The age of the Argiles àBucaillellaof Normandy, the systematic position of the Cretaceous ammonite...

Cretaceous Research (1999) 20, 609–628Article No. cres.1999.0170, available online at http://www.idealibrary.com on

The age of the Argiles a Bucaillella ofNormandy, the systematic position of theCretaceous ammonite genera Bucaillella andArcthoplites, and the delimitation of theAptian/Albian boundary

Raymond Casey

Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Revised manuscript accepted 17 June 1999

The Argiles a Bucaillella of Bec de Caux, Normandy (NW France) are of Early Albian age and represent a local horizon(Subzone of Bucaillella cayeuxi) lying within the Zone of Leymeriella tardefurcata of the standard European sequence. This agedetermination rests mainly on the recognition of a species of Arcthoplites among the fauna of the Argiles a Bucaillella, describedherein as Arcthoplites (A.) marechali sp. nov. Both Bucaillella and Arcthoplites are referred to the family Hoplitidae as primitivemembers of the Gastroplitinae, a subfamily that reached its peak of development in the Boreal–Arctic regions. The Argiles aBucaillella are thus the repository of a gastroplitinid fauna that is unique in western Europe and critical for the study of theorigin and dispersal of the Albian ammonite superfamily Hoplitaceae. Records of the Aptian genus Acanthohoplites from theArgiles a Bucaillella are incorrect, though its successor, Hypacanthoplites, is well represented. Owing to the limitedgeographical distribution of early Leymeriella and the extended upwards range of species of the Hypacanthoplites jacobi group,the H. jacobi/L. schrammeni junction—the currently accepted Aptian/Albian boundary—is difficult to recognize outsidenorthern Germany. From a global perspective, the first occurrence of the ammonite genus Hypacanthoplites offers a moresatisfactory marker for the base of the Albian Stage. Accordingly, the Zone of H. jacobi is here removed from the Aptian andattached to the Lower Albian. The H. anglicus Subzone of southern England and northern France, previously regarded as theupper part of the jacobi Zone, is redefined and recognized as a subdivision of the tardefurcata Zone, and considered to embracethe Subzone of B. cayeuxi (Argiles a Bucaillella) and probably part of the underlying Sables ferrugineux.

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K W: Cretaceous; Aptian; Albian; boundary; ammonites; Bucaillella; Arcthoplites.

1. Introduction

In the course of their study of the Aptian–Albiandeposits exposed along the coast north of Le Havre,Normandy, Juignet et al. (1973) introduced the terms‘Argiles a Bucaillella’ and ‘Argiles a Bucaillella deCauville’ for a sequence of clays found at the top ofthe Sables ferrugineux. This paper anticipated anotherby the same authors (Destombes et al., 1974) in whichthe eponymous ammonite, Bucaillella, was describedand illustrated for the first time. Opinions have dif-fered as to the precise position that the Argiles aBucaillella occupy in the Cretaceous time-scale, aproblem made more acute by the fact that this ammo-nite genus is apparently endemic to Normandy. Mostsubsequent workers (Juignet, 1974, 1980; Breton,1981; Marechal et al., 1988) have followed Juignetet al. (1973) and Destombes et al. (1974) in assigning

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this unit to the topmost level of the Upper Aptian,generally as a special Subzone of B. cayeuxi above theHypacanthoplites anglicus Subzone of the H. jacobiZone of southern England. However, Marechal’s(1994) study of the fauna of the Argiles a Bucaillellaled him to conclude that this biostratigraphical unitshould be placed in the Lower Albian as a division ofthe Zone of Leymeriella tardefurcata and correlatedwith the Subzone of Farnhamia farnhamensis, whichhad been assigned to the base of the English Albian(Casey, 1954, 1961).

Provincial differences in faunas has always bedevil-led long-range correlation by ammonites. In particu-lar, the difficulty of integrating the various regionaloccurrences that characterized the change fromAptian to Albian time in western Europe—Leymeriellain northern Germany, Farnhamia in southern England

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610 R. Casey

and Bucaillella in Normandy—was quoted as a primeexample (Casey, 1996, p. 73). This truism drew fromOwen (1996a, p. 76) the comment that Caseyhad given an incorrect interpretation of the LateAptian–Early Albian sediments in Normandy and here-asserted the jacobi age of Bucaillella.

The present contribution was made in connec-tion with my revision of the ammonoidea of theLower Greensand Group (Aptian–Lower Albian) ofEngland. It was hoped that a closer look at the faunaof the Argiles a Bucaillella would throw light on theEnglish succession, in which no single section showsa continuous ammonite record across the Aptian/Albian boundary.

Examination of an extensive collection ofammonites from the Argiles a Bucaillella at theMuseum d’Histoire Naturelle, Le Havre, has providedunequivocal evidence to support Marechal’s datingof this unit as Lower Albian (tardefurcata Zone).Correlation of the Subzones of Bucaillella cayeuxi andFarnhamia farnhamensis is, however, in my opinion,open to debate. The age-diagnostic feature of theNormandy deposit is the occurrence of the genusArcthoplites side by side with Bucaillella. These twogenera are considered to be closely allied members ofthe Hoplitidae and are here treated as primitiverepresentatives of the subfamily Gastroplitinae. This isbelieved to be the first authentic record of Arcthoplitesin the classic regions of western Europe.

Previous dating of the Argiles a Bucaillella as Aptianmay be ascribed in part to misidentification, notablyof the Aptian genus Acanthohoplites, but also toreliance on Hypacanthoplites anglicus as a guidefossil for the topmost Aptian. Re-appraisal of theposition of this ammonite in relation to the ‘stan-dard’ sequence of northern Germany, aided by studyof the Argiles a Bucaillella, now places the anglicusSubzone in the lower–middle levels of the broadtardefurcata Zone. This broad tardefurcata Zone isalso considered to embrace the higher levels of theSables ferrugineux immediately below the Argiles aBucaillella.

Figure 1. Sketch-map showing geographical setting of Becde Caux and Cauville (modified from Destombes et al.,1974).

2. Stratigraphy and localization of ammonites

The Argiles a Bucaillella (Subzone of Bucaillella ca-yeuxi of Destombes et al., 1974) consist of a succes-sion of grey to blackish clays, mostly sandy, withbands of phosphatic, ferruginous and pyritic nodules,and range from 2.10 m to 4.20 m in thickness, pre-served beneath the transgressive Poudingue ferru-gineux. Whether they should be treated as a discretelithological unit overlying the Sables ferrugineux ormerely a lateral facies of the topmost beds of that

formation (e.g., Breton, 1981) is open to question.The Argiles a Bucaillella are best exposed in the cliffsand foreshore near Cauville, nearly 40 km NNE of LeHavre (Figure 1), where the section shown in Figure2 (based on Marechal, 1994) may be seen. Moredetailed accounts of the lithostratigraphy have beengiven by the authors quoted above.

Figure 2 shows the distribution of the variousammonite genera throughout the strata studied. Thedistribution is uneven. Whereas Bucaillella is foundthroughout the five divisions recognized by Marechal,the genus Hypacanthoplites, already present in theunderlying beds C2–C3 of the Sables ferrugineux, hasnot been found in beds C6 base and C6.2, is very rarein bed C6.1, but appears in strength in beds C6.3 andC6.4. To date Arcthoplites has been collected onlyfrom these higher beds of the Argiles a Bucaillella(C6.3–4). This part of the succession has a morehomogeneous lithology (Marechal et al., 1988), sug-gesting that the distribution of ammonites within thewhole formation was subject to palaeoecological influ-ences. The apparent absence of Arcthoplites from thelower part of the Argiles a Bucaillella is not, therefore,regarded as of biochronological significance.

The junction with the immediately underlying bedsof the Sables ferrugineux (C4–5) is poorly known,though when seen it is clearly marked by a bored

Argiles a Bucaillella and the Aptian/Albian boundary 611

surface (J.-P. Debris, pers. comm., December 1998).The overlying Poudingue ferrugineux is a condenseddeposit (high Lower Albian–Middle Albian), itsbasement-bed containing reworked ammonites de-rived from the Argiles a Bucaillella and other pre-existing deposits of middle–latest tardefurcata Zoneage. The presence of Sonneratia of the group ofS. kitchini Spath in this basement-bed at Cauville(Marechal, 1991) shows that the indigenous fauna ofthis horizon cannot be earlier than basal mammillatumZone (kitchini Subzone of Casey, 1961), as indicatedby Owen (1971), not topmost tardefurcata Zone (regu-laris Subzone). The occurrence of Sonneratia in associ-ation with ammonites of the tardefurcata Zone referredto by Breistroffer (1947) and quoted by Marechal(1991) relate to condensed tardefurcata-mammillatumdeposits (Perte-du-Rhone and England) and to anunsubstantiated record from Germany (Stolley,1908). Wherever the two zones are separated strati-graphically, Sonneratia is confined to the mammillatumZone, as in southern England (Casey, 1965) andMangyshlak, Kazakhstan (Saveliev, 1992), the two

regions which have contributed most to the study ofthe genus and its vertical range.

3. Systematic section

Superfamily Hoplitaceae H. Douville, 1890Family Hoplitidae H. Douville, 1890Subfamily Gastroplitinae Wright, 1952

Discussion. Gastroplitinae was proposed by Wright(1952) as a subfamily of Hoplitidae to accommodatethe two genera Gastroplites McLearn and Neogastrop-lites McLearn, first described from the Middle–UpperAlbian of Arctic Canada. Subsequently Casey (1954)added a further two genera of early Albian age,Arcthoplites Spath and Subarcthoplites Casey, andtreated the subfamily as an independent boreal off-shoot of the Hoplitidae originating in the Desmo-ceratidae, possibly by way of Cymahoplites Spath.These views were accepted in a major referencebook on the Ammonoidea, part of the ‘Treatise oninvertebrate paleontology’ (Wright, 1957) and in

Figure 2. Section of the Argiles a Bucaillella at Cauville (after Marechal, 1994) showing distribution of ammonite genera.

612 R. Casey

consequence were widely quoted. Many new taxahave since been added amid a confusing diversity ofopinions regarding the circumscription of the sub-family and its relationship to the other two branches ofthe early Hoplitidae, the Cleoniceratinae and theSonneratinae. Saveliev (1973), for example, dealingwith the Mangyshlak faunas, retained Arcthoplites(tardefurcata Zone) in the Gastroplitinae, thoughSubarcthoplites, which Jeletsky (1964) had foundinseparable from Arcthoplites, was conceived as theparent stock of a new subfamily of the Hoplitidae(‘Vnigriceratinae’) derived from the Desmoceratidaeby way of Uhligella in the jacobi Zone. At the sametime he referred to the Cleoniceratinae, under thegeneric name Bellidiscus, a group of ammonitesdoubtfully separable from Subarcthoplites. In turn,Subarcthoplites was considered to have given rise latein the Early Albian to the important Arctic genusFreboldiceras Imlay. In continuance of his work on theMangyshlak faunas, Saveliev (1992) later brought inentirely different phylogenetic concepts: Bellidiscuswas retained in the Cleoniceratinae, but Arcthopliteswas removed to the Sonneratinae, while theGastroplitinae was made to include Protohoplites(Hemisonneratia) and Protohoplites s.s., which Wright(1957) and Casey (1965) had placed in theHoplitinae. Uhligella still retained its position at theroot of Saveliev’s new phylogenetic tree, thoughSubarcthoplites and Freboldiceras had slipped out of thepicture.

