Carnets de Géologie / Notebooks on Geology - Article 2011/01 (CG2011_A01)

The Dichotomus Horizon: proposal for a new biochronologic unit of the Giraudi Zone of the Upper Barremian of southeastern France, and considerations regarding the genus Imerites ROUCHADZÉ (, Gassendiceratinae)

1 Didier BERT 2 Gérard DELANOY 3 Stéphane BERSAC

Abstract: Recent revisions of the genus Imerites ROUCHADZÉ make it possible to introduce a new bio- chronologic horizon to define more precisely the lower boundary of the Giraudi Zone: the Dichotomus Horizon. Using the concept of 'interval zone', this new horizon maintains the current lower boundary of the Giraudi Zone as accepted by authors, and thus contributes to the stabilization of the Barremian zonal system. This stabilization is also strengthened by abandonment of the use of "Crioceras" cristatus d'ORBIGNY (nomen dubium) that ought not be used as an index species in detriment of Imerites giraudi (KILIAN). The classification, origin, and intraspecific variation of the genus Imerites ROUCHADZÉ are exa- mined. Key Words: Tethyan realm; Upper Barremian; biostratigraphy; Interval zone; southeastern France; ammonites.

Citation: BERT D., DELANOY G. & BERSAC D. (2011).- The Dichotomus Horizon: proposal for a new bio- chronologic unit of the Giraudi Zone of the Upper Barremian of southeastern France, and considerations regarding the genus Imerites ROUCHADZÉ (Ammonoidea, Gassendiceratinae).- Carnets de Géologie / Notebooks on Geology, Brest, Article 2011/01 (CG2011_A01) Résumé : L'horizon à Dichotomus : proposition d'une nouvelle unité biochronologique de la zone à Giraudi du Barrémien supérieur du Sud-Est de la France, et considérations sur le genre Imerites ROUCHADZÉ (Ammonitina, Gassendiceratinae).- Les récentes révisions du genre Imerites ROUCHADZÉ permettent à présent d'introduire un nouvel horizon biochronologique afin de mieux définir la limite inférieure de la Zone à Giraudi : l'horizon à Dichotomus. Par l'application du concept de la zone d'intervalle, l'utilisation de cet horizon permet de conserver la limite inférieur actuelle de la zone à Giraudi telle qu'elle a été acceptée par les auteurs, et ainsi de contribuer à la stabilisation du schéma zonal du Barrémien. Cette stabilisation est aussi renforcée par l'abandon de l'usage de "Crioceras" cristatus d'ORBIGNY (nomen dubium) qui ne devrait pas être utilisé comme espèce indice au détriment de Imerites giraudi (KILIAN). La classification, l'origine et la variabilité intraspécifique du genre Imerites ROUCHADZÉ sont aussi discutées. Mots-Clefs : Domaine téthysien ; Barrémien supérieur ; biostratigraphie ; zone d'intervalle ; Sud-Est de la France ; ammonites. Introduction producibility by specialists working in discrete localities (REBOULET et alii, 2007, 2009 - see After a period of instability, in recent years BERT et alii, 2008 for a historical account). It several studies have helped to fix the calibra- now includes the Vandenheckei, Sartousiana tion of the Upper Barremian biostratigraphy of and Giraudi zones (Fig. 1), their limits based on southeastern France that increased its value for faunal changes commonly associated with se- practical use and increased the degree of its re- quence boundaries developed in relation to

1 * Corresponding author Université de Bourgogne, Laboratoire Biogéosciences, UMR CNRS 5561, 6 bd Gabriel, F-21000, Dijon (France) [email protected] 2 Département des Sciences de la Terre, Université de Nice-Sophia-Antipolis, Faculté des Sciences, 28 avenue Valrose, 06108 Nice Cedex 2 (France) [email protected] 3 945 route de Gattières, F-06640 Saint Jeannet (France) [email protected] Manuscript online since January 17, 2011

1 Carnets de Géologie / Notebooks on Geology - Article 2011/01 (CG2011_A01) eustasy (ARNAUD, 2005). In accord with the (DELANOY, 1995, 1997, 1998; BERT et alii, 2008; recommendations of the IUGS Lower Creta- BERT & DELANOY, 2009; BERT et alii, 2010) has ceous Ammonite Working Group, the KILIAN contributed significantly to a refinement of the Group, stabilization of the boundaries of these biostratigraphic pattern of the Tethyan Upper zones led to a preference for the use of interval Barremian of southeastern France. zones rather than zones based on the range of This work revises the definition of the lower a taxon. With good reason, for the boundaries boundary of the Giraudi Zone [index species: of zones based on individual ranges are subject Imerites giraudi (KILIAN, 1888)] and is a mani- to repeated change in range limits caused by festation of progress in the continuation of the new finds or by tergiversation resulting from a revision of Upper Barremian biostratigraphy in revision of index taxa. Thus it seems preferable southeastern France through emendation to the to choose stable and precise horizons for defi- ammonite faunas which are a major element of ning the base of zones (THIERRY, 1997). The its framework (here Imerites ROUCHADZÉ, 1933). introduction of several biochronological horizons W Figure 1: Zonal scheme amended after BERT et alii, 2008, and REBOULET et alii, 2009. In red the Dichotomus Horizon (new). Figure 1 : Schéma zonal modifié d'après BERT et alii, 2008, et REBOULET et alii, 2009. En rouge, l'horizon à Dichotomus (nouveau).

