [-rnrberti subchronozoncs.;rs frequently u,ith better preserved ,rnd more diverse f,ru- proposcrl lrv Crrlkrnron 3. Svkcs (19S0). Thc fornrcr is lccognised on nas inst:rnce, the terr.r.rinll pductcostLltut/t (for C,rllovian thc basis of thc inrler species. in;rssoci.rtion *irh Peltrnnu'pltitc., sp. in Biohorizon nray be 4 m or so thick, irs compirrcd to l the top -5:tt or so oî tlìc lri.rscirllv Siltstonc Mcnrber, Brot'rr Argillrtccous maximum of 0.45 rn in Yorkshire). The section is rrlso Ironrrrtion. Thc ovcrlr.ing lrrscrllv Srnrlstone Mcnrber vielcls frrr-rna oi Callovian-Oxfordian boun darlt in Britain 203

the lon,er part of the Lamberti Subchronozone, vith Q. ex er. Ldnber- sampled for microfossil analysis but has not yer been described in full ti and. Kosmocerzr ex gr con?pressum (Quenstedt) with the succeedins (the diagramrnatic sunlnlary of Chapman ( I 999) is conjectural and cor- Clynelish Quarrv Sandstone Member yielding a typicrrl lamberti Bio' relations hypothetical). horiz-on fauna with, in addition to the index, comnlon Euaspidoceras The top of the Sten'artby Member comprised around 2 m of birsutum (including E. clynelisbense Arkell) end sonre hecticoceratids greenish grey clays with trvo calcareous bands in its upper part - around (? Putealiceras sp.). The base of the Oxfordian is presun.red to lie in the 0.3 rn above the higher band, a 0.2 m thick marl bed with abundant Gry- succeeding Brore Arenaceous Member, althoush no anmonires have phaea yielded a rich Lamberti Subchronoz-one faunas including Qwenst- currently been recorded (Sykes 1975; Page in Cox Er Sumbler 2002, edtoceras ex gr. Larnberti, (K.) spinosum, (Peltomor- pp.373-376). phites) cf. subtense,Grossoutria (Poculispbinctes) poculun, Euaspidoceras

birsutum, H ect i coceras (Putealiceras) puteale rnd Reineckeìa (C ollotìa) 3. Balintore, Rosshire, Scotland oxyptychoides (Spath). The top of the bed is locally marked by a layer of The Callovian is exposed in this area on rhe shore at Cadh'h-an- broken shells, overlain by a darker, marly clay wirh a heavily burrowed Rirh INH851227 a.rea,), the boundary with the Oxfordian lyine u'ithin base. This level marks the base of the \Weymouth Menrber and yields the Shandwick Clav Men.rber of the Brora Arenaceous Fornration (Sykes typical coarsely rrbbed Cardioceras tooodbamense Arkell with frequent 19l5; \Yr/right in Vright & Cox 2OO1; Page in Cox & Sumbler 2002, pp. snrall, weakly ornanrented hecticoceratids (possibly ìncludins. Fehlman- 376-379). Faunal records are scxnry however, althoueh Q. lamberti is nites sp.). Higher levels ìn the Scarbursense Subchronozone àre as re- recorded at around 9.7 n.r above the base of rhe menrber wirh C. scar- corded by Spath (1919) and Callonron (196S), rhe recently observed burgense irt 1 2.3 m above the blse. Callovian-Oxfordian boundary lyine at 6 n.r below the base of lìnresrone Bed A of these authors. 4. Scarborough-Cunstone Nab, North Yorkshire, England The bound:rry between the Callovian and Oxfordian stages lies 6. Stewartby, Bedfordshire, England at or close to the junction between the Hackness Rock Member of the The disused Rockery Pit at Stewarrby, near Bedford ITLO I 54 1 5] Osgodby Formation (cf. Vright 1968, 197S) and the Oxford Cl.ry For- forn.rerly showed a somewhlr wearhered section across the Callovian- matìon (formerly included in rhe "Upper ", but in a dis- Oxfordian boundary, sp:rnning the Stewartby-Veymourh Member tinctive silty f,icies when conrpared to rhe nlore calcareous cliÌys of the boundrry. The locality is very briefly nrentioned bv Callomon (1990) \ù/eynrouth Menrber of centr,rl and southern Eneland). and recorded by Page (1990) and showed a succession sin.ril:rr to that The Hrckness Rock is tl,pically a thin (0-1.5 m) condensed cha- recorded by Callomon (in Vyatt et al. 1988) in tempor;rry excrvrrions r.nosìte oolite, ofien sandy or calcareous, prinrarily represenunq parrs rt nearby Millbrook. The top of rhe Callovian is marked by a 0.2-0.35 of the Athleta Chronozone and the late Lan.rberrì Chronozone (termi- m argillaceous Iimestone or "Lanrberti Bed", althoueh very locally the nal Callovian). Thìckness variations of such a deposit ìnevitably nreans strse boundarv lies within this bed. Around 2 cm of marl irlmediately th;rt the preserved sequence sìgnificantly varies from site to site. Never- bef ow has yielded Q. henrici, Kosmoceras (K.) sp. and Hect;coceras sp. theless, sood boundary sequences have been recorded at four locations of the Henrici Subchronozone, and the bed itself has yielded Quenst, - Scarboroush Castle Hill [TA0589 ;rrea], Osgodby Nab [TAO99S3O] edtoceras ex gr. lambenì, KÒsmocer"ts (K.) ex gr. spinosilm,