In the meantime, Owen (1988b) thought thatthe Gastroplitinae had not emerged until themammillatum Zone, its supposed root-form,Sokolovites, being linked to Sonneratinae throughTetrahoplites. This author took Arcthoplites andSubarcthoplites out of the Gastroplitinae, believingthem to be connected independently with theDesmoceratidae through Freboldiceras. And becauseFreboldiceras was believed to have been derived fromCallizoniceras (currently placed in the Puzosiinae),whereas the mainstream Hoplitidae (Sonneratinae,Hoplitinae) were considered to have originatedin another branch of the Desmoceratidae(Beudanticeratinae) by way of Uhligella (Spath,1942; Casey, 1965), Owen deemed it necessary tomake further radical changes in classification. TheCleoniceratinae, which had been subordinated to theHoplitidae as a subfamily (Wright, 1952, 1957), wasrestored to family rank and divided into three sub-families, Cleoniceratinae Whitehouse, VnigriceratinaeSaveliev and Lemuroceratinae Owen. Freboldiceras,Arcthoplites, Subarcthoplites and Bellidiscus wereassigned to the Vnigriceratinae; besides the nominategenus, Lemuroceratinae was said to embrace

Cymahoplites Spath and Puzosigella Casey. The genusFarnhamia Casey, known only from the Lower Albianof SE England, which Casey (1954) and Wright(1957) had placed at the root of the mainstreamHoplitidae, was treated by Owen as a synonym ofArcthoplites. Some years earlier, Jeletsky & Stelck(1981) had gone a step further in isolating theCleoniceratinae by taking this taxon out ofthe Hoplitaceae altogether and transferring it to theDesmocerataceae as a subfamily of the Desmo-ceratidae. This move was based on a perceivedrelationship between the Cleoniceratinae and theBeudanticeratinae.

Many of the ideas of Owen and Jeletsky & Stelck(1981) were taken up by Wright (1996) in the revisedaccount of the Cretaceous Ammonoidea written forthe ‘Treatise’. Accepting the diphyletic origin of thegenera traditionally grouped in the Hoplitaceae, hefollowing Jeletsky & Stelck (1981) in transferringthe genera centred nominally on Cleoniceras to thesuperfamily Desmocerataceae. Vnigriceratinae andLemuroceratinae were dismissed as synonyms of anundivided Cleoniceratidae, which had Freboldicerasand Arcthoplites (embracing Subarcthoplites andBellidiscus) as its root-forms. Arcthoplites was thoughtto have given rise to Leconteites Casey, AnadesmocerasCasey and Cleoniceras Parona & Bonarelli as one earlyside branch and Cymahoplites and Lemuroceras asanother. Like Owen (1988b), Wright believed theGastroplitinae to have commenced with Sokolovites ofthe mammillatum Zone.

None of these schemes of classification and conjec-tural phylogenies can be regarded as convincing. Inparticular, the concept of a diphyletic origin for theammonites long grouped in the Hoplitaceae restsupon very fragile foundations and other phylogeneticpossibilities need to be explored. Jones (1967, p. 37)drew attention to the basic similarities in the suture-lines of Freboldiceras, Arcthoplites and the beudanticer-atinid Grantziceras, pointing to a common ancestry forthese three taxa. Sutural characters and general mor-phology suggest that a connection between Cleonicerasand the Beudanticeratinae is just as credible as a linkwith the Puzosiinae by way of the Cymahoplites-Anadesmoceras stock, Freboldiceras and Callizoniceras.In any case, Callizoniceras is not a typical member ofthe Puzosiinae; with its relatively simple suture-lineand ribbing it is not far removed from Uhligella(Beudanticeratinae) and the allocation of thesetwo desmoceratids to different subfamilies may bequestioned.

Freboldiceras and its presumed descendant,Arcthoplites, are here seen as primitive Gastro-plitinae. The striking similarity between Arcthoplites


(Bellidiscus) probus (Saveliev) of the Lower Albian(tardefurcata Zone) of Transcaspia (Saveliev, 1973,pl. 9, figs 3a–v) and Gastroplites (‘Anagastroplites’)tozeri (Jeletsky, 1980, pl. 8, figs 1, 5, 6) from thepresumed topmost Middle Albian of Canada, arguesagainst their placement in different sections of theHoplitidae, still less in different superfamilies. Con-versely, Sokolovites, which Wright (1996), followingOwen (1988b), tentatively placed at the root of theGastroplitinae by way of Tetrahoplites, is here placed inthe Cleoniceratinae. Originally described as linkingthe Cleoniceratinae with the Hoplitinae (which thenembraced the Sonneratinae) rather than with theGastroplitinae (Casey, 1965, p. 553), the affinities ofSokolovites have been shown by its sutural ontogenyto lie firmly with Cleoniceras and Anacleoniceras(Mikhailova, 1975).

Although Freboldiceras now replaces Cymahoplites (=Leconteites) as the front-runner candidate for thestarting-point of the Gastroplitinae, the latter genusis still an important strand in the evolving hoplitidplexus. The holotype of Ammonites kerenskianusBogoslowsky (1902), the type-species of CymahoplitesSpath, from the condensed Albian of the Moscowregion, being inadequate, present-day interpretation ofthis genus rests on illustrations in Casey (1966),Mikhailova (1974) and, especially, Saveliev (1973). Thelast author described a broad spectrum of Cyma-hoplites species from Mangyshlak under Vnigriceras(Vnigriceras) and V. (Astrodiscus). All of these subse-quent records of Cymahoplites from the Russian Plat-form fix its position in the tardefurcata Zone. Taken inconjunction with elucidation of the North AmericanLeconteites by Jones et al. (1965), it is possible torationalize nomenclature and sink not only Vjasems-kiceras Sazonova, Puzosigella Casey, Vnigriceras s.s. andV. (Astrodiscus) Saveliev in the synonymy of Cymahop-lites, but also Leconteites Casey; compare ‘Vnigriceras(V.)’ kelendensis Saveliev (1973, pl. 18, fig. 2) fromMangyshlak with ‘Leconteites’ deansi (Whiteaves) fromstrata of about the same age on Russia’s Pacific rim(Alabushev & Wiedmann, 1994, fig. 4A).

Saveliev’s monograph on the ammonites of thetardefurcata Zone of Mangyshlak also demon-strated the close relationship between Cymahoplites(=Vnigriceras) and Anadesmoceras, another LowerAlbian form of world-wide distribution. Indeed,the type-species of ‘Vnigriceras’, ‘V.’ emendatumSaveliev is a species of Cymahoplites transitional toAnadesmoceras. Its borderline status is indicated by thefact that Wright (1996, pp. 96–98, fig. 74.3) figuredC. (‘V.’) emendatus as an example of Anadesmoceraswhile at the same time citing Vnigriceras as a synonymof Leconteites (=Cymahoplites herein).

Currently, Cymahoplites and Anadesmoceras areaccepted as early members of the Cleoniceratinae.Relevant to this issue is a series of forms illustratedfrom the Lower Albian of Alaska by Jones (1967) asArcthoplites talkeetnanus (Imlay), which are linked tocontemporary Freboldiceras. They include morpho-types whose emphasized umbilical rib-endings andearly onset of smoothness foreshadow Cymahoplites(Jones, 1967, pl. 8, figs 1–3); others, with more dis-tinct umbilical bullae (Jones, pl. 8, figs 4–10) suggestprogression towards Tetrahoplitoides Casey andCleogastroplites Jeletsky, both on the borderline of theGastroplitinae and the Cleoniceratinae. There arethus grounds for postulating a common origin forthese two subfamilies in Early Albian times, withFreboldiceras near the point of divergence.

Bucaillella, discussed below, introduces anotherfactor into the debate. Its ties with contemporaryArcthoplites place it in the Gastroplitinae; equally, itsSonneratia-like juvenile stage compels us to recognizealso the relationship with the Sonneratinae. For thepresent, therefore, I acknowledge the descent of theHoplitidae from the Desmoceratidae in Early Albiantimes and its more-or-less simultaneous radiationinto the three subfamilies Cleoniceratinae, Gastro-plitinae and Sonneratinae, the last giving rise to theHoplitinae before the end of the Early Albian. It isuncertain, however, that these conventional taxaformed a simple evolutionary ‘tree’; some degree ofanastomosis may have taken place and flexibility ofclassification may be expected for some time in thefuture.

Genus Arcthoplites Spath, 1925

Type species. Hoplites jachromensis Nikitin (1888),Albian, Russian Platform, by original designation.

Discussion. When proposing the generic name Arcthop-lites, Spath (1925, p. 76) cited Nikitin’s species as‘genotype’ but gave no differentiating characters be-yond placing it in the Hoplitidae along with Sonneratiaand comparing it to the (unrelated) genus Hypacan-thoplites. The best source of information on the genusin the region of its typical development is Saveliev’s(1973) monograph.

Arcthoplites is here taken to comprise two subgenera,Arcthoplites s.s. and Bellidiscus Saveliev (type-speciesB. probus Saveliev, 1973, tardefurcata Zone,Mangyshlak). The latter was originally proposed as anindependent genus and differs from typical Arcthoplitesin its relatively more compressed and involute shell-form and closer ribbing which tends to weaken alongthe siphonal line. It is with some hesitation that the

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Figure 3. Distribution of Arcthoplites.

name Bellidiscus is preferred for this taxon insteadof Subarcthoplites Casey (1954), proposed for‘Lemuroceras’ belli McLearn from the Albian of ArcticCanada. Workers in North America (e.g., Jeletsky,1964; Jones, 1967) have found it difficult to separateSubarcthoplites from Arcthoplites. Moreover, accordingto Jones (1967, p. 40) ‘L.’ belli bears low, indistinctumbilical bullae. This is not obvious in Jeletsky’sillustrations of the holotype of ‘L.’ belli (Jeletsky, 1964,pl. 26, figs 3a–e), though clearly shown in anotherspecimen described as Arcthoplites aff. belli (McLearn)(Jeletsky, 1964, pl. 26, figs 2a, b). Study of a popu-lation of the gastroplitinid Neogastroplites americanus(Reeside & Weymouth) from the Cenomanian MowryShale of the western interior of the USA showsconsiderable variation in the strength of the umbilicalrib-endings (Reyment & Kennedy, 1998), so thisfeature may have little taxonomic significance. How-ever, it is characteristic of the typical, Eurasian,species of Arcthoplites that umbilical bullae are absent,even on the innermost whorls (see Saveliev, 1973,pl. 4, figs 1–3). For this reason the forms with bullateor emphasized rib-endings in the young illustrated byJones (1967) from the Lower Albian of Alaska asArcthoplites talkeetnanus (Imlay) do not, in my opinion,belong either to Arcthoplites s.s. or to Bellidiscus. Sub-arcthoplites may prove to be an appropriate subgenericname for this species, which according to Birkelund &Hakansson (1983, p. 13) preceded typical Arcthoplites.Wright (1996) considered both Subarcthoplites andBellidiscus to be junior synonyms of Arcthoplites.

