Monday, May 6, 2013

The soils of the Champagne wine region

In a recent post I refuted a winegeeks assertion that Kimmeridgian soil extended across the wine regions of Champagne, Burgundy, and the Loire Valley. I was, instead, able to show that the primary Kimmeridgian vineyard sites in France are: (i) the Aube sub-region of Champagne; (ii) the Chablis, Tonnerre, and Auxerrois sub-regions of Burgundy; and (iii) the Pouilly, Sancerre, and Menetou-Salon sub-regions of the Loire Valley. This finding begs the question "If not Kimmeridgian in those three regions, then what?" I will attempt to answer that question in this and two subsequent posts.

The figure below places a map of the French wine regions side-by-side with a geological map of the country. The geological map clearly shows that, contrary to the winegeeks article, a single soil type is not possible for the three wine regions under discussion. If we just follow the course of the Loire as it wends its way through the Loire region, we see it passing through Jurassic period stratigraphy, then through the Cretaceous and Tertiary stratigraphy of the Paris Basin, then through the paleozoic rocks of the Massif Amoricain before debouching into the Atlantic Ocean.

So lets look at each one of the regions of interest, beginning with Champagne.

The soil in Champagne is, for the most part, comprised of massive chalk deposits interspersed with rocky outcroppings and covered with a thin layer of topsoil (mix of sand, marl, clay and lignite) which requires constant renewal through fertilization.

Champagne soil (Source: Fatcork via

The slow sagging of the Paris Basin caused an upthrusting of ancient geologic formations at the outer perimeter with each formation exhibiting as a concentric, outward-facing escarpment. One such escarpment was the Kimmeridgian chain of Jurassic soils discussed previously. In the case of Champagne, the escarpment is comprised of sands, marls, and lignitic clays of the Tertiary period capping chalk from the upper Cretaceous and, below Chalons, clays and sands of the lower Cretaceous. It is the marriage of the Tertiary and upper Cretaceous strata that "is the parentage of the unique soils of Champagne."

The components of the Tertiary strata function as follows (Wilson):
  • Sands -- provide coarse ingredients which help in building good soil structure
  • Clays, marls, weathered chalk -- bond with particles to give good body to the soil
  • Lignite -- a soft, low-grade coal which "seasons" the soil. Rapid burial resulted in concentration with iron, sulfur, and zinc from plant material.
Chalk, according to Wilson, is composed of calcareous algae (a form of seaweed) and shells of tiny organisms that settled in a uniform manner at the bottom of the Cretaceous seas. The chalk deposits in Champagne are finer-grained and more porous than other French limestone soils -- and have extremely high concentrations of the mineral marls Belemnite (younger and found higher up on the growing slopes) and Micraster (older and located on the valley floors). Chalk has excellent drainage as well as water-retention properties in that its micro-pores can absorb water during wet periods and slowly release it during drier periods. In addition chalk will also reflect sunlight and heat thus aiding in the ripening of the grapes. The chalk soil allows the vine roots to dig freely and deeply in search of water and nutrients and also retains a constant temperature year round. Chalk weathers to a fine dust which is easily dispersed. In the case of Champagne, the Tertiary slope wash collects in the belly of the concave hills serving a binding function as well as providing mineral content. The chalk provides excellent drainage and water retention, which, when combined with the Tertiary soils, results in one of the best vine-growing soils in France.

The soils in the defined Champagne region is not monolithic, however. The Côte de Bars region of Champagne has Kimmeridgian soil of the same construct as the soils that underpin the vineyards of Chablis and Sancerre. In the Aisne region the upper Cretaceous has dipped into the Paris Basin  and the soil is comprised entirely of Tertiary clays and sands. In the area below Chalone -- referred to as wet Champagne -- the poor-permeability clays and sands of the lower Cretaceous period are dominant.

The Champagne soils distribution is illustrated graphically below.

©Wine -- Mise en abyme

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