The Kimmeridgian of the "Champagne Berrichonne"

Marls of St Doulchard

This formation covers part of the north of the Champagne berrichonne, from Bourges to the little town Sancerre near the Loire valley. The vineyards of Menetou-Salon and Sancerre, well known for their most characteristic type of vine, the Sauvignon, prefer before all, the marly limestone grounds of the Kimmeridgian stage.

Alas, if the marls are as well used for the viticulture, they are hardly exploited in quarries. The "good old quarries" are filled and closed today. No wonder that our materiel mainly comes from accidental outcrops : road workings, foundation of houses, digging out of the wines...
Vineyard of the Menetou-Salon area

Age

Lower Kimmeridgian stage p.p. (Cymodoce zone p.p.) - upper Kimmeridgian stage (Mutabilis, Eudoxus and Autissiodorensis zones)

Deposits

The layers are about 60-80m thick and spread out over 3-5km (Debrand-Passard, 1982)

Lithology

At the base of the formation, a level with green lumachellic conglomerate separates the "Marls from St Doulchard" and the "Limestones of Buzançais" ( lower Kimmeridgian, Cymodoce zone p.p.). Than follows an alternation of gray marls, becoming black in the depth, and fine limestone of clear gray to dark gray color, sometimes covered with a beige patina. The marly deposits nevertheless dominate. At the top, the layers of limestones become more significant and are accompanied by many lumachelles of Nanogyra striata (Smith). These deposits are very irregular, often lenticular.

Macrofauna

Apart from the small oyster Nanogyra that Berrichons formerly called "sheepdewclaw ", the macrofauna is composed in the following way : bivalves - Pholadomia, Trigonia.. brachiopods - Xestosina..., (rares) sea-urchins and ammonites.
Nanogyra striata or "sheep dewclaw"

Environment

The variations of facies and fauna indicate a succession of two environments. First is agitated and not very deep (presence of pebbles and remains of fossils). The second, calmer and deeper, probably following a new marine invasion, is characterized by the lacking of pebbles and the presence of pelagic organisms, like ammonites. It is also in the "Marls of St Doulchard " where had been discovered the plesiosaure of Berry-Bouy, exhibited in the Natural history museum of Bourges (Cher) France.

Microfauna

Foraminifera, mainly of the family of Lituolidae and rare Lenticulina.

Microflora

Primarily pollens and spores.