The boundary between the northern portion. The Barremian here is cha- racterized by pelagic sediments, mainly alterna- Sartousiana and Giraudi zones, and tion of marls and limestones in decimetric to the new Dichotomus Horizon metric beds. Given the relative continuity of deposits and the paleontological record, it is 1- Geological setting possible to track in considerable detail the suc- cession and evolution of their ammonite faunas. The Lower of southeastern Fran- Thus, following up on the work of DELANOY ce is marked by the evolution of a large intra- (1995, 1998), several sections of this area cratonic subsident area known as the Vocontian expose the boundary between the Sartousiana Basin (PAQUIER, 1900). The area of the historical and the Giraudi zones well enough that they Barremian stratotype (Angles-Barrême-Castel- can be examined minutely: they are the Vignon lane area – Fig. 2), is in the southern part of section (VIG, Fig. 3), the Descouère section the Vocontian Basin which is less affected by (DES, Fig. 4), and the Grande-Terre section gravity remodelling and Alpine orogeny than its (GT, Fig. 5).

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W Figure 2: Barremian paleo- geography of southeastern France and location of the area studied (from ARNAUD, 2005, amended). Figure 2 : Cadre paléogéographi- que du Sud-Est de la France et localisation du secteur d'étude (modifiée d'après ARNAUD, 2005).

Subzone (Autrani Horizon) but is extremely 2- The boundary between the Sartousiana rare, for at this level and time it is only a very and Giraudi zones in southeastern France minor element of the ammonite fauna. In the The base of the Giraudi Zone is charac- lower portion of the Giraudi Subzone the situa- terized by an important phase of marine trans- tion is reversed: the Hemihoplitinae and the gression (ARNAUD, 2005), marked lithologically Pulcheliidae are gone and turriculate morpho- by the "vire marneuse à Heteroceras" of au- logy dominates quantitatively, first briefly with thors. It is associated with a major faunal turn- Imerites (Gassendiceratinae), and later with over (DELANOY, 1990, 1995, 1997, 1998; BERT et Heteroceras which begin an increase in abun- alii, 2008). This turnover is relatively progres- dance at the base of the Giraudi Zone and proli- sive in strata at the top of the Feraudianus Sub- ferate accompanied by a morphological explo- zone and at the base of the Giraudi Subzone. In sion in the Emerici Horizon (DELANOY, 1990, fact, all change occurs between the lower part 1995, 1997, 1998; DELANOY & EBBO, 2000; DELA- of the Feraudianus Subzone and the Emerici NOY & BERT, 2006). Horizon of the Giraudi Subzone (Fig. 1) where Above the Autrani Horizon (Feraudianus the Hemihoplitinae are progressively replaced Subzone, Sartousiana Zone, Fig. 1), the appea- quantitatively by the Heteroceratidae. At the rance of the genus Imerites ROUCHADZÉ is cur- base of the Feraudanus Subzone Hemihoplitinae rently accepted by authors as the valid marker are the major components of the ammonite of the lower limit of the Giraudi Zone (see fauna with a preponderance of the genus Hemi- historical account in KAKABADZE, 1989; HOEDE- hoplites SPATH. The Pulcheliidae and the Pei- MAEKER & BULOT, 1990; DELANOY, 1990, 1995, rescinae are quite rare, as are the Gassendice- 1998; REBOULET et alii, 2006, 2007, 2009; BERT ratinae (genera Gassendiceras BERT, DELANOY & et alii, 2008). Revisions of this genus by DELA- BERSAC, 2006, and Pseudoshasticrioceras DELA- NOY (1998) and BERT et alii (2009), improved NOY, 1998) which become more numerous at understanding of the stratigraphic distribution the top of the Subzone (i.e. in the Bersaci and of the species of Imerites. Their development Autrani horizons). The genus Heteroceras over time is coincident with the evolutionary d'ORBIGNY (with a turriculate morphology) is framework of the last Gassendiceratinae BERT, present at the upper limit of the Feraudianus DELANOY & BERSAC, 2006. So in the succession