(the proposed Stratotl,pe for the Scrrbursense Subchronozone of Cal- (Putealiceras) cf. puteale, ? Euaspidoceras sp., Crossoutn"ia ( Poculisphinc- lomon 1990), C;ryton Bay foreshore;rnd at Cunstone Nab [TA064854] tes) sp., Pachycer4J sp., erc. (\lright 1968, 1983, in Vright Et Cox 2001; Cox 1988; Callomon 6i Where the base of the Oxfordian lies within rhis bed it is niarked \Wright 1989; Page in Cox Er Sumbler 2002, pp.333-340; Cox tr Par.e by a line of rolled shells, includine Grypbaea,;rnd the loq.est faunas in Cox & Sumbler 2002, pp. 323-333). recorded are relatively stronely ribbed CardiocerLls Lroodhamense, \Woodhan, ^s The Henrici Subchronozone is not clearly recoenisable in this at (see below), associated with contmon Tar,tmelliceras sp., area but the l-anrberri Subchronozone vìelds rich flunas as described also Properispbinctes sp.; Q. p,tucicostatun has nor been recorded and by Leckenby (1859), Buckman (1909-1930), \Wrisht (1983), Cor as the Lamberti Subchronozone is only around O.l-0.15 nt rhick and (1988), Callomon tt Vrighr (1989) and Page (1991), includine Qaen- even locally absent, it is clear that a non-sequence is also present here stedtocer"ts ex gr. lamberti, Peltoceras (Peltotnotpbites) subtense (Betn), at the boundary. Higher faunas in the 80 cn.r or so of clay ,rbove the Grossoutria ( Poculispbinctes) poculum (Leckenby), Euaspidoceras hir, Lan.rberti Bed have yielded typical Cardioceras scarburgense in rssocia- sutum, B inatisphinctes binatus (Leckenby), H ecticoceras (Putealiceras) tion with Properisphinctes ex gr. bernensis (de Loriol), ?Crossoulria sp., putedle (Leckenby) rvith rarer Kosmoceras (K.) gr. spínosum (J. de C. Hectococet'as ex er. bonarellii de Loriol and, notably, a fragrrentary large

