◄ Carnets Geol. 21 (4) ►
Outline:
[1. Introduction]
[2. Regional geological setting]
[3. Description of sections studied]
[4. Ammonite stratigraphy]
[5. Temporal distribution of the belemnites]
[6. General and stratigraphic remarks about the belemnite taxa]
[7. Conclusions] [Bibliographic references] and ...
[Plates]
Published online in final form (pdf) on February 28, 2021
DOI 10.2110/carnets.2021.2104
[Editor: Bruno R.C. Granier; language editor:
Simon F. Mitchell]
A zonation based on the temporal distribution of belemnites is presented for the Valanginian and its boundaries. It is calibrated on ammonite controlled and bed-by-bed correlated sections from the pre-Vocontian Basin (southeast France). Three new sections are introduced herein that have previously not been investigated. All together, seven zones and six subzones are introduced. In addition, both within the Vocontian area, as well as outside (Bulgaria, Crimea, Czech Republic, France, Hungary, Morocco, Romania, Slovakia, Spain, Switzerland), differences regarding the spatial distribution of belemnites are investigated. Also, in two addenda, some remarks are given regarding lithological oddities.
• Belemnites;
• Neocomian;
• Valanginian;
• Hauterivian;
• zonation
Janssen N.M.M. (2021).- Mediterranean Neocomian belemnites, part 5: Valanginian temporal distribution and zonation (and some lithological remarks).- Carnets Geol., Madrid, vol. 21, no. 4, p. 67-125.
Les bélemnites néocomiennes méditerranéennes, 5e partie : Distribution temporelle et zonation du Valanginien (avec quelques remarques sur la lithologie).- Une zonation établie sur la distribution temporelle des bélemnites est présentée pour le Valanginien et ses limites. Elle est calibrée sur des coupes du bassin pré-vocontien (sud-est de la France) datées par ammonites et corrélées banc par banc. Trois coupes inédites sont présentées ici. Ce sont au total sept zones et six sous-zones qui sont proposées ici. De plus, les différences concernant la répartition spatiale des bélemnites sont analysées au sein du domaine vocontien ainsi que dans d'autres régions (Bulgarie, Crimée, Espagne, France, Hongrie, Maroc, Roumanie, Slovaquie, Suisse, Tchèquie). Enfin, deux addenda présentent des remarques concernant certaines particularités lithologiques.
• Bélemnites ;
• Néocomien ;
• Valanginien ;
• Hauterivien ;
• zonation
This
paper is devoted to the temporal distribution of belemnites in the Valanginian,
including across its upper and lower boundaries, and refines, extends, and
provides further evidence regarding the temporal and spatial distribution of
Valanginian belemnites in the pre-Vocontian Basin (Arnaud,
2005),
previously published in Janssen and Clément
(2002) and Janssen
(2009). The distribution pattern is compared to more proximal parts of that
basin, i.e., sections in proximity to Les Allaves (Thieuloy
et al., 1991) and Preynes (Fig. 1 
).
However,
most of the material originates from the more distal parts. The zonation herein
proposed, based on belemnites, is helpful when ammonites are rare and gives
additional tie points around stage/substage boundaries and helps with
proximal-distal correlation within the basin.
|
Figure 1:
Geographical
distribution of areas and sections studied. Fig. 1.A. Details of outlined area in the Baronnies. Fig.
1.B. Details of
position of sections in Preynes area. Abbreviations used: ACL (Ravin du Coteau d'Acle), ALL
(Les Allaves), ANG (Angles), AUL
(Aulan), BEG (La Bégude), BLB (Barret-le-Bas),
BME (Barret-sur-Méouge), CAR
(Carajuan), CHE (Cheiron), CLZ (Col de Lazarier), FCH
(Farme de Chilet), GIN (Ginestous), GM
(Gros Mas; see Fig. 1.B), GRAU (Grau
de Lèbres), LBL (Laborel), LCH (La Charce), PIL (Piloubeau),
PRY (Preynes), SCL
(Saint Colombe), SCX (Serre de la
Croix), SLD (Saut de la Drôme),
SPA (St. Pierre-Avez), SVJ
(St. Vincent-sur-Jabron), TM (Terre
Masse), VBL (Vaubelle), VGL
(Vergol), and VPE (Vallon des Péchières). |
The
recent fine-tuning of ammonite zones in the lower Valanginian resulted in a
fundamentally different ammonite zonation/subzonation for the interval due to
revision of the taxonomy and stratigraphy as discussed by Company
and Tavera
(2015). These changes are implemented to the stratigraphical data previously
published (Table 1 
). However, as the investigated sections in the pre-Vocontian
Basin for the most part (Hirsutus Subzone to Furcillata Zone) can be correlated
bed-by-bed, ammonite divisions (Subzone, Sz, and Zone, Z) are herein used as
Chronozones (cf. Salvador, 1994, p. 83-84). In the French literature the
term "Horizon" is often used; it can mean both zonule as well as subzone.
Table 1: Stratigraphical data for the Vergol section (VGL), modified after Reboulet (1996), Kenjo (2014), Company and Tavera (2015) (= C&T, 2015), and field observations (range of Baronnites hirsutus in VGL). Both Saynoceras contestanum and Valanginites are extremely rare in the distal parts of the pre-Vocontian Basin, therefore there Neocomites (Eristavites) platycostatus and Busnardoites subcampylotoxus are more appropriate as subchronozonal index ammonites (see text for explanation). Abbreviations used: neocom. = neocomiensis. For affiliation of ammonite genera see references cited. |
|
Previously,
only informal belemnite zonal schemes have been proposed for the pre-Vocontian
Valanginian. Largely, the zones herein established will be based on the first
occurrence (hereafter FO) and associations of belemnites that characterize
certain stratigraphic intervals. Herein, the outcrops at Vergol/Aulan/Fm.Chilet,
Angles/Cheiron/Source de l'Asse de Moriez, and Vaubelle/St.Vincent-sur-Jabron
serve as reference sections as most of the material originates from them. The
latter two sections are new and described here. In addition several sections
(see Fig. 1 ) have not been investigated as
intensively, but provided interesting or
additional material important for parts of this work.
In the investigated sections ammonites provide the foundation of the temporal framework, to which the distribution of the belemnites will be compared. These sections combined, cover the whole of the Valanginian. Bed-by-bed correlation is possible in the investigated distal sections for parts of the lowest Valanginian (Pertransiens Zone). The distal sections typically show the alternation of limestone and calcareous-clay (marl; marlstone) beds (Cotillon et al., 1980; Giraud et al., 1995; Reboulet & Atrops, 1997), sometimes with slumped beds or sets of beds, characteristic of the more distal parts of the basin. Some intervals show intercalated with thin to very-thin (a few mm's thick, but ocassionally up to 50 cm thick) brown-weathering layers (see Appendix A), the so-called "plaquettes calcaréo-gréseuses rousses" (calcarenitic brownish beds).
A distal to proximal, bed-by-bed correlation is not possible for some parts of the basin, except for certain sets of beds, based on their fauna (mainly ammonites) and overall lithology (limestone vs. marlstone dominated sets of beds; Ferry & Monier, 1987; Thieuloy et al., 1991; Reboulet, 1996). The more proximal (hemipelagic: Cotillon et al., 1980) sections, are typically composed of sets of limestone beds intercalated with marlstone dominated sets of beds (Cotillon, 1971; Thieuloy et al., 1991). These beds and/or sets of beds often yield large amounts of almost monospecific associations of various fossil groups, among which small brachiopods (Pugitella) or echinoids (Toxaster) are most typical. In the area surrounding Preynes (PRY), sedimentary rocks were deposited on an outer ramp (Robert, 1994, p. 10; Blanc, 1996, Fig. 59), between the distal sediments of the basin and the more proximal sediments of the more southern areas (hemipelagic area and "Provence platform area", cf. Masse et al., 2009).
The distal settings
Most
of the investigated sections are from the deeper parts of the pre-Vocontian
basin (Figs. 2
- 3
- 4
- 5
- 6 ). As not all of the sections have been extensively investigated in regard to
ammonites, bed-by-bed correlation of these sections provides a satisfying
alternative, at least from the Hirsutus Sz up into younger levels. In general,
ammonites are common, generally as haematitic casts in the marls and as
calcareous casts in the limestone beds. In addition, aptychi (Vašíček
et al., 2016a, 2016b,
2016c), rhyncholites, belemnites, porifera (Hérenger,
1944;
Pl. 1 , figs. 3-11, 14-16), and
gastropods ("pelican-feet"), occur in varying abundance. Other macrofossil
groups, such as, bivalves, brachiopods, corals, echinoids, and vertebrates, are
less common.
Angles
(ANG-V) and surrounding.
These sections are situated roughly to the north-east of Castellane and are
exposed in a wide area around lake Castillon. The uppermost lower and upper
Valanginian at ANG-V yield abundant ammonites (Thieuloy,
1979; Le Hégarat
& Ferry, 1990; Bulot et
al., 1993a; Bulot, 1995; Reboulet,
1996). It was chosen as a
complementary section for the Valanginian (hypostratotype; Busnardo et
al., 1979). The Berriasian-Valanginian boundary is placed - based on
calpionellids - at a slumped interval (beds ANG-V201-207; Le Hégarat
& Ferry, 1990, p. 371). Some belemnites have been mentioned by Combémorel
(1979) and Janssen (2009). Bed numbers for ANG-V follow Busnardo
(1979). The exposures known as Source de l'Asse de Moriez (SAM) and especially
Cheiron (CHE) cover the whole Valanginian and belong to the classical areas in
which at the beginning of the 19th century many macrofossils were collected.
Nowadays, the amount of exposure varies due to the level of water in the
artificial lake Castillon, but belemnites and ammonites occur quite commonly in
the surrounding hills. Here, especially, the interval from the upper Valanginian
to lowermost Hauterivian is well-exposed (Fig.
2 ), and compares well
lithologically with ANG-V. In the late Valanginian (Niclesi Sz and Furcillata Z)
at CHE there are intervals with small-scale slumping.
|
Figure 2:
Stratigraphic
distribution of belemnites in the upper Valanginian (p.p.) and lowermost
Hauterivian (Peregrinus to Radiatus Zones pro parte). The legend is applicable
for Figs. 2
- 3 |
|
Figure 3:
Stratigraphic
distribution of belemnites in the lowermost upper Valanginian ("Neocomiensis
Subzone" (Verrucosum Zone) to Peregrinus Zone pro parte). For explanation of
abbreviations of sections mentioned see Fig. 1 |
Vergol (VGL) and surroundings.
The hamlet of Vergol (05°25'01"E - 43°12'27"N) is situated to the
north of Montbrun-les-Bains. Valanginian sedimentary rocks are well exposed in
the area. Details of bed numbers can be found in Reboulet (1996,
2015, 2017a, 2017b), McArthur et al.
(2007), Janssen (2009), Kenjo et al.
(2014), and herein. The Verrucosum Zone is exposed in an area running approximately south of
Vergol, to the farm of Chilet (section FCH; Fig. 1 ). As macrofossils (chiefly ammonites; Blanc et
al., 1994; Reboulet, 1996; Kenjo,
2014) are abundant and the
area is easily accessible and continuous over large areas, the Vergol succession
has a well-developed, ammonite-based, stratigraphical framework, especially in
the upper Valanginian (Reboulet, 1996, 2015). The lower Valanginian is
slightly more problematic as in parts of the lithological column ammonites
appear rather scarce, especially in the lower Pertransiens Zone. Blanc et
al. (1994) and Blanc
(1996, p. 85-88) investigated the Vergol section as a potential reference
section for the Berriasian-Valanginian boundary.
The
succession around the boundary between the lower and upper Valanginian yields
abundant taxa. The base of the Verrucosum Zone is placed at the inter-bed
VGL102-103 (Reboulet, 1996; Reboulet & Atrops,
1997) (Fig.
4 ). The index-species (Saynoceras
verrucosum) is ubiquitous and abundant in a few beds that can be traced
across the pre-Vocontian Basin and into its more proximal parts (Thieuloy,
1973; Cotillon et al.,
1980; Bulot
et al., 1993a; Bulot & Thieuloy,
1995). It is succeeded by a marlstone-dominated interval that is poorly
characterized by ammonites. So far, it has yielded only long ranging species.
