Le Naturaliste Vendéen, Numéro 3 (2003)
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Hettangian stratotype shows an example of preservation and valorisation of a scientifical historical place. Earth Story is understood thanks to geological heritage; this heritage is very vulnerable. Judicial framework and mentality evolution allow us to make a conservation of particularly interesting places.
The Liassic Talmont-Saint-Hilaire (Vendée, France) outcrop has been studied here according to the abundance of fossil plants of the Cheirolepidiaceous family (Gymnosperms, Coniferales). A new species of Brachyphyllum has been studied in light microscopy, even in scanning electron microscopy and transmission electron microscopy. It is, at that time, one of the most complete study realized on a fossil taxon. Epidermal cells, subsidiary cells and guard cells have been described on both adaxial and abaxial surfaces, in transversal and longitudinal sections. Cuticle ultrastructural variations have been observed between epidermal and stomatal cells. To conclude, we propose a discussion about the cuticle structure variations related to environmental conditions and the functional morphology of the different cells.
Analyse d'un exemple de fossilisation d'une trace de pas de Dinosaure (Lias inférieur des Causses)
(2003)
A calcareous block made of algo-laminated (stromatolitic) material exhibits at its upper surface a foot print of a Dinosaurian. A vertical section (sawing) and a thin section allow to make detailed observations. The early diagenesis permits the preservation of the deformations caused by the foot print.
In the inter/supratidal algal mats, the early diagenesis products a progressive induration. It is enough to preserve all the deformations affecting the mats, including footprints of vertebrates, tracks and burrows of small invertebrates, and physical actions (desiccation cracks).
Comparaison des ichnopopulations des Grands Causses (Sud de la France) et du Veillon (Vendée)
(2003)
From descriptive statistic method concerning length (L), width (W) and L/W, it is suggested that Grallator variabilis samples from Vendée (Le Veillon) and Grands Causses belong to the same ichnospecies. Also, by this way, G. maximus of Hettangian of Vendée could be synonym of G. minusculus from USA Hettangian.
Numerous footprints areas has been found, since 1962, in Permian, Triassic and Hettango-Sinemurian. All show precised oriented trackways. So that they were undestood like walking ways but their precise meaning is still enigmatic.
Footprints are numerous in France where they found from Carboniferous to Quaternary levels. Those of Middle Triassic (Anisian-Ladinian) are especialy interesting because they are tridactyl footprints made probably by first dinosaurs. First skelettons are known from Upper Ladinian / lower Carnian.
The Veillon ichnofauna, early Liassic in age, includes various Reptile taxa: quadruped Pseudosuchian, Coelurosaurians, Theropods, primitive Iguanodon – like Ornithopods and some unspecified forms. This ichnofauna is very comparable to the early Liassic footprint assemblage of the Connecticut.
Clastic deposits related to alluvial and estuarine environments sedimented during the early Liassic in the Veillon area (south of Talmont-Saint-Hilaire, Vendée, France). A reptile fauna including various taxa, just known by innumerable footprints, lived in that environment, in rather hot and dry climatic conditions.
In the Talmondais (Vendée) the Hettangian sedimentation locally begins with fluviatil clastic deposits prior to the deposition of shallow marine carbonates. These clastics, including the footprint-bearing beds of Le Veillon (south of Talmont- Saint-Hilaire) are subject to important and frequent variations in thickness. Drilling and geophysic data indicate a tectonic control of these variations. A fault-block pattern is proposed. At a small scale, it gives an illustration of the extensional tectonic processes related to the evolution of the Biscay rift during the early Liassic.