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Imerites dichotomus ERISTAVI, 1955 appears nication of COMPANY, see DELANOY, 1998, p. 207), before Imerites giraudi (KILIAN, 1888). The use Bulgaria, Romania and Georgia (see BERT et alii, of an interval zone allows a redefinition of the 2009), a distribution that augers an extensive lower boundary of the Giraudi Zone without application of the Dichotomus Horizon. change of level by use of the new Dichotomus Faunal assemblages: The index species is Horizon (defined below). This usage preserves generally fairly well represented in the French' the integrity and stability of Barremian zonation sections. It is associated with (see DELANOY, (BERT et alii, 2008). There is no need to move 1995, 1998; BERT et alii, 2008): Macroscaphites the lower limit of the Giraudi Zone upward to yvani (PUZOS) macro- and microconchs, Acan- make it coincident with the appearance of its tholytoceras pseudoaudouli (THOMEL) macro- index species, or to rename the Giraudi Zone as and microconchs, Jaubertites collignoni SARKAR, the Dichotomus Zone, because I. dichotomus Protetragonites crebrisulcatus (UHLIG), Euly- ERISTAVI is the first species of Imerites of which toceras phestus (MATHERON), Silesites seranonis the appearance coincides with the accepted (d'ORBIGNY), Melchiorites melchioris (TIETZE), definition of the lower limit of the Giraudi Zone. Barremites difficilis (d'ORBIGNY), Barremites In any event, any shift in level would dissociate strettostoma (UHLIG), Phyloceras ponticuli the base of the Giraudi Zone from the faunal (ROUSSEAU), and with Heteroceras coulleti DELA- turnover and the sequence boundary with which NOY, Heteroceras baylei REYNES and Spinocrio- it is coincident (ARNAUD, 2005); application ceras trachyomphalus (UHLIG). either of these options would change the level of the base of the zone and return to the insta- Considerations regarding the genus bility that has long characterized Barremian Imerites ROUCHADZÉ, 1933 zonation and should cease. 1- Remarks on the classification and origin 3- The Dichotomus Horizon (new) of Imerites In France Imerites dichotomus ERISTAVI has a The genus Imerites ROUCHADZÉ has traditio- very limited and precise stratigraphic position. nally been classified as a Heteroceratidae, but it By anagenesis (BERT et alii, 2009) it is the suc- is now recognized as a representative of the cessor of the index species Pseudoshasticrio- family Hemihoplitidae (see BERT et alii, 2009 for ceras autrani (DELANOY), and the ancestor of the an historical account) despite the presence of a index species Imerites giraudi (KILIAN). In the turricone in the juvenile part of the shell (heli- stratotype area (Vocontian Basin, southeastern coidal coiling). SARKAR was the first to classify France – Fig. 2) its appearance in the stratigra- Imerites (his Escragnolleites) in the Hemihopli- phic succession is in agreement with its biologic tidae (1955, p. 24) because it has a hemihopli- relationships. These facts, and the need for the tid ancestor (1955, p. 18, 22), although KILIAN establishment of a high resolution biostrati- (1907-1913) saw "some similarities" between graphy for the whole of the Barremian (REBOU- Heteroceras giraudi (=Imerites) and some LET et alii, 2006; REBOULET et alii, 2007; BERT et Hemihoplitidae [=Ancyloceras (Crioceras) he- alii, 2008; REBOULET et alii, 2009), has impelled berti in KILIAN's time]. It has been recognized us to propose Imerites dichotomus ERISTAVI as a for a long time that helicoidal coiling is not new biostratigraphic marker in the Vocontian restricted to the Heteroceratidae. Indeed, KILIAN Basin. This species occurs in strata immediately (1888, 1889) was the first to restrict the genus above the major beds of the Autrani Horizon at Heteroceras d'ORBIGNY only to those Barremian the top of the Feraudianus Subzone (Sartousia- taxa that have a turricone. But d'ORBIGNY classi- na Zone), and immediately precedes those of fied one Senonian species (1851, p. 222) as a the Giraudi Horizon where Imerites giraudi (KI- heteroceratid, and MEEK (1876) included heli- LIAN) occurs (Figs. 3 - 4 - 5). coidal forms from the Upper Cretaceous of the Index species: Imerites dichotomus ERISTA- United States of America (Nostoceratidae) in VI, recently revised by BERT et alii (2009). that group, thus indicating broader criteria for Status: This horizon is defined by the first their classifications. This type of coiling is appearance of its index species (bed No. 436 in known to have developed repeatedly in the the Vignon [VIG] section, Fig. 3), and its upper evolutionary history of the ammonoids (e.g. limit is currently set at the base of the Giraudi Cochloceras; some Bajocian Spiroceras; Horizon (bed No. 439 in the VIG section) with Uppermost Barremian Kutatissites; some Lower the first appearance of Imerites giraudi (KILIAN). Cretaceous Leptoceratoidae; Albian Mariella, The Dichotomus Horizon is also present in the Turrilitoides, Helicoceras or Pseudhelicoceras; sections near La Baume (Castellane area): beds Cenomanian Turrilites, Hypoturrilites, Meso- 151 to 152 in the Descouère section (DES, Fig. turrilites and Ostlingoceras; Axonoceras, Joua- 4), and bed 679 in the Grande-Terre section niceras, Anaklinoceras and some other Nostoce- (GT, Fig. 5) [see also DELANOY, 1995, 1998]. ratidae from the Upper Cretaceous, etc. – see Paleobiogeographic distribution: Imeri- ARKELL et alii, 1957 and WRIGHT et alii, 1996). tes dichotomus ERISTAVI is present in south- But these authors did not remark a connection eastern France but also in Spain (oral commu- between these homeomorphs and the Hetero- ceratidae. More recently, KAKABADZE (2004, p.