The index-species for the underlying and overlying subzones are absent. This is
the Neocomiensis Horizon of Atrops and Reboulet
(1993). It is in
this interval, characterized by many rust-coloured intercalations, that the
typical lower Valanginian and lowermost upper Valanginian (Verrucosum Horizon)
belemnites disappear. In the Inostranzewi Zone the Barrande levels are clearly
visible (Pl. 4 , fig. 8), and pre-date the Valanginian positive carbon excursion.
The
section herein called Col d'Aulan (AUL) is comparable to the Morénas section
of Reboulet (1996). It is generally similar to VGL, but in the latest
early Valanginian (part of the Platycostatus Sz) the intervals that are
partially slumped in VGL are undisturbed (Fig.
4 ).
|
Figure 4:
Stratigraphic
distribution of belemnites in the upper lower Valanginian to lowermost upper
Valanginian (Inostranzewi Zone to Verrucosum Horizon). For explanation of
abbreviations mentioned see Fig. 1 |
|
Figure
5:
Stratigraphic
distribution of belemnites in the lower Valanginian (Pertransiens Zone pro parte
to Neocomiensiformis Zone). For explanation of abbreviations mentioned see Fig. 1 |
Vaubelle (VBL) - St.Vincent-sur-Jabron (SVJ). These
sections are located to the WSW of Sisteron. Valanginian sedimentary rocks are
exposed over a wide area around the farm of Vaubelle. Sections to the west and
north-west of the farm (at the southern, western and eastern foot of the Serre
Michel) were measured (Pl. 2 , figs. 1-2). SVJ is located to the west of VBL.
Exposures are numerous, but sometimes complicated by faults and changes in
lithology caused by mass-flow deposits. Belemnites are generally common. The
lower part of the Hirsutus Sz yields a level with abundant large haematitic
specimens of the ammonite Olcostephanus
stephanophorus (VBL048-049). In the Hirsutus Sz the characteristic belemnite
Duvalia superconstricta occurs. Typically, the Berriasibelus conicus-group
is most common together with Mirabelobelus
blainvillei, whereas some levels yield large numbers of Castellanibelus.
The Verrucosum Horizon is characterized by abundant Duvalia
emericii, succeeded by sediments of
the "Neocomiensis Sz" dominated by Hibolites
aff. jaculoides, aptychi and many
small brown-weathered beds. Younger levels were not investigated.
The
so-called Barrande levels (B1-4) are present (Pl. 2 , figs. 4-5; see beds VBL087
and 088 in Fig.
4 ), and in the inter-bed between VBL091-092 an ochre-coloured
level occurs and may correspond to O4 of Fresneau et
al. (2009). Several slumped intervals are common to many of the investigated
sections: i.e., at the base of the
Valanginian, below the Hirsutus Sz (Pl. 3 , figs. 1, 3), in the Neocomiensiformis
Zone (Pl. 3 , figs. 6-7), and at the top of the Inostranzewi Zone
(Platycostatus Sz) (Pl. 3 , fig. 5). A thin calcarenitic bed occurs in the lower Pertransiens
Zone and yields many fragmented aptychi and some belemnites (mainly M.
blainvillei).
In
contrast to the other investigated sections, there are occurrences of
redepositional deposits consisting of micro-conglomerates, redeposited
macrofossils (mainly early-middle Berriasian ammonites), and variously sized
calcareous clasts, nodules and boulders (Fig. 6 ;
Pl. 3 , fig. 4; see
Appendix B).
These sediments are often overlain by brownish-weathering calcarenites with
thickness of 2-50 cm (VBL042, Pl. 4 , fig. 5), which sometimes containing
ichnofossils (Chondrites isp.) at top.
|
Figure 6:
Stratigraphic
distribution of belemnites in the uppermost Berriasian to lowermost Valanginian
(Alpillensis Zone (p.p.) - Pertransiens Zone). Bed-by-bed correlation appears to
be difficult, coloured bands indicate possible correlative (sets of) beds. Also
the abundant occurrence of the ammonite Leptoceras
(indicated by yellow band) is a possible correlative level. The belemnites B.
exstinctorius, C.
orbignyanus, and M. blainvillei
are the first typical members of Valanginian belemnite associations. For
explanation of abbreviations used see Fig. 1 |
To date, the following sections have been less completely investigated with respect to the bed-by-bed distribution of belemnites. However, they confirm the general stratigraphi distributions seen in other sections or provide valuable additional information. They include:
La Charce (LCH). Here, the upper Valanginian and especially the Hauterivian have been extensively investigated with regards to ammonites (Thieuloy, 1977b; Ferry & Rubino, 1988; Reboulet et al., 1992; Bulot et al., 1993a; Bulot, 1995; Bulot & Thieuloy, 1995; Reboulet, 1996). The lower Valanginian is also well developed, but has only been partially investigated to date (Ferry & Rubino, 1988; Reboulet, 1996), even though both belemnites and ammonites are quite common.
The lower/upper Valanginian boundary appears to be disturbed.
Here, these sediments
are characterised by many small, generally only few mm thick, but sometimes up
to 20 cm thick brownish-weathering calcilutitic to (calc)arenitic beds ("la
Zone Jaune" or "yellow zone" of Le Doeuff, 1977). These beds yield
trace-fossils (e.g., Palaeodictyon, Zoophycos),
scour marks, ripple marks, and parallel and convolute laminations. These
marlstone-dominated sedimentary successions succeed a calcareous bed dated as
belonging to the lowermost Inostranzewi Zone (bed LCH098; this bed correlates to
bed VGL085) and the succeeding sediments appear in part to be missing (a.o. the
Barrande levels are missing). The upper part of this marly sedimentary unit
consists of relative thinly-bedded, brownish-weathering layers and few
calcareous beds that are slumped and is followed by a succession of undisturbed,
well-bedded typical alternations of limestone and marlstone. Below the
thin-bedded slump deposit is a rather large slump (MKIII) that consists of a
thick calcareous bed that yielded the belemnite Duvalia elongata (Pl.
9 ,
figs. 31-32). This species first occurs in
the upper parts of the "Neocomiensis Horizon", indicating these slumps are
of post "Verrucosum Horizon" time. The index species of the latter horizon
appears to be absent here, although Ferry et
al. (1989, p. 777) indicate Saynoceras
in the lower part of the slumped beds above LCH098. Most probably this record
refers to "S. fuhri" (sensu Reboulet).
Just above the first calcareous bed (LCH100 sensu
Reboulet) Pseudobelus sp. B occurs. This calcareous series of bedsets also yields many specimens of H.
aff. jaculoides, Duvalia binervia,
and D. elongata.
Several levels with slumped beds occur in the lower Valanginian. In the Pertransiens Zone, calcareous ammonites are quite common, but belemnites and haematitic ammonites are relatively scarce. Some limestones beds show burrows filled with phosphatised faecal pellets (LCH065 and LCH066), whereas a thick limestone bed (LCH055) shows fluid-escape structures. It is interesting to note the presence of the so-called "Teschener fauna" (Uhlig, 1902). Herein, ammonites like Fuhriella and Sarasinella occur abundantly (det. J. Klein) in the upper part of the Pertransiens Zone, below the Hirsutus Sz. This part is not divided into subzones, but is, in the pre-Vocontian Basin, characterized by the (near) absence of the nominal species of the Pertransiens Zone. The Otopeta Sz, very rich in ammonites, also yielded the nautilus Xenocheilus.
Vallon des Péchières (VPE). This outcrop is exposed in a valley to the north of Buis-les-Baronnies and shows the upper lower Valanginian and lowermost upper Valanginian. In the "Neocomiensis Sz", which is up to 10 mm thick, non-continuous beds occur that are completely made up of fragments of aptychi. Thin brownish-weathering levels occur frequently; they are typically up to several mm's thick, often are up to several centimetres thick. Also, the Barrande levels B1-4 occur.
The Baronnies. The
sections described below, roughly occur in an area to the north of the Lure
Mountain and west of Sisteron (Fig. 1.A ). They crop out
in five E-W orientated valleys. From
north to south they include:
(1) the valley W of Montclus of the Blème (a tributary of the Buëch),
(2) the valley of the Blaisance (a tributary of the Buëch),
(3) the valley of the Céans (a tributary of the Buëch), north of the Chadre Mountain, in the valley of the river Céans sections (Laborel, LBL; St. Colombe, SCL), yields late early Valanginian to late Valanginian belemnites (cf. Clément, 1999). Here, no apparent brownish-weathering levels were observed in the lowermost upper Valanginian. The lowest beds exposed at SCO are from the Hirsutus Sz and above these beds, slumping is observed in the interval below the Subcampylotoxus Sz and in the Platycostatus Sz, and
(4) the valley of the Méouge (a tributary of the Buëch); this valley yields the section known as Barret-le-Bas (BLB), east of the village of Barret-sur-Méouge. Valanginian outcrops are widespread in this area to the south of the Chadre Mountain (Barret-le-Bas, BLB; Barret-sur-Méouge, BME (Le Hégarat, 1973, p.423-425); St.-Pierre-Avez, SPA) where ammonites, calpionellids (Le Hégarat, 1973; Remane & Thieuloy, 1973; Busnardo et al., 1979; Bulot, 1995), and belemnites (Combémorel, 1979; Clément, 1999) have been investigated. The BLB section was selected as a Valanginian hypostratotype (Busnardo et al., 1979). The interval around the lower/upper Valanginian boundary commonly yields Berriasibelus heres and Duvalia emericii. Thin brownish-weathering beds occur in the "Neocomiensis Sz" and yield many broken aptychi (see Appendix A).
North
of this valley, west of Laragne-Montéglin (Fig. 1 ), the classical outcrops of
Serre de la Croix (SCX) and Piloubeau (PIL) can be found. Here, in the eastern
part of the Chadre Mountain the earliest Valanginian is exposed yielding at SCX
abundant belemnites in the Hirsutus Sz. In addition, many haematitic fossils
occur in these beds, among these are ammonites, corals, porifera (Pl. 1 , figs.
3-11), and small bivalves. At PIL the Pertransiens Zone and older leves occur,
in part slumped, but are currently largely obscured by vegetation. However, a
few belemnites (e.g., Berriasibelus
incertus, however not in situ)
could be collected, among which Pseudobelus
and Castellanibelus are the most common. The slumped beds are succeeded by a thick limestone bed
(corresponding
to BLB 000), that in turm is overlain by a series of undisturbed beds that are
exposed in some small gullies in an otherwise forested area. At PIL, the
Pertransiens Zone yields ammonites, such as, Platylenticeras, especially well-known from higher-latitudes (Thieuloy,
1977a, p. 402-404) and rare species like Cantianiceras?
diense (det. J. Klein).
(5) the valley of the Jabron, which is located further to the south. In this valley sections around Vaubelle were investigated (see above).
All the above mentioned sections are from the more distal parts of the Vocontian Basin. More proximal areas, so-called hemipelagic settings, are characterized by alternating sets of limestone and marlstone dominated beds, hiatuses, condensed deposits, different fossil abundances, and the absence of slumps. Here, cephalopods (ammonites, belemnites, nautiloids) may be abundant, but aptychi and rhyncholiti are extremely rare. Benthic macrofossils are common to very abundant and include bivalves, brachiopods, and echinoids, whereas corals, crustacean, and vertebrate remains are rare. Intermediate settings show characteristics of both the distal and proximal areas. Deposition was often fault-related and during compressional tectonic episodes, movements along several of these faults led to the development of sub-basins (i.e., the Preynes-Majastres unit).
The sections investigated - intermediate settings
Preynes (PRY).
Localities within
intermediate palaeogeographical affinity between the distal and proximal
settings are uncommon in the investigated area. One example is found in a valley
east of the Pas d'Escale, around the farm of Preynes (PRY) and "Gros
Mas" (= GM; Fig. 1.B ). Sections here were previously studied (ammonites and
calpionellids) and logged by Arnaud et al. (1993), Robert
(1994), and Blanc (1996). However, belemnites were not mentioned in these
studies, despite their relative abundance. Nautiloids are extremely rare and
only one strongly weathered Xenocheilus was obtained from the
Pertransiens Zone. The
middle Berriasian (indicated by the abundance of Dalmasiceras dalmasi and other
species) to upper Berriasian is
mainly calcareous, with subordinate thin to very thin marl intercalations.
