◄ Carnets Geol. 19 (9) ►
[1. Introduction] [2. Palaeogeographic, structural and stratigraphic framework]
[3. Historical account of the Aptian ammonite palaeontology in the Les Ferres area]
[4. Methods] [5. Results] [6. Conclusion] [Bibliographic references] and ... [Plates]
Laboratoire du Groupe de recherche en paléobiologie et
biostratigraphie des Ammonites, Bois-Mésanges, quartier Saint-Joseph, 04170
La Mure-Argens (France)
Laboratoire du Groupe de recherche en paléobiologie et
biostratigraphie des Ammonites, Bois-Mésanges, quartier Saint-Joseph, 04170
La Mure-Argens (France)
Réserve naturelle nationale géologique de Haute-Provence, service Environnement, Conseil départemental des Alpes de Haute-Provence, 13, rue du Docteur-Romieu, CS 70216, 04995 Digne-Les-Bains cedex 9 (France)
Laboratoire Géosciences, UMR-CNRS 6118, université de Rennes-1, campus Beaulieu, bâtiment 15, 35042 Rennes cedex (France)
Published online in final form (pdf) on August 8, 2019
[Editor: Michel Moullade; language editor: Simon Mitchell; technical editor: Bruno Granier]
On the southern margin of the Vocontian Basin (SE France), for taphonomic reasons (fragmentation, reworking, pyritization), lower Aptian (Lower Cretaceous) deposits of the interval between the Deshayesites deshayesi and Dufrenoyia furcata zones are usually not suitable for studying the late ontogenetic developments of ammonites (fossil cephalopods). In the vicinity of the village of Les Ferres (Department of the Alpes-Maritimes, SE France), a relatively thick sedimentary succession with well-preserved ammonites, representative of the zones mentioned above, is found in a small basin called the "Les Ferres Aptian Basin" (LFAB). The 1262 ammonites collected or studied in situ are dated from the Deshayesites forbesi Zone through the top of the Dufrenoyia furcata Zone. This study presents the lithostratigraphy, biostratigraphy derived from these ammonites, and the respective range of these taxa. This is an introductory contribution to any future palaeontological study of the lower Aptian ammonites in the Les Ferres area. The lithologic unit overlying the Hauterivian-Aptian limestones is introduced herein as the Les Graous Formation. It is subdivided in three members, from bottom to top: 1) the Combe de Joinet Member, 2) the Pont de la Cerise Member, and 3) the Les Graous Member. In addition, two remarkable levels are identified: the Ammonitoceras level (outstandingly abundant) and the Toxoceratoides bed.
• Southeast of France;
• lower Aptian;
Bersac S. & Bert D. (2019).- The lower Aptian ammonites of the Les Ferres Aptian Basin (Lower Cretaceous, Southeast of France). Part I: Introduction and biostratigraphy.- Carnets Geol., Madrid, vol. 19, no. 5, p. 149-183.
Les ammonites de l'Aptien inférieur du bassin aptien de Les Ferres (Crétacé inférieur, SE de la France). Ière partie : Introduction et biostratigraphie.- Sur la marge méridionale du Bassin Vocontien (SE de la France), les dépôts d'âge aptien inférieur (Crétacé inférieur) de l'intervalle situé entre les zones à Deshayesites deshayesi et Dufrenoyia furcata ne sont habituellement pas favorables à l'étude des développements ontogénétiques tardifs des ammonites (céphalopodes fossiles) pour des raisons taphonomiques (fragmentation, remaniement, pyritisation). Dans les environs du village de Les Ferres (département des Alpes-Maritimes, SE de la France), des sédiments aptiens relativement épais et riches en ammonites bien conservées relevant de l'intervalle stratigraphique précité se sont déposés dans un petit bassin structural dénommé ici bassin aptien de Les Ferres (LFAB). Les 1262 ammonites collectées ou étudiées in situ sont datées de la Zone à Deshayesites forbesi jusqu'au sommet de la Zone à Dufrenoyia furcata. La lithostratigraphie, la biostratigraphie fondée sur les ammonites et la distribution de leurs taxons respectifs sont décrits dans ce travail qui constitue une introduction litho- et biostratigraphique à de futurs travaux paléontologiques sur les ammonites de l'Aptien inférieur du secteur des Ferres. Au-dessus des calcaires hauteriviens à aptiens, une nouvelle formation lithologique est décrite, la Formation de Les Graous. Elle est divisée en trois membres, de bas en haut : 1) Membre de la Combe de Joinet, 2) Membre du Pont de la Cerise et 3) Membre de Les Graous. Deux niveaux remarquables y sont identifiés : le niveau à Ammonitoceras (exceptionnellement abondants) et le banc à Toxoceratoides.
• sud-est de la France ;
• Aptien inférieur ;
• biostratigraphie ;
In the Vocontian Basin (Southeast of France), upper lower Aptian ammonite faunas (middle Deshayesites deshayesi to Dufrenoyia furcata zones sensu Bersac et al., 2012; see Fig. 1 ) have been repeatedly described and figured (Sayn, 1920; Thomel, 1963, 1964, 1968; Dauphin, 2002; Dutour, 2005; Joly & Delamette, 2008). Nevertheless, their study is limited by several factors:
they are generally preserved as small pyrite nuclei, which makes the study of their ontogeny difficult;
heteromorph ammonites are generally underrepresented in the Vocontian Basin for taphonomical reasons (Dauphin, 2002; Dutour, 2005) and because they were not adapted to a pelagic environment (Westermann, 1996; Lukeneder, 2015);
the conditions are usually unfavorable for preservation of large heteromorph ammonites in the neritic margins of the Vocontian Basin, with the upper lower Aptian either being absent or represented by reworked deposits yielding only fragmented ammonites (Bersac et al., 2010; Pictet et al., 2015).
Most of the large lower Aptian heteromorph ammonites in the Vocontian Basin that have been figured in the literature are older than the middle D. deshayesi Zone (sensu Bersac et al., 2012; see Fig. 1 and Roch, 1927; Delanoy, 1998; Delanoy et al., 2008; Pictet et al., 2009, 2015). A few of the more recent species that have been reported include Ammonitoceras ucetiae Dumas, 1876 (Dumas, 1876) and Toxoceratoides? sp. inc. "Gigantomorph" godeti Thieuloy, 1990 [Thieuloy, 1990 = Lithancylus godeti (Thieuloy, 1990), see Conte, 1999 and Mikhailova & Baraboshkin, 2001] from the Serviers-et-Labaume and Montaren-et-Saint-Médiers area (Gard department, southeastern France; Dumas, 1876). These ammonites come from the Deshayesites multicostatus Subzone (D. deshayesi Zone sensu Bersac et al., 2012) based on the evolutionary characters of the associated Douvilleiceratinae Parona & Bonarelli, 1897 (see Bersac & Bert, 2018).
The Les Ferres area is located in the lower Esteron Valley (Alpes-Maritimes Department, SE France), in the southern part of the Vocontian Basin. It was situated at the boundary between the neritic and hemipelatic domains during the early Aptian (Figs. 2 - 3 ). The Aptian series were deposited in a small E-W structural basin, within a series of tilted blocks. This palaeostructure, which is named herein the Les Ferres Aptian Basin (LFAB), was the site for the deposition of a relatively thick sedimentary sequence with numerous large ammonites. The interval from the Deshayesites forbesi to the Dufrenoyia furcata zones does not include any polyzonal or condensed intervals. The ammonite fauna is represented by the "classical" taxa described and figured in the pelagic domain (Dufrenoyia Kilian & Reboul, 1915, Cheloniceras Hyatt, 1903, Pseudohaploceras Hyatt, 1900, Toxoceratoides Spath, 1924 and Colombiceras Spath, 1923, etc., see for example Dutour, 2005) associated with numerous heteromorph ammonites that belong mainly to the genera Ammonitoceras Dumas, 1876, Lithancylus Casey, 1960, and Tropaeum J. de C. Sowerby, 1837, which were previously poorly known in SE France. This material is sufficiently abundant and stratigraphically constrained to allow the study of evolutionary trends and intraspecific variability. In a nutshell, the LFAB is a unique locality to study ammonites of this time interval.