Sowerbv) md Alligaticeras (A.) alligatum (Leckenby) and Disticboceras phylloceratid (? C all ip b1, llo ceras sp.). bicostatum (Srlhl\. The fauna of the succeedins termìnal Callovian paucicostatunt 7. Voodham, Buckinghamshire, England lù/oodhan.r Bìohorizon, rvas fìrst recosnised in this area by\fri5;ht (1983), at Cun- The famous fornrer brick pit at lSP7ll7l, as described stone Nrb rnd Cayton Bay foreshore, with Quenstedtocer,ts pducicos, by Arkell (1939) and Callonron (1968) rvas lost in the 19ZOs due to in- t'ttun a.s figured bv Vright (1983). This fruna ìs not recorded;rt C;rl- fill bv refuse, despite irs supposed protected site status. The top of rhe lomon's crndidate Oxfordìan srratotype (1990), although rhe early Celìovian is nrerked by the L;rmberti Bed 1= Bed C of Arkell), r 0.3 Oxfordian scarburgense Biohorizon is here better preserved. Similar m thick nrarly limesrone band rt the top of the Stew,rrtby Member of levels also appeiìr ro vield a few Peltomotpbítes l'nd Euaspidoceras in the Oxford Clay Formation, considered to be the type horizon for the the district. Nevertheless,:rs none of the sites in the district îppears ro I-amberti Subchronozone by Callonron in Cope er al. ('1980). The fauna have vieided a basel Oxfordìl.n t,oodbantettse faunrr, there mlv still be is abundant and dominated by Quenstedtocerdr ex sr. Lunberti, showing a small non-seqLlence rt the stage bound,rry. a remarkable rrnge of presunred intraspecifìc varìltjon (as illustrated by Caflonron 1985), in association wirh Peltocer,ts (Peltornoryhites) subtense, 5. Varboys, Cambridgeshire, England Grossour.,ria (Poculisphinctes) poculun,?Grossouoria rrira (Br"rckrnan), lV;rrbovs Pit fTL308818], now 11 \vasre disposal site and partlv Euaspidoceras hirsutum, Binatisphinctes binatus, Hecticoceras (Puteal- infilled, has long been known for its ìmportant sections in Veymouth iceras) puteale, Kosntoceras (K.) zr. spinosutn, Alligaticeras (A.) alliga- Menrber cl:rys of the Marìae Chronozone,;rs recorded by Spath (1939), tun and Disticboceras bicostatunt. Great rarities include (P.) Crllomon (1968) and \fright (in Wright & Cox 2001). The base of the lalandeauum (D'Orbigny) and. Reinecleeia (Collotia) sp.. Oxfordian had never been recorded, hower.er, until 1990, wnen excr- The overlyine clays of Bed B, at the base of the Veymouth vations for landfill cells, revealed the top of the Stewartby Member Menrber, yield pvritised Cardioceras spp. including C. iroodhamense below and hence the Callovian-Oxfordian boundarr.'. This sectron was Arkell non Fortwengler Er Marchand and C. ex gr. scarburgense - the 244 K. N. Page

Fig.2 - The C.rllovian-Oxfordian boundary sequence at Ham Cardioceras ú. scarburgense, Peltoceras sp., near È Hecticoceras sp., Fehlmannites sp., Cliff/Redclil[ Point, o tVeymouth, Dorset (bed € numbers after Callon.ron in o È co g o o Callomon & Cope 1995). è N z o co s c o o o E É. oN o o -o l! o J X c o o o o0) É 0) C Cardioceras scarb urgense, Pelfoceras sp., uJ o í) I o) í Hectiaceras sg. ú. chatillonense, I 3 o f o .ct ) = o oo ì \ Cardioce ras woodhamense

J Q u e n stedto@ra s ú. pauci@statu m, Euaspidoceras sp., Hecficoceras sp Pelfoceras sp.,

t E È o (ú c.' o o- g q) o c z c o o N oN co o C J o J EI -co -o Quenstedtoeras ex grp. lamberti c) o l o \Quensfedfoceras lambefti, Kosmocrvras (K.) ex grp. É. o tu _o I spi nosum, Peltoceras (Peltonorphites) sp. ú. fL Eq) E suótense, Grossouvia (Poculisphinctes) poculum, fL (ú o f J E Ailigaticeras sp. d. alligatum, Her,ticr,ce.ras o (Putealiceras) J sp., ?Bem,beras sp., Di stichoce ra s bi@stat u m

Q u e n stedtoeras prael am beft i

Quensfedfooera s praelambefti, Euaspldoceras sp.