Conglomeratic (mud flows) and/or gully-like calcareous levels occur. The
uppermost Berriasian contains variable proportions of glauconite, phosphate, and
iron-rich concretions, especially in the Alpillensis Z. Herein, erosional
surfaces occur, expressed as partially eroded ammonites. This set of beds is
covered by an iron crust and shows a rather irregulair surface. A conspicuous
bed yielding abundant rhynchonellids occurs in the lower part of the Alpillensis
Sz (Bulot, 1995, p. 278; Blanc,
1996, p. 89). These calcareous
dominated sediments (upper Berriasian - lowermost Valanginian) precede lower
Valanginian marl dominated sediments, yielding abundant belemnites (mainly B.
gr. conicus, C. orbignyanus, and M.
blainvillei) separated by slumped beds (Fig. 7 ). Apparently, beds with common T.
pertransiens are absent or the latter species is extremely rare.
In the
Valanginian, the initially marl-dominated sediments actually consist of
alternating sets of marlstone- or limestone-dominated beds (Pl. 6 , figs. 3, 5)
with a "sandy" appearance. In the depicted section, for this part,
individual beds are not figured, but for sets of beds (calcareous complex,
indicated by A to M). Bed-numbers of Arnaud et
al. (1993) are, where possible, indicated (e.g., PRY148). In the lower marly
intervals especially, Megagyrolites-like
burrows (Gaillard, 1980) or concretions occur with sizes ranging from a few
centimetres to several decimetres. In addition, some porifera (Pl. 1 , figs.
15-16) and decapods (Pl. 1 , fig. 17) occur. Slightly higher in the section, the
marly levels yield a few haematitic ammonites (Platylenticeras, Sarasinella,
and more abundantly Lytoceras and Phylloceras)
and driftwood. Here, belemnites are quite frequent, indicating the Hirsutus Sz (D. superconstricta, Castellanibelus
vaubellensis). Higher up in the sequence, limestone sets of beds are more
pronounced and calcareous ammonites (det. J. Klein) become progressively more
abundant. Initially, these sets of beds are dominated by Olcostephanus
gr. drumensis, and above by Olcostephanus
guebhardi, accompanied by "Busnardoites
roberti" and Neocomites
neocomiensiformis. Thereafter, Bochianites,
Olcostephanus, Vergoliceras, and Busnardoites
become the dominant ammonites with subordinate Valanginites. The latter beds weather out as thin bedded limestones
(Pl. 6 , figs. 1, 5; just below the light blue line). They are succeeded by
several tens of metres of marly sediments yielding turbiditic limestone beds
with an abundant ichnofauna (Pl. 6 , fig. 4). Above these beds, two succeeding,
thick limestone sets of beds occur with Duvalia
crassa and few Castellanibelus.
These beds yield, besides O.
guebhardi, many macroconchs of neocomitidae, indicating the Subcampylotoxus
and Inostranzewi Zones. However, these sediments were only briefly investigated
for this paper.
Ginestous (GIN).
The
Ginestous section is situated in the so-called "depression of Nimes" ("la Gouttière némausienne"; Gayte,
1984), a western extension of the pre-Vocontian Basin, and is the westernmost
section investigated (Fig. 1 ). It
is situated approximately at the boundary between the basin and the outer ramp. Here
especially, the uppermost Berriasian yields many belemnites (Fig. 7 ). The section has previously been investigated for belemnites (Gayte,
1984, p. 35-36). Ammonites have been studied (Le Hégarat,
1973, p. 251-259, 344-348; Le
Hégarat
& Remane, 1968, 1973, p. 79-85) in complementary sections, known as
Ginestous-La Garenne, Les Oliviers, and Lacisterne. In the uppermost Berriasian
conspicuous barite nodules occur and there is also a level (marly bed
GIN108-109; Fig. 7 ) that has the
potential to be correlated across this area that yields abundant Leptoceras. This level can be found throughout the investigated area
and was mentioned by Thieuloy (1966) from the Grande-Chartreuse.
The uppermost Berriasian yields B. aff. exstinctorius sp. 1, B. incertus, and M.? orbignyi. Castellanibelus is very frequent, but the other genera are rather rare. These sediments are succeeded by a number of slumped limestone beds, among which one bed yields the ammonite Pseudohimalayites gr. nieri in abundance, in a marly matrix containing large angular quartz grains. The sedimentary succession shows characteristics from both distal (slumps) as well as from more proximal (marl dominance) sets of beds. Given this section's palaeogeographical position, it was probably formed in an "intermediate" setting.
|
Figure 7:
Stratigraphic
distribution of belemnites in PRY (see Fig. 1.B |
The sections investigated - proximal settings
Valanginian
sedimentary successions, on the southern margin of the pre-Vocontian Basin yield
abundant cephalopods (Thomel, 1964; Cotillon,
1971; Thieuloy et
al., 1991; Autran, 1993; Bulot,
1995; Reboulet, 1996;
and refs. therein). Among these, ammonites and nautilids are most abundant,
while belemnites sometimes occur in large quantities (e.g., in condensed
glauconite rich beds; cf. Janssen, 2009), but in general are rare as
compared to other cephalopods. The sediments were deposited between the open
marine (distal) parts of the basin and a carbonate platform situated to the
south. The upper Valanginian is characterized by relatively thin limestone beds
intercalated with rather thick marlstone successions. Large differences can be
observed between the amount of condensation, extension of the hemipelagic
sediments and cephalopod richness in certain sections. Several sections (Fig.
8 )
have been investigated, including: Les
Allaves (ALL), Ravin du Couteau d'Acle (ACL), La Bégude (BEG), Grau de Lèbres
(GRAU), and Carajuan (CAR), all
located in the Moustiers-La
Palud area. This area is well known
for the "canyon du Verdon". In general, sections are easily accessible, but
especially the softer, calcareous-clayey sediments (marlstones) can be covered
by lush vegetation. Also, weathering can be quite strong and as some beds appear
to be rather patchy, eventually parts of these sections might turn out to be
unaccessible from time to time. All sections show more-or-less condensed upper
Valanginian sediments and apparently less condensed lower Valanginian sediments.
In all investigated areas the Verrucosum Sz is well developed. In general,
cephalopod abundances fluctuate heavily within these sediments. Notably, the
lower Valanginian (but for the uppermost) is nearly barren of belemnites and
nautiloids. Other macrofossil groups, especially brachiopods and echinoids show
fluctuating, but often high abundances, especially in the marl dominated
intervals. In several of these sections the Platycostatus Sz and the Verrucosum Sz
show tubular concretions, such as, Tisoa
siphonalis Serres, 1840 (comparable to Friren,
1876, Pl. II,
figs. 6-9), that are more-or-less perpendicular to bedding. These structures
probably represent fluid-escape structures (venting conduits), remobilized along
existing burrows (often several meters long). They are often associated with
cold-seep deposits (Knaust, 2019). Also, irregular beds with abundant
small oysters and patches of bivalves occur and are apparently associated with
these concretions.
Nautilids are common, especially Cymatoceras, but also some other genera occur sporadically, such as Angulithes and Xenocheilus. The latter genus occurs in the Platycostatus Sz of TM, while Angulithes occurs in ALL and in BEG (in both sections as single specimens), in the "Neocomiensis Sz". Among the belemnite "Belemnites pistilliformis" is relatively common in the proximal areas. These include juvenile to sub-adult hibolitid belemnites of the genera Hibolites and Adiakritobelus.
Initially Busnardo and Cotillon (1964), but more extensively and covering a wider area Cotillon (1971, p. 25-34), based on lithostratigraphy, defined various formations within these proximal deposits. Fossil abundances and lithological differences were obvious, and several sets of beds were defined, such as the "Grand Lumachelle" (GL) and the "Petite Lumachelle" (PL), or as marly successions with abundant small brachiopods (Pugitella; Sandy, 1987) or echinids (Toxaster; David, 1979, 1980; François & David, 2006).
Terre Masse (TM). This exposure, previously
known as Chabrières (Thomel, 1964), located to the north of PRY,
yields few belemnites (Fig.
8 ), except for a
condensed level at the base of bed TM108. Herein belemnites are abundant (a.o. Adiakritobelus
peyroulesensis). Also, the uppermost lower Valanginian yields few belemnites.
This section was reinvestigated by Thieuloy et
al. (1991) and Bulot (1995). The
lowermost Hauterivian is typically developed in a glauconitic facies with an abundance
of cephalopods.
Tubular
concretions occur around the lower/upper Valanginian boundary. Bed TM102 yields
the nautiloid Xenocheilus malbosi (Pictet, 1867) (Pl. 1 , fig. 12).
Les Allaves (ALL). This section was investigated and illustrated by Thieuloy et al. (1991). The GL is well exposed, but most of the beds above it, and below the glauconitic uppermost Valanginian - lowermost Hauterivian on top, are not always easily accessible or exposed. At the base of the GL, bed ALL106 is especially rich in large nautiloids. Contrary to the ACL section, ammonites and belemnites appear to be rare in the GL. This is in part due to the poor accessibility of these sections. However, the lower beds yield abundant belemnites (Hibolites), visible as cross-sections in the outcrop. The sediments below the GL are generally well exposed and visible in several outcrops along a small gully. The latter overlies the PL, and is overlain, though the contact is not exposed, by marly calcareous sediments of the Verrucosum Horizon. These highly bioturbated sediments are approximately 1 m thick, and yield irregular marly calcareous nodules, with many small bivalves, echinoids (a.o. Salinaria; Toxaster), and ammonites. Among the latter, S. verrucosum and Valanginites are especially common. Tubular concretions also occur. The glauconitic lowermost Hauterivian is very rich in belemnites (Janssen, 2009).
La Bégude (BEG). In this section (Fig.
8 ),
located to the east of Les Allaves, the general development of the GL is
comparable to ALL and ACL, but individual beds vary in thickness. The section is
illustrated in Thieuloy et al. (1991,
Fig. 7, p. 62). The sediments between the GL and the succeeding marls are
not well exposed anymore, while small faults and lush vegetation disturbs the
continuity of the younger succession. On top of the GL, condensed sediments
occur, yielding abundant ammonites, belemnites, and brachiopods (a.o. Peregrinella). The glauconitic lowermost Hauterivian yields: Adiakritobelus,
Hibolites and abundant "Belemnites
pistilliformis", together with a few Duvalia
and Pseudobelus, and in the upper
Valanginian Duvalia gr. binervia
occurs.
Grau de Lèbres
(GRAU). This
section (Fig.
8 ) is situated slightly to the east of ACL (see below). The GL is
not well exposed (covered by vegetation). The top of the PL forms the crest of a
small hill and the preceding Karakaschiceras-beds
are well exposed. The section is illustrated in Bulot
(1995,
Figs. 11 and
34). The PL is especially rich in O.
guebhardi and few boreal ammonites also occur. However, belemnites appear to
be very rare. Only, in the marly inter-bed GRAU112-113 of the Subcampylotoxus Sz,
a single belemnite (Hibolites lebresensis) was found.
Ravin du Coteau d'Acle (ACL). This
section, previously not described, is exposed to the west of BEG and indicated
on the topographic map as Ravin du Côte d'Acle. Belemnites are rather common,
but in the lowermost upper Valanginian only (Fig.
8 ). Here, post Verrucosum Horizon sediments are well exposed,
especially the GL. The latter consists of hard-wearing calcareous sediments with
often a characteristic appearance of ball-like structures (called
"boules" in French). These beds yield nautilids (Cymatoceras), ammonites (especially Karakaschiceras), and commonly the belemnite H. aff. jaculoides. On top
of the GL two thin calcareous beds (ACL097 and ACL098) are developed that
contain a few belemnites (Hibolites),
some boreal ammonites (Dichotomites
and Prodichotomites) occur and the
ammonite Neohoploceras is present in
abundance. Bed ACL098a consists of two more or less nodular levels. The upper
bed shows traces of glauconite, abundant bivalves and reworked and in
situ cephalopods. Among the cephalopods the most common are: Cymatoceras,
Varlheideites peregrinus, Neocomites
neocomiensis (with fine ribbing), Duvalia
gr. binervia and Pseudobelus. The marly sediments above bed ACL098a are poorly
exposed, but some small marly-limestones could be recognized that yielded few
ammonites (a.o. Teschenites robustus).
