The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 89

The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP

Kevin N. PAGE 1, Guillermo MELÉNDEZ 2 and John K. WRIGHT 3

1 School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK; e-mail: [email protected] 2 Paleontología, Dpto. Geología, Universidad de Zaragoza, Zaragoza 50009, Spain; e-mail: [email protected] 3 Department of Earth Sciences, Royal Holloway, University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK; e-mail: [email protected]

Key-words: ammonites, stratigraphy, palaeobiogeography, Jurassic, Callovian, Oxfordian, GSSP, Europe, Cardiocer a- tidae, Perisphinctoidea.

ABSTRACT: The latest Callovian and Early Oxfordian are characterised by one of the highest levels of mixing of Boreal, Submediterranean and even Mediterranean faunas. In particular the massive expansion of Boreal Cardioceratidae from their original “home” in Arctic areas as far south as south-east France, brings them into contact with Mediterranean- style faunas rich in Phylloceratidae. This so-called “Boreal Spread” provides the framework within which high- resolution inter-bioprovincial correlations are possible and hence the context for a successful GSSP designation for the base of the Oxfordian Stage within Europe (and hence the beginning of the Upper Jurassic). Associated with the Cardioceratidae, especially in more Tethyan areas is a great variety of Perisphinctoidea, including Aspidoceratidae, Periphinctinae, Grossouvrinae and rarer Pachyceratidae as well as frequent Hecticoceratinae and rarer Phylloce- ratidae. As several of these persist beyond Europe they therefore provide tantalising indications that a truly global correlation of any GSSP established in Europe will ultimately be possible. The stratigraphical, taxonomic and palaeobiogeographical context and significance of the trans Callovian-Oxfordian boundary faunas within Europe is here reviewed and the faunas of the candidate GSSP at Redcliff Point, Weymouth, SW England are described, including the basal Oxfordian species Cardioceras (Pavloviceras ) redcliffense sp. nov.

INTRODUCTION into contact with diverse Mediterranean-style faunas rich in Phylloceratidae (Pantethyan Realm The latest Callovian and Early Oxfordian or Superrealm). Not surprisingly, this intermixing represent one of the most dynamic intervals in the means that exceptionally detailed high-resolution history of Jurassic Ammonoidea and is characte- correlations are possible across the area, this rised by one of the highest levels of mixing of providing one of the best contexts for establishing Boreal, Submediterranean and even Mediterranean the Global Stratotype Section and Point for the base faunas. The key event is a massive expansion of the of any Jurassic Stage. range of Boreal Cardioceratidae from their original Associated with the Cardioceratidae in the home in Arctic Province areas (Panboreal Realm south is a great variety of Perisphinctoidea, inclu- or Superealm sensu Westermann 2000), across ding Aspidoceratidae, Periphinctinae, Grossouvri- Europe to as far south as SE France, bringing them nae and rarer Pachyceratidae as well as frequent 90 Volumina Jurassica, Volumen VII

