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d. STOP 6 : The Autunian paleoflora (JGa, JB)

Fossil macrofloras from the Lodève basin have been known since the 18 th century and have been the object of numerous studies with a special mention to the works of ZEILLER (1898), FLORIN (1938, 1944) and DOUBINGER (1956). These studies concerned mainly plants from the lower deposits belonging to the Usclas – St-Privat Formation. The microflora has been studied by DOUBINGER (1963) and DOUBINGER et al. (1987).

* Flora from the Usclas – St-Privat Formation :
Above the basal conglomerate, black bituminous shales contain fishes and rare plant fragments mainly walchian conifers mentioned by BERGERON (1889) and DOUBINGER (1956). However the most well known flora has been collected from the overlying dark grey pelites in the tile or ‘Tuilières’ quarries near Soumont. Plants are preserved as compressions. Specimens representative of this famous flora are present in many Museum collections in France and abroad. DOUBINGER (1956) listed 46 species for the ‘Tuilières’ flora ; she emphasized the abundance and diversity of the walchian conifers (12 species) and of the callipterids (11 species). Recent quantitative study of more than one thousand specimens in the collections of the Université des Sciences, Montpellier (BERTHOLON 1996) revealed in fact an assemblage strongly dominated by the conifers Walchiaceae with more than 85% specimens (Walchia piniformis and Culmitzchia frondosa being the most common species) whilst callipterids are the second most important group but with less than 10% of specimens. The other taxa (Cordaitales, Ginkgoales, Cycadales, Medullosaceae, lycopsids, sphenopsids and ferns) represent less than one to a few percent of the total specimens. According to DOUBINGER (1956) the flora from the Assise de Millery (Upper Autunian) in the Autun basin is very similar to this Lodève flora ; indeed the two have 18 species in common however in Autun (BROUTIN et al. 1999) the callipterids are more abundant in relative number whilst less diversified (only 5 species). Floras from the Lower Rotliegend of Germany are quite comparable to the Lodève flora ; as an example the flora of the Oberhausen locality of the Saar-Nahe Basin described by KERP et al. (1990) is also strongly dominated by conifers (particularly Otovicia hypnoides which is also present at Lodève). The Lodève flora has been sometimes interpreted as having affinities with the Stephanian but it is noteworthy that its dominant elements (conifers and callipterids) have never been found in the nearby Stephanian basin of Graissessac.

Microflora : DOUBINGER (1963, 1974) and DOUBINGER et al. (1987) described an association LO1 dominated by Potoneisporites and monosaccate pollen (about 70%) with bisaccate pollen as second group which reflect the radiation of conifers. DOUBINGER suggested, on this basis, a correlation with the Assise de Muse of the Autun basin referred to the late lower Autunian (BROUTIN et al. 1999).

* Floras from the Tuilères – Loiras Formation :
DOUBINGER (1963) briefly described but not illustrated a plant assemblage from the transition zone of the ‘Alternating Autunian’ collected near Mas d’Alary and DOUBINGER & KRUSEMAN (1965) mentionned a small contemporaneous assemblage collected between St-Alban and St-Martin-du-Bosc. Recently GALTIER & BROUTIN (1995) described a similar flora from an abundant material collected in the COGEMA uranium mine : plants occurred in a light grey silstone at the base of bed 3, several meters above the cinerite VIII. Therefore it is situated near the top of the Tuilières – Loiras Formation. The plant assemblage is equally dominated by Autunia conferta and Walchia piniformis and characterized by a diversity of callipterids and conifers, all present in the underlying flora from the Tuilières with the exception of Peltaspermum martensii. The occurrence of ‘Stephanian elements’ like Calamites, Annularia, Sphenophyllum thonii is noteworthy and has been interpreted (DOUBINGER 1963, GALTIER & BROUTIN 1995) as evidence that small areas of coal swamp-type persisted during the Autunian. This is supported by the occurrence of some microfloras dominated by monolete spores (DOUBINGER & KRUSEMAN 1965). However most microfloras (association LO2 of DOUBINGER et al. 1987) reflect the overall dominance of conifers with monosaccate pollen first and bisaccate much more abundant than in the underlying LO1 association. According to DOUBINGER et al. (1987) this LO2 microflora is similar to several american ones of Leonardian age.

