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c. STOP n° 5 : The Autunian Group (fig. 16-20).
* Lithostratigraphy (JG, fig. 4)
It is well known through the Gogema works (GARRIC unpublished, Laversanne 1976). The names ‘Grey Autunian’, ‘Alternating Autunian’, ‘Red Autunian’ were utilized as a result of long-standing use by their field geologists (Jacques GARRIC being the discoverer of the Uranium site). Later, ODIN (1986) abandoned this nomenclature and proposed the 3 names of Formations which are used in fig. 4.
The following text is taken from BROUTIN et al. (1992) :
“ •… The F1 Usclas – St-Privat Formation
Fluvio-deltaic deposits that constitute the base of the grey Permian. Their thickness varies considerably, from some 20 m on the sides of palaeovalleys to 100 m in their deepest parts. Lying unconformably on the Cambrian or Stephanian, they are organized into a succession of poorly bedded, approximately 10 m fining-upward sequences, in which the first organic material appears. From fluviatile conglomeratic bases, they pass upwards to deltaic-lacustrine sediments at their tops, with lateral facies variations, deposited under moist tropical climatic conditions.
“ • The F2 Tuilières – Loiras Formation
Lacustrine deposits constituting the greater part of the grey and the red-and-grey Autunian average 300 m thick. These are fine-grained sediments, essentially well-bedded siltstone to mudstone, characterized by the thickening (bed 30) and then thinning (bed 15) of ‘beds’. They are organized in elementary sequences, each one including the following, succession : basal siltstones, carbonaceous ‘bed’ (in French = couche) and calcareous siltstones or shales toward the top. Pyroclastic or dolomitic horizons are often interbedded in the two last layers of the sequence. The Formation was divided by Cogema into three Members (L1 to L3, see Fig. 4), in the upper of which the first red beds appear. The climate was thus characterized by alternating seasons.
“ • The Viala Formation
This formation corresponds to the lower part of the red Permian, and consists of flood-plain deposits. It is truncated at its top by an erosional surface upon which rests the succeeding Rabejac Formation, and which has resulted in a variation of thickness from 50 m at Lunas, in the west, to 330 m at St-Jean-de-la-Blaquière, in the east. The formation is red throughout the basin, consisting of a sandstone-siltstone lower member and a sandstone-mudstone, and thus is overall fining-upwards. A few grey intervals, including ‘bed a’, are nevertheless present and so indicate the accumulation of organic carbon. The climatic condition were those of a dry tropical climate… ”
* The elementary sequence (= facies ‘couche’) (Fig. 16-17). The following text is taken from BROUTIN et al. (1992)

Fig 16 –; Vertical organisation of the sequence type (Autunian Group).

Fig 17 Séquences 46 and 47 of the Usclas - St Privat Formation

“ There are 57 principal elementary sequences averaging about 12 m thick (numbered in Arabic numerals) that are distributed in the F1-F2 Formations described above.They are characterized by grey intervals appearing within compact, uniform grey, green or red pelites. The elementary sequences are composed essentially of two components. A lower siltstone, from 10 cm to several metres thick, with cross-stratification and a slightly erosional base and commonly traces of plants and animal tracks, which is overlaid by interlaminated pale calcareous siltstone and carbonaceous often bituminous mudstone (‘bed’) that may attain 2 m thickness. Mudcracks are commonly present in the top of the sequence. These sequences are very constant and can be traced over fifteen kilometres or more in some instances ; they can be clearly recognized in boreholes.
“ In the upper ‘grey Autunian’ and in the ‘alternative Autunian’ some half dozen of these sequences include other rock types : hard, pale beds of pyroclastic material, including spherolitic and shardy fragments, of extreme regularity and constituting good marker beds, in the middle of the interlaminated unit, and beds of massive dolomite about 10 cm thick in the mud-cracked zone in the upper part of the interlaminated unit. The pyroclastic beds (cinerites, numbered in Roman numerals) also exist elsewhere than in the elementary units. ”
After JG, the paleoenvironmental vertical successions of this sequence are fluviatile to a flood plain passing through a lacustrian background.

* Volcanic-ashes (cinerites) (JG, fig. 18).
They are pyroclastic horizons numbered I to XXIV. Their extent and continuity in the basin allow to do correlations between different areas of the Lodève basin. For description, see fig. 18 legend.

Fig 18– Repères volcaniques du Groupe Autunien. Les bancs de « cinérites » I à X sont présentés dans toute leur épaisseur. Une partie de l’encaissant bitumineux est restée collée au banc X (partie blanche). Ces repères majeurs sont uniques et tous d’aspect différent par la couleur blanche (X) ou gris-noir (III), la structure litée (II, VI), la présence d’une structure en nuages (I et III), en flammèches noires (V et VII), la dolomitisation sommitale (I, II et VI) ou la silicification à la base (I) etc. ; I-X volcanic ashes markers ( = Cinérites) of the Autunian Group (after Jacques Garric). The n° X is white. It is surrounded by bituminous shales. II and X have a rather regular bedding. Others have a « clouded structure » with silice in the base of n° I, carbonates at the top of n° II and VI, asphalt in III, V and VII.