The objective of the present work is to describe the lithostratigraphy and biostratigraphy of the lower Aptian of LFAB, with the aim of supporting our future palaeontological studies of ammonites from this area.
Biostratigraphic charts used in the present work. SZS: Standard Mediterranean
Zonal Scheme. St.: stages.
Location of the Les Ferres area in the Vocontian Basin (figure after Bersac
et al., 2010, amended).
The studied outcrops all are located on the northern flank of Cheiron Mountain, in the vicinity of the village of Les Ferres (Fig. 3 ).
The study area belongs to the southern subalpine Castellane Arc, at the southern margin of the Vocontian Basin. It is part of a tectonic structure on the southern boundary of the Esteron Syncline, at the junction between two tilted blocks. This tectonic structure is characterized by the presence of WNW-ESE oriented half-grabens. The (synsedimentary) tectonics were active from the Valanginian to the Albian, and are responsible for the rapid lateral change in thickness and the numerous gaps that characterize the Lower Cretaceous succession in this area (Dardeau, 1987; Dardeau & Graciansky, 1987). This tectonic structure has also resulted in the formation of a small EW-oriented basin, in which the lower Aptian sediments were deposited. The Lower Cretaceous strata were deposited in the outer neritic domain. Their facies are intermediary between those of the hemipelagic units located to the northeast and those of the condensed neritic series located to the southeast (Cotillon, 1971; Bersac et al., 2010; Fig. 2 ).
The Aptian of the LFAB is represented by two main lithological units: a calcareous unit overlain by a plurimetric marly unit (Cotillon, 1971, 2010; Ragazzi, 1982; Fig. 4 ); the calcareous unit and the lower part of the marly unit are referred to the lower Aptian and the rest of the marly unit to the upper Aptian. These deposits form a transgressive sequence (Cotillon, 1971) related to the "middle Bedoulian drowning event" (Bréheret, 1997; Cotillon, 2010; Masse & Fenerci-Masse, 2011, p. 671). The present work focuses on the marly lower Aptian of the LFAB. Newly identified lithostratigraphic units are formally described in Chapter 5.2.
Figure 3: Map of the Les Ferres area with location of the studied or mentioned
sections. 1: Conségudes section; 2:
Les Graous 2 section (GRS 2); 3: Les Graous 1 section (GRS 1); 4: unnamed
section of the La Vallière locality studied by Ragazzi (1982, p. 73),
then Bréheret (1997, p. 267, Figs. 114-115); 5: La Vallière section
(VAL); 6: La Graou section (GRO); 7: Combe de Joinet section (CHP); 8: Pont de
la Cerise section (CLE); 9: Combe de Marin section (CRS); 10: Pont Païré
section (PPR); 11: Colle-Belle section.
Synthetic log of the Lower Cretaceous of the Les Ferres area. J.-B.: Jurassic
and Berriasian; Cenom.: Cenomanian; Form.: Formation; CJ: Combe de Joinet
Member; AL: Ammonitoceras Level; TB: Toxoceratoides Bed.
Fallot (1885, p. 128) was the first author to indicate the possible presence of Aptian strata in the vicinity of Les Ferres. Subsequently, Goguel (1944), Cotillon (1971), Ginsburg et al. (1980), Ragazzi (1982), and Bréheret (1997) have documented the lithostratigraphy and ammonite biostratigraphy of this area (see detailed historical accounts in Ragazzi, 1982, and Bréheret, 1997). Cotillon (1971, p. 146), for instance, was the first to mention the presence of the ammonite genus Dufrenoyia (and consequently the presence of the D. furcata Zone, see Fig. 1 ) in the LFAB. However, several occurrences of ammonite taxa reported in these contributions were not supported by any illustrations. Our own investigations in the area started in the early 2000s and resulted in preliminary publications (Bert & Bersac, 2011; Bert, 2014) including illustrations of few specimens. More recently, Delanoy et al. (2018) revisited the site. They figured and described these faunas in detail. These latter authors, focused on large heteromorphic ammonites and described ten new taxa.
To date, the lithostratigraphic units of the LFAB have not been formally described in the scientific literature. In the present work, we propose a formal lithostratigraphic scheme for the marly lower Aptian of the LFAB (Fig. 4 and see Chapter 5.2). The name of the recognized units is that of the outcrop where they are visible under the best conditions. Two remarkable levels are recognized and named according to the characteristics of their respective ammonite faunas.
The biostratigraphic scheme used in the present work is that previously proposed by Bersac et al. (2012) for the lower Aptian, based on a review of the Deshayesitidae Stoyanow, 1949 (Ammonoidea, Bersac & Bert, 2012, 2015; Fig. 1 ).
Our objective was to prospect all the Aptian outcrops of the LFAB. Nine sections were then identified and 8 of them were sampled (Fig. 3 ). Two other sections close to the study area were also studied: the Conségudes and the Colle-Belle sections. A total of 1,262 ammonites was bed-by-bed sampled or studied in situ between 2000 and 2017. This material is deposited in the collections of the Laboratory of the Research Group for Paleobiology and Biostratigraphy of the Ammonites (G.P.A., France).
We were both present in the field when all the material published by Delanoy et al. (2018) was extracted and we reviewed it once prepared. Therefore, we deemed it necessary to include it in our study. Our own field data differ somewhat from those of Delanoy et al. (2018), and we will explain these differences below where necessary. It should be noted that the designation of specimens published by Delanoy et al. (2018) is complicated by the fact that several specimens may bear the same number, or that several numbers may be assigned to the same specimen. The problematic numbers are 28754, 28756, 28767, 28766, 28768, and 28769. Similarly, it should be noted that the holotype of Proaustraliceras bournaudi Delanoy et al. 2018, numbered AP-001 (Delanoy et al., 2018, p. 47 and Fig. 7) does not belong to the Bersac's collection contrary to the statement by these authors.
In this chapter, we briefly discuss the taxonomic assignments used in our study for the sole purpose of providing support for the presentation of the lithostratigraphic and biostratigraphic results. In particular, according to our data, the new taxa introduced by Delanoy et al. (2018) are all subjective synonyms of taxa already described. For this reason, these taxa are not quoted in the stratigraphic logs (Figs. 5 , 7 , 9 - 10 , 12 , 14 - 15 ). We will expose our taxonomic positions in detail in future works.
5.1.1. The Deshayesitidae and Douvilleiceratidae Parona & Bonarelli, 1897
These two ammonite families provide lower Aptian zonal and subzonal index species for different palaeogeographic domains (Casey et al., 1998; Baraboshkin & Mikhailova, 2002; Reboulet et al., 2018). The criteria for identifying Deshayesitidae used in this work are those proposed by Bersac & Bert (2012, 2015). They rely on the morphology of the ventral area and the suture lines. The taxa we identified in the LFAB are Deshayesites sp. (Pl. 1 , figs. 4-5), Deshayesites multicostatus Swinnerton, 1935 (Pl. 2 , figs. 6-8, 13-15, 19), Deshayesites grandis Spath, 1930 (Pl. 3 , figs. 9-12), Dufrenoyia furcata (J. de C. Sowerby, 1837) (Pl. 5 , figs. 5-9), and Dufrenoyia dufrenoyi (Orbigny, 1841) (Pl. 5 , figs. 30-32). The lower Aptian Douvilleiceratidae of the LFAB are only represented by Douvilleiceratinae. Their identification is based on the duration of their ontogenetic stages (see Bersac & Bert, 2018, and references therein). The identified taxa are Procheloniceras sp. (Pl. 1 , figs. 6-7), Cheloniceras sp. and Cheloniceras crassum Spath, 1930 (Pl. 2 , figs. 16-17; Pl. 3 , figs. 5-6; Pl. 4 , figs. 8-9).