Hecticoceratinae, Phylloceratidae and Lytocera- ceratidae, with cadoceratids in the Lower and tidae. Most of these groups are commonest in Sub- Middle Callovian which evolve into Longaeviceras mediterranean and Mediterranean Province areas, in the early Upper Callovian and eventually but the Aspidoceratidae do persist well into the give rise to Cardioceras at the end of the terminal Pan-Boreal Realm and are locally common amongst Callovian , Lamberti Chronozone. The expansion the latest Callovian Subboreal faunas of England of Quenstedtoceras into Subboreal and Subme- and Scotland. Crucially, several groups of Peri- diterranean province areas – the Boreal Spread of sphinctoidea, including Peltoceratinae, do range Callomon (1985) – provides an excellent corre- beyond Europe and are known in East Pacific and lative event, now established as the base Indo-Pacific areas (Westermann 1992), therefore of the Lamberti Chronozone. Detailed records of providing tantalising indications that a truly global trans-boundary ammonite faunas from the Arctic correlation of any GSSP established in Europe will Province are few although there is no reason to ultimately be possible. suspect that the basic succession of Quenstedto- The current paper will review the stratigra- ceras to Cardioceras faunas differs in any phical, taxonomic and palaeobiogeographical con- significant way from that in adjacent Subboreal texts and significances of the trans-Callovian- areas, as described below. The local persistence Oxfordian boundary faunas within Europe, building of Longaeviceras into the Lower Oxfordian, on recent results from the candidate Oxfordian however, is noteworthy . GSSP near Redcliff Point, Weymouth, Dorset. There is some evidence, however, of ende- mic cardioceratid species in Boreal-Pacific areas (sensu Westermann 2000) of North America as BIOPROVINCIAL CONTEXT suggested by reviews in Westerman (1992, for instance pp. 29-92, 225 -272) . The East Pacific The marked north to south zonation of ammo- context of these faunas, however, may suggest nite faunas during the latest Callovian and Early that assignment to a different biogeographic pro- Oxfordian in Europe reflects a transition from vince might be more appropriate, perhaps even the relatively environmentally restricted and cooler a Northwest Pacific Province as is recognised at waters of the circum-polar Arctic Sea to the warm the end of the Jurassic and into the Lower Creta- margins of the Tethys Ocean. As would be expected, ceous ( cf . Page 1996). diversity increases steadily southwards and as a result a series of essentially east-west trending Boreal-Atlantic Realm: Subboreal Province bioprovinces are recognisable, as reviewed by Page (including England, Normandy, southern (1996, 2008 ). Although overlapping geographi- Germany, northern Poland, Russian platform) cal ranges facilitate some correlations between adjacent provinces, it is the sudden spread of the Subboreal Province Late Callovian to Early Cardioceratidae southwards from their Arctic home Oxfordian faunas are also dominated by Cardio- in the latest Callovian, that provides the context for ceratidae, but in addition include levels with correlation of the interval across Europe. The frequent Perisphinctoidea , especially Euaspido- character of each successive bioprovincial belt is ceras and Peltoceras (both Aspidoceratidae) and reviewed below. locally also Oppeliidae, including Hecticoceratinae. The Upper Callovian, Lamberti Subchronozone, Arctic or Boreal-Atlantic Realm: Arctic Province in particular the lamberti Biohorizon is particular (including Greenland,Spitzbergen, Alaska, diverse with a wide variety of Tethyan forms and western Canada, far eastern Russia, Scotland) also frequent Kosmoceras (K.) which is characte- ristic of the province , for instance in North York- A distinct Arctic Province for ammonoids shire (Wright 1968) . In the Lower Oxfordian, was already established in the Triassic and its although no clearly endemic Subboreal taxa are use in the Jurassic is reviewed by Page (1996). currently recognised (comparable for instance It is equivalent to the “inner Boreal ” Province of with Lower Callovian Proplanulitinae or Upper Callomon (1985), although often referred to as Oxfordian to Kimmeridgian Aulacostephanidae), simply a “Boreal Province ” by many authors. the Province maintains a clear Boreal character Callovian and Oxfordian Arctic Province faunas due to the dominance of Cardioceratidae. The pre- are virtually exclusively composed of Cardio- sence of frequent Tethyan forms, however, demon- The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 91 strates a classic “Subboreal ” character within an rare Phyllo- and Lytoceratidae. Representative Arctic to Mediterranean province spectrum of boundary sections are few, however, and most of the increasing Tethyan influence as has been described recorded fauna has been recovered from stratigra- by many authors ( e.g . Enay 1980; Page 1996, etc. ). phically condensed levels associated with a major A synthesis of typical Subboreal ammonite faunas regional non-sequence which typical omits most of in the UK is provided by Page (2004) and the can- the Middle and Upper Callovian and the Lower and didate GSSP near Redcliff Point in Dorset, SW basal Middle Oxfordian. Where typical faunas have England, as described in more detail below, been recorded, the Upper Callovian, including is characteristic. equivalents of the Lamberti Chronozone is chara- In Scotland (as reviewed by Page 2004) cterised by common Hecticoceratinae with varied the fauna is much less diverse and more Arctic Perisphinctoidea including Peltoceras , Alligati- in style. Latest Callovian faunas include typi- ceras and Poculisphinctes (Meléndez et al. 1982; cal Boreal Quenstedtoceras spp. with occasional Page et al. 2004). Remarkably, a few very rare Kosmoceras (K. ). With the exception of Eu- Kosmoceras (K.) are also known. Lower Oxfordian aspidoceras at one level, no other genera seem faunas are also dominated by Perisphinctoidea, to have been recorded. Early Oxfordian faunas although equivalents of the Mariae Chronozone are of the Mariae Subchronozone are virtually exclu- difficult to recognise. Peltoceras , Properisphin- sively of Cardioceras (Pavloviceras ) and only very ctes , Mirosphinctes and Oppeliidae are typical. rare late Longaeviceras (L. staffinense Sykes) Phylloceratidae, including Sowerbyceras , are appears to be present – other Perisphinctoidea ( e.g . only locally recorded, and never common. As in Peltoceras and very rare Mirosphinctes ) not being the Mediterranean Province (see below), in the recorded until the Costicardia Subchronozone of absence of Cardioceratidae, reliable correlation the Cordatum Chronozone . of the terminal Callovian, Lamberti Chronozone and the basal Oxfordian Mariae Chronozone is Mediterran-Caucasian Realm: Submediterra- currently problematic. nean or Mediterranean Province – east (SE France, etc.) Mediterran-Caucasian Realm: Mediterranean Province [including Italy, Sicily, Eastern Submediterranean Province faunas S Spain (Betics)] have a strong Mediterranean Province flavour and are characterised by a remarkable mixing In addition to abundant Phylloceratidae, of Boreal and Tethyan faunas with frequent Mediterranean faunas of the latest Callovian and Cardioceratidae, varied Perisphinctoidea (Pelto- earliest Oxfordian include a wide range of Peri- ceras , Poculisphinctes , Alligaticeras , etc. ) and sphinctoidea which are broadly similar to those common Hecticoceratinae in association with of Submediterranean areas ( e.g . as recorded by common Mediterranean Province Phylloceratidae, Checa and Sequiros 1990). In the absence of chara- including Sowerbyceras . Subboreal Kosmoceras is cteristic Cardioceratidae, however, the Callovian- rare as is Tethyan Pachyceras . The faunas of Oxfordian boundary becomes difficult to recognise the alternative candidate Oxfordian GSSP at Sa- with precision. vournon and Thoux in SE France exemplify such assemblages and have been described by Fortwen- gler and Marchand (1994, 1997) and Bonnot et al . THE AMMONITE FAUNAS OF THE CANDIDATE (1995 ) (see also Cariou et al. 1997, and Thierry et OXFORDIAN GSSP AT REDCLIFF POINT, al. 1997). Similar faunas are also known as far east WEYMOUTH, DORSET, SW ENGLAND AND as Iran (Seyed-Emami et al. 1995). THEIR CORRELATION

