Geol. Mag.: page 1 of 21
c
Cambridge University Press 2013 1
doi:10.1017/S0016756813000927
Palaeoenvironmental changes at Col des Tribes (Montagne Noire,
France), a reference section for the Famennian of north
Gondwana-related areas
CATHERINE GIRARD
∗
†, JEAN-JACQUES CORNÉE‡, CARLO CORRADINI§,
AURÉLIEN FRAVALO
∗
& RAIMUND FEIST
∗
∗
Université Montpellier 2, UMR 5554 CNRS, Institut des Sciences de l’Evolution C.C. 64,
Place Eugène Bataillon, F-34095 Montpellier, France
‡Université Montpellier 2, UMR 5243 CNRS, Géosciences Montpellier C.C. 60,
Place Eugène Bataillon, F-34095 Montpellier, France
§Università di Cagliari, Dipartimento di Scienze Chimiche e Geologiche, Via Trentino 51, I-09127 Cagliari, Italy
(Received 12 August 2013; accepted 27 September 2013)
Abstract – We present detailed biostratigraphy based on conodonts and palaeoenvironmental trends
deduced from microfacies and conodont abundance through the Famennian (Late Devonian) at Col
des Tribes (Montagne Noire, France). The succession is characterized by micritic limestones deposited
in settings oscillating between mid to outer ramp. Facies contain poor fauna, widely dominated by
nektonic organisms. This section is complete and one of the most conodont-rich for the Famennian
of the north Gondwana-related area. The Upper Kellwasser event (Frasnian–Famennian boundary)
and the Hangenberg (Devonian–Carboniferous boundary) have been lithologically identified. They
are characterized by decimetre-thick black dysoxic to anoxic argillaceous sediments. The Condroz
and annulata events, although not materialized by lithological changes, have been positioned due
to the precise stratigraphy. The first event occurred during the deposition of condensed ferruginous
facies (griotte limestones) and the second event during the deposition of micrites barren of benthic
fauna. The combination of information from both facies and conodont biofacies changes allows a
general sea-level curve through the entire Famennian for north Gondwana to be proposed for the
first time. At Col des Tribes, the general trend is a slight deepening upwards from triangularis to
trachytera zones, then a pronounced shallowing-upwards trend from upper trachytera to praesulcata
zones. This curve correlates with the well-known reference curve from Euramerica concerning the late
Famennian (trachytera to praesulcata Zones). There are some discrepancies in minor cycles which can
be explained by tectonical phenomena at the onset of the edification of the Variscan belt in Europe.
Keywords: conodonts, microfacies, Devonian, Montagne Noire, sea level.
1. Introduction
The Famennian (Late Devonian epoch) is a stage
marked by important changes in the biosphere and a
period of recurrent environmental perturbations. Seven
global events occurred over an interval of c. 15 Ma.
At its base, the Frasnian–Famennian (F/F) boundary is
known as one of the five most drastic episodes of bio-
logical extinction of the Phanerozoic and has recently
also been considered as a biodiversity crisis due to
speciation rate drop (Racki, 2005; Stigall, 2012). This
episode is called the Kellwasser event. At the top of
the Famennian, the Devonian–Carboniferous boundary
is also characterized by a worldwide extinction event
called the Hangenberg event (Walliser, 1984). Other
global events occurred during the Famennian such as
Nehden (House et al. 1985; Schülke, 2003; Schülke &
Popp, 2005), Enkeberg (House, 1985; Becker, 1993),
Condroz (Schülke & Popp, 2005), annulata (Becker,
1993; Schülke & Popp, 2005) and Dasberg (Becker,
†Author for correspondence: catherine.girard@univ-montp2.fr
1993; Hartenfels, 2010; Marynowski, Filipiak & Zaton,
2010). They are generally marked by palaeontological
and/or environmental changes (Walliser, 1996; House,
2002).