latter also beine present in Bed A above (these levels form the strato- dominated by pvritìsed nuclei of Q. benrici (R. Douvillé), with occa- type of the Scarburgense Subchronozone of Arkell 1941). The .rpp.rr- sional Kosmoceras (K.) spinosum, hecticoceratìds and perisphinctids. ent absence of Q. paucicostatzm an]ongst the thousands of ammonites Tr,rces of large body chanrbers of poorly preserved ex known from this site suggests that,;rs elservhere in central England, ir gr. lanberti were present in an overlying sequence of around 2.5 m of non-sequence is present at the stalle boundarl'. silty calcareous bands and marl. The overlvins Mlriae Chronozone rvas rlso presenr iìs Hollingu,orth & \fiignall (1992, p.17) recorded at 8. Stanton Harcourt, Oxfordshire, England least 0.6 nr of cltrys with Cardioceras spp., including, S. scarburgense - Terrpor.rrv excavetions for refuse disposal operations below althoueh it is uncle:rr whether cross-boundary pducicostdtum or uood- River Terrace travels, near Stanton Harcourt, north-rvest hanense biohorìzon faunas are present. of Oxford [N2413047], reverled a Callovian-Oxfordian boundary se- Elservhere in the district, in further temporxry excavxtlons at quence in Oxford Clay facies as described by Hollingworth er Vignall Linch Hill [N2424036], the Lamberti Subchronozone yielded relatively (1992), but without any rnalysis of the ammonite faunas. rvell preserved Quenstedtoceras ex gr. lamberti in ;r preserv.rtìon simi- In 1994, exposures were already in :r poor condition and are lar ro th;rt recorded at \Woodhan.r, although no section appelrs to hrve norv lost. Prominent at thrt time l'ere Henrici Subchronozone faunas been recorded (per. obs. 1990). 9. Redcliff Point/ Ham Cliff, Dorset, England 3) Grcv nrilrl \\'ith shelll seanr rrnd scattcred c;rlcareous len- Historicall,v the Oxford Cl;ry lìorm;ition of the Vel,nrouth clis- ':,,:::' *::1 trict hls yielded rich termin,rl Crrllovian, Larnberti Chronoz.onc frtunls ::l:: :::l:i:* :::::i'l': ': ::':::"à1,5i':ll from now-obliterated brick pits ancl also fron low slunrped cliffs ,rround Tidrloor Point (Arkell l94Z; Crrllonron 1993; Callomon c\ Copc 1995; 2) Grev nr,rrl l'ith sonre calcareous lenticles lnd in Q. lanberti Chrpnr;rn I999; Cox Ei Page in Cox $i Sumbler 2002, pp.20-29). Thesc inlos'erptn[lanbtrtiBiohorizon,part]...... (c.O.7m); f,run,rs include the tr-pe specinen of Q. lantberti (J. de C. Sos'erbv) it- self. Unfortunatelv no sections s'ere rccorded in the brick pits,rnd the Bed I, Level z) Grev m,rrl s'ith son.ìe c:rlcareous lenticles. Com- c.\posures of the Tidnroor Point :rrea ;rre lo\\,, slumped degr.rded. mon fauna, ofren rvith pvritised nuclei, includes ,rbundent 'rnd Quensted- More complete exposure s of these levels h;rve nevertht'less [.rccn tocerds e\ grp. lanbarti, Kosntocer,ts (K.) ex gr. spittosun (J. de C. Sor- knos,n for nlanv vears near Redcliff Point, east of Ve1'nrouth .rt ;r lo- erby), Peltoceras (PcbonotVhites) sp. cf. subtense, Hecticocerrzs (Puteal- 1W61 cality often referred to;ìs H;rnr Cliff fSYZl68l8] (Arkell 19471 Wright rcerzs) sp., Allig'ttit'eras sp.c'i.alligatum. Probably irrcludes levcl of I 9t16, in Wright & Cox 200I ; Citllorron 1993; Callonron & Cope 19951 Chapnran (1999), rvhich is rcported to vield: Distic'hoceras bicostatum,

