Geobios 35 (2002) 397–409
www.elsevier.com/locate/geobio
Small shelly fossils from the Lower Cambrian Lastours Formation,
southern Montagne Noire, France
Microfossiles à paroi squelettique de la Formation de Lastours
(Cambrien inférieur) en Montagne Noire méridionale, France
J. Javier Álvaro a,*, Olaf Elicki b, Françoise Debrenne c, Daniel Vizcaïno d
a
Université des sciences et techniques de Lille I, Laboratoire de paléontologie et paléogéographie du paléozoïque, UPRESA 8014 CNRS,
Cité Scientifique SN5, 59655 Villeneuve d’Ascq, France
b
Institut für geologie, TU bergakademie Freiberg, Bernhard von Cotta strasse 2, 09596 Freiberg-Sachsen, Germany
c
Muséum national d’Histoire naturelle, laboratoire de paléontologie, UMR 8569 CNRS, 8, rue Buffon, 75005 Paris, France
d
7, rue Jean-Baptiste Chardin, Maquens, 11090 Carcassonne, France
Received 10 November 2001; accepted 23 January 2002
Abstract
The paper presents the first description and illustration of archaeocyaths and small shelly fossils from the lower member of the Lower
Cambrian Lastours Formation (southern Montagne Noire). The outcrops of the Caunes–Minervois sheet thrust (Pardailhan nappe) represent
alternation of relatively low-energy, shallow subtidal substrates (highly bioturbated mottled limestones), and reef flanks or inter-reef settings
surrounded by winnowed archaeocyath-spiculate shelly pavements. The archaeocyathan assemblage (Botoman in age) is dominated by the
genera Anthomorpha and Inessocyathus, from which the species Inessocyathus levis is reported for the first time in the southern Montagne
Noire. Phosphate-shell microfossils comprise hyolithelminths (Hyolithellus and Torellella) and conodont-related sclerites (Yunnanodus), the
latter having previously only been reported from the Meishucunian of south China. © 2002 Éditions scientifiques et médicales Elsevier
SAS. All rights reserved.
Résumé
Ce travail présente la première description et illustration d’archéocyathes et de microfossiles à paroi squelettique du membre inférieur
de la Formation de Lastours (Cambrien inférieur de la Montagne Noire méridionale). Les affleurements de l’écaille tectonique de
Caunes–Minervois (nappe de Pardailhan) montrent une alternance de dépôts marins peu profonds à basse énergie (fortement bioturbés
donnant un aspect de calcaires « mouchetés »), et de flancs récifaux ou de domaines inter-récifaux entourés de lumachelles à archéocyathes
et spicules transportés. L’assemblage d’archéocyathes (d’âge Botomen) est dominé par les genres Anthomorpha et Inessocyathus ; il
comprend l’espèce Inessocyathus levis, citée pour la première fois en Montagne Noire méridionale. Les microfossiles à paroi phosphatée
sont représentés par des hyolithelmintidés (Hyolithellus et Torellella) et des sclérites conodontiformes (Yunnanodus), ces derniers cités
jusqu’à présent uniquement dans le Meishucunien de la Chine méridionale. © 2002 Éditions scientifiques et médicales Elsevier SAS. Tous
droits réservés.
Keywords: Small shelly fossils; Archaeocyaths; Carbonates; Lower Cambrian; Montagne Noire; France
Mots clés: Microfossiles; Archéocyathes; Carbonates; Cambrien inférieur; Montagne Noire; France
* Corresponding author.
E-mail address: Jose-Javier.Alvaro@univ-lille1.fr (J. Javier Álvaro).
© 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
PII: S 0 0 1 6 - 6 9 9 5 ( 0 2 ) 0 0 0 3 6 - 0
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J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
1. Introduction
The Lower Cambrian strata of the Montagne Noire
(southern France) have been classically the focus of studies
on the early radiation of metazoans and the environments in
which the “Cambrian explosion” occurred. Since the discovery of archaeocyaths (Bergeron, 1894), these rocks have
contributed to the understanding of the Lower Cambrian
fauna through studies on archaeocyaths (Debrenne, 1964),
trilobites (Cobbold, 1931, 1935; Courtessole et al., 1971;
Courtessole and Jago, 1980; Geyer, 1992; Álvaro et al.,
1998b), brachiopods (Termier and Termier, 1974), chancelloriids (Geyer, 1986) and ichnofossils (Álvaro and Vizcaïno,
1999). However, although local zonations have been established (last revision in Álvaro et al., 2001), convincing
inter-regional correlations remain difficult due to the rare
and scattered occurrence of biostratigraphically significant
fossils. This is mostly controlled by a high degree of
recrystallization and selective dolomitization of carbonates,
and severe tectonic deformations leading to diverse kind of
fossil preservation related to the original texture and mineralogy of skeletal remains: e.g. the micritic skeletons of
archaeocyaths rarely reproduce their original texture due to
neomorphic replacement and mechanical stress inducing
stretched and folded frameworks on larger skeletons, contrasting with the micritized outlines on small and/or midsized cups. As a result, specific and even generic determinations are frequently impossible.
