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II. STOPS N° 1-6

A. STOP N° 1 : THE STEPHANIAN BASIN OF GRAISSESSAC (FIG. 1 ; JGA)
The Graissessac coal basin has a simple overall structure consisting of a long, narrow syncline, 22 km by 3 km, running on a E-W axis and dipping towards the east under the Permian Lodève basin. It is located along the northern border of the axial zone of the Hercynian Montagne Noire. It is filled by fluvio-torrential, fluviatile and lacustrine deposits typical of an intra-mountain basin. Deposits are transgressive on Hercynian structures to the north but are bounded by a fault in contact with the axial metamorphic zone and the Cambrian of the Saint-Gervais mountains to the south. The geology of the basin has been investigated by LOUIS (1954), BECQ-GIRAUDON (1973, 1984) and more recently SAINT-MARTIN (1993) who recognized features characterizing active synsedimentary extensive tectonic (such as stretched pebbles in conglomerates, metric to large scale south-verging recumbent folds resulting from shearing along series tilted toward the bounding fault ; early normal faults). The East-West syncline is eroded and sealed by the unconformable sedimentary deposits of the Permian of the Lodève basin. According to SAINT-MARTIN (1993) the Graissessac basin does not correspond to a typical extensional half graben basin such as the Lodève basin ; the setting and structure of the two neighbouring and successive basins do not agree with the hypothesis (BECQ-GIRAUDON & VAN DEN DRIESSCHE 1993) of a single Stephano-Permian extensional tectonic event. To the south, the Graissessac basin is bounded by normal faults that correspond to a North-South extensive phase. This extension is superimposed on the extensional ductile deformation which affects the eastern part of the Axial Zone gneissic dome (SAINT-MARTIN 1993).
BECQ-GIRAUDON (1973) described the basin as a torrential detritic cone and distinguished an area of conglomerates in the west and a zone of worked coal seams on the east.
The Graissessac coal field has been worked since the 18th century and reached its peak of production in about 1918. It stopped only a few years ago after the closure of several opencast quarries.
Rich and well preserved floras have been collected in many localities (GRAND’EURY 1877 ; BECQ-GIRAUDON 1973). A list of about sixty species (DOUBINGER et al. 1983) is characteristic of a Late Stephanian age as recently defined by DOUBINGER et al. (1995). The major groups of plants are represented : lycopsids with locally abundant Sigillaria (in contact with coal seams), sphenopsids with very common Calamites, Asterophyllites, Annularia and Sphenophyllum ; filicopsids with the abundant arborescent psaroniaceous ferns (diverse species of Pecopteris) and the smaller Renaultia – Sphenopteris ; a great diversity of pteridosperms (Alethopteris, Callipteridium, Dicksonites, Neuropteris, Odontopteris and diverse seeds) ; and finally cordaites which are common in coarser sediments. Trunks and fossil woods of Calamites and Cordaites have also been recognized (GALTIER et al. 1997). Work in progress on the palaeoecology (MARTIN-CLOSAS & GALTIER 1998) allows recognition of different contemporaneous plant associations characterized by differences in taphonomy and transport.
The microflora is not well preserved, DOUBINGER provided a list of about twenty species with dominant monoletes spores (Laevigatosporites, Punctatosporites) corresponding to the arborescent ferns whilst pollen grains are represented by Wilsonites and Florinites (DOUBINGER et al 1983).
The fauna is rare ; fishes have been recorded by BERGERON (1889) and LOUIS (1954) ; BECQ-GIRAUDON (1973) mentioned invertebrates bivalves (Carbonicola) and insects (Blattinopsis and one Protorthoptera) ; other arthropods and insects have been recently collected by GALTIER and are currently under study by BETHOUX.

B. STOPS N° 2-6 : THE LODEVE BASIN AND THE TRIASSIC COVER.

1. Between stops 1 and 2, presentation in the bus of the Lodève basin and its triassic and hettangian cover (fig. 2-4 ; GG, JG, JGa)

Fig 2 –; The Lodève permian basin : stops 2-6

* Structural setting (fig. 2, 3 and 4).