* Floras from the Viala Formation
DOUBINGER & KRUSEMAN (1965) and DOUBINGER & HEYLER (1975) described plants preserved as impressions or casts, without organic matter from the Fm. de Rabejac. and ‘Red Autunian’. These plants are difficult to identify at the specific if not generic level. The assemblage comprises some taxa with a large stratigraphic range (Autunia conferta, Ernestiodendron filiciforme) whilst Supaia is mentionned for the first time in west Europe. Microfloras (association LO3 of DOUBINGER et al. 1987) show the dominance of bisaccate pollen and the regression of monosaccate and some pollen of the genus Lueckisporites (L.globosus, L. singhii) known in European ‘Thuringian’ strata.

Fig 20–West-part of the the Tréviels quarry after Jacques Garric. At the top of the quarry, one can see the alpha bone-bed of the Lower Viala Member. They are rich with amphibian and reptile remains ; stratigraphical marks are precised with arabic numbers for beds and with roman numbers for ashes (= cinérites) (location after JG) ; Faults cut up into blocks the Autunian Group. They were active during the sedimentation and bear U, Pb, Cu and Zn mineralizations coming from the bituminous shales.

III. THE GRAISSESSAC, LODEVE BASINS AND TRIASSIC COVER AGES.

A. THE GRAISSESSAC BASIN (JGA, JB).

Carboniferous deposits from the Graissessac basin are definitely of Late Stephanian age s.l. (DOUBINGER et al. 1995) with the notable absence of any remains of walchiaceans and callipterids (see the stop 1 text).

B. THE LODEVE BASIN (FIG. 4 ; 10)

1. the Autunian Group.
* Flora (JGa, JB). In contrast the macrofloras found in the lower Formations (Usclas, Tuilières–Loiras) of the Lodève bsin are dominated by the walchiaceans and callipterids and the macro- and microfloral assemblages are almost identical to the Autunian floras as defined in the Autun Basin.
It must be noted that in the basal part of the Saar-Nahe Basin, the most recent radiometric datings give ages of 298.7 ± 5.3 m.y. and 297.8 ± 5.8 m.y. According to SCHÄFER and KORSCH (1998) who positioned the Carboniferous – Permian boundary at 298 m.y. the entire Lower Rotliegend would possibly be Carboniferous in age.
In the absence of any radiometric data for the Lodève Basin this question remains open in this area. If the hypothesis is true that the lower deposits of the Lodève Basin are synchroneous with the Lower Rotliegend, this would imply that the Usclas more Tuilières–Loiras Formations are of Late Carboniferous age. In consequence the entire stratigraphic succession of the Graissessac more Lodève deposits should be reconsidered.
See the stop 6 text

2. The Saxonian Group.
* Insects (AN, JS, OB).
• Results of 1997.
The Phyloblatta specimens from Vignasses and Arièges (F34 and F19, figures 4), are similar to Phyloblatta compactiformis, P. praecurvata, P. cf. deserta from Upper Rotliegend I of the Boskovice furrow (Czech) and to P. compacta from Leonardian of Kansas (SCHNEIDER, 1984 a and b). From this, the F34-F39 insect levels could be dated as Leonardian in age. In addition, the presence of a Diaphanopterodea : Martinoviidae, in the Arièges outcrop and present in the Lower Leonardian of Kansas and Oklahoma, supports this age.
Nevertheless, the Typinae of Arièges, close to Typus of Leonardian and to Arctotypus from the Russian Late Permian, seems rather to indicate Lower Kazanian age for the Arièges level.
This conclusion is also inferred from the new taxa of Protozygoptera, found in Canals (F23) and Bouisset (F31) sites (figure 4) : Epilestes gallica and Lodevia longialata are very similar to Epilestes kargalensis and Permepallage angustissima from the Russian Lower Kazanian. Therefore the range of insects suggests Leonardian – Lower Kazanian ages for the F30-F31 period of the Salagou Formation (figure 4).
• Results of 2001.
Detailed study concerning Odonatoptera (NEL A., GAND G. & GARRIC J., 1999 ; NEL A., GAND G., FLECK G., BETHOUX O., LAPEYRIE J & GARRIC J., 1999) suggested an age as low as Lower Kazanian for the F23-F31 part of the Salagou Formation (fig. 4 B, C). Nevertheless, the above taxa were either unknown before or have a so little known vertical extension that the previous age is, or may not be, accurate. As new and so far unpublished insects coming from the F26-F31 sites are distributed from Lower Kazanian to Ufimian (= Roadian) in others basins, undoubtedly, it is better, to infer the same age for the same part of the Salagou formation (fig. 4). Future investigations will permit us to be more precise of inferred age at stage rank. (OB).
Blattoid insects of the Salagou Fm. indicate an Kungurian to lower Lopingian age. The La Lieude fm. could be therefore of higher Lopingian age (JS).