The purpose of this paper is to characterize, for the first
time, the fossil record of the lower member of the Lastours
Formation, in order to improve the paleoecological and
biostratigraphic knowledge of Lower Cambrian carbonate
strata preserved in the southern Montagne Noire. Due to the
recrystallized nature of these limestones, the analysis is
approached in two ways: selected archaeocyathan-rich
samples were determined using polished slabs and thin
sections, whereas phosphate-shell microfossils were released by acid digestion. Our study of this newly discovered
macro- and microfossil assemblage is a contribution toward
the larger purpose of elucidating the biodiversity of the
Lower Cambrian, microbial–archaeocyathan reef complexes that colonized the western Gondwana margin.
2. Geological setting, stratigraphy and facies
The lower member of the Lastours Formation (sensu
Álvaro et al., 1998a) is exposed in discontinuous, somewhat
faulted bands throughout the Pardailhan nappe. This member consists of massive to bedded, white, grey and black
limestones (locally dolomitized) lacking shaly intercalations. The last character permits differentiation of this
member from the underlying Pardailhan Formation and the
upper members of the Lastours Formation.
The pond studied in this work is located approximately
2.5 km eastwards of the village of Caunes–Minervois
(Fig. 1), on the Pardailhan nappe. It was reported by
Debrenne (1964, Fig. 13) under the name « Notre-Dame du
Cros » (x = 617, y = 113.8 in Berger et al., 1993), where
scarce, highly broken and badly preserved archaeocyathan
cups were then observed but not described. The outcrop is
located in one of the thrust sheets that characterize the
southwesternmost edge of the nappe, bounded by Tertiary
sediments. In fact, this small thrust sheet was first reported
as Tertiary limestones in the first edition of the geological
map (Thoral et al., 1951), and definitively assigned to
Cambrian rocks in the second one (Berger et al., 1993). The
ravines associated with the pond provide a reliable section,
up to 30 m thick, of the lower member of the Lastours
Formation (Fig. 2). Major lithostratigraphic boundaries are
not exposed, and the top of the limestone has yielded an
abundant and determinable fossil record composed of archaeocyaths and phosphatic microfossils.
In the area investigated, the limestone outcrops can be
subdivided into five subunits (I to V), whose lithologic and
petrographic characters are summarized in Table 1. The
subunits I, III and V are highly recrystallized, and their
original microfacies difficult to recognize. Calcareous skeletons (such as archaeocyaths, trilobites and echinoderm
ossicles) are commonly preserved as spar-filled moulds of
blocky calcite cements (50–200 µm across). In some cases,
the sparry mosaics do not mimic any bioclast shape, but
display more irregular outlines that cannot be attributed to
any specific taxon. The matrix is heterogeneously recrystallized to microsparite.
Although all the subunits are partially bioturbated, the
subunit II exhibits a dominant burrow-mottled aspect. The
fine- to medium-crystalline limestone, variably to completely burrow-mottled, is nearly unfossiliferous and originally dominantly micritic. Patches of orange-colored ferroan dolomite (composed of subelliptical sucrosic mosaics
of euhedral dolomite rhombs, up to 300 µm across) form a
network of irregular thin nodular interbeds. Locally, bioturbation is so pervasive that bedding is lost.
Finally, subunit IV (on which this work is focused)
consists of microbial boundstones and archaeocyathan–microbial floatstones. Its bottom is marked by a sharp decrease
in the amount of bioturbation with concomitant preservation
of physical sedimentary structures. The abundant fossil
content of the subunit (comprising archaeocyaths, calcisponge spicules, trilobites, echinoderm ossicles, brachiopods, hyoliths, phosphatic small shelly fossils, etc.) forms a
shell coquina in a limestone matrix. Fossils are commonly
visible in low relief on outcrop surfaces, after weathering
out of the matrix. Skeletons are not aligned in any distinct
direction, reflecting an apparent random embedding pattern
of the bioclasts. Archaeocyaths are preserved lying parallel
to bedding and not in life position. The poorly sorted,
abraded skeletons suggest that the fossils were reworked
and transported a short distance. Some skeletons are infilled
with micritic matrix, commonly forming geopetal fabrics
paralleling stratification. The most common sediment is
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
399
Fig. 1. (A) Geological sketch map of the Caunes–Minervois thrust sheet at the contact between the Minervois and Pardailhan nappes in the southern
Montagne Noire. (B) Map of the Caunes–Minervois thrust sheet, geological sections and stratigraphic log.
Fig. 1. (A) Schéma géologique de l’écaille tectonique de Caunes–Minervois sur le contact entre les nappes du Minervois et de Pardailhan en Montagne Noire
méridionale. (B) Carte de l’écaille tectonique de Caunes–Minervois, sections géologiques et coupe stratigraphique.
micrite and fine silt-size skeletal debris with numerous
calcisponge spicules and calcareous microspheres of uncertain affinity. The spicules are composed of optically single
crystals of calcite, and both monoaxon and polyaxon in
shape, suggesting provenance from vanished sponges, originally very abundant. The subunit contains the most abundant and diverse fauna of determinable archaeocyaths,
including the following taxa: Inessocyathus levis DEBRENNE, 1964, ?Afiacyathus sp., Carinacyathidae gen. et
sp. indet, Erismacoscinina gen. et sp. indet, Erismacoscinus
cf. elongatus (BORNEMANN, 1886), Erismacoscinus cf.