This sequence is overlain by lowermost Hauterivian glauconitic limestones that
yield belemnites (A.
robustus, Pseudobelus sp. A).
At the base of the gully, a single D. cf. emericii was found, in a patch of oyster and bivalve rich sediment. However, the contact with the underlying PL, which forms a ridge in the forested area, is not exposed. The marl-dominated sediments at the base of the exposure yield patches of nodular limestones very rich in small oysters and sometimes other molluscs (various double-valved bivalves), while the marls themselves yield abundant small Toxaster. Tubular concretions also occur commonly.
Carajuan (CAR).
Carajuan is seen as the reference section for the outer platform facies (see Thieuloy
et al., 1991, p. 57 and references therein; Arnaud et
al., 1993; Bulot, 1995; Bulot et
al., 1995; Reboulet,
1996). In recent years an increasingly detailed
framework based on the distribution of ammonites was presented by these authors.
Cephalopods, occur but are not common, except in a few beds. A few belemnites
were found mainly in the upper Valanginian (Fig.
8 ). The sediments above the GL are partially covered by vegetation,
but generally well exposed. On top of bed CAR084 a glauconitic phosphatic bed of
2 cm thickness, with an accumulation of rolled and fragmented belemnites could
be observed; it mainly yielding "B.
pistilliformis" and Hibolites.
In addition a few D. gr. binervia and Pseudobelus
occur. It was not possible to see if this was only represented by pockets filled
with reworked clasts, or if there was any lateral continuation.
Apparently, CAR077 yielded the ammonite Karakaschiceras (cf.) pronecostatum (see Hennig Fischer, 2003, Fig. 4.17; Bulot, 1995, p. 253). However, this seems to contradict with the belemnites that occur, and most probably it represents a conch of the K. inostranzewi-biassalense-group; unfortunately it has not been figured nor described. The marly bed below CAR078 yielded D. emericii. The latter species belongs to the belemnite association that characterizes the pre-Verrucosum-event association sensu Janssen and Clément (2002). However, the base of bed CAR078 yields already D. elongata indicating a post-Verrucosum-event belemnite association.
|
Figure 8:
Stratigraphic
distribution of belemnites and a few nautiloids in the proximal settings. Indicated
are bed-numbers, ammonite (sub-)zonation (see text for references), belemnite
(sub-)zonation, lithology and geography. Bed-numbers
of Terre Masse, La Bégude, Les Allaves, and Carajuan after Thieuloy et
al., 1991, while alternative bed-numbers TM (in green) after Thomel
(1964)
and in blue (CAR) after Reboulet (1996). Ravin du Côte
d'Acle is herein first presented. Abbreviations used: GL = Grande Lumachelle, "GL" = correlative part with GL (but not defined there), PL = Petite
Lumachelle, Callid. = Callidiscus, Sub. = Subheterocostata. B = Dichotomites
occurrence, Abr = Adiakritobelus
brevirostris, Dge = Duvalia gervaisiana, P.B?
= possibly Pseudobelus sp. B, R
= Adiakritobelus robustus. For the
legend see Fig.
2 |
General remarks
Much
of the belemnite material originated from sections that have been investigated
for ammonites (Le
Hégarat,
1973; Le Hégarat & Remane,
1973; Thieuloy, 1973; Busnardo et al.,
1979; Thieuloy et al., 1991; Atrops
& Reboulet, 1993, 1995; Bulot et al.,
1993a, 1993b; Bulot & Thieuloy,
1995; Reboulet, 1996). In some cases data were used from unpublished works (Robert,
1994; Bulot, 1995; Blanc,
1996; Kenjo, 2014). For the lower Valanginian, as a result, many
discrepancies occur and various groups of researchers have used different
ammonites in their zonal schemes (compare Bulot, 1995;
Reboulet, 1996;
Kenjo, 2014). Recently, Company and Tavera (2015) published a
modified zonation to the standard that was in use (Reboulet et
al., 2011) to accommodate for some of the discrepancies and taxonomical
problems that existed between the "standard zonation" and their findings in
the SE of Spain (Betic Cordillera). In their text, they gave supporting evidence
that this new zonation can also be applied outside the Betic Cordillera. At the
moment, differences appear to be largely the result of variations in the
abundance of certain ammonites (hence the different subzones) and in part due to
taxonomical discrepancies, as explained by Company and Tavera
(2015). Therefore,
the work of Company and Tavera (2015) is extremely useful to shed new light on the temporal
and spatial distribution and the taxonomical interpretation of ammonites for
this sub-stage. However, Company and Tavera
(2015) used several
subzonal index species that do not occur in abundance in the more distal parts
of the pre-Vocontian Basin, but do in the more proximal parts. For that reason,
some different taxa are herein used to characterize some of the subzonal
ammonite associations (see Table 1 ). The newly introduced zonal (not subzonal)
scheme was proposed in advance (Reboulet et
al., 2014) to be valid as a "standard zonation" for the Valanginian of
the Mediterranean Tethys. However, at the moment, papers that confirm the
zonation proposed for the lower Valanginian are lacking for the pre-Vocontian
Basin except for the unpublished work of Kenjo (2014). In
Table 1
the
different zonations (Reboulet et al., 2011, 2014; Company & Tavera, 2015) are
shown and the correlation for the lower Valanginian as proposed by the latter
authors, is partially followed.
At present, the modified ammonite zonation as proposed by Company
and Tavera (2015)
appears to deviate, at the boundary of the Pertransiens Zone to
Neocomiensiformis Zone, when applied to the pre-Vocontian Basin. The nominal
species for the Hirsutus Sz (Baronnites
hirsutus; Pl. 1 , fig. 14) is quite frequent in Vergol (but not mentioned by
Reboulet, 1996, or Kenjo,
2014) (see Fig. 5 ; indicated by ammonite symbol). It occurs first in the inter-bed
VGL045-046 (= V47-48), i.e., several beds below the FO of the index species of the Neocomiensiformis Zone of
Company and Tavera (2015). The latter is mentioned by Kenjo
(2014) and Reboulet (2017b) from bed V53 (= VGL051), but specimens
comparable to Kenjo (2014, Pl. 1 , fig. 5) occur also one bed lower (det.
J. Klein).
Other striking differences that exist between the two palaeogeographical domains are in the relative abundance of several ammonite taxa. These differences are most apparent in the rarity of Valanginites in the proximal parts of the pre-Vocontian Basin in the lower Valanginian, and the near absence of species like Saynoceras contestanum. However, these differences might be artificial, and be based on the more thorough investigations in the Betic Cordillera and, in part, this might be explained by the high abundance of (juvenile) haematitic internal casts in the pre-Vocontian Basin.
In
the pre-Vocontian Basin the upper Valanginian (Figs.
2
- 3 ) is more thoroughly investigated regarding ammonites as compared to the
lower Valanginian, resulting in a much more uniform distribution pattern.
However, some additions are
made to the proposed scheme, because of their significance in the temporal
distribution of the belemnites. These include the use of the "Neocomiensis
Sz" (Fig. 3 ) introduced by Atrops and Reboulet
(1993) for the upper
part of the Verrucosum Sz without the index specimen, either of the name-giving
Subzone or with the index specimen of the following Subzone. This interval is of
special interest for belemnites in the pre-Vocontian Basin, as it includes the
transition from typical early to late Valanginian faunas, the "Verrucosum-event" of Janssen and Clément (2002).
The Berriasian-Valanginian boundary
The
boundary between the Berriasian and Valanginian, i.e., the base of the Valanginian
is placed at the FO of Calpionellites darderi, apparently almost
co-occurring with the FO
of the ammonite T.
pertransiens (Blanc et al., 1994; Bulot
et al., 1995, 1996; Aguado
et al., 2000; Company & Tavera,
2015). Blanc
et al. (1994)
placed this boundary in Vergol at the bed Mb210 (= VGL014; = V01; Fig. 6 ).
However, the FO
of T. pertransiens appears to be earlier (det. J. Klein), bed W93 (= base
B138; Fig. 6 ), and thus occurring throughout the larger part of the latest Berriasian
Otopeta Sz sensu Blanc et
al. (1994). Kenjo (2014) placed this boundary at a different, even
slightly early, level (B136; Fig. 6 ; see also Reboulet,
2017a) based on the FO of the ammonite Neocomites
premolicus and doubtful T. pertransiens
(see Kenjo, 2014, p. 30). Thus, the recent work of Kenjo
(2014)
and the findings presented here indicate that the FO of C.
darderi and T. pertransiens are even
further apart than previously assumed.
In
the lowest Valanginian bed-by-bed correlation appears to be more difficult (but
see coloured bands in Fig.
4 ). In addition there is a lack of ammonite data in
several sections mentioned. Still some biostratigraphical tie points are
potentially present. In several sections an abundance of Leptoceras
occurs, apparently being a correlative level in the upper Berriasian Otopeta Sz
(Fig. 6 ). This level can be found throughout the
investigated area and was mentioned by Thieuloy (1966) from the
Grande-Chartreuse. So for the
moment, within the Pertransiens Zone and latest Berriasian some correlation
points seem to exist, i.e., the abundance of Leptoceras in the Otopeta Sz and some beds in the Pertransiens Zone
(Fig. 6 ), resulting in the relative position of belemnites (FO of) that occur
around the base of the Valanginian (as based on belemnites). However, this level
does not coincide with the FO of any species hitherto used to fix the lower
boundary of the Valanginian in the pre-Vocontian Basin (the calpionellid C.
darderi or the ammonite T.
pertransiens).
The Valanginian-Hauterivian boundary
The
base of the Hauterivian is defined by the FO of the ammonite genus Acanthodiscus,
which marks the base of the Radiatus Zone (Mutterlose et al.,
2020). The GSSP for the base of the Hauterivian Stage is
defined in the La Charce section (LCH) at the base of bed 189 (Reboulet et
al., 1992). This bed corresponds to bed 380a in ANG and CHE (Fig.
2 ).
In Figures 2
- 3
- 4
- 5
- 6
the occurrences of the belemnites are
shown for the most extensively investigated sections. Based on the temporal
distribution in these sections combined, a zonal scheme is proposed (see below).
In Figure 9
the temporal distribution of belemnites is shown for the latest Berriasian to
earliest Hauterivian. As
mentioned previously, correlations between sections become complicated below the
Hirsutus Sz. This is due to lithological differences caused by slumping and
debris-flows, and also because the sedimentary succession appears more variable,
resulting from differences in weathering patterns and primary
limestone-dominated intervals.
It turns out that characteristic Valanginian belemnite species, such as, B. exstinctorius, C. orbignyanus, M. blainvillei, and H. aff. pistilliformis, do have their FOs above the FO of the ammonite T. pertransiens.
In
addition, some belemnites that show their FOs in the uppermost Berriasian
disappear shortly after the FO of T. pertransiens. One of
these species is D. tornajoensis. However, in the southeast of Spain it ranges into the Hirsutus Sz
(Fig. 9 ),
while Castellanibelus sp. E and D.
lata lata range into the lowermost
Valanginian. Duvalia lata
constricta and Pseudobelus gr. bipartitus
are taxa typical of the uppermost Berriasian ranging in the Valanginian.
The earliest Valanginian belemnites (Pertransiens Z) in the pre-Vocontian Basin are largely dominated by taxa icluding B. gr. conicus, C. orbignyanus, H. aff. pistilliformis, and M. blainvillei, while D. lata constricta is common and a few typical Berriasian species occur rarely (Castellanibelus sp. E, D. lata lata, and D. tornajoensis). In the Hirsutus Sz a few characteristic belemnites have their FOs, including C. vaubellensis and D. superconstricta, while B. (gr.) conicus, B. exstinctorius, C. orbignyanus, H. aff. pistilliformis, and M. blainvillei occur abundantly. Above, in the Subcampylotoxus Sz, new taxa appear, such as, D. crassa, D. hispanica, and H. lebresensis, while B. exstinctorius becomes common but disappears shortly after.