Undisputed occurrences of Arcthoplites are confinedto the northern hemisphere, where the genus has apatchy distribution stretching from Iran northwards tothe Mangyshlak Peninsula of Kazakhstan, through theMoscow and Novaya Zemlya regions of the RussianPlatform, Svalbard (Spitsbergen), east and northGreenland, and thence to Arctic Canada, Alaska andthe Pacific rim of Siberia. Figure 3 shows that recordsof Arcthoplites are concentrated in the Boreal–Arcticrealm, suggesting that this was the origin and centre ofdispersal of the genus. The unexpected discovery ofArcthoplites in Normandy, associated with its allyBucaillella, indicates a southwards penetration of thegastroplitinid stock in parallel with that of Mangyshlakand Iran. Because of the apparent absence of Arcthop-lites in western Europe and of Leymeriella in centralRussia, Birkelund & Hakansson (1983, p. 15) postu-lated different routes of migration for these two gen-era: an Atlantic–European seaway for Leymeriella anda Russian–Arctic seaway for Arcthoplites. This newlyfound western outpost of Arcthoplites thus gives scopefor further palaeobiogeographical speculation. Thepossibility cannot be ruled out that the boreal

influences in the Aptian–Albian of Normandy de-tected by Juignet et al. (1973) were augmented by anorth–south marine communication on the Atlanticside of the British Isles, comparable with that whichhad brought the boreal genus Prodeshayesites to the Isleof Wight and SE England at the beginning of theAptian transgression.

Unlike the solitary example of Gastroplites found inthe Gault (cristatum Subzone, basal Upper Albian) ofFolkestone, SE England (Casey, 1936) and assumedto be a straggler from the north (Spath, 1937), thegastroplitinid fauna of Normandy was a thrivingindigenous population.

A previous record of Arcthoplites from the Albian ofCauville (Cayeux, 1961) refers properly to Bucaillella,as explained by Destombes et al. (1974, p. 76). Otherwestern European forms incorrectly referred toArcthoplites in the past (e.g., Breistroffer, 1947) wereassigned by Casey (1952) to Tetrahoplites, Proto-hoplites s.s. and P. (Hemisonneratia) (Sonneratinae-Hoplitinae). Another member of the Sonneratinaewrongly synonymized with Arcthoplites is the genusFarnhamia Casey (1954) of the tardefurcata Zone ofSE England. The statement by Owen (1988b, p. 215)that the inner whorls of Farnhamia show that theybelong to species of Arcthoplites is untrue. On thecontrary, it is the inner whorls of Farnhamia, withtheir umbilical bullae or bulges, persistent to 100 mmdiameter or more, that reveal affinity with Sonneratia(Casey, 1965, pl. 77, fig. 2a; pl. 78, figs 3, 5, 6, 8).


A group of Arcthoplites-like forms were describedfrom Madagascar by Collignon (1963) under Pseudo-sonneratia, one of which (‘P.’ sakalava Collignon) wasreferred positively to Arcthoplites by Owen (1988a,p. 483, table 2). Reference to Collignon’s illustrations(Collignon, 1963, pl. 282) shows ‘P.’ sakalava to havea distinctive blunt style of ribbing, with primaries thatare distantly spaced on the inner whorls and cross theumbilical shoulder obliquely in a manner reminiscentof Lemuroceras but not seen in typical Arcthoplites.Whether these Tethyan forms have a genetic connec-tion with their Boreal–Arctic analogues is an interest-ing question of palaeobiogeography that cannot bepursued here.

Subgenus Arcthoplites s.s.Arcthoplites (Arcthoplites) marechali sp. nov.Figures 4, 6.10–13

1988 Bucaillela cayeuxi Destombes, Juignet & Rioult;Marechal et al., 1988, pl. 1, fig. 10 only.

Holotype. No. 531 MHNH (Museum d’HistoireNaturelle, Le Havre), Argiles a Bucaillella, bed C6.4Cauville, Bec de Caux, Normandy (M. Marechalcollection).
Etymology. The trivial name of this species honoursM. Marc Marechal, whose dedicated collecting andobservations have made the present paper possible.
Description. Compressed, moderately involute (umbili-cus c. 30% of diameter), whorls subrectangular, withflat sides converging slightly to well-rounded ventralshoulders, flattish–gently convex venter and steep um-bilical wall. Costation of about 20 primary ribs at60 mm diameter, with 10–15 secondaries; primariesleave top of umbilical wall and lean a little forwards onpassing over flank, either very gently sigmoidal or,when preceding a secondary rib, sickle-shaped, cross-ing venter with slight forward bend; secondaries short,mostly free-ending, some uniting with a primary atmid-flank or just above. Body-chamber occupies 180�and tends to inflate rapidly to subquadrate shape to-wards peristome. Suture-line with symmetrically bifidsaddles and asymmetrically trifid L.

Remarks. This species is close to a specimen from thecondensed Albian of the Moscow region attributed toA. (A.) jachromensis by Baraboshkin & Mikhailova(1988, p. 84, pl. 2, figs 2a, b), though the Russian formhas less flexuous ribs. The original A. jachromensis(Nikitin, 1888, pl. 4, figs 1, 2, 5) has more convexwhorl-sides, and more definite and frequent union ofprimary and secondary ribs at a higher point on the

flank. Arcthoplites (A.) subjachromensis Saveliev (1973)from the tardefurcata Zone of Mangyshlak also has ahigher point of branching of the ribs, and the ribs areless flexuous and with fewer single primaries. Arctho-plites (A.) bogoslowskyi Saveliev (1973), from thecentre of the Russian Platform, has a subrectangularwhorl-shape similar to that of the present species and alow point of bifurcation of the ribs, though the ribbinghas a simple forward curvature and lacks the sickle-shaped tendency seen in A. (A.) marechali. The ventralribbing of this Russian form is also much more stronglyprojected forwards. The same features distinguish an-other taxon from the same region, A. (A.) gerassimoviBaraboshkin & Mikhailova (1988), perhaps conspecificwith A. (A.) bogoslowskyi. The asymmetry of the firstlateral lobe is especially marked in A. (A.) marechali,though an approach to this condition is seen in thesuture-line of the Mangyshlak A. (A.) aff. jachromensisillustrated by Saveliev (1973, p. 104, fig. 14) and to alesser extent in that of the Alaskan species A. (s.l.)talkeetnanus (Imlay) (Jones, 1967, p. 40, fig. 19).

The largest example of A. (A.) marechali examined(Figure 4.1a, b) is 125 mm in diameter. The body-chamber occupies the last half-whorl (180�) and iscomplete to the (crushed) peristome, which is pre-ceded by two ventral riblets. Specimens of Arcthoplitesfrom the Moscow region attain up to twice thatdiameter, at which size the last whorl is almost com-pletely smooth (E. J. Baraboshkin collection, GeologyFaculty, Moscow State University). A stout, coarsely-ribbed variant of the present species (Figure 4.5a, b)has an expanding body-chamber and apparently leadsto Bucaillella cayeuxi moricei Destombes, Juignet &Rioult (compare Marechal et al., 1988, pl. 1, figs 8, 9).The sudden expansion of the body-chamber towardsthe peristome has been noted in some specimens of A.(A.) marechali and may be characteristic of the species.Examples of A. (A.) jachromensis from northernGreenland (Birkelund & Hakansson, 1983, pl 2, figs5b, 6b) seem to show the same phenomenon to alesser degree. It is unknown whether this phase ofbody-chamber expansion in the present species wasfollowed by contraction, as in Bucaillella cayeuxi wattei(Destombes et al., 1974, pl. 1, figs 2a, b).

Genus Bucaillella Destombes, Juignet & Rioult, 1974

Type species. B. cayeuxi Destombes, Juignet & Rioult,Argiles a Bucaillella, Bec de Caux, Normandy, byoriginal designation.

Discussion. The nominal genus Bucaillella and thecombination Bucaillella cayeuxi first appeared in apaper by Juignet et al. (1973, p. 309). Although this

616 R. Casey


Figure 4. Arcthoplites (Arcthoplites) marechali sp. nov., Argiles a Bucaillella, Cauville, Bec de Caux, Normandy. 1, side (a) andventer (b) of large example with half-whorl body-chamber and inner whorls partly preserved as an external mould, lastseptum at position of ‘1a’, No. MHNH 8105; 2, side (a), venter (b) and plaster cast of inner whorls (c) of (septate)holotype, No. MHNH 9026; 3, side (a) and venter (b) of fragment with beginning of body-chamber No. MHNH 9028;4, side (a) and venter (b) of body-chamber fragment, No. 326; 5, side (a) and venter (b) of coarse example with large partbody-chamber showing expansion towards mouth-border, No. MHNH 9027. The originals of all figures are phosphoriteinternal moulds and are all shown natural size. Figures 4.1–3, 5 are from bed C6.4, M. Marechal collection, Museumd’Histoire Naturelle, Le Havre; Figure 4.4 is from bed C6.3, F. Amedro collection (ex M. Marechal collection).Photography by Phil Hurst, The Natural History Museum, London.

new specific name was attributed to Destombes,Juignet & Rioult, in a paper listed in the bibliography asalready published in 1973, the paper in question did notappear until 1974. The 1973 use of these names, beingwithout diagnoses or indications, was therefore nudeand invalid. Both genus and species were fully andvalidly described by Destombes et al. in 1974.

The holotype of B. cayeuxi came from an oldcollection (‘collection Bucaille’) in the Museumd’Histoire Naturelle, Rouen. It was originally re-corded by Destombes (1958, p. 306) as a species ofHemisonneratia (mammillatum Zone) and thought tohave come from the Poudingue ferrugineux. Later(Destombes et al., 1974, p. 75) it was attributed to theArgiles a Bucaillella of Cauville. Re-examination ofthis specimen by Marechal (1990) has led him toconclude from the mode of preservation that it wasobtained most likely from the lateral equivalent of theArgiles a Bucaillella exposed at Saint-Jouin, about7 km NE of Cauville.