5.1.2. The Parahoplitidae Spath, 1922
The collected material is assigned to the D. furcata Subzone (D. furcata Zone) (Pl. 5 , figs. 10-12). All intermediates can be observed from slender forms having a Colombiceras crassicostatum-type shape to robust forms with a Gargasiceras gargasensis-type shape. Consequently we consider Gargasiceras gargasensis (Orbigny, 1841) as a subjective synonym of Colombiceras crassicostatum (Orbigny, 1841), as already suggested by Jacob (1907), Dutour (2005) and Bulot (2010). Possible primitive representatives of Parahoplitidae occur in the Deshayesites grandis Subzone (D. deshayesi Zone) and are identified as ?Colombiceras sp.
5.1.3. The Ancyloceratidae Meek, 1876
The genus Ammonitoceras is represented by large ammonites with criocone, aspinoceratic or ancyloceratic coiling, characterized by the presence of a particular ontogenetic stage in the inner whorls: the Ammonitoceras stage. This stage is characterized by the presence of bituberculated main ribs bearing an umbilical tubercle and a lateral tubercle of larger size. In a future article, we will publish a detailed study of Ammonitoceras from the D. deshayesi and D. furcata zones of the LFAB.
Preliminary results from this study suggest that:
the genus Ammonitoceras shows significant intraspecific variability that mainly relates to the duration of the ontogenetic Ammonitoceras stage;
Ammonitoceras macroconchs of the D. furcata Zone (Pl. 4 , figs. 1-3) have on average an Ammonitoceras stage disappearing later during ontogeny and a narrower spiral hiatus than those of the D. multicostatus Subzone (Pl. 2 , figs. 1-2);
Ammonitoceras of the D. multicostatus Subzone can be assigned to the species Ammonitoceras ucetiae and those of the D. furcata Zone to Ammonitoceras lahuseni (Sinzow, 1906);
we interpret Ammonitoceras dumasi Delanoy et al., 2018 as the macroconch of A. ucetiae and regard it as a subjective synonym of that species;
we interpret the following species and specimens as microconchs of A. ucetiae: Caseyites esteronensis Delanoy et al., 2018, Caseyites vermeuleni Delanoy et al., 2018, Ammonitoceras madouxi Delanoy et al., 2018, Proaustraliceras bournaudi Delanoy et al., 2018, the specimen identified under ?Proaustraliceras sp. numbered 28766 or 28767 in Delanoy et al. (2018, p. 50-51, Fig. 9.A) and the specimen of Ammonitoceras aff. madouxi numbered 28764 in Delanoy et al. (2018, p. 71-72, Fig. 19);
according to our interpretation, A. leiferrasensis Delanoy et al., 2018, Caspianites ragazziae Delanoy et al., 2018, and the specimen figured under ?Caspianites sp. and numbered 28744 or 28754 in Delanoy et al., (2018, p. 83, Fig. 25.A-B and p. 84) are all macroconchs of A. lahuseni and thus subjective synonyms of that species;
in our view, Caseyites morenobedmari Delanoy et al., 2018 is a microconch of A. lahuseni and consequently a subjective synonym of that species; and
Ammonitoceras specimens from the D. grandis Subzone are too incomplete to be identified at the specific rank.
Lithancylus of the D. multicostatus Subzone of the LFAB (Pl. 2 , figs. 11-12) appear to have significant intraspecific variability, which concerns both their ontogenetic sequence and adult size. In our opinion, these specimens belong to the species Lithancylus grandis (J. de C. Sowerby, 1828), and consequently we interpret Lithancylus bifurcatus Delanoy et al., 2018 as a subjective synonym of that species.
5.1.4. The Helicancylidae Hyatt, 1894
On the basis of the diagnostic characteristics proposed by Bulot et al. (2017) and Frau et al. (2017), we identified Toxoceratoides sp., Toxoceratoides aff. royerianus (Orbigny, 1842) (Pl. 3 , figs. 13-16) and Toxoceratoides rochi Casey, 1961 (Pl. 5 , figs. 1-4).
5.1.5. The Ptychoceratidae Gill, 1871
The genus Ptychoceras Orbigny, 1842, is represented by rare specimens we identified as Ptychoceras emericianum Orbigny, 1842 (Pl. 5 , fig. 15) on the basis of the revision work of Vermeulen et al. (2015).
5.1.6. The Desmoceratidae Zittel, 1895
We identified the Desmoceratidae of the LFAB on the basis of the diagnostic criteria proposed by Dutour (2005), in particular the aspect of the whorl section. In this respect, identification of the collected specimens at the specific rank was made difficult by the fact that they are almost always deformed and crushed. The taxa identified are: Pseudohaploceras sp. (Pl. 1 , fig. 8), Pseudohaploceras liptoviensis (Zeuschner, 1856) (Pl. 2 , figs. 9-10; Pl. 4 , figs. 6-7), Pseudosaynella sp., Aconeceras nisum (Orbigny, 1841) (Pl. 5 , figs. 13-14) and ?Aconeceras sp.
5.1.7. The Lytoceratidae Neumayr, 1875
Representatives of this family are rare in the LFAB and are attributed to Lytoceras sp. (Pl. 4 , figs. 10-11).
5.1.8. The Macroscaphitidae Hyatt, 1900
Based on Busnardo’s remarks (in Gauthier, 2006), we identified Macroscaphites aff. yvani (Puzos, 1832) and Macroscaphites striatisulcatus (Orbigny, 1841) (Pl. 2 , fig. 20; Pl. 3 , figs. 3-4; Pl. 5 , fig. 16).
Following the works of Wright et al. (1996), Klein et al. (2007) and Vašíček et al. (2014), we consider Pseudocrioceratites Egoian, 1969, as a subjective synonym of Acantholytoceras Spath, 1923. The Acantholytoceras we collected in the LFAB are too fragmented to be identified to specific level (Pl. 4 , figs. 4-5).
5.1.9. The Phylloceratidae Zittel, 1884
In the LFAB, this family is represented only by the subgenus Hypophylloceras Salfeld, 1924 (Phylloceras Suess, 1865). Joly & Delamette (2008, Fig. 74) recognized 6 species of Phylloceras (Hypophylloceras) ranging through the D. deshayesi and D. furcata zones (sensu Reboulet et al. 2018) in the Vocontian Basin. The diagnostic characters are subtle variations in ornamentation, section or morphology of the suture line. Our specimens are not sufficiently well preserved to be identified to the specific level (Pl. 3 , fig. 1; Pl. 4 , fig. 12).
5.2.1. Top of the Hauterivian-Aptian limestones (Fig. 4 )
In the neritic domain of the Castellane Arc, Hauterivian to lower Aptian deposits are represented by a pluridecametric succession of massive limestone beds. Cotillon (1971) divided it into a series of formations (formations 17 to 25, Cotillon, 1971, p. 34 and Fig. 12bis). In the LFAB, the Hauterivian-Aptian limestones are represented by a plurimetric succession of massive decimetric limestone beds separated by centimetric marly intervals (Fig. 4 ) that have already been described in the literature under various names ("Calcaire blanc compacte" in Fallot, 1885, p. 127, "Barrémo-Bédoulien" in Ragazzi, 1982, p. 73).
The highest beds in the upper part of this lithological unit contain increasing amount of sandstone and glauconite (Ragazzi, 1982), and corresponds to Cotillon's (1971) Formation 25, and these are assigned to the lower Aptian (pars, Ginsburg et al., 1980; Ragazzi, 1982). The upper limit of the Hauterivian-Aptian limestones is represented by a firmground-type, with iron crust layers and extensive bioturbation by Rhizocorallium Zenker, 1836 (Fig. 8.D ). This discontinuity surface is correlated with the "early Aptian unconformity" (Cotillon, 2010, p. 4) that is related to the "middle Bedoulian drowning event" (Masse & Fenerci-Masse, 2011, p. 671). It corresponds to a large-scale discontinuity surface formed during the flooding of the Provençal platform (Bréheret, 1997; Cotillon, 2010; Masse & Fenerci-Masse, 2011). This event is assigned to the upper D. forbesi Zone (Pictet et al., 2015; Fig. 1 ).
