Sables du Castrais Formation

The Sables du Castrais Formation, also known as the Molasses du Castrais, is a geologic formation of Eocene (Ypresian to Bartonian) age, outcropping in the Montagne-Noire region of France.

History
"Petrified fossil remains" were known from the Sables du Castrais Formation since at least the 18th century, and several of these fossils were described by Cuvier (1804) and Cuvier (1822) as belonging to Palaeotherium and Lophiodon.

In 1845, a jaw assigned to Lophiodon lautricensis was discovered in the formation and was described by Noulet (1851); Noulet also mentioned that he had himself collected fossils from the formation alongside pharmacist J. Parayre as early as c. 1843.

Léonce Roux du Carla discovered several more fossils from the Grès d'Issel Mermber of the Sables du Castrais formation from February 1855 until his death in 1859, and this helped Noulet (1858) to confirm the Eocene age of the deposit. Despite this, all that remains today of du Carla's collection is a single jaw of Palaeotherium castrense from the Sables du Castrais Formation.

Between 1850 and 1868, during the construction of the Castres - Albi railroad, several more fossils were recovered from the Sables du Castrais Formation, including M. Zebrowsky's 1868 discovery of fossils within the area.

The Grès d'Issel Member was identified by Henri de Sévérac in 1873, and the Sables du Castrais Formation was first described by M. Richard in 1946.

The Grès d'Issel Member is located in a quarry which closed around 1966 and is now inaccessible due to it currently being located underneath a private garden.

Age of the formation
The age of the Sables du Castrais Formation was listed as Eocene by Noulet (1858) and in 1867, Gervais noted that the Issel Member likely dated to the Early Eocene, while the Villeneuve-la-Comptal Member likely dated to the Middle Eocene.

Caraven-Cachin (1898) was the first to assign the Sables du Castrais Formation to the Bartonian. Stehlin (1910) and Escarguel (1999) dated the formation to the Lutetian-Bartonian and found it to overlie the Molasses de Saix et de Lautrec Formation. Fauré (2011) agreed with the more recent dating of the formation to the Ypresian-Bartonian.

Geology
The base of the Sables du Castrais Formation, which overlies Danian rocks, is made up of Ypresian gravel clays and the Issel Sandstones, which range from 15-40 m, and the Argiles rutilants d'Issel et de Saint-Papoul Member is deposited within the gravel clays, and is between 20-30 m thick.

The Argiles rutilants d'Issel et de Saint-Papoul Member is overlain by the Lutetian Grès d'Issel Member, which is between 50-100 m thick, and is overlain by the Bartonian Molasses du Castelnaudary Member. The whole formation underlies the Molasses de Saix et de Lautrec Formation.

The Grès de Carcassonne Member also appears to be slightly younger than the Grès d'Issel Member, likely dating to the late Lutetian or early Bartonian.

The Sables du Castrais Formation was described by Capera and Baillet (2014) as a typical fluviatile formation, with lenticular channels, formed by conglomerates and sandstones, with calcareous cement and large trough cross-strata.

Mammals

 * Artiodactyl
 * Lipotyphia
 * Marsupial


 * Pan-Carnivora


 * Perissodactyl


 * Primates
 * Rodent

Reptiles

 * Crocodilians


 * Turtles