Shortly after the original citation of the specimen(Destombes, 1958) it was shown to me, and, in apersonal communication to Dr Destombes, I con-sidered it to represent an undescribed genus close toArcthoplites. According to Destombes et al. (1974,p. 76) this information was passed to M. L. Cayeuxand resulted in the name Arcthoplites being applied toa specimen of Bucaillella from the Pays de Caux(Cayeux, 1961). When discussing Hemisonneratia,Casey (1965, p. 486) referred to Destombes’ originalspecimen as belonging to a new genus resembling aninflated Arcthoplites. In their detailed description ofBucaillella, Destombes et al. (1974, pp. 75–77) re-ferred to the similarity in costation between the twogenera, but emphasized the relatively depressedwhorl-shape of Bucaillella, as well as a difference instratigraphical position (the latter no longer valid, asshown below). Above all, the Sonneratia-like earlywhorls of Bucaillella (up to 40 mm in diameter), withflanks converging to an arched venter and the pres-ence of feeble umbilical bullae, distinguish theNormandy form from Arcthoplites and persuadedDestombes et al. (1974) to place Bucaillella in theirnewly created subfamily Sonneratinae.

Bucaillella cayeuxi was found to display a widespectrum of variability. Two extremes were selectedfor description by Destombes et al. (1974)—a globose,depressed form with rounded venter and a contractingbody-chamber, designated morphotype wattei (Figure5.1a, b), and a relatively compressed form with sub-quadrate whorls and flat venter, named morphotypemoricei (Figure 5.2a, b). These two ‘morphotypes’ arehere treated as subspecies. Other variants are repre-sented by boldly sculptured specimens almost devoidof secondary ribs (Marechal et al., 1988, pl. 2, figs 12,13) and another form, closely ribbed with secondariesbifurcating from near the umbilical border (Marechalet al., pl. 1, fig. 5).

Bucaillella is here regarded as a member of theGastroplitinae proceeding towards the Sonneratinae,either as a specialized offshoot of Arcthoplites or ashaving a common ancestry with that genus. Thesubspecies moricei of B. cayeuxi is transitional betweenthe two genera. Material available to me is insufficientto confirm the presence of the ‘Sonneratia’ stage in thejuvenile of this form and its attribution to Bucaillellarather than to Arcthoplites is purely arbitrary.

Another genus that invites comparison withBucaillella is the primitive sonneratinid Farnhamia,at present known only from the Lower Albian(tardefurcata Zone) of SE England. The more distinctand persistent umbilical bullae of Farnhamia wouldseem to place it closer to the mammillatum ZoneSonneratia, though its wide, symmetrically trifid firstlateral lobe with shallow central tine (Casey, 1965,p. 467, fig. 175b) is not duplicated in other membersof the Sonneratinae.

Superfamily Parahoplitaceae Schindewolf, 1968Family Parahoplitidae Spath, 1922Subfamily Acanthohoplitinae Stoyanow, 1949Genus Acanthohoplites Sinzow, 1907

Type species. Parahoplites aschiltaensis Anthula, UpperAptian, Caucasus, by subsequent designation ofRoman, 1938.

Discussion. Destombes et al. (1974) described ammo-nites from the Argiles a Bucaillella (C6) and thePoudingue ferrugineux (C7) as Acanthohoplites aff.

618 R. Casey


Figure 5. Bucaillella cayeuxi Destombes et al., Argiles a Bucaillella, Cauville, Bec de Caux, Normandy. 1, side (a) and venter(b) of B. cayeuxi wattei Destombes et al., holotype of subspecies (‘morphotype’), J. Watte collection, MHNH 9025; 2,side (a) and venter (b) of B. cayeuxi moricei Destombes et al., holotype of subspecies (‘morphotype’), M. Vaast collection,MHNH 7216. Copies of Destombes et al., 1974, pl. 1, figs 2a, b and pl. 2, figs 1a, b. Natural size. Originals in Museumd’Histoire Naturelle, Le Havre.

bigoureti (Seunes) (C6), ‘Acanthohoplites’ aff. seunesi(Jacob) (C7) and ‘Acanthohoplites’ pachys sp. nov.(C7) Marechal (1994, p. 85) recorded Acanthohoplitesbigoureti (Seunes) from beds C6.4 and C7 and A.seunesi (Jacob) from beds C6.3 and C6.4 and noted aprevious record of the latter species from bed C7.These two species of Acanthohoplites belong properlyto the ‘Clansayes’ horizon or Zone of A. (Nolaniceras)nolani of the Aptian and in my opinion have not beencorrectly identified from the Argiles a Bucaillella andthe Poudingue ferrugineux. The Normandy forms areall coarsely sculptured Hypacanthoplites comparable tothe early whorls of H. shepherdi Casey and H. corruga-tus Casey of the anglicus/farnhamensis Subzones ofsouthern England (Casey, 1965, pl. 76, figs 5a, b).Although in the past the nominal genus Acanthoho-plites has been used to embrace species of Hypacan-thoplites, it is today used exclusively for those Aptianforerunners of Hypacanthoplites that lack the sharplyangulated and tuberculated venter exhibited in theearly–middle growth stages of the latter genus. As thusdefined, Acanthohoplites reached its peak of develop-ment in the nolani Zone and possibly survived into thebase of the jacobi Zone (rubricosus Subzone).

Genus Hypacanthoplites Spath, 1923

Type species. Acanthoceras milletianum (d’Orbigny) var.plesiotypica Fritel, jacobi Zone, Germany, by originaldesignation.

Remarks. No attempt is made here to discuss in detailthe rich Hypacanthoplites faunas of the Argiles aBucaillella, the underlying Sables ferrugineux and theoverlying Poudingue ferrugineux, all of which areconsidered to fall within the broad tardefurcata Zone.The following notes focus on a few critical forms inneed of elucidation.

Hypacanthoplites anglicus Casey

1939 Acanthohoplites jacobi (Collet); Spath, p. 287(pars).

1950 Hypacanthoplites anglicus Casey, p. 291, pl. 14,fig. 1.

1953 Hypacanthoplites kopetdagensis Glazunova, p. 49,pl. 10, figs 1–3.

1965 Hypacanthoplites anglicus Casey; Casey, p. 427,pl. 51, figs 4–7; pl. 64, fig. 2.

1975 Hypacanthoplites anglicus Casey; Kemper, p. 98,pl. 2, figs 10–13 only.

Remarks. This species was recorded from thebasement-bed of the Folkestone Formation atFolkestone, SE England, by Spath (1939) as Acantho-hoplites jacobi (Collet). He noted, however, that theFolkestone specimens were not typical and were as-sociated with forms reminiscent of H. milletianus ofthe tardefurcata Zone. When splitting H. anglicus fromH. jacobi, Casey (1950, 1965) observed that hisspecies did not occur in the classic jacobi faunaof northern Germany but showed affinities withspecimens from the mid-tardefurcata Zone ofAltwarmbuchen, near Hannover. Nevertheless, be-cause of the absence in the anglicus fauna of Leymeriellaor other ammonites diagnostic of the tardefurcata Zone,he accepted the species as belonging to the ‘wider jacobizone’ of Spath. Hypacanthoplites anglicus was subse-quently designated index-species for the upper part ofthe jacobi Zone of SE England (Casey, 1961).

Kemper (1973, 1975), who followed Brinkmann(1937) in treating the schrammeni, tardefurcata andregularis horizon as independent zones, showedthat H. anglicus occurred in the restricted tardefurcataZone (germanica Subzone), as for example, atAltwarmbuchen. He has since shown that other formsof the H. jacobi group range well into the tardefurcataZone of northern Germany (Kemper, 1982).Hypacanthoplites anglicus anglicus Casey and H.anglicus audax Casey have been collected at Vohrum,Hannover (H. M. Bayliss collection) at a level nohigher than the schrammeni Subzone (H. M. Bayliss,pers. comm., December 1998). In Normandy H.anglicus occurs in the Argiles a Bucaillella (Marechal,1994), now firmly dated as tardefurcata age (germanicaSubzone) by the presence of Arcthoplites. Judgingby material preserved in the Museum d’HistoireNaturelle, Le Havre, the same species or closely alliedforms are found also in the Sables ferrugineux in thevicinity of Cauville. It thus appears that H. anglicusand its associated fauna fall within the schrammeni–germanica interval of the sequence in northernGermany and are of post-jacobi age. The absence ofLeymeriella from the ammonite fauna of the anglicusSubzone can no longer be ascribed to age-difference,but rather to palaeoecological factors that excluded

620 R. Casey

Figure 6. 1, Bucaillella cayeuxi Destombes et al., whorl-section of holotype, presumed lateral equivalent of Argiles aBucaillella, Bec de Caux, Normandy; 2, B. cayeuxi wattei Destombes et al., whorl-section, Argiles a Bucaillella, locality asbefore; 3, B. cayeuxi moricei Destombes et al., whorl-section, horizon and locality as before; 4, B. cayeuxi Destombeset al., juvenile, suture-line,�3.3, horizon and locality as before; 5, Arcthoplites (Arcthoplites) bogoslowskyi Saveliev,whorl-section, condensed Albian, central Russian Platform; 6, Arcthoplites (A.) jachromensis (Nikitin) (s.l.), whorl-section,condensed Albian, Moscow region, Russia; 7, Arcthoplites (A.) nikitini Saveliev, whorl-section of holotype, tardefurcataZone, Kugusem, Mangyshlak, Kazakhstan; 8, Arcthoplites (A.) subjachromensis Saveliev, section, horizon and locality asfor Figure 6.7; 9, Arcthoplites (A.) aff. jachromensis (Nikitin), external suture-line,�c. 5, horizon and locality as for Figure6.7; 10, Arcthoplites (A.) marechali sp. nov., whorl-section of holotype, Argiles a Bucaillella (bed C6.4), Cauville,Normandy; 11, Arcthoplites (A.) marechali sp. nov., whorl-section of example illustrated in Figure 4.4., Argiles aBucaillella (bed C6.3), Cauville, Normandy; 12, Arcthoplites (A.) marechali sp. nov., whorl-section near peristome ofexample illustrated in Figure 4.1, Argiles a Bucaillella (bed C6.4), Cauville, Normandy; 13, Arcthoplites (A.) marechali sp.nov., external suture-line of example illustrated in Figure 4.3,�1.3 (H. M. Bayliss del.), horizon and locality as forFigure 6.13; 14, Arcthoplites (s.l.) talkeetnanus (Imlay), external suture-line,�4, Lower Albian, Alaska. Figures 6.1-4after Destombes et al., 1974; Figures 6.5-9 after Saveliev, 1973; Figure 6.14 after Jones, 1967. All figures reduced to0.66 unless otherwise stated.


the genus from the whole of the Anglo–Paris Basinuntil regularis Subzone times.

Hypacanthoplites anglicus rigidus subsp. nov.