calathus (BORNEMANN, 1886), Protopharetra stipata
DEBRENNE, 1964, ?Chouberticyathus sp., Dictyocyathus
cf. verticillus (BORNEMANN, 1891), Anthomorpha margarita BORNEMANN, 1886 and Anthomorpha immanis
DEBRENNE, 1964 (Fig. 3). Archaeocyath content varies
from 10% to 40%. Two types of micrite occur as background matrix: (i) a microbioclastic spiculite, with scattered
intraclasts, and disarticulated and broken trilobites and
brachiopods; and (ii) a mottled micrite composed of unidentified thromboids replaced by microsparite and sparry
masses of lighter colored micrite; the latter does not display
any direct evidence of the former presence of calcimicrobes
at the microscopic level, but shows characteristic clotted
and branching morphologies at centimetric and decimetric
scale, displaying decimetre-scale microbial patch reefs.
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J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
the aperture. Their cross-section can be circular (Hyolithellidae Walcott, 1886) or elliptical (Torellellidae Holm,
1893). The outer surface of the tubes may be ornamented by
distinct striae or ribs, whereas their inner surfaces seem to
be smooth. In contrast to the original description by Billings
(1871) and the original diagnosis of the order by Fisher
(1962), hyolithelminths lacked mineralized operculum
(Bengtson et al., 1990).
The subdivision of hyolithelminths into two families was
established more than a century ago, and is only based on
few morphological features: the distinction between hyolithellids and torellellids is mostly based on cross-sections.
The existence of keels and pronounced striae in Torellellidae is not obligatory. Consequently, the diagnostic basis
for both families is rather imprecise, mainly studying
microfossils from highly deformed strata. This problem
persists and intensifies the ambiguities between numerous
definitions of genera and species (for a discussion see
Landing, 1988; Brasier, 1986, in Cowie and Brasier, 1989:
127). Further research and discussions are necessary to
clarify if the diagnostic characters between species are
really justifiable, which is beyond the scope of this paper.
Family Torellellidae HOLM, 1893
Genus Torellella HOLM, 1893
Type species: Torellella laevigata (LINNARSSON,
1871).
Diagnosis: Small, narrow, conical, calcium–phosphatic
tube, curved and irregularly shaped near the closed apex and
straighten toward aperture; low angle of wall divergence;
elliptical to biconvex (lens-shaped) cross-section; aperture
perpendicular to shell axis; exterior surface with transverse
striae and ribbing more pronounced than in the hyolithellids; inner surface smooth.
Fig. 2. Lower and lowermost Middle Cambrian stratigraphic units of the
southern Montagne Noire, based on Álvaro et al. (1998a), Álvaro and
Vizcaïno (1999), and this work.
Fig. 2. Unités stratigraphiques du Cambrien inférieur et moyen (d’après
Álvaro et al. 1998a; Álvaro et Vizcaïno 1999, et ce travail).
3. Systematic paleontology of the small shelly fossils
Illustrated fossil specimens, polished slabs and thin
sections are housed in the Muséum national d’Histoire
naturelle of Paris (Laboratoire de Paléontologie; acronyms
MNHN and R). Phosphatic microfossils were extracted
from the limestone matrix by dissolving the rock in a dilute
(10% by volume) acetic acid solution. The acid-resistant
skeletons were manually picked from the residues.
Phylum and Class uncertain
Order Hyolithelmintes FISCHER, 1962
Remarks: This order, widely accepted as worm tubes, is
characterized by small conical phosphatic tubes with an
irregular curved apical area, elongate and straighter toward
Torellella mutila MISSARZHEVSKY, 1989
Fig. 4(1–4)
1989 Torellella mutila nov. sp. (Missarzhevski, 1989, p.
195; pl. 24, Fig. 8).
1994 Torellella mutila (Elicki, 1994, p. 77; pl. 7, Fig. 11).
Diagnosis: Species of Torellella, straight and narrow,
displaying a low rate of wall divergence and two keels at the
aperture section.
Description: Elongated, narrow, hollow, phosphatic tube
fragments bearing elliptical cross-sections. One specimen
(Fig. 4(1–2)) shows two indistinctly developed keels on the
tapered parts of the cross-section. The narrowest and proximal part of the tube is strongly curved, and in all specimens
irregular depending on growth stages. The tubes, with
diameter up to 270 µm, show a variable wall-thickness
between 5 and 10 µm. No different shell-layers are visible.
