Kimmeridgian soil is a very unique type of soil found in the grape growing areas of eastern Loire Valley, southern Champagne and at the core of the Chablis wine region. The soil was classified in the middle of the 18th century - by a French geologist Alcide d'Obigny, while working in Dorset near the town of Kimmeridge in the south of England. He identified a unique layer of dark marl which he named Kimmeridgian.
It must be noted that the Kimmeridgian soils found in France, differ from that found in England. The layer is a relatively uniform chalky marl, though with thin marly limestone containing rich layers of seashells. Strata formed from the post Jurassic period continued to be deposited in the shallow sea areas which once covered this part of France.

 

These layers were forced to the surface when the area known today as the Paris Basin began a slowly tilt up during the late Tertiary and Quaternary periods. This slow tilting of the basin allowed the Seine, Aube, Yonne and Loire Rivers to erode, cutting through the rising ridges of Kimmeridgian-Portlandian outcrop into a large collection of wine areas.
These unique Kimmeridgian outcrops, are sometimes called the 'Kimmeridgian Chain' in that they are distinct and separate from their associated wine regions. The primary Kimmeridgian vineyard sites in France include: The Aube sub-region of Champagne, Chablis, Tonnerre and the Auxerrois wine areas of northern Burgundy. Along with the Pouilly, Sancerre and Menetou-Salon wine areas of the Loire Valley.
The quality of the vineyards resting on top of these chalky soils has been known for centuries. And for as long as anyone can remember, attempts have been made to duplicate these characters. Quality sparkling wines are made in several places around the world, but it is not Champagne. The best wines of the Loire Valley still have a special combination of terroir, fruit, structure and a nuance that is impossible to duplicate elsewhere. As there are vibrant, crisp Chardonnay wines made all over the world - but they are not Chablis.
The Kimmeridgian soils are possibly the most famous and important in the world, when it comes to 'fine' wine. The quality, longevity and unique ingredients of this particular blend of limestone and clay have captivated the wine world for centuries. There is simply no comparison.
A key to the Kimmeridgian soils is how the layers work together. The marly soil of the Kimmeridgian layer provide good structure, ideal water-retention and is easy to cultivate. The hard limestone Portlandian layer contains numerous fossil fragments and has been cracked by frost - offering good aeration and ideal drainage, along with those gentle slopes.
Chablis is a significant part of the Kimmeridgian chain and is home to some of the finest Chardonnay wines. The defined wine region was recognised as growing on a sub-soil of Kimmeridgian limestone - while wine grown elsewhere in Chablis would be classified Petit Chablis. The mid-slope in Chablis maps almost perfectly to the Kimmeridgian outcrop with the soft, carbonate-rich rock being covered by Portlandian limestone and supported by other limestone deposits. The south-facing Kimmeridgian slope also has significant exposure to the sun and is home to the Chablis Grand Cru vineyards.
Geologic conditions identical to those found in Grand Cru slopes, also extend both north-east and south-west, but the vineyards on these sites are classed as Premiers Cru. This confirms that the Kimmeridgian soil is not the only ingredient in the making of a Grand Cru Chablis. And in 1976 the reference to Kimmeridgian limestone in the definition of Chablis was discontinued. As it is believed - it is also a combination of the slope and orientation of each site, along with micro-climate that are of importance to producing quality Chardonnay in Chablis.
In the vicinity of Sancerre and Pouilly-sur-Loire wine areas of the Loire Valley, faulting has caused the east bank of the river (the Pouilly side) to lower. Thus causing the Kimmeridgian slope to lie flat, exposing elements of the Tertiary period - (sands, clays, and freshwater limestone) and Quaternary period - (with high-river-terrace sands, gravel and clay). The town of Sancerre sits on top a fault ridge, the eastern side has a layer of Cretaceous soils while the west side is covered with brush and gravel slopes. Further west the best vineyards sit on the classic Portlandian-Kimmeridgian soil combination - a classic example of 'terroir'.