1965 Hypacanthoplites anglicus Casey, late mutant;Casey, p. 428, pl. 51, 51, fig. 6, text-fig. 162d.

Holotype of subspecies. The specimen illustrated byCasey (1965) from the Folkestone Formation (tardefur-cata Zone, farnhamensis Subzone), Coxbridge pit,Farnham, Surrey, SE England (Wright brothers’ collec-tion No. 4571; now C84760 in the Department ofPalaeontology, The Natural History Museum, London).

Description. Costation slightly more rigid than inH. anglicus s.s. and whorls stouter with subquadratetendency.

Remarks. This subspecies is represented in the collec-tions (M. Marechal and F. Deschandol) by severalspecimens from the Argiles a Bucaillella, along withH. anglicus anglicus and H. anglicus audax. Somespecimens are precisely localized in bed C6.4 ofCauville (e.g., M. Marechal collection MHNH 9029).A Cauville specimen illustrated by Destombes et al.(1974, p. 66, pl. 1, figs 1a, b) as H. aff. jacobi (Collet)seems to be closer to the present form than to Collet’sspecies. The horizon of this specimen needs to beclarified as it is ambiguously described as originatingin ‘‘Couche C2, sommet des Sables ferrugineux’’. Thesummit of the Sables ferrugineux at Cauville is bedC5, bed C2 being near the base.

Hypacanthoplites anglicus rigidus connects thetypical H. anglicus with H. trivialis Breistroffer of themilletioides Subzone. No examples of this subspecieshave been found in the Folkestone area, suggestingthat here the anglicus Subzone, with its eroded top,does not represent the total range of the index-species.Presumably the highest part of the anglicus Subzoneis contained in the unfossiliferous sands below thefarnhamensis Subzone in the Folkestone Formation ofSurrey and Sussex.

Hypacanthoplites trivialis cauvillensis Destombes,Juignet & Rioult

1974 Hypacanthoplites anglicus var. cauvillensis nov.var., Destombes et al., p. 67, pl. 5, figs 6a, b.

Remarks. The holotype of this subspecies was col-lected from the reworked debris at the base of thePoudingue ferrugineux (bed C7) at Cauville. Itsmangled condition makes it difficult to interpret,though topotypes collected by M. Marechal have beenmade available for study. On account of its rectiradi-ate costation this taxon is here attached to H. trivialis

Breistroffer rather than to H. anglicus and suggeststhe former presence of the milletioides Subzone inthe Cauville area. Compared with typical H. trivialisit is distinguished by its density of ribbing. AnAltwarmbuchen ammonite, figured by Kemper (1975,pl. 3, figs 1a, b only) as H. anglicus, also has arectiradiate though coarser style of costation withshort secondaries, recalling H. milletianus (d’Orbigny).

Hypacanthoplites cf. spathi (Dutertre)

1965 Hypacanthoplites cf. spathi (Dutertre); Casey,p. 442, text-fig. 164d, e.

Remarks. A cast taken from the hollow nucleus of amacroconch species of Hypacanthoplites from theSables ferrugineux (bed C2) of Cauville (Marechalcollection MHNH 9030) shows good agreement withseptate fragments found in the anglicus Subzone ofFolkestone, Kent, and Wissant, Boulonnais (e.g., Casey,1965, p. 442, text-fig. 164d, e). As usual in this genus,the Cauville specimen shows that the umbilical tuberclesof the inner whorls were more pronounced on the ex-terior of the shell than on the internal mould. Evidentlythese specimens represent an undescribed species com-parable to H. spathi (Dutertre) of the jacobi Zone butwith strong ribbing persisting to a much larger diameterand, apparently, no lateral tubercles in the young.

The Cauville form illustrated from the Argiles aBucaillella (bed C6.4) by Marechal (1994, pl. 1, fig. 7)as H. spathi is here re-determined as H. aff. milletioidesCasey. It is one of a number of forms from this depositthat foreshadow H. milletioides and H. subelegansBreistroffer of higher horizon.

Hypacanthoplites rubricosus Casey

1950 Hypacanthoplites rubricosus sp. nov., Casey,p. 290, pl. 14, figs 3–10.

1965 Hypacanthoplites rubricosus Casey; Casey, p. 436,pl. 73, figs 2–4, pl. 74, figs 5a, b, text-fig. 162e.

Remarks. The imprint of a little ammonite of 22 mmdiameter found in the Argiles a Bucaillella of Cauvillewas referred to H. rubricosus by Destombes et al.(1974, p. 66, fig. 5.3). This record cannot be ac-cepted. Only the whorl-section was illustrated and thisis too depressed for H. rubricosus, which characterizesthe base of the jacobi Zone at Folkestone.

4. The age of the Argiles a Bucaillella

Since Bucaillella is apparently endemic to Normandyand the associated species of Hypacanthoplites, such asH. anglicus, are also under review as to their precisezonal position, dating of this unique deposit turns onthe genus Arcthoplites.

622 R. Casey


Figure 7. Tentative correlation of the Argiles a Bucaillella and adjacent formations with sequences in other key areas, and, at right,various schemes of ammonite zonation that have been applied to these strata. Regional columns at left are composite and drawnmainly from the following sources: Mangyshlak—Baraboshkin, 1992, 1996; northern Germany—Brinkmann, 1937 and Kemper,1973, 1975, 1982; SE England—Casey, 1961; Normandy—Destombes et al., 1974 and Marechal et al., 1988; with modificationsintroduced in the present text. Broken lines with a question mark indicate correlation lines that are especially conjectural.

Before reviewing the distribution of Arcthoplites, it isnecessary to correlate the various schemes of zonalclassification that have been applied to the Leymeriellahorizons of northern Germany, which form part ofthe ‘standard’ European scale for the Lower Albian.The first detailed subdivision of these beds was byBrinkmann (1937), who recognized three zones,in ascending order: Leymeriella schrammeni, L.tardefurcata and L. regularis, each comprising twosubzones. The tardefurcata Zone was divided intoa Subzone of L. tardefurcata anterior below and aSubzone of L. tardefurcata tardefurcata above. Becausethe subspecific name ‘anterior’ had been appliedalready to the forerunner of L. schrammeni schrammeni,Casey (1957) renamed L. t. anterior as L. germanica.In the meantime, Spath (1941), reverting to formerusage, had reduced Brinkmann’s three zones to asingle Zone of L. tardefurcata, with three subzones: L.schrammeni, L. acuticostata and L. regularis. Spath’sacuticostata Subzone thus corresponds to the whole ofBrinkmann’s Zone of L. tardefurcata, embracing boththe Subzones of L. germanica and L. tardefurcata s.s. Itshould be noted that Brinkmann did not himself employL. acuticostata as a subzonal index; its occurrence in theGerman sequence was shown to cover only a smallinterval near the base of the vertical range of L. ger-manica (Brinkmann, 1937, p. 2, fig. 2). AlthoughSpath’s classification of these beds has been widelyquoted, in those areas where the Leymeriella sequence isbest developed, e.g., the Hannover region of Germanyand in Mangyshlak, workers have preferred Brinkmann’sscheme (e.g., Kemper, 1973, 1975; Saveliev, 1973;Baraboshkin, 1992, 1996). The term ‘tardefurcata Zone’thus has quite different meanings for different authors:(1) a broad tardefurcata Zone covering the whole intervalbetween the jacobi and mammillatum Zones, as used bySpath, and (2) a restricted tardefurcata Zone, which,following Brinkmann, lies between the Zones of L.schrammeni and L. regularis and is equivalent to theacuticostata Subzone of Spath. For the present, Icontinue to use the more conservative scale ofSpath, though acknowledging its inadequacy forhigh-resolution correlation.

The abrupt replacement of Leymeriella (Leymeriella)by L. (Neoleymeriella) in the classic successions ofnorthern Germany and Mangyshlak suggests thepossibility that they are incomplete at the base of the

regularis Zone/Subzone, as shown tentatively in Figure7. If the horizon of L. (L.) acuticostata has beencorrectly identified there by Baraboshkin (1992),the Mangyshlak succession may also lack the toppart of Brinkmann’s tardefurcata Zone. However,Baraboshkin’s Subzone of L. (L.) acuticostata restssolely on specimens determined as L. (L.) cf. acuticos-tata, and while it falls within the broad acuticostataSubzone of Spath, correlation with the narrow band ofdistribution attributed to L. (L.) acuticostata in theGerman succession should not be assumed. In phos-phatic but relatively uncondensed regularis deposits atWrecclesham, Surrey, SE England, the ranges ofLeymeriella s.s. and L. (Neoleymeriella) are shown tooverlap at a level where Anadesmoceras reaches its peakof abundance (Casey, 1961, p. 554; 1978).

The type species of Arcthoplites, A. jachromensis(Nikitin), is found in the Moscow region of Russia incondensed deposits which include ammonites ofMiddle Albian age, leading to the idea that Arcthop-lites may range as high as the Zone of Hoplitesdentatus (Nikitin, 1888; Baraboshkin & Mikhailova,1988). Similar species of Arcthoplites were illustratedby Bogoslowsky (1902) from the Ryazan area, SE ofMoscow, accompanied by Cymahoplites, but again ina condensed deposit that does not permit dating ofthese two genera. Finds of Arcthoplites in reworkedsediments on Novaya Zemlya, Kolguev Island andin Cheshskaya Guba, at the extreme north of theRussian Platform, are also impossible to date pre-cisely (Cherkesov & Burdykina, 1979). It was thediscovery of a species of Arcthoplites (A. birkenmayeriNagy) in association with Leymeriella (L.) germanicaCasey in the Lower Albian of Svalbard (Spitsbergen)that gave the first positive clue as to the position ofArcthoplites in the Eurasian time-scale (Nagy, 1970).This association placed A. birkenmayeri in the lowerpart of the tardefurcata Zone (in Brinkmann’s sense),germanica Subzone, equivalent to the lower part ofthe acuticostata Subzone of Spath. Nevertheless,Nagy thought that Arcthoplites might range as high asthe lower part of the Zone of Douvilleiceras mammil-latum because of the presence of the genus in bedsunderlying those with Otohoplites of upper mammilla-tum age.

More definite evidence of the position of Arcthopliteswas obtained by Saveliev (1973), who showed that in

624 R. Casey

the tardefurcata-mammillatum sequence of Mangyshlak,Kazakhstan, A. jachromensis and congeneric forms wereconfined to the restricted tardefurcata Zone, togetherwith strong representations of Leymeriella, Cymahoplites(=Vnigriceras Saveliev) and Anadesmoceras. South ofMangyshlak, at the southern extremity of the Caspianregion, Arcthoplites has been found in association withLeymeriella of the restricted tardefurcata Zone in the IranBasin (Sayed-Emami, 1980).