Approaching the upper
Valanginian, several earliest Valanginian species are replaced and
characteristic species like D. emericii
and B. heres occur. Eventually,
though some species are already rare, the uppermost lower to lowermost upper
Valanginian is characterized by the last occurrence (hereafter LO) of almost all
taxa so far present (Figs. 3
- 4 ). Characteristic taxa that do not occur in
stratigraphically younger sediments include: Berriasibelus, Castellanibelus,
Mirabelobelus, D. emericii, D.
gr. lata, and some species of Hibolites
(see Janssen & Clément, 2002; data herein presented, Fig. 9 ).
Only taxa that relate to P.
bipartitus range up to the base of the Pronecostatum Sz succeeded by a new
species herein called Pseudobelus sp. B.
This assemblage change is accompanied by the abundant occurrence of belemnites that are either homeomorphic, or identical to H. jaculoides. The latter species is well-known from the Boreal-Atlantic and Boreal-Arctic Provinces (eastern England, northern Germany, noth-east Greenland, Svalbard; Swinnerton, 1937; Mutterlose, 1978, 1990; Doyle & Kelly, 1988; Alsen & Mutterlose, 2009).
In
France, at least from the top of the Verrucosum Sz up to the Peregrinus Sz a
specimen very similar to H. jaculoides (herein
named H. aff. jaculoides) occurs regularly and commonly in abundance in the
investigated sections in the distal areas. In addition, a few occurrences are
recorded at the top of the Peregrinus Sz and the base of the Nicklesi Sz.
Moreover, it constitutes a near mono-specific association in the sediments of
the younger parts of the Verrucosum Zone in the more proximal parts of the
Vocontian Basin (Fig.
8 ), and apparently disappears in the Nicklesi Sz.#
The post-Verrucosum-event
succession is further characterized by D.
binervia and D. elongata. In younger levels the genus Adiakritobelus occurs, while H.
aff. jaculoides becomes rare and
disappears. Now, Adiakritobelus become
an important constituent of the belemnite associations and also the species that
relate to D. binervia
diversify further, with D. gervaisiana,
D. kleini, D. oehlerti
(however, so far not known from the southeast of France), and
D. variegata. Several of the
groups of species that characterize the upper Valanginian can be found up to and
including the sediments that are attributed to the lowermost Hauterivian
Radiatus Zone (Fig.
2 ), being replaced in the younger part of the latter zone by a
different association of belemnites (cf. Janssen, 2009) characterized by Duvalia
gr. dilatata and Hibolites gr.
subfusiformis.
|
Figure 9:
Stratigraphic
distribution of belemnites in the Valanginian of ANG/CHE, VBL, VGL, LCH, and BLB
(all SE of France),
and to sections Y.Cl(2), Y.G, Y.T, and Tornajo (all SE of Spain). Bed numbers of French sections
after personal field observations and after Busnardo (1979), Reboulet et al.
(1992), Bulot et al.
(1993a), Blanc et al.
(1994), Bulot (1995), McArthur et al.
(2007), Kenjo
(2014), and Reboulet
(1996). Bed numbers of Spanish sections after personal
field observations, Company and Tavera
(2015) and Aguado et al.
(2018). The positions of the published "possible Berriasian/Valanginian
boundaries", based on data from VGL, are indicated by black arrows and are
indicated by circled "1"
and "2".
For the legend see Fig.
2 |
The distal - proximal trends in the distribution of the belemnites
In general, belemnites are more abundant and more diverse in distal sections,
except for some condensed levels in the proximal areas. However, in distal
sections, abundances and diversities fluctuate (Figs. 2
- 3
- 4
- 5
- 6
- 7
- 8 ). In the pre-Vocontian
Basin belemnites appear most common in the Hirsutus Sz (Fig. 5 ), around the
boundary between the lower and upper Valanginian (Figs. 3
- 4 ), and in the
lowermost upper Valanginian (Fig. 3 ). This is
partly explained by lithology, as
this interval consists of more marly sediments; however similar marl dominated
intervals in the upper Valanginian and uppermost lower Valanginian do not yield
abundant belemnites. Therefore these differences in abundance are likely due to
palaeoenvironmental causes, such as higher sea-levels, accommodation space,
food-supply, and also selective processes due to mass-flows.
In
the proximal areas, belemnites become significant from the uppermost lower
Valanginian onwards (Fig.
8 ). They occur only very sporadically in older
sediments. However, in PRY and GIN (Fig. 7 ; intermediate sections), the
uppermost Berriasian and the lowermost Valanginian yield belemnites in
abundance.
Some
genera and/or species do occur solely in the distal parts of the basin, or are
very rare in the more proximal parts, these include: Berriasibelus,
Castellanibelus, and Mirabelobelus.
While Duvalia, Adiakritobelus, and hibolitids are sometimes very common in the
proximal parts, but also occur in the distal parts in abundance. Size
differences are noted among some belemnites (see Reboulet,
2001, regarding
ammonites) related to combinations of intrinsic and external factors, like
species longevity, maturity time, temperature, environmental range, and
food-supply. This is especially noticeable in H. aff. jaculoides. Rather
robust specimens (Pl. 11 , fig.
7) can be found in the more distal sections (ALL, ACL) as compared to the
proximal area.
Belemnite zonation for the Valanginian
In
the 19th century French researchers discriminated roughly between "Valanginian" (zone à Belemnites bicanaliculatus; zone à Duvalia
lata/conica, zone à Duvalia emericii) and "Hauterivian"
sediments (zone à Belemnites dilatatus). It was only recently (Table
2 )
that in the southeast of France, a
preliminary proposal for a zonation based on belemnites was introduced in a
congress abstract and a manuscript (Gayte, 1982, 1984). This was based on
duvaliids for
parts of the Valanginian-Hauterivian, but without further explanation. This was
partially copied and published by Christensen and Combémorel
(1998, chart 5), but has never been elaborated on or formalized (e.g., no type section
or bed-numbers were indicated).
More
or less simultaneously with the latter paper, Janssen
(1997) and Clément (1999) defined zonations
based on belemnites from the Betic Cordillera (Spain) and the Barret-sur-Méouge
area, respectively (Table
2 ). However, the first (Janssen,
1997) is no
longer applicable as some of the material that was used for that zonation was
misidentified (see Janssen, 2003, and subsequent papers), and the latter (Clément,
1999) was published as a master's thesis and never formalized. Eventually, Janssen
and Clément (2002) divided part of the Valanginian sedimentary record
into three assemblage zones based on the temporal distribution of belemnites
based on a few sections in the southeast of France (Table
2 ).
Table 2: Different zonal schemes compared, as proposed by the various authors in the pre-Vocontian Basin. (A)Z = (ammonite) zone, (A)Sz = (ammonite) subzone, SBZ = superbiozone, BZ = biozone, Hor. = Horizon. BA = belemnite association. J&C = Janssen & Clément. For generic affiliation see text. Ammonite subzones in blue are (at the moment) not included in the recommended zonation, but are sometimes used in the papers indicated in the text. |
|
The
framework for the zonation herein proposed is based on bed-by-bed correlation in
the pre-Vocontian Basin, resulting in 6 zones (Fig. 10 ). All the Valanginian
zones and subzones are defined by the FO (except for one) of the index species
and are furthermore characterized by distinctive associations of belemnites.
However, to date no species or assemblages of belemnites appear to clearly mark
the position of the Berriasian-Valanginian boundary hitherto proposed in the
pre-Vocontian Basin. Typical Valanginian belemnites (C.
orbignyanus, B.
conicus, B. exstinctorius,
M. blainvillei, and H.
aff. pistilliformis) occur already within the Pertransiens Zone, while a
few typical Berriasian species have there LOs approximately there (Fig. 9 ).
Herein, the uppermost Berriasian has yielded several belemnites that appear to be restricted to this substage. However, to date, their exact distribution is as-of-yet unknown and it is out of the scope of this paper (but will be treated in a subsequent paper). Among others, these belemnites include: B. aff. exstinctorius sp. 1, B. incertus, D. miravetesensis, D. papretravinensis, G. mayeri, and M.? orbignyi.
The
Berriasian-Valanginian boundary is defined by the FO of C.
darderi (Fig. 6
indicated by (1.)) in VGL and is about 6 m higher as
compared to this boundary based on ammonites (Fig. 6
indicated by (2.)).
The
following zonation based on belemnites is proposed for the pre-Vocontian Basin (Fig. 10
). This zonation is based mainly on the succession of different species
of Duvalia (Fig. 11 ) because they are
generally common, sometimes abundant, have relatively short stratigraphic
ranges, and probably the most easily recognizable among the various belemnite
taxa. Herein "(Range) (Sub)Zones", "Taxon-range (Sub)Zones", and "Abundance (Sub)Zones" are defined based on the first appearance datum(s)
(which
are biohorizons; hereafter FAD). They are actually the FOs (lowermost documented
occurrences of the taxon in the specific sections) combined.
|
Figure 10:
Stratigraphic
(sub-)zonation for the Valanginian of the pre-Vocontian Basin. Circled "1" and "2" indicate possible position of Berriasian-Valanginian
boundary. Yellow band indicates relative position of Leptoceras
abundance. For generic affiliation of belemnites see text. Bed numbers in type
sections (Cheiron-Angles, CHE-ANG; Vergol, VGL, and VBL, Vaubelle) are indicated,
e.g., bed "367 m" indicates marl on top of calcareous bed 367. In VGL the
marl bed above V11 corresponds to B150 sensu
Kenjo
(Fig.
4 |
|
Figure 11: Distribution and relative abundances of the belemnites in the pre-Vocontian Basin. Here, "duration" of each belemnite-subzone (left column) is arbitrarily equalized. Ammonite subzones are indicated to the right. Stage and sub-stage boundaries are indicated by hatched red lines and red arrows. Abbreviations used: Haut. = Hauterivian, u.Be. = upper Berriasian. |
(1) Castellanibelus orbignyanus Zone
Lower
boundary definition: FAD of the index species (Pl. 7 , figs. 7-10).
Secondary markers: FOs of B. exstinctorius, B. conicus, H. aff. pistilliformis, and M. blainvillei.
Correlation to Ammonite Zones: restricted to the Pertransiens zone.
Type section: VGL (interbed V11-12 to bed 042).
Auxiliary reference section: VBL (interbed P06-07 to bed 044).
Remarks: This is the first typical Valanginian belemnite association. The LOs of Berriasian taxa, such as D. lata lata, D. lata constricta and D. tornajoensis occur within this zone.
(2) Duvalia superconstricta Taxon-range Zone
Lower
boundary definition: FAD of the index species (Pl. 7 , figs. 27-28).
Definition: total range of the index species.
Secondary markers: total range of C. vaubellensis.
Correlation towards Ammonite Zone: From to the uppermost part of the Pertransiens zone to the middle part of the Neocomiensiformis Zone.
Type section: VGL (interbeds 042-043 to 072-073).
Auxiliary reference section: VBL (interbeds 044-045 to 072-073).
Remarks: several taxa are very abundant, especially B. gr. conicus, C. orbignyanus, and M. blainvillei. The FO of H. lebresensis is in the uppermost part.
(3) Duvalia crassa Zone
Lower
boundary definition: FAD of the index species (Pl. 8 , figs. 1-6).
Secondary markers: LOs of B. exstinctorius, B. conicus, C. orbignyanus, and H. aff. pistilliformis. In addition, the FO of D. hispanica, while B. aff. exstinctorius sp.2 is restricted to this zone.
Correlation to Ammonite Zones: Upper part of the Neocomiensiformis Zone to lower part of the Inostranzewi Zone.
Type section: VGL (bed 073 to interbed 089-090).
Auxiliary reference section: VBL (bed 073 to interbed 089-090).
Remarks: Most taxa common in the previous zone prevail here too. Gradually Hibolites become more abundant and Pseudobelus becomes more and more omnipresent and abundant. The FOs C. picteti and H. laryi is in the uppermost part.
(4) Duvalia emericii Zone
Lower
boundary definition: FAD of index species (Pl. 8 , figs. 9-10, 19-22).
Secondary marker: the FO of B. heres.