Mediterran-Caucasian Realm: Submediterra- As discussed by Page (1994, 2004), one of nean Province – west (including Spain) the stratigraphically most complete trans Callo- vian-Oxfordian boundary sequences in the UK is In contrast to eastern Submediterranean exposed near Redcliff Point, west of Weymouth, areas, faunas in the west are characterised by a on the Dorset coast (SW England; National map virtually absence of Boreal forms – Cardioceratidae grid reference SY716818). The section is developed in particular appear to be unrecorded – and only in the mudrock facies of the Oxford Clay Formation 92 Volumina Jurassica, Volumen VII

ZONATION SUBBOREAL SUBMEDITERRA- consecutively, however, in a style analogous to that (Submediterra- PROVINCE NEAN PROVINCE used for the Aalenian and Bajocian by Callomon nean/Subboreal BIOHORIZONS (UK) (EAST) and Chandler (1990), using the prefix “Ox ”. As for- /Arctic) HORIZONS Woodhamense mal stratigraphical units biohorizons are conven- (sensu Fortwengler lamberti , tionally quoted as, for instance, either a

e Ox4: aff. scarburgense and Marchand) n

e Biohorizon or a Lamberti Biohorizon (Fig. 1). o e n z N s o o n A z I n e o Ox3: scarburgense D o g n r r Upper Callovian, Lamberti Chronozone, R o h u r O b C h F r

Lamberti Subchronozone

c Scarburgense a e X b c a Ox2: woodhamense i O u S r S a LL1: praelamberti Biohorizon. M Ox1: redcliffense Index: Quenstedtoceras praelamberti (R. Dou- villé ). Author: Marchand (1986). LL3d: pauci. γ, Peltomorphites Thouxensis (?) Reference: 3.0-2.75 m below the top of Bed 1(=Da- tum), Stewartby Member, Oxford Clay Forma-

e LL3c: paucicostatum γ , n tion, Redcliff Point/Ham Cliff, Weymouth, Dorset, e o n z o o UK. z n

o LL3b: paucicostatum N

o β n r Fauna: Relatively evolute but closely ribbed Quens- A Paucicostatum I o h r c V tedtoceras praelamberti (R. Douvillé) is typical h b O C u L

LL3a: paucicostatum i S L α (cf . Douvillé 1912, pl. 4: 34-36), associated with t

i r A t e r C occasional Euaspidoceras sp. b e b m LL2b: Quenstedtoceras sp. 1 Comments: For consistency with Thierry et al . a m Lamberti L a

L (1997), the praelamberti Biohorizon is taken as LL2a: lamberti the lowest within the Lamberti Subchronozone.

Praelamberti LL2a: lamberti Biohorizon. LL1: praelamberti Index: Quenstedtoceras lamberti (J. Sowerby). Fig. 1. Correlation of ammonite biohorizons and horizons across the Callovian-Oxfordian boundary between the UK and SE France. Author: Callomon (1964). Reference (provisional): c. 2 m + below top of Bed 1, Stewartby Member, Oxford Clay Formation, Redcliff Point/Ham Cliff, and includes the boundary between its component Weymouth, Dorset, UK. Stewartby and Weymouth members (see also Arkell Fauna: Quenstedtoceras lamberti (J. Sowerby) 1947; Callomon in Callomon and Cope 1995; Chap- sensu stricto abundant with characteristic man 1999; Page et al. 2003; Page 2004 ). As well as evolute microconchs with arcuate, forward a remarkably complete sequence of ammonite curving ribbing, well developed ventral chevrons faunas, which includes assemblages not clearly and well space primary ribbing with up to 4 sec- recorded elsewhere, the site has also now yielded ondary ribs developing between each. rich microfossil assemblages and high resolution Comments: The characteristic fauna was recorded geochemical data which confirms its suitability as low in the Ham Cliff section during initial sam- a GSSP (see Page, Meléndez, Hart et al ., 2009 , this pling in 2002, but appears to have been covered volume). by beach material by 2003. The exact level has The sequence of ammonite faunas now re- not been established relative to the Datum used corded can become a standard for correlation for sampling from 2003 onwards and therefore throughout Subboreal areas and is described below requires confirmation when beach levels lower as a sequence of biohorizons ( sensu Page 1995). once more. By comparison with other localities Biohorizonal labelling for the Callovian follows in the UK, the associated fauna is likely to be Page (2004) with new units accommodated in a con- relatively diverse, with Hecticoceras (Puteali- ventional way, for instance biohorizon LL2 is now ceras ) puteale (Leckenby), Peltoceras (Pelto- separated into biohorizons LL2a and LL2b ( n.b . morphites ) sp. cf. subtense (Bean), Grossou- each unit is of full biohorizonal status as subunits vria (Poculisphinctes) poculum (Leckenby), are not permitted by the methodology; see Page Euaspidoceras hirsutum (Bayle), Kosmoceras 1995, etc. ). Oxfordian biohorizons are renumbered (K.) ex gr. spinosum (J. de C. Sowerby), Alliga- The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 93