The rate of ellipcticity increases gradually and the angle of
divergence is low (less than 20°), and mostly constant, so
that the tubes are more flattened on their elongated straight
(distal) part. Preservation is incomplete, so that only some
areas display simple and more or less regular ring-like
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
401
Table 1
Characteristics of facies comprising the lower member of the Lastours Formation on the Caunes–Minervois thrust sheet; M, mudstone; W, wackestone; P,
packstone; B, boundstone; F, floatstone
Tableau 1
Caractéristiques principales des faciès reconnues dans le membre inférieur de la Formation de Lastours (écaille tectonique de Caunes–Minervois); M,
mudstone; W, wackestone; P, packstone; B, boundstone; F, floatstone
Sub-units
Composition
Physical structures
Biogenic structures
Skeletal components
I
Archaeocyathanmicrobial lenses
distinct, dm-thick
lenticular geometries
dispersed burrows
highly recrystallized fabric
II
Burrow-mottled micritic
limestones irregularly
dolomitized
Lenticular, fossil-poor
limestones
Burrow-mottled microbial
Limestones
dark grey to black, mediumbedded to lenticular,
archaeocyathan-Microbial F and
W
Locally bioturbated
light to medium grey, thickbedded to massive, weakly
stylo-nodular, M to W
light to medium grey, lenticular,
fossil-poor M to W
light to medium grey thickbedded to massive,
archaeocyathan f interbedded
with microbial-Dominant B and
cm-thick P
bedded
burrows fillwed with
discrete sucrosic
none
nodular patterns lenticular
geometries
dm-thick bedded strata
with erosive storminduced bioclastic
coquinas
slightly bioturbated
scarce and small fragments
of undetermined biolcasts
Ephiphyton-like
thromboids, archaeocyaths,
brachiopods, calcisponge
spicules, phosphatic
microfossils, echinoderms,
etc.
archaeocyaths,
calcumicrobes, etc.
III
IV
V
Lenticular, Fossil-poor
Limestones
light to medium grey, thinbedded to lenticular, M to W
nodular patterns due to
mica-rich stylo-nodular
fabric
structures (Fig. 4(1)), and some weak growth lines on the
straight part of the outer surface (Fig. 4(1,3–4)). The
distance between the rings can reach 40 µm depending on
their position on the tube. The inner surface is smooth.
Discussion: The general growth patterns, type of curvature and cross-section of the specimens indicate its affiliation to the genus Torellella HOLM, 1893 (in Fisher, 1962).
The specimens show morphological features shared by
several species. Strong similarities exist with T. mutila
MISSARZHEVSKY, 1989 and T. lentiformis (SYSOIEV,
1962): both species apparently differ only in the lower and
rather continuous rate of wall divergence in T. mutila (so
that this tube is straighter and narrower), and in the
occurrence of keels. Although their value as a diagnostic
tool is questionable, the specimens are assigned to T. mutila
on the basis of the morphological features described above.
Occurrence: Torellella mutila is known from the early
Botoman of Siberia and Mongolia (Missarzhevsky, 1989),
and the middle–late Marianian of Germany (immediately
overlying the Ferralsia saxonica-bearing layer; Elicki,
1994).
Torellella lentiformis (SYSOIEV, 1962)
Fig. 4(5–8)
1962 Lentitheca lentiformis nov. sp. (Sysoiev, 1962, pl. 1,
Fig. 1).
1963 Lentitheca lentiformis (Sysoiev, 1963, pl. 49,
Fig. 1a).
1969 Torellella lentiformis (Rozanov et al., 1969, pl. 8,
Fig. 2).
1974 Torellella lentiformis (Meshkova, 1974, pl. 19,
Fig. 1).
highly bioturbated
slightly bioturbated
1982 Torellella lentiformis (Rozanov et al., 1982, p. 57,
pl. 5, Figs. 6–7).
1983 Torellella lentiformis (Sokolov and Zhuravleva,
1983, pl. 60, Fig. 9).
1986 Torellella lentiformis (Brasier, 1986, pl. 9,
Figs. 1–r).
1989 Torellella lentiformis (Missarzhevski, 1989, pl. 24,
Fig. 6).
1989 Torellella lentiformis (Cowie and Brasier, 1989,
pl. 7.1, Fig. 13).
1994 Torellella lentiformis (Elicki, 1994, p. 78; pl. 7,
Figs. 9–10).
Diagnosis: Species of Torellella irregular and curved in
shape; angle of wall divergence variable, increased sharply
near the proximal part.
Description: Small phosphatic, elongated, tube fragments of narrow shape and elliptical cross-section. Keels are
not developed. Nearly all tubes show a distinct irregular and
curved tube shape, both laterally and dorsoventrally. The
thickness of the tube walls ranges from 5 to 10 µm. No
different shell-layers are visible. The angle of divergence is
not constant and increases sharply near the narrowest
(proximal) part of the tube. The largest (distal) part of each
tube is clearly more elliptical in section, as in T. mutila.
Most specimens display growth lines, well preserved on
outer surfaces: these structures are regular (e.g. on Fig. 4(6))
or irregular (Fig. 4(8)), and depend on the relative position
(juvenile vs. adult). Ring-like or other ornamentation characters are not observed on outer walls. The inner surfaces of
these hollow tubes are smooth.
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J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
Discussion: As in the case of T. mutila, the material,
growth and curvature patterns, and cross-sections indicate
the affiliation to the genus Torellella.
Occurrence: T. lentiformis is known from the Tommotian of Siberia (Rozanov and Sokolov, 1984), the Tommotian levels of Nuneaton (Brasier, in Cowie and Brasier,
1989), and occurs in Germany overlying lower–middle
Ovetian archaeocyath-bearing carbonates (Elicki, 1994). In
addition, the species is known from Tommotian–Botoman
strata of Mongolia (Rozanov, 1982), and probably from
Massachusetts and Shropshire (Brasier, in Cowie and
Brasier, 1989).
Torellella sp. indet,
Fig. 4(9)
Discussion: This specimen fits with the hitherto described Torellella species in its main tube characteristics.