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21) made the following observation about cer- the systematic position as to family". And DELA- tain genera with helicoidal coiling and the NOY (1998, p. 184) said about Imerites that "the absence of any relationship to the Heteroce- presence of the turricone would be only the ratidae: "the similarity in the mode of coiling expression of a homeomorphism that affects (helicoidal, planispiral or helicoidal, planospiral the early developments of these forms" (trans- and uncoiled) is not important for identifying lation pars).

W Figure 3: Distribution of the ammonites in the Vignon (VIG) section pars (Barrême area, Alpes-de-Haute-Provence). Figure 3 : Répartition des faunes d'ammonites dans la coupe du Vignon (VIG) pars (secteur de Barrême, Alpes-de-Haute-Proven- ce).

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BERT et alii (2009) were the first to distin- monstrate that Imerites is a direct descendant guish and define evolutionary processes in the of the genus Pseudoshasticrioceras DELANOY origin and development of species in the genus (Gassendiceratinae BERT, DELANOY & BERSAC). Imerites of the Hemihoplitidae. Their work This taxonomic distinction between genera of involved study of an evolved "Pseudoshasti- the same lineage is based on the early appea- crioceras" ornament in Imerites dichotomus rance of a turricone during the growth of ERISTAVI (see BERT et alii, 2006). In that stage of Imerites (BERT et alii 2009). development weaker peri-ventral tubercules de-

Figure 4: Distribution of the ammonites in the Descouère (DES) section pars (La Baume in the Castellane area, Alpes-de-Haute-Provence). Figure 4 : Répartition des faunes d'ammonites dans la coupe du Descouère (DES) pars (La Baume, secteur de Castellane, Alpes-de-Haute-Provence).

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Figure 5: Distribution of the ammonites in the Grande-Terre (GT) section pars (La Baume in the Castellane area, Alpes-de-Haute-Provence). Figure 5 : Répartition des faunes d'ammonites dans la coupe de la Grande-Terre (GT) pars (La Baume, secteur de Castellane, Alpes-de-Haute-Provence).

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We welcome acceptance of the genus Imeri- would be necessary: renaming the Giraudi Zone tes into the Gassendiceratinae but we do not as the Cristatus Zone [note that this is not obli- agree with the broader generic limits proposed gatory, for the International Stratigraphic Guide for Imerites by VERMEULEN & LEPINAY (2010, p. (SALVADOR, 1994, p. 67) states that "if it is desi- 18, 20). Their diagnosis includes some non- rable to continue use of a taxonomic term turriculate Hemihoplitidae, which would cause which is no longer valid, the term should be in problems that preclude its acceptance: quotation marks"]. 1. the large range of variation in morpholo- However new data obtained in the recent gy and ornament proposed for their Ime- revision of Imerites by BERT et alii (2009, p. 32- rites by these authors requires a rede- 33) found the syntypes of "Crioceras" cristatus finition of this genus to include criteria d'ORBIGNY of the d'ORBIGNY's collection are too much broader in scope than those com- fragmented to be identified at a specific level, monly acceptable to specialists. Their and the fragments may not be of just one proposal widely depasses the intent of specimen but may even represent more than the author of the genus Imerites ROU- one species. These facts render this taxon CHADZÉ and that of subsequent workers. unusable and a nomen dubium. Moreover, This new definition would produce a d'ORBIGNY's (1842, Pl. 115, figs. 4-8) original genus-group taxon which would greatly illustrations are probably a synthetic compi- lessen the precision of identification and lations (i.e. a picture based on several different make correlation with previous work but fragmentary specimens assembled and difficult. So nomenclatural stability restored to appear as if they were a single would be threatened and Upper Barre- specimen). They were recognized as such by mian biostratigraphy again subject to KILIAN (1888, 1889). In the original illustration revision because of confusion regarding the turricone is replaced by planispiral whorls the stratigraphic ranges of the species of for the stages of growth of the actual syntypes the genus Imerites ROUCHADZÉ; (particularly fragmented) when compared to the 2. the ornamental and morphological original picture make this obvious. So the reha- characteristics specified in the emended bilitation of "Crioceras" cristatus d'ORBIGNY, diagnosis of VERMEULEN & LEPINAY, would 1842, to replace Imerites giraudi (KILIAN, 1888), include in their genus Imerites species of a long-used, well defined taxon (recognized by Hemihoplitinae currently assigned to many authors), is not desirable. Moreover, the other genera, although they lack any purpose of the ICZN principle of priority is phyletic link to them. So Imerites in VER- explained by Article 23.2 which states very MEULEN & LEPINAY'S usage, might well explicitly that it must foster nomenclatural sta- include the taxa Hemihoplites SPATH, bility: "it is not intended to be used to upset a Camereiceras DELANOY, Pachyhemihopli- long-accepted name in its accustomed meaning tes DELANOY or Ancylezeiceras VERMEULEN. by the introduction of a name that is its senior synonym or homonym, or through an action This problem is particularly evident in the taken following the discovery of a prior and taxon "I." stephaniae VERMEULEN & LEPINAY, 2010 hitherto unrecognized nomenclatural act"; a (found in the Provincialis Subzone: One sub- fortiori when the older name is based on a syn- zone separates it from the appearance of the thetic compilations and can be considered as a first Imerites s. str.) that they attribute to the nomen dubium because it differs from cha- genus Imerites ROUCHADZÉ, but do not compare racteristics found in its syntypes. On the other it with contemporary Hemihoplitids. "I." stepha- hand, the proposal of invalidation by VERMEULEN niae VERMEULEN & LEPINAY is a fragmentary speci- & LEPINAY (2010, p. 17-18) of the d'ORBIGNY's men (VERMEULEN & LEPINAY, 2010, p. 21, Pl. 1, syntypes in favour to a more complete neotype fig. 7) particularly close in aspect to contempo- (not among the syntypes) does not comply with rary Hemihoplites of the group H. casanovai the provisions of the ICZN (Art. 75, and in DELANOY (=H. intermedius VERMEULEN - currently particular, § 75.3.4) and therefore cannot be under study). implemented. At most it might be possible to designate one of the original syntypes as a 2- The case of "Crioceras" cristatus d'ORBI- lectotype (n°5405-1 of the d'ORBIGNY's collec- GNY, 1842 tion), but the basic problem remains As DELANOY (in GAUTHIER et alii, 2006, p. 138- unchanged... 139), maintained "Crioceras" cristatus d'ORBIGNY Whatever the nomenclatural possibilities should be considered synonymous with Imerites mentioned earlier (DELANOY in GAUTHIER et alii, ILIAN) and according to the principle of giraudi (K 2006, p. 139), Imerites giraudi (KILIAN) is the priority of the International Code of Zoological type-species of the genus Imerites ROUCHADZÉ Nomenclature (ICZN - Art. 23.1) has seniority. and we strongly recommend "Crioceras" crista- ERMEULEN & LEPINAY (2010, p. Consequently, for V tus d'ORBIGNY be considered invalid. 20) another amendment of Barremian zonation