ticeras (A. ) alligatum (Leckenby), etc . Represen- costatum fauna is included within the Callo- tative figures of these and other typical Lamber- vian. ti Subchronozone taxa are listed by Page (2004). LL3c: paucicostatum transient γ Biohorizon nov. LL2b: Quenstedtoceras sp. 1 Biohorizon nov. Index: Q. ex gr. paucicostatum transient γ nov . Index: Quenstedtoceras sp. with common coarsely Reference: Bed 2, +?1.55-2.1 m above the base of ribbed and relatively involute microconchs Bed 2, Weymouth Member, Oxford Clay Forma- (= “Vertumniceras spp. ” sensu Buckman 1909- tion, Redcliff Point/Ham Cliff, Weymouth, Dorset, 1930 ). UK. Reference: 1.65 to 0.2 m below top of Bed 1, Ste- Fauna: Q. ex gr. paucicostatum including forms wartby Member, Oxford Clay Formation, Redcliff showing features transitional to C. ( Pavlovi- Point/Ham Cliff, Weymouth, Dorset. ceras ) scarburgense (Young and Bird) as Fauna: Characterised by relatively coarsely ribbed occasional microconch specimens show body and involute microconchs of Quenstedtoceras chambers with a fine, scarburgense -style sp.; associated fauna includes Euaspidoce- forwards swept ribbing and reduced ventral rib- ras hirsutum , Hecticoceras (Putealiceras ) sp., chevrons and a consequently an incipient keel. Alligaticeras (A.) alligatum , Grossouvria Rare Alligaticeras sp. also present. (Poculisphinctes) poculum and Kosmoceras (K.) ex gr. spinosum . LL3d: paucicostatum – Peltomorphites sp . Bio- horizon nov. . LL3a. paucicostatum transient α Biohorizon nov. Indices : Q. paucicostatum transient γ, Peltoceras Index: Quenstedtoceras ex gr. paucicostatum (Peltomorphites ) sp. Lange transient α nov. Reference: Bed 2, 2.2-2.3 m above the base of Bed 2, Reference: Bed 2, 0.1-0.8 m above base, Weymouth Weymouth Mem-ber, Oxford Clay Formation, Member, Oxford Clay Formation, Redcliff Point/ Redcliff Point/Ham Cliff, Weymouth, Dorset, UK. Ham Cliff, Weymouth, Dorset, UK. Fauna: Q. paucicostatum transient γ abundant Fauna: Quenstedtoceras transitional between (Pl. 1 H) with common nuclei of Peltoceras Q. ex gr. lamberti and Q. paucicostatum sensu (Peltomorphites ) sp. stricto . Although dominated by the latter Comments: The stratigraphical position of this rela- morphology (see below) frequent forms retain tively Peltoceras -rich fauna, immediately below a lamberti -style with relatively widely primary the first Cardioceras ex gr. scarburgense is spacing. Overall, however, the fauna is notice- highly suggestive of a correlation with the lower ably more involute than typical lamberti group. part of the Elisabethae Horizon in SE France of Rare Hecticoceras sp. and ? Poculisphinctes Fortwengler and Marchand (1994), a level also sp. also present. with common Peltoceras eugenii (Raspail) (Bonnot et al. 1995; Fortwengler and Marchand LL3b: paucicostatum transient β Biohorizon. 1997). Index: Q. ex gr. paucicostatum transient β (= Q. pau- cicostatum Lange sensu stricto ). Lower Oxfordian, Mariae Zone, Author: Marchand (1979). Scarburgense Subzone Reference: Beds 2-4, 0.85-1.45 m above the base of Bed 2, Weymouth Member, Oxford Clay Forma- Ox1: Cardioceras (Pavloviceras ) redcliffense Bio- tion, Redcliff Point/Ham Cliff, Weymouth, Dorset, horizon nov. UK. Index: Cardioceras (Pavloviceras ) redcliffense Fauna: Dominated by typical Q. paucicostatum sp. nov. (Pl. 1A-G; see Appendix for description). morphs, with ribbing bending forward from Reference: Bed 2, 2.4-2.5 m above the base of Bed 2, relatively straight primary ribs at around 45º Weymouth Member, Oxford Clay Formation, towards the venter on the outer part of the whorl Redcliff Point/ Ham Cliff, Weymouth, Dorset, UK. sides and with a tendency to swell towards the Fauna: Cardioceratid fauna transitional between venter. Ventral rib chevrons persist. Euaspi- Quenstedtoceras ex gr . paucicostatum and C. doceras hirsutum frequent. (Pavloviceras ) ex gr . scarburgense ; scarbur- Comments: Following Callomon (1990) and Fort- gense -morphs with a keel developed through wengler and Marchand (1994, etc. ), the pauci- most of their ontogeny represent around 20% of 94 Volumina Jurassica, Volumen VII