Hence, the general tube growth pattern, the characteristic
cross-section, and also the tube material is the same. The
degree of divergence is low compared to tube length. The
fossil remain shows a rather long part of the tube with a
more or less circular cross-section. Only at the distal “end”
of the preserved fragment a distinct increase of the angle of
divergence, as well as a change from relatively circular to
elliptical cross-section and a change in direction is present.
The preservation, however, is poor and incomplete, and no
further details can be seen. The mentioned main features of
the tube indicate that the fossil fragment belongs to the
genus Torellella. Neither growth lines, rings nor ridge
structures are observed because of the poor preservation.
Regarding the taxonomic uncertainties of this group, the
specimen is described in open nomenclature.
Family Hyolithelidae WALCOTT, 1886
Genus Hyolithellus BILLINGS, 1871
Type species: Hyolithellus micans (BILLINGS, 1871).
Diagnosis: Small, narrow, conical, calcium–phosphatic
tube, curved and irregular near the closed apex and
straighten toward the aperture; low angle of wall divergence; circular cross-section; shell composed of thin lami-
nae that thicken progressively toward the aperture; the latter
perpendicular to shell axis; exterior surface sometimes
covered by small transverse ridgelets and striae, inner
surface smooth.
Remarks: In the original diagnosis an “operculum” was
included that was later identified as a fossil remain of
another organism (Bengtson et al., 1990). Several uncertainties need to be addressed: the specific affinity of this genus
is taxonomically very problematic by comparison with the
other Hyolithelmintes group (Torellella). The poor preservation of the observed specimens does not allow classification at the species level. Distinct thickness variation is not
useful as a diagnostic character.
Hyolithellus sp. indet,
Fig. 5(1–3).
Description: Narrow, curved, phosphatic tube fragments
with a circular cross-section. The curved (proximal) part
occupies a significative part of the total length. The angle of
divergence is low and constant. Preservation is poor, but
some more or less regular ridges are visible on the outer
surface (Fig. 5(1,2)); the distance between these structures
is around 15 µm. An increase in ridge separation on the
“proximal” part may be present. Other ornamental characters are not observed. The inner surface is generally smooth.
The maximum diameter of the tube fragments is about
200 µm. The wall-thickness is irregular and ranges from 14
to 20 µm in the same level of the tube (Fig. 5(2)). The tube
wall of the specimens seems to be three-layered (Fig. 5(3)):
the poor and only locally preserved inner and outer layers
are less than 7 µm thick, whereas the middle (main) layer is
11–18 µm thick. None of the layers show any distinct
internal pattern (sublayering, crystal orientation, etc.).
Discussion: Because of the tube composition, the circular cross-section and the general shape, the described
specimens are assigned to the genus Hyolithellus.
Occurrence: Hyolithellus display a wide paleogeographic distribution (Siberia, Mongolia, India, North and
South America, Australia, Antarctica, Europe) in Lower to
Fig. 3. Archaeocyaths of the Caunes–Minervois thrust sheet. (1) Anthomorpha margarita BORNEMANN; longitudinal section of an intervallum fragment,
MNHN M84265 (AL 15a.2). (2) Anthomorpha immanis DEBRENNE; longitudinal section with exocyathoid outgrowths at the base, MNHN M84266 (AL
CMO). (3) Protropharetra stipata DEBRENNE; transverse section of a young cup, MNHN M84261 (AL 2.2). (4) Dictyocyathus cf. verticillus
(BORNEMANN); stretched transversal cup, MNHN M84263 (AL 15a.1). (5) Carinacyathidae gen et sp. indet; longitudinal section showing the S-shaped,
outer wall with non-communicating canals, MNHN M84268 (AL 15c.2). (6) ?Afiacyathus sp.; rare synapticulae, MNHN M84267 (AL 1). (7) ?Chouberticyathus sp.; transverse section of a skeleton replaced by sparry calcite, surrounded by sponge spicules (AL 15b). (8) Anthomorpha margarita BORNEMANN;
transverse basal section with vesicular tabulae, MNHN M84264 (AL 2). (9) Erismacoscinus cf. elongatus (BORNEMANN); oblique longitudinal section,
MNHN M84259 (AL 6). (10) Inessocyathus levis DEBRENNE; oblique longitudinal section, MNHN M84258 (AL 1a). (11) Erismacoscinus cf. calathus
(BORNEMANN); longitudinal section of an intervallum fragment (AL 4a).
Fig. 3. Archéocyathes de l’écaille tectonique de Caunes–Minervois. (1) Anthomorpha margarita BORNEMANN; fragment d’intervallum, MNHN M84265
(AL 15a.2). (2) Anthomorpha immanis DEBRENNE; section longitudinale avec excroissances exocyathoïdes à la base, MNHN M84266 (AL CMO). (3)
Protropharetra stipata DEBRENNE; section transversale d’un calice jeune, MNHN M84261 (AL 2.2). (4) Dictyocyathus cf verticillus (BORNEMANN);
section transversale d’un calice étiré, MNHN M84263 (AL 15a.1). (5) Carinacyathidae; section longitudinale montrant les canaux non-communiquants en
S, MNHN M84268 (AL 15c.2). (6) ?Afiacyathus sp.; rares synapticulae, MNHN M84267 (AL 1). (7) ?Chouberticyathus sp.; section transversale, le squelette
est remplacé par de la sparite (AL 15b). (8) Anthomorpha margarita Bornemann; section transversale basale avec tabulae vésiculaires, MNHN M84264 (AL
2). (9) Erismacoscinus cf. elongatus (BORNEMANN); section oblique longitudinale, MNHN M84259 (AL 6). (10) Inessocyathus levis DEBRENNE; section
longitudinale oblique, MNHN M84258 (AL 1a). (11) Erismacoscinus cf. calathus (BORNEMANN); fragment d’intervallum (AL 4a).