* Conchostracans (JS).

In comparison to the forms of the Permian of Russia and North America as well as of the German Rotliegend (MARTENS 1983, KOZUR & SITTIG 1981, SCHNEIDER et al., 1995) the profile between Sallèles and Arièges could be Artinskian to Kungurian/Ufimian or even Upper Sakmarian to Kazanian in age. The occurrence of Supaia, a characteristic plant of the Lower Leonardian (READ & MAMAY, 1964) at the Rabejac site (DOUBINGER and HEYLER, 1975) supports a Kungurian age for the base of the Salagou Formation (= Sallèles levels). In the higher Merifons facies of the upper Salagou Formation as well as some ten of metres above the base of the la Lieude Fm., conchostracans with ornamentation typical of Mesozoic forms suggest a Tatarian age (Capitanian to ? Changxingian).
Summing up : Insects and conchostracans of the Salagou fm. indicate a Kungurian to lower Lopingian age. The La Lieude fm. could therefore be of higher Lopingian, i.e. Changxingian age, as suggested from insects, conchostracans and climatic signals.

* Palichnofauna (GG)
The strata containing footprints have been precisely located in the lithostratigraphy which is well known from uranium prospecting. This has formed the basis of a palichnostratigraphic scale on which several ichno-associations have been identified (G. GAND 1987 ; CHATEAUNEUF & GAND 1989 ; GAND 1993).
But, now, if we take into consideration the equivalence between Salichnium decessus, S. pectinatus undertracks, Gilmoreichnus brachydactylus and Anthichnium salamandroides ; D. nicolasi undertrack of Dimetropus leisnerianus, it can be seen that Autunian Group contains footprints confined there as with A. salamandroides, Limnopus zeilleri, Dromopus lacertoides, Amphisauropus latus and Ichniotherium. After age of this similar association, Autunian Group could be Pennsylvanian (Gzhelian) – Sakmarian.
The base of the F4 Formation of the Saxonian Group sees the first appearance of Varanopus curvidactylus / Microsauripus acutipes, Dromopus didactylus and Hyloidichnus major. The three four footprints are known from levels located at the top of the Leonardian Series, near the Castle-Peak (Choza Formation, Clear-Fork Group, Texas). One may date them as Upper Kungurian – Early Ufimian by using the ROSS & ROSS, 1994 scale.
Near the top of the F5 Salagou Formation (la Lieude level) appears a new association with Brontopus giganteus, B. circagiganteus, Merifontichnus thalerius, Planipes brachydactylus, Lunaepes ollierorum. The two last ichnogenus belong also to the ‘Pradineaux Formation’ dated Lower Tatarian (LETHIERS et al. 1993) or Early Thuringian (VISSCHER 1968). So that, based on present data, a large part of the Saxonian Group could range from, at least, the Upper Kungurian to Lower Tatarian.

3. The Triassic cover.

From flora, the series has been dated from Anisian to Rhaetian (fig. 6). The Lower Mudstones Formation (t4-5) is Lower Anisian from the macroflora and palichnological data (Demathieu 1984) but only Middle Anisian from microflora (see above the stop n° 2). On the east and south border of the ‘Massif Central’, it is clear that the Scythian is absent. This means a permotriassic gap of probably 10 m.y. !