Paléontologie de Lodève

article paru en français et en anglais dans les bull N° 185 et 186

Bassins Carbonifère de Graissessac et Permien de Lodève

Dans le cadre du congrès international de Sienne (Italie), consacré aux « Événements du Paléozoïque terminal au Trias précoce de l’Europe méditerranéenne et de quelques autres régions », les auteurs du livret-guide ont organisé l’excursion n° 3 dans les bassins de Graissessac et de Lodève. Grâce à des affleurements naturels importants et aux travaux miniers (charbon, uranium), nombreux sont les sondages, les découvertes et les galeries de mines qui ont permis de bien connaître l’organisation spatiale de ces bassins. La version française du livret-guide est publiée dans les bulletins 185 et 186 de la SHNA

EXCURSION N° 3 : THE GRAISSESSAC CARBONIFEROUS

AND LODÈVE PERMIAN BASINS ; (LANGUEDOC – FRANCE)

par GAND Georges, GALTIER Jean, GARRIC Jacques, SCHNEIDER Jörg,
KÖRNER Franck et BETHOUX Olivier

Guide book redaction : GAND, G. ; GALTIER, J. ; GARRIC, J. ; SCHNEIDER, J. ; KÖRNER, F., BETHOUX, O. with a contribution for the text of HOERNES, S. ; KLEEBERG, R. ; NEL, A. ; DEMATHIEU, G. ; LAPEYRIE, J. ; ODIN, B. ; CONRAD, G. ; MATHIS, V. ; BRULHET, J. ; BROUTIN, J. ; CHATEAUNEUF, J. J. ; CABANIS, B. ; LEROY, B. ; NMILA ; MERABET, N. ; GUILLAUME, A. ; HENRIOT, O. ; contribution for definitive figures : BUSSIERE Annie (Burgundy University) ; general coordination : GAND Georges.
Organisation of the excursion : Dr GALTIER Jean (Montpellier University & Cirad), Dr GAND Georges (Burgundy University), GARRIC Jacques (Geologist Engeneer, retired Gogema, Montpellier).
Stops :
* n° 1 — The Stephanian basin of Graissessac (Dr Jean GALTIER = JGa).
n° 2-6 — The Lodève basin and the triassic cover.
Between stops 1 and 2, presentation in the bus of the Lodève basin and its triassic and hettangian cover (Dr Georges GAND = GG, Dr Jean GALTIER, Jacques GARRIC = JG)
* n° 2 — The Triassic of Dio : Stratigraphy and Palichnofauna (Dr Georges GAND), Paleoflora (Dr Jean GALTIER)
n° 3-6 — The Lodève basin. The Saxonian Group
* n° 3 — The Saxonian Group near la Lieude : sequential organisation, Geochemistry (Dr Georges GAND : classical data ; Pr Dr Jörg SCHNEIDER (JS) and Frank KÖRNER (FK) : new data ; Palichnofauna (Dr Georges GAND) ; Paleoflora (Pr Dr Jörg SCHNEIDER, Dr Jean GALTIER).
* n° 4 — Fossiliferous sandstones rills of the Salagou Formation (Saxonian) near Salasc ; the fossiliferous rills : structure and origine (Jacques GARRIC) ; Palaeontology : insects (Pr Dr Jörg SCHNEIDER, Olivier BETHOUX (OB), Triopsids (Dr Georges GAND, Dr Jean LAPEYRIE (JL),Conchostracans (Pr Dr Jörg SCHNEIDER).
n° 5-6 — The Lodève basin. The Autunian Group.
*n° 5 — The Autunian Group near Mas d’Alary. Lithostratigraphy, Volcanic-ashes (cinérites), Uraniferous mineralizations (Jacques GARRIC) ; Palaeontology (Dr Georges GAND)
* n° 6 — The Autunian paleoflora near St-Jean-de-la-Blaquière (Dr Jean GALTIER) ; ages of the Carboniferous, Permian, Triassic series : collective discussion.

I. SITUATION AND GENERAL FEATURES (FIG. 1 ; JGA)

Situated on the southern border of the Massif Central, the Lodève basin is surrounded by the Palaeozoic Montagne Noire to the west, the Mesozoic Causses Plateau to the north and the Languedoc Tertiary plain to the south (Fig.1).

Fig 1 – The Graissessac carboniferous and Lodève permian basin, stops 1-6.

The Permian crops out over an area of about 150 km2, dipping uniformly at about 15° to the south ; it is about 2500 m thick and consists predominantly of (dark grey, grey and red) mudstones.
The Permian deposits rest unconformly on Precambrian and Cambrian schists and dolomites of the Lodève ridge in the north and west. In the western end of the basin the Orb faults bring into contact the Carboniferous basin of Graissessac with the Permian ; however elsewhere, Stephanian beds extend beneath the Permian as recognized in one drill core.
The Mesozoic (Triassic and Liassic deposits) is subhorizontal and rests unconformably on the Permian. The Permian basin is bounded to the south by extensions of the E-W faults of the Espinouze and to the east by the Cévennes faults which separate the Permian from the Oligocene plain of Languedoc.
In order to observe the geological context of the Lodève Permian basin, the field trip will start in the nearby Late Carboniferous basin of Graissessac then the Triassic border will be examined before the detailed visit of the Permian sequence.

* Outcrops : between stops 1-2. From the bus, the Salagou Formation with La Tour and Octon facies = 2 characteristic Members of an arid playa environment.