The Lodève Basin is a half graben scaled to the south. It is, above all, filled up by Permian deposits resting unconformably on Carboniferous sediments (fig. 3A).
The following text is taken from BROUTIN, CHATEAUNEUF & MATHIS 1992

Fig3AC–A = N-S cross - section of the permian Lodève basin ; B = F1-F5 Formations, A = Autunian Group, B : Saxonian Group (Odin 1986, part) ; C = sedimentological interpretation of the Salagou Formation on the west border (Garric 2001).

“ The basin is crossed by three sets of faults :
“ – NNE-SSW, the Orb fault zone. This brings into contact the Upper Carboniferous-Permian Graissesac basin with the Upper Permian of the extreme western end of the Lodève Basin. The Olmet Fault divides the basin in two parts, letting down the Mesozoic plateau between Lunas and Lodève. The Cevennes faults, with deep-seated strike-slip movement, separate the Permian basin from the Oligocene plain of Languedoc.
“ – ENE-WSW (N 70°-N 110°’). These are common and the main sources of mineralization (in particular uranium, but also galena, sphalerite, etc.), extending from the east to the centre of the basin along its long axis. These faults have commonly convexly curved, north-dipping fault planes, rooted in the Cambrian basement, and are associated with south-dipping antithetic faults. They were active during and immediately after the Permian sedimentation and disappear beneath the Mesozoic deposits. They have in general been reactivated during later tectonic phases, in particular under the effect of north-directed Alpine compression. In the south, the Aires Fault bounds the southern part of the basin where it is bordered by the minor Mourèze through.
“ – N-S. This direction is represented by a system of simple open fractures along which basic dykes have been emplaced, feeding the Pliocene-Quaternary (1,6-0,7 Ma) volcanic structures aligned north-south.”

Fig 3DE. D = la Tour faciès : fan conglomerats outcrops with debris-flow, mass-flow, stream-flow; E = The typical "Ruffes" landscape : alternation of thin sand/siltstones beds with mud-cracks and thick red mud/siltstones layers; S = "le lac du Salagou", Ls = basalte of la Sure (Odin 1986).

* Lithostratigraphy (GG, JS).
Permian deposits were subdivided for a long time (FEYS & GREBER 1972) into 2 large megasequences. The basalmost is the Autunian Group. It will be studied during stops n°5 and 6. The second is the Saxonian Group. It rests unconformably upon the preceding one.
The Saxonian is about 2500 m thick. It is a vertical succession of predominantly fine grained deposits ; in the western part of the basin conglomeratic levels are intercalated. They are successively, from base to top : St Xist, la Tour, la Lieude ‘facies’ (KRUSEMAN 1965). ODIN (1986) has distinguished 2 Formations in the Saxonian :
– F4 is the Rabejac Formation in which, from west to east part of the basin, ODIN has described St-Xist, Rabejac and Lafont facies. This Formation starts with conglomerates erosive on the Autunian. They extend the entire basin but are thicker and coarser from East to West. Near la Tour-sur-Orb area (fig. 2), they are clearly fan conglomerates (St-Xist facies) meaning that the Bousquet d’Orb / la Tour-sur-Orb border fault was very active, creating a source area that provides a persistent supply of coarse debris spreading to the east. Above the conglomerates follow red sandstones and mudstones with abundant sedimentary structures indicating a subaerial deposition : ripple marks, desiccation cracks, footprints and invertebrates tracks.
The Rabejac Formation consists generally of alluvial fan deposits and may be connected with the Saalian volcano-tectonic events.
– F5 is the Salagou Formation about 2000 m thick against the Aires fault. From east to west, one can see the following facies. The Octon facies is made of very fined grained deposits outcrouping widely in the west part of the basin (= regional ‘Ruffes’ landscape). It is a cyclic alternation of 1-meter to 10-meter thick red massive (hitherto unfossiliferous) mud / siltstones with cm thick yellowish-gray carbonaceous siltstone horizons with desiccation cracks, water ripples, invertebrate tracks and arthropod remains. Some of these siltstone horizons were mapped and numbered (N°. 100 – 1000 ; R in fig. 4) by HENRIOT (1988, unpublished) of COGEMA. (For more details see stop 3 : NMILA, A., CABANIS, B., LEROY, S., HENRIOT, O. & MATHIS, V. (1992) ; KÖRNER (1999).
Westward of the Octon village, the transition to the following Merifons facies could be observed. The frequency of the cycles increased drastically – the red mudstone / siltstone part decreased to decimetres and the carbonaceous desiccation crack-horizons are apparently more frequent. The colour of the latter one changed to pale green ; often they form large surfaces with beautiful desiccation cracks. The La Lieude facies in the top of the Merifons facies should be regarded as a separate formation in the future. Their base is marked by the sudden shedding of debris flow fanglomerates after hundreds of metres of nearly exclusive pelitic sediments. Just within this level Therapsida footprints occur (GAND et al. 2000). Higher up in the profile, the pelitic intercalations disappear between stacked fanglomerates and sandstone horizons. The very coarse La Tour facies in the south-west corner of the basin represents the proximal fan deposits of the La Lieude facies. The drastic facies change from the Merifons to the La Lieude facies is now under discussion in terms of climatic change and/or tectonic activation (KÖRNER et al. 2001).