In northern Greenland, A. jachromensis occurs withAnadesmoceras a few metres above an assemblage withFreboldiceras and Leymeriella (Proleymeriella) trolleiBirkelund & Hakansson (schrammeni Zone), consist-ent with a level for Arcthoplites in the tardefurcata Zone(germanica Subzone) (Birkelund & Hakansson, 1983).Comparing the Greenland occurrences with thoseof Alaska, Svalbard and Mangyshlak, Birkelund &Hakansson (1983, p. 13) considered that the tardefur-cata Zone (=Spath’s acuticostata Subzone) embraced asuccession of four Arcthoplites horizons, in ascendingorder: A. talkeetnanus, A. birkenmayeri, A. jachromensisand A. spp. (e.g., A. subjachromensis Saveliev). In NorthAmerica the absence of Leymeriella places constraintson direct correlation of the Arcthoplites-bearing stratawith their Eurasian equivalents. However, in a review ofthe Lower Albian ammonite faunas of that continent,Owen (1988a) adduced indirect evidence for aligningthese strata with the restricted tardefurcata Zone andeliminating the mammillatum Zone from the frame.

In recent years a more detailed biostratigraphicalscheme for the important Mangyshlak succession hasbeen proposed by Baraboshkin (1992, 1996), basedon the stratotype section of Kugusem (Figure 7). Foursubzones were recognized in Saveliev’s Zone ofLeymeriella (L.) tardefurcata, in ascending order: L.(L.) recticostata, Arcthoplites (A.) jachromensis, Arctho-plites (Bellidiscus) probus and L. (L.) acuticostata.Arcthoplites first appears in the recticostata Subzonein the form of A. (B.) cf. subplanus Saveliev. In thejachromensis Subzone, Arcthoplites s.s. predominates(A. jachromensis Nikitin, A. subjachromensis Saveliev,A. nikolskensis Saveliev), while the succeeding probusSubzone yields only the subgenus Bellidiscus—A. (B.)probus, A. (B.) angustus, A. (B.) crassus and A. (B.)subplanus—all Saveliev species. The acuticostataSubzone has yielded only Leymeriella comparable toL. (L.) acuticostata Brinkmann.

The foregoing review confirms the placing ofArcthoplites in Spath’s acuticostata Subzone (of whichBaraboshkin’s acuticostata Subzone is only a smallpart). In Brinkmann’s more refined scale the Arctho-plites levels fall within the germanica Subzone of hisrestricted tardefurcata Zone. It may be assumed, there-fore, that the Argiles a Bucaillella, with Arcthoplites (A.)

marechali, are also of germanica Subzone age and liewell above the base of the Albian. The presence ofHypacanthoplites anglicus in the Argiles a Bucaillellais consistent with the record of this species in therestricted tardefurcata Zone of Altwarmbuchen,northern Germany (Kemper, 1975).

In Figure 7 the greater part of the Sablesferrugineux at Cauville is shown tentatively as corre-sponding to the schrammeni Zone/Subzone of northernGermany in accordance with the post-jacobi aspect ofthe small fauna of Hyacanthoplites collected from thesebeds. As yet the basal levels of the Sables ferrugineuxhave yielded no ammonites but are unlikely to beolder than jacobi Zone in my opinion.

Above the Argiles a Bucaillella, the base of thePoudingue ferrugineux contains a remanie assemblageof ammonites that includes Hypacanthoplites trivialiscauvillensis Destombes et al. and Leymeriella (Neo-leymeriella) aff. regularis (d’Orbigny) (Destombeset al., 1974), suggesting the former existence of themilletioides and regularis Subzones in the Cauville area.

Marechal’s correlation of the Argiles a Bucaillellawith the English Subzone of Farnhamia farnhamensis(Marechal, 1994) is questionable. The genus Farn-hamia is endemic to SE England and in its stratotypearea of Farnham, Surrey, occurs in isolation within asuccession of largely unfossiliferous sands of theFolkestone Formation of the Lower GreensandGroup. A variable thickness of such sands, terminat-ing at an angular unconformity, separate the Farn-hamia horizon from the overlying regularis Subzone(Casey, 1961). Farnhamia is associated with a suite ofHypacanthoplites showing affinities both with those ofthe (presumably earlier) anglicus Subzone and the(presumably later) milletioides Subzone; also rareAnadesmoceras, a genus which places the Subzoneof F. farnhamensis in the broad tardefurcata Zone.Originally, the Farnhamia horizon was thought tocorrespond to the schrammeni Subzone of northernGermany (Casey, 1954). However, because of thepresence of Anadesmoceras in the fauna, Birkelund &Hakansson (1983) equated the Subzone of F. farnha-mensis with the restricted tardefurcata Zone of northernGermany and Mangyshlak (=Spath’s acuticostataSubzone). Owen (1988a, b) reached the same conclu-sion, based on the idea that Farnhamia was congenericwith or very close to Arcthoplites. The grounds for anacuticostata Subzone age for Farnhamia advanced bythese authors are here regarded as tenuous in the onecase and invalid in the other. It is not known preciselyat which level Anadesmoceras first appears in the broadtardefurcata Zone; the synonymy of Farnhamia andArcthoplites is not accepted (Casey, 1996, p. 72;Wright, 1996, p. 114) and the subjective assessment


of a close relationship between these two genera doesnot imply contemporaneity. Nevertheless, their con-clusions are endorsed in the new alignment of therelevant strata shown in Figure 7.

The species of Hypacanthoplites found as faunal as-sociates of Bucaillella and of Farnhamia exhibit simi-larities, but the only form in common so far identifiedis H. anglicus rigidus subsp. nov. This late mutation ofH. anglicus occurs in bed C6.4 at Cauville and as ararity in the farnhamensis Subzone. The presence of H.anglicus s.s. in the Argiles a Bucaillella and its absencefrom the farnhamensis Subzone suggests that the latteris slightly younger. On this slender evidence the Sub-zone of Farnhamia farnhamensis is placed a little higherin the column than the Argiles a Bucaillella and on alevel with the middle of Spath’s acuticostata Subzone.

1Despite recent denials of the existence of these two subzones(Ruffell & Owen, 1995; Owen, 1996a, b), new excavations atFolkestone have confirmed the rubricosus-anglicus succession(Casey, in prep.). Primitive Hypacanthoplites of the rubricosus levelare found also in a phosphatic nodule-bed near the base of theSandrock Formation in the Isle of Wight (Casey, 1961, p. 514) andin a similar bed, below the anglicus fauna, at the base of the WissantFormation in the Boulonnais (F. Amedro collection).

5. Delimitation of the Aptian/Albian boundary

Present-day thinking on this boundary dates fromBreistroffer (1947), who considered the AlbianStage to commence with the Zone of Leymeriella (L.)tardefurcata, with an horizon of L. (Proleymeriella)schrammeni at the base. The stratotype section for thissuccession is in the Hannover region of northernGermany. The underlying ‘Clansayes’ horizon, orZone of Diadochoceras nodosocostatum, which Jacob(1905), Spath (1923, 1941) and others had taken as thebasal unit of the Albian, was divided into two subzonesand elevated to a separate substage (‘Clansayesian’) atthe top of the Aptian. Following Spath (1941) andBreistroffer (1947), the index-species for these twodivisions of the ‘Clansayesian’ have been accepted asAcanthohoplites (Nolaniceras) nolani below and Hypa-canthoplites jacobi above, now generally regarded asindependent zones (cf. Erba, 1996).

The limited geographical range of species of theschrammeni group (Proleymeriella) has posed problemsover the use of L. (P.) schrammeni as the marker forthe base of the Albian (Hart et al., 1996). As yet thereis no consensus as to a suitable substitute marker,either from the ammonite options presented or fromother organisms.

In the Folkestone area of SE England the jacobiZone was considered to comprise two subzones,Hypacanthoplites rubricosus below and H. anglicusabove1 (Casey, 1950, 1961). An isolated occurrence

in Surrey, SE England, of a fauna containing speciesof Hypacanthoplites similar to those of the anglicusSubzone but with the genus Anadesmoceras and aprimitive hoplitid, Farnhamia, was taken to representa subzone at the base of the broad tardefurcata Zone(Subzone of Farnhamia farnhamenis) analogous to thatof L. (P.) schrammeni (Casey, 1954). Much of theevidence for drawing the Aptian/Albian boundary atthe anglicus/farnhamenis level in the English scale hascrumbled, however, as research in other regions hasprogressed. As stated above, the horizon of Farnhamiais now determined as well above the base of theAlbian. Moreover, the status of the anglicus fauna asan indicator of latest Aptian time can no longer bemaintained, as shown in the systematic section, de-spite recent affirmations of its Aptian age (Ruffell &Owen, 1995; Casey, 1996; Owen, 1996b). In particu-lar, the statements by Owen (1996b, p. 467) that‘‘In . . . the Subzone of Hypacanthoplites anglicus . . .we can recognise the well-known and geographicallywidely distributed Hypacanthoplites jacobi fauna’’ andthat this ‘‘interval of time is best regarded as aSubzone of Hypacanthoplites jacobi’’ need to becorrected.

The anglicus fauna is not, of course, the same as thatof the Hannover jacobi Zone. As originally described(Casey, 1950, 1965), it included H. simmsi (Forbes),H. newingtoni Casey and other macroconch species,which, together with H. anglicus itself, are lacking inthe jacobi fauna of Vohrum and Algermissen (Casey,1965, p. 427), presumably due to palaeoecologicalfactors as well as a time-difference. Hypacanthoplitesanglicus is now known to be a species of the broadtardefurcata Zone. In the vicinity of Sandling Junction,near Hythe, where the succession is more expandedthan at Folkestone, it has been found only in theupper levels of the strata hitherto assigned to theanglicus Subzone (Casey, 1961). Conversely, H.simmsi occupies the lower part, which can now beextended down from the Folkestone Formation intothe Sandgate Formation of the Lower GreensandGroup of SE England following the finds reported byRuffell & Owen (1995). It is here proposed to detachthis lower part of the succession from the anglicusSubzone as a Subzone of Hypacanthoplites simmsi. Forthe present this simmsi Subzone is retained in thejacobi Zone, notwithstanding the absence of the index-species from the classic jacobi fauna of Germany. Thebase of the redefined anglicus Subzone is taken at thefirst occurrence of the index species, H. anglicus,which is in bed 5 of the Sandling Junction section(Casey, 1961, p. 533), the Subzone here embracingbeds 5–9 only. As shown in Figure 7, it is by no meanscertain that the simmsi/anglicus contact corresponds

626 R. Casey

to the jacobi/schrammeni junction of the ‘standard’sequence.