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Figure 6: Dimorphism and variability in shell morphology in Imerites. Figure 6 : Dimorphisme et variabilité morphologique de la coquille chez Imerites.

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ERISTAVI seem quite rare, but adult 3 - Intraspecific variability in Imerites and macroconchs are also few. The adult mechanical constraints associated with the form of the macroconch was unknown presence of turricone prior to the recent revision by BERT et alii Intraspecific variability in species of Imerites (2009). Juvenile or fragmentary speci- involves ornamentation, some dimensional mens of this species that are difficult to parameters of the shell and the size and orien- place because of uncertainty regarding tation of the turricone (Fig. 6c). The relation- which dimorph they represent are relati- ship of turricone size and placement to changes vely common; in shell morphology has been studied by DELA- 4. Variability in the size of the turricone NOY (1998, p. 53) for the genus Heteroceras versus that of the morphology of the and was illustrated by KAKABADZE (2004, Fig. 10) shell is well expressed in the macro- for the Kutatissites. In Imerites, the phenome- conchs of Imerites dichotomus ERISTAVI, non is the same: a larger turricone generally is just as it is in Imerites giraudi (KILIAN) accompanied by a less regular or triangular (Fig. 6c). This is the same in the micro- coiling before normal involution resumes. Ho- conchs of I. dichotomus (Fig. 6b): the wever, contrary to the views of VERMEULEN & type specimen of I. rarecostatus (=I. LEPINAY (2010) these purely mechanical dichotomus [m]) has a large turricone constraints are not comparable with the dimor- and minute coil, whereas the specimen phic differentiation in Imerites dichotomus figured Pl. 2, fig. 2 (in BERT et alii, 2009) ERISTAVI where tripartite adult microconch [m] has a well-developed coil and a relatively are associated with large planospiral adult small turricone; macroconch [M] (see BERT et alii, 2009, Pl. 2, 5. The specimens of I. giraudi (=I. cristatus fig. 2 versus Pl. 1, fig. 1 – Fig. 6a) for several in VERMEULEN & LEPINAY, 2010) cannot be reasons: used to suggest the absence of dimor- 1. The dimorphs of the adult stages of I. phism in I. dichotomus, since the tripar- dichotomum ERISTAVI are very different tite coiling of the microconchs is current- and there are, to our knowledge, no ly recognized with certainty only in I. di- intermediaries (Fig. 6a); chotomus. 2. The presence of such intermediaries was Conclusions assumed by VERMEULEN & LEPINAY (2010) because of the existence of specimens Recent revisions of the genus Imerites ROU- with a triangular coil ("I. cristatus favrei CHADZÉ provide an increased understanding of morphotype" of Pl. 1, figs. 5-6). These its variability and its evolution, so now permit specimens of which the whorl "may the introduction of a new biochronologic hori- represent a draft shaft" (p. 18) are too zon, the Dichotomus Horizon (Fig. 1), to define small in size and incomplete. They are the lower boundary of the Giraudi Zone more only juvenile whorls with triangular coi- precisely. Using the interval zone concept, the ling that wraps the turricone, but lack an addition of this horizon maintains the current uncoiling of the outer whorls to form a lower boundary of the Giraudi Zone as accepted shaft (Fig. 6c). Only the specimens figu- by authors (the appearance of the genus Ime- red Pl. 1, figs. 1-2 of their publication rites), and thus contributes to the stabilization may be adult, but they are crioconic with of the Barremian zonal scheme. This stabili- no shaft. Consequently, no adult speci- zation is also strengthened by the abandonment men with a morphology intermediate of "Crioceras" cristatus d'ORBIGNY (nomen du- between those of micro- and macro- bium) that ought not be used as index species conchs are known; instead of Imerites giraudi (KILIAN). Following 3. The tripartite Imerites raricostatus (KA- THIERRY (1997), in general (as it is for the KABADZE) has a well expressed orna- Barremian) it is preferable to use interval zones mental stage with fibular ribs (the type rather than the stratigraphic range of any one specimen is refigured in KOTETISHVILI et taxon for example, to avoid constant changes of alii, 2005, Pl. 87, fig. 2) and its ontoge- boundaries that discoveries and systematic nic sequence is very similar to the tripar- reviews of index taxa might impose, thus threa- tite specimen figured in BERT et alii tening the stability of the zonation. The intro- (2009, Pl. 2, fig. 2 – Fig. 6a). Therefore duction of a new biochronologic horizon increa- I. raricostatus (KAKABADZE) is a micro- ses the precision of the biostratigraphic zona- conch of I. dichotomus ERISTAVI and not tion of the Barremian stage in southeastern a morphotype of I. giraudi (KILIAN) (VER- France which is a requirement for the study in MEULEN & LEPINAY, 2010). Complete adult detail of the evolution of ammonites and their microconch specimens of I. dichotomus populations.