Among these events, the Kellwasser, annulata, Das-
berg and Hangenberg are related to worldwide anoxic
events. In most of the cases these anoxic events have
been studied when easily identified based on facies de-
posits, i.e. when black shales are present (Becker, 1993;
Racka et al. 2010). The Condroz event is not paired
with anoxia spread, but with termination of black Chei-
loceras shale due to regression (Walliser, 1996). Inde-
pendently of any lithological signature, following the
Late Devonian conodont zonation established by Zie-
gler & Sandberg (1990) all these events can be dated
and globally correlated. Assumed to be synchronous
at the global scale, these events are sometimes related
to a glacioeustatic mechanism (Sandberg, Morrow &
Ziegler, 2002; Racka et al. 2010) and generally to sea-
level fluctuations (Walliser, 1996).
Sea-level fluctuations through the Devonian are
well known on the east European platform (Alekseev,
2 C. GIRARD AND OTHERS
Devonian
10 km
100 km
the Mediterranean
Marseille
Montpellier
Toulouse
Bédarieux
Cabrières
Bédarieux
Mont Peyroux
Cessenon
Clermont l'Hérault
3 5'
43
32'
Col des Tribes
Col des Tribes
Causses et
Veyran
Causses et
Veyran
Mont Peyroux
0
10 20 30
m
D
C
cherts
36
22
35
N
F
F
a
c
b
Figure 1. Location of the Col des Tribes section (Montagne Noire, south France). Maps showing: (a) the position of the Montagne
Noire in southeastern France; (b) the Col des Tribes section near Causses and Veyran; and (c) the position of the sampled levels
(modified from House, 1985; Becker, 1993). F/F --- Frasnian/Famennian boundary; D/C --- Devonian/Carboniferous boundary.
Kononova & Nikishin, 1996) and at the scale of
the Euramerica supercontinent (Johnson, Klapper &
Sandberg, 1985; Johnson & Sandberg, 1989; Sand-
berg, Morrow & Ziegler, 2002; Haq & Schutter; 2008;
Racka et al. 2010). Because of the absence of con-
tinuous sections through the Famennian on the north
Gondwana-related area (Galatian superterrane, Stamp-
fli et al. 2013), sea-level fluctuations are poorly con-
strained.
The present study focuses on the tracing of Famen-
nian sea-level fluctuations and related events in the
Montagne Noire (France). Previous biostratigraphic
works at Col des Tribes (CT) were principally based
on goniatites (J.D. Price, unpubl. thesis, University of
Hull, UK, 1982; Becker, 1993; Becker & Weyer, 2004).
The presence of variously abundant conodonts in a
series of reconnaissance samples was discovered by
G. Klapper in the early 1980s (unpublished results)
but detailed conodont biostratigraphy of the entire Fa-
mennian sequence remained largely incomplete (Boyer
et al. 1968). These works however suggested that there
were no major biostratigraphical gaps or discontinuities
allowing for both microfacies investigations and evalu-
ation of conodont faunal changes to be made through-
out the entire Famennian interval.
In this regard we aim to: (1) establish a detailed strati-
graphy based on conodont biozonation; (2) establish a
model of depositional environments using the evolu-
tion of microfacies; and (3) use conodont assemblages
to obtain an insight into particular sea-level changes.
2. Geological setting
The Col des Tribes section is located in the Montagne
Noire, France (Fig. 1). The Montagne Noire is part
of the external tectonic zone of the Variscan belt in
southern France (Matte, 1991; Ballèvre et al. 2009;
Faure, Lardeaux & Ledru, 2009; Fig. 1a), composed of
a south-facing pile of low-grade to non-metamorphic
rocks (Arthaud, 1970). Even if the palaeolocation of
the Montagne Noire during Late Devonian time is
still under debate, most authors consider it was on
the northern-most margin of Gondwana or on an in-
termediate block rifted off Gondwana during Early
Palaeozoic time and located between Laurussia and
Gondwana (Tait, Bachtadse & Dinarès-Turell, 2000;
Golonka, 2002; Nysaether et al. 2002). During Famen-
nian time, the Montagne Noire should have been part
of the Galatian superterrane which was bouded to the
SE by the Palaeotethys Ocean and bounded to the NW
by the Rheic Ocean (Stampfli et al. 2013). The stud-
ied section belongs to the inverse limb of the Mont-
peyroux nappe which suffered very low-grade meta-
morphism (anchizonal to non-metamorphic, Wiederer
Late Devonian environmental changes in the Montagne Noire 3
et al. 2002). It is composed of oxidized sediments as-
sumed to have been deposited on an outershelf submar-
ine rise (Engel, Feist & Franke, 1982).