A B

1 cm 1 cm

1 cm E D 1 cm 1 cm C 1 cm F

H G

1 cm 1 cm The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 95

the assemblage but are still associated with slightly flexuous primary ribs on inner whorls paucicostatum morphs. and secondaries which curve on the outer half of Comments: The incoming of scarburgense morphs the whorl side towards a carinate venter. Rare alongside paucicostatum morphs in SE France Peltoceras (Peltomorphites ) also present and corresponds to a level near the middle of the probably also hecticoceratids. Elisabethae “Horizon ” of Fortwengler and Mar- Comments: Relatively inflated and more strongly chand (1994), thereby, providing a very accurate ribbed morphs resembling “Q.” mariae Douvillé correlation between the two regions. The bio- common. horizon is, therefore, potentially recognisable across Europe from the UK to SE France based Ox4: aff. scarburgense Biohorizon . on this association of morphs. C. redcliffense is Index: Cardioceras (Pavloviceras ) aff. scarbur- also present in Russia in the key Callovian- gense (Young and Bird). Oxfordian boundary section of Kislev et al. Author: Page et al . (2003), broadly equivalent to (2006) (JKW observation 2007). the Woodhamense “Horizon ” of Fortwengler and Marchand (1994, 1997). Ox2: woodhamense Biohorizon. Reference: Bed 3, Weymouth Member, Oxford Clay Index: Cardioceras (Pavloviceras ) woodhamense Formation, Warboys Clay Pit, Cambridgeshire Arkell (non Fortwengler and Marchand 1994, (Spath 1939; Callomon 1968). 1997). Fauna: Cardioceras (Pavloviceras ) aff. scarbur- Author: Page et al . (2003). gense is typical, a species including morpho- Reference: Bed 2, 3.1-3.2 m above the base of Bed 2, logies transitional to C. praecordatum Douvillé Weymouth Member, Oxford Clay Formation, (with a more accentuated forward sweep of the Redcliff Point/Ham Cliff. secondary ribbing towards a more prominent Fauna: Cardioceras (Pavloviceras ) woodhamense keel). Arkell (non Marchand) is typical and characteri- Comments: The characteristic fauna is present in sed by common relatively strongly ribbed morphs. the Redcliff Point area, but not in a conti- Occasional Euaspidoceras sp. also present. nuous succession with the Callovian-Oxfordian Comments: The use of a woodhamense Biohori- boundary exposure. zon follows Callomon ’s (1993) interpretation of Arkell ’s (1939) species as basal Oxfordian. “C. woodhamense ” of Fortwengler and Mar- CONCLUSIONS: GLOBAL CORRELATION chand (1994, etc .) is a later form, from the upper POTENTIAL OF EUROPEAN CALLOVIAN- part of the Scarburgense Subchronozone (Page OXFORDIAN BOUNDARY FAUNAS 2004). Detailed correlations are possible between Ox3: scarburgense Biohorizon. the UK Subboreal sequence of ammonite faunas, Index: C. (Pavloviceras ) scarburgense (Young and as exemplified by the Redcliff Point/Ham Cliff sec- Bird). tion and the alternative candidate GSSP localities Author: Buckman (1913). at Savournon and Thuoux in SE France , in an east- Reference: Bed 3 (4.5 to at least +6.2 m above ern Submediterranean or Mediterranean context the base of Bed 2), Weymouth Member, Oxford (see Page, Meléndez, Hart et al. 2009, this volume). Clay Formation. Faunas in the latter area facilitate correlations with Fauna: C. (P. ) scarburgense sensu stricto is com- both the cardioceratid-free western Submediterra- mon with typical compressed variants with nean Province (Iberia) and Mediterranean areas

Plate 1 Quenstedtoceras and Cardioceras from the Callovian/Oxfordian boundary interval at Redcliff Point / Ham Cliff, Weymouth, Dorset, UK. A-G : Cardio- ceras (Pavloviceras ) redcliffense sp. nov. ; Bed 2, 2.4-2.45 m above base [ redcliffense Biohorizon (Ox1)]. D : Holotype (inner whorls of macroconch?). A, B: Typical relatively involute macroconchs with ribbing fading on whorl sides. C, E-G: Microconchs with keel and tendancy towards slightly flexuous ribbing and forward curving secondary ribs. H : Quenstedtoceras paucicostatum Lange transient γ nov.; Bed 2, 2.2-2.3 m above base [paucicostatum, Peltomorphites Biohorizon (LL3d)]. Large specimen is typical relatively evolute macroconch with ventral rib chevrons; small specimen is finely ribbed microconch transistional to Cardioceras (Redcliff Ox.1). All specimens currently housed in SoGEES, University of Plymouth. Scale bar is 1 cm. 96 Volumina Jurassica, Volumen VII through various Perisphinctoidea. Beyond Europe, acknowledge the assistance of English Nature the Arctic Province provides