Pliensbachian of the motorway A71 (Cher)

Lower Pliensbachian page below

Upper Pliensbachian

Let's follow in the traces of the famous french paleontologist Alcide d'Orbigny, who used to work with ammonites of the St. Amand-Montrond (Cher, Berry) area for creating several lower pliensbachian (carixian) types. The setting is the 19th century. These well-known deposits have since turned into meadows. Traditionally, this is a cattle-rearing region and there are not very many accessible outcrops. So, we made the most of our good fortune, when, 10 years ago, the motorway building works (A71) cut across the south of our départment.
orbigny
Alcide d' Orbigny

Lithology

The Carixian deposits of the southern Berry show a marly facies with some rare limestone levels. These limestones, of the same color that the marls, are often a little clayey, but of relatively fine texture and sometimes nearly hard. They contain moults of ammonites, preserved in pyrite or limonite.

Environnement

The thick layers of marls seem to be a sign of a slow sedimentation and weak energy in rather calm seawater.

Macrofauna

Beside the cephalopods (Ammonoidae, Belemnitidae, Nautiloidae) we mainly found brachiopods (Zeilleriidae, Terebratulidae, Rhynchonellidae...), lamellibranchs (Pectinidae, Limidae, Plicatulidae...), gastropods (Eotomariidae, Zygopleuridae...) and also some echinoderms (Pentacrinidae and fairly rare Echinidae). But ammonites remained the most important group of the Pliensbachian fauna.

Deposits

The thickness of the layers reaches approximately 35 m (Geological map 1/50 000 St. Amand-Montrond).

Microflora

Principally pollens and spores.

Age

Lower Pliensbachian stage (Carixian), from the Jamesoni subzone, top of the Jamesoni zone to the Figulinum subzone, top of the Davoei zone .
Bridge under the old road of Arcomps