In contrast to Palaeozoic rocks of the Pyrenees and
southern Alps, those of the Montagne Noire did not
suffer any alpine deformation which explains the com-
paratively good preservation of fossils and sedimentary
fabrics. The investigated section near Col des Tribes
is situated on the eastern slope of the Mont Peyroux
summit (Fig. 1), IGN sheet 1:25 000 St Chinian
2544 E, between 43° 29
26.65
N, 3° 5’ 26.28
E and
43° 29
23.94
N, 3° 5
27.50
E.
3. Methods
3.a. Palaeoenvironments
A total of 71 samples were collected (Figs 1b, 2a),
marked in the field by pink numbers. Bed numbers
mostly coincide with those formerly marked by House
& Price (in Becker, 1993, pp. 91–92). Many covered in-
tervals were made accessible by hand digging. A total of
71 thin-sections were cut for microfacies analysis from
the same samples used for conodont studies. Based on
field and microscopic observations (semi-quantitative
estimate of the relative abundance of bioclasts) and
palaeontological qualitative results, four facies types
are distinguished (Flügel, 2004). As facies are poorly
diversified at Col des Tribes where the carbonates gen-
erally yield few bioclastic debris (only one sample
provided up to 15 % of bioclasts), we chose the follow-
ing ratios of bioclast abundance to illustrate vertical
changes along the section: very rare: <1 %; rare: 1–
2 %; frequent: 2–6 %; and abundant: 6–15 %. In order
to characterize the depositional environment, we in-
troduced the ratio N/(N+B) where N is the abundance
of debris of nektonik organisms, B is the abundance of
benthic organisms and N+B represents the total abund-
ance of bioclasts (nektonik + benthic) (see Flügel,
2004 for palaeoenvironmental setting of organisms).
Even if such a ratio is dependent upon very differ-
ent palaeoenvironmetal parametres (dysoxia, nature of
bottom, currents, etc.), we consider it useful for dis-
crimating large-scale proximal to distal trend changes.
The most frequent pieces of benthic organisms are
issued from thin-shelled and less than 500-μm-long
ostracods, echinoids (crinoids), trilobites, brachiopods
and, to a lesser extent, gastropods, bivalves, silicified
foraminifers, sponges and possibly microbes. Nektonic
organisms are represented by cephalopods (ammon-
oids), thin-shelled pelagic molluscs (‘filaments’ in thin-
section), pelagic ostracods (entomozoans) and calcified
radiolarians (<200 μm). Most foraminifers, conodont
elements and fish teeth were also found from residues of
washed samples. The lithological description is based
on Dunham’s (1962) carbonate rock classification re-
fined by Embry & Klovan (1971). Each facies is related
to a depositional environment according to the zona-
tions proposed by Wright & Burchette (1996) and Flü-
gel (2004). The pelagic carbonate systems of Devonian
time are known to be large-extent platforms (Peterhän-
sel & Pratt, 2001; Morrow & Sandberg, 2008). The ver-
tical change of facies during Famennian time suggests
a low-angle ramp depositional system. Inner-ramp de-
posits correspond to marine sediments which were de-
posited above the base of the fair-weather wave ac-
tion. Mid-ramp deposits were deposited between the
lower limit of fair-weather wave action and the base of
storm-wave action. Outer-ramp – basinal deposits were
deposited under the lower limit of storm-wave action
(Fig. 2b).