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Acknowledgments ces de la Terre et des Planètes), t. 311, p. 259-264. We wish to express our thanks to Mr. Ray- DELANOY G. (1995).- Les biozones à Feraudia- mond ENAY, and to the anonymous reviewer, nus, Giraudi et Sarasini du Barrémien supé- Mr. Stephane REBOULET and to Mr. Jaap KLEIN for rieur de la région stratotypique d'Angles- their valuable advice. We thank the Réserve Barrême-Castellane (Sud-Est de la France).- Géologique de Haute Provence and Mrs. Myette Géologie Alpine, Grenoble, Mémoire H.S., n° GUIOMAR who have allowed us access to the 20 (1994), p. 279-319. areas studied. One of us (D.B.) has interesting DELANOY G. (1997).- Biostratigraphie haute discussions with Gerd E.G. WESTERMANN about résolution du Barrémien supérieur du Sud- stratigraphical nomenclature, and we warmly Est de la France.- Comptes Rendus de l'Aca- thank him. We want especially and sincerely to démie des Sciences, Paris, (Série II, Scien- thank Nestor SANDER who kindly corrected our ces de la Terre et des Planètes), t. 325, p. English in the final version. 689-694. Bibliographic references DELANOY G. (1998).- Biostratigraphie des faunes d'Ammonites à la limite Barrémien-Aptien ARKELL W.J., KUMMEL B. & WRIGHT C.W. (1957).- dans la région d'Angles-Barrême-Castellane. Mesozoic Ammonoidea. In: MOORE R.C. (Ed.), Étude particulière de la Famille des Hetero- 4.- Treatise on Invertebrate Paleon- ceratidae (, Ammonoidea).- tology, Geological Society of America, New Annales du Muséum d'Histoire Naturelle de York; University of Kansas, Lawrence, Part L, Nice, t. XII (1997), 270 p. p. L80-L437. DELANOY G. & BERT D. (2006).- Nouvelles unités ARNAUD H. (2005).- The South-East France Ba- taxinomiques de la famille des Heterocerati- sin (SFB) and its Mesozoic evolution.- Géo- dae SPATH, 1924.- Annales du Muséum logie Alpine, Grenoble, (série spéciale "Collo- d'Histoire Naturelle de Nice, t. XXI, p. 255- ques et Excursions"), n° 7, p. 5-28. 295. BERT D. & DELANOY G. (2009).- Pseudoshasticrio- DELANOY G. & EBBO L. (2000).– Une nouvelle ceras bersaci nov. sp. (Ammonoidea, Gas- espèce d'Heteroceras: H. mascarelli sp. nov. sendiceratinae), and new ammonite bioho- (Ancyloceratina, Ammonoidea) dans le rizon for the Upper Barremian of south- Barrémien supérieur du S-E de la France.- eastern France.- Carnets de Géologie / Note- Annales du Muséum d'Histoire Naturelle de books on Geology, Article 2009/02 Nice, t. XV, p. 1-17. (CG2009_A02), 22 p. ERISTAVI M.S. (1955).- Nizhnemelovaja fauna BERT D., DELANOY G. & BERSAC S. (2006).- Des- Gruzii (Lower Cretaceous fauna of Georgia).- criptions de représentants nouveaux ou peu Institut Geologii i Mineralogii Akademii Nauk connus de la Famille des Hemihoplitidae G.S.S.R., Monografii, Tbilisi, 6, 224 p. (en SPATH, 1924 (Barrémien supérieur, Sud-Est russe). de la France) : conséquence taxinomique et GAUTHIER H. avec la collaboration de BUSNARDO phylétiques.- Annales du Muséum d'Histoire R., COMBÉMOREL R., DELANOY G., FISCHER J.-C., Naturelle de Nice, t. XXI, p. 179-253. GUÉRIN-FRANIATTE F., JOLY B., KENNEDY W.J., BERT D., DELANOY G. & BERSAC S. (2008).- Propo- SORNAY J. & TINTANT H. (eds.) (2006).- Révi- sitions pour un nouveau découpage biozonal sion critique de la Paléontologie Française ammonitique, et nouveaux biohorizons pour d'Alcide d'ORBIGNY, Vol. IV, Céphalopodes le Barrémien supérieur.