links to Eastern (Dorset Team, now Natural England) and wish to Pacific areas through its cardioceratid faunas and thank Mr Peter Broatch (Osmington) for permission the widespread distribution of Peltoceratinae into to extensively sample the section and Carolina Pacific areas also has a potential to aid the global d’Arpa (Palermo ) for assistance in the field . The correlation of the Callovian-Oxfordian boundary. authors would like to thank Professor A. Wierzbo- The very wide correlation potential of the wski and Dr M. Rogov for a critical review of the Callovian-Oxfordian boundary using ammonites – original text. This research contributes to Project at the level of “Horizon ” within central Europe, CGL2004-02694/BTE (MEC-CSIC) (GM) and has close to subchronozone level elsewhere in Europe been sub-sidised by the Fundación María-José and probably at around chronozonal level else- Bello-Villalba (KP). where – still provides the highest resolution method for correlating the stage boundary within marine sequences globally. Underpinning this correlation REFERENCES potential is a major bioevent, the “Boreal Spread ” (sensu Callomon 1985, etc .) of the Cardioceratidae Arkell W. J. 1939. The ammonite succession at from their Arctic Province homeworld across the Woodham Brick Company ’s Pit, Akeman Europe to the Mediterranean. Whatever oceano- Street, Buckinghamshire, and its bearing on graphic or palaeogeographic changes facilitated the classification of the Oxford Clay. Quarterly this colonisation is unclear, but it also enabled Journal of the Geological Society of London , Tethyan Perisphintoidea and Oppeliidae to reach 95 : 135-122. at least as far north as Britain in reasonable Arkell W. J. 1947. The geology of the country around numbers at times. Crucially, it also facilitated Weymouth, Swanage, Corfe and Lulworth. a northwards movement of ocean-going Mediterra- Memoir of the Geological Survey of Great nean Province Phylloceratidae, especially in the Britain (England and Wales) , 386 pp. Early Oxfordian, most abundantly so in Sub- Bonnot A., Fortwengler D. and Marchand D. 1995. mediterranean, SE France, but also in small num- Les Peltoceratinae (Ammonitina, Aspidocera- bers into Iberia and even as very rare occurrences tidae) au passage Callovien-Oxfordien dans les in Subboreal Britain (Page 2004). Terres Noires du sudouest (France). Geobios , Whatever processes affected the distribution 30 : 651-672. of ammonite faunas would be expected to have Buckman S. S. 1909-1930. Yorkshire type ammoni- affected other groups. Changes in belemnite faunas tes (1, 2) and Type Ammonites (3-7), 790 pla- across the boundary in the UK have been observed, tes. London & Thame: Wheldon & Wesley (1), with Tethyan forms becoming dominant in England the author (2-7). in the Lower Oxfordian (see Page , Meléndez, Hart Buckman S. S. 19 13. The “Kellaways Rock ” of Scar- et al. 2009, this volume) but for other groups borough. Quarterly Journal of the Geologi- information is patchy. Probably the most signi- cal Society of London , 69 : 152-158. ficant, however, is the flood of early planktonic fora- Callomon J. H. 1964. Notes on the Callovian and minifera in the earliest Early Oxfordian (Oxford Oxfordian Stages. In : Colloque du Jurassique, et al . 2002), a bioevent recognisable elsewhere. Luxembourg, 1962, Comptes Rendues et Clearly whatever happened oceanographically or Mémoires de Institute Grand Ducal, Section biogeographically during the Callovian-Oxfordian des Sciences naturelles , physiques et mathé- “transition ” had a major effect across Europe – and matiques, Luxembourg : 269-291. not only on ammonite faunas … Callomon J. H. 1968. The Kellaways Beds and Ox- ford Clay. In : P. C. Sylvester-Bradley and T. D. Acknowledgements Ford ( Eds ), The geology of the east Midlands. University Press Leicester : 264-290. Dorset County Council (on behalf of the Dorset Callomon J. H. 1985. The evolution of the Jurassic & East Devon World Heritage Site) provided finan- ammonite family Cardioceratidae . Special cial assistance for initial field work, isotopic analy- Papers in Palaeontology , 33 : 49-90. sis and some photography. A contribution from the Callomon J. H. 1990. On the definition of the basal same source towards the costs of presenting this boundary stratotype of the Jurassic Oxfordian work is gratefully acknowledged. The authors also Stage. In: G. Meléndez ( Ed .), 1 st Oxfordian The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 97