Fig 4
The Permian series of the Lodève basin. A =Autunian group with F1-F3 Formations, B = Saxonian Group with F4, F5 Formations (Odin 1986), C = F12-F35 saxonian fossiliferous sites ; Stratigraphy : COGEMA = Compagnie Générale d’Exploitation des Matières Nucléaires, E = Members (Laversanne 1976), V.a. = volcanic ashes indicated by roman numbers, Beds from 57 to 00 with alpha, béta, gamma = bone beds, R = 100-1000 COGEMA markers ; Palaeontology : Traces Inv. = invertebrates ; Traces Ver. = footprints ; Flora, M.f = macroflora, P.a = palynology ; Fauna Ver = vertebrates, Inv. = invertebrates.

* Paleomagnetism
Reproduced from MERABET, N. & GUILLAUME, A.(1988) :

“ The Lodève basin is a reference site for the determination of the Permian magnetic poles of the Western European Block.
“ Sedimentary formations (pelites) from the Lodève basin (43°41.5’N latitude, 3°21’E longitude), of Permian age, have been studied by applying thermal and alternating fields, and thermal followed by alternating field demagnetization. The principal Saxonian magnetization has a mean, derived from 93 specimens giving unit weight to the six sites, of D = – 160.6°, I = – 11.8°, alpha 95 = 1.5° ’, and a corresponding north paleopole at 48.6° N, 153.5° E, K = 2096, A95 = 1.2°. The mean direction of the principal Autunian magnetization from 65 specimens, giving unit weight to each of the eight sites, is D = – 169.7°, I = 6.4°, alpha 95 = 3.0°. This direction corresponds to a north paleopole at 42.2° N, 169.4° E, K=517, 95 = 2.2°. These Autunian and Saxonian poles are very close, respectively, to intervals 270-290 Ma and 240-260 Ma of the European polar wander path, close to the Permian poles derived from the Lodève basin by KRUSEMAN (1962) (Saxonian and Autunian poles are situated, respectively, at 48° N, 164° E). 44.5’N, 178’E).”

* Flora, Fauna, Palichnofauna (fig. 5 ; GG).
• Connected with the colour of the Formations, Macro and microflora are only really present in grey levels of the Autunian (F1 Usclas and St-Privat – F2 Tuilières-Loiras Formations ; fig. 4). Nevertheless, sometimes in red layers (Rabejac) and especially in green beds of the Salagou Formation, a macroflora may be found but it is rather indeterminable. The main Autunian taxa are located at stop n° 5 stop as are vertebrates. These were first mentioned in the 19th century and also come from the Autunian. They include a skeleton of an Araeoscelidian, some remains of amphibians and fishes and bones-beds from the Viala Formation are also found at the top of the Salagou Formation.

