Monday, May 13, 2013

The soils of the Burgundy wine region

Winegeeks has identified Kimmeridgian soil as the top vineyard soil in the world but has erroneously attributed that soil type to the totality of vineyards in Burgundy, Champagne, and the Loire Valley. I have begun a process to set the record straight by, first, identifying the locations where Kimmeridgian soils can actually be found and, second, clarifying what soil types are to be found in Champagne, Burgundy, and the Loire. In this post I identify the soils of Burgundy.

Excluding Chablis, the Burgundy vineyards occupy hills and slopes along a 100-mile (160-km) stretch of the western side of the Sâone Valley. The region is noted for its diversity of soils -- both within and between vineyards -- but bourgogne-wines.com still sees "a unity of geology and soil" from north to south; a unity characterized by sedimentary soils comprised of clay, marls, and limestone over an older substrate of granite, lava, and schist.

During the Mesozoic era, most of mainland France was covered under a warm sea which was favorable for coral development and limestone deposits. During the Jurassic period (150 million+ years ago), calcareous sedimentation converted the deposits into rocks comprised of clay, marls, and limestones. The sea withdrew approximately 65 million years ago and erosion of the exposed sedimentary rocks led to the creation of valleys and clay-limestone soils. Thirty million years ago (Tertiary era), the action of the African plate pushing against the European plate resulted in the formation of Mont Blanc and the Massif Central as well as the landscape in evidence today between Dijon and Macon. Glacial activity during the Quaternary period eroded existing slopes to form the Côtes we know today.

Faulting has been a key contributor to the lay of the Burgundy land. Wilson (Terroir) describes a fault zone that runs the entire length of the Sâone Valley and provides a "profound break between two different geologic worlds." The faulting lowered the strata one mile deep into the trough and fractured its western edge into the scarps and hills of Burgundy. Upslope of the fault the soil is comprised of Jurassic limestone and marls while the valley-side soils are comprised of Tertiary era sands and clays which filled in the trough (All of the great Grand Cru vineyards are located upslope of the fault line.). Faulting in the Dijon-Macon corridor has also served to create three of the four distinct viticultural compartments extant today(Wilson). The Blanzy Rift separates the Côte d'Or from the Chalonnais which is, in turn, separated from the Mâconnais by the Grosne Rift. The fourth viticultural zone -- Beaujolais -- is the result of a bulge in basement granite.

The Côte d'Or "dominates the Bressan plain from Dijon to Maranges at a height of 150 - 200 metres" (bourgogne-wines.com). Rendzinas (a type of shallow intrazonal soil rich in lime and formed from  underlying limestone or chalk rocks -- botanydictionary.org) and brown limestone soils with a covering of broken rock fragments predominate in this zone with Côte de Nuit soils dating to the mid-Jurassic (175 million years ago) and Côte de Beaune soils dating to the Upper Jurassic (150 million years ago). Gravel and red silts have slipped down the slopes and come to rest on marl or limestone bases. The arable land is generally very shallow and in close contact with the source rock but the vine roots are able to exploit any weaknesses in the rock to dive deep for water and nutrients. The cap rock from Dijon to Prémeaux is Comblanchien limestone (hard pink-beige limestone laid down during the Bathonian epoch) which re-appears at Puligny and is the cap rock for the rest of the Côte de Beaune. The cap rock from the Hill of Corton to Puligny-Montrachet is Nantoux limestone (Wilson). The bedrock in the Côte de Nuits is calcaire à entroques, a crinoidal limestone whose many fractures provide a water-storage system for the thin soils.

The soils of the Hautes-Côtes are a mix of hard limestones and clays with pebbly limestones on the flank and limestone pavement and gravel at the foot of the slope. The cap rock is Rauracian limestone.

Côte Chalonnais is part of the northeast face of the Massif Central with differing soils characteristics in its northern and southern portions. The cap rock in the north is Nantoux limestone with Jurassic limestone soils dominant. In some villages, Liassic and Triassic soils surface. In the south the cap rock is Bajocian limestone while some soils are Liassic/Triassic assemblages with a high clay content while others are mid- and upper Jurassic assemblages where hard limestones and softer marls alternate. The lower slopes exhibit leached-out brown soils -- the result of a pebbly alluvium overlaying the limestone -- while the base of the hills are covered with sand and flinty clay.

Variations in the Maconnais landform has led to a diversity of soils to include rendzinas and brown limestone and flinty, clayey, and sandy soils mixed with sandstone pebbles. Vines growing around the base of Solutre are rooted in reddish Liassic marls that have washed down the slopes and have been covered with limestone scree.

Beaujolais and Chablis soils have been covered elswhere.

The soils of Burgundy are summarized in the following figure.


©Wine -- Mise en abyme

No comments:

Post a Comment