From a geodynamic perspective the geological region is attached to the Burgundy plate. It is bordered on the west by the Loire trench which is juxtaposed with the Sancerre fault and the underlying Biturige immediately to the west.
The oldest lands are from the Jurassic period and are around 160 million years old. These are formed from calcareous marine deposits, with the fossils (remnants of organisms and shell debris) found in their heart testifying to their past life. Amongst these, the presence of corallum indicate that the climate at the time was tropical.
The sea receded from the area for the first time 140 million years ago, recovered it 20 million years later, then finally receded at the end of the Cretaceous period (70 M.a.), when the climate was colder than during the Jurassic period.
From this time onwards the area went through a strong erosive period. The calcareous deposits dissolved partially, leaving behind residues which were more or less clayey (flinty clays or cherts). A powerful Eocene river flowed from the Massif Central along the current bed of the Loire, leaving deposits in the north of the region (around Cosne). The climate was once more tropical during this period (35 M.a.).
An important tectonic phase then stretched across Western Europe from west to east. This created the Alsace, Bresse and Limagne trenches and in this region, the Loire trench. Many faults in a north-westerly direction appeared at the same time and sculpted the current hilly relief.
Four very different soil types can be differentiated in the vineyards:
Villiers limestone of the Oxfordian
Marls with oyster shells of the Kimmeridgian
Barrois limestone of the Portlandian
Flinty clays of the Cretaceous
||Nanogyra Virgula marls
||Terres blanches (white soil)