Type section: VGL (bed 090 to interbed 105b-106).
Correlation to Ammonite Zones: Inostranzewi to lower part of the Verrucosum Zone (Verrucosum Subzone).
Auxiliary reference section: ANG (bed 295 to interbed 306b2-307).
Remarks: Pseudobelus is very common and often abundant. This Zone includes two Subzones which mark the boundary between the lower and upper Valanginian.
(4a) Berriasibelus heres Subzone
Lower boundary definition: FAD of D. emerici.
Secondary
marker: FO of B. heres (Pl. 8 , figs. 23-27).
Correlation to Ammonite Zones: Restricted to the Inostranzewi Zone.
Type section: VGL (bed 090 to interbed 102-103).
Auxiliary reference section: ANG (bed 295 to interbed 304a-305).
Remarks: Pseudobelus, C. picteti and H. laryi are common.
(4b) Duvalia emericii Abundance Subzone
Definition: the abundant occurrence of the index-species.
Additional characteristics: the abundance occurrence of H. aff. jaculoides.
Correlation to Ammonite Zones: Restricted to the Verrucosum Subzone.
Type section: VGL (interbeds 102-103 to 105b-106).
Auxiliary reference section: ANG (interbeds 304a-305 to 306b2-307).
Remarks: Both diversity and abundances are generally high. The transition to the next Zone is marked by the so-called "Verrucosum-event" of Janssen and Clément (2002). Herein, most of the typical early Valanginian taxa vanish.
(5) Duvalia elongata Zone
Definition:
the total range of the index species (Pl.
9 , figs. 21-22, 31-32).
Secondary marker: the FO of D. binervia.
Correlation to Ammonite Zones: Verrucosum Zone (from the "Neocomiensis" Subzone) to the Peregrinus Zone (chiefly Peregrinus Subzone).
Type section: VGL (interbeds 105b-106 to 137-138).
Auxiliary reference section: ANG (interbeds 306b2-307 to 338b-c).
Remarks: Characteristicly, the belemnite association is of low diversity and high abundance; in addition it is characterized by the size decrease of the Pseudobelus taxa and the general abundance of H. aff. jaculoides. This Zone includes two Subzones.
(5a) Duvalia elongata Subzone
Lower boundary definition: the FAD of the index species.
Secondary marker: the FAD of D. binervia.
Correlation to Ammonite Zones: Restricted to the "Neocomiensis" Subzone.
Type section: VGL (interbeds 105b-106 to 122-123).
Auxiliary reference section: ANG (interbeds 306b2-307 to 312d-e).
Remarks: H. aff. jaculoides, Pb. gr. bipartitus and the index species are (very) abundant, while the overall diversity is low.
(5b) Pseudobelus sp. B Subzone
Lower
boundary definition: FAD of the index species (Pl. 10 , figs. 1-4).
Correlation to Ammonite Zones: Pronecostatum Subzone to Peregrinus Subzone but for the uppermost part.
Type section: VGL (interbeds 122-123 to 137-138).
Auxiliary reference section: ANG (interbeds 312d-e to 338c).
Remarks: Adiakritobelus occurs first (A. gr. rogeri and A. brevirostris) in the uppermost part.
(6) Duvalia variegata Zone
Lower
boundary definition: FAD of the index species (Pl. 10 , figs. 13-18).
Secondary markers: FOs of D. kleini and A. minaret.
Correlation to Ammonite Zones: Uppermost part of the Peregrinus Subzone to Furcillata Zone (but for the Callidiscus Subzone).
Type section: VGL (interbeds 137-138 to 184-185).
Auxiliary reference section: ANG (beds 338c to 374).
Remarks: This zone is characterized by the radiation and dominance of Adiakritobelus taxa. Duvaliids become less abundant, and H. aff. jaculoides disappears from the assemblage. Tentatively this zone can be divided into intervals based on the succession of Adiakritobelus (abundance of A. brevirostris and A. minaret; FO of A. peyroulensis; FO of A. rogeri), but more material is needed to confirm the succession of assemblages. In addition, very elongated hibolitid belemnites (H. gr. longior and/or Vaunagites?) and Pseudobelus sp. A occur for the first time. With the exception of Adiakritobelus, the latter species typically characterize the sediments around the Valanginian-Hauterivian boundary.
(7) Duvalia gervaisiana Zone
Lower
boundary definition: FAD of the index species (Pl. 10 , figs. 25-28).
Upper boundary definition: FAD of D. dilatata (cf. Janssen, 2009, Fig. 11).
Correlation to Ammonite Zones: Callidiscus Subzone (topmost part of the Furcillata Zone) to the boundary between the Radiatus and Loryi Zone (not exactly known yet).
Type section: CHE (beds 374 to interbed 401-402).
Auxiliary reference section: ANG (beds 374 to interbed 401-402).
Remarks: Typical late Valanginian taxa, such as, Duvalia gr. binervia and Adiakritobelus disappear within this zone. Hibolitid taxa are relatively common. Apparently, A. robustus has a short range in the upperpart of this zone. This zone includes the Valanginian-Hauterivian boundary. It includes two Subzones and an undefined upper part.
(7a) Duvalia gervaisiana Subzone
Lower boundary definition: FAD of the index species.
Correlation to Ammonite Zones: Callidiscus Subzone to lower part of the Radiatus Zone.
Type section: CHE (bed 374 to interbed 390-391).
Auxiliary reference section: ANG (bed 374 to interbed 390-391).
Remarks: includes the LO A. peyroulesensis, while A. rogeri is relatively common. It includes the Valanginian-Hauterivian boundary.
(7b) Adiakritobelus robustus Taxon-range Subzone
Definition:
total range of the index species (Pl. 12 , figs. 7-9).
Correlation to Ammonite Zones: Part of the upper part of the Radiatus Zone.
Type section: CHE (beds 391-394).
Auxiliary reference section: ANG (beds 391-394).
Remarks: includes the LO of D. gervaisiana.
(7c) the upperpart of this zone is not subzoned.
The
zonation above, as applied in the pre-Vocontian Basin, is chiefly defined on the
FOs of belemnite taxa and correlated to ammonite datums available from various
sources (see text above for references). Outside the investigated areas,
ammonite datums might be available, but details about the temporal distribution
of belemnites are generally lacking except for some sections in the southeast of
Spain (Fig. 9 ). These sections have been investigated for ammonites by
Company and Tavera (2015). Despite the relatively low abundances of belemnites,
it is obvious that some differences occur between the ammonite and belemnite
datums, which is especially apparent in the latest early Valanginian (the FO of D.
emericii) and in the earliest late
Valanginian (the FO of H. aff. jaculoides).
Otherwise, the general succession of species seems to be comparable except for
individual abundances.
Table 3:
Ammonite
(sub-) zonation versus Belemnite (sub-) zonation for the pre-Vocontian Basin.
Ammonite subzones in blue are not (yet) formalized at the moment. |
|
Family Duvaliidae Pavlow, 1914
Genus Duvalia Bayle, 1878
Type: Belemnites dilatatus Blainville, 1827
Typically, members of this genus are more or less strongly compressed (laterally-compressed), characterized by a dorsally placed alveolar groove and an asymmetrical profile. Among the Valanginian Duvalia two morphological (stratigraphical) groups can be distinguished (Janssen, 2018), principally based on common taxa: the lata-group (Berriasian - early Valanginian) and the binervia-group (late Valanginian - earliest Hauterivian).
The binervia-group is characterized by strongly-compressed (laterally-compressed), small to medium sized rostra, with a short alveolar groove. The outline (lateral view) is leaf-like to elongated, while the profile (dorsal or ventral view) is hastate to elongate sub-conical. Principally, these taxa occur in the late Valanginian to earliest Hauterivian, except for their predecessor D. emericii, which first occurs in the latest early Valanginian. The binervia-group including its predecessor is derived through species that relate to the lata-group. The latter is especially abundant and diverse in the uppermost Berriasian (Alpillensis-Otopeta Sz) and lowermost Valanginian (Pertransiens Zone), but is much more uncommon throughout the rest of the lower Valanginian.
The
lata-group includes: D.
lata constricta, D. lata
lata (Pl. 7 , figs. 11-12), D. miravetesensis
(Pl. 7 , figs. 13-14), D. tornajoensis
(Pl. 5 , figs. 3-6), D. aff. tornajoensis
(Pl. 5 ,
figs. 7-8), D. superconstricta (Pl. 7 ,
figs. 27-28), D. crassa
(Pl. 8 , figs. 1-6), and D. hispanica
(Pl. 8 , figs. 7-8, 11-14;
Pl.
9 , figs. 33-34). In between the lata- and
the succeeding binervia-group, Duvalia
emericii (Pl. 8 , figs. 9-10, 19-22) is common in the uppermost lower
Valanginian and lowermost upper Valanginian. In the upper Valanginian the binervia-group
dominates (Fig.
2 ). The latter group is common both in the distal as well as the
proximal parts of the basin. The binervia-group includes: D. binerva
(Pl.
9 , figs. 3-20, 23-30), D. elongata
(Pl.
9 , figs. 31-32; Pl. 10 , figs. 11-12), D.
kleini (Pl.
9 , figs. 1-2), D.
variegata (Pl. 10 , figs. 13-18), D.
oehlerti (Pl. 10 , figs. 19-20), and D.
gervaisiana (Pl. 10 , figs. 25-28).
Genus Berriasibelus Delattre, 1952b
Type: Belemnites exstinctorius Raspail, 1829 (OD)
The
genus occurs abundantly in the distal parts of the pre-Vocontian basin, is
common in the intermediate sections, but appears to be very rare in the proximal
settings investigated. Most of the specimens can be attributed to B. (gr.) conicus
(Pl. 7 ,
figs. 15-24) which is especially abundant in the Hirsutus Sz. In the
investigated distal sections B.
exstinctorius (Pl. 2 , figs. 22-23) occurs regularly, being characterized by
a sudden and strong lateral flattening (compression) of the apex, the broad
alveolar groove, the deep alveolus and the short conical shape of the rostrum;
it appears first in the lower part of the Pertransiens Zone and disappears in
the uppermost lower Valanginian (Inostranzewi Zone). It is preceded by Berriasibelus
aff. exstinctorius sp. 1 (Pl. 5 ,
figs. 20-21, 24-25) which is characterized by a tapering-down-the-apex aspect of
the rostrum and a well-rounded cross-section in the apical region, that lacks
the lateral flattened apex. The youngest morphologically comparable specimens
show a very robust outline (B. aff. exstinctorius
sp.2; Pl. 8 , figs. 15-18). These rostra are succeeded by Berriasibelus
heres (Pl. 8 , figs. 23-27), disappearing in the lowermost upper Valanginian
(Verrucosum Sz).
Typically,
but being rare, B. incertus occurs in the
uppermost Berriasian (Pl. 5 ,
figs. 26-27) to lowermost Valanginian. The
conglomerate in VBL yields a.o. B. kabanovi
(Pl. 5 ,
figs. 9-10) and B.
triquetrus. The temporal distributions of the latter species are not yet
known, but the few bed-by-bed records from Spain suggest occurrences in the
uppermost Berriasian and possibly lowermost Valanginian (Fig.
4 ). Actually, the
latter species does not occur together with B.
exstinctorius, a characteristic early
Valanginian taxon. Among the Duvaliidae, Berriasibelus
appears to be the most abundant taxon in the lower Valanginian, followed by Castellanibelus.
Genus Castellanibelus Combémorel, 1972
Type: Belemnites Orbignyanus Duval-Jouve, 1841 (SD)
The
genus occurs very abundantly in the distal
parts of the basin, is common in intermediate sections, but appears to be very
rare in the most proximal settings investigated. The genus occurs at
least from the uppermost Berriasian onwards, ranging into the lowermost upper
Valanginian (Verrucosum Sz). The latest Berriasian species is characterized by a
rather elongated cylindrical rostrum (Castellanibelus
sp. E; Pl. 5 ,
figs. 1-2; Pl. 7 , figs. 3-4). Most
common is C. orbignyanus (Pl. 7 , figs. 7-10). It first occurs in the lowermost
Pertransiens Z, co-occurring with a robust morph (C. vaubellensis; Pl. 7 ,
figs. 1-2) in the Hirsutus Sz and eventually being replaced by another near
cylindrical morph in the uppermost lower Valanginian (C. picteti; Pl. 7 ,
figs.