- Carnets de Géolo- Crétacés, sous la direction de J.C. FISCHER.- gie / Notebooks on Geology, Brest, Article Backhuys Publisher, Leiden, 292 p. 2008/03 (CG2008_A03), 18 p. HOEDEMAEKER P.J. & BULOT L. (reporters), AVRAM BERT D., DELANOY G. & CANUT L. (2009).- L'origi- E., BUSNARDO R., COMPANY M., DELANOY G., ne des Imerites ROUCHADZÉ, 1933 : résultat KAKABADZE M., KOTETISHVILI E., KRISHNA J., d'une innovation chez les Gassendiceratinae KVANTALIANI I., LATIL J.L., MEMMI L., RAWSON BERT, DELANOY & BERSAC, 2006 (Ammonoidea, P.F., SANDOVAL J., TAVERA J.M., THIEULOY J.-P., Ancyloceratina).- Annales de Paléontologie, THOMEL G., VASICEK Z. & VERMEULEN J. Paris, vol. 95, p. 21-35. (1990).- Preliminary ammonite zonation for BERT D., BUSNARDO R., DELANOY G. & BERSAC S. the lower Cretaceous of Mediterranean (2010).- Problems in the identity of "Crio- region (Lower Cretaceous team, ceras" barremense KILIAN, 1895 (Ancyloce- Working Group of IGCP, Project 262).- ratida, Late Barremian), and their proposed Géologie Alpine, Grenoble, t. 66, p. 123-127. resolution.- Carnets de Géologie / Notebooks KAKABADZE M.V. (1989).- The Barremian biostra- on Geology, Brest, Article 2010/01 tigraphical subdivisions of Georgia and (CG2010_A01), 17 p. comparison with some western mediter- DELANOY G. (1990).- Précisions nouvelles sur ranean regions. In: WIEDMANN J. (ed.), Creta- "Emericiceras" collignoni THOMEL (Ammonoi- ceous of the Western Tethys.- Proceedings dea) et proposition d'un nouveau schéma 3rd International Cretaceous Symposium, zonal dans le Barrémien supérieur du Sud- Tubingen (1987), E. 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generic variabilities and their implication for SADAT N., ROPOLO P., SANDOVAL J., TAVERA J.M., the systematics of the Cretaceous hetero- VAŠÍČEK Z., VERMEULEN J., ARNAUD H., GRANIER morph ammonites; a review.- Scripta Geolo- B. & PREMOLI-SILVA I. (2006).- Report on the gica, Leiden, vol. 128, p. 17-37. second international meeting of the IUGS KILIAN W. (1888).- Sur quelques fossiles du Lower Cretaceous Ammonite Working Group, Crétacé inférieur de la Provence.- Bulletin de the "KILIAN Group" (Neuchâtel, Switzerland, la Société Géologique de France, Paris, 8 September 2005).- Cretaceous Research, (3ème série), t. XVI, p. 663-691, pls. XVII- London, vol. 27, n° 5, p. 712-715. XXXI. REBOULET S. & KLEIN J. (reporters), BARRAGAN R., KILIAN W. (1889).- Description géologique de la COMPANY M., GONZALEZ-ARREOLA C., LUKENEDER montagne de Lure.- Thèse, Masson édit., A., RAISOSSADAT S.N., SANDOVAL J., SZIVES O., Paris, 458 p. TAVERA J.M., VAŠÍČEK Z. & VERMEULEN J. KILIAN W. (1907-1913).- Das Mezosoïcum (2009).- Report on the 3rd International Unterkreide (Palaeocretacium).- Lethaea Meeting of the IUGS Lower Cretaceous Geognostica, Stuttgart, Teil III, Bd. 3, p. Ammonite Working Group, the "KILIAN 234-279. Group" (Vienna, Austria, 15th April 2008).- KILIAN W. & REBOUL P. (1915).- I. La faune de Cretaceous Research, London, vol. 30, n° 2, l'Aptien inférieur des environs de Montélimar p. 496-502. (Drôme) (Carrière de l'Homme d'Armes). In: ROUCHADZÉ J. (1933).- Les ammonites aptiennes KILIAN W. (ed.), Contribution à l'étude des de la Géorgie occidentale.