Chrrpnran 1999; Pase in Cox c\ Sunrbler 2002, pp. 3l-34). Despite thc Grossout,ria (Poculisphinctes) poculunt, T Bemiceras sp. irnd a Peltoceras qu;llitv of exposure being variable - rs erosion is limited to exception.rl ( Pehont ory h i t es) sp. ( f i gured by' Chapman | 999, lig.7, 13) ll a n ben i Bio- st()rÍn evenrs - a more complete stxge boundan'sequence h:rs been rc- horizon.part]...... (c.0.4m); corded herc than at TidnToor Point. The latter l'as iirst published bv Clllornon (1993; see also Callorrron Ei Cope 1995) but has recenth'been Bed f ,levels x-v) Grev m,rrl s'ith Q. pr.tel.tnberti and Euaspi- re-exrmined b1'Chapnran (1999). As the ts'o sections.rre difficult to doceras sp. in los,er pirt (: level x, c.2nr belos'the top of the bed [: corìlprre, the subdivision into beds of the forner schenre is rcproduccd praelamberti Biohorizonl...... (c.2.6 nr recorded). hcre (liig.2 and belor,). Additions arc brsed on pers. obs. irncl possiblc corrclirtions with the scction of Chrpman (1999), r'hich uses levcl or slnrple numbers rather than a division into beds. The sequence of ammonite faunas across the Callovian- Oxfordian boundary MARIAE CHRONOZONE, SCARBURGENSE SUB- The followins ammonite faunas or biohorizons CHRONOZONE (sensu Page 1995) characterise the Callovian-Oxfordian

5) (part) Grev nrarl wirh scrrrercd amnronires and a line of Grr'- boundary inter-val in Britain. Examples of most of the taxa pltrca c. 1.5 rr above the base, llso l,ielding C. scarbutgense lscdrburge nse listed below are figured by Arkell (1939), Spath (1939), Biohrrrizon, partl. The Cryphaea bcd eppears to be equivalent to level Wright (1983), Cox (1988) and Page (1991). Abbrevia- \lZ3.l of Chapman (1999), rvith levcl 25.l rround 0.5 nr higher. Thc tions used for denoting biohorizons derived from zonal lrrtter is reported to yield C. scarburgense (including Chapnran 1999, assignment (e.g. Lamberti Lamberti fig,6, G-N and fig.5, G-J, N-Y rhc latter misidentified s"C. pauci- LL = Chronozone, utst,rtuni', also fie.6, O-T, identificd as"Quenstedtoceras" nrariae), Hcc- Subchronozone). ticoccras sp. cf. chatillonerse (repolted bv Chapman 1999 as including a nr icroconch form resenr blin g, " Il ri ght i a" t h u o u xen s i s ; Forrn'e'n gler et al., fig. 7, H) md Peltocetz.s sp. (including Chapnran 1999, fig. 7, I-O) UPPER CALLOVIAN, LAMBERTI CHRONOZONE, LAMBERTI lscarbutgense Biohorizon, panl. An additional fauna, denoted V79, SUBCHRONOZONE around 4 nr higher, is reported as including C. scarburgensa (including Chapnran 1999, fig.8, G), Heticoceras sp. (Chapnan 1999, fig. 8, A- LLI: praclanbcrti Biohorizon. Reference: Lorvest c.1.5 m of ?F), Feblmannires sp. (Chapnran 1999, fig.8, H-N) and Peltocer,ts sp., Unìt 1, Stewartby/?Vcynrouth Menrber, Oxford CIay iìorrr.ration, Red- although biohorizon assignnrent is uncertain ...... (6 nr+); cliff Point/Hanr Cliff, Veymouth, Dorset. h.llunt Quenstedtoceras prlze- lamberti (R. Douvillé) md Eu,tspidoceras sp.. Comnrenrs: rhe praelam- 5) (part) Grey nrarl s'ith scattc'red ammonires including Crr- berti Bìohoriz,on is presentlv the lor.est distinguished in the Lamberti dioceras uoodhamense (Arkell) non Forts,engler Et Marchand and C. Subzone in Britain. l" Q u en st e d t oceras"l m ari ae (d'Orbir:nr.) (Callomon | 99 3) lr"' o od ha - menseBiohonz-on] .... (c.0.7 m); LL2: lanberti Biohorizon. Reference: upper c.40 crn of Unit 1, and Unit 2, Stervrrtbr,/?Vcvmouth Menrber, Oxford Clal' Formation, LAMBERTI CHRONOZONE, LAMBERTI SUBCHRO- Redcliff Point/Hrnr Clifl Wevmourh, Dorset. Faunl: Qaensledtoceras NOZONE latnberti (J. de C. Sorvcrby) [often abundant, nracnrconchs very vari- able from inflated fornrs (including Q. cadìforne Buckrnrn) to com- 4e-f) Grey marl rvith scattered lmnronites includinu Q. cf. pressed (includins Q. Lmbeti auct.) and fronr involute nrorphologies pt1tcircst,lturil (Lange) near the top (=$gd 4f). Probably equir',rlent (includins Q. sutherhndiae J. de C. Sorverbv) to rehtively evolute to fcvef V7l.l of Chapm;rn (1999) rvith C. paucicost.ttun (including forms (includinu Q. gregrriunt Leckenbv), as illustr;rted bv Callonron Chapnran 1999, fig. 5, M), also Euaspidoceras sp., Hecticocerdr sp. irnd 1985, text-fig. 5). Conrpressed :rcute ventered rnd intermediate forms Peltoceras sp. Includes level WZl.l wirh"C."paucicostdttlm, probablv at n,ith a short *'horl section and an arched venter (includingQ. dissin- *:::: i1e Brown) donrinatc nrost assenrblases (Plge l99l). Typical micro- t:::::' 1:t::t: ::::i:1':::',::':"- :t:T: [ì:i::il conchs have a chlracteristic ribbing st,v-le n'ith three to four secondan' ribs per prinrarr, (: Q. fexicostarzzi (Phillips), figured b1'Callonron Er 4b-d) Double rorv of calcareous lenticles. Probably ecluìv;rlent \fright 1989, pl.95, figs.2r, b, also Page 1991, pl. 17, figs. 7,8); coars- ley ribbed infl;rted r';rrients include leacbi to lcvels \Y/65-\167 of Chapnrrn (1999) lpaucicostatutn Biohoriz,on, Q. [. Sowerby));associated p:ìrtl.. (c.0.4nt); fauna includes Peltoceras (Peltontoryhites) subtense (Bern) (includine Page 1991, pl. 25, fir:. 10, p|.27, fig. l), Grossoat'ria (Poculispbinctes) poculunt (Leckenbv) (including Page 1991, pl.2l, fig. Cox, 1988, -ta) Dark clavs s,ith Q. paucitostatun in upper c. 0.8m [= par- l,4; cicost.ttun Biohorizon, pxrtl .. . . . (c.t.8 m); text iig.1, pl. 12. fiss.9, I l, l.{, l6; pl. 13, figs. l-5),Tcrossouxria tri- 206 K. N. Page