The schrammeni fauna is missing, not only in theAnglo–Paris Basin, but also over the whole of theRussian Platform, the Crimea and Transcaspia(Baraboshkin, 1996, 1997; in Hart et al., 1996), aswell as over much of Central Asia (Krymgolts, 1977).On the other hand, the jacobi Zone is widely reportedin many of these regions, where it invariably suc-ceeded by strata of middle tardefurcata age. In theKopet–Dag area of Turkmenistan, for example,Glazunova (1953) has attributed to the jacobi Zone alarge assemblage of Hypacanthoplites, including formsconspecific with or analogous to H. anglicus (e.g.,H. kopetdagensis Glazunova). While the absence of theschrammeni fauna is in places clearly associated witha break in the stratigraphical succession (e.g., inMangyshlak, Kazakhstan), elsewhere over this vastexpanse of territory there may be another explanation.It must be asked whether the widespread gap in thetheoretical ammonite sequence at the jacobi/tardefurcata junction observed in eastern Europe andwestern Asia is due, in part at least, to strata ofschrammeni age being included in an amplified jacobiZone, as has happened in the Anglo–Paris basin.

When pointing out the important changes in theammonites at the base of the broad tardefurcata Zone,with the evolution of Leymeriella from Callizoniceras(Wollemanniceras), Breistroffer (1947) did not giveweight to the equally important changes within thenodosocostatum Zone (his ‘Clansayesian’ Substage),perhaps because in SE France, where he worked, thisbroad biostratigraphical unit is represented mainly bycondensed deposits. The constituent members of thisnodosocostatum ‘Zone’ are the Zones of Acanthohoplites(Nolaniceras) nolani below and Hypacanthoplites jacobiabove. Wherever these two zones are found in un-condensed deposits the faunas are seen to be verydistinct. The ammonite fauna of the so-called ‘Zone’of Diadochoceras nodosocostatum (the index-species ofwhich is known only from the Tethyan realm) is inessence the fauna of the nolani Zone, being character-ized by Acanthohoplites s.s., A. (Nolaniceras), Dia-dochoceras and Eodouvilleiceras. It is here that thewidespread Aptian genus Acanthohoplites reached itspeak of abundance and diversity. The most significantammonite events in the jacobi Zone were the evolutionof Hypacanthoplites from Acanthohoplites and thedisappearance of Diadochoceras and Eodouvilleiceras.

Outside northern Germany early members of theLeymeriella stock, i.e., the group of L. (Proleymeriella)schrammeni, are known from only a few localitieswithin the narrow corridor of distribution of the genus,stretching from Iran to northern Greenland (see

Birkelund & Hakansson, 1983, fig. 6). By comparison,the Acanthohoplites–Hypacanthoplites lineage has acircum-global distribution that takes in Europe,the Caucasus, western Asia, north and east Africa,Madagascar, Mexico, Arizona, California and Japan(Wright, 1996). In view of the difficulty in fixing theAptian/Albian boundary on the basis of the H. jacobi/L.schrammeni contact, it is here suggested that the firstoccurrence of the genus Hypacanthoplites offers a moresatisfactory marker for the base of the Albian.

There are a few drawbacks to taking Hypa-canthoplites as the basal marker for the Albian.Differentiation of early Hypacanthoplites from lateAcanthohoplites can be readily made only in micro-conchs or juveniles; the flat, delicately noded venterdiagnostic of Hypacanthoplites being in these earlyforms a transient feature of the first few whorls. Thegenus has not been recorded from the Arctic andin some regions where faunas of primitive Hypa-canthoplites are well represented in continuousammonitiferous sequences, as in the Kopet-Dag areaof Turkmenistan, the published stratigraphy (e.g.,Glazunova, 1953) is not sufficiently refined topin-point the nolani–jacobi contact. However, the firstoccurrence of Hypacanthoplites is well documentedin the stratigraphical column of Western Europe andcan be determined in the expanded succession ofthe Vocontian Trough, France, one of the chiefcandidate-regions for Aptian/Albian boundarystratotype selection.

Not only does the appearance of Hypacanthoplitesprovide a practical baseline for the Albian Stage ofwide applicability, but the return of the jacobi Zone tothe Albian would go a long way towards eliminatinga troublesome issue concerning the Aptian Stage.This is the question of whether the Aptian should bedivided into two or three substages. Since Breistroffer(1947) added to the classic Lower (‘Bedoulian’)and Upper (‘Gargasian’) Aptian an uppermost‘Clansayesian’ Substage (=nolani and jacobi Zones ofpresent usage), different practices have developed. Ingeneral, though not universal, workers in the Borealrealm tend to retain the classic twofold division, whilethose concerned with the Tethyan realm havefavoured a threefold division by employing a ‘MiddleAptian’ (Casey et al., 1998).

It is here proposed that the concept of a‘Clansayesian’ or third substage of the Aptian bedropped, with the jacobi Zone being transferred to theAlbian and the nolani Zone accepted as the topmostzone of the Upper Aptian. This would obviate theneed for a ‘Middle Aptian’ and encourage inter-national agreement on a simple bipartite division ofthe Aptian into Lower and Upper substages.


Acknowledgements

I am indebted to M. G. Breton for access to thecollections in the Museum d’Histoire Naturelle,Le Havre; to Dr M. D. Belonin of VNIGRI, StPetersburg, for permission to examine the collectionsof the late A. A. Saveliev; and to Dr E. J. Baraboshkinfor showing me relevant ammonites from the RussianPlatform at Moscow State University. The co-operation of M. M. Marechal is especially appreci-ated, as also the computer skill of Mr M. Cuddeford.Mr C. J. Wood made helpful comments on the draftmanuscript. Thanks are due also to M. F. Amedro,Mr H. M. Bayliss, Mr J. Craig, M. J.-P. Debris, M. F.Deschandol and Mr D. Searle. The work has beenaided by a grant from the Royal Society.

References

Alabushev, A. & Wiedmann, J. 1994. Palaeogeographic significanceof the distribution of Albian (Cretaceous) ammonite faunas in thePacific coast of North-East Russia. Neues Jahrbuch fur Geologieund Palaontologie, Monatshefte 1994, 193–204.

Baraboshkin, E. J. 1992. The Lower Albian of the central regionsof the Russian Platform. In Phanerozoic stratigraphy of the centralpart of the East-European Platform (ed. Shik, S. M.), pp. 20–36(‘Centrgeologia’, Moscow). [In Russian]

Baraboshkin, E. J. 1996. The Russian Platform as a controller ofthe Albian Tethyan/Boreal ammonite migrations. GeologicaCarpathica 47, 275–284.

Baraboshkin, E. J. 1997. A new stratigraphical scheme for theLower Cretaceous deposits between Kacha and Bodrak (south-west Crimea). Vestnik Moskovskogo Universiteta, Geologiya 1997(3), 22–29. [In Russian]

Baraboshkin, E. J. & Mikhailova, I. A. 1988. Ammonites andstratigraphy of the Middle Albian in the northern Moscow region.Article 2. Ammonites. Byulleten Moskovskogo ObshchestvaIspytatelei Prirody, Geologiya 63, 75–88. [In Russian]

Birkelund, T. & Hakansson, E. 1983. The Cretaceous of NorthGreenland—a stratigraphic and biogeographical analysis.Zitteliana 10, 7–25.

Bogoslowsky, N. A. 1902. Material for the study of the LowerCretaceous ammonite fauna of central and northern Russia.Memoires du Comite Geologique de la Russie (New Series) 2 vi+1–161, pls 1–18. [In Russian with German translation]

Breistroffer, M. 1947. Sur les zones d’ammonites dans l’Albien deFrance et d’Angleterre. Travaux du Laboratoire de Geologie de laFaculte des Sciences de l’Universite de Grenoble 26, 1–88.

Breton, G. 1981. Excursions geologiques sur le littoral entre LeHavre et Etretat. Bulletin Trimestriel de la Societe Geologique deNormandie et des Amis du Museum du Havre 68(3), 1–54.

Brinkmann, R. 1937. Biostratigraphie des Leymeriellenstammesnebst Bemerkungen zur Palaogeographie des nordwestdeutschenAlb. Mitteilungen aus dem Geologischen Staatsinstitut Hamburg 16,1–18.

Casey, R. 1936. Recent additions to the Albian ammonoid faunasof Folkestone. Geological Magazine 73, 444–448.

Casey, R. 1950. The junction of the Gault and Lower Greensand inEast Sussex and at Folkestone, Kent. Proceedings of the Geologists’Association 61, 268–298.

Casey, R. 1952. The ammonite genera Arcthoplites Spath andTetrahoplites gen. nov. Abstracts of Proceedings of the GeologicalSociety, London 1490, 134–135.

Casey, R. 1954. New genera and subgenera of Lower Cretaceousammonites. Journal of the Washington Academy of Sciences 44,106–115.

Casey, R. 1957. The Cretaceous ammonite genus Leymeriella, witha systematic account of its British occurrences. Palaeontology 1,29–59, pls 7–10.

Casey, R. 1961. The stratigraphical palaeontology of the LowerGreensand. Palaeontology 3, 487–621, pls 77–84.

Casey, R. 1965. A monograph of the Ammonoidea of the LowerGreensand, Part 6, pp. 399–546, pls 67–90 (PalaeontographicalSociety, London).



Casey, R. 1996. Correspondence. Lower Greensand ammonitesand ammonite zonation. Proceedings of the Geologists’ Association107, 69–74.

Casey, R., Bayliss, H. M. & Simpson, M. I. 1998. Observations onthe lithostratigraphy and ammonite succession of the Aptian(Lower Cretaceous) Lower Greensand of Chale Bay, Isle ofWight, UK. Cretaceous Research 19, 511–535.

Cayeux, L. 1961. L’Albien des environs du Havre. Bulletin de laSociete Geologique de Normandie 1, 21–26.

Cherkesov, O. V. & Burdykina, M. D. 1979. Descriptions of newammonite finds in Novaya Zemlya. In Upper Palaeozoic andMesozoic of the of the islands and coasts of the Arctic seas of the USSR.(ed. Shulgina, N. I.), pp. 43–66 (Nauchno-issledovatelskiiInstitut Geologii Arktiki, Leningrad). [In Russian]

Collignon, M. 1963. Atlas des fossiles caracteristiques deMadagascar (Ammonites). X (Albien), pp. 1–84, pls 1–37 (ServiceGeologique, Tananarive).

Destombes, P. 1958. Revision de l’Albien de la region du Havre.Deductions paleogeographiques sur le NW du Bassin Parisien auCretace moyen. Bulletin de la Societe geologique de France, Serie 6,8, 305–313.

Destombes, P., Juignet, P. & Rioult, M. 1974. Ammonites del’Aptien–Albien du Bec-de-Caux, Normandie (NW France).Bulletin Trimestriel de la Societe Geologique de Normandie et des Amisdu Museum du Havre 61, 49–115, pls 1–6.

Erba, E. 1996. The Aptian stage. In Proceedings, Second InternationalSymposium on Cretaceous Stage Boundaries, Brussels, 8–16September 1995 (eds Rawson, P. F., Dhondt, A. V., Hancock,J. M. & Kennedy, W. J.), Bulletin de l’Institut Royal des SciencesNaturelle de Belgique, Sciences de la Terre 66-supplement,31–43.