We only sampled the last Hauterivian-Aptian limestone bed: it is represented by a centimetric level of grey to yellowish sandstone relatively rich in internal moulds of ammonites, nautiloids and belemnites (Fig. 13.A ). Ragazzi (1982, p. 74-75) reported the following ammonite fauna: Ancyloceras audouli (Astier, 1851), Deshayesites latilobatus (Sinzow, 1910) [= ‘D. latelobata (Sinzow)' in Ragazzi, 1982, p. 75], Deshayesites sp., Cheloniceras sp., Procheloniceras sp., Pseudohaploceras sp., Costidiscus recticostatus (Orbigny, 1841). We identified: Ancyloceras rochi Sarkar, 1955 (Pl. 1 , figs. 1-2), Ancyloceras sp. (Pl. 1 , fig. 3), Toxoceratoides sp., Deshayesites sp. (Pl. 1 , figs. 4-5), Procheloniceras sp. (Pl. 1 , figs. 6-7), Pseudohaploceras sp. (Pl. 1 , fig. 8), Pseudohaploceras liptoviensis, Hypophylloceras sp. This fauna is associated with numerous nautiloids [Cymatoceras neckerianus (Pictet, 1847) (Pl. 1 , fig. 9)] and belemnites (Mesohibolites sp.).
We could not identify any Deshayesites from this bed at the specific rank because the characteristics of their ventral area in the inner whorls and their suture line could not be observed (Bersac & Bert, 2012, 2015). Nevertheless, their rounded ventral areas on the phragmocone suggests that they are older than the D. grandis Subzone (Pl. 1 , fig. 5).
The Douvilleiceratidae collected in this bed have a relatively long and well expressed Procheloniceras stage and no Cheloniceras stage was observed (Bersac & Bert, 2018), but the innermost whorls of the studied specimens are not preserved: if the Cheloniceras stage occurs, it is restricted to innermost whorls only (Pl. 1 , figs. 6-7). The shape of these specimens with more primitive features than Cheloniceras cornuelianum (Orbigny, 1841) leads us to attribute them to the genus Procheloniceras Spath, 1923. This genus seems to occur at the top of the D. forbesi Zone (sensu Bersac et al., 2012), whereas the genus Cheloniceras succeeds it from the base of the D. deshayesi Zone (Bersac & Bert, 2018). It should be noted that we have not collected any representative of the stratigraphically significant family Roloboceratinae Casey, 1961. Their representatives occur in the lower part of the D. forbesi Zone (sensu Bersac et al., 2012) in the Boreal realm and at least from the upper part of the D. forbesi Zone or from the base of the D. deshayesi Zone (sensu Bersac et al., 2012) in the Tethysian realm (Casey et al., 1998; Bersac & Bert, 2012, Fig. 17, 2015, Fig. 15).
Small Ancyloceras Orbigny, 1842, similar to those collected at the top of the Hauterivian-Aptian limestones, were reported in the Deshayesites weissi Zone (= D. forbesi Zone sensu Reboulet et al., 2018) by Ropolo et al. (1998, p. 171) in the Roquefort-la Bédoule area (SE France); they were identified as Ancyloceras matheronianum Orbigny, 1842. Pierre Ropolo provided photographs of these specimens to us and, from our point of view, they are similar to the type specimen of Ancyloceras rochi, originally described and figured by Roch (1927, p. 29, Pl. IV, fig. 2) as "Ancyloceras Binelli Astier".
5.2.2. The Les Graous Formation
This formation is formally defined for the first time in the present work (Fig. 4 ) and is restricted to the LFAB. It is represented by dark green glauconitic sandstones in its lower part and grey-blue marls in its upper part. Its lower limit is the terminal discontinuity of the Hauterivian-Aptian limestones. Its upper limit is located at the top of a marly-limestone level just below a dark grey glauconitic level (Fig. 4 ). This glauconitic level yielded the oldest Epicheloniceras martini (Orbigny, 1842) of the study area and was therefore assigned to the upper Aptian Epicheloniceras debile Subzone (Epicheloniceras martini Zone, see Dutour, 2005 and Fig. 1 ). The Les Graous Formation type section is Les Graous 1 (GRS1, Figs. 3 , 5 - 6 , and see Chapter 5.3.1), where it is observable in its entirety. The Les Graous Formation is the equivalent of Cotillon's (1971, p. 69) formations ab1 and ab2 of the neritic domain of the Castellane Arc. At Les Ferres, this author (ibid., p. 146) named it "[a, b]".
Figure 5: Log of the Les Graous 1 section
(GRS 1) with distribution of the ammonite taxa, see Fig. 4
for caption. HA: Hauterivian-Aptian limestones. PC: Pont de la Cerise Member. D. for.: Deshayesites
forbesi. D. d.: Deshayesites deshayesi. D. m.: Deshayesites
multicostatus. D. gr.: Deshayesites grandis. E. m.: Epicheloniceras
martini. E. d.:
Epicheloniceras debile. [M]: macroconch, [m]: microconch.
Figure 6: Field photographies of the Les Graous 1 section
(GRS 1). Log of this section
is figured in Fig. 5 .
A: Beds 95 to 98 at the base of the section in 2009.
Length of the hammer: 330 mm. B: Beds 100 to 104 in the lower part of the
Les Graous Member in 2005. C: specimen No. 28750, holotype of Caseyites
morenobedmari Delanoy et al., 2018 (Delanoy et al.,
2018, Fig. 15, = Ammonitoceras lahuseni (Sinzow, 1906) [m]
in Fig. 5 )
during extraction from Bed 102 of GRS 1 in 2006. Length of the
ammonite: 468 mm (Delanoy et al., 2018, p. 63). D: lower
Aptian deposits of GRS 1, overlain by upper Aptian and Albian in 2010; a: top of
the Hauterivian-Aptian limestones.
We propose to divide the Les Graous Formation into several lithostratigraphic members, described here for the first time:
This lithostratigraphic unit is restricted to the LFAB (Fig. 4 ). It was previously mentioned by Ragazzi (1982, p. 76), who named it "marnes bleutées" ("bluish marls").
The Combe de Joinet Member is represented by 1.10-1.50 m of light grey marly limestone in which are sometimes intercalated two more indurated decimetric levels or a glauconitic decimetric level. The lower limit of this member is the discontinuity surface at the top of the Hauterivian-Aptian limestones. Its upper limit is an intensely bioturbated discontinuity surface (ichnogenus Thalassinoides Ehrenberg, 1944; Fig. 13.B ). The type section of this member is the Combe de Joinet section (CHP, Figs. 3 , 10 - 11 , and see Chapter 5.3.4). The ammonite fauna of the Combe de Joinet Member is particularly rare and only represented by fragmented internal moulds of Ancyloceras sp., Deshayesites sp., Cheloniceras crassum, Macroscaphites aff. yvani, Pseudohaploceras liptoviensis and Pseudohaploceras sp. This member crops out in the following sections: La Vallière (VAL, see Figs. 3 , 7 - 8 , and Chapter 5.3.2), Combe de Joinet (CHP), Pont de la Cerise (CLE, see Figs. 3 , 12 - 13 , and Chapter 5.3.5) and Combe de Marin (CRS, see Figs. 3 , 14 , and Chapter 5.3.6). It also partly crops out in the Pont Païré section (PPR, see Figs. 3 , 15 - 16 , and Chapter 5.3.7).
Field photographies of the La Vallière section (VAL). Log of this section is
figured in Fig. 7 .
A: general view (2004) of the upper part of the
section, located against a palaeo-escarpment. B: Beds 403 to 405 of the
Pont de la Cerise Member in 2010. Bed 405 is interpreted to be the local
equivalent of the Ammonitoceras Level. 8.C: upper surface of the last
bed (400) of the Hauterivian-Aptian limestones with Rhizocorallium.