Fig 5– Permian footprints of the Lodève basin.La Lieude : Dl = Merifontichnus thalerius, D2 = Lunaepes ollierorum, D3 = Planipes brachydactylus, D4 = Brontopus circagiganteus, D5 = Brontopus giganteus ; Rabejac et Cambouras : C1 = Varanopus curvidactylus, C2 et C3 = : Dimetropus leisnerianus ; C4 = Anthichnium salamandroides, C5 = : Dromopus didactylus, C6, C7 = Hyloidichnus major ; C8 = Limnopus sp. ; Formation du Viala et Membre du Mas d’Alary : B1 et B2 = Salichnium decessus, B3 = Salichnium pectinatus, B4 et B5 = Anthichnium salamandroides, B6 et B7 : Limnopus zeilleri, B8 = Limnopus regularis, B9 = Varanopus cf rigidus, B10 = Amphisauropus latus, B11 = Dimetropus leisnerianus, B12 = D. nicolasi, Bl3 = Dromopus lacertoides, B14 et B15 : cf Ichniotherium ; Formations F1 et F2 ; A1 et A2 = Limnopus zeilleri, A3 = Anthichnium salamandroides, A4 = Dromopus lacertoides, A5 = cf. Anthichnium sp., A6 = Dimetropus nic

• Invertebrate tracks and footprints are common in all Formations with 3 remarkable sites : Cogema quarry (Mas d’Alary Member), Rabejac quarry (Rabejac Formation) and the paleontological slab of ‘la Lieude’ (Salagou Formation top). First observations of footprints were made by F. and P. ELLENBERGER (1959) with new findings and studies provided by HEYLER & LESSERTISSEUR 1962 who described 14 new genera and 16 new ‘species’. ELLENBERGER (1983-1984) distinguished and named‘almost 130 new ichnotypes’. After undertaking a revision of French Permian footprints from prospecting in all the French basins and visiting several European fossil collections or sites, GAND 1987 proposed only 14 ichnogenera and 22 ichnospecies. The following list is a little shorter with 16 ichnospecies.
+ Traces attributed to Temnospondyls (Branchiosauridea and Micromelerpetondidea ?) = Anthichnium salamandroides (GEINITZ, 1861) HAUBOLD, 1971 with undertracks of Salichnium decessus or S. pectinatus (HEYLER & LESSERTISSEUR, 1963) ; Eryopsidea : Limnopus zeilleri(DELAGE, 1912) GAND, 1985 ; Amphisauropus latus HAUBOLD, 1970.
+ Traces ascribable to Amniotes ; Captorhinomorpha with Hyloïdichnus major (HEYLER & LESSERTISSEUR, 1963), HAUBOLD, 1971 ; Varanopus curvidactylus MOODIE, 1929 (SARJEANT, 1971), Microsauripus acutipes MOODIE, 1929 (SARJEANT, 1971) ; Varanopus rigidus GAND, 1989 ; Pelycosauria Eupelycosauria with Dimetropus leisnerianus (GEINITZ, 1863) HAUBOLD, 1971, Dimetropus nicolasi GAND & HAUBOLD, 1971 being its undertrack ; Edaphosauria : Ichniotherium cottae (POHLIG, 1886) HAUBOLD, 1971 ; Eosuchia et Araeoscelidia : Dromopus lacertoides (GEINITZ, 1863) HAUBOLD, 1971 ; Dromopus didactylus (MOODIE, 1930) GAND & HAUBOLD, 1984 ; Therapsida or Therosauria : Lunaepes ollierorum, Merifontichnus thalerius, Planipes brachydactylus GAND et al. 2000 ; Caseamorpha or Therapsida : Brontopus circagiganteus, B. giganteus.

Invertebrates tracks are also frequent, above all in the Salagou Formation (see below stop n° 3 ; fig. 6)