5-6).
Genus Gillieronibelus Janssen, 2003
Type: Belemnites Mayeri Gilliéron, 1873 (SD)
This
genus occurs in the uppermost Berriasian, but reworked specimens can be found in
the Pertransiens Z (lowermost Valanginian) at VBL (Fig.
4 ). The exact temporal
distribution is not known, but it has been mentioned previously from the
Paramimouna to Alpillensis Z from the southeast of Spain (Janssen,
2003).
It is very rare in GIN (Pl. 5 , figs. 28-30), but occurs quite in abundance in
the conglomerate at VBL (Pl. 5 , figs. 11-15).
Genus Pseudobelus Blainville, 1827
Type: Pseudobelus bipartitus Blainville, 1827 (SMT)
Pseudobelus
occurs in fluctuating abundances from the distal to the more proximal areas. It
is characterized by the 8-shaped cross-section of the rostrum
solidum. Typically, the temporal distribution shows size decrease from the
Berriasian into the upper Hauterivian (Rouville, 1872). Pseudobelus
gr. bipartitus (Pl. 10 , figs. 5-8) occurs at least from the upper
Berriasian onwards, ranging into the lowermost upper Valanginian Pronecostatum
Sz. Herein, it is replaced by a new species Pseudobelus
sp. B; Pl. 10 , figs. 1-4). In the uppermost Valanginian, from the topmost part
of the Peregrinus Zone, another new species Pseudobelus
sp. A (sensu Janssen, 2009) occurs.
Family Hibolitidae Nerodenko, 1983
Among this family, Hibolites dominates in the Valanginian, but abundances can fluctuate heavily. In addition, Mirabelobelus occurs quite abundant and regularly in the lower Valanginian but it is only in the upper Valanginian that various other genera appear, like Adiakritobelus and Vaunagites. However, so far, the latter, extremely elongated taxon is unequivocally known only from proximal areas (Combémorel & Gayte, 1981), and possibly Morocco (Mutterlose & Wiedenroth, 2008). Juvenile or sub-adult specimens might occur in more distal areas, but could not be recognized as such so far. Especially at the transition from the early to the late Valanginian, Hibolites become extremely abundant. They diminish in the late Valanginian in favour of Adiakritobelus. While in the Hauterivian and earliest Barremian, Hibolites become dominant again, while other genera like Adiakritobelus and Vaunagites disappear in the earliest Hauterivian. In the late Valanginian, at least from the Peregrinus Sz on, in the proximal facies, very elongated hibolitid belemnites occur (Vaunagites or Hibolites gr. longior), however, with a relatively short but clear alveolar groove.
Genus Hibolites auctorum (non Hibolithes Denys de Montfort, 1808)
The monotypical genus Hibolithes Denys de Montfort, 1808, is clearly an Early Cretaceous duvaliid. Given the taxonomic conundrum this implies, for which the solution is outside of the scope of this paper, the most commonly used 'alternative' is for the moment preferred.
Within
the Valanginian taxa several hibolitid species can be distinguished. The
lowermost Valanginian yields a slender very elongated hibolitid often without a
clear alveolar groove (H. aff. pistilliformis; Pl. 11 , figs. 10-13; note the figured specimens show a faint alveolar groove).
This species is especially abundant in the Hirsutus Sz. It is succeeded by a
less elongate, slightly depressed taxon with a clear alveolar groove, reaching
well beyond the protoconch (H. lebresensis, Pl. 11 ,
figs. 14-23) and eventually the less elongate,
slightly stout, H.
laryi (Pl. 11 , figs. 8-9). The latter species is generally pitted by Acrothoracia
and first occurs in the late early Valanginian and disappears in the earliest
late Valanginian. Hereafter, the Valanginian hibolitids are dominated by the (sudden)
appearance of H.
aff. jaculoides (Pl. 11 , figs. 1-7). It occurs from the Verrucosum
Horizon onwards, being especially abundant in the younger parts of the
Verrucosum Zone and is also very common in the proximal part of the basin.
Apparently size differences exist between specimens from the proximal parts of
the basin and those from the distal part of the basin. The specimens from the
proximal areas appear to be more robust, or of larger size. This is a common
phenomenon among cephalopods and probably relates a.o. to the availability of
more food (Reboulet, 2001). Among the
Tethysian hibolitids morphological variation, possibly
expressed as dimorphism, has been suggested (Gayte, 1984). After the
Verrucosum-event H. aff.
jaculoides is extremely common and abundant. However, it disappears in the
Peregrinus Zone, in the base of the Nicklesi Sz, both in the proximal as well as
in the distal areas. Apparently, both Adiakritobelus
and H.
gr. longior are the succeeding
taxa. However, long elongated hibolitid taxa (H. gr. longior) occur
already from the Peregrinus Sz on, at least in the proximal setting. They
eventually gave rise to the extremely elongated Vaunagites.
Genus Adiakritobelus Janssen & Főzy, 2004
Type: Hibolites rogeri Delattre, 1952a (OD)
A
genus characterized by a hibolitid morphology, often more robust as compared to
typical elongated and subhastate Hibolites.
The genus occurs from the late Valanginian onwards, and disappears in the
earliest Hauterivian. In the pre-Vocontian Basin, the genus is quite common.
Both distal as well as proximal areas yield Adiakritobelus
commonly. Among the first are A. brevirostris
and A. minaret (Pl. 12 , figs.
12-17). These are followed by the more elongate A. gr. rogeri and
extremely elongate A. peyroulesensis
(Pl. 12 , figs. 1-6). The youngest species is very robust (A.
robustus; Pl. 12 , figs. 7-9). Outside
the area of investigation the genus is so far rarely described or recognized. It
occurs in Hungary (Janssen & Főzy,
2004, Pl. II, figs.
11-12; and possibly Bujtor et al., 2013, Fig. 6.Q1-2),
the southeast of Spain (Pl. 12 ,
figs. 10-11, 16-17; Janssen, 2009,
Pl. 5 ,
figs. 11-13), the Czech Republic (Vanková & Kosták,
2019), Rumania
(Constantin, 2001), and Morocco (pers. obs.; specimens in the collection
of Wiedenroth, University of Bochum, Germany). However, they were neither
mentioned nor figured by Mutterlose and Wiedenroth
(2008).
Genus Mirabelobelus Janssen & Clément, 2002
Type: Belemnites bicanaliculatus Blainville, 1827 (OD)
This
small sized genus is very common in the lower Valanginian in the pre-Vocontian
Basin. Apparently, The FO of Mirabelobelus
blainvillei is in the Pertransiens Z. Lateral lines can be well-developed
giving the taxon a superficial pseudobeloid appearance. The Valanginian species
shows some morphological plasticity (Pl. 12 , figs. 24-39). Exceptionally,
specimens show a short alveolar groove on the rostrum solidum. Lateral lines can
be rather insignificant, like thin scratches, but often like in Pseudobelus, produce a symmetric 8-shaped cross-section of the
rostrum. Size differences are apparent without clear indication of ontogenetical
differences, some species appear more slender and elongate, while others appear
stouter. However, in all specimens, the alveolar area is missing, apparently
being very fragile or non-calcitic. It is only known from a few examples and a
few specimens outside this geographical area (Janssen, 2003,
Tornajo,
Spain; coll. A. Ippolitov, Crimea).
Janssen and Clément (2002) originally include two species within this
genus. The second is an enigmatic species depicted by Orbigny
(1840),
that originates from Andruze (= Anduze), north-east of GIN (Fig.
1 ). It is
figured by Janssen (2003, Pl. 1, figs. 8-9; erroneously indicated as figs.
5-6 in plate explanation) from Mirabel and here refigured (Pl. 12 , figs. 40-41).
However, attribution to the genus is highly uncertain and most likely the
figured specimen represents a duvaliid.
Mirabelobelus?
orbigny is a late Berriasian species. It occurs in the Picteti and
Alpillensis Z of PRY, the Alpillensis Z of GIN, and few species are known from
the upper Berriasian (Picteti Z) of BME. Contrary to the type species, it shows
a clear alveolar groove and the alveolar area is well-preserved. It is without
the alveolar constriction seen in M. blainvillei.
The pseudobeloid appearance, i.e., the 8-shaped cross-section, is most apparent in the apical
area.
In this aspect there seems to be some relation to, or it is homeomorphic with,
the Late Jurassic - early Berriasian "Pseudobelus"
around Belemnites zeuschneri Oppel, 1865, or more like "Pseudobelus"
gr. pilleti (Pictet, 1868; Pl. 12 , figs. 42-46). Otherwise the apical area is characterized by some lateral
compression, while the alveolar area shows a much more angular, rounded
cross-section.
1.)
Based on the temporal distribution of belemnites in the Valanginian of the
Vergol, Vaubelle, and Angles-Cheiron sections, a zonal scheme for the
pre-Vocontian Basin is presented (Table 4 ). The zonation is based on bed-by-bed
distribution and correlation. The latter is, at least in the distal settings,
possible from the Hirsutus Sz up to the Furcillata Sz. Lowermost
Valanginian sediments are apparently not well correlatable resulting in a more
tentative temporal distribution of the belemnite taxa.
Table 4:
Distribution of belemnite taxa through various
palaeogeographical areas. Taxa in blue are used as (sub-) zonal index taxa.
Abbreviations used: Bg = Bulgaria, Ch = Switzerland, Cr = Crimea, CzS = Czech
Republic + Slovakia, E = Spain, F = France, Hu = Hungary, Mor = Morocco, Ro =
Romania, (d) = distal, (i) = intermediate, (p) = proximal, ? = unsure, x =
present, xx = common, xxx = very common, and (#) = principally upper Berriasian
taxon. |
|
2.)
The stratigraphic distribution pattern of the belemnites, based on a combination
of distinguished assemblages and subzonal indexes, seems to provide a
comparable resolution as compared to the zonal scheme established for the
ammonites (Fig. 11 ). However, both the lower as well as the upper boundary of
the Valanginian do not exactly coincide with any species of belemnite, or any
assemblage changes. Yet, the lower stage boundary, especially, appears to be
recognizable by a suite of FOs of belemnites, see (3).
3.)
The first typical Valanginian belemnites are B.
exstinctorius, B.
conicus, C. orbignyanus,
H. aff. pistilliformis,
and M. blainvillei (Figs. 6 ,
9 ). They show their FOs separated by a few
beds only.
4.) Except for some long-ranging taxa (D. lata constricta, P. bipartitus), few typical Berriasian species extend their ranges into the earliest Valanginian (Castellanibelus sp.E, D. lata lata, D. tornajoensis).
5.)
Differences exist between belemnite taxa and abundances in the proximal,
intermediate, and distal parts of the basin that involves both genera and
species. High abundances in the more proximal facies are often the result of
condensation, but not always as can be seen from the large numbers of H.
aff. jaculoides in both distal and
proximal facies. Berriasibelus, Castellanibelus,
and Mirabelobelus are (nearly) absent
from proximal facies, while species of Duvalia
are ubiquitous. Adiakritobelus,
although having a more patchy distribution, appears to be quite common overall.
Also Pseudobelus shows a patchy
distribution in proximal facies, but seems to be most common in more distal
facies (Figs. 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9 ).
6.)
The species H. aff. jaculoides
occurs suddenly and in abunadnce, first in basinal, and later in more proximal
facies. It originated most probably from the Boreal-Atlantic and would indicate
that exchange was possible in that period. The population yields juvenile and
adult specimens, indicating successful conditions. However, only a few
occurrences are recorded in the top of the Peregrinus Sz and the base of the
Nicklesi Sz, in which it disappears. In Spain, the taxon first occurs at the
base of the Pronecostatum Sz. Either, the Neocomiensis Sz in France correlates
with the base of the Pronecostatum Sz in Spain (Fig. 9 ), and/or there is a
sampling bias, as differences in conditions between both areas, and/or (causing)
a time delay in the spread of H. aff. jaculoides,
seem to be unlikely.