This member is restricted to the LFAB (Fig. 4 ) and is represented by massive glauconitic sandstones (Ragazzi, 1982; Bréheret, 1997) in which are often intercalated more or less continuous light grey decimetric beds (Figs. 8.A-B , 16.A ). The thickness of this member varies from less than one metre in the Les Graous 1 section (GRS1) to 15 m in the La Vallière section (VAL, Fig. 17 ). The lower limit of this member is represented by the discontinuity surface at the top of the underlying Combe de Joinet Member. Its upper limit is characterized by the abrupt end of the glauconitic sandstones, which are overlain by a characteristic, more or less marly, grey limestone bed, here named the "Toxoceratoides Bed" (which belongs to the overlying Les Graous Member, see Chapter 184.108.40.206). The type section of the Pont de la Cerise Member is at the Pont de la Cerise section (CLE, see Figs. 3 , 12 - 13 , and Chapter 5.3.5). The first decimetres of this member are relatively rich in phosphate nodules, belemnite fragments and fish teeth. When this member reaches a plurimetric thickness, the first two meters display cross-stratifications. Bioturbation is frequent throughout the Pont de la Cerise Member, especially in the more indurated levels (Figs. 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 , Thalassinoides in Fig. 13.C ).
The glauconitic sandstones of the Pont de la Cerise Member were first mentioned by Goguel (1944, p. 21) who assigned them to the Albian. Ginsburg et al. (1980) and Ragazzi (1982, p. 74) dated them as Aptian. A level remarkably rich in ammonites generally occurs in the upper 0.5 m of this member. It is named here the "Ammonitoceras Level" and will be described below. The Pont de la Cerise Member crops out in the following sections: Les Graous 1 (GRS1), Les Graous 2 (GRS2), La Vallière (VAL), Combe de Joinet (CHP), Pont de la Cerise (CLE), Combe de Marin (CRS), and Pont Païré (PPR).
11: Field photographs of the Combe de Joinet section (CHP). Log of this section
is figured Fig. 10 .
A: top of the
Hauterivian-Aptian limestones and lower
part of the section in 2004. B-C: top of the Pont de la Cerise
Member and lower part of the Les Graous Member in 2004. AL: Ammonitoceras
Level. D: ammonites in situ in the Ammonitoceras Level in
2009 (refigured from Bert, 2014, p. 393). a: specimen No.
"28769" identified as Caseyites esteronensis Delanoy et
al., 2018 in Delanoy et al. (2018, p. 58, Fig.
quoted as Ammonitoceras ucetiae Dumas, 1876 [m] in Fig. 10 .
b: specimen No. AP-001, holotype of Pseudocrioceras bournaudi Delanoy
et al., 2018 in Delanoy et al. (2018, p. 47,
Figs. 7, 8.A),
quoted as Ammonitoceras ucetiae Dumas, 1876 [m] in Fig. 10 .
Length of the hammer: 330 mm.
Apart from the Ammonitoceras Level, the ammonite fauna of the Pont de la Cerise Member is represented by rare and poorly preserved internal moulds (Fig. 13.D ). We recognized the following taxa: Ammonitoceras sp., Lithancylus grandis, Deshayesites sp. Cheloniceras sp., Pseudohaploceras liptoviensis and a fragmentary Ancyloceratidae unidentifiable at the generic rank. Belemnites are represented by Neohibolites aptiensis (Stolley, 1913) and Duvalia grasi (Duval-Jouve, 1841). A level one centimetre above the Ammonitoceras Level yielded small internal phosphate moulds of Macroscaphites striatisulcatus and Pseudohaploceras liptoviensis.
The Ammonitoceras Level is a 0.20 m-thick level particularly rich in ammonites. It is located approximately 0.50 m below the upper limit of the Pont de la Cerise Member (Figs. 4 , 11.C-D ). This level provided an abundant cephalopod fauna mainly consisting of deformed internal moulds of ammonites and nautiloids, and belemnite rostra (Pl. 2 , figs. 1-17, 19-20). The proportion of subcomplete representatives of the heteromorphic ammonite family Ancyloceratidae, especially Ammonitoceras, is noteworthy (Fig. 11.D ; Pl. 2 , figs. 1-5). The type section of this reference level is the Combe de Joinet section (CHP) where it crops out under particularly favourable conditions (see Chapter 5.3.4). Heteromorph ammonites are deposited without preferential orientation (Fig. 11.D ). Bert (2014, p. 393) figured this level for the first time (Fig. 11.D ), and Delanoy et al. (2018) described and figured many ammonites. We identified the following taxa in the Ammonitoceras Level: Ammonitoceras ucetiae macroconchs (Pl. 2 , figs. 1-2) and microconchs (Pl. 2 , figs. 3-5), Lithancylus grandis (Pl. 2 , figs. 11-12), Deshayesites multicostatus (Pl. 2 , figs. 6-8, 13-15, 19), Cheloniceras crassum (Pl. 2 , figs. 16-17), Cheloniceras sp., Pseudohaploceras liptoviensis (Pl. 2 , figs. 9-10), Pseudosaynella sp., Macroscaphites striatisulcatus (Pl. 2 , fig. 20). Belemnites are represented by Neohibolites aptiensis and Duvalia grasi. Nautiloids are frequent and represented by Cymatoceras neckerianus, Eucymatoceras plicatum (Fitton, 1836) and Anglonautilus sp. The level 405 of the La Valliere section (VAL) is a possible local representative of the Ammonitoceras Level (see Chapter 5.3.2) and additionally provided Toxoceratoides aff. royerianus. Gastropods, bivalves and ahermatypic corals are relatively rare (Pl. 2 , fig. 18).
Deshayesitidae of the Ammonitoceras Level have a smooth siphonal band ending at a diameter between 15 and 18 mm and their ventral area is not subtabulated on the phragmocone (Pl. 2 , figs. 8, 14). These characters correspond to the index species D. multicostatus (Bersac & Bert, 2015). The genus Cheloniceras is represented by two distinct morphologies:
a relatively frequent one, characterized by a long Cheloniceras stage and a short Procheloniceras stage. The "intermediate stage" of Cheloniceras parinodum Casey, 1961, is present in some specimens between the Cheloniceras and Procheloniceras stages (Bersac & Bert, 2018). For these reasons, we attributed this morphology to a primitive form of C. crassum (Pl. 2 , figs. 16-17);
a much rarer second morphology, with evolute coiling and with relatively short Cheloniceras stage. This form we left in open nomenclature, resembles the primitive parahoplitid Colombiceras and could be its ancestor.
The presence of D. multicostatus and C. crassum with primitive morphology in the Ammonitoceras Level indicates an age corresponding to the late part of the D. multicostus Subzone (D. deshayesi Zone) sensu Bersac et al. (2012; Fig. 1 ). The morphology of the Ammonitoceras in the Ammonitoceras Level, with a short Ammonitoceras ontogenetic stage and an important spiral hiatus in macroconchs (Pl. 2 , fig. 1), is consistent with such an age.
The absence of Deshayesites bearing a longer smooth siphonal band and a subtabulated ventral area on the phragmocone (corresponding to the index species D. grandis, see Bersac & Bert, 2012), allows us to exclude the presence of the D. grandis Subzone in the Ammonitoceras Level.
The Ammonitoceras Level crops out in the following sections: Les Graous 1 (GRS1), Les Graous 2 (GRS2), La Vallière (VAL), Combe de Joinet (CHP), Pont de la Cerise (CLE) and Pont Païré (PPR).
13: Field photographs of the Pont de la Cerise section (CLE). Log of this
section is available in Fig. 12 .
A: top of the
Hauterivian-Aptian limestones, Combe de Joinet Member and Pont de la Cerise Member in 2004.
B: Thalassinoides at the top of the Combe de Joinet Member (bed 404) in
2004. Length of the hammer: 330 mm. C: Thalassinoides in Bed 408
of the Pont de la Cerise Member. Length of the hammer: 290 mm. D:
ammonites fragments in Bed 409 (Cheloniceras sp. and Pseudohaploceras
sp. in Fig. 12 ). Tape measure with centimetre markings.