Glazunova, A. E. 1953. Ammonites of the Aptian and Albian ofKopet-Dag, Lesser and Greater Balkhans and Mangyshlak, 156 pp.(Trudy VSEGEI, Moscow). [In Russian]

Hart, M., Amedro, F. & Owen, H. 1996. The Albian Stage andSubstage boundaries. In Proceedings, Second International Sympo-sium on Cretaceous Stage Boundaries, Brussels, 8–16 September1995 (eds Rawson, P. F., Dhondt, A. V., Hancock, J. M. &Kennedy, W. J.), Bulletin de l’Institut Royal des Sciences Naturelle deBelgique, Sciences de la Terre 66-supplement, 45–56.

Jacob, C. 1905. Eutude sur les ammonites et sur l’horizonstratigraphique du gisement de Clansayes. Bulletin de la SocieteGeologique de France, Serie 4, 5, 339–432, pls 12, 13.

Jeletsky, J. A. 1964. Illustrations of Canadian fossils. LowerCretaceous marine index fossils of the sedimentary basins ofWestern and Arctic Canada. Geological Survey of Canada, Paper64–11, 1–101, pls 1–36.

Jeletsky, J. A. 1980. New or formerly poorly known, biochronologi-cally and palaeobiogeographically important gastroplitinid andcleoniceratinid (Ammonitida) taxa from Middle Albian rocks ofmid-western and Arctic Canada. Geological Survey of Canada,Paper 79–22, 1–63, pls 1–10.

Jeletsky, J. A. & Stelck, C. R. 1981. Pachygrycia, a new Sonneratia-like ammonite from the Lower Cretaceous (earliest Albian?) ofnorthern Canada. Geological Survey of Canada, Paper 80–20,1–25, pls 1–4.

628 R. Casey

Jones, D. L. 1967. In Jones, D. L. & Grantz, A., Cretaceousammonites from the lower part of the Matanuska Formation,southern Alaska. United States Geological Survey, Professional Paper547, iv+49 pp., pls 1–9.

Jones, D. L., Murphy, M. A. & Packard, E. L. 1965. The LowerCretaceous (Albian) ammonite genera Leconteites and Brew-ericeras. United States Geological Survey, Professional paper 503-F,1–22, pls 1–11.

Juignet, P. 1974. La transgression cretacee sur la bordue orientale duMassif Armoricain. Aptien, Albien, Cenomanian de Normandie et duMaine. These de Doctorat d’Etat, Universite de Caen, 810 pp.,28 pls.

Juignet, P. 1980. Bucaillella (Argiles noires a). In Megnien, C.,Synthese geologique du Bassin de Paris, 3, Lexique des noms deformations. Memoires du Bureau de Recherches Geologiques etMinieres 103, 256 pp.

Juignet, P., Rioult, M. & Destombes, P. 1973. Boreal influences inthe Upper Aptian–Lower Albian beds of Normandy, northwestFrance. In The Boreal Lower Cretaceous (eds Casey, R. & Rawson,P. F.), Geological Journal, Special Issue 5, 303–326.

Kemper, E. 1973. The Aptian and Albian stages in northwestGermany. In The Boreal Lower Cretaceous (eds Casey, R. &Rawson, P. F.), Geological Journal, Special Issue 5, 345–360.

Kemper, E. 1975. Die Cephalopoden aus dem Unter-Alb (Zoneder Leymeriella tardefurcata) von Altwarmbuchen. Berichten derNaturhistorische Gesellschaft zu Hannover 119, 87–111.

Kemper, E. 1982 Die Ammoniten des spaten Apt und fruhen AlbNordwestdeutschlands. Geologisches Jahrbuch A 65, 553–577.

Krymgolts, G. Ya (president of editorial board) 1977. Decisions ofthe interdepartmental stratigraphical conference on the Mesozoic ofCentral Asia (Samarkand, 1971), with unified stratigraphical corre-lation tables, pp. 1–48, 14 tables (Interdepartmental Stratigraphi-cal Committee, VSEGEI, Leningrad). [In Russian]

Marechal, M. 1990. L’holotype de Bucaillella cayeuxi Destombes,Juignet & Rioult, 1974 (Hoplitidae, Ammonitina) et son originegeographique et stratigraphique. Bulletin Trimestriel de la SocieteGeologique de Normandie et des Amis du Museum du Havre 77(2),44.

Marechal, M. 1991. Decouverte d’especes du genre Sonneratia a labase de l’Albien inferieur de Cauville. Bulletin Trimestriel de laSociete Geologique de Normandie et des Amis du Museum du Havre78(2), 21–31.

Marechal, M. 1994. Les Hypacanthoplites Spath, 1923 des Argiles aBucaillella cayeuxi de Cauville et leur position stratigraphique.Bulletin Trimestriel de la Societe Geologique de Normandie et des Amisdu Museum du Havre 81(2), 83–96.

Marechal, M., Lepage, G., Breton, G., Debris, J-P., Freneix, S.& Secretan, S. 1988. Les Argiles a Bucaillella de L’Aptiensuperieure de Cauville (Seine-Maritime, Normandie) et leurcontenu paleontologique. Bulletin Trimestriel de la SocieteGeologique de Normandie et des Amis du Museum du Havre 75(4),5–24.

Mikhailova, I. A. 1974. The genus Cymahoplites Spath from theAlbian deposits of Mangyshlak. Vestnik Moskovskogo Universiteta4, 1974, 37–43. [In Russian]

Mikhailova, I. A. 1975. The genus Sokolovites Casey and itsstratigraphical significance. Vestnik Moskovskogo Universiteta 6,1975, 38–45. [In Russian]

Nagy, J. 1970. Ammonite faunas and stratigraphy of Lower Creta-ceous (Albian) rocks in southern Spitsbergen. Norsk PolarinstituttSkrifter 152, 58 pp., 9 pls.

Nikitin, S. N. 1888. Les vestiges de la periode Cretacee dans laRussie centrale. Memoires du Comite Geologique de St. Petersbourg5(2), 1–205, pls 1–5.

Owen, H. G. 1971. Middle Albian stratigraphy in the Anglo–ParisBasin. Bulletin of the British Museum (Natural History), Geology,Supplement 8, 1–164, pls 1–3.

Owen, H. G. 1988a. Correlation of ammonite faunal provinces inthe Lower Albian (mid-Cretaceous). In Cephalopods—present and

past (eds Wiedmann, J. & Kullman, J.), pp. 477–489(Schweizerbart’sche Verlagsbuchhandlung, Stuttgart).

Owen, H. G. 1988b. The ammonite zonal sequence and ammonitetaxonomy in the Douvilleiceras mammillatum Superzone (LowerAlbian) in Europe. Bulletin of the British Museum (NaturalHistory), Geology 44, 177–231.

Owen, H. G. 1996a. Correspondence. ‘‘Uppermost Wealden faciesand Lower Greensand Group (Lower Cretaceous) in Dorset,southern England: correlation and palaeoenvironment’’ byRuffell & Batten (1994) and ‘‘The Sandgate Formation of theM20 Motorway near Ashford, Kent and its correlation’’ byRuffell & Owen: reply. Proceedings of the Geologists’ Association107, 74–76.

Owen, H. G. 1996b. Boreal and Tethyan late Aptian to late Albianammonite zonation and palaeobiogeography. Mitteilungen ausdem Geologish-Palaontologischen Institut der Universitat Hamburg77, 461–481.

Reyment, R. A. & Kennedy, W. J. 1998. Taxonomic recognitionof species of Neogastroplites (Ammonoidea, Cenomanian) bygeometric morphometric methods. Cretaceous Research 19, 25–42.

Ruffell, A. H. & Owen, H. G. 1995. The Sandgate Formation ofthe M20 Motorway near Ashford, Kent, and its correlation.Proceedings of the Geologists’ Association 106, 1–9.

Saveliev, A. A. 1973. Stratigraphy and ammonites of the LowerAlbian of Mangyshlak (Zones of Leymeriella tardefurcata andLeymeriella regularis). Trudy VNIGRI 323, 339 pp., 44 pls, foldingchart (‘Nedra’, Leningrad). [In Russian]

Saveliev, A. A. 1992. The Lower Albian ammonites of Mangyshlak,their phylogeny and significance for zonal stratigraphy of theAlbian of the southern USSR (Superzone of Cleonicerasmangyschlakense), 138 pp., 48 pls, folding chart (VNIGRI,‘Nedra’, St. Petersburg). [In Russian]

Sayed-Emami, K. 1980. Leymeriella (Ammonoidea) aus dem unternAlb von Zentraliran. Mitteilungen Bayerische Staatssammlung furPalaontologie und Historische Geologie 20, 17–27.

Spath, L. F. 1923. On the ammonite horizons of the Gault andcontiguous deposits. Appendix II in Summary of Progress of theGeological Survey for 1922 139–149.

Spath, L. F. 1925. A monograph of the Ammonoidea of the Gault,Part 2, pp. 73–110, pls 5–8 (Palaeontographical Society,London).

Spath, L. F. 1937. The Canadian ammonite genus Gastroplites inthe English Gault. Annals and Magazine of Natural History 19(10), 257–260.

Spath, L. F. 1939. Problems of ammonite nomenclature. V.On Acanthohoplites jacobi (Collet) and the Jacobi Zone of theFolkestone Sands. Geological Magazine 76, 236–239.

Spath, L. F. 1941. A monograph of the Ammonoidea of the Gault,Part 14, pp. 609–668, pls 65–72 (Palaeontographical Society,London).

Spath, L. F. 1942. A monograph of the Ammonoidea of the Gault, Part15, pp. 669–720 (Palaeontographical Society, London).

Stolley, E. 1908. Die Gliederung der norddeutschen UnternKreide. Centralblatt fur Mineralogie, Geologie und Palaontologie 9,107–124, 244–247.

Wright, C. W. 1952. A classification of Cretaceous ammonites.Journal of Paleontology 26, 213–222.

Wright, C. W. 1957. Cretaceous ammonites. In MesozoicAmmonoidea (eds Arkell, W. J., Kummel, B. & Wright, C. W.),Treatise on invertebrate paleontology (ed. Moore, R. C.), L, Mol-lusca 4. Cephalopoda, Ammonoidea, pp. L80–490 (GeologicalSociety of America, Boulder, and University of Kansas Press,Lawrence).

Wright, C. W. 1996 (with contributions by Callomon, J. H. &Howarth, M. K.). Treatise on invertebrate paleontology. L, Mollusca4 revised. Volume 4, Cretaceous Ammonoidea, xx+362 pp.(Geological Society of America, Boulder, and University ofKansas Press, Lawrence).

The age of the Argiles àBucaillellaof Normandy, the systematic position of the Cretaceous ammonite...

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