* Geochemical characteristics of the Autunian. (from BROUTIN et al. 1992) :

• Vertical variation in the carbonates
Ankeritic dolomite is present throughout the Autunian and predominates in the ‘upper grey Autunian’, whereas calcite is present only in the ‘red Autunian’ from progressively different sources upwards in the succession, or to progressive variation in the chemistry of the volcanic material that formed the main constituent of the sediments.
• Variation in clay minerals
Illite is present throughout the succession, but kaolinite only in the ‘red Autunian’. Gypsum appears in the upper red Autunian only, but dolomite pseudomorphs of gypsum are present at the base of the Autunian.
* Uraniferous mineralizations. (from CONRAD et ODIN 1984) :
The first signs of uranium were discovered in the Lodève basin in 1957 by the Atomic Energy Commission and it has since been mined by the COGEMA. Open cast mining began in 1978 and mines were productional in 1979. A processing plant works on the mining site. The quantity of exploitable ore has been evaluated at 20 000 tons for an ore of about 0.2%.
Mineralization in the Lodève Autunian are of 3 sorts. BRULHET et al. (1979) have defined these mineralizations :
– An early diagenetic mineralization. It can be found in beaches in the thin levels of bituminous laminites in the ‘red Autunian’ (The red and grey Autunian in our classification). Organic matter has trapped the uranium from the packing waters of the subjacent red sediments.
– A late diagenetic mineralization in the mid Autunian in relation with the molybdenum. It is a result of the trapping of the uranium from volcanic glasses, from montmorillonites etc., from red sediments at the border of synsedimentary breaks, from bituminous laminites and grey arkosic silts, in contact with incipient oils.
– An epigenetic mineralization, the most considerable and the richest, linked to Pre Triassic fracturing. Sulphatic carbonated waters, having crossed the karst Cambrian bedrock, diffused through the Autunian along faults. A reducing environment, rich in organic matter, made possible the precipitation of uranium.

* The outcrops route and the Tréviels quarry (JG, fig. 19-20).
In the west-part of the Tréviels quarry, Uranium was worked by Cogema from the Mas d’Alary Member (beds 00-3) and from the Viala Formation (this last is now embankmented). At the top of the quarry, one can see the alpha, beta bone-beds of the Lower Viala Member. They are rich with amphibian and reptilian remains. Also are beds 00-3 and volcanic ashes II of the Mas d’Alary Member.

Fig 19–Situation of main volcanic ashes in Autunian Group (Mas d’Alary-Mas Lavayre areas) ; They are precised in roman numbers (after Jacques Garric).

Faults cut up into blocks within the Autunian ; they were active during the sedimentation and bear U, Pb, Cu and Zn minerals coming from the bituminous shales.
* Palaeontology (body fossils and footprints ; GG).
• Fauna. It has been found in :
– F1 Usclas and St-Privat – F2 Tuilières–Loiras Formations : Aphelosaurus lutevensis (GERVAIS, 1859) THEVENIN, 1910 (Araeoscelidian, Reptiles) ; ‘Branchiosaurus’, ‘Actinodon’, Discosauriscus (Amphibians) ; Acanthodes sp (Acanthodii), Pygopterus sp. ? (Actinopterygii), Palaeonisciformes, Usclasichthys macrodens HEYLER, 1977 (indet. family Fishes),
– In F3 Viala Formation (alpha, beta, gamma bones-beds) : ‘Actinodon’ (Amphibian), Eryops (Pelycosaurian), Branchiosauroides ?, Expleuracanthus ? (Pleuracanthiformes).(HEYLER 1969, 1997 ;) (cf. fig. 4 A legend).
• Palichnofauna (fig. 5)
There are numerous footprint levels in the Autunian. Some of them are very notable and were discovered in the Uranium quarry opened by Cogema (Mas d’Alary Member). In this way, two large areas bearing several hundred of tracks were studied (GAND 1989). The first reachs 500 m2. It is the ‘C3 surface or Cogema slab’ with more than 500 footprints : Dimetropus leisnerianus and cf. Ichniotherium sp. The second mentioned ‘C" 3 area’ measures about 69 m2 and shows 300 Limnopus zeilleri tracks distributed between 13 trackways. Except Ichniotherium, which is rare and atypical, the two previous others taxa are observed from the base to the top of the Autunian. They are often combined and occur commonly with Anthichnium salamandroides and Dromopus lacertoides. Amphisauropus latus is also found and is apparently as rare as Varanopus rigidus which has been seen once in the upper part of the Autunian (F3 Viala Formation).
The association Dromopus / Anthichnium / Limnopus is very characteristic in the lower Autunian. We have also observed it in the Pennsylvanian (USA), Saar-Nahe basin (Germany), Enville Beds of Hamstead (England). It suggests that Areoscelidia, Temnospondyls trackmakers in the basin known also from bones (see above). Dimetropus and Varanopus reveal also the presence of Pelycosauria and Captorhinomorpha