ra (Buckman) (Cox 1988, pl. t+, figs. ?2, elso 3-5). Euaspidoceras bir- C. praecordatum (with a developine keel; includes specimens figured sutum (Bavle) (including Page 1991, pl. 22, figs. 6.7), Binatislthinctes as C. scarburgense ?var. crassa nor'." b1' Spath 1939, pl. 76, figs. 4 and binatus (Leckenb.v), Hecticoceras (Putealiceras) pir teale (Leckenbl') wrth 12, nray also include var. nornundiana Spath 1919, pl. 7, figs. 9). Com- ra.re Kosmoceras (K.) ex gr. spinosunt (J. de C. Sorverbv), AlLigaticeras nrents: succeeding falunas are included in the Praecordatum Subzone. (A.) alLigatutn (Leckenbv)(including Page 1991, pl. 20, fig. 15; pI.21, The aff. scarburgense Biohorizon ìs broadlv equivalent to the "?middle figs.5,6; Cox 1988, pI.23, figs. 3,5,6,7) and Disticboceras bicostatunt subzone of the Mariae zone ?with scdrburgense and, praecordatum" of (Stahl). Great rarities ìnclude P,tcb)tceras (P.) lalandeanut;'r (D'Orbign1,) Arkell (1941) and the index species is broadlv equivalent to C. u'ood- and (ColLotia) oxl,ptichoides (Spath). Comments: Rich lant- bamense sensu Fortrvengler & Marchand non Arkell. beti tsiohorizon frunas as knortn from the Scrrborough district (North Yorkshire), \Woodhan.r (Buckinghanrshire) ;rnd the Wevmouth district, Dorset, especiallv from Tidnroor Point and Redcliff Point/Hanr Cliff. Correlations with the candidate GSSP in Haute Pro- Cardiocerarids are the onl,y truly diagnostic taxa, all other species be- vence ing very close to earlier or later forms. The very expanded sequences of the Terre Noire LL3: paucicostatunt Biohorizon Reference: Unit .1, Stew:rrtbv/ ?Veymouth Menrber, Oxford Clay Formation, Redcliff Point/Hanr in south east France allowed Fortwengler and Marchand Cliff. Fauna: Quenstedtoceras pducicostdtum (Lange) is typical and lo- (1994, 1997) to construct a very detailed sequence of cally comnron; microconchs are nlost typical and characteristic forms faunas across the Callovian-Oxfordian boundary - the have a continuous kecl and ribbing which does not form ventral cher'- Scarburgense Subchronozone, for instance, is around 48 rons unlike typical Q. larnberti (fìgured by \lright 1 983, pl. I 8 figs. 1 -3, m thick at Savournon, as opposed to a maximum of only also Page 1991, pl. 17, ttg. 9; Chapman 1 999, Fig.5, M); Peltoceras (Pel- tomorybites) sp. , Euaspìdocerz-, sp. lnd Hecticoceras sp. are occasional around 9 m at Warboys and possibly similar at Redcliff andT Longaericer4s sp. very rare (figured by Wright, I 983, pl. 1 8, fig. 8). Point/Ham Cliff. In addition, the Submediterraneanf Comments: follon'ìng Callonron (1990) and Fortu.enqler & Marchand Mediterranean character of the faunas inevitably meant (1994, etc.), the paucicostatum fauna. is included s,ithin the Callovian. that assemblages were richer in Tethyan groups such as hecticoceratinids and peltoceratinids, thereby facilitat- LOVER OXFORDIAN. MARIAE ZONE, SCARBUR- ing the recognition of a more detailed sequence of fau- GENSE SUBZONE nas than is currently possible in Britain, at least in the early Oxfordian. Not surprisingly, therefore, sections at MSl: tpoodhanrezse Biohorizon. Reference: lower c. 0.2 m of Thuoux and Savournon v/ere subsequently proposed to Unit 5, Veyrnouth Member, Oxford Clav Fornration, Redcliff Point/ the International Subcommission on Jurassic Stratigra- Hanr Cf iff. F auna: Cardi oceras (S carburgiceras) "ooo dhamezse Arkell phy, 1998, as a Stratotype Section and Point non March:rnd (including fornrs resembling Q. mariae R. Douvillé; in