- Bulletin de l'Insti- faunes paléocrétacées du Sud-Est de la tut géologique de Géorgie, Tbilisi, vol. 1 France.- Mémoires pour servir à l'Explication (1932), n° 3, p. 165-273. de la Carte Géologique détaillée de la Fran- SALVADOR A. (ed., 1994).- International strati- ce, Paris, n° 14, 221 p. graphic guide. A guide to stratigraphic clas- KOTETISHVILI E.V., KVANTALIANI I.V., KAKABADZE sification, terminology and procedures.- M.V. & TSIREKIDZE L.R. (eds., 2005).- Atlas of I.U.G.S. & Geological Society of America, Early Cretaceous fauna of Georgia.- Procee- 214 p. dings of the Georgian Academy of Sciences, SARKAR S.S. (1955).- Révision des Ammonites A. Janelidze Geological Institute, Tbilisi, (n. déroulées du Crétacé inférieur du SE de la ser.), vol. 120, 788 p. France.- Mémoires de la Société Géologique MEEK F.B. (1876).- A report on the invertebrate de France, Paris, (N.S.), t. XXXIV, n° 72, Cretaceous and Tertiary fossils of the Upper 176 p. Missouri Country.- Report of the United Sta- THIERRY J. (1997).- La biostratigraphie, du taxon tes Geological Survey of the Territories, à la biozone et aux échelles biozonales. In: Washington, vol. IX, 629 p. REY J. (éd.), Stratigraphie, Terminologie ORBIGNY A. d' (1840-1842).- Paléontologie fran- Française.- Bulletin des Centres de Recher- çaise. Description des mollusques et rayon- ches Exploration-Production elf-aquitaine, nés fossiles - Terrains crétacés. Tome Pre- Pau, Mémoire 19, p. 63-89. mier. Céphalopodes.- Masson, Paris, 662 p. VERMEULEN J. (2000).- Nouvelles données sur les ORBIGNY A. d' (1851).- Notice sur le genre Hete- répartitions stratigraphiques, les évolutions roceras, de la classe des Céphalopodes.- et les classifications de trois familles d'am- Journal de Conchyliologie, Paris, tome monites du Crétacé inférieur.- Géologie second, p. 217-222. Alpine, Grenoble, n° 75, p. 123-132. PAQUIER M.V. (1900).- Recherches géologiques VERMEULEN J. (2006).- Nouvelle classification à dans le Diois et les Baronnies orientales.- fondement phylogénétique des ammonites Travaux du Laboratoire de Géologie de la hétéromorphes du Crétacé inférieur.- Faculté des Sciences de l'Université de Annales du Muséum d'Histoire Naturelle de Grenoble, t. 5, p. 149-556. Nice, t. XXI, p. 137-178. REBOULET S. (reporter), ATROPS F., BERT D., BULOT VERMEULEN J. & LEPINAY P. (2010).– Nouvelles L., BUSNARDO R., DELANOY G. & VERMEULEN J. données sur le genre Imerites ROUCHADZÉ, (2007, unpublished).- Zonation Hauteri- 1933 (Ammonidita, Ancyloceratina) ; répon- vien – Barrémien.- Compte rendu de la ses et précisions apportées au travail de réunion des biostratigraphes français du BERT, DELANOY et CANUT, 2009.- Annales de KILIAN Group (IUGS Lower Cretaceous Am- Paléontologie, Paris, vol. 96, p. 13-23. monites Working Group), Digne-les-Bains (2 WRIGHT C.W., CALLOMON J.H. & HOWARTH M.K. Mai 2007), 14 p. (eds., 1996).- Cretaceous Ammonoidea. In: REBOULET S. & HOEDEMAEKER P.J. (reporters), KAESLER R.L. (ed.), Mollusca 4 (revised).- AGUIRRE URRETA M.B., ALSEN P., ATROPS F., Treatise on Invertebrate Paleontology, Geo- BARABOSKIN E.Y., COMPANY M., DELANOY G., logical Society of America, New York; Uni- DUTOUR Y., KLEIN J. LATIL J.L., LUKENEDER A., versity of Kansas, Lawrence, Part L, 362 p. MITTA V., MOURGUES F.A., PLOCH I., RAISSOS-

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