Working Group Meeting, Zaragoza 1988 . Kiselev D., Rogov M., Guzhikov A., Pimenov M., Publicaciones Sepaz Paleontología ,. Zara- Tesakova E. and Dzyuba O. 2006. Dubki (Sara- goza , 2: 119-127. tov Region, Russia), the reference section for Callomon J. H. 1993. Oxford Clay. In : J. H. Callomon the Callovian/Oxfordian boundary. Volumina and J. C. W. Cope The Jurassic geology of Jurassica , 4: 177-179. Dorset, guide to excursions. Arkell Interna- Marchand D. 1979. Un nouvel horizon paléontolo- tional Symposium, September 1993, Univer- gique: l ’horizon ∫ paucicostatum (Oxfordien sity College London : 41-48, London. inférieur, zone ∫ Mariae, base de la sous-zone Callomon J. H. and Chandler R . B. 1990. A review of ∫ Scarburgense), Compte Rendu Sommaires the ammonite horizons of the Aalenian-Lower des Séances de la Societé Géologique de Bajocian stages in the Middle Jurassic of France , 1979: 122-124. southern England. Memoire Descrittivo della Marchand D. 1986. L ’évolution des Cardioceratidae Carta Geologica d’Italia . 40 : 85-112. d’Europe occidentale dans leur contexte paléo- Callomon J. H. and Cope J. C. W. 1995. The Jurassic biogéographique (Callovien supérieur-Oxfor- Geology of Dorset. In : P. D. Taylor ( Ed. ) Field dien moyen). These Doctoral, Université de Geology of the British Jurassic: 51-104. Geo- Dijon: 601p. logical Society, London. Meledina S. V. 1987. Ammonity i zonalnaya stra- Cariou E., Enay R., Atrops F., Hantzpergue P., Mar- tigrafiya kelloveya Sibiri, Trudy Akademii chand D. and Rioult M. 1997. Oxfordien. In : Nauk SSSR, Sibirskoye otdelenye Instituta E. Cariou and P. Hantzpergue ( Coord. ), Geologii Geofizikii, Nauka, Moscow, 184pp. Biostratigraphie du Jurassique ouest européen Meléndez G., Atrops F. and Page K. N. 2007 . The et méditerranéen. Bulletin du Centre des cardioceratid succession and the recognition Recherches Elf Exploration Production, of the Callovian-Oxfordian boundary at Savou- Mémoire, 17 : 79-86. rnon (SE France). 23 rd Annual Meeting of the Chapman N. D. 1999. Ammonite assemblages of Spanish Palaeontological Society: Carava- the Upper Oxford Clay (Mariae Zone) near ca (Murcia), 4-6 October 2007 : Abstract Weymouth, Dorset. Proceedings of the Dorset Volume. Natural History and Archaeological Socie- Meléndez G., Sequeiros L. and Brochwicz-Lewiƒski ty , 121 : 77-100. W. 1982. Lower Oxfordian in the Iberian Chain Checa A. and Sequeiros L. 1990. New data on the (Spain). Part 2: Ammonite fauna. Bulletin de Lower Oxfordian from the Subbetic Zone l’Academie Polonaise des Sciences (Sciences (Betic Range, SE Spain). In : G. Meléndez ( Ed .), de la Terre ), 30 : 173-181. 1st Oxfordian Meeting, Zaragoza 1988 Publi- Oxford M. J., Gregory F. J., Hart M. B., Henderson A. caciones Sepaz Paleontología. Zaragoza , 2: S., Simmon M. D. and Watkinson M. P. 2002. 153-160. Jurassic planktonic foraminifera from the Douvillé R. 1912. Étude sur les Cardiocératides de United Kingdom. Terra Nova , 14 : 205-209. Dives, Villers-sur-Mer et quelques autres gise- Page K. N. 1991. Ammonites. In : D. M. Martill, and ments. Memoire de la Societé Géologique de J. D. Hudson ( Eds ), Fossils of the Oxford Clay. France, 19 : 77pp. Palaeontological Association Field Guides to Enay R. 1980. Paléobiographie et ammonites Jura- Fossils, 4: 86-143. ssiques: Rhythmes fauniques et variations du Page K. N. 1994. A review of the suitability of key niveau marin; voies et changes, migrations et British Callovian-Oxfordian and Oxfordian domaines biogéographiques. Livres Jubilaire Kimmeridgian sites as Global Stratotype sec- Society Géologique de France, Mémoire N. - tions and Points (GSSPs) for stage boundaries S. 10 : 261-281. (Abstract). In : F. Atrops ( Ed .), Guide book and Fortwengler D. and Marchand D. 1994. Nouvelles abstracts , 4 th Oxfordian and Kimmerdgian unités biochronologiques de la zone ∫ Mariae Working Groups Meeting, Lyon, France, (Oxfordien inférieur), Geobios Mémoire Spe- June 1994 : 15-16, Lyon. cial , 17 : 203-209. Page K. N. 1995. Horizons; Intra-subzonal units in Fortwengler D. and Marchand D. 1997. Les coupes Jurassic ammonite stratigraphy. Palaeonto- de Thuoux et de Savournon (SE de la France logy, 38 : 801-814. et la limite Callovien-Oxfordien. Geobios , 30 : Page K. N. 199 6. Mesozoic ammonoids in space and 519-540. time. In : N. H. Landman, K. Tanabe, R. A. Davis 98 Volumina Jurassica, Volumen VII