Global teste Crllomon 1993; probirblv includes specìmens fìgured by Arkell for the base of the Stage (although ratification has not 1939, pl.10, figs. 2-4); typicrl coarsely rìbbed compressed fornrs have yet been achieved). c:rrinate venters. Feeblv ribbed becticoceretids ma1- be locally frequent Figure 3 shows the correlation of the current Sub- (including ?Fehlntannites sp.), also T.tr.lmellicerus sp.. Conrments: the mediterranean sequence of horizons (: "zonules" sensu woodhamense feuna is placed at the base of the Oxfordian followins Callon.ron (1993) and in Callomon and Cope (1995), despìte its rpprr- Page 1995) as established by Fortwengler and Marchand ent predating of a Yorkshire scarburgense fauna, selected by Callomon (1994,1997) and reviewed by Thierry et al. (1997) and (1990) as the basal horizon of the stage (see comment to MS2). The Cariou et aI. (1997\ with that described here for Sub- carinate venter indicates that generic assignnlent to Cardioceras rather boreal Province sequences in Britain. Correlation of the rha,n is probably most appropriate. C. zaoodhamense Quenstedtoceras Subboreal pra elamberti and lamberti biohorizons and the of Fortwengler & Marchend is a later form, from the upper part of the name is Scarburgense Subchronozone. Submediterranean horizons of the same straight- forward. The Submediterranean Thuouxensis (or Elisa- MS} scarburgelse Biohorizon. Reference: lWeynouth Mem- bethae) Horizon is more problematic however, as the car- ber, Forn.ration. Fruna: C. (Scarburgiceras) scarburgense Oxford Clay dioceratid fauna is dominated by Q. paucicostatum,blt (Young & Bird) sensu stricto is conlmon (typìcal conrpressed variants with occasional forms resembling true C. scarburgense have relativell, straìght primary ribs on their inner whorls and second- (Cariou er 1997). As Subboreal paucicostatum Bio- aries u'hich curve on the outer half of the whorl sìde towlrds a carinate ^1. venter; includes Chapman 1999, Fig.5, G-J, N-Y Fig.6, G-N, O-T), also horizon faunas are relatively uncon-ìmon and therefore Hecticoceras spp. iincludinu Ch.rpm.rn 1999. Fi{r.7, H) tnd Peltoceras poorly characterised, it is not unlikely that they could sp. (including Chapn.ran 1999, Fig.7, I-O). Comment: the fauna fig- span the Paucicostatum-Thuouxensis boundary and hence ured by Sflright (1983) from Bed 1O of the Oxford Clay Formation on the Submediterranean Callovian-Oxfordian boundary (as rhe north side of Osgodby Nrb, Scarborough (e.g. pl. t 8, figs. 4-7; and especially the less common scarbur- Page 199l,pl. 1/,figs. IO, 1I,pl. 18,figs. 10, 11)maybelongtoasimi- shown on Fig. 3), if lar level as the Dorset reference, although further material is required gense morphs have not been recovered in UK sections. to confirm. This Yorkshìre fauna rrtrrked the base of the Oxfordian in The position of the Subborealwoodhamen.te (sensu the proposal of Callonron (1990). stricto) Biohorizon in the Submediterranean sequence is problematic, as the characteristic morphology is not MS3: aff. scarburgezse Biohorizon. Reference: Bed 3, Vevmouth clearly represented in assemblages figured from France. Member, Oxford Clay Forrnation, Varboys Clav Pit, Cambridgeshire (Spath 1939; Caflonron 1968). Fauna: Cardioceras (Scarburgiceras) alf. The relatively common occurrence of feebly ribbed hec- scarburgense is typical, r species including morplroloeies transitional to ticoceratids in Britain, however, su€igests that the Bioho- C a I I oi., i an - O {ord i an bo un tlaD' i n B rita i n 2Q7