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
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Middle Cambrian strata, and is not indicative of a distinct
biostratigraphic level (Matthews and Missarzhevsky, 1975;
Brasier and Singh, 1987; Landing, 1988, 1991; Missarzhevsky, 1989; Bengtson et al., 1990; Landing and Bartowski, 1996), although its species could display biostratigraphic utility. This genus is known in Europe from England
and Scandinavia (Fisher, 1962). An old report of a single
finding from Germany (Schwarzbach, 1934: “...slim and
round small rods maybe belong to the genus Hyolithellus...”) is ambiguous. No further findings are reported since
then, and re-investigation is not possible because the material is neither figured nor described, and was lost during the
Second World War.
Phylum, Class, Order and Family uncertain
Genus Yunnanodus WANG and JIANG (in Jiang, 1980)
Type species: Yunnanodus dolerus WANG and JIANG
(in Jiang, 1980).
Diagnosis: Small (about 1 mm), spine-shaped sclerites
with small basal plate, the latter bearing short denticles; thin
wall, of unknown composition; internal cavity extending
throughout the spine length of spine (after Wang and Jiang
(in Jiang, 1980); Qian and Bengtson, 1989).
Yunnanodus dolerus WANG and JIANG (in Jiang, 1980).
1980 Yunnanodus dolerus nov. sp. (Jiang, 1980, p. 86; pl.
2, Figs. 13–16).
1980 Yunnanodus doleres (Luo et al., 1980, pl. 1, Fig.
11).
1984 Yunnanodus doleres (Xing et al., 1984, pl. 10, Fig.
6).
1984 Yunnanodus doleres (Qian, 1984, pl. 3, Figs. 9–10).
1984 Yunnanodus doleres (Luo et al., 1984, pl. 11, Fig.
7).
1989 Yunnanodus dolerus (Qian and Bengtson, 1989,
Figs. 44–45).
Yunnanodus cf. dolerus WANG and JIANG (in Jiang,
1980),
Fig. 5(4–5).
Description: Tooth-like fragments consisting of a flat,
more or less slightly concave base (plate), with a large
internal cavity, and one predominant straight spine flanked
by several minor denticles. The cavity continues into the
slightly inclined main spine. The latter is about 1 mm long
with a basal diameter of about 430 µm. Its cross-section is
circular and very slightly flattened. The phosphatic wall is
corroded, so that its detailed internal structure is not visible;
rib-like features on spine and denticles seem to be related to
preservational conditions. Four flanking minor denticles are
preserved (three on one side, one on the opposite one). Their
length decreases with distance from the main spine: the
largest (and nearest) denticle is 280 µm long, and the
smallest (and distal) 200 µm. The denticles show a slightly
flexural aspect, and point to the same direction than the
main spine. Their cross-section is not determinable.
Discussion: Despite its poor preservation, the specimen
described shows all the characters necessary to assign to the
conodont-related genus Yunnanodus WANG and JIANG,
1980 (in Jiang, 1980), presently a monospecific taxon
(Yunnanodus dolerus WANG and JIANG, 1980 (in Jiang,
1980)), and hitherto known only from the middle Meishucunian of south China. The sclerite presented herein differs
from Wang and Jiang’s description by the apparent fewer
number of minor denticles (this, however, could be an effect
of preservation) and a larger plate. Nevertheless, specimens
described and illustrated by Qian and Bengtson (1989)
coincide with the French material in such a fewer number of
(bent) denticles. A difference between the French specimen,
the type species and Qian and Bengtson’s specimens is the
shape of the main spine, which is straight in the former and
slightly curved in the latter ones. Furthermore, the length of
the denticles is slightly bigger in the French specimen
(200–280 µm), in contrast to the Chinese forms which are
100–150 µm. Comparing the type material from Wang and
Jiang (in Jiang, 1980), the specimens of Qian and Bengtson
(1989) and the Lastours one, their morphological differences appear to be of minor importance, quite possibly
representing intraspecific morphological variability. Further
Fig. 4. (1) Torellella mutila MISSARZHEVSKY, 1989; strongly curved initial part with ring-like structures; see two slightly developed keels and the low
angle of divergence (R 11084). (2) Torellella mutila MISSARZHEVSKY, 1989; a detail of the enlarged initial part of the previous tube with well-preserved
ring-like structures (R 11084). (3) Torellella mutila MISSARZHEVSKY, 1989; growth lines on the middle and flattened part of the tube (R 11085). (4)
Torellella mutila MISSARZHEVSKY, 1989; clearly visible regular growth lines on the flattened part of a specimen displaying a low angle of divergence (R
11086). (5) Torellella lentiformis (SYSOIEV, 1962); distinct increase of the tube’s angle of divergence (R 11087). (6) Torellella lentiformis (SYSOIEV, 1962)
(R 11088). (7) Torellella lentiformis (SYSOIEV, 1962); distinct increase of the tube’s angle of divergence and well-developed growth lines (R 11089). (8)
Torellella lentiformis (SYSOIEV, 1962); more irregular growth lines on the middle part of the tube (R 11090). (9) Torellella sp. indet. (R 11091). All scale
bars = 500 µm, except 4.2, 4.6 and 4.8 where = 200 µm.