3.b. Faunas
A total of 71 samples were sampled for conodont stud-
ies. The weight of the samples analysed varied within
the range 50–730 g depending on the abundance of con-
odonts (Table 1). The samples were taken at intervals
of 0.1–1.0 m over the entire section in order to capture
the changes in lithology. The samples were dissolved in
dilute formic acid (10 %). The insolute residues were
separated through two sieves (100 μm and 1 mm). The
two fractions were dried and picked up under a bin-
ocular microscope in order to collect the microfossils.
All conodonts (Table 1) occurring in the residues were
picked up. Some conodont elements were identified at
the specific level for biostratigraphy (Fig. 3). For biod-
iversity analyses, the absolute and relative abundances
of the different genera present in the samples have been
investigated. When present, trilobites provided addi-
tional information about palaeoenvironment.
3.b.1. Conodont absolute and relative abundances
Absolute abundance was estimated as the number of
platform elements (P1) per kilogram of rock. Since the
differences in absolute abundances reach several orders
of magnitude, these data have been log-transformed.
Very different weight of rocks have been analysed in
order to obtain a total close to 100 platform elements for
each level, allowing for a reliable estimation of relative
abundances. When the number of platform elements
was <100, values were excluded from the analyses
(see Table 1). Among these platform elements, several
genera can be identified that have been related to differ-
ent environmental preferences (Seddon & Sweet, 1971;
Sandberg, 1976). The variations of the relative propor-
tion of the different genera are assumed to provide an
indirect water depth proxy.
Such an approach is called biofacies analysis (Sed-
don & Sweet, 1971; Sandberg, 1976). In this study
the procedure established by Sandberg (1976) has been
followed. Each biofacies was named after the one or
two most abundant genera among the conodont plat-
form elements, usually constituting at least 75–80 %
of the total platform elements. During the investigated
period, Icriodus and Protognathodus are considered as
characteristic of shallow marine environments (Sand-
berg & Dreesen, 1984), whereas Palmatolepis and Si-
phonodella have been interpreted as associated with
4 C. GIRARD AND OTHERS
Figure 2. (Colour online) Col des Tribes section with microfacies interpretations and proposed relative sea-level changes. Conodont
zones after Ziegler & Sandberg (1990). Estimated sea-level variations based on N/(N+B) ratio, where N represents nektonic faunas and
B benthic faunas. Blackish argillaceous sediments are depicted in grey, shadings represent the tentative position of some Famennian
events. lo – lower; up – upper; um – uppermost.
Late Devonian environmental changes in the Montagne Noire 5
Figure 3. Famennian biostratigraphic species. (a) Palmatolepis triangularis Sannemann, 1955; (b) Palmatolepis minuta minuta Branson
& Mehl, 1934; (c) Palmatolepis termini Sannemann, 1955; (d) Palmatolepis crepida Sannemann, 1955; (e) Palmatolepis glabra prima
Ziegler & Huddle, 1969; (f) Palmatolepis rhomboidea Sannemann, 1955; (g) Palmatolepis gracilis gracilis Branson & Mehl, 1934; (h)
Palmatolepis marginifera marginifera Helms, 1959; (i) Polygnathus glaber bilobatus Ziegler, 1962; (j) Scaphignathus velifer velifer
Helms, 1959; (k) Palmatolepis perlobata helmsi Ziegler, 1962; (l) Palmatolepis gracilis sigmoidalis Ziegler, 1962; (m). Palmatolepis
perlobata postera Ziegler, 1960; (n) Polygnathus styriacus Ziegler, 1957; (o) Palmatolepis gracilis expansa Sandberg & Ziegler,
1979; (p) Bispathodus costatus Ziegler, Sandberg & Austin, 1974; (q) Bispathodus ultimus Bischoff & Ziegler, 1957; (r) Siphonodella
sulcata Huddle, 1934; (s) Protognathodus meischneri Ziegler, 1962; (t) Siphonodella quadruplicata Branson & Mehl, 1934; (u).
Pseudopolygnathus triangulus triangulus Voges, 1959; (v) Siphonodella duplicata Branson & Mehl, 1934; (w) Siphonodella cooperi
Hass, 1959.