rizon corresponds with part of the Scarburgense Hori- STANDARD BIOHORIZONS HORIZONS zon, as described by Cariou er aL. (1997). The Subboreal ZONATION (UK) (SE FRANCE) scd.rburgense Biohorizon would therefore correspond to a higher part of the same Horizon. As indicated previously, C. woodbamense Fort- E È o o -o "Woodhamense" g o. wensler & Marchand non Arkell includes forms identi- o afl. scahurgense (Fortwengler & z N Marchand non Arkell) cal to C. a[f. scarburgense, as interprered here a correla- o o - c tion between the subboreal aff . scarbwrgense Biohorizon o o o E o) and the Subrnediterranee.n o O scarburgense s.s. woodbAmense is consecuentlv xlt o -o Scarburgense clear. o .g o o a J woodhamense Thuouxensis/ Conclusions Elisabethae t E o g(! o paucicostatum Althoueh British sections have played a key role in N the development of understanding of the Callovian-Ox- z o o Paucicostatum c fordian boundary, the majority are nor suitable as GSSP =< N I o o candidates due to stratigraphical incompleteness. One key J -o J Y o section, however, at Redcliff Point/Ham Cliff near Wey- O C) E lamberti Lamberti mouth, Dorset, has the porenrial to yield stratigraphi- É. E o ul o -o cal inforn-ration to complement any proposed or ratified (L -o E n E o GSSB as the lithologies present are suitable for micro- f J -E praelamberti Praelamberti p:rlaeontological analysis.

Fig. 3 - Thc. correlltion of the sequence of Subbore;rl biohorizons rccosnisecl in thc UK (this r.ork) r'ith the'sequcncc of Subnrcditerr;rrrean horizons (;rfter Fortr.engler & March- ancl 1994. 199l; Thierrv et rl. 1992;rnd Crriou cr rl. 199l; Adenotledgenerits. M. Hlrt (Universin' of Pli'rrouth) con- for the tcnrin;rl Callovi,rn encl b;rsal Oxforcli.rn. Thc. double lirnred the potentirl of the Redcliff Poìnt/Hanr Cliff section for nri- johorizons linc bctl een rrcl jrce nr b inclic;rtcs the stntigraphi- cropaliìeontolosic;rl studies. The author *'ould also like to thank the cll intervrrl conceptu;rllv present bctu'c-en e;rch dcfinc'd unit revies,ers R. Enal'and B. Mltvj;r for their critic;rl reviews and suuges- (scc P;rge 1995). tion. rhrt irrrproved rhe nr,rnuscripr.

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