(Eds ): Ammonoid Paleobiology. Topics in Geo- and nomenclature. Palaeogeography, Palaeo- biology , 13 : 755-794. climatology, Palaeoecology, 163 : 49-68. Page K. N. 2004 . The Callovian-Oxfordian boundary Wright J. K. 1968. The stratigraphy of the Callovian in Britain: A review of key sections and their rocks between Newtondale and the Scar- correlation with the proposed Global Stra- borough Coast, Yorkshire. Proceedings of the totype Section and Point for the Oxfordian in Geologists’ Association, 84 : 447-457. Haute Provence, France. Rivista Italiana di Wright J. K. 1983. The Lower Oxfordian (Upper Paleontologia e Stratigrafia, 110 : 201-208. Jurassic) of north Yorkshire. Proceedings of Page K. N. 2008. The evolution and geography of the Yorkshire Geological Society, 44 : 249-281. Jurassic ammonites. Proceedings of the Geo- logists’ Association, 119 : 35-57. Page K. N., Hart M. B. and Oxford M. J. 2003. The APPENDIX: DESCRIPTION OF NEW SPECIES search for a Global Stratotype Section and (INCLUDING NOTES ON CARDIOCERATID Point (GSSP) for the base of the Oxfordian GENERA AND SUBGENERA) Stage. Geoscience in south-west England, 10 : 435-441 . Cardioceras (Pavloviceras ) redcliffense sp. nov. Page K. N., Bello J., Lardiés M. D., Meléndez G., Ramajo J. and Ziani H. 2004. The stratigraphy TYPE : Original of Plate 1: A , ( Specimen “Redcliff of the Upper Bathonian to Middle Oxfordian M1”, SoGEES, University of Plymouth ). Bed 2, 2.4- succession of the Aragonese branch of the 2.5 m above the base of Bed 2, Weymouth Member, Cordillera Ibérica (Spain) and its European Oxford Clay Formation, Redcliff Point/ Ham Cliff, context. Rivista Italiana di Paleontologia e Weymouth, Dorset, UK. Additional topotype mate- Stratigrafia, 110 : 191-200. rial available. Page K. N., Meléndez G., Hart M. B., Price G. D., Wright J. K., Bown P. and Bello J. 2009 . DESCRIPTION : Cardioceratid species transistional Integrated stratigraphical study of the can- between “Q.” ex gr . paucicostatum Lange and C. didate Oxfordian Global Stratotype Section (Pavloviceras ) ex gr . scarburgense (Young and and Point (GSSP) at Redcliff Point, Weymouth, Bird) in which around 20% of the assemblage Dorset, UK. Volumina Jurassica , 7: 101-111. contains variants or morphologies ( “morphs ”) Seyed-Emami K., Schairer G. and Zeiss A. 1995. resembling the typical C. scarburgense (e.g. as Ammoniten aus der Dalichai-Formation (Mitt- figured by Wright 1983). The latter have a keel lerer bis Obere Jura) und der Lar-Formation developed through most if not all of their phragmo- (Obere Jura), N Emanzadeh-Has-hem (Zen- cone and consequently ribbing does not form tralalbirz Nordiran). Mittelungen der Bayeri- ventral chevrons and the lateral profile is not sche Staatssammlung für Paläontologie und therefore serrated or significantly undulose ( i.e. Historische Geologie , 35 : 39-52. where remnants of secondary ribbing crosses) . Spath L. F. S. 1939. The ammonite zones of the The remainder of the assemblage, has a more pau- Upper Oxford Clay of Warboys, Huntingdon- cicostatum style, however, as Quenstedtoceras - shire. Bulletin of the Geological Survey of style rib-chevrons persist and ribbing is not as fine. Great Britain , 1: 82-98. Thierry J., Cariou E., Elmi S., Mangold C., Mar- Microconchs of C. redcliffense show a similar chand D. and Rioult M. 1997. Callovien. In : involution to those of Q. paucicostatum but E. Cariou and P. Hantzpergue ( Coord. ), Bio- typically have slightly flexuous ribbing (biconvex) stratigraphie du Jurassique ouest-européen et with forward curving secondaries, rather than the méditerranéen. Bulletin du Centre des straight primary ribs and more angular inflexion of Recherches Elf Exploration, Production, the latter. The keel is present on most although may Mémoire 17 : 63-78. be very slightly undulose on some, secondaries Westermann G. E. G. 1992. The Jurassic of the typically fading towards it and merging with it (in Circum-Pacific. Cambridge University Press, Q. paucicostatum ribs – the secondary ribs typical 675 pp. do not significantly weaken even when an incipient, Westermann G. E. G. 2000. Marine faunal realms gently undulose keel is present). Maximum, size of the Mesozoic: review and revision under the observed is around 40 mm. Complete macroconchs new guidelines for biogeographic classification are not yet available at the type locality, although The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP 99 available material indicates a greater involution nuously evolving lineage, however, such assign- (c. 13-20%) than is observable in paucicostatum ments are biological meaningless and as is admira- specimens (c. 30%). In addition ribbing appears to bly shown by the Redcliff Point sections, transitio- fade earlier on the whorl sides ( e.g. by 40 mm) but nal assemblages are to be expected. with more pronounced secondaries on the outer- most part of the whorl sides. In paucicostatum , As already suggested by Callomon (1990), in however, blunt swollen ribbing often appears to a nomenclatural sense it is desirable to reduce persist to larger diameters. No specimens larger this subjectivity by using a single genus to describe than around 60 mm have currently been observed, this lineage. As Quenstedtoceras Hyatt 1877 has suggesting a relatively small species. priority over Cardioceras Neumayr and Uhlig 1881, however, its use for Oxfordian forms might meet DISTRIBUTION : Characteristic of the redcliffense resistance from some quarters. In addition, Mele- Biohorizon nov. (Ox1) (basal Oxfordian, Scarbur- dina (1987) has reported some sutural differences gense Subchronozone, Mariae Chronozone) at the between certain Quedstedtoceras and Cardioce- type locality although probably absent at most ras which lead to her proposal of a new subfamily, other well known English localities due to the the Quedstedtoceratinae. Clearly, however, in the widespread non-sequence at this level (see Page case of the Q. paucicostatum group, evolution 2004). Potentially recognisable across Europe directly into the C. scarburgense is demonstrable, where cardioceratid assemblages are reported to so the significance of Meledina ’s observations include a “mixing ” of C. paucicostatum and remains unclear, at least at this stratigraphical C. scarburgense as in the upper part of the Elisa- level. Pending a full revision of the Cardioceratinae, bethae “Horizon ” of Fortwengler and Marchand however, the conventional usage of the two genera (1994) and the lowest part of the Scarburgense is retained here, but noting that the disappearance Zonule (fauna 8A) of Fortwengler and Marchand of the genus Quenstedtoceras is a nomenclatural (1997) in the Thoux-Savournon area of SE France . artefact – a true “pseudoextinction ”. Later ( i.e . post The species is now independently confirmed paucicostatum ) records of “Quenstedtoceras ” in through new sampling at Savournon (April 2007; the Lower Oxfordian, such as “Q. ” mariae Douvillé Meléndez et al . 2007 ). Now also noted at Dubki in are simply coarsely ribbed and inflated variants of Russia (JKW observation, 2007; section cited by Cardioceras such as are known throughout the Kiselev et al . 2006). history of the group well into the Middle Oxfordian (cf . Callomon 1985 , for example “Goliathiceras ” DISCUSSION : The transition between Quenstedto- Buckman 1918 ). ceras and Cardioceras has become established as the “event ” through which the the Callovian-Oxfor- Mariae Chronozone faunas are sufficient dian boundary can be correlated ( cf . Callomon distinct from earlier and later assemblages to 1964, 1990, etc. ). The recognition of “Cardioceras ” warrant subgeneric assignment as a distinguisha- paucicostatum Lange as a form at the boundary ble segment of the overall Cardioceras lineage. level by Marchand (1979), however, precipitated a As already implemented by Page (1991 ), Pavlovice- subjective discussion as to which genus the species ras Buckman 1920 – based on a macroconch should be assigned to. As a consequence, the pau- morphospecies – has priority over Scarburgiceras cicostatum “Horizon ” has been juggled up and Buckman 1924 – based on a microconch form – and down between the Callovian and the Oxfordian the former is therefore used here to identify this depending on what genus its index was considered group. to be best assigned (Callomon 1990). In a conti-