Fig. 4. (1) Torellella mutila MISSARZHEVSKY, 1989; partie initiale fortement courbée munie de structures ressemblant à des anneaux; il est remarquable
la présence de deux légères quilles et l’angle faible de divergence (R 11084). (2) Torellella mutila MISSARZHEVSKY, 1989; détail de la partie initiale du
tube antérieur montrant des structures ressemblant des anneaux bien préservées (R 11084). (3) Torellella mutila MISSARZHEVSKY, 1989; stries
d’accroissement sur la partie médiane et applatie du tube (R 11085). (4) Torellella mutila MISSARZHEVSKY, 1989; stries régulières d’accroissement nettes
sur la partie applatie de l’exemplaire qui montre un angle faible de divergence (R 11086). (5) Torellella lentiformis (SYSOIEV, 1962); augmentation nette
de l’angle de divergence (R 11087). (6) Torellella lentiformis (SYSOIEV, 1962) (R 11088). (7) Torellella lentiformis (SYSOIEV, 1962); augmentation nette
de l’angle de divergence et développement des stries d’accroissement (R 11089). (8) Torellella lentiformis (SYSOIEV, 1962); plan irrégulier des stries
d’accroissement sur la partie moyenne du tube (R 11090). (9) Torellella sp. indet. (R 11091). Toutes les échelles = 500 µm, à l’exception des Figs. 4.2, 4.6
et 4.8 où sont = 200 µm.
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
405
406
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
findings and more material are necessary to clarify if
attributing these morphological variations to one species is
justifiable.
Yunnanodus? sp.,
Fig. 5(6–7)
Description: Two badly preserved specimens lacking
denticles are questionably assigned to this genus on the
basis of phosphatic conical morphologies with a strongly
corroded plate and a well-preserved, straight, main spine.
The latter is slightly inclined, 1.100 µm long and displays a
distinct deep internal cavity. The basal diameter of the spine
is subcircular and about 500 µm. The morphology of the
plate is not determinable and minor denticles are not
observed, both characters seemingly due to poor preservation.
The other fragmented sclerite shows a badly preserved
spine, slightly curved, about 1 mm long, and contains a
distinct deep internal cavity. The basal diameter of the
phosphatic spine is subcircular and about 500 µm. No
morphological features are visible on the surface of the
spine. Minor denticles or other elements are not observed.
Discussion: These specimens differ from these assigned
positively to Y. dolerus in the morphology of the plate,
which is only partly preserved, and the primary existence of
minor denticles. Because of the size and material of the
sclerites, the shape and inclination of the main spine, and
the existence of the characteristic internal cavity, the specimens reported here are related to the genus Yunnanodus.
However, due to the lack of denticles (preservational
aspects?), which is a diagnostic character by original
definition, the specimen is reported in open nomenclature.
4. Paleoecological and biostratigraphic implications
The described subunits were deposited in a spectrum of
environments ranging from calm settings, seldom affected
by turbulence, to those frequently washed by waves and
currents. Lower energy deposits dominate the mottled
limestones, whereas sediments deposited under higher conditions are floatstones and packstones. The mottled limestones are interpreted to represent deposition in a moder-
ately shallow, open-platform setting below weather wave
base, but within the episodic action of storm waves. Storms
were probably responsible for the generation of intraclasts,
and packstone and floatstone beds. The lack of evidence for
gravity-driven flow suggest that the topographic relief was
minor. Neither consistent paleocurrent directions were determined nor channel-like features observed.
The lower member of the Lastours Formation contains
the youngest archaeocyathan assemblage of the southern
Montagne Noire. Fossiliferous beds in the Lower Cambrian
of the Montagne Noire are scarce and bounded by thick
intervening barren intervals. This is particularly true for
trilobite-bearing beds, whereas archaeocyaths are found in a
considerable greater number on the Pardailhan and the
lower part of the Lastours Formations. In summary, the
whole siliciclastic–carbonate sections of the Pardailhan
Formation and the lower member of the Lastours Formation
can be correlated with the Siberian Botoman stage (Fig. 2),
based on the presence of the archaeocyath-index Anthomorpha, while trilobites appear as isolated assemblages both in
the Pardailhan Formation and the upper member of the
overlying Lastours Formation.
5. Conclusions
The Lastours Formation represents a small piece of a
wide carbonate platform that bordered the western Gondwana margin in Early Cambrian time (Álvaro et al., 2000).
