Kimmeridgian soil is a unique type of soil found in the wine areas of eastern Loire Valley, southern Champagne, and is at the heart of the Chablis wine region. The soil was identified by a French geologist Alcide d'Obigny, while working in Dorset near the town of Kimmeridge in the south of England in the middle 18th century. He identified a unique layer of dark marl which he named Kimmeridgian.
Though it must be noted that the Kimmeridgian soils found in France differs from that found in England. As it is a relatively uniform chalky marl with thin marly limestone containing rich layers of mixed seashells. Strata formed from the post Jurassic period continued to be deposited in the shallow sea areas which 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 band 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 Auxerrois wine areas of northern Burgundy; and the Pouilly, Sancerre and Menetou-Salon wine areas of the Loire Valley.
The success of the vineyards resting on top of these chalky soil has been widely known for centuries. For just as long as anyone can remember, attempts have been made to duplicate their characters. Quality sparkling wine is now made in several places around the world, but it is not Champagne. The best wines of the Loire Valley still have a special mix of terroir, fruit, structure and a nuance that is impossible to duplicate elsewhere. And 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 on earth when it comes to fine wine. The quality, longevity and unique features of this particular blend of limestone and clay have driven the wine world for centuries. There is simply no comparison.
A key to Kimmeridgian soil is the way it works with its Portlandian partner. The marly soil of the Kimmeridgian layer develops good structure and ideal water-retention and is easy to cultivate. The hard limestone of the Portlandian contains numerous fossil fragments and is cracked by frost. This enables good aeration of the gentle slopes as well as aiding in ideal drainage.
Chablis is a significant part of the Kimmeridgian chain and is home to some of the finest Chardonnay wines. The defined wine region was recognized 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.
The geologic conditions identical to those found in the Grand Cru slopes, also extend both north-east and south-west, but the vineyards on these sites are classed as Premiers Crus. This is an indication that Kimmeridgian soil is not the only ingredient in the making of a Grand Cru Chablis. As a matter of fact, the reference to Kimmeridgian limestone in the definition of Chablis was discontinued in 1976, as many believe it is also a combination of the slope and orientation of each site is 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 (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.