7.) Regarding the newly established ammonite zonation of Company and Tavera (2015), it can be applied more easily to the proximal part of the basin, but appears to be more difficult in the more distal sections, either due to lacking ammonite data, or differences in the spatial distribution of some ammonite taxa.
8.)
Validation of the proposed belemnite zonation outside the pre-Vocontian Basin is
not yet possible because of the lack of sufficient bed-by-bed investigation of
sections with respect to belemnites. Only a few sections have been investigated
in the southeast of Spain and show several common species, but their ranges
appear not always comparable, either due to the amount of available belemnites,
uncertainty of some correlations, or the possible absence of some species (Fig. 9 ). The same holds true for the moment for other areas, such as, Hungary (Hu),
the Crimea (Cr), the Czech Republic and Slovakia (CzS), Bulgaria (Bg), Romania (Ro),
Switzerland (Ch), and Morocco (Mor) (Tab. 4).
Kind and warm gratitude goes to Willem Bont (Amsterdam, NL) for making the photos; Myette Guiomar and Didier Bert (Réserve géologique, Digne, F) for permission of sampling some protected sections; Arnaud Clément (Gap, F), Gero Moosleitner (Vienna, AT), and Paul Floor (Zwolle, NL) for sharing and donating materials; Martin Schobben and Bas van de Schootbrugge (Utrecht University, NL) for joining in some fieldwork and without the continuous contribution and inspiration of Jaap Klein (Vinkeveen, NL; Oraison, F) this work would not have been possible at all. Also, I would like to acknowledge the influence and inspiration of Wolfgang Riegraf on my work over the years, who unfortunately was lost to the coleoid community earlier this year.
Finally, I thank the reviewers Alexei Ippolitov, Oksana Dzyuba, and Simon F. Mitchell for their valuable suggestions and linguistic corrections that significantly improved this paper.
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Plate
1: fig.
1. Orientated group of belemnites (CLZ 104, Col Lazarier, Verrucosum Sz).; |
|
|
Plate
2:
Vaubelle: |
|
|
Plate
3:
Vaubelle: |
|
|
Plate
4: Vaubelle and Vergol: |
|
|
Plate
5: Preyes (PRY):
|
|
|
Plate 6: Berriasian
belemnites: VBL and GIN; Dorsal view to the left unless otherwise indicated (d). |
|
|
Plate
7: figs. 1-2. Castellanibelus vaubellensis Janssen,
2018, RGM543617; PRY E-mid, Hirsutus
Sz;
Dorsal view to the left unless otherwise indicated (d). |
|
|
Plate
8: figs. 1-3. Duvalia crassa Janssen, 2018, RGM613215; VBL077, Subcampylotoxus
Sz;
Dorsal view to the left unless otherwise indicated (d). |
|
|
Plate
9: figs. 1-2. Duvalia kleini Janssen,
2018 (gr. binervia), RGM560708; SAM343b-c, Nicklesi
Sz;
Dorsal view to the left unless otherwise indicated (d). |
|
|
Plate
10: figs. 1-2. Pseudobelus sp. B, RGM560733; SAM320-321, Pronecoststum
Sz;
Dorsal view to the left unless otherwise indicated (d). |
|
|
Plate
11: figs. 1-2. Hibolites aff. jaculoides Swinnerton,
1937, RGM583889, Y.G16, Pronecostatum
Sz;
Ventral view to the right unless otherwise indicated (v). |
|
|
Plate
12: figs. 1-2. Adiakritobelus peyroulesensis Janssen, 2009, RGM543245, TM108b
Nicklesi-Furcillata Sz;
Ventral view to the right unless otherwise indicated (v). |
|
Appendix A (calcilutites, -siltites, or -arenites)
Thin brownish-coloured layers, so-called "plaquettes calcaréo-gréseuses rousses" (calcarenitic rust-coloured layers), are often quite common in the uppermost lower Valanginian (Platycostatus Sz) to lowermost upper Valanginian (Verrucosum and "Neocomiensis" Sz). Only occasionally they occur in older or younger parts of the Valanginian. Generally, they are several mm's thick but in exceptional cases up to 50 cm.
The
thicker layers are generally associated with slumped beds and often occur on top
of the disturbed sets of beds. They generally lack abundant macrofossils except
for ichnofossils, which are clearly visible on the upper surface. The thinner
beds contain a few echinoid spines, but more often, variable amounts of
cephalopod remains (aptychi, rhyncholiti, and belemnites). Frequently
these beds are characterized by abundances of (debris of) aptychi, the so-called
"Lumachelle à Aptychus", as mentioned by Paquier (1900, p. 109-110)
from the lowermost upper
Valanginian. It occurs in the following sections: BLH, LBL, VBL, VGL, and VPE, and Montclus
(Fig. 1 ). Paquier
(1900) also mentions
Raton, to the NW of Rosans.
In VBL a thin aptychi rich calcarenite, additionally yielding belemnites (mainly M. blainvillei), occurs in the Pertransiens Zone, with a restricted lateral extension. In other sections rust-coloured calcarenitic layers of this age were not found.
In LCH these brownish weathered beds (generally only few mm thick, but sometimes up to 20 cm thick) and calcareous slumps occur in abundance between the Subcampylotoxus Sz (p.p.) and the Pronecostatum Sz ("la Zone Jaune" or "yellow zone" of Le Doeuff, 1977). They are difficult to assess, but it appears as if the base of this unit truncates the upper part of the Subcampylotoxus Sz (and probably also the Platycostatus Sz and Verrucosum Horizon). These beds show laminated parallel bedding, sometimes convolute bedding at the base, wavy structures on top, scour marks, and abundant ichnofossils (a.o. Paleodictyon, Zoophycos). However, the presence of large-scale hummocky cross-bedding is not evident, giving direct evidence for tempestites.
Tangri (1980, p. 30-31) mentioned the occurrence of thin beds (generally several cm's thick, occasionally up to 10-20 cm) separated by marly sediments of several cm's to metres in thickness, situated above the Verrucosum Horizon. The area investigated by this author is situated to the north of our area (around the town of Die, northern edge of the pre-Vocontian). Apparently, calcarenitic beds appear to be much more abundant there (15-20% of the total lithology). Several sedimentary structures can be noted within, and on top of these calcarenites (Tangri, 1980, p. 82-85). Tangri (1980, p. 83) mentions the occurrence of a flute cast probably as a result of a transported belemnite. However, fossils were not mentioned from these calcarenitic beds.
Occasionally
belemnites occur within, or on top of these beds, either as orientated groups of
rostra (Pl. 1 , fig. 1), as randomly orientated, but size-sorted, or as single
specimens (Pl. 1 , fig. 2). The following sections yielded belemnites associated
with these layers: CLZ, VBL, VGL, Gouravour and Chanousse.
These beds are either interpreted as turbidites or tempestites, indicating the occurrence of transported material into the proximal areas of the basin. Apparently, cephalopod remains were incorporated and eventually sorted during transport. They are most abundant in the uppermost lower to lowermost upper Valanginian. They occur also outside this time-frame, but are rare and often confined to the bottom or top of slumped sedimentary units most probably indicating a turbiditic origin. The peak of their occurrence appears to be around the major excursion of the Valanginian positive C-isotope excursion. As this event might well be connected to climatic change (a wetter climate), these beds are here probably best explained as originating through tempestites in the more proximal areas, becoming turbiditic in the more distal parts of the pre-Vocontian Basin.
Appendix B (debris flows/slumps VBL)
In
contrast to all other investigated sections are the occurrences of
redepositional deposits (debris-flows) consisting of micro-conglomerates,
redeposited macrofossils (mainly early-middle Berriasian ammonites; both in
nodules as well as loose steinkerns), and variously sized calcareous clasts,
nodules and boulders (Pl. 3 , fig. 4; Pl. 4 , figs. 1-3) in the Vaubelle area (VBL
and SVJ). Sometimes these sediments are covered by brownish-weathered
calcarenites of 2-50cm (Pl. 4 , fig. 5; see
Appendix A), yielding traces of
ichnofossils (Chondrites) on top.
These
redeposited sediments (debris flows) were also mentioned from nearby sections by
Le Hégarat (1973), and are especially common in the latest Jurassic and
earliest Berriasian (Remane, 1960, 1973, Fig. 2; Ferry et
al., 2015). However here, these sediments occur below the Hirsutus Sz, in
the Pertransiens Zone (slumps and debris flows; Pl. 3 , fig. 1), and at the base
of the Valanginian.
The
deposits at the base of the Valanginian yield in its top part, a poorly sorted
conglomerate (VBL B100; Pl. 3 , fig. 2; Pl. 4 , figs. 1-3), deposited in
gully-like structures, often ranging to a micro-conglomerate and being covered
by a brownish weathered calcarenitic bed (VBL Psst; Pl. 4 , figs.
1-3) (cf. Ferry, 2017, Fig. 20D). This conglomerate yields fossils
including brachiopods, aptychi, belemnites and ammonites.
The ammonites (det. J. Klein) indicate redeposition from the uppermost Tithonian
(Moravisphinctes cf. moravica),
but mainly from the lower Berriasian (Berriasella
jacobi, B. cf. subatasi?, B. cf. moesica,
Delphinella subchaperi, Malbosiceras
cf. chaperi, Pseudosubplanites cf. grandis,
Ps. cf. combesi, Picteticeras elmii,
P. enayi, P. oxycostata,
Pseudargentiniceras sp. (Jacobi Z), and Delphinella sp. (Jacobi-Privasensis Z). In addition, a few late
Berriasian ammonites occur, e.g., Berriasella
(Hegaratella) kaffae
(Paramimouna-Picteti Z), besides long-ranging taxa like Ptychophylloceras,
Haploceras, Lytoceratinae and many indeterminable, badly and/or partially
preserved, berriasellids. They occur both
in calcareous clasts as well as loose fossils. So, the majority of the ammonites
point to redeposition from lower Berriasian sediments, while most typical upper
Berriasian ammonites appear to be absent. On the other hand, the belemnites
herein, point mainly to the latest Berriasian (Picteti-Alpillensis Z), including
species like: Castellanibelus sp. E, D.
(aff.) tornajoensis, Gillieronibelus
mayeri, and Mirabelobelus?
orbignyi. In addition, the bed yields taxa of the Duvalia
lata-group and several Berriasibelus species.
The latter include a.o. Berriasibelus
kabanovi, B. cf. triquetrus,
and B. aff. exstinctorius
sp. 1. Possible early Berriasian belemnite taxa are rare and include: Conobelus
sp. (Pl. 6 , figs. 18-19), incomplete fragments of a long grooved hibolitid,
probably like H. cf. fellabrunensis (Vetters,
1905), and "Pseudobelus" gr. pilleti (Pictet,
1868; Pl. 6 ,
figs. 28-29). The latter taxon is comparable to specimens from the
Jacobi Z of SLD (Pl. 6 , figs. 30-34).
Below
these deposits the sediments consist of, several tens of metres, the base is not
exposed, marlstone dominated, mud-flows with various sized calcareous clasts and
fine dispersed silica, yielding a few ammonites, such as, Berriasella
privasensis, Jabronella cf. jabronensis,
and J. cf. cisternensis,
indicating the Privasensis-Paramimouna Z (det. J. Klein) besides indeterminable
ammonite specimens and only a few belemnites (Fig. 6 ). Above these sediments, in
bed VBL P02, slightly above the sandstone bed (Fig. 6 ) the ammonite Kilianella
chamalocensis (Pl. 4 , fig. 4) occurs. Here, in addition, T.
gr. pertransiens and Erdenella
paquieri occur, indicating the latest Berriasian to earliest Valanginian.
Thus in VBL mass transport deposits, such as debris flows and slumps, are quite common, indicating transport/reworking - mainly based on ammonites - from uppermost Tithonian(?) to upper Berriasian. These sediments, either expressed as conglomeratic levels (in the uppermost Berriasian or lowermost Valanginian) or as debris flows (in the upper Berriasian and in the upper Pertransiens Zone), might be of local origin, resulting from paleofault activity. The general picture indicates reworking of younger to older strata and their fossils in progressively younger sediments. It should be noted that most belemnites indicate the latest Berriasian while most ammonites have older ages (Jacobi-Privasensis Zones, early-middle Berriasian).