The limestones of the lower member of the Lastours
Formation, cropping out in the Caunes–Minervois thrust
sheet (Pardailhan nappe, southern Montagne Noire), represent alternation of two marine depositional environments:
relatively low energy, shallow subtidal substrates, highly
bioturbated (mottled limestones); and reef flanks or interreef settings, containing centimetre-thick microbial patch
reefs surrounded by washed archaeocyath-spiculate shelly
pavements. Sedimentary structures related to wave, current
and/or storm action (erosional surfaces, graded beds and
packstone textures) are common, recognized as laterally
correlatable layers (up to 20 cm thick), which reflect intensive washing and winnowing. The common development of
Fig. 5. (1) Hyolithellus sp. indet; round cross-section showing some ridges on the outer surface (scale bar = 200 µm) (R 11092). (2) Hyolithellus sp. indet;
a detail of the previous specimen with a smooth inner surface and ridge-like ornamentation (scale bar = 100 µm) (R 11092). (3) Hyolithellus sp. indet; variable
thickness of the three-layered wall on the same specimen; inner and outer layer altered (scale bar = 50 µm) (R 11092). (4) Yunnanodus cf. dolerus WANG
and JIANG, 1980; flat base with one inclined main spine and four minor denticles (scale bar = 1 mm) (R 11093). (5) Yunnanodus cf. dolerus WANG and
JIANG, 1980; a detail of the previous specimen exhibiting well-preserved four minor denticles (scale bar = 500 µm) (R 11093). (6) Yunnanodus? sp.; large
basal cavity, corroded plate and main spine (scale bar = 500 µm) (R 11094). (7) Yunnanodus? sp. (scale bar = 500 µm) (R 11095).
Fig. 5. (1) Hyolithellus sp. indet; section transversale subcirculaire montrant quelques crêtes sur la surface extérieure (échelle = 200 µm) (R 11092). (2)
Hyolithellus sp. indet; détail de l’exemplaire antérieur avec une surface intérieure lisse et une ornementation à partir de crêtes légères (échelle = 100 µm) (R
11092). (3) Hyolithellus sp. indet; épaisseur variable de la paroi composée de trois couches, l’intérieur et l’extérieur altérées (échelle = 50 µm) (R 11092).
(4) Yunnanodus cf. dolerus WANG and JIANG, 1980; base plate avec une épine majeure inclinée et quatre denticules (échelle = 1 mm) (R 11093). (5)
Yunnanodus cf. dolerus WANG and JIANG, 1980; détail de l’exemplaire antérieur montrant quatre denticules bien préservés (échelle = 500 µm) (R 11093).
(6) Yunnanodus? sp.; cavité basale large, plaque corrodée et épine principale (échelle = 500 µm) (R 11094). (7) Yunnanodus? sp. (échelle = 500 µm) (R
11095).
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
407
408
J. Javier Álvaro et al. / Geobios 35 (2002) 397–409
microbial boundstones, abundant infaunal activity, and a
diversity of shelly fauna indicate a well-oxygenated, openmarine setting. Quieter parts of the platform recorded
carbonate mud substrates characterized by burrow mottling.
Due to the abundance of mud matrix there is no evidence
of synsedimentary and cementation. This is corroborated by
medium to high degree of bioturbation. Most of the biogenic
disturbance appears as nondiagnostic, centimetre-sized mottling recognized as burrow systems. They form irregular,
vertical and horizontal networks, whose fills lack any
lamination and walls are sharp and sinuous. The burrow fill
is composed of sucrosic dolomite reflecting cementation in
a biogenically induced, diagenetic microenvironment.
An archaeocyathan assemblage (dominated by Anthomorpha and Inessocyathus) is composed of the following
species: Inessocyathus levis DEBRENNE, 1964 (reported
for the first time in the southern Montagne Noire), ?Afiacyathus sp., Carinacyathidae gen. et sp. indet, Erismacoscinina gen. et sp. indet, Erismacoscinus cf. elongatus
(BORNEMANN, 1886), Erismacoscinus cf. calathus
(BORNEMANN, 1886), Protopharetra stipata DEBRENNE, 1964, ?Chouberticyathus sp., Dictyocyathus cf.
verticillus (BORNEMANN, 1891), Anthomorpha margarita
BORNEMANN, 1886 and Anthomorpha immanis DEBRENNE, 1964. Phosphate-shell microfossils are dominated by hyolithelminths (genera Hyolithellus and Torellella) and conodont-related sclerites (genus Yunnanodus).
Other abundant but unidentified fossil debris consist of
calcisponge spicules, linguliformean brachiopods, trilobite
debris, hyoliths and echinoderm ossicles. The fossil assemblage is Botoman in age, dated on the basis of archaeocyaths.
From a biofacies and sedimentological point of view, the
Caunes–Minervois thrust outcrops are similar to those of the
Orbiel valley (whose sections were named Artigues, Caunette and Grézilhou by Debrenne, 1964), where the stratotypes of both the Pardailhan and Lastours Formations were
defined (Álvaro et al., 1998a). Retecoscinus boyeri, relatively abundant in the underlying Pardailhan Formation
(Debrenne, 1964), is absent in the lower member of the
Lastours Formation. However, this lack is difficult to
interpret in terms of biostratigraphy versus paleoecological
conditions.
Acknowledgements
The authors are indebted to Brian Pratt and another
anonymous referee who kindly improved the ideas expressed in this manuscript. Laboratory work and access to
scanning microscopy facilities were arranged in the laboratory LP3 of Lille by G. Ponchel. Assistance in collecting
samples was undertaken by Z.A. Herrera and E. Villas. Field
work was supported by Project ATI 15–52. This paper is a
contribution to PICS French–Chinese Project.
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