This member is restricted to the LFAB (Fig. 4 ). It starts with a marly limestone level of about 0.2 m thickness, named here the Toxoceratoides Bed (Figs. 4 , 11.C ). The type section of the Les Graous Member is at the Les Graous 1 section (GRS1).
The levels of the Les Graous Member above the Toxoceratoides Bed are represented in the sections at Les Graous 1 (GRS1) and Les Graous 2 (GRS2) by blue-grey sandy marls. A bundle of 6 more indurated beds is intercalated in the lower part of these marls (Figs. 6.B , 11.C-D ). Within the Les Graous Member, pyrite nodules and centimetre-thick pyrite alteration beds are relatively common. The upper limit of this member can only be observed at the GRS 1 and GRS 2 sections: it corresponds to a discontinuity surface with numerous Thalassinoides located at the top of a 0.80 m-thick marly limestone bed (GRS 1 and GRS 2 bed 113; Figs. 5 , 6.D ).
The Toxoceratoides Bed provided a large number of deformed internal moulds of ammonites, nautiloids, belemnites (Pl. 3 , figs. 7-8), bivalves, gastropods, corals, and fish scales. The ammonite fauna is represented by Ammonitoceras sp., Lithancylus sp., Toxoceratoides aff. royerianus (Pl. 3 , figs. 13-16), Deshayesites grandis (Pl. 3 , figs. 9-12), Cheloniceras crassum (Pl. 3 , figs. 5-6), ?Colombiceras sp., Pseudohaploceras liptoviensis, ?Aconeceras sp., Macroscaphites striatisulcatus (Pl. 3 , figs. 3-4), Acantholytoceras sp., Ptychoceras emericianum, Hypophylloceras sp. (Pl. 3 , fig. 1) and Lytoceras sp.
The Deshayesites in this level have a well-expressed smooth siphonal band and a subtabulated ventral area on the phragmocone (Pl. 3 , figs. 9, 12). The Cheloniceras have a long Cheloniceras stage and a short or absent Procheloniceras stage (Pl. 3 , fig. 5). These characters indicate an age corresponding to the D. grandis Subzone (Fig. 1 ).
Above the Toxoceratoides Bed, the lower part of the Les Graous Member yielded an abundant ammonite fauna represented by deformed internal moulds (Fig. 6.C ). Within these levels, belemnites (Pl. 5 , figs. 17-21) and fish scales (Pl. 5 , fig. 26) are relatively frequent. Nautiloids, echinoids (Pl. 5 , figs. 27-28), brachiopods (Pl. 5 , fig. 29), gastropods (Pl. 5 , figs. 22-23), bivalves (Pl. 5 , fig. 24) and small ahermatypic corals (Pl. 5 , fig. 25) are rarer. Fossils are noticeably more frequent in the more indurated beds. Pyritic internal moulds of ammonites are extremely rare and poorly preserved. In the lower part of the grey-blue marls, we identified the following ammonitic taxa: Ammonitoceras lahuseni macroconchs (Pl. 4 , figs. 1-3) and microconchs, Tropaeum bowerbankii, Toxoceratoides rochi (Pl. 5 , figs. 1-4), Dufrenoyia furcata (Pl. 5 , figs. 5-9), Cheloniceras crassum (Pl. 4 , figs. 8-9), Colombiceras crassicostatum (Pl. 5 , figs. 10-12), Pseudohaploceras liptoviensis (Pl. 4 , figs. 6-7), Aconeceras nisum (Pl. 5 , figs. 13-14), Ptychoceras emericianum (Pl. 5 , fig. 15), Macroscaphites striatisulcatus (Pl. 5 , fig. 16), Acantholytoceras sp. (Pl. 4 , figs. 4-5), Lytoceras sp. (Pl. 4 , figs. 10-11), Hypophylloceras sp. (Pl. 4 , fig. 12). Nautiles are represented by Cymatoceras neckerianus (Pl. 4 , figs. 13-14) and Anglonautilus sp.
In the upper part of the Les Graous Member, we identified Toxoceratoides rochi, Dufrenoyia dufrenoyi (Pl. 5 , figs. 30-32), Cheloniceras crassum, Pseudohaploceras liptoviensis, Aconeceras nisum, Hypophylloceras sp.
The grey-blue marls of the Les Graous Member are assigned to the D. furcata Zone (Fig. 1 ): their lower part is assigned to the D. furcata Subzone and their upper part to the D. dufrenoyi Subzone.
16: Field photographies of the Pont de la Cerise section (CLE). Log of this
section is available in Fig. 15 .
A: Pont de la Cerise Member in 2017. B: top of the Pont de la Cerise Member and base of the Les Graous Member
in 2017. AL: Ammonitoceras Level.
Eight sections were sampled between 2000 and 2017. They are located along an E-W axis on either side of the village of Les Ferres (Fig. 3 ). These sections are (from W to E):
These sections are located about 1.65 km to the WSW of the village of Les Ferres. Les Graous 1 (GRS 1, Fig. 3 , lat.: 43°50'31.8"N, long.: 7°4'35.4"E) crops out on the eastern flank of the Les Graous cuesta and Les Graous 2 (GRS 2, Fig. 3 , lat.: 43°50'31.0"N, long.: 7°4'27.3"E) on its western flank. Because of their similar lithostratigraphy, the log of GRS 1 only is figured (Fig. 5 ). Field photographs and log section of GRS 1 were given by Bert & Bersac (2011, Figs. 30, 32-37, 40-47), but the exact location of this section was not indicated because fieldwork had not been completed then. In this section, the marly Aptian can be observed continuously from the top of the Hauterivian-Aptian limestones to the Albian (Fig. 6.B, .D ). The Combe de Joinet Member is absent and the Pont de la Cerise Member lies directly on the Hauterivian-Aptian limestones. The Pont de la Cerise Member is only 0.90 m thick in GRS 1 (Figs. 5 , 6.A ). A bed of phosphate nodules can be observed at 15 cm above its base. At the top of this member the Ammonitoceras Level provided some poorly preserved ammonite fragments. In addition to the ammonite taxa cited in Fig. 5 , the Pont de la Cerise Member provided Cymatoceras neckerianus (20 cm above its base), Anglonautilus sp. (30 cm above its base) and several specimens of Neohibolites aptiensis.
The Toxoceratoides Bed is present at the base of Les Graous Member (Figs. 5 , 6.A ). It is relatively marly here and yielded a fairly abundant fauna of ammonites, belemnites and nautiloids. Above the Toxoceratoides Bed, the first 5 metres of this member are represented by a bundle of 6 sandy and marly limestone beds separated from each other by marly intervals (Figs. 5 , 6.B ). A rich ammonite fauna assigned to the D. furcata Subzone (Fig. 6.C ; Pl. 4 , figs. 8-12; Pl. 5 , figs. 1-16) was collected mainly from the first 5 sandy and marly limestone beds and Bed 99 (Fig. 5 ).
The upper part of the Les Graous Member is attributed to the D. dufrenoyi Subzone. It is marlier and only the sandy and marly limestone beds yielded ammonites. Bed 110 yielded the earliest D. dufrenoyi (Fig. 5 ). The upper limit of this member is represented by a sandy limestone bed (Bed 113, Fig. 5 ) that is relatively rich in ammonites (especially in D. dufrenoyi, Pl. 5 , fig. 32). It is overlain by upper Aptian dark glauconitic marls. All the material from "les Graoux" published by Delanoy et al. (2018) was collected from Beds 99, 100 and 102 of the GRS 1 section in our presence.
Ragazzi (1982, p. 73) and Bréheret (1997, p. 267, Figs. 114-115) studied a section located in the La Vallière area (Fig. 3 , lat.: 43°50'32.6"N, long.: 7°5'29.9"E). This section is nowadays almost completely covered by vegetation and located in a private fenced property.
We studied an outcrop near this section (VAL section, Figs. 3 , 7 , lat.: 43°50'32.1"N, long.: 7°5'48.4"E). It is located in a half-graben, against a vertical decametric palaeo-escarpment, about 0.6 km SSW of the village of Les Ferres (Fig. 8.A ). A cross-section of this tectonic structure was figured by Dardeau & Graciansky (1987, Figs. 1-2). In this outcrop, the Pont de la Cerise Member reaches its maximum thickness (15 m) and is overlain by a 0.2 m-thick sandstone level (Bed 417, Fig. 7 ), which is the probable local equivalent of the Toxoceratoides Bed (Fig. 8.A ). Bed 405, located at 3.70 m from the base of the Pont de la Cerise Member (Figs. 7 , 8.B ), yielded a relatively abundant, but fragmentary, ammonite fauna very similar to that of the Ammonitoceras Level. A level located at the top of the Pont de la Cerise Member (top of Level 416, Fig. 7 ) yielded rare representatives of Toxoceratoides, Deshayesites and Cheloniceras, but they are too fragmentary to be identified to specific level. Nevertheless, the lithological and palaeontological characteristics of this last bed are not equivalent to the Ammonitoceras Level. For this reason, we consider Bed 405 as a local equivalent of the Ammonitoceras Level. This all implies that the glauconitic sandstones overlying the Ammonitoceras Level of VAL are therefore considerably more developed here than in other sections (Fig. 17 ). The Les Graous Member of VAL is almost completely covered by vegetation and thus could not be studied.
The La Graou section (GRO, lat.: 43°50'36.2"N, long.: 7°6'0.0"E) was described by Ragazzi (1982, p. 73), then by Bréheret (1997, p. 264, Fig. 114). It is located 0.5 km SW to the village of Les Ferres (Figs. 3 , 9 ). The Lower Aptian is nowadays almost totally covered by vegetation and only a small part of the Les Graous Member can be observed.
The CHP section (lat.: 43°50'42.7"N, long.: 7°6'9.5"E) is located 0.8 km ESE of the village of Les Ferres, along a track leading to the Pont de la Cerise Figs. 3 , 10 - 11 ). Bert (2014, p. 393) figured the Ammonitoceras Level at the CHP section for the first time (Fig. 11.D ). Delanoy et al. (2018, Fig. 2) published a log of this section and described and figured many ammonites, mainly from the Ammonitoceras Level (Bed 107 in Delanoy et al., 2018 = Bed 415 in the present work, Figs. 10 , 11.C-D ). Unfortunately, several levels located at the base of the marly Aptian were not figured in the log of Delanoy et al. (2018, Fig. 2), including the Combe de Joinet Member. For this reason, we did not use the bed numbering system of this latter work for our own log (Fig. 10 ). At CHP, the Combe de Joinet Member (Bed 401) crops out in good conditions along the track between the D1 road and the Pont de la Cerise (Figs. 3 , 11.A ). It is represented by massive sandy and marly limestones and provided some rare fragments of ammonite. The Ammonitoceras Level crops out under good conditions, allowing the collecting of abundant ammonites (Delanoy et al., 2018; Fig. 11.C-D ; Pl. 2 , figs. 1-19). Only the lower part of the Les Graous Member is visible, its upper part being covered with dense vegetation (Fig. 11.B ).
This section (lat.: 43°50'42.7"N, long.: 7°6'9.5"E) was first published by Ragazzi (1982, p. 75) who named it "Pont de la Cerise" despite the fact that another section closer to the Pont de la Cerise locality was named "Combe de Marin" by Ragazzi (1982, p. 77 and Fig. 3; Fig. 3 and see Chapter 5.3.6). The CLE section crops out on the right bank of the Esteron River in the locality of the Clot d'Estéron, 1.95 km east of the village of Les Ferres (Figs. 3 , 12 ). The top of the Hauterivian-Aptian limestones, the Combe de Joinet and Pont de la Cerise members, as well as the Toxoceratoides Bed crop out under favourable conditions (Fig. 13.A ). As Ragazzi noticed (1982, p. 76), the Combe de Joinet Member (Beds 401 to 404 in CHP) is represented by 1.1 m of marly limestone and two decimetric limestone beds (Figs. 12 , 13.A ). The top of this member is intensely bioturbated (Fig. 13.B ). The Pont de la Cerise Member crops out in very good conditions and is 5.5 m thick at that point (Fig. 13.A, .C-D ). In its lower and middle parts, rare and poorly preserved fragments of Ancyloceratidae gen. ind., Deshayesites sp., Cheloniceras sp., and Pseudohaploceras liptoviensis (Fig. 13.D ) were recorded. The Ammonitoceras Level (Bed 415, Fig. 12 ) occurs at the top of this member and its ammonite fauna appears to be slightly less abundant and less well-preserved than that at CHP (Pl. 2 , fig. 20). Only the Toxoceratoides Bed (Bed 416, Fig. 12 ) of the Les Graous Member crops out under good conditions, the rest of the formation being entirely covered by vegetation.
This section was figured by Ragazzi (1982, p. 77 and Fig. 3). It is located on the left bank of the Esteron River, opposite to the Pont de la Cerise locality, 2.69 km east of the village of Les Ferres (Fig. 3 ). The CRS section crops out at the top of a cliff mainly formed by the Hauterivian-Aptian limestones (Fig. 14 ). Our own observations differ slightly from those of Ragazzi (1982): only the Combe de Joinet Member and the lower 5.4 m of the Pont de la Cerise Member are currently observable. The rest of the Aptian marls is covered by vegetation. The Combe de Joinet Member is represented by 0.80 m of marly limestones, with a dark brown clay level, 0.10 m thick, in its lower part. The ammonite fauna is rare and fragmentary, but includes: Ancyloceras sp., Deshayesites sp., Pseudohaploceras liptoviensis and Macroscaphites aff. yvani.
Ragazzi (1982) already mentioned this section ("ravin de Pont de Payre" in Ragazzi, 1982, p. 77) where she observed that the Pont de la Cerise Member was reduced to a thickness of 3.5 metres. This section (lat.: 43°51'11.6"N, long.: 7°7'49.0"E, Fig. 15 ) crops out in a ravine perpendicular to the track between the D17 road and Pont de la Cerise (Fig. 3 ). Our own observations differ from Ragazzi’s (1982): the Pont de la Cerise Member is separated from the Hauterivian-Aptian limestones by a metre-thick covered section and is 11 m-thick (Figs. 15 , 16.A-B ). This member can be observed under good conditions along the ravine, for a distance of about 100 m. The Ammonitoceras Level (top of Bed 414 in PPR, see Fig. 15 ) is present at its top (Fig. 16.B ), immediately above a level particularly rich in large pyrite nodules. The levels of the Pont de la Cerise Member below the Ammonitoceras Level reach their maximum thickness in this section. Ammonites are very rare in the Pont de la Cerise Member in this section, except in the Ammonitoceras Level. Only the first 3.3 m of the Les Graous Member are observable (Fig. 16.B ); they are richer in glaucony than in the other sections. The Toxoceratoides Bed is marlier than in the CHP and CLE sections, and yielded some ammonites (Figs. 15 , 16.B ).
Lithostratigraphic correlation between the studied sections and the adjacent
The Combe de Joinet Member appears at VAL, where it reaches its maximum thickness (taking into account that this member could not be measured at PPR). It gets thinner towards the east (Fig. 17 ). The Pont de la Cerise Member appears at GRS 1 and GRS 2 with a thickness of only 0.9 m. The interval of this member beneath the Ammonitoceras Level gradually thicken towards the east (taking into account that we have no thickness data at CRS, Fig. 17 ) reaching their maximum thickness at PPR. The interval of the Pont de la Cerise Member above the Ammonitoceras Level are generally a few centimeters-thick, except at VAL where they exceptionally reach a thickness of 11 m (Figs. 7 , 8.A , 17 ). This may be due to the palaeogeographic context of VAL: the presence of a decametric fault palaeo-escarpment in this area probably allowed an accumulation of a large amount of sediment above the Ammonitoceras Level (Dardeau & Graciansky, 1987). Our observations differ from those of Ragazzi (1982) who observed a thickness reduction of the Pont de la Cerise Member ("accumulation glauconitique" in Ragazzi, 1982, p. 78) at CRS and PPR (Fig. 17 ) compared to more westerly sections. The thickness variation of the Les Graous Member could not be studied because this latter is completely visible only at GRS 1 and GRS 2.
The nearest outcrop west of GRS 2 (Fig. 3 ) confirms the westward thickness reduction of the Pont de la Cerise Member, as already observed by Ragazzi (1982). This section, named "Conségudes" by Ragazzi (1982, Fig. 3), crops out along the D1 road next to the village of Conségudes (lat.: 43°50'26.5"N, long.: 7°2'58.3"E, Fig. 3 ): the "Early Aptian unconformity" (Cotillon, 2010, p. 4) is located at the top of the upper Barremian limestones and is directly covered by Albian dark marlstones (Ragazzi, 1982, p. 73 and Pl. 3; Fig. 17 ). The Aptian is therefore totally absent in this section.
East of the study area, the Aptian is also totally missing in the Colle-Belle section (Cotillon, 1971, p. 147, lat.: 43°51'10.4"N, long.: 7°8'32.3"E, Fig. 17 ), with Albian marlstones lying directly on Barremian limestones (Cotillon, 1971, p. 132 and 147; Fig. 17 ). The sudden demise of the marly Aptian between the PPR and the Colle-Belle section is probably related to the presence of a decametric synsedimentary fault forming the eastern limit of the LFAB.
North of the study area, Aptian deposits can be observed only on the northern flanks of the Roccaforte and Vial mountains and near the village of Tournefort, where they are represented by plurimetric dark marlstones with pyritized ammonites characteristic of the pelagic domain (Ragazzi, 1982, p. 61 and personal observations).
To the south, the Aptian is missing or represented in the Coursegoules and Ruth Mountain areas by thin reworked layers (Cotillon, 1971, p. 145; Bersac et al., 2010; Bert & Bersac, 2011, Figs. 4-6, 20, 67-70; Bert et al., 2013, p. 361, Fig. 9).
The faunal spectrum study of the ectocochleate cephalopods of the LFAB is based on 1,262 ammonites and 58 nautiloids collected or studied in situ, and by 29 ammonites and 1 nautiloid published in Delanoy et al. (2018).
The most represented ammonites families in the lower Aptian of the LFAB are Ancyloceratidae, Deshayesitidae, Douvilleiceratidae, and Desmoceratidae (Fig. 18 ). This faunal spectrum is consistent with the palaeogeography of the LFAB during the early Aptian times, located in the outer neritic domain. Ancyloceratidae and Nautiloidea (Ward, 1987; Hewitt, 1989; Westermann, 1990, 1996) have a preferential tropism for the neritic domain, Deshayesitidae are open oceanic surface organisms, Douvilleiceratidae are opportunistic (Bulot et al., 2005; Dutour, 2005) and Desmoceratidae, Phylloceratidae and Lytoceratidae are deeper water environmental representatives (Westermann, 1990, 1996; Bulot et al., 2005).
The most spectacular character of the lower Aptian ammonite fauna of the LFAB is the abundance of the heteromorphic genus Ammonitoceras in the D. deshayesi and D. furcata Zones, with 80.2% of the Ancyloceratidae of the D. deshayesi Zone and 91.9% for the D. furcata Zone respectively. Such an abundance has never been reported previously in the literature (Kakabadze, 1981; Kakabadze & Hoedemaeker, 2004). It may be related to particularly favourable environmental conditions in the LFAB.
The scarcity of representatives of the genus Tropaeum in the LFAB may be related to the fact that this is a boreal taxon (Casey, 1960; Aguirre-Urreta, 1985). Nautiloidea never represent more than 13.5% of the ectocochleate cephalopod fauna (Fig. 18 ).
The proportion of each group of ectocochleate cephalopods varies over the stratigraphic interval considered: excluding data from the Combe de Joinet Member and the Pont de la Cerise Member below the Ammonitoceras Level due to the small amount of material collected (respectively 10 and 15 specimens; Fig. 18 ), there is a decrease in the proportion of Nautiloidea and Ancyloceratidae over time and an increase of Deshayesidae and Desmoceratidae (the latter being related to the "bloom" of the genus Aconeceras Hyatt, 1903, in the D. furcata Zone). This is strongly consistent with the transgressive trend of the studied series (see Chapter 2), where open marine environment taxa become progressively more prevalent. At the top of the studied series, in the D. dufrenoyi Subzone, this phenomenon leads to a faunal spectrum similar to that observed in hemipelagic environments, where the ammonite populations are mainly composed of Deshayesitidae and Desmoceratidae (Dutour, 2005, Fig. 22). The proportion of Helicancylidae is higher when Ancyloceratidae decrease, as a result of ecological interactions between these two families.
Nautiloidea and Ammonoidea faunal spectrum of the lower Aptian of les Ferres
area. HAL: Hauterivian-Aptian limestones, n: number of specimens studied, CJ:
Combe de Joinet Member, PC: Pont de la Cerise Member, AL: Ammonitoceras
Level, TB: Toxoceratoides Bed, LG: Les Graous Member.
The marly deposits of the Les Ferres Aptian Basin (LFAB) are located in one of the few areas of the southern margin of the Vocontian Basin where ammonites from the D. deshayesi – D furcata Zones can be studied under favourable conditions. An abundant bed-by-bed collection of ammonites, constrained at the subzone level and represented by a significant proportion of adult or subadult specimens was collected. The lithostratigraphy and biostratigraphy of the marly Aptian of Les Ferres presented in the present article aims to serve as a basis for our future palaeontological work in this area. The whole marly Aptian of the LFAB is represented by a newly described lithological unit: the Les Graous Formation. This unit is divided into 3 members (from bottom to top): 1) the Combe de Joinet, 2) the Pont de la Cerise and 3) the Les Graous Members. Most of the collected ammonites come from a precise level at the top of the Pont de la Cerise Member, the Ammonitoceras Level (upper D. multicostatus Subzone, D. deshayesi Zone), and from the lower part of the Les Graous Member (D. grandis and D. furcata Subzones). One of the most remarkable features of this fauna is the abundance of the heteromorphic ammonite genus Ammonitoceras (Ancyloceratidae). The abundant collected material allows us to formulate hypotheses on the intraspecific variability and the evolutionary modalities of several taxons of the families Ancyloceratidae, Douvilleiceratidae, Deshayesitidae, Parahoplitidae, and Desmoceratidae, which will be the topic of forthcoming contributions.
We warmly thank Pierre Ropolo for providing data about the lower Aptian Ancyloceras of the Cassis-La Bédoule area. The constructive comments of the Editor-in-chief and reviewers Ottilia Szives (Budapest, Hungary) and Yves Dutour (Aix-en-Provence, France) are highly appreciated and greatly improved the manuscript. We are grateful to Simon Mitchell for the improvement of the English manuscript.
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of the last bed of the Hauterivian-Aptian limestones (Deshayesites
forbesi Zone). All specimens: Bersac's collection.
the Ammonitoceras Level (top of the Pont de la Cerise Member, Dehayesites
deshayesi Zone, Deshayesites multicostatus Subzone). Scale bar
50 mm for figures 1 to 17. Scale bar 10 mm for figures 18 to 20. All
specimens: Bersac's collection.
of the Toxoceratoides Bed (base of the Les Graous Member, Dehayesites
deshayesi Zone, Deshayesites grandis Subzone). All specimens: Bersac's
of the Les Graous Member (Dufrenoyia furcata Zone, Dufrenoyia
furcata Subzone). All specimens: Bersac's collection.
the Les Graous Member. Figures 1-29: Dufrenoyia furcata Zone, Dufrenoyia furcata Subzone.
Figures 30-32: Dufrenoyia furcata Zone, Dufrenoyia dufrenoyi
specimens: Bersac's collection.