Understanding the Terroir of Burgundy: Part 3.4 The Grand Crus

 By Dean Alexander

While working my first wine shop job twenty years ago, I asked the store manager – who was a Burgundy guy of significant reputation: “Why is Rousseau’s Ruchottes-Chambertin not as good as as his Clos de Bèze and Chambertin?”  The answer I got was honest: “I don’t know. I’ll have to ask next time I’m there.”

It years later that realized that I had asked the wrong question. The question I should have asked was: What causes these neighboring vineyards to produce wines of such different character? 

Today, twenty years later, I can answer that question. If you have read my previous 12 articles in this series on Understanding the Terroir of Burgundy, it is likely you can answer it too. More importantly, some of the lessons here can be used to understand other appellations where less concrete information is known.

Clos des Ruchottes to the right, and Ruchottes du bas, on the left. photo: googlemaps

Clos des Ruchottes to the right, and Ruchottes du bas, on the left. photo: googlemaps

The short answer

Chambertin, Chambertin-Clos de Bèze, and Ruchottes-Chambertin

These three grand cru vineyards sit in a row, shoulder to shoulder on the same hillside. All have their upper-most vines smack up against the forested hillside, and all have virtually the same exposition. The legendary domaine of Armand Rousseau farms and makes wine from all three of these vineyards; yet one, the cru of Ruchottes-Chambertin, does not seem to be cut from the same cloth. The wine made from Ruchottes is not as rich or opulent. It tends to be lighter, more fine-boned, and more angular in its structure. The primary reason for this difference in wine character is that right at the border of Clos de Bèze and Ruchottes, the limestone beneath changes significantly. Unlike the other two vineyards, Ruchottes-Chambertin sits over very hard and pure limestone that is composed of almost completely of calcium carbonates and very little in the way of impurities, such as mud or clay.

The impurities within the stone, (bonded by the calcite) is what determines how much clay and other materials will be left behind as bedding materials when the stone has weathered. The more impurities in the limestone, the more nutrients will be available for the vines when the stone weathers chemically.  Further, it will reflect not just how fractured the stone has become due to extensional stress, but it will have often been the determining factor of whether the bedding has become friable as well. The wines of Chambertin and Clos de Bèze have this sort of impure limestone as a bedding under three-quarters of its surface area. It is a significant factor in giving the wines of Chambertin and Clos de Bèze a heavier weight and richer character than the wines from Ruchottes.

Another major factor in this differential in wine weight is that Ruchottes is a much smaller appellation, which confines it solely to the upper-slope. Its location makes it subject to all of the factors that challenge upper slope vineyards, details that are examined in Part 3.3.  Conversely, both Chambertin or Clos de Beze extend almost three times farther down the hill, all the way to the curb of the slope. Additionally, while the degree of slope may kick up in the upper final meters of the Clos de Bèze and Chambertin, the area under vine upon upper slope (that will produce a lighter wine) is relatively small compared to the entire surface area of those vineyards.  

Unlike Ruchottes, the long slopes of Chambertin and Clos de Bèze will reach down to almost to where the slope completely leveled off. There at the base of the slope, rock and soil colluvium will have been transported by gravitational erosion, adding generously to the depth the soil. This depth allows more water to be absorbed and retained for use by the vines. It is rich in limestone rubble, gravel, and catches and holds more fine earth fractions including transported clay that has flocculated there. Above ground scree litters the vineyards

The fact that most ownership parcels run in vertical rows, from the top of the vineyard, to the bottom, assures that any lighter, more finessed wines will contribute, but not dominate the overall blend. In other words, blending of heavier wines lower on the slope masks the lighter wines from the top of the slope. 

It is abundantly clear that the vines benefit from the higher levels of nutrients in these deeper soils. They develop grapes that carry more color (anthocyanins) and brings many times more dry extract to the wine. This translates as the wines of these vineyards having a richer, more velvety texture, increased depth, all of which covers the structure. On the opposite end of the spectrum, the upper-slope position of Ruchottes-Chambertin dictates that the soils there are very shallow, and while there is a high percentage of colluvium, it is not as rich in sand, silt or clay sized particles.  In fact, there are places the topsoil has completely eroded away, leaving fractured stone and primary clay and marly-limestone between the voids and breaks in the rock.

New research allows new understanding

Today we can examine this variation of limestone within a vineyard with a precision that was not possible a decade ago. This is due to the groundbreaking work of geologist Françoise VannierPetit and her mapping of the dominant limestone beddings of Gevrey. Through her work, we know that Ruchottes is a very homogeneous terroir, one with a very pure and hard limestone bedding dominating the vineyard. While the stone does not provide much in the way of nutrients to nurture the vines, we know it is well-fractured by two large faults that run through the vineyard.  Because of the vigorous faulting and fracturing throughout the vineyard, Ruchottes does produce a grand cru class wine, but it is a grand cru of a different character.

The geological factors in Ruchottes do not typically produce a wine with the substantial fruit or thickness of a Chambertin, and this ‘reduced’ level fruit often does not completely ‘blanket’ of structure in the wines from Ruchottes. This obvious structure is often mentioned in wine reviews, noting heightened acids and tannins, lending the wines a more angular construction than in other grand crus. By the same token, the wine from Ruchottes is often quite aromatic, with finer bones, for this wine, it means exhibiting more finesse, as well as giving the taster a heightened awareness of the wine’s precise rendering of detail. In another vineyard, this might be attributed to the grapes achieving less phenolic maturity, but the wines of Ruchottes are ripe, they just aren’t typically as large scaled or heavy. Moreover, they can be remarkably beautiful wines that can age effortlessly, for decades; often gaining poise, polish, and balance while doing so.

The gentle slopes of Chambertin. Photo: googlemaps

The gentle slopes of Chambertin. Photo: googlemaps

The substrata of Chambertin and Clos de Bèze is much more varied. With Vannier-Petit’s mapping information, we know that 35 million years ago the vineyards of Chambertin and Clos de Bèze were opened up by a large fault. This exposing the older (2 million years +/-) of softer bedding planes below.  They are both divided by four bedding planes, three of them being of soft, friable, impure materials, giving excellent nutrients.  This softer, highly fractured bedding allows the vines to thrive, and produce wines with much higher levels of fruit. This is the heart of Chambertin and Clos de Bèze.

Additionally, the twin vineyards are perfectly situated, mostly upon a gentle gradient which will resist erosion, or better yet, at the curb of the slope, where the soil is deeper,  The vineyards are well protected from wind, being squarely behind the hillside of Montagne de Combe Grisard. These two vineyards sit in the sweet spot of the heat trap formed by the hyperbolic concave of the slope. This positioning allows ripening occur even in most cold, wet years. Ruchottes, while fairly well protected, it is nearer the Combe de Lavaux through which cooling winds flow down the vast gorge.

All of these factors make the wines made from Chambertin and Clos de Bèze much easier wines to understand because they have so much to give. They can be very seductive and complex, and can be drunk either young or old.  Are they typically better wines than can be made in Ruchottes?  The knee-jerk reaction is yes, as Ruchottes can be equated to the man fighting with one hand tied behind his back. But when a well-made wine from Ruchottes is opened at the right time, and served with the right meal, it can be perfection.

Armand Roussaux parcel map

Chambertin clos de Beze

 

Digging deeper 

Gevrey-Chambertin topography

Generally speaking, when compared to vineyards in some of other villages, the grand vineyards of Gevrey are fairly mild in their gradient. The uppermost vineyard sites of the Chambertin-named vineyards butt up against the Montagne de Combe Grisard’s “chaumes”, (or ‘scruff ‘ in English). But unlike the steep upper hillsides of Vosne or Volnay that were able to be planted to vine, there is an unarable, rocky, forested landscape. Here in the chaumes, where no vines are planted, the hillside above Gevrey becomes steep.

The premier cru of Bel-Air is the one real exception. Carved out of a void in the rocky forest, and perched directly above Chambertin Clos de Bèze, Bel Air is a steep vineyard. It is a superb example of the struggles upper-slope vineyards face. See Part 3.3.1 for more on this. According to Vannier-Petit, a white Oolite formation underlies the uppermost section of Bel Air, and Premeaux Limestone underlies the lower part. Several writers have describe Clos de Bèze as having Oolite formations below the soils, but Vannier-Petit does not note this. Instead, it is likely that Oolite has slid, as scree, or even in large chunks as a rock slide, into Clos de Bèze, from Bel Air above.

A prominent feature of the area, as outlined by the late James E. Wilson, a geologist, and author of Terroir (1998), is a rocky outcropping he referred to as a “Comblanchien cap“. While this was not part of the vineyard landscape, he described it as a major feature of the “Nuits Strata Package.” This term,“Nuits Strata Package,” as coined by Wilson, is an overarching reference to the bands of limestone bedding that stretch from Marsannay to Nuits-St-George, a layering of limestones unique to the Côte de Nuits. An upper-band of Comblanchien stone, he wrote, formed a structural bulwark or ‘cap’ which has allowed the upper-hillside to resist erosion, while the softer center eroded more quickly. This has caused the Côte de Nuits to develop its hyperbolic concave slope-shape. This concave slope relief, as I wrote earlier, allows the heat of the sun is trapped, allowing fruit to ripen fully. This is particuularly true for vineyards such as this that sit in a wind shadow which is created by the trees and hillside above.

Interestingly, a much more recent map of Gevrey by Vannier-Petit, does not deem it necessary to include hillside construction above the vineyards.  So while she shows no Comblanchien cap rock at the edge of the Gevrey’s vineyards, as it seems Wilson described them, she does shows that the Premeaux stone extends one hundred or so meters up-slope. This extends well beyond the farthest, uppermost edges of the vineyard land.  While she may have felt the composition was outside the scope of the project, certainly anything that will wash, slide, or roll into a vineyard, is of great importance to our understanding of the physical vineyard makeup.

Ruchottes-Chambertin: a largely homogeneous appellation 

Here, a photo by Armand Rousseau illustrating the lack of topsoil, and the width of the fractures in the Premeaux limestone. No doubt this is a more extreme section, but it gives us the understanding of the relationship between the hard stone, fracturing and the difficulty of dealing with erosion in these vineyards.

Here, a photo from Armand Rousseau illustrates the lack of topsoil, and the width of the fractures in the Premeaux limestone. No doubt this is a more extreme section, but it gives us the understanding of the relationship between the hard stone, fracturing and the difficulty of dealing with erosion in these vineyards.

Ruchottes-Chambertin, and it’s ying-yang partner. Mazy-Chambertin (also spelled Mazis-Chambertin), sit at the tail end of the string of grand cru vineyards. The primary limestone beneath both vineyards is the significantly calcium-pure, Premeaux. Premeaux limestone, which is marketed as marble, is highly desirable for construction and prized for its pink color. It is very similar to Comblanchien (which is a creamy white), but slightly less pure, (hence the color), and slightly less resistant to geological strain. See Part 1.1 for detailed compressional strengths of various commercial limestones.

Technically, the Ruchottes appellation is made up of three small, roughly equally-sized vineyards:  Ruchottes Bas, (meaning the below) Ruchottes Hauts, (meaning above), and next to that, against the forested outcroppings at the top of the hill, Clos des Ruchottes. The Clos, is a monopole owned by the firm of Armand Rousseau.

While the lower half of the Clos des Ruchottes shares the rest of Ruchottes’ Premeaux limestone, the uppermost section, is covered in a layer of white Oolitic stone. Oolitic stone is made up of millions of small, oval, carbonate Oolite (egg stone) pellets that are fused by mineral cement. This composite construction makes the stone more susceptible to fracture, and the vines find it far easier to penetrate the many weak spots in this more porous stone. If anything, this is a benefit that the Clos des Ruchottes has over the rest of the Ruchottes appellation, especially since it is so high upon the hill. However we don’t know if the Oolite is of significant depth, and it is likely that Premeaux lies directly beneath it anyway. In either case, as vineyards go, the entire appellation of Ruchottes-Chambertin, is remarkably homogeneous in character.

The excellent Armand Rousseau website discusses Ruchottes Oolitic limestone, as well as shows the firm’s holdings in the vineyard, and is fairly detailed, and seemingly competent in their geological explanations, a surprising rarity in Burgundian marketing. Below is an excerpt.

The soil is composed of a shallow layer of red marl up to the top of the area. It is very pebbly, shallow and not fertile. The vines are based on oolithic limestone dating from Bathonien which disintegrates if frozen producing scree. This soil type forces the roots to go deeper into the rock. This results in a more fragrant, mineral style of wine that is lighter in colour but with a fine and elegant body. domaine-rousseau.com/en

Examining Ruchottes faulting and fracturing

We know through of the study of fracturing along the Arugot fault in the Dead Sea Basin, that as the distance from the fault increases, fracturing diminishes in frequency. This means that fracturing still occurs in its clusters, but the spacing between clusters is farther apart, leaving stretches of relatively undisturbed stone between areas of fracturing. As Ruchottes is located at the farthest possible distance in Gevrey from the main Saône fault, we rightly might expect this hard stone to be only intermittently fractured. Certainly there have been numerous accounts over the past century of vignerons having to dynamite sections of these vineyards to break up the stone enough to plant their vines.

Mazy and Ruchottes Chambertin with dip and strike oriented faults. Significant outcropping has emerged from this hard Premeaux stone at the convergence of these faults. Interestingly its both parallel and perpendicular to the extensional, horizontal faulting

Mazy and Ruchottes Chambertin with dip and strike oriented faults. Significant outcropping has emerged from this hard Premeaux stone at the convergence of these faults. Interestingly its both parallel and perpendicular to the extensional, horizontal faulting

Unknown before Vannier-Petit’s work were the locations of sub-faulting that occurred at the same time that the Saône Fault developed.(1) Two sub-faults bi-sect Ruchottes and Mazy, right at the border with Clos de Bèze. The vertical fault-line follows the boundary between the Premeaux stone and the various beddings that make up Clos de Bèze.

Ruchottes origin during of the Côte’s creation 

The once level Premeaux limestone bedding of Ruchottes came under great strain as the land that now forms the Saône Valley Basin pulled away and began its slide down. As the limestone slab was pulled extensionally, the once solid piece of limestone bedding first began to microfracture, then to fracture throughout the body of the stone. As understood by the study of fluid mechanics, stress intensifies exponentially upon weakest areas of the stone, from which fracturing propagates, until the main horizontal break, or fault occurs.

As this faulting occurred, the neighboring blocks of limestone were pulled downward by the void made by the dropping/falling off the fledgling Saône Valley. As this happened, bedding of Ruchottes began to tilt and slide downwards, both pulled and sliding with the adjacent formations. It is not clear if this was a rapid, cataclysmic event, or that it happened over the span of hundreds of thousands, or even millions of years. Either way, the stress upon the Premeaux bedding of Ruchottes was extraordinary, and what fracturing that was not caused the faulting, certainly occurred as it tilted and moved its position downward.

Often times, faulting can cause one plate to sit significantly higher than the next, forming a drop off which may or may not fill with soil.  In some locations, such as the fault between Chevalier-Montrachet and Le Montrachet, this has occurred What soil was lost by Chevalier to erosion, found a fine resting place in Le Montrachet, allowing the soils of Le Montrachet to become much deeper (and richer).  In other instances, erosion may once again level any difference in bedding height created by faulting. Alternately, the bedding may remain at the same height following the fault creation.  To the best of my knowledge, any height differential between Ruchottes du bas and Mazy Hauts is not documented.

Looking at the satellite image, there are certainly several visual clues that this faulting exists. Most obvious are the signs of significant stress are the limestone ridges, where the bedding has folded upon itself, that pushed above the topsoil. These are dominate features directly above the southern end of Mazy Haut, and just like the walls of Clos, these limestone ridges greatly reduce erosion in these areas, which results in deeper richer soils and thus weightier wines, not only in Mazy, but in that area of Ruchottes du Dessus.

Clos de Beze & Chambertin: four distinct bedding planes

Here the soft friable makeup explains the ease that the vines have in extracting nutrients and water from the base rock

Here the soft friable makeup explains the ease that the vines have in extracting nutrients and water from the base rock

While Chambertin and Chambertin Clos de Bèze are very similar to each other, they are unique to all other vineyards in Gevrey. Both vineyards share the same four bands of bedding planes, in roughly the same proportions. The one largest difference between them is that there is a higher percentage of Crinoidal stone in Clos de Bèze than exists in the northern end of Chambertin.  However, what is farmed depends completely on the parcels owned, not what exists in the vineyard itself.  It is increasingly clear is that a parcel is a vineyard in itself, and sections within parcels can hold wide variation in the character of wine it will produce.

Upper-slope Bathonian beddings:

Premeaux limestone and Argillaceous limestone/Shaley limestone

The uppermost sections of both Clos de Bèze and Chambertin sit over the very pure, and hard, Premeaux limestone, formed during the Bathonian which is a 2 million year period of the upper middle Jurassic. As in Ruchottes, we can expect this Premeaux limestone to be fairly well-fragmented. If this were the only stone found below the surface of these vineyards, the wines would taste much more like Ruchottes, but that is not the case.

The middle-upper section of these sibling vineyards is argillaceous limestone. This is a calcium-rich clay matrix may be indurated into stone, or it also may be soft and more marly. The clay, or argile as it is called in French, normally composes up to 50% the matrix, with roughly the balance being calcium carbonate and impurities. To this Vannier-Petit adds the word hydraulique, (in parenthesis), which refers to the fact that this particular limestone contains silica and alumina, that will yield a lime that will harden under water.  The assumption is that this Calcaire Argilleux formed underwater in the Jurassic lagoon or seashore, by secreting quicklime which bound with the clay, 168 million years ago.

Decanter Magazine alternately, and perhaps inaccurately, translates from the French Calcaire Argilleux, into Shaley Limestone, (as seen in the map box). That said, Françoise VannierPetit describes in an interview, that the relationship of clay and shale, is almost as one material that continually is in a transition from clay to shale – and back again, depending on how hardened (indurated) it becomes, or degraded. That stated, shale is generally regarded as lithified clay mixed with silt, the blend of which causes the notable horizontal striations, while a body of transported clay (of a single type, ie. Kaolin) that has been indurated (hardened) is termed claystone. Geologist are notorious for their loose use of terms, which makes it challenging for the rest of us to catch up, and I suspect Vannier-Petit is often guilty of this. AC Shelly is credited with writing in 1988 that “The term shale, however, could perhaps be usefully abandoned by geologists, except when communicating to engineers or management‟

Nothing is as simple as a name. Shale can be found in many forms. The relationship between clay and shale is very tight, just like water and ice.

Nothing is as simple as a name. Shale can be found in many forms. The relationship between clay and shale is very tight, just like water and ice.

Middle to lower slope Bajonien beddings: 

Marnes à Ostrea acuminata & Crinoidal Limestone

The oyster, and other fossils that sedimentologists are constantly mentioning as being present the bedding is really only relevant because it allows the scientist to easily reference age of the material. The fact certain creatures lived only during distinct periods of time, and only in certain environments. So not only does it give scientists the age of the strata, but it tells them a lot about the particular conditions that existed in that location, quickly allows the scientist to assign the formation of the bedding material to a particular period of time. As the fossils display different signs of evolution, (in the case some oysters, their valve position changed over long periods of time) the sedimentologist can establish the age bedding, and allow them to recognize a change of bedding (at on the surface) simply by the fossils in each location.

Using this methodology, the scientist gleans information about how the bedding has shifted position, or even its location. These shifts have been very significant in the Côte. By categorizing strata by type, and fossil type. and date, they can match one strata in one location with its mate in another.  This methodology allows sedimentologists to correlate strata worldwide.

Oyster bedIn the vineyard of Chambertin, the marl (Marnes à Ostrea acuminata) lies in a layer just beneath the argillaceous material that once was an ancient oyster bed. It is loaded with fossilized oyster shells (Ostrea)  from the upperBajocien period. This soil, into which the fossils are bedded, contains a large amount of the clay, montmorillonite, which has a very high cation exchange rate, and such soils, with their negative charge, attract and hold positively charged ions called cations (minerals like calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), hydrogen (H+) and sodium (Na+) that are crucial for plant growth. This makes this particular marl which lies in the heart of Chambertin, a particularly sweet spot for vines. And because this is a bedding plane that underlies the Argillaceous material above it, those vines whose roots can reach that deeply, may benefit from the Marnes à Ostrea acuminata too. That said, the deeper roots, it is reported, do not typically supply vines significantly with nutrients, that vines rely on their shallower root systems for this function.

gevrey pre slideThe age of the Marnes à Ostrea acuminata dates back to the very late Bajocian, parkinsoni zone 168.3 +/-, well before the Premeaux which lies above it was formed on top of it. This important because this decisively shows that the Comblanchien bedding, which lies at the base of the hillside (and was formed later in the Bathonian), slid down slope, and was pulled eastward with the falling valley. This slide of the Comblanchien, which at one time overlaid the argillaceous and oyster marl material and lay next to the Premeaux, moved downward almost 100 meters and eastward by roughly 200 meters. exposing this older marl and crinoidal bedding to the air, after having been buried underground for the previous 133 million years. The next bedding plane is the also Bajocien in origin, again being older than the Premeaux higher on the hill, and older than the Comblanchien which sits below both Chambertin and Clos de Beze.

The lowest section of Chambertin, and the largest percentage of Clos de Beze’s acreage consists of the well-fractured Crinoidal Limestone. This is the most common base rock upon which, the classified crus of Gevrey are planted.

Crinoids were extremely prevalent the lagoons and Jurassic seas worldwide, until the Permo-Triassic extinction when they were virtually wiped off of the geologic record. Their fossilized remains create weakness in the stone that encases them. This weakness in the stone, coupled with the geological fracturing of the area, has made it relatively easy for the vine’s roots to penetrate deep into this rock strata. Impurities in the stone’s construction, allows for chemical weathering, brought about by rainwater infiltration, to create rich primary clay bedding for the vines, within the breaks and gaps in the rock. These factors have proved that Crinoidal limestone provides a very effective and fertile bedding for Pinot Noir to grow.

Wilson described the Crinoidal limestone as being “cracked by numerous small faults which ‘shuffle the cards’ of strata, but generally are not large enough to ‘cut the deck’ to introduce markedly new strata.” Terroir (1998) p.131.  This is typical of his breezy style, and while it is visual (in terms of cards), it really doesn’t have much concrete meaning, other than being a colorful way to say the crinoidal stone is well-fractured. He does go on to say that this extensive fracturing allows the stone to be a good aquifer for the vines.

crinoids

Colluvium: atop the bedding planes

Almost every grand cru vineyard in the Côte de Nuits has significant amounts of colluvium mixed in their soils. While Ruchottes-Chambertin does have colluvium is one of the most glaring exceptions it is not significant in quantity.  Typically, this colluvium is accompanied by a fair amount of transported clay, which when together often forms marl.(2)  Rarely does one exist without the other in vineyards that have been classified as grand cru.

In the Côte de Nuits, there tends to be more colluvium in the colluvium to clay matrix, while in the Côte de Beaune, there tends to be more clay.  This tends to the case because there are many more marl bedding planes in the Côte de Beaune than there are in the Côte de Nuits, where marl bedding is rarer. There may be more shale in the Côte de Beaune as well.

 

The tête de cru, –  the very finest of the grand cru vineyards, have relatively equal proportions of marl and colluvium and sit only upon the slightest of slopes. This applies to the vast majority of Chambertin and Clos de Bèze vineyard area. These crus possess a perfect planting bed for vines: they have colluvium/marl based topsoil that is at least 50 cm (19 inches) deep where the absorbing roots are active.(3)  Because of this construction, the soil has good porosity for root and water infiltration but is not so porous a material that the water does not drain right through it, or cause it evaporates quickly from it. Additionally, because of its rocky nature, the grand cru soils tend to resists compaction.

While there is a band of harder, less fertile Premeaux stone on the uppermost slopes of Chambertin and Clos de Bèze, this represents a minority proportion of these vineyards. Parcels that have vines on these upper slopes, often lend a measure of finesse to the finished wine, without impacting the palate impression of the finished blend. For these reasons, Chambertin and Chambertin Clos de Bèze are among the finest vineyards in the Côte de Nuits.

Clos des Ruchottes, (and Ruchottes in general) is a far different vineyard than its two neighbors. With the near-pure calcium stone beneath its shallow soils, the low levels of impurities mean that when it weathers,  very little clay is produced. Because of the scant soil, the vineyard their neither contains nor can it attract, as much in the way of nutrients for the vines as can Clos de Bèze with which it shares a border. The resulting wines typically have less fruit, less color, seem more structured or tannic, and have a finer, though thinner texture. On the upside, the vineyard produces a very classy wine that can have excellent aromatics, remarkable finesse, and has excellent age ability.

Agree? Disagree? Comments are welcome and encouraged! Please feel free to like or share this, or any other article in this series!


Note: Many authors note that Clos de Bèze has Oolitic limestone. Vannier-Petit does not note this on her map. Instead, she places the Oolitic stone in the premier cru of Bel Air, which sits directly above it. A likely explanation of Oolite being cited as existing in Chambertin is scree/colluvium from Bel Air has slid down, to litter Clos de Bèze from above.

(1) The problem with always talking about the Saône Fault, is it ignores the fact that the fault is really the most minor part of the geological event that happened. It was a continent being pulled apart, that caused a void into which the land adjacent to the Cote d’Or fell into a trough which would become the Saône Valley. The Saône Fault is nothing more than as scar marking that event. And in fact, the Saône Fault lies buried quite deeply underground – its general location is only estimated.

(2) Marl would require a smaller particle size than just rock and gravel sized limestone pieces to produce the non-clayey consistency that marl displays.

(3) Despite the conventional wisdom to the contrary, it is this shallow absorbing root system that gathers the majority of nutrients that vines require.

 

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Understanding the Terroir of Burgundy: Part 2.1 From Limestone to Clay

© BiVB Latricieres

Latricieres under brewing storm clouds.  photo © BiVB

by Dean Alexander

The weathering of limestone: let it rain

flooding

Rain and Flooding

For the past 35 million years, rainwater has endlessly and relentlessly washed across the limestone escarpment. To varying degrees, the limestone will absorb water through its pores, but stone that has been damaged by ductile deformation is much more easily infiltrated. Faster still, water fills the cracks and fissures created by geologic strain, finding freshly broken calcium carbonate to wetten, and begin the process of chemical weathering called carbonation.

Rain rainwater, it seems is more than just H2o.  From the storm clouds above, H2o binds to with carbon dioxide (CO2) to form carbonic acid (H2CO3). And although carbonic acid is typically a mild acid when carried by the rainwater, it does slowly act as a solvent to the calcium carbonate (CaCO3) that holds the limestone together. This carbonation frees the carbonate from the calcium, and will metamorphose the calcium into calcium hydrogen bicarbonate Ca(HCO3)2, which technically only exists in solution. (1)  The material that remains behind once it is no longer bound by bonds of the stone, is whatever impurities that were in the stone when it formed. This could include clay, fossils, feldspar which is the most common mineral on earth), among many other possibilities.

Nature’s Highly Engineered, Deconstruction of Limestone

Calcium Bicarbonate photo credit: Frank Baron/Guardian

The calcium carbonate in limestone is made solvent by the carbonic acid in rainwater.  The calcium carbonate is metamorphosed into calcium hydrogen bicarbonate  or Ca(HCO3)2. Technically calcium bicarbonate exists only as a water solution. As long as enough CO2 remains in the water, calcium bicarbonate is stable. But once excess Co2 is released, calcium carbonate is dropped out of solution resulting in the scale like on the facet above. photo credit: Frank Baron/Guardian

Calcium carbonate is more soluble in colder temperatures.  If you aren’t paying attention, this, along with so many other pieces of information might seem fairly unrelated. But like everything else, it is an important piece of the puzzle. It is all part of nature’s finely detailed engineering, where every element directly is related to, and influences the next.

This fact that calcium is more soluble in colder temperatures folds beautifully together with the freeze-thaw fracturing of the limestone that I detailed in Limestone: Part 1.2. The acidic water enters the more porous limestone, where it then freezes. This exerts immense internal pressure on the rock, which causes it to split along the pores, can cause various types of fractures within the stone.  Then when the acidic ice within the rock begins to melt, it erodes the stone along the fissures, being aided by the cold temperatures. The more acidic the rainwater, the more minerals the groundwater can dissolve and be held in solution. Interestingly, because lime is alkaline (a base as opposed to acid) it naturally balances the ph of the water, and thus the soil, which is good for the health the vines.

Clay Development = great vineyards

Puligny excavation at Alex Gamble

An excavation of the village cru, Les Grands Champs by Alex Gamble and Francoise Vannier-Petit. According to Vannier-Petit’s analysis, below the first 30 centimeters of dark clay-loam soil, lies a fine-grained, yellow clay. In its most pure form it is typical of transported clay being less than 2 microns, before mixing with heavier soils of increasing size down to an 80 cm depth. Here it transitions to more loosened substratum of “angular gravel” of 2 mm in size, which she also terms “heterometric stones”, providing good drainage for the site. See more at alexgamble.com

Les Grands Champs

Visual observation: Les Grands Champs is located on the eastern edge of the village of Puligny. The land here is be quite flat, with less than a one percent grade.  It sits at the foot of the 1er cru Clavillions (where the road turns to head up hill). Folatieres lies just above that, the bottom of which is denoted by the by the plot being replanted.

Every Burgundy vineyard that is considered to be great has at least some clay and some limestone in their makeup. But that is not surprising since  clay, is the byproduct of the chemical weathering of stone. The silicate materials (essentially the building blocks almost all minerals) in the stone are metamorphosed into phyllosilicate minerals. Putting that more simply: after stone is eroded by acid, some of the weathered material (depending on what the stone was made of) is transformed into a material that will become clay – once it attracts the needed aluminum, oxygen, and water.

Clays first forms at the site (in situ) of the stone that is being weathered, and this typically is a form of surface weathering. This new material is a primary clay, and sometimes referred to as a residual clay. These primary clays tend to be grainy, lack smoothness, and do not typically have qualities that are described as plasticity. As primary clays are eroded, (typically by water) and are moved to reform in another location, they are called transported clays.

This transportation changes the clay’s properties; this is likely because the water carries the lighter, smaller gains together, away from the larger, coarser material that remains in the in situ location. When transported clay reforms, the reformation is called flocculation. This natural attraction that clays have toward homogeneous groupings, are due not only to their similar size but because they carry a net negative electrical charge, which the particles gain by adsorption. Adsorption is not to be confused with absorption, is like static-cling. Items are added, or adhered by an electrical charge, to the grains, not absorbed by the grains.

In flocculation, particles are attracted to one another, by their uniform size (typically very small, under 2 micrometers), and shape (tetrahedral and octahedral sheets). These phyllosilicate sheets organize themselves, layering one upon another, like loose pages of sheet music. Between these silicate sheets, aluminum ions and oxygen are sandwiched. These elements bind together to form a clay aggregate, even in the confluence of water. Clay formations can carry with them, varying mineral components such as calcium, titanium, potassium, sodium and iron and other minerals, making them available to the vines. To say that the chemistry of clay gets very complicated, very quickly, is an understatement.

Transported clay has plasticity, which primary clays do not. When a clay is very wet, beyond its liquid limit, (meaning the most water a clay structure can hold before it de-flocculates), the sheets slide apart, giving clay its slippery feeling. Any thick area of clay found at a location is likely to a be transported clay, as the adsorption characteristic of clay allows it to achieve significant mass.

Sand 0.02 – 2.00 mm in diameter
Silt 0.002 – 0.02 mm in diameter
Clay < 0.002 mm in diameterClay types

Francoise Vannier Petit at AlexGamble

Francoise Vannier Petit, inspects the yellow ocher-colored clay in Puligny-Montrachet, Les Grands Champs.  Clays get their pigmentation from various impurities. Brown clays get their color from partially hydrated iron-oxide called Goethite. This yellow ocher clay gets its color from hydrated iron-hydroxide, also known as limonite. Clay type, however, is not determined by its color, but instead by its chemical and material organization.

Different clay types can be found next to each other or layered on top of one another. This layering is called a stacking sequence. photo source: alexgamble.com

The type of clay that is produced from the weathering of rock depends on the what minerals make up the stone.  In the case of granite (the stone which existed in the Burgundy region, before the creation of limestone), is constructed of up to 65% feldspar, and a minimum of 20% quartz, along with some mica. While quartz will not chemically degrade in contact with the carbonic acid carried in rainwater, feldspar and mica will. Even though they originate from the same stone, these two minerals will metamorphose into two different of types clay, that belongs to two different clay family groupings. Feldspar weathers into Kaolinite clay minerals and mica weathers to an Illite clay mineral. These tend to be non-swelling clays. (3)

I probably spent twenty hours trying to figure out what kind of clay eroded from limestone, before I realized that it would depend on what impurities were mixed into the calcium carbonate when it was brewed up during the Jurassic period.  Limestone can produce any of the four families of clay.

Kandites (of which Kaolin(ite) is a subgroup), are the most common clay type, because feldspar, which is the world’s most common mineral, metamorphoses into it.

The other three clay groupings are smectite, illite, and chlorite.(4) Within these clay family groupings, there are 30 subtypes. As might be suggested by the example of the weathering of granite above, it is very common for different kinds clays reside adjacent to, or in layers with other clays. This layering of clay types is called a stacking sequence, and it can occur in either ordered or random sequences. Each are attracted to formations of its own type, by size weight, and electrical charge.

The Effect of  Weathered Limestone on Soil Quality

effect of lime on Clay

effect of lime on Clay

There are a number of significant benefits to the high levels of limestone in the soils of Burgundy. The world over, farmers make soil additions of agricultural lime (which is made from grinding limestone or chalk), in order to balance and strengthen their soils. These are additions that are unnecessary in Burgundy.  Soil salinity is increased by the calcium bicarbonate that is released by chemical weathering of limestone. This increase in soil salinity (which raises the pH) of the soil, is cited as a condition for the flocculation of the clay, allowing the phyllosilicates (clay minerals) to bind together into aggregates. But of course, citing a high ph is required for flocculation (as I have seen written by several authors) this is the chicken or the egg debate. The flocculation requires a low pH environment to occur because it creates that environment in process of its development.

Lime additions to agricultural lands are also beneficial in that it increases soil aeration, which in turn improves water penetration. The calcium loosened soils allow for better root penetration, and because of that root growth is improved. Additionally, agricultural lime strengthens vegetation’s cell walls, increases water and nitrogen intake, and aids in developing enzyme activity. Too much lime (and its accompanying salinity) in the soil, however, can be lethal to the vines, and various rootstock has been identified as being more resistant to the effects of high levels of limestone in the soil than others.

This loosening of soil by addition of lime/calcium carbonate is caused by the disruption of the alignment of the clay particles. Rather than doing a poor job paraphrasing an already excellent article from soilminerals.com, called “Cation Exchange Capacity,” which will I quote below.  To put the article in a frame of reference, it explains to farmers interested in organic and biodynamic farming, the proper mineral balance for healthy soils. These are conditions often exist naturally in the best sections of the slope in the Cote d’Or.

“Because Calcium tends to loosen soil and Magnesium tightens it, in a heavy clay soil you may want 70% or even 80% Calcium and 10% Magnesium; in a loose sandy soil 60% Ca and 20% Mg might be better because it will tighten up the soil and improve water retention. If together they add to 80%, with about 4% Potassium and 1-3% Sodium, that leaves 12-15% of the exchange capacity free for other elements, and an interesting thing happens. 4% or 5% of that CEC will be filled with other bases such as Copper and Zinc, Iron and Manganese, and the remainder will be occupied by exchangeable Hydrogen , H+. The pH of the soil will automatically stabilize at around 6.4 , which is the “perfect soil pH” not only for organic/biological agriculture, but is also the ideal pH of sap in a healthy plant, and the pH of saliva and urine in a healthy human.” soilminerals.com

Mud is the problem, lime is the solution

On construction sites, mud is a problem, and lime is the solution.

The industrial of use of limestone to control wet and unstable soil

The soil strengthening properties of lime is well known by the construction industry. It is used as a soil stabilizer in the construction of buildings and roadways, as well as being used to stabilize wet ground to improve the mobility of trucks and tractors. In the vineyard, soils with high levels of limestone provide the good porosity, soil structure, and drainage to clay soils, and as this construction advertisement depicts, the same for mud/dirt soils as well.

Lime is also the binding agent in cement. The first known use of lime in construction was 4000 BC when it was used for plastering the pyramids, and later the Romans extensively used lime in the preparation of mortar for various constructions. They found that mortars prepared from lime, sand, and water, would harden to a man-made limestone, with exposure to the carbon dioxide provided by the air. This, of course, sounds very familiar, knowing the formation and chemical weathering of stone.


 Next Up Soil Formation: Part 2.2, Soil, Slope and Erosion

NOTES

(1) I should note, that within the span of this short paragraph, carbon has seen several forms: in the air (in carbon dioxide CO2), as an acid (in carbonic acid CO3) carried by water, in stone as calcium carbonate CaCO3, as a mineral bi-product (as calcium bicarbonate Ca(HCO3)2 which exists in liquid solutions. This is all part of the carbon cycle, where carbon is regenerated in the air we breath, the water we drink, the earth we grow our food in.

(2) The fact that CO3 is now carried by water, is important in terms of vineyard development.

(3) Kaolinite clays are the type used in pottery.

(4) As Granite was the primary stone formation in the region prior to the development of limestone, it is likely that Kaolinite and Illites are the most common clay families in Burgundy today.

Understanding the Terroir of Burgundy: Part 1.2 Limestone: stress, deformation and fracturing

by Dean Alexander

The first steps toward vineyard formation

The world was a very different place 160 million years ago when the limestone was formed. Dinosaurs roamed the earth and Pangea was breaking apart.

The world was a very different place 160 million years ago when the limestone of the Cote d’Or was formed. Dinosaurs roamed the earth and Pangea were breaking apart.

Burgundy’s story really is one of stone into the earth, and pivots on a cast of geological stress, sub-freezing temperatures, and the simple, transformative power of water. Just how the forces of nature may have acted upon the limestone and transformed it into the great wine region it is today, is the subject of this article. Meanwhile, the ultimate goal of this series explains the intimate relationship limestone has with the wines of Burgundy.

I suspect that we all have this image of the Côte, post-Fault Event (however long that took), to be this raw 400-meter face of sheared limestone. But even then, the Côte was not a solid piece of stone. The incredible extensional forces the broke the Côte d’Or free from the Saône would have caused significant tension fracturing throughout the Côte before this much more massive fault gave way.

Just Add Water

just add water

just add water

This tensile fracturing, which surely was extensive, would allow rainwater to deeply infiltrate these fine crevices of the stone. And then, upon each surface that the water contacted, depending on the specific porosity and permeability of the limestone, rain water would penetrate the surface of the stone. This contact with water would set the stage for two very different yet significant developments in the stone.

With winter temperatures below freezing, the water in the stone will expand between 8 and 11 percent. This will yield 2000 pounds per square inch, or 150 tons per square foot of internal pressure which is more than enough  to cleave the stone. Geologists call this frost wedging, a form of mechanical weathering which breaks apart the stone due to thermal expansion and further with the eventual contraction. Thermal expansion has a culprit in shattering the stone: the cold. Most materials are inherently brittle in colder temperatures, and the limestone which has more elastic than brittle tendencies is more vulnerable to fracturing in freezing temperatures. Frost wedging is so successful in nature that the stone industry mimics it as a non-explosive technique to separate pieces of stone.

The effect of successive freeze thaw cycles, even upon undamaged exposed stone can cause the development of micro-fissures that influence the stone’s fatigue strength, and can produce vertical cracking called exfoliation joints, as well as flaking, and spalling. All along the Côte, there are numerous scars on hillsides where limestone has in the past loosened, to slide off of even moderate slopes, sending scree down the hillside to rest at the curb of the slope. Geologists refer to this rubble pile as colluvium, and it has proved a near perfect vineyard soil solution. The sliding and falling of rock further degrades the stone, abrading it as it slides, and breaking as it falls, allowing fresh broken surfaces for water to act on. Frost wedging which in part created this colluvium rubble pile, is considered mechanical weathering, and is the first development that I mentioned water would bring. Equally important to vineyard formation, is the second significant development that rainwater brings, is chemical weathering. The acid carried by the rainwater, will metamorphose these freshly broken limestone surfaces. And like magic, it will slowly dissolve the calcium carbonate which binds the stone, leaving behind clay minerals and other material.  (This process will be covered in Part 1.3 Clay and Soil Development)

Exfoliation and Other Theories on Geologic Structures with Unobservable Change

Gilbert's 1904 exfoliation weathering and unloading theory explained. Girraween National Park, Queensland

Gilbert’s 1904 exfoliation weathering and unloading theory explained. Girraween National Park, Queensland

Consider for a moment: most significant geologic changes occurs over a time frame that is far longer than the entire the evolution of mankind. This fact alone might best explain the difficulties of studying events that happen so slowly that change is not observable. These are geologic forces that can not be seen, felt, or measured. If we didn’t have evidence that these changes had occurred, we would

Like this granite, softer, more impure limestone can be prone to spalling, in part because of its porous nature. Stones, like granite, and softer limestones that have a significant amount of feldspar in their makeup, are more brittle because feldspar, and its bonds, are more brittle. Conversely, the calcium carbonate in limestone makes the material more elastic, because the chemical bonds of CO3 will tend to move or realign if the stress upon them is long and gradual. So the makeup of each limestone is critical to how prone it is to fracturing.

Like this granite, softer, more impure limestone can be prone to spalling, in part because of its porous nature. Stones, like granite, and softer limestones that have a significant amount of feldspar in their makeup. Feldspar, the most common mineral on earth, and its bonds, are brittle than calcium carbonate. Conversely, the calcium carbonate in limestone makes the material more elastic, because the chemical bonds of CaCO3 will tend to move or realign if the stress upon them is long and gradual. So the makeup of each limestone is critical to how prone it is to fracturing.

never know they were still continuing to occur around us. The scale of time and shear size and immobility of the objects makes many traditional scientific methods impossible.

Exfoliation Theory: G.K. Gilbert 1904

We know that exfoliation joints exist, but scientists are at odds about how they occur. It is agreed that mechanical strain results in large horizontal sheets of stone separating itself from the mother rock. Half Dome in Yosemite has achieved its shape in this manner. The first, and once long-held theory, was put forth by the ground breaking U.S. geologist Grove Karl Gilbert.  Gilbert’s theory of Mechanical Exfoliation concerned stone formations that had previously been buried in the earth’s crust, which were later were forced to the surface by geological up-shifts. The theory explained that the removal of the overburden (the weight of the rock or earth above) had caused unloading of stress in one direction. The resulting release of stress once on the surface and not confined upwardly, caused expansion and tensile cracking along unloading joints, eventually creating loose sheets of stone on the upper surface of these rock structures. These outer layer of stone were thusly being exfoliated. This website for Girraween National Park in Queensland, Australia, has an excellent explanation of exfoliation weathering.

Challenges to Exfoliation Theory

However, this theory has had it challenges by the mid 20th century, and is to some extent (depending on the point of view), muted or discredited.  Situations were sited that didn’t fit all of the theory’s criteria, like rocks that with exfoliation joints which have never been deeply buried, and evidence that many exfoliation joints exist in compressive stress environments, rather than being produces by extensional stress as the theory suggests. Alternative theories are thermal expansion, (and even wide diurnal expansion), and hydraulic expansion, , (which I discussed above with frost wedging), compressional stress, and in the case of Half Dome, the weight of gravity, or a combination of all of the above, including exfoliation weathering.

Along the same lines, theories revolve around minerals that are created in an anaerobic environment. These stipulate some minerals molecular structure are changed (metamorphized) when exposure to oxygen, creating new minerals. While oxygen is the most common element in the earth’s crust, most of it is bonded with silicates and oxide materials and is not free to act as a weathering agent. But when minerals are exposed to free O2 above ground, they undergo chemical weathering, that produces new minerals that are stable on the surface.  The most obvious example is when iron ions lose an electron with exposure to oxygen, rust is formed.

Bedding planes

bedding fold types: Caused by compressional stress. Although extensional stress is the major shaper of the Cote, there are some folds in the North-South direction, due to compressional stress.

bedding fold types: Caused by compressional stress. Although extensional stress is the major shaper of the Cote, there are some folds in the North-South direction, due to a compressional stress of bedding plates pushing against one another.

In many ways, I’ve put the cart before the horse by talking about the escarpment, before covering even more fundamental ideas. But that is how storytelling goes: sometimes you have to fill in the back story.

The world was a very different place 160 million years ago. This was five million years before the Allosaurus and Apatosaurus (formerly known as the Brontosaurus) roamed the earth. The limestone of the Côte, being a sedimentary material, was laid down in big, flat, shallow beds between the reef barrier that protected the lagoon, and the shore. Each layer was put down, one at a time, chronologically by age, marking millions of years. As the seas receded, and this is the main point, this would become a wide, flat valley of young, sedimentary limestone. It is likely that this bedding would eventually, be completely covered by wind-blown soils. We don’t know what happened to this young Burgundian stone in the intervening 130 million years between formation and the Fault Event, 35 million years ago, but it is unlikely it remained there unchanged. As geological stress acted upon the bedding, it would be pulled, pushed, deformed, and in all likelihood, in some way, fractured.

Author’s Note: For the remainder of this article, I will describe the stress and deformation, and potential fracturing of the stone in the body of the text, and in the photos I will show some of the results (that I am aware of), of that stress. Hopefully the two together will paint a complete picture.

It takes more than just ‘X’ to fracture

Bedding dips Bedding planes. All bedding started out horizontal, but through various stresses, the bedding planes often shift and compress one another causing folds or change their orientation.


Tilted Bedding Planes: While all sedimentary bedding was laid out horizontally, various stresses can shift the bedding planes into other orientations. Geologist measures the tilt by dip, the up/down angle, and strike the percentage off of an east-west axis.

I would love to be able to write that a particular limestone will fracture under the “X” conditions, but just doesn’t seem to be that simple. First, there are too many variables. How stone reacts to geological stress is directly related to its composition and construction as well as: its temperature, the amount of stress, multiplied by the duration of  stress. Most materials tend to be more elastic under higher temperatures and more brittle in low temperatures. It would be reasonable to assume that there was significantly more geological fracturing during ice ages because stone is more brittle in cold temperatures. At least in warmer temperatures, calcium carbonate stones tend to have good elasticity, depending on how pure their construction, as the chemical bonds in CO3 will move if pressure is applied very slowly. However, that elasticity is finite before the stone is structurally damaged as it passes its elastic limit; but more on that later.

Secondly, like I mentioned before, science cannot measure the stress, but rather the deformation due to the stress. For this geologists use a strainmeter, which they measure changes in the distance between two points. For greater distances technology has brought the laser interferometer. These tools allow the scientist to measure frequencies that represent deformation.  Over short periods of time, they record tides (I had never before considered the stress created by a 1.5 quintillion tons of water moving position above earth) and the seismic waves of earthquakes, while over longer periods of time, it can record the gradual accumulation of stress of rock formations.

The mission of this article? What I am looking for here, are some kind of answers these two questions: What conditions would make it possible for vine roots to bed into limestone bedrock? and What limestone types will fracture enough to allow this to happen? Anything learned along the way will be a bonus.

Stresses and the resulting strain

The ductile bending of this folded limestone was made under compressional stresses for a considerably long period of time. Ductile folds are not elasticity as, if released, this rock would not return to its original shape. Note the fractures that have developed almost vertically through the layers of stone.

The bending of this folded limestone was made under compressional stresses over a very long period of time. This stone. well beyond its elastic limit, has experienced a high degree of ductile strain, and is now brittle and structurally degraded. Note the fractures that have developed almost vertically through the layers of stone.

Stress causes strain of various types. Like I mentioned before, we are not able to measure the stress itself, rather only its effect by measuring the stone’s deformation. Below are the basic stresses upon objects and the resultant strains and deformations associated with them. Any deformation is considered flow (as science calls this) and it is domaine of an interdisciplinary study called Rheology. Here it is again, more simply, because its getting more complicated: Stress first.  It, in turn, causes strain. The result can be deformation, and this deformation is studied as if it were a liquid: as flow by Rheologists (a group of engineers, mathematicians, geologists, chemists, and physicists), who work together in an attempt to answer questions that transcend all of these disciplines.

6 Most Common Geologic Stresses (the first two are the most relevant to Burgundy)

  • Tensile, Tension, or extensional stress which stretch the rock or lengthen an object, will cause longitudinal or linear strain, and its effect is to lengthen an object, and can pull rocks apart. Like a rubber band pulled longitudinally, this is known as extensional rheology. As the rubber band breaks, that is called shearing flow. Rocks are significantly weaker in tension than in compression, so tensile fractures are very common. Tension stress formed the Côte d’Or.
  • Compressional stress that squeezes the rock and the resulting strain shortens an object. This too can be a linear or longitudinal strain. Stone under compressional stress can either fold (as in the photo to the right) or fault.
  • Normal Stress (can be either compressional or extensional) Normal stress that acts perpendicular to the stone.
  • Directed stress is typically a compressional stress, that comes from one direction with no perpendicular forces to counteract it. The higher the directed pressure the more deformation that occurs.
  • Lithostatic> and hydrostatic stresses are the compressional pressure of being underground or underwater. The force of the stress is uniform, causing compression from all sides.
This limestone jutting out of the vines in the Puligny vineyard, Les Combettes. Wine writers typically cite this common rock features as evidence of shallow soils, but these rock features are more likely a fold (plunging anticline) caused by compressional stress.

Wine writers typically cite these limestone outcroppings as evidence of shallow soil. But these rock features are more likely a fold (plunging anticline) caused by compressional stress. Location: Puligny, Les Combettes.

Interestingly, the effects of hydrostatic stresses upon an object are mitigated by oppositional forces. For example, the stress from below counteracts much of the force from above, and the forces from the right side counteracted by those from the left as they push against each other. So unlike directed stress, (the kind of stress that a 2 ton object exerts on top of a man), hydrostatic stress is like a scuba diver in the ocean. The stress of water upon the diver can be the same as the heavy weight upon the man, but because of counteracting stresses, strain is not expressed in the same way.

  • Shear stress is that which is parallel to an object. Shear strain (caused by shear stress) changes the angle of an object. It can cause slippage between two objects when the frictional resistance is exceeded, or even failure within an object. Faulting is an example of slippage under shear stress. I would be remiss to note that faults in Burgundy, at least to my anecdotal eye, often occur between limestone types.

 

Coaxial strain

Coaxial strain

 

The Magnitude of  Strain

Elastic strain and ductile deformation

stressesThere are two levels of strain. Elastic strain, in the effects of the strain, are reversible. The stone will change shape or deform under stress, with minimal damage to its structure, and then return to its original shape and position.

Ductile strain, is the area of strain once past the elastic level. The stone is now developing microscopic fissuring, and the stone can not return completely to its original size, shape, or position. Although the stone may not appear to be visibly damaged, any deformation into the ductile range, will harm the stone’ structural integrity. Additionally, in comparison to the deformation of the stone in the elastic range, the speed and ease of ductile deformation increases quickly (in structural geologic terms).  The deformation is now the result of micro-fissures that have emerged throughout the stone, and are now both propagating and enlarging. It is during this phase of rapid deformation that the stone can achieve dramatic folding from what had previously been flat, sedimentary stone.

By The Numbers: limestone limits

Elasticity in stone

Elasticity in stone

Author’s note: The measuring of deformation and the related stress involved becomes a bit more technical, and requires a number of lingo words to be used in the same sentence. I resist this as much as possible, because it requires the reader to be very familiar with the terms. Skip ahead if this doesn’t interest you, but it gives a numerical frame of reference for limestone fracturing.

The deformation under applied pressure is called flow, and the material’s resistance to deformation is measured (in newtons). The measurement of a stone’s elasticity is called it’s Elastic Modulus  (a.k.a. Young’s Modulus).

Elasticity of rock groups. Click to enlarge

The elasticity of rock groups. Click to enlarge

The Elastic Modulus measures the tensile elasticity, meaning when a material is pulled apart by extensional stress.  This resistance to deformation is expressed in gigapascals (GPa) which are one billion newtons per square meter. 

Additionally, there is Bulk Modulus, the measurement of a stone’s lithostatic (compressed from all sides) elasticity. This is expressed in Gigapascals, (GPa) or one million newton units.

And Shear Modulus, also known as the Modulus of Rigidity, in which the elasticity of a stone under shear forces is measured.  It is defined as “the ratio of shear stress to the displacement per unit sample length (shear strain)”.

Scarp Cutaway. Click to enlarge

Scarp Cutaway. Click to enlarge

I gave the MPa compressional strength (loads that tend to shorten) of various limestone types in part 1.1. Note here MPa is used, or one million newtons per square meter. The elastic modulus of most limestone can be as low as 3 GPa for very impure limestone (we don’t know what was sampled), and up to 55 GPa depending on purity of the calcium carbonate. As a comparison of elastic modulus: Dolomite (limestone with a magnesium component) typically ranges between 7 to 15 GPa, while Sandstone typically runs 10 to 20 GPa.

  • click to enlarge

    click to enlarge

    General Limestone Modulus Ranges (the range of deformation before fracture)

  • Elastic modulus range: 3 GPa – 80 GPa  
  • Bulk modulus range: 5 GPa – 66.67 GPa
  • Shear modulus range: 3.5 GPa to 33 GPa

 

The strain rate is important: which is expressed as elongation over time (e/t). The longer the period of time, the more the material can “adapt” to the strain. The faster the stress is applied exceeding the plastic elastic limit, the shorter the plastic region. The plastic region fracture where the material breaks and is considered brittle behavior.

  • Brittle materials can have either a small (or a large) region of elastic behavior, but only a small region of ductile behavior before they fracture.
  • Ductile materials have a small region of elastic behavior and a large region of ductile behavior before they fracture.

 

From Strain to Total Failure of Stone

The description of how stone reacts to crushing pressures reminds me of those submarine movies, where the hull is slowly being strained with a chorus of creepy groaning sounds, rivets popping and water spraying from leaks in the hull. In the laboratory, geologists study stones they crush, in order to understand what has occurred to rock materials over hundreds of thousands, to several million of years.

Infinitesimal strains refer to those that are small, a few percent or less, and is part of a mathematical approach material that is “assumed to be unchanged by the deformation” (Wikipedia).  As deformation increases, micro-cracks and pores in the stone are closed and depending on the orientation of the pores in relation to the direction of the stress, this can cause the stone to begin to deform in a coaxial manner. This non-linear deformation is obvious in weaker or more porous stone.

The goal is to explain how this happens in limestone with high calcium carbonate

The goal is to explain how this happens in limestone with high calcium carbonate content. photo alexgambal.com

While in the elastic region, stone adjusts to the pressure applied to it. Micro-cracks don’t appear in the stone until it reaches the 35%-40% way-point in elastic region. At this point structural strain is largely recoverable with little damage. At 80% of the elastic limit, micro cracks are developing independently of one another, and are evenly dispersed throughout the stone’s structure, despite the fact that the stone is at maximum compaction with no volume change. As the stone nears its elastic limit, micro-cracks are now appearing in clusters as the their growth accelerates in both speed and volume. The stones appearance and size remains intact as it passes its peak strength, although the structure is highly disrupted. The crack arrays fork and coalesce, as they begin to form tensile fractures or shear planes, depending on the strength” of the limestone.(1) The rock is now structurally failing, and considered to have undergone “strain softening”.  Additional strain will be concentrated on the most fractured, weakest segments of the stone, creating strain and shear planes in these specific zones, which as it nears the fracture point will essentially become two or more separate stones, ironically bound together only by frictional resistance and the stress that divided them. information source: Properties of Rock Materials, Chapter 4 p.4-5, (LMR) at the Swiss Federal Institute of Technology, Lausanne

The Bottom Line on the Fracturing of Limestone

Roche de Solutre and Vergisson, are large, tilted bedding planes. What little information that I have found of their formation (non-scientific) claims these are plateaus which raised when the Saone Valley was formed, and have later tilted to the East. Plateaus are often formed by magma pressure causing the ground swell upwards, or by glacial erosion. The theory that 400 meters of stone were reabsorbed back into the earth by tilting, sounds like sketchy science to me. I would consider a second option more likely: only one end of this structure was pushed above ground by geologic forces.

Roche de Solutre and Vergisson, are large, tilted bedding planes. What little information that I have found of their formation (non-scientific) claims these are plateaus which raised when the Saone Valley was formed, and then later “tilted” to the East.  The theory that 400 meters of stone were reabsorbed back into the earth by “tilting”, sounds like sketchy science to me. I would consider a second option more likely: only one end of this structure was pushed above ground by geologic forces.

The truth is that we don’t have any records detailing the condition of the limestone base that lies below the topsoil. Certainly the limestone base has been exposed often enough over the past century, that had some academic organization wanted to catalog this kind of information, there would now be a large database to refer to by now. Moreover this would be a substantial advance in the knowledge of how to farm these vineyards. Today, the most progressive vignerons are now making these inquiries themselves, digging trenches to find out what lies below in order to make the best replanting and farming decisions possible. But it is unlikely that even these recent efforts are being catalogued, as they investigated.

Vineyard Development: Limestone

Tilted bedding plane, whether a plateau as one source describes or not As a tilted bedding plane, The Roche (Roc) de Solutre and Vergisson, despite their distance South of the Cote de Nuits, and their slightly more youthful age, gives an unique glimpse into the layers of limestone in Burgundy. It reminds us, that whatever the top layer is, there lies different strata just below it. Click to enlarge

Tilted bedding plane, whether a plateau as one source describes or not
As a tilted bedding plane, The Roche (Roc) de Solutre and Vergisson, despite their distance South of the Cote de Nuits, and their slightly more youthful age, gives an unique glimpse into the layers of limestone in Burgundy. It reminds us, that whatever the top layer is, there lies different strata just below it. Click to enlarge

Limestone fracturing and shallow soiled vineyards

Since deeper soils do not require the vine to penetrate the bedrock in order to have a successful vineyard, fracturing there is not required for vineyard vitality.

However any vineyard where there is shallow soil, the limestone below must be compromised structurally, to some degree, for the vines to penetrate the stone. In this way, the vines themselves are a contributor to mechanical weathering of stone in the vineyards. Limestone varieties with a high percentage of impurities, are typically more easily fractured; although they may actually be soft enough, or porous enough stone for the vines to penetrate on their own.  It is documented that composite formations with heavy fossilization (like crinoidal), or clay content (like argillaceous limestone)  are less elastic than purer limestones with high levels of CaCO3, and are much more friable. You can read about limestone construction in Limestone: part 1.1.

With a harder stone, would significant ductile deformation with fissuring make the stone weak enough for the vine roots to penetrate?  Or does a limestone based vineyard need to be significantly fractured before vines can sufficiently take root? That answer to this question is not apparent with the information available at this time, but the answer is probably yes.

Mazy and Ruchottes Chambertin with dip and strike oriented faults. Significant outcropping has emerged from this hard Premeaux stone at the convergence of these faults. Interestingly its both parallel and perpendicular to the extensional, horizontal faulting

Mazy and Ruchottes Chambertin with dip and strike oriented faults. Significant outcropping has emerged from this hard Premeaux stone at the convergence of these faults. Interestingly its both parallel and perpendicular to the extensional, horizontal faulting

Vineyards like Mazy-Chambertin and Ruchottes-Chambertin give evidence that the more brittle Premeaux limestone (with its lower compressive strength, and higher porosity), if fractured enough, can support vineyards, despite there being very shallow topsoil. There are a number of linear, east-west oriented, limestone outcroppings in these two vineyards, indicating this area has seen significant compressional stress to the bedrock there over the last 35 million years, in addition to the tensile faulting caused by extensional stress that created the region. These two stresses would have created vertical dip joints, and horizontal, strike joints, and very possibly diagonal oblique joints, and fissuring in the bedrock. Enough for the vines to survive well enough for these two vineyards to be awarded grand cru status in the late 1930s.There has been a question in my mind whether Comblanchien, which is so dense that water cannot penetrate enough to effect freeze thawing, and is also very elastic due to its 98% calcium carbonate content, would fracture enough in a vineyard location to support a vineyard in shallow soils. In fact that has been a driving question throughout this piece, and which I was inclined to believe the answer was no, until evidence proved otherwise.  Apparently that has happened. 

The Rise of Colluvium

In terms of vineyard soil development itself, geologic pressures have worked extensively to prepare the limestone bedrock. Primarily with extensional stress, but also exerting compressional stress, the strain significantly weakened and fractured the limestone bedding. This deformation and the ensuing fracturing allowed water to infiltrate its cracks and crevices. During periods of cold weather it would freeze within the fissuring, causing frost wedging. Exfoliation would ensue, ultimately causing significant limestone debris to be pulled away by gravity, itself a powerful force of mechanical weathering, to slide (and tumble) down the hillside.  As the stones fell, they would further break and abrade into yet smaller pieces. Abrasion is another agent of weathering. There they would stop at the curb of the slope, where eventually they form deep, limestone-based “colluvium” soils. This is what Coates is speaking of when he wrote “rock and more limestone on the section closest to the over-hang, and there is some sand” in AmoureusesThese are the colluvium soils that would with enough time would generate the vineyards upon the the red grand cru vines of the Cote de Nuits would grow.

But first, the story of chemical weathering would have to play out, creating clay and soil needed to feed the vines. The slopes of the Cote d’Or would slowly evolve geologically for millions of years, awaiting the arrival Roman agriculturalists who would recognize and exploit the vinous wealth of this thin strip of the hillside.

Next up: Part 1.3 Amoureuses and Parallel Evidence of Shallow Soils over Comblanchien

 

Please feel free to comment, like, follow, share, or re-blog this or any of this terroir series!

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(1) Because it is often difficult to distinguish between the different types of fractures and  faulting once the fracture has occurred, I will leave it at this. There are 3 kinds of fractures born from the three major stresses: Shear, tensile, and extensional.

(2) I have not been able to determine if  crystallization is a definition of Comblanchien limestone, or if the Comblanchien limestone in the villages Corgoloin and Comblanchien just happen to have been metamorphosed into marble, and that is why it is quarried there.

Previous articles on Terroir

Limestone Construction: part 1.1 (click here)

Introduction to Terroir (click here)

Preface to my article on Terroir (click here)

Marl: The Most Misused and Misunderstood